High magneto-optical performance in metal-dielectric magnetoplasmonic nanodisks

Abstract

The term magnetoplasmon, or magnetoplasma surface wave, was first introduced in the early 70’s, motivated by a renovated interest in surface plasmons in metals and degenerate semiconductors. Nowadays, the phenomenology associated to systems where plasmonic and magneto-optical (MO) properties coexist has become an active area of investigation. These magnetoplasmonic systems have opened new routes for the development of e.g. high performance gas and biosensing platforms as well as the exploitation of non-reciprocal effects in devices with potential applications in the telecom area. In magnetoplasmonic structures, MO and plasmonic properties are intertwined, allowing for plasmonic properties to become tunable upon application of a magnetic field (active plasmonics), or the MO effects to be largely increased by plasmon resonance excitation, as a consequence of the enhancement of the electromagnetic (EM) field in the MO active component of the structure. In this last case, the study of the enhanced MO activity in structures with subwavelength dimensions is especially interesting since the properties of these systems upon plasmon resonance excitation bring as a consequence an enhanced EM field in its interior, and more interestingly in the region where the MO active component is present. Unfortunately, it is not straightforward to experimentally determine the intensity of the EM field inside a nanostructure. Here we show how the EM profile related to the localized surface plasmon resonance can be probed locally inside the nanostructure by measuring the MO activity of the system as a function of the position a MO active probe (a Co nanolayer). At this stage, optimizing the EM field distribution within the structure by maximizing it in the MO components region while simultaneously minimizing it in all the other, non MO active, lossy components, will allow for the development of novel systems with high MO activity and reduced losses, becoming an alternative to state of the art dielectric MO materials, like garnets. We will show how the insertion of a dielectric layer in Au/Co/Au magnetoplasmonic nanodisks induces an EM field redistribution in such a way to concentrate it in the regions of interest of the nanostructure. The metallo-dielectric system exhibits large MO activity and low optical extinction in a specific wavelength range (around 780 nm). It will be demonstrated this is due to a EM field redistribution at this wavelength, controlled by the insertion of the dielectric layer. If time permits we will also show some examples in which the MO effect is used to control the plasmon properties, such as magnetoplasmon interferometry.