Excitation and Amplification of Spin Waves by Spin–Orbit Torque

Abstract

The emerging field of nanomagnonics utilizes high-frequency waves of magnetization-spin waves-for the transmission and processing of information on the nanoscale. The advent of spin-transfer torque has spurred significant advances in nanomagnonics, by enabling highly efficient local spin wave generation in magnonic nanodevices. Furthermore, the recent emergence of spin-orbitronics, which utilizes spin-orbit interaction as the source of spin torque, has provided a unique ability to exert spin torque over spatially extended areas of magnonic structures, enabling enhanced spin wave transmission. Here, it is experimentally demonstrated that these advances can be efficiently combined. The same spin-orbit torque mechanism is utilized for the generation of propagating spin waves, and for the long-range enhancement of their propagation, in a single integrated nanomagnonic device. The demonstrated system exhibits a controllable directional asymmetry of spin wave emission, which is highly beneficial for applications in nonreciprocal magnonic logic and neuromorphic computing.

Optically Inspired Nanomagnonics with Nonreciprocal Spin Waves in Synthetic Antiferromagnets

“…However, the emission of spin waves with sub‐micrometric wavelength is challenging due to the slow spatial decay of the field and the high impedance of the antennas as the size approaches nanoscale dimensions . Ferromagnetic nanostructures, spin‐transfer torque, spin‐orbit torques, spin currents, magnetoelastic coupling, and multiferroic heterostructures are alternative methods used for spin‐wave generation; however, they do not provide a straightforward control of the wavefront and beam shape. Other methods for spatially controlling the spin‐wave propagation include using the natural anisotropy of the spin‐wave dispersion, or physically micro/nanopatterning the spin‐wave medium, but their flexibility and scalability to multi‐beam configurations is limited.…”

Towards magnonic devices based on voltage-controlled magnetic anisotropy

“…Therefore, one of the challenges of magnonics is to increase the propagation length of SWs in ultrathin FM films. Although, several charge current-induced SW amplification methods 2,3,23,24,77 are available, the main drawback of these methods is, again, Joule heating and higher power consumption. Alternatively, this problem can be solved by reducing the overall dimension of the device below SW propagation length.…”

“…There are several wellknown charge current induced methods available for SW amplification. For instance, the SWs can be amplified by passing current through conducting WG 77 , by microwave magnetic field through parametric pumping 24 , by modulating Gilbert damping through spin-orbit torque (SOT) 2,3,23 , which can be even modulated by electric field 103 . Alternatively, VCMA can be used for SWs amplification in order to design low power magnonic devices.…”

“…Generally, thin films made of ordered magnetic materials are used as SWWGs. Later in this article, we shall describe various methods of SW excitation 1,[12][13][14][15] , manipulation [16][17][18][19] , channeling 17,[20][21][22] , amplification 2,[23][24][25] , and detection 14,15,26 . Although different kinds of methods are available for all the above-mentioned operations, all-electrical methods are preferable for application of magnonics into onchip-integrated devices.…”

Inverse Spin Hall Effect in Electron Beam Evaporated Topological Insulator Bi2Se3 Thin Film

“…Spintronics has been the major focus topic of research in last three decades . Devices based on spintronics have shown potential applications in the data storage devices, non‐volatile magnetic random‐access memory (MRAM), spin torque oscillators, magnonics, spin Hall magnetic sensor, spin orbit torque (SOT)‐induced magnetic switching, etc. Giant magnetoresistance (GMR)‐based devices utilized spin polarized current to switch the magnetization .…”