Improvement of the magnetic properties of SrFe12O19 ceramics by tailored sintering with SiO2 addition

Abstract

In order to obtain competitive strontium ferrite sintered magnets, SiO2 and CaO are added to avoid exaggerated grain growth. Besides favoring proper densification, these additives prevent the collapse of coercivity associated to grain growth. However, these additives may lead to slight decreases in density and the formation of paramagnetic α-Fe2O3 that hampers magnetization. Here, with the motivation of simplifying the production process, we present a study to maximize the magnetic performance of strontium ferrite ceramics using silica as the sole additive. A microscopic study offers insights into the grain growth mechanism activated by Silica. As a result, a compromise between relative density, coercivity and saturation magnetization is attained. It is found that sintering for 4 h up to 1200 °C with a SiO2 content of 1 wt% leads to the best compromise between coercivity, magnetization and density values. Competitive densities are reported in the absence of CaO, the usual co-additive. In addition, Confocal Raman Microscopy is employed for the first time to characterize the decomposition of strontium ferrite onto α-Fe2O3.