Critical behavior near the paramagnetic to ferromagnetic phase transition temperature in La0.7Pb0.05Na0.25MnO3

Critical behavior in La0.7Pb0.05Na0.25MnO3 has been investigated by dc magnetization measurements. Magnetic data indicate that the compound exhibits a continuous (second-order) paramagnetic (PM) to ferromagnetic (FM) phase transition. Estimates of critical exponents yield delta = 4.80 +/- 0.01, gamma = 1.296 +/- 0.002 and beta = 0.344 +/- 0.007 (consistent with both the predictions for the three-dimensional-Heisenberg model and with those reported for materials when the FM transition is ascribed to the double exchange (DE) mechanism as a major origin) with T-C = 334.54 +/- 0.08. The critical exponent gamma is slightly inferior than predicted from the 3D Heisenberg model. Such a difference may be due, within the context of the quenched disorder, to the presence of some alterations of short-range magnetic order of FM clusters in the PM phase. The temperature variation in the effective exponent (gamma(eff)) is similar to those for disordered ferromagnets. (C) 2010 Elsevier Ltd. All rights reserved.