Contributions to Hysteresis in Magnetocaloric Materials

Hysteresis is detrimental to the refrigeration cooling cycle efficiency and yet many of the magnetocaloric materials under consideration as solid state refrigerants possess this property. This article discusses some aspects related to the factors leading to hysteresis in real materials. In the absence of high quality single crystals, determining the intrinsic energy cost associated with the transformation between metastable phases is an experimental challenge. We describe a micro‐calorimetric method that provides valuable insight into intrinsic behavior with the sensitivity to measure micro‐crystallites. We show that there is no correlation between the strength of first order character and magnitude of hysteresis between material families. We review some of the extrinsic factors which contribute to the hysteresis in real materials particularly those that can be accounted for using local imaging techniques such as scanning Hall probe microscopy. We discuss a number of mechanisms by which the extrinsic hysteretic properties of a material can be modified.