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 δ=4.80±0.01δ=4.80±0.01, γ=1.296±0.002γ=1.296±0.002 and β=0.344±0.007β=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 TC=334.54±0.08TC=334.54±0.08. The critical exponent γγ 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 (γeffγeff) is similar to those for disordered ferromagnets.

Research highlights
► Critical exponents are consistent with those for the 3D-Heisenberg model.
► Effective exponent (γoffγoff) is similar to those for disordered ferromagnets.
► Critical behavior reveals the presence of ferromagnetic clusters in the paramagnetic phase.