Berlin 2012 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 25: Electron Theory of Magnetism
MA 25.2: Vortrag
Mittwoch, 28. März 2012, 09:45–10:00, H 0112
Magnetic anisotropy energy of disordered and ordered tetragonal FeCo alloys — •Ilja Turek1,3, Josef Kudrnovsky2, and Karel Carva3 — 1Institute of Physics of Materials ASCR, Brno, Czech Republic — 2Institute of Physics ASCR, Prague, Czech Republic — 3Dept. of Condensed Matter Physics, Charles Univ., Prague, Czech Republic
We present results of ab initio calculations of the uniaxial magnetic anisotropy energy (MAE) in disordered body-centered tetragonal (bct) FeCo alloys as well as in alloys with a partial L10 order. The latter systems are simulated by a two-sublattice model with different sublattice compositions. The calculations employ the relativistic TB-LMTO method and the coherent potential approximation (CPA) which enables us to scan the entire intervals of both concentration variables and a broad range of the bct c/a-ratio. For the homogeneous alloys, we have found that the huge maximum MAE of about 800 µeV/atom, obtained previously in a simple virtual crystal approximation, overestimates the MAE of the random alloys in the CPA at least by a factor of four. This effect is due to the strong disorder-induced scattering in the minority spin channel, manifested by a strong broadening of the Bloch spectral functions near the Fermi energy. For the ordered alloys, we have found that the maximum L10 order compatible with a given Co concentration can bring the MAE up to high values around 500 µeV/atom. However, these high MAEs are significantly reduced by small perturbations of the perfect atomic order. Relation of the MAEs to the orbital magnetic moments will also be presented and discussed.