Abstract
This work presents a Monte Carlo study of the phase transition in the perovskites La0.7Sr0.3Mn0.73+Mn0.3-x4+ TixO3 (x=0.1, 0.2, and 0.25). We take into account nearest-neighbor (NN) interactions between magnetic ions Mn3+(S=2) and Mn4+(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 Mn3+ and Mn4+ which is at the origin of the ferromagnetic ordering. Effects of the very small interaction J2 between NN Mn3+ is analyzed: we show that it can cause an antiferromagnetic phase above Tc which disappears at smaller J2 or at Mn3+ 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%.
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