Measurement of spin current using spin relaxation modulation induced by spin injection

Ferromagnetic resonance spectra affected by the spin-Hall effect (SHE) and the spin torque were measured for a Ni81 Fe19 /Pd bilayer film. A charge current applied to the Pd layer is converted into a spin current via SHE, which propagates into the Ni81 Fe19 layer through the interface as a spin current. The spin current exerts the torque on the magnetization, modulating the spin relaxation in the Ni81 Fe19 layer. By monitoring the spin relaxation modulation, we estimated the spin current amplitude injected into the Ni81 Fe19 layer. This method enables the quantitative measurement of spin currents without assuming any microscopic material parameters.