摘要:

The conversion of electromagnetic power into spin‐wave power and vice versa is investigated from a theoretical point of view. The analysis applies to a rod of ferromagnetic material whose two ends are each in a resonant cavity that is connected to a waveguide. The dc magnetic field is assumed to be nonuniform in such a way that the effective wavelength of the spin waves becomes large in those regions of the sample that protrude into the cavities. The theoretical analysis of the excitation process leads to a differential equation which is of the same form as the well‐known wave equation except that the wavenumber is a function of position. The conversion efficiency depends on the solution of this wave equation through a simple integral over the wavefunction which has the physical significance of a coupling length. A numerical estimate indicates that substantially complete conversion should be possible.

ISSN:0021-8979    

DOI:10.1063/1.1713058

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The coupling length is calculated by using two approaches: (a) For a simple model the wavefunction and the coupling length are determined rigorously; (b) More general, approximate results are obtained by means of the WKB method, which is valid if the dc magnetic field varies sufficiently slowly. It is shown that the coupling length is inversely proportional to the square root of the field gradient at the turning point.

ISSN:0021-8979    

DOI:10.1063/1.1713060

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The electrical polarization produced in solid dielectrics by gamma ray bombardment is treated as a space charge resulting from the production and absorption of Compton electrons. For a gamma‐ray beam in equilibrium with secondary electrons, the calculated net space charge is negative in sign and decreases with distance in proportion to gamma ray attenuation. The distribution of polarization was studied experimentally by cutting away sections of irradiated carnauba wax and measuring the charge released on heating for each section. The relationship of thermally released charge to sample polarization and the effect of a temperature gradient are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1713061

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The elastic constants of a (73.8% Ni‐26.2% Fe) ferromagnetic alloy have been measured at 300°K with the following results:C11=23.04,C12=14.44, andC44=11.92 (in units of 1011dyn cm−2). These results are compared with previously reported work on pure Ni and a (30% Ni‐70% Fe) alloy.

ISSN:0021-8979    

DOI:10.1063/1.1713062

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Measurements of Young's modulus as a function of pressure up to 10 000 bars at 20°C show that the glass‐transition temperature in natural and synthetic rubbers is raised by pressure. For natural gum rubber, the transition occurs at 5100 bars at 20°C and Young's modulus increases 1000‐fold on passing through the transition.

ISSN:0021-8979    

DOI:10.1063/1.1713063

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

According to a theory developed by Landau and Khalatnikov, the approach of long‐range order to equilibrium can be characterized by a relaxation time with a temperature dependence of the form: &tgr;=&bgr;/(Tc−T), where &bgr; is constant andTcis a second‐order phase transition temperature. The ferroelectric material, triglycine sulfate, is known to undergo a second‐order phase transition at its Curie temperature. The long‐range order is identifiable with the spontaneous polarization directed along the crystallographicBaxis. Ultrasonic waves traveling perpendicularly to theBaxis coupled to the spontaneous polarization and exhibited marked relaxational effects forT<Tc. Detailed absorption measurements verified the Landau‐Khalatnikov relation, yielding &bgr;=2.25×10−10sec/deg C andTc=49.09°C. Using this value of &bgr;, the kinetic coefficient &ggr; was calculated to be 8.0×1010cgs. With the absorption results, a calculation of the accompanying rise in the sound velocity asTincreases throughTcwas performed. This rise was only 40% of the rise actually measured, indicating that long‐range order is not sufficient to explain the temperature dependence of sound velocity forTnearTc. Substantial scattering losses were observed for temperatures aboveTc. These are attributed to needle‐shaped domains, which retain polarization forT>Tc. These domains, which point along theBaxis, have cross sections comparable in size to the sound wavelengths.

ISSN:0021-8979    

DOI:10.1063/1.1713064

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Near the Suhl second‐order threshold for spin‐wave excitation in ferrimagnetic resonance the spin waves have, in general, important influences on harmonic generation which can be predicted from the theory of spin waves in ferrites. These influences are potentially useful for experimental studies of the properties of spin waves, and their understanding is important for the operation of practical frequency multipliers that use ferrites. The second‐harmonic generation from the uniform mode itself is described by a simplified theory in which the only influence of spin waves is to alter the loss parameter of the resonant component. Two further effects are then predicted which are of interest: (1) A strong enhancement of the third and fourth harmonics of the uniform mode occurs above threshold, resulting from interaction of a nonresonant uniform mode component with the spin‐wave dipolar field. (2) Random inhomogeneities or crystalline anisotropy can lead to a direct radiation of spin‐wave energy into an external second‐harmonic circuit, since the spin waves are elliptically polarized and the proper coupling mechanisms to produce coherence exist. Experimental results in certain instances give quantitative agreement with the theory of direct spin‐wave contribution to second‐harmonic generation, and a study of harmonic generation can lead to conclusions as to the nature of spin waves excited in resonance experiments.

ISSN:0021-8979    

DOI:10.1063/1.1713065

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

A theoretical analysis of the efficiency of a magnetic triode thermionic converter is presented, and expressions for maximum obtainable efficiencies at given emitter temperature and collector work function are evaluated. A comparison with the thermionic vacuum diode efficiency shows similar efficiencies, but at considerably lower values of optimum current density for the triode.

ISSN:0021-8979    

DOI:10.1063/1.1713067

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The model of a magnetic film as one domain with a single anisotropy axis is often an inadequate approximation to true film behavior. A better approximation considers the film to consist of many uniaxial regions, with a range of anisotropy constants and of axis orientations in the plane of the film. The dispersion of values results in considerable confusion and awkwardness when using the single domain representation to understand magnetic switching. It is shown here that the total anisotropy distribution can be displayed on a polar plot in which each film region is characterized by a single point with the coordinates:Hk, its anisotropy field, and &agr;, its axis orientation. In this (Hk,&agr;) plane the switching effectiveness of the applied field is represented by a curve which is fixed in size and orientation relative to the field vector. Switching occurs in those parts of the film whose anisotropy points fall within the curve. The field figure is extended to include magnetization reversal by domain wall motion. Inverted switching behavior and switching time measurements are briefly discussed. Interactions between regions are not considered.

ISSN:0021-8979    

DOI:10.1063/1.1713069

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

An experimental study has been made of the effect of high‐temperature vacuum heat treatment on the infrared reflectivity of heavily doped germanium and silicon. The heat treatment produces a layer on the surface with optical properties differing from those of the bulk material. From a Kramers‐Kronig analysis of the reflectivity data for ann‐type silicon sample, where the time of heating is sufficiently short to make impurity out‐diffusion unimportant, it is concluded that the changes in free‐carrier electric susceptibility indicate a decrease in the low‐frequency‐scattering relaxation time. The change in relaxation time is attributed to the introduction of extensive surface fracture from the heating. The extinction coefficient was not obtained over a sufficient spectral range to ascertain whether it follows the classical expression; however, the results for the extinction coefficient indicate an increase in the high‐frequency relaxation time.

ISSN:0021-8979    

DOI:10.1063/1.1713070

出版商:AIP    

年代:1964

数据来源: AIP