Plasmonic structures enable sensing with optical readout, thanks to their environmental sensitivity and their strong interaction with light. When they display optical chirality, such structures become appealing for the detection of small concentrations of chiral molecules. Furthermore, a modulation of their optical chirality during a sensing experiment might allow lowering the limit of detection. In this context, chiral plasmonic structures, including magneto-optic building blocks, are interesting candidates because their optical chirality can be modulated in a contactless way by an external magnetic field. A convenient means for monitoring such modulation relies on measuring the circular dichroism of the structures. However, this dichroism results from several contributions (intrinsic optical chirality, magneto-optic modulation, and anisotropy) and separating them is a challenging task. In this paper, the authors establish a method for extracting by simple measurements the contributions of the intrinsic optical chirality and of the magneto-optic modulation in Au split ring/ring—Au/Co cylinder nanostructures. Upon suitable nanostructure design, including a multilayer configuration for the cylinders, a 25% modulation of the optical chirality is reported at visible frequencies using a small magnetic coil.

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