Ion dependence of magnetic anisotropy in MFe2O4 (MFe, Co, Mn) nanoparticles synthesized by high-temperature reaction

The influence of different M2+ cations on the effective magnetic anisotropy of systems composed of MFe2O4 (M=Fe, Co and Mn) nanoparticles was investigated. Samples were prepared by the high-temperature (538 K) solution phase reaction of Fe (acac)3, Co (acac)2 and Mn (acac)2 with 1,2 octanodiol in the presence of oleic acid and oleylamine. The final particles are coated by an organic layer of oleic acid that prevents agglomeration. Transmission electron microscopy (TEM) images show that particles present near spherical form and a narrow grain size distribution, with mean diameters in the range of 4.5–7.6 nm. Powder samples were analyzed by ac susceptibility and Mössbauer measurements, and Keff for all samples was evaluated using both techniques, showing a strong dependence on the nature of the divalent cation.