Influence of cation disorder on the magnetic properties of ball-milled ilmenite (FeTiO₃)

We have investigated the evolution of crystal structure, cation disorder and magnetic properties of ilmenite (FeTiO3) after increasing time of high-energy ball-milling in an inert atmosphere. Refinement of X-ray diffraction data show that the hexagonal crystal structure of ilmenite is maintained after high-energy ball-milling of up to 128 h, but neutron diffraction studies reveal significant cation redistribution of Fe2+ and Ti4+ ions in the ball-milled samples. Mössbauer spectroscopy studies show that the magnetic hyperfine field of Fe2+, which is around 5 T before ball-milling, increases, and after milling times longer than 4 h a broad distribution of hyperfine fields with values up to around 40 T for Fe2+ is seen. This can be explained by the cation disorder induced by the ball-milling which affects the orbital contribution to the magnetic hyperfine field. In contrast to some ball-milled spinel ferrites, the Néel temperature of ilmenite is not significantly affected by the cation disorder.