A novel annealing technique for the magneto-impedance effect in amorphous Co66Fe4Ni1B14Si15 alloy

The magnetoimpedance effect in amorphous Co66Fe4Ni1B14Si15 alloy has been improved drastically by using a novel annealing technique invented by authors where a high-frequency driving current is applied to the longitudinal direction of the sample during the thermal treatment in a vacuum. The AC current annealing has been performed at various temperatures (150 deg. C, 250 deg. C, and 350 deg. C for 1 h) and frequencies (100 kHz, 1 MHz, and 5 MHz of 10 mA). Despite a large increment of magnetoimpedance effect in our annealed samples a noticeable structural change was not observed. The thermal treatment seems to help softening the magnetic properties of the sample especially near the surface within skin depth. Therefore, the AC current annealing is found to be useful for improving the giant magnetoimpedance effect