Polarization Analyzed Small Angle Neutron Scattering Of Ferrite Nanoparticles

Ferromagnetic nanoparticles offer a range of possible applications in nanotechnology, biomedical practices, and data storage, but important issues exist regarding their true magnetic structure. We have been investigating 9 nm diameter Fe3 O4 nanoparticles and 11 nm diameter CoFe2 O4 nanoparticles coated with an oleic acid shell. The nanoparticles were synthesized by solution chemistry methods and characterized by X-ray diffraction, SQUID, and vibrating sample magnetometry. Polarization Analyzed Small Angle Neutron Scattering (PASANS) was used under various temperatures and applied magnetic fields to investigate the magnetic structure of the particles. PASANS has revealed the iron oxide particles have a canted magnetic shell in high field that disappears in lower field, while the cobalt iron oxide particles are fully canted. We have developed an energy-based model to explain the origins of this canting and shell formation that agrees with the experimental results.