Monte Carlo Simulation of the Vacancies and Thickness Effects on the Magnetic Behavior of La Ca MnO Thin Films

摘要

Monte Carlo simulations of La$_{0.67}$ Ca$_{0.33}$ MnO$_{3}$ thin films by using the Metropolis algorithm and a nearest neighbor classical Heisenberg model were carried out. Films were simulated by considering system sizes of $L times L times d$ magnetic ions, being $d$ the film thickness, which was varied, and $L$ the linear dimension of the basal plane, which was kept fixed at a high enough value. In the simulation we have differentiated three types of ions, namely Mn$^{4+ d3}$, Mn$^{3+e{rm g}}$ , and Mn$^{3+e{rm g}'}$ with their corresponding coupling constants. Hence, the effect of substituting Mn ions by vacancies upon the magnetic properties of the films was addressed. Magnetization, magnetic susceptibility, and specific heat curves as a function of temperature were obtained. Results indicate that the paramagnetic to ferromagnetic transition temperature $T_{c}$ increases until reaching the value reported for the bulk material (${sim}$ 260 K) as the film thickness increases above 9 magnetic unit cells. Moreover, as the vacancies percentage increases, $T_{c}$ exhibits a linear decrease without depending of the sample thickness; this is caused by the decrease in the magnetic -nonds density.