Critical parameters near the ferromagnetic–paramagnetic phase transition in La 0.7A0.3(Mn 1−xb x)O 3 ( A=Sr; B=Ti and Al; x=0.0 and 0.05) compounds

Abstract

The critical parameters provide important information concerning the interaction mechanisms near the paramagnetic-to-ferromagnetic transition. In this paper, we present a thorough study for the critical behavior of La 0.7 A 0.3(Mn 1− xB x )O 3 ( A=Sr; B=Ti and Al; x=0.0 and 0.05) polycrystalline samples near ferromagnetic–paramagnetic phase transition temperature by analyzing isothermal magnetization data. We have analyzed our dc-magnetization data near the transition temperature with the help of the modified Arrot plot, Kouvel–Fisher method. We have determined the critical temperature T C and the critical parameters β, γ and δ. With the values of T C, β and γ, we plot M×(1− T/ T C) − β vs. H×(1− T/ T C) − γ . All the data collapse on one of the two curves. This suggests that the data below and above T C obey scaling, following a single equation of state. Critical parameters for x=0 and x Ti=0.05 samples are between those predicted for a 3D-Heisenberg model and mean-field theory and for x Al=0.05 samples the values obtained for the critical parameters are close to those predicted by the mean-field theory.