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 Ni50Mn30Ga20 and Ni50Mn18.5Cu6.5Ga25 micro-meter and sub-micro-meter 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 increase of phase homogeneity, decrease of thermal hysteresis and increase of saturation magnetization, by decreasing the particles' size of the examined compounds. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study presents a top-down method using ball-milling techniques to prepare micro-meter and sub-micro-meter sized particles of Ni50Mn30Ga20 and Ni50Mn18.5Cu6.5Ga25. The research shows that lattice defects and atomic disorder induced during milling have a detrimental effect on magnetic properties and magneto-structural phase transitions, but can be recovered by subsequent annealing. Furthermore, tuning the particle size can improve magnetic properties, such as phase homogeneity, thermal hysteresis reduction, and saturation magnetization increase.