Plasmon-Induced Magneto-Optical Activity in Nanosized Gold Disks

In this Letter we show that nanostructures made out of pure noble metals can exhibit measurable magneto-optic activity at low magnetic fields. This phenomenon occurs when the localized surface plasmon resonance of the nanostructure is excited in the presence of a static magnetic field parallel to the propagation of incident light. The large magneto-optical response observed comes from an increase of the magnetic Lorentz force induced by the large collective movement of the conduction electrons in the nanostructures when the resonance is excited.

Figure 1

(a) Schematic of the MO effect induced by the Lorentz force in a metal nanoparticle. (b) Magneto-optic Kerr polar experimental configuration. (c) SEM images of the gold nanodisk arrays.

Figure 2

Experimental optical and magneto-optical effects in Au nanodisk arrays: (a) optical extinction, (b) Kerr rotation, and (c) ellipticity of nanodisk arrays with aspect ratios (AR) 2.2 ($D=70$, $h=32$) (squares) and 6 ($D=120$, $h=20$) (circles). The inset in (b) represents the Kerr rotation variation as a function of the magnetic field for the Au nanodisks with aspect ratio 2.2.

Figure 3

Theoretical Kerr rotation (top panel) and ellipticity (bottom panel) in gold nanoparticles and films. Comparison of the Maxwell-Garnett (MG) model for arrays of randomly distributed nanoparticles [dark gray (red) lines and black lines), the scattering matrix (SM) model for ordered arrays of nanoparticles (symbols), and the MO effects of a continuous 20 nm Au film [light gray (green) line].