Magnetic Nanostructures Grown on Vertically Aligned Carbon Nanotube Templates

We describe the growth of magnetic nanostructures on carbon nanotube templates. The nanotubes were grown by microwave plasma enhanced chemical vapor deposition. The as-grown nanotubes were aligned reasonably well around the substrate normal directions. However, it was found that the nanotubes grown on magnetic catalysts tend to regroup into microumbrella-like structures under an external magnetic field due to the dipole interactions among the magnetic particles at the top tips of the nanotubes. To prevent the regrouping of nanotubes and also facilitate the study of magnetic properties of subsequently formed magnetic nanostructures, antiferromagnetic materials have been used for the formation of nanotubes. The hysteresis loops of the nanostructures have been measured using a vibrating sample magnetometer at both room and elevated temperatures. The shape of the hysteresis loops suggested that there exists a strong magnetostatic interaction in this system. Multiple steps have been observed in the coercivity versus temperature curves, which are attributed to the size-effect of the magnetic nanostructures.