Dresden 2006 – wissenschaftliches Programm
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MA: Magnetismus
MA 25: Spin-Electronics I
MA 25.2: Vortrag
Donnerstag, 30. März 2006, 10:30–10:45, HSZ 103
Magnetic properties and disorder effects in diluted magnetic semiconductors — •Lars Bergqvist1,2, Olle Eriksson2, Josef Kudrnovsky3, Vaclav Drchal3, Anders Bergman2, Lars Nordström2, and Ilja Turek4 — 1Institut für Festkörperforschung, Forschungszentrum Jülich,Forschungszentrum Jülich, D-52428 Jülich, Germany — 2Department of Physics, Uppsala University, Box 530, S-75121 Uppsala, Sweden — 3Institute of Physics, Academy of Sciences of the Czech Republic,Na Slovance 2, CZ-182 21 Prague 8, Czech Republic — 4Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, CZ-616 62 Brno, Czech Republic
We present calculations of the exchange interactions and critical temperatures for several diluted magnetic semiconductor systems with an impurity band. It is shown that the exchange interactions are dominated by short ranged interactions that have a strong directional dependence. Using a combination of first principles calculations of the exchange interactions together with Monte Carlo simulations of the classical Heisenberg model, in which the positional disorder and spin fluctuations are properly included, the calculated critical temperatures are in good agreement with experimantal observations. It is showed that agreement between theory and experiment, as regards ordering temperatures, is obtained only when the magnetic atoms are randomly positioned in a simulation cell which proves that disorder effects play a very important role. The effect of strong electron-electron interaction has been studied by means of the LSDA+U scheme. We investigate in detail the nature of the anisotropic exchange interactions by means of a Fermi surface analysis.