Angular Dependence of Vortex Annihilation Fields in Asymmetric Co Dots

TL;DR

This study explores how the angular orientation of magnetic fields affects vortex annihilation in asymmetric cobalt nanodots, revealing angle-dependent control over vortex chirality and annihilation fields.

Contribution

It demonstrates the influence of field angle on vortex reversal and chirality control in asymmetric Co dots, highlighting a crossover behavior in annihilation fields.

Findings

Vortex annihilation fields depend on the angle of the applied magnetic field.

Chirality control is effective at small angles but diminishes at intermediate angles.

A crossover in annihilation field behavior occurs at certain angles.

Abstract

Shape asymmetries in nominally circular nanomagnets provide a potential means for vortex chirality control. However, in realistic arrays their effects are challenging to probe since asymmetric magnetization reversal processes are often averaged to include distributions over all angles. Here we investigate how shape asymmetry influences the vortex reversal in arrays of sub-micron edge-cut Co dots. We find that the vortices can be manipulated to annihilate at particular sites under different field orientations and cycle sequences. The vortex annihilation field and degree of chirality control depend sensitively on the angular position of the applied field relative to the flat edge of the dots. For small angles, the major loop annihilation field is significantly larger than that found from the half loop and the vortex chirality can be well controlled. At intermediate angles the chirality control is lost and an interesting crossover in the annihilation field is found: the half loop actually extrudes outside of the major loop, exhibiting a larger vortex annihilation field. At large angles the annihilation fields along major and half loops become degenerate.