182 research outputs found
Hybrid chiral domain walls and skyrmions in magnetic multilayers
Noncollinear spin textures in ferromagnetic ultrathin films are currently the
subject of renewed interest since the discovery of the interfacial
Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange
interaction selects a given chirality for the spin textures and allows
stabilising configurations with nontrivial topology. Moreover, it has many
crucial consequences on the dynamical properties of these topological
structures, including chiral domain walls (DWs) and magnetic skyrmions. In the
recent years the study of noncollinear spin textures has been extended from
single ultrathin layers to magnetic multilayers with broken inversion symmetry.
This extension of the structures in the vertical dimension allows very
efficient current-induced motion and room-temperature stability for both N\'eel
DWs and skyrmions. Here we show how in such multilayered systems the interlayer
interactions can actually lead to more complex, hybrid chiral magnetisation
arrangements. The described thickness-dependent reorientation of DWs is
experimentally confirmed by studying demagnetised multilayers through circular
dichroism in x-ray resonant magnetic scattering. We also demonstrate a simple
yet reliable method for determining the magnitude of the DMI from static
domains measurements even in the presence of these hybrid chiral structures, by
taking into account the actual profile of the DWs. The advent of these novel
hybrid chiral textures has far-reaching implications on how to stabilise and
manipulate DWs as well as skymionic structures in magnetic multilayers.Comment: 22 pages, 5 figure
Exploring ultra-fast charge transfer and vibronic coupling with N 1s RIXS maps of an aromatic molecule coupled to a semiconductor
We present for the first time two-dimensional resonant inelastic x-ray scattering (RIXS) maps of multilayer and monolayer biisonicotinic acid adsorbed on the rutile TiO2(110) single crystal surface. This enables the elastic channel to be followed over the lowest unoccupied molecular orbitals resonantly excited at the N 1s absorption edge. The data also reveals ultra-fast intramolecular vibronic coupling, particularly during excitation into the LUMO-derived resonance. Both elastic scattering and the vibronic coupling loss features are expected to contain the channel in which the originally excited electron is directly involved in the core-hole decay process. This allows RIXS data for a molecule coupled to a wide bandgap semiconductor to be considered in the same way as the core-hole clock implementation of resonant photoemission spectroscopy (RPES). However, contrary to RPES measurements, we find no evidence for depletion of the participator channel under the conditions of ultra-fast charge transfer from the molecule to the substrate densities of states, on the timescale of the core-hole lifetime. These results suggest that the radiative core-hole decay processes in RIXS are not significantly modified by charge transfer on the femtosecond timescale in this system
Irreversible transformation of ferromagnetic ordered stripe domains in single-shot IR pump - resonant X-ray scattering probe experiments
The evolution of a magnetic domain structure upon excitation by an intense,
femtosecond Infra-Red (IR) laser pulse has been investigated using single-shot
based time-resolved resonant X-ray scattering at the X-ray Free Electron laser
LCLS. A well-ordered stripe domain pattern as present in a thin CoPd alloy film
has been used as prototype magnetic domain structure for this study. The
fluence of the IR laser pump pulse was sufficient to lead to an almost complete
quenching of the magnetization within the ultrafast demagnetization process
taking place within the first few hundreds of femtoseconds following the IR
laser pump pulse excitation. On longer time scales this excitation gave rise to
subsequent irreversible transformations of the magnetic domain structure. Under
our specific experimental conditions, it took about 2 nanoseconds before the
magnetization started to recover. After about 5 nanoseconds the previously
ordered stripe domain structure had evolved into a disordered labyrinth domain
structure. Surprisingly, we observe after about 7 nanoseconds the occurrence of
a partially ordered stripe domain structure reoriented into a novel direction.
It is this domain structure in which the sample's magnetization stabilizes as
revealed by scattering patterns recorded long after the initial pump-probe
cycle. Using micro-magnetic simulations we can explain this observation based
on changes of the magnetic anisotropy going along with heat dissipation in the
film.Comment: 16 pages, 6 figure
Holographic imaging of antiferromagnetic domains with in-situ magnetic field
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
polarised 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.Comment: 14 pages, 6 figure
Tracing intensive fish and meat consumption using Zn isotope ratios: evidence from a historical Breton population (Rennes, France)
International audienceHere we report Sr and Zn isotope ratios of teeth of medieval to early modern Breton people a population whose diet is known from historical, archeological and collagen isotope data. Most of the population, buried in the Dominican convent of Rennes, France, consists of parliamentary nobles, wealthy commoners and ecclesiastics, who had a diet rich in animal products. Our aim is to assess how the Zn isotope ratios of their teeth compare to those of other French historical populations previously studied, which were characterized by cereal-based diets, and those of modern French individuals, who daily eat animal products. We describe a clear offset (∼0.35‰) between local and non-local human individuals in Zn isotope ratios. The δ 66 Zn tooth values of local individuals overlap that of modern French people, and are lower than those of local carnivores. Non-local δ 66 Zn values are similar to those of historical individuals analyzed previously. We conclude the lower Zn isotope ratios of local humans relative to the associated fauna can be explained by the consumption of carnivorous fish and pork, in agreement with historical, zooarchaeological and collagen (C, N, S) isotope data. Zn isotopes could therefore be a tracer of fish and/or substantial meat consumption in ancient populations
Recent developments of marine ingredients for food and nutraceutical applications: a review.
