SIZE EFFECTS ON THE MAGNETIC-PROPERTIES OF FINE FE-CR PARTICLES

The magnetic and structural properties of Fe100-xCrx ultrafine particl es with x = 5-20 have been studied as a function of particle size. Par ticles with a size in the range of 80-360 angstrom were prepared by ga s evaporation under argon atmosphere. The particles with smaller diame ter had a high coercivity at low temperatures and showed a stronger te mperature dependence of coercivity. The x = 20 particles with a size 8 0 angstrom had a coercivity about 2100 Oe at 10 K with a superparamagn etic blocking temperature about 150 K. Mossbauer spectra showed the pr esence of Fe-Cr, alpha-Fe and Fe-oxide components in the bigger partic les, and Fe-Cr and Fe-oxides in the smaller particles. The coercivity at low temperatures increased with decreasing particle size and this w as attributed to the higher percentage of Fe-oxide on the surface of t he smaller particles. This interpretation was further supported by the temperature dependence of coercivity of Fe-Cr particles sandwiched be tween two Ag films.