Small angle x-ray and neutron scattering study of disordered and three dimensional-ordered magnetic protein arrays

The magnetic nanoparticles of Fe(3)O(4)-gamma-Fe(2)O(3) grown inside the cavity of globular proteins (apoferritin)-magnetoferritin proved to be a useful model system for studying the fundamental effects of magnetostatic interactions in nanoparticle assemblies. In this work the main focus is on structural characterization of such new nanocomposites by small angle x-ray scattering (SAXS) and small angle neutron scattering to evaluate interparticle separation (center to center) in two types of assemblies: three dimensional periodic arrays and disordered (amorphous) assemblies. Straightforward analysis of the face-centered cubic pattern of periodic arrays revealed that the interparticle spacing is 9.9 nm, whereas the SAXS pattern of disordered assembly reveals three correlation lengths, one of which is 10.5 nm and corresponds to the interparticle (center-to-center) nearest neighbor distance. The magnetic behaviors of the two systems are distinctly different. Given that the interparticle separation differs by only similar to 0.6 nm, the main structural factor contributing to the observed differences in magnetic properties is likely to be the array order. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3075865]