Direct Observation of Spin-Wave Focusing by a Fresnel Lens

Spin waves are discussed as promising information carrier for beyond complementary metal-oxide semiconductor data processing. One major challenge is guiding and steering of spin waves in a uniform film. Here, we explore the use of diffractive optics for these tasks by nanoscale real-space imaging using x-ray microscopy and careful analysis with micromagnetic simulations. We discuss the properties of the focused caustic beams that are generated by a Fresnel-type zone plate and demonstrate control and steering of the focal spot. Thus, we present a steerable and intense nanometer-sized spin-wave source. Potentially, this could be used to selectively illuminate magnonic devices like nano-oscillators.