Clausius–Mossotti relation revisited: Media with electric and magnetic response

A reexamination of the Clausius–Mossotti relation in which material with both electric and magnetic responses yields surprising results. Materials with indices near zero and with real parts less than zero, that is the real part of both the permeability and permittivity are negative, are found to emerge from the interaction of electric and magnetic responses in a self-consistent theory. The new results point the way to artificial and natural materials with exotic responses. A simulation with ∼10¹⁰ particles shows good agreement with the analytical results.