Exchange-Biased Magnetic Vortices

Abstract

This paper reviews our work on the interplay between exchange bias due to the coupling of a ferromagnet to an antiferromagnet and the formation of magnetic vortices, which occur due to the patterning of a ferromagnet. Depending on the thermal and magnetic history, a variety of different effects can be observed. Thermal annealing in a saturating magnetic field establishes a spatially homogeneous exchange bias with a uniform unidirectional anisotropy. This results in an angular dependence of the magnetization reversal mode, which can be either via magnetization rotation or vortex nucleation and annihilation. In contrast, thermal annealing in a field smaller than the vortex annihilation field imprints the ferromagnetic vortex configuration in the antiferromagnet with high fidelity resulting in unusual asymmetric hysteresis loops. Furthermore, we discuss how the interfacial nature of the exchange bias can modify the vortex magnetization along the thickness of the ferromagnet.