Crystal growth of Co ferrite on fine acicular γ-Fe2O3 particles

Highly coercive magnetic powder was obtained by growing cobalt ferrite on the surface of γ-Fe₂O₃ particles in highly alkaline suspensions containing cobalt and ferrous ions in a Co/Fe molar ratio = $\text{1}\text{2}$. The mechanism of the growth and the structure of cobalt ferrite on γ-Fe₂O₃ were studied by X-ray diffraction and electron diffraction techniques. Results show that crystals of cobalt ferrite CoFe₂O₄ with a spinel type crystal structure of lattice constant 8.415 Å grew epitaxially on γ-Fe₂O₃. The acicular direction of the epitaxially grown Co-γ-Fe₂O₃ as well as γ-Fe₂O₃ was in the $\text{1}$01] direction. It was found that from the lattice constant value and the half width of X-ray diffraction peaks, the lattice constant epitaxially grown Co γ-Fe₂O₃ may be attributed to two kinds of crystals, viz., seed γ-Fe₂O₃ ($\text{a = 8.35 ～ 8.37}\text{A}\text{?}$) which was partly reduced to Fe₃O₄, and surface layer CoFe₂O₄ ($\text{a = 8.415}\text{A}\text{?}$). The crystal growth in the interface between the seed crystals and the growth layer was affected by the crystal structure of the seed crystals. The lattice constant of CoFe₂O₄ which was located in the vicinity of the interface was almost equal to that of the seed crystals.