Abstract
We have fabricated high-coercivity nanocomposites constituted of Fe2O3 or CoFe2O4 nanocrystals embedded in amorphous silica matrix by a single-molecule precursor sol-gel method. Our approach enables smooth variation of the Fe(Co) : Si ratio up to 40 weight % of the magnetic phase, resulting in high density nanocomposite.
Final crystallite size and phase composition was adjusted by subsequent heat treatment. The Fe2O3/SiO2 samples annealed at 1000 and 1100 degrees C revealed coercivity, H-c similar to 2 T at 300 K due to formation of the metastable epsilon-Fe2O3 phase.
The CoFe2O4/SiO2 composites exhibit enhancement of the H-c value with increasing annealing temperature. Origin of the large coercivity in the two types of the magnetically hard nanocomposites will be discussed.