Hexagonal SrFe12O19 ferrites: Hydrothermal synthesis and their sintering properties

Hexagonal M type SrFe12O19 (SrM) ferrites were synthesized by the hydrothermal method, and the effects of molar ratio of OH-/NO3- (R-O/N), the atomic ratio of Fe/Sr (R-F/S) and sintering on the phase composition and magnetic properties of as-synthesized specimens are studied. It is found that the R-O/N and R-F/S in starting materials affect the phase composition and magnetic properties greatly. Fe2O3 is found as impurity in some specimens, while in all as-synthesized specimens, SrCO3 forms inevitably during the synthesis process. After sintering at 1100 degrees C, the perovskite type SrFeO3-x ferrite forms as the product of SrCO3 and Fe2O3 at high temperature, and the specimens exhibit the Perminvar magnetic hysteresis loops which show two-phase magnetic behaviors. However, when sintered at 1200 degrees C, SrFeO3-x further reacts with Fe2O3 to produce SrFe12O19, and the specimens with R-F/S=8, 9 and 10 exhibit the single-phase hexagonal structure and magnetic behavior. It is also found that the saturation magnetization and coercivity are both enhanced after sintering at high temperatures due to the elimination of impurities. (C) 2012 Elsevier B.V. All rights reserved.