Control of magnetic vortex chirality in square ring micromagnets

A.Libál, M.Grimsditch,V.Metlushko,P. Vavassori, B. Jankó

We investigate the effect of a deliberately introduced shape asymmetry on magnetization reversal in small, square-shaped, magnetic rings. The magnetization reversal process is investigated using the diffracted magneto-optical Kerr effect (D-MOKE) combined withmicromagnetic simulations. Experimentally we find that the reversal path is sensitive to a small changes in the direction of the applied field. Micromagnetic simulations that reproduce the measured 0th and 1st order loops, allow us to identify the reversal mechanisms as due to different intermediate states;namely the so called vortex and horseshoe states. Based on our results we are now able to prescribe a methodology for writing a vortex
state with specific chirality in these asymmetric rings. Such control will be necessary if patterned arrays of this kind are to be used as magnetic storage elements.

A Scanning Electron Microscope (SEM) Image of the fabricated permalloy open-slit square ring lattice

 

The two possible ways of switching for the magnetization: vortex state (top three slides) and the horseshoe state (bottom three slides). In both cases we are approaching the switching from large negative fields

 

The 1st diffracted order for the 0th direction. The peaks in the full hysteresis loop correspond to vortex states with different chirality. The direction of the applied magnetic field to archive a desired chirality is also shown below the magnetization slides