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Galanakis I.,University of Patras | Sasoglu E.,Peter Grnberg Institute and Institute for Advanced Simulation | Sasoglu E.,Fatih University
Journal of Applied Physics | Year: 2011

We use a rigid band model to simulate doping in half-metallic NiMnSb and CoMnSb semi-Heusler alloys. Using first-principles calculations we calculate the intrasublattice exchange constants and the Curie temperature for these alloys as a function of the shift of the Fermi level and compare them also with the case of half-metallic CrAs and CrSe zinc-blende alloys. We show for all four compounds that the interactions between Cr-Cr(Mn-Mn) nearest neighbors are sufficient to explain the behavior of the Curie temperature. The interplay between the ferromagnetic RKKY-like and the antiferromagnetic superexchange interactions depends strongly on the details of the density of states around the minority-spin gap and thus it is found to be alloy-dependent. © 2011 American Institute of Physics. Source


Fukushima T.,Osaka University | Katayama-Yoshida H.,Osaka University | Sato K.,Osaka University | Bihlmayer G.,Peter Grnberg Institute and Institute for Advanced Simulation | And 4 more authors.
Journal of Physics Condensed Matter | Year: 2014

On the basis of constrained density functional theory, we present ab initio calculations for the Hubbard U parameter of transition metal impurities in dilute magnetic semiconductors, choosing Mn in GaN as an example. The calculations are performed by two methods: (i)the Korringa-Kohn-Rostoker (KKR) Green function method for a single Mn impurity in GaN and (ii)the full-potential linearized augmented plane-wave (FLAPW) method for a large supercell of GaN with a single Mn impurity in each cell. By changing the occupancy of the majority t2 gap state of Mn, we determine the U parameter either from the total energy differences E(N + 1) and E(N - 1) of the (N 1)-electron excited states with respect to the ground state energy E(N), or by using the single-particle energies for occupancies around the charge-neutral occupancy n0 (Janak's transition state model). The two methods give nearly identical results. Moreover the values calculated by the supercell method agree quite well with the Green function values. We point out an important difference between the 'global' U parameter calculated using Janak's theorem and the 'local' U of the Hubbard model. © 2014 IOP Publishing Ltd. Source

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