Reciprocal space mapping of magnetic order in thick epitaxial MnSi films

We report grazing incidence small angle neutron scattering (GISANS) and complementary off-specular neutron reflectometry (OSR) of the magnetic order in a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit. Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a magnetic modulation perpendicular to the films under magnetic fields parallel and perpendicular to the film, where additional polarized neutron reflectometry (PNR) and magnetization measurements are in excellent agreement with the literature. Regardless of field orientation, our data does not suggest the presence of more complex spin textures, notably the formation of skyrmions. This observation establishes a distinct difference with bulk samples of MnSi of similar thickness under perpendicular field, in which a skyrmion lattice dominates the phase diagram. Extended x-ray absorption fine structure measurements suggest that small shifts of the Si positions within the unstrained unit cell control the magnetic state, representing the main difference between the films and thin bulk samples

Element-Specific Depth Profile of Magnetism and Stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 Interface

Depth-sensitive magnetic, structural and chemical characterization is important in the understanding and optimization of novel physical phenomena emerging at interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant X-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers with sub-nanometer resolution. In particular, the X-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element specific depth profile of the ferromagnetic moments in both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in contrast to previous observations on inversely deposited layers. Additional resonant X-ray reflection measurements indicate a region of an altered Mn- and O-content at the interface, with a thickness matching that of the magnetic diluted layer, as origin of the reduction of the magnetic moment.Comment: 13 pages, 4 figures, supplemental material include

Local effects of large food-falls on nematode diversity at an arctic deep-sea site: results from an <i>in situ</i> experiment at the deep-sea observatory HAUSGARTEN

To study the response of the smaller benthic biota to larger food-falls and their possible effects on the biodiversity at the deep seafloor, we deployed the halves of a sagittally bisected porpoise (1.3 m in length: each half approximately 18 kg) at 2500 m and 5400 m water depth at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the eastem Fram Strait. Five weeks after the porpoise deployment, sediments beneath the carcasses and at different distances (0, 20, 40 cm) from these artificial food-falls were sampled with push-corers handled by a Remotely Operated Vehicle. The samples provided empirical evidence for a quick response by sediment-inhabiting bacteria and metazoan meiofauna to the carcasses at both water depths. Compared to control sediments, the substantial pulse of organic matter also led to generally increased meiofauna/nematode densities around the artificial food-falls. The comparison of nematode communities in sediments affected by the carcasses with those in control sediments exhibited shifts in the structural composition and the associated trophic and functional diversity of the nematodes. Our results confirmed that the impact of large food-falls on the deep benthic community largely depend on environmental factors (water depth, alternative food sources) as well as the background species composition, i.e., the structure of the prevailing meiofauna/nematode assemblages and the composition of the necrophagous community present in the wider area

Interfacial roughness and proximity effects in superconductor/ferromagnet CuNi/Nb heterostructures

© 2015 AIP Publishing LLC. We report an investigation of the structural and electronic properties of hybrid superconductor/ferromagnet (S/F) bilayers of composition Nb/Cu60Ni40 prepared by magnetron sputtering. X-ray and neutron reflectometry show that both the overall interfacial roughness and vertical correlations of the roughness of different interfaces are lower for heterostructures deposited on Al2O3(1 1 ¯ 02) substrates than for those deposited on Si(111). Mutual inductance experiments were then used to study the influence of the interfacial roughness on the superconducting transition temperature, TC. These measurements revealed a ∼4% higher TC in heterostructures deposited on Al2O3, compared to those on Si. We attribute this effect to a higher mean-free path of electrons in the S layer, caused by a suppression of diffusive scattering at the interfaces. However, the dependence of the TC on the thickness of the ferromagnetic layer is not significantly different in the two systems, indicating a weak influence of the interfacial roughness on the transparency for Cooper pairs

Trends in biomass, density and diversity of North Sea macrofauna

Total biomass and biomass of large taxonomic groups (polychaetes, molluscs, crustaceans, echinoderms) and species diversity of the macrofauna were determined for almost 200 North Sea stations sampled synoptically by seven vessels during Spring 1986 and for 120 additional stations sampled in earlier years by the Marine Laboratory in Aberdeen. There exists a clear and significant decreasing trend in biomass with latitude, both in total biomass and for the different taxonomic groups. Apart from latitude, sediment composition and chlorophyll a content of the sediment also infuence total biomass and biomass of most groups significantly. Biomass increases consistently in finer sediments and sediments with a higher chlorophyll a content. The same trends are found for the results within laboratories. Some interaction exists, indicating weak laboratory and zonal effects. Diversity, as measured by Hill's diversity index N1 = (exp H′) shows a clear and significant trend with latitude. Towards the north of the North Sea diversity increases considerably. The trend is also found for laboratories separately and is everywhere equally strong. Also longitude and depth show an effect on diversity. Sediment variables have no clear influence on diversity. Other diversity measures show the same trend but are more variable than N1,. Total density tends to increase towards the north, but sediment related variables have a larger influence. Mean individual weight becomes considerably smaller towards the northern part of the North Sea

HAUSGARTEN: Multidisciplinary investigations at a deep-sea, long-term observatory in the Arctic Ocean

The marine Arctic has played an essential role in the history of our planet over the past 130 million years and contributes considerably to the present functioning of Earth and its life. The global cycles of a variety of materials fundamental to atmospheric conditions and thus to life depend to a signifi cant extent on Arctic marine processes (Aargaard et al., 1999). The past decades have seen remarkable changes in key Arctic variables. The decrease of sea-ice extent and sea-ice thickness in the past decade is statistically signifi - cant (Cavalieri et al., 1997; Parkinson et al., 1999; Walsh and Chapman, 2001; Partington et al., 2003; Johannessen et al., 2004). There have also been large changes in the upper and intermediate layers of the ocean, which have environmental implications. For instance, the deep Greenland Sea has continued its decadal trend towards warmer and saltier conditions, with a corresponding decrease in oxygen content, refl ecting the lack of effective local convection and ventilation (Dickson et al., 1996; Boenisch et al., 1997). Changes in temperature and salinity and associated shifts in nutrient distributions will directly affect the marine biota on multiple scales from communities and populations to individuals, consequently altering food-web structures and ecosystem functioning (Benson and Trites, 2002; Moore, 2003; Schumacher et al., 2003; Wiltshire and Manly, 2004; Perry et al., 2005). Today, we do not know whether the severe alterations in abiotic parameters represent perturbations due to human impacts, natural long-term trends, or new equilibriums (Bengtson et al., 2004). Because Arctic organisms are highly adapted to extreme environmental conditions with strong seasonal forcing, the accelerating rate of recent climate change challenges the resilience of Arctic life (Hassol, 2004). The entire system is likely to be severely affected by changing ice and water conditions, varying primary production and food availability to faunal communities, an increase in contaminants, and possibly increased UV irradiance. The stability of a number of Arctic populations and ecosystems is probably not strong enough to withstand the sum of these factors, which might lead to a collapse of subsystems. To detect and track the impact of large-scale environmental changes in the transition zone between the northern North Atlantic and the central Arctic Ocean, and to determine experimentally the factors controlling deep-sea biodiversity, the German Alfred Wegener Institute for Polar and Marine Research (AWI) established the deepsea, long-term observatory HAUSGARTEN, representing the fi rst, and by now only, open-ocean, long-term station in a polar region