Study of strontium hexaferrite prepared by solid state reaction using celestite and hematite

Abstract

Abstract Strontium hexaferrite (SrM) powders were prepared by solid-state reaction using celestite and magnetite/hematite. Energy dispersive X-ray fluorescence spectrometry, X-ray diffractometry (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry were used for analyses. The precursor ores were purified by hand-sorting and magnetic separation. Magnetic separation yielded 75% magnetite and 25% hematite in iron ore. Strontium reached a single phase of $$\rm SrSO_4$$ via hand-sorting. XRD confirmed single-phase $$\rm SrFe_{12}O_{19}$$ sample with hexagonal symmetry (space group $$\rm P6_{3}/mmc$$ ). EDS analyse confirmed that the percentage of elements is in agreement with the expected stoichiometry for the hexaferrite phase. Initial SrM sample exhibited magnetization at maximum field of $$\rm 56~emu/g$$ and coercive field of $$\rm 632~Oe$$ . Although remanence and coercivity were lower than expected for the initial SrM sample, due to wide particle size distribution observed in SEM images, by optimizing synthesis parameters, particularly annealing at $$950^\circ $$ C, the coercivity increased by nearly eightfold, reaching 4.96 kOe. The sample annealed at 950 $$^\circ $$ C also exhibited a maximum energy product of $$\rm (BH)_{max}\approx 3.20~MGOe$$ and an estimated magnetocrystalline anisotropy constant of $$\rm K_1\sim 3.6\times 10^6~erg/cm^3$$ . Microstructural evidence confirmed the predominance of particles in the monodomain regime, which justifies the increase in the coercive field. The results demonstrate that microstructural control is decisive for tuning the magnetic response of SrM, enabling the large-scale viability of this synthesis route for the production of high-coercivity hexaferrites, using a direct mixture of minerals instead of conventional industrial reagents.