Successive weak-ferromagnetic transitions in α-Sm2S3

Magnetization and specific heat have been investigated for a single crystal and a sintered sample of α-Sm2S3 having an orthorhombic crystal structure. The weak-ferromagnetic transitions have been found and the Curie temperatures are determined as TC1 = 3.6 K and TC2 = 1.8 K from the magnetic specific heat Cmag(T) of a single crystal under no magnetic field. The weak-ferromagnetic features are extremely anisotropic, and the easy-magnetization axis is c which is perpendicular to the longitudinal direction of the needle-like single crystal. The saturation magnetization at T = 2.0 K and H = 100 Oe along the c-axis after field-cooling (FC) is so small as 1/18 of the full moment of Sm3+. The magnetization M(T) after zero-field cooling (ZFC) shows a curious peak at about 4.5 K just above TC1 regardless of the direction of the applied magnetic field for the single crystal. While both M(T) curves of FC/ZFC for the sintered sample show such peaks at about 4.0 K. The Cmag(T) behaves characteristically depending on the direction of the applied magnetic field. The magnetic entropy Smag(T) is also extremely anisotropic for the magnetic-field direction, and the Smag(T) under H//a is almost invariant to the field within 70 kOe. Therefore, it might be useable for controlling MCE effect by its rotating in magnetic field.