摘要:

A monolithic process has been used to produce superconducting materials by controlled precipitation of theA‐15 (V3Ga) phase inside the bcc matrix of a V‐rich solid solution. Ingots of V‐(17∼19 at.%)Ga were prepared by arc melting, homogenization, and quenching, were deformed at intermediate temperature into tape, and were aged at temperatures in the range 600–1000 °C to precipitate theA‐15 phase. The maximum critical transition temperature (∼14.8 °K) was found in materials aged at temperatures of 750 °C or below. At these aging temperatures theTcinitially increases with aging time, and passes through a distinct maximum. The source of the exceptionally highTcis not clear, but may be attributable to a combination of high solute content and internal strain in the smallA‐15 precipitate particles.

ISSN:0021-8979    

DOI:10.1063/1.327940

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

High wall and bubble velocities have been observed in garnet films having a strong orthorhombic anisotropy. This anisotropy is induced by compressive misfit stress in garnets containing Mn3+ions. The magnetostatics of bubbles in these orthorhombic materials differs from that in uniaxial materials, e.g., no hard bubbles have been observed for large in‐plane anisotropies. Under certain conditions automotion of bubbles has been observed indicating that vertical Bloch lines may be present. Wall mobilities of 55 m s−1Oe−1and velocities up to 1400 m s−1have been observed. The possibilities for small bubble diameter applications will be shown.

ISSN:0021-8979    

DOI:10.1063/1.327941

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The theory of the photomagnetoelectric effect has been worked out for the case in which the lifetime is dependent on the injection level and the recombination mechanism is described by the Shockley‐Read statistics. Under the small signal hypothesis, the nonlinear continuity equation has been solved by perturbative method. An example is presented which evidences the deviation of the theoretical behavior of the spectral distribution of the short‐circuit current from the standard case in which the linear continuity equation is considered and the lifetime is constant.

ISSN:0021-8979    

DOI:10.1063/1.327942

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

For monocrystalline MnZn ferrous ferrite the magnetocrystalline anisotropy constantsK1andK2, the initial permeability &mgr;i, and the saturation magnetizationMshave been measured in considerable detail as functions of temperatureT. The effect ofK2has been incorporated in the commonly used expressions describing the dependence onK1andMsof &mgr;idue to rotation of magnetization and displacement of domain walls. It is shown that a nonzeroK2can limit considerably the secondary maximum of &mgr;i(T) at the temperature of anisotropy compensation. The results of measurements on monocrystalline Mn0.42Zn0.44Fe2.145O4are interpreted with the aid of the theoretical expressions obtained for &mgr;ias a function ofK1,K2, andMs. Special attention has been paid to the temperature range around the secondary maximum of &mgr;i(T) at −82 °C and the temperature range around the primary maximum of &mgr;i(T) close to the Curie temperature.

ISSN:0021-8979    

DOI:10.1063/1.327943

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The magnetic properties of several amorphous alloys prepared by melt spinning have been studied. These comprise alloys of the series Tb1−xCox, Y1−xCox(0.25⩽x⩽0.60), andR69Co31(R=La, Nd, Sm, Gd, Tb, Dy, Ho, and Er). Most of the alloys in which theRcomponent has an orbital momentum were found to exhibit large intrