  Spin-orbit torque (SOT) can drive sustained spin wave (SW) auto-oscillations
in a class of emerging microwave devices known as spin Hall nano-oscillators
(SHNOs), which have highly non-linear properties governing robust mutual
synchronization at frequencies directly amenable to high-speed neuromorphic
computing. However, all demonstrations have relied on localized SW modes
interacting through dipolar coupling and/or direct exchange. As nanomagnonics
requires propagating SWs for data transfer, and additional computational
functionality can be achieved using SW interference, SOT driven propagating SWs
would be highly advantageous. Here, we demonstrate how perpendicular magnetic
anisotropy can raise the frequency of SOT driven auto-oscillations in magnetic
nano-constrictions well above the SW gap, resulting in the efficient generation
of field and current tunable propagating SWs. Our demonstration greatly extends
the functionality and design freedom of SHNOs enabling long range SOT driven SW
propagation for nanomagnonics, SW logic, and neuro-morphic computing, directly
compatible with CMOS technology.
