Self-Induced Spin Pumping and Inverse Spin Hall Effect in Single FePt Thin Films

Abstract

Self-induced spin Hall effect and self-torque hold great promise in the field of spintronics,offering a path toward highly efficient spin-to-charge interconversion, a pivotal advancement for datastorage, sensing devices, or unconventional computing. In this study, we investigate the spin-chargecurrent conversion characteristics of chemically disordered ferromagnetic single FePt thin films byspin-pumping ferromagnetic resonance experiments performed on both a resonance cavity and onpatterned devices. We clearly observe a self-induced signal in a single FePt layer. The sign of asingle FePt spin pumping voltage signal is consistent with a typical bilayer with a positive spinHall angle layer such as that of Pt on top of a ferromagnet (FM), substrate//FM/Pt. Structuralanalysis shows a composition gradient due to natural oxidation at both FePt interfaces, with theSi substrate and with the air. The FePt-thickness dependence of the self-induced charge currentproduced allowed us to obtain λFePt = (1.5 ± 0.1) nm and self-induced θself-FePt = 0.047 ± 0.003,with efficiency for reciprocal effects applications θself-FePt × λFePt = 0.071 nm which is comparableto that of Pt, θSH-Pt × λPt = 0.2 nm. The spin pumping voltage is also observed in a symmetricalstacking, Al/FePt/Al with a lower overall efficiency. Moreover, by studying bilayer systems suchas Si//FePt/Pt and Si//Pt//FePt we independently could extract the individual contributions ofthe external inverse spin Hall effect of Pt and the self-induced inverse spin Hall effect of FePt.Notably, this method gives consistent values of charge currents produced due to only self-inducedinverse spin Hall effect in FePt layers. These results advance our understanding of spin-to-chargeinterconversion mechanisms in composite thin films and pave the way for the development of next-generation spintronics devices based on self-torque.