摘要:

The demagnetization effect of a single‐layered superconducting coil made of a cylindrical multifilamentary wire on its eddy‐current loss is studied for the case of ac magnetic fields parallel to the coil axis. An expression for an effective demagnetization coefficient of the wire is obtained by taking account of the interaction among turns of the coil. It is shown from this expression that the magnitude of the eddy‐current loss increases remarkably with the distance between neighboring turns of the coil. The experimental loss values of the wires wound into various kinds of coils are within 20% of the theoretical values.

ISSN:0021-8979    

DOI:10.1063/1.328119

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

ac lossesPLof bronze‐processed (Nb0.99Zr0.01)3Sn strips have been measured between 4.2 and 16.5 K in the presence of a dc magnetic fieldH0. The measurements were performed using an electronic wattmeter with both ac and dc fields parallel to the long flat surfaces of the sample. A minimum in the functionPL(H0) was observed for fixed ac amplitudesh0. This minimum was found to occur in the entire temperature range between 4.2 and 16.5 K. A similar minimum was recently reported in Nb3Ge [Thompsonetal., J. Appl. Phys. 50, 3514 (1979)] at 4.2 K. The position of the minimum is explained here by the same physical model as in Thompsonetal. [J. Appl. Phys. 50, 3514 (1979)]; and Clem (ibid. 3518), but extending the model to include the temperature dependence of the entry surface shielding fields &Dgr;Hen(B,T) for flux density in the sampleB=0. It is also shown here that loss minimum measurements can be used for the determination of &Dgr;Hen(0,T) in the temperature range 4.2–16.5 K.

ISSN:0021-8979    

DOI:10.1063/1.328120

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The wall resonance frequencies of bubble and stripe lattices in the hexagonal ferrites BaFe12O19and PbFe12O19have been measured as a function of crystal thickness and magnetic fields applied parallel and perpendicular to thecaxis, which is oriented normal to the crystal surface. The dependence of the resonance frequencies on the normal field is in agreement with theory. For the dependence on the in‐plane field, however, a similar deviation between theory and experiment occurs, as is observed in garnet bubble materials; furthermore, the resonance frequencies increase stronger with decreasing thickness of the crystals than is predicted by theory.

ISSN:0021-8979    

DOI:10.1063/1.328121

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A ferromagnetic resonance (FMR) study of the effects of ion implantation into La, Ga:YIG (yttrium iron garnet) films is presented. H+, Ne+, and Ar+are used with doses ranging from 1014to 1016ions/cm2and implantation energies up to 200 keV. It is observed that the field for uniform resonance changes, and also that the magnetic film thickness decreases, depending on the ion and dose used. The experimental spin‐wave spectra are compared with theoretical spectra, yielding a profile for the anisotropy through the film thickness. It is argued that the observed changes in the magnetic film thickness are due to the existence of paramagnetism in the implanted top layer of the film.

ISSN:0021-8979    

DOI:10.1063/1.328122

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We report on measurements of conduction and threshold switching in organic polymer films using a new lateral geometry with very small (∼4 &mgr;m2) metallic contact areas. This geometry is shown to be quite useful in the study of both the conduction and switching mechanisms in thick (1–2 &mgr;m) polymethylmethacrylate (PMMA) films and should be equally useful in the study of switching mechanisms in other organic, semiconducting, or insulating materials. Results are presented showing reproducible and consistent ’’zero‐voltage’’ resistance values. Evidence is presented which suggests that filament formation occurred during threshold switching in our polymethylmethacrylate films.

ISSN:0021-8979    

DOI:10.1063/1.328123

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Dielectric hysteresis of stretched polyvinylidene fluoride films under a sinusoidal electric field of a period of 300 sec with an amplitude of 240 MV/m is observed by the aid of a minicomputer. It is found that the coercive field is about 50 MV/m and the remanent polarization is about 65 mC/m2. The dipolar polarization initially present in the sample is determined from the shape of the hysteresis loop for the first cycle. If the poled film is annealed at 100 °C for 1 h, the hysteresis loop becomes distorted for the first cycle, but returns to the normal shape after two or three cycles. The linear relationship between the residual dipolar polarization and the piezoelectric stress constant is determined.

ISSN:0021-8979    

DOI:10.1063/1.328124

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

In this paper it has been shown that a large reflectance modulation of light may be obtained with the help of a piezoresistive semiconducting circular membrane under forced vibrations due to sound waves. The membrane is fitted to the base of a Helmholtz resonator so that it responds even to weak sound waves incident at the mouth of the resonator. Numerical calculations show that the relative change in reflectivity for Ge as well as GaSb in the infrared region is so large that this method of light intensity modulation may be used fruitfully for communication purposes.

ISSN:0021-8979    

DOI:10.1063/1.328125

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A time‐resolved measurement on the recovery of saturation inp‐Ge was performed with picosecond CO2laser pulses. It was directly confirmed that the relaxation of hole excitation inp‐Ge was faster than 40 psec and that this type of measurement can provide additional temporal information on picosecond pulses.

ISSN:0021-8979    

DOI:10.1063/1.328126

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The influence of light scattering on photoacoustic signals is treated. Theoretical and experimental results are compared. The theoretical results are based on a model in which the photons diffuse through the sample. An equation governing the diffusion process is solved with appropriate boundary conditions. This gives the distribution of photons in the sample. The photoacoustic signal is then calculated and the result is compared with the result for nonscattering samples, giving the influence of the light scattering. The experimental results are obtained by measuring the photoacoustic signal for both scattering and nonscattering samples. The experimental and theoretical results are in good agreement. The differences are mainly due to the incompleteness of the original diffusion theory. An improved theory incorporating internal reflection at the sample surface is also analyzed. The paper illustrates the effects of light scattering on photoacoustic signals. It also shows how to estimate theoretically the photoacoustic signal from a light‐scattering sample.

ISSN:0021-8979    

DOI:10.1063/1.328127

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The refractive indices of Tl3AsSe3as a function of wavelength and temperature are reported. Also included are the variations with temperature of the coefficients of thermal expansion. Within the context of a simplified LCAO theory the apparent anomalous temperature dependences of the refractive indices are explained.

ISSN:0021-8979    

DOI:10.1063/1.328128

出版商:AIP    

年代:1980

数据来源: AIP