Magnon-Cherenkov effect from a picosecond strain pulse

Radiation from an uniformly moving source, referred to as the Cherenkov effect, is a universal phenomenon, which enables emission of waves and finds important applications in various areas of physics from particle physics to plasmonics and beyond. Currently, unveiling the potential of Cherenkov emission of coherent spin waves, or magnons, is hampered by a lack of experimentally implemented fast-moving magnetic perturbations. In this work, we uncover the magnon-Cherenkov effect demonstrating experimentally the emission of the exchange spin waves enabled by an optically induced picosecond strain pulse, which acts as a spatially localized propagating perturbation of the internal effective magnetic field as a result of magnetoelastic coupling. Through time-resolved measurements and micromagnetoelastic simulations, we reveal the sagittal propagation of a strain pulse in a dielectric ferrimagnet followed by the emitted SWs fully in line with the conditions of the Cherenkov effect. The spectral characteristics of the emitted spin waves are controlled with an applied magnetic field and the shape of the strain pulse itself. Establishing a picosecond strain pulse as a source for the magnon-Cherenkov effect significantly expands the possibilities to realize and control non-dissipative spin transport in various laterally and vertically structured magnonic devices.