Development of Co-Fe-Si-B-Ni-Mo amorphous microwires with unique combination of high GMI effect and fast single DW propagation

The influence of annealing on the magnetic properties and Giant Magnetoimpedance (GMI) effect of Co 68.7 Fe 4 Si 11 B 13 Ni 1 Mo 2.3 glass-coated amorphous microwires was systematically studied. Upon thermal treatment, a remarkable transformation in the hysteresis loop shape from inclined to almost perfectly rectangular and, simultaneously, a significant enhancement in the GMI ratio, ΔZ/Z, to an unprecedented 470% under optimal annealing conditions were recorded. This enhancement is accompanied by a significant modification in the magnetic field dependence of the GMI ratio (ΔZ/Z), characterized by a shift of the GMI peaks to much lower magnetic fields. The onset of a rectangular hysteresis loop after annealing is associated with magnetization switching by the propagation of a single domain wall, DW, in the inner axially magnetized single-domain core, which is confirmed by direct measurements that revealed a rapid and uniform DW propagation reaching velocities of up to 850 m/s in sample annealed at 350 °C. The observed changes in magnetic properties are discussed in terms of the internal stresses relaxation, the domain wall stabilization, and modification in the magnetostriction coefficient. These factors affect the magnetoelastic anisotropy and promote a substantial change in the domain structure of studied microwire. This work highlights that appropriate annealing is critical for the optimization of magnetic properties and GMI performance and thus allowing the development of microwires with a unique combination of high GMI effect and fast single DW propagation, paving the way for development of advanced magnetic sensors and devices.