Computational Analysis of a Spiral Thermoelectric Nanoantenna for Solar Energy Harvesting Applications

Thermo-electrical nanoantennas have been proposed as an alternative option for conversion solar energy harvesting applications. In this work, the response of a spiral broadband antenna has been obtained from numerical and theoretical simulations perspectives. The results show that this device exhibits a responsivity of 20mV/W under 117W/cm2, for a single-frequency radiation. We discuss strategies for enhanced efficiency

Seebeck Nanoantennas for Infrared Detection and Energy Harvesting Applications

In this letter we introduce a new type of infrared sensor, based on thermocouple nanoantennas, which enables the energy detection and gathering in the mid-infrared region. The proposed detector combines the Seebeck effect, as a transduction mechanism, with the functionalities of the optical antennas for optical sensing. By using finite-element numerical simulations we evaluate the performance and optical-to-electrical conversion efficiency of the proposed device, unveiling its potential for optical sensing and energy harvesting applications.Comment: 4 pages, 3 figures, Invited paper at EUCAP 201

Optimal design of nanomagnets for on-chip field gradients

The generation of localized magnetic field gradients by on-chip nanomagnets is important for a variety of technological applications, in particular for spin qubits. To advance beyond the empirical design of these nanomagnets, we propose a systematic and general approach based on the micromagnetic formulation of an optimal field gradient source. We study the different field configurations that can be realized and find out quantitatively the most suitable ferromagnetic layer geometries. Using micromagnetic simulations, we then investigate the minimum requirements for reaching magnetic saturation in these nanomagnets. In terms of either longitudinal or transverse field gradient, the results provide an optimal solution for uniform, saturated nanomagnets, where the magnetic material can be selected according to the strength of the external fields that can be used.Comment: 10 pages, 4 figures, supplemental material. All comments most welcom

Fragmentation of magnetism in artificial kagome dipolar spin ice

Geometrical frustration in magnetic materials often gives rise to exotic, low-temperature states of matter, like the ones observed in spin ices. Here we report the imaging of the magnetic states of a thermally-active artificial magnetic ice that reveal the fingerprints of a spin fragmentation process. This fragmentation corresponds to a splitting of the magnetic degree of freedom into two channels and is evidenced in both real and reciprocal space. Furthermore, the internal organization of both channels is interpreted within the framework of a hybrid spin-charge model that directly emerges from the parent spin model of the kagome dipolar spin ice. Our experimental and theoretical results provide insights into the physics of frustrated magnets and deepen our understanding of emergent fields through the use of tailor-made magnetism.Comment: 9 pages, 5 figures. Published version available on the Nat. Comm. web site: http://www.nature.com/ncomms/2016/160513/ncomms11446/full/ncomms11446.htm

Tunable stochasticity in an artificial spin network

Metamaterials present the possibility of artificially generating advanced functionalities through engineering of their internal structure. Artificial spin networks, in which a large number of nanoscale magnetic elements are coupled together, are promising metamaterial candidates that enable the control of collective magnetic behavior through tuning of the local interaction between elements. In this work, the motion of magnetic domain-walls in an artificial spin network leads to a tunable stochastic response of the metamaterial, which can be tailored through an external magnetic field and local lattice modifications. This type of tunable stochastic network produces a controllable random response exploiting intrinsic stochasticity within magnetic domain-wall motion at the nanoscale. An iconic demonstration used to illustrate the control of randomness is the Galton board. In this system, multiple balls fall into an array of pegs to generate a bell-shaped curve that can be modified via the array spacing or the tilt of the board. A nanoscale recreation of this experiment using an artificial spin network is employed to demonstrate tunable stochasticity. This type of tunable stochastic network opens new paths towards post-Von Neumann computing architectures such as Bayesian sensing or random neural networks, in which stochasticity is harnessed to efficiently perform complex computational tasks.Comment: 24 pages, 10 figure

Vers la mesure de nano-objets uniques, réalisation de nanogaps par électromigration

