Backscattering-Immune Chiral Spin-Wave Modes for Protected Magnon Transport at the Nano-Scale

Protected energy transport is a key element in future data processing devices. Spin waves and their quanta, magnons are one of the promising alternative candidates for the aim of low energy wave-based computing systems. However, their protected transport with suitable propagation characteristics remains a big challenge since backscattering at defects is a loss channel. Here, we report on the identification of backscattering-immune spin-wave modes by studying the propagation of spin waves in magnetic thin films. Our results reveal that chiral Magneto Static Surface Waves (cMSSWs) in films with nano-scale thickness are robust against backscattering from surface defects. cMSSWs propagate perpendicular to the magnetisation direction in an in-plane magnetised thin film and their reciprocity is broken due to dipolar interaction. As long as their frequency lies inside the gap of the volume modes, they are protected against various types of surface inhomogeneities and defects. The distinct robustness of the cMSSWs is demonstrated by comparing it to other types of spin-wave modes that can propagate in such systems. Our results open a new direction in designing highly efficient magnonic logic elements and devices employing cMSSWs in thin films.