14 research outputs found
Dynamique ultrarapide de l'aimantation dans les alliages de métaux de transitions et de terres rares
My PhD work describes the pico and femtosecond magnetization dynamics using the time structure of X-rays. I studied the ultrafast demagnetization of thin films (~ 20 nm) for various transitions metals (TM) - rare earths (RE) alloys. My studies have been performed by using two experimental techniques which are sensitive to the magnetization and which are time resolved: tr-XMCD and tr-MCDAD. These two experimental techniques also show chemical selectivity allowing to distinguish the TM and RE dynamics. They are both based on pump-probe experiments which were used at the SOLEIL and BESSY II synchrotrons.Mon travail décrit la dynamique de l'aimantation pico et femtoseconde mesurée grùce à la structure temporelle des rayons X. J'ai étudié la désaimantation ultrarapide des métaux de transitions (MT) et des terres rares (TR) dans différents alliages MT-TR sous forme de films minces (~ 20 nm). Mes études reposent principalement sur les techniques expérimentales sensibles à l'aimantation et résolues en temps : tr-XMCD et tr-MCDAD. Ces deux techniques expérimentales offrent par ailleurs une sélectivité chimique qui permet de mesurer séparément la désaimantation ultrarapide des MT et des TR. Elles reposent sur des montages expérimentaux pompe-sonde que j'ai utilisé dans les synchrotrons SOLEIL et BESSY II
Ultrafast magnetization in transition metals and rare earths alloys
Mon travail décrit la dynamique de l'aimantation pico et femtoseconde mesurée grùce à la structure temporelle des rayons X. J'ai étudié la désaimantation ultrarapide des métaux de transitions (MT) et des terres rares (TR) dans différents alliages MT-TR sous forme de films minces (~ 20 nm). Mes études reposent principalement sur les techniques expérimentales sensibles à l'aimantation et résolues en temps : tr-XMCD et tr-MCDAD. Ces deux techniques expérimentales offrent par ailleurs une sélectivité chimique qui permet de mesurer séparément la désaimantation ultrarapide des MT et des TR. Elles reposent sur des montages expérimentaux pompe-sonde que j'ai utilisé dans les synchrotrons SOLEIL et BESSY II.My PhD work describes the pico and femtosecond magnetization dynamics using the time structure of X-rays. I studied the ultrafast demagnetization of thin films (~ 20 nm) for various transitions metals (TM) - rare earths (RE) alloys. My studies have been performed by using two experimental techniques which are sensitive to the magnetization and which are time resolved: tr-XMCD and tr-MCDAD. These two experimental techniques also show chemical selectivity allowing to distinguish the TM and RE dynamics. They are both based on pump-probe experiments which were used at the SOLEIL and BESSY II synchrotrons
Ultrafast magnetization in transition metals and rare earths alloys
Mon travail décrit la dynamique de l'aimantation pico et femtoseconde mesurée grùce à la structure temporelle des rayons X. J'ai étudié la désaimantation ultrarapide des métaux de transitions (MT) et des terres rares (TR) dans différents alliages MT-TR sous forme de films minces (~ 20 nm). Mes études reposent principalement sur les techniques expérimentales sensibles à l'aimantation et résolues en temps : tr-XMCD et tr-MCDAD. Ces deux techniques expérimentales offrent par ailleurs une sélectivité chimique qui permet de mesurer séparément la désaimantation ultrarapide des MT et des TR. Elles reposent sur des montages expérimentaux pompe-sonde que j'ai utilisé dans les synchrotrons SOLEIL et BESSY II.My PhD work describes the pico and femtosecond magnetization dynamics using the time structure of X-rays. I studied the ultrafast demagnetization of thin films (~ 20 nm) for various transitions metals (TM) - rare earths (RE) alloys. My studies have been performed by using two experimental techniques which are sensitive to the magnetization and which are time resolved: tr-XMCD and tr-MCDAD. These two experimental techniques also show chemical selectivity allowing to distinguish the TM and RE dynamics. They are both based on pump-probe experiments which were used at the SOLEIL and BESSY II synchrotrons
Insight into the magnetic properties of Pb-dopped iron oxide nanoparticles during Fe(III) bio-reduction by Shewanella oneidensis MR-1
