Flux Reversal at Low Temperatures

Abstract

Fast flux reversal in thin (2000 Å) Permalloy films has been observed at 77° and 4°K and compared to room temperature. The inverse of the reversal time as a function of drive field with initial angle as a parameter was plotted. The switching coefficient Sw of the low-drive region increased threefold which is inconsistent with a simple, eddy-current-damped domain wall motion model since the conductivity changed only 17% over the same range. The switching coefficient for the intermediate-drive region is essentially constant to 77°K and then increases as the temperature is reduced in a manner inconsistent with an intrinsically damped nonuniform rotational mechanism. The thresholds in this region doubled, as did the anisotropy field HK between 296° and 4°K. The high-drive region does not change with temperature consistent with a coherent rotational model.