Junji Sakurai

Crystallographic, Magnetic, and Superconductive Transitions in (La1-xBax)2CuO4-y

Three types of phase transitions in (La1-xBax)2CuO4-y–orthorhombic to tetragonal, spin density wave (SDW) and superconductive–were traced as a function of the Ba concentration, x. The obtained phase diagram indicates that the SDW state does not coexist with superconductivity, whereas samples both in orthorhombic and tetragonal phases can be superconducting.

Unusual low-temperature properties of Ce compounds

Abstract Low-temperature properties of Ce-based ternary compounds are reviewed. The groundstate of 4f electrons from Ce exhibits a wide variety of unusual features, including magnetic ordering, nonmagnetic or superconductive heavy-fermion state, valence fluctuation, etc. Especially we will concentrate on the equi-atomic series CeTIn and CeTSn (T: transition element), of which the unusual properties will be discussed in terms of competition between the Kondo effect and the indirect RKKY interaction among Ce spins. CeNiSn is a specially interesting example which has a small energy gap growing at low temperature, probably due to coherence effect of heavy quasiparticles in the Kondo lattice.

Magnetic Field Effects on Thermopower of Fe/Cr and Cu/Co/Cu/Ni(Fe) Multilayers

We measured the thermopower under magnetic field (magneto-thermopower) on artificial metallic mutilayers, Fe/Cr and Cu/Co/Cu/Ni(Fe), which have been reported to show the giant magnetoresistance. The magneto-thermopower for these samples was also found to be remarkably large, corresponding to their giant magnetoresistance. The magneto-thermopower on Fe/Cr multilayers was observed to change its sign with temperature variation.

Magnetic and Transport Properties of New Kondo Compounds CeTIn (T=Ni, Pd and Pt)

Measurements of magnetic susceptibility, electrical resistivity and thermoelectric power have been made on the CeTIn system (T=Ni, Pd and Pt) with the hexagonal Fe2P-type structure. The results suggest that CeNiIn is an intermediate valence compound with Kondo-like anomalies in resistivity ?m(T), and CePdIn is a heavy fermion compound with doubie-peak structures in both ?m(T) and S(T) and exhibits an antiferromagnetic order at TN=1.8 K, whereas CePtIn is a heavy fermion peak in ?m(T) and shows no magnetic and superconducting transitions.

Heavy-Fermion and Semiconducting Properties of the Ternary Uranium Compounds U3T3Sn4 and U3T3Sb4 (T=Ni, Cu, Pd, Pt and Au)

We present results of magnetic, transport and calorimetric measurements on U 3 T 3 X 4 with T=Ni, Cu, Pd, Pt and Au and X=Sn and Sb. A heavy-fermion behavior manifests itself in U 3 T 3 Sn 4 , where the electronic specific-heat coefficient increases from 90 mJ/K 2 mol U for T=Ni and Pt to about 300 mJ/K 2 mol U for T=Cu and Au. We ascribe the mass enhancement to the dehybridization of 5 f electrons with the d electrons derived from the T atom. On the other hand, U 3 T 3 Sb 4 with T=Ni, Pd and Pt shows a semiconducting behavior with a band gap of about 0.2 eV, whereas U 3 Cu 3 Sb 4 is a metallic ferromagnet with T c =91 K. In these antimonides, 5 f electrons are localized because of the weak hybridization with the 5 p electrons from the Sb atom. These results indicate that the number of 5 p electrons in the present system determines whether the system shows heavy-fermion or semiconducting behavior.

Magnetic and transport studies on RPdSn (R= rare earth)

Abstract Magnetic and electrical properties of a series of ternary compounds, RPdSn (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy or Ho) were studied from electrical resistivity, thermopower, magnetic susceptibility and 119 Sn Mossbauer absorption. They were found to be antiferromagnetic. However, the values of T N are not in accordance with the De Gennes factor of rare earth elements. CePdSn was found to be a Kondo compound, SmPdSn and DyPdSn to have a secondary phase transition at a temperature below T N .

Metamagnetic Behavior of the Heavy-Fermion Compound CeNi2Ge2.

We have studied the temperature dependence of the electrical resistivity, the magnetic susceptibility and the high-field magnetization of CeNi 2 Ge 2 . Quadratic temperature dependence of the resistivity is observed below 0.7 K. The susceptibility exhibits a broad maximum at 28 K. Magnetization shows metamagnetic behavior at H M ∼42 T as in CeRu 2 Si 2 . These results indicate that CeNi 2 Ge 2 is a new heavy-fermion compound showing the metamagnetic behavior in the nonmagnetic ground state.

Magnetic, transport and specific heat measurements on CeTX (T = Pd and Pt, X = Ga, Ge and Sn)

Magnetic susceptibility, electrical resistivity, thermopower and specific heat measurements were carried out on a series of ternary compounds of Ce, CeTX (T = Pd and Pt, X = Ga, Ge and Sn). They were found to be dense Kondo compounds with an antiferromagnetic ordering at low temperatures.

X-Ray Study of Crystal Distortions in RMn2 Compounds (R: Y, Pr, Nd, Sm and Gd)

Powder X-ray diffraction measurements on intermetallic compounds RMn 2 (R: Y, Pr, Nd, Sm and Gd) have been made in a temperature range from 69 to 300 K. Below T N , every sample shows a large volume expansion, being as large as 4.6% for YMn 2 . In addition, PrMn 2 and NdMn 2 having the hexagonal C14 type of crystal structure are distorted into monoclinic below T N . On the other hand, SmMn 2 having the same C14 type structure is distorted into orthorhombic. On the basis of a theory of magnetoelastic coupling the directions of magnetization of these compounds below T N were determined. The cubic C15 type YMn 2 shows a very small and probably rhombohedral distortion below T N , whereas the same C15 type GdMn 2 shows no symmetry change.

Magnetic susceptibility and electrical resistivity of RGa6 (R rare earth metals)

Abstract The evistence and the crystal structure of RGa6 (R  rare earth metals) have been reported recently. We measured the magnetic susceptibility and electrical resistivity of these compounds in a temperature range from livuid helium temperature to room temperature, and found antiferromagnetic transitions for RGa6 (R  Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er), a superconducting transition for YGa6 and anomalous temperature dependences of the resistivity for CeGa6 and YbGa6.