  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.
