Band structure reconfiguration and surface
Faraday rotation in Bi-substituted iron garnets
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Posted on 2024-02-12 - 14:51
Bismuth-substituted lutetium iron garnets have exhibited a remarkable enhancement
in Faraday rotation (FR) for films thinner than 50 nm. A sevenfold amplification in the
magneto-optic gyrotropy was found to occur within 2 nm of the air-surface interface at 532 nm
wavelength. The present study delves into the underlying physical mechanisms contributing to
such amplification. Near-surface changes in band structure in these materials and their connection
to the magneto-optic response are explored. Density functional theory is employed to investigate
the changes in density of states and overall band structure reconfiguration of surface atoms. The
transition dipole matrix (TDM) model is then applied to both bulk and surface states, correctly
predicting a Faraday rotation enhancement at the surface as a result of overall surface band
structure reconfiguration and resulting bandgap reduction. Surface versus bulk FR spectral
response is extended beyond prior studies over the full visible and the near-infrared spectral
ranges, predicting significant amplification across the telecom band. Experimental analysis
through X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy reveal a reduction
in bandgap as films are thinned down from 200 nm to 40 nm. By providing a deeper physical
understanding of the origin of enhanced Faraday rotation at the surface, this work opens up
avenues for more efficient miniaturized Faraday rotation applications. Knowledge of the band
structure information thus uncovered may be used to demonstrate novel and more advanced
applications.
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Dash, Sushree; Odegard, Gregory; Levy, Miguel (2024). Band structure reconfiguration and surface
Faraday rotation in Bi-substituted iron garnets. Optica Publishing Group. Collection. https://doi.org/10.6084/m9.figshare.c.7059221.v2