Magnetic Circular Dichroism Study on Dual Plasmonic Au@CuS Core–Shell Nanoparticles: Effects of Shell Thickness and Uniformity

Dual plasmonic metal–semiconductor hybrids exhibit multifunctionalities for broad photophysical and photochemical applications. In this study, we focus on the magneto-optical (MO) properties of Au@CuS core–shell nanoparticles examined by magnetic circular dichroism (MCD) spectroscopy. The core–shell nanoparticles are prepared by a seeded growth protocol. The MCD response in the CuS (covellite) spectral region [= near-IR (NIR) region] has an inverted sign with respect to that of Au, demonstrating that the charge carriers inducing the surface plasmon behavior are different between CuS (p-type) and Au (n-type). The hole effective mass of covellite CuS is estimated on the basis of the cyclotron-derived MCD signal analysis. The MO activity, defined here as the maximum MCD amplitude normalized to extinction, is significantly damped when the shell is thin and nonuniform. Thicker and more uniform shell formation leads to the MO activity increase in the NIR region, but it is overall smaller than that of pure CuS nanoparticles, suggesting the existence of magnetoplasmonic coupling between the Au and CuS counterparts. We then believe our work will put forward developments toward the realization of flexible controllability of MO responses in dual plasmonic nanostructures.