Processing Effects on the Martensitic Transformation and Related Properties in the Ni 55 Fe 18 Nd 2 Ga 25 Ferromagnetic Shape Memory Alloy.

The influence of processing on the martensitic transformation and related magnetic properties of the Ni 55 Fe 18 Nd 2 Ga 25 ferromagnetic shape memory alloy, as bulk and ribbons prepared by the melt spinning method and subjected to different thermal treatments, is investigated. Structural, calorimetric, and magnetic characterizations are performed. Thermal treatment at 1173 K induces a decrease in both the Curie and the martensitic transformation temperatures, while a treatment at 673 K produces the structural ordering of the ribbons, hence an increase in T C . A maximum value of the magnetic entropy variation of -5.41 J/kgK was recorded at 310 K for the as quenched ribbons. The evaluation of the magnetoresistive effect shows a remarkable value of -13.5% at 275 K on the bulk sample, which is much higher than in the ribbons.