Viscosity field and magnetic aftereffects in amorphous (Fe-Ni-P-B) alloys

The viscosity field giving rise to the magnetic permeability relaxation in amorphous soft magnetic materials is studied. The nature of the activated processes hindering the wall motion in amorphous ferromagnets is discussed. The viscosity field acting on 180° walls is derived both for single step and periodic wall motion. Experimental results of the aftereffect of the magnetic induction as a function of magnetization in Fe80B20and Fe40Ni40P14B6are reported. A comparison is made with the viscosity field results to get information on mean wall thickness and induced anisotropy coefficients in these materials.