  We theoretically investigate the creation of a magnetic moment in gold
nanoparticles by circularly polarized laser light. To this end, we describe the
collective electron dynamics in gold nanoparticles using a semiclassical
approach based on a quantum hydrodynamic model that incorporates the prin-
cipal quantum many-body and nonlocal effects, such as the electron spill-out,
the Hartree potential, and the exchange and correlation effects. We use a
variational approach to investigate the breathing and the dipole dynamics
induced by an external electric field. We show that gold nanoparticles can
build up a static magnetic moment through the interaction with a circularly
polarized laser field. We analyze that the responsible physical mechanism is a
plasmonic, orbital inverse Faraday effect, which can be understood from the
time-averaged electron current that contains currents rotating on the
nanoparticles surface. The computed laser-induced magnetic moments are
sizeable, of about 0.35 muB/atom for a laser intensity of 450 GW/cm2 at plasmon
resonance.
