Chiral protection of dipole-exchange spin-waves

Protected energy transport is a key element in future data processing devices. Here, we report on the identification of backscattering-immune spin-wave modes by studying the propagation of spin waves in magnetic thin films of nano-scale thickness. Our results reveal that chiral Magneto Static Surface Waves (cMSSWs), which propagate perpendicular to the magnetization direction in an in-plane magnetized thin film, are robust against backscattering from surface defects. cMSSWs are protected against various types of surface inhomogeneities and defects as long as their frequency lies inside the gap of the volume modes. This protection is a consequence of symmetry breaking of the dynamic magnetic fields of cMSSWs due to the off-diagonal part of the dipolar interaction tensor, which is present both for long- (dipole dominated) and short-wavelength (exchange dominated) spin waves. Our results open a new direction in designing highly efficient magnonic logic elements and devices employing cMSSWs in nano-scale thin films.