The structure, morphology and magnetic properties of Sr-ferrite powder prepared by the molten-salt method

Sub-micrometre high-performance Sr-ferrite powder was prepared by a molten-salt method using Na_2SO4 as the fluxing agent. In the reaction process, a mixture of superfine powder was pre-sintered at 1150°C for 3h and then annealed at 850°C for 2h. The as-obtained Sr-ferrite powder is SrFe_12O19 with a hexagonal magnetoplumbite structure. We observe that with raising the pre-sintering temperature as well as increasing the annealing temperature and time, there is an enlargement of particle size. We regulated the reaction parameters to optimize the magnetic properties of the Sr-ferrite powder. The structure with the best magnetic properties is quasi-cubic in shape and relatively uniform in size, showing a coercivity of 471.89kAm^-1, a saturation magnetization of 91.51μWbmkg^-1, a remanence ratio of 0.50 and a maximum magnetic energy product of 7.89kJm^-3. We then studied the effects of particle size, demagnetization factor and magnetocrystalline anisotropy on coercivity. Compared with the conventional ceramic process, the one presented here is more convenient and economical for the production of homogeneous hexagonal ferrite powders of high magnetic performance.