〔Major achievements〕Continuously evolving antiferromagnetic order within the superconducting phase in Zn-doped CeCoIn5
Kaede Inoh; Ryosuke Koizumi; Teppei Takahashi; Hayao Fujimoto; Hideaki Ebisawa; Azumi Yashiro; Mika Kohinata; Asuka Hosogai; Akira Matsuo; Koichi Kindo; Ikuto Kawasaki; Daisuke Okuyama; Hung-Cheng Wu; Taku J. Sato; Kenichi Tenya; Kenji Ohoyama; Kazuaki Iwasa; Makoto Yokoyama, Last, American Physical Society (APS)
Physical Review B, 17 Mar. 2025, [Reviewed]

〔Major achievements〕Quantum criticality linked to the suppressed superconducting upper critical field in Ni-doped CeCoIn5
Azumi Yashiro; Rahmanto; Kaketo Inami; Kohei Suzuki; Kaede Inoh; Teppei Takahashi; Ryosuke Koizumi; Yohei Kono; Shunichiro Kittaka; Yusei Shimizu; Fuminori Honda; Dai Aoki; Kenichi Tenya; Makoto Yokoyama, Last, American Physical Society (APS)
Physical Review Materials, 08 Aug. 2024, [Reviewed]

Modulation vector of the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn5 revealed by high-resolution magnetostriction measurements
S. Kittaka; Y. Kono; K. Tsunashima; D. Kimoto; M. Yokoyama; Y. Shimizu; T. Sakakibara; M. Yamashita; and K. Machida, American Physical Society
Physical Review B, Jun. 2023, [Reviewed]

Weyl-Kondo semimetal behavior in the chiral structure phase of Ce3Rh4Sn13
K. Iwasa; K. Suyama; S. Ohira-Kawamura; K. Nakajima; S. Raymond; P. Steffens; A. Yamada; T. D. Matsuda; Y. Aoki; I. Kawasaki; S.-i. Fujimori; H. Yamagami; and M. Yokoyama, Last, American Physical Society (APS)
Physical Review Materials, Jan. 2023, [Reviewed]

〔Major achievements〕Nested antiferromagnetic spin fluctuations and non-Fermi-liquid behavior in electron-doped CeCo1-xNixIn5
H. Sakai; Y. Tokunaga; S. Kambe; J.-X. Zhu; F. Ronning; J. D. Thompson; H. Kotegawa; H. Tou; K. Suzuki; Y. Oshima; and M. Yokoyama, Last, American Physical Society (APS)
Physical Review B, Dec. 2022, [Reviewed]

〔Major achievements〕Direct measurement of the evolution of magnetism and superconductivity toward the quantum critical point
W. Higemoto; M. Yokoyama; T. U. Ito; T. Suzuki; S. Raymond; and Y. Yanase, Corresponding, Nontrivial quantum states can be realized in the vicinity of the quantum critical point (QCP) in many strongly correlated electron systems. In particular, an emergence of unconventional superconductivity around the QCP strongly suggests that the quantum critical fluctuations play a central role in the superconducting pairing mechanism. However, a clear signature of the direct coupling between the superconducting pairing states and the quantum criticality has not yet been elucidated by the microscopic probes. Herein, we present muon spin rotation/relaxation and neutron diffraction measurements in the superconducting dome of CeCo(In1 - xZnx)5. It was found that a magnetically ordered state develops at x≥ 0.03, coexisting with the superconductivity. The magnitude of the ordered magnetic moment is continuously reduced with decreasing x, and it disappears below x∼ 0.03, indicating a second-order phase transition and the presence of the QCP at this critical Zn concentration. Furthermore, the magnetic penetration depth diverges toward the QCP. These facts provide evidence for the intimate coupling between quantum criticality and Cooper pairing.
Proceedings of the National Academy of Sciences of the United States of America, Nov. 2022, [Reviewed]

〔Major achievements〕Evolution of the electronic structure and correlations accompanied by suppression of itinerant ferromagnetism in Sr1−x(La0.5K0.5)xRuO3
Ikuto Kawasaki; Shin-ichi Fujimori; Yukiharu Takeda; Hiroshi Yamagami; Rahmanto; Yutoku Honma; Kensuke Matsuoka; and Makoto Yokoyama, Last, We have carried out soft x-ray photoemission experiments on itinerant ferromagnet Sr1-x(La0.5K0.5)xRuO3 to investigate how the electronic state varies with doping concentration. The Ru 4d-derived coherent part of the valence spectra develops significantly with increasing x for x≤0.3, which can be explained by the suppression of the ferromagnetic exchange splitting. With further increasing x, this development is overwhelmed by the spectral weight transfer from the coherent to the incoherent parts due to the electron correlation. The enhancement of the electron correlation effect with doping is also confirmed by the Ru 3d core-level spectra as the suppression of the well-screened peak. In contrast to the remarkable variation of the Ru 4d spectral intensity as a function of x, the valence spectra hardly depend on temperature and do not show any noticeable change across the magnetic transition temperatures, indicating that the temperature dependence of the exchange splitting cannot be explained by a simple Stoner picture. We compare the present photoemission results with those for isostructural Sr1-xAxRuO3 (A=La and Ca) and discuss the origin of the difference in the magnetic property between these doped compounds.
Physical Review B, May 2022, [Reviewed]

〔Major achievements〕Nature of field-induced antiferromagnetic order in Zn-doped CeCoIn5 and its connection to quantum criticality in the pure compound
M. Yokoyama; Y. Honma; Y. Oshima; Rahmanto; K. Suzuki; K. Tenya; Y. Shimizu; D. Aoki; A. Matsuo; K. Kindo; S. Nakamura; Y. Kono; S. Kittaka; and T. Sakakibara, Lead
Physical Review B, Feb. 2022, [Reviewed]

〔Major achievements〕Nanoscale heterogeneity induced by nonmagnetic Zn dopants in the quantum critical metal CeCoIn5: 115In NQR/NMR and 59Co NMR study
H. Sakai; Y. Tokunaga; S. Kambe; J.-X. Zhu; F. Ronning; J. D. Thompson; S. K. Ramakrishna; A. P. Reyes; K. Suzuki; Y. Oshima; M. Yokoyama, Last, American Physical Society (APS)
Physical Review B, Aug. 2021, [Reviewed]

Strong magnetic anisotropy and unusual magnetic field reinforced phase in URhSn with a quasi-kagome structure
Y. Shimizu; A. Miyake; A. Maurya; F. Honda; A. Nakamura; Y. J. Sato; D. Li; Y. Homma; M. Yokoyama; Y. Tokunaga; M. Tokunaga; and D. Aoki, American Physical Society (APS)
Physical Review B, Oct. 2020, [Reviewed]

〔Major achievements〕Avoided quantum criticality and cluster-glass formation in itinerant ferromagnet Sr1-x(La0.5K0.5)xRuO3
R. Iwahara; R. Sugawara; Rahmanto; Y. Honma; K. Matsuoka; A. Matsuo; K. Kindo; K. Tenya; and M. Yokoyama, Last
Physical Review Materials, Jul. 2020, [Reviewed]

〔Major achievements〕Anisotropic magnetic-field response of quantum critical fluctuations in Ni-doped CeCoIn5
M. Yokoyama; K. Suzuki; K. Tenya; S. Nakamura; Y. Kono; S. Kittaka; and T. Sakakibara, Lead
Physical Review B, 2019, [Reviewed]

〔Major achievements〕Observation of a new field-induced phase transition and its concomitant quantum critical fluctuations in CeCo(In1-xZnx)5
M. Yokoyama; H. Mashiko; R. Otaka; Y. Oshima; K. Suzuki; K. Tenya; Y. Shimizu; A. Nakamura; D. Aoki; A. Kondo; K. Kindo; S. Nakamura; and T. Sakakibara, Lead, We demonstrate a close connection between observed field-induced antiferromagnetic (AFM) order and quantum critical fluctuation (QCF) in the Zn7%-doped heavy-fermion superconductor CeCoIn5. Magnetization, specific heat, and electrical resistivity at low temperatures all show the presence of new field-induced AFM order under the magnetic field B of 5-10 T, whose order parameter is clearly distinguished from the low-field AFM phase observed for B < 5 T and the superconducting phase forB < 3 T. The 4f electronic specific heat divided by the temperature, C-e/T, exhibits - ln T dependence at B similar to 10 T (equivalent to B-0), and furthermore, the C-e/T data for B >= B-0 are well scaled by the logarithmic function of B and T : ln[ (B - B-0)/T-2.7]. These features are quite similar to the scaling behavior found in pure CeCoIn5, strongly suggesting that the field-induced QCF in pure CeCoIn5 originates from the hidden AFM order parameter equivalent to high-field AFM order in Zn7%-doped CeCoIn5., AMER PHYSICAL SOC
Physical Review B, 2017, [Reviewed]

〔Major achievements〕Correlation effect in Sr1-xLaxRuO3 studied by soft x-ray photoemission spectroscopy
I. Kawasaki; Y. Sakon; S.-i. Fujimori; H. Yamagami; K. Tenya; and M. Yokoyama, Last, To clarify how the electronic state of Sr1-xLaxRuO3 evolves with La doping, we conducted photoemission (PES) experiments using soft x rays. The spectral shape of the Ru 4d-derived peak near the Fermi level changes significantly with increasing x. This variation indicates that a spectral weight transfer from the coherent to the incoherent component occurs due to an enhancement of the electron correlation effect. Resonant PES experiments at the La 3d(5/2) edge have confirmed that there is no significant contribution of the La 5d state in the energy range where the spectral weight transfer is observed. Using the dependence of the photoelectron mean-free path on the photon energy, we subtracted the surface components from the PES spectra and confirmed that the enhancement of the electron correlation effect with La doping is an intrinsic bulk phenomenon. On the other hand, a large portion of the coherent component remains at the Fermi level up to x = 0.5, reflecting that the Ru 4d state still has itinerant characteristics. Moreover, we found that the PES spectra hardly depend on the temperature and do not exhibit a discernible change with magnetic ordering, suggesting that the temperature variation of the exchange splitting does not follow the prediction of the Stoner theory. The presently obtained experimental results indicate that the electron correlation effect plays an important role in Sr1-xLaxRuO3 and that the Ru 4d electrons possess both local and itinerant characteristics., AMER PHYSICAL SOC
Physical Review B, Nov. 2016, [Reviewed]

〔Major achievements〕Superconductivity and non-Fermi-liquid behavior in the heavy-fermion compound CeCo$_{1-x}$Ni$_x$In$_5$
Ryo Otaka; Makoto Yokoyama; Hiroaki Mashiko; Takeshi Hasegawa; Yusei Shimizu; Yoichi Ikeda; Kenichi Tenya; Shota Nakamura; Daichi Ueta; Hideki Yoshizawa; Toshiro Sakakibara, Corresponding, The effect of off-plane impurity on superconductivity and non-Fermi-liquid
(NFL) behavior in the layered heavy-fermion compound CeCo$_{1-x}$Ni$_x$In$_5$
is investigated by specific heat, magnetization, and electrical resistivity
measurements. These measurements reveal that the superconducting (SC)
transition temperature T$_c$ monotonically decreases from 2.3 K (x=0) to 0.8 K
(x=0.20) with increasing x, and then the SC order disappears above x=0.25. At
the same time, the Ni substitution yields the NFL behavior at zero field for
x=0.25, characterized by the -ln T divergence in specific heat divided by
temperature, C$_p$/T, and magnetic susceptibility, M/B. The NFL behavior in
magnetic fields for x=0.25 is quite similar to that seen at around the SC upper
critical field in pure CeCoIn$_5$, suggesting that both compounds are governed
by the same antiferromagnetic quantum criticality. The resemblance of the
doping effect on the SC order among Ni- , Sn-, and Pt-substituted CeCoIn5
supports the argument that the doped carriers are primarily responsible for the
breakdown of the SC order. The present investigation further reveals the
quantitative differences in the trends of the suppression of superconductivity
between Ce(Co,Ni)In$_5$ and the other alloys, such as the rates of decrease in
T$_c$, dT$_c$/dx, and specific heat jump at T$_c$, d($\Delta$C$_p$/T$_c$)/dx.
We suggest that the occupied positions of the doped ions play an important role
in the origin of these differences.
Journal of the Physical Society of Japan, 29 Jul. 2016, [Reviewed]

Muon Spin Relaxation and Neutron Diffraction Studies of Cluster-Glass States in Sr1-xLaxRuO3
I. Kawasaki; K. Fujimura; I. Watanabe; M. Avdeev; K. Tenya and M. Yokoyama, Corresponding, To clarify the magnetic properties of cluster-glass states in Sr1-xLaxRuO3 (0.3 <= x <= 0.5), we report herein the results of muon spin relaxation (mu SR) and neutron powder diffraction measurements. The mu SR experiments showed that magnetic clusters start developing well above the peak temperature T* in the ac susceptibility. The volume fraction of the magnetically ordered region increases continuously with decreasing temperature, showing no anomaly at T*, and reaches nearly 100% at the lowest temperature. The temperature variation of the volume fraction is essentially independent of the La concentration in the x range presently investigated, although the dc magnetization is significantly suppressed with increasing x. Neutron powder diffraction experiments revealed that the ground state for x = 0.3 is a long-range ferromagnetic ordered state. These results indicate that, with decreasing temperature, cluster-glass states in Sr1-xLaxRuO3 gradually develop into long-range ferromagnetic ordered states with decreasing temperature, and that the magnetic ordering process differs strikingly from that expected for a conventional second-order ferromagnetic transition., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2016, [Reviewed]

Enhancement of ferromagnetism by oxygen isotope substitution in strontium ruthenate SrRuO3
H. Kawanaka; Y. Aiura; T. Hasebe; M. Yokoyama; T. Masui; Y. Nishihara; and T. Yanagisawa, The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature T-c of 160 K is studied. We observed for the first time a shift of Delta T-c similar to 1 K by oxygen isotope substitution of O-16 -> O-18 in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient alpha = -partial derivative ln T-c/partial derivative lnM. The Raman spectra indicate that the main vibration frequency of O-16 at 363 cm(-1) shifts to 341 cm(-1) following oxygen isotope substitution O-18. This shift is remarkably consistent with the Debye frequency being proportional to proportional to 1 root M where M is the mass of an oxygen atom. The positive isotope shift of Delta T-c can be understood by taking account of the electron-phonon interaction., NATURE PUBLISHING GROUP
Scientific Reports, 2016, [Reviewed]

〔Major achievements〕Pauli-limited superconductivity and antiferromagnetism in the heavy-fermion compound CeCo(In1-xZnx)5
M. Yokoyama; H. Mashiko; R. Otaka; Y. Sakon; K. Fujimura; K. Tenya; A. Kondo; K. Kindo; Y. Ikeda; H. Yoshizawa; Y. Shimizu; Y. Kono; T. Sakakibara, Lead, We report on the anisotropic properties of Pauli-limited superconductivity (SC) and antiferromagnetism (AFM) in the solid solutions CeCo(In1-xZnx) 5 (x <= 0.07). In CeCo(In1-xZnx) 5, the SC transition temperature T-c is continuously reduced from 2.3 K (x = 0) to similar to 1.4 K (x = 0.07) by doping Zn, and then the AFM order with the transition temperature of T-N similar to 2.2 K develops for x larger than similar to 0.05. The present thermal, transport, and magnetic measurements under magnetic field B reveal that the substitution of Zn for In yields little change of low-temperature upper critical field mu H-0(c2) for both the tetragonal a and c axes, while it monotonically reduces the SC transition temperature Tc. In particular, the magnitudes of mu H-0(c2) at the nominal Zn concentration of x = 0.05 (measured Zn amount of similar to 0.019) are 11.8 T for B parallel to a and 4.8 T for B parallel to c, which are as large as those of pure compound though T-c is reduced to 80% of that for x = 0. We consider that this feature originates from a combination of both an enhanced AFM correlation and a reduced SC condensation energy in these alloys. It is also clarified that the AFM order differently responds to the magnetic field, depending on the field directions. For B parallel to c, the clear anomaly due to the AFM transition is observed up to the AFM critical field of similar to 5 T in the thermodynamic quantities, whereas it is rapidly damped with increasing B for B parallel to a. We discuss this anisotropic response on the basis of a rich variety of AFM modulations involved in the Ce115 compounds., AMER PHYSICAL SOC
Physical Review B, 2015, [Reviewed]

〔Major achievements〕Possible Evolution of Antiferromagnetism in Zn-Doped Heavy-Fermion Superconductor CeCoIn5
M. Yokoyama; K. Fujimura; S. Ishikawa; M. Kimura; T. Hasegawa; I. Kawasaki; K. Tenya; Y. Kono and T. Sakakibara, Lead, We have succeeded in growing single crystals of the heavy-fermion
superconductor CeCo(In1-xZnx)5 with x<=0.07. Measurements of specific heat,
electrical resistivity, dc magnetization and ac susceptibility revealed that
the superconducting (SC) transition temperature Tc decreases from 2.25 K (x=0)
to 1.8 K (x=0.05) by doping Zn into CeCoIn5. Furthermore, these measurements
indicate a development of a new ordered phase below T_o ~ 2.2 K for x=>0.05,
characterized by the reduced magnetization and electrical resistivity in the
ordered phase, and the enhancement of specific heat at T_o. This phase
transition can be also recognized by the shoulder-like anomaly seen at H_o ~ 55
kOe in the field variations of the magnetization at low temperatures, which is
clearly distinguished from the superconducting critical fields Hc2=49 kOe for
x=0.05 and 42 kOe for x=0.07. We suggest from these results that the
antiferromagnetic (AFM) order is generated by doping Zn, and the interplay
between the SC and AFM orders is realized in CeCo(In1-xZnx)5.
Journal of the Physical Society of Japan, 2014, [Reviewed]

Novel Magnetic Chiral Structures and Unusual Temperature Hysteresis in the Metallic Helimagnet MnP
T. Yamazaki; Y. Tabata; T. Waki; T. J. Sato; M. Matsuura; K. Ohoyama; M. Yokoyama and H. Nakamura, We have reinvestigated the magnetic properties of the classical metallic helimagnet MnP by magnetization and neutron scattering experiments. Our neutron scattering results indicate that the previously reported magnetic structure in the low-temperature (LT) helimagnetic phase (T < 47 K) should be modified to an alternately tilted helimagnetic structure produced by the Dzyaloshinsky-Moriya interaction. In the intermediate temperature (IT) range between the LT helimagnetic phase and the high-temperature (HT) ferromagnetic phase along the c-axis, 47 < T < 252 K, we have found a weak ferromagnetic behavior along the b-axis. Surprisingly, the IT weak ferromagnetic phase has two different states, namely, the large magnetization (LM) and small magnetization (SM) states. The SM state emerges with cooling from the paramagnetic phase above 292K via the HT ferromagnetic phase and LM state emerges with warming from the LT helimagnetic phase. The weak ferromagnetism along the b-axis and the unusual temperature hysteresis in the IT phase can be understood by assuming a spontaneous formation of the stripe structure consisting of alternately arranged HT ferromagnetic and LT helimagnetic domains., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2014, [Reviewed]

〔Major achievements〕Ferromagnetic Cluster-Glass State in Itinerant Electron System Sr1-xLaxRuO3
I. Kawasaki; M. Yokoyama; S. Nakano; K. Fujimura; N. Netsu; H. Kawanaka and K. Tenya, Corresponding, The magnetic and electronic properties of Sr1-xLaxRuO3 were studied by means of dc-magnetization, ac-susceptibility, specific heat, and electrical resistivity measurements. The dc-magnetization and ac-susceptibility measurements have revealed that the transition temperature and the ordered moment of the ferromagnetic order are strongly suppressed as La is substituted for Sr. The ac-susceptibility exhibits a peak at T* due to the occurrence of spontaneous spin polarization. Furthermore, we observed that T* shows clear frequency variations for x >= 0.3. The magnitude of the frequency shifts of T* is comparable to that of cluster-glass systems, and the frequency dependence is well described in terms of the Vogel-Fulcher law. On the other hand, it is found that the linear specific heat coefficient gamma enhances with the suppression of the ferromagnetic order. The relatively large gamma values reflect the presence of the Ru 4d state at Fermi level, and hence, the magnetism of this system is considered to be tightly coupled with the itinerant characteristics of the Ru 4d electrons. The present experimental results and analyses suggest that the intrinsic coexistence of the spatially inhomogeneous magnetic state and the itinerant nature of the Ru 4d electrons is realized in this system, and such a feature may be commonly involved in La- and Ca-doped SrRuO3., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2014, [Reviewed]

