Martyn J. Bull

Neutron intermultiplet spectroscopy of UPd3 and UPt3

Abstract Neutron intermultiplet spectroscopy has been used to re-examine UPd3 and UPt3 at 17 K. In UPd3, the 3H4 → 3F2 transition is observed at 395 meV, confirming a localised 5f2 state for the uranium ions. In the heavy fermion compound UPt3, only a small trace of this transition remains, indicating that the 5f electrons in this material are of a predominantly itenerant nature. The Q dependence of the transition in UPd3 has also been determined. The transition intensities are found to differ by a factor of ∼ 2 from that predicted by calculations.

Alternative explanation of “gravitational screening” experiments

Abstract We show that the phenomena tentatively ascribed by Podkletnov and Nieminen [Physica C 203 (1992) 441] to gravitational screening may be easily understood in terms of a buoyancy correction to the authors weighting procedure.

Classical properties in spin dynamics in the S = 2 one-dimensional Heisenberg antiferromagnet, CsCrCl3

We performed inelastic neutron scattering experiments, in order to investigate the spin dynamics in the S =2 one-dimensional (1D) Heisenberg antiferromagnet, CsCrCl 3 , above the three-dimensional ordering temperature ( T N =16 K). We deduced the static correlation function from the dynamical structure factor. The inverse correlation length showed a linear temperature dependence and was described by quantum and classical theories with the exchange constant determined from the dispersion relation of the magnetic excitations. The temperature dependence of the dynamical structure factor was also determined. We demonstrated that the spin dynamics in CsCrCl 3 above T N is quantitatively well described by classical theory for a 1D Heisenberg antiferromagnetic system.

A novel double-crystal analyser system for the PRISMA spectrometer at ISIS

Abstract The crystal analyser spectrometer PRISMA has proven to be particularly successful at surveying extended areas of (κ, e) space, efficiently collecting high-quality inelastic and critical scattering data sets from single-crystal samples. In the inelastic mode, mechanical constraints upon the 16 analyser-detector arms limit the final energy to Ef > 12 meV. To overcome this constraint, a novel double-crystal analyser system has recently been installed on the PRISMA spectrometer. Neutrons scattered from the sample are analysed by five groups of paired pyrolytic graphite analysers allowing final energies 2.25 meV

Localized excitations in UPdSn

The authors have measured the inelastic neutron-scattering response of UPdSn at various temperatures using the HET and PHAROS spectrometers at the ISIS and MLNSC facilities, respectively. UPdSn shows some quasielastic scattering, which may be attributed to the hybridization of the 5f electrons with the conduction electrons. Furthermore, they find a clear excitation around 40meV above 40K in addition to the phonon contribution. While this excitation may be indicative of crystal fields in UPdSn, its strong temperature dependence seems to contradict a simple crystal-field picture. Below T{sub N}, the unusual temperature dependence may be attributed to magnetically-driven distortions (and subsequent changes in the local surrounding of the U ions), but there is some evidence that other additional mechanism(s) may contribute above T{sub N}. Some possible mechanisms will be discussed.

Neutron scattering studies of UxY1−xPd3 compounds

We have examined the spin dynamics of U 0.2 Y 0.8 Pd 3 and U 0.45 Y 0.55 Pd 3 , at low temperatures, using inelastic neutron scattering techniques. In U 0.45 Y 0.55 Pd 3 we observe excitations at 2-5 meV and 36 meV, which we attribute to crystal field levels. The energy of the lower branch shows a dispersion characteristic of antiferromagnetic correlations. The magnetic scattering from U 0.2 Y 0.8 Pd 3 is much weaker, and the excitations are strongly damped with a Lorentzian (relaxational) response