Spin polarization at the NiMnSb/MgO(1 0 0) interface

The half-metallic NiMnSb alloy was tested as a possible fully polarized electrode in a magnetic tunnel junction. For this purpose, epitaxial NiMnSb(0 0 1) and NiMnSb/MgO(0 0 1) systems were grown by molecular beam epitaxy. Spin-polarized photoemission experiments using the synchrotron radiation at the ESRF were performed on both the uncovered NiMnSb(0 0 1) surface and on the NiMnSb/MgO(0 0 1) interface. Starting from a NiMnSb(0 0 1) uncovered surface presenting at room temperature a 40% polarization at the Fermi level measured in the whole Brillouin zone, this polarization was observed to dramatically decrease when a MgO(0 0 1) epitaxial barrier was grown on top of it. On the other hand, the X-ray absorption experiments clearly show some oxidization of Mn after growing the MgO layer. This behavior was confirmed by testing the electronic and chemical properties of a unique atomic plane of Mn grown on a Fe buffer layer, before and after growing a MgO layer on top of it.