Mie Magnetic\nStructural Colors from Short Chains of\nTiO<sub>2</sub> Nanospheres

We demonstrate distinctive structural colors within a\nsmall footprint\nby using a short chain of nanospheres. Rather than using high-index\nmaterials like Si (<i>n</i> ∼ 4), which ensure strong\nmodal confinement, TiO<sub>2</sub> is employed. TiO<sub>2</sub> has\nan intermediate index (<i>n</i> ∼ 2), promoting stronger\nmodal coupling between the magnetic dipoles of each particle. This\napproach enables selective engineering of the magnetic response and\nyields larger spectral changes compared to that of Si. Despite the\nlower refractive index, the absence of absorption in TiO<sub>2</sub> also produces higher scattering intensities than Si. We develop\na quasistatic analytical model that describes the dipolar modal coupling\nin a trimer and use it to reveal distinct magnetic field strengths\nin the outer or central particle depending on the polarization of\nincident light. These results suggest pathways to manipulate the magnetic\nfield in chains of particles and create vibrant structural colors\nwith simple configurations.