Catalytic effect of the spinel ferrite nanocrystals on the growth of   carbon nanotubes
  We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe2O4), (ii) ferrite where cobalt was substituted by nickel (NixCo1-xFe2O4, with x= 0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (ZnyNi1-yFe2O4 with y= 1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the grain size by FE-SEM images in the range of 10-70 nm, and their magnetic properties by VSM. Next, carbon nanotubes were grown on these nanocatalysts by the CCVD method. We show that the catalytic effects of these nanocrystals on the carbon nanotube growth depend on cation distributions in the octahedral and tetrahedral sites, structural isotropy and catalytic power due to cations. Our study can have applications in finding a suitable candidate of doped ferrite nanocrystals as catalysts for carbon nanotube growth. More interestingly, the yield of the fabrication of carbon nanotubes can be considered as an indirect tool to study catalytic activity of ferrites. 
R. Hosseini Akbarnejad, V. Daadmehr, F. Shahbaz Tehrani, F. Aghakhani,   and S. Gholipour
cond-mat.mtrl-sci