Yannick Dusch

Avec le développement des nouvelles technologies de l'information et de la communication (NTIC), la consommation énergétique des systèmes de traitement et de stockage de données est devenue un problème majeur. Les limites des systèmes actuels à cet égard impliquent le besoin de technologies de rupture ultra-basse consommation.Cette thèse propose une approche originale de cette problématique, basée sur l'utilisation d'un élément magnétoélectrique composite (piézoélectrique/magnétostrictif) bistable et commandable de façon univoque, baptisé MELRAM.L'étude énergétique statique montre que la combinaison d'une anisotropie uni-axiale et d'un champ de polarisation magnétique statique définit deux positions d'équilibre stables perpendiculaires pour l'aimantation dans la partie magnétostrictive. L'application de contraintes piézoélectriques sur celle-ci permet de contrôler électriquement la position de l'aimantation. L'étude énergétique du système permet également de montrer la stabilité du système à long terme (10 ans), dans une large gamme de températures autour de l'ambiante, avec une barrière énergétique de 60kBT. L'étude dynamique, utilisant le modèle du macrospin, permet quant à elle d'exhiber un temps de réponse inférieur à 1ns. L'énergie dissipée lors de l'écriture, d'origine électrique et magnétique, est évaluée à 261kBT (1,1aJ), soit quatre ordres de grandeur en dessous de l'état de l'art.Plusieurs stratégies de lecture par vanne de spin et jonction tunnel magnétique sont proposées et commentées. Les premières réalisations d'éléments nanométriques magnétostrictifs sont présentées ainsi qu'une solution de polarisation magnétique intégrée par aimant permanent

Optically pumped spintronic terahertz emitters (STEs) have, in less than a decade, strongly impacted terahertz (THz) source technology, by the combination of their Fourier‐limited ultrafast response, their phononless emission spectrum and their wavelength‐independent operation. However, the intrinsic strength of the inverse spin Hall effect governing these devices introduces a challenge: the optical‐to‐terahertz conversion efficiency is considerably lower than traditional sources. It is therefore primordial to maximize at least their electromagnetic efficiency independently of the spin dynamics at play. Using a rigorous time‐domain treatment of the electromagnetic generation and extraction processes, an optimized design is presented and experimentally confirmed. With respect to the strongest reported spintronic THz emitters it achieves a 250% enhancement of the emitted THz field and therefore an 8 dB increase of emitted power. This experimental achievement brings STE close to the symbolic barrier of mW levels. The design strategy is generically applicable to any kind of ultrafast spin‐to‐charge conversion (S2C) system. On a broader level, our work highlights how a rigorous handling of the purely electromagnetic aspects of THz spintronic devices can uncover overlooked aspects of their operation and lead to substantial improvements.

We demonstrate the creation and control of magnetic topological textures in thin film structures by plasmonic effects. From electromagnetic and photothermal models, the heat and absorption were determined, then the results were implemented in micromagnetic formalism to study the dynamics of magnetization under various conditions. The laser pulse duration and the contact area between nanoparticles and the magnetic layer are key parameters in the formation of topological textures. It is possible to generate a single skyrmion, multiple skyrmions, and skyrmioniums in the range of picoseconds. These results highlight the possibility of manipulating magnetic textures by using plasmonic effects, which presents significant opportunities for spintronics and non-conventional computer applications.

In this paper, we introduce a gas sensor concept consisting of a nanostructured gold grating coupled with a Distributed Bragg Reflector. This coupling makes it possible to obtain plasmonic Tamm states where excitation is possible at normal incidence and does not require the use of Kretschmann configuration. Through parameters optimization of the gold nanostructured grating, we achieved well-defined and localized Tamm resonances between the gold nanostructured grating and the Distributed Bragg Reflector composed of SiO ₂ /Si ₃ N ₄ . To exploit the spatial confinement of the energy of the Tamm states in order to measure the change in refractive index, we propose three configurations in which we substitute the last nitride layer in the Bragg Reflector with porous materials. In the first configuration, we use a porous nitride portion with 30% porosity, producing sensitivity S = 170nm/RIU and figure of merit FOM = 27.1 RIU ^-1 . In the second configuration, we use a porous nitride layer with a porosity of 30% (S = 175nm/RIU, FOM = 27.3 RIU ^-1 ). Finally, the third configuration adopts a 66% porous silicon layer (S = 268nm/RIU, FOM = 43.6 RIU ^-1 ). These values show significant potential for sensing applications.

This theoretical study unveils the potential for ultrafast skyrmion generation in magnetic thin films, driven by the remarkable plasmonic properties of gold nanoparticles. By combining the plasmonic, photothermal, and micromagnetic analysis, we explore size-dependent light absorption, resonance wavelength, and electric field distribution around the nanoparticles. Our findings highlight the crucial role of the insulating layer's thickness in enhancing plasmonic effects, offering tunable absorption characteristics. Micromagnetic calculations demonstrate the efficient creation of Néel skyrmions in the range of a few tens of ps, showcasing a breakthrough in magnetic phenomena and opening thus a path for functional skyrmionic-based devices.

In this work, we propose a sensor based on Tamm plasmonic resonance; the structure is composed of gold nanoribbons deposited on a Distributed Bragg Reflector (DBR) (SiO₂/Si₃N₄)₆. We have enhanced the sensitivity of our sensor from 40 nm/RIU to 200 nm/RIU for a refractive index change of 1% by replacing the last layer of Si₃N₄ in contact with gold with porous Si₃N₄ with a porosity of p = 40%.