Orientational order of self-assembled magnetic nanocrystals

The magnetization directions of self assembly of monodispersed magnetic nanocrystallites with different shapes have been revealed by a direct probe. The orientations of monodispersed maghemite nanocrystallites with spherical and cubic shapes, which are prepared through a drying process, are studied by means of magnetic Compton scattering. By utilizing this technique, a direct measurement of nanocrystallite orientation is possible, and we find that the shape of magnetic Compton profiles is different between spherical and cubic nanocrystallites. The preferential orientation of the spherical nanocrystallites is the [100] direction along the applied magnetic field, while for the cubic ones it is a mix of the [100], [110], and [111] directions. This result indicates that the shape of nanocrystallites is one of the important intrinsic factors that controls the assembly of nanocrystallites under a magnetic field.