Magnetic properties of MFe2O4 (M=Fe, Co, Ni) nanoparticles synthesized by high-temperature reaction

H R RECHENBERG; A D ARELARO; ENIO LIMA JR.; P K KIYOHARA; L M ROSSI

Dublin, Ireland

Simposio; JEMS 08 – IV Joint European Magnetic Symposia; 2008

MFe2O4 ferrites with the spinel structure are an important class of iron oxide materials, whcih in nanoparticle form (NPs), have long been of scientific and technological interest. The magnetic characateristic of ferrite NPs, such as the mean magnetic moment and the magnetic anisotropy, may be tuned by adjusting the chemical indetity of the ion M2+, grain size and morphology, as well as the surface chemistry. IN this study, MFe2O4 (M = Fe, Co, Ni) NPs were synthesized by high temperature decomposition of Fe(acac)3 and the corresponding M2+ compound in the presence of a long chain alcohol. The morphology was investigated by TEM and XRD. Nearly spherical and well crystaline NPs with narrow size distribution were found, with = 5-8 nm range. Magnetization characterization was carried out through M vs. H isotherms and ac susceptibility at different frequencies. Mössbauer spectra were collected at 4.2 K, in applied fields up to 12 T. All spectra could be fitted with two hyphefine sextets, corresponding to the A and B sites occupied by Fe in the spinel structure. Spin canting was observed in both sites. On the other hand, there was no evidence for a third component contribution arising from randomly oriented Fe spins near to the surface - such as has been observed - In accordance with core-shell model for more conventionally prepared ferrite NPs. This result suggests that a high crystallinity inhibits the appearence of surface spin disorder.