Fiber optics for spin waves

Xiangjun Xing,Yan Zhou

doi:10.1038/am.2016.25

Abstract

Chiral magnets can guide spin waves and hence act as the magnonic equivalent of optical fibres, researchers in China theoretically show. Circuits that use spin currents rather than conventional electrical currents are anticipated to have considerably higher throughputs and be suitable for tasks such as image processing and speech recognition. Now, Xiangjun Xing at Wenzhou University and Yan Zhou at Nanjing University have performed simulations that show that deep one-dimensional potential wells can be created in chiral magnets. Such wells can guide spin waves, acting as magnonic waveguides that resemble optic fibres with a graded refractive index. The pair also designed simple logic gates based on these waveguides. They claim that this will open up new avenues for guiding spin waves in ultrathin magnetic structures.

Highlights

Magnonic circuits are estimated to be capable of providing substantial throughput enhancement compared with those circuits currently based on complementary metal-oxide-semiconductor technology; special tasks such as advanced image processing and speech recognition that benefit from parallel processing of information will be possible.[1,2] To achieve multifunctionality of magnonic circuits, controlled propagation and manipulation of spin waves (SWs) in a rich variety of magnetic nanostructures are required
We show by micromagnetic simulations that the potential well caused by a strip-domain wall (SDW) can serve as an internal channel to guide spin-wave (SW) propagation, which makes the ultrathin chiral magnet including the SDW become a reconfigurable self-cladding optic-fiber-like magnonic waveguide with a graded refractive index
With the continued downscaling of magnetic films, the antisymmetric Dzyaloshinskii–Moriya interaction (DMI)[3,4] arising from spinorbit scattering of itinerant electrons has manifested its roles in ultrathin samples with inversion-asymmetric interfaces,[5,6] where various spin textures such as spin spirals,[7] chiral domain walls[8,9] and skyrmions[10] were observed recently

Summary

Introduction

Magnonic circuits are estimated to be capable of providing substantial throughput enhancement compared with those circuits currently based on complementary metal-oxide-semiconductor technology; special tasks such as advanced image processing and speech recognition that benefit from parallel processing of information will be possible.[1,2] To achieve multifunctionality of magnonic circuits, controlled propagation and manipulation of spin waves (SWs) in a rich variety of magnetic nanostructures are required. Ultrathin nanostructures with interface-induced DMI will become promising candidates for the construction of magnonic devices with versatile functionalities.[1,16,17,18] So far, guided propagation and manipulation of SWs in chiral nanostructures containing unique spin textures have not yet been addressed, despite their strong relevance to potential applications of chiral magnets in magnonics as well as to understanding the strength of relevant interactions.[19,20] In the widely used Damon–Eshbach (DE) propagation geometry,[21] SWs in a strip-type waveguide—regardless of the center or edge modes22— have nonzero precession amplitude at the boundary;[23] they might suffer from undesired scattering caused by boundary irregularities that have been found to result in reduced attenuation length.[22] The self-cladding waveguide with well-defined internal channels suggested by Duerr et al.[13] can resolve the edge-scattering problem, but the channels must be maintained by an applied field, which is not preferred in real devices

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