摘要:

Simultaneous measurements have been made of the absorption at 8.5 kMc and of the second harmonic magnetization generated in single crystal Zn2Y. The high planar anisotropy of this ferrite enhances its frequency doubling behavior. The results agree well with the predictions of the equation of motion for the magnetization with anisotropy and losses included.

ISSN:0021-8979    

DOI:10.1063/1.1728743

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The space potential of the plasma contained in the DCX‐1 has been investigated using a beam of lithium ions. The ions were accelerated through a variable potential from a thermionic source and directed toward the plasma. The beam energy at which the transmission became significant was defined as the plasma space potential. The potentials obtained in this way have shown an increase with plasma density but have only a weak dependence on the background gas pressure.

ISSN:0021-8979    

DOI:10.1063/1.1728744

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

High resolution Bitter pattern studies of the domain structure of permalloy films, with uniaxial anisotropyHkand under the influence of applied fields in the film plane, are reported, and from these studies are inferred some aspects of noncoherent flux reversal processes. The threshold field for irreversible domain propagation across the film is measured for a variety of films differing in thickness (150 to 1100 A), rate of deposition (30 to 1100 A/min), substrate temperature (100 to 350°C), and composition (80 to 83.5% Ni), as a function of the angle &agr; between the reversing field and the easy axis, after saturating along the opposite easy direction. For &agr;<&agr;c, where &agr;cdepends on thickness and preparation variables and varies from 0° to about 60°, reversal takes place by parallel wall displacement, with a wall coercive forceHwcharacteristic of the film. Two principal structural features have been identified as affectingHw: Nonmagnetic inclusions, and local easy axes in the film plane normal to the main easy axis (negativeHk). In films thin enough to support Ne´el‐type walls, long perturbation walls are generated when a domain wall collides with an inclusion (or hole); these perturbation walls, which appear to be some form of 360° (or 720°, etc.) wall separating head‐on parallel domains, require several hundred oersteds for removal. NegativeHk, which is demonstrated by high‐angle buckling combined with low angular anisotropy dispersion, is readily found in films withhw=Hw/Hk>1, and is believed to be directly correlated withhw. For &agr;>&agr;c, reversal takes place by labyrinth propagation, in which the walls remain relatively fixed, and long, slender domains develop from the tip leaving behind regions of unswitched material, resulting in a labyrinth‐like flux pattern. The labyrinth threshold is nearly parallel to the threshold for coherent rotation, but below it by an amount which increases with decreasing film thickness. A model for labyrinth propagation, which treats the film as being composed of regions of differingHk, with magnetostatic interactions coupling a region undergoing switching to unswitched and previously switched regions, predicts the direction of propagation and its thickness dependence in reasonable agreement with experiment, and is partially successful in explaining the labyrinth threshold. It is suggested that labyrinth propagation is the primary mechanism of intermediate‐speed pulse switching (switching time ≳0.1 &mgr;sec); the correlation between intermediate‐ and high‐speed threshold fields, and angular and amplitude anisotropy dispersion, is examined. Finally, the high‐speed switching mode (&tgr;<0.1 &mgr;sec) is considered; the intrinsic damping for this mode is found to be about four times the damping deduced from ferro‐magnetic resonance linewidth or from free oscillations of the magnetization, indicating that even for switching times approaching 1 m&mgr;sec reversal does not take place by a completely coherent rotation.

ISSN:0021-8979    

DOI:10.1063/1.1728745

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An investigation has been carried out of the current and electric field distributions in the end region of a crossed field MHD device (accelerator or generator), with skewed electrodes, for the case in which the plasma exhibits the Hall effect. In order to simplify the situation enough to permit analytic solutions, a two‐dimensional problem was considered wherein the plasma velocity and properties, and magnetic field intensity were taken to be constant and uniform. Solutions were obtained for several values of &ohgr;&tgr; (&ohgr;=electron cyclotron frequency, &tgr;=electron mean free time); they show that current flows a considerable distance upstream of the beginning of the electrodes, that some current concentration exists at one of the electrode corners, and that displacing this electrode upstream reduces this current concentration somewhat.

ISSN:0021-8979    

DOI:10.1063/1.1728746

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The rate at which contamination forms on surfaces exposed to electron beams in reflection electron diffraction has been investigated for electropolished single crystals of copper and cleavage faces of alkali halide crystals by observing the decrease of the intensity in the diffraction pattern. It was found that a cold chamber at liquid nitrogen temperatures surrounding the specimen reduces the contamination rate on copper by an amount directly proportional to the solid angle through which the specimen is exposed to the vacuum system, and at the smallest aperture lowers the rate by as much as 2 orders of magnitude. Color centers were produced in the alkali halide crystals exposed to the electron beam. The resultant imperfections in the crystal lattice apparently affected the diffraction spot intensity, making measurement of contamination rates by this method unsatisfactory.

