A comparative study of BaxSr1-xFe12O19 ferrite permanent magnets prepared by ball milling and sol-gel routes

Given the huge and increasing global demand for permanent magnet supply, even slight improvements of the magnetic properties and cost effectiveness of permanent magnet materials could incur huge energy and money savings. This article is concerned with the optimization of the experimental conditions for the production of pure M-type BaxSr1-xFe12O19 hexaferrites with improved magnetic properties. X-ray diffraction analysis revealed the formation of a single M-type hexaferrite in the ball milling route at a sintering temperature of 1100 degrees C for the samples with x = 0.0 and 0.5, and at 1200 degrees C for x = 1.0. In the sol-gel route, however, a single M-type phase was successfully synthesized at a significantly lower temperature of 890 degrees C. The magnetic parameters of the samples prepared by ball milling exhibited an improvement at lower Ba contents. On the other hand, the samples prepared by sol-gel method exhibited a significant improvement of the intrinsic coercivity (H-cM) compared with those prepared by ball milling, with the highest value of 5.9 kOe observed at x = 0.0 and sintering temperature of 1000 degrees C. The saturation and remnant magnetization, however, were not influenced significantly by the synthesis route, and remained relatively high, comparable with the best parameters for ferrite isotropic magnets. The sample with x = 1.0 prepared by sol-gel method and sintering at 890 degrees C exhibited the highest residual induction B-r = 2509 G, practical coercivity H-cB = 1919 Oe, and maximum energy product (BH)(max) = 9.9 kJ m(-3).