Unusual nature of electronic and magnetic states of Sm_1.85Ce_0.15CuO_4-δ

Temperature-dependent magnetization (M(T)) and specific heat (C_P(T)) measurements were carried out on single-crystal Sm_1.85Ce_0.15CuO_4-δ (T_C=16.5K). The magnetic anisotropy in the static susceptibility, x = M/H, is apparent not only in its magnitude but also in its temperature dependence, with Χ_⊥ for H ⊥ c larger than Χ_∥ for H ∥ c. For both field orientations, Χ does not follow the Curie-Weiss behavior due to the small energy gap of the J = 7/2 multiplet above the J = 5/2 ground-state multiplet. However, with increasing temperature, Χ_∥(T) exhibits a broad minimum near 100 K and then a slow increase while Χ_⊥(T) shows a monotonic decrease. A sharp peak in C_P(T) at 4.7 K manifests an antiferromagnetic ordering. The electronic contribution, 7, to C_P(T) is estimated to be γ = 103.2 (7) mJ/mole·Sm·K². The entropy associated with the magnetic ordering is much smaller than Rln2, where R is the gas constant, which is usually expected for the doublet ground state of Sm⁺³. The unusual magnetic and electronic properties evident in M(T) and C_P(T) are probably due to a strong anisotropic interaction between conduction electrons and localized electrons at Sm⁺³ sites.