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  • 1
    Electronic Resource
    Electronic Resource
    Investigations of nuclear magnetism in silver down to picokelvin temperatures. I (1991)
    Springer
    Journal of low temperature physics 85 (1991), S. 1-24 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nuclear magnetic ordering in silver has been investigated by the low-field NMR technique using an rf SQUID. Spin entropies down to 0.50 · R ln 2, corresponding to polarizations up to 78%, were obtained. An indication of antiferromagnetic ordering was observed in the static magnetic susceptibility, which showed clear saturation at the beginning of warmup after cooling to T〈1 nK by adiabatic demagnetization to B=10±5 µT; the critical entropy of the transition was found to be Sc=(0.60±0.04) · R ln 2. The NMR absorption increased in the ordered state at frequencies around 75 Hz. Remnants of this increase were observed in the paramagnetic phase as well. The feasibility of experiments at negative spin temperatures was demonstrated by a quick reversal of the external magnetic field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683319
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Indirect nuclear spin interactions and nuclear ordering in metals (1987)
    Springer
    Journal of low temperature physics 66 (1987), S. 155-167 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract All conduction electron-mediated nuclear spin interactions that arise from the electron-nuclear hyperfine Hamiltonian are calculated using Bardeen's spherical approximation for electronic wave functions. The results are applied to nuclear magnetic ordering in copper, where non-s-electron-mediated interactions are found to be important for the understanding of the ordered state properties. The ordered structure of silver nuclei is predicted to be a generalized form of a type I antiferromagnet due to the dominating Ruderman-Kittel interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681818
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  • 3
    Electronic Resource
    Electronic Resource
    Investigations of nuclear antiferromagnetic ordering in copper at nanokelvin temperatures (1986)
    Springer
    Journal of low temperature physics 62 (1986), S. 433-487 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nuclear magnetism in metallic copper has been studied by demagnetizing highly polarized spins to low fields where spin-spin interactions dominate. In earlier experiments anomalous spin-lattice relaxation caused by impurities warmed up nuclear spins too fast; this adverse effect was overcome by selective oxidation of impurities. In zero field the critical temperatureT c of the antiferromagnetic transition is 58±10 nK, and during the first-order phase change the entropy increases from (0.48±0.03)ℛ ln 4 to (0.61±0.03)ℛ ln 4. The critical fieldB c =0.27±0.01 mT. The entropy and the static susceptibility of the nuclear spins were measured as a function of temperature whenB=0. These curves agree with theory in the paramagnetic state. In a polycrystalline sample two anomalies were observed at the lowest entropies in the NMR line shapes of the dynamic susceptibility and in the behavior of the static susceptibility. However, when measuring the static susceptibility of a single-crystal specimen in the three Cartesian directions, three different ordered phases were found. These antiferromagnetic states are described and theB-S phase diagram is presented. Metastability and nonadiabaticity are discussed. The observed large reduction ofT c from the mean field calculationT MF=230 nK is caused by fluctuations. The free electron model of the Ruderman-Kittel (RK) interaction seems to be able to explain only one ordered phase. However, relatively small changes to the RK range function or inclusion of non-s-electron-mediated interactions to the Hamiltonian may increase the number of ordered phases to three. Long-living metastable states are another possible explanation for the observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683405
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  • 4
    Electronic Resource
    Electronic Resource
    A Versatile Nuclear Demagnetization Cryostat for Ultralow Temperature Research (2000)
    Springer
    Journal of low temperature physics 120 (2000), S. 121-150 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new cascade nuclear demagnetization cryostat has been designed and constructed. Our aim was to build a versatile, modular cryostat, with a large experimental space providing an excellent platform for various types of ultralow temperature measurements. A powerful dilution refrigerator, combined with a massive copper nuclear cooling stage, enables us to reach lattice temperatures below 100 μK continuously for more than two months. The cryostat is equipped with a second magnet for operating a double-stage nuclear demagnetization setup. Details of the design and performance are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004665020659
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