Evolution of Ferromagnetic Clusters Originating from Itinerant Ru 4d Electrons in Sr1-xLaxRuO3　　　　　　　　　　　　　　　
M. Yokoyama; S. Nakano; S. Ishikawa; N. Wada; S. Takeuchi; I. Kawasaki; H. Kawanaka and K. Tenya, Lead
JPS Conference Proceedings, 2014, [Reviewed]

Polarized Light Microscopic Study of the Hidden Order Phase in URu2Si2　　　　　　　　　　　　　　　
C. Tabata; M. Tokunaga; M. Yokoyama; H. Hidaka; T. Yanagisawa and H. Amitsuka
JPS Conference Proceedings, 2014, [Reviewed]

X-ray backscattering study of crystal lattice distortion in hidden order of URu2Si2
C. Tabata; T; Inami; S. Michimura; M. Yokoyama; H. Hidaka; T. Yanagisawa and H. Amitsuka, We performed synchrotron X-ray diffraction measurements on a small single crystal of
[GRAPHICS]
with approximate dimensions of
[GRAPHICS]
. A backscattering diffraction set-up (2
[GRAPHICS]
) in combination with a Si(660) monochromator ensures a high instrumental resolution of
[GRAPHICS]
, where
[GRAPHICS]
denotes a lattice-plane spacing and
[GRAPHICS]
is its spread expressed as the full width at half maximum (FWHM). We carefully measured the (550) Bragg peak in the temperature range between 5 and 25K, and found it to show no signature of broadening and splitting when "Hidden Order (HO)" sets in below 17.5K. Temperature variation of the peak position closely follows the behaviour of the known linear thermal expansion coefficient. Detailed analysis of the peak width reveals that the tetragonal fourfold rotational symmetry of
[GRAPHICS]
is conserved in HO within the experimental accuracy of the orthorhombicity of
[GRAPHICS]
. We also found that the (550) peak profile exhibits a temperature-independent fine structure, which indicates that the tetragonal
[GRAPHICS]
-axis lattice parameter of the used crystal is distributed with a FWHM of
[GRAPHICS]
., TAYLOR & FRANCIS LTD
Philosophical Magazine, 2014, [Reviewed]

Investigation of Local Symmetries in the Hidden-Order Phase of URu2Si2
T. Mito; M. Hattori; G. Motoyama; Y. Sakai; T. Koyama; K. Ueda; T. Kohara; M. Yokoyama and H. Amitsuka, The local symmetry at the Ru(4d) and Si(4e) sites in URu2Si2 was investigated above and below the hidden-order temperature T-O = 17.5K by measuring Ru-101-nuclear quadrupole resonance (NQR) and Ru-99-nuclear magnetic resonance (NMR) in single-crystalline samples and Ge-73-NMR in a 10%-Ge-73-substituted polycrystalline sample. For both sites, no evidence of symmetry change below T-O was observed. The asymmetry parameter eta of the electric field gradient, which reflects the local rotation symmetry, was estimated to be zero with accuracies of 0.0010-0.0015 and 0.05 for the 4d and 4e sites, respectively. The results suggest that the symmetry change at T-O is extremely small or intrinsically invisible by the present method., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2013, [Reviewed]

〔Major achievements〕Emergence of Magnetic Long-range Order in Frustrated Pyrochlore Nd2Ir2O7 with Metal-Insulator Transition
K. Tomiyasu; K. Matsuhira; K. Iwasa; M. Watahiki; S. Takagi; M. Wakeshima; Y. Hinatsu; M. Yokoyama; K. Ohoyama; and K. Yamada, In this study, we performed powder neutron diffraction and inelastic scattering measurements of frustrated pyrochlore Nd2Ir2O7, which exhibits a metal-insulator transition at a temperature T-MI of 33 K. The diffraction measurements revealed that the pyrochlore has an antiferromagnetic long-range structure with propagation vector q(0) of (0, 0, 0) and that it grows with decreasing temperature below 15 K. This structure was analyzed to be of the all-in all-out type, consisting of highly anisotropic Nd3+ magnetic moments of magnitude 2.3 +/- 0.4 mu(B), where mu(B) is the Bohr magneton. The inelastic scattering measurements revealed that the Kramers ground doublet of Nd3+ splits below T-MI. This suggests the appearance of a static internal magnetic field at the Nd sites, which probably originates from a magnetic order consisting of Ir4+ magnetic moments. Here, we discuss a magnetic structure model for the Ir order and the relation of the order to the metal-insulator transition in terms of frustration., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2012, [Reviewed]

Symmetry of the Hidden Order in URu2Si2 from Nuclear Magnetic Resonance Studies
S. Takagi; S. Ishihara; M. Yokoyama and H. Amitsuka, The hidden order (HO) in URu2Si2 has been investigated by both Si-29 and Ru-99 NMR on a single crystal. Tiny, but finite additional broadening of the spectrum in the HO phase in both Si-29 and Ru-99 NMR with external magnetic field applied along the crystallographic [100] or [110] direction, and its persistence as H-ext -> 0 in Si-29 NMR clearly indicate the existence of internal hyperfine field, and the breaking of the time-reversal symmetry in the HO phase can therefore be concluded. We discuss which symmetry of the D-4h symmetry group of the URu2Si2 crystal structure is compatible with the observed dependence on the crystal-axis direction of the existence or nonexistence of the internal hyperfine field. Then, by imposing a strong constraint that the wave-vector of the HO is also Q(0) = [0, 0, 1], the wave-vector of the pressure-induced antiferromagnetism, we show that the two-dimensional representation E-remains as the only possible candidate for the HO symmetry. Since dipoles are obviously excluded from the major HO parameter, we conclude the E-multipole (octupole or triakontadipole) to be the HO parameter. We further discuss that the E- multipole, but with no associated dipoles, seems to be a key feature of the HO in URu2Si2., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2012, [Reviewed]

Neutron Scattering Study on Commensurate and Incommensurate Antiferromagnetic Phases in UPd2Si2 under Uniaxial Stress
T. Nakada; M. Yokoyama; C. Tabata; H. Igarashi; H. Hidaka; H. Amitsuka; K. Tenya and T. J. Sato, Corresponding, The nature of competition between incommensurate (IC) and commensurate (C) antiferromagnetic (AF) orders in UPd2Si2 was investigated by performing elastic neutron scattering experiments under uniaxial stress σ. It is found that applying σ along tetragonal [010] direction reduces the IC-AF order, and then stabilizes the C-AF order. The transition temperature from IC- to C-AF phases TNl is enhanced from 109 K (σ = 0) to 112.5 K at (0.8 GPa), while the onset of IC-AF transition TNh is unchanged from 132 K under σ. In addition, c-axis component qz of the IC-AF modulation at 115 K also increases from 0.736 (σ = 0) to 0.747 (0.8 GPa). The magnitude of C-AF moment at 5 K is estimated to be 2.2 μB/U in the entire σ range presently investigated (σ ≤ 0.8 GPa). These features are similar to those obtained from the investigations using hydrostatic pressure p, indicating that applications of p and σ∥ [010] commonly induce the crystal strains which inherently affect a delicate balance of frustrated magnetic interactions between uranium 5f moments. © 2012 The Physical Society of Japan.
Journal of the Physical Society of Japan, 2012, [Reviewed]

Low-temperature specific heat for ferromagnetic and antiferromagnetic orders in CaRu1-xMnxO3
M. Yokoyama; S. Nakano; S. Someya; T. Nakada; N. Wada; H. Kawanaka; H. Bando; K. Tenya; A. Kondo and K. Kindo, Lead, Low-temperature specific heat of CaRu1-xMnxO3 was measured to clarify the role of d electrons in ferromagnetic and antiferromagnetic orders observed above x = 0.2. Specific heat divided by temperature C-p/T is found to roughly follow a T-2 function, and relatively large magnitudes of electronic specific heat coefficient gamma were obtained in wide x range. In particular, gamma is unchanged from the value at x = 0 (84 mJ/K-2 mol) in the paramagnetic state for x <= 0.1, but linearly reduced with increasing x above x = 0.2. These features of gamma strongly suggest that itinerant d electrons are tightly coupled with the evolution of magnetic orders in small and intermediate Mn concentrations., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2012, [Reviewed]

NMR and NQR investigations of local symmetry in the hidden order phase of URu2Si2
T. Mito; M. Hattori; G. Motoyama; Y. Sakai; T. Koyama; K. Ueda; T. Kohara; M. Yokoyama and H. Amitsuka, In order to study local symmetries at the 4e(Si)- and 4d(Ru)-sites above and below hidden order transition temperature T-O = 17.5 K in URu2Si2, we have investigated the nuclear quadrupole interaction by Ge-73-nuclear magnetic resonance (NMR) measurement on a 10% Ge-73-substituted sample URu2(Si0.9Ge0.1)(2), and by Ru-101-nuclear quadrupole resonance (NQR) measurement on a pure single crystal sample. The present Ge-73-NMR measurements do not give any evidence for change in the local symmetry at 4e-site within experimental accuracy. On the other hand, the precise measurement of Ru-101-NQR frequency has detected an anomaly just below T-O as sensitively as the thermal expansion measurement dose. Its temperature dependence shows a linear relation with that of the in-plane lattice parameter, which may be a clue to clarify a modification in microscopic charge distribution at T-O., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2012, [Reviewed]

Thermal fluctuations in perpendicular recording media: New methodology for estimation of activation moment
H. Mamiya; H. Hagiya; Y. Oba; M. Ohnuma; T. Oku; J. Suzuki; M. Yokoyama; T. Katayama; Y. Nishihara; H. Awano and T. Koda, In nanoparticulate films with perpendicular magnetic anisotropy, a large demagnetizing field almost compensates for the experimentally designed change in the magnetic field applied parallel to the film normal. We propose a new method based on field-cycling to eliminate the uncertainty in the demagnetizing response from the analysis of the activation volume of the reversal or magnetic activation moment in such films. In this method, the applied field induced variation in the magnetic relaxation rate is measured before the effect of the demagnetizing field becomes dominant. We also discuss an analogical thermal-cycling method to clarify the temperature dependence of the barrier height for magnetization reversal in a magnetic field. We apply these methods to a Co74Pt16Cr10-SiO2 nanoparticulate film as an example. The results demonstrate that these methods are useful for studying thermal fluctuations in perpendicular recording media., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2011, [Reviewed]

Interplay between quantum criticality and geometric frustration in Fe3Mo3N with stella quadrangula lattice
T. Waki; S. Terazawa; T. Yamazaki; Y. Tabata; K. Sato; A. Kondo; K. Kindo; M. Yokoyama; Y. Takahashi and H. Nakamura, We propose the eta-carbide-type correlated-electron metal Fe3Mo3N as a new candidate for testing geometric frustration in itinerant-electron magnets. In this compound, ferromagnetism is abruptly induced from a non-magnetic non-Fermi-liquid ground state either when a magnetic field (similar to 14T) applied to it or when it is doped with a slight amount of impurity (similar to 5%Co). We observed a peak in the paramagnetic neutron scattering intensity at finite wave vectors, revealing the presence of the antiferromagnetic correlation hidden in the magnetic measurements. It causes a new type of geometric frustration in the stella quadrangula (SQ) lattice of the Fe sublattice, which is a corner-shared lattice of two nested regular tetrahedrons. Although the SQ lattice is one of pyrochlore-derived lattices, we anticipate the unique nature of the frustration due to the competition between first-and second-neighbour interactions, J(1) and J(2), possibly of direct exchange type. We propose that the frustrated antiferromagnetic correlation suppresses the ferromagnetic correlation to its marginal point and is therefore responsible for the origin of the ferromagnetic quantum critical behaviour in pure Fe3Mo3N Copyright (C) EPLA, 2011, EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY
EPL(Europhysics Letters), 2011, [Reviewed]

73Ge-NMR Investigation of the Hidden Order in URu2Si2
T. Mito; M. Hattori; G. Motoyama; H. Sakai; T. Koyama; K. Ueda; T. Kohara; M. Yokoyama and H. Amitsuka, In order to investigate the local symmetry at the Si(4e)-site above and below hidden order temperature T-O = 17.5 K in URu2Si2, we have carried out Ge-73-nuclear magnetic resonance (NMR) measurement on 10% Ge-73-substituted sample URu2(Si0.9Ge0.1)(2). The specific heat measurement on the present sample shows a clear second-order transition, indicating that the hidden order is still a bulk property. Besides, equally split Ge-73-NMR lines due to the nuclear quadrupole interaction gives evidence for fairly uniform electric-field gradient at the Ge-substituted sites, Although this is the first attempt to investigate the local symmetry at the 4e-site by proving electric interactions, no evidence for symmetry lowering below T-O has been obtained at present., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2011, [Reviewed]

Crystalline electric field study in the pyrochlore Nd(2)Ir(2)O(7) with metal-insulator transition
M. Watahiki; K. Tomiyasu; K. Matsuhira; K. Iwasa; M. Yokoyama; S. Takagi; M. Wakeshima; Y. Hinatsu, We carried out inelastic neutron scattering measurements to identify crystalline electric field (CEF) states of Nd(3+) (a total angular momentum J = 9/2) in Nd(2)Ir(2)O(7), which exhibits a metal-insulator transition at T(MI) = 36 K. Excitation peaks observed around 26 and 41 meV are interpreted as CEF excitations within five Kramers doublets. It is notable that splitting of the ground doublet by 1.3 meV was microscopically observed at 3 K for the first time, indicating emergence of magnetic long-range order despite geometrical frustration. The splitting width decreases with increasing the temperature towards T(MI) like an order parameter of the transition. We discuss the results in light of Nd-Ir interactions., IOP PUBLISHING LTD
INTERNATIONAL CONFERENCE ON FRUSTRATION IN CONDENSED MATTER (ICFCM), 2011, [Reviewed]

Molecular spin-liquid state in the spin-3/2 frustrated spinel HgCr2O4
K. Tomiyasu; H. Ueda; M. Matsuda; M. Yokoyama; K. Iwasa and K. Yamada, A hexamer-type spin excitation seen in spinel chromates ACr(2)O(4) (A = Mg, Zn, or Cd) is the representative spin-liquid-like state caused by geometrical frustration. To clarify an origin of the state, we comparatively studied spin excitations in an isomorphic material HgCr2O4 by inelastic neutron scattering and observed a different molecular-type excitation. Numerical analyses performed using model Hamiltonians suggest that these two types of spin excitations originate from a spin-3/2 molecular singlet hidden in a magnetically ordered phase. The difference between the molecular types is explained by the difference in the kind of exchange interactions occurring in the chromates., AMER PHYSICAL SOC
Physical Review B, 2011, [Reviewed]

Elastic constants of U(Ru1-xRhx)2Si2
T. Yanagisawa; H. Saito; T. Mayama; Y. Ikeda; H. Hidaka; M. Yokoyama and H. Amitsuka, {IOP} Publishing
Journal of Physics: Conference Series, 2010, [Reviewed]

Elastic constants of U(Ru1-xRhx)(2)Si-2
T. Yanagisawa; H. Saito; T. Mayama; Y. Ikeda; H. Hidaka; M. Yokoyama; H. Amitsuka, Ultrasonic measurements on Rh-substitution system U(Ru1-xRhx)(2)Si-2 (x = 0,0.02 and 0.07) were performed in order to investigate lattice properties for low temperature phase transitions of 'hidden order'(HO) phase and antiferromagnetc (AFM) phase. Elastic constant C-11 vs. T of the x = 0.02 and 0.07 samples exhibit a depression below 80 K, which is similar to a softening in the non-doped sample which had already been reported. The C-11 of x = 0.02 exhibits a step-like anomaly at 14.0 K and an additional softening of 3.2% with minimum at 6.7 K, which correspond to HO and AFM transitions, respectively. The C-11 in x = 0.07 sample only exhibits a shoulder-like anomaly at around 17 K and continue to depress down to 4.2 K., IOP PUBLISHING LTD
INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009), 2010, [Reviewed]

Coexistence of Ferromagnetic and Antiferromagnetic States in CaRu1-xMnxO3
H. Kawanaka; A. Noguchi; M. Yokoyama; H. Bando and Y. Nishihara, Effect of Mn substitution in paramagnetic metal CaRuO3 was studied by magnetization measurements. Development of ferromagnetic order was observed for x >= 0.2 in CaRu1-xMnxO3. The ratio of the effective moment and the spontaneous magnetization P-eff/M(0) is much larger than one in this ferromagnetic state. At low temperatures the antiferromagnetic order coexists with the ferromagnetic one and the magnetization is significantly suppressed with decreasing temperature. The magnetic phase diagram in CaRu1-xMnxO3 with 0.3 <= x <= 0.8 estimated from the magnetization measurements is reported., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2010, [Reviewed]

Search for Hidden Order Parameter of URu2Si2 by Neutron-Scattering Experiment under Uniaxial Stress
Y. Ikeda; M. Yokoyama; D. Nishikawa; H. Hidaka; T. Yanagisawa; K. Tenya; S. Kawarazaki; T.J. Sato; H. Yoshizawa and H. Amitsuka, Elastic neutron-scattering experiment was performed on the heavy-fermion superconductor URu2Si2 under uniaxial stress in order to search a sign of a hidden order parameter. Contour maps of neutron-scattering at 1.5 K were achieved by mesh scanning. No additional magnetic signal exists in (h0l) and (hhl) planes except for a well-known weak antiferromagnetic signal with magnetic-propagation vector of Q = (100) within the present experimental accuracy and scanned area. © 2010 IOP Publishing Ltd.
Journal of Physics: Conference Series, 2010, [Reviewed]

Resonant X-ray Scattering Study of Hidden Order in URu2Si2 using a Low-Stress Single Crystal
H. Amitsuka; T. Inami; M. Yokoyama; S. Takayama; Y. Ikeda; I. Kawasaki; Y. Homma; H. Hidaka and T. Yanagisawa, We have studied a puzzling phase below 17.5 K of URu2Si2 by means of resonant Xray scattering (RXS) near the U M-IV absorption edge (E similar to 3.73 keV), using a high-quality single-crystalline sample with low residual stress. We reconfirm that a commensurate (003) superlattice reflection comes purely from antiferromegnetic dipolar order with ordering wave vector Q(AF) = (1, 0, 0). No other traces of significant RXS have been detected in a major region of (h0l) plane, indicating absence of quadrupolar order within a searched Q range including a conceivable nesting vector Q* = (1.4, 0, 0)., IOP PUBLISHING LTD
Journal of Physics: Conference Series, 2010, [Reviewed]

Magnetic-field dependence of antiferromagnetic structure in CeRh(1-x)Co(x)In(5)
M. Yokoyama; Y. Ikeda; I. Kawasaki; D. Nishikawa; K. Tenya; K. Kuwahara; H. Amitsuka, Lead, We investigated effects of magnetic field H on antiferromagnetic (AF) structures in CeRh(1-x)Co(x)In(5) by performing the elastic neutron scattering measurements. By applying H along the [1 (1) over bar0] direction, the incommensurate AF state with the propagation vector of q(h1) = (1/2, 1/2, 0.297) observed at H = 0 is replaced by the commensurate AF state with the q(c2) = (1/2, 1/2, 1/4) modulation above 2 T for x = 0.23, while the AF states with the q(c1) = (1/2, 1/2, 1/2) and q(h2) = (1/2, 1/2, 0.42) modulations seen at H = 0 change into a single q(c1)-AF state above similar to 1.6 T for x = 0.7. These results suggest the different types of AF correlation for Co concentrations of 0.23 and 0.7 in an applied magnetic field H., IOP PUBLISHING LTD
INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009), 2010, [Reviewed]

