Heavy fermion like behavior in layered Ce-based oxysulfides

Abstract

We have succeeded to obtain an almost single phase of layered oxysulfide CeOCuS and found a heavy fermion like behavior in this compound. It crystallizes in tetragonal LaOAgS-type structure and the lattice parameters a and c are 0.3923 and 0.8333 nm, respectively. They are smaller than those expected for trivalent Ce ion. This suggests that Ce ions exist in a mixed valence state. The temperature dependence of the specific heat, C shows an upturn below about 7 K. It is expressed by the following relation, C = γ T + β T 3 + δ T 3 ln ⁡ T . The value of γ is about 324 mJ/mol K 2, which is comparable with that of conventional heavy fermion compounds. The temperature dependence of the electrical resistivity is metallic and obeys the following relation, ρ = ρ 0 + ρ 1 T 2 + ρ 2 T 2 ln ⁡ T , below 100 K. The temperature dependence of the magnetic susceptibility is expressed by the sum of Pauli paramagnetic and Curie Weiss terms. The Pauli paramagnetic term has a large value, which corresponds to about 10% that estimated from γ . The effective magnetic moment μ eff , 1.62 μ B , is smaller than the free ion value of trivalent Ce and indicates about 64% of Ce ions is trivalent.