Effect of calcium deficiency on the critical behavior near the paramagnetic to ferromagnetic phase transition temperature in La0.8Ca0.2MnO3 oxides

The critical behavior associated with the magnetic phase transition has been investigated by magnetization isotherms in La0.8Ca0.2MnO3 and La0.8Ca0.1 square 0.1MnO3 (square is the calcium deficiency). The critical exponents are estimated by various techniques such as the Modified Arrott plot, Kouvel-Fisher plot and critical isotherm technique. The critical exponents values for La0.8Ca0.2MnO3 are very close to those found out by the 3D-Ising model (beta = 0.328, gamma = 1.180, and delta = 4.826 at an average T-C = 181.676 K). Moreover, the estimated critical exponents of La0.8Ca0.1 square 0.1MnO3 are consistent with the prediction of the 3D-Heisenberg model (beta = 0.357, gamma = 1.167, and delta = 4.802 at an average T-C = 178.182 K). We noted that the critical exponents gamma are almost similar to the value of the mean-field theory which can be explained by the existence of a long-range dipole-dipole interaction. Following the Harris criterion, we deduced that the disorder in our case is relevant, which can be the cause of the change in the universality class. (C) 2012 Elsevier B.V. All rights reserved.