Spin-dependent tunneling from Fe(001): Effect of resonant interface states

Tsymbal \textit{et al.} [1] have studied the electronic structure of the oxidized Fe(001) surface and found positive spin polarization of the oxygen density of states. Here we study spin-dependent tunneling from clean and oxidized Fe surface through vacuum using the principal-layer Green's function technique and the tight-binding LMTO basis. We found large negative spin polarization in both cases. Although the spin polarization of the oxygen DOS is positive tor the oxidized surface, the tunneling current primarily flows directly from Fe atoms. The dominating minority-spin channel is controlled by resonant surface states, which are sensitive to the detailed structure of the charge density at the interface. We also found that interface resonant states control the minority-spin tunneling conductance in epitaxial Fe/MgO/Fe tunnel junctions. As confirmed by a full-potential LMTO calculation, the resonant interface band is very flat, and its bottom is very close to the Fermi level. As a result, the tunneling conductance is very sensitive to variations of the surface electronic structure. [1] E. Y. Tsymbal, I. I. Oleinik, and D. G. Pettifor, J. Appl. Phys. \textbf{87}, 5230 (2000).