Polarization transformation and destructive interference on subwavelength magnetic domains in magneto-plasmonic systems.

We demonstrate magneto-optical (MO) polarization transformation due to surface plasmons in CoPt perpendicular magnetic films in the polar Kerr geometry. An extraordinary Kerr rotation angle (θ =  ± 88.9°) that almost reaches the upper limit of polarization is produced in the attenuated total reflection (Kretschmann) configuration. P-polarized incident radiation is almost transformed upon reflection to s-polarized radiation, which may be out of phase depending on whether the magnetization of CoPt is up or down. Moreover, the reflected intensity may be drastically modulated by applying an external magnetic field. The reflectivity goes almost to zero in the demagnetized state and increases with increasing external magnetic field. This drastic optical response is attributed to the MO destructive interference produced by the subwavelength magnetic domain structure.