TEM micrographs showing nearly spherical Fe oxide nanoparticles with mean diameters: (a) 4.5 and (b) . The inset in each panel is the histogram of the particle diameter distribution.
Magnetization curves of the alumina supported Fe oxide nanoparticles before carbon SWNT growth at 300 and corresponding to samples (a) 1, (b) 2, (c) 3, and (d) 4. No hysteresis loop was observed for S4 at all studied temperature region. Magnetization units are emu/g of total sample (iron oxide ). Units on the insets are also emu/g for magnetization value and kilogauss for external magnetic field.
Temperature dependence of the magnetization curves under ZFC and FC for S1. The inset is the thermal variation of under ZFC showing interacting particles in S1.
Magnetization curves of the alumina supported Fe particles after carbon SWNT growth corresponding to samples (a) 1, (b) 2, (c) 3, and (d) 4. Only catalyst S4 shows superparamagnetic behavior at temperatures lower than after nanotube growth. Units on the inset to panel (d) are emu/g for magnetization value and kilogauss for external magnetic field.
The best fit for Langevin function for (a) catalyst S1 before carbon SWNT growth and (b) catalyst S4 after carbon SWNT growth.
Temperature dependence of the magnetization curves under ZFC and FC for S4 after carbon SWNT growth.
Magnetization vs applied magnetic field for catalyst S4 at 5 and after heat treatment at under mixed gases flow.
TEM images of the carbon nanotubes synthesized using catalyst S1. The carbon material contains (a) very broad distribution of nanotube diameter, (b) SWNTs with big diameter and relatively thick walls, and multiwall nanotubes and (c) carbon SWNTs with different bundle sizes.
Carbon SWNT diameters estimated from radial breathing mode (RBM) frequencies of Raman spectra. The diameters were estimated from , where is the tube diameter (nm) and the RBM frequency . The data with “+” are tubes which are out of resonance for particular laser excitation energy. The letters “vw,” “w,” “m,” and “s” mean that the RBM signal is very weak, weak, moderate, or strong, respectively.
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