Self-induced spin pumping and inverse spin Hall effect in single FePt thin films

Abstract

In this study, we investigate the spin-charge current conversion characteristics of chemically disordered ferromagnetic single FePt thin films by spin-pumping ferromagnetic resonance experiments performed on both a resonance cavity and on patterned devices. We clearly observe a self-induced signal in a single FePt layer. The sign of a single FePt spin pumping voltage signal is consistent with a typical bilayer with a positive spin Hall angle layer such as that of Pt on top of a ferromagnet (FM), substrate//FM/Pt. Structural analysis shows a strong composition gradient due to natural oxidation at both FePt interfaces, with the Si substrate and with the air. The FePt-thickness dependence of the self-induced charge current produced allowed us to obtain ${\lambda }_{\text{FePt}}=(1.5\pm 0.1)$ nm and self-induced ${\theta }_{\text{self-FePt}}=0.047\pm 0.003$, with efficiency for reciprocal effects applications ${\theta }_{\text{self-FePt}}\times {\lambda }_{\text{FePt}}=0.071$ nm which is comparable to that of Pt, ${\theta }_{\text{SH-Pt}}\times {\lambda }_{\text{Pt}}=0.2$ nm. Moreover, by studying bilayer systems such as Si//FePt/Pt and Si//Pt//FePt we independently could extract the individual contributions of the 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-induced inverse spin Hall effect in FePt layers. These results advance our understanding of spin-to-charge interconversion mechanisms in composite thin films and pave the way for the development of next-generation spintronics devices based on self-torque.

13 pages, 7 figures

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