Reflection of cold atoms by a cobalt single crystal

We have demonstrated. that a cobalt single crystal can be used to make a re markably smooth retro-reflector for cold paramagnetic atoms. The crystal is cut so that its surface lies in the (0001) plane and the atoms are reflect ed by the magnetic field above the surface due to the self-organized patter n of magnetic domains in the material. We find that the reflectivity for su itably polarized atoms exceeds 90% and may well be unity. We use the angula r spread of a reflected atom cloud to measure the roughness of the mirror. We find that the angular variation of the equivalent hard reflecting surfac e is (3.1 +/- 0.3 degrees)rms for atoms dropped onto the mirror from a heig ht of 2 cm.