Cobalt ferrite nanoparticles in a mesoporous silicon dioxide matrix

We have studied magnetic nanoparticles of cobalt ferrite obtained by the extraction-pyrolysis method in a mesoporous silicon dioxide (MSM-41) molecular sieve matrix. The X-ray diffraction data show evidence for the formation of CoFe2O4 particles with a coherent scattering domain size of ∼40 nm. Measurements of the magnetization curves showed that powders consisting of these nanoparticles are magnetically hard materials with a coercive field of Hc(4.2 K) = 9.0 kOe and Hc(300 K) = 1.8 kOe and a reduced remanent magnetization of Mr/Ms(4.2 K) = 0.83 and Mr/Ms(300 K) = 0.49. The shape of the low-temperature (4.2 K) magnetization curves is adequately described in terms of the Stoner-Wohlfarth model for randomly oriented single-domain particles with a cubic magnetic anisotropy.