Abstract
The critical behavior and magnetocaloric effect (MCE) in the perovskite system La0.7-xPrxBa0.3MnO3 (x = 0.05, and 0.15) have been carefully investigated via dc-magnetization measurement. With the increase in Pr-doping, the universality class shifts from the predicted 3d-Heisenberg model characterized by a short-range coupling [beta = 0.371 +/- 0.008, gamma = 1.351 +/- 0.002 and delta = 4.634 +/- 0.002, for x = 0.05] to an unknown one [beta = 0.385 +/- 0.004, gamma = 1.324 +/- 0.001 and delta = 4.435 +/- 0.006, for x = 0. 15]. The critical exponents, however, obey the scaling behavior for both samples. Likewise, this series of compounds displays rescaled magnetic entropy data that plead in favor of a non-universal MCE behavior. Moreover, the field dependence of the magnetic entropy change (Delta SM) gives rise to critical exponents (beta and gamma) which are not consistent with that estimated through the critical behavior. Unexpectedly, the renormalization group approach revealed critical exponents for both samples comparable to those calculated for 3dXY spin interactions. All three exponents vary with Pr concentration, indicating the violation of both universality and weak universality hypotheses that may lead to several critical points. The unconventional outcomes suggest that, in addition to the correlation between quenched disorder and accommodation strain, magnetic anisotropy plays a major role with increasing Pr - x, opposing the exchange mechanisms. Pr - x enhanced the peak of Delta SM around TC and the relative cooling power (RCP). The broad operating temperature range along with a negligible hysteresis make Pr - 15% a promising candidate for magnetic refrigerant material near room temperature.