Towards high performance CoFe₂O₄ isotropic nanocrystalline powder for permanent magnet applications

We report on a comparative study of high performance isotropic cobalt ferrite (CoFe₂O₄) 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$−3$ (2.34 MGOe) has been obtained for isotropic powder after post-processing annealing. This magnetic performance combined with the required short processing times and the unnecessary requirement of oxygen avoidance in the milling process, makes this CoFe₂O₄ powder a good candidate for permanent magnet applications.