Tyndall National Institute - Journal Articles
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Item Graphene field effect transistor on silicon nitride devices for near-infrared wavelength tuning(Optica Publishing Group, 2024) Vorobev, Artem S.; Mendoza-Castro, J. H.; Iadanza, S.; Jastan, S.; Bianco, G. V.; Bruno, G.; D’Orazio, A.; O’Faolain, Liam; Grande, M.; Horizon 2020In this work, we present the Graphene Field Effect Transistor (GFET) on Silicon Nitride waveguides for achieving the wavelength tuning in the Near-Infrared (NIR) range. The obtained Electrolyte-Graphene-Waveguide fabrication and characterization results are demonstrated.Item Investigation of transverse exchange-springs in electrodeposited nano-heterostructured films through first-order reversal curve analysis(AIP Publishing, 2024-09-19) Samanta, Arindam; Roy, Saibal; Science Foundation Ireland; National Science FoundationThe prerequisite of efficient exchange-spring nano-heterostructures, i.e., tuning both hard and soft phases at a nanometer level, has posed significant preparation challenges to ensure effective exchange-coupling. Here, we present a novel approach to fabricate transverse exchange-spring nano-heterostructures using single starting material through an “in situ” electrodeposition technique at room temperature. Utilizing modified acidic bath chemistry and controlled hydrogen evolution, we successfully prepared stress-free, shiny, fine-grained amorphous, and nanocrystalline Co-rich cobalt phosphorus films. These nano-heterostructured films exhibit a unique non-collinear anisotropy-driven transverse exchange-spring behavior, investigated systematically under ambient conditions. The comprehensive functional analyses reveal that intricate interplay between in-plane (IP) anisotropy of amorphous phase and out-of-plane (OOP) anisotropy generating from a nanocrystalline structure compete with each other, while producing characteristic stripe domain structures to novel corrugated stripe domain shapes. The angle-dependent first-order reversal curve distributions demonstrate new insights into the magnetic reversal mechanisms, further confirming the non-exchange-spring and exchange-spring nature of the films depending on the prevalent interfacial exchange coupling. Formation of anisotropy-driven metastable-state due to competition between IP and OOP anisotropy at a particular OOP orientation has led the normal exchange-spring structures to a transverse exchange-spring structure. Micromagnetic simulations, in excellent agreement with experimental data, further elucidate the formation of characteristic stripe domain patterns and the influence of anisotropy on the magnetic properties. The innovative methodology and detailed functional analysis presented here offer significant understanding to the field of exchange-spring magnetic materials, including anisotropy-driven metastable states, demonstrating the potential for scalable and cost-effective fabrication of advanced nano-heterostructures with tailored magnetic properties.Item Tunable power-phase distributions in a phonon-magnon-coupled magnon microwave antenna for reservoir computing(American Physical Society, 2024-11-26) Samanta, Arindam; Roy, Saibal; Science Foundation Ireland; National Science Foundation; Department for Education, UK GovernmentExploring the power and phase profiles of spin waves not only enhances our fundamental understanding of magnetic materials but also opens up avenues for energy-efficient technologies such as spintronics, magnonics, and potentially reservoir computing. Here, we present the power-phase distributions and their tunability of a surface-acoustic-wave-driven “magnon microwave antenna” (MMA), comprising patterned arrays of magnetostrictive nanomagnets embedded in piezoelectric heterostructures. The MMA generates tunable microwave frequencies without external bias fields, thanks to phonon-magnon coupling, producing multimode microwave frequencies with nonvolatile spin textures. A comprehensive static magnetic study elucidates the crucial role of the demagnetization energy distribution, rather than its overall magnitude in magnetization reversal processes. Additionally, functional tunability could be achieved through amplitude-dependent training using various combinations of nanowire and nanodot dimensions, topologies, material properties, and array configurations. The nonvolatile nature of the spin textures generated in the MMA under bias-field-free conditions is promising for energy-efficient logic and low-power computing applications. Thus this work introduces a novel alternative approach, paving the way to utilize these MMAs for on-chip reservoir computing, where amplitude varies at the operating frequency.Item Determining the effective permeability of a laminated CoZrTaB (CZTB) film, through consideration of demagnetisation effects and eddy-displacement currents(Institute of Electrical and Electronics Engineers (IEEE), 2024-11-08) Murphy, Ruaidhrí; Wei, Guannan; Masood, Ansar; O’Mathúna, Cian; Pavlovic, Zoran; McCloskey, Paul; O’Driscoll, Séamus; Enterprise Ireland; Horizon 2020Multi-laminated thin film inductors are a key emerging technology to enable highly integrated, on-chip, voltage regulators. The permeability of a magnetic core at high frequency is a key determiner of inductance density. In this paper, a multi-lamination magnetic core made up of alternate CZTB amorphous, uniaxially anisotropic magnetic films and AlN dielectric layers is investigated. The individual films are approximately 200 nm thick, appropriate for operation at over 100 MHz, but the laminated structure and overall thickness of several micrometres mean that analytical methods are impractical for computing demagnetisation. Magnetostatic Finite Element Analysis (FEA) is used to model the magnetic core demagnetisation, accounting for various length/width dimensions, magnetic film thicknesses and dielectric thicknesses. At higher frequencies, the dielectric layers, which are included in the structure to suppress induced eddy-currents allow displacement currents to flow through the dielectric layers and lead to increased eddy currents circulating around the overall core structure and thus further increasing loss and reducing permeability. Eddy-current FEA simulations which include the displacement currents, and an analytically derived Equivalent Circuit Model (ECM) are used to model the real and imaginary (loss) components of permeability spectra. The work, therefore determines the combined contributions of both demagnetisation effects and eddy-displacement currents to the reductions in real permeability and the increase in loss components for thicker multi-laminated magnetic cores. Permeameter measurements on fabricated cores, having ten laminations, and with various AlN thicknesses (10, 20, 40 and 60 nm) gave excellent agreement with the predicted effective permeability through the approach of combining the FEA and ECM models, over the 10 MHz to 1 GHz frequency range. It was shown, that at 100 MHz, for multi-laminated cores with thin or higher k dielectric layers, that displacement-eddy currents are dominant, giving a power loss an order of magnitude higher than would be for magnetically induced eddy currents alone.Item A robust sensor for inline pH measurements(Institute of Electrical and Electronics Engineers (IEEE), 2024-11-07) Nair, Nikila; Akshaya, A.V.; Bosco, Michael John; Ananthasuresh, G. K.; Joseph, Jose; Ministry of Electronics and Information technologyConventionally, a pH sensor having a glass bulb and a liquid-based reference electrode is used for accurate, real-time pH measurement. However, glass bulb-based pH sensors suffer wear and tear in harsh operating conditions and yield erroneous readings in strong alkaline and acidic media. This necessitates the development of a robust pH sensor that renders stable performance in harsh operating conditions. This paper reports the fabrication and characterization of an all-solid-electrode pH sensor with excellent linearity in the pH range of 4 to 9 with a sub-Nernstian slope of -43.18 mV/pH. The fabrication process of the sensor is explained in detail, and the performance of the sensor is validated with extensive characterization. Furthermore, the efficacy of the sensor in practical applications is established by measuring the pH of idli batter during its fermentation process. The proposed sensor is also used to measure the pH of soil solutions, wherein the pH of soil samples showed an error of less than ±0.15 pH when compared with a laboratory pH meter.