Abstract
Large surface plasmon polariton assisted enhancement of the magneto-optical activity has been observed in the past, through spectral measurements of the polar Kerr rotation in Co hexagonal antidot arrays. Here, we report a strong thickness dependence, which is unexpected given that the Kerr effect is considered a surface sensitive phenomena. The maximum Kerr rotation was found to be -0.66 degrees for a 100 nm thick sample. This thickness is far above the typical optical penetration depth of a continuous Co film, demonstrating that in the presence of plasmons the critical lengthscales are dramatically altered, and in this case extended. We therefore establish that the plasmon enhanced Kerr effect does not only depend on the in-plane structuring of the sample, but also on the out-of-plane geometrical parameters, which is an important consideration in magnetoplasmonic device design.
Highlights
Plasmonics allow for the confinement of light on length-scales smaller than the incident wavelength, leading to dramatic enhancements of the electric field within the confining material
We establish that the plasmon enhanced Kerr effect does depend on the in-plane structuring of the sample, and on the out-of-plane geometrical parameters, which is an important consideration in magnetoplasmonic device design
A similar feature is observed in the 20 nm continuous film, thereby suggesting it has no correspondence to the antidot array or any plasmonic origin
Summary
Plasmonics allow for the confinement of light on length-scales smaller than the incident wavelength, leading to dramatic enhancements of the electric field within the confining material. Scitation.org/journal/adv magnetic layer due to the SPP excitation at the Au/air interface is the strongest Since they were investigating a hybrid structure, whereby the SPP was excited at the Au interface, their study was limited to a maximum Co thickness of just 9 nm. It is interesting to consider the thickness dependence when working in reflection, which would not be subject to the same thickness limitations, as it is inherently a surface sensitive probe In this communication, we investigate the thickness dependence of the polar Kerr effect in reflection, for a series of Co antidot films with thicknesses in the range 20 - 100 nm. We reveal a strong dependence of the polar Kerr rotation on the magnetic layer thickness when the effect is coupled to resonant plasmonic excitations. The study is focused on Co films, with film thicknesses (t) smaller than the wavelength of the incident light (λ), but larger than the penetration depth (δ) of the bulk Co metal
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