Magnetically Reconfigurable Toroidal Metasurfaces

• Published in: Advanced optical materials 2024-05, Vol.12 (13), p.n/a
• Main Authors: Acharyya, Nityananda, Mallick, Soumyajyoti, Rane, Shreeya, Upadhyay Kahaly, Mousumi, Roy Chowdhury, Dibakar
• Format: Article
• Language: English
• Subjects: Dipoles; Electromagnetic radiation; Electron spin; Electrons; Ferromagnetism; Magnetic fields; magnetotransport; metasurface; Metasurfaces; Multilayers; terahertz; Terahertz frequencies; Thin films; time domain spectroscopy; toroidal resonance; Transport phenomena
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202303045

Harnessing electron spin within limited dimensions under applied magnetic fields can lead to spin‐assisted tunable light‐matter interactions, which form a crucial step in developing frequency‐agile opto‐spintronic structures toward next generation photonic devices. For this purpose, spin‐dependent magneto transport phenomena derived from ferromagnetic (FM)/nonmagnetic (NM) multilayer structures have recently emerged as a useful tool for dynamically tailoring electromagnetic waves. With this pretext, five layers of aluminum (Al)/nickel (Ni) based multilayer thin films in sub skin depth regime are studied in terahertz domain under low‐intensity (0 to 30 mT) magnetic fields while systematically varying the NM spacer layer (sandwiched between the FM layers) from 8 to 18 nm. Such thin multi‐layer films demonstrate conductivity variations up to ≈40% for 30 mT of applied field. Utilizing the same multilayer configurations, magnetic field induced tunability in a metasurface design is investigated that simultaneously manifests toroidal, dipolar, and other higher‐order modes. Further, multipolar analysis reveals that the nonradiative toroidal and radiative dipole modes can be enhanced by almost 56% and 183%, respectively, under 0–30 mT magnetic fields. Such magnetic field‐induced simultaneous control over radiative and non‐radiative resonances can be pivotal for next generation terahertz magnetophotonic devices. Al/Ni based multilayer metasurfaces are studied under 0–30 mT of applied magnetic fields in order to demonstrate spin‐valve effect induced toroidal resonances. In this study, multipolar analysis reveals that the toroidal and dipole modes can be enhanced by almost 56% and 183%, respectively, with 30 mT of magnetic field. This work can pave pathways toward the development of advanced meta devices that relies on the spin dependent magnetotransport phenomena.