  The temporal evolution of pulsed Spin Hall Effect - Spin Transfer Torque
(SHE-STT) driven auto-oscillations in a Yttrium Iron Garnet (YIG) / platinum
(Pt) microdisc is studied experimentally using time-resolved Brillouin Light
Scattering (BLS) spectroscopy. It is demonstrated that the frequency of the
auto-oscillations is different in the center and at the edge of the
investigated disc that is related to the simultaneous STT excitation of a
bullet and a non-localized spin-wave mode. Furthermore, the magnetization
precession intensity is found to saturate on a time scale of 20 ns or longer,
depending on the current density. For this reason, our findings suggest that a
proper ratio between the current and the pulse duration is of crucial
importance for future STT-based devices.
