595 research outputs found
Collapse of ferromagnetism and Fermi surface instability near reentrant superconductivity of URhGe
We present thermoelectric power and resistivity measurements in the
ferromagnetic superconductor URhGe for magnetic field applied along the hard
magnetization b axis of the orthorhombic crystal. Reentrant superconductivity
is observed near the the spin reorientation transition at =12.75 T,
where a first order transition from the ferromagnetic to the polarized
paramagnetic state occurs. Special focus is given to the longitudinal
configuration, where both electric and heat current are parallel to the applied
field. The validity of the Fermi-liquid dependence of the resistivity
through demonstrates clearly that no quantum critical point occurs at
. Thus the ferromagnetic transition line at becomes first order
implying the existence of a tricritical point at finite temperature. The
enhancement of magnetic fluctuations in the vicinity of the tricritical point
stimulates the reentrance of superconductivity. The abrupt sign change observed
in the thermoelectric power with the thermal gradient applied along the b axis
together with the strong anomalies in the other directions is a definitive
macroscopic evidence that in addition a significant change of the Fermi surface
appears through .Comment: 6 pages, 5 figure
Continental shelves as potential resource of rare earth elements
International audienceThe results of this study allow the reassessment of the rare earth elements (REE) external cycle. Indeed, the river input to the oceans has relatively flat REE patterns without cerium (Ce) anomalies, whereas oceanic REE patterns exhibit strong negative Ce anomalies and heavy REE enrichment. Indeed, the processes at the origin of seawater REE patterns are commonly thought to occur within the ocean masses themselves. However, the results from the present study illustrate that seawater-like REE patterns already occur in the truly dissolved pool of river input. This leads us to favor a partial or complete removal of the colloidal REE pool during estuarine mixing by coagulation, as previously shown for dissolved humic acids and iron. In this latter case, REE fractionation occurs because colloidal and truly dissolved pools have different REE patterns. Thus, the REE patterns of seawater could be the combination of both intra-oceanic and riverine processes. In this study, we show that the Atlantic continental shelves could be considered potential REE traps, suggesting further that shelf sediments could potentially become a resource for REE, similar to metalliferous deep sea sediments.
Rare earth element sorption onto hydrous manganese oxide: A modeling study
International audienceManganese oxides are important scavengers of rare earth elements (REE) in hydrosystems. However, it has been difficult to include Mn oxides in speciation models due to the lack of a comprehensive set of sorption reactions consistent with a given surface complexation model (SCM), as well as discrepancies between published sorption data and predictions using the available models. Surface complexation reactions for hydrous Mn oxide were described using a two surface site model and the diffuse double layer SCM. The specific surface area, surface side density, and pHzpc were fixed to 746 m2/g, 2.1 mmol/g, and 2.2, respectively. Two site types (triple bond; length of mdashXOH and triple bond; length of mdashYOH) were also used with pKa2 values of 2.35 (triple bond; length of mdashXOH) and 6.06 (triple bond; length of mdashYOH). The fraction of the high affinity sites was fixed at 0.36. Published REE sorption data were subsequently used to determine the equilibrium surface complexation constants, while considering the influence of pH, ionic strength, and metal loading. Log K increases from light REE to heavy REE and, more specifically, displays a convex tetrad effect. At low metal loading, the triple bond; length of mdashYOH site type strongly expresses its affinity toward REE, whereas at higher metal loading, the same is true for the triple bond; length of mdashXOH site type. This study thus provides evidence for heterogeneity in the distribution of the Mn oxide binding sites among REE
Characterization of metal binding sites onto biochar using rare earth elements as a fingerprint
International audienc
It’s time to replace the term “heavy metals” with “potentially toxic elements” when reporting environmental research
International audienceEven if the Periodic Table of Chemical Elements is relatively well defined, some controversial terms are still in use. Indeed, the term "heavy metal" is a common term used for decades in the natural sciences, and even more in environmental sciences, particularly in studies of pollution impacts. As the use of the term appears to have increased, we highlight the relevance of the use of the term "Potentially Toxic Element(s)", which needs more explicit endorsement, and we illustrate the chemical elements that need to be considered
Drastic change in transport of entropy with quadrupolar ordering in PrFeP
The antiferroquadrupolar ordering of PrFeP is explored by
probing thermal and thermoelectric transport. The lattice thermal conductivity
drastically increases with the ordering, as a consequence of a large drop in
carrier concentration and a strong electron-phonon coupling. The low level of
carrier density in the ordered state is confirmed by the anomalously large
values of the Seebeck and Nernst coefficients. The results are reminiscent of
URuSi and suggest that both belong to the same class of aborted
metal-insulator transitions. The magnitude of the Nernst coefficient, larger
than in any other metal, indicates a new route for Ettingshaussen cooling at
Kelvin temperatures.Comment: final published versio
Nernst effect in the phase-fluctuating superconductor InO
We present a study of the Nernst effect in amorphous 2D superconductor
InO, whose low carrier density implies low phase rigidity and strong
superconducting phase fluctuations. Instead of presenting the abrupt jump
expected at a BCS transition, the Nernst signal evolves continuously through
the superconducting transition as previously observed in underdoped cuprates.
This contrasts with the case of NbSi, where the Nernst signal
due to vortices below T and by Gaussian fluctuations above are clearly
distinct. The behavior of the ghost critical field in InO points to a
correlation length which does not diverge at , a temperature below which
the amplitude fluctuations freeze, but phase fluctuations survive.Comment: 4 pages, 4 figure
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