Towards 100% spin-polarized charge-injection : The half-metallic NiMnSb/CdS interface

Spin-electronics requires an electron source with a spin-polarization as high as possible. For this, half-metallic materials seem ideally suited as they exhibit 100% spin polarization. Because of its high Curie temperature and compatibility with existing semiconductor technology, NiMnSb is a most desirable half metal. However, using first-principles calculations we find that NiMnSb surfaces are not half metallic, even if they are stoichiometric and perfectly ordered. Moreover, several surface and interface sensitive experiments have reported polarizations far less than 100%. These findings are easily rationalized, as they result from the symmetry breaking at the surface. We show that it is possible to restore half metallicity at interfaces, by a proper engineering at the microscopic level. Therefore the half metal NiMnSb is, in principle, a suitable source material for 100% spin-polarized charge carriers.