Backscattering immunity of dipole-exchange magnetostatic surface spin waves

TL;DR

This paper demonstrates that chiral magneto static surface waves in nano-scale magnetic thin films are immune to backscattering from surface defects, due to symmetry breaking in their dynamic magnetic fields, promising for magnonic device design.

Contribution

It reveals backscattering immunity of cMSSWs in thin films, independent of mode topology, due to symmetry breaking caused by dipolar interactions.

Findings

cMSSWs are robust against surface defects within the mode gap

Robustness is due to symmetry breaking of dynamic magnetic fields

Confirmed by micromagnetic simulations

Abstract

The existence of backscattering-immune spin-wave modes is demonstrated 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. Our explanation is independent of the topology of the modes and predicts that this robustness 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. Micromagnetic simulations confirm the robust character of the cMSSWs. Our results open a new direction in designing highly efficient magnonic logic elements and devices employing cMSSWs in nano-scale thin films.