Critical parameters near the ferromagnetic-paramagnetic phase transition in La0.7A0.3(Mn1-xbx)O3 (A=Sr; B=Ti and Al; x=0.0 and 0.05) compounds

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 La0.7A0.3(Mn1-xBx)O3 (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 TC and the critical parameters β, γ and δ. With the values of TC, β and γ, we plot Mx(1-T/TC)-β vs. Hx(1-T/TC)-γ. All the data collapse on one of the two curves. This suggests that the data below and above TC obey scaling, following a single equation of state. Critical parameters for x=0 and xTi=0.05 samples are between those predicted for a 3D-Heisenberg model and mean-field theory and for xAl=0.05 samples the values obtained for the critical parameters are close to those predicted by the mean-field theory.