Tellegen particles and magnetoelectric metamaterials

In 1948 Tellegen [Philips Res. Rep. 3, 81 (1948)] suggested that an assembly of the lined up electric-magnetic dipole twins can construct a new type of an electromagnetic material. Until now, however, the problem of creation of the Tellegen medium is a subject of strong discussions. An elementary symmetry analysis makes questionable an idea of a simple combination of two (electric and magnetic) dipoles to realize local materials with the Tellegen particles as structural elements. In this paper we show that in search of sources with local junctions of the electrical and magnetic properties one cannot rely on the induced parameters of small electromagnetic scatterers. No near-field electromagnetic structures and no classical motion equations for point charges give a physical basis for realization of sources with a local junction of the electrical and magnetic properties. We advance a hypothesis that local magnetoelectric (ME) particles should be physical objects with eigenmode oscillation spectra and nonclassical symmetry breaking effects. Our studies convincingly prove this assumption. We show that a quasi-two-dimensional ferrite disk with magnetic-dipolar-mode oscillations is characterized by unique symmetry features with topological phases resulting in appearance of the ME properties. An entire ferrite disk can be characterized as a combined system with the eigenelectric and eigenmagnetic moments. The fields near such a particle are distinguished by special symmetry properties. The questions raised in this paper give new insights into a problem of realization of local ME composites.