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

Hysteresis loops in mesoscopic narrow rings with cubic anisotropy have been computed. A two-step switching process is found. The first transition corr esponds to vortex formation and has been studied in detail. Starting from a well defined remanent state with two opposite head-to-head walls, the vort ex 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 a xis due to the combined action of the magneto-crystalline anisotropy and th e magnetostatic dipolar fields. (C) 2001 American Institute of Physics.