Crossover of the magnetocaloric effect and its importance on the determination of the critical behaviour in the La0.67Ba0.33Mn0.9Cr0.1O3 perovskite manganite

The magnetic phase transition and the magnetic entropy change (-Delta S-M) in the La0.67Ba0.33Mn0.9Cr0.1O3 manganite were investigated by measuring the magnetization as a function of temperature. The maximum magnetic entropy change (-Delta S-M) and the relative cooling power (RCP) are found to be, respectively, 4.20 J kg(-1) K-1 and 238 J kg(-1) for a 5-T field change, making of this material a promising candidate for magnetic refrigeration near room temperature. To investigate the nature of the paramagnetic (PM) to ferromagnetic (FM) phase transition, found to be of second-order, we performed a critical exponents study by dc-magnetization M(H,T) measurements around the Curie temperature T-C, in a temperature range including the critical region vertical bar epsilon vertical bar = vertical bar T-T-C vertical bar/T-C <= 0.05. From the derived values of the critical exponents (beta = 0.380, gamma = 1.345), we conclude that La0.67Ba0.33Mn0.9Cr0.1O3 belongs to the three-dimensional Heisenberg class with short-range interaction. Scaling relations are obeyed, indicating renormalized interactions around T-C. By investigating the field dependence of RCP and Delta S-M, it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method. (C) 2012 Elsevier B.V. All rights reserved.