Direct measurement and imaging of magnetocaloric effect inhomogeneities at the microscale in Ni44Co6Mn30Ga20 with infrared thermography

To study the MCE at the microscale with infrared thermography, a bulk Ni44Co6Mn30Ga20 sample was investigated. Direct measurements of the MCE were performed for temperatures around the reverse and direct martensitic transformation, by applying and removing a ~1.2 T magnetic field to the sample and recording the changes in its surface temperature with an IR camera. This was done for different sample temperatures on heating (from 273 K to 327 K) and cooling (from 327 K to 267 K). For sample temperatures around the reverse martensitic transformation, the inverse MCE is observed, with ΔT between −0.04 K and −0.54 K. The effect displays strong spatial inhomogeneity at the microscopic scale, which varies considerably with the progress of phase transformation. This behavior is not observed for the direct martensitic transformation (on cooling). The study reveals substantial novelty in the manifestation of the MCE at the microscopic scale, associated with phase dynamics, showing a different and inhomogeneous behavior on heating and cooling of a FSMA around the martensitic transition.