Nonreciprocities and relaxations of magnetostatic surface spin waves in ferromagnetic bilayers
Phys. Rev. B 114, 144421 – Published 23 September, 2026
DOI: https://doi.org/10.1103/bgbx-czbt
Abstract
We investigate theoretically and numerically the nonreciprocal propagation and relaxation properties of magnetostatic surface spin waves (MSSWs) in dipolar-coupled ferromagnetic bilayers. The in-phase acoustic and out-of-phase optic modes are identified with distinct cross-thickness localization profiles. We trace the direction-dependent interlayer dipolar coupling strength to the intrinsic chirality of single-layer MSSWs and their associated dipolar fields, providing an intuitive physical picture for the dispersion nonreciprocity. For relaxation properties, we extend the geometry-corrected relaxation model to bilayer systems and apply the magnon-number-weighted effective damping formalism to structures with distinct Gilbert damping factors in the two sublayers. Systematic micromagnetic simulations confirm the accuracy of the quadratic energy-weighted damping scheme and quantify the relation between mode localization and total dissipation in hybrid magnonic waveguides. Combining dispersion-relation-determined characteristic frequencies and damping-related decay lengths, we establish quantitative design guidelines for nonreciprocal magnonic functionalities including frequency-division multiplexing and damping-tunable isolation. In this work, we offer quantitative reference for evaluating and optimizing the performance of multilayer magnonic waveguides and provide practical design criteria for bilayer-based nonreciprocal magnonic components.
