Origin of Strong Two-Magnon Scattering in Heavy Metal/Ferromagnet/Oxide Heterostructures

TL;DR

This study reveals that strong two-magnon scattering in heavy-metal/ferromagnet/oxide heterostructures mainly originates at the HM/FM interface, influenced by interfacial spin-orbit coupling and magnetic roughness, affecting spin torque efficiency.

Contribution

It identifies the primary location and factors contributing to two-magnon scattering in HM/FM/oxide heterostructures, highlighting the role of the HM/FM interface and interfacial properties.

Findings

TMS is strongest at the HM/FM interface.

Interfacial spin-orbit coupling correlates with TMS strength.

TMS at the FM/oxide interface remains weak despite strong anisotropy.

Abstract

We experimentally investigate the origin of the two-magnon scattering (TMS) in heavy-metal (HM)/ferromagnet (FM)/oxide heterostructures (FM = Co, Ni81Fe19, or Fe60Co20B20) by varying the materials located above and below the FM layers. We show that strong TMS in HM/FM/oxide systems arises primarily at the HM/FM interface and increases with the strength of interfacial spin-orbit coupling and magnetic roughness at this interface. TMS at the FM/oxide interface is relatively weak, even in systems where spin-orbit coupling at this interface generates strong interfacial magnetic anisotropy. We also suggest that the spin-current-induced excitation of non-uniform short-wavelength magnon at the HM/FM interface may function as a mechanism of spin memory loss for the spin-orbit torque exerted on the uniform mode.