Effect of shape on magnetic response for slotted Co nanorings

Remanent states and magnetization reversal for slotted Co nanorings have been investigated using Lorentz microscopy and off-axis electron holography. The 30-nm -thick Co slotted rings were patterned individually and in arrays using electron-beam lithography and lift-off. Different combinations of ring sizes, ring widths, slot angles, and interelement distances were studied using orthogonal applied field directions (perpendicular and parallel to the slot direction). Typical outer diameters (ODs) were in the range of 300-650 nm with slot angles (α) from 30° to 180°. Single-vortex, double-vortex, and flux-closure states without any vortex were found to be the most common remanent configurations. The nanorings showed considerable flux leakage near the slotted region for some size and shape combinations. Slotted Co nanorings with small OD (300 nm or less) and moderate slot angles (α=30°) would be strong candidate shapes for future patterned media applications.