摘要:

A zero‐frequency bridge has been developed for measuring the inductance and the current‐vs‐quantum‐phase relation of superconductors. The current null detector is a SQUID magnetometer coupled to the bridge by a superconducting transformer. The bridge is balanced by adjusting precision resistors at room temperature. The theory of the bridge and analysis of the null‐detector circuit for optimizing the sensitivity are given. For current‐dependent inductors, a definition of inductance based on the quantum‐phase difference is shown to be useful. Construction and operation of the bridge are described and measurements of inductance vs temperature for Al thin‐film meander lines are presented. Zero‐frequency measurements avoid the stray coupling to capacitances and normal metal inductances found in high‐frequency measurements and the method could give high‐precision absolute measurements. The sensitivity of the present instrument is such that an inductor of 4×10−7H was measured to a relative precision of one part in 104with a measuring current of 5×10−6A. Considerable improvement is possible, especially for circuit elements of very small inductance such as Josephson junctions and weak‐link superconductors.

ISSN:0021-8979    

DOI:10.1063/1.1663097

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

ac losses of commercial Nb3Sn tapes have been measured before and after removal of the normal metal cladding which is used to stabilize the superconductor. It is shown that materials which are frequently used to assist in bonding the normal metal to the Nb3Sn surface give rise to hysteretic losses which are much larger than those of the Nb3Sn itself in the low‐field region of interest for power transmission, below 1000 Oe. Examples of such materials are superconductive Pb&sngbnd;Sn solders used in cladding tin‐diffused tapes and ferromagnetic nickel flashes used in silver plating vapor‐deposited tapes. These lossy materials are not essential and can be eliminated in tapes which are properly designed for power transmission. It is also shown that eddy current losses are acceptably small for normal metal cladding thickness of the order of 25 &mgr;m (&rgr;∼10−8&OHgr; cm).

ISSN:0021-8979    

DOI:10.1063/1.1663098

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A simple, versatile, and inexpensive technique for the fabrication of superconducting microbridges and small Josephson tunnel junctions is described. The technique is based on the use of fiber masks for the production of precisely controlled substrate channels and yields device dimensions of 1 &mgr;m or less.

ISSN:0021-8979    

DOI:10.1063/1.1663099

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A magnetic annealing effect has been observed in a ferromagnetic MnBi single crystal. It was found that by heating an MnBi single crystal in a magnetic field perpendicular to the easy axis of magnetization of the crystal, the easy axis of the magnetization and the hexagonalcaxis of the crystal would change into the direction parallel to the field through a recrystallization process induced by the magnetic annealing. This recrystallization phenomenon is similar to that observed by Boothbyet al.on a polycrystalline sample. Based on the microstructure investigation and transformation kinetic analysis, it was found that the mechanism of the recrystallization in a single crystal is a thermally activated nucleation and interface controlled growth process. It was established that the magnetocrystalline anisotropy energy of the crystal is responsible for the recrystallization.

ISSN:0021-8979    

DOI:10.1063/1.1663100

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The theoretical field positions of the standing spin‐wave modes for selected Permalloy films and YIG films were obtained from a numerical solution of the spin‐wave equation for the case of perpendicular resonance for different pinning conditions. The static magnetizationM(z)was assumed to have an asymmetrical variation in which the magnetization has a minimum value at the substrate‐film interface (z=0) and increases to a maximum value at the film‐air interface (z=L). Comparisons of theoretical and experimental field positions show that a good fit of the experimental data occurs when the magnetization has a polynomial‐type variation.

ISSN:0021-8979    

DOI:10.1063/1.1663101

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Many laser drilling applications require that the shape of the drilled hole be carefully controlled. In order to successfully do this it is necessary to understand the laser drilling process. This paper reports on a quantitative model which predicts the depth and shape of a hole drilled in alumina ceramic by a ruby laser. Both experimental and theoretical results indicate that the predominant drilling mechanism for this application is not one of surface absorption and conduction inward, but one in which laser energy is absorbed throughout the bulk of the ceramic. The depth and shape of holes drilled in ceramic have been accurately predicted from the measured beam energy density distribution. Finally, it is shown that the radiation pressure of the focused beam plays an important role in the romoval of molten material from the heated region.

ISSN:0021-8979    

DOI:10.1063/1.1663102

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The voltage dependence of the electron sensitivity of photographic emulsions is analyzed in terms of experimentally established relations between (i) track density and energy loss rate (ii) incident energy and range. It is found that the latter strongly dominates the functional sensitivity at high energies. Calculated values are compared with experimental data by Dudley. The detective quantum efficiency of standard electron microscope plates is computed as a function of energy.

ISSN:0021-8979    

DOI:10.1063/1.1663103

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The specific heats of four samples of 2H NbSe2have been measured in the temperature range from 1 to 54 K. No anomalous behavior was found near 40 K where x‐ray, NMR, and Hall‐effect measurements have indicated the presence of a phase transition. An upper limit of 0.3 J/mole K has been placed on the magnitude of any anomaly in the heat capacity associated with this transition. Measurements of high‐purity stoichiometric 2H NbSe2sample gave a superconducting transition temperature of 7.23 K, a specific heat jump (&Dgr;C) in zero field of 240 mJ/mole K, and a Debye temperature of 204 K. A deviation from the usualT3behavior for the lattice contribution to the heat capacity was observed and assumed to be due to the two‐dimensional layer structure of the compound. Our best estimate for the electronic coefficient of specific heat (&ggr;) is about 10±5 mJ/mole K2. Based on the values forTcand &Dgr;C, the value for &ggr; calculated from BCS theory is 23 mJ/mole K2for 2H NbSe2which is in disagreement with our estimated value for &ggr; by a factor of 2.

ISSN:0021-8979    

DOI:10.1063/1.1663104

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The authors apply knowledge of spall phenomena and a simple pressure wave propagation model as a tool in solving gun explosion problems. An example with an explosive‐loaded cylinder serves to illustrate the approach.

ISSN:0021-8979    

DOI:10.1063/1.1663105

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Two recent papers have dealt with the observation that the Schottky barrier height,Vb′, of the gold‐gallium arsenide system increases linearly with the thickness of an interfacial oxide layer,l. In this paper it is shown how this linear relationship can be derived by considering the cause to be the same as that of the flat‐band voltage shift in MOS devices. That is, charge trapped at the oxide‐semiconductor interface creates an image charge in the semiconductor bulk. The slope,dVB′/dl, predicted by this analysis is in good agreement with the 1.75×10−6V/cm value experimentally derived. The predicted barrier height also varies linearly with the amount of trapped surface charge,Qss.

ISSN:0021-8979    

DOI:10.1063/1.1663106

出版商:AIP    

年代:1974

数据来源: AIP