Pri diplomskem delu smo raziskovali postopek sinteze kompozitnih nanodelcev, kjer smo različne jedrne nanodelce (silicijev dioksid – SiO2 in barijev heksaferit – BaFe12O19) prevlekli s plastjo spinelnega ferita. Plast spinelnega ferita je nastala s soobarjanjem Fe3+/M2+ ionov (M2+ = Fe2+, Co2+) ter heterogeno nukleacijo trdnega produkta na površino jedrnih nanodelcev. Sintezo kompozitnih nanodelcev prekritih s plastjo kobaltovega ferita smo naredili s stehiometričnim razmerjem Fe3+/Co2+ ionov in povečano koncentracijo Co2+ ionov.
Z izbrano metodo smo na površino jedrnih nanodelcev nukleirali plast spinelnega ferita (maghemit ali kobaltov ferit). Plast kobaltovega ferita ni imela stehiometrične sestave. Pri sintezi kompozitnih nanodelcev, kjer smo kot jedrne nanodelce uporabili nanodelce barijevega heksaferita velikosti 5 − 70 nm, smo dobili nehomogen vzorec. Vzorec je vseboval majhne nanodelce (13 nm), pri katerih so oborjeni ioni zreagirali z jedrnimi nanodelci ter večje kompozitne nanodelce, kjer je bila spinelna plast heterogeno nukleirana na bazalnih površinah ploščatih heksaferitnih nanodelcev. Pri pripravi kompozitnih nanodelcev, kjer smo heksaferitne nanodelce prevlekli s plastjo kobaltovega ferita, smo v primeru stehiometrične in povečane koncetacije Co2+ ionov dobili nestehiometrično sestavo spinelne pasti na površini jedrnih nanodelcev.
Magnetne meritve so pokazale, da se je nasičena magnetizacija v primeru kompozitov s spinelno plastjo maghemita povečala, kakor se je povečala tudi remanenca. Pri kompozitih s plastjo kobaltovega ferita na površini se je zmanjševala tako nasičena magnetizacija kot koercitivnost.The preparation of the composite nanoparticles using coating of different core nanoparticles (silicion dioxide – SiO2 or barium hexaferrite - BaFe12O19) with thin layer of spinel ferrites was studied. The spinel layer was formed by a heterogeneous nucleation of the solid phase on the surfaces of the core nanoparticle during co-precipitation of the Fe3+/M2+ ions (M2+= Fe2+, Co2+). The stoichiometric ratio of Fe3+/Co2+ ions and an increased concentration of Co2+ ions were used for the synthesis of the composite nanoparticles with the cobalt ferrite layer.
With selected method we managed to synthesize the composite nanoparticles with the thin layer of spinel (maghemite and cobalt ferrite) on the SiO2 core nanoparticles, however the cobalt-ferrite layer didn’t have the stoichiometric composition. With synthesis of the composite nanoparticles, where we used barium-hexaferrite nanoparticles (diameter 5 − 70 nm) as the cores, a nonhomogeneous product was obtained. The synthesised product consisted of small composite nanoparticles (13 nm) where the precipitated ions reacted with the core nanoparticles resulting in new compound, and of the larger composite nanoparticles that had the spinel layer located on the basal planes of the hexaferrite platelet cores. When the cobalt-ferrite layer was coated onto the barium-hexaferrite nanoparticles, the product was similar than on the SiO2 core nanoparticles - a thin layer of cobalt ferrite had the nonstoichiometric composition.
With magnetic measurement we discovered, that saturated magnetization and remanence increased for the composite nanoparticles with maghemite layer compared to the hexaferrite core nanoparticles. For the composite nanoparticles with the cobalt-ferrite layer, the saturated magnetization and coercivity decreased compared to the hexaferrite cores
