Thickness dependent enhancement of the polar magneto-optic Kerr effect in Co magnetoplasmonic nanostructures

TL;DR

This study reveals that the magneto-optic Kerr effect in Co nanostructures is significantly enhanced by surface plasmons and strongly depends on film thickness, challenging the notion that Kerr effect is purely surface sensitive.

Contribution

It demonstrates a novel thickness dependence of the plasmon-enhanced Kerr effect in Co nanostructures, highlighting the importance of out-of-plane parameters in magnetoplasmonic devices.

Findings

Maximum Kerr rotation of -0.66 degrees at 100 nm thickness

Kerr effect enhancement extends beyond typical optical penetration depth

Out-of-plane geometrical parameters influence magneto-optical responses

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.