Vortex formation in magnetic narrow rings:: The role of magneto-crystalline anisotropy

Hysteresis loops in mesoscopic narrow rings with cubic anisotropy have been computed. A two-step switching process is found. The first transition corresponds to vortex formation and has been studied in detail. Starting from a well defined remanent state with two opposite head-to-head walls, the vortex is created when, due to any asymmetry, one wall depins first, propagates, reaches the other and they annihilate one another. It is also found that, in this geometry, the crystallographic hard axis becomes the global easy axis due to the combined action of the magneto-crystalline anisotropy and the magnetostatic dipolar fields. (C) 2001 American Institute of Physics.