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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Magnesium diboride, MgB2, has a relatively high superconducting transition temperature, placing it between the families of low- and high-temperature (copper oxide based) superconductors. Supercurrent flow in MgB2 is unhindered by grain boundaries, making it potentially ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 410 (2001), S. 563-565 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The recently discovered superconductor magnesium diboride, MgB2, has a transition temperature, Tc, approaching 40 K, placing it intermediate between the families of low- and high-temperature superconductors. In practical applications, superconductors are permeated ...
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In doped perovskite manganites of the form Rj _ xAJVlnC)3, where R and A are rare-earth and alkaline-earth elements respectively, a marked polarization of charge carriers due to strong intra-atomic Hund interactions on the manganese sites leads to a dependence of the electrical resistivity on the ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4081-4084 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A c-axis oriented YBa2Cu3O7−δ film, 180–230 nm thick, deposited onto 〈100〉 LaAlO3 by dc sputtering was irradiated at room temperature with 50 keV 2H+ (deuterium) ions to a dose of 1×1016 cm−2. Secondary-ion-mass spectroscopy analysis shows that after implantation the implanted 2H is trapped in both the film and the substrate. For example, when the thickness of the YBCO film is equal to ∼180 nm, it contains about 4.5% of the retained dose. The as-implanted 2H distribution is essentially Gaussian-like and the depth (Rˆp) of maximum 2H concentration is ∼485 nm. It is obvious that the target crystallinity has to be taken into account for the range data, since the experiment values (Rˆp,R¯p, and ΔRp) are obviously larger than the corresponding values from the transport of ions in matter code. This implantation makes the YBa2Cu3O7−δ film more granular. Within the irradiated LaAlO3 substrate, a damaged band was observed by cross-sectional transmission electron microscopy, which was centered at about 85% of Rˆp(exp).
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4703-4708 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of polycrystalline La0.7−xYxCa0.3MnO3 samples were studied, where x=0, 0.07, 0.1, 0.15, and 0.2. Measurement of the dc resistivity, microwave surface resistance, ac susceptibility, and dc magnetization were made. As expected, the magnetic state becomes more frustrated as Y is added. It is found that the dc resistivity is approximately two orders of magnitude larger than the 9 GHz resistivity for all samples, however, both increase with Y doping by the same multiplicative factor. From circumstantial evidence and estimation of the grain boundary response time, it is found that the microwave measurement short circuits the grain boundaries. We assume that the dc resistivity is dominated by grain boundary properties and the microwave resistivity reflects intragranular behavior. Analysis of the electrical transport at dc and microwave frequencies is carried out and a phenomenological model proposed which agrees well with observation. The model implies that the influence of Y is modified by the underlying static disorder in which it is placed. © 2000 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1005-1007 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of colossal magnetoresistance (MR) material La0.7Ca0.3MnO3 were implanted with 200 keV Cr ions over a range of fluence from 1×1013 to 5×1015 ions/cm2. Resistance measurements were made in zero and applied magnetic fields of up to 8 T. At fluences of 1×1014 and 5×1014 Cr+/cm2, the resistance was much greater than in the unimplanted material and the metal–insulator transition temperature was suppressed to values below 20 K. For the highest fluence (5×1015 ions/cm2), a reentrant metal–insulator-type transition was observed and the resistance dropped significantly. Furthermore, improvement in the low-field MR was observed between the virgin and high fluence implanted films for fields less than 500 mT. These results are interpreted in terms of changes in magnetic properties with depth, defect creation, and the influence of oxygen deficiency. © 1998 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2929-2934 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Patterns on YBa2Cu3O6.87 films, laser written in O2 or N2 atmospheres, and with various writing power densities and scanning speeds, have been studied by Raman scattering. For laser writing in O2 at atmospheric pressure, with low power density and fast scanning speed, it is found systematically that the oxygen content of YBa2Cu3Ox can be reduced. Only when the writing power density is high and the scanning speed is low (e.g., 2.3 mW/μm2 and 1 μm/s), do the laser-irradiated lines in an O2 atmosphere approach full oxygenation (x→7). For laser writing in N2 at atmospheric pressure, the oxygen stoichiometry always decreases, rendering the lines nonsuperconducting. The structural phase transition from orthorhombic to tetragonal can be identified with laser writing in a N2 atmosphere with a writing power density of 1.9 mW/μm2 and a scanning speed of 20 μm/s. The oxygen O(4) line (∼500 cm−1) and the Ba line (115 cm−1) disappear, and the intensity of the Cu(2) line (144 cm−1) rises sharply when the phase transition occurs. This study shows how Raman scattering can be used as a routine technique, which is fast, sensitive, and nondestructive, and is able to measure oxygen content on a fine scale (a few μm) during high-Tc superconductor device processing. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 394-399 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been found that the synthesis conditions and subsequent annealing treatments can significantly change the magnetic and transport behavior of the colossal magnetoresistive materials of the general formula La1−zAzMnO3, where A is a divalent ion. In order to clarify the role of vacancies within this structure, resistivity and magnetization measurements have been carried out on a series of samples derived from the parent compound LaMnO3, with La and Mn vacancies introduced by systematically varying the oxygen annealing conditions. Previous studies have shown that for a given carrier concentration, the Curie temperature of the paramagnetic to ferromagnetic transition (Tc) increases as the tolerance factor of the perovskite structure increases and then begins to decrease slowly for even higher tolerance factors. Generally, Tc also increases with the Mn4+ content, consistent with a double exchange mechanism responsible for ferromagnetism. In this study Tc was found to decrease as the vacancy concentration (and therefore the Mn4+ concentration) and tolerance factor both increase. The magnetic and transport data are discussed in the light of structural information obtained from neutron diffraction studies. In the present study it is found that La and Mn vacancies play a significant role in determining the physical properties of these materials: for high vacancy concentrations (x,y≥0.080) the magnetic properties are analogous to those of spin glasses associated with disorder and frustration. Semiconductorlike resistivity was observed for all samples at all temperatures. © 1998 American Institute of Physics.
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  • 9
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract It was found from plan-view transmission electron microscopy (TEM) observations that c-oriented YBa2Cu3O7−δ (YBCO) films on LaAlO3, prepared by the magnetron sputtering technique had a single crystalline-like YBCO matrix, but always contained some precipitates of impurity phases. A large number of highly defective twin boundaries were also observed in all of these epitaxial films. Such highly defective twin boundaries are thought to be flux pinning centres and also paths for the diffusion of water into YBCO films. Therefore the films need to be passivated against attack from humid air.
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  • 10
    ISSN: 1572-9605
    Keywords: Bi2Sr2CaCu2O10/Ag ribbons ; I–V characteristics ; flux creep ; anisotropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Current-voltage characteristics of high-critical-current Bi2Sr2CaCu2O10/Ag ribbons were measured using both transport and magnetization techniques. The slope of these curves changes with magnetic field and temperature in a way very similar to the observedj c (H, T) behavior. This correspondence between the critical current and the slope of theI–V characteristics can be explained within the thermally activated flux creep framework. The dependence ofj c on the angle between field and ribbon is compared to the existing intrinsic anisotropy models.
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