The valence electronic states at the model tunneling junction interface $\mathrm{MgO}∕\mathrm{Fe}\left(001\right)$ system were systematically studied by comparing the spin-resolved photoemission spectroscopy of clean $\mathrm{Fe}\left(001\right)$ and $\mathrm{MgO}$ covered $\mathrm{MgO}∕\mathrm{Fe}\left(001\right)$ surfaces using linearly $p$-polarized light. For the clean $\mathrm{Fe}\left(001\right)$ film on $\mathrm{GaAs}\left(001\right)$, five distinct features including bulk and surface-related transitions are found. The bulk and surface-state transitions are well-accounted for by the direct transition model based on the calculated energy band structure of bcc bulk $\mathrm{Fe}\left(001\right)$. The previously observed minority feature at a binding energy $E_B=-1.3\mathrm{eV}$ is reinterpreted as a surface roughness associated transition. Upon the $\mathrm{MgO}$ adsorption on $\mathrm{Fe}\left(001\right)$, the surface-state transitions at $E_B=-0.3\mathrm{eV}$ below Fermi energy $E_F$ appearing in both the majority and minority spin spectra at low photon energy ($18\mathrm{eV}$ to $35\mathrm{eV}$) were quenched. This is also the first direct experimental evidence of a minority spin surface state located just below the Fermi energy as predicted previously. The bulk states at the $\mathrm{MgO}∕\mathrm{Fe}\left(001\right)$ interface exhibit a layer-dependent modification, i.e., the bulk states in the deeper Fe layer(s) remain unaffected, while the states of ${\Delta }_5^{\downarrow }$ band symmetry in the Fe layer(s) closest to the $\mathrm{MgO}∕\mathrm{Fe}\left(001\right)$ interface are strongly modified, in contrast to the states of ${\Delta }_1^{\uparrow }$ symmetry. As a consequence of this interface effect, the “partial spin polarization” at the Fermi level changes sign from negative to positive values as seen in the spin asymmetry spectra at photon energies of $40\mathrm{eV}$ and $60\mathrm{eV}$. The origin of this spin- and symmetry-dependent modification observed at $\mathrm{MgO}∕\mathrm{Fe}\left(001\right)$ interfaces is discussed.

• Received 6 April 2007

DOI:https://doi.org/10.1103/PhysRevB.77.064421