Au cours de ce travail de thèse, nous avons étudié la formation de nanogaps par électromigration dans des nanofils d'or. Cette technique consiste à provoquer la rupture d'un nanofil en lui appliquant de fortes densités de courant et peut être utilisée pour la caractérisation électrique de nano-objets. Néanmoins, les mécanismes de formation des nanogaps ne sont, à ce jour, pas encore totalement compris. L'étude en temps réel du processus d'électromigration par microscopie à force atomique a permis d'apporter un éclairage nouveau de la dynamique du processus. En effet, il apparaît que la structure globale du dispositif est définie dans les premiers temps de l'électromigration et nous avons montré que cette structure est directement liée à la microstructure du film métallique. Pour la première fois, des nanogaps ont été élaborés par électromigration dans des films monocristallins. Malgré l'absence de joints de grain, il est possible de former des nanogaps dans un matériau épitaxié. L'utilisation de ces matériaux permet d'obtenir des nanogaps avec une morphologie plus reproductible. Les propriétés de transports des nanogaps obtenus à partir de films polycristallins ont été caractérisées. Les caractéristiques obtenues présentent toutes des signatures particulières, attribuées à la présence d'agrégats d'or provenant de la procédure d'électromigration et/ou de polymères issus du procédé de nanofabrication. Ces résultats montrent la difficulté à réaliser des mesures à l'échelle de la molécule uniqueWe have studied the formation of nanogaps by électromigration of gold nanowires. Electromigration relies on large current densities to break a thin and narrow metallic wire and can be used for the electrical characterization of nanometer scale objects. Nevertheless, a complete description of the electromigration process is lacking. Real time atomic force microscopy during the electromigration process gave a new view the dynamic of the process. Indeed, this study reveals that the major structural changes appear at the early stage of the process and that the final global structure of the device is directly linked to the pre-existing microstructure. For the first time, we make nanogaps by électromigration of monocrystalline nanowires. We show that despite the lacking of grain boundaries, it is possible to form nanogaps in epitaxial materials. The morphology of those nanogaps is more reproducible. The electrical transport properties of the polycristalline nanogaps have been measured. The entire obtained characteristics show particular signature that can be attributed to the presence of gold cluster formed during the électromigration process and / or to polymer from the nanowire fabrication. These results show the difficulty to measure at the molecular scaleMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Nouveaux ligands hétérocycliques et leurs complexes métalliques (étude des propriétés magnétiques)

Dans le premier temps, nous avons préparé de nouveaux hétérocycles azotés comprenant des unités 1,2,4-triazine : btrz, cpytrz, pytrz, bpy-pytrz et pytrz. Ensuite, nous avons observé leur aptitude à la complexation des ions métalliques d10 (CuI, AgI, ZnII) en utilisant l analyse en spectrométrie UV-Visible, spectrométrie de Masse ESIMS, Résonance Magnétique Nucléaire, et Diffraction de Rayons X. En outre, avec le ligand bpy-pytrz, son complexe CuI est un hélicate double-brin dinucléaire dont l orientation H-H (Head to Head) ou H-T (Head to Tail) sera déterminée grâce à la structure RX. Par ailleurs, nous avons obtenu pour la première fois des monocristaux d un complexe entre l ion uranium UO2(NO3)2 et le ligand bpy-pytrz. Dans une seconde partie, la synthèse de séquences bipyridine-bisdiazines-pont 2-oxapropylène est présentée à savoir les séquences : bpy-bpz, bpy-bpm, bpy-btz2,2 et bpy-btz4,4 . L étude de leurs modes de complexation avec des ions métalliques 3dn (NiII, CoII, CuII) a été réalisée. Enfin, des résultats intéressants sur les propriétés magnétiques (ferromagnétisme) de ces complexes ont été obtenus et concernent en particulier des complexes neutres dinucléaires du NiII .Fistly, new nitrogen heterocycles containing 1,2,4-triazine units have been prepared: btrz, cpytrz, pytrz, bpy-pytrz et pytrz. Then, their complexation behaviour have been studied with d10 transition metal ions (CuI, AgI, ZnII) by UV-Vis, Nuclear Magnetic Resonance, ESI-MS and X-ray diffraction spectrometries. Particularly, the bpy-pytrz ligand CuI complex gave a dinuclear double-strand helicate, of which H-H (Head to Head) or H-T (Head to Tail) conformation will be determined by X-ray diffraction. Elsewere, for the first time we were able to obtained suitable single crystals of the Uranium (UO2(NO3)2) complex with bpy-pytrz ligand. Secondly, the synthesis of sequential 2-oxapropylene-bridged bipyridine-bisdiazine strands (bpy-bpz, bpy-bpm, bpy-btz2,2 , bpy-btz4,4 ) has been reported. Their complexation behaviour with 3dn transition metal ions (CoII, NiII, CuII) have been studied in solution and in solid phases. Finally, preliminary interesting results have been achieved on the magnetic properties of their complexes and concerned particularly the dinuclear NiII neutral complexes.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Anisotropie magnétique induite par modulation de surface et étude de la propagation de parois de domaines dans des nanostructures magnétiques