Specific-heat study for ferromagnetic and antiferromagnetic phases in SrRu(1-x)Mn(x)O(3)
A. Yamaji; M. Yokoyama; Y. Nishihara; Y. Narumi; K. Kindo, Corresponding, Low-temperature electronic states in SrRu(1-x)Mn(x)O(3) for x <= 0.6 have been investigated by means of specific-heat C(p) measurements. We have found that a jump anomaly observed in C(p) at the ferromagnetic (FM) transition temperature for SrRuO(3) changes into a broad peak by only 5% substitution of Mn for Ru. With further doping Mn, the low-temperature electronic specific-heat coefficient gamma is markedly reduced from the value at x = 0 (33 mJ/K(2) mol), in connection with the suppression of the FM phase as well as the enhancement of the resistivity. For x >= 0.4, gamma approaches to similar to 5 mJ/K(2) mol or less, where the antiferromagnetic order with an insulating feature in resistivity is generated. We suggest from these results that both disorder and reconstruction of the electronic states induced by doping Mn are coupled with the magnetic ground states and transport properties., IOP PUBLISHING LTD
INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009), 2010, [Reviewed]

Electronic structure of SrRu1-xMnxO3 studied by photoemission and x-ray absorption spectroscopy
K. Horiba; H. Kawanaka; Y. Aiura; T. Saitoh; C. Satoh; Y. Kikuchi; M. Yokoyama; Y. Nishihara; R. Eguchi; Y. Senba; H. Ohashi; Y. Kitajima and S. Shin, In order to investigate the change in the electronic structure with Mn doping of SrRu1-xMnxO3 (SRMO), we have performed soft x-ray synchrotron photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). In the soft x-ray PES spectra, the sharp peak structure near the Fermi level (E-F), which was clearly observed in SrRuO3, was suppressed accompanied with Mn doping in SRMO. In the Mn 2p XAS and Mn 2p-3d resonant PES spectra, we have confirmed the existence of Mn3+ ions with the electron doping to Mn 3d e(g) states and Mn 3d partial density of state never have finite intensity at E-F in SRMO. These results suggest that the metal-insulator transition of SRMO with Mn doping is originated from the charge transfer from the itinerant Ru 4d t(2g) bands to the localized Mn 3d e(g) orbitals., AMER PHYSICAL SOC
Physical Review B, 2010, [Reviewed]

Itinerant electron magnetism in CaRu_1-xMn_xO₃ (0 ≦ x ≦ 0.5)
H. Kawanaka; M. Yokoyama; A. Noguchi; H Bando; Y. Nishihara, Corresponding, The effect of Mn substitution in paramagnetic metal CaRuO3 was studied by magnetization and neutron diffraction measurements. Development of ferromagnetic order is observed for x >= 0.2 in CaRu1-xMnxO3. For the sample with x = 0.4, the Curie temperature of similar to 160 K is obtained from the Arrott plot and the ratio of effective moment and saturation moment P-eff/M(0) is estimated to be similar to 4.8. We further found that the magnetization is significantly suppressed with decreasing temperature T below similar to 90 K. In the neutron diffraction experiment at T = 15 K, we observed the evolution of a magnetic Bragg peak originating from the G-type antiferromagnetic order as well as the ferromagnetic one. This strongly suggests that both ferromagnetic and antiferromagnetic states are coexistent with each other at low temperatures. In the M(T)(0)(2) against T-2 plot (here, M(T)(0) is a spontaneous magnetization estimated from the Arrott plot), M(T)(0)(2) linearly increases with decreasing T-2 in the ferromagnetic region between similar to 90 and 160 K. The ferromagnetic properties of the CaRu1-xMnxO3 system (x <= 0.5) are well explained in terms of spin fluctuation theory based on the itinerant electron model rather than the localized spin model., IOP PUBLISHING LTD
Journal of Physics: Condensed Matter, 2009, [Reviewed]

Effects of Co doping on antiferromagnetic structure in CeRhIn₅
M. Yokoyama; I. Kawasaki; S. Oinuma; N. Oyama; K. Tenya; H. Amitsuka, Lead, We performed the elastic neutron scattering experiments on the mixed compounds CeRh1-xCoxIn5, and found that doping Co into CeRhIn5 dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of q(h) = (1/2,1/2,similar to 0.3) observed in pure CeRhIn5 is suppressed with increasing x, and new AF states with an incommensurate q(1) = (1/2,1/2,similar to 0.4) and a commensurate q(c) = (1/2,1/2,1/2) modulations simultaneously develop near the AF quantum critical point: x(c)similar to 0.8. These results suggest that the AF correlations with the q(c) and q(1) modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above x similar to 0.4. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2009, [Reviewed]

Small-angle polarized neutron scattering study of spherical Fe₁₆N₂ nano-particles for magnetic,recording tape
T. Oku; T. Kikuchi; T. Shinohara; J. Suzuki; Y. Ishii; M. Takeda; K. Kakurai; Y. Sasaki; M. Kishimoto; M. Yokoyama; Y. Nishihara, We have performed small-angle polarized neutron scattering experiments of spherical Fe16N2 nanoparticles, which are potential candidate materials for high density magnetic recording tape. The results were analyzed based on a core-shell model, and we evaluated the magnetic structure of the particles. The correlation between the magnetic structure and magnetic stability of the particles were discussed in terms of high density recordings. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2009, [Reviewed]

Magnetic properties around quantum critical point of CePt_1-xRh_x
I. Kawasaki; D. Nishikawa; H. Hidaka; T. Yanagisawa; K. Tenya; M. Yokoyama; H. Amitsuka, In order to investigate magnetic properties around a quantum critical point of CePt1-xRhx alloys, we have performed the ac-susceptibility (chi(ac)) measurements with field frequency ranging from omega/2 pi = 0 (dc magnetization) to 1113 Hz for temperature down to 100mK on polycrystalline CePt1-xRhx (x = 0.5, 0.6). The in-phase component of chi(ac) exhibits a pronounced peak at T-f. The peak magnitude and T-f show significant field-frequency dependence. In addition, a staircaselike hysteresis loop of magnetization was observed below 200mK. From the dynamical analyses of chi(ac) we suggest that CePt0.5Rh0.5 and CePt0.4Rh0.6 can be described as cluster-glass systems. (C) 2009 Published by Elsevier B.V., ELSEVIER SCIENCE BV
Physica B, 2009, [Reviewed]

〔Major achievements〕Change of antiferromagnetic structure near a quantum critical point in CeRh1-x Cox In5
M. Yokoyama; N. Oyama; H. Amitsuka; S. Oinuma; I. Kawasaki; K. Tenya; M. Matsuura; K. Hirota; T. J. Sato, Lead, The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-x Cox In5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: xc ∼0.8. The incommensurate AF order with the wave vector of qh = (1/2,1/2,∼0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate qc = (1/2,1/2,1/2) and an incommensurate q1 = (1/2,1/2,∼0.42) AF structures evolve at intermediate Co concentrations. The AF orders with qc and q1 are enhanced at x=0.7, and furthermore, the qh AF order vanishes. These results suggest that the AF correlations with the qc and q1 modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x∼0.3. © 2008 The American Physical Society.
Physical Review B - Condensed Matter and Materials Physics, 03 Jun. 2008, [Reviewed]

〔Major achievements〕Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu(2)Si(2)
K. Yano; T. Sakakibara; T. Tayama; M. Yokoyama; H. Amitsuka; Y. Homma; P. Miranovic; M. Ichioka; Y. Tsutsumi; K. Machida, To identify the superconducting gap structure in URu(2)Si(2), we perform field-angle-dependent specific heat measurements for the two principal orientations in addition to field rotations, and a theoretical analysis based on microscopic calculations. The Sommerfeld coefficient gamma(H)'s in the mixed state exhibit a distinctly different field dependence. This comes from point nodes and the substantial Pauli paramagnetic effect of URu(2)Si(2). These two features combined give rise to a consistent picture of superconducting properties, including a possible first order transition of H(c2) at low temperatures., AMER PHYSICAL SOC
PHYSICAL REVIEW LETTERS, Jan. 2008, [Reviewed]

Polarized neutron scattering study on antiferromagnetic states in CeRh_0.6Co_0.4In₅
M. Yokoyama; N. Oyama; H. Amitsuka; S. Oinuma; I. Kawasaki; K. Tenya; M. Matsuura; K. Hirota, Lead, Polarized neutron scattering experiments were performed on mixed compound CeRh0.6Co0.4In5 to clarify the nature of the low-temperature ordered states. Three nonequivalent Bragg peaks, characterized by the wave vectors of q(h)similar to(1/2,1/2,0.3), q(1)similar to(1/2,1/2,0.4) and q(c) = (1/2, 1/2, 1/2), were observed at 1.4K. These Bragg peaks are found to occur entirely in spin-flip channel. This indicates that these Bragg peaks originate from the magnetic scattering, i.e., the antiferromagnetic orders with three different modulations appear in this compound. (c) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2008, [Reviewed]

Dependence of pressure-induced phase transitions on pressure-transmitting media in the heavy-electron superconductor URu₂Si₂
H. Amitsuka; K. Matsuda; M. Yokoyama; I. Kawasaki; S. Takayama; Y. Ishihara; K. Tenya; N. Tateiwa; T.C. Kobayashi; H. Yoshizawa, Elastic neutron-scattering and ac-susceptibility measurements have been performed on a 20 single crystal of URu2Si2 under hydrostatic pressure up to similar to 1.1 GPa using Fluorinert 70 & 77 and Daphne oil 7373 as pressure-transmitting media. Daphne oil produces better hydrostaticity of the applied pressure than Fluorinert, resulting in a slight shift of the phase boundary between hidden order and antiferromagnetic order to a lower pressure. The superconducting phase is also influenced, but never overlaps with the antiferromagnetic phase. (c) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2008, [Reviewed]

Probing the nodal structures of heavy electron superconductors by means of specific heat measurements in magnetic fields
T. Sakakibara; J. Custers; K. Yano; A. Yamada; T. Tayama; Y. Aoki; H. Sato; H. Sugawara; H. Amitsuka; M. Yokoyama, Last, Measurements of the angle-resolved specific heat C(H, theta) have been performed on PrOs4Sb12 and PrOs4Sb12 in order to examine their superconducting gap structures. In the filled skutterudite PrOs4Sb12, a clear fourfold angular dependence is observed with H rotated in the (10 0) planes, whose field variation suggests gap minima along [10 0] directions. Interestingly, a reversed angular oscillation of C(H, theta) has been observed in the normal state above H-c2 which continues to grow as the high-field antiferroquadrupole phase is approached. In URu2Si2, C(H, theta) with H rotated around the tetragonal c-axis suggests that the nodal structure has rotational symmetry. Comparison between the C(H) data for a- and c-axes indicates the existence of point nodes along the [0 0 1] direction. (c) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2008, [Reviewed]

Anomalous pinning behavior in Sr₂RuO₄
K. Tenya; R. Yamahana; M. Yokoyama; H. Amitsuka; K. Deguchi; Y. Maeno, In order to investigate the chiral-superconducting characteristics as well as the vortex-pinning properties, detailed magnetization measurements of the single crystal Sr2RuO4 have been performed in the field parallel to the [0 0 1] direction. Anomalous pinning features are found at weak fields in the magnetization curves: Tiny flux-jumps successively appear around zero field at temperatures up to at least 0.2 K. At higher temperatures, a small peak of the hysteretic magnetization is observed below 0.1 kOe, which is so-called second magnetization peak (SNIP). The magnitude of the hysteretic magnetization is strongly dependent on (independent of) the field-gradient in the field region below (above) the field where the SNIP appears. Possible origins are discussed from the viewpoints of the pairing symmetry together with the topological change in the vortex-lattice configuration. (C) 2007 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2008, [Reviewed]

Quantum critical phenomena of ferromagnetic CePt_1-xRh_x
I. Kawasaki; K. Tenya; M. Yokoyama; H. Amitsuka, We have performed specific heat C and magnetic susceptibility chi measurements on the pseudo-binary alloys CePt1-xRhx, synthesized by mixing CePt (a ferromagnetic Kondo-lattice system) and CeRh (an intermediate valence system). As Rh is substituted for Pt, CePt1-xRhx shows a continuous change in the ground state from ferromagnetic order (T-C similar to 6K at x = 0) to a nonmagnetic valence-fluctuation state for x > 0.8. We found a non-Fermi-liquid-like behavior which is characterized by the power law T dependence of C(T) and chi(T), for a wide x range above the ferromagnetic quantum critical point (x(c)similar to 0.8). (C) 2007 Elsevier B.V. All rights reserved., ELSEVIER
Physica B, 2008, [Reviewed]

Low-energy magnetic fluctuations in U(Ru1-xRhx)(2)Si-2(x <= 0.02)
M. Yokoyama; K. Matsuda; H. Amitsuka; K. Tenya; N. Aso; H. Yoshizawa, Lead, Inelastic neutron scattering experiments were performed on U(Ru1-x xRh(x))(2)Si-2 with x 0 and 0.02 in order to investigate the variations of the antiferromagnetic ( AF). fluctuations with doping Rh. We have found that the energy of the magnetic excitation observed at Q (1, 0, 0) in the hidden order (HO) phase markedly decreases from similar to 2.6meV (x = 0) to similar to 0 (x = 0.02) with increasing x. In addition, the staggered susceptibility chi Q estimated from the inelastic peak develops in the HO phase at x 0.02, while it is suppressed at x = 0. These results indicate that the AF. fluctuation in the HO phase is signifi. cantly enhanced with doping Rh. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, Mar. 2007, [Reviewed]

Neutron-scattering and magnetization study on URu₂Si₂ under hydrostatic pressure using a Cu-Be pressure cell
K. Matsuda; M. Yokoyama; K. Tenya; H. Amitsuka; H. Yoshizawa, We have performed the elastic neutron-scattering and the AC magnetic susceptibility measurements under hydrostatic pressure for URu2Si2 to construct a reliable T-P phase diagram, focusing on the relationship between the hidden order (HO), pressure-induced antiferromagnetism (AF), and non-BCS-type superconductivity (SC). For this purpose, we used the same pressure condition and the same single crystalline sample through all the measurements, because the HO-to-AF phase transition is very sensitive to the experimental conditions such as the quality of sample and applied pressure. The neutron scattering experiment performed under pressures ranging from P = 0.5 to 1.07 GPa showed that the phase transition between HO and AF occurs very sharply at P-M = 0.7GPa for T -> 0. The ordered moment mu(o) of the high-pressure AF phase is estimated to be similar to 0.4 mu(B)/U. (c) 2006 Elsevier B. V. All rights reserved., ELSEVIER SCIENCE BV
Journal of Magnetism and Magnetic Materials, 2007, [Reviewed]

Pressure-temperature phase diagram of the heavy-electron superconductor URu₂Si₂
H. Amitsuka; K. Matsuda; I. Kawasaki; K. Tenya; M. Yokoyama; C. Sekine; N. Tateiwa; T.C. Kobayashi; S. Kawarazaki; H. Yoshizawa
Journal of Magnetism and Magnetic Materials, 2007, [Reviewed]

Magnetism of insulator phase in SrRu_1-xMn_xO₃ (0.4 ≦ x ≦ 0.6)
H. Kawanaka; C. Satoh; M. Yokoyama; H. Kitazawa; O. Suzuki; G. Kido; H. Bando; Y. Nishihara, Temperature dependence of magnetization was measured in the insulator phase of SrRu1-xMnxO3 (0.4 <= x <= 0.6) at magnetic fields up to 15 T. For the sample with x = 0.6, the peak of the magnetization changes from 210 to 250 K with increasing magnetic field up to 5 T and slightly decreases above it. The paramagnetic Curie-Weiss temperature is positive (180 K). The anti-ferromagnetic Neel temperature obtained from the neutron diffraction experiment agrees with the peak temperature measured in high magnetic fields. Discussion of the magnetization peak in high and low magnetic fields is given. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Journal of Magnetism and Magnetic Materials, 2007, [Reviewed]

No Evidence for “Small-Moment Antiferromagnetism” under Ambient Pressure in URu₂Si₂: Single-Crystal ²⁹Si NMR Study
S. Takagi; S. Ishihara; S. Saitoh; H. Sasaki; H. Tanida; M. Yokoyama; H. Amitsuka, The still unidentified hidden order (HO) phase below T-0 = 17.5 K in the heavy-electron superconductor URu2Si2 has been investigated by Si-29 NMR on a single crystal under external magnetic field H-ext || c-axis and ambient pressure P. For a previously proposed model of the small-moment antiferromagnetism (SMAF), in which tiny-moment antiferromagnetism (AF) under ambient P is ascribed to spatially homogeneous AF with an ordered moment mu(SMAF) = 0.02-0.04 mu(B), splitting of the line would be expected on the basis of a scaling from the corresponding splitting in the P-induced AF. However, we observed at T = 4.5 K no splitting of the line. This clearly indicates that the SMAF model cannot describe the ambient-P properties. Below To down to similar to 14 K, the 29 Si NMR line shows additional broadening over the paramagnetic width. The additional contribution, however, disappears below similar to 14 K, which indicates that the HO itself produces almost zero internal field at the 29Si site along the c-axis at low temperatures in the HO phase., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2007, [Reviewed]

Relation between magnetism and metal-insulator transition in Mn-doped SrRuO₃　　　　　　　　　　　　　　　
M. Yokoyama; C. Satoh; K. Fujita; Y. Nishihara; H. Kawanaka and H. Bando, Lead
Topological Aspects of Critical Systems and Networks (World Scientific Publishing), 2007, [Reviewed]

”Magnetization study of pairing and vortex states in Sr₂RuO₄　　　　　　　　　　　　　　　
K. Tenya; R. Yamahana; A. Ishii; H. Amitsuka; M. Yokoyama; K. Deguchi and Y. Maeno
Topological Aspects of Critical Systems and Networks (World Scientific Publishing), 2007, [Reviewed]

〔Major achievements〕Evolution of Heterogeneous Antiferromagnetic State in URu₂Si₂: Study of Hydrostatic-Pressure, Uniaxial-Stress and Rh-Dope Effects
M. Yokoyama and H. Amitsuka, Lead, We have investigated the nature of the competition between hidden order and antiferromagnetic (AF) order in URu2Si2 by performing the neutron scattering experiments under hydrostatic-pressure P, uniaxial-stress sigma, and Rh-substitution conditions. Hidden order observed at ambient pressure in pure URu2Si2 is found to be replaced by the AF order by applying P, s along the tetragonal basal plane, and by doping Rh. We discuss these experimental results on the basis of the crystalline strain calculations, and suggest that this phase transition is generated by the 0.1% increase of the tetragonal c/a ratio. We have also found that the magnetic excitation observed in the hidden order phase vanishes in the AF phase. We show that this variation can be qualitatively explained by assuming the hidden order parameter to be quadrupole., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2007, [Reviewed], [Invited]

Uniaxial-stress effect on the antiferromagnetic state in CePd₂Si₂
M. Yokoyama; A. Gawase; H. Amitsuka; K. Tenya; H. Yoshizawa, Lead, We have performed the elastic neutron scattering measurements under the uniaxial stress sigma for the antiferromagnetic (AF) state in CePd2Si2, and found an anisotropy in the sigma dependence of the AF state. The magnitude of the staggered moment is reduced with increasing sigma applied along the tetragonal [110] direction, while it shows nearly independent of sigma for sigma parallel to [001]. Similar behavior is also observed in the sigma dependence of the Neel temperature. From these results, we suggest that both the volume compression and the increase of the c/a ratio lead to the suppression of the AF state. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2006

Magnetization study of the superconductivity in Sr₂RuO₄
K. Tenya; S. Yasuda; M. Yokoyama; H. Amitsuka; K. Deguchi; Y. Maeno, Static magnetization measurements of Sr2RuO4 have been performed down to 0.1 K. An anomalous increase of magnetization is observed at H-2 which is located just below H-c2. The onset field H-2 gradually decreases with temperature and seems to merge with H-c2 around I K. Besides the above anomaly, a small kink is found in the magnetization curves at around 9 kOe. These magnetization behaviors are analyzed from the viewpoint of the Ginzburg-Landau theory. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2006, [Reviewed]

