We study the interaction of electromagnetic waves with a cluster composed of gyromagnetic and dielectric spheres. We expand the electromagnetic fields in terms of the vector multipole fields and relate the expansion of the scattered field to that of the incident field. We apply this generalized multisphere Mie theory to dimers and hexamers containing one dielectric sphere and similar gyromagnetic spheres. We observe multiple Fano resonances in the extinction, circular extinction, and optical activity spectra of the oligomers. Fano resonances can be engineered by adjusting the geometrical and structural parameters of the system. More importantly, Fano resonances can be dynamically tuned by an external magnetic field. A Fano resonance frequency shift as large as 0.5–1 GHz for a magnetic field increase of $200\mathrm{G}$ is achievable.

• Received 13 August 2019
• Revised 5 February 2020
• Accepted 11 February 2020

DOI:https://doi.org/10.1103/PhysRevB.101.064426