Growth and Nanoscale Magnetic Properties of Ferromagnetic Nanowire Encapsulated Inside Carbon Nanotubes (original) (raw)
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Magnetism of Fe, Co, and Ni nanowires encapsulated in carbon nanotubes
Journal of Magnetism and Magnetic Materials, 2008
We have investigated the electronic and magnetic properties of Fe, Co, and Ni nanowires encapsulated in carbon nanotubes (CNTs) using spin polarized ab initio calculation. The incorporated systems with hollow region between the nanowire and the C shell have the enhanced magnetic moments compared to the ferromagnetic nanowires tightly wrapped by CNTs. The Co nanowire encapsulated in CNTs is a strong ferromagnet and has high spin polarization regardless of the distance between the nanowire and the C shell. The results show that the Co-filled CNTs are useful for spin polarized transport nanodevice.
Journal of Physics D: Applied Physics, 2009
High-quality cobalt nanowires have been grown by focused-electron-beam-induced deposition (FEBID) and their magnetic and transport properties determined. The nanowires contain up to about 95% Co atomic percentage, as measured by EDX spectroscopy, which remarkably represents a high value compared to other metal deposits grown by the same technique. The Co content has been found to correlate with the beam energy used for the growth. The magnetotransport properties have been studied on individual nanowires through 4-probe measurements. For the nanowires with the highest Co content, the resistivity at room temperature is low (~40 µΩcm), and shows metallic temperature dependence. The magnetotransport properties clearly demonstrate the ferromagnetic nature of the nanowire, with a saturation magnetization of M s =1329±20 emu/cm 3 , very close to the bulk one. Due to the local character of this type of growth at targeted places and its high lateral resolution, these results pave the way for the creation of magnetic nanostructures and devices with the full potentiality of high-quality Co.
Nano Letters, 2008
Magnetic nanowires of CoFe 2O4 were casted inside the channel of multiwall carbon nanotubes by mild chemical synthesis. A detailed investigation of these nanowires was performed using mainly the electron tomography technique; this study provides a complete characterization of their microstructure in terms of the spatial organization and the size distribution of individual particles forming the nanowire as well as its residual porosity. In particular, we have shown that the size of the CoFe 2O4 monocrystalline particles is closely dependent on the location of the particle within the nanotube, i.e., small particles close to the tube tip (5 nm) and bigger particles inside the tube channel (15 nm). As the theoretical critical size for superparamagnetic relaxation in CoFe 2O4 is estimated within the range of 4-9 nm, the size distribution obtained by 3D-TEM agrees with the Mossbauer study that suggests the presence of two different magnetic components inside the nanowire. We have shown also that, by using this preparation method and for this internal diameter of nanotube, the CoFe 2O4 nanowire exhibits a continuous structure along the tube, has a residual porosity of 38%, and can fill the tube at only 50%, parameters which influence in a significant manner the magnetic behavior of this system.
High temperature structural and magnetic properties of cobalt nanowires
2012
We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant and Ms the saturation magnetization. Hc decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300 - 500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation.
Understanding and measuring the magnetic properties of an individual nanowire and their relationship with crystalline structure and geometry are of scientific and technological great interest. In this work, we report the localized study of the magnetic flux distribution and the undisturbed magnetization of a single ferromagnetic nanowire that poses a bar-code like structure using off-axis electron holography (EH) under Lorentz conditions. The nanowires were grown by template-assisted electrodeposition, using AAO templates. Electron holography allows the visualization of the magnetic flux distribution within and surroundings as well as its quantification. The magnetic analysis performed at individual nanowires was correlated with the chemical composition and crystalline orientation of the nanowires.
Journal of Crystal Growth, 2015
We report on the study of two-step grown crystalline II-VI semiconductor nanowires (NWs) covered with ferromagnetic metal. In the first step ZnTe nanowires were grown by a vapor-liquid-solid mechanism (VLS) on GaAs (1 1 1)B substrates covered with Au thin film. Solid source molecular beam epitaxy and Au-based nanocatalysts were used for these purposes. The nanowires were smooth, slightly tapered and mostly oriented along the axis perpendicular to the substrate. The diameters of the obtained nanowires were from 30 to 70 nm and their length was around 1 mm. In the second step the nanowires were covered with Co shell of different thicknesses. As a result magnetic nanotubes were formed. Structural characterization of the nanowires was performed using scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy techniques. Initial roughness of the nanowires influences the growth of Co shell with the increment of deposition thickness. Deposited Co formed nanograins having hexagonal closed packed structure, however face cubic centered grains were also observed. Magnetic force microscopy experiments on an individual Co nanotube revealed magnetic anisotropy of the investigated structures.
Magnetism of Fe nanowires encapsulated in carbon nanotube.pdf
2005
We have investigated the electronic structures and magnetism of Fe nanowires encapsulated in carbon nanotube. We have calculated the magnetic moment, spin polarization, and conductance channel for Fe nanowires encapsulated in carbon nanotube. The magnetic moment of an encapsulated system is decreased compared with that of freestanding Fe nanowires and the spin polarization and conductance channel are also decreased. The decrease of magnetic moment and spin polarization is caused by a strong hybridization between the Fe nanowire and the carbon shell, The overall charge transfer occurs from Fe wire to C shell, which is consistent with experimental result. However since the Fe-C distance is large enough to have hollow region between Fe wire and C shell, the magnetic moment and spin polarization are close to those of freestanding Fe nanowire, and the conductance channel is almost same with that of freestanding Fe nanowire.
Magnetic properties of self-assembled Co nanowires of varying length and diameter
Journal of Applied Physics, 2000
Ferromagnetic Co nanowires have been electrodeposited into self-assembled porous anodic alumina arrays. Due to their cylindrical shape, the nanowires exhibit perpendicular anisotropy. The coercivity, remanence ratio, and activation volumes of Co nanowires depend strongly on the length, diameter, and spacing of the nanowires. Both coercivity and thermal activation volume increase with increasing wire length, while for constant center-to-center spacing, coercivity decreases and thermal activation volume increases with increasing wire diameter. The behavior of the nanowires is explained qualitatively in terms of localized magnetization reversal.
Ferromagnetic CoPt 3 Nanowires: Structural Evolution from fcc to Ordered L1 2
Journal of the American Chemical Society, 2009
The synthesis of nanostructural materials has been an important area of research for decades owing to their extensive use in electronics, photonics, catalysis, information storage, optical sensing, biological labeling, imaging, and sur face -enhanced Raman scattering studies. In particular, the fabrication of metal nanowires has recently attracted substantial attention because they have unique magnetic properties and other potential technological applications. Significant progress in the preparation of transition metal nanowires has been achieved by utilizing porous alumina templates. Co-Pt alloy films exhibit strong perpendicular magnetic anisotropy and high chemical stability.