Boosting optical nonreciprocity: surface reconstruction in iron garnets
Bi-substituted iron garnet films are extensively used in the fabrication of nonreciprocal devices in optical telecommunications. The miniaturization of these devices for on-chip integration requires the development of more efficient magneto-optic materials than presently available. Recent evidence has emerged of large nearsurface enhancements in the magneto-optic response in these materials. However, their operative mechanisms at the atomic and electronic levels are not as yet understood. We report significant differences in the ionic structure between surface and bulk in bismuth-substituted iron garnet materials. It is found that the unit cell is elongated normal to the surface, thus enlarging the separation between Fe3+ ions. These ions play a central role in the magneto-optic response of this material. A marked displacement of Fe ions creates gaps at the surface that are populated in the bulk. Concomitantly, surface- and bulksensitive measurements of spin-polarized 3d Fe3+ states show significant differences in the magnitude of L2 edge xray magnetic circular dichroism, as well as differences in L3 edge dichroism which in the presence of spin-orbit coupling in 3d states can be assigned to high-energy states. An increase in magnetic circular dichroism correlates with larger Faraday rotation. These findings provide a deeper understanding of the role of the surface in the electronic transitions to excited Fe3+ 3d states, responsible for these nonreciprocal phenomena. Together with the surface reconstruction underlying these effects reported here, they provide a useful tool for the further development of improved materials technologies to advance the integration of nonreciprocal devices in optical circuits.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF); Air Force Research Laboratory (AFRL)
- Grant/Contract Number:
- AC02-06CH11357; MRI 1429232; FA8650-17-C-5072
- OSTI ID:
- 1650221
- Alternate ID(s):
- OSTI ID: 1712696
- Journal Information:
- Optica, Journal Name: Optica Vol. 7 Journal Issue: 9; ISSN 2334-2536
- Publisher:
- Optical Society of AmericaCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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