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Solid State Sciences, Volume 18, April 2013, Pages 24-35.
Kin Mun Wong, S.M. Alay-e-Abbas, A. Shaukat, Yong Lei.
Institut für Physik & IMN MacroNano® (ZIK), Technische Universität Ilmenau, Prof. Schmidt-Str. 26, Ilmenau 98693, Germany and
Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000, Pakistan and
Department of Physics, University of Sargodha, 40100 Sargodha, Pakistan.
Abstract
We use first-principles full-potential method to study the structural and electronic properties of the ferromagnetic (FM) and antiferromagnetic (AF) ordering in the PbS-based ternary alloys Pb1−xEuxS (0 ≤ x ≤ 1). It is shown that the generalized gradient approximation (GGA) functional of DFT in its standard form is not sufficient for obtaining the correct physical interpretation of the binary PbS and EuS compounds and, therefore, the calculations have been extended by considering spin-orbit coupling (SOC) in the Pb atoms and by treating strongly localized f electrons of Eu by the self-interaction correction (SIC) scheme. The Wu and Cohen (WC) generalized gradient approximation (GGA) functional has been used for structural optimization, whereas the GGA parameterization scheme formulated by Engel and Vosko (EV) has also been utilized for calculating the electronic properties of all the compounds. The experimental value of Coulomb parameter (Uf-expt.) within the SIC provide good description for the structural properties of all compounds but fails to predict an accurate EuS energy band structure. A comparison of the results obtained using the WC GGA + SOC + U and EV GGA + SOC + U shows that the later deliver much better band structure profiles of the ferromagnetic EuS and non-magnetic PbS. The ternary alloys constructed by substituting Eu for the Pb atoms in the rocksalt PbS have been used for computing the structural and electronic properties of FM and AF ordering in the Pb1−xEuxS. The stability of the alloys with respect to two magnetic orders has been analyzed and the effect of FM and AF coupling on the electronic properties of the alloys are carefully studied. In particular, the variation of the degree of contribution from the various electronic energy states from the different elements in the alloys has been elucidated in terms of the total and partial density of states for all the composition ranges. Importantly, our results predict that the ternary Pb1−xEuxS alloys have a direct band gap nature and AF is the preferred magnetic order.
