Magnetic interactions in high-energy ball-milled NiZnFe2O4/SiO2 composites

G. POZO LÓPEZ; S.P. SILVETTI; S.E. URRETA; E.D. CABANILLAS

Buenos Aires

Congreso; At the Frontiers of Condensed Matter III: New Trends in Structural, Electronic and Magnetic Properties of Matter; 2006

Centro Atómico Constituyentes - Comisión Nacional de Energía Atómica

Composites Ni0:5Zn0:5Fe2O4=SiO2 are obtained after high-energy ball milling precursor oxides, in stoichiometric proportions, for 200 h at room temperature and further isothermal annealing for 1 h at 1273 K, under air and argon atmosphere, respectively. After 200 h grinding, a complex microstructure develops with small hematite crystals mixed with SiO2 and remanent NiO and ZnO particles, and very small NiZn ferrite clusters, reaching a mean size of 9 nm. The high temperature treatments remove the hematite grains from the powder and promote the growth of NiZn ferrite grains to reach mean sizes nearly 20 nm. For treatments in oxidizing atmospheres, the major phases are SiO2 and NiZn ferrite, while for annealing in Ar a new phase appears, fayalite, which is paramagnetic at room temperature. The M–H loops are all well described by the sum of a ferromagnetic and a superparamagnetic-like contribution. The observed properties are interpreted considering the different magnetic phases obtained, their crystal sizes and their mutual interactions.