FINE POWDERS OF CO-MN CATION DEFICIENT SPINEL FERRITES FOR MAGNETOOPTICAL PIGMENTS

Very small particles of Go-Mn defect spinel ferrites with acicular and spherical shape were prepared. Their magnetic and magneto-optical pro perties were measured in function of their oxidation state and their s ite. It was shown that the coercivity of acicular (AP) and spherical ( SP) particles with a mean crystallite size close to 20 nm, reached 380 0 and 2950 Oe respectively, The SP coercivity decreases when the grain s sizes become lower than 20 nm, but remains higher than 1000 Oe for p articles having crystallites close to 10-15 nm, The Curie temperature decreases also sligthly when the grains are smaller than 20 nm, while the remanent Faraday rotation falls from 0.6 to 0 deg/mu m when the cr ystallite size is reduced from 40 to 7-8 nm. The Go-Mn ferrite particl es studied have interesting properties, even they have not, for now, a ll the required properties to be high performance pigments for magneto -optical recording.