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  • 1
    Electronic Resource
    Electronic Resource
    Enhancement of room temperature magnetoresistance in double perovskite ferrimagnets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5037-5039 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The double perovskite Sr2FeMoO6 is a half-metallic ferrimagnet exhibiting significant magnetoresistance (MR) at 300 K in a magnetic field H〈2 kOe. A preliminary study of the influence of isovalent and aliovalent substitutions for Sr2+ on the magnitude of the room-temperature MR is reported. Of the polycrystalline samples, Sr1.9A0.1FeMoO6 (A=Ca, Ba, La or Pr), the best result was obtained with the Ba(0.1) sample, which showed a factor of 2 enhancement of the MR over that previously reported for Sr2FeMoO6. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373240
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  • 2
    Electronic Resource
    Electronic Resource
    Grain-boundary room-temperature low-field magnetoresistance in Sr2FeMoO6 films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6761-6763 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited or LaAlO3 and SrTiO3 (001) substrates by pulsed laser deposition. The deposition conditions were optimized. Single-phase Sr2FeMoO6 was obtained in 100 mTorr 99.999% Ar gas at 825 °C. Transport and magnetic data showed a metallic temperature dependence and a saturation magnetization Ms at 10 K of 3.2μB/f.u. However, the Curie temperature TC(approximate)380 K was reduced from 415 K found for tetragonal polycrystalline best ceramics, which lowers Ms at 300 K in the thin films to 1.5μB/f.u. compared to 2.2μB/f.u. in the ceramics. A low remanence was attributed to the presence of antiphase boundaries. A Wheatstone bridge arrangement straddling a bicrystal boundary was used to verify that spin-dependent electron transfer through a grain boundary and not an antiphase boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372833
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  • 3
    Electronic Resource
    Electronic Resource
    Intra- versus intergranular low-field magnetoresistance of Sr2FeMoO6 thin films (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2812-2814 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of (001)-oriented Sr2FeMoO6 have been epitaxially deposited on LaAlO3 and SrTiO3 (001) substrates. Comparison of their transport and magnetic properties with those of polycrystalline ceramic samples shows a metallic versus semiconductor temperature dependence and a saturation magnetization Ms at 10 K of 3.2 μB/f.u. in the film as against 3.0 for a tetragonal polycrystalline sample. However, the Curie temperature TC(approximate)389 K is reduced from 415 K found for the tetragonal ceramic, which lowers Ms at 300 K in the thin films to 2.0 μB/f.u. compared to 2.2 μB/f.u. in the ceramics. A Wheatstone bridge arrangement straddling a bicrystal boundary has been used to verify that spin-dependent electron transfer through a grain boundary is responsible for the low-field magnetoresistance found in polycrystalline samples below TC. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125158
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  • 4
    Electronic Resource
    Electronic Resource
    Physical and chemical properties of (Y1−xCax)(Ba2−xLax)Cu3O7−δ (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 651-652 
    Details
    ISSN: 1572-9605
    Keywords: High-Tc superconductor ; chain conduction ; thermopower ; chemical stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The metallic conductivity of both the CuO2 sheets and the CuOx chains of YBa2Cu3O7−δ has been established. We have used double doping in (Y1−xCax)(Ba2−xLax)Cu3O7−δ to destroy the integrity of the CuO1−δ chains while keeping constant the total oxidation state of the Cu-O array. A break-up of the chain segments allows us to establish the temperature dependence of the Seebeck coefficient, α(T), due to the CuO2 sheets and, by difference, that of the CuO1−δ chains in YBa2Cu3O7−δ. We also show that double doping enhances significantly the chemical stability of the superconductive phase. The origin of the chemical stability and of the behavior of α(T) is interpreted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00727461
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  • 5
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    Biogeochemical Impact of Snow Cover and Cyclonic Intrusions on the Winter Weddell Sea Ice Pack (2017)
    In:  EPIC3Journal of Geophysical Research: Oceans, ISSN: 21699275
    Details
    Publication Date: 2020-06-14
    Description: Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R. V. Polarstern AWECS cruise, June–August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992. The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southward from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll-a (Chl-a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large-scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice, and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker, and more concentrated ice are sufficient to increase the snow depth and, somehow counterintuitively, to warm the ice.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    The role of surface-active carbohydrates in the formation of transparent exopolymer particles by bubble adsorption of seawater (1998)
    In:  EPIC3Limnology and oceanography, 43, pp. 1860-1871
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Anisotropy of magnetic susceptibility of rocks induced by experimental deformation (2006)
    Details
    Publication Date: 2019-11-04
    Description: In the present paper, the influence of the rheological process on the Anisotropy of Magnetic Susceptibility (AMS) of rocks is studied experimentally. The cylindrical samples of quartz-magnetite rock undergo a process under the confining stress of 300 MPa, temperature of 500-800 °C and strain rate of 5 ´ 10-5 - 1 ´ 10-4/s. The residual deformation after the above process ranges 9-42%, depending on the experimental condition. It is found that the magnetic susceptibilities and the shapes of magnetic grains in these samples are almost isotropic before deformation. After being deformed, these samples show certain amounts of anisotropy of magnetic susceptibility and the axes of maximum principal susceptibilities deviate from the original ones more or less. Furthermore, the grains become oblate-ellipsoidal and a certain preferred orientation occurs. The grain shape anisotropy seems to be the main reason for AMS formation. It appears that there is a limitation of the piezomagnetic theory in explaining some tectonomagnetic phenomena. The results obtained in this study imply that ductile deformation at high temperature and pressure in depth during a long time-process may result in another kind of response in rock magnetism, which could be a new mechanism of tectonomagnetic variation.
