Influence of Pb Doping on the Magnetocaloric Effect and Critical Behavior of (La0.9Dy0.1)0.8Pb0.2MnO3

We used the modified Arrott plot method to analyze the magnetic field dependence of the magnetization, M(H), for a perovskite-type manganite (La0.9Dy0.1)(0.8)Pb0.2MnO3, and determined the critical parameter values T (C) = 248.4 K, beta = 0.484 +/- A 0.002, gamma = 0.961 +/- A 0.012, and delta = 2.90 +/- A 0.01. With these exponent values, the M(H) data around T (C) fall on two universal branches of a scaling function M(H,epsilon) = |epsilon| (beta) f (+/-)(H/|epsilon| (beta + gamma) ), where epsilon = (T - T (C))/T (C) is the reduced temperature, f (+) for T > T (C) and f (-) for T < T (C). Comparing with theoretical models, the exponent values obtained in our work are quite close to those expected from mean-field theory (with beta = 0.5, gamma = 1, and delta = 3). This reveals nearly long-range ferromagnetic order existing in (La0.9Dy0.1)(0.8) Pb0.2MnO3. From the M(H) data, we also found that, around the ferromagnetic-paramagnetic phase-transition temperature (T (C)), the magnetic entropy change reaches a maximum value (|delta S (max)|) of about 1.1 J kg(-1) K-1 for H = 10 kOe, corresponding to relative cooling power (RCP) of 50 J/kg. In addition to the above investigation, the temperature dependence of the magnetization, remanent magnetization (M (r)), and coercivity (H (c)) were recorded to learn about the physical processes taking place in (La0.9Dy0.1)(0.8)Pb0.2MnO3.