Ni59.0Mn23.5In17.5 Heusler alloy as the core of glass-coated microwires: Magnetic properties and magnetocaloric effect

Abstract

Heusler Ni59.0Mn23.5In17.5 alloy was prepared as the metallic core of a glass-coated microwire with a total diameter of 41.8 μm. X-ray diffractograms performed at room temperature and 100 K show a highly ordered L21 cubic structure characteristic of the austenitic phase in Heusler alloys. Thermomagnetic curves measured in the temperature range from 50 K up to 400 K show ferromagnetic coupling in the austenite with the Curie temperature around 246 K. Hysteresis loops measured at different temperatures indicate a soft ferromagnetic behaviour, confirming the microwire axis as the magnetization easy direction. The magnetic entropy variation reaches a maximum value of 1.75 J/kgK at the ferro-to-paramagnetic phase transition for a magnetic field change of 30 kOe. After short annealing, the Curie temperature is almost unchanged while the maximum entropy change increases up to 2.01 J/kgK. Refrigerant capacity and its dependence on both working temperature range and applied field value are evaluated for all microwire samples, reaching 120 J/kg for a 30 kOe magnetic field variation. We analyze the possibility of employing microwire shape Heusler alloys as low field magnetocaloric micro-devices and solid-state actuators.