Magnetic modulation of mid and far-infrared plasmon resonances using the orientational magneto optical effect

Arrays of in plane randomly placed aligned slits were engraved on an anisotropic magneto resistance Ni81Fe19 film, a material whose optical properties depend on the relative orientation of the light polarization and the magnetization direction (orientational magneto optical effect). In the 3-14 mu m spectral range and for light polarized perpendicular to the slit axis, the reflectivity of the arrays presents a dip related to the excitation of the slit plasmon longitudinal resonance. We show that the intensity of this feature is different if the direction of the magnetization is parallel or perpendicular to the light polarization that excites this resonance. By varying the slit length, the spectral dependence of this magnetic modulation of the plasmon resonance has been analyzed. The results suggest that the orientational magneto optical effect could be used for magnetic modulation of plasmon resonances from the mid-infrared to the far-infrared spectral ranges.