Ferrimagnetic resonance induced by the spin Hall effect

A bilayer consisting of a ferrimagnetic insulator (FiM) and a heavy metal (HM) can be used as a pump-probe system to analyze the magnetic properties of the FiM. An oscillating electric current in the HM induces spin current injection into the FiM via the spin Hall effect. The resulting magnetization dynamics of the FiM, in turn, causes spin pumping back into the HM and modifies its conductivity via the inverse spin Hall effect (ISHE). We present a phenomenological theory to model the ISHE output spectrum, in which the Landau-Lifshitz-Gilbert equations governing the FiM dynamics are coupled to the spin-diffusion equations governing the spin and charge transports in the HM. It is found that the ISHE signal is greatly enhanced at the magnetization compensation point of the FiM. Furthermore, the peak frequencies and amplitudes of the ISHE spectrum are strongly correlated to the magnetic properties of the FiM sublattices. Most interestingly, the ISHE output can be increased by several orders of magnitude by tuning the on-site-sublattice and cross-sublattice damping constants. Our analysis shows the possibility of using the FiM/HM bilayer system as a sensitive probe into the magnetic parameters of the FiM sublattices. Conversely, the drastically enhanced ISHE signal with appropriate tuning of the damping parameters suggests a means to substantially improve the spin torque efficiency in FiM-based heterostructures.