Ferrite-Based Exchange-Coupled Hard-Soft Magnets Fabricated by Spark Plasma Sintering

Ferrite-based, hard-soft magnetic nanocomposites with the composition (100% - x)SrFe12O19-xCoFe(2)O(4), where x = 5, 10, and 15 wt%, were prepared by mixing the constituent powders, followed by spark plasma sintering. In order to control the particle size of the constituent materials, the SrFe12O19 and CoFe2O4 powders were synthesized using the hydrothermal method, mixed and then consolidated with spark plasma sintering. The conditions during the spark plasma sintering process (sintering temperature, time, and applied pressure) were varied in order to prepare composites with a high density and exchange-coupled hard and soft magnetic phases, leading to an increase in the maximum energy product, when compared with pure SrFe12O19. The microstructural analysis revealed that the relative density of the sintered composite exceeded 90% of the theoretical value and that the CoFe2O4 was uniformly distributed in the SrFe12O19 matrix. Magnetic measurements of the sintered composites showed a single-phase magnetic behavior. When compared with the single-phase SrFe12O19 used in this study, the SPS composites exhibited a 22% increase in the maximum energy product (26.1 kJ/m(3)).