Study of frequency dependencies of the complex magnetic ac-permeability aftereffect in amorphous Fe64Co21B15 and Fe8Co77B15 alloys

The frequency dependencies of the complex magnetic permeability and its aftereffect phenomenon in as-cast and annealed Fe64Co21B15 and in as-cast Fe8Co77B15 amorphous ribbons were studied. The measurements of these properties were carried out at frequencies between 1 and 120 kHz. The behavior of the frequency dependence of real and imaginary parts of the ac permeability and aftereffect were analyzed using the magnetic domain wall motion model. A change of the restoring force coefficient and the damping parameter with time was considered for the study of frequency dependency of the magnetic relaxation.