In-plane hysteresis of permalloy nanorings: a study of micromagnetic simulation

Abstract

Magnetic hysteresis of isotropic permalloy nanorings with outer diameter 200 nm and thickness 20 nm has been studied. The inner diameter is varied from 0 to 190 nm to accommodate wide range of samples from nanodisk to thin nanorings. Micromagnetic simulation of in-plane hysteresis curve of these nanorings reveals that the magnetic properties change gradually with the change of inner diameter. The hysteresis loss indicated by the area of the hysteresis loop, increases gradually with the increase in inner radius up to d _in = 174 nm. For inner diameter of 176 nm, the loop area decreases drastically and remains so for up to d _in = 180 nm. After that, a small increment of d _in results in a large increment of loop area. The remanent states are found to be vortex states for d _in = 0–180 nm and onion states for d _in > 180 nm. The changes are attributed to two parameters mainly: exchange energy and demagnetization energy. These two parameters depend on inner curvature of the ring, which is treated as a variable in this simulation work. The changes in loop area have been discussed in light of variation of these parameters.