Micromagnetic simulation of hysteresis loop of elliptic permalloy nanorings

Magnetic hysteresis behavior of isotropic permalloy elliptic nanorings of outer semi major axis length (a(out)) 100 nm and thickness (t) 20 nm were studied with respect to the variation of two parameters: outer semiminor axis length (b(out)) and the difference between outer and inner dimensions (r). The outer semiminor axis length (b(out)) varied from 90 nm to 20 nm which covers from nearly circular nanoring to elliptic nanoring of high aspect ratio. The value of r varied in steps of 10 nm. Micromagnetic simulation of in-plane hysteresis curve of these nanorings revealed that the remanent state of all of these elliptic rings are onion states if the magnetic field is applied along the longer side of the elliptic rings. If the magnetic field is applied along the shorter side, then the remanent states turn out to be vortex state. The hysteresis loss indicated by area of the hysteresis loop was found to be decreasing gradually with the increment of either r or b(out). On the other hand, the remanent magnetization increased with increment of r but decreased with the increment of b(out). The changes were attributed to three parameters mainly: inner curvature, exchange energy and demagnetization energy. The changes in loop area were discussed in light of variation of these three parameters.