Dresden 2003 – scientific programme

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MA: Magnetismus

MA 7: Spin-Elektronik

MA 7.2: Talk

Monday, March 24, 2003, 15:30–15:45, HSZ/401

Curie temperatures and exchange mechanisms in diluted magnetic semiconductors — •Kazunori Sato¹, Peter Dederichs¹, Hiroshi Katayama-Yoshida², and Josef Kudrnovsky³ — ¹IFF, Forschungszentrum Juelich — ²ISIR, Osaka Univ., Japan — ³Academy of Sciences of the Czech Republic, Prague

Based on ab initio calculations of Curie temperatures for Mn-doped GaN, GaP, GaAs and GaSb, we discuss the origin of ferromagnetism in diluted magnetic semiconductors (DMS). The electronic structure of DMS is calculated in the local spin density approximation by using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation to describe the substitutional and spin disorder. From the total energy differences between the ferromagnetic state and the spin-glass state, realistic estimations of Curie temperatures are achieved by using a mapping on the Heisenberg model in the mean field approximation. If impurity bands are formed in the gap, as it is the case for (Ga, Mn)N, double exchange dominates leading to a characteristic √c-dependence of T_C as a function of the Mn concentration c. On the other hand, if the d-states are localized, as in (Ga, Mn)Sb, Zener’s p-d exchange prevails resulting in a linear c-dependence of T_C. (Ga, Mn)As is an intermediate case, showing a √c-like behavior in the local density approximation (LDA), but a nearly linear c-dependence, if the LDA+U method, with U = 4 eV, is used.