Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 12: Spindependent Transport I
MA 12.4: Talk
Tuesday, March 27, 2007, 11:00–11:15, H22
Electronic structure of Fe/MgOx interfaces studied by photoemission — •Martina Müller, Frank Matthes, and Claus Schneider — Institut für Festkörperforschung, Forschungszentrum Jülich, D-52428 Jülich, Germany
Ferromagnet/insulator (FM/I) systems have experienced a long-term interest by providing fundamental insights in the physics of spin-dependent transport. A critical factor concerns the electronic structure of the FM/I boundary which is considered to act decisive on the tunneling spin-polarization. Whereas the interface of nearly stoichiometric Fe/MgO systems is well characterized, the interaction mechanisms with off-stoichiometric MgOx barriers remain concealed so far.
We present results on modifications of the Fe(001) 3d electronic structure at Fe/MgOx interfaces resulting from variations of the MgOx stoichiometry. Spin- and angle-resolved photoemission spectroscopy experiments have been performed at low photon energies (< 40eV) at the beamline U250-PGM of the storage ring DELTA (Germany). Fe(001)/GaAs samples have been prepared under UHV conditions covered with ultrathin MgOx layers. Their degree of oxidation was monitored via Mg 2p core-level shifts. We found a noticeable dependence of the magnitude of the interfacial spin-polarization P on the MgOx degree of oxidation. P is strongly enhanced for oxygen-deficient MgOx overlayers, whereas it drops down in case of an oxygen excess at the interface. We ascribe these findings to well-defined chemical bonding mechanisms between the Fe 3d and O 2p electronic states, thereby taking into account the particular occupancy of the MgOx lattice sites.