Spin diffusion in Pt as probed by optically generated spin currents
Résumé
We investigate the dependence of the photoinduced inverse spin-Hall effect (ISHE) signal in a set of Pt/Ge(001) junctions as a function of the Pt thickness t(Pt) in the 1-20-nm range at room temperature. The spin-polarized electrons, photoexcited through optical orientation at the direct gap of bulk Ge, diffuse towards the Pt layer, where spin-dependent scattering yields a transverse electromotive field E-ISHE. We show that the experimental data can be properly interpreted in the frame of the spin diffusion model, provided that we consider a variation of the spin diffusion length L-s in platinum when the Pt film thickness is increased. Indeed, for t(Pt) > 10 nm we estimate L-s = 8.2 +/- 3.5 nm, whereas for t(Pt) < 10 nm the spin diffusion length decreases to L-s = 3.5 +/- 2.1 nm. Moreover, the experimental results clearly indicate that for t(Pt) < 10 nm the spin Hall angle. is three times larger than the value corresponding to thick Pt layers, suggesting a drastic change of the spin-dependent scattering mechanism for very thin Pt films.