Resonant magneto–optical Kerr effect induced by hybrid plasma modes in ferromagnetic nanovoids**Project supported by the Natural Science Foundation of Shandong Province, China (Grant No. ZR2015AM024) and the Doctoral Research Started Funding of Qufu Normal University, China (Grant No. BSQD20130152).

Abstract

With nanovoids buried in Co films, resonant structures were observed in spectra of polar magneto–optical Kerr effect (MOKE), where both a narrow bandwidth and high intensity were acquired. Through changing the thickness of Co films and the lattice of voids, different optical modes were introduced. For a very shallow array of voids, the resonant MOKE was induced by Ag plasma edge resonance, for deeper ones, hybrid plasma modes, such as void plasmons in the voids, surface lattice plasmons between the voids, and the co-action of them, etc. resulted in resonant MOKE. We found that resonant MOKE resulted from the void plasmons resonance which possesses the narrowest bandwidth for the lowest absorption of voids. The simulated electromagnetic field (EF) distribution consolidated different effects of these three optical modes on resonant MOKE modulation. Such resonant polar MOKE possesses high sensitivity, which might pave the way to on-chip MO devices.