Koji Kaneko

Direct observation of quadrupolar excitons in the heavy-fermion superconductor PrOs4Sb12

We report inelastic neutron scattering experiments performed to investigate the low energy magnetic excitations on single crystals of the heavy-fermion superconductor PrOs(4)Sb(12). The observed excitation clearly softens at a wave vector Q=(1,0,0), which is the same as the modulation vector of the field-induced antiferro-quadrupolar ordering, and its intensity at Q=(1,0,0) is smaller than that around the zone center. This result directly evidences that this excitonic behavior is derived mainly from nonmagnetic quadrupolar interactions. Furthermore, the narrowing of the linewidths of the excitations below the superconducting transition temperature indicates the close connection between the superconductivity and the excitons.

Detailed Measurements of Characteristic Profiles of Magnetic Diffuse Scattering in ErB2C2

Detailed neutron diffraction measurements were performed on a single crystalline sample of Er 11 B 2 C 2 . We observed magnetic diffuse scattering, which consists of three components, just above the transition temperatures. This scattering is also observed in anomalous antiferroquadrupolar ordering compounds,TbB 2 C 2 and HoB 2 C 2 . The results of the experiments indicate that the antiferroquadrupolar interaction is not essential for the origin of the magnetic diffuse scattering.

Basic Concepts of Polarisation Analysis for Neutron Chopper Spectrometer POLANO at J-PARC

The basic concept underlying the use of neutron polarisers and analysers in a polarised neutron spectrometer which will be constructed in J-PARC/MLF is discussed. The spectrometer, named POLANO, is a compact chopper spectrometer for polarisation analysis in the energy region up to Ei ~200u2005meV. In the first stage of this project, a 3He spin filter polarised by the spin exchange optical pumping method will be used as the polariser. Based on the optimisations of the filter parameters, we confirm that the designed optimised 3He spin filters will be feasible for use up to 80u2005meV.

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.

Magnetic properties of U2RhGa8 and U2FeGa8

We have grown single crystals of U2FeGa8 and U2RhGa8 with the tetragonal structure by the self-flux method. Both compounds are Pauli paramagnets and possess relatively large γ-values of 52 and 43xa0mJxa0K−2/molxa0U, respectively.

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.

Inelastic Neutron Scattering Study of the Heavy Fermion Superconductor PrOs4Sb12

We review inelastic neutron scattering experiments performed on single crystal of the heavy fermion superconductor PrOs 4 Sb 12 . The low lying excitation spectrum consist of a singlet–triplet crystal field transition modulated by quadrupolar intersite interactions. The evolution of this so-called quadrupolar exciton on crossing the superconducting transition was studied both as a function of temperature and magnetic field. Our measurements point out the coupling between the quadrupolar fluctuations and the superconductivity.

Resonant x-ray scattering study ofNpRhGa5andNpCoGa5

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.

Resonant x-ray scattering study of NpRhGa_5 and NpCoGa_5

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.

Crystal and magnetic structure in the itinerant 5f antiferromagnet UCr2Si2

We have grown a single crystal of UCr2Si2 for the first time. UCr2Si2 exhibits a structural transition from the ThCr2Si2-type structure (I4/mmm) to the triclinic (P) structure below Ta = 210 K. An antiferromagnetic structure was determined by neutron diffraction below TN = 27xa0 K, with a propagation vector Q = [−1/2, 1/2, 0] and a magnetic moment 0.65xa0μB/U oriented along [0, 0, 1] direction.