  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.
