Unusually high magnetic hardness, characterized by a coercive field of 2 T at 2 K, has been observed for 12 nm particles of CoFe2O4 (15%) in amorphous silica prepared by the sol-gel technique and sintered at 1000degreesC. 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.