Magnetic properties and magnetocaloric effect in Heusler-type glass-coated NiMnGa microwires

We studied magnetic properties, structure and magnetocaloric effect (MCE) in thin NiMnGa glass-coated microwires. After annealing studied microwires exhibit ferromagnetic behavior at room temperature. We directly measured the temperature change, Delta T, originated from the MCE in annealed NiMnGa glass-coated microwires and after glass removal. After glass removal Delta T increases from 0.06-0.08 K to 0.22 K. Observed temperature dependence of magnetization and MCE should be associated with both magnetic (paramagnetic-ferromagnetic) and structural (austenite-martensite) phase transitions. Considerable magnetization increase in vicinity of Curie temperature can be also attributed to the Hopkinson effect. We evaluated the possibility to prepare the magnetocaloric materials for magnetic refrigerators in the form of glass-covered microwires and showed that glass-coated microwires might be interesting for the MCE applications owing to high ratio of surface to volume. (c) 2013 Elsevier B.V. All rights reserved.