MAGNETIC PIGMENTS FOR RECORDING MEDIA

CrO2 doped with 1-2 wt% Fe3+ on Cr4+ positions is one of the most impo rtant materials for magnetic recording in audio, data and video tapes. Fe-57 Mossbauer spectroscopy was applied to determine the level of ir on doping in newly developed high coercivity CrO2 particles. It was fo und that, compared with the conventional preparation process, the new particles contain increased amounts of Fe3+ ions in the CrO2 crystal l attice giving rise to higher magnetocrystalline anisotropy. This is re flected in coercivities of up to over 900 Oe. All samples contain as a secondary iron-containing phase alpha-(Cr1-xFex)(2)O-3, the amount of which is higher in samples of the conventional preparation process th an in those of the new BASF process. Details about the mechanism of th e development of doped CrO2 particles in both types of processes were obtained by means of Mossbauer, XRD and wet chemical investigations ma king possible an optimization of the new BASF process.