On the broadening of the martensitic transition in Heusler alloys: from microscopic features to magnetocaloric properties

We report on the sharpness of the magnetostructural transition in a Ni-Co-Mn-Ga-In Heusler alloy, which has a key role in defining the magnetocaloric effect exploitable in efficient and environmentally friendly magnetic refrigerators. Magnetic and calorimetric analysis together with optical microscopy in phase-imaging mode are compared to correlate the transition broadening with microscopic features of the sample. The three techniques give the same temperature behavior of the martensitic transition. Microscopy analysis of different sample areas and during cycles in temperature reveals the spatial homogeneity of the transition width and its reproducibility in subsequent transformations.