  "Spin pumping" is the injection of spin angular momentum by a time-dependent
magnetization into an adjacent normal metal proportional to the spin mixing
conductance. We study the role of electrostatic interactions in the form of
crystal fields on the pumped spin currents generated by insulators with
exchange-coupled local moments at the interface to a metal. The crystal field
is shown to render the spin currents anisotropic, which implies that the spin
mixing conductance of insulator|normal metal bilayers depends on crystal cut
and orientation. We interpret the interface "effective field" (imaginary part
of the spin mixing conductance) in terms of the coherent motion of the
equilibrium spin density induced by proximity in the normal metal.
