Magnetic interactions in SrFe12O19/CoFe2O4 composite: Influence of ball milling frequency and annealing temperature

SrFe12O19/CoFe2O4 magnetic composites were fabricated by mixer ball milling technique (with the oscillating frequency of 10, 15, 20 and 25 Hz) using hexagonal ferrite (80 wt%) and cubic ferrite (20 wt%) powders as precursors. The composites were divided into three groups for thermal treatments: i) 700 degrees C, 3 h; ii) 900 degrees C, 3 h; iii) 900 degrees C, 5 h. X - ray powder diffraction was carried out for structural analysis. Transmission electron microscopy was applied to investigate the morphology of the final products. Magnetic properties were studied at room temperature by measurements of magnetization versus applied external magnetic field, direct current demagnetization and isothermal remanence magnetization. A relationship was established between magnetic properties and the structural parameters of the composites and correlated to the oscillating frequency of ball milling. From all the groups, the samples processed at 10 Hz -frequency stand out in terms of magnetic properties. Annealing at 900 degrees C for 3 h allowed obtaining the composite with the energy product (BH)(max) value about 20 % larger than its parent compound. The existence of the exchange coupling effect was derived from constructing Henkel plots and can explain the improved magnetic characteristics of the standing-out composite.