Size and thickness dependencies of magnetization reversal in Co dot arrays

The magnetization reversal properties of high-resolution Co dot arrays fabricated by nanoimprint lithography have been studied as a function of both diameter and thickness. Both vortex and single-domain states were observed by measuring the hysteresis loops, which result in an experimental phase diagram in the diameter-thickness plane. In the vortex state, magnetization reversal proceeds by vortex nucleation, growth, and subsequent annihilation under relatively high field. The vortex growth has been shown to be reversible in a wide field range, in agreement with micromagnetic simulations. Finally, a distribution of annihilation fields in patterned dot arrays was studied experimentally.