NiGa 2 S 4 While neutron scattering is often the ultimate tool for elucidating atomic scale structure and dynamics, the complexity of the experiments has sometimes limited early impact in the materials development cycle. Our experiments on NiGa 2 S 4 are an exception to this. Through collaboration with Dr. Satoru Nakatsuji and Prof. Y. Maeno who embody a leading materials synthesis group at Kyoto University in Japan, we have been fortunate to work on a very interesting new material. NiGa 2 S 4

more »

... s a triangular lattice spin-1 antiferromagnet with unusual bulk properties indicating that there might be something new for us to learn about cooperative effects in this basic physical system. The specific heat shows two maxima versus temperature none of which indicate a phase transition to long range magnetic order. This is very unusual for a Bravais lattice with no apparent disorder. Our pulsed neutron scattering experiments carried out at the NIST Center for Pyrochlore magnets display a vast range of interesting physical effects related to geometrical frustration and weak connectivity. As opposed to more conventional antiferromagnets where near neighbor antiferromagnetic interactions select a specific long range ordered state, these interactions only define a low energy manifold on a pyrochlore lattice. The situation becomes particularly interesting forf metallic systems as strong fluctuations in the low energy manifold can have qualitative effects on charge transport and thermodynamic properties. Our inelastic scattering experiments on pyrochlore Pr 1-x Bi x Ru 2 O 7 revealed a novel effect wherein a non-Kramers doublet ground state undergoes inhomogeneous level splitting due to a distribution of electro-static environments. We combined bulk measurements with inelastic scattering data to reach a comprehensive understanding of the anomalous properties of this alloy. Figure 4 shows that were able to calculate temperature dependent specific heat and susceptibility data from inelastic neutron scattering data with no truly adjustable parameters. The results were recently published in Physical Review Letters. Figure 4. Specific heat and susceptibility data for the pyrochlore antiferromagnet Pr 1-x Bi x Ru 2 O 7 , which contains non-Kramers Pr ions in an inhomogenous environment. The solid lines were calculated on the basis of inelastic neutron scattering data from the IRIS instrument at ISIS. The good agreement between calculations and bulk data indicate that our interpretation in terms of inhomogeneous level splitting of a non-Kramers ion is correct. The results were recently published in Phys. Rev. Lett. Product Developed Under the Award Published papers (the publications are attached to this document) 1. "Unconventional Magnetic Correlations in DyB2Cand HoB2C studied by μSR",