Dresden 2006 – scientific programme
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MA: Magnetismus
MA 25: Spin-Electronics I
MA 25.3: Talk
Thursday, March 30, 2006, 10:45–11:00, HSZ 103
Ferromagnetism in (GaV)As and (Zn,Co)O — •Brahim Belhadji1, Peter H. Dederichs1, Kasunori Sato2, Voicu Popescu3, and Hubert Ebert3 — 1Institut fuer Festkoerperforschung, Forschungszentrum juelich — 2The institute of Scientific and Industrial Research, Osaka University, Osaka 567-0047, Japan — 3Department Chemie/Physikalishe Chemie, University of Muenich, Butenandtstr. 5-13, D-81377 Muenich
The exchange interactions in dilute magnetic semiconductors can take very different forms. While in the model system (Ga,Mn)A s ferromagnetism is favored by Zener’s p-d exchange, in systems with impurity bands in the bandgap the situation is more complicated. If the Fermi level lies in the impurity band, ferromagnetism is favored by Zener’s double exchange. However if the F ermi level is outside the impurity band, the interaction is determined by super-exchange, and is usually antiferromagnetic, l ike e.g. in (Ga,Fe)As or (Cd,Mn)Te. However, in constrast to this we find that in (Ga,V)As and (Zn,Co)O, where the Fermi leve l lies between the eg and t2g states, that the interaction is ferromagnetic. Our calculations are based on the local density approximation the Korringa-Kohn-Rostoker method in connection with the Coherent-Potential-Approximation (KKR-CPA). For (Ga,V )As the calculated coupling constants Jij between two V atoms are ferromagnetic, short ranged and nearly independant of the V concentration. Due to the short range the Curie temperature is strongly suppressed for small V concentrations. We discuss th e reason for the occurrance of ferromagnetic super-exchange on these systems.