  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 a magnetophotonic crystal that exhibit abrupt and narrow
magneto-optical spectral features that are both magnetic field 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, in both optical and
magneto-optical spectra, which we demonstrate and explain using Maxwell-theory
simulations. This robust magnetophotonic crystal opens 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.
