摘要:

A simple model which allows spin‐½ nuclei in antiferromagnetic crystals to interact with phonons is presented and an order of magnitude calculation predicts the one‐ and two‐phonon effects observed in KMnF3.

ISSN:0021-8979    

DOI:10.1063/1.1659083

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Data on the parallel pump and subsidiary absorption threshold at 9.1 GHz and effective linewidth &Dgr;Heffat 9.9 GHz have been obtained for polycrystalline YIG materials with an average grain diametera0from 1 to 30 &mgr;. The fine‐grain samples (1–10 &mgr;) were made by hot pressing. The parallel pump spin‐wave line‐widths extrapolated to zero wavenumber, &Dgr;Hk→0, vary asa0−1, with &Dgr;Hk→0=25 Oe ata0=1 &mgr;. The &Dgr;Hkfor the fine‐grain samples (a0≈ 1 &mgr;) show an inversek‐dependence. A simple model in which the spin‐wave transit time across individual grains limits &Dgr;Hkappears to explain thea0−1dependence but not the observedk‐dependences for &Dgr;Hk. The high‐field &Dgr;Heffis 5.5 Oe fora0=1 &mgr; and varies asa0−1/2. The low‐field values are slightly larger, due to a small two‐magnon contribution arising from coupling to degenerate short‐wavelength spin waves. Even though the high‐field &Dgr;Heffcontains no two‐magnon contribution, it is significantly larger than linewidths in single crystals. A recently proposed magnetostriction mechanism is consistent with thea0−1/2dependence, but the predicted magnitude of &Dgr;Heffis much smaller than observed.

ISSN:0021-8979    

DOI:10.1063/1.1659084

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Saturation magnetization and Mo¨ssbauer measurements at different temperatures from 4.2° to 623°K have been made on samples of composition Cu0.5Fe2.5O4sintered at different temperatures between 1210° and 1350°C and quenched to room temperature. The Mo¨ssbauer spectra consist of a superposition of two six‐line patterns, which are attributed to iron onBsites andAsites, on the basis of the change in the intensity of the spectra with the substitution of a small amount of Sc in Cu0.5Fe2.5O4. The relative isomer shifts and hyperfine fields also confirm this assignment. The internal magnetic field at the iron nucleus at 300°K isH&bgr;= 473±2 kOe andHA= 402±2kOe. The isomer shifts relative to metallic iron and theAandBsites are found to be characteristic of the iron in the trivalent state. The saturation magnetization, Curie temperature, and hyperfine fields are found to be practically independent of the sintering temperature. The ratio of the iron site occupancy factor is determined from the intensity ratio of the Lorentzian fits of the two patterns and is compared to the value deduced from magnetization measurements. The various models proposed for this system are discussed in the light of the present work.

ISSN:0021-8979    

DOI:10.1063/1.1659085

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The minimum transition length for the arctangent magnetization transition is calculated. Readback voltage for the arctangent transition, where the magnetization contains components both in and normal to the coating plane, is calculated via the reciprocity theorem and Karlquist's fringe field equations. Several misconceptions currently existing in the literature are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659086

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A physical model is proposed for the photoplastic effect in ZnO, i.e., the reversible increase in flow strength upon illumination. The model is based on the assumption of Coulomb interaction between dislocations, which are negatively charged, and photoionized traps, which contain excess positive charge. Negative charge on dislocations has been observed in silicon, germanium, cadmium sulfide, and other semiconductors. The excess positive charge appears when interstitial Zn+atoms are doubly ionized to Zn2+under the influence of light. Several measurements were made of the photoplastic effect which confirmed the proposed model. First it was found that the photoplastic effect depended on the deformation rate so that at a high strain rate, 5×10−2sec−1, the effect disappeared, presumably because of the high propagation velocity of the dislocations, which did not allow sufficient time for the photoionization to grow. At lower strain rates, 5×10−4sec−1, a repeated yielding occurred, also explained by the model. In a second experiment photoconductivity at high dislocation densities was studied. An analysis of the photoconductivity data made it possible to predict the saturation illumination intensity and the time constant of the photoplastic effect. Agreement with the observed values was found. In a third experiment it was found that the flow stress, with and without illumination, depended on the square root of the density of interstitial zinc atoms.

ISSN:0021-8979    

DOI:10.1063/1.1659087

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The main purpose of the present investigation was to characterize the behavior ofS‐glass fibers at quasistatic strain rates. The experimental results presented herein, representing over 1600 individual tests, are a first step in the statistical characterization of fiber properties. It has been established that fiber strength decreases with increasing strain rate. Moreover, the experimental results demonstrate that Weibull distribution can adequately represent fiber strength distribution for quasistatic strain rates. For the type of glass tested, strength was observed to be maximum at or near room temperature (+75°F). The strength dependence on strain rate is greatest at room temperature. At higher or lower temperatures the dependence on strain‐rate is not so marked. Tests were also performed to determine the elastic modulus at various temperatures and strain rates. The elastic modulus increases with both an increase in strain rate and a decrease in temperature.

ISSN:0021-8979    

DOI:10.1063/1.1659088

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In a carbide or biboride the excess binding energy associated with metal—metalloid interactions must be overcome for a dislocation to move through the crystal structure. This makes possible a simple calculation of the indentation hardness number in terms of the heat of formation and the molecular volume. Good agreement with measurements is found for twelve representative compounds.

ISSN:0021-8979    

DOI:10.1063/1.1659089

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A complete theory of Maker fringes in nonabsorbing isotropic and uniaxial crystals has been derived which includes all the corrections necessary for making precise determinations of nonlinear optical co‐efficients. These corrections include finite beamwidth effects and multiple reflection corrections. Comparison of this theory with extensive experimental data on the Maker fringes in quartz, ADP, and KDP shows agreement to within the experimental accuracy of about 5&percent; on the Maker fringe envelopes and to better than 1&percent; on the coherence lengths. We conclude from this study that a careful analysis of Maker fringes can yield precise values of the nonlinear optical coefficients and coherence lengths in isotropic and uniaxial crystals. This is of great importance in establishingaccurateandreliablestandards in the field of nonlinear optics.

ISSN:0021-8979    

DOI:10.1063/1.1659090

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The effects of intenseQ‐switched ruby laser radiation on the colloidal systems NaCl[Au] and CaF2[Ca] were investigated by microscope and absorption spectroscopy techniques. A dependence of the width and depth of the surface crater on the incident laser pulse energy was established. In the case of NaCl[Au] a shift of the absorption maximum towards shorter wavelengths was observed. This was interpreted in terms of Mie's theory. Calculations on the temperatures generated in the colloids and its surroundings were done using Goldenberg's theoretical results.

ISSN:0021-8979    

DOI:10.1063/1.1659091

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The optical transmission of CdS single crystals has been changed using a laser. With ac techniques, these changes have been observed from 530 to 2000 nm in the transmission spectrum, and include both increased and decreased transmission. Comparison between the intensity dependence and the temperature dependence of photoconductivity and of change of transmission suggest a mechanism. The effect is a change of optical absorption produced primarily by the change in hole population of imperfection levels in the band gap. Changes in transmission due to population changes of approximately 1012cm−3have been observed.

ISSN:0021-8979    

DOI:10.1063/1.1659092

出版商:AIP    

年代:1970

数据来源: AIP