‘‘Multifunctional Ni-Mn-Ga and Ni-Mn-Cu-Ga Heusler particles towards the nanoscale by ball-milling technique’’

This work presents a top-down method, based on ball-milling techniques, for the preparation of and micro-meter and sub-micrometer sized particles. The structural, morphological, and magnetic features of the as milled and annealed particles are investigated. First, we observe a detrimental effect on the magnetic properties and magneto-structural phase transitions of the induced lattice defects and atomic disorder, and second, we demonstrate the possibility to recover the original configuration by subsequent annealing. The optimization of the latter is strongly dependent on the initial milling energy, but, generally, a fast recovery of the Heusler and martensitic phases is observed. Further, we can tune the transformation temperatures or even improve the magnetic properties, in terms of phase homogeneity, thermal hysteresis and saturation magnetization, by decreasing the particles’ size of the examined compounds.