Magneto-caloric properties of La-based compounds

摘要

The magneto-caloric effect and magnetization behavior have been analyzed in the La_(0.7)Ca_(0.3)(Mn_(1-x)Nb_x)O_3 (x=0, 0.02, 0.04, 0.06, 0.08, 0.1) compound. Polycrystalline samples were prepared by standard solid-state reaction in a stream of 5% H_2/Ar gas. X-ray diffraction patterns revealed that all the samples had a single phase with an orthorhombic structure. The temperature dependence of the magnetization was measured with a commercial vibrating sample magnetometer (VSM) at various temperatures from 100 K to 300 K in fields up to 10 kOe. The Curie temperature is decreasing slightly with increasing of Nb concentration from 275 K to 248 K. The values of magnetic entropy change, ΔS_M are decreased with increasing Nb content. The substitution of Nb for Mn affects the bond length and bond angle, which thereby change the strength of magnetic interactions and the magnetic entropy.