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

•Micro and sub-micro-meter sized particles of Ni-Mn-Ga/Ni-Mn-Cu-Ga Heusler compounds by top-down ball-milling technique.•Recovery of the original phase transitions through optimization of the annealing treatments even for long-milled powders.•Tunability and improvement of the magneto-structural prop...

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Bibliographic Details
Published in:Journal of alloys and compounds 2021-08, Vol.872, p.159747, Article 159747
Main Authors: Cavazzini, Greta, Cugini, Francesco, Delmonte, Davide, Trevisi, Giovanna, Nasi, Lucia, Ener, Semih, Koch, David, Righi, Lara, Solzi, Massimo, Gutfleisch, Oliver, Albertini, Franca
Format: Article
Language:English
Subjects:
Annealing
Ball milling
Copper
Crystal defects
Heusler alloys
Homogeneity
Magnetic nanoparticles
Magnetic properties
Magnetic saturation
Manganese
Martensitic transformation
Mechanical milling
Nickel
Optimization
Phase transitions
Transformation temperature
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Summary:•Micro and sub-micro-meter sized particles of Ni-Mn-Ga/Ni-Mn-Cu-Ga Heusler compounds by top-down ball-milling technique.•Recovery of the original phase transitions through optimization of the annealing treatments even for long-milled powders.•Tunability and improvement of the magneto-structural properties with respect to the bulk.•Avoidance of sintering and agglomeration for particles heat-treated at high temperature and/or for a long time.•Higher phase stability and better accommodation of stresses for Ni-Mn-Cu-Ga than the ternary Ni-Mn-Ga compound. [Display omitted] 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.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2021.159747