Absence of spin transport in amorphous YIG evidenced by nonlocal spin transport experiments

Abstract

It remains highly controversial whether long-distance spin transport or only Joule heating without spin transport exists in the disordered magnetic amorphous ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (a-YIG). Here, we carefully check and analyze the origin of the observed electrical signals in the Py/a-YIG/Pt-based nonlocal spin-transport experiments with both horizontal and vertical geometries, based on the ferromagnetic resonance (FMR)-induced spin pumping and inverse spin Hall effect. In all lateral nonlocal devices with a distance from 2.0 \ensuremath{\mu}m to 200 nm and vertical structures with a $\ensuremath{\ge}\text{40-nm-thick}$ a-YIG spacer layer, the spin-current-induced direct voltage peak signal is absent under FMR conditions, indicating that a-YIG does not possess long-distance spin transport. Furthermore, we demonstrate that a weak spin-torque FMR voltage signal, which gradually reduces to zero with increasing a-YIG thickness in the vertical geometry, is attributed to the leaked spin rectification voltage generated in the Py layer due to the electric leakage between the top Pt layer and the bottom Py layer through the pinhole defects in the thin middle a-YIG layer. Additionally, we find an improvement of the interfacial spin-mixing conductance due to spin accumulation in the interface of a-YIG/Py, which can significantly enhance spin-orbit torque efficiency in the ferromagnet/heavy metal systems with a disordered magnetic a-YIG buffer layer.