摘要:

The motion of flux line dislocation (FLD) dipoles is shown to be a more important mechanism for flux transport than the motion of individual FLDs. The electric field generated by FLD dipoles moving at a terminal velocityvisE=(Bbys)&Lgr;v,whereBis the magnetic induction,bis the magnitude of the Burgers vector,ysis the separation between the individual FLDs in each dipole, and A is the density of moving FLD dipoles. The terminal velocity is found to be proportional to (J‐Jc), whereJcis a critical current density. The analogy between the above equation and the corresponding equation for the plastic‐shear strain rate in metals is explored in order to qualitatively explain yield phenomena and time‐dependent hysteresis inE‐Jcurves. Possible FLD dipole sources and the portion of experimentalE‐Jcurves likely to be affected by FLD motion are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658723

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The temperature dependence of the induced anisotropy constantKand saturation magnetizationMsin evaporated polycrystalline Ni&sngbnd;Fe films was determined relative to room‐temperature values over a broad alloy range from 100° to 293°K. Within experimental error,K(T)/K(293°K) = [Ms(T)/Ms(293°K)]q, whereq=3.6±0.2 for all compositions. This result suggests that the anisotropy in evaporated films is a single‐ion effect. Further, if the anisotropy can be described by a combination of pair ordering and constraint release, both mechanisms are single‐ion effects.

ISSN:0021-8979    

DOI:10.1063/1.1658724

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Anomalously large changes in the magnetization as a function of hydrostatically applied pressure have been observed over a range of sample densities and applied fields in porous polycrystalline (ceramic) ferrites such as NiFe2O4and YIG. These changes can be explained on the basis of anisotropy energy resulting from nonisotropic strain. The experimental results show that large nonisotropic strains can obtain in porous samples and thus, care must be exercised in interpreting ``hydrostatic'' measurements on porous materials especially when the property being measured is known to be strongly dependent on the nature of the induced strain. For single‐crystal YIG, the saturation magnetization per unit mass is found to be independent of pressure as is expected since its magnetic moment is the spin‐only value.

ISSN:0021-8979    

DOI:10.1063/1.1658725

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The dependence of Mo¨ssbauer‐line‐area ratio as function of thickness of iron films in the range of 100 to 3000 Å was investigated experimentally, and was related to the magnetic structure of the film. The results were explained by either of two indistinguishable models. In one model all the magnetic dipoles have the same polar angle with respect to the normal to the film. In the second model the magnetic dipoles can be only normal and tangential to the film. In both models no dependence on the azimuthal angle was found. This thickness dependence is discussed on the basis of the film formation.

ISSN:0021-8979    

DOI:10.1063/1.1658726

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Precise measurements of the temperature dependences of the53Cr,79Br, and81Br nuclear resonance frequencies in ferromagnetic chromium tribromide have been carried out between 4.2°K and the Curie temperature (32.56°K). The resonances are found to be sensitive and reproducible indicators of temperature. Several of the resonances can be used for thermometers with millidegree sensitivity in the range 2°–25°K. This range includes the 4°–14°K range between the hydrogen and helium vapor‐pressure curves, where a reliable secondary standard is needed.

ISSN:0021-8979    

DOI:10.1063/1.1658727

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

This paper presents the ultrasonic measurements of the elastic constants of RbCl, RbBr, and RbI as a function of pressure up to approximately 4 kbars in the temperature range of 120° to 300°K. The reduction of the raw data is analyzed according to the self‐consistent method suggested by Cook and is discussed at length so as to clarify the limitations as well as the precision of the final results presented in this paper. The results of adiabatic as well as the isothermal values of the elastic‐constant measurements at pressure are given together. Pressure derivatives of the elastic constants of the above salts under different thermodynamic conditions are calculated and are given separately. Finally the Cauchy relation and anisotropy are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1658728

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In order to estimate accurately the values of the elastic constants of a solid at high pressure and at an arbitrary temperatureTfrom the ultrasonic measurements of the velocities of elastic waves propagated in solids as a function of pressure at the temperatureT, it is necessary to knowa priorithe compressibility of the solid as a function of pressure at the temperatureT. However, this latter information is not always available. Hence, one has to make some kind of approximation to estimate the values of the elastic constants of solids at high pressure. The procedure developed here is more consistent than previous procedures. It requiresa prioriknowledge of the following values: the thermal expansion coefficient, its temperature derivative, the specific heat at constant pressure of a solid at one atmosphere, and the travel‐time measurements of the elastic waves propagated through the solid as a function of pressure at a temperatureTor at more than one temperature.

ISSN:0021-8979    

DOI:10.1063/1.1658729

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Small‐scale indentation experiments performed on nonmetallic specimens are reported. These experiments are very similar to others performed by one of us (N.G.) on metal specimens and reported in a previous issue of this journal. Again, it is believed that the theoretical strength of the perfect lattice is being observed.

ISSN:0021-8979    

DOI:10.1063/1.1658730

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Impact shear tests have been used to study the dependence of shear stress with shear‐strain rate at strain rates ranging from 0.5×104to 2.2×104sec−1in pure Al, prestrained Al, and Al‐2 at. % Cu alloy. Within this strain‐rate range a linear relationship was found between shear‐stress and shear‐strain rates, indicating the presence of a viscous drag on dislocations. The dependence on temperature of this viscous damping was investigated between 10° and 293°K. The results are discussed in terms of theories of phonon viscosity and phonon scattering, and of electron viscosity at low temperatures.

ISSN:0021-8979    

DOI:10.1063/1.1658731

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Energy spectra of electrons transmitted through targets of Be, Al, and Au were measured for incident electron energies of 4.0 and 8.0 MeV. The target thicknesses corresponded to ⅕ or ½ the range (calculated in the continuous slowing‐down approximation) for the incident electron energy. Transmitted electron spectra were measured as a function of emission angle in the forward hemisphere using a magnetic spectrometer. Angular distributions and energy spectra are compared with results calculated with a Monte Carlo computer program (the NBS ETRAN‐15 program). The calculations agree with the experimental data within the experimental error of measurement, except for the aluminum target where spectral comparison agree but there exists a normalization discrepancy. A spectral shift is observed in the data from a beryllium target.

ISSN:0021-8979    

DOI:10.1063/1.1658732

出版商:AIP    

年代:1970

数据来源: AIP