Magnetic form factor of URu₂Si₂
K. Kuwahara; M. Kohgi; K. Iwasa; M. Nishi; K. Nakajima; M. Yokoyama; H. Amitsuka, We report the field-induced magnetic form factor of the heavy-electron system URu2Si2 obtained by using polarized neutrons. The neutron experiments were performed on the two single crystals at 60 K by applying a magnetic field of 6 T along the tetragonal c-axis. The observed magnetic form factor is close to the theoretical 5f form factor of the free U3+ or U4+ ions calculated by the dipole approximation as other U-based intermetallic superconductors. However, the extrapolated value at sin theta/lambda = 0 (0.07 mu(B)/U) is smaller than the bulk magnetization value (0.10 mu(B)/N). Therefore, this result indicates some contribution other than 5f electrons to the bulk magnetization of URu2Si2. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2006, [Reviewed]

Unusual Magnetic Response in Superconducting Mixed State of Sr₂RuO₄
K. Tenya; S. Yasuda; M. Yokoyama; H. Amitsuka; K. Deguchi; Y. Maeno, We report on detailed measurements of the magnetization of Sr2RuO4 in the superconducting mixed state, performed on a high-quality single crystal in a magnetic field parallel to the [100] axis. A small but distinct kink structure is found at around 9 kOe in the magnetization curve, indicating the presence of an additional superconducting phase transition that has been theoretically predicted to be evidence of the superconductivity with a two-component order parameter. An anomalous increase of magnetization is also observed just below the upper critical field. These anomalies disappear when the field is tilted from the [100] axis by only 3-5 degrees. Possible origins of such magnetization behavior are discussed from the viewpoint of a spin-triplet pairing scenario with a two-component order parameter., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2006, [Reviewed]

Heterogeneous Metallic State in URu₂Si₂
H. Amitsuka; M. Yokoyama; K. Matsuda; K. Tenya; H. Yoshizawa, A review of recent attempts to understand the pressure-temperature phase diagram of URu2 Si-2 is given. At ambient (and weak) pressures, the low-T properties of this system are dominated by an unidentified ordered state (hidden order: HO) and non-trivial superconductivity, while by applying hydrostatic (or uniaxial or chemical) pressures, a change to a regime dominated by antiferromagnetic order (AF) is observed. In between these two regimes, an unusual heterogeneous metallic state is found. This change in regime is clearly demonstrated by neutron scattering, NMR and mu SR measurements. The experimental results and strain analyses show that the low-T state of this system is extremely sensitive to the shape effects, and a slight increase in the axial strain delta(c/a)/( c/a ) (equivalent to(eta) over cap) can easily change the ground state from HO to AF. The critical value is estimated to be very small ((eta) over capc similar to 10(-3) ), suggesting that a strain distribution in a crystal is responsible for the observed heterogeneity. We will demonstrate this by showing our recent neutron-scattering experimental data using a high-quality single crystal., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2006, [Reviewed], [Invited]

〔Major achievements〕New Magnetic State in Incommensurate Magnetic Phase of Heavy-Fermion Superconductor CeRh_0.6Co_0.4In₅
M. Yokoyama; H. Amitsuka; K. Matsuda; A. Gawase; N. Oyama; I. Kawasaki; K. Tenya; H. Yoshizawa, Lead, We performed elastic neutron scattering experiments on solid solution CeRh1-xCoxIn5 with x = 0.4 to clarify the nature of the antiferromagnetic (AF) phase in the vicinity of the quantum critical point. We observed the incommensurate AF order below T-Nh = 3.5 K. The structure of the incommensurate AF order is basically unchanged from that for pure CeRhIn5. We further found the evolution of a new commensurate AF order with the modulation of q(c) = (1/2, 1/2, 1/2) below T-Nc, = 2.9 K. The volume-averaged moments for the incommensurate and commensurate AF phases are 0.38 mu(B)/Ce and 0.21 mu(B)/Ce, respectively, which are reduced from the incommensurate AF moment (0.75 mu(B)/Ce) for pure CeRhIn5. We suggest from these results that the commensurate magnetic correlation may be tightly coupled with the superconductivity observed below T-c = 1.4 K., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2006, [Reviewed]

Antiferromagnetic defects in non-magnetic hidden order of the heavy-electron system URu₂Si₂　　　　　　　　　　　　　　　
H. Amitsuka; K. Tenya; M. Yokoyama
Topology in Ordered Phase (World Scientific Publishing), 2006, [Reviewed]

Superconductivity in URu₂Si₂ under high pressure　　　　　　　　　　　　　　　
K. Tenya; I. Kawasaki; H. Amitsuka; M. Yokoyama; N. Tateiwa; T.C. Kobayashi
Topology in Ordered Phase (World,Scientific Publishing), 2006, [Reviewed]

〔Major achievements〕Antiferromagnetic order in disorder-induced insulating phase of SrRu1-xMnxO3 (0.4 <= x <= 0.6)
M Yokoyama; C Satoh; A Saitou; H Kawanaka; H Bando; K Ohoyama; Y Nishihara, Lead, We have performed powder neutron diffraction measurements on the solid solutions of SrRu1-xMnxO3, and found that the itinerant ferromagnetic order observed in pure SrRuO3 changes into the G type antiferromagnetic (AF) order with nearly localized d electrons in the intermediate Mn concentration range between x = 0.4 and 0.6. With increasing x, the AF moment is strongly enhanced from 1.1 mu(B) (x = 0.4) to 2.6 mu(B) (x = 0.6), which is accompanied by the elongation of the tetragonal c/a ratio. These results suggest that the substitution of Mn for Ru suppresses the itinerant characteristic of the d electrons, and induces the superexchange interaction through the compression in the c plane. We have also found that the magnetic and transport properties observed in our tetragonal samples are similar to those of recently reported orthorhombic ones., PHYSICAL SOC JAPAN
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, Jun. 2005

Magnetic excitations in U(Ru1-xRhx)(2)Si-2 (x <= 0.03)
M Yokoyama; H Amitsuka; S Roh; Kawasaki, I; K Tenya; H Yoshizawa, Lead, We have investigated magnetic excitations for a mixed phase of hidden order (HO) and the anti ferromagnetic (AF) order in U(Ru1-xRhx)(2)Si-2 (x <= 0.03) by means of inelastic neutron scattering. The inelastic peaks observed at Q = (1, 0, 0) and (1,0.4,0) in the HO phase for x = 0 and 0.015 at 1.4 K are found to be strongly reduced in the AF dominant compositions of x = 0.02 and 0.03. Similar behavior is observed as the HO is replaced by the AF order upon cooling for x = 0.02. The x-T region in which the strong reduction of inelastic peaks is observed corresponds to the AF-rich region, indicating that the magnetic excitations typical for the HO-phase vanish in the AF phase. (c) 2005 Published by Elsevier B.V., ELSEVIER SCIENCE BV
PHYSICA B-CONDENSED MATTER, Apr. 2005

〔Major achievements〕Competition between hidden order and antiferromagnetism in URu₂Si₂ under uniaxial stress studied by neutron scattering
M. Yokoyama; H. Amitsuka; K. Tenya; K. Watanabe; S. Kawarazaki; H. Yoshizawa; J.A. Mydosh, Lead, We have performed elastic neutron scattering experiments under uniaxial stress sigma applied along the tetragonal [100], [110], and [001] directions for the heavy-electron compound URu2Si2. We found that antiferromagnetic (AF) order with large moment is developed with sigma along the [100] and [110] directions. If the order is assumed to be homogeneous, the staggered ordered moment mu(o) continuously increases from 0.02 mu(B)/U(sigma=0) to 0.22 mu(B)/U (0.25 GPa). The rate of increase partial derivative mu(o)/partial derivative sigma is similar to 1.0 mu(B)/GPa, which is four times larger than that for the hydrostatic pressure (partial derivative mu(o)/partial derivative P similar to 0.25 mu(B)/GPa). Above 0.25 GPa, mu(o) shows a tendency to saturate, similar to the hydrostatic pressure behavior. For sigma parallel to[001], mu(o) shows only a slight increase to 0.028 mu(B)/U(sigma=0.46 GPa) with a rate of similar to 0.02 mu(B)/GPa, indicating that the development of the AF state highly depends on the direction of sigma. We have also found a clear hysteresis loop in the isothermal mu(o)(sigma) curve obtained for sigma parallel to[110] under the zero-stress-cooled condition at 1.4 K. This strongly suggests that the sigma-induced AF phase is metastable, and separated from the "hidden order" phase by a first-order phase transition. We discuss these experimental results on the basis of crystalline strain effects and elastic energy calculations, and show that the c/a ratio plays a key role in the competition between these two phases., AMER PHYSICAL SOC
Physical Review B, 2005

¹⁰¹Ru NQR and Hidden Order in URu₂Si₂
S. Saitoh; S. Takagi; M. Yokoyama; H. Amitsuka, The still unclarified hidden order phase below To = 17.5 K in the heavy-electron system URu2Si2 has been studied by Ru-101 NQR on a single crystal under H-ext = 0 and ambient P. Considering an invariant form of the quadrupole coupling between a Ru-101 nucleus and U 5f electrons, which is compatible with the symmetry of the U-Ru bonds, it is shown that U 5f quadrupoles can be probed by Ru-101 NQR and that the singlet ground-state models for the (5f)(2) configuration of U can naturally explain the observed large T-dependence of the NQR frequency (101)v(2Q)(T) above T-o. (101)v(2Q)(T) shows a slight but significant increase below TQ congruent to 13.5 K. Combining with general considerations on the effects on Ru-101 NQR of a possible symmetry-breaking electric field gradient (EFG) or hyperfine field due to hidden order, we discuss that the increase can be interpreted as arising from symmetry -breaking EFG components of V-yz and/or V-zx, due to quadrupole order. In this interpretation the onset of the quadrupole order is retarded by about 4 K below T-o. which is discussed in connection with related measurements., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2005, [Reviewed]

Magnetization study of heavy Fermion superconductor URu₂Si₂ under high pressures
K. Tenya; I. Kawasaki; K. Tameyasu; S. Yasuda; M. Yokoyama; H. Amitsuka; N. Tateiwa; T.C. Kobayashi, Magnetization measurements of URu2Si2 have been performed under hydrostatic pressures. The superconducting transition temperature decreases linearly with pressure up to 1.1 GPa and disappears above 1.5 GPa. The hysteretic magnetization shows characteristic behaviors at high pressures, suggesting that the pinning properties are changed due to the switch of the normal state to the antiferromagnetic state. (c) 2005 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2005, [Reviewed]

〔Major achievements〕Neutron scattering study on competition between hidden order and antiferromagnetism in U(Ru1-xRhx)2Si(2) (x <= 0.05)
M Yokoyama; H Amitsuka; S Itoh; Kawasaki, I; K Tenya; H Yoshizawa, Lead, We have performed elastic and inelastic neutron scattering experiments on solid solutions of U(Ru1-xRhx)(2)Si-2 with Ru-rich concentrations: x = 0, 0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with increasing x, and correspondingly, the onset temperature T-m (similar to 17.5 K at x = 0) of weak antiferromagnetic (AF) Bragg reflection decreases. For x = 0.04 and 0.05, no magnetic order is detected in the investigated temperature range down to 1.4 K. In the intermediate range, 0.02 less than or equal to x less than or equal to 0.03, We found that the AF Bragg reflection is strongly enhanced. At x = 0.02, this enhancement takes place at similar to7.7 K (drop T-M), which is significantly lower than T-m (similar to 13.7 K). T-M increases with increasing x, and seems to merge with T at x = 0.03. If the AF state is assumed to be homogeneous, the staggered moment mu(0), estimated at 1.4 K increases from 0.02(2) mu(B)/U (x = 0) to 0.24(l) mu(B)/U (x = 0.02). The behavior is similar to that observed under hydrostatic pressure (mu(0) increases to similar to0.25 mu(B)/U at 1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an increase in the AF Volume fraction. We also found that the magnetic excitation observed at (1, 0, 0) below T-m disappears as T is lowered below T-M., PHYSICAL SOC JAPAN
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, Mar. 2004, [Reviewed]

High pressure X-ray diffraction study of URu2Si2
K Kuwahara; H Sagayama; K Iwasa; M Kohgi; S Miyazaki; J Nozaki; J Nogami; M Yokoyama; H Amitsuka; H Nakao; Y Murakami, We have performed high pressure X-ray diffraction measurements on a powder sample of the tetragonal heavy-electron compound URu2Si2 at low temperatures and pressure up to 3 GPa, in order to investigate a pressure-induced phase transition at P-c = similar to1.5 GPa, which was indicated in the neutron diffraction experiment under pressure. The pressure variations of the lattice parameters a and c at 15 K decrease monotonously with increasing pressure. No discontinuity of the lattice parameters of URu2Si2 around P-c is observed within experimental error., JAGIELLONIAN UNIV PRESS
ACTA PHYSICA POLONICA B, Aug. 2003, [Reviewed]

Nonequilibrium antiferromagnetic state in the heavy electron compound URu2Si2
M Yokoyama; J Nozaki; H Amitsuka; K Watanabe; S Kawarazaki; H Yoshizawa; JA Mydosh, Lead, We have investigated the nature of the antiferromagnetic (AF) phase induced by uniaxial stress sigma in URu2Si2, by performing elastic neutron scattering measurements up to 0.4 GPa. We have found that the AF Bragg-peak intensity shows a clear hysteresis loop with sigma under the zero-stress cooling condition. The result strongly suggests that the sigma-induced AF phase is metastable and separated from the coexisting "hidden ordered" phase by a first-order phase transition. We also present the analyses of the crystalline strain effects, and suggest that the c/a ratio plays an important role in the competition between these two phases., JAGIELLONIAN UNIV PRESS
ACTA PHYSICA POLONICA B, Feb. 2003, [Reviewed]

Magnetic properties of Sm-based filled skutterudite phosphides
R. Giri; C. Sekine; Y. Shimaya; I. Shirotani; K. Matsuhira; Y. Doi; Y. Hinatsu; M. Yokoyama; H. Amitsuka, Filled skutterudites SmFe4P12 and SmOs4P12 have been prepared at high temperature and high pressure. The temperature dependence of electrical resistivity in both compounds shows metallic behavior. The magnetic susceptibility and specific heat measurements indicate that indicate that SmFe4P12 shows a ferromagnetic ordering at 1.5 K, whereas SmOs4P12 is an antiferromagnet with a T-N of 4.6 K. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2003, [Reviewed]

Inhomogeneous Magnetism and Hidden Order in URu₂Si₂
H. Amitsuka; M. Yokoyama, Recent high-pressure studies have been particularly effective in revealing unusual properties of inhomogeneous magnetism in the heavy-electron superconductor URu2Si2, In this paper a narrow selection of the important experimental observations elucidating the pressure-induced two-phase competition is reviewed. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2003, [Reviewed], [Invited]

Inhomogeneous Magnetism in URu₂Si₂ Studied by Muon Spin Relaxation under High Pressure
H. Amitsuka; K. Tenya; M. Yokoyama; A. Schenck; D. Andreica; F.N. Gygax; A. Amato; Y. Miyako; Ying Kai Huang; J.A. Mydosh, We have studied the low-temperature phase below 17.5 K in the heavy-fermion superconductor URu2Si2 using the zero-field muSR technique under hydrostatic pressures P up to 0.85 GPa. The measurements qualitatively confirm the previous results of NMR and neutron scattering that pressure induces unusual evolution of an inhomogeneous antiferromagnetic (AF) phase which spatially competes with some nonmagnetic 'hidden order'. The AF volume fraction, however, develops abruptly at around a pressure of 0.6 GPa, in contrast to the P-linear variations in the NMR results. Moreover, the onset temperature of the AF-volume evolution is clearly lower than 17.5 K, whereas the nominal Neel temperature seems to be about 20 K. These experimental results suggest that the AF phase exists as a metastable state. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2003, [Reviewed], [Invited]

〔Major achievements〕Anomalous Fermi Liquid Behavior of the Dilute Uranium Alloys La_1-xU_xRu₂Si₂ (x≦0.07)　　　　　　　　　　　　　　　
M. Yokoyama; H. Amitsuka; K. Kuwahara; K. Tenya; T. Sakakibara, Lead
Journal of the Physical Society of Japan, 2002

Effects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu₂Si₂
M. Yokoyama; H. Amitsuka; K. Watanabe; S. Kawarazaki; H. Yoshizawa; J.A. Mydosh, Lead, We have performed the elastic neutron scattering experiments under uniaxial stress sigma along the tetragonal [100], [110] and [001] directions for URu2Si2. For sigma parallel to [100] and [110], the antiferromagnetic moment mu(0) is strongly enhanced from 0.02 mu(B)/U (sigma = 0) to 0.22 mu(B)/U (sigma = 0.25 GPa) at 1.5 K. The rate of increase partial derivative mu(0)/partial derivative sigma is roughly estimated to be similar to 1.0 mu(B)/GPa, which is much larger than that for the hydrostatic pressure (similar to 0.25 mu(B)/GPa). Above 0.25 GPa, mu(0) shows a tendency to saturate similar to the behavior in the hydrostatic pressure, For sigma parallel to [001], on the other hand, mu(0) shows only a slight increase to 0.028 mu(B)/U (sigma = 0.46 GPa) with a rate of similar to 0.02 mu(B)/GPa. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu2Si2 is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio, or both., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2002

Thorium Dilution Effects of the Heavy Electron Compound URu₂Si₂
M. Yokoyama; K. Tenya; H. Amitsuka, Lead, We have investigated Th dilution effects for URu2Si2 by performing magnetic susceptibility chi and specific heat C measurements in a rich U-concentration range. We have observed that sharp and clear anomalies seen in chi and C of the pure URu2Si2 at T-0 = 17.5 K become weak and unclear by substituting only five percent of U with Th. At the same time, the magnitude of the c-axis susceptibility chi(c) and C/T at low temperature is enhanced, indicating that the gap formation in the density of states for heavy quasi-particles is sensitively suppressed. For 10% of Th substitution, on the other hand, we have found a new kink anomaly to appear in chi(c) at similar to 13.7 K, where C also shows a hump. This suggests the presence of antiferromagnetic instability in URu2Si2. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2002, [Reviewed]

Cryogenic System for Neutron Scattering Experiments with In Situ Pressure Tuning Mechanism: Response of the Antiferromagnetism of URu₂Si₂ to Uniaxial Stress
S. Kawarazaki; Y. Uwatoko; M. Yokoyama; Y. Okita; Y. Tabata; T. Taniguchi; H. Amitsuka, A handy insertable device to manipulate hydrostatic pressure or uniaxial stress on a sample in a cryostat for neutron scattering experiments is described. The pressure that is generated in a miniature hydraulic oil-cylinder on the top of the inserting stick is transmitted to the sample via a long piston-cylinder unit made of a thick stainless-steel tube and a fiber-reinforced plastics (FRP) rod. One can thus in situ tune the pressure or the stress on the sample without handling the pressure-cell at room temperature outside the cryostat. The device is designed to fit into the ILL-type Orange cryostat so that it can he used ill many neutron scattering facilities. A newly designed uniaxial-stress cell and hydrostatic pressure cell to he used with this system are also described. The result of measurement of the hysteresis effect of uniaxial stress oil the antiferromagnetism of URu2Si2 at 1.4 K is presented., JAPAN SOC APPLIED PHYSICS
Japanese Journal of Applied Physics, 2002, [Reviewed]

Multipole Ordering in f Electron Systems
T. Sakakibara; T. Tayama; K. Tenya; M. Yokoyama; H. Amitsuka; D. Aoki; Y. Onuki; Z. Kletowski; S. Kunii, We discuss multipole ordering in two cubic f-electron compounds. Field variation of the antiferroquadrupolar transition temperature T-Q in PrPb3 is determined by the specific heat and the magnetization measurements. It is found that T-Q(H) shows a pronounced increase for H parallel to <100>, which has been successfully explained by the antiferromagnetic interaction between the field-induced staggered moment in the 0(2)(0)(proportional to 2J(z)(2) - J(x)(2) - J(y)(2)) AFQ phase. From the analysis of the anisotropy in T-Q(H), the importance of an octupolar interaction is pointed out. The new ordered state in CexLa1-xB6 (x < 0.8), called phase IV, has been examined by magnetization measurements under uniaxial pressures. A pronounced anisotropy is observed at a relatively weak pressure, and the ordering temperature seems to increase in magnetic field. The results are discussed in view of a possible octupolar ordering in phase IV. (C) 2002 Elsevier Science Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD
Journal of Physics and Chemistry in Solids, 2002, [Reviewed]

