Search results for "Electrical Resistivity"

Exchange bias in epitaxial Mn2Au (0 0 1)/Fe (0 0 1) bilayers

2019

Epitaxial Mn2Au thin films for antiferromagnetic spintronics

2015

Mn2Au is one of the few candidate materials for antiferromagnetic spintronics requiring ordered metals with a high Neel-temperature and strong spin–orbit coupling. We report the preparation of epitaxial Mn2Au thin films by rf-sputtering. Structural characterization by x-ray and electron diffraction demonstrates a high degree of atomic order and the temperature dependence of the resistivity is typical for a good metal. The magnetic properties of the samples are studied by the investigation of Mn2Au/Fe bilayers. Exchange bias effects are observed, which present strong evidence for antiferromagnetic order in the Mn2Au thin films. Small domains of 500 nm are visualized in the exchange coupled F…

Conductimetry and impedance spectroscopy study of low pressure metal organic chemical vapor deposition TiN O films as a function of the growth temper…

2001

Abstract Titanium oxinitride thin films have been grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) using titanium isopropoxide, Ti(OCH(CH 3 ) 2 ) 4 (TIP) and NH 3 precursors in a growth temperature range from 450 to 750°C on sapphire substrates. The electrical behaviour of these films was studied between 400 and 173 K, revealing three different behaviours, ranking from a hopping conductivity (450–500°C) to a conducting one (700–750°C), with a dual behaviour for the intermediate growth temperatures. Moreover, at room temperature, both conductimetry and impedance spectroscopy highlighted a percolation behaviour, interpreted in terms of continuum percolation. The effect…

(La0.8Sr0.2)(Mn1−yFey)O3±δ oxides for ITSOFC cathode materials?

2005

The oxygen transport properties in (La 0.8 Sr 0.2 )(Mn 1-y Fe y )O 3±δ (LSMF) with various iron contents y = 0, 0.2, 0.5, 0.8 and 1 were determined by the IEDP technique. Both oxygen diffusion and surface exchange coefficients were found to be greater for y = 0.8 and 1 than those of LSM (y=0). Moreover, for y ≤0.5, grain boundary diffusion was the rate limiting step especially at lower temperatures. Thus, in the LSMF perovskite materials, the oxygen diffusion via oxygen vacancies is enhanced by Fe. The LSMF electrical performances were measured by impedance spectroscopy. Compared to LSM and LSF (y= 1), porous LSMF cathodes with y= 0.2-0.8 exhibit poor electronic conductivity: Fe, by reducin…

Electrical Transport in Lead-Free [(1−x)(Na0.5Bi0.5)-xBa]Zr1 - yTiyO3Ceramics (x = 0, 0.06, and y = 0, 0.96)

2009

Lead-free ceramics based on (Na 0.5 Bi 0.5 TiO 3 , NBT)-(Ba(Ti,Zr)O 3 , BTZ) were prepared by solid phase hot pressing sintering process and their ac (σ ac ) and dc (σ dc ) conductivity have been studied (303–753 K). Low frequency (100 Hz–100 kHz) ac conductivity obeys power law σ ac ∼ ω s characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperatures. Dc conductivity has thermally activated character and possesses four linear parts with four different activation energies and some discontinous changes. However, σ ac (T) possesses two linear parts with two different activation energies and more discontinuous ch…

Structural, electrical and optical properties of zinc‐iridium oxide thin films deposited by DC reactive magnetron sputtering

2014

ZnO-IrO2 thin films were deposited on glass by DC reactive magnetron sputtering at room tem-perature. Structural, electrical and optical properties were investigated as a function of iridium atomic concentra-tion in the films. XRD data shows that ZnO-IrO2 thin films are X-ray amorphous and Raman spectrum resembles the spectrum of IrO2, without any distinct features of wurtzite ZnO structure. The lowest film resistivity and the highest transmittance achieved in the present study were 1.4 × 10-3 Ωcm and 33% at 550 nm, respectively. However, resistivity and transmittance are inversely related to the iridium concentration in the films.

Surface-state electrons on a hydrogen film. 1. Annealing of the film

1991

We have investigated the surface of thin films (thickness ∼2 µm) of solid H2 between 1.5 and 4.2 K by measuring the ac conductivity of surface-state electrons (SSE). The films were prepared on a glass substrate by quench condensation at 1.5 K and were therefore initially strongly disordered. In fact the surface of the virgin films before any heat treatment was so rough that no current due to SSE could be observed. Annealing the films decreased the surface roughness and gave rise to a thermal-activation-type temperature dependence of the SSE conductivity. By proper heat treatment up to 8 K the activation energy could be reduced to 10kB.

Stability, sub-gap current, 1/f-noise, and elemental depth profiling of annealed Al:Mn-AlOX-Al normal metal-insulator-superconducting tunnel junctions

2016

In this paper we report a study of the effect of vacuum annealing at 400◦C on the properties of normal metal-insulator-superconductor (NIS) tunnel junctions, with manganese doped aluminium (Al:Mn) as the normal metal, aluminum as the superconductor and amorphous aluminum oxide as the tunneling barrier (Al:Mn-AlOx-Al). The annealing treatment improves the stability of the junctions, increases their tunneling resistance and does not have a negative impact on the low-temperature current-voltage characteristics. The measured 1 / f resistance noise of the junctions also changes after annealing, in the best case decreasing by over an order of magnitude. All these observations show that annealing …

Tuning the Direct and Indirect Excitonic Transitions of h-BN by Hydrostatic Pressure

2021

The pressure dependence of the direct and indirect bandgap transitions of hexagonal boron nitride is investigated using optical reflectance under hydrostatic pressure in an anvil cell with sapphire windows up to 2.5 GPa. Features in the reflectance spectra associated with the absorption at the direct and indirect bandgap transitions are found to downshift with increasing pressure, with pressure coefficients of −26 ± 2 and −36 ± 2 meV GPa–1, respectively. The GW calculations yield a faster decrease of the direct bandgap with pressure compared to the indirect bandgap. Including the strong excitonic effects through the Bethe–Salpeter equation, the direct excitonic transition is found to have a…

Epoxy Resin/Carbon Black Composites Below the Percolation Threshold

2013

International audience; A set of epoxy resin composites filled with 0.25-2.0 wt.% of commercially available ENSACO carbon black (CB) of high and low surface area (CBH and CBL respectively) has been produced. The results of broadband dielectric spectroscopy of manufactured CB/epoxy below the percolation threshold in broad temperature (200 K to 450 K) and frequency (20 Hz to 1 MHz) ranges are reported. The dielectric properties of composites below the percolation threshold are mostly determined by alpha relaxation in pure polymer matrix. The glass transition temperature for CB/epoxy decreases in comparison with neat epoxy resin due to the extra free volume at the polymer-filler interface. At …