Ultra-low Gilbert damping and self-induced inverse spin Hall effect in GdFeCo thin films

Ferrimagnetic materials have garnered significant attention due to their broad range of tunabilities and functionalities in spintronics applications. Among these materials, rare earth-transition metal GdFeCo alloy films have been the subject of intensive investigation due to their spin-dependent transport properties and strong spin-orbit coupling. In this report, we present self-induced spin-to-charge conversion in single-layer GdFeCo films of different thicknesses via inverse spin Hall effect. A detailed investigation of spin dynamics was carried out using broadband ferromagnetic resonance measurements. The anisotropy constant and the effective g-factor are found to decrease with thickness, and they become nearly constant for thicknesses beyond 25 nm. A remarkably low damping constant of 0.0029±0.0003 is obtained in the 43-nm-thick film, which is the lowest among all previous reports on GdFeCo thin films. Furthermore, we have demonstrated self-induced inverse spin Hall effect, which has not reported so far in a single-layer of GdFeCo thin film. Our analysis shows that the inverse spin Hall effect becomes increasingly dominant over the spin rectification effect with increasing film thickness. The in-plane angular-dependent voltage measurement of the 43-nm-thick film reveals a spin pumping voltage of 1.64 µV. The observation of spin-to-charge current conversion is attributed to the presence of high spin-orbit coupling element Gd in the film as well as co-existence of mixed phases (nanocrystalline and amorphous) in our films. Our findings underscore the potential of GdFeCo as a prime ferrimagnetic material for emerging spintronic technologies.