Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 24: Magnetic Semiconductors

MA 24.11: Vortrag

Mittwoch, 25. März 2009, 17:30–17:45, HSZ 401

Ferromagnetism in MgO_1−xN_x: density-functional calculations — •Phivos Mavropoulos, Marjana Ležaić, and Stefan Blügel — Institut für Festkörperforschung and Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany

We examine the possibility of a magnetic state in Nitrogen-doped MgO. To this end, we discuss results of density-functional calculations within the Korringa-Kohn-Rostoker Green-function method in the coherent potential approximation for the description of disorder in MgO_1−xN_x and within the pseudopotential method for structural relaxations. We find that, when Nitrogen is substituted in MgO, a spin-polarized impurity band emerges close to the MgO valence band, with a ferromagnetic state stabilized by the double-exchange mechanism. The Curie temperature, estimated within the random phase approximation with exchange constants calculated by the Liechtenstein formula, is found to increase linearly above a percolation threshold of x≈ 2%, reaching 35 K at 10% and 90 K at 20% concentration. While for isolated substitutional impurities structural relaxation is insignificant, for dimers or trimers we find that it can lead to an insulating but still magnetic state. In the case of interstitial impurities we see that the O atom is pushed out of the ideal lattice position, forming a dumbell configuration around it together with the N atom. A pair of close-by N interstitials also push the two associated O atoms out of their lattice positions, resulting in a non-magnetic configuration.