Anomalous Uniaxial Pressure Effect on the Phase IV Ordering in Ce_xLa_1-xB₆
T. Sakakibara; K. Tenya; M. Yokoyama; H. Amitsuka; S. Kunii, We have examined the magnetization M of Ge0.75La0.25B6 under uniaxial pressures applied along the [001] direction, focusing our attention on the mysterious phase IV ordering, Magnetization of phase IV, which is nearly isotropic at an ambient pressure, becomes strongly anisotropic at a relatively weak uniaxial pressure of 60 MPa. On entering phase IV from the paramagnetic phase I, M(T) increases (decreases) for the field direction II parallel to [001] ([110]), suggesting that the order parameter is intrinsically anisotropic. Interestingly, M(T) for H parallel to [001] exhibits an upward-bending at the ordering temperature TI-IV, and TI-IV (H) seems to increase in magnetic field unlike the case of ordinary antiferromagnetic orderings. The results are discussed in view of a spontaneous ordering of an octupole moment in phase IV., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2002, [Reviewed]

Low-Temperature Magnetization Study on the non-Kramers Cubic System Pr₃Pd₂₀Ge₆
H. Amitsuka; A. Nogami; K. Tenya; M. Yokoyama; S. Miyazaki; T. Sakakibara; M. Nakayama; N. Kimura; H. Aoki; T. Komatsubara, We report on high-precision magnetization measurements on the non-Kram.ers cubic compound Pr3Pd20Ge6 for temperatures down to similar to 80 mK, in fields applied parallel to the [100] and [110] directions up to 8.5 T. Multistep-like structures of the magnetization curves are fourid below about 1 K for both the field directions. Temperature variations of the magnetic susceptibility show no tendency to saturate down to 80 inK, implying that the crystalline-electric-field (CEF) lowest state of 4f electrons for at least one of the Pr sites is the magnetic triplet Gamma(5). No significant anomaly is observed at 0.26 K, where quadrupole order is suggested front ultrasonic sound velocity measurements. An application of a simple CEF model is discussed., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2002, [Reviewed]

Hidden Order and Weak Antiferromagnetism in URu₂Si₂
H. Amitsuka; M. Yokoyama; S. Miyazaki; K. Tenya; T. Sakakibara; W. Higemoto; K. Nagamine; K. Matsuda; Y. Kohori; T. Kohara, The origin and nature of the low-temperature please appearing below 17.5 K (equivalent to T-0) in URu2Si2 is still not fully understood. Since the weak antiferromagnetic state (WAF; mu(ord) similar to0.02-0.04 muB) developing below around To is not simply reconciled with a large reduction in the magnetic entropy (similar to0.2R ln 2), the existence of some hidden order parameter has been argued, where WAF is considered to be of a secondary nature. The paper reviews recent development of microscopic characterization of WAF based on neutron scattering and Si-29 NMR under high pressure. It is demonstrated that, at least, for pressures ranging from similar to0.3 to similar to0.83 GPa, there are spatially competing two different ordered states in the crystal: a normal-moment (similar to0.25 mu(B)/U) antiferromagnetic state and some unknown, non-magnetically ordered state. Simple extrapolation to ambient pressure suggests that WAF originates from one percent volume fraction of this antiferromagnetic phase. We also discuss the unusual magnetic properties at ambient pressure, presenting our latest results of zero-field and longitudinal-field muSR experiments. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2002, [Reviewed]

〔Major achievements〕Antiferro-quadrupolar ordering and multipole interactions in PrPb3
T Tayama; T Sakakibara; K Kitami; M Yokoyama; K Tenya; H Amitsuka; D Aoki; Y Onuki; Z Kletowski, Antiferro-quadrupolar (AFQ) ordering in the cubic Gamma (3) ground state system PrPb3 has been studied by means of magnetization and specific heal measurements under magnetic fields Ii. Field variation of the AFQ transition temperature T-Q (0.4K at H 0) has teen determined for the three crystallographic directions (100), (110) and (111). The obtained T-Q(H) is strongly anisotropic, with T-Q((100))(H) the largest (similar to0.7K at 6T). The AFQ phase diagram and the magnetization behavior observed for H \ \ (100) are well explained by a model that incorporates both antiferromagnetic and antiferroquadrupolar interactions. The interactions between field-induced staggered magnetic moments stabilize the AFQ order. This simple model, however, seriously fails to explain the observed anisotropy: T-Q((100))(H) > T-Q((110))(H) > T-Q((111))(H). Reconsidering the field-induced multipole moments in the AFQ phase, we propose that inclusion of a weak ferro-octupolar interaction between rs type octupole moments is important in reproducing the anisotropic phase diagram of PrPb3., PHYSICAL SOC JAPAN
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, Jan. 2001, [Reviewed]

Magnetic and Fermi surface properties of the ferromagnetic compound UGa2
T Honma; Y Inada; R Settai; S Araki; Y Tokiwa; T Takeuchi; H Sugawara; H Sato; K Kuwahara; M Yokoyama; H Amitsuka; T Sakakibara; E Yamamoto; Y Haga; A Nakamura; H Harima; H Yamagami; Y Onuki, We have studied the magnetic and Fermi surface properties in a ferromagnet UGa2. The electrical resistivity, elastic constant, thermal expansion coefficient: thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal-structure. The 5f(2)- and 5f(3)-CEF schemes, based on the localized 5f-electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5f(2)- and 5f(3)-core models nor by the spin-polarized 5f-itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m(0), which is consistent with the electronic specific heat coefficient of 11mJ/K-2.mol., PHYSICAL SOC JAPAN
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, Aug. 2000, [Reviewed]

Unusual low-temperature behavior of the dilute uranium alloys La1-xUxRu2Si2 (x <= 0.07)
M Yokoyama; H Amitsuka; K Kuwahara; A Okumura; K Tenya; T Sakakibara, We have investigated single-U-site properties of the dilute U alloys La1-xUxRu2Si2 for x less than or equal to 0.07. Contrary to usual Kondo effect, electrical resistivity due to U ions shows a In T decrease as temperature decreases. The 5f specific heat C-P(5f)/T exhibits a broad peak at similar to 10 K, and entropy change associated with this anomaly below 30 K is estimated to be only about 0.3 R In 2. These properties differ greatly from those seen in the usual dilute magnetic alloys. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
PHYSICA B, Jun. 2000, [Reviewed]

Non-Fermi-liquid behavior in R1-xUxRu2Si2 (R = Th, Y and La; x <= 0.07)
H Amitsuka; K Kuwahara; M Yokoyama; K Tenya; T Sakakibara; M Mihalik; AA Menovsky, Single-U-ion properties of heavy-electron compound URu2Si2 have been investigated by a series of diluting experiments on R1-xUxRu2Si2 (R = Th, Y, and La: x less than or equal to 0.07). A strong uniaxial magnetic anisotropy of local 5f moments is commonly observed throughout the dilutions. From a large enhancement of chi and C/T as T-->18, we suggest a non-Kramers, magnetic doublet Gamma(5) (f(2)) to be eminently suitable for the crystal-field lowest level, contrary to general Views of low-lying singlets for the periodic system. We further demonstrate the absence of the conventional Kondo effect in all these dilutions. A strong suppression of 5f moments at low temperatures accompanies a non-trivial In T decrease in rho and a small change in the magnetic entropy. Specific-heat measurements in magnetic fields up to 12 T have revealed no sign of the residual entropy, eliminating the simple application of the two-channel Kondo theory to the present alloys. We also discuss a puzzling phase transition at 17.5 K of URu2Si2 in relation to the single-ion physics, providing our latest results of neutron-scattering experiments under high pressure, (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
PHYSICA B, Jun. 2000, [Reviewed]

Neutron scattering studies on heavy-fermion superconductors
N Metoki; Y Koike; Y Haga; T Honma; M Sato; Y Onuki; N Kimura; K Maesawa; H Amitsuka; M Yokoyama; K Kuwahara; Y Miyako, We review recent neutron scattering studies on uranium-based heavy-fermion superconductors. The coupling between magnetic and superconducting order parameters was observed in UPt3, UPd2Al3, URu2Si2, and UhTi(2)Al(3). In UPd2Al3, the superconducting gap appears in the spin excitation spectra. These results are indicative of the strong interplay between magnetism and superconductivity. We also report the unusual behaviors of the weak antiferromagnetic ordering, the long-range magnetic correlation in UPt3 at ultra-low temperatures, and the pressure-induced magnetic transition from the weak (0.02 mu(B)/U) to a high moment state (0.4 mu(B)/U) at 1.5 GPa in URu2Si2. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
PHYSICA B, May 2000, [Reviewed]

Interplay of Orbital and Magnetic Degrees of Freedom in f-Electron Systems: The case of PrPb₃ and TmTe
T. Sakakibara; T. Tayama; K. Kitami; M. Yokoyama; K. Tenya; H. Amitsuka; T. Matsumura; D. Aoki; Y. Onuki; Z. Kletowski; T. Suzuki, Effect of magnetic field on the antiferro-quadrupolar (AFQ) phase in the cubic compounds PrPb3 and TmTe has been studied by means of magnetization and specific heat measurements. In PrPb3, it is found that the AFQ transition temperature T-Q (=0.4 K at H=0) remarkably increases in magnetic field. This behavior is well explained by antiferromagnetic interactions between the field-induced staggered magnetic moment in the AFQ phase. Analysis of the observed anisotropy T-Q([100])(H) > T-Q([110])(H), however, strongly suggests the presence of a weak ferro-octupolar interaction. In TmTe, magnetic susceptibility chi(T) increases enormously on cooling and appears to diverge upon an antiferromagnetic (AF) transition at T-N=0.22 K. The results imply that a ferromagnetic moment is induced in the AF phase by an alternating anisotropy due to the preexisting AFQ order at T(Q)approximate to 1.8 K. This is possible when both AF and AFQ states are described by the same wave vector, in agreement with recent neutron diffraction studies., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2000, [Reviewed]

Pressure-Induced Magnetic Phase Transition of the 5f Electron System URu₂Si₂
H. Amitsuka; M. Yokoyama; K. Tenya; T. Sakakibara; K. Kuwahara; M. Sato; N. Metoki; T. Honma; Y. Onuki; S. Kawarazaki; Y. Miyako; J.A. Mydosh, A puzzling phase transition at T-o similar to 17.5 K of the heavy-electron 5f system URu2Si2 is characterized by development of an unusually small staggered moment mu(o) concomitant with large bulk anomalies and sharp magnon excitations. Through elastic and inelastic neutron scattering, we have studied the influence of pressure P up to similar to 2.8 GPa on this phase transition. For pressures less than 1.3 GPa, mu(o) at 1.4 K is quasi-linearly enhanced from similar to 0.017(3) mu(B) to similar to 0.25(2) mu(B), while its onset temperature increases only ten present. We have also observed a sharp phase transition at P-c similar to 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu(o) similar to 0.4 mu(B)) appears. Sharp magnon excitations at Q = (1,0,0) and (1,0.4,0) collapse in this high-P phase. The lattice parameter a decreases discontinuously at P-c even for T > T-o, indicating that pressure induces a significant change in electronic states in a higher characteristic energy scale. We show that the observed magnetic instability could qualitatively well be explained by competition between quadrupolar and dipolar interactions in a non-trivial Gamma(5) doublet., PHYSICAL SOC JAPAN
Journal of the Physical Society of Japan, 2000, [Reviewed]

Elastic Constants of URu₂Si₂ in Magnetic Fields
K. Kuwahara; A. Okumura; M. Yokoyama; K. Tenya; H. Amitsuka; T. Sakakibara, In previous ultrasonic measurements on the tetragonal compound URu2Si2 in zero magnetic field, we found a tendency of the softening below similar to 70 K in the transverse 1/2(c(11) - c(12)) mode. The results strongly suggest the presence of the lattice instability in this system. We here present the experimental results of the temperature dependence of elastic constants, c(11-) 1/2(c(11) - c(12)) and c(66) in magnetic fields along the tetragonal c-axis up to 12 T. The 1/2(c(11) - c(12)) mode increases as the magnetic field is increased, while the c(11) and c(66) modes decrease. The small but distinct held effects imply that the elastic anomaly in the transverse mode is caused by electrons. (C) 2000 Published by Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2000, [Reviewed]

The specific heat of the filled skutterudite PrRu₄P₁₂ in magnetic fields
C. Sekine; T. Inaba; I. Shirotani; M. Yokoyama; H. Amitsuka; T. Sakakibara, We have investigated the field dependence of the metal-insulator (MI) transition displayed by the filled skutterudite PrRu4P12 by means of specific heat measurements. The MI transition is not caused by a crystallographic transformation with breaking cubic symmetry, a valence transition nor a magnetic phase transition. Although the origin of the MI transition is still unclear, it is possible that an antiferro-quadrupolar ordering or a local-structure change of P atom is related to this transition. A lambda-like second order-type anomaly is observed at T-MI = 62.3 K. No field dependence of the MI transition is detected up to 12 T. A held-induced peak is observed much below T-MI (below 10 K). The magnetic entropy approaches the value similar to R In 2 above 10 K, which suggests that the crystalline-electric-field ground state of PrRu4P12 is the non-Kramer's doublet Gamma(3). (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
Physica B, 2000, [Reviewed]

〔Major achievements〕Effect of pressure on tiny antiferromagnetic moment in the heavy-electron compound URu(2)Si(2)
H Amitsuka; M Sato; N Metoki; M Yokoyama; K Kuwahara; T Sakakibara; H Morimoto; S Kawarazaki; Y Miyako; JA Mydosh, We have performed elastic neutron-scattering experiments on the heavy-electron compound URu(2)Si(2) for pressure P up to 2.8 GPa. We have found that the antiferromagnetic (100) Bragg reflection below T(m) similar to 17.5 K is strongly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu(0) at 1.4 K increases linearly from similar to 0.017(3)mu(B) to similar to 0.25(2)mu(B), while T(m) increases slightly at a rate similar to 1 K/GPa, roughly following the transition temperature T(0) determined from macroscopic anomalies. We have also observed a sharp phase transition at P(0) similar to 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu(0) similar to 0.4 mu(B)) appears with a slightly reduced lattice constant., AMER PHYSICAL SOC
PHYSICAL REVIEW LETTERS, Dec. 1999, [Reviewed]

〔Major achievements〕Zn置換したCeCoIn5において観測された磁気量子臨界点と超伝導の共存　　　　　　　　　　　　　　　
髭本 亘; 横山 淳
固体物理, Mar. 2025, [Reviewed], [Invited]
Last

Ce(Co_1-xNi_x)In₅における量子臨界揺らぎ
鈴木康平; 横山淳; 大島佳樹; 天谷健一; 近藤晃弘; 金道浩一; 中村翔太; 橘高俊一郎; 榊原俊郎
日本物理学会講演概要集(CD-ROM), 23 Mar. 2018

Zn置換CeCoIn₅におけるNQR/NMR研究
酒井宏典; 服部泰佑; 徳永陽; 神戸振作; RONNING Filip; ZHU Jianxin; 鈴木康平; 大島佳樹; 横山淳
日本物理学会講演概要集(CD-ROM), 23 Mar. 2018

21aPS-45 Study on resonant photoemission spectroscopy for itinerant ferromagnet Sr_<1-x>La_xRuO_3
Sakon Y.; Kawasaki I.; Yokoyama M.; Fujimori S.-i.; Yamagami H.
Meeting Abstracts of the Physical Society of Japan, 2016

20pPSB-6 Low-temperature properties of heavy-fermion superconductor Ce(Co1_<1-x>Ni_x)In_5
Otaka R.; Yokoyama M.; Mashiko H.; Tenya K.; Ikeda Y.; Shimizu Y.; Kono Y.; Yoshizawa H.; Sakakibara T.
Meeting Abstracts of the Physical Society of Japan, 2016

Spin dynamics in itinerant ferromagnet Sr_1-xLa_xRuO₃
Hasebe Takayuki; Yokoyama Makoto
Meeting Abstracts of the Physical Society of Japan, 2016

High-field and low temperature phase and non-Fermi-liquid behavior in CeCo(In,Zn)₅
Mashiko H.; Yokoyama M.; Tenya K.; Kondo A.; Kindo K.; Nakamura S.; Kono Y.; Shimizu Y.; Sakakibara T.
Meeting Abstracts of the Physical Society of Japan, 2016

20pPSB-8 Entropy and Electronic State of CeRh_2Si_2 in high magnetic field
Kohama Yoshimitsu; Otaka Ryo; Yokoyama Makoto; Matsuo Akira; Kindo Koichi
Meeting Abstracts of the Physical Society of Japan, 2016

24aPS-110 Effect of magnetic field on electrical resistivity for cluster-glass state of Sr_<1-x>La_xRuO_3
Fujimura K.; Sakon Y.; Kondo A.; Kindo K.; Ikeda Y.; Yoshizawa H.; Kawanaka H.; Tenya K.; Yokoyama M.
Meeting Abstracts of the Physical Society of Japan, 2015

17aPS-11 Magnetic field versus temperature phase diagram of the heavy-fermion superconductor CeCo(In_<1-x>Zn_x)_5
Mashiko H.; Yokoyama M.; Sakon Y.; Tenya K.; Kondo A.; Kindo K.; Kono Y.; Shimizu Y.; Sakakibara T.
Meeting Abstracts of the Physical Society of Japan, 2015

17aPS-12 Field-induced non-Fermi liquid state in Zn-doped CeCoIn_5
Otaka R.; Yokoyama M.; Sakon Y.; Tenya K.; Ikeda Y.; Yoshizawa H.; Shimizu Y.; Sakakibara T.
Meeting Abstracts of the Physical Society of Japan, 2015

22aPS-40 Specific heat and resistivity of heavy-fermion superconductor CeCo(In,Zn)_5 under magnetic field
Mashiko H.; Otaka R.; Fujimura K.; Sakon Y.; Ikeda Y.; Yoshizawa H.; Kondo A.; Kindo K.; Tenya K.; Yokoyama M.
Meeting Abstracts of the Physical Society of Japan, 2015

21aBB-7 Upper critical field of heavy-fermion superconductor CeCo(In_<1-x>Zn_x)_5
Yokoyama M.; Fujimura K.; Kawasaki I.; Tenya K.; Kono Y.; Sakakibara T.; Ikeda Y.; Yoshizawa H.; Kondo A.; Kindo K.
Meeting Abstracts of the Physical Society of Japan, 2015

23pBC-14 Entropy in Heavy Fermion Antiferromagnet CeRh_2Si_2
Kohama Y.; Yokoyama M.; Kindo K.; Amitsuka H.
Meeting Abstracts of the Physical Society of Japan, 2015

9aPS-103 Magnetic relaxation for ferromagnetic clusters in itinerant electron system Sr_<1-x>La_xRuO_3
Fujimura K.; Kawasaki I.; Tenya K.; Yokoyama M.
Meeting abstracts of the Physical Society of Japan, 22 Aug. 2014

7pBK-2 Superconductivity and magnetism in Zn-doped heavy-fermion CeCoIn_5
Yokoyama M.; Fujimura K.; Kawasaki I.; Tenya K.; Kono Y.; Sakakibara T.; Ikeda Y.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 22 Aug. 2014

8aPS-35 Development of the apparatus to measure the low-temperature specific heat under uniaxial pressure and its application to CeCoIn_5
Kittaka S.; Sakakibara T.; Yokoyama M.
Meeting abstracts of the Physical Society of Japan, 22 Aug. 2014

28aPS-50 Study of four-fold rotational symmetry in URu_2Si_2 by Ru-NMR measurement
Miki T.; Emi N.; Hattori M.; Mito T.; Motoyama G.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.; Amitsuka H.; Matsumoto Y.; Haga Y.
Meeting abstracts of the Physical Society of Japan, 05 Mar. 2014

