Experimental investigation of the effect of thermal hysteresis in MnFeP_1-x As_x materials applied in an AMR device

The magnetocaloric material series MnFeP1-xAsx, exhibiting a 1st order phase transition are possibly good candidates for magnetic refrigeration devices operating at room temperature (Brück et al., 2005). These materials have intrinsic hysteresis (thermal and magnetic) and the impact of this on magnetic refrigeration devices has not yet been thoroughly investigated in the literature.

Here, the thermal hysteretic magnetocaloric properties are studied using vibrating sample magnetometry (VSM) and how this influences actual refrigeration performance, using an established active magnetic regenerator (AMR) test device (Bahl et al., 2008) with a flat plate regenerator of a single Curie temperature (TC) material.

We find that the maximum adiabatic entropy change does not depend on the thermal history of the material, but the peak temperature is shifted 1.5 K for fields up to 1.5 T when measured at a constant field during heating or cooling. There is possibly an increase of the entropy change peak width of 0.3 K when cooling compared to heating.

These results are confirmed by experiments on an AMR test device.