Theoretical description of the magnetocaloric effect in Mn-Fe-P-Si alloys.

We apply a thermodynamic model describing magnetoelastic effects and based on mean field theory to understand the physical origin of the first order ferro- to paramagnetic magnetostructural transition occurring in Mn1.3Fe0.65P0.5Si0.5. The phenomenological parameters of the model are determined through comparison with the entropy data measured by Peltier calorimetry under magnetic field. The values obtained support the idea that: the phase transition is driven by the strong magnetoelastic coupling present along the a lattice axis; the spin entropy plays a key role in the transition; the structural contribution has a minor counteracting role. Moreover, the number of magnetic moments derived from the model agrees with the picture describing the paramagnetic phase of the system as due to the disordered magnetic moments at the Mn sites only.

我们采用一种基于平均场理论（mean field theory）、描述磁弹性效应的热力学模型，以理解Mn1.3Fe0.65P0.5Si0.5中发生的一级铁磁-顺磁磁结构转变的物理起源。该模型的唯象参数通过与磁场下珀尔帖量热法（Peltier calorimetry）测得的熵数据对比确定。所得参数值支持以下观点：该相变由沿晶格a轴存在的强磁弹性耦合驱动；自旋熵在相变中起关键作用；结构贡献则具有次要的抵消作用。此外，由模型推导的磁矩数量与下述图像一致：该体系的顺磁相仅由Mn位点的无序磁矩所致。