28aPS-49 Ru-NQR study of local symmetry in URu_2Si_2
Emi N.; Miki T.; Mito T.; Motoyama G.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.; Amitsuka H.; Matsumoto Y.; Haga Y.; Yamamoto E.; Fisk Zachary
Meeting abstracts of the Physical Society of Japan, 05 Mar. 2014

URu₂Si₂の隠れた秩序における構造変化の検証
網塚浩; 田端千紘; 日高宏之; 柳澤達也; 熊井玲児; 小林賢介; 中尾裕則; 村上洋一; 稲見俊哉; 道村真司; 横山淳
物構研サイエンスフェスタ要旨集, 2014

Anomaly of Ru-NMR/NQR spectra on URu_2Si_2
Emi N.; Miki T.; Hattori M.; Mito T.; Motoyama G.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 26 Aug. 2013

High-resolution X-ray diffraction study of URu_2Si_2
Tabata C; Inami T; Michimura S; Yokoyama M; Hidaka H; Yanagisawa T; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 26 Aug. 2013

URu₂Si₂のX線構造解析 III
田端千紘; 日高宏之; 柳澤達也; 横山淳; 網塚浩; 小林賢介; 熊井玲児; 中尾裕則; 村上洋一
日本物理学会講演概要集, 05 Mar. 2013

UPd₂Si₂の整合-不整合反強磁性に対する一軸応力効果
横山淳; 中田崇寛; 田端千紘; 日高宏之; 網塚浩; 天谷健一; 佐藤卓
日本物理学会講演概要集, 2013

26aXA-6 Uniaxial-stress effect on commensurate-incommensurate antiferromagnetic orders in UPd_2Si_2
Yokoyama M; Nakada T; Tabata C; Hidaka H; Amitsuka H; Tenya K; Sato T. J
Meeting Abstracts of the Physical Society of Japan, 2013

URu₂Si₂における放射光X線構造解析
田端千紘; 日高宏之; 柳澤達也; 横山淳; 網塚浩; 小林賢介; 熊井玲児; 中尾裕則; 村上洋一
物構研サイエンスフェスタ要旨集, 2013

18pGA-6 Symmetry of the Hidden Order in URu_2Si_2 and Single-Crystal NMR
Takagi S.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 24 Aug. 2012

URu₂Si₂のX線構造解析 II
田端千紘; 三浦植幸; 安孫子和弘; 日高宏之; 柳澤達也; 横山淳; 網塚浩; 小林賢介; 熊井玲児; 中尾裕則; 村上洋一
日本物理学会講演概要集, 24 Aug. 2012

24pPSB-30 Microscopic investigation on URu_2Si_2 by NMR/NQR measurement
Hattori M.; Mito T.; Motoyama G.; Sakai Y.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 05 Mar. 2012

URu₂Si₂のX線構造解析
田端千紘; 三浦植幸; 安孫子和弘; 日高宏之; 柳澤達也; 横山淳; 網塚浩; 小林賢介; 熊井玲児; 中尾裕則; 村上洋一
日本物理学会講演概要集, 05 Mar. 2012

URu₂Si₂の隠れた秩序状態における磁気励起
網塚浩; 田端千紘; 日高宏之; 柳澤達也; 横山淳; LUMSDEN M. D; KANCHANAVATEE N; BUTCH N. P; MAPLE M. B
NSL News Lett, 2012

共鳴X線散乱によるURu₂Si₂の隠れた秩序状態の解明
網塚浩; 田端千紘; 門別翔太; 柳澤達也; 横山淳; 桑原慶太郎; 須田山貴亮; 岡本淳; 山崎裕一; 中尾裕則; 村上洋一
PFシンポジウム要旨集, 2012

単結晶構造解析によるURu₂Si₂の隠れた秩序状態の解明
田端千紘; 三浦植幸; 安孫子和弘; 日高宏之; 柳澤達也; 横山淳; 網塚浩; 小林賢介; 熊井玲児; 中尾裕則; 村上洋一
PFシンポジウム要旨集, 2012

〔Major achievements〕Neutron Scattering for Heavy-Fermion Compounds　　　　　　　　　　　　　　　
M. Yokoyama
Bussei-Kenkyu, 2012, [Reviewed], [Invited]
Lead

24aGC-11 Does the hidden order of URn_2Si_2 break time-reversal symmetry?
Takagi S.; Misawa Y.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 24 Aug. 2011

24aGC-9 Elastic Response of Rh-substitution System of URu_2Si_2
Watanabe Y; Saito H; Hiura K; Shimizu Y; Yanagisawa T; Hidaka H; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 24 Aug. 2011

23aPS-31 Attempt to detect the symmetry lowering of hidden order in URu2Si2 : NMR/NQR measurement
Hattori M.; Amitsuka H.; Mito T.; Inoue K.; Motoyama G.; Sakai H.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.
Meeting Abstracts of the Physical Society of Japan, 2011

27pPSB-5 NMR/NQR studies of symmetry in URu_2Si_2
Hattori M.; Amitsuka H.; Mito T.; Inoue K.; Motoyama G.; Sakai H.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.
Meeting Abstracts of the Physical Society of Japan, 2011

UPd₂Si₂の一軸応力下中性子散乱
中田崇寛; 横山淳; 五十嵐英紀; 田端千紘; 日高宏之; 網塚浩; 天谷健一; 佐藤卓
日本物理学会講演概要集, 2011

25aEC-13 Neutron scattering study for UPd_2Si_2 under uniaxial-stress
Nakada T; Yokoyama M; Igarashi H; Tabata C; Hidaka H; Amitsuka H; Tenya K; Sato T. J
Meeting Abstracts of the Physical Society of Japan, 2011

25pWJ-11 Is the hidden order of URu_2Si_2 really quadrupolar?
TAKAGI Shigeru; KUNO Daisuke; YOKOYAMA Makoto; AMITSUKA Hiroshi
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2010

25pWJ-4 Angle resolved magnetization measurements of URu_2Si_2
Kurahashi Y; Nishikawa D; Shimizu Y; Hidaka H; Yanagisawa T; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2010

25pWJ-7 Elastic response of heavy fermion compound U(Ru_<1-x>Rh_x)_2Si_2
Saito H; Yanagisawa T; Mayama T; Ikeda Y; Hidaka H; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2010

強相関5f電子系化合物における量子異常の研究と新規物性の探索
網塚浩; 柳澤達也; 日高宏之; 池田陽一; 清水悠晴; 西川大地; 田中淳; 真山太一; 横山淳; 芳賀芳範; 本間佳哉
東北大学金属材料研究所附属量子エネルギー材料科学国際研究センター共同利用研究経過報告書(CD-ROM), Jul. 2010

21pGF-1 Magnetization Measurements of URu_2Si_2 under High Pressure II
Nishikawa D; Ikeda Y; Shimizu Y; Hidaka H; Yanagisawa T; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 01 Mar. 2010

21aPS-16 Ultrasonic measurement of heavy fermion compound U(Ru_<1-x>Rh_x)Si_2
Saito H; Yanagisawa T; Mayama T; Ikeda Y; Hidaka H; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 01 Mar. 2010

20aPS-17 Quantitative evaluation of magnetic cluster size in perpendicular magnetic recording media
Hagiya H; Oku T; Suzuki J; Kira H; Shinohara T; Kakurai K; Yokoyama M; Nishihara Y; Mamiya H; Oba Y; Ohnuma M
Meeting abstracts of the Physical Society of Japan, 01 Mar. 2010

25pWJ-10 NMR/NQR investigations of the hidden order in URu_2Si_2
Mito T.; Hattori M.; Motoyama G.; Koyama T.; Ueda K.; Kohara T.; Yokoyama M.; Amitsuka H.
Meeting Abstracts of the Physical Society of Japan, 2010

23aWP-6 Possibility of the inverse Dzyaloshinsky-Moriya interaction in metallic helical magnet MnP
Yamazaki T; Tabata Y; Waki T; Nakamura H; Matsuura M; Ohoyama K; Yokoyama M
Meeting Abstracts of the Physical Society of Japan, 2010

25aPS-49 Single site effects in La-diluted clathrate system of R_3Pd_<20>Ge_6(R=Ce, Pr)
Wakabayashi T; Hidaka H; Yanagisawa T; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2009

25pTJ-6 Specific Heat Measurement of URu_2Si_2 under High Pressure II
Ikeda Y; Nishikawa D; Tanaka A; Kurahashi Y; Shimizu Y; Hidaka H; Yanagisawa T; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2009

25pTJ-7 Development of Measurement Method with NiCrAl Piston Cylinder Cell and Magnetization Measurements of URu_2Si_2 under High Pressure
Nishikawa D; Ikeda Y; Hidaka H; Yanagisawa T; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2009

URu₂Si₂の高圧下磁化測定
西川大地; 石原祐子; 高山茂貴; 日高宏之; 柳澤達也; 横山淳; 網塚浩; KREITLOW Jan; SULLOW Stefan
日本物理学会講演概要集, 03 Mar. 2009

Pr₃Pd₂₀Ge₆の低温磁場中構造解析
若林琢巳; 川崎郁斗; 日高宏之; 網塚浩; 柳澤達也; 横山淳; 天谷健一
日本物理学会講演概要集, 03 Mar. 2009

27aTD-3 Elastic Neutron Scattering Experiment on URu_2Si_2 under Uniaxial Stress
Ikeda Y; Yokoyama M; Nishikawa D; Hidaka H; Yanagisawa T; Tenya K; Kawarazaki S; Sato T. J; Yoshizawa H; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2009

27aTD-5 Weak Magnetism of Uranium Compounds Studied by Resonant X-ray Scattering Measurements
Amitsuka H; Takayama S; Ikeda Y; Kawasaki I; Hidaka H; Yanagisawa T; Yokoyama M; Inami T; Haga Y; Homma Y
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2009

27aTD-6 Systematic Study of Crystalline-Electric-Field Effect in Dilute Magnetic Systems La_<1-x>R_xRu_2Si_2 (R: Rare Earth; x≤0.1): Part II
Morishita A; Hidaka H; Yanagisawa T; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2009

27aPS-36 Magnetic Clustering and Non-Fermi-Liquid Behavior Accompanying Suppression of Long-Range Ferromagnetic Order in CePt_<1-x>Rh_x
Kawasaki I; Hidaka H; Yanagisawa T; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2009

27aPS-87 Structure analysis of Pr_3Pd_<20>Ge_6 in low temperature and magnetic field
Wakabayashi T; Kawasaki I; Hidaka H; Amitsuka H; Yanagisawa T; Yokoyama M; Tenya K
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2009

CePt_1-xRh_xの強磁性長距離秩序の抑制に伴う磁気クラスター形成および非フェルミ液体異常
川崎郁斗; 日高宏之; 柳澤達也; 横山淳; 天谷健一; 網塚浩
日本物理学会講演概要集, 2009

立方晶希土類化合物R₃Pd₂₀Ge₆(R=Ce,Pr)におけるLa希釈効果
若林琢巳; 日高宏之; 柳澤達也; 横山淳; 天谷健一; 網塚浩
日本物理学会講演概要集, 2009

21aPS-100 Search for the Hidden Order parameter in URu_2Si_2
Takayama S.; Ikeda Y.; Kawasaki I.; Yokoyama M.; Inami T.; Honma Y.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2008

21aPS-43 Systematic Study of Magnetic Anisotropy and Crystalline-Electric-Field Effect in Dilute Magnetic Systems La_<1-x>R_xRu_2Si_2 (R=Rare Earth; x≤0.1)
Morishita A.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2008

21aPS-102 Magnetization Measurements under Hydrostatic Pressureon URu_2Si_2 II
Ishihara Y; Takayama S; Morishita A; Hidaka H; Amitsuka H; Yanagisawa T; Tenya K; Yokoyama M; Kreitlow Jan; Sullow Stefan; Sawai Y; Kindo K; Honma Y
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2008

21aPS-57 Field Induce Phase Transition on Clathrate Compound Pr_3Pd_<20>Ge_6 II
Wakabayashi T; Kawasaki I; Morishita A; Hidaka H; Amitsuka H; Yanagisawa T; Yokoyama M; Tenya K
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2008

21aPS-101 Heat Capacity Measurement for URu_2Si_2 Under High Pressure
Ikeda Y; Tanaka A; Takayama S; Ishihara Y; Hidaka H; Yanagisawa T; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2008

22pQC-12 Magnetic properties and ferromagnetic quantum critical behavior of CePt_<1-x>Rh_x
Kawasaki I; Nishikawa D; Hidaka H; Yanagisawa T; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2008

24aYB-6 Systematic Study of Crystalline-Electric-Field Effect in Dilute Magnetic Systems La_<1-x>R_xRu_2Si_2(R=Rare Earth;x&pve;0.1)
Morishita A.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 29 Feb. 2008

24aYB-1 Ferromagnetic quantum critical behavior in CePt_<1-x>Rh_x
Kawasaki I.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 29 Feb. 2008

24pWR-11 Neutron-scattering study under magnetic field on Ce(Rh,Co)In_5
Yokoyama M.; Oyama N.; Oinuma S.; Kawasaki I.; Amitsuka H.; Tenya K.; Matsuura M.; Hirota K.
Meeting abstracts of the Physical Society of Japan, 29 Feb. 2008

URu₂Si₂の静水圧下磁化測定
石原祐子; 高山茂貴; 森下明; 日高宏之; 網塚浩; 横山淳; 天谷健一; KREITLOW Jan; SUELLOW Stefan
日本物理学会講演概要集, 2008

CePt_1-xRh_xの磁性状態と強磁性量子臨界現象
川崎郁斗; 西川大地; 日高宏之; 柳澤達也; 横山淳; 天谷健一; 網塚浩
日本物理学会講演概要集, 2008

Pr₃Pd₂₀Ge₆の磁場誘起相転移 II
若林琢巳; 川崎郁斗; 森下明; 日高宏之; 網塚浩; 柳澤達也; 横山淳; 天谷健一
日本物理学会講演概要集, 2008

23pPSB-41 Magnetization Measurements under Hydrostatic Pressure on URu_2Si_2
Ishihara Y; Takayama S; Morishita A; Hidaka H; Amitsuka H; Yokoyama M; Tenya K; Kreitlow Jan; Sullow Stefan
Meeting Abstracts of the Physical Society of Japan, 2008

21pPSA-85 Magnetization and Superconductivity of Ce(Rh, Co)In_5
Oinuma S.; Kawasaki I.; Yokoyama Y.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 21 Aug. 2007

21pPSA-10 Systematic Study of Single-Site Electronic Correlation in Dilute Magnetic System La_<1-x>RE_xRu_2Si_2 (RE : Rare-Earth Elements ; x≤0.1)
Morishita A.; Oinuma S.; Ikeda Y.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 21 Aug. 2007

21pPSB-35 Crystal Electronic Field Effects m Pr_3Pd_<20>Ge_6 III
Wakabayashi T.; Kawasaki I.; Tennya K.; Amitsuka H.; Yokoyama M.
Meeting abstracts of the Physical Society of Japan, 21 Aug. 2007

22aXA-10 Antiferromagnetic state in Co-doped CeRhIn_5 II
Yokoyama M.; Oyama N.; Oinuma S.; Kawasaki I.; Amitsuka H.; Tenya K.; Matsuura M.; Hirota K.; Sato T. J.
Meeting abstracts of the Physical Society of Japan, 21 Aug. 2007

18pPSB-26 Specific Heat Measurements of Ce(Rh,Co)In_5 in Magnetic Fields
Oinuma S.; Ibuka S.; Kawasaki I.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 28 Feb. 2007

20pWP-10 Antiferromagnetic state in Co-doped CeRhIn_5
Yokoyama M.; Oyama N.; Oinuma S.; Kawasaki I.; Tenya K.; Amitsuka H.; Sato T.J.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 28 Feb. 2007

21aWP-2 Single-crystal NMR studies on hidden order in URu_2Si_2
Takagi S.; Nakamaru Y.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 28 Feb. 2007

18pPSB-46 Low-Temperature Properties of Dilute System RR_xLa_<1-x>Ru_2Si_2(R: Rare-Earth Element)
Morishita A.; Oinuma S.; Tasaka A.; Yamahana R.; Matsuda K.; Wakabayashi T.; Kawasaki I.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 28 Feb. 2007

25pZR-3 The neutron scattering experiments on URu_2Si_2 under high pressure III
Matsuda K.; Yokoyama M.; Tenya K.; Amitsuka H.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 18 Aug. 2006

30aTD-3 The neutron scattering experiments on URu_2Si_2 under high pressure II
Matsuda K.; Yokoyama M.; Tenya K.; Amitsuka H.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 04 Mar. 2006

22aXD-2 The neutron scattering experiments on URu_2Si_2 under high pressure
Matsuda K.; Yokoyama M.; Amitsuka H.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 19 Aug. 2005

22aXD-3 Neutron scattering study on "weak ferromagnetism" in URu_2Si_2
Yokoyama M.; Gawase A.; Amitsuka H.; Tenya K.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 19 Aug. 2005

22aXD-1 NQR/NMR study of hidden order in URu_2Si_2
Ishihara S.; Takagi S.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 19 Aug. 2005

21aYJ-5 Static Magnetization Study of Sr_2RuO_4 at Very Low Temperatures III
Tenya K.; Yokoyama M; Amituka H.; Deguchi K.; Maeno Y.
Meeting abstracts of the Physical Society of Japan, 19 Aug. 2005

27aWA-12 Magnetic form factor of URu_2Si_2
Kuwahara K.; Kohgi M.; Iwasa K.; Nishi M.; Nakajima K.; Yokoyama J.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 04 Mar. 2005

25aPS-1 NQR/NMR study of hidden order in URu_2Si_2 II
Ishihara S.; Saito S.; Takagi S.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 04 Mar. 2005

〔Major achievements〕URu₂Si₂における隠れた秩序と不均一磁性の競合
横山 淳; 網塚 浩
波紋, 2005, [Reviewed], [Invited]
Lead

15aRD-1 ^<101>Ru NQR/^<29>Si NMR in Single Crystalline URu_2Si_2
Saito S; Takagi S; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2004

14pPSA-11 Neutron scattering study under uniaxial stress for the heavy fermion compound CePd_2Si_2
Yokoyama M; Gawase A; Amitsuka H; Tenya K; Yoshizawa H
Meeting abstracts of the Physical Society of Japan, 25 Aug. 2004

27aXC-1 Static Magnetization Study of Sr_2RuO_4 at Very Low Temperatures II
Tenya K; Yasuda S; Tameyasu K; Yokoyama M; Amituka H; Deguchi K; Maeno Y
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2004

28aXD-8 Magnetic Phase Diagram of U(Ru_<1-x>Rh_x)_2Si_2 (x≤0.05)
Yokoyama M; Amitsuka H; Itoh S; Kawasaki I; Tenya K; Yoshizawa H
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2004

28aXD-10 ^<29>Si NMR/^<101>Ru NQR in Single Crystalline URu_2Si_2
Saito S; Takagi S; Yokoyama M; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2004

28aXD-9 Metamagnetism in U(Ru_<1-x>Rh_x)_2Si_2(x≤0.04)
Amitsuka H; Tenya K; Yokoyama M; Kim Kee Hoon; Harrison Neil; Jaime Marcelo; Mydosh John A
Meeting abstracts of the Physical Society of Japan, 03 Mar. 2004

Low Temperature Magnetic Propertles of U(Ru_<1-x>Rh_x)_2Si_2 (x≤0.07)
Itoh S.; Yokoyama M.; Tenya K.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 15 Aug. 2003

Inhomogeueous Magnetism and Magnetic Excitations in U(Ru_<1-x>Rh_x)_2Si_2 (x≤0.05)
Yokoyama M.; Itoh S.; Amitsuka H.; Tenya K.; Yoshizawa H.
Meeting abstracts of the Physical Society of Japan, 15 Aug. 2003

Static Magnetization Study of Sr_2RuO_4 at Very Low Temperatures
Yasuda S.; Tameyasu K.; Yokoyama M.; Tenya K.; Amituka H.; Deguchi K.; Maeno Y.
Meeting abstracts of the Physical Society of Japan, 15 Aug. 2003

