Magnetic properties of perovskites Pr0.9Sr0.1 Mn0.93+Mn0.14+O3: Monte Carlo simulations and experiments

This work presents the remarkable experimental magnetocaloric properties of the perovskites Pr0.9Sr0.1Mn0.93+ Mn0.14+O3, including the magnetic entropy change |ΔSm| and the Relative Cooling Power (RCP). To understand these striking properties, we elaborate in this paper a model and use Monte Carlo (MC) simulations to study it for comparison. For the model, we take into account nearest-neighbor (NN) interactions between magnetic ions Mn3+ (S=2) and Mn4+ (S=3/2) and the interactions between these Mn ions with the magnetic Pr ions. The crystal is a body-centered tetragonal lattice where the corner sites are occupied by Mn ions and the center sites by Pr and Sr ions in their respective concentrations given in the compound formula. We use an Ising-like spin model describing a strong anisotropy on the z axis. We show that pairwise interactions between ions cannot reproduce the large plateau of the magnetization experimentally observed below the phase-transition temperature. By introducing for the first time a many-spin interaction between Mn ions, we obtain an excellent agreement with experiments. Fitting the experimental Curie temperature TC with the MC transition temperature, we estimate the value of the effective exchange interaction in the system. From this value, we estimate various exchange interactions between ions: the dominant one is that between Mn3+ and Mn4+ which is at the origin of the ferromagnetic ordering below TC. We also studied the applied-field effect on the magnetization in the region below and above TC. The obtained MC results for |ΔSm| are in agreement with experiments performed for applied fields from 1 to 5 T. MC results of RCP are also shown and compared to experimental ones. Various other physical quantities obtained from MC simulations including internal energy and specific heat, versus temperature are also shown and discussed.