Chemical trend of exchange coupling in diluted magnetic II-VI semiconductors: Ab initio calculations

Abstract:

We have calculated the chemical trend of magnetic exchange parameters Jdd, N , and N of Zn-based II-VI semiconductors ZnA A=O, S, Se, and Te doped with Co or Mn. We show that a proper treatment of electron correlations by the local spin-density approximation LSDA +U method leads to good agreement between experimental and theoretical values of the nearest-neighbor exchange coupling Jdd between localized 3d spins in contrast to the LSDA method. The exchange couplings between localized spins and doped electrons in the conduction band N are in good agreement with experiment as well. But the values for N coupling to doped holes in the valence band indicate a crossover from weak coupling for A=Te and Se to strong coupling for A=O and a localized hole state in ZnO:Mn. This hole localization explains the apparent discrepancy between photoemission and magneto-optical data for ZnO:Mn.

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