High Coercive Field for Nanoparticles of CoFe₂O₄ in Amorphous Silica Sol–Gel

Unusually high magnetic hardness , characterized by a coercive field of 2 T at 2 K, has been observed for 12 nm particles of CoFe 2 O 4 (15%) in amorphous silica prepared by the sol–gel technique and sintered at 1000 °C. Field‐ and temperature‐dependence magnetization data (see Figure) for these particles and those of 3.2 nm suggest that dipolar interaction between particles is responsible for this enhancement.