Sol-gel fabricated CoFe/sub 2/O/sub 4//SiO/sub 2/ nanocomposites: synthesis and magnetic properties

Well-defined CoFe/sub 2/O/sub 4/ nanoparticles embedded in an amorphous SiO/sub 2/ matrix have been synthesized by a sol-gel method, characterized and investigated by Mo/spl uml/ssbauer spectroscopy and magnetic properties measurements. The mean particle size increases from 3 to 15nm consistently with the temperature of the subsequent annealing, which varied from 800/spl deg/C to 1100/spl deg/C, respectively. The composites exhibit superparamagnetic behavior with the blocking temperature T/sub B/ increasing with the mean particle size from 80 to 350 K, respectively. Sufficiently high value of H/sub c//spl sim/2.5 T (at 2 K) has been observed for the sample annealed at 1100/spl deg/C.