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  • Articles: DFG German National Licenses  (3)
  • 1985-1989  (3)
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  • Articles: DFG German National Licenses  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Nuclear spin-lattice relaxation in metals at low temperatures (1988)
    Springer
    Journal of low temperature physics 70 (1988), S. 151-172 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In NMR experiments performed on metals at low temperatures, the analysis to obtain the nuclear spin-lattice relaxation time τ1 can be quite complicated. The electronic heat capacity ultimately becomes less than that of the nuclear spins, and the characteristic times for heat flow through the various resistances between the nuclear spins and the thermal bath can become long relative to τ1. This makes it necessary to solve the full set of coupled differential equations describing the thermal relaxation. This problem has been examined because τ1 is used as a thermometric parameter, and we consider the cases when the radiofrequency field penetrates the sample completely (powders and foils) and when only the skin-depth nuclei are excited (bulk specimens). Using our theoretical model, we analyze experimental results for platinum powder and a thallium bulk sample and obtain consistent values for κ=τ1 T over a wide range of experimental conditions, even when thermal bottlenecks occur and the apparent relaxation time is much longer than τ1. These values are κ(Pt)=(34.2±0.6)×10−3 sec K and κ(Tl)=(4.37±0.08)×10−3 sec K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683249
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Comment on pulsed NMR thermometry at very low temperatures (1988)
    Springer
    Journal of low temperature physics 73 (1988), S. 207-219 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract At temperatures below 1 mK the rf power in pulsed NMR experiments is normally kept as low as possible in order to minimize eddy current heating in the metallic samples used for thermometry. However, for metallic samples with short Korringa constants a temperature dependence enters via the spin-lattice relaxation mechanism in addition to the paramagnetic dependence. It may cause systematic errors if the temperature of the conduction electrons is raised by eddy current heating due to the action of the rf pulse to a temperatureT e which is not very small compared to ω1κ, with κ being the Korringa constant and ω1 the rotation frequency of the nuclear moments in the rf field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681977
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Very low temperatures and their applications in nuclear orientation (1985)
    Springer
    Hyperfine interactions 22 (1985), S. 221-234 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In NO-experiments at very low temperatures problems arise from the finite life-time of the nuclei and the radioactive self-heating of the source. Recent developments of top loading hyperfine enhanced nuclear demagnetization cryostats of small cooling power give fast access to temperatures around 1 mK. To reach lower temperatures the bottleneck of thermal contact must be overcome in order to cool samples which are themselves the main source of heat. In this context the limitations of nuclear demagnetization cryostats are discussed with respect to their application in “brute force”- and NQR/NMR-experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02063996
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    Paper (German National Licenses)
    Fulltext
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