Lorentz microscopy of elliptical magnetic rings

A study of the magnetization reversal process of NiFe elliptical rings has been made as a function of ring size and ring orientation with respect to the applied field. The long axis of the rings ranged from 600 nm to 6 μm and the ring width and thickness were fixed at ∼220 and 20 nm, respectively. The magnetization reversal mechanism was characterized using Lorentz transmission electron microscopy as a function of the angle between the long axis of the ellipse and the applied field. A decrease in the range of stability of the intermediate vortex state with increasing angle between the long axis and the applied field was observed. The structure of the remanent domain walls was dependent on the size of the ring, and a phase diagram of domain-wall type as a function of ring geometry calculated from Landau-Lifshitz-Gilbert simulations is presented for comparison with the experimental data.