Change of permeability and GMI in amorphous Co{sub 71}Fe{sub 1}Mo{sub 1}Mn{sub 4}Si{sub 14}B{sub 9} alloy before and after heat treatments

The complex permeability spectra of amorphous ribbons were measured as a function of ac magnetic field. At relatively high magnetic field, the spectra showed the superposition of two Debye type dispersions attributed to the relaxation processes of domain wall motion and rotational magnetization. The permeability from the wall motion was maximum in the sample annealed at 250 C, while the permeability from rotational magnetization was maximum at the sample annealed at 350 C. The magneto-impedance (MI) profile changed sensitively with measuring frequency and annealing temperature. The changes of magneto-impedance with annealing temperature were discussed in terms of magnetic softness and domain change due to the annealing.