Structural Colors from Mie Magnetic Dipoles Engineered with Short Chains of TiO2 Nanoparticles

We demonstrate notable structural color variations from a basic and compact configuration made from a chain of one, two, or three nanoparticles. Instead of relying on high-index materials like Si for strong modal confinement, we utilize TiO₂, which has an intermediate refractive index, to enhance modal coupling between the magnetic dipoles of each particle. This approach allows for selective engineering of the magnetic response, resulting in larger spectral changes compared to those with Si. Despite its lower refractive index, TiO₂ leads to higher scattering intensities than Si. We develop a quasistatic analytical model to describe dipolar modal coupling in a trimer and use it to uncover distinct magnetic field strengths in the outer or central particle based on the polarization of incident light. These results highlight new methods to control the magnetic field in particle chains and create vibrant structural colors with simple configurations.