Magnetic-field-dependent assembly of silica-coated magnetite nanoclusters probed by Ultra-Small-Angle X-ray Scattering (USAXS)

• In situ analysis of Magnetically tunable colloidal nanocluster using Ultra Small Angle X-ray Scattering (USAXS) under uniform magnetic field.
• The colloidal super-lattice structure was analyzed in magnetic field along the direction parallel and perpendicular to scattering vector.
• Structure factors were extracted by subtracting form factor from the USAXS data using Irena software tool.
• The observed super-lattice structural spacing can be tuned by extent of the strength of external magnetic field.
• The structure factor calculations showed that the colloidal crystal has the hexagonal packing.

Colloidal suspension of the silica coated magnetic nanoclusters (MNCs) was used to study the magnetic field mediated assembly of magnetic nanoparticles. The spatial arrangement of these MNCs in colloidal suspension was studied using the ultra-small-angle X-ray scattering (USAXS) technique with magnetic field applied in directions orthogonal and parallel to the scattering vector. In situ magnetic field analysis of the USAXS scattering measurement showed anisotropic behavior that can be attributed to the formation of colloidal crystals. During magnetization, the clustered magnetic core induces a large dipole moment, and the thickness of the silica shell helps keep distance between the neighboring particles. The assembly of these hybrid nanostructured particles was found to be dependent on the strength and orientation of this external magnetic field. The dipolar chains formed of MNCs arranged themselves into colloidal crystals formed by two-dimensional magnetic sheets. The structure factor calculations suggested that the lattice parameters of these colloidal crystals can be tuned by changing the strength of the external magnetic field. These experiments shed light on the stimuli-responsive assembly of magnetic colloidal nanoparticles that leads to the creation of tunable photonic crystals.