Neutron Scattering Study of Crystal Field Energy Levels and Field Dependence of the Magnetic Order in Superconducting HoNi2B2C

Elastic and inelastic neutron scattering measurements have been carried out to investigate the magnetic properties of superconducting (Tc~8K) HoNi2B2C. The inelastic measurements reveal that the lowest two crystal field transitions out of the ground state occurat 11.28(3) and 16.00(2) meV, while the transition of 4.70(9) meV between these two levels is observed at elevated temperatures. The temperature dependence of the intensities of these transitions is consistent with both the ground state and these higher levels being magnetic doublets. The system becomes magnetically long range ordered below 8K, and since this ordering energy kTN ~ 0.69meV << 11.28meV the magnetic properties in the ordered phase are dominated by the ground-state spin dynamics only. The low temperature structure, which coexists with superconductivity, consists of ferromagnetic sheets of Ho{3+ moments in the a-b plane, with the sheets coupled antiferromagnetically along the c-axis. The magnetic state that initially forms on cooling, however, is dominated by an incommensurate spiral antiferromagnetic state along the c-axis, with wave vector qc ~0.054 A-1, in which these ferromagnetic sheets are canted from their low temperature antiparallel configuration by ~17 deg. The intensity for this spiral state reaches a maximum near the reentrant superconducting transition at ~5K; the spiral state then collapses at lower temperature in favor of the commensurate antiferromagnetic state. We have investigated the field dependence of the magnetic order at and above this reentrant superconducting transition. Initially the field rotates the powder particles to align the a-b plane along the field direction, demonstrating that the moments strongly prefer to lie within this plane due to the crystal field anisotropy. Upon subsequently increasing the field atComment: RevTex, 7 pages, 11 figures (available upon request); Physica

t→bWt \to b W in NonCommutative Standard Model

We study the top quark decay to b quark and W boson in the NonCommutative Standard Model (NCSM). The lowest contribution to the decay comes from the terms quadratic in the matrix describing the noncommutative (NC) effects while the linear term is seen to identically vanish because of symmetry. The NC effects are found to be significant only for low values of the NC characteristic scale.Comment: 11 page Latex file containing 2 eps figures (redrawn). More discussion included. To appear in PR

Synthesis and characterization of Ba3(Pb1-xBix)2O7

The synthesis and initial characterization of a layered perovskite-based lead-bismuth oxide are reported. The phase, Ba3(Pb1-xBix)2O7, for 0≤x≤0.5, is the n=2 member of the Ruddlesden-Popper series An+1BnO3n+1. It can be synthesized only under very narrowly defined conditions. Despite the analogy to the well-known three-dimensional perovskite superconductor BaPb0.75Bi0.25O3, layered Ba3Pb2O7 does not become superconducting (down to 1.8 K) on doping with Bi.

Cs8.5W15O48 and CsW2O6: Members of a New Homologous Series of Cesium Tungsten Oxides

The crystal structures of two new reduced cesium tungsten oxides are reported. Along with the previously reported compound Cs6W11O36, they represent several members of a homologous series of layer compounds between the hexagonal tungsten bronze and pyrochlore structure types. The series formula is [A] Cs2nW4n–1O12n, where n – 1 is the number of pyrochlore layers.

Promoting children's positive intergroup attitudes towards stigmatized groups: Extended contact and multiple classification skills training

Two studies were conducted to evaluate interventions, based upon the extended contact hypothesis and multiple classification skills training, which aimed to promote children's positive intergroup attitudes towards two stigmatized groups. Study I tested whether extended contact and multiple classification skills training changed out-group attitudes towards the disabled among 6-9 year-old children. Out-group attitudes were significantly more positive only in the extended contact condition compared to the control. Study 2 involved four conditions: control, extended contact, modified multiple classification skills training and a combination of both interventions. Again, only the 6-11 year-old children who experienced the extended contact interventions (extended contact and combined) showed significantly more positive attitudes towards the refugee out-group compared to the control. The implications of these findings for the development of prejudice-reduction strategies in children will be discussed

Superconductivity at 28 K in a cuprate with a niobium oxide intermediary layer

A new copper oxide based superconductor is reported based on the ordered interleaving of NbO6 or TaO6 octahedra between the apices of copper oxide pyramids. Good bulk superconductivity is observed for only a narrow range of temperatures, annealing times and cooling rates. The relatively low Tc of the prototype compound Sr2Nd1.5Ce0.5NbCu2O10–δ, may be due to the presence of the insulating NbO6 layers or the wide (Nd, Ce)2O2 layers which separate the CuO2 planes