Abstract
9Be NMR spectra have been studied in the heavy-fermion compound UBe13 as functions of spectrometer frequency, crystal orientation, and temperature. BeI-site isotropic Knight shift and BeII-site anisotropic shifts, corresponding hyperfine fields, and quadrupolar tensors have been determined. For T ⪅ 10 K a typical heavy-fermion Knight shift anomaly is observed.
Highlights
IntroductionThe mtermetalllc compound UBe~ has attracted much attentton since its discovery as a heavy-electron system [1], In large part because ~ts superconductingtransition at 0 84 Kmakes it one of the heavy-electron superconductors [2] Previous nuclear magnetic resonance (NMR) studies of UBe~s have concentrated on the 9Be spin-lattice relaxation rate [3,4] The noise power of local field fluctuattons at 9Be sites is three orders of magnitude larger than in the non-5f reference compound ThBe~, and the relaxation rate in the superconducting state follows a power law in temperature instead of the conventional activated BCS temperature dependence In addition, prehminary measurements of NMR spectra [3] lndtcated little change of frequency of hne-width upon enteremg the superconducting state
In this paper we report measurements of 9Be nuclear magnetic resonance (NMR) absorption spectra m single-crystal UBe~ m the normal state as a function of spectrometer frequency, crystal orientation, and temperature Knight shifts, hyperfine fields, and quadrupolar couphngs are derived from the data The hyperfine fields are found to be no smaller than m lSOStructural 4 f B e j~ compounds
The observed 9Be (! = 3/2) field-swept NMR spectra consmted of ten lines due to the existence of two mequlvalent Be sites, Be ~ and Be H The Be I site is of cubic point symmetry (m3), while the symmetry of the Be I~ site is q m t e low (m), this leads to an anlsotrop~c Kmght shift and quadrupolar splitting [6] of the spectra from Be H nuclei After the mdivldual lines were ~dentified, the temperature dependence of the Kmght shift was obtained for the mequlvalent Be ~ and Be ~j sites The relation between shift and bulk magnetic susceptibility was used to obtain the corresponding hyperfine fields Approximate corrections for the demagnettzatlon and Lorentz fields were
Summary
The mtermetalllc compound UBe~ has attracted much attentton since its discovery as a heavy-electron system [1], In large part because ~ts superconductingtransition at 0 84 Kmakes it one of the heavy-electron superconductors [2] Previous nuclear magnetic resonance (NMR) studies of UBe~s have concentrated on the 9Be spin-lattice relaxation rate [3,4] The noise power of local field fluctuattons at 9Be sites is three orders of magnitude larger than in the non-5f reference compound ThBe~, and the relaxation rate in the superconducting state follows a power law in temperature instead of the conventional activated BCS temperature dependence In addition, prehminary measurements of NMR spectra [3] lndtcated little change of frequency of hne-width upon enteremg the superconducting state. II Laboratonum fur Festkorperphyslk, ETH-Honggerberg, CH-8903 Zurich, Switzerland Supported by the Schwelzerlsche Natlonalfonds zur Forderung der Wmsenschafthchen Forschung. In this paper we report measurements of 9Be NMR absorption spectra m single-crystal UBe~ m the normal state as a function of spectrometer frequency, crystal orientation, and temperature Knight shifts, hyperfine fields, and quadrupolar couphngs are derived from the data The hyperfine fields are found to be no smaller than m lSOStructural 4 f B e j~ compounds
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