Predicting tunable nonreciprocal spin wave generation mediated by interfacial Dzyaloshinskii-Moriya interaction in magnonic heterostructures

Thin, metallic magnetic films can support nonreciprocal spin waves due to the interfacial Dzyaloshinskii-Moriya interaction (iDMI). However, these films typically have high damping, making spin wave propagation distances short (less than one micrometer). In this work, we theoretically study a thin ferromagnetic strip with iDMI and excite spin waves by driving a central segment of the strip. Spin waves propagate with different amplitudes to the left versus to the right from the driving region (i.e. nonreciprocity occurs) due to the iDMI. Our calculation based on spin-wave-dispersion plus our micromagnetic simulations both show that changing the driving segment width, driving frequency and static applied field strength tunes the nonreciprocity. Our calculation based on spin-wave-dispersion, using a so-called “overlap function” will allow researchers to predict conditions of maximum nonreciprocity, without the need for computational solvers. Moreover, to circumvent the issue of short propagation distances, we propose a geometry where iDMI is only present in the driving region and low-damping materials comprise the remainder of the strip. Our calculations show significant spin wave amplitudes over several microns from the excitation region.

💡 Research Summary

This paper presents a comprehensive theoretical and numerical study on the generation of tunable nonreciprocal spin waves in magnonic heterostructures mediated by the interfacial Dzyaloshinskii-Moriya interaction (iDMI). The core challenge addressed is that while iDMI in ultrathin metallic ferromagnetic films enables nonreciprocal spin wave propagation—where waves traveling in opposite directions have different properties—it is often accompanied by high magnetic damping, severely limiting propagation distances to less than a micrometer.

The research focuses on a quasi-one-dimensional ferromagnetic strip (modeled as a spin chain) with iDMI. Spin waves are excited by a spatially localized, oscillating magnetic field applied to a central segment (the “driving region”) of the strip. Due to the iDMI, the spin wave dispersion relation becomes asymmetric