Remerciements à l'éditeur pour son accord de diffusion. L'article original est aussi accessible sur le site de l'éditeur à l'adresse : http://www.halieutique.org/23201b.htmlInternational audienceIn a global context of marine biological resource overexploitation, a better upgrading of fish and shellfish biomass is a challenge for the 21st century. One of the main and promising issues will be the production of marine bio-ingredients using enzymatic hydrolysis. This paper presents the key steps in the production of enzymatic hydrolysates, such as (i) enzymatic treatment for the bioconversion of solid discards, and more particularly, use of proteases, (ii) quantification of the proteolysis extend and procedures of quality-control and (iii) identification of biological activity, using in vitro and in vivo methods. In the last part, examples of marine, commercially available functional foods or nutraceutical ingredients carrying bioactive properties are presented in order to demonstrate the interest of biotechnological exploitation of marine resources
Ultra-fast intramolecular vibronic coupling revealed by RIXS and RPES maps of an aromatic adsorbate on TiO2(110)
Two-dimensional resonant inelastic x-ray scattering (RIXS) and resonant photoelectron spectroscopy (RPES) maps are presented for multilayer and monolayer coverages of an aromatic molecule (bi-isonicotinic acid) on the rutile TiO2(110) single crystal surface. The data reveals ultra-fast intramolecular vibronic coupling upon core-excitation from the N 1s orbital into the lowest unoccupied molecular orbital (LUMO) derived resonance. In the RIXS measurements this results in the splitting of the participator decay channel into a purely elastic line which disperses linearly with excitation energy, and a vibronic coupling channel at constant emission energy. In the RPES measurements the vibronic coupling results in a linear shift in binding energy of the participator channel as the excitation is tuned over the LUMO-derived resonance. Localisation of the vibrations on the molecule on the femtosecond timescale results in predominantly inelastic scattering from the core-excited state in both the physisorbed multilayer and the chemisorbed monolayer
Skyrmions in Magnetic Multilayers: Chirality, Electrical Detection and Current-induced Motion
Sub-100-nm skyrmions are stabilized in magnetic metallic multilayers and observed using transmission electron microscopy, magnetic force microscopy, scanning transmission X-ray microscopy and X-ray resonant magnetic scattering. All these advanced imaging techniques demonstrate the presence of 'pure' Neel skyrmion textures with a determined chirality. Combining these observations with electrical measurements allows us to demonstrate reproducible skyrmion nucleation using current pulses, and measure their contribution to the transverse resistivity to detect them electrically. Once nucleated, skyrmions can be moved using charge currents. We find predominantly a creep-like regime, characterized by disordered skyrmion motion, as observed by atomic force microscopy and scanning transmission X-ray microscopy. These observations are explained qualitatively and to some extent quantitatively by the presence of crystalline grains of about 20nm lateral size with a distribution of magnetic properties
Trophic position of Otodus megalodon and great white sharks through time revealed by zinc isotopes
Diet is a crucial trait of an animal’s lifestyle and ecology. The trophic level of an organism indicates its functional position within an ecosystem and holds significance for its ecology and evolution. Here, we demonstrate the use of zinc isotopes (δ66Zn) to geochemically assess the trophic level in diverse extant and extinct sharks, including the Neogene megatooth shark (Otodus megalodon) and the great white shark (Carcharodon carcharias). We reveal that dietary δ66Zn signatures are preserved in fossil shark tooth enameloid over deep geologic time and are robust recorders of each species’ trophic level. We observe significant δ66Zn differences among the Otodus and Carcharodon populations implying dietary shifts throughout the Neogene in both genera. Notably, Early Pliocene sympatric C. carcharias and O. megalodon appear to have occupied a similar mean trophic level, a finding that may hold clues to the extinction of the gigantic Neogene megatooth shark.publishedVersio
Exploring ultra-fast charge transfer and vibronic coupling with N 1s RIXS maps of an aromatic molecule coupled to a semiconductor
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