Glass-coated Ni2MnGa microwires with narrow structural transition range and enhanced magnetocaloric effect at low fields

Abstract

The structural, magnetic and magnetocaloric properties of glass-coated magnetic microwires, composed of Ni2MnGa and produced with the Taylor-Ulitovski technique, have been investigated with XRD, EBSD, SEM and magnetization measurements. At room temperature, the microwires exhibit a monocrystalline phase with a Cu2MnAl-type crystal structure (space group Fm-3m; cell parameter a = 5.832 Å). The microwires in this study show a magnetocaloric effect with a sharp martensitic transformation in the range of 185–195 K, as well as a magnetocaloric effect owing to the magnetic phase transition at the Curie temperature. Due to the different strength of anisotropy and easy magnetization axis, the magnetocaloric effect during the martensitic transformation exhibit a maximum at low fields (0.5 T), and high efficiency (defined as a ratio between refrigerant capacity and applied magnetic field) at 0.2 T.