Magnetism in uranium and praseodymium intermetallic compounds studied by inelastic neutron scattering
The dispersion of magnetic excitations in PrNiSn has been studied using inelastic neutron scattering. The dispersion relations along [0 0 Q] and [Q 0 0] have been determined for the excitations observed at 1.5, 2.5 and 5.2 meV. The two lower excitations are proposed to be modes originating from the 2 meV level predicted by earlier inelastic measurements. Additional measurements of the 3.5 meV excitation already studied were performed to provide higher resolution data and improved statistics. Preliminary measurements on NdNiSn were also made. Searches have been made using inelastic neutron scattering to look for crystalline electric field (CEF) excitations in the uranium-based intermetallics UPdSn, UCu2Sn and U3Pd20Si6. In UPdSn, a distinct CEF excitation has been observed at 50 meV in the paramagnetic phase. On cooling, the excitation shifts to lower energies and its temperature dependence exhibits marked changes at the antiferromagnetic transition temperatures of TN =25 and 40 K. The quasielastic scattering below 20 meV is found to increase significantly below the lower transition temperature. A set of Stevens parameters have been proposed to account for the observed data. The magnetic scattering observed in UCu2Sn is a broad, asymmetric peak centred at 7 meV which disappears above the quadrupolar ordering temperature of TQ = 16.5 K. The temperature dependence of the peak has been determined and comparisons with two different energy level schemes have been made. Three clear CEF excitations, which are visible in both the paramagnetic and ordered phase, have been observed at energies of 14.3, 23.9 and 31.6 meV in U3Pd20Si6. The temperature dependence of the excitations has been followed and a tentative level scheme proposed. A sharp, intense peak at 3 meV is visible at low temperatures and has been attributed to the exchange induced splitting of the 8c ground state below TN =19 K.