Electronic and magnetic properties of the electron-doped superconductor Sm_1.85Ce_0.15CuO₄-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=16.5 K). The magnetic anisotropy in the static susceptibility χ ≡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. With increasing temperature, however, 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, γ, 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 R In 2, 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.