Browsing by Author "Salah Eldin Ashamalla Yousif"

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    The investigation Thermal Stability of optical properties of metallic Paints under different temperatures
    (Al Neelain University, 2010) Salah Eldin Ashamalla Yousif
    v ABSTRACT In this thesis, electronic structure calculations for some selected double perovskite oxides have been done, using two electronic structure codes, via Mindlab and WIEN2k. The selected compounds are Sr 2 CrZrO 6 , Sr 2 MnNbO 6 , Sr 2 FeMoO 6 and Sr 2 NiRuO 6 . A systematic study was carried out adopting dif ferent approximation methods viz , LMTO - ASA and LMTO - P LW for the cubic structure, FP - LAP W method for pseudo cubic and tetragonal crystalline structures. The calculation of the density of the states (DOS) was performed in terms of the local spin density approximation and Hubbard potential (LSDA+U), including the spin - orbit coupling. In the LM TO - ASA and LMTO - PLW approximation methods, the DOS of Sr 2 FeMoO 6 was obtained and found to agree very well with published reports. Half metallic character through the spin down channel and the ferrimagnetic ordering were observed with notable hybridization among the 3d, 4d and Oxygen within Fermi level. A ll methods used here, show that, the half - metallic character through different bands and channels was seen in all compounds except Sr 2 NiRuO 6 compound, which shows normal metallic conduction in LMTO - ASA and L MTO - PLW methods. For the two methods, the obtained values of the magnetic moments indicate that, the Sr 2 CrZrO 6 is frustrated system, while the Sr 2 MnNbO 6 compound has a ferrimagnetic ordering v ABSTRACT In this thesis, electronic structure calculations for some selected double perovskite oxides have been done, using two electronic structure codes, via Mindlab and WIEN2k. The selected compounds are Sr 2 CrZrO 6 , Sr 2 MnNbO 6 , Sr 2 FeMoO 6 and Sr 2 NiRuO 6 . A systematic study was carried out adopting dif ferent approximation methods viz , LMTO - ASA and LMTO - P LW for the cubic structure, FP - LAP W method for pseudo cubic and tetragonal crystalline structures. The calculation of the density of the states (DOS) was performed in terms of the local spin density approximation and Hubbard potential (LSDA+U), including the spin - orbit coupling. In the LM TO - ASA and LMTO - PLW approximation methods, the DOS of Sr 2 FeMoO 6 was obtained and found to agree very well with published reports. Half metallic character through the spin down channel and the ferrimagnetic ordering were observed with notable hybridization among the 3d, 4d and Oxygen within Fermi level. A ll methods used here, show that, the half - metallic character through different bands and channels was seen in all compounds except Sr 2 NiRuO 6 compound, which shows normal metallic conduction in LMTO - ASA and L MTO - PLW methods. For the two methods, the obtained values of the magnetic moments indicate that, the Sr 2 CrZrO 6 is frustrated system, while the Sr 2 MnNbO 6 compound has a ferrimagnetic ordering. The results for the pseudo cubic and tetragonal structures show that there is hybridization among the 3d and 4d states in the spin - up channels where as a gap is found in the spin - down channels in both Sr 2 MnNbO 6 and Sr 2 NiRuO 6 . T he conduction band is seen in the spin - up and spin - down channels in Sr 2 CrZrO 6 and Sr 2 FeMoO 6 respectively. The resulting magnetic moments indicate that all the pseudo cubic and tetragonal structures are having ferromagnetic ordering except the Sr 2 FeMoO 6 having a ferrimagnetic ordering. The values of the spin magnetic moments of the 3d elements ar e in the range of 1.737 μ B to 3.949 μ B for pseudo cubic and 1.710 μ B to 3.971 μ B for tetragonal structure. The values of the spin magnetic moments of the 4d elements are in the range of 0.013 μ B to 1.058 μ B and 0.001 μ B to 1.225 μ B for pseudo cubic and te tragonal structures respectively. The values of the orbital magnetic moments of the 3d elements are in the range of 0.004 μ B to 0.20 μ B and 0.0044 μ B to 0.22 μ B for the two structures respectively. For the 4d elements , the range of 0.002 μ B to 0.10 μ B and 0.0001μ B to 0.1 μ B for the two structures respectively. These values indicate that the effect of the orbital magnetic moment vary from quenched to weakly unquenched to unquenched as going from Zr to Nb to Ru. A similar trend is observed in the 3d orbitals as going from Cr to Mn to Ni. For the Sr (5s) and O(2p) orbital, the orbital moments are negligibly small. The Sr 2 NiRuO 6 shows ferromagneti c ordering in accordance with the super exchange interaction 푒 푔 2 − 푂 − 푒 푔 0 of Goodenough - Kanamori - Anderson (GKA).