Magnetotransport Properties in Semimetallic Bismuth Thin Films

The magnetotransport properties of the electroplated and sputtered Bi thin films have been investigated in the range 4 – 300 K. A marked increase from 5,200 % to 80,000 % in the ordinary magnetoresistance (MR) for the electroplated Bi thin film was observed after thermal anneal at 4 K. The MR ratios for the as-grown and the annealed Bi thin films were found to exhibit 560 % and 590 %, respectively, at 300 K. On the other hand, the MR for the sputtered Bi film grown by sputtering was hardly observed at 4 and 300 K, whereas the MR ratios after anneal were found to reach 30,000 % at 4 K and 600 % at 300 K. We find that the room temperature MR in the sputtered films depends on the trigonal-axis oriented microstructures and grain size, in contrast to the electroplated films. Our results demonstrate the very large room temperature MR in the electroplated and sputtered Bi thin films, which can be used for spintronic device applications.

Processing and Characterization of High-conductance Bismuth Wire Array Composites

We fabricated Bi nanowire array composites with wire diameters from 30 to 200 nm by high-pressure injection (HPI) of Bi melt into porous anodic alumina templates. The composites were dense, with Bi volume fraction in excess of 50%. The parallel Bi nanowires, whose length appeared to be limited only by the thickness of the host template (up to 55 μm), terminated at both sides of the composite in the Bi bulk. The individual Bi nanowire crystal structure was rhombohedral, with the same lattice parameters as that of bulk Bi; the wires in the array were predominantly oriented with the trigonal axis along the wire length. Low contact resistance was achieved by bonding the composite to copper electrodes.

Static and dynamic properties of hydrogen sulphide in hydroquinone clathrates

A variety of investigations has been undertaken on hydrogen sulphide hydroquinone clathrates, with the aim of achieving a better understanding of the motions of the guest molecules and of the phase transition near 8 K, Measurements have been made, over a wide temperature range including the phase transition, of heat capacities on H2S, D2S, and HDS clathrates, dielectric constants perpendicular and parallel to the trigonal axis of single crystal specimens, incoherent quasi-elastic neutron scattering, and neutron diffraction. All of the data are consistent with the H2S molecular dipole being able to rotate rather easily about an axis parallel to the trigonal crystal c axis. Rotations about the other axes are much more difficult. The rotation about the trigonal axis is almost free at high temperatures but there is evidence for three preferred orientations at temperatures just above the phase transition. No discrete energy states are observed at any temperature due to strong guest–cage and guest–guest interactions. The experiments provide direct evidence that the phase transition is associated with a cooperative freezing out of the dipole reorientations.

Molecular reorientation in sodium hydrosulfide: a deuterium nmr study

Deuterium nmr provides a unique opportunity to verify that the molecular motion in sodium hydrosulfide, NaSH, in the trigonal phase is the flipping of the SH− ion between two positions parallel and antiparallel to the trigonal axis. Measurements of the spin–lattice relaxation time show that motion of the hydrosulfide ion is not influenced substantially by deuteration. Measurements of the deuterium nuclear quadrupole splitting, ΔνQ, over the range of temperatures where the correlation time, τc, describing the motion changes from [Formula: see text] show little change. The molecular motion of the SD− ions must, therefore, not change the deuterium quadrupolar interaction and 180° flipping of the SD− ion is the only reasonable model which fits this criterion.Spin–lattice relaxation times have also been measured in the high temperature cubic phase. At 376 K, τc was found to be 0.40 ps in agreement with neutron quasielastic scattering measurements.

Sodium NMR in the trigonal phase of sodium hydrosulfide

Measurements of the sodium nuclear quadrupole coupling constant and spin–lattice relaxation time, while confined mainly to the trigonal phase, show the existence of the two known phase transitions at 358 and 113 K. The quadrupole coupling constant is 206 kHz at 358 K and decreases roughly linearly with decreasing temperature at a rate of about 0.66 kHz/K. The satellite peaks in the quadrupolar split powder pattern disappear above 358 K in the cubic phase. Below 130 K. where there is no known phase transition, the satellites broaden and again disappear but in this case it is because the fluctuation rate of the electric field gradient at the sodium site due to reorientation of the SH− ion is about equal to the quadrupolar splitting of the spectrum at this temperature. Only the resonance from the −1/2 ↔ 1/2 transition is observed down to 77 K.The spin–lattice relaxation of the sodium spins shows a very strong temperature dependence and a well-defined minimum similar to the previously observed results for the protons. The relaxation is caused by the nuclear quadrupole interaction made time dependent by the reorientation of the neighbouring SH− ions. A simple model calculation gives reasonable agreement between the calculated and experimental values of T1 at the minimum if the SH− ion is considered to move between two positions parallel and antiparallel to the trigonal axis. An extension of this model suggests that the lack of an enhanced relaxation rate at the 113 K phase transition may be a result of a parallel ordering of neighbouring SH− ions along the trigonal axis in the lowest temperature phase.