Dresden 2003 – wissenschaftliches Programm

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MA: Magnetismus

MA 7: Spin-Elektronik

MA 7.4: Vortrag

Montag, 24. März 2003, 16:00–16:15, HSZ/401

Exchange interactions in diluted magnetic semiconductors — •Josef KUDRNOVSKY¹, Ilja TUREK², Vaclav DRCHAL¹, Patrick BRUNO³, and Peter WEINBERGER⁴ — ¹Institute of Physics AS CR, Prague — ²Institute of Physics of Materials, Brno — ³MPI fuer Mikrostrukturphysik, Halle — ⁴Center for Computational Materials Science, Vienna

The effective pair exchange interactions between Mn-atoms in diluted GaMnAs and GeMn semiconductors are obtained by mapping total energies associated with rotations of the corresponding magnetic moments onto the effective classical Heisenberg Hamiltonian. The electronic structure is described in the framework of the local spin density approximation by including both the substitutional and magnetic disorders treated in the coherent potential approximation. The ground state with partial disorder of local moments appears in GaMnAs due to the presence of As-antisites with a reduced total magnetic moment. A detailed study of the behavior of pair exchange interactions as a function of the distance between Mn-atoms as well as a function of the concentration of Mn- and defect-atoms is presented including the low-concentration limit. We have found that pair exchange interactions are exponentially damped with increasing distance between Mn-atoms due to disorder and the semimetallic character of systems. The period of damped oscillations is inversely proportional to the concentration of Mn-atoms and is small compared to the corresponding Mn-Mn distance leading thus to the ferromagnetic coupling. Pair exchange interactions are also reduced with increasing concentrations of Mn-atoms.