Cationic distribution and spin canting in CoFe2O4 nanoparticles

CoFe2O4 nanoparticles ( ∼ 6 nm), prepared by a thermal decomposition technique, have been investigated through the combined use of dc magnetization measurements, neutron diffraction, and 57Fe Moessbauer spectrometry under high applied magnetic field. Despite the small particle size, the value of saturation magnetization at 300 K (Ms ≅ 70 A m2 kg-1) and at 5 K (Ms ≅ 100 A m2 kg-1) are rather close to the bulk values, making the samples prepared with this method attractive for biomedical applications. Neutron diffraction measurements indicate the typical ferrimagnetic structure of the ferrites, showing an inversion degree (γNPD = 0.74) that is in very good agreement with cationic distribution established from low temperature (10 K) Moessbauer measurements in high magnetic field (γmoss = 0.76). In addition, the in-field Moessbauer spectrum shows the presence of a non-collinear spin structure in both A and B sublattices. The results allow us to explain the high value of saturation magnetization and provide a better insight into the complex interplay between cationic distribution and magnetic disorder in ferrimagnetic nanoparticles. (paper)