Influence of K addition on the magnetic and magnetocaloric properties of La2-xKxNiMnO6 (x = 0, 0.2 and 0.4) double perovskite

The structural and magnetic properties of La2-xKxNiMnO6 (x = 0, x = 0.2 and x = 0.4) synthesized by a sol gel method have been investigated. Refinements of X-ray diffraction data reveal that our compositions crystallized in monoclinic structure with P21/n space group. Double magnetization transition are observed from the magnetization measurements versus temperature (TC1 at high temperature and TC2 at low temperature) and can be ascribed to Ni2+-O-Mn4+ and Ni3+-O-Mn3+ superexchange interactions, respectively. Based on Banerjee criterion, the nature of magnetic transition is of second order for all synthesized samples. The magnetic entropy change was calculated from the measurement of isothermal magnetization versus magnetic field at different temperatures. The maximum (−ΔSMmax) under a magnetic field of 5 T is found to be 1.17 J/kg K, 1.10 J/Kg and 0.96 J/Kg K for x = 0, x = 0.2 and x = 0.4, respectively. The relative cooling power (RCP) increases with K doping and reaches 173 J/kg for x = 0.4.