Magnetic properties of perovskites La${}_{0.7}$Sr${}_{0.3}$Mn${}_{0.7}^{3+}$Mn${}_{0.3-x}^{4+}$Ti${}_x$O${}_3$:Monte Carlo simulation versus experiments

Abstract

This work presents a Monte Carlo study of the phase transition in the perovskites La${}_{0.7}$Sr${}_{0.3}$Mn${}_{0.7}^{3+}$Mn${}_{0.3-x}^{4+}$Ti${}_x$O${}_3$ ($x$= 0.1, 0.2, and 0.25). We take into accountnearest-neighbor (NN) interactions between magnetic ions Mn${}^{3+}$($S=2$) and Mn${}^{4+}$($S=3/2$) using a spin model describing a strong anisotropy on the $z$ axis. We have calculated the uniform and staggered magnetizations as well as the Edwards-Anderson order parameter as functions of temperature, with and without an applied magnetic field. Fitting the experimental Curie temperature at $x=0$, we estimated values of various exchange interactions in the system. The dominant one is that between Mn${}^{3+}$ and Mn${}^{4+}$ which is at the origin of the ferromagnetic ordering. Effects of the very small interaction $J\_2$ between NN Mn${}^{3+}$ is analyzed: we show that it can cause an antiferromagnetic phase above $T\_c$ which disappears at smaller $J\_2$ or at Mn${}^{3+}$ concentrations smaller than 0.55. Our results show a good agreement with experiments on the magnetizations for substitution concentration $x=0.1$, 0.2 and 0.3. We also studied the applied-field effect on the magnetization and our obtained results are compared with experiments performed at $x=10\%$.

To appear in J. Mag. Magn. Materials