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Computing Studies on Magnetic Properties and Electronic Structure of Rare Earths (Gd, La, Y) Doped Materials Based on Density Function Theory

Author: YanKai
Tutor: ZhaoHaoFeng
School: Nanjing University of Information Engineering
Course: Applied Mathematics
Keywords: Density functional theory Rare Earth Elements Zinc oxide Diluted magnetic semiconductors p-type
CLC: O482.51
Type: Master's thesis
Year: 2011
Downloads: 116
Quote: 0
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Based on density functional theory a First Principle package Materials Studio CASTEP for rare earth elements Re (Re = Y, La, Gd) doped oxygen vacancies (Vo) and rare earth elements Re (Re = Y La, Gd) coexist, rare earth element Re (Re = Y, La, Gd) respectively, co-doped with C and N 2 × 2 × 2 zinc oxide supercell changes in cell structure, electronic structure, magnetic properties, optical properties calculated . Finally, through analysis and comparison to experiment developed characteristics of p-type zinc oxide dilute magnetic semiconductor provide some guidance, at the same time reveal the physical mechanism behind the related phenomena. Concluded that the analysis of this paper is as follows: rare earth Y single-doped zinc oxide supercell weak moment 0.02μB. Rare Earth La doped zinc oxide supercell, although the cause local spin polarization of the atoms, but did not appear magnetic supercell. Rare earth elements Gd single doped zinc oxide supercell magnetic moment significantly increased 7μB band gap of 0.133eV. Overall, Vo supercell improve magnetic properties of rare earth elements Re doping has little effect on the magnetic supercell mainly from the rare-earth doped own. This is mainly the role of the half full 4f electron shell, in addition, the rare earth-doped more performance for a trivalent donor forms exist, while Vo As another donor forms exist, which will cause the ZnO semiconductor rendered n-type characteristics, making doped miscellaneous supercell Fermi level into the top of the valence band. Therefore, irrespective of the single rare earth doped the coexistence Vo and Re (Re = Y, La, Gd), zinc oxide supercell are unable to achieve p-type. REE Re (Re = Y, La, Gd) with N-doped zinc oxide supercell, can effectively increase the supercell band gap, but the improvement effect of the supercell magnetic moment little supercell the magnetic moments of still the main source of in doped rare earth elements. Calculated, Gd-N co-doped zinc oxide supercell higher the magnetic moment 6.96μB well as the wide band gap of 0.608eV. This is mainly due to N as by the presence of impurities, and can effectively absorb REE produce free electrons. Thus, Gd-N of zinc oxide-doped zinc oxide semiconductor of a p-type as well as improvement of the magnetic moments conducive supercell. The rare earth elements Re (Re = Y, La, Gd) and C co-doped zinc oxide supercell, can effectively improve the supercell magnetic moment, especially YC, La-C co-doped magnetic moment of the system relative Y-, La single mixed with improved significantly, which Gd-C co-doped zinc oxide supercell magnetic moment up to 8.0μB. However, co-doped with C elements the supercell band gap disappeared. This is mainly due to the rare earth element Re (Re = Y, La, Gd) larger radius, which can easily lose the valence electrons. Secondly, C atomic radius is larger than N, and C atomic number smaller than N 1, C-2p orbit can accommodate four electrons, but the binding force of electronic without N. Again, C-doped although able to absorb and reduce the free electrons generated by the rare earth element, but it also can make the increase in the number of the hole carriers, thereby improving the system conductivity, and eventually causes the disappearance of the system band gap. In addition, rare earth element Re element doped the supercell level position of the optical properties of the principal effects of ZnO, and the peak strength, the same time, so that the doped systems, a significant change in the optical properties of the high energy region. N, C alternative O bit doped ZnO supercell such that the system has significant changes in the optical properties of the low-energy region. This change was mainly due to the N, C doping at the Fermi level due to the impurity level.

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