31The spin glass behavior of Y 2 Mo 2 O 7 has puzzled physicists for nearly three decades. Free of bulk 32 disorder within the resolution of powder diffraction methods, it is thought that this material is a rare 33 realization of a spin glass resulting from weak disorder such as bond disorder or local lattice distortions.

We present time-of-flight inelastic neutron scattering measurements at low temperature on powder samples of the magnetic pyrochlore oxides Tb2Ti2O7 and Tb2Sn2O7. These two materials possess related, but different ground states, with Tb2Sn2O7 displaying "soft" spin ice order below TN ∼ 0.87 K, while Tb2Ti2O7 enters a hybrid, glassy spin ice state below Tg ∼ 0.2 K. Our neutron measurements, performed at T = 1.5 K and 30 K, probe the crystal field states associated with the J = 6 states of Tb 3+ within the appropriate F d3m pyrochlore environment. These crystal field states determine the size and anisotropy of the Tb 3+ magnetic moment in each material's ground state, information that is an essential starting point for any description of the low-temperature phase behavior and spin dynamics in Tb2Ti2O7 and Tb2Sn2O7. While these two materials have much in common, the cubic stanate lattice is expanded compared to the cubic titanate lattice. As our measurements show, this translates into a factor of ∼ 2 increase in the crystal field bandwidth of the 2J + 1 = 13 states in Tb2Ti2O7 compared with Tb2Sn2O7. Our results are consistent with previous measurements on crystal field states in Tb2Sn2O7, wherein the ground-state doublet corresponds primarily to mJ = |±5 and the first excited state doublet to mJ = |±4 . In contrast, our results on Tb2Ti2O7 differ markedly from earlier studies, showing that the ground-state doublet corresponds to a significant mixture of mJ = |±5 , |∓4 , and |±2 , while the first excited state doublet corresponds to a mixture of mJ = |±4 , |∓5 , and |±1 . We discuss these results in the context of proposed mechanisms for the failure of Tb2Ti2O7 to develop conventional long-range order down to 50 mK.

The geometrically frustrated double perovskite Ba2YRuO6 has magnetic 4d 3 Ru 5+ ions decorating an undistorted face-centered cubic (FCC) lattice. This material has been previously reported to exhibit commensurate long-range antiferromagnetic order below TN ∼ 36 K, a factor f ∼ 15 times lower than its Curie-Weiss temperature ΘCW = −522 K, and purported short-range order to T * = 47 K. We report new time-of-flight neutron spectroscopy of Ba2YRuO6 which shows the development of a ∼5 meV spin gap in the vicinity of the [100] magnetic ordering wavevector below TN =36 K, with the transition to long-range order occurring at T * = 47 K. We also report spin waves extending to ∼14 meV, a surprisingly small bandwidth in light of the large ΘCW . We compare the spin gap and bandwidth to relevant neutron studies of the isostructural 4d 1 material Ba2YMoO6, and discuss the results in the framework of relatively strong spin-orbit coupling expected in 4d magnetic systems.

In this work we investigate the electrical transport properties and growth conditions of tungsten carbon (WC) and palladium carbon (PdC) nanostructures on Si substrates using a focused ion beam and scanning electron microscope. In situ energy dispersive x-ray (EDX) characterizations reveal that electron-beam-induced WC and PdC nanostructure depositions (EBID) show a lower metal concentration (below 3% atomic percentage) than in ion-beam-induced deposition (IBID) (above 20%). In the case of PdC the growth pattern and the Pd/C content were optimized by adjusting the deposition temperature of the precursor material. In situ measurements of the resistivity of the nanostructures as a function of thickness reveal a minimum at a thickness approximately 200 nm. The lowest resistivity obtained for the PdC and WC structures is two orders of magnitude higher than the corresponding bulk values for pure Pd and W. The EBID samples show a non-metallic behaviour due to the low metal content. The temperature and magnetic field dependence of the IBID structures reveal a behaviour similar to disordered or granular conductors. The upper critical field and critical current density of the WC structures were measured below the superconducting critical temperature of approximately 5 K.

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