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First - principles calculations of the electronic structure and magnetic properties of iron nanowire filled boron nitride nanotubes

Author: WangSuFang
Tutor: ZhangJianMin
School: Shaanxi Normal University
Course: Optics
Keywords: Fe nanowires BNNTs Geometries Electronic structure First-priciples
CLC: TB383.1
Type: Master's thesis
Year: 2010
Downloads: 71
Quote: 3
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Abstract


Metal-encapsulated boron nitride (BN) nanomaterials in the experiment studies have achieved great success has been reported. Nanowires constructed from magnetic materials, especially Fe, Co and some Fe-based alloys are of interest, because they are likely to be used in nanoelectronics devices, magnetic recording media and biological sensors. However, the oxidation-and corrosion resistances of surface are weak point of the metallic nanowires. BN nanocables are of potential use for nanoscale electronic devices and nanostructured ceramic materials because of providing good stability at high temperatures with high electronic insulation in air. Metal-encapsulated BN nanomaterials, therefore, would have significant advantages for technological application.Under GGA, the structural, electronic and magnetic properties of Fe nanowire encapsulated in BNNTs have been investigated systematically using the first-principles PAW potential within DFT. In detailed, the structural, electronic and magnetic properties of BCC Fen nanowire encapsulated in (8,8) BNNT is given in chapter 3; the structural, electronic and magnetic properties of Fe nanowire encapsulated in zigzag (n,0) BNNTs (8≤n≤15) given in chapter 4; the electronic and magnetic properties of the three types of the ferromagnetic nanowires (FN4) (Fe4, Co4 and Ni4) encapsulated in (m,m) BNNTs is given in chapter 5. Following conclusions are obtained:(1) Form the results of structural, electronic and magnetic properties of BCC Fen nanowire encapsulated in (8,8) BNNT, the initial shapes (quadratic-prismatic Fe wire and cylindrical (8,8) BNNT) are preserved without any visible changes and no one relative rotation is taken place after optimization for the thin nanowires encapsulated inside BNNTs, and the formation processes of such systems are exothermic due to the weaken interactions between them. The magnetic moments analyses show that no magnetization is found on the B and N atoms, but a significant enhancement of the magnetic moments is found for Fen@(8,8) systems, especially for thin nanowires encapsulated in (8,8) BNNT due to increased ratio of the surface atoms with less coordination number compared to bulk Fe, and very weak influence of outer nanotubes leading to their magnetic moments are similar to those of the freestanding nanowires. Both the total density of states (DOS) and charge density analyses show that the spin polarization and the magnetic moment of Fen@(8,8) systems come solely from the Fen nanowire, implying the Fe5@(8,8) and Fe9@(8,8) systems can be applied to the circuits that demand preferential transport of electrons with a specific spin.(2) Form the results of the structural, electronic and magnetic properties of Fe nanowire encapsulated in zigzag (n,0) BNNTs (8≤n≤15), among the eight Fe@(n,0) systems, only the Fe@(8,0) system is formed endothermically, the other larger systems are formed exothermically. Therefore it is expected that thicker Fe nanowires would be pulled spontaneously into larger BNNTs by forces amounting to a fraction of a nanonewton. The high spin polarization and magnetic moments of the Fe@(n,0) systems coming solely from the Fe nanowire imply the Fe@(n,0) systems can be applied to the circuits that demand preferential transport of electrons with a specific spin, in particular for Fe@(12,0) and Fe@(13,0) systems.(3) Form the results of the electronic and magnetic properties of the ferromagnetic nanowires (FN4) (Fe4, Co4 and Ni4) encapsulated in (m,m) BNNTs, all three types of the FN4 encapsulated into the narrower (6,6) BNNT are endothermic while they are encapsulated into the broader (8,8) BNNT are exothermic. Both the spin polarization and the magnetic moment of the FN4@(8,8) systems are larger than those of FN4@(6,6) systems due to weaker restriction of the broader (8,8) BNNT, but those of these two combined systems are smaller than those of the corresponding freestanding FN4. And the spin polarization of Co4@(8,8) system is larger than that of either Fe4@(8,8) system or Ni4@(8,8) system means that the Co4@(8,8) system can be used as spinvalve in spin-dependent transport nanodevice.

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