摘要:

The prospect of incorporating Josephson tunnel junctions into future device technologies requires that fabrication procedures be developed which assure high junction yield, uniform quality, and reproducibility. Critical‐current distributions which are extracted from theI‐Vcharacteristics of series‐connected lead and lead‐alloy junction arrays provide a quantitative measure of the yield, as revealed by a direct count of the 2&Dgr; increments, and the quality or uniformity, as revealed by the width of the distribution. Examples of the effects of oxidation parameters, junction area, electrode thickness, magnetic fields, and thermal cycling on the critical‐current distributions demonstrate the ease in which significant statistical information on simultaneously prepared junctions is obtained. As a further illustration of the use of this diagnostic method, we present results on flux‐trapping experiments together with a preliminary survey of the effectiveness of a simple technique in which lead alloys are evaporated from a single source to completion and then oxidized in an acidic‐oxygen environment.

ISSN:0021-8979    

DOI:10.1063/1.324392

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Approximate formulas that yield the resonance amplitude of symmetric two‐junction interferometers have been derived using step‐by‐step linearizations and approximations based on physical arguments. The resonance amplitude is found to strongly depend on the deviceQ. It increases asQincreases, reaches a peak, and subsequently decreases again. In the low‐Qregion, the resonance step is very broad and largely independent of rapid changes in device current. This is not the case in the high‐Qregion where the resonance amplitude increases with decreasing device current rise time. In the range of validity of the approximations, the results were compared to computer solutions, and reasonable agreement was found for arbitrarily chosen test cases. Although derived for two‐junction interferometers, the results can be extended directly to certain symmetric three‐junction interferometers.

ISSN:0021-8979    

DOI:10.1063/1.324393

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Theoretical investigations based on the Ginzburg‐Landau theory and the consideration of the lifetime of normal particles and superparticles yields a new acceleration equation of superparticles and a diffusion‐type equation for normal current in nonequilibrium superconductors. Derived relations are used to examine the experiments on normal‐current injection in supernormal junctions and on the effective capacitance in superconducting microbridges. Good agreement is found between theory and experiment.

ISSN:0021-8979    

DOI:10.1063/1.324394

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Gallium additions to the Cu‐Sn bronze matrix in the production of Nb3Sn wires by solid‐state diffusion raiseHc2(4.2 K) of the resulting compound to ∼25 T. This increase inHc2, which is not accompanied by any significant increase inTc, is associated with the incorporation of gallium into theA‐15 compound which has the approximate composition Nb3(Sn0.9Ga0.1). Critical currents in a variety of Ga‐containing wires, all reacted at 700 °C, have been measured in fields up to 23.5 T. This is the highest field at which steady‐state current measurements have yet been made. The pinning force is found to be closely proportional toh1/2(1−h)2, wherehis the reduced field.

ISSN:0021-8979    

DOI:10.1063/1.324395

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We present our latest results on the fabrication and properties of high‐TcNb3Sn thin‐film weak links and SQUID’s prepared by radiation damage of localized regions. Using radiation damage, we have successfully fabricated high‐temperature thin‐film weak links with current‐voltage characteristics similar to those produced either by proximity effect or ion‐implantation techniques. The critical current of these weak links obey a relationIc∝ (T′c‐T)3/2forT<T′c, andIc∝exp(−&ggr;T) forT≳T′c, whereT′cis the intrinsic transition temperature of the radiation‐damaged region. High‐temperature (operation temperature ≳14.5 K) Nb3Sn thin‐film SQUID’s with sensing area ∼3 mm2have been successfully fabricated using these weak links.

ISSN:0021-8979    

DOI:10.1063/1.324397

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We have examined the dependence of various properties of sputter‐deposited amorphous GdCo, GdFe, and GdCoX(X=Mo,Cu,Au) films upon substrate bias and annealing. Particular interest was directed to changes in magnetization, anisotropy, composition, x‐ray diffraction patterns, and Ar content of the films. In the case of the binary films, we applied substrate bias voltages to 400 V. We found that for the GdCo system,Kurises with increasingly negative bias voltage to aboutVb=−200 V. Further increases inVbcauseKuto decrease, so thatKu?0 forVb?−400 V. Furthermore, it was found that the Ar content of the films tends to correlate withVb, reaching a maximum forVb?−200 V. X‐ray diffraction patterns of these films also appear to correlate withKubut in a more subtle manner than has been suggested by other workers. The results for amorphous GdFe films were considerably different. In particular, it was found thatKuwas large forVb?0 but decreased rapidly with negative bias. The behavior of ternary GdCoXfilms was similar to that of the binary GdCo films, except that the x‐ray diffraction patterns showed little dependence onVb. On being annealed for 4 h at 200 °C, the binary films show no change in magnetization, composition, or x‐ray diffraction profile, but do experience a decrease inKuby about a factor of 2. The situation is similar for the GdCoCu and GdCoAu films except that the temperature dependence of the magnetization also changes dramatically. In contrast to these results, amorphous GdCoMo films undergo little or no change on annealing. Our results suggest that the incorporation of Ar into the films is closely related to the mechanism responsible forKuin these materials; however, there exist data which conflict with this interpretation, so that the origin ofKuremains in doubt. On the other hand, we have established the limits to the effects ofVbon the material’s properties, and we present a comprehensive collection of empirical facts which will prove useful for preparing this class of materials with desired properties.

ISSN:0021-8979    

DOI:10.1063/1.324344

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The dispersion relation of the magnetostatic volume wave in a normally magnetized ferromagnetic slab placed between two metal plates is analyzed. When the normalized spacesA=D1/SandB=D2/S, whereD1andD2are the spaces between the slab and the metals andSis the slab thickness, are finite, the cutoff frequency &OHgr;cexists in the dominant mode and becomes {&OHgr;H[&OHgr;H+1/(A+B+1)]}1/2, where &OHgr;H=Hi/4&pgr;Ms,Hiis the internal magnetic field, and 4&pgr;Msis the saturation magnetization. This frequency &OHgr;cgives the lower limit of the frequency region in which the magnetostatic volume wave exists and varies withA+Bfrom &OHgr;Hto [&OHgr;H(&OHgr;H+1)]1/2. The experimental values on the change of &OHgr;cwithA+Bhave agreed well with the theoretical results.

ISSN:0021-8979    

DOI:10.1063/1.324398

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The real and imaginary parts of complex relative permittivity along thebaxis of antiferroelectric Cu(HCOO)24H2O single crystals were measured at 1 kHz over a temperature range −10 to −45 °C under various uniaxial stresses. The antiferroelectric phase transition temperatures (&Vthgr;c) under uniaxial stress along thecaxis (&sgr;3) and thea′ axis (&sgr;1) vary linearly with the stress coefficients ofd&Vthgr;c/d&sgr;3=3.3×10−8K/(N/m2) andd&Vthgr;c/d&sgr;1=2.6×10−8K/(N/m2), respectively, and these values agree well with the values calculated by the Clausius‐Clapeyron equation. The temperature dependence of the real part of complex permittivity in the paraelectric phase under various uniaxial stresses obeys the Curie‐Weiss law. The characteristic temperatures (&Vthgr;0) under &sgr;3and &sgr;1vary linearly with the stress coefficients ofd&Vthgr;0/d&sgr;3=−6.7×10−7K/(N/m2) andd&Vthgr;0/d&sgr;1=−10.8×10−7K/(N/m2), respectively. The dielectric properties under uniaxial stresses are elucidated by the phenomenological theory for the antiferroelectrics under uniaxial stresses, and the electrostrictive coefficients are estimated from the stress dependence of &Vthgr;cand &Vthgr;0. The activation energy for the flip‐flop of the dipole (&Dgr;&fgr;) is found to increase with applied stresses, and &ggr; which stands for the stress dependence of &Dgr;&fgr; has a large anisotropy and its values are 1.1×10−9/(N/m2) along thecaxis and 60.0×10−9/(N/m2) along thea′ axis.

ISSN:0021-8979    

DOI:10.1063/1.324399

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The dependence of the absorptivity and emissivity of lead sulfide films on thickness was investigated. Theoretical calculations were made using the bulk–lead sulfide model. Reflectance measurements in the visible and infrared regions of the spectrum were made to determine absorptivity and emissivity values. Both the theoretical and experimental results predict optimuma/evalues for the lead sulfide thickness range 300–800 A˚.

ISSN:0021-8979    

DOI:10.1063/1.324345

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

In order to obtain more accurate information of Compton profiles a new technique, the Compton fluorescence scattering (CFS), was further developed. The most important advantage of the CFS compared with the conventional x‐ray technique is that the background is small and well defined. With respect to &ggr; radiation the resolution is much better and influences of multiple scattering are less serious. As an example the results on aluminum with AgK&agr; radiation and a LiF 600 analyzer demonstrate that deviations between previous results with the MoK&agr; conventional method and 412‐ and 59‐keV &ggr; measurements respectively could be interpreted. The best agreement was found with the 412‐keV &ggr; results.

ISSN:0021-8979    

DOI:10.1063/1.324346

出版商:AIP    

年代:1978

数据来源: AIP