Vortex Nucleation in Exchange Biased Magnetic Nanoelements

We report a theoretical investigation of vortex nucleation along the hysteresis curves of flat iron and permalloy nanoelements exchange coupled to an antiferromagnetic substrate. Contrary to common intuition, the interface exchange field favors vortex nucleation. For lateral dimensions in the sub-100 nm range, vortex nucleation in iron nanoelements require smaller values of the interface field strength. For both materials, strong values of the interface field strength leads to double loop curves, with the magnetization driven by vortex motion in most part of both branches of the hysteresis curve.