Low-frequency magnetoimpedance: domain wall magnetization processes

A systematic study of the magnetization processes underpinning the giant ma gnetoimpedance phenomenon at low frequencies (f < 10 MHz) is presented. Ins tead of observing only the total impedance as the main parameter, in this p aper we make use of the complex permeability formalism, by calculating perm eabilities from complex impedance results. We first investigate the effects of the ac magnetic field amplitude (as produced by the ac current flowing through the sample). Results point to domain wall bulging as the dominant m agnetization process for low ac field amplitude. As this amplitude increase s, domain walls are unpinned and displaced, leading to hysteresis. As frequ ency increases, a clear relaxation behavior is observed. The effects of the de field are then studied. This parameter produces a damping of domain wal l processes, leading to a serious decrease in permeability. Very high frequ encies are also considered (f in the GHz range) from results recently publi shed, which lead to a complete image of all the magnetization processes, si nce these results clearly show spin rotation and resonance. (C) 2001 Elsevi er Science B.V. All rights reserved.