Magnetic properties of perovskites La0.7Sr0.3Mn0.73+ Mn0.3-x4+TixO3: Monte Carlo simulation versus experiments

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%.