Quantitative determination of magnetic fields from iron particles of oblong form encapsulated by carbon nanotubes using electron holography (original) (raw)
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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.
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The magnetization state of ball-milled nanocrystalline Fe particles is studied by electron holography. The flux lines of the stray field leaking out from free magnetic poles in the particles are visualized in a wide temperature range. The variations of the exchange length, brought about by temperature changes, are discussed taking into account the random anisotropy model, microstructural characterization data and the known magnetic properties. A correlation between the intensity of the stray field and the value of the exchange length is observed. We suggest that a transition between two different kinds of magnetization patterns takes place depending on the ratio between exchange length and particle size.
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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...
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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.
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Journal of Physics: Conference Series, 2010
We present results on the application of an iron filled carbon nanotube (Fe-CNT) as a probe for magnetic force microscopy (MFM) in an external magnetic field. If an external field is applied parallel to the sample surface, conventional ferromagnetically coated MFM probes often have the disadvantage that the magnetization of the coating turns towards the direction of the applied field. Then it is difficult to distinguish the effect of the external field on the sample from those on the MFM probe. The Fe-CNT MFM probe has a large shape anisotropy due to the high aspect ratio of the enclosed iron nanowire. Thanks to this the direction of the magnetization stays mainly oriented along the long nanotube axis in in-plane fields up to our experimental limit of 250 mT. Thus, the quality of the MFM images remains unchanged. Apart from this, it is shown that Fe-CNT MFM probe yields a very good magnetic resolution of about 25 nm due to the small diameter of the iron filling.