Caballero-Flores R, Bingham N S, Phan M H, Torija M A, Leighton C, Franco V, Conde A, Phan T L, Yu S C, Srikanth H
Department of Physics, University of South Florida, Tampa, FL 33620, USA. Departamento de Física de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, 41080 Sevilla, Spain. Departamento de Física, Universidad de Oviedo, 33007 Oviedo, Spain.
J Phys Condens Matter. 2014 Jul 16;26(28):286001. doi: 10.1088/0953-8984/26/28/286001. Epub 2014 Jun 19.
The Maxwell relation, the Clausius-Clapeyron equation, and a non-iterative method to obtain the critical exponents have been used to characterize the magnetocaloric effect (MCE) and the nature of the phase transitions in Pr0.5Sr0.5MnO3, which undergoes a second-order paramagnetic to ferromagnetic (PM-FM) transition at TC ~ 247 K, and a first-order ferromagnetic to antiferromagnetic (FM-AFM) transition at TN ~ 165 K. We find that around the second-order PM-FM transition, the MCE (as represented by the magnetic entropy change, ΔSM) can be precisely determined from magnetization measurements using the Maxwell relation. However, around the first-order FM-AFM transition, values of ΔSM calculated with the Maxwell relation deviate significantly from those calculated by the Clausius-Clapeyron equation at the magnetic field and temperature ranges where a conversion between the AFM and FM phases occurs. A detailed analysis of the critical exponents of the second-order PM-FM transition allows us to correlate the short-range type magnetic interactions with the MCE. Using the Arrott-Noakes equation of state with the appropriate values of the critical exponents, the field- and temperature-dependent magnetization [Formula: see text] curves, and hence the [Formula: see text] curves, have been simulated and compared with experimental data. A good agreement between the experimental and simulated data has been found in the vicinity of the Curie temperature TC, but a noticeable discrepancy is present for [Formula: see text]. This discrepancy arises mainly from the coexistence of AFM and FM phases and the presence of ferromagnetic clusters in the AFM matrix.
麦克斯韦关系、克劳修斯 - 克拉佩龙方程以及一种获取临界指数的非迭代方法已被用于表征Pr0.5Sr0.5MnO3中的磁热效应（MCE）和相变性质。Pr0.5Sr0.5MnO3在TC约247 K时经历二级顺磁到铁磁（PM - FM）转变，在TN约165 K时经历一级铁磁到反铁磁（FM - AFM）转变。我们发现，在二级PM - FM转变附近，磁热效应（由磁熵变ΔSM表示）可以通过使用麦克斯韦关系从磁化测量中精确确定。然而，在一级FM - AFM转变附近，在AFM和FM相发生转变的磁场和温度范围内，用麦克斯韦关系计算的ΔSM值与用克劳修斯 - 克拉佩龙方程计算的值有显著偏差。对二级PM - FM转变的临界指数进行详细分析，使我们能够将短程型磁相互作用与磁热效应联系起来。使用具有适当临界指数值的阿罗特 - 诺克斯状态方程，模拟了场和温度依赖的磁化强度[公式：见原文]曲线，从而得到了[公式：见原文]曲线，并与实验数据进行了比较。在居里温度TC附近，实验数据和模拟数据之间取得了良好的一致性，但对于[公式：见原文]存在明显差异。这种差异主要源于AFM和FM相的共存以及AFM基体中存在铁磁团簇。
