Takemi Komatsubara

Magnetic Properties of Single Crystals of CexLa1-xB6

Measurements of the magnetization process at 4.2 K and 1.3 K for magnetic field up to about 150 kOe and of the temperature dependence of the susceptibility between 4.2 K and room temperature have been done in order to investigate Kondo states of dilute and dense Kondo system in single crystalline Ce x La 1- x B 6 (0.03 ≦ x ≦1.0). The magnetic phase diagram is constructed above 0.6 K for Ce 0.5 La 0.5 B 6 , Ce 0.75 La 0.25 B 6 and CeB 6 . A largely anisotropic magnetization and the temperature dependence of susceptibility in dilute alloys indicate the \(\varGamma _{8}\) quartet Kondo state contrary to the previous report. Dependence of Kondo temperature on the Ce concentration is very weak.

Coherent Kondo State in a Dense Kondo Substance: CexLa1-xCu6

The electrical resistivity, magnetoresistance and magnetic susceptibility of single crystalline Ce x La 1- x Cu 6 ( x =0-1) have been measured down to mK region. As the Ce concentration is increased, the consecutive change from the dilute (incoherent) Kondo regime to the Kondo lattice (coherent) regime is observed. The characteristic features in the coherent Kondo regime are clearly observed in the resistivity and the magnetoresistance above x =0.7. The low temperature resistivity in Ce x La 1- x Cu 6 shows a T 2 dependence and the residual resistivity follows the Nordheim law. As for the coherence effect in CeCu 6 , the resistivity follows a T 2 dependence below 0.1 K, the magnetoresistance changes from negative to positive below about 0.15 K within applied magnetic fields and the susceptibility shows an enhanced Pauli paramagnetism below 1 K.

Anomalous specific heat of CeB6

Abstract Specific heat measurement of CeB6 has been performed over the temperature region 1.6–77 K. Particularly the low-temperature anomaly, which consists of a sharp peak and a broad satellite, was examined in applied magnetic field up to 1.8 T. The observed field dependence and the entropy consideration reveal that both the two peaks are related to some intrinsic phase transitions which involve a complicated process of magnetic ordering. In the light of the reported data on magnetic properties, the anomalous features of this compound are discussed in terms of the unusual exchange interaction which differs remarkably in magnitude between the ground state and the excited state.

Heavy fermion state in CeCu6

Abstract Studies of the electrical resistivity, magnetoresistance, magnetic susceptibility, nuclear spin-lattice relaxation rate, specific heat, thermoelectric power, and Hall coefficient in Ce x La 1- x Cu 6 are reported. The magnetic properties of Ce x La 1− x Cu 6 scale with the cerium concentration, that is, the Kondo temperature is almost independent of the cerium concentration. The characteristic temperature in the heavy fermion state of CeCu 6 is about one order smaller than the Kondo temperature.

Electrical resistivity and magnetoresistance of CeB6

Abstract Electrical resistivity and magnetoresistance of CeB6 single crystal have been measured in the temperature range from 1.3 to 300 K under the magnetic field up to 85 kOe. Three characteristic phases are distinguished consistently with other measurements. The Kondo like behaviour in the resistivity observed in the high temperature phase is fitted by the conventional form for the dilute Kondo state with the Kondo temperature TK = 5 ∼ 10K and the unitarity limit resistivity ϱ u ≅ 110 μΩ cm/Ce-atom. The negative magnetoresistance in the middle phase is stronger with increasing magnetic field and with decreasing temperature suggesting rapid destruction of the Kondo state. The magnetoresistance in the low temperature phase exhibits some anomalies suggesting sub-phases corresponding to several kinds of spin ordering.

Magnetic properties of CeB6 single crystal

Abstract Magnetic measurements of CeB6 have been made in fields up to 80 kOe at temperatures up to 1000 K. Below 2.3 K, each magnetization vs field curve shows several critical points depending on the direction of field, but between 2.3 and 3 K, the curve is smooth. Above about 3 K, the magnetization curve has a break point at a certain field which increases monotonically with increasing temperature. The paramagnetic susceptibility has been analysed by assuming appropriate values of crystal-field splitting and exchange interactions. From these results, a magnetic phase diagram for CeB6 has been proposed.

Specific heat of the dense Kondo compound CeCu6

Abstract The specific heat of CeCu6 has been measured over a wide temperature range 150 mK–70 K. The ratio C/T was found to be as large as 1.45 J/K2 mol at low temperatures, indicating the heavy Fermi-liquid nature of a Kondo-lattice ground state.

Anisotropy in a Heavy Fermion Superconductor: UPd2Al3

We report on the anisotropy of magnetization, electrical resistivity and upper critical magnetic fields ( H C2 ) of UPd 2 Al 3 . The magnetization curve in the antiferromagnetically ordered state shows large anisotropy, indicating that the sublattice moments lie in the basal hexagonal plane. The value of -( d H C2 / d T ) at T C is estimated to be about 36 (kOe/K) for the magnetic field parallel and perpendicular to the hexagonal c -axis, and the upper critical field seems to be rather isotropic.

Characterization of Kondo Lattice Substance: CeCu6

Impurity effects of the starting material Ce and the crucible on the Kondo lattice formation of CeCu 6 have been studied through the measurements of the electrical resistivity, thermoelectric power, negative magnetoresistance and magnetic susceptibility.

Dense Kondo behavior in CeB6 and its alloys

Abstract CeB 6 shows a typical dense Kondo behavior and reveals three characteristics phases, named I, II and III. The phase I is characterized by the incoherent Kondo state, the mysterious phase II seems to be the quadrupolar ordering of the Γ 7 –Γ 8 mixing type, and in phase III the complicated multi-Q ordering due to the competition between the exchange and the coherent Kondo lattice appear. The substitution of nonmagnetic atoms for Ce atom causes no clear change in the Kondo temperature T K . Also, no visible change in the magnetic properties in the phase I was observed, while the decrease of ordered temperatures is observed in common for all types of substitution.