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ABSTRACT: We report a novel magnetic phenomenon consisting of the formation of helical spin configurations during the magnetization of densely packed ferromagnetic nanowires encapsulated inside carbon nanotubes. We studied the hysteresis loops when the magnetic fields are applied parallel and perpendicular to the nanotubes axes. We also performed theoretical calculations on aligned nanowire arrays that clearly indicate the creation of helical spin vortices in the hysteresis loops. The latter are caused by the presence of strong dipolar interactions among neighboring wires.
Physical Review Letters 07/2005; 94(21):216102. · 7.37 Impact Factor
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Advanced Materials 05/2005; 17(10):1239 - 1243. · 13.88 Impact Factor
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ABSTRACT: The magnetization reversal and magnetoresistance of two-dimensional arrays of aligned Fe-filled carbon nanotubes have been investigated. Our results show a linear temperature dependence of the coercivity above 10 K and a relative large hysteresis for the applied field perpendicular to the nanowires axes. A continuous decrease of the magnetoresistance for both field directions is observed. We attribute this behavior to the anisotropic nature of the system.
Journal of Magnetism and Magnetic Materials 01/2004; 272-276:e1255. · 1.78 Impact Factor
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M. Terrones,
D. Golberg,
N. Grobert,
T. Seeger, M. Reyes-Reyes,
M. Mayne,
R. Kamalakaran,
P. Dorozhkin,
Z.-C. Dong,
H. Terrones,
M. Rühle,
Y. Bando
Advanced Materials 10/2003; 15(22):1899 - 1903. · 13.88 Impact Factor
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ABSTRACT: Transport and field-emission properties of as-synthesized CNx and BNCx (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those
were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron
microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CNx nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100kΩ or less at room temperature, whereas
those made of BNCx nanotubes exhibited semiconducting properties and high resistivities of ∼50–300MΩ. Both types of ropes revealed good field-emission
properties with emitting currents per rope reaching ∼4μA(CNx) and ∼2μA (BNCx), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CNx or BNCx nanotubes displayed low and similar turn-on fields of ∼2–3V/μm. 3mA/cm2 (BNCx) and 5.5mA/cm2 (CNx) current densities were reached at 5.5V/μm macroscopic fields. At a current density of 0.2–0.4mA/cm2 both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing
the current density to 0.2–0.4A/cm2, only CNx films continued to emit steadily, while the field emission from BNCx nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating.
Applied Physics A 02/2003; 76(4):499-507. · 1.63 Impact Factor
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Y. M. Choi,
D S Lee,
R. Czerw,
P. W. Chiu,
N. Grobert,
M Terrones, M. Reyes-Reyes,
H. Terrones,
J-C Charlier,
P M Ajayan,
S Roth,
D. L. Carroll,
Y W Park
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ABSTRACT: The temperature dependent thermoelectric power (TEP) of boron and nitrogen doped multi-walled carbon nanotube mats has been measured showing that such dopants can be used to modify the majority conduction from p-type to n-type. The TEP of boron doped nanotubes is positive, indicating hole-like carriers. In contrast, the nitrogen doped material exhibits negative TEP over the same temperature range, suggesting electron-like conduction. Therefore, the TEP distinct nonlinearites are primarily due to the formation of donor and acceptor states in the B- and N- doped materials. The sharply varying density of states used in our model can be directly correlated to the scanning tunneling spectroscopy studies of these materials.
05/2002;
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Nano Letters, v.3, 275-277 (2003).
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M Terrones,
D Golberg,
N. Grobert,
T. Seeger, M. Reyes-Reyes,
M. Mayne,
R. Kamalakaran,
P. Dorozhkin,
Z. C. Dong,
H. Terrones,
M. Rühle,
Y Bando
Advanced Materials, v.15, 1899-1903 (2003).
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Applied Physics A-Materials Science & Processing, v.76, 499-507 (2003).
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Applied Physics Letters, v.82, 1275-1277 (2003).
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ABSTRACT: We report on the synthesis and elemental mapping of ropes composed of aligned multi-walled B–C–N nanotubes using energy-filtered (Omega filter) high-resolution transmission electron microscopy. The nanotube ropes were synthesized by reacting aligned nanotubes with B2O3 in a N2 atmosphere at 1985–2113 K. It was found that the overall B–N content within the ropes increases with temperature. Furthermore, BN-rich tubular ropes obtained at higher synthesis temperatures exhibit complex shell assembly: BN-rich, C-rich and B–C–N layers were found to exist. The latter nanostructure represents a unique `nanocable' with either conducting or semiconducting shells shielded with insulating BN-rich layers. We envisage that the novel nanocables will also exhibit high-oxidation resistance at elevated temperatures.
Chemical Physics Letters 360:1-7. · 2.34 Impact Factor
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ABSTRACT: High yields of dense, ‘clean’ and uniform arrays of well-aligned carbon nanotubes, with bamboo-like structure encapsulating gaseous nitrogen, were obtained by thermolyzing uniform aerosols of ferrocene/benzylamine solutions at 850 °C. Electron energy loss spectroscopy (EELS) studies reveal that up to 90% of these tubes contain molecular nitrogen in their cores. The materials were characterized by scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and EELS elemental mappings using an Omega Filter microscope. We envisage the material useful for storing large concentrations of relatively heavy gases such as nitrogen in confined volumes.
Chemical Physics Letters 396:167-173. · 2.34 Impact Factor
