山口 明

Abstract The thermal expansion of a diluted Ce system La_1-xCe_xCu₆ for (0.6 ≤ x ≤ 1) has been measured between 10 and 150 K to reveal the change from the coherent heavy Fermion state (0.9 ≤ x ≤ 1) to the incoherent Kondo state (0 < x ≤ 0.73). The large Ce concentration x dependence of the linear thermal expansion coefficient along b-axis α_b(T) suggests that the coupling between the 4f¹ electron and the lattice strain is the largest along the b-axis in the three crystallographic axes. The maximum of the magnetic contribution to the volume thermal expansion coefficient β_m(T) at T = 50 K is retained in the x range of 0.6 ≤ x ≤ 1, suggesting the crystalline electric field (CEF) level for x = 1 doesn’t change by the substitution. Furthermore, the upturn in β_m(T) below 25 K, which should be a precursor of the maximum at T = 2.5 K reported for x = 1, is retained when we decrease x from 1 to 0.6. Because the ground state for x = 0.6 is the incoherent Kondo state, the robustness of the maximum at T = 50 K and upturn in the current x value implies that β_m(T) in 10 ≤ T ≤ 150 K is attributed to the CEF and Kondo effects rather than the formation of the heavy Fermion state.

Abstract We performed electrical resistivity measurements of Ce₃TiSb₅ under pressure. From the pressure dependences of antiferromagnetic ordering temperature T_N and lower anomalous temperature T*, temperature–pressure phase diagram of Ce₃TiSb₅ up to 2.3 GPa has been constructed. T* rapidly decreases with increasing pressure and disappears around 1 GPa. T_N increases with increasing pressure, however a hump structure of electrical resistivity below T_N becomes small. Hence, some change for the magnetic ordered state is expected to occur in higher pressure region.