Depth profile of transverse permeability spectrum in an annealed Co-based amorphous ribbon

Amorphous Co/sub 66/Fe/sub 4/B/sub 15/Si/sub 15/ ribbons were annealed at a temperature of 380(degree)C for 8 h in open air under a field of 3 Oe applied along the sample axis. The annealed samples were etched in hydrofluoric acid solution during various times from 10 s to 30 min in order to the different thickness of material, t/sub etch/, from ribbon surface. The static permeabilities due to domain wall motion (mu)/sub s,dw/ and magnetization rotation (mu)/sub s,rot/ are separated from the permeability extracted from the magnetoimpedance spectra. For the samples with thickness t/sub etch/ less than 2 (mu)m, both (mu)/sub s,dw/ and (mu)/sub s,rot/ are nearly zero at H=-3 Oe, while they are relatively large at H=+3 Oe. As the etched thickness increases over 2 (mu)m, (mu)/sub s,dw/ and (mu)/sub s,rot/ at H=-3 Oe start to increases and eventually reach similar values to those at H=+3 Oe. The variations of (mu)/sub s,rot/ and (mu)/sub s,rot/ with t/sub etch/ reflect that the sample annealed in open air is nearly saturated in the direction opposite to that of annealing field. This is due to antiferromagnetic coupling between the inner amorphous phase and the surface crystalline phase with thickness about 2 (mu)m.