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Abstract All‐optical control and detection of magnetic states for high‐density recording necessitate nanophotonic approaches to amplify local light intensity below the diffraction limit. Sculpting the near‐field phase and polarization can additionally strengthen magneto‐optical effects that rely on circularly polarized pulses, such as all‐optical helicity‐dependent switching, imaging, and spin‐wave excitation. Here, high‐refractive‐index dielectric nanoantennas illuminated with circularly polarized light resonantly enhance local electric field rotation by more than sixfold within [Pt/Co]Nthin films. Sub‐wavelength arrays of amorphous Si nanodisks, or metasurfaces, patterned on perpendicularly magnetized films support Mie‐type resonances that modulate reflection and transmission dissymmetry by >±2% in experiments. Spatial and spectral interference between dipolar modes, proximity effects, and gain are evaluated by varying disk aspect ratio, metasurface–metal separation, and magnetic film thickness, respectively. Simulated enhancements in magnetic circular birefringence and differential absorption are correlated with amplified local field rotation at electric dipolar modes. Greater achievable amplifications are shown via simulations with single‐crystalline Si metasurfaces exhibiting lower losses, including a 12‐fold strengthened electric field rotation within ferromagnetic layers. The metasurface design rules established here could enable nanoscale localization of all‐optical magnetic switching with lowered laser fluence thresholds, as well as enhanced magneto‐optical responses for light‐assisted reading in spintronic devices.
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Optical response of finite-thickness ultrathin plasmonic films
We show that the optical response of ultrathin metallic films of finite lateral size and thickness can feature peculiar magneto-optical effects resulting from the spatial confinement of the electron motion. In particular, the frequency dependence of the magnetic permeability of the film exhibits a sharp resonance structure shifting to the red as the film aspect ratio increases. The films can also be negatively refractive in the IR frequency range under proper tuning. We show that these magneto-optical properties can be controlled by adjusting the film chemical composition, plasmonic material quality, the aspect ratio, and the surroundings of the film.
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- Award ID(s):
- 1830874
- PAR ID:
- 10476982
- Publisher / Repository:
- Materials Research Society
- Date Published:
- Journal Name:
- MRS Communications
- Volume:
- 8
- Issue:
- 3
- ISSN:
- 2159-6859
- Page Range / eLocation ID:
- 1092 to 1097
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1557/mrc.2018.153
