Spin transport in antiferromagnetic insulators: progress and challenges

Abstract

Spin transport is a key process in the operation of spin-based devices that has been the focus of spintronics research for the last two decades. Conductive materials, such as semiconductors and metals, in which the spin transport relies on electron diffusion, have been employed as the channels for spin transport in most studies. Due to the absence of conduction electrons, the potential to be a spin channel has long been neglected for insulators. However, since the demonstration of spin transmission through a ferromagnetic insulator, it was realized that insulators with magnetic ordering can also serve as channels for spin transport. Here, the recent progress of spin transport in antiferromagnetic insulators is briefly described with an introduction to the experimental techniques. The observations regarding the temperature dependence of spin transmission, spin current switching and the negative spin Hall magnetoresistance are discussed. We also include the challenges for developing the functionality of antiferromagnetic insulators as well as the unresolved problems from the experimental observations.

All‐Electrical Magnon Transport Experiments in Magnetically Ordered Insulators

“…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.…”

Coherent Transfer of Spin Angular Momentum by Evanescent Spin Waves within Antiferromagnetic NiO

“…The need for energy efficient information technology has generated intense interest in media for processing data using new carriers including sound [1], light [2], and electron spin [3]. Recently, insulating antiferromagnets (AFMs) were shown to transport spin angular momentum via spin waves [4][5][6][7][8]. While robustness against magnetic perturbations and functionality at THz frequencies [9,10] are common to most AFMs, exceptionally long-distance spin transport [4] and current induced switching of the Néel vector by antidamping torques [11][12][13] have only been reported for insulating phases.…”

Modulating the Spin Seebeck Effect in Co2FeAl Heusler Alloy for Sensor Applications

“…However, usually, these systems present a high heat resistance, leading to limitations in biosensor applications [4]. On the other hand, thermoelectric effects based on spin dynamics have received increasing attention in recent past, not just to the great technological potential in power-saving electronic devices [5][6][7][8][9], but also for photodetectors [10,11], diode [12], and temperature sensor [13].…”