Magnetization mechanism in high-energy ball-milled (NiZnFe2O4)/(SiO2) composites

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

San Nicolás, Buenos Aires

Congreso; Congreso SAM/CONAMET 2007; 2007

Universidad Tecnológica Nacional, Facultad Regional San Nicolás.

Magnetic composites Ni0.5 Zn0.5 Fe2O4 /SiO2 were obtained by high energy ball milling precursor oxides at room temperature for 200 h. Some specimens were further isothermally annealed for 1 h at 1273 K, under air and Argon atmosphere, respectively. After 200 h grinding, small hematite crystals mixed with SiO2, NiO and ZnO particles are found together with very small NiZn ferrite clusters, with a mean size of about 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 near about 20 nm. For treatments in air, the major phases are SiO2 and NiZn ferrite, while for annealing in Ar a new paramagnetic phase appears, identified as fayalite. The M-H loops may all be described by the sum of a ferromagnetic and a superparamagnetic-like contribution. Relatively broad effective blocking temperature distributions are found in all the specimens and coherent rotation is confirmed as the magnetization inversion mechanism operating in the annealed specimens.