Correlation between particle size and magnetic properties in soft-milled Ni45Co5Mn34In16 powders

Abstract

The effect of microstructural defects induced by mechanical milling has been studied in a Ni–Mn–In–Co metamagnetic shape memory alloy. The martensitic transformation and Curie temperatures do not change with grinding, thus pointing out to a null variation of long range atomic order as a consequence of the deformation. Nevertheless, the enthalpy change of the martensitic transformation highly decreases. This, and the large thermal stabilization of the martensite (with shifts on the temperature of the first reverse martensitic transformation up to 60 K), indicate the presence of a huge amount of internal stresses and microstructural defects in the obtained micro-particles. The presence of such defects considerably affects the saturation magnetization in austenite whereas almost no effect is observed in martensite. The magnetocaloric effect has been evaluated in samples with three different particle sizes. In spite of the MCE value is lower than in the bulk, the broader temperature range for the martensitic transformation in the powders makes the relative cooling power be comparable to that in the bulk. The as-milled micro-particles can be then considered as good preliminary candidates for magnetic refrigeration applications at the microscale.