Large Spin-Wave Bullet in a Ferrimagnetic Insulator Driven by the Spin Hall Effect

Because of its transverse nature, spin Hall effects (SHE) provide the possibility to excite and detect spin currents and magnetization dynamics even in magnetic insulators. Magnetic insulators are outstanding materials for the investigation of nonlinear phenomena and for novel low power spintronics applications because of their extremely low Gilbert damping. Here, we report on the direct imaging of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the ferrimagnetic insulator Y3Fe5O12 based on the excitation and detection by SHEs. The driven spin dynamics in Y3Fe5O12 is directly imaged by spatially resolved microfocused Brillouin light scattering spectroscopy. Previously, ST-FMR experiments assumed a uniform precession across the sample, which is not valid in our measurements. Astrong spin-wave localization in the center of the sample is observed indicating the formation of a nonlinear, self-localized spin-wave "bullet".