Electromechanically reconfigurable terahertz stereo metasurfaces

Advanced Materials Wiley (2024) 2402069

Authors:

Saurav Prakash, Prakash Pitchappa, Piyush Agrawal, Hariom Jani, Yunshan Zhao, Abhishek Kumar, John Thong, Jian Linke, Ariando Ariando, Ranjan Singh, Thirumalai Venkatesan

Abstract:

Dynamic terahertz devices are vital for the next generation of wireless communication, sensing, and non-destructive imaging technologies. Metasurfaces have emerged as a paradigm-shifting platform, offering varied functionalities, miniaturization, and simplified fabrication compared to their 3D counterparts. However, the presence of in-plane mirror symmetry and reduced degree of freedom impose fundamental limitations on achieving advanced chiral response, beamforming, and reconfiguration capabilities. In this work, a platform composed of electrically actuated resonators that can be colossally reconfigured between planar and 3D geometries is demonstrated. To illustrate the platform, metadevices with 3D Split Ring Resonators are fabricated, wherein two counteracting driving forces are combined: i) folding induced by stress mismatch, which enables non-volatile state design and ii) unfolding triggered by the strain associated with insulator-to-metal transition in VO2, which facilitates volatile structural reconfiguration. This large structural reconfiguration space allows for resonance mode switching, widely tunable magnetic and electric polarizabilities, and increased frequency agility. Moreover, the unique properties of VO2, such as the hysteretic nature of its phase transition is harnessed to demonstrate a multi-state memory. Therefore, these VO2 integrated metadevices are highly attractive for the realization of 6G communication devices such as reconfigurable intelligent surfaces, holographic beam formers, and spatial light modulators.

Spatially reconfigurable antiferromagnetic states in topologically rich free-standing nanomembranes

Nature Materials Nature Research 23:5 (2024) 619-626

Authors:

Hariom Jani, Jack Harrison, Sonu Hooda, Saurav Prakash, Proloy Nandi, Junxiong Hu, Zhiyang Zeng, Jheng-Cyuan Lin, Charles Godfrey, Ganesh ji Omar, Tim A Butcher, Jörg Raabe, Simone Finizio, Aaron Voon-Yew Thean, A Ariando, Paolo G Radaelli

Abstract:

Antiferromagnets hosting real-space topological textures are promising platforms to model fundamental ultrafast phenomena and explore spintronics. However, they have only been epitaxially fabricated on specific symmetry-matched substrates, thereby preserving their intrinsic magneto-crystalline order. This curtails their integration with dissimilar supports, restricting the scope of fundamental and applied investigations. Here we circumvent this limitation by designing detachable crystalline antiferromagnetic nanomembranes of α-Fe2O3. First, we show—via transmission-based antiferromagnetic vector mapping—that flat nanomembranes host a spin-reorientation transition and rich topological phenomenology. Second, we exploit their extreme flexibility to demonstrate the reconfiguration of antiferromagnetic states across three-dimensional membrane folds resulting from flexure-induced strains. Finally, we combine these developments using a controlled manipulator to realize the strain-driven non-thermal generation of topological textures at room temperature. The integration of such free-standing antiferromagnetic layers with flat/curved nanostructures could enable spin texture designs via magnetoelastic/geometric effects in the quasi-static and dynamical regimes, opening new explorations into curvilinear antiferromagnetism and unconventional computing.

Holographic imaging of antiferromagnetic domains with in-situ magnetic field.

Optics express 32:4 (2024) 5885-5897

Authors:

Jack Harrison, Hariom Jani, Junxiong Hu, Manohar Lal, Jheng-Cyuan Lin, Horia Popescu, Jason Brown, Nicolas Jaouen, A Ariando, Paolo G Radaelli

Abstract:

Lensless coherent x-ray imaging techniques have great potential for high-resolution imaging of magnetic systems with a variety of in-situ perturbations. Despite many investigations of ferromagnets, extending these techniques to the study of other magnetic materials, primarily antiferromagnets, is lacking. Here, we demonstrate the first (to our knowledge) study of an antiferromagnet using holographic imaging through the 'holography with extended reference by autocorrelation linear differential operation' technique. Energy-dependent contrast with both linearly and circularly polarized x-rays are demonstrated. Antiferromagnetic domains and topological textures are studied in the presence of applied magnetic fields, demonstrating quasi-cyclic domain reconfiguration up to 500 mT.

Holographic imaging of antiferromagnetic domains with in-situ magnetic field

University of Oxford (2024)

Abstract:

Dataset accompanying the publication

Spatially reconfigurable antiferromagnetic states in topologically rich free-standing nanomembranes

University of Oxford (2024)

Authors:

Hariom Jani, Jack Harrison, Sonu Hooda, Saurav Prakas, Proloy Nandi, Junxiong Hu, Zhiyang Zeng, Jheng-Cyuan Lin, Charles Godfrey, Ganesh ji Omar, Tim A Butcher, Jörg Raab, Simone Finizio, Aaron Voon-Yew Thean, A Ariando, Paolo G Radaelli

Abstract:

The datasets included herein contain experimental results (Scanning transmission X-ray microscopy, X-ray diffraction, electron diffraction, confocal microscopy etc.) and related theoretical analysis for the investigation of antiferromagnetic topological textures in freestanding membranes. The steps used in the obtaining, reducing and analysing the datasets can be found in the Methods and Supplementary Information sections of the published manuscript.