Analysis of magnetocaloric effect in Ni2FeGa-based glass-coated microwires

Abstract

Enhancement of magnetocaloric effect by proper tuning of phase transition temperatures was analysed on a series of Ni2FeGa Heusler glass-coated microwires. By a targeted combination of the structural and magnetic transition, the magnetic entropy change was enhanced more than three times from ≈ −0.25 J.kg−1.K−1 at 125 K to ≈ −0.8 J.kg−1.K−1 at the human body temperature 310 K, and cooling power increased significantly. In the presented investigation, different analytical approaches like the temperature-dependent magnetisation, magnetic entropy change, Arrott plots, universal curves analysis, n-exponent and Kouvel-Fisher method were performed to verify the presence and contribution of both types of transitions. The results show the possibility of establishing a phase diagram with the correlation between the structural and magnetic transition temperature as a function of the valence electrons concentration ratio (e/a) – chemical composition. Moreover, obtained results point to the fact that the transition temperatures are invariant under different analytical approaches. The phase diagram allows fine-tuning of the magnetocaloric effect in Ni2FeGa-based Heusler alloys in the form of glass-coated microwires and opens the opportunity to achieve higher efficiency of magnetocaloric effect by a slight change of alloy’s composition.