Composition dependence of physical properties in Pr0.7Ca0.3Mn1−xNixO3

We have prepared orthorhombic Pr0.7Ca0.3Mn1−xNixO3 ceramics by conventional solid-state reaction. Then, we have studied their electrical, magnetic and magnetocaloric properties. From electrical conductivity study, it is found that Ni-doped PrCaMnO3 systems exhibit a semiconductor behavior. In conductance versus temperature curves, a specific saturation region appears for x = 0, 0.02 and 0.05. Such behavior seems to appear at high temperature (T > 300 K) for x = 0.1. The evolution of such behavior with nickel content is attributed to the variation of the density of trapped charge and to the capture efficiency of charge traps. It is also found that electrical transport is governed by thermally activated hopping process. The activation energy of such process is sensitive to the nickel concentration. It increases from Ehop = 35 meV for x = 0 to Ehop = 128 meV for x = 0.1. The temperature dependence of dielectric permittivity is characterized by the appearance of dielectric transition and it is described by the Curie-Weiss law. The transition temperature Td does not change for small Ni content (Td = 145 K for x = 0.02 and 0.05), but it increases for x = 0.1 (Td = 155 K). Impedance study indicates the presence of a non-Debye relaxation phenomenon in the investigated materials and approves the applied role of the grain boundary in electrical transport process. The magnetic measurements reveal that an x increase in Pr0.7Ca0.3Mn1−xNixO3 enhances the ferromagnetic-paramagnetic transition temperature. Based on the isothermal curves we have calculated the magnetic-entropy which persistently increases with the increase of magnetic field. The magnetic-entropy has been also deduced from the Landau theory. Satisfactory agreement between the theoretical curves and the experimental dependencies has been found.