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Yoshichika Onuki,Rikio Settai,Kiyohiro Sugiyama,Tetsuya Takeuchi,Fuminori Honda,Yoshinori Haga,Etsuji Yamamoto,Tatsuma D. Matsuda,Naoyuki Tateiwa,Dai Aoki,Ilya Sheikin,Hisatomo Harima 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The f-electron system in rare-earth and actinide compounds exhibit a variety of characteristicproperties including heavy fermions and unconventional superconductivity. The Fermi surface propertiesin rare-earth and actinide compounds are clarified by the de Haas-van Alphen experimentson the basis of the results of energy band calculations. The effect of pressure on the electronicstates of CeRhIn5, CeIrSi3, and YbIr2Zn20 is studied in magnetic fields. An electronic instability,including unconventional superconductivity, occurs at 2.4 GPa in CeRhIn5 and 2.6 GPa in CeIrSi3. An abrupt non-linear increase in the magnetization, namely, a metamagnetic behavior, is found inthe heavy fermion compounds, including YbT2Zn20 (T: Co, Rh, Ir). A super-heavy fermion statewith a specific heat coefficient of 10 J/(K2·mol) is realized in YbIr2Zn20 under pressure.
Magnetization Steps in Yb2Pt2Pb with the Shastry-Sutherland Lattice
Yasuyuki Shimura,Toshiro Sakakibara,Ken Iwakawa,Yoshichika Onuki,Kiyohiro Sugiyama 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We measured the DC magnetization of the antiferromagnet Yb2Pt2Pb (TN ~ 2.1 K) with theShastry-Sutherland lattice for two in-plane directions H k[100] and [110] down to 0.08 K. Multiplemetamagnetic transitions are found to develop in the field dependence of the magnetization M(H). Substantial anisotropy is observed in M(H) and is discussed on the basis of a two-sublattice modelwith strong Ising anisotropy along the orthogonal [110] ([1¯10]) directions recently proposed byOchiai et al.
Magnetism and Superconductivity in CeCu2Ge2 under High Pressures and Magnetic Fields
Fuminori Honda,Takashi Maeta,Yusuke Hirose,Yoshichika Onuki,Atsushi Miyake,Rikio Settai 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We measured the electrical resistivity of CeCu2Ge2 under various high pressures and strongmagnetic fields. Beyond the previous antiferromagnetic critical pressure Pc ' 8 GPa, the antiferromagneticphase is found to exist at much higher pressure of 10.9 GPa even in magnetic fields upto 8 T. The pressure vs. temperature phase diagram and the magnetic field vs. temperature phasediagram under high pressure were constructed. The pressure-induced antiferromagnetic phase isstill observed and coexists with pressure-induced superconductivity at 10.9 GPa.
Magnetic Phase Diagram of UCoAl
Tatsuma D. Matsuda,Naoyuki Tateiwa,Etsuji Yamamoto,Yoshinori Haga,Yoshichika Onuki,Dai Aoki,Jacques Flouquet,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We report precision c-axis magnetic measurements on a high-quality single crystal of the heavyfermion metamagnet UCoAl. The metamagnetic transition at HM changes from 1st order at lowtemperature to a crossover at high temperature. HM is nearly linearly increasing with increasingtemperature up to a critical temperature T0. The critical temperature T0 is determined from boththe field and the temperature dependences of magnetization to be 11 K. The field dependence ofthe Sommerfeld coefficientis estimated from M(T) by using a Maxwell relation. (H) shows astep-like decrease at HM. This behavior is consistent with the previous reports of specific heat andresistivity measurements at low temperatures.
Specific-Heat Study on the Noncentrosymmetric Heavy-Fermion Superconductor CePt3Si
Tetsuya Takeuchi,Masahiko Tsujino,Takashi Yasuda,Shin Hashimoto,Rikio Settai,Yoshichika Onuki 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
Specific-heat measurements were performed on a high-quality single crystal of CePt3Si without inversion symmetry in the tetragonal crystal structure. We observed distinct peaks in the specific-heat C at the superconducting transition temperature Tc =0.46 K and the antiferromagnetic ordering temperature TN =2.25 K, compared to the previous data, indicating an improvement of the sample quality. The temperature dependence of the electronic specific-heat coefficient Ce=T below about 0.3 K is well described y the equation of Ce/T = γs + βsT with γs =34.1 mJ/K2·mol and βs =1290 mJ/K3·mol, evidencing the existence of line nodes in the superconducting energy gap. Furthermore, the electronic specific-heat coefficient γs in the superconducting state indicates a nonlinear magnetic eld dependence s(H) / pH, which also supports the presence of line nodes. Specific-heat measurements were performed on a high-quality single crystal of CePt3Si without inversion symmetry in the tetragonal crystal structure. We observed distinct peaks in the specific-heat C at the superconducting transition temperature Tc =0.46 K and the antiferromagnetic ordering temperature TN =2.25 K, compared to the previous data, indicating an improvement of the sample quality. The temperature dependence of the electronic specific-heat coefficient Ce=T below about 0.3 K is well described y the equation of Ce/T = γs + βsT with γs =34.1 mJ/K2·mol and βs =1290 mJ/K3·mol, evidencing the existence of line nodes in the superconducting energy gap. Furthermore, the electronic specific-heat coefficient γs in the superconducting state indicates a nonlinear magnetic eld dependence s(H) / pH, which also supports the presence of line nodes.
