Critical phenomena and estimation of the spontaneous magnetization through magnetic entropy change in La0.67Ba0.33Mn0.98Ti0.02O3

The critical properties of the manganese perovskite La0.67Ra0.33Mn0.98Ti0.02O3 around the paramagnetic-ferromagnetic phase transition were investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis based on the data of static magnetic measurements recorded around the Curie temperature T-C. The magnetic data analyzed in the critical region using the above methods yield the critical exponents beta = 0.551 +/- 0.008 with T-c = 310.47 K +/- 0.10 (from the temperature dependence of the spontaneous magnetization below T-C) and gamma = 1.020 +/- 0.024 with T-C = 310.11 K +/- 0.14 (from the temperature dependence of the inverse initial susceptibility above T-C) and delta = 2.826, determined separately from the isothermal magnetization at T-C. These critical exponents fulfill the Widom scaling relation delta = 1 + gamma/beta, implying that the obtained values of beta and gamma are reliable. Based on these critical exponents, the magnetization field temperature (M-H-T) data around T-c collapse into two curves obeying the single scaling equation M(H, epsilon) = epsilon(beta)integral(+/-)(H/epsilon(beta+gamma)) The values deduced for the critical exponents in La0.67Ba0.33Mn0.98Ti0.02O3 are close to the theoretical prediction of the mean-field model rather than the universal theory of 3D-Heisenberg, 3D-Ising and tricritical mean-field models. Moreover we have investigated the validity and usefulness of the theoretical modeling in our compound La0.67Ba0.33Mn0.98Ti0.02O3 based on the mean-field analysis of the magnetic entropy change (-Delta S-M) versus the magnetization data. Results obtained through this approach are compared to those obtained from extrapolation of the Arrott curves. An excellent agreement was obtained between this approach with the one obtained from the extrapolation of the Arrott curves. (C) 2011 Elsevier Masson SAS. All rights reserved.