Theoretical aspects of near-field magneto-optics and scanning magneto-optical microscopy

A general theory for near-field optics of in-surface homogeneous ferromagnets and scanning microscopy of inhomogeneous ones is reviewed. The model under discussion assumes the near field to be provided by a small metal particle placed above and near the plane surface of a magnetizable medium. Light is scattered by the combined system "particle plus medium" and is detected in the far field, where the characteristics of radiation are related to the magnetic properties of scattering volume. The particle-sample interaction, mediated by surface plasmons, is treated to all orders of multiple-scattering theory, and the magneto-optical interaction is considered to first-order terms in magnetization. Both cross-sections and ellipticity parameters are evaluated. The problem of scanning near-field magneto-optical. microscopy is formulated within the model of a domain wall formed inside of an atomically thin near-surface magnetic layer. A description is given of surface-plasmon-enhanced magneto-optical effects excitable via the near field. Restrictions to the spatial resolution of the near-field magneto-optical contrast are discussed in terms of geometrical parameters such as the subwavelength size of a magnetic inhomogeneity and the spacing between it and a probing particle.