Characterization of the structural, magnetic and magnetocaloric properties of double perovskite La_(1.95)Sr_(0.05)BMnO_6 (B = Ni and Co)

摘要

An exhaustive study of structural, magnetic and magnetocaloric properties on La1.95Sr0.05BMnO6 (B=Ni and Co) double perovskite were performed. The samples were prepared by the sol-gel method. The crystallographic structure was studied by the X-ray diffraction patterns and Rietveld refinement which revealed that all samples crystallize in a monoclinic structure with P2(1) space group. The magnetic behaviors of these double perovskite have been studied in detail. For La1.95Sr0.05NiMnO6, the M(T) curves exhibit double magnetization transition temperature at 68K and 266K which can be ascribed to Ni3+-O-Mn3+ and Ni2+-O-Mn4+ superexchange interaction, respectively. However, unique magnetic transition has been observed for the La1.95Sr0.05CoMnO6 double perovskite at 210K due to Co2+-O-Mn4+ superexchange interaction. A deep investigation based on the Landau Theory and Arrot analysis confirmed a second order ferromagnetic phase transition for both samples. Besides, the magnetocaloric behaviors of these new samples have been studied by analysis the magnetic entropy change. This latter reached maximum values of 1.01 and 1.35J/kg/K for La1.95Sr0.05NiMnO6 and La1.95Sr0.05CoMnO6, respectively, under mu H-0=5T. Moreover, the relative cooling power values for La1.95Sr0.05NiMnO6 and La1.95Sr0.05CoMnO6 are found to be 94J/kg and 116J/kg, respectively, under mu H-0=5T. Based on the obtained S-M data, we have also described the universal master curve for (S-M/< versus rescaled temperature to confirm the order magnetic phase transition. Interestingly, all the S-M(T, H) data points are collapsed into a universal curve in the whole temperature range. The significant values of relative cooling power for both samples suggest that they might be an interesting candidate for exploring a new kind of magnetic refrigerants.