Cavity-enhanced near-field optical magnetometry

Abstract

We present the first near-field scanning optical magneto-optic Kerr effect (MOKE) of sub-micron magnetic structures, where a Kerr rotation of 0.11º from a 0.25µm nickel magnet was observed. This is enabled by a cavity based technique to enhance the Kerr rotation of light reflected from a magnetized surface. Spatially resolved magneto-optic measurements are performed involving both conventional microscopy and near-field scanning optical microscopy (NSOM). Cavity enhancement is achieved with either a single dielectric coating or a dielectric-metal bilayer coating applied to the ferromagnetic structure of interest. We present a scattering matrix approach to calculating the enhancement resulting from a multilayer dielectric coating and show good agreement with experiment. This demonstrates a non-invasive optical technique for magnetometry with ultrahigh spatial resolution.