Self-propagating high-temperature synthesis of barium-chromium ferrites BaFe12-xCrx O19 (0 x6.0)

Abstract

Pure and chromium substituted barium ferrites BaFe12-xCrxO19 (0 x6.0) have been synthesised in air by self-propagating high-temperature synthesis (SHS): a combustion process involving a reaction of barium peroxide, iron oxide, chromium oxide and iron metal powder. Two series of SHS samples were produced: series 1 - zero field SHS, and series 2 - SHS in a magnetic field of 1.1 T, both followed by sintering at 1200 °C for 2 h. X-ray data showed that hexagonal ferrites were produced, and systematic changes in lattice parameters were seen as a function of the Cr content. Scanning electron microscopy indicated crystallites of order 1 µm. Energy dispersive x-ray analysis (EDAX) showed that the samples were homogeneous with the expected Ba:Fe:Cr ratios. Mössbauer, x-ray and magnetic hysteresis data showed a progressive change in the sublattice occupancy and magnetization with Cr content. Some differences in magnetic parameters were observed between series 1 and 2, implying that the use of a magnetic field during SHS can influence product microstructure. In particular, the coercive forces in the Cr doped ferrites showed maxima at x = 1.5 and x = 1.0 for series 1 and 2 respectively, with the series 2 coercivities being consistently 40-50% smaller than their series 1 counterparts. This indicates that applied field SHS provides an alternative route to reducing coercivity in hexagonal ferrites in lieu of conventional approaches such as cationic doping.