The effect of ferromagnetic layer structure on the magnetization reversal processes in (NiFe/Co)/Al–O/NiFe [formula omitted] and (Co/NiFe)/Al–O/NiFe [formula omitted] films was investigated. The films were fabricated by sputter deposition, and the Al–O layer was prepared by oxidizing an Al layer in air. Two distinct magnetization processes were observed by transmission Lorentz microscopy (TLM) with increasing in situ applied field. Reversal of the NiFe/Co bilayer in [formula omitted] occurs via moment rotation, while reversal of the Co/NiFe bilayer in [formula omitted] occurs by domain wall motion, in both cases at higher field than the top NiFe layer. The difference can be ascribed to the difference in the deposition order of the ferromagnetic bilayers (FMBs). High resolution electron microscopy shows that the grains in the top NiFe layer are randomly oriented in both films. In [formula omitted] the NiFe grains in the FMB are randomly oriented, with columnar grains present in the Co. In [formula omitted] a columnar grain structure of NiFe in the FMB is induced by the Co underlayer. The rough FMB/Al–O interface in [formula omitted] leads to weak biquadratic interlayer coupling, which will slightly reduce the field range of the antiparallel magnetization configuration. Hysteresis loops of [formula omitted] and [formula omitted] show two stage magnetization reversals in each sample, which are consistent with TLM results.
ASJC Scopus subject areas
- General Physics and Astronomy