  Magnetic metamaterials consist of magnetic resonators smaller in size than
their excitation wavelengths. Their unique electromagnetic properties were
characterized by the effective media theory at the early stage. However, the
effective media model does not take into account the interactions between
magnetic elements; thus, the effective properties of bulk metamaterials are the
result of the "averaged effect" of many uncoupled resonators. In recent years,
it has been shown that the interaction between magnetic resonators could lead
to some novel phenomena and interesting applications that do not exist in
conventional uncoupled metamaterials. In this paper, we will give a review of
recent developments in magnetic plasmonics arising from the coupling effect in
metamaterials. For the system composed of several identical magnetic
resonators, the coupling between these units produces multiple discrete
resonance modes due to hybridization. In the case of a system comprising an
infinite number of magnetic elements, these multiple discrete resonances can be
extended to form a continuous frequency band by strong coupling. This kind of
broadband and tunable magnetic metamaterial may have interesting applications.
Many novel metamaterials and nanophotonic devices could be developed from
coupled resonator systems in the future.
