Tuning the Colloidal Crystal Structure of Magnetic Particles by External Field

Manipulation of the self‐assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X‐ray scattering technique we have investigated the different crystal structures exhibited by self‐assembly of core–shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close‐packed (RHCP) one. External field drives the self‐assembly toward a body‐centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles. An external magnetic field stimulates core–shell magnetite/silica nanoparticles to self‐assemble to a body‐centered tetragonal crystalline structure. In the absence of magnetic field, the self‐organization is governed by the hard‐sphere repulsion between the particles and a combination of electrostatic repulsion and van der Waals attraction, leading to the formation of a random hexagonal close‐packed structure.