  We theoretically consider the spin-wave mode- and wavelength-dependent
enhancement of the Gilbert damping in magnetic insulator--normal metal bilayers
due to spin pumping as well as the enhancement's relation to direct and
alternating inverse spin Hall voltages in the normal metal. In the
long-wavelength limit, including long-range dipole interactions, the ratio of
the enhancement for transverse volume modes to that of the macrospin mode is
equal to two. With an out-of-plane magnetization, this ratio decreases with
both an increasing surface anisotropic energy and mode number. If the surface
anisotropy induces a surface state, the enhancement can be an order of
magnitude larger than for to the macrospin. With an in-plane magnetization, the
induced dissipation enhancement can be understood by mapping the anisotropy
parameter to the out-of-plane case with anisotropy. For shorter wavelengths, we
compute the enhancement numerically and find good agreement with the analytical
results in the applicable limits. We also compute the induced direct- and
alternating-current inverse spin Hall voltages and relate these to the magnetic
energy stored in the ferromagnet. Because the magnitude of the direct spin Hall
voltage is a measure of spin dissipation, it is directly proportional to the
enhancement of Gilbert damping. The alternating spin Hall voltage exhibits a
similar in-plane wave-number dependence, and we demonstrate that it is greatest
for surface-localized modes.
