  Spin pumping is an interfacial spin current generation from the ferromagnetic
layer to the non-magnetic metal at its interface. The polarization of the
pumped spin current $\textbf{J}_s \propto \textbf{m}\times \dot{\textbf{m}}$
depends on the dynamics of the magnetic moment $\textbf{m}$. When the materials
are based on light transition metals, mechanism behind the spin current
transfer is dominated by the exchange interaction between spin of localized
d-electrons and itinerant conduction electrons. In heavier transition metals,
however, the interaction is not limited to the exchange interaction. The spin
of the conduction electron can interact to its nuclear spin by means of
hyperfine interaction, as observed in the shift of NMR frequency. By studying
the spin polarization of conduction electron of the non-magnetic metallic layer
due to a nuclear magnetic moment $\textbf{I}$ of the ferromagnetic layer, we
show that the hyperfine interaction can mediate the spin pumping. The
polarization of the spin current generation is shown to have a similar form
$J_s\propto \textbf{I}\times\dot{\textbf{I}}$.
