HIGH COERCIVITY SINGLE-DOMAIN PARTICLES IN GLASS MATRIX

Impregnating transition metallic compounds into porous glass is a simp le way to form ultrafine particles in a glass matrix. In our studies, ultrafine particles were prepared by impregnating Fe compounds into po rous glasses (pore size 70+/-21 Angstrom) and annealing. After anneali ng, the samples were studied at different temperatures with a vibratin g sample magnetometer. In the annealed glasses two types of particles were formed: (a) superparamagnetic particles and (b) ferromagnetic par ticles with exceedingly high coercivity (Hc=13 kOe at 298 K). The rati o between superparamagnetic and high coercivity particles depends on t he annealing temperature and time. In samples annealed at lower temper atures or at high temperature for short times, only superparamagnetic particles were found. In those annealed at high temperatures after cer tain times, only high coercivity particles were found. It was also fou nd 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.