Self-Induced Spin\nPumping and Inverse Spin Hall Effect\nin Single FePt Thin Films

Self-induced spin Hall effect and self-torque hold great\npromise\nin the field of spintronics, offering a path toward highly efficient\nspin-to-charge interconversion, a pivotal advancement for data storage,\nsensing devices, or unconventional computing. In this study, we investigate\nthe spin-charge current conversion characteristics of chemically disordered\nferromagnetic single FePt thin films by spin-pumping ferromagnetic\nresonance experiments performed on both a resonance cavity and on\npatterned devices. We clearly observe a self-induced signal in a single\nFePt layer. The sign of a single FePt spin pumping voltage signal\nis consistent with a typical bilayer with a positive spin Hall angle\nlayer such as that of Pt on top of a ferromagnet (FM), substrate//FM/Pt.\nStructural analysis shows a composition gradient due to natural oxidation\nat both FePt interfaces, with the Si substrate and with the air. The\nFePt-thickness dependence of the self-induced charge current produced\nallowed us to obtain λ<sub>FePt</sub> = (1.5 ± 0.1) nm\nand self-induced θ<sub>self‑FePt</sub> = 0.047 ±\n0.003, with efficiency for reciprocal effects applications θ<sub>self‑FePt</sub> × λ<sub>FePt</sub> = 0.071 nm which\nis comparable to that of Pt, θ<sub>SH‑Pt</sub> ×\nλ<sub>Pt</sub> = 0.2 nm. The spin pumping voltage is also observed\nin a symmetrical stacking, Al/FePt/Al with a lower overall efficiency.\nMoreover, by studying bilayer systems such as Si//FePt/Pt and Si//Pt//FePt\nwe independently could extract the individual contributions of the\nexternal inverse spin Hall effect of Pt and the self-induced inverse\nspin Hall effect of FePt. Notably, this method gives consistent values\nof charge currents produced due to only self-induced inverse spin\nHall effect in FePt layers. These results advance our understanding\nof spin-to-charge interconversion mechanisms in composite thin films\nand pave the way for the development of next-generation spintronics\ndevices based on self-torque.