N. Metoki

Effects of pressure on tiny antiferromagnetic moments in the heavy-electron compound URu2Si2

We have performed elastic neutron-scattering experiments on the heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. We have found that the antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu_o at 1.4 K increases linearly from ~ 0.017(3) mu_B to ~ 0.25(2) mu_B, while T_m increases slightly at a rate ~ 1 K/GPa, roughly following the transition temperature T_o determined from macroscopic anomalies. We have also observed a sharp phase transition at P_c ~ 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu_o ~ 0.4 mu_B) appears with a slightly reduced lattice constant.

Magnetic properties of a pressure-induced superconductor UGe2

We performed DC-magnetization and neutron scattering experiments under pressure P for a pressure-induced superconductor UGe 2 . We found that the magnetic moment is enhanced at a characteristic temperature T * in the ferromagnetic state, where T * is smaller than a Curie temperature T C . This enhancement becomes remarkable in the vicinity of P C * =1.20 GPa, where T * becomes 0 K and the superconducting transition temperature T SC shows a maximum. The characteristic temperature T * , which decreases with increasing pressure, also depends on the magnetic field.

Neutron-diffraction study of the unusual ordered phases of Ce0.75La0.25B6

Abstract Ce0.75La0.25B6 shows paramagnetic phase (phase I), 4f-electron quadrupolar ordered phase (II), magnetically ordered phase (III), and an unknown phase IV. In order to investigate order parameters in phases III and IV, neutron diffraction experiments were performed down to 74 mK . Magnetic diffraction pattern measured in phase III is reproduced by a model in which spin arrangement is modified from the previously suggested structure for CeB6. No magnetic reflections were observed in phase IV. Thus, the order parameter in phase IV is expected to be 4f-electron multipoles rather than magnetic dipoles.

Strong correlation between magnetism and superconductivity in a single crystalline UNi2Al3 and UPd2Al3

Abstract The anisotropy of upper critical magnetic fields is remarkably different between UPd 2 Al 3 and UNi 2 Al 3 . The low-energy excitations observed in inelastic neutron scattering experiments of UPd 2 Al 3 are suggested to be those associated with nodes of a gap function. The temperature dependence of the magnetic Bragg peak intensity in UNi 2 Al 3 shows coupling between antiferromagnetism and superconductivity.

Magnetization dynamics in the normal and superconducting phases of UPd2Al3: I. Surveys in reciprocal space using neutron inelastic scattering

This topical review presents results from neutron inelastic scattering experiments on single crystals of UPd2Al3. The focus is on the experimental situation, while the sequel paper advances theoretical perspectives. We present a detailed and complete characterization of the wavevector- and energy-dependent magnetization dynamics in UPd2Al3 as measured by neutron inelastic scattering primarily in the form of extensive surveys in energy–momentum space under a wide range of experimental conditions, and put our observations in context with data that has been published previously by two independent groups. In this way we emphasize the robustness of the results, which indicate the intricate nature of the dynamic magnetic susceptibility of this material. This study yields unique insight into the low-temperature ground state, which exhibits a microscopic coexistence of antiferromagnetism and superconductivity, making UPd2Al3 one of the most accessible heavy-fermion superconductors that can be fully characterized by neutron spectroscopy.

Neutron diffraction study of antiferromagnetic order in UGa3 under pressure

Abstract The unique magnetic structure and property of intermetallic uranium compounds UGa 3 have been investigated by neutron diffraction measurements. With applying pressure we succeeded in revealing the magnetic structure of UGa 3 . We suppose that the magnetic moment of UGa 3 at low pressures is along the 〈011〉 direction and that at 2.2xa0GPa along the 〈111〉 direction. The Neel temperature and magnetic moment are reduced with applied pressure.

Magnetization dynamics in the normal and superconducting phases of UPd2Al3: II. Inferences on the nodal gap symmetry

This paper provides an analysis of neutron inelastic scattering experiments on single crystals of UPd(2)Al(3). The emphasis is on establishing robust general inferences on the joint antiferromagnetic-superconducting state that characterizes UPd(2)Al(3) at low temperatures. A distinction is drawn between these conclusions and various theoretical perspectives of a more model-sensitive nature that have been raised in the literature.

Neutron diffraction study of 5f itinerant antiferromagnet UPtGa5 and UNiGa5

Abstract Magneto-striction and magnetic form factors in 5f itinerant antiferromagnets UNiGa5 and UPtGa5 are studied by means of neutron scattering. Remarkable magneto-striction was observed around TN, indicating large spin–orbit coupling in the itinerant system. The orbital magnetic moment is found to be strongly suppressed due to the hybridization of uranium 5f with Ga-4p electron.

Neutron scattering study of the antiferromagnetic ordering in UPt3 at mK-temperatures

Abstract Neutron scattering experiments have been performed in order to study the antiferromagnetic correlation in UPt3 at ultralow temperatures. The (0.5xa00xa01) antiferromagnetic peak was observed down to 20xa0mK. The linewidth exhibits a remarkable narrowing with decreasing temperature, and a resolution-limited peak is observed below 20xa0mK. This is direct evidence for the long-range antiferromagnetic correlation in UPt3.

Resonant x-ray scattering study of NpRhGa5 and NpCoGa5

We report a resonant x-ray scattering (RXS) study of antiferromagnetic neptunium compounds NpCoGa_5 and NpRhGa_5 at the Np M_4 and Ga K-edges. Large resonant signals of magnetic dipole character are observed below the Neel temperatures at both edges. The signals at the Np edges confirm the behaviour determined previously from neutron diffraction, i.e. the moments along [001] in NpCoGa_{5} and in NpRhGa_5 a reorientation of the moments from the c-axis direction to the ab plane. In the latter material, on application of magnetic field of 9 Tesla along the [010] direction we observe a change in the population of different [110]-type domains. We observe also a magnetic dipole signal at the Ga K-edge, similarly to the reported UGa_3 case, that can be interpreted within a semi-localized model as an orbital polarization of the Ga 4p states induced via strong hybridization with the Np 5f valence band. Quantitative analysis of the signal shows that the Ga dipole on the two different Ga sites follows closely the Np magnetic moment reorientation in NpRhGa_5. The ratios of the signals on the two inequivalent Ga sites are not the same for the different compounds.