  The polarization of the spin current pumped by a precessing ferromagnet into
an adjacent normal metal has a constant component parallel to the precession
axis and a rotating one normal to the magnetization. The former component is
now routinely detected in the form of a DC voltage induced by the inverse spin
Hall effect (ISHE). Here we compute AC-ISHE voltages much larger than the DC
signals for various material combinations and discuss optimal conditions to
observe the effect. Including the backflow of spins is essential for distilling
parameters such as the spin Hall angle from ISHE-detected spin pumping
experiments.
