  We study the magneto-optical response of noble metal nanoparticle clusters.
We consider the interaction between the light-induced dipoles of particles. In
the presence of a magnetic field, the simplest achiral cluster, a dimer,
exhibits circular dichroism (CD). The CD of a dimer depends on the directions
of the magnetic field and the light wave vector. The CD of a populous cluster
weakly depends on the magnetic field. Upon scattering from the cluster, an
incident linearly polarized light with polarization azimuth $\varphi$, becomes
elliptically polarized. The polarization azimuth rotation and ellipticity angle
variation are sinusoidal functions of $2 \varphi$. The anisotropy and the
chirality of the cluster control the amplitude and offset of these sinusoidal
functions. The Faraday rotation and Faraday ellipticity are also sinusoidal
functions of $2 \varphi$. Near the surface plasmon frequency, Faraday rotation
and Faraday ellipticity increase.
