Towards isotropic negative magnetics in the visible range
  The idea of isotropic resonant magnetism in the visible range of frequencies known from precedent publications is developed having in mind achievements of the modern chemistry. Plasmonic colloidal nanoparticles covering a silica core form a cluster with resonant and isotropic magnetic response. Two approximate models giving the qualitative mutual agreement are used to evaluate the magnetic polarizability of the cluster. It is shown that the electrostatic interaction of nanocolloids decreases the resonant frequency of an individual complex magnetic scatterer (nanocluster) compared to the previously studied variant of a planar circular nanocluster with same size. This means the reduction of the optical size of nanoclusters that presumably allows one to avoid strong spatial dispersion within the frequency range of the negative permeability. 
C.R. Simovski, S.A. Tretyakov