    Description: JCR Journal
    Description: open
    Keywords: anisotropy ; rheology ; ductile deformation ; high-temperature ; high-stress experiment ; seismomagnetism ; 04. Solid Earth::04.02. Exploration geophysics::04.02.04. Magnetic and electrical methods ; 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2607730 bytes
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  • 8
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    Assessing the O2 budget under sea ice: An experimental and modelling approach (2015)
    Elementa: Science of the Anthropocene
    In:  EPIC3Elementa: Science of the Anthropocene, Elementa: Science of the Anthropocene, pp. 1-11, ISSN: 3: 000080
    Details
    Publication Date: 2016-01-05
    Description: The objective of this study was to assess the O2 budget in the water under sea ice combining observations and modelling. Modelling was used to discriminate between physical processes, gas-specific transport (i.e., ice-atmosphere gas fluxes and gas bubble buoyancy) and bacterial respiration (BR) and to constrain bacterial growth efficiency (BGE). A module describing the changes of the under-ice water properties, due to brine rejection and temperature-dependent BR, was implemented in the one-dimensional halo-thermodynamic sea ice model LIM1D. Our results show that BR was the dominant biogeochemical driver of O2 concentra- tion in the water under ice (in a system without primary producers), followed by gas specific transport. The model suggests that the actual contribution of BR and gas specific transport to the change in seawater O2 concentration was 37% during ice growth and 48% during melt. BGE in the water under sea ice, as retrieved from the simulated O2 budget, was found to be between 0.4 and 0.5, which is in line with published BGE values for cold marine waters. Given the importance of BR to seawater O2 in the present study, it can be assumed that bacteria contribute substantially to organic matter consumption and gas fluxes in ice-covered polar oceans. In addition, we propose a parameterization of polar marine bacterial respiration, based on the strong temperature dependence of bacterial respiration and the high growth efficiency observed here, for further biogeochemical ocean modelling applications, such as regional or large-scale Earth System models
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 9
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    The impact of dissolved organic carbon and bacterial respiration on pCO2 in experimental sea ice (2016)
    PERGAMON-ELSEVIER SCIENCE LTD
    In:  EPIC3Progress In Oceanography, PERGAMON-ELSEVIER SCIENCE LTD, 141, pp. 153-167, ISSN: 0079-6611
    Details
    Publication Date: 2016-06-07
    Description: Previous observations have shown that the partial pressure of carbon dioxide (pCO2) in sea ice brines is generally higher in Arctic sea ice compared to those from the Antarctic sea ice, especially in winter and early spring. We hypothesized that these differences result from the higher dissolved organic carbon (DOC) content in Arctic seawater: Higher concentrations of DOC in seawater would be reflected in a greater DOC incorporation into sea ice, enhancing bacterial respiration, which in turn would increase the pCO2 in the ice. To verify this hypothesis, we performed an experiment using two series of mesocosms: one was filled with seawater (SW) and the other one with seawater with an addition of filtered humic-rich river water (SWR). The addition of river water increased the DOC concentration of the water from a median of 142 µmol Lwater-1 in SW to 249 µmol Lwater-1 in SWR. Sea ice was grown in these mesocosms under the same physical conditions over 19 days. Microalgae and protists were absent, and only bacterial activity has been detected. We measured the DOC concentration, bacterial respiration, total alkalinity and pCO2 in sea ice and the underlying seawater, and we calculated the changes in dissolved inorganic carbon (DIC) in both media. We found that bacterial respiration in ice was higher in SWR: median bacterial respiration was 25 nmol C Lice-1 h-1 compared to 10 nmol C Lice-1 h-1 in SW. pCO2 in ice was also higher in SWR with a median of 430 ppm compared to 356 ppm in SW. However, the differences in pCO2 were larger within the ice interiors than at the surfaces or the bottom layers of the ice, where exchanges at the air–ice and ice–water interfaces might have reduced the differences. In addition, we used a model to simulate the differences of pCO2 and DIC based on bacterial respiration. The model simulations support the experimental findings and further suggest that bacterial growth efficiency in the ice might approach 0.15 and 0.2. It is thus credible that the higher pCO2 in Arctic sea ice brines compared with those from the Antarctic sea ice were due to an elevated bacterial respiration, sustained by higher riverine DOC loads. These conclusions should hold for locations and time frames when bacterial activity is relatively dominant compared to algal activity, considering our experimental conditions.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment (2014)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Chemistry, ELSEVIER SCIENCE BV, 166, pp. 59-69, ISSN: 0304-4203
    Details
    Publication Date: 2014-12-10
    Description: We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14 °C for 14 days after which ice decay was induced by increasing the air temperature to −1 °C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.
    Repository Name: EPIC Alfred Wegener Institut
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