We have nanofabricated a medium with strong magnetic response at visible-light frequencies, including a band with negative m. A medium is made of electromagnetically coupled pairs of gold dots with geometry and symmetry carefully designed at nanometre level. The 600-700Thz magnetic response arises due to the excitation of an antisymmetric plasmon resonance.

The high-frequency permeability qualitatively reveals itself in a novel effect of optical impedance matching. Our approach shows for the first time the feasibility of magnetism at visible frequencies and paves a way towards magnetic and left-handed components for visible optics.