MAGNETIC-PROPERTIES AND MORPHOLOGIES OF RAPIDLY-SOLIDIFIED IRON-OXIDES WITH SILICA

Rapid solidification of iron oxides with silica was investigated as a method of making fine dispersions of magnetic phases within a non-magnetic matrix. Such a process applied to amorphous thin films may ultimately lead to solid-state dispersions of particles that possess magnetic properties suitable for magnetic recording purposes. Ceramic powders of four different compositions were pressed into rods, sintered and then rapidly solidified using the double roller quench method. The compositions of these powders were 1) pure Fe3O4; 2) 82 wt% Fe3O4 + 18 wt% SiO2; 3) 77 wt% Fe3O4 + 18 wt% SiO2 + 5 wt% CoO and 4) 46 wt% Fe3O4 + 26 wt% SiO2 + 28% CoO. SEM and XRD studies were done on as-quenched flakes produced from each of the starting compositions. The flakes produced from pure Fe3O4 are composed of crystals of Fe2O3·Fe3O4, with a mean particle size of 5 μm. For this sample, σ2 was 85 emu/g and Hc was 30 Oe. An AES study was done on a flake produced from composition 2). The flakes produced from starting compositions of 2) and 3) consisted of equiaxed precipitates of Fe2O3·Fe3O4 (Berthollide oxide) growing within a glassy matrix in an oriented manner. The average size of these precipitates is 1500 Å on edge. Flakes produced from sample 2) possess a σs of 54 emu/g and Hc of 245 Oe: flakes produced from sample 3) have σs of 50 emu/g and Hc of 550 Oe. The flakes that were produced from starting composition 4) consisted of separate precipitates and dendrites of cobalt ferrite with an average size of 2000 Å on edge. The σs of this sample was 10 emu/g and the Hc was 650 Oe. © 1990.