Preparation and magnetic properties of La-Mn and La-Co doped barium hexaferrites prepared via an improved co-precipitation/molten salt method

摘要

La-Mn and La-Co doped barium hexaferrites of formula Ba_((1-x))La_xFe_((12-x))M_xO_(19) (M=Mn, Co) (x=0.05 to 0.40) were prepared with an improved co-precipitation/molten salt method. For the synthesis, aqueous solutions of the appropriate metal chlorides were prepared in the ratio required except that the initial mole ratio of Fe and dopants to Ba was chosen to be 11:1, and then mixed with excess Na_2CO_3. The solutions were then cooled, filtered off, dried, then mixed with KCI flux, and heated at 450 ℃ and for 2 h. The temperature was then raised to 950 °C and kept for 4 h, then cooled. This new synthesis method, which employs a lower temperature and shorter reaction time, gives products with improved crystallinity and purity while the saturation magnetization and coercivity values are comparable with those synthesized via the high temperature method.