Komatsubara Takemi

Magnetic Property of a New Kondo Lattice Intermetallic Compound: CeCu6

CeCu 6 is shown to be a typical substance in the Kondo lattice ground state, having no magnetic ordering. The anisotropic negative magnetoresistance is found at low temperatures, which probably reflects the orthorhombic crystal structure.

Anisotropic Magnetic Property of Kondo Lattice Substance: CeCu6

We have measured the electrical resistivity, magnetoresistance, magnetic susceptibility and magnetization of CeCu 6 in the temperature region of 0.6 K to room temperature. The magnetic property is extremely anisotropic, reflecting the orthorhombic crystal structure. The anisotropy of negative magnetoresistance can be qualitatively understood by the corresponding magnetization. We have found that CeCu 6 is a typical Kondo lattice substance, having no magnetic ordering. The Kondo temperature is estimated as 2–3 K.

Dense Kondo Behavior in CexLa1-xAl2

We have measured the electrical resistivity and the magnetic susceptibility of Ce x La 1- x Al 2 ( x =0–1) single crystals to study the dense Kondo phenomenon. The magnetic resistivities per molar cerium, which result from the combined effect of the crystalline field and the Kondo scattering, are found to be almost the same at higher temperatures than ca. 50 K. The Curie temperature of ca. 30 K and the effective Bohr magneton of ca. 2.5 µ B are also independent of the concentration of cerium ion. These data show that the dilute Kondo state is continuously connected to the dense Kondo state as a linear function of cerium concentration in the paramagnetic region.

Fermi Surface and Cyclotron Mass of CeB6

The angular dependence of the de Haas-van Alphen (dHvA) frequency has been studied in the Kondo lattice compound CeB 6 . The Fermi surface of CeB 6 is quite similar to that of PrB 6 or LaB 6 , with an electron pocket of almost the same size as that in PrB 6 . We have also determined the field dependence of the heavy cyclotron mass for the main belly orbit in CeB 6 and have confirmed a discrepancy between the present mass and the one estimated from the low temperature specific heat coefficient.

Kondo Lattice Formation in CexLa1-xCu6

We have measured the electrical resistivity, Hall coefficient, magnetoresistance, magnetic susceptibility and magnetization of a dense Kondo substance Ce x La 1- x Cu 6 ( x =0-1). The dilute Kondo impurity state is found to be retained below x =0.1-0.2 in Ce x La 1- x Cu 6 , having a constant value of the unitarity limit in the magnetic resistivity. On the other hand, the Kondo lattice is formed above x =0.8-0.9 because the magnetic resistivity decreases with the decrease of the temperature and the temperature dependence of negative magnetoresistance shows a minimum around 1 K.

Magnetic Property of a Dense Kondo Substance: CeCu2

We have measured the electrical resistivity, specific heat, magnetoresistance, magnetic susceptibility and magnetization of CeCu 2 single crystal in the temperature region of 1.4 K to room temperature. CeCu 2 is found to be a so-called dense Kondo substance with a large specific heat coefficient of 180 mJ/mole·K 2 around 10 K. The magnetic susceptibility and the negative magnetoresistance are extremely anisotropic, reflecting the orthorhombic crystal structure. The antiferromagnetic ordering is suggested below 3.0 K.

Low Temperature Magnetic Resistivity in a Dense Kondo Substance: CexLa1-xCu6

We have measured the low temperature electrical resistivity down to 18 mK in a dense Kondo substance Ce x La 1- x Cu 6 . The dilute Kondo impurity state is found to exist below x =0.1–0.2 in Ce x La 1- x Cu 6 , whereas the Kondo lattice is formed above x =0.8. The n-value in the resistivity of ρ m =ρ m0 + A T n in CeCu 6 is highly anisotropic with respect to the current direction; n=2.01, 1.71 and 2.07 for J // a -, b - and c -axes, respectively.

Elastic Soft Mode and Crystalline Field Effect of Kondo Lattice Substance; CeCu6

Temperature dependences of the elastic constants of the Kondo lattice substance CeCu 6 have been measured by the ultrasonic method. The transverse C 66 mode exhibits a complete softening, which is associated with the structural phase transition from the orthorhombic D 16 2h to the monoclinic C 5 2h structures at T c =168 K. The crystalline electric field effect has been observed in the softening of the elastic constants below about 100 K. The longitudinal C 11 and C 33 modes show a remarkable softening below 10 K, which is related to the excitation of the Kondo lattice.

Spin Fluctuations in the Heavy Fermion Superconductor UPd 2Al 3 Studied by Neutron Inelastic Scattering

We have found that there are two contributions to the dynamical response in UPd 2 Al 3 . The first is a heavily damped spin-wave, which has been observed previously. It shows no appreciable change on warming through T c , but softens and becomes overdamped as T approaches T N . The second is a quasielastic-like component that exists in the antiferromagnetically ordered state and is strongly localized around the ordered wavevector. As a function of temperature this component exhibits a minimum at the superconducting transition temperature T c , and increases strongly below T c . Its width in the momentum space at T = 0.5 K corresponds to a correlation length of ∼50 A, which is close to the superconducting coherence length of ∼85 A.

Superconductivity of the Kondo Lattice Substance: CeCu2Si2

Superconductivity has been ascertained in CeCu 2 Si 2 single crystals, which were grown from a tungsten crusible by the Czochralski pulling method. The anisotropic electrical resistivity and magnetic susceptibility are also presented.