73 research outputs found
Electronic ground states of Fe and Co as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy
The electronic ground state of the Co diatomic molecular cation
has been assigned experimentally by x-ray absorption and x-ray magnetic
circular dichroism spectroscopy in a cryogenic ion trap. Three candidates,
, , and , for the electronic ground state of Fe
have been identified. These states carry sizable orbital angular momenta that
disagree with theoretical predictions from multireference configuration
interaction and density functional theory. Our results show that the ground
states of neutral and cationic diatomic molecules of transition elements
cannot generally be assumed to be connected by a one-electron process
Spin and orbital magnetic moments of size-selected iron, cobalt, and nickel clusters and their link to the bulk phase diagrams
Spin and orbital magnetic moments of cationic iron, cobalt, and nickel
clusters have been determined from x-ray magnetic circular dichroism
spectroscopy. In the size regime of atoms, these clusters show
strong ferromagnetism with maximized spin magnetic moments of 1~ per
empty state because of completely filled majority spin bands. The
only exception is where an unusually low average spin
magnetic moment of ~ per unoccupied state is
detected; an effect, which is neither observed for nor
.\@ This distinct behavior can be linked to the existence
and accessibility of antiferromagnetic, paramagnetic, or nonmagnetic phases in
the respective bulk phase diagrams of iron, cobalt, and nickel. Compared to the
experimental data, available density functional theory calculations generally
seem to underestimate the spin magnetic moments significantly. In all clusters
investigated, the orbital magnetic moment is quenched to \,\% of the
atomic value by the reduced symmetry of the crystal field. The magnetic
anisotropy energy is well below 65 eV per atom
Large orbital magnetic moments of small, free cobalt cluster ions Co n with n lt; 9
The size dependent electronic structure and separate spin and orbital magnetic moments of free Co cluster ions have been investigated by x ray absorption and x ray magnetic circular dichroism spectroscopy in a cryogenic ion trap. A very large orbital magnetic moment of per atom was determined for Co, which is one order of magnitude larger than in the bulk metal. Large orbital magnetic moments per atom of amp; 8201; amp; 8201; amp; 8776;1 were also found for Co, Co, and Co. The orbital contribution to the total magnetic moment shows a non monotonic cluster size dependence The orbital contribution increases from a local minimum at n amp; 8201; amp; 8201; amp; 8201; amp; 8201;2 to a local maximum at n amp; 8201; amp; 8201; amp; 8201; amp; 8201;5 and then decreases with increasing cluster size. The 3d spin magnetic moment per atom is nearly constant and is solely defined by the number of 3d holes which shows that the 3d majority spin states are fully occupied, that is, 3d hole spin polarization is 10
Mn-Acetate Complexes Studied as Single Molecules
The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn12 coordination clusters of general formula [MnMnO(RCOO)(HO)] had been exemplified by bulk samples of the archetypal [MnMnO(CHCOO)(HO)] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn12 system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [MnO(CHCOO)(CHCN)] (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [MnO(CHCOO)(CHCN)] (1), [[MnO(CHCOO)] (2), [MnO(CHCOO)(HO)] (3), and the complex in bulk geometry [MnMnO(CHCOO)(HO)] (5). The found magnetic fingerprints – experiment and theory alike – are of a remarkable robustness: The Mn core bears almost no magnetic anisotropy while the surrounding MnIII8 ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects
Positive impacts of important bird and biodiversity areas on wintering waterbirds under changing temperatures throughout Europe and North Africa
Migratory waterbirds require an effectively conserved cohesive network of wetland areas throughout their range and life-cycle. Under rapid climate change, protected area (PA) networks need to be able to accommodate climate-driven range shifts in wildlife if they are to continue to be effective in the future. Thus, we investigated geographical variation in the relationship between local temperature anomaly and the abundance of 61 waterbird species during the wintering season across Europe and North Africa during 1990-2015. We also compared the spatio-temporal effects on abundance of sites designated as PAs, Important Bird and Biodiversity Areas (IBAs), both, or neither designation (Unlisted). Waterbird abundance was positively correlated with temperature anomaly, with this pattern being strongest towards north and east Europe. Waterbird abundance was higher inside IBAs, whether they were legally protected or not. Trends in waterbird abundance were also consistently more positive inside both protected and unprotected IBAs across the whole study region, and were positive in Unlisted wetlands in southwestern Europe and North Africa. These results suggest that IBAs are important sites for wintering waterbirds, but also that populations are shifting to unprotected wetlands (some of which are IBAs). Such IBAs may therefore represent robust candidate sites to expand the network of legally protected wetlands under climate change in north-eastern Europe. These results underscore the need for monitoring to understand how the effectiveness of site networks is changing under climate change.Peer reviewe
Landscape structure, human disturbance and crop management affect foraging ground selection by migrating geese
It is well known that agricultural intensification has caused severe population declines among bird species which use farmland for breeding and overwintering, while migrating bird species may benefit from intensive farming, but in turn damage crops. Knowledge of the habitat selection of migrating birds is important from both a conservation and agro-economic point of view. We investigated the habitat preferences of three common migrating goose species: White-fronted Goose Anser albifrons, Bean Goose A. fabalis and Greylag Goose A. anser during the autumn of 2009 in western Poland. A total of 24 flocks of these species were identified. Geese preferred large, elevated fields that were remote from forests and human settlements but in close proximity to a lake. Geese selected maize stubbles and avoided winter cereals. They selected sites in landscapes with a lower diversity of crops. Flock size was negatively correlated with the proportion of pastures in the landscape, but it increased with field size, distance to forest and distance to town. Our results are in contrast with the paradigm that less intensive farmland positively influences habitat use by birds during foraging. We advise the delayed ploughing of stubbles with the aim of creating appropriate foraging habitats for geese and minimizing damage to cereal crops
Fluoride concentrations in the pineal gland, brain and bone of goosander (Mergus merganser) and its prey in Odra River estuary in Poland
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