Magneto‐Optical Metamaterials: Nonreciprocal Transmission and Faraday Effect Enhancement

Abstract

the effective medium regime, known for its tolerance to small-scale geometry variations. [9][10][11][12][13] We present comprehensive theoretical, experimental, and numerical analysis of the electromagnetic properties of the magneto-optical metamaterial, demonstrating both the rotation of the polarization plane and nonreciprocal transmission, two phenomena that can be controlled by the direction of the external magnetic field. This enhanced response is the result of the combination of the introduced magneto-optical properties and strong anisotropy of the metamaterial. We demonstrate rotation of the polarization plane with the effective Verdet constant equivalent of at least 10 5 rad m −1 T −1 , significant enhancement with respect to bulk ferromagnetic materials, [14] suggesting that nanostructured magnetic materials have much stronger magneto-optical response than their bulk counterparts. Overall, plasmonic magneto-optical nanorods combine the benefits of sub-wavelength light manipulation offered by metamaterials and of strong magneto-optics offered by plasmonic nanocomposites, leading to a promising material platform for integrated nanophotonic applications.The magneto-optical metamaterial geometry and its optical response are illustrated in Figure 1. The composite is formed by an array of aligned plasmonic (gold) nanorods with magnetooptical (nickel) shells inside a dielectric (alumina) matrix (note that in the composites the Ni shells extend only part-way along the rod; see the Experimental Section). As follows from the geometry, in the absence of an external static magnetic field and in the limit when the unit cell is much smaller than the wavelength (a << λ 0 ), the optical response of the composite can be described by a diagonal permittivity tensor with Cartesian components = ⊥ ⊥ zẑ { , , }     . Effective medium theory can be used to relate the components of the effective permittivity  ⊥ and  zz to the permittivity of the constituent materials as well as to the geometrical parameters of a metamaterial, such as a unit cell a, and radii of the rod r 1 and of the shells around the rod r i , with i = 2, …, N. Existing analytical and numerical tools allow calculations of the optical response of metamaterials composed of rods without shells, with plasmonic and magneto-optical material constituents and in the limit r 1 << a, [1,11,13,15] as well as shelled nanorod composites, comprising nonmagneto-optical materials with arbitrary rod concentration. [12,16] Here, we present a formalism that can incorporate magneto-optical response in the effective-medium description of shelled rod metamaterials and even in the limit  r a i 2 . We consider a metamaterial with a = 64 nm, r 1 = 15 nm, and r 2 = 23 nm and assume that the Magneto-optical effects are at the heart of modern technologies providing opportunities for polarization control in laser physics and optical communications, metrology, and in high-density data storage. Here a new type of a hyperbolic magneto-optical metamaterial based on Au-Ni nanorod arrays ...

Nitride‐Oxide‐Metal Heterostructure with Self‐Assembled Core–Shell Nanopillar Arrays: Effect of Ordering on Magneto‐Optical Properties

“…[ 18 ] Taking advantage of lithographic patterning, hybrid nanostructures such as stacked nanodisks or core–shell nanoparticles can be produced at relatively large scale. [ 18,19 ] Using porous alumina templates to coat pure or core–shell nanowires [ 20–24 ] enables interesting vertical coupling scheme, which realizes enhanced and tunable MO activity despite the fact that the alumina template material is fragile and limited for integration. [ 25 ]…”

Fiber Optic Sensors Based on the Faraday Effect

“…Gigantic FR has been reported for thin films [ 187 , 188 , 189 , 190 ], magneto-optical photonic crystals [ 20 , 191 , 192 , 193 ] and ferrofluids [ 22 , 194 , 195 , 196 , 197 ]. A few exotic structures possessing or mimicing FR have been reported [ 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 , 206 , 207 , 208 , 209 ]. A Verdet constant three orders of magnitude higher than one of CMT has been achieved [ 189 ].…”

Fluctuational Electrodynamics in Atomic and Macroscopic Systems: van der Waals Interactions and Radiative Heat Transfer

“…Treating inherently nonreciprocal materials like topological insulators [99][100][101][102] (which could break reciprocity in the presence of an applied magnetic field) or other intrinsic nonreciprocal magneto-optic media [103,104] would require an extension of this formalism beyond the scope of this paper, but metamaterials that exhibit emergent nonreciprocal magneto-optic responses in an effective medium framework [105,106] can be treated using our framework if the underlying materials obey reciprocity. As these definitions are common in continuum EM theory but may be less familiar in the context of quantum chemistry, we point out three items of note.…”