  We study spin pumping in a
$\mathrm{Y_3Fe_5O_{12}(YIG)/Pt/Ni_{81}Fe_{19}(Py)}$ trilayer film by means of
the inverse spin Hall effect (ISHE). When the ferromagnets are not excited
simultaneously by a microwave, ISHE-induced voltage is of the opposite sign at
each ferromagnetic resonance (FMR). The opposite sign is consistent with spin
pumping of bilayer films. On the other hand, the voltage is of the same sign at
each FMR when both the ferromagnets are excited simultaneously. Futhermore, the
voltage greatly increases in magnitude. The observed voltage is unconventional;
neither its sign nor magnitude can be expected from spin pumping of bilayer
films. Control experiments show that the unconventional voltage is dominantly
induced by spin pumping at the Py/Pt interface. Interaction between YIG and Py
layers is a possible origin of the unconventional voltage.
