Magnetically responsive photonic film with high tunability and stability

We demonstrate the fabrication of magnetically assembled one-dimensional chain-like photonic nanostructures with significantly high photonic stability. The key lies in the use of agarose hydrogel to prevent the magnetic assemblies from coagulation. When exposed to an external magnetic field, negatively charged Fe3O4@SiO2 particles can effectively assemble in the hydrogel matrix into onedimensional chains with internal periodicity and display a fast, fully reversible, and tunable photonic response to the changes in the external field. The steric hindrance and the hydrogen bonding from the agarose network effectively limit the migration of the Fe3O4@SiO2 particles and their chain-like assemblies. As a result, the system shows remarkable stability in photonic response under external magnetic fields of large gradients, which has been a challenge previously. The ability of stabilizing the magnetic particle assemblies over a long period represents a major stride toward practical applications of such field-responsive photonic materials.