  Superconductor-Ferromagnet (SF) heterostructures are of interest due to
numerous phenomena related to the spin-dependent interaction of Cooper pairs
with the magnetization. Here we address the effects of a magnetic insulator on
the density of states of a superconductor based on a recently developed
boundary condition for strongly spin-dependent interfaces. We show that the
boundary to a magnetic insulator has a similar effect like the presence of
magnetic impurities. In particular we find that the impurity effects of
strongly scattering localized spins leading to the formation of Shiba bands can
be mapped onto the boundary problem.
