摘要:

The effect of longitudinal magnetic fields up to 60 kOe on the electrical resistivity of chromium‐iron alloys containing 0.9, 2.3, 3.3, 4.9, 9.5, and 11.2 at. % iron, have been studied at 4.2°K. All these alloys, except that with 0.9 at. % iron, exhibit negative total magnetoresistivity. The role of temperatures on the transverse magnetoresistivity at 12 kOe has been explored using the chromium‐9.5‐at. %‐iron alloy. The change in the magnetic component of the total magnetoresistivity has been calculated from the experimental data. This quantity is discussed from the viewpoint of a localized‐magnetic‐moment model.

ISSN:0021-8979    

DOI:10.1063/1.1709779

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The present work is concerned with determining the factors controlling the adhesion of metal couples. Most previous studies have been done in the presence of contaminants and, under these conditions, an energy barrier for adhesion has always been observed. This barrier has been ascribed to various factors: the need to disperse the contaminants so that metal‐metal contact and, consequently, adhesion, can occur; the energy required to realign the surface metal atoms to form an interfacial bond; and, for lightly loaded conditions, the necessity to overcome the elastic relief stresses which may break any bond formed during the unloading of the couple. A further condition for adhesion which has been postulated, is that the metal couples must be mutually soluble.The present adhesion experiments show that contaminant dispersal is the major barrier to adhesion. Thus, spontaneous adhesion occurred under vacuum conditions for the three systems studied when the surfaces were sufficiently clean, whereas subsequent contamination resulted in nonadhesion. Substantial amounts of contamination could, however, be tolerated. The contaminants may be divided into two classes, stable surface films and mobile gaseous or liquid films. While both are barriers to adhesion, the latter may be removed by application of a vacuum, whereas the former requires a more rigorous treatment.Because adhesion occurred for clean surfaces under vacuum conditions, even where elastic deformation predominated, the postulated energy barrier of adhesion due to the realignment of the surface atoms is considered of minor importance, at least for the softer metals studied here. Further, no evidence for rupture of the bonds by the elastic relief forces on unloading such lightly loaded clean couples has been observed. The latter effect, however, is thought to become more important whenever stable surface films are present, because of the limited metal‐metal contact.Since the one immiscible system studied here showed as great a tendency to adhesion as the miscible systems, the condition of bulk miscibility is considered no criterionper sefor adhesion.

ISSN:0021-8979    

DOI:10.1063/1.1709780

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Up to 6.0 wt % SrSO4, CaSO4, and BaSO4were added to strontium ferrite magnets consisting of the magnetoplumbite phase SrO·6 Fe2O3. The hysteresis loop, density, saturation moment per gram, and the degree of orientation were measured. The magnets were analyzed by standard chemical methods and by x‐ray diffraction techniques. The microstructures of the magnets were examined with a light microscope and with an electron‐beam microanalyzer. It was found that approximately 0.1 to 2.0 wt % SrSO4, CaSO4, or BaSO4are extremely beneficial in activating the ferrite magnet formation and in improving the magnet properties. SrSO4is particularly effective. With only 0.22 wt % SrSO4and at a sintering temperature of 2250°F, the remanence is increased from 3425 to 4150 G, the saturation moment from 65.2 to 69.1 G·cm3/g, the density from 4.21 to 4.86 g/cm3, and the degree of orientation from 81% to 87%. X‐ray scanning micrographs show that the solubility of SrSO4in SrO·6 Fe2O3is greater than 0.22 and less than 1.1 wt % at 2250°F.

ISSN:0021-8979    

DOI:10.1063/1.1709781

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The resistivity and mobility ofp‐type andn‐type silicon films grown epitaxially on (0001) and (11¯02) sapphire have been measured as a function of substrate prefiring, growth parameters, and film postfiring. Sapphire preheated in hydrogen produced the highest mobility silicon films. Preheating the substrate in helium resulted in films with low mobility. The growth temperature at which the maximum mobility was obtained was found to be about 1200°C on the (0001) sapphire and about 1115°C on the (11¯02) sapphire. The electrical properties were found to be relatively insensitive to growth rate in the range between 0.3 &mgr;/min and 3 &mgr;/min except that slower growth rates and longer growth times lead to relatively more auto‐doping from the substrate. The auto‐doping was linked to the hydrogen reduction of sapphire (Al2O3) resulting in aluminum‐doped silicon. Postfiring of the films below 1250°C resulted in no gross crystal changes but could result in appreciable electrical changes. Postfiring in hydrogen introduced aluminum into the films and postfiring in oxygen removed aluminum. Postfiring in helium resulted in little change in the doping of the films.

