| We investigated deviations of magnetic nanoparticle behavior from the ideal, non-interacting behavior in the superferromagnetic regime. These deviations can be understood in greater detail by considering the magnetic components oriented orthogonally to the applied magnetic field. We demonstrated the novel measurement of the transverse magnetization of 7 nm iron oxide crystals and showed that it agrees qualitatively with the deviations between proposed interaction models and our experimental, longitudinal magnetization curves. Using polarization analyzed small angle neutron scattering (PASANS), we demonstrated the ability to probe the 3D magnetic structure in a sample of 9 nm iron oxide nanoparticle crystals, and discovered a 1.0 to 1.5 nm thick shell with the spins coherently oriented perpendicular to a 7 nm core aligned with the applied field, between temperatures of 160 K and 320 K under a nominally saturating 1.2 T field. Finally, we developed a novel synthesis for of highly monodisperse, 30 nm diameter MnO nanoparticles. These were oxidized to create an Mn3O4 shell of controllable thickness. We found the exchange bias parameters in this MnO/Mn3O4 core/shell system to be significantly lower than those commonly reported for the same system. We believe the anomalous literature values to be due to spin-glass like behavior and/or thermal training resulting from the use of poorly crystalline, or polycrystalline particles. |
