Effective Heisenberg exchange integrals of diluted magnetic semiconductors determined within realistic multi-band tight-binding models

Abstract

Abstract. Diluted magnetic semiconductors (DMS) like Ga1−xMnxAs are described by a realistic tightbinding model (TBM) for the (valence) bands of GaAs, by a Zener (J-)term modeling the coupling of the localized Mn-spins to the spins of the valence band electrons, and by an additional potential scattering (V-) term due to the Mn-impurities. We calculate the effective (Heisenberg) exchange interaction between two Mn-moments mediated by the valence electrons. The influence of the number of bands taken into account (6-band or 8-band TBM) and of the potential (impurity) scattering V-term is investigated. We find that for realistic values of the parameters the indirect exchange integrals show a long-range, oscillating (RKKYlike) behavior, if the V-term is neglected, probably leading to spin-glass behavior rather than magnetic order. But by including a V-term of a realistic magnitude the exchange couplings become short ranged and mainly positive allowing for the possibility of ferromagnetic order. Our results are in good agreement with available results of ab-initio treatments.

Determination of the Fermi level position in dilute magnetic Ga1-xMnxN films

“…In order to model the electronic properties of the dilute magnetic semiconductor Ga 1−x Mn x N with x = 10% the following multiband V-J model Hamiltonian 11,12 is used:…”

“…For the simulation of magnetic impurities, the EBOM is augmented by a potential scattering and a spin-spin interaction term (V-J model). 11,12 Then, the frequency-dependent conductivity is evaluated via the kernel polynomial method (KPM) 13 The paper is structured as follows: First, the experimental setup for the ellipsometric characterization is explained, followed by a description of the applied theoretical approaches. Then, the experimentally determined optical constants between 200 nm and 12 400 nm of Ga 1Àx Mn x N layers with x ¼ 4% and x ¼ 10% and corresponding theoretical results for x ¼ 10% of the real part of the AC-conductivity, DOS, and Fermi level are discussed.…”

“…Thereby, the difficulties in first principle calculations regarding the role of correlations can be avoided and the lattice model can account for disorder effects by means of an ensem-ble average over different configurations with random impurity positions. For the simulation of magnetic impurities, the EBOM is augmented by a potential scattering and a spin-spin interaction term (V-J model) 11,12 . Then the frequency-dependent conductivity is evaluated via the kernel-polynomial method (KPM) 13 The paper is structured as follows: First, the experimental setup for the ellipsometric characterization is explained, followed by a description of the applied theoretical approaches.…”

Exchange couplings for Mn ions in CdTe: Validity of spin models for dilute magnetic II-VI semiconductors

“…The unexpected non-monotonous decay of J n as a function of the Mn-Mn separation, and also the over-all size of the exchange couplings, are unexplained. Only the nearest-neighbor exchange couplings J 1 for Mndoped II-VI semiconductors were calculated using the superexchange approach, [15][16][17][18] or density-functional theory (DFT) in the local-density approximation, DFT (LSDA), and in DFT(LSDA)+U . 19,20 In this work, we calculate the exchange couplings J n≤4 using three itinerant-electron approaches, (i), the generalized-gradient approximation (GGA) to DFT with the functional of Perdew, Burke, and Ernzerhof, 21 , (ii) GGA+U as implemented in the FLEUR package, 22 and, (iii), GGA+Gutzwiller for a suitable two-ion Hubbard model.…”