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Evidence of a Rattling Transition in the Caged Compounds LaRu2Zn20 and LaIr2Zn20: 139La NMR Studies
Hideki Tou,Kenji Asaki,Hisashi Kotegawa,Takahiro Onimaru,Keisuke T. Matsumoto,Yukihiro F. Inoue,Toshiro Takabatake 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We report a study of 139La(I=7/2) nuclear magnetic resonance (NMR) to investigate the structuralphase transition in the two caged compounds LaIr2Zn20 and LaRu2Zn20 from microscopic viewpoints. The former compound shows a second-order structural phase transition around Ts = 200 Kwhereas the latter one shows a first-order structural phase transition at Ts = 150 K. For both compounds,quite narrow La-NMR lines of less that 10 kHz without any electric field gradient (EFG) atthe La site were observed at temperatures above Ts, indicating that the local symmetry at the Lasite holds a cubic symmetry. On the other hand, an EFG at La site appears at temperatures belowTs, evidencing symmetry lowering occurs at the La site at temperatures below Ts. At temperaturesaround Ts, both the nuclear spin-lattice relaxation rate (1/T1) and the nuclear spin-spin relaxationrate (1/T2) show unusual enhancements associated with the slowing down of the EFG fluctuations. However, the temperature dependences of 1/T1T and 1/T2 are different from the typical slowingdownphenomena of the EFG fluctuations due to the classical motional narrowing. The lowering ofthe local symmetry at the La site is ascribed to a freezing of the rattling motion.
Thermoelectric properties in Mn-doped Bi<sub>2</sub>Se<sub>3</sub>
Kim, C.M.,Kim, S.H.,Onimaru, T.,Suekuni, K.,Takabatake, T.,Jung, M.H. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.8
Using n-type and p-type Mn-doped Bi<SUB>2</SUB>Se<SUB>3</SUB> single crystals, a thin-film-type thermoelectric (TE) module was fabricated and the TE characteristics were investigated. The Seebeck coefficient at room temperature was about 100 μV K<SUP>-1</SUP> with different sign for both materials. From the Seebeck coefficient and resistivity values, the electric power of our TE module was evaluated to be 90 μW for a single couple at the temperature difference of 10 K. This value is compared to that (~21 μW) of commercialized TE device. Nevertheless, the actual power was measured to be quite small around 0.74 μW, which is much higher than other homemade TE power level. This small power is attributed to the high electrical contact resistance between the TE material and the heat source and sink. Assuming the contact resistance level ~0.1 Ω similar to that of commercialized TE devices, the electric power should be about 41 μW, which is almost 2 times higher than that in commercialized TE devices. These results propose that the Mn-doped Bi<SUB>2</SUB>Se<SUB>3</SUB> system is another promising TE material, which can be replaced with the commercialized Bi<SUB>2</SUB>Te<SUB>3</SUB> system.
Satoshi Okajima,Yasuyuki Shimura,Takahiro Onimaru 한국물리학회 2023 새물리 Vol.73 No.12
When spins of s = 1/2 form a triangular lattice and antiferromagnetic interactions work between them, magnetic order is suppressed due to geometrical frustration. Our research is centered on Yb-based semiconductors Yb₂Cu<SUB>2n</SUB>S<SUB>n+3</SUB> (2 ≤ n ≤ 5) which crystallize in a trigonal CaAl₂Si₂-type structure. These semiconductors feature a defective triangular lattice made up of Yb ions. We synthesized two polycrystalline Yb₂Cu<SUB>2n</SUB>S<SUB>n+3</SUB>, with n values of 2.2 and 3.6. The former has a defect rate of 24% for Yb sites, while the latter has a defect rate of 45%. The specific heat and magnetization were measured down to 0.4 and 1.8 K, respectively. For n = 2.2, there was no indication of a phase transition. On the other hand, for n equal to 3.6, the specific heat exhibits a cusp at T₁ = 4.1 K and a peak at T₂ = 2.3 K. It is suggested that the deficiency of Yb sites in the triangular lattice induces phase transitions as a way to release geometrical frustration.
Anisotropic c − f Hybridization in the Kondo Semiconductor CeFe2Al10
Yuji Muro,Keiske Yutani,Jumpei Kajino,Takahiro Onimaru,Toshiro Takabatake 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We report a single-crystal study on the Kondo semiconductor CeFe2Al10 in which we measuredthe magnetic susceptibility, electrical resistivity, thermopower and thermal conductivity. The highlyanisotropic behavior in all measurements indicates an anisotropic electronic structure that couldoriginate from a c−f hybridization in an orthorhombic YbFe2Al10-type structure. The anisotropicc−f hybridization effect is manifested in the different peak temperatures of the electrical resistivityand the thermopower along the three principal axes.
Thermoelectric properties in Mn-doped Bi2Se3
C.M. Kim,S.H. Kim,T. Onimaru,K. Suekuni,T. Takabatake,정명화 한국물리학회 2014 Current Applied Physics Vol.14 No.8
Using n-type and p-type Mn-doped Bi2Se3 single crystals, a thin-film-type thermoelectric (TE) module was fabricated and the TE characteristics were investigated. The Seebeck coefficient at room temperature was about 100 mV K1 with different sign for both materials. From the Seebeck coefficient and resistivity values, the electric power of our TE module was evaluated to be 90 mW for a single couple at the temperature difference of 10 K. This value is compared to that (~21 mW) of commercialized TE device. Nevertheless, the actual power was measured to be quite small around 0.74 mW, which is much higher than other homemade TE power level. This small power is attributed to the high electrical contact resistance between the TE material and the heat source and sink. Assuming the contact resistance level ~0.1 U similar to that of commercialized TE devices, the electric power should be about 41 mW, which is almost 2 times higher than that in commercialized TE devices. These results propose that the Mn-doped Bi2Se3 system is another promising TE material, which can be replaced with the commercialized Bi2Te3 system.
Magnetic and Transport Properties of a New Caged Compound PrOs2Zn20
K. Wakiya,N. Nagasawa,K. T. Matsumoto,T. Onimaru,K. Umeo,T. Takabatake 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
The magnetic and transport properties of a Pr-encaged compound PrOs2Zn20 have been studiedby the electrical resistivity (T), magnetic susceptibility ρ(T), and specific heat C(T) measurementsdown to 2 K. The (T) and the C(T) show distinct anomalies at Ts = 87 K, which resemble theanomalies in the isostructural and isoelectronic compound PrRu2Zn20 with the structural phasetransition at Ts = 138 K. Above 50 K, the ρ(T) follows the Curie-Weiss law with the effectivemagnetic moment of 3.64 µB/f.u., which indicates the trivalent state of the Pr ion. The saturatedbehavior of ρ(T) below 5 K indicates the Van-Vleck paramagnetic state. Hence, the Pr3+ ion fallsin a nonmagnetic ground state under the crystalline electric field.
Tuning of magnetic and transport properties in Bi2Te3by divalent Fe doping
Jo, N. H.,Lee, K. J.,Kim, C. M.,Okamoto, K.,Kimura, A.,Miyamoto, K.,Okuda, T.,Kim, Y. K.,Lee, Z.,Onimaru, T.,Takabatake, T.,Jung, M. H. American Physical Society 2013 Physical review. B, Condensed matter and materials Vol.87 No.20