Transient Enhancement Studies of Domain-Wall Pinning in Ferromagnetic Metals

The technique of transient enhancement of initial ac susceptibility is introduced. The time dependence of the low-field ac susceptibility of ferromagnets is observed in the presence of a second time-varying field. The technique enables the diffusion of domain-wall pinning centers to be studied and also acts as a sensitive indicator of domain nucleation for magnetic critical-phenomena studies near the Curie temperature. Preliminary results for ferromagnetic gadolinium over the temperature range 240-292 K yield an activation energy for the pinning centers of {~}0.7 eV.