Ultra-Low-Intensity Magneto-Optical and Mechanical Effects in Metal Nanocolloids

Magneto-plasmonics is a designation generally associated with ferromagnetic-plasmonic materials since such optical responses from non-magnetic materials alone are considered weak. Here, we theoretically analyse, numerically investigate, and experimentally show that there exists a magneto-optical switching behaviour in noble-metal nanocolloids. The response is observable at ultra-low illumination intensities <1 W/cm$^2$ with DC magnetic fields <1 mT. Polarization-dependent nonzero time-averaged plasmonic loops and vortex power flows subsequently produce significant torque on nanoparticles and nanoclusters via dipole-dipole interactions. This work provides a new framework for the dynamical interaction between light polarization, nano-surfaces and material magnetization.