Tuning Giant magnetoimpedance and magnetic properties of glass-coated co-Fe-Si-B-Ni-Mo microwires via isothermal annealing

We evaluated how annealing affects the magnetic properties and Giant Magnetoimpedance (GMI) response of Co 68.7 Fe 4 Si 11 B 13 Ni 1 Mo 2.3 glass-coated microwires with nearly zero magnetostriction. We used microwires with the fixed dimensions and annealed them at 350 °C for 30, 45, 60, and 90 min. X-ray diffraction confirmed that the amorphous structure was maintained after l the annealing. Annealing brought substantial changes in the hysteresis loops. At first, the loops were almost linear and unhysteretic and, hence, showed low remanence, M r , about 0.045. After annealing, they acquired rectangular shapes with M r ≈ 0.95, making the microwires magnetically bistable. The GMI response improved the most. As-prepared microwires started with the GMI ratio, ∆Z/Z , about 370%. After annealing for 30 min, the GMI ratio increased to about 500% —a huge 31% boost at practical frequencies (100–150 MHz). But, if we pushed annealing to 90 min, performance actually dropped to about 400%. Accordingly, with careful control of annealing conditions we can obtain microwires with unique combination of magnetic properties, i.e. showing both magnetic bistability and outstanding GMI sensitivity. This kind of performance makes these microwires especially promising for cutting-edge magnetic sensing and bio-magnetic detection technologies.