  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.
