EFFECT OF COMPOSITION AND ANNEALING ON LOCAL ATOMIC ORDER AND MAGNETIC PROPERTIES OF FECO AND SILICA-COATED FECO NANOPARTICLES SINTERED BY CO-PRECIPITATION

Phase composition and magnetic properties of FexCo1-x (25 <= x <= 75, wt.%) and (FeCo)(70)(SiO2)(30) (wt.%) nanoparticles (NPs) were studied by Fe-57 Mossbauer spectroscopy and magnetometry. By varying the Fe:Co ratio in NPs, we established the optimal composition (Fe25Co75), which reveals the highest value of magnetization (up to 76.9 emu/g). Study of (FeCo)(70)(SiO2)(30) NPs proved that coverage of Fe25Co75 cores with SiO2 shells resulted in the decrease of the medium core's diameter and inhibits formation of undesirable surface Fe(Co) hydroxides. Annealing of (FeCo)(70)(SiO2)(30) NPs draw to perfect crystallization of FeCo cores and full diminishing of Fe(Co) hydroxides.