Microstructure and magnetic properties of tubular cobalt–silica nanocomposites

Co-based (Co and Co3O4) nanoparticles were self-integrated into SiO2 nanotubes with a methodology based on the use of a Co salt as a template structure for the formation of SiO2 nanotubes. Within the confinement of tubular matrix of SiO2, the nanofibres of cobalt precursor, i.e., [Co(NH3)6](HCO3)(CO3)·2H2O, were treated in a H2 atmosphere with different parameters. With a sufficient reduction on the cobalt precursor, sphere-like Co-based nanoparticles are obtained, being well aligned in the interior space of the SiO2 nanotubes. With an insufficient reduction, platelet-like Co-based nanoparticles are formed, being arranged in a random manner inside the SiO2 nanotubes. The sufficiently reduced Co–SiO2 nanocomposite exhibits an open hysteresis loop in the low field region (<3 kOe) and a paramagnetic response in high field (>3 kOe) at 300 K. An observed wide separation between the zero-field-cooling (ZFC) and field-cooling (FC) curves over the whole temperature region has demonstrated a characteristic feature of ferromagnetism with a magnetically anisotropic barrier diverting the easy axis from the axis of the applied field. The predominant factor leading to this anisotropic potential barrier is attributed to the shape anisotropy native to the one-dimensional arrangement of Co-based nanoparticles within the tubular matrix, i.e. SiO2 nanotubes.