Direction-sensitive magnetophotonic metasurfaces.

Nanometer-thin rare-earth-transition metal (RE-TM) alloys with precisely controlled compositions and out-of-plane magnetic anisotropy are currently in the focus for ultrafast magnetophotonic applications. However, achieving lateral nanoscale dimensions, crucial for potential device downscaling, while maintaining designable optomagnetic functionality and out-of-plane magnetic anisotropy is extremely challenging. Here we integrate nanosized Tb$_{18}$Co$_{82}$ ferrimagnetic alloys, having strong out-of-plane magnetic anisotropy, within a gold plasmonic nanoantenna array to design micrometer-scale magnetophotonic metasurfaces that exhibit abrupt and narrow magneto-optical spectral features that are both magnetism and light incidence direction controlled. The narrow Fano-type resonance arises through the interference of the individual nanoantenna's surface plasmons and a Rayleigh anomaly of the whole nanoantenna array, which we demonstrate and explain using Maxwell-theory simulations. These robust magnetophotonic metasurfaces open the way for conceptually new high-resolution light incidence direction sensors, as well as for building blocks for plasmon-assisted all-optical magnetization switching in ferrimagnetic RE-TM alloys.