  We experimentally demonstrate generation of coherent propagating magnons in
ultra-thin magnetic-insulator films by spin-orbit torque induced by dc electric
current. We show that this challenging task can be accomplished by utilizing
magnetic-insulator films with large perpendicular magnetic anisotropy. We
demonstrate simple and flexible spin-orbit torque devices, which can be used as
highly efficient nanoscale sources of coherent propagating magnons for
insulator-based spintronic applications.
