Spin current and spin waves at a platinum/yttrium iron garnet interface: impact of microwave power and temperature

The spectra of ferromagnetic resonance and spin current of the heterostructure consisting of an epitaxial film of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) grown on a gallium gadolinium garnet (Gd₃Ga₅O₁₂) substrate and with 10 nm thick platinum (Pt) film on top were studied at frequencies f = 2–18 GHz under applied power in the range of 20 μW–50 mW as well as temperatures T = 77–300 K. The standing spin-wave resonances (SWRs) with both magnetostatic backward volume spin waves and magnetostatic surface spin waves (MSSWs) were detected. The SWR evolution was investigated with change of microwave power. Due to generation of spin current perpendicular to the Pt/YIG interface and the inverse spin Hall effect the charge current on the Pt film was registered and analyzed. The SWR resulted in deviations of spin current spectral lines from a Lorentz line form, indicating that at high microwave power the main contribution is made by MSSW. As the temperature decreases, the amplitude of the spin current decreases, although the width of the spectral line remains the same while the magnetization increases at lower temperatures. A decrease in spin Hall angle with cooling may explain this behavior of the spin current at low temperatures. (paper)