Generation of coherent spin-wave modes in yttrium iron garnet microdiscs by spin-orbit torque.

M Collet,V E Demidov,X De Milly,S O Demokritov,O D’Allivy Kelly,G De Loubens,J L Prieto,V V Naletov,O Klein,R Bernard,P Bortolotti,A Anane,V Cros,J Ben Youssef,M Muñoz

doi:10.1038/ncomms10377

Abstract

In recent years, spin–orbit effects have been widely used to produce and detect spin currents in spintronic devices. The peculiar symmetry of the spin Hall effect allows creation of a spin accumulation at the interface between a metal with strong spin–orbit interaction and a magnetic insulator, which can lead to a net pure spin current flowing from the metal into the insulator. This spin current applies a torque on the magnetization, which can eventually be driven into steady motion. Tailoring this experiment on extended films has proven to be elusive, probably due to mode competition. This requires the reduction of both the thickness and lateral size to reach full damping compensation. Here we show clear evidence of coherent spin–orbit torque-induced auto-oscillation in micron-sized yttrium iron garnet discs of thickness 20 nm. Our results emphasize the key role of quasi-degenerate spin-wave modes, which increase the threshold current.

Highlights

In recent years, spin–orbit effects have been widely used to produce and detect spin currents in spintronic devices
This finding has created a great excitement in the community for two reasons: first, one could control electronically the damping of insulators, which can offer improved properties compared with metals, here YIG has the lowest damping known in nature; second, the damping compensation could be achieved on large objects, a relevant point for the field of magnonics[6,7] whose aim is to use spin waves as carriers of information
Using a metal with large YSH, such as Pt, a charge current flowing in plane generates a pure spin current flowing perpendicular to the plane, which can eventually be transferred through an interface with ferromagnetic metals, resulting in the coherent emission of spin waves[12], and with non-metals such as YIG5