摘要:

Extensive studies of the low frequency1/fnoise in high-temperature superconducting (HTS) Josephson junctions of various types and materials have been performed for a wide range of operating parameters. The origin of the measured voltage fluctuations can be traced back to the trapping and release of charge carriers in trapping centers in an insulating barrier, giving rise to correlated fluctuations of the junction critical currentIcand normal-state resistanceRn.We observed a linear dependence of the normalized critical current and resistance fluctuations onRn, which suggests a constant density of trapping centers for the HTS Josephson junctions. The scaling of the normalized fluctuations is in good agreement with the previously found scaling relationIcRn∝1/Rnand supports a junction model assuming a leaky tunnel barrier. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119281

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A process to fabricate epitaxial YBaCuO suspended microbolometers using silicon separated by implanted oxygen (SIMOX) substrates is reported. Unlike the other micromachining techniques, no process step is needed after film deposition and the YBaCuO air-bridge retains excellent superconducting qualities. The support membrane is constituted of a 80-nm-thick CeO2/YSZ buffer layer on a 150-nm-thick silicon layer. The critical temperatureTc(R=0)is 88 K and the transition width is 2.5 K. Current-voltage characteristics directly measured on a 10-&mgr;m-wide, 100-&mgr;m-long suspended bridge show a critical current density of7.5×105A/cm2at 80 K. The thermal conductanceGof this bridge is2×10−5W/K. An optical noise equivalent power (NEP) of6.1×10−12 W/Hzat 1 kHz is deduced from optical sensitivity and noise measurements. The time constant is 6 &mgr;s, which is the lowest value reported on such suspended structures. Comparison with a similar suspended bridge fabricated without a silicon layer shows that the sensitivity–bandwidth product of the SIMOX bridge is improved by one order of magnitude, thus demonstrating the feasibility of sensitive and fast YBaCuO bolometers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119282

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the growth and properties of (Sr1−xCax)RuO3and Sr (Ru1−xTix)O3thin films obtained by sequential deposition of submonolayers from end members of each compound. Magnetization measurements as well as transport properties exhibit a very different behavior for each type of substitution. A simple model, which assumes a random distribution of the substituted sites, allows us to account quantitatively for the reduction of the magnetization with increased doping and further confirms the homogeneity of our samples. A strong distortion due to the presence of the Ti on the Ru site could explain the different behavior observed between both types of doping. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119283

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We study the magnetic properties of Fe thin films epitaxially grown on GaAs (001) for a large range of substrate temperature. Magnetization deficiency has been observed and studied. Its dependence on both thickness and temperature clearly show the existence of a nearly half-magnetized phase at the interface, covered by “as-bulk” Fe. Furthermore, reflection high-energy electron diffraction studies show a transition between two bcc structures with different crystalline parameters. Transmission electron microscopy confirms the formation of this interfacial phase, for which the compoundFe3Ga2−xAsxseems to be the best candidate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119284

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The sign and strength of the dominant magnetic interactions inCo34Fe8Ag54Cu4granular films were modified by changing the microstructure through annealing. Magnetic force micrographs showed that in the as-cast sample the magnetic moments of neighboring grains tended to be arranged parallel along a direction out of the film plane, forming elongated magnetic clusters that were themselves aligned antiparallel, with dominant demagnetizing interactions. This is a direct evidence that an uncompensated antiferromagneticlike microstructure is stabilized below the volume percolation threshold. However, in the sample annealed at 750 °C the particle growth led to large in-plane ferromagneticlike clusters with dominant magnetizing interactions. Thus, in this letter we present direct correlation of interactions effects with magnetic measurements and show that &Dgr;Mplots correlate with changes in the magnetic microstructure in these systems. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119285

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have used superparamagnetic magnetic force microscopy (MFM) tips to obtain high spatial resolution MFM images of recording heads. Profiles of the magnetic field gradient above a thin-film recording head under 3 mA bias current to the head and various tip-head distance conditions are presented. At a low tip-head distance, the gap width, gap location, and gap-field structure can be well resolved in these MFM images. Superparamagnetic tips show promise for the magnetic imaging of recording heads with gap widths below 200 nm. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119286

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We demonstrate improvement in fatigue resistance and other ferroelectric properties through cerium doping in sol–gel derived lead zirconate titanate thin films. We have studied frequency dependence of fatigue behavior and show that the loss of polarization due to fatigue follows a universal scaling behavior withN/f2,whereNis the number of switching cycles andfthe frequency. The origin of the scaling is attributed to the drift of oxygen vacancies, which is the rate limiting process in the growth of the interface layer responsible for fatigue. Empirical fits for both undoped and cerium-doped samples show that switchable polarization follows stretched exponential decay with time orN/f. Cerium doping is shown to improve fatigue resistance by impeding the motion of oxygen vacancies. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119287

出版商:AIP    

年代:1997

数据来源: AIP