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  • 11
    Digitale Medien
    Digitale Medien
    Nuclear spin-lattice relaxation of isotopic impurities in solid hydrogen (1992)
    Springer
    Journal of low temperature physics 89 (1992), S. 699-702 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report calculations of the nuclear spin-lattice relaxation of isotopic impurities (HD) in solid hydrogen. The temperature-independent relaxation observed at low temperatures is attributed to the quantum tunneling of the impurities, and the pronounced minimum observed at intermediate temperatures is associated with scattering from thermally excited vacancies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00694120
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  • 12
    Digitale Medien
    Digitale Medien
    Population difference thermometry for ultra-low temperatures (1992)
    Springer
    Journal of low temperature physics 89 (1992), S. 715-718 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report measurements of the asymmetry of the intensities of the quadrupolar fine structure of NMR lines in ferromagnetic MnSb down to 30 mK. The asymmetry ratios provide a means of measuring the temperature, and is an example of the use of population difference thermometry as a primary thermometer for ultra-low temperatures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00694124
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  • 13
    Digitale Medien
    Digitale Medien
    Nuclear demagnetization cryostat at University of Florida Microkelvin laboratory (1992)
    Springer
    Journal of low temperature physics 89 (1992), S. 719-722 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Two nuclear-demagnetization cryostats, each containing 173 mol of copper coolant in a 8 T magnetic field and based on an Oxford Instruments model 1000 dilution refrigerator, have been under development at the University of Florida Microkelvin Laboratory for studies of nuclear magnetic ordering in metals and in solid3He, properties of superfluid3He at T≈0, and mesoscopic systems, and for development of primary thermometers based on population differences in nuclear quadrupole systems. The performance of the first cryostat is analyzed with emphasis on improvements to be made.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00694125
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  • 14
    Digitale Medien
    Digitale Medien
    Measurements of the nuclear spin-lattice relaxation times in BCC3He for high magnetic fields, high molar volumes, and low temperatures (1985)
    Springer
    Journal of low temperature physics 59 (1985), S. 45-81 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Experimental studies of the nuclear spin-lattice relaxation times in BCC helium three are reported for high molar volumes and low temperatures close to the minimum in the melting curve. The results show the existence of a new relaxation mechanism at low temperatures with an approximately linear temperature dependence (T 1 ∝T −1). An analysis of the vacancy-induced relaxation shows that both the vacancy formation energy and the vacancy mobility decrease dramatically as a function of density on approaching the maximum possible molar volume (minimum density) of the solid. A possible interpretation of both the new relaxation mechanism and the vacancy properties is outlined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00681504
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  • 15
    Digitale Medien
    Digitale Medien
    Local ordering in dilute ortho-para-hydrogen mixtures at low temperatures (1988)
    Springer
    Journal of low temperature physics 72 (1988), S. 1-24 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report experimental observations of the local orientational ordering of ortho-H2 molecules in dilute solid ortho-para mixtures for low temperatures. The results indicate a smooth, continuous freezing of the rotational degrees of freedom without any evidence for a distinct discontinuity in the temperature dependence of the local order parameters for the 37–600 mK temperature range.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00681725
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  • 16
    Digitale Medien
    Digitale Medien
    Spectral inhomogeneity of nuclear spin-lattice relaxation in orientationally ordered solid hydrogen (1986)
    Springer
    Journal of low temperature physics 65 (1986), S. 1-11 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The results of calculations of the nuclear spin-lattice relaxation time of orientationally ordered ortho-hydrogen molecules for the case of the local ordering in the orientational “glass” phase of ortho-para-hydrogen mixtures are given. A strong dependence on the position of the NMR isochromat in the line shape is found and this is in good agreement with the experimental results of the Duke group, provided that the cross-relaxation is taken into account. The relaxation is found to deviate considerably from an exponential recovery.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00685399
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  • 17
    Digitale Medien
    Digitale Medien
    NMR studies of molecular hydrogen in zeolite (1995)
    Springer
    Journal of low temperature physics 98 (1995), S. 383-401 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We report new pulsed NMR studies of the supercooling of molecular hydrogen constrained to the interior of the molecular cages of zeolite. Measurements of the supercooling for the ultra-small structure of zeolite-5A in comparison with earlier studies show that the substantial supercooling observed does not depend strongly on the characteristic dimensions and is interpreted as a class-II growth attributed to imperfect wetting. Studies of the supercooling of HD and detailed analyses of the orientational ordering of molecular H2 show that the abrupt transitions observed in the pulsed NMR studies are associated with the supercooled liquid/solid transitions and are not associated with orientational ordering.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00752275
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  • 18
    Digitale Medien
    Digitale Medien
    The Orientational Ordering of Molecular Hydrogen in 2D (2000)
    Springer
    Journal of low temperature physics 120 (2000), S. 89-106 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The orientational ordering of ortho-hydrogen molecules on a triangular lattice is calculated as a function of ortho concentration using the method of restricted traces. The calculated temperatures for the transitions from the disordered phase to the long range pinwheel ordered phase show a strong concentration dependence with a critical concentration X c=73% below which the long range ordering is not realized in this model. The results are consistent with recent NMR studies of ortho-para hydrogen mixtures adsorbed as a commensurate $$\sqrt 3 $$ × $$\sqrt 3 $$ structure on hexagonal boron nitride for which X c=69±4%. The values of the observed transition temperatures can only be understood if there is a large renormalization of the effective quadrupolar interaction constant in 2D.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004660919750
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  • 19
    Digitale Medien
    Digitale Medien
    Anomalous nuclear spin lattice relaxation of3He adsorbed on porous material (1976)
    Springer
    Journal of low temperature physics 22 (1976), S. 313-323 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Measurements of the nuclear spin lattice relaxation times of3He adsorbed on porous material for a wide range of temperatures (0.33〈T〈1.5 K) and applied magnetic fields (3.75〈H〈25 kG) indicate that the relaxation time of the adsorbed atoms is anomalously short with respect to the minimum allowable value for internuclear dipolar interactions, and the observed temperature and field dependence establishes that paramagnetic impurities on the surface do not play a major role in the relaxation process. Comparison with the relaxation rates of129Xe adsorbed on Vycor glass suggests that the relaxation is intimately related to the mobility of the3He adatoms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00654710
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  • 20
    Digitale Medien
    Digitale Medien
    Orientational Ordering in Monolayer Films of Molecular Hydrogen on Boron Nitride (1999)
    Springer
    Journal of low temperature physics 114 (1999), S. 173-201 
    Details
    ISSN: 1573-7357
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract NMR studies of monolayer hydrogen films for both the expected $$\sqrt {\text{3}} \times \sqrt {\text{3}} $$ commensurate solid and the incommensurate solid (for full monolayer coverage) on hexagonal boron nitride (BN) are reported for ortho-H 2 concentrations 0.30≤X≤0.74 and temperatures 0.08〈T〈4.2 K. Phase diagrams for these systems are mapped out in terms of X and T from clear structural changes of the NMR spectra, including the observation of a 2D orientational quadrupolar glass ordering for X〈X crit =0.69, and long range orientational ordering for X〉X crit for commensurate films.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021858021708
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