  Spin pumping enables the vertical transport of pure spin current through Al
in a Pd/Al/Ni80Fe20(Py) trilayer film, in which the Py acts as a spin battery.
The spin current injected into the Al flows through the Al to reach the Pd,
resulting in the generation of electromotive forces due to the inverse spin
Hall effect in the Pd. The electromotive forces decreased with increasing
thickness of the Al layer. A simple model based on the theory by Tserkovnyak et
al., [Phys. Rev. B, 66, 224403 (2002)] allows an estimation of the spin
coherence of the perpendicular spin transport in the Al of 61 nm. This
comparatively short coherence is attributed to a reduction in spin pumping
efficiency because of the roughness of the Al/Py interface.
