Spin-wave caustics in an extended thin film excited by a nanoconstriction

International audienceThe ability to control the directionality of spin waves is important for magnonic logic and computing application. Here, we demonstrate the emission of caustic-like spin waves in an extended yttrium iron garnet (YIG) thin film of 200 nm thickness by a nano-constricted rf waveguide. Using spatial resolved micro-focused Brillouin light spectroscopy technique in both the backward volume and the Damon-Eshbach geometry, we reveal the spin-wave directional spin-wave propagation in the YIG film. We excite spin waves in the film by passing a rf current through a constricted waveguide patterned on the top of the extended YIG film by electron-beam lithography. When the direction of the group velocity is the same for waves of different wavevectors, caustic beams are formed which propagate in two directions perpendicular to the isofrequency curve. We find that these beams are symmetric in intensity for a rf magnetic field perpendicular to the biasing magnetic field. On the other hand, one beam is more intense than the other one for a rf magnetic field parallel to the biasing field. We further show that the propagation direction of caustic-like spin-wave beams is frequency dependent. Our findings have important implications for the development of switchable spin wave splitters, passive spin-wave frequency-division demultiplexers[1, 2] and magnonic interferometry