  The magnetic-field-induced assembly of magnetic nanoparticles (NPs) provides
a unique and flexible strategy in the design and the fabrication of functional
nanostructures and devices. We have investigated the field-driven self-assembly
of core-shell magnetite NPs dispersed in toluene by means of in situ small
angle neutron scattering (SANS). The form factor of the core-shell NPs was
characterized and analyzed using SANS with polarized neutrons. Large-scale
aggregation of magnetite NPs has formed above 0.02 T as indicated by very-small
angle neutron scattering measurements. Three-dimensional long-range ordered
superlattice of magnetite NPs was revealed under the application of moderate
magnetic field. The crystal structure of the superlattice has been identified
as a face-centered cubic one.
