The Magnetic and Magnetocaloric Properties of the Perovskite La_0.7Ca_0.3Mn_1-xNi_xO₃

This paper studies the effects of the Mn-site substitution by nickel on the magnetic properties and the magnetocaloric properties of $La_0.7Ca_0.3Mn_1-xNi_xO_3$ (x = 0, 0.05 and 0.1). The orthorhombic crystal structures of the samples are confirmed by the room temperature X-ray diffraction. The dependence of the Curie temperature ($T_C$) and the magnetic entropy change (${\Delta}S_M$) on the Ni doping content was investigated. The samples with x = 0 had the first order phase transition, while the samples with x = 0.05 and 0.1 had the second order phase transition. As the concentration of Ni increased, the maximum entropy change (${\mid}{\Delta}S_M{\mid}_max$) decreased gradually, from 2.78 $J{\cdot}kg^-1{\cdot}K^-1$ (x = 0) to 1.02 $J{\cdot}kg^-1{\cdot}K^-1$ (x = 0.1), in a magnetic field change of 15 kOe. The measured value of $T_C$ was 185 K, 150 K and 145 K for x = 0, 0.05 and 0.1, respectively. The phase transition temperatures became wider as x increased. It indicates that the Mn-site substitution by Ni may be used to tailor the Curie temperature in $La_0.7Ca_0.3Mn_1-xNi_xO_3$.