ISSN:0021-8979    

DOI:10.1063/1.1709782

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The transient growth of the spin‐wave population in a microwave magnetic field applied parallel to the dc field is investigated. It is assumed that the sample is in thermal equilibrium before the initiation of the microwave pulse, and that the rf field amplitude remains constant during the pulse. According to the theory the absorption coefficient approaches a steady‐state value below threshold, and grows indefinitely (as long as the field amplitude remains constant) above the threshold. The results of detailed calculations concerning the steady‐state and the transient absorption are described. Above threshold the time dependence of the absorption coefficient is characterized by a very fast initial rise to an intermediate plateau or hump, a subsequent more gradual rise, and an approximately exponential rise at later times. As the absorption coefficient increases, the field amplitude in the cavity decreases (assuming that the incident power remains constant). This reaction of the sample upon the field amplitude is taken into account in an approximate fashion. Because of this reaction the absorption coefficient approaches a new steady state above the threshold.

ISSN:0021-8979    

DOI:10.1063/1.1709783

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Measurements have been made of the attenuation of longitudinal waves along the ⟨110⟩ direction in a lead single crystal over a frequency range from 30 to 150 Mc/sec and in a temperature range from 60° to 300°K. The attenuation can be divided into a square‐law frequency term and a term consistent with the theoretical form of dislocation attenuation at high frequencies. By determining the high‐frequency asymptote of the dislocation internal friction and by assuming a reasonable dislocation density, the drag coefficient for the dislocations can be evaluated. The measurements are consistent with the sum of a phonon scattering term and a phonon viscosity term. The square‐law attenuation is about twice as large as the thermoelastic loss and over a temperature range is in agreement with the sum of a thermoelastic loss plus a phonon viscosity loss.

ISSN:0021-8979    

DOI:10.1063/1.1709784

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Ultra‐high vacuum pumps of the sputter‐ion pattern have been investigated from the standpoint of origin and destination of electrically charged particles constituting pump current. It has been found that secondary electron emission is responsible for a large portion of total current, that ion energies range from 0.50 to 0.80 of applied pump potential, and that needle crystals (whiskers) that grow progressively from pump electrodes cause pump current to depart from its linear dependence on pressure.

ISSN:0021-8979    

DOI:10.1063/1.1709785

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The refractive index vs wavelength of LiNbO3has been measured between 0.42 &mgr; and 4.0 &mgr; at 25°C and 80°C. The measured values have been expanded in a three‐term polynomial by a least‐squares best fit and the temperature dependence of the polynomial coefficients determined. The results are used to calculate the phase‐matching temperatures normal to the optic axis in nonlinear optical second‐harmonic generation and parametric experiments. The calculated results are compared with experimentally measured values.

ISSN:0021-8979    

DOI:10.1063/1.1709786

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The elastic moduli of hexagonal beryllium oxide, zinc sulfide, and cadmium selenide at 25°C have been determined by measuring ultrasonic wave velocities in the 20‐ to 50‐MHz frequency range. The data are compared with other literature data and discrepancies are discussed. The adiabatic bulk modulus, volume compressibility, and Debye temperatures are also computed.

ISSN:0021-8979    

DOI:10.1063/1.1709787

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The theory underlying the operation of metal‐insulator‐piezoelectric (MIPS) electromechanical transducers is verified experimentally for time‐varying loads on devices made from CdS piezoelectric film materials. Experimental transducers exhibit sensitivities of the same order as those observed under static loading within times shorter than one microsecond after the application of mechanical stress. The frequency limitations for the transducer appear to be determined by the electrical properties of the MOS structure. The MIPS effect is demonstrated experimentally in CdSe transducers. Transducers fabricated on a flexible polyimide film are described, and a microphone embodying this construction is discussed. Transducers made with CdS films have properties which are more reproducible than are obtained from transducers using CdSe films. X‐ray studies show this result to be linked to crystal structure in the semiconductor layers.

ISSN:0021-8979    

DOI:10.1063/1.1709788

出版商:AIP    

年代:1967

数据来源: AIP