Topological spin Hall effects and tunable skyrmion Hall effects in uniaxial antiferromagnetic insulators

Abstract

Recent advances in the physics of current-driven antiferromagnetic skyrmions have observed the absence of a Magnus force. We outline the symmetry reasons for this phenomenon, and show that this cancellation will fail in the case of spin polarized currents. Pairing micromagnetic simulations with semiclassical spin wave transport theory, we demonstrate that skyrmions produce a spin-polarized transverse magnon current, and that spin-polarized magnon currents can in turn produce transverse motion of antiferromagnetic skyrmions. We examine qualitative differences in the frequency dependence of the skyrmion Hall angle between ferromagnetic and antiferromagnetic cases, and close by proposing a simple skyrmion-based magnonic device for demultiplexing of spin channels.arXiv:1902.09382v2 [cond-mat.mes-hall]

All‐Electrical Magnon Transport Experiments in Magnetically Ordered Insulators

“…Moreover, several proposals to realize topological magnon insulators, where edge channels provide momentum-locked pure spin current transport, have been put forward (see Figure 8b). [154,167] If such effects can be verified in the experiment, they will provide fruitful grounds for new functionalities in magnonic applications. In regard to applications and further developments in the field, it will be crucial to determine efficient ways to tune and engineer emergent spin-orbit effects in antiferromagnetic magnonics.…”

“…There is a growing number of theoretical concepts already out exploiting this equivalent nature, predicting, for example, the existence of topological magnon states in AFIs or emergent spin-orbit coupling effects in magnon transport. [37,154,[163][164][165][166][167][168][169][170] First experiments on magnon transport via all-electrical means in AFIs were fully compatible with a simple diffusive magnon spin transport, where the injected spin orientation is maintained within the AFI. [71,[77][78][79] However, within the past year, new experiments emerged, which confirm the electronic transport analogy via the observation of the magnon Hanle effect in easy-plane AFIs.…”

“…Many theoretical concepts exploit the intrinsic two-level properties of magnons in antiferromagnets and the coupling to, for example, magnetic anisotropy or dipolar fields to construct emergent spin-orbit phenomena in analogy to electronic transport. [154,[163][164][165][166][167][168][169]256] In terms of emergent spin-orbit coupling, the magnon spin Nernst effect, [163,169] i.e., the generation of a transverse magnonic pure spin current by driving a magnon current via a thermal gradient, is one of the prototype examples awaiting experimental verification (see Figure 8a). A major challenge in the experiment will be the detection of the transverse magnon spin accumulation and careful control experiments to disentangle the magnon SHE from other effects driven by the applied thermal gradient.…”

“…[124,[131][132][133][134][136][137][138][139][140][141][142][143][144][145] In addition, based on the SMR effect, it is possible to quantify spin-orbit torque effects [36,[146][147][148][149][150][151] and investigate topological spin textures in MOIs. [152][153][154][155][156][157][158] For the all-electrical magnon transport experiments, we consider the case that s and n are arranged collinear to each other. For this arrangement, the interfacial spin-transfer torque acts on the thermally excited magnons in the MOI.…”

Suppression of Skyrmion Hall Motion in Antiferromagnets Driven by Circularly Polarized Spin Waves

“…Thus, the skyrmion Hall motion could be also driven by the spin wave even in AFM systems. Interestingly, the scattering direction of the magnon and the deflection direction of skyrmion are determined by the chirality of the spin wave, allowing the skyrmions work as spin splitters in AFM magnon devices [26]. However, skyrmion Hall motion is detrimental for data propagation in future skyrmion-based devices, as discussed above.…”