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  • 1995-1999  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Effects of the microstructure on the magnetotransport properties of polycrystalline manganite films grown by metalorganic chemical vapor deposition (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6945-6955 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of the microstructure on the magnetoresistance of polycrystalline manganite (La1−xSrxMnO3) thin films have been investigated. The films have been grown by metalorganic chemical vapor deposition on silicon (001) substrates covered with a native silica layer. Different microstructures were obtained by varying the substrate temperature in the range (550–750 °C). The films exhibit a ferromagnetic/paramagnetic transition around 325 K. The grain size is in the range 20–100 nm and, for deposition temperature lower than 650 °C, weak links appear in the films as the grains are mostly noncohesive. The low-field contribution to the magnetoresistance is independent of the grain size in the studied range. A factor of ∼1.8 is gained in this contribution as the substrate temperature is lowered below 650 °C, which can be related to the occurrence of noncohesive grains in the films. The largest low-field magnetoresistance obtained is about 20% at 22 K (under 0.2 T). The high-field contribution to the total magnetoresistance appears to be independent of the microstructure of the films. Our results are discussed in the framework of spin-dependent transport mechanisms (tunneling or scattering). Finally, the low-temperature (T≤20 K) resistivity upturn observed for all the polycrystalline films is discussed. It can be attributed to activated transport phenomena (Coulomb blockade tunneling or tunneling through impurities, with activation energies on the order of 0.05 meV) or to localized states in the material. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371777
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The surface structure of icosahedral Al68Pd23Mn9 measured by STM and LEED (1995)
    Springer
    Applied physics 61 (1995), S. 491-501 
    Details
    ISSN: 1432-0630
    Keywords: 61.44.+p ; 68.35.Bs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract For the first time the surface structure of an icosahedral quasicrystal has been successfully investigated in Ultra-High Vacuum (UHV) by Scanning Tunneling Microscopy (STM) and Low-Energy Electron Diffraction (LEED). After cleaning an i-Al68Pd23Mn9 sample in UHV by cycles of ion-sputtering and annealing at temperatures close to the melting point atomically flat terraces are observed by STM. Successive step heights show quasiperiodic order according to the Fibonacci chain. The normals of these terraces are parallel to a five-fold axis as revealed by highly resolved STM images. On the terraces five-fold stars and pentagonal holes are observed. Their orientation is the same on all terraces investigated. Additionally to this long-range orientational order, a high degree of quasiperiodic order is found for the pentagonal holes. This indicates that the quasiperiodic order of this highly ordered and thermodynamically stable quasicrystal extends even up to the surface. Both the step heights and the distances between the pentagonal holes well agree with the values derived from a structural model of this material. Five-fold symmetric LEED patterns can be analysed by means of the Fourier transform of a Fibonacci pentagrid as suggested by the STM data. The analysis yields the same line separations within the pentagrid as deduced from the STM experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01540250
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The surface structure of icosahedral Al68Pd23Mn9 measured by STM and LEED (1995)
    Springer
    Applied physics 61 (1995), S. 491-501 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 61.44.+p; 68.35.Bs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  For the first time the surface structure of an icosahedral quasicrystal has been successfully investigated in Ultra-High Vacuum (UHV) by Scanning Tunneling Microscopy (STM) and Low-Energy Electron Diffraction (LEED). After cleaning an i-Al68Pd23Mn9 sample in UHV by cycles of ion-sputtering and annealing at temperatures close to the melting point atomically flat terraces are observed by STM. Successive step heights show quasiperiodic order according to the Fibonacci chain. The normals of these terraces are parallel to a five-fold axis as revealed by highly resolved STM images. On the terraces five-fold stars and pentagonal holes are observed. Their orientation is the same on all terraces investigated. Additionally to this long-range orientational order, a high degree of quasiperiodic order is found for the pentagonal holes. This indicates that the quasiperiodic order of this highly ordered and thermodynamically stable quasicrystal extends even up to the surface. Both the step heights and the distances between the pentagonal holes well agree with the values derived from a structural model of this material. Five-fold symmetric LEED patterns can be analysed by means of the Fourier transform of a Fibonacci pentagrid as suggested by the STM data. The analysis yields the same line separations within the pentagrid as deduced from the STM experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01540250
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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