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- Kudrnovsky, Josef, et al.
(författare)
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Exchange interactions and critical temperatures in diluted magnetic semiconductors
- 2004
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16:48, s. S5571-S5578
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Tidskriftsartikel (refereegranskat)abstract
- A first-principles approach to magnetic properties of diluted magnetic semiconductors (DMS) is presented that is based on the local spin-density approximation (LSDA) as implemented in the framework of the tight-binding linear muffin-tin orbital method, while the effect of randomness is described by the coherent potential approximation. Application of a real-space Green-function formalism yields the exchange pair interactions between distant magnetic atoms that are needed for quantitative studies of magnetic excitations including the Curie temperatures. We have found that the pair exchange interactions exhibit a strong directional dependence and are exponentially damped with increasing distance between magnetic atoms due to disorder and the half-metallic character of the DMS. As a case study we consider (Ga, Mn) As, (Ga, Mn)N, and (Zn, Cr)Te alloys. The calculations demonstrate that inclusion of disorder and, in particular, realistic distances among magnetic impurities, are needed to obtain critical temperatures which are in good agreement with available experiments.
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| 2. |
- Kudrnovsky, Josef, et al.
(författare)
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Exchange interactions and magnetic percolation in diluted magnetic semiconductors
- 2005
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Ingår i: Local-Moment Ferromagnets. - Berlin/Heidelberg : Springer Berlin/Heidelberg. - 3540272860 ; , s. 131-145
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Konferensbidrag (refereegranskat)abstract
- We propose a theory that combines first-principles evaluations of inter-atomic exchange interactions with a classical Heisenberg model and Monte Carlo simulations. Exchange interactions are determined using the magnetic force theorem and the one-electron Green functions. The magnetic properties of diluted magnetic semiconductors are dominated by short ranged interatomic exchange interactions that; have a strong directional dependence. We show that; critical temperatures of a broad range of diluted magnetic semiconductors, involving Mn-doped GaAs and GaN as well as Cr-doped ZnTe, arc reproduced with a good accuracy only when the magnetic atoms arc randomly positioned on the Ga (Zn) sites, whereas in ordered structure of the magnetic atoms results in critical temperatures that are too high. This suggests that the ordering of diluted magnetic semiconductors is heavily influenced by magnetic percolation, and that the measured critical ternperatures should be very sensitive to the details of the sample preparation, in agreement with observations.
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