Towards high performance CoFe_2O_4 isotropic nanocrystalline powder for permanent magnet applications

摘要

We report on a comparative study of high performance isotropic cobalt ferrite (CoFe_2O_4) powder processed by dry and surfactant assisted (wet) ball milling. Milling times as short as 1.5 min (dry) and 6 min (wet) have resulted in a 4-fold increase in coercivity, with a maximum achieved value above 318 kA/m (4 kOe). The use of surfactant is shown to be advantageous in the formation of a more homogeneous structure constituted by non-agglomerated and strained nanoparticles. A record (BH)_(max). value of 18.6 kJ m~(-3) (2.34MGOe) has been obtained for isotropic powder after postprocessing annealing. This magnetic performance combined with the required short processing times and the unnecessary requirement of oxygen avoidance in the milling process, makes this CoFe_2O_4 powder a good candidate for permanent magnet applications.