Vortex states in patterned exchange biased NiO/Ni samples

TL;DR

This study explores vortex states in patterned NiO/Ni squares, revealing how shape and exchange bias influence magnetization reversal, with implications for magnetic device design.

Contribution

It demonstrates the impact of square size and shape on vortex formation and exchange bias behavior in NiO/Ni nanostructures, combining experimental and simulation approaches.

Findings

Vortex-like hysteresis loops observed in NiO/Ni squares.

Sign change in exchange bias field for 1.5 μm squares.

Vortex nucleation driven by shape and unidirectional anisotropy interplay.

Abstract

We investigated the magnetization reversal of arrays of exchange biased NiO/Ni squares with superconducting quantum interference device magnetometry and micromagnetic simulations. The edges of the squares were 0.5, 1.5, and 3.0 $\mu$m long. The NiO/Ni structures exhibit vortexlike hysteresis loops and micromagnetic calculations show that this feature is due to several vortices nucleating in the islands. Furthermore, for the arrays with squares of 1.5 $\mu$m edge length, the sign of the exchange bias field changes, as compared to the same continuous NiO/Ni layer. We attribute the vortex nucleation and the change of the exchange bias field to the interplay between shape and unidirectional anisotropy.