Slow magnetization dynamics of small permalloy islands

Abstract

The conditions that lead to specific domain configurations and the associated switching characteristics of small permalloy islands were studied by using magnetic force microscopy. By measuring a large number of particles, it was established that islands that have nonzero remanent moments (nonsolenoidal) exist in one of three distinct configurations, namely: (a) true single domain, (b) quasisingle domain with edge closure patterns, and (c) multidomain with nonuniform internal magnetization. The configuration depended upon the island width as well as the aspect ratio. Islands that are 310 nm wide or less are true single domain particles at low aspect ratios (similar to 1.87) and higher, while islands wider than 500 nm always exhibited edge closure domains even for very large aspect ratios. In the range between 310 and 500 nm, the onset of single domain behavior was a function of the aspect ratio and thickness. Our studies involving in situ applied field similarly revealed the mechanisms of the reversal processes for each of the configurations, which correlated quite well with the values of the switching fields. (C) 2000 American Institute of Physics. [S0021-8979(00)37308-X].