ISSN:0021-8979    

DOI:10.1063/1.1728747

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An apparatus is described in which a pure dynamic shear strain is produced in a small sample of liquid or other material, and the resulting shear stress is measured in the frequency range between 20 and 1000 cps. The shear stress is decomposed into its real and imaginary parts, which yield the shear rigidity and the shear viscosity. Design and working equations are derived. Two liquids are investigated and the data shown. The effect of impurity molecules is discussed, and a possible application to lubrication theory is suggested.

ISSN:0021-8979    

DOI:10.1063/1.1728748

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Irradiation damage of nickel single crystals bombarded with 3 Mev electrons has been studied by Kossel line techniques. Changes of lattice parameter and x‐ray line breadth were determined for crystals bombarded with integrated dosages of 1016, 1017, and 1018electrons/cm2at liquid nitrogen temperature. It is concluded that the formation of Frenkel defects in the lattice due to the electron bombardment is consistent with the data obtained. Subsequent annealing studies support this conclusion.Using an electron microbeam probe to obtain the Kossel patterns, the absolute precision of the lattice parameter obtained is better than 1 part per 100 000 or ±0.00003 A. The limit of relative precision of change in lattice parameter of a given crystal is 3 parts per 1 000 000 or 0.00001 A. Basic principles of the formation of Kossel lines, experimental arrangements, various errors, and related models are presented.

ISSN:0021-8979    

DOI:10.1063/1.1728749

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

On aging at 120°C two annealed alpha brasses containing 30 and 35% Zn, respectively, a small (about 0.0003 to 0.0006 A) reduction in the lattice parameter occurs. In the present work all diffraction lines in the spectrum were measured using monochromated CuK&agr;iradiation, and all indicated the same change. Cold work induced by filing produced a measurable amount of stacking faults as detected by the shifts in the diffraction lines and in addition caused an apparent increase in lattice parameter of about 0.0008 A. On aging these cold‐worked alloys for over 1000 hr at 120°C, the lattice parameter decreased. For the Cu‐35Zn the decrease was 0.0037 A and was accompanied by the precipitation of a small but measurable amount of beta phase. Thereby the solubility limit of the alpha phase was placed between 33 and 34% Zn. The Cu‐30Zn alloy also showed a decrease in the lattice parameter of 0.0029 A but, as expected, no beta phase. In neither case was there any observable change in the stacking fault density. These data are interpreted in terms of solute clustering, possibly to stacking faults, as considered by Suzuki. It is suggested that solute clustering may also be the cause of the decrease in lattice parameter for the annealed and aged alloys, rather than short‐range ordering.

ISSN:0021-8979    

DOI:10.1063/1.1728750

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Permalloy films (83 wt.% Ni‐17 wt.% Fe) epitaxially grown on NaCl, were annealed by electron bombardment in an electron microscope. Perfect single‐crystal diffraction patterns indicated the presence of the [100] parent crystal and [122] twin crystals. Fringe patterns observed on electron micrographs were identified by dark field microscopy and electron diffraction as being caused by platelets of twins, 100–400 A thick, lying parallel to {111} planes of the parent crystal. The nonintegral reflections, commonly observed in conjunction with twin reflections, were shown to be caused by double diffraction.

ISSN:0021-8979    

DOI:10.1063/1.1728751

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Recent experimental results from a cesium thermionic converter reported by Houston and Gibbons show that at low emitter temperatures and high cesium pressures the output current approaches an asymptotic value as the emitter is made more and more negative with respect to the collector. With further decrease in voltage the current jumps to much higher values. The assumption was made by Houston and Gibbons that the operation of the converter under these conditions is electron space‐charge‐limited and that in the high current mode, collision ionization is present. In the present communication a quantitative analysis of this electron space‐charge‐limited operation is presented. On the basis of this assumption an expression for the limiting value of the output current is obtained. A method is outlined by means of which the difference in emitter and collector work functions can be found from an experimental current‐voltage characteristic and conversely such a characteristic can be plotted if sufficient information is given. This method is applied to experimental I–V curves obtained from a parallel plate converter with a tantalum emitter. From these curves the emitter work function and the true saturation current have been estimated. These values of work function are approximately 0.5 v less than extrapolated values obtained from other experiments reported in the literature for cesium on tantalum. With the assumption that ions are introduced in the interelectrode spacing only by surface ionization, the magnitudes of the emitter and collector sheaths are computed at different points of the I–V curve.

ISSN:0021-8979    

DOI:10.1063/1.1728752

出版商:AIP    

年代:1962

数据来源: AIP