Berlin 2005 – scientific programme
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MA: Magnetismus
MA 33: Messmethoden, Anisotropie, Spinelektronik/Spininjektion
MA 33.8: Talk
Wednesday, March 9, 2005, 12:45–13:00, TU EMH225
Half-Metallic and Metallic Phases of Magnetite probed by Raman Spectroscopy — •Martin Friák1, Arno Schindlmayr1,2 und Matthias Scheffler1 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4–6, 14195 Berlin-Dahlem, Germany — 2Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany
Half-metals, which are metallic in only one spin channel and can thus sustain ideal 100% polarized currents, are excellent candidates for future spintronics technologies. Factors like strain may destroy this desirable property, but as the spin polarization is difficult to measure directly, there are so far no comprehensive data. We therefore studied thermodynamic properties that are more readily accessible by spectroscopy and can be probed to distinguish the half-metallic and metallic phases. For magnetite we identify the A1g Raman-active phonon mode as a possible indicator. Our density-functional theory (DFT-GGA) calculations, employing the all-electron FLAPW method, predict the mode frequency under equilibrium conditions in good agreement with experiments and also reproduce the observed kink in the frequency as a function of applied pressure around 15 GPa. We explain this behavior as a direct consequence of the strain-induced half-metal to metal transition, which changes the lattice dynamics. Explicit boundaries for the half-metallic phase of magnetite are given for different forms of strain.