Transverse magneto-optical effects in nanoscale disks

Abstract

We have investigated the optical and magneto-optical responses of nanoscale ferromagnetic disks by means of numerical simulations, using an extension of the discrete-dipole approximation. Specifically, we studied the case of $5\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ thick cobalt disks in the diameter range from 200 to $1000\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$, illuminated under normal incidence with a wavelength of $\ensuremath{\lambda}=632.8\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$. We furthermore assumed the magnetization to lie in the plane of the disk and to be oriented perpendicular to the electric field of the incoming electromagnetic wave, i.e., the transverse magneto-optical Kerr effect configuration. The induced polarization pattern and the near- and far-field optical and magneto-optical responses have been calculated, finding clear nanoscale confinement effects as one reduces the diameter of the disks. However, we also observe that the rather weak magneto-optical response essentially mimics the optical response, and we demonstrate that it can be calculated as a perturbation of the latter with a high degree of accuracy. This strong similarity between the optical and magneto-optical nanoscale confinement effects also results in the fact that the normalized magneto-optically induced far-field light intensity change, which is the quantity measured in experiments, is only weakly affected even in the case of sub-wavelength-sized disks.