Magnetic and structural features of glass-coated Cu-based (Co,Fe,Ni,Mn–Cu) alloy microwires

The various factors (compositional and geometrical) which determine the microstructural and magnetic behaviour of glass-coated microwires are described. The discussion is based on results performed on microwires at several compositions (Co,Fe,Ni,Mn–Cu, Cu-based). The structural changes (experimentally determined by XRD diffraction) due to variations of the chemical composition, geometry (ratio, ρ, of the metallic core to the total diameter of the microwire) and heat treatment can be correlated with the evolution of the hysteresis behaviour. A significant change of the magnetization curve is observed in Fe30Cu70 microwire, which is ascribed to the presence of two different magnetic phases depending on ρ. Enhanced magnetic hardness (up to 800 Oe) is obtained for Co29Ni25Cu45Mn1 microwire after annealing at 700°C for 1 h, which could be correlated with phase separation during heat treatment. Variations of the coercivity evidence a certain correlation with the grain size and ρ parameter, which could be ascribed to the effect of the internal stresses on the grain size.