International audienceAnthropogenic activities have led to a significant accumulation of Pb in the environment, posing a threat to ecosystems. Iron oxides that display magnetic properties are ubiquitous in the environment and Pb partitioning onto these minerals is considered one of the most critical geochemical processes controlling its environmental fate. In anoxic environments, iron oxides undergo redox cycling due to biotic and abiotic routes, resulting in their transformation/dissolution and evolution of their magnetic characteristics. However, there is still a lack of knowledge on the impact of Pb on the dynamic of iron oxides bioreduction. Furthermore, there is little information available regarding the nature of biogenic minerals and their magnetic signatures.Here we incubated Pb-bearing ferrihydrites (Fh_Pb) with various Pb/(Fe + Pb) molar ratios (i.e., 0, 2 and 5%) with the iron-reducing bacterium Shewanella oneidensis MR-1, for 21 days.XRD analyses of the initial Fh_Pb displayed characteristic features of Fh and a decrease of magnetization in the presence of Pb. During the bio-reduction process, Pb doping led to a drop in the rate and extent of reduction. At the end of the incubation period, the analysis of the aqueous solutions revealed a minor proportion of Pb in solution, indicating that a significant proportion of the Pb is sorbed onto the biogenic minerals. Magnetite (95%) and siderite (5%) formed during the bioreduction of Fh, while magnetite (~80%) and goethite (~20%) precipitated in the presence of Pb as revealed by transmission Mössbauer spectroscopy. Furthermore, the size of the magnetite particles decreased from about 11 nm in absence of Pb to 6 nm with 2% of Pb-bearing, while 5% of Pb led to particles too small to be quantified with our TEM measurements. The combined effect of the decrease in particle size of magnetite, substitution of Pb and the precipitation of goethite in the Pb-dopped assay led to a significant decrease of magnetization at room temperature. Overall, this study highlights the effect of Pb on iron oxides bio-reduction and transformation processes and the sensitivity of magnetism to serve as a monitoring method
Effect of Sb on precipitation of biogenic minerals during the reduction of Sb-bearing ferrihydrites
International audienceAntimony (Sb) is a naturally occurring element; it is enriched in the environment by anthropogenic activities. Like other metalloid species, Sb partitions to mineral phases such as oxyhydroxides. In reducing environments, Fe(III) may serve as a terminal electron acceptor during dissimilatory iron reduction leading to its transformation. Relatively little is known concerning the effect of Sb(V) on the precipitation of biogenic minerals in relation to microbiologically mediated redox reactions. To further our understanding, Sb-bearing ferrihydrites (0.5âŻg) with variable Sb/(FeâŻ+âŻSb) molar ratios of 0.04, 0.06 and 0.1, were incubated in the presence of Shewanella oneindensis MR-1 (1âŻĂâŻ108âŻcell mLâ1) under N2 atmosphere. Additionally, we synthesized abiotic GR1(CO32â) in the presence of Sb(V) to examine the effect of Sb(V) on this mineral formation and stabilization. A combination of wet chemistry and solid analysis techniques (XRD, Mössbauer and Raman spectroscopies) was used to characterize the reactions.The Sb loading affected the rate and the extent of bio-reduction compared with pure ferrihydrite. Only a minor fraction of the total Sb, less than 0.5%, was released into the solution by the end of the incubation period, suggesting that the metalloid partitioned mainly in a newly formed phase. Furthermore, XPS analyses showed the presence of Sb(V) and Sb(III) species on the biogenic minerals. Magnetite was the main biogenic precipitate (91%) in the absence of Sb(V). Increasing of the molar ratios [Sb/(FeâŻ+âŻSb)] to 0.1 resulted mainly in the precipitation of carbonated green (47%) rust and goethite (37%). Abiotic green rust synthesis carried out in the presence of Sb(V) indicated the latterâs stabilizing effect on the green rust structure, as for phosphate species. Thus, it is likely that Sb(V) preserve biogenic green rust, hindering its transformation to more thermodynamically stable phases
Dynamique ultrarapide de spins 3d et 4f dans des alliages CoDy ferrimagnétique en fonction de la température
International audienceWe report an element-and time-resolved investigation of femtosecond laser induced ultrafast dynamics of the Co 3d and Dy 4f spins in a ferrimagnetic Co80Dy20 alloy as a function of the temperature. We observe that the Co characteristic demagnetization time (ÏCo) remains nearly constant (~0.2 ps) on increasing the temperature. Conversely, the Dy characteristic demagnetization time (ÏDy) decreases from ~1 ps to ~0.4 ps with the rise of temperature. Comparing our experimental data with literature shows that ÏCo and ÏDy are independent of the alloy composition or the demagnetization amplitude and that ÏDy scales with the relative temperature T* = TCurie-T
