Magnetization changes visualized using photoemission electron microscopy

Abstract

Photoemission electron microscopy was used to visualize the motion of magnetic domains on a sub-nanosecond timescale. The technique exploits the imaging of magnetic domains using soft X-ray circular dichroism, with the special feature that the instrument utilizes a fast image acquisition system with intrinsic 125ps time resolution. The overall time resolution used is about 500ps. Different domains and domain movements have been observed in lithographically-produced Permalloy structures on a copper microstrip-line. A current pulse of I=0.5A with rise times of about 300ps switched the Permalloy islands from a Landau-Lifshitz type domain configuration into metastable s-state domain configurations. A pulse with opposite direction could reverse these s-type patterns. Photoemission electron microscopy was employed to observe the domain movements while repeating current pulses passed the microstrip-line. Using small unipolar amplitudes, only the cross-tie walls of the s-type patterns disappear and the pattern becomes "fuzzy", e.g. the domain rims are not sharp and some domains change their size. Before the structure switches at a current threshold, it is more fluctuating as shown by significant differences in sharpness of the islands rim and the inter-domain boundaries show. The device behavior complicates when a bi-polar pulse is applied. Switching and oscillating of domains is observed in various manners, e.g. very tiny domains appear and unify again. © 2004 Elsevier B.V. All rights reserved.