Terahertz magneto-plasmonics using cobalt subwavelength aperture arrays

We characterize the terahertz (THz) magneto-plasmonic response of a cobalt-based periodic aperture array. The bare cobalt surface allows for low loss propagation of surface plasmon-polaritons, as evidenced by comparing the reflection from aperture arrays coated with Au and with Co. When an external magnetic field is applied in a polar Kerr geometry, we observe a maximum polarization rotation of ~0.6° and an ellipticity of ~0.35° from the Co-based array. These values are larger than expected based on existing models that include only interband transitions in ferromagnetic metals. We discuss possible reasons for the difference between experiment and theory.