Active Ferromagnetic Metasurface with Topologically Protected Spin Texture for Spectral Filters

Electromagnetic metasurfaces modulate a material's response to electromagnetic waves by specifically arranged elements with dimensions below the wavelength. They have opened new fields of research, including flat optics and nanophotonics on a chip. Ferromagnetic metasurfaces could become the building blocks for manipulation of both microwaves and spin waves (magnons). So far, the functionality of magnonic devices has been limited by high intrinsic damping of the materials employed, suppressing long-distance spin-wave propagation. Here ferromagnetic metasurfaces are reported, which are created from periodic arrays of either 15 nm thick Co₂₀Fe₆₀B₂₀, Ni₈₀Fe₂₀ or Co nanodisks on ferrimagnetic yttrium iron garnet (YIG) hosting topologically protected vortex states. This device, a reconfigurable spectral filter, operates in the microwave regime near 0.9 GHz and manipulates long-distance spin-wave transmission in thin YIG. An efficiency of 98.5% is demonstrated, with the metasurface covering only 15% of the microwave antenna. This first demonstration of a ferromagnetic metasurface opens unprecedented possibilities for on-chip control of microwaves in low-damping ferrimagnetic insulators.