Arrays of epitaxial Co submicron particles: Critical size for single-domain formation and multidomain structures

Arrays of Co particles with well-defined geometry and lateral sizes in the range 0.1-0.5 mum were prepared by electron beam lithography and studied by magnetization measurements and magnetic force microscopy. The starting mat erials were epitaxial Co films, with in-plane magnetic anisotropy, having t hicknesses in the range 10-50 nm. The particles change from multidomain beh avior to that of stable single domains in zero field, as the lateral dimens ion decreases within these ranges. For particles of circular shape, i.e., w ithout in-plane shape anisotropy, the critical size for forming single doma ins was found to be about 200 nm in lateral extension and 20 nm thickness. Elliptical particles prepared with 20 nm thickness and lateral dimensions 1 50 by 450 nm were found to be stable single domains, of good uniformity, in zero field. The switching of these particles from one magnetization direct ion along the long axis to the other, requires an applied field B(S)approxi mate to (100 +/- 20)mT. A comparison with other published results leads to the conclusion that although the critical volume for single domains may be about the same, the final microscopic magnetic structure and the processes for magnetic switching for particles in the actual range of sizes, are stro ngly governed by the intrinsic properties of the Co films, which may vary w idely. (C) 2001 American Institute of Physics.