Spin polarization at ferromagnet-insulator interfaces: The important role of stoichiometry in MgO/Fe(001)

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Abstract
The electronic structure of ferromagnet-insulator interfaces plays a key role in spin-dependent transport processes by determining the spin polarization of the tunneling charge carriers. Employing spin-polarized, angle-resolved photoelectron spectroscopy we studied the spin-resolved electronic structure in the model system MgO/Fe(001) and observed a surprisingly multifaceted influence of the MgO stoichiometry. In particular, oxygen-deficient MgO barriers are found to strongly enhance the interfacial spin polarization. The results highlight the important role of the specific nature of the oxygen bonding and its relevance for the tunnel magnetoresistance effect.