Correlation of edge roughness to nucleation field and nucleation field distribution in patterned Permalloy elements

The effects of edge roughness on vortex nucleation field and its distribution are measured in Permalloy nanostructured arrays. Teardrop-shaped elements, 250 nm wide and 30 nm thick, were fabricated using electron beam lithography and lift-off. Roughness variations were created by varying the electron dose during patterning, and measured by analysis of in-focus transmission electron microscopy (TEM) images. In situ measurements of the vortex nucleation fields and the nucleation field distributions of the dose arrays were performed with Lorentz mode TEM. In combining the measurements of edge roughness with measurements of nucleation field and its distribution, we show that edge roughness increases the probability for vortex nucleation and thus permits vortices to nucleate at larger applied fields, but at the same time, edge roughness broadens the nucleation-field distribution in magnetic nanostructured arrays.