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Theoretical Study of Magnetic Properties of Doped Zno Nano Wires

Author: MaShiJia
Tutor: LuPengFei
School: Beijing University of Posts and Telecommunications
Course: Physical Electronics
Keywords: Dilute magnetic semiconductors first-principleszinc oxide ferromagnetism Curie Temperature
CLC: TN304.21
Type: Master's thesis
Year: 2013
Downloads: 23
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Abstract

As we all know, electrons have two freedoms which are charge and spin. The traditional microelectronics mainly use the charge freedom of electrons rather than the spin freedom. Spintronics is a new branch of science which uses the spin and charge properties of electrons in order to overcome the limits of traditional microelectronics. Dilute magnetic semiconductors (DMSs) are the most promising materials for spintronics application which can be obtained by doping3d transition-metals (TMs) in host semiconductor. Searching for DMSs with high Curie Temperature(Tc)(the critical temperature when materials changes from ferromagnetism to antiferromagnetism) is significant to the applications of such spintronics applications.ZnO has a direct wide band gap (3.35eV) and large excitonic binding energy (60meV), and was widely used in the optical and piezoelectric field. In2000, Dielt predicted ZnO is a promising host material to achieve DMS with Curie temperature above room temperature. However, theoretical conclusions cannot explain those observed phenomena in experiments and the origin of FM has not been well understood. In this paper, we studied the electronic and magnetic properties of ZnO bulk and nanowires DMSs from first-principles calculations. It includes several parts as follows:first, The electronic and magnetic properties of Mn-doped ZnO bulk materials have been studied. In this part different positions of Mn ions results in different configurations. For each configuration, we calculate parallel and antiparallel spin alignments between Mn ions which correspond to FM and AFM orderings, respectively. We use the energy difference between AFM and FM orderings to indicate magnetic stability. In all configurations, AFM is always more stable than FM ordering in Mn-doped ZnO system. The two doped Mn ions mediate superexchange interaction through O ion and result in a stable AFM coupling.second, The electronic and magnetic properties of (Mn,Li)-codoped ZnO bulk materials have been studied. Doping Li to ZnO introduces holes which can change the groud state of ZnMnO system from AFM to FM with high Curie temperature. We restrict different configurations to near group and far group based on the Mn-Mn distance. The FM stabilization is largely affected by Mn-Mn distance rather than the position of dopant Li. We proposed that dopant Li mediates FM coupling through double exchange interaction and RKKY interaction when Li locates near and far from Mn ions, respectively.third, The electronic and magnetic properties of V-doped ZnO nanowires have been studied. In the beginning of this part we studied-the geometry optimizations of intrinsic ZnO nanowires. We passivate the bonds of Zn and O atoms on the surface of the nanowire using pseudo-H to avoid additional surface states. The energy of FM state is lower than that of AFM state which means high Curie temperature ferromagnetism could be obtained in such a system. V-doped ZnO nanowire has half-metal property and the observed stable ferromagnetism can be explained by the p-d hybridization between V-3d and O-2p orbit.

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