Magnetism of sol-gel fabricated CoFe2O4/SiO2 nanocomposites -: art. no. 124304

Details of synthesis and characterization of sol-gel-produced CoFe2O4 nanoparticles embedded in the amorphous SiO2 matrix are presented together with results of an extended magnetization study of these materials. The particle size was found to increase from 6 to 15 nm by varying the temperature of a subsequent annealing from 800 to 1100 degrees C. All samples exhibited superparamagnetic behavior with values of the blocking temperature T-B increasing with the particle size. At temperatures above T-B the magnetization curves follow the expected Langevin scaling of M vs H/T, which is consistent with the formation of the superparamagnetic state. For T < T-B, the coercivity field H-c was found to be proportional to root T and the frequency-dependent ac susceptibility was found to obey the Neel-Arrhenius law. Both observations are compatible with a model of noninteracting randomly oriented single-domain particles. (c) 2005 American Institute of Physics.