Naoyuki Tateiwa,Yoshinori Haga,Tatsuma D. Matsuda,Etsuji Yamamoto,Yoshichika Onuki,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have studied the high-pressure magnetic property in UGe2 where ferromagnetic superconductivityappears under high pressure. In this study, we focus on the magnetic property at pressuresabove the ferromagnetic critical pressure Pc =1.6 GPa. The temperature and magnetic field dependencesof the dc-magnetization have been measured under high pressures up to 5.1 GPa by using aceramic anvil high pressure cell. At pressures above Pc, the magnetic susceptibility χ shows a broadmaximum around Tχmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetictransition) at Hc. With increasing pressure, the peak structure in χ becomes broader, and thepeak position Tχmax moves to the higher temperature region. The metamagnetic field Hc increasesrapidly with increasing pressure. At pressures above 4.1 GPa, χ shows a simple temperature dependence,and the magnetization increases linearly with increasing field. These phenomena in UGe2resemble to those in the intermetallic compounds of 3d transition metals such as Co(S1−xSex) andYCo2. We discuss the experimental results by using the phenomenological spin-fluctuation theory.
Pressure Evolution of the Metamagnetic Transition in UCoAl As Measured Using 59Co NMR
Hisashi Kotegawa,Hiroki Nohara,Hideki Tou,Tatsuma D. Matsuda,Etsuji Yamamoto,Yoshinori Haga,Zachary Fisk,Yoshichika Onuki,Dai Aoki,Jacques Flouquet 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have performed NMR measurements under pressure in UCoAl with a quantum critical endpointof the metamagnetic transition from the paramagnetic phase to the ferromagnetic (FM) phase. 59Co-NMR sensitively detects the evolution of the internal field caused by applying the externalfield. The metamagnetic field Hm increases with increasing pressure consistently with other experimentalmethods, accompanied by the suppression of the magnetization in the field-induced FMphase and the magnetization jump at Hm. The loss of the NMR signal on approaching the QCEPindicates the development of the spin fluctuations.
Effect of Pressure on the Field-induced Ordered Phase in the Heavy-fermion Compound YbCo2Zn20
Tetsuya Takeuchi,Yuki Taga,Shingo Yoshiuchi,Masahiro Ohya,Yusuke Hirose,Fuminori Honda,Rikio Settai,Yoshichika Onuki 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
The effect of pressure on the field-induced ordered phase for H k h111i in the heavy-fermioncompound YbCo2Zn20, which is presumably a field-induced antiferro-quadrupolar (FI-AFQ) phase,was investigated in the pressure range up to 4.5 GPa and under magnetic fields up to 80 kOe. When pressure is applied, the metamagnetic-like transition at Hm =6 kOe shifts to lower fieldsand disappears around the quantum critical pressure Pc 1.8 GPa. A pressure-induced antiferromagnetic(PI-AFM) phase appears at pressures above about 2 GPa, and the critical field Hc ofthe PI-AFM phase increases with increasing pressure. On the other hand, the transition field HQof the FI-AFQ phase decreases gradually without showing any anomalous behavior around Pc andbecomes obscure around 4 GPa, where Hc of the PI-AFM phase and HQ of the FI-AFQ phasebecome comparable. The magnetic field versus pressure, H-P, phase diagram for H k h111i at0.1 K was constructed in the pressure range up to 4.5 GPa.
Single Crystal Growth and Various Electronic States in Yb-based Compounds
Yusuke Hirose,Shingo Yoshiuchi,Naoto Nishimura,Junya Sakaguchi,Kentaro Enoki,Ken Iwakawa,Yasunao Miura,Kiyohiro Sugiyama,Yoshichika Onuki,Rikio Settai,Tetsuya Takeuchi,Fuminori Honda,Tatsuma D. Matsud 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We succeeded in growing single crystals of YbTIn5 (T : Co, Rh, Ir), YbGa4, YbT2Zn20 (T : Co,Rh, Ir), YbPdGe, Yb2Pt2Pb, and YbPd5Al2. The electronic and magnetic properties are clarifiedby measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat and deHaas - van Alphen effect.