Plasmon-induced 0.13 T optomagnetic field in a gold coaxial nanoaperture

We theoretically investigate a resonant inverse Faraday effect within individual coaxial nanoapertures. Upon illumination with circularly polarized light, resonant gold coaxes are shown to develop an optomagnetic field that is controllable by the helicity of the light. This magnetic field is found to reach 0.13 T upon excitation at an intensity of 0.5 · 1011W.cm−2 that is typical from sub-ps light pulses. At an intensity of 2.4 · 108W.cm−2 (consistent with the CW regime), we obtain a static magnetic field of about 1 mT, leading to a helicity-dependent magnetic force of 4.5 · 106 N onto a point-like magnetic dipole of unit moment. Given their submicron footprint, individual coaxial nanoapertures open new prospects towards ultrafast and polarization-controlled tunable magnetism on the nanoscale, thus potentially impacting a large panel of application and techniques including all optical magnetization switching, spin-wave excitation and optomagnetic tweezing of nano-objects.