  We present here the design of nano-inclusions made of properly arranged
collections of plasmonic metallic nano-particles that may exhibit a resonant
magnetic dipole collective response in the visible domain. When such inclusions
are embedded in a host medium, they may provide metamaterials with negative
effective permeability at optical frequencies. We also show how the same
inclusions may provide resonant electric dipole response and, when combining
the two effects at the same frequencies, lefthanded materials with both
negative effective permittivity and permeability may be synthesized in the
optical domain with potential applications for imaging and nano-optics
applications.
