Dynamic susceptibility of dipolar coupled magnetic vortices

Abstract

We report a calculation of the dynamic susceptibility of a pair of ferromagnetic circular nanocylinders stacked along the common axis, one on the other, and separated by a thin nonmagnetic spacer. Our theoretical model considers the dipolar energy without restrictions on dipolar sums, along with the anisotropy and exchange energies. Our results indicate that the nanocylinders dipolar interaction may affect the susceptibility spectrum. We have found, for instance, that a 30nm thick, 70nm diameter Fe nanocylinder holds a single magnetic vortex, and the planar susceptibility (χxx) spectrum displays two low-frequency peaks (at 0.37 and 1.00 GHz). We have also found that the χxx susceptibility spectrum of dipolar-coupled vortices in a pair of Fe nanocylinders with a 5 nm spacer exhibits peaks at 0.3, 0.7, 1.2, and 1.4 GHz. Furthermore, the relative weight of the peaks is controlled by the degree of spatial localization of these excitations.