We have measured the momentum and energy dependence of the spin fluctuations in the low-temperature mixed-valent state and the high-temperature integral-valent state of (Formula presented), using flux-grown single crystals and a triple axis spectrometer. The magnetic scattering can be fit with a Lorentzian power spectrum, with positions and halfwidths equal (Formula presented)=2.3 meV and (Formula presented)=1.8 meV in the high-temperature state at 50 K and (Formula presented)=40.2 meV and (Formula presented)=12.3 meV in the low-temperature state at 20 K. Within the experimental uncertainties, the line shape as a function of energy transfer (i.e., the power spectrum) does not depend on momentum transfer Q. The static susceptibility χ(Q) is no more than 10% larger at the zone boundary than at zone center for the [1,0,0] direction. The results compare reasonably well to the predictions of the Anderson impurity model and to earlier measurements on polycrystalline samples. © 1997 The American Physical Society.

Neutron-diffraction measurements have been made on polycrystalline samples of UBe13 and ThBe13 at several temperatures between 10 and 250 K. Refinement of the powder patterns using the Rietveld method of profile analysis yields structural parameters in substantial agreement with previous work [space group Og6 (Fm3c); 8 U in 8(a); 8 Be(I) in 8(b); 96 Be(II) in 96(i)]. Values for the (y,z) coordinates of the 96 Be(II) are (0.1763, 0.1150) and (0.1745, 0.1129) for UBe13 and ThBe13, respectively. They correspond very closely to those values required for regular snub-cube coordination of the Be(II) around the uranium atoms. © 1985 The American Physical Society.

We present the results of polarized and unpolarized inelastic neutron scattering measurements of the heavy-fermion superconductor UBe13 at 10 K. At this temperature, the energy spectrum of the magnetic scattering is characterized by a broad quasielastic Lorentzian line shape modified by the Bose occupation factor, with a width of 132 meV (half-width at half maximum). No evidence of a narrow (few meV) f-level resonance predicted by the electronic specific-heat coefficient is observed. The energy-integrated magnetic scattering yields a susceptibility which is consistent with bulk measurements, indicating that any additional response must have a small spectral weight. © 1986 The American Physical Society.

Inelastic neutron scattering from the antiferromagnetic (TN=9.7 K) heavy-fermion system U2Zn17 reveals magnetic fluctuations which are highly localized in reciprocal space and broad in frequency. At higher energies, the fluctuations persist almost unchanged to temperatures well above Tn. Analysis of the neutron and bulk susceptibility data in terms of Kondo-type single-ion response functions modified by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions between ions indicates that it is the temperature dependence anticipated theoretically of the effective RKKY coupling which drives the magnetic phase transition in U2Zn17. © 1987 The American Physical Society.

Neutron scattering measurements were performed on polycrystalline samples of UBe13 in order to establish more accurately the structure and probe the dynamics of the spin fluctuations. The structure was confirmed to be cubic with space group O6h (Fm3c) with BeII positional parameters y = 0.1763(1) and z = 0.1150(1). The inelastic spectrum at T = 10 K exhibits a broad response with half width at half maximum of 15 meV. © 1985.

The phase transition of U2Zn17 at 9.7 K has been investigated by neutron powder diffraction. The transition corresponds to the onset of antiferromagnetic order where the U moments are oriented antiparallel to their nearest neighbors within the basal planes and the near neighbor along the c^ axis of this rhombohedral compound. At 5 K, the ordered moments lie within the basal planes and are of magnitude (0.8±0.1)1/4B, which is substantially below the paramagnetic moment of 2.251/4B/U atom given by high-temperature susceptibility data. © 1986 The American Physical Society.