Helical shell-domain structure in laser-annealed Co-based amorphous microwires analyzed by giant magnetoimpedance

A commercial glass-covered, Co-based amorphous microwire (Co₆₇Fe_3.8Ni_1.4B_11.5Si_14.6 Mo_1.7) is etched in order to remove its glass cover in a 60.51% hydrofluoric acid solution, and annealed in air by illuminating with a pulsed Nd:YAG laser beams with an energy E of 48 mJ/pulse. Giant magnetoimpedance (GMI) profiles at a frequency f are measured as function of the angle θ of the external field, H, with respect to the wire axis. The sign of the H values at the peak of the GMI profiles for f = 100 kHz and at the dip of the GMI profiles for f = 10 MHz, H_p and H_d, respectively, change at θ = 85-90°, reflecting that the tilt angle of the helical domains is between 0° and 5° from the circular direction for the as-etched samples. The variations of H_p and H_d with θ for the sample with E = 48 mJ/pulse and H_a = 20 Oe show a change in sign of H_p and H_d at θ = 90-100°, reflecting that the tilt angle of the helical domains is decreased by about -10° compared to that of the as-etched sample.