Spin Wave Excitation in Magnetic Insulator Thin Films by Spin-Transfer Torque

We describe excitation of dipole-exchange spin waves in insulating magnetic thin films by spin current injection at the surface of the film. An easy-axis magnetic surface anisotropy can induce a non-chiral surface spin wave mode with penetration depth inversely proportional to the strength of the surface anisotropy, which strongly reduces the critical current and enhances the excitation power. The importance of the interface spin wave modes on the excitation spectrum is reduced by spin pumping, which depends on the quality of the interface as expressed by the spin mixing conductance.