  Single-crystal Heusler atomic-scale superlattices that have been predicted to
exhibit perpendicular magnetic anisotropy and half-metallicity have been
successfully grown by molecular beam epitaxy. Superlattices consisting of
full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity
were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy
loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers
with high cobalt or high iron concentrations for samples grown near room
temperature on GaAs (001). Superlattice structures grown with an excess of
aluminum had significantly lower thin film shape anisotropy and resulted in an
out-of-plane spin reorientation transition at temperatures below 200 K for
samples grown on GaAs (001). Synchrotron-based spin resolved photoemission
spectroscopy found that the superlattice structure improves the Fermi level
spin polarization near the X point in the bulk Brillouin zone. Stoichiometric
Co$_2$MnAl terminated superlattice grown on MgO (001) had a spin polarization
of 95%, while a pure Co$_2$MnAl film had a spin polarization of only 65%.