Muon Spin Relaxation Study of U(Ru_<1-x>Rh_x)_2Si_2 (x≤0.05)
Yokoyama M.; Itoh S.; Amitsuka H.; Andreica D.; Schenck A.; Gygax F. N.; Amato A.; Mydosh J. A.
Meeting abstracts of the Physical Society of Japan, 06 Mar. 2003

^<29>Si NMR Studies of Hidden Order in Single Crystalline URu_2Si_2
Sasaki H.; Saitoh S.; Muraoka H.; Takagi S.; Yokoyama M.; Amitsuka H.
Meeting abstracts of the Physical Society of Japan, 06 Mar. 2003

High-Pressure μSR Measurements on URu2Si2
Amitsuka H; Yokoyama M; Tenya K; Miyako Y; Schenck A; Andreica D; Gygax F.N; Amato A; Kai Huang Ying; Mydosh J.A
Meeting abstracts of the Physical Society of Japan, 13 Aug. 2002

29Si-NMR Study of U(Ru1-xRhx)2Si2
Sawa T; Furukawa Y; Kumagai K; Ito S; Yokoyama M; Tenya K; Amitsuka H
Meeting abstracts of the Physical Society of Japan, 13 Aug. 2002

High pressure X-ray diffraction study of URu2Si2
Kuwahara K; Sagayama H; Iwasa K; Kohgi M; Miyazaki S; Nozaki J; Nogami J; Yokoyama M; Amitsuka H; Nakao H; Murakami Y
Meeting abstracts of the Physical Society of Japan, 13 Aug. 2002

Field-Induced Quadrupole Order in TmCo2Si2
網塚 浩; 横山 淳; 野崎 順; 天谷 健一; 東方 綾; 大山 研司; 榊原 俊郎
Meeting abstracts of the Physical Society of Japan, 13 Aug. 2002

Hidden Order and Antiferromagnetism in U(Ru1-xRhx)2Si2
Amitsuka H; Yokoyama M; Itoh S; Tenya K; Yoshizawa H
Meeting abstracts of the Physical Society of Japan, 13 Aug. 2002

27pWB-4 Neutron Scattering Study of URu_2si_2 under Uniaxial Stress
Yokoyama M.; Nozaki J.; Amitsuka H.; Watanabe K; Kawarazaki S.; Yoshizawa H.; Mydosh J.A.
Meeting abstracts of the Physical Society of Japan, 01 Mar. 2002

Uniaxial Stress Effects of the Heavy Electron Compound URu_2Si_2
Yokoyama M.; Amitsuka H.; Watanabe K.; Kawarazaki S.; Yoshizawa H.; Mydoh J. A.
Meeting abstracts of the Physical Society of Japan, 03 Sep. 2001

μSR study on the ordered state of URu_2Si_2
Miyazaki S.; Yokoyama M.; Teramae S.; Tenya K.; Amitsuka H.; Higemoto W.; Nagamine K.
Meeting abstracts of the Physical Society of Japan, 03 Sep. 2001

μSR Study on the Small-Moment Antiferromagnetic State in URu_2Si_2
Amitsuka H.; Miyazaki S.; Yokoyama M.; Tenya K.; Sakakibara T.; Higemoto W.; Nagamine K.
Meeting abstracts of the Physical Society of Japan, 09 Mar. 2001

Th dilution effects of the heavy electron compound URu_2Si_2
Yokoyama M.; Amitsuka H.; Tenya K.
Meeting abstracts of the Physical Society of Japan, 09 Mar. 2001

Anisotropy of the phase diagram of Ce_<0.75>La_<0.25>B_6
Sakakibara T.; Yokoyama M.; Amitsuka H.; Tenya K.; Kunii S.
Meeting abstracts of the Physical Society of Japan, 10 Sep. 2000

Low temperature magnetic properties of the rare-earthe compounds TmM_2Si_2 (M: Transition metals)
Yokoyama M.; Nozaki J.; Miyazaki S.; Tenya K.; Amitsuka H.; Sakakibara T.
Meeting abstracts of the Physical Society of Japan, 10 Sep. 2000

Magnetization and Specific Heat Studies of UR_2Si_2 in the Supersonducting State
Tenya K.; Yokoyama M.; Amitsuka H.; Sakakibara T.; Ohkumi H.; Inada Y.; Onuki Y.; Yamamoto E.; Haga Y.; Honma T.
Meeting abstracts of the Physical Society of Japan, 10 Mar. 2000

Themal properties of Y-doped URu_2Si_2 : Speciffic heat measurements in High field
Yokoyama M.; Amitsuka H.; Okumura A.; Tenya K.; Sakakibara T.
Meeting abstracts of the Physical Society of Japan, 10 Mar. 2000

25aH-1 Effect of Pressure on"Weak Antiferromagnetic"of Uru_2Si_2
Amitsuka H; Yokoyama M; Kuwahara K; Sato M; Metoki N; Kawarazaki S; Miyako Y; Sakakibara T; Mydosh J.A.
Meeting Abstracts of the Physical Society of Japan, 1999

25aH-3 Effect of Pressure on the magnetic excitation of Uru_2Si_2 at low temperature
Sato M; Metoki N; Honma T; Onuki Y; Amitsuka H; Yokoyama M; Kuwahara K; Sakakibara T
Meeting Abstracts of the Physical Society of Japan, 1999

Smイオン置換したCeCoIn5における超伝導の抑制と磁気秩序の誘起
小泉遼介; 高橋哲平; 富士本駿; 海老澤秀明; 松尾晶; 金道浩一; 那波和宏; 金城克樹; 佐藤卓; 天谷健一; 横山淳
日本物理学会2025年春季大会, 20 Mar. 2025

重い電子超伝導体CeCoIn5のNi 置換系における量子臨界点　　　　　　　　　　　　　　　
横山淳
東北大学金属材料研 究所大洗・アルファ合同研究会, Sep. 2024

Zn置換したCeCoIn5の超伝導相内における反強磁性秩序　　　　　　　　　　　　　　　
横山淳; 井能楓; 矢代安澄; 小泉遼介; 高橋哲平; 海老澤秀明; 富士本駿; 大山研司; 岩佐和晃; 天谷健一; 松尾晶; 金道浩一
日 本物理学会第79回年次大会, Sep. 2024

比熱や磁化から見るNi置換系CeCoIn5の零磁場量子臨界点　　　　　　　　　　　　　　　
高橋哲平; 横山淳; 鈴木康平; 小泉遼介; 海老澤秀明; 松尾晶; 金道浩一; 中村翔太; 清水悠晴; 榊原俊郎
日本物理学会第79回年次大会, Sep. 2024

CaRuO3のLa0.5K0.5イオン置換系における非フェルミ液体状態と磁気相関の関連　　　　　　　　　　　　　　　
海老澤秀明; 塩澤悠花; 杉谷美奈; 松尾晶; 金道浩一; 横山淳
日本物理学会第79 回年次大会, Sep. 2024

ホール抵抗測定で見た重い電子系超伝導体CeCo1−xNixIn5の量子臨界揺らぎ　　　　　　　　　　　　　　　
小泉遼介; 矢代安澄; 高橋哲平; 富士本駿; 清水悠晴; 青木大; 天谷健一; 横山淳
日本物理学会第79 回年次大会, Sep. 2024

Carrier-doping effect and quantum criticality in Ni-doped CeCoIn5 investigated by Hall-resistivity measurements　　　　　　　　　　　　　　　
Ryosuke Koizumi; Azumi Yashiro; Teppei Takahashi; Yusei Shimizu; Dai Aoki; Kenichi Tenya; Makoto Yokoyama
International Conference on Magnetism 2024, 03 Jul. 2024

Relationship between quantum criticality and superconducting upper critical field in Ni-doped CeCoIn5　　　　　　　　　　　　　　　
Makoto Yokoyama; Azumi Yashiro; Rahmanto; Kaketo Inami; Kohei Suzuki; Kaede Inoh; Teppei Takahashi; Ryosuke Koizumi; Yohei Kono; Shunichiro Kittaka; Kenichi Tenya; Fuminori Honda; Yusei Shimizu; Dai Aoki
International Conference on Magnetism 2024, 01 Jul. 2024

Quantum criticality in Ni-doped CeCoIn5 investigated by specific heat and magnetization measurements　　　　　　　　　　　　　　　
Teppei Takahashi; Kohei Suzuki; Akira Matsuo; Koichi Kindo; Shota Nakamura; Yusei Shimizu; Toshiro Sakakibara; Makoto Yokoyama
International Conference on Magnetism 2024, 01 Jul. 2024

CaRuO3のLa0.5K0.5イオン置換系における非フェルミ液体からフェルミ液体へのクロスオーバー　　　　　　　　　　　　　　　
海老澤秀明; 塩澤悠花; 杉谷美奈; 松尾晶; 金道浩一; 横山淳
日本物理学会2024年春季大会, 20 Mar. 2024

ホール抵抗測定で探るNi置換したCeCoIn5のキャリアドープ効果と量子臨界現象　　　　　　　　　　　　　　　
小泉遼介; 矢代安澄; 高橋哲平; 清水悠晴; 青木大; 天谷健一; 横山淳
日本物理学会2024年春季大会, 18 Mar. 2024

Ce3T4Sn13(T = Co, Rh, Ir)のカイラル相における4f 電子状態とWeyl-Kondo半金属　　　　　　　　　　　　　　　
岩佐和晃; 河村聖子; 村井直樹; 中島健次; J.-M. Mignot; S. Raymond; Paul Steffens; 松田達磨; 青木勇二; 川崎郁斗; 藤森伸一; 山上浩志; 横山淳
日本物理学会第78 回年次大会, Sep. 2023

Znイオン置換したCeCoIn5の超伝導と反強磁性秩序の共存　　　　　　　　　　　　　　　
井能楓; 小日向実佳; 細貝明日香; 岩佐和晃; 大山研司; 松尾晶; 金道浩一; 天谷健一; 横山淳
日本物理学会第78 回年次大会, Sep. 2023

比熱や磁化測定から見るCeCo(1−x)NixIn5 の量子臨界揺らぎ　　　　　　　　　　　　　　　
高橋哲平; 鈴木康平; 横山淳; 松尾晶; 金道浩一; 中村翔太; 清水悠晴; 榊原俊郎
日本物理学会第78回年次大会, Sep. 2023

Ce(Co1−xNix)In5の超伝導状態のミュオンスピン回転法による観測　　　　　　　　　　　　　　　
髭本亘; 横山淳; 中野裕章; 高久雅暉; 宮田侑; 伊藤孝
日本物理学会第78 回年次大会, Sep. 2023

Ni置換したCeCoIn5 における量子臨界性の磁場角度依存性　　　　　　　　　　　　　　　
井波駆; 橘高俊一郎; 河野洋平; 横山淳
日本物理学会第78回年次大会, Sep. 2023

Ni置換したCeCoIn5の超伝導相近傍で発達する量子臨界ゆらぎ　　　　　　　　　　　　　　　
矢代安澄; ラフマント; 鈴木康平; 清水悠晴; 本多史憲; 青木大; 天谷健一; 横山淳
日本物理学会第78回年次大会, Sep. 2023

重い電子系超伝導体CeCo1−xNixIn5の超伝導抑制と結晶格子の関連　　　　　　　　　　　　　　　
小泉遼介; 井能楓; 矢代安澄; 杉谷美奈; 横山淳
日本物理学会第78回年次大会, Sep. 2023

重い電⼦超伝導体CeCoIn5のZnイオン置換系における反強磁性秩序と量⼦臨界現象　　　　　　　　　　　　　　　
横山淳
東北⼤学⾦属材料研究所⼤洗・アルファ合同研究会, Sep. 2023, [Invited]

Lattice Properties in Heavy-fermion Superconductor CeCo1−xNixIn5　　　　　　　　　　　　　　　
R. Koizumi; K. Inoh; A. Yashiro; and M. Yokoyama
International Conference on Strongly Correlated Electron Systems SCES 2023, Jul. 2023

Neutron-Scattering Study for Antiferromagnetic Order in Zn-doped CeCoIn5　　　　　　　　　　　　　　　
K. Inoh; A. Yashiro; A. Hosogai; R. Koizumi; H. Ebisawa; T. Takahashi; I. Kawasaki; D. Okuyama; Hung-Cheng Wu; T. J. Sato; K. Iwasa; K. Ohoyama; S. Raymond; K. Tenya; and M. Yokoyama
International Conference on Strongly Correlated Electron Systems SCES 2023, Jul. 2023

Weyl-Kondo Semimetal Behavior in the Chiral Structure Phase of Ce3Rh4Sn13　　　　　　　　　　　　　　　
K. Iwasa; K. Suyama; S. Ohira-Kawamura; K. Nakajima; S. Raymond; P. Steffens; A. Yamada; T. D. Matsuda; Y. Aoki; I. Kawasaki; S.-i. Fujimori; H. Yamagami; and M. Yokoyama
International Conference on Strongly Correlated Electron Systems SCES 2023, Jul. 2023

磁場角度分解磁歪測定から探るCeCoIn5のFFLO相転移　　　　　　　　　　　　　　　
橘高俊一郎; 綱島海斗; 木元大介; 河野洋平; 清水悠晴; 山下穣; 榊原俊郎; 横山淳; 町田一成
日本物理学会2023年春季大会, Mar. 2023

ミュオンで見たZn置換CeCoIn5の超伝導状態における磁性　　　　　　　　　　　　　　　
髭本亘; 横山淳; 伊藤孝; 中野裕章; 鈴木泰雅; Stephane Raymond; 栁瀬陽一
日本物理学会2023年春季大会, Mar. 2023

中性子散乱で見るZnイオン置換したCeCoIn5の反強磁性構造　　　　　　　　　　　　　　　
井能楓; 矢代安澄; 小泉遼介; 細貝明日香; 海老澤秀明; 高橋哲平; 川崎郁斗; 奥山大輔; Hung-Cheng Wu; 佐藤卓; 岩佐和晃; 大山研司; Stephane Raymond; 天谷健一; 横山淳
日本物理学会2023年春季大会, Mar. 2023

Ni置換したCeCoIn5の超伝導消失と量子臨界ゆらぎ　　　　　　　　　　　　　　　
矢代安澄; ラフマント; 鈴木康平; 清水悠晴; 本多史憲; 青木大; 天谷健一; 横山淳
日本物理学会2023年春季大会, Mar. 2023

重い電子系超伝導体CeCo1-xNixIn5の結晶格子特性　　　　　　　　　　　　　　　
小泉遼介; 井能楓; 矢代安澄; 横山淳
日本物理学会2023年春季大会, Mar. 2023

CeCo1-xNixIn5の量子臨界揺らぎと超伝導上部臨界磁場　　　　　　　　　　　　　　　
横山淳
東北大学金属材料研究所大洗・アルファ合同研究会, 29 Sep. 2022, [Invited]

重い電子超伝導体CeCo1-xNixIn5の結晶格子特性　　　　　　　　　　　　　　　
小泉遼介
東北大学金属材料研究所大洗・アルファ合同研究会, 29 Sep. 2022

CeCoIn5における磁場誘起非フェルミ液体異常のNi置換効果　　　　　　　　　　　　　　　
矢代安澄
東北大学金属材料研究所大洗・アルファ合同研究会, 29 Sep. 2022

CeCoIn5 の量子臨界揺らぎとZn置換系における磁場誘起反強磁性の関係　　　　　　　　　　　　　　　
横山淳; 本間友徳; 大島佳樹; ラフマント; 鈴木康平; 天谷健一; 清水悠晴; 青木大; 松尾晶; 金道浩一; 中村翔太; 河野洋平; 橘高俊一郎; 榊原俊郎
日本物理学会2021年秋季大会, Sep. 2021

重い電子系超伝導体CeCoIn5におけるNi置換効果とZn置換効果」　　　　　　　　　　　　　　　
酒井宏典; 徳永陽; 芳賀芳範; 神戸振作; J.-X. Zhu; F. Ronning; S. K. Ramakrishna; A. P. Reyes; 小手川恒; 藤秀樹; 鈴木康平; 大島佳樹; 横山淳
日本物理学会2021年秋季大会, Sep. 2021

重い電子超伝導体CeCo1−xNixIn5の量子臨界揺らぎ　　　　　　　　　　　　　　　
横山淳
東北大学大洗・アルファ合同研究会, Sep. 2021

重い電子超伝導体CeCoIn5における縦波弾性定数の静水圧依存性　　　　　　　　　　　　　　　
徳永淳志; 佐藤晴耕; 赤津光洋; 根本祐一; 横山淳
日本物理学会第76回年次大会, Mar. 2021

重い電子系超伝導体CeCoIn5におけるNi 置換効果のNMR　　　　　　　　　　　　　　　
酒井宏典; 徳永陽; 芳賀芳範; 神戸振作; J.-X. Zhu; F. Ronning; 小手川恒; 藤秀樹; 鈴木康平; 大島佳樹; 横山淳
日本物理学会第76回年次大会, Mar. 2021

Relationship between quantum critical fluctuations and anomalous superconductivity in CeCoIn5 and its ionic substitutions　　　　　　　　　　　　　　　
Makoto Yokoyama
GIMRT Joint International Symposium on Radiation Effects in Materials and Actinide Science, Oct. 2020, [Invited]

重い電子系超伝導体CeCoIn5においてZn置換による不均一電子状態　　　　　　　　　　　　　　　
酒井宏典; 徳永陽; 芳賀芳範; 神戸振作; J.-X. Zhu; F. Ronning; S. K. Ramakrishna; A. P.; Reyes; 鈴木康平; 大島佳樹; 横山淳
日本物理学会2020 年秋季大会, Sep. 2020

重い電子超伝導体CeCoIn5の弾性的性質に対する圧力効果　　　　　　　　　　　　　　　
徳永淳志; 佐藤晴耕; 赤津光洋; 根本祐一; 横山淳
日本物理学会2020 年秋季大会, Sep. 2020

CeCo(In1−xZnx)5のZn濃度-温度-磁場相図　　　　　　　　　　　　　　　
長谷川奈那; 田山孝; 横山淳
日本物理学会2020 年秋季大会, Sep. 2020

CeCo(In1-xZnx)5のmuSR法による研究III　　　　　　　　　　　　　　　
髭本亘; 宮崎一輝; 網田裕斗; 伊藤孝; 鈴木康平; 大島佳樹; 横山淳
日本物理学会第75回年次大会, Mar. 2020

重い電子系超伝導体CeCoIn5におけるZnおよびNi置換効果のNMR　　　　　　　　　　　　　　　
酒井宏典; 徳永陽; 芳賀芳範; 神戸振作; J.-X. Zhu; F. Ronning; S. K. Ramakrishna; A. P. Reyes; 小手川恒; 藤秀樹; 鈴木康平; 大島佳樹; 横山淳
日本物理学会第75回年次大会, Mar. 2020

CeRhIn5のヘリカル反強磁性秩序に対するNi置換効果　　　　　　　　　　　　　　　
菅原良馬; 横山淳; 植田大地; 益田隆嗣; 近藤晃弘; 金道浩一
日本物理学会第75回年次大会, Mar. 2020, 名古屋大学

CeCo(In1-xZnx)5の精密磁化・熱膨張・磁歪測定による熱力学的考察　　　　　　　　　　　　　　　
長谷川奈那; 田山孝; 横山淳
日本物理学会第75回年次大会, Mar. 2020

CeCoIn5のNi置換系における異方的量子臨界揺らぎ　　　　　　　　　　　　　　　
横山淳; 鈴木康平; 天谷健一; 中村翔太; 河野洋平; 橘高俊一郎; 榊原俊郎
日本物理学会第74回年次大会, 2019

Sr1-x(La,K)xRuO3における遍歴強磁性秩序の消失　　　　　　　　　　　　　　　
岩原諒也; 横山淳
日本物理学会第74回年次大会, 2019

CeCoIn5のZnイオン置換系における磁場誘起量子臨界現象　　　　　　　　　　　　　　　
横山淳; 大島佳樹; 鈴木康平; 天谷健一; 中村翔太; 橘高俊一郎; 榊原俊郎
日本物理学会2019年秋季大会, 2019

