Structure and magnetic properties of multi-walled carbon nanotubes modified with cobalt

The magnetic properties of multi-walled carbon nanotubes (MWCNTs) modified with cobalt nanoparticles were studied in the temperatures and magnetic field range of (4.2–290) K and (0.03–5) T, respectively. Nanoparticles of cobalt encapsulated inside MWCNTs were obtained by using the chemical vapor deposition technique. The low temperature SQUID magnetization measurements were supplemented with structural investigations by means of high-resolution transmission electron microscopy, scanning electron microscopy as well as thermogravimetric and X-ray diffraction analysis. X-ray diffraction revealed the presence of MWCNTs, f.c.c. Co and h.c.p. Co phases. The magnetic characterization provided the remanent magnetization value (MR) of about 0.07 emu/g (∼40% of the saturation moment), while the coercive field (HC) value amounts to 600 Oe. Both parameters MR and HC slightly decrease with the rise of temperature. The substantial magnetization increase observed at low temperatures suggests the existence of nano Co clusters (in the atomic scale size).