Structural dynamics during laser-induced ultrafast demagnetization
The mechanism underlying femtosecond laser-pulse-induced ultrafast magnetization dynamics remains elusive, despite two decades of intense research on this phenomenon. Most experiments focused so far on characterizing magnetization and charge carrier dynamics, while the first direct measurements of structural dynamics during ultrafast demagnetization were reported only very recently. We here present our investigation of the infrared laser-pulse-induced ultrafast demagnetization process in a thin Ni film, which characterizes simultaneously magnetization and structural dynamics. This is achieved by employing femtosecond time-resolved x-ray resonant magnetic reflectivity (tr-XRMR) as the probe technique. The experimental results reveal unambiguously that the subpicosecond magnetization quenching is accompanied by strong changes in nonmagnetic x-ray reflectivity. These changes vary with reflection angle, and changes up to 30% have been observed. By modeling the x-ray reflectivity of the investigated thin film, we can reproduce these changes by a variation of the apparent Ni layer thickness of up to 1%. Extending these simulations to larger incidence angles, we show that tr-XRMR can be employed to discriminate experimentally between currently discussed models describing the ultrafast demagnetization phenomenon.Funding from the European Community's Seventh Framework Programme under Grant Agreement No. 312284 (CALIPSO Project) is gratefully acknowledged, as well as financial support received from the following agencies: (i) The French âAgence National de la Rechercheâ (ANR) via the projects UMAMI, ANR-11-LABX-0058_NIE and the EQUIPEX UNION (ANR-10-EQPX-52), and (ii) the CNRS-PICS program
DEOGEN2: prediction and interactive visualization of single amino acid variant deleteriousness in human proteins
High-throughput sequencing methods are generating enormous amounts of genomic data, giving unprecedented insights into human genetic variation and its relation to disease. An individual human genome contains millions of Single Nucleotide Variants: to discriminate the deleterious from the benign ones, a variety of methods have been developed that predict whether a protein-coding variant likely affects the carrier individual's health. We present such a method, DEOGEN2, which incorporates heterogeneous information about the molecular effects of the variants, the domains involved, the relevance of the gene and the interactions in which it participates. This extensive contextual information is non-linearly mapped into one single deleteriousness score for each variant. Since for the non-expert user it is sometimes still difficult to assess what this score means, how it relates to the encoded protein, and where it originates from, we developed an interactive online framework (http://deogen2.mutaframe.com/) to better present the DEOGEN2 deleteriousness predictions of all possible variants in all human proteins. The prediction is visualized so both expert and non-expert users can gain insights into the meaning, protein context and origins of each prediction.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Quantum advantage in a spintronic engine with coherently coupled ultrafast strokes using molecular superexchange
Recent theory and experiments have showcased how to harness quantum mechanics
to assemble heat/information engines with efficiencies that surpass the
classical Carnot limit. So far, implementing work-producing quantum resources
has required atomic engines driven by external laser and microwave energy
sources We propose a spin electronic implementation that operates autonomously.
Our concept heuristically deploys several known quantum resources upon placing
a quantum-entangled chain of spin qubits formed by the Co centers of
phthalocyanine (Pc) molecules between electron-spin selecting Fe/C60
interfaces. Density functional calculations reveal that transport fluctuation
strokes across the interfaces can stabilize spin coherence on the Co
paramagnetic centers, which host spin swap engine strokes. Across solid-state
vertical molecular nanojunctions, we measure large enduring dc current
generation, sizeable output power above room temperature, and two quantum
thermodynamical signatures. The Fe/C60 interface's record 89% spin polarization
also enables a spintronic feedback and control over the flow and direction of
charge current. Beyond these first results, further research into spintronic
quantum engines, and retooling the spintronic-based information technology
chain7, could help accelerate the transition to clean energy.Comment: