Electron holography of ferromagnetic nanoparticles encapsulated in three-dimensional arrays of aligned carbon nanotubes (original) (raw)
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Applied Physics A, 2009
Using electron holography (interference electron microscopy) we have made measurements of the magnetic flux and magnetic field distribution around a carbon nanotube filled with iron. At the surface of the carbon nanotube, an iron particle with a radius of 30 nm and a length of 200 nm created a magnetic flux of 10 −15 Wb (Weber) and a magnetic field of 0.3-0.4 T (Tesla). The theory developed in this work is constrained to the case of cylindrical symmetry of the investigated ferromagnetic particles, but, in general, such studies can be made for ferromagnetic particles of any shape.
Magnetic properties of Fe nanoparticles trapped at the tips of the aligned carbon nanotubes
Journal of Magnetism and Magnetic Materials, 2001
The magnetic properties of iron nanoparticles partially encapsulated at the tips of aligned carbon nanotubes have been studied. The carbon nanotube wall not only protects the metallic particles from oxidization, but also reduces the inter-particle dipolar interaction by non-magnetic separation. Magnetic characterizations performed in the temperature range of 5-350 K with magnetic field up to 3 T show that these carbon-nanotube-supported iron particles are good candidates for high-density magnetic recording media.
physica status solidi (c), 2014
We present results of study of magnetic properties of nanocomposite formed in situ during the synthesis of aligned carbon nanotube (CNT) arrays. CNTs were grown by the atmospheric pressure floating catalyst chemical vapor deposition method. High temperature pyrolysis of ferrocene/xylene solution injected into the quartz tube at high temperature was carried out. By varying the ferrocene content (C F) in the ferrocene/xylene solution we tuned the concentration, location, size, shape and chemical state of iron based catalytic ferromagnetic nanoparticles. The variation of these parameters was reflected in the magnetic properties of the CNT based nanocomposite. In particular, it is shown, that the main interaction mechanism between ferromagnetic nanoparticles for high C F contents is the exchange coupling, while the magnetic anisotropy dominates at low ferrocene concentration. The role of the orientation of the nanotubes is decisive for the observation of magnetic anisotropy. When the alignment is destroyed, the exchange coupling mechanism starts to dominate also for low C F samples.
Carbon, 2014
In this work, we investigate magnetic properties of iron based nanoparticles (NP) intercalated into carbon nanotube (CNT) aligned arrays synthesized by injection chemical vapor deposition. We have analyzed the temperature (T) and the ferrocene concentration (C F ) dependences of the macroscopic magnetic parameters. From these experiments a weaker interaction between magnetic moments of NP was obtained for low C F values. The random anisotropy model for the experimental data analysis was applied and micromagnetic parameters were evaluated. The law of the approach to magnetic saturation (LAS) was analyzed using the general expression with the correlation function C(r = x/R a ) of magnetic axes, R a being the magnetic anisotropy correlation length. We obtained that, while for C F = 0.5% C(r) is a step-like (C(r < 10) = 1, C(r > 10) = 0), for C F P 1% C(r) decays rapidly on a short range, (2-3)R a . Such extended correlations for C F = 0.5% could be associated with the dominant role of the coherent anisotropy, which is caused by the influence of the alignment of CNT. When the aligned CNTs for C F = 0.5% are destroyed into powder, the LAS is changed to H À1/2 , which means the dominant role of the exchange mechanism.
Magnetization of carbon-coated ferromagnetic nanoclusters determined by electron holography
Journal of Materials Research, 1999
The magnetic properties of carbon-coated Co and Ni nanoparticles aligned in chains were determined using transmission electron holography. The measurements of the phase change of the electron wave due to the magnetization of the sample were performed. The ratio of remnant magnetization to bulk saturation magnetization Mr/Ms of Co decreased from 53% to 16% and of Ni decreased from 70% to 30% as the particle diameter increased from 25 to 90 nm. It was evident that the inhomogenous magnetic configurations could diminish the stray field of the particles. After being exposed to a 2-Tesla external magnetic field, the Mr/Ms of Co increased by 45% from the original values with the same dependency on the particle size. The Mr/Ms of Ni particles, on the other hand, increased only 10%. The increased magnetization could be attributed to the merging of small domains into larger ones after the exposure to the external magnetic field. The validity of the interpretation of the holograms was establi...
Magnetic properties of Fe 3 C ferromagnetic nanoparticles encapsulated in carbon nanotubes
Physics of The Solid State, 2007
The low-temperature dependences of magnetic characteristics (namely, the coercive force H c , the remanent magnetization M r , local magnetic anisotropy fields H a, and the saturation magnetization M s ) determined from the irreversible and reversible parts of the magnetization curves for Fe3C ferromagnetic nanoparticles encapsulated in carbon nanotubes are investigated experimentally. The behavior of the temperature dependences of the coercive force H c (T) and the remanent magnetization M r (T) indicates a single-domain structure of the particles under study and makes it possible to estimate their blocking temperature T B = 420–450 K. It is found that the saturation magnetization M s and the local magnetic anisotropy field H a vary with temperature as ∼T 5/2.
Iron nanoparticles in aligned arrays of pure and nitrogen-doped carbon nanotubes
Carbon, 2012
Arrays of aligned carbon nanotubes (CNTs) and nitrogen-doped carbon (CN x) nanotubes have been grown on silicon substrates as the result of thermolysis of ferrocene/toluene and ferrocene/acetonitrile mixture. The microstructure of materials was studied by transmission and scanning electron microscopy, and X-ray diffraction was used to control the carbon and iron forms. The composition and properties of iron nanoparticles developed in the CNT and CN x nanotube samples were determined from Mö ssbauer spectroscopy data. The total iron content in CN x nanotubes was found to be considerably higher than that in CNTs. Three forms of iron nanoparticles a-Fe, c-Fe, and Fe 3 C were detected in CNTs and only two last of them in CN x nanotubes. In the interior of CNT channels the a-Fe and Fe 3 C nanoparticles were observed to be coupled by a strong exchange interaction and to exhibit magnetic behavior at room temperature.
Electron Holography of Magnetic Nanostructures
2005
Electron holography is an electron microscope imaging technique that permits quantitative measurement of magnetic fields with spatial resolution approaching the nanometer scale. The theoretical background and usual experimental setup for electron holography are first briefly described. Applications of the technique to magnetic materials and nanostructures are then discussed in more detail. Future prospects are summarized.
Electron holography of gas-phase condensed Fe nanoparticles
Journal of Magnetism and Magnetic Materials, 2003
Electron holography observations were performed on Fe nanoparticles with a mean size of about 50 nm synthesized by gas-phase condensation. Phase maps were obtained which represent the magnetic field both inside and around nanoparticle chains. The results suggest the presence of flux-closure magnetic configurations inside the particles, in agreement with recent micromagnetic calculations. r