Temperature Dependence of Magnetoresistance in Ni3Al System

The transverse magnetoresistance of stoichiometric and off-stoichiometric polycrystalline samples of the Ni3Al system has been measured over the temperature range 1.2C. The data are in qualitative agreement with the theoretical predictions of Chang et al. based on a model of the magnetoresistance of an itinerant ferromagnet, but the observed magnetoresistance is considerably larger than predicted

Study of Lattice Instabilities in Snx Euy-x Mo6S8 (y=1.0 and 1.2)

An anomaly in the heat capacity of Eu1.2Mo6S8 at ∼120 K (T0) has been observed and identified as a structural transformation. The heat capacity, electrical resistance, and Hall coefficient for the Eu-rich pseudoternaries have been measured under pressure to obtain the pressure dependence of T0. The depression of T0 by pressure is used to explain the pressure dependence of the superconducting transition temperature and the anomalous temperature dependence of the critical field

Slightly Conductive Transparent Films for Space Applications — Manufacturability and Durability

ABSTRACT Highly transparent, slightly conductive films of co-deposited indium tin oxide (ITO) and MgF 2 have possible applications for environmental protection of exterior surfaces of spacecraft. Reliable preparation of films with the desired sheet resistivity (~10 8 ohms/square) is difficult because the electrical properties of ITO-MgF 2 are highly dependent on film composition. We have investigated the use of plasma emission monitoring to improve the reproducibility of films prepared by RF magnetron sputtering. While considerable improvement was observed, it appears that some in-situ electrical or optical characterization will be needed for reliable production coating with ITO-MgF 2 . We have also done further evaluation of a possibly undesirable photoconductive effect previously observed in these films

Observation of the Transition from Semiconductor to High-Tc Superconductor in (SnxEu1-X)YMo6S8 Under High Pressure

Pressure-induced high-temperature superconductivity is observed in semiconducting (SnxEu1-x)yMo6S8, where 0\u3c~x\u3c~0.1 and y=1.0 and 1.2, having a carrier concentration ≃1019/cm3 at 4.2 K as determined from Hall-effect measurements. Above a threshold pressure ≃7 kbar, superconductivity appears with dTc/dP≃2 K/kbar. The maximum superconducting temperature (Tc∼10 K), reached at ∼ 12 kbar, represents the highest pressure-induced Tc in any semiconductor. For P\u3e~13 kbar, the temperature-dependent resistance appears metallic

Mixed composition materials suitable for vacuum web sputter coating

Ion beam sputter deposition techniques were used to investigate simultaneous sputter etching of two component targets so as to produce mixed composition films. Although sputter deposition has been largely confined to metals and metal oxides, at least one polymeric material, poly-tetra-fluorethylene, has been demonstrated to produce sputtered fragments which repolymerize upon deposition to produce a highly cross-linked fluoropolymer resembling that of the parent target Fluoropolymer-filled silicon dioxide and fluoropolymer-filled aluminum oxide coatings have been deposited by means of ion beam sputter coat deposition resulting in films having material properties suitable for aerospace and commercial applications. The addition of fluoropolymer to silicon dioxide films was found to increase the hydrophobicity of the resulting mixed films; however, adding fluoropolymer to aluminum oxide films resulted in a reduction in hydrophobicity, thought to be caused by aluminum fluoride formation

Transport Critical Current and Magnetization Measurements of Melt-Processed YBa2Cu3O7-X

We report magnetic field dependence of the transport critical current and dc magnetic susceptibility measurements on YBa2Cu3O7−x superconductors formed by melt-solid reactions at 950 °C between Ba-Cu-O (or Tb-Ba-Cu-O) and solid nonstoichiometric Y-Ba-Cu-oxide. Four-probe dc critical current measurements at 77, 64, and 4.2 K show strong depression of the critical current density with increasing magnetic field in agreement with a model of weakly linked superconducting regions. Diamagnetic shielding and Meissner flux expulsion measurements in the temperature range 10–300 K show about one third volume fraction of perfect superconductivity. Both shielding and flux expulsion were observed to be approximately temperature independent below 60 K indicating strong coupling between the grains throughout the entire volume below this temperature

Transport Critical Current and Magnetization Measurements of Melt-Processed YBa2Cu3O7-X

We report magnetic field dependence of the transport critical current and dc magnetic susceptibility measurements on YBa2Cu3O7−x superconductors formed by melt-solid reactions at 950 °C between Ba-Cu-O (or Tb-Ba-Cu-O) and solid nonstoichiometric Y-Ba-Cu-oxide. Four-probe dc critical current measurements at 77, 64, and 4.2 K show strong depression of the critical current density with increasing magnetic field in agreement with a model of weakly linked superconducting regions. Diamagnetic shielding and Meissner flux expulsion measurements in the temperature range 10–300 K show about one third volume fraction of perfect superconductivity. Both shielding and flux expulsion were observed to be approximately temperature independent below 60 K indicating strong coupling between the grains throughout the entire volume below this temperature