Impact of interfacial chemical state on spin pumping and inverse spin Hall effect in YIG/Pt hybrids

The interface between ferromagnetic (FM) and nonmagnetic (NM) metal plays a fundamental role in the generation, transmission, detection of spin current, and spin-based devices. The impact of physical properties on the interface such as roughness, crystallization conditions, and even impedance matching has been widely investigated. In this work, the effects of interfacial chemical state at the interface of ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ and Pt (YIG/Pt) are systematically investigated through spin injection. Prior to Pt deposition, the spin mixing conductance and inverse spin Hall voltage of YIG/Pt hybrids increased up to 300%, using surface chemical processing on YIG. The interfacial chemical state is identified from x-ray photoelectron spectroscopy spectra and peak decomposition. Both ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ cations appear at the interface and higher content of ${\mathrm{Fe}}^{3+}$ enhances the interface magnetic moment which consequently plays a crucial role in spin injection efficiency and inverse spin Hall voltage. In order to prevent the influence of magnetic proximity effect of Pt layers close to the FM/NM interface, a Cu spacer is inserted. It is found that the improved spin injection efficiency due to iron cations still exists in the YIG/Cu/Pt structure, which confirms the universal influence of the interfacial chemical state on spin pumping efficiency. This discovery has potential implications for spin generation, detection, and even optimization of spintronic devices.