  We formulate a theory of the AC spin Hall magnetoresistance (SMR) in a
bilayer system consisting of a magnetic insulator such as yttrium iron garnet
(YIG) and a heavy metal such as platinum (Pt). We derive expressions for the DC
voltage generation based on the drift-diffusion spin model and quantum
mechanical boundary condition at the interface that reveal a spin torque
ferromagnetic resonance (ST-FMR). We predict that ST-FMR experiments will
reveal valuable information on the current-induced magnetization dynamics of
magnetic insulators and AC spin Hall effect.