CeCo(In1-xZnx)5のμSR法による研究II　　　　　　　　　　　　　　　
髭本亘; 網田裕斗; 宮崎一輝; 伊藤孝; 鈴木康平; 大島佳樹; 横山淳
日本物理学会2019年秋季大会, 2019

遍歴強磁性化合物Sr1-x(La,K)xRuO3におけるクラスター形成に伴う比熱の変化　　　　　　　　　　　　　　　
岩原諒也; 横山淳; 菅原良馬
日本物理学会2019年秋季大会, 2019

CeCoIn5のNi 置換系における異方的量子臨界揺らぎ　　　　　　　　　　　　　　　
横山淳
東北大学金属材料研究所附属量子エネルギー材料科学国際研究センター2019 年度大洗アルファ合同研究会, 2019

Transport properties in quantum critical CeCo0.75Ni0.25In5　　　　　　　　　　　　　　　
Rahmanto; M. Yokoyama; K. Suzuki; K. Tenya; Y. Shimizu; A. Nakamura; F. Honda; and; D. Aoki
International Conference on Strongly Correlated Electron Systems SCES2019, 2019

Emergence of cluster-glass state in itinerant ferromagnetic compound Sr1-x(La0.5K0.5)xRuO3　　　　　　　　　　　　　　　
R. Iwahara and M. Yokoyama
International Conference on Strongly Correlated Electron Systems SCES2019, 2019

Anisotropic Quantum Critical Fluctuations and Superconductivity in Ni-doped CeCoIn5　　　　　　　　　　　　　　　
M. Yokoyama; K. Suzuki; K. Tenya; S. Nakamura; Y. Kono; S. Kittaka; and T. Sakakibara
International Conference on Strongly Correlated Electron Systems SCES2019, 2019

エキゾチック超伝導体における量子臨界揺らぎ: 量子ビーム実験に向けた展望　　　　　　　　　　　　　　　
横山淳
茨城大学フロンティア応用原子科学研究センター研究会, 2018

Zn 置換CeCoIn5 におけるNQR/NMR 研究　　　　　　　　　　　　　　　
酒井宏典; 服部泰佑; 徳永陽; 神戸振作; 鈴木康平; 大島佳樹; 横山淳
日本物理学会第73 回年次大会, 2018

Ce(Co1-xNix)In5 における量子臨界揺らぎ　　　　　　　　　　　　　　　
鈴木康平; 横山淳; 大島佳樹; 天谷健一; 近藤晃弘; 金道浩一; 中村翔太; 橘高俊一郎; 榊原俊郎
日本物理学会第73 回年次大会, 2018

Non-Fermi-liquid behavior in heavy-fermion compound CeCo1-xNixIn5　　　　　　　　　　　　　　　
K. Suzuki; M. Yokoyama; Y. Oshima; T. Hasegawa; K. Tenya; S. Nakamura; S. Kittaka; T. Sakakibara; I. Kawasaki; W. Higemoto; and I. Watanabe
International Conference on Magnetism ICM2018, 2018

Thermal Conductivity of Heavy-Fermion Superconductor CeCo(In1-xZnx)5　　　　　　　　　　　　　　　
A. Osawa; Y. Oshima; K. Suzuki; K. Tenya; and M. Yokoyama
International Conference on Magnetism ICM2018, 2018

Field-induced antiferromagnetic order and its quantum critical fluctuations in CeCo(In1-xZnx)5　　　　　　　　　　　　　　　
M. Yokoyama; Y. Oshima; K. Suzuki; H. Mashiko; K. Tenya; Y. Shimizu; A. Nakamura; D. Aoki; A. Kondo; K. Kindo; S. Nakamura and T. Sakakibara
International Conference on Magnetism ICM2018, 2018

CeCo(In1-xZnx)5のmuSR　　　　　　　　　　　　　　　
髭本亘; 網田裕斗; 岡澤赳; 大嶋浩平; 伊藤孝; 鈴木康平; 大島佳樹; 横山淳
日本物理学会2018年秋季大会, 2018

CeCoIn5のZnイオン置換系における中性子散乱　　　　　　　　　　　　　　　
横山淳; Stephane Raymond
日本物理学会2018年秋季大会, 2018

CeCoIn5のNi置換系における量子臨界揺らぎの磁気異方性　　　　　　　　　　　　　　　
鈴木康平; 横山淳; 大島佳樹; 天谷健一; 中村翔太; 河野洋平; 橘高俊一郎; 榊原俊郎
日本物理学会2018年秋季大会, 2018

重い電子系超伝導体CeCo(In1-xZnx)5における熱伝導率　　　　　　　　　　　　　　　
大澤篤史; 横山淳; 大島佳樹; 鈴木康平; 天谷健一
日本物理学会2018年秋季大会, 2018

CeCoIn5のZnイオン置換により誘起される反強磁性の磁気構造　　　　　　　　　　　　　　　
横山淳; Stephane Raymond
日本中性子科学会第18回年会, 2018

CeCoIn5のイオン置換系における磁場誘起反強性と量子臨界揺らぎ　　　　　　　　　　　　　　　
横山淳
第三回強相関電子系研究会, 2018, [Invited]

遍歴強磁性体SrRuO3における強磁性転移の酸素同位体効果　　　　　　　　　　　　　　　
川中浩史; 相浦義弘; 長谷部敬之; 横山淳; 増井孝彦; 西原美一; 柳澤孝
日本物理学会 第72回年次大会, 2017

CeCo1-xNixIn5における非フェルミ液体異常　　　　　　　　　　　　　　　
鈴木康平; 大高凌; 益子寛明; 横山淳; 天谷健一; 中村翔太; 榊原俊郎; 清水悠晴; 仲村愛; 青木大
日本物理学会 第72回年次大会, 2017

CeCoIn5のZn置換系における磁場中輸送特性　　　　　　　　　　　　　　　
大島佳樹; 大高凌; 鈴木康平; 益子寛明; 横山淳; 天谷健一; 清水悠晴; 仲村愛; 青木大
日本物理学会 第72回年次大会, 2017

CeCo(In1-xZnx)5の低温高磁場相　　　　　　　　　　　　　　　
横山淳; 益子寛明; 大高凌; 天谷健一; 近藤晃弘; 金道浩一; 中村翔太; 榊原俊郎; 清水悠晴; 仲村愛; 青木大
日本物理学会 第72回年次大会, 2017

CeCo(In1-xZnx)5 の低温高磁場相における磁化測定　　　　　　　　　　　　　　　
大島佳樹; 横山淳; 鈴木康平; 益子寛明; 天谷健一; 中村翔太; 橘高俊一郎; 榊原俊郎
日本物理学会2017 年秋季大会, 2017

Ce(Co1-xNix)In5 の量子臨界揺らぎに対する極低温磁化測定　　　　　　　　　　　　　　　
鈴木康平; 横山淳; 大島佳樹; 大高凌; 天谷健一; 近藤晃弘; 金道浩一; 中村翔太; 榊原俊郎
日本物理学会2017 年秋季大会, 2017

CeCo(In1-xZnx)5 の精密熱膨張測定による量子臨界点の研究　　　　　　　　　　　　　　　
田山孝; 湯谷大志郎; 杉本成駿; 横山淳
日本物理学会2017 年秋季大会, 2017

CeCo(In,Zn)5 における磁場誘起量子臨界揺らぎ　　　　　　　　　　　　　　　
横山淳; 益子寛明; 大島佳樹; 鈴木康平; 天谷健一; 清水悠晴; 近藤晃弘; 金道浩一; 中村翔太; 榊原俊郎
日本物理学会2017 年秋季大会, 2017

重い電子系超伝導体CeCoIn5 のZn 置換系における磁場誘起量子臨界現象　　　　　　　　　　　　　　　
横山淳
東北大学金属材料研究所附属量子エネルギー材料科学国際研究センター平成２９年度大洗研究会, 2017

Field-induced antiferromagnetism and its concomitant quantum critical fluctuation in Zn-doped CeCoIn5　　　　　　　　　　　　　　　
Makoto Yokoyama
2nd International Symposium of Quantum Beam Science, 2017, [Invited]

重い電子系超伝導体Ce(Co1-xNix)In5 の低温物性　　　　　　　　　　　　　　　
大高凌; 横山淳; 益子寛明; 天谷健一; 河野洋平; 清水悠晴; 池田陽一; 吉澤英樹; 榊原俊郎
日本物理学会 第71 回年次大会, 2016

高磁場領域でのCeRh2Si2 のエントロピーと 電子状態　　　　　　　　　　　　　　　
小濱芳允; 大高凌; 横山淳; 松尾晶; 金道浩一
日本物理学会 第71 回年次大会, 2016

光電子分光によるSr1-xLaxRuO3 におけ るRu4d 電子状態の研究　　　　　　　　　　　　　　　
川崎郁斗; 佐近優美; 横山淳; 藤森伸一; 山上浩志
日本物理学会 第71 回年次大会, 2016

遍歴強磁性体Sr1-xLaxRuO3 の光電子分 光による電子状態の研究　　　　　　　　　　　　　　　
川崎郁斗; 佐近優美; 横山淳; 藤森伸一; 山上浩志
日本物理学会2016 年秋季大会, 2016

CeCoIn5 のZn 置換系における精密熱膨張・磁歪測定　　　　　　　　　　　　　　　
湯谷大志郎; 田山孝; 横山淳; 益子寛明; 榊原俊郎
日本物理学会2016 年秋季大会, 2016

CeCo(In1-xZnx)5 における低温高磁場相と非フェルミ液体異常　　　　　　　　　　　　　　　
益子寛明; 横山淳; 天谷健一; 近藤晃弘; 金道浩一; 中村翔太; 河野洋平; 清水悠晴; 榊原俊郎
日本物理学会2016 年秋季大会, 2016

遍歴強磁性体Sr1-xLaxRuO3 におけるスピンの動的性質　　　　　　　　　　　　　　　
長谷部敬之; 横山淳
日本物理学会2016 年秋季大会, 2016

強相関f 電子系の超伝導　　　　　　　　　　　　　　　
横山淳
平成28 年度物質科学研究会, 2016

重い電子系CeCoIn5 の超伝導および非フェルミ液体異常に対するZn 置換効果　　　　　　　　　　　　　　　
横山淳
第二回強相関電子系研究会, 2016

高磁場領域でのCeRh2Si2 のエントロピーと,電子状態　　　　　　　　　　　　　　　
小濱芳允; 大高凌; 横山淳; 松尾晶; 金道浩一
日本物理学会 第71 回年次大会, 2016

光電子分光によるSr1-xLaxRuO3 におけ,るRu4d 電子状態の研究　　　　　　　　　　　　　　　
川崎郁斗; 佐近優美; 横山淳; 藤森伸一; 山上浩志
日本物理学会 第71 回年次大会, 2016

遍歴強磁性体Sr1-xLaxRuO3 の光電子分,光による電子状態の研究　　　　　　　　　　　　　　　
川崎郁斗; 佐近優美; 横山淳; 藤森伸一; 山上浩志
日本物理学会2016 年秋季大会, 2016

非従来型超伝導を示す新規金属間化合物の開発　　　　　　　　　　　　　　　
横山淳
第５回「量子ビームを用いた材料・生体の構造と機能の研究」成果報告会, 2015

Sr1-xLaxRuO3 のクラスター状態における磁場中電気抵抗　　　　　　　　　　　　　　　
藤村健司; 近藤晃弘; 金道浩一; 池田陽一; 吉澤英樹; 川中浩史; 天谷健一; 横山淳
日本物理学会第70 回年次大会, 2015

重い電子系反強磁性体CeRh2Si2 におけるエントロピー　　　　　　　　　　　　　　　
小濱芳允; 横山淳; 金道浩一; 網塚浩
日本物理学会第70 回年次大会, 2015

近藤半導体YbB12 の電気抵抗率における表面とバルクの効果　　　　　　　　　　　　　　　
石井克弥; 林健人; 和田徹; 伊賀文俊; 左近優美; 横山淳
日本物理学会第70 回年次大会, 2015

重い電子系超伝導体CeCo(In,Zn)5 の磁場中比熱および電気抵抗　　　　　　　　　　　　　　　
益子寛明; 大高凌; 藤村健司; 佐近優美; 池田陽一; 吉澤英樹; 近藤晃弘; 金道浩一; 天谷健一; 横山淳
日本物理学会第70 回年次大会, 2015

重い電子系超伝導体CeCo(In1-xZnx)5 の上部臨界磁場　　　　　　　　　　　　　　　
横山淳; 藤村健司; 川崎郁斗; 天谷健一; 河野洋平; 榊原俊郎; 池田陽一; 吉沢英樹; 近藤晃弘; 金道浩一
日本物理学会第70 回年次大会, 2015

近藤半導体YbB12 における表面／バルク効果　　　　　　　　　　　　　　　
伊賀文俊; 和田徹; 石井克弥; 林健人; 左近優美; 横山淳; 佐藤桂輔; 近藤晃弘; 金道浩一
日本物理学会2015 年秋季大会, 2015

CeCoIn5 のZn 置換系における磁場誘起非フェルミ液体異常　　　　　　　　　　　　　　　
大高凌; 横山淳; 佐近優美; 天谷健一; 池田陽一; 吉澤英樹; 河野洋平; 清水悠晴; 榊原俊郎
日本物理学会2015 年秋季大会, 2015

重い電子系超伝導体CeCo(In1-xZnx)5 の温度-磁場相図　　　　　　　　　　　　　　　
益子寛明; 横山淳; 佐近優美; 天谷健一; 近藤晃弘; 金道浩一; 河野洋平; 清水悠晴; 榊原俊郎
日本物理学会2015 年秋季大会, 2015

Ru-NQR によるURu2Si2 の局所対称性　　　　　　　　　　　　　　　
江見直哉; 三木俊宙; 水戸毅; 本山岳; 小山岳秀; 上田光一; 小原孝夫; 横山淳; 網塚浩; 松本裕司; 芳賀芳範; 山本悦嗣; Zachary Fisk
日本物理学会第69回年次大会, 2014, 日本物理学会

Sr1-xLaxRuO3 の不均一強磁性クラスターの性質および輸送特性　　　　　　　　　　　　　　　
藤村健司; 横山淳; 根津正謙; 竹内伸吾; 皆川由貴; 川崎郁斗; 川中浩史; 天谷健一
日本物理学会第69回年次大会, 2014, 日本物理学会

重い電子系CeCoIn5 のZn 置換系における超伝導と磁性　　　　　　　　　　　　　　　
横山淳; 藤村健司; 川崎郁斗; 天谷健一; 河野洋平; 榊原俊郎; 池田陽一; 吉澤英樹
日本物理学会2014 年秋季大会, 2014

一軸性圧力下での極低温磁場中比熱測定装置の開発とCeCoIn5 への応用　　　　　　　　　　　　　　　
橘高俊一郎; 榊原俊郎; 横山淳
日本物理学会2014 年秋季大会, 2014

遍歴電子系Sr1-xLaxRuO3 の強磁性クラスター状態における磁気緩和　　　　　　　　　　　　　　　
藤村健司; 川崎郁斗; 天谷健一; 横山淳
日本物理学会2014 年秋季大会, 2014

Sr1-xCaxRuO3における強磁性クラスターグラス状態　　　　　　　　　　　　　　　
皆川由貴; 野中麻美; 藤村健司; 川中浩史; 川崎郁斗; 天谷健一; 横山淳
日本物理学会2014 年秋季大会, 2014

ミュオンスピン緩和法からみたSr1-xLaxRuO3 における不均一強磁性クラスターの形成　　　　　　　　　　　　　　　
川崎郁斗; 横山淳; 藤村健司; 渡邊功雄; 天谷健一
日本物理学会2014 年秋季大会, 2014

Inhomogeneous cluster-glass state and thermal transport properties in Sr1-xLaxRuO3　　　　　　　　　　　　　　　
K. Fujimura; M. Yokoyama; N. Netsu; S. Takeuchi; Y. Minagawa; I. Kawasaki; H. Kawanaka and K. Tenya
International Conference on Strongly Correlated Electron Systems SCES2014, 2014

Superconductivity and magnetism in heavy-fermion compound CeCo(In1-xZnx)5　　　　　　　　　　　　　　　
M. Yokoyama; M. Kimura; K. Fujimura; T. Hasegawa; K. Tenya; I. Kawasaki; Y. Kono and T. Sakakibara
International Conference on Strongly Correlated Electron Systems SCES2014, 2014

Study of local symmetry in URu2Si2 by Ru-NMR/NQR measurements　　　　　　　　　　　　　　　
N. Emi; T. Miki; T. Mito; G. Motoyama; T. Koyama; K. Ueda; T. Kohara; M. Yokoyama; H. Amitsuka; Y. Matsumoto; Y. Haga; E. Yamamoto and Z. Fisk
International Conference on Strongly Correlated Electron Systems SCES2014, 2014

Synchrotron X-Ray Diffraction Study of Single-Crystalline URu2Si2　　　　　　　　　　　　　　　
C. Tabata; R. Kumai; H. Nakao; K. Kobayashi; Y. Murakami; M. Yokoyama; H. Hidaka; T. Yanagisawa; H. Amitsuka
International Conference on Strongly Correlated Electron Systems SCES2014, 2014

High-Resolution X-Ray Diffraction Study on URu2Si2　　　　　　　　　　　　　　　
C. Tabata; T. Inami; S. Michimura; M. Yokoyama; H. Hidaka; T. Yanagisawa and H. Amitsuka
11th Prague Colloquium on f-electron systems, 2014

一軸性圧力下での極低温磁場中比熱測定装置の開発とCeCoIn5,への応用　　　　　　　　　　　　　　　
橘高俊一郎,榊原俊郎,横山淳
日本物理学会2014 年秋季大会, 2014

Polarized Light Microscopy Observations of the Hidden Order Phase in URu2Si2　　　　　　　　　　　　　　　
C. Tabata; M. Tokunaga; M. Yokoyama; H. Hidaka; T. Yanagisawa and H. Amitsuka
International Conference on Strongly Correlated Electron Systems SCES2013, 2013

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

茨城大学

American Physical Society

International Society for μSR Spectroscopy

The Physical Society of Japan

エキゾチック超伝導および非フェルミ液体異常をもたらす量子臨界状態の包括的理解
基盤研究（C）
Apr. 2023 - Mar. 2026

極低温無冷媒冷凍機で比熱を測定するための技術指導　　　　　　　　　　　　　　　
Aug. 2023 - Mar. 2024

Research on the mechanism of exotic superconductivity coupled with quantum critical fluctuations
Grant-in-Aid for Scientific Research (C)
Ibaraki University
Apr. 2020 - Mar. 2023

Interplay between unusual superconducting critical field and magnetic correlation in Pauli-limited superconductors
Grant-in-Aid for Scientific Research (C)
Ibaraki University
Apr. 2017 - Mar. 2021

Analysis on the multiphase diagram of spin-triplet superconductivity by micromagnetization measurements
Grant-in-Aid for Scientific Research (C)
Shinshu University
Apr. 2013 - Mar. 2016

一軸応力下微視測定による重い電子系の隠れた秩序の観測
新学術領域研究(研究領域提案型)
茨城大学
Apr. 2011 - Mar. 2013

Study on the superconducting micro-flux-jumps which successively appear around zero-field at low temperatures
Grant-in-Aid for Scientific Research (C)
Shinshu University
2009 - 2011

Development and application of a neutron polarizing and focusing system based on magnetic field gradients
Grant-in-Aid for Scientific Research (B)
Japan Atomic Energy Agency
2008 - 2010

Study of Weak Magnetism and It's Relationship to Hidden Order and Superconductivity in 5f-Electron Systems
Grant-in-Aid for Scientific Research (B)
Hokkaido University
2007 - 2009

重い電子系における量子臨界現象の制御パラメータの決定
若手研究(B)
茨城大学
2006 - 2007

一軸応力下微視実験による強相関f電子系の新奇な磁性と超伝導の制御
若手研究(B)
茨城大学
2004 - 2005

微視測定および希釈法によるウラン化合物の軌道秩序とゆらぎの研究
特別研究員奨励費
北海道大学
2000 - 2002