Filling carbon nanotubes with metals by the arc-discharge method: the key role of sulfur

PACS. 61.16.Bg Transmission, reflection and scanning electron microscopy (including EBIC) - 81.05.Tp Fullerenes and related materials; diamonds, graphite,

Magnetization reversal by uniform rotation (Stoner-Wohlfarth model) in f.c.c. cobalt nanoparticles

9 pages, 10 figures; conference proceeding: 1st Joint European Magnetic Symposia (JEMS\'01), Grenoble (France), 28th August - 1st September, 2001The combination of high sensitive superconducting quantum interference device (SQUID) with high quality nanoparticles allowed to check the simplest classical model describing the magnetisation reversal by uniform rotation which were proposed more than 50 years ago by Neel, Stoner and Wohlfarth. The micrometer sized SQUIDs were elaborated by electron beam lithography and the nanoparticles were synthesised by arc-discharge. The measured angular dependence of switching fields of nearly all f.c.c. Co nanoparticles revealed a dominating uniaxial magnetic anisotropy. This result suggests that twin boundaries and stacking faults strongly alter the cubic magnetocrystalline anisotropy leading to dominating uniaxial anisotropy. However, few particles were sufficiently \"perfect\" in order to show a more complex switching field surface and a field path dependence of the switching field which is the important signature of the cubic magnetocrystalline anisotropy

Experimental Evidence of the Néel-Brown Model of Magnetization Reversal

International audiencePresented are the first magnetization measurements of individual ferromagnetic nanoparticles (15–30 nm) at very low temperatures (0.1–6 K). The angular dependence of the hysteresis loop evidenced the single domain character of the particles. Waiting time, switching field, and telegraph noise measurements showed for the first time that the magnetization reversal of a well prepared ferromagnetic nanoparticle can be described by thermal activation over a single-energy barrier as originally proposed by Néel and Brown. The “activation volume” estimated by these measurements was close to the particle volume

Experimental Evidence of the Néel-Brown Model of Magnetization Reversal

International audiencePresented are the first magnetization measurements of individual ferromagnetic nanoparticles (15–30 nm) at very low temperatures (0.1–6 K). The angular dependence of the hysteresis loop evidenced the single domain character of the particles. Waiting time, switching field, and telegraph noise measurements showed for the first time that the magnetization reversal of a well prepared ferromagnetic nanoparticle can be described by thermal activation over a single-energy barrier as originally proposed by Néel and Brown. The “activation volume” estimated by these measurements was close to the particle volume

Cap structure of the coaxial BCN nanotubes investigated by nano-EELS

Communication to : Conference EMAG'97, Cambridge (GB), September 2-5, 1997SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1998 n.18 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Graphitic encapsulation of catalyst particles in carbon nanotube production

A new model is proposed for the encapsulation of catalyst metal particles by graphite layers that are obtained, for example, in low-temperature chemical vapor deposition production of carbon nanotubes (CNTs). In this model graphite layers are primarily formed from the dissolved carbon atoms in the metal-carbide particle when the particle cools. This mechanism is in good agreement with molecular dynamics simulations (which show that precipitated carbon atoms preferentially form graphite sheets instead of CNTs at low temperatures) and experimental results (e.g., encapsulated metal particles are found in low-temperature zones and CNTs in high-temperature regions of production apparatus, very small catalyst particles are generally not encapsulated, and the ratio of the number of graphitic layers to the diameter of the catalyst particle is typically 0.25 nm(-1))