Magnetism in carbon structures filled with ferromagnetic crystals: filling-control, phase-transitions and shell manipulation

Carbon nanotubes filled with ferromagnetic metal or alloy nanocrystals have recently attracted significant attention thanks to their tunable coercivities and saturation magnetizations. Continuous filling of the nanotube’s central capillary as well as nanotube-shell manipulation remain important steps towards application of this category of materials. In this seminar I will present possible solutions that can be employed towards control of both filling and shell-composition parameters.

I will firstly outline the importance of CVD growth methods which exploit self-organizational processes in a locally perturbed viscous boundary layer (between a flowing thermally decomposed metallocene vapour and a textured substrate). Interestingly, K-type substrate roughness produces flower-like morphologies continuously filled with Fe-based nanowires with length in the order of many micrometers. Together with these methodologies, I will outline the importance of chlorine and sulfur as additional filling-promoters. Careful control of the chlorine-concentration allows fabrication of cm-scale films of continuously filled carbon nanotubes. The relation between chlorine-concentration and CNT-filling rate will be outlined. Finally, the role of sulfur will be described also from the perspective of CNT-shell manipulation, opening up possible future applications in superconductivity, with a predicted Tc~35K (on the basis of literature observations). Finally, I will compare the properties of these materials with those of other ferromagnetically filled systems.