Post-Annealing Influence on Magnetic Properties of Rapidly Quenched Ni-Mn-Ga Glass-Coated Microwires

In this article, we showed how the post-annealing process affects the magnetic properties of rapidly quenched Ni-Mn-Ga glass-coated microwires. Microwires with Ni63Mn12Ga25 chemical composition, total diameter D = 54.6 mu m and metallic nucleus diameter d = 26.7 mu m, were prepared by the Taylor-Ulitovsky technique. The annealing temperature was fixed at 873 K, and the time was 1 and 10 h. The microwires were slowly cooled to room temperature after annealing. Based on thermomagnetic curves and hysteresis loops, we suggest crystallographic texture in the wires that considerably affect magnetic properties. The wires' internal structure indicates nanocrystalline state with radial micrometers and submicrometer grains distribution in the wire annealed during 10 h. A ferromagnetic-to-paramagnetic phase transition occurs around room temperature. No signs of a martensitic transformation were found. The difference in magnetization saturation, remanence, and Curie temperature values for 1- and 10-h annealed microwires indicates the influence of internal stresses and that created by the presence of a glass coating.