  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.
