High coercivity single-domain particles in glass matrix

Impregnating transition metallic compounds into porous glass is a simple way to form ultrafine particles in a glass matrix. In our studies, ultrafine particles were prepared by impregnating Fe compounds into porous glasses (pore size 70+/-21 Angstrom) and annealing. After annealing, the samples were studied at different temperatures with a vibrating sample magnetometer. In the annealed glasses two types of particles were formed: (a) superparamagnetic particles and (b) ferromagnetic particles with exceedingly high coercivity (Hc=13 kOe at 298 K). The ratio between superparamagnetic and high coercivity particles depends on the annealing temperature and time. In samples annealed at lower temperatures or at high temperature for short times, only superparamagnetic particles were found. In those annealed at high temperatures after certain times, only high coercivity particles were found. It was also found that the blocking temperature T-B Of the high coercivity particles depends on the annealing process. Moreover it was found that the Curie temperature of the high coercivity particles is below 520 K. (C) 1996 American Institute of Physics.