Novel SHS routes to CoTi-doped M-type ferrites

Cobalt and titanium substituted barium ferrites BaFe(12-2x)Co(x)Ti(x)O(19) with 0 less than or equal to x less than or equal to 1.5 have been made by self-propagating high-temperature synthesis (SHS). Comparison was made between the SHS samples and x=0 and 0.75 materials prepared commercially by conventional methods. X-ray and Mossbauer data for all the SHS samples showed that the majority product was M-type hexagonal ferrite, with up to 10 wt% hematite impurity. Systematic changes in the hexagonal unit cell lattice parameters were seen as a function of CoTi content. Scanning electron microscopy and X-ray line broadening showed that the SHS crystallites were comparable in size and morphology to those prepared by conventional routes. Mossbauer and magnetic hysteresis data showed no significant change in sublattice and net magnetizations in the SHS samples, in contrast to the reduction found in CoTi-doped conventional ferrites. The coercive forces in the CoTi-doped SHS ferrites are larger than those in conventional samples at the same doping level, implying that a greater concentration of pinning centers are introduced via the SHS reaction route. (C) 2001 Kluwer Academic Publishers.