Abstract
The critical properties of the manganese perovskite La-0.7(Ba,Sr)(0.3)Mn1-xGaxO3 (x = 0.0, 0.1 and 0.2) around the paramagnetic-ferromagnetic phase transition were investigated using modified Arrott plots and Kouvel-Fisher method based on the data of static magnetic measurements recorded around the Curie temperature T-C. For all compounds, the obtained values of critical exponents were found to satisfy the scaling theory. Moreover, the critical exponents are confirmed by the field dependence of the magnetic entropy change relation Delta S-M = aH(n) The critical exponents values of our samples are very close to those found by the mean-field model (beta = 0.5, gamma = 1 and delta = 3). These results indicate long-range ferromagnetic coupling in La-0.7(Ba,Sr)(0.3)Mn1-xGaxO3 (x = 0.0, 0.1 and 0.2), which cannot be explained by the nearest-neighbor interaction proposed for the double-exchange mechanism. (C) 2016 Elsevier B.V. All rights reserved.