Cobalt(II)-titanium(IV)-substituted barium ferrite forming the chemical formula of BaCoxTixFe12-2xO19(x=1-6)havebeen investigated using Xray diffraction spectroscopy (XRD), Superconducting Quantum Interference Device (SQUID) and high-resolution transmission electron microscopy (HRTEM). The specimen of magnetoplumbite (M-type) Co-Ti-substituted BaFe12O19 were synthesised via sol-gel method using ethylene glycol as precursor. Significant increase in line broadening of the XRD pattems were observed indicating the decrease of particle sizes due to the Co(II)-Ti(IV) substitution. BaCo3Ti3Fe6O19 showed the highest coercivity but moderate saturation and remnant magnetisations. HRTEM imaging showed that Co(II)-Ti(IV) substitution in the system of BaCoxTixFe12-2xO19 (x = 1-6) produced no drastic change in the structure of the M-type ferrites. Most of the M-types crystals examined by HRTEM displayed a long axis perpendicular to the c-axis of the M-type structure. Disordered crystals showing the intergrowth between Co-Ti-substituted barium ferrite and the spinel-structured iron oxide were detected. (c) 2007 Elsevier B.V. All rights reserved.