Effect of Annealing Temperature and Boron Addition on Magnetic Properties of Hexaferrites Synthesized by Standard Ceramic Method.

The barium and strontium hexaferrites (BaM and SrM) were successfully prepared by the standard solid-state reaction method. To inhibit crystal growth, 1 wt % BO was added into the initial mixture. The structural and magnetic properties of pure hexaferrites were compared with the samples prepared with boron addition. Powders were annealed at temperatures between 800 and 1200 C. The crystal structure, morphology, and magnetic properties of hexaferrites were investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). BaM was synthesized at temperatures as low as 800 C with boron addition having saturation magnetization of ∼50 emu/g and coercivity of ∼3 kOe. At the same temperature, pure sample has very low magnetization about 1.3 emu/g. Moreover, at higher sintering temperatures, boron-containing samples have higher magnetization values compared to pure BaM. The optimal Fe/Ba ratio was determined as 10.5 for boron-containing samples, while it is 11.5 for the pure one. The coercivity started to decrease at 1100 C indicating that single to multi-domain transition occurs. The saturation magnetization values are nearly equal in pure- and boron-containing SrM samples in the whole temperature range. However, maximal coercivities occurred at different temperatures for boron-containing and the pure samples as 1000 and 1100 C, respectively. Magnetic interactions deduced from the Stoner-Wohlfarth model using the isothermal magnetization and demagnetization measurements showed that boron addition suppresses the destructive (demagnetizing-like) interactions among domains in both SrM and BaM samples, and thus, stabilizes the remanence. [ABSTRACT FROM AUTHOR]