Demonstration of a micron-scale spin-orbit-torque emitter for coherent magnonics

Using micro-focus Brillouin light scattering (BLS), we experimentally demonstrate generation of coherent propagating magnons in ultra-thin magnetic-insulator films by spin-orbit torque induced by dc electric current [1]. We show that this challenging task can be accomplished by utilizing magnetic-insulator films with large perpendicular magnetic anisotropy (PMA) possessing ultra-low Gilbert damping ( ≈ 8 10^-4 for 20 nm thick Bismuth substituted YIG [2]). Fine tuning of the PMA allows to exactly cancel the dipolar field (the effective magnetization M_eff ≈ 0). As a result, the usually observed non-linear shift of the auto-oscillation frequency is suppressed. Hence, the dominant mechanism for self-localization of the auto-oscillations is inhibited. We demonstrate simple and versatile spin-orbit torque devices, which can be used as highly efficient nanoscale sources of coherent propagating magnons for insulator-based spintronic applications.

[1] M. Evelt et al., “Emission of coherent propagating magnons by insulator-based spin-orbit torque oscillators”. Phys. Rev. Applied 10, 041002 (2018)
[2] L. Soumah et al., Ultra-low damping insulating magnetic thin films get perpendicular. Nat. Commun. 9, 3355 (2018).