Une étude de l induction d une anisotropie magnétique d origine magnétostatique dans une couche mince magnétique (Ni81Fe19) à topologie modulée a été effectuée grâce aux observations réalisées à l aide de mesures de magnéto-transport (AMR). La modulation à l échelle nanométrique est obtenue avec une nouvelle approche basée sur la lithographie électronique. La présence d une anisotropie uniaxiale orientée parallèlement à la modulation a été mise en évidence. Ce denier a permis la définition de deux axes orthogonaux d anisotropie dans un même substrat et l exploration de la faisabilité d un capteur de champ magnétique bidimensionnel. Une géométrie de capteur à Effet Hall Planaire est proposée. Le développement et la fabrication d un dispositif permettant l étude de la propagation d une paroi de domaines dans une piste submicronique effectué sur une vanne de spin ont été accomplis. Dans ces dispositifs, la position de la paroi est déterminée par la mesure de la magnétorésistance géante (GMR). L étude systématique des champs d injection et de dépiégeage a montré l existence une asymétrie de la propagation de la paroi entre les transitions P ® AP et AP ® P. Il a été montré, grâce à une série de simulations micro magnétiques, que cette asymétrie résulte de l influence du champ dipolaire créé par la couche fixe sur les configurations adoptées par la paroi dans la couche libre. Des mesures de relaxation de temps ont permis d obtenir la probabilité cumulée de dépiégeage de la paroi à partir de la constriction. Une variété de comportements a été ainsi mise en évidence.A study on the induction of a magnetic anisotropy of magnetostatic origin in a magnetic thin layer (Ni81Fe19) having a modulated topology was carried out by performing magneto-transport measurements (AMR). Modulation in the nanometric scale is obtained with a new approach based on the electronic lithography. The presence of a uniaxial anisotropy along the modulation was highlighted. This latter allowed the definition of two orthogonal axes of anisotropy in the same substrate and the exploration of the feasibility of a 2D dimensional magnetic sensor. A sensor geometry based on the Planar Hall effect is proposed. The development and the fabrication of a device allowing studying the domain wall propagation in a sub-micronic wire based on a spin-valve element have been accomplished. In such devices the domain wall position is determined by probing the Giant Magneto-Resistance (GMR). The systematic study of the injection and depinning fields showed the existence of an asymmetry in the propagation of the wall between the transitions P ® AP and AP ® P. It was shown, thanks to a series of magnetic micro simulations, that this asymmetry results from the influence of the dipolar field created by the fixed layer on the configurations adopted by the wall in the free layer. Relaxation time measurements made it possible to obtain the cumulated probability for the depinning of the domain wall from the constriction. A variety of behaviors was thus highlighted.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Probing the antiferromagnetic-paramagnetic transition in artificial spin ice by tuning interactions

International audienceArtificial spin ice systems, two-dimensional arrays of interacting nanomagnets, provide a playground to directly observe competing interactions. Due to the anisotropic nature of the dipolar interactions, rotation of nanomagnets is a powerful way of tuning the interactions. In this paper, we experimentally examine the ground state transition from antiferromagnetic to ferromagnetic order triggered by this transformation. The as-grown magnetic configurations well agree with Monte Carlo simulations and ascribe a unique effective temperature independent of the rotation angle. Deviations from the theoretical ground state and behavior at transition are therefore well explained