  We study a periodic arrangement of magnetic regions in a one-dimensional
superconducting wire. Due to the local exchange field, each region supports
Andreev bound states that hybridize forming Bloch bands in the subgap spectrum
of what we call the Andreev crystal (AC). As an illustration, ACs with
ferromagnetic and antiferromagnetic alignment of the magnetic regions are
considered. We relate the spectral asymmetry index of a spin-resolved
Hamiltonian to the spin polarization and identify it as the observable that
quantifies the closing and reopening of the excitation gap. In particular,
antiferromagnetic ACs exhibit a sequence of gapped phases separated by gapless
Dirac phase boundaries. Heterojunctions between antiferromagnetic ACs in
neighboring phases support spin-polarized bound states at the interface. In a
close analogy to the charge fractionalization in Dirac systems with a mass
inversion, we find a fractionalization of the interface spin.
