Magnetic Properties of the Heavy-Fermion Antiferromagnet Ce_7Ni_3

抄録

We report on the magnetic, transport, and thermal properties of a heavy-fermion antiferromagnet Ce₇Ni₃. The Ce ions in the three nonequivalent sites are found to be very close to trivalent from L_III X-ray absorption spectroscopy and magnetic susceptibility measurements. The magnetic susceptibility along the c axis exhibits a pronounced peak at the Néel temperature T_N=1.9, K, while that along the b axis defined perpendicular to the a axis shows a rounded maximum at 0.6, K. The magnetization curve for B//c at 1.4, K exhibits a metamagnetic transition at 0.2, T, and reaches a value of 1.0, μ _B/Ce at 36, T. The electrical resistivity ρ (T) for I//c turns up below T_N, whereas those for I//a and I//b decrease. These results suggest that the antiferromagnetic order creates a partial gap along the c axis on the Fermi surface. The magnetic entropy due to 4f electrons reaches 0.47R ln 2 at T_N. The magnetic moment and magnetic entropy in the antiferromagnetic state are substantially reduced by the combination of the Kondo effect and crystalline electric field (CEF) effect. The Kondo temperature and energy of the first CEF level are estimated to be 7, K and 240, K, respectively, by the analysis of the specific heat.