MAGNETISM IN ULTRAFINE FE AND CO PARTICLES

The magnetic properties of vapor deposited Fe and Co particles in the size range of 50-350 angstrom have been studied. Magnetization, Mossbauer and structural data show a ''core-shell'' morphology, where the core is metallic and the shell is a poly-crystalline Fe (Co)-oxide. A sharp reduction in magnetization was observed in particles with a size below 100 angstrom and this has been attributed to surface/interface spin canting brought about by the ferrite oxide shell. We have systematically studied the effect of various surface chemistries on the hysteretic behavior. The results clearly indicate that the oxide shell controls both the magnitude and the temperature dependence of coercivity.