There are two types of magnetocaloric effects that are the so-called direct and inverse effects originating from ferromagnetic–paramagnetic (FM–PM) and antiferromagnetic–ferromagnetic (AFM–FM) phase transitions, respectively. Here, the magnetocaloric effects of FeRh alloy, which exhibit both the direct and inverse effects, have been studied by combining first-principles calculations and Monte Carlo simulations. The magnetic exchange coupling constants in the AFM and FM phases are evaluated by first-principles calculations based on the Liechtenstein formula. The Monte Carlo calculations considering the two-phase mixtures of AFM and FM well reproduce the experimental magnetization curves at zero external magnetic field. It is also shown that the isothermal magnetic entropy changes near the AFM–FM transition temperature under magnetic fields are successfully reproduced based on the Maxwell relation. The entropy changes in a wide range of the magnetic fields near the AFM–FM and FM–PM transition temperatures are investigated and the direct and inverse magnetocaloric effects of FeRh are discussed. The giant relative cooling power of FeRh alloy is achieved due to the large saturation magnetizations and the first-order AFM–FM phase transition.

有两种类型的磁热效应，分别是源自铁磁-顺磁（FM-PM）和反铁磁-铁磁（AFM-FM）相变的所谓直接效应和逆效应。在这里，结合第一性原理计算和蒙特卡罗模拟，研究了 FeRh 合金的磁热效应，它表现出正向和反向效应。AFM 和 FM 相中的磁交换耦合常数通过基于列支敦士登公式的第一性原理计算来评估。考虑 AFM 和 FM 的两相混合物的蒙特卡罗计算很好地再现了在零外部磁场下的实验磁化曲线。还表明，基于麦克斯韦关系成功地再现了磁场下 AFM-FM 转变温度附近的等温磁熵变化。研究了在 AFM-FM 和 FM-PM 转变温度附近的大范围磁场中的熵变化，并讨论了 FeRh 的直接和反向磁热效应。由于大的饱和磁化强度和一级 AFM-FM 相变，FeRh 合金具有巨大的相对冷却能力。