摘要:

The variation of a transverse magnetic field induces a magnetic moment along the axis of a cylinder of a hysteretic type‐II superconductor provided that a static axial field is present. We argue that an axial moment appears perpendicular to the inducing field in order to relax the magnetic pressure or Lorentz forces. Our observations show that the induced electric currents do not flow exactly along the direction of the impressed (induced) electric fields.

ISSN:0021-8979    

DOI:10.1063/1.1659073

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Point‐contact devices are described which have exhibited long‐term stability and reliability. A particular mode of operation of the devices as rf‐biased low‐frequency detectors is described in detail, including a description of how the device drives a resonant circuit to which it is coupled. In this mode of operation the sensitivity of the devices to low‐frequency fields is of the order of 10−9G per root cycle bandwidth. Perfectly clean contacts were made by breaking a notched niobium member at 4.2°K and then remaking contact at the break. Quantum behavior of such contacts is identical to that of ordinary contacts, but effects of microscopic multiple connections at the contact were not observed.

ISSN:0021-8979    

DOI:10.1063/1.1659074

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experimental evidence is presented which shows that quantization of the phase integral is not a necessary condition for the occurrence of quantum interference effects in superconducting weak‐link circuits. Interference patterns observed with weak‐link geometries containing resistive sections differ from their superconducting couterparts only in the effect of Johnson noise which causes a random walk in quantum phase.

ISSN:0021-8979    

DOI:10.1063/1.1659075

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Several modes of operation of point contacts as heterodyne detectors in the frequency range 0 to 1010Hz were investigated experimentally. A point contact in a superconducting loop, under the application of two externally generated ac fields, behaved as expected on the basis of a model given previously. Likewise, a point contact in a partly resistive loop, in which an externally generated signal is heterodyned with the Josephson oscillation of the contact, gave the expected results. In both cases the heterodyne signal amplitude exhibits a decaying oscillatory (Bessel‐function‐like) dependence on applied signal level; the heterodyne power at the first peak being approximately 0.1&phgr;02f0/L, wheref0is the heterodyne frequency,Lthe loop inductance, and &phgr;0the flux quantum. On the other hand, an anomalously large heterodyne signal was obtained from a pair of closely coupled Josephson‐oscillating contacts. No explanation of this result is offered, but it appears that a sort of amplification of the heterodyne signal is effected when the Josephson frequencies are larger than the heterodyne frequency.

ISSN:0021-8979    

DOI:10.1063/1.1659076

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A method is presented for transforming hysteretic magnetization curves into their corresponding reversible magnetization curves. This procedure permits the determination of the thermodynamic critical fieldHc; the lower critical fieldHc1; the upper critical fieldHc2; and the Ginzburg‐Landau parameters &kgr;1and &kgr;2, which are found to be equal for each corrected magnetization curve for samples containing up to 28 at.&percent; In. Large, composition‐dependent, hysteresis effects are noted in the magnetization curves of these Pb&sngbnd;In samples.

ISSN:0021-8979    

DOI:10.1063/1.1659077

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Steady‐state measurements were made of the optical emission and electrical properties of amphoteric Si‐doped GaAs diodes. The width of the emitting region of these diodes is explained in terms of a theory involving the drift of electrons across a semi‐insulatingp‐region. At low currents radiative recombination occurs in thep‐region within a diffusion length of the junction. However, at high currents a considerable number of injected electrons drift across thep‐region and light emanates from the entirep‐region. The theory is consistent with the observedI‐Vcharacteristics and also with the spreading of the emission into thep‐region.

ISSN:0021-8979    

DOI:10.1063/1.1659078

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An electrical and optical study has been made of the transient response of amphoteric Si‐doped GaAs diodes. The luminescent turn‐on and turn‐off times were found to increase both with decreasing photon energy and with decreasing current drive. These results are consistent with a theory based on the wavy band model in which the recombination is from deep localized donor states and deep localized acceptor states.

ISSN:0021-8979    

DOI:10.1063/1.1659079

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The field asymmetries introduced in winding air‐cored solenoids are investigated theoretically by treating the solenoid as a suitably deformed single turn. Regarding the solenoid as an electron lens, aberrations are calculated for the various field integrals. Using a novel method of measuring aberrations, these are compared with results obtained from carefully wound test lenses.

ISSN:0021-8979    

DOI:10.1063/1.1659080

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The magnetic field generated by the magnetization has been calculated for films with arbitrarily rough surfaces for the case in which the magnetization is uniform throughout the film. Simple results are obtained on the assumption that the film surface is not too ``ragged,'' i.e., for the case in which the inclination of the local film surface relative to the mean surface is fairly small (<45°). A rough estimate of the demagnetizing factor for a direction in the plane of the film is given by&pgr;⟨p2⟩/&lgr;d, where⟨p2⟩is the mean square deviation of actual film surface from the mean surface, &lgr; the predominant wavelength of the surface roughness, anddthe film thickness. The results are discussed in the context of induced uniaxial anisotropy and ferromagnetic resonance.

ISSN:0021-8979    

DOI:10.1063/1.1659081

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Polycrystalline nickel films between 26 and 296 Å in thickness were obtained by evaporation at normal incidence from tungsten filaments onto microscope‐slide glass substrates maintained at 75°C, at pressures between 6×10−10and 12×10−10Torr. In the same vacuum the substrates with their films were arranged to be parts of an automated torsion magnetometer in which the sample rotated about an axis in its own plane perpendicular to the magnetic field. Measurements were made of the torque as a function of the magnetic field required to maintain the plane of the sample at various fixed angles &thgr;0ranging from 3° to 84° with respect to the magnetic field, at sample temperatures of about 300°, 77°, and 4.2°K. The torque data were analyzed by a new method which permits detailed investigation of models for the magnetization. It is shown that for a single‐domain model with an out‐of‐plane uniaxial anisotropy, the saturation magnetizationMSand the total anisotropy fieldScan be calculated from the magnitude and slope of the torque/field curve at any field strengthH′and any angle &thgr;0. The single‐domain model was verified for four samples with thicknesses of 87, 109, 182, and 296 Å. For these samples, bothMSandSwere independent ofH′and &thgr;0. This shows that for films thicker than 87 Å,MSis independent of thickness within the experimental error of ±2&percent;, and has the temperature dependence of bulk material, decreasing by 6.2±1.0&percent; between 4.2° and 300°K. The anisotropy field was completely accounted for by the shape demagnetizing field, and by magnetostriction and strain in nickel film. The torque data from the thinnest film, which was 26‐ Å thick and electrically discontinuous, did not fit the single‐domain model. The characteristic torque behavior of such very thin films probably indicates that they contain islands small enough to be superparamagnetic, This conclusion was supported by a theoretical analysis which showed that a film model consisting of identical, noninteracting, superparamagnetic particles does indeed give rise to torque curves like those of the 26‐ Å film. If such a superparamagnetic film is erroneously assumed to be a single domain, itsMSvalues appear to be less than the bulk values. Therefore, a detailed analysis of torque curve shapes is required to obtain reliable values forMS.

ISSN:0021-8979    

DOI:10.1063/1.1659082

出版商:AIP    

年代:1970

数据来源: AIP