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Keywords:

  • Magnetic hysteresis;
  • Nanoparticles, magnetic;
  • Spinels;
  • Superparamagnetism

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 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.