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  • 1995-1999  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of experimental and theoretical physics 87 (1998), S. 996-1002 
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An investigation based on the coupled Maxwell-Bloch equations for a system of equivalent exchange-coupled spins is performed in order to explain a number of features of NMR spectra obtained in metals by Fourier-transforming of the free-induction decay at ultralow temperatures. Small angles of tilting of the nuclear magnetization by the exciting rf field are considered. It is shown that the free precession inherits the nonuniformity in the distribution of the rf field and the magnetization produced at the excitation stage inside the sample on account of the skin effect. As a result, the NMR spectrum is found to consist of a set of peaks—signals due to standing spin waves. However, such a spectrum can be observed only when the detuning of the exciting rf field is sufficiently large relative to the Larmor frequency of the spins. Otherwise, the rf field does not penetrate into the sample because of strong absorption by the spins. If the detuning is large, the dispersion signal and part of the NMR absorption signal are proportional to the equilibrium magnetization to the power 3/2. Such behavior is expected at low temperatures so that the coupling of the magnetization with the rf field is strong. The results obtained qualitatively explain the experimentally observed characteristics of the NMR spectra: the presence of kinks and structure of the NMR lines, the dependence of the shape and intensity of the spectrum on the detuning of the exciting rf field, and the nonlinear dependence of the nuclear susceptibility on the reciprocal of the sample temperature.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The self-aligned in-line technique has been applied to the preparation of ultrasmall low-capacitance metallic tunnel junctions. By using e-beam lithography the area of Al/AlOx/Al contacts has so far been reduced to less than 0.005 μm2. At low temperatures high-ohmic double junctions with a small metallic island between them show the Coulomb blockade effect. The current through such a device could be modulated by a voltage applied to a gate electrode capacitively coupled to the island (single-electron transistor). Both single-charge phenomena have been observed at temperatures up to 1 K. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 101 (1995), S. 767-773 
    ISSN: 1573-7357
    Keywords: 67.50.Fi ; 43.25.+y
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sound absorption of3He-B at 0 bar was studied at a frequency of 10 MHz. We performed pulsed experiments with different pulse lengths (4 to 15 μs) and pulse powers (0.1 to 160 μW) in the temperature range 0.2 〈 T/TC 〈 2. For pulse power less than pth ∼ 50 μW, and in the temperature range 0.4 to 0.8 Tc and zero field, the attenuation coefficient a decreases monotonically at about 0.2 cm−1 per decade of power. Above pth. α increases up to values of 3.5 cm−1 and 1.9 cm−1 at highest power for temperatures of 0.8 Tc and 0.4 Tc, respectively. At pulse power around 100 μW and at the lowest temperatures, the attenuation changes within the first 200 μs after the application of the pulse; α also increases with increasing field. In the normal fluid α decreases with increasing power. All of our observations are lacking a rigorous theoretical understanding.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 110 (1998), S. 467-472 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Novel attenuation effects and the generation of the third harmonic frequency in nonlinear zero and first sound in 3 He were found in pulsed sound-transmission experiments at various pressures (0, 10 bar), frequencies (10-50 MHz), sound-pulse energies (0.01-110 nJ) and temperatures ranging from 0.8 mK to 200 mK. The nonlinear damping of zero sound increases with the square of the frequency and demonstrates that quantum-damping exists in a Fermi liquid even for low frequency phonons at temperatures as high as 1 mK due to multiple phonon absorption processes. The origin of the additional damping found in first sound at high temperatures and sound pulse powers is unclear, but part of the apparent attenuation is caused by third harmonic generation which was also found in superfluid 3 He-B. In zero- as well as in first sound the third harmonic generation takes place in the leading edge of the propagating sound pulse at times when the fundamental frequency has not even developed to its full amplitude.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 101 (1995), S. 253-258 
    ISSN: 1573-7357
    Keywords: 76.60.−k ; 76.60.Jx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The big indirect exchange interaction and the huge nuclear magnetic moments of the two Tl-isotopes makes Tl useful at low temperatures for non linear pulsed NMR studies of inter- and intra-spin interactions mediated by the conduction electrons. We extended earlier experiments to higher fields (0.1 T 〈 Bo 〈 1 T) on a cylindrically shaped sample of 6N purity and found the proposed spin waves trapped in the skin depth of the sample which manifest themselves in line splitting with increasing tipping angles. We also found frequency shifts in partial agreement with the expectations. However, the spin susceptibility was enhanced above the paramagnetic value at temperatures below 2 mK, whereas the line width decreased by a factor of two between 5 and 1 mK. Thus, while solving the high spin-polarization puzzle of Tl (line splitting of already merged lines) we were left with two other unexplained observations.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-7357
    Keywords: 67.70.+n ; 67.80.Jd ; 75.10.J
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present measurements of the magnetization of pure3He films adsorbed on graphite at a density of p = 0.235 atoms/Å2, which corresponds to the 2D Heisenberg ferromagnetic regime. Different NMR frequencies (461.3kHz and 1.004 MHz) were used to study the magnetic field dependence of the nuclear magnetization. Measurements were performed on a Papyex sample to investigate the influence of the platelet size. The results are discussed in the context of theoretical models presented recently to describe these systems.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 101 (1995), S. 657-663 
    ISSN: 1573-7357
    Keywords: 76.60.-k ; 76.60.Lz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigated several AuIn2 samples of similar purity by spin-echo techniques. The temperatures and fields ranged from 0.5 to 20 mK and from 0.06 to 0.8 T, respectively. Our results are: The Knight-shift changed from sample to sample within about 5%. Spin-echoes could not be found in all samples. T2 ranged from about 40 μs in one sample, to a temperature and field independent T2 = 83 μs for another sample, to a field and temperature dependent T2 which varied for this sample from 2 ms at low B/Tn-values (∼5 T/K) to 0.3 ms at B/Tn ∼300. We have shown that the temperature of the conduction electron system is the relevant temperature in the problem, and not the nuclear spin-temperature of In. From the amplitudes of multiple spin-echo structures we conclude that demagnetizing fields are not the only origin for their occurrence.
    Type of Medium: Electronic Resource
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