Magnetization Reversal in Thin Films

The magnetization reversal of thin films (≈1000 A thick) of 80-20 Permalloy has been studied in a strip transmision line. These films are evaporated onto a heated glass substrate in the presence of an orienting field. Magnetization reversal along the axis of initial orientation takes place in times less than 20 mμsec in any reversing field large enough to overcome the orienting energy. The switching coefficient $S_w$ is defined by $S_w=H_m\tau$, with $\tau$ the reversal time and $H_m$ the reversing field. The experiment gives $H_m=1\mathrm{}$ oe and $\tau <2\mathrm{}\times {10}^{-8\mathrm{}}$ sec, from which $S_w<2\mathrm{}\times {10}^{-8\mathrm{}}$ oe-sec. Reversal by rotation of the magnetization as a whole in the plane of the film yields a model which is consistent with the observed reversal times. Preliminary measurements of the initial permeability perpendicular to the orientation axis have been carried out to 2000 Mc/sec and do not yet reveal the expected frequency dispersion of the initial permeability. This is an indication that $S_w$ may be another order of magnitude smaller than reported here.