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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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All‐Optical Helicity‐Dependent Switching in Hybrid Metal–Ferromagnet Thin Films
Abstract Over the past decades, optical manipulation of magnetization by ultrafast laser pulses has attracted extensive interest. It not only shows intriguing fundamental science arising from the interactions between spins, electrons, phonons, and photons, but also manifests the potential to process and store data at a speed that is three orders of magnitude faster than the current technologies. In this paper, all‐optical helicity‐dependent switching (AO‐HDS) in hybrid metal–ferromagnet thin films, which consist of Co/Pt multilayers with perpendicular magnetic anisotropy and an Au film capping layer on the top, is experimentally demonstrated. The switching behaviors of the hybrid Co/Pt–Au material, with various laser repetition rates, scanning speeds, and fluencies, are systematically studied. In comparison with bare Co/Pt multilayers, the hybrid metal–ferromagnet thin films show pronounced AO‐HDS when the number of laser pulses per μm along the scanning direction gradually increases. In addition, the AO‐HDS effect is very robust against laser fluences. A possible mechanism is further proposed based on numerical simulations of the optomagnetic coupling model. These findings promise a new material system that exhibits stable AO‐HDS phenomena, and hence can transform future magnetic storage devices, especially with the addition of plasmonic nanostructures made of noble metals.
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- PAR ID:
- 10457606
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 8
- Issue:
- 13
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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