Enhanced MOKE Via Tunable Plasmon Resonance Field in the Otto Configuration

Here, we demonstrate the enhancement of the transverse magneto-optical Kerr effect (TMOKE) signal, due to surface plasmon resonance in the Otto configuration, where the low index dielectric has a variable thickness. This constitutes a demonstration that, in principle, a separation of the magnetic sample from the plasmonic device and the modulation of the plasmon resonance with an enhancement of the MOKE signal is possible. We have achieved this by using air as a low index dielectric where the evanescent wave extends, preceding to excitation of surface plasmons. The magnetic sample under consideration is a thin layer of cobalt coated by an ultrathin silver layer, on a silicon substrate (Ag/Co/Si). The sample is brought close enough to the prism/air interface, allowing surface plasmon excitation in the air/Ag interface. This leads to an increase of the TMOKE signal up to ~ 2 ‰ with respect to the incident light. This is about 7 times the traditional MOKE signal in the absence of plasmons. This is comparable with previous works using the Kretschmann-Raether configuration. Furthermore, the fact that the plasmon field generated at the metal-air interface substitutes the laser light used in traditional MOKE allows new functionalities such as controlling the penetration depth of the plasmonic field into the sample. This should find applications in magnetometry and related technology.