Spin wave emission by spin-orbit torque antennas

TL;DR

This paper investigates how spin-orbit torque antennas can generate and control propagating spin waves in magnetic waveguides, comparing their efficiency and characteristics to traditional inductive antennas, with implications for spintronic device development.

Contribution

It demonstrates the generation of high wavevector spin waves by spin-orbit torque antennas and analyzes the contributions of spin-Hall and Oersted fields, highlighting their relative effects and efficiency.

Findings

Spin-orbit torque antennas can excite spin waves with wavevectors up to 6 rad/μm.

Both spin-Hall and Oersted fields contribute roughly equally to the effective field.

Oersted field dominates the torque due to precession ellipticity and field orientation.

Abstract

We study the generation of propagating spin waves in Ta/CoFeB waveguides by spin-orbit torque antennas and compare them to conventional inductive antennas. The spin-orbit torque was generated by a transverse microwave current across the magnetic waveguide. The detected spin wave signals for an in-plane magnetization across the waveguide (Damon-Eshbach configuration) exhibited the expected phase rotation and amplitude decay upon propagation when the current spreading was taken into account. Wavevectors up to about 6 rad/$\mu$m could be excited by the spin-orbit torque antennas despite the current spreading, presumably due to the non-uniformity of the microwave current. The relative magnitude of generated anti-damping spin-Hall and Oersted fields was calculated within an analytic model and it was found that they contribute approximately equally to the total effective field generated by the spin-orbit torque antenna. Due to the ellipticity of the precession in the ultrathin waveguide and the different orientation of the anti-damping spin-Hall and Oersted fields, the torque was however still dominated by the Oersted field. The prospects for obtaining a pure spin-orbit torque response are discussed, as are the energy efficiency and the scaling properties of spin-orbit torque antennas.