STRUCTURAL, ELECTRONIC, MAGNETIC AND OPTICAL PROPERTIES OF FERROMAGNETIC Pb1-xEuxSe AND Pb1-xEuxTe ALLOYS (x = 0, 0.25, 0.50, 0.75 AND 1)

Abstract

First-principles total energy calculations have been performed using full potential linear-augmented-plane-wave method within the framework of density functional theory to study the structural, electronic, magnetic and optical properties of the Pb 1-x Eu x Se and Pb 1-x Eu x Te (0 ≤ x ≤1) alloys in the ferromagnetic (FM) ordering. The calculations have been extended to treat the strongly localized f electrons of Eu atom by the self-interaction correction (SIC) approach. For structural optimization, the Wu and Cohen generalized gradient approximation (GGA) functional has been used, whereas for calculating electronic properties, the GGA parameterization scheme formulated by Engel and Vosko (EV) has also been utilized. It has been observed that the use of experimental value of Coulomb parameter (Uf- expt. ) within the SIC does not yield an accurate EuSe and EuTe energy band structure. The improvement in the electronic band structures of nonmagnetic PbSe / PbTe and ferromagnetic EuSe / EuTe have been achieved by considering the effects of spin–orbit coupling for Pb atoms, by a suitable choice of U and by treating the U values for Eu atom's f and d electrons as parameters. The electronic and optical properties of FM Pb 1-x Eu x Se in agreement with experiments can be achieved by combining EV GGA with a Hubbard U < Uf- expt. , however, a stronger and stable AFM coupling in EuTe leaves the above scheme unable to provide good electronic structure of FM Pb 1-x Eu x Te . In case of Pb 1-x Eu x Se the nonlinear behaviour of electronic structure is reflected in the optical properties of Eu -doped PbSe that have been studied in terms of incident photons' energy dependent complex dielectric function.