Faraday-Rotation in Iron Garnet Films Beyond Elemental Substitutions

TL;DR

This paper reports a novel enhancement of the Faraday Effect in nanoscale iron garnet films, caused by symmetry-breaking at the air-surface interface, enabling potential applications in light control with monolayer magnetic garnets.

Contribution

It reveals a new mechanism for Faraday rotation enhancement in ultrathin films, independent of elemental substitution or optical resonance effects.

Findings

Seven-fold increase in Faraday rotation at 2 nm interface

Enhancement due to symmetry-breaking at the air-surface interface

Potential for monolayer magnetic garnets in optical devices

Abstract

In previous decades significant efforts have been devoted to increasing the magneto-optical efficiency of iron garnet materials for the miniaturization of nonreciprocal devices such as isolators and circulators. Elemental substitutions or proper nano-structuring to benefit from optical resonances have been pursued. However, all these approaches still require film thicknesses of at least several tens of microns to deliver useful device applications, and suffer from narrow bandwidths in the case of optical resonance effects. This Letter reports on a newly discovered enhancement of the Faraday Effect observed experimentally in nanoscale bismuth-substituted iron garnet films. It is shown here that this enhancement is not due to elemental substitution or compositional variations. Nor is it due to photon trapping or resonance effects. Comprehensive experimental and theoretical analysis of the Faraday rotation reveals a dramatic seven-fold amplification in the magneto-optic gyrotropy within only 2 nm of the air-surface interface, corresponding to just a couple of atomic monolayers as a result of symmetry-breaking at the air-film interface. This finding opens up an avenue to the application of monolayer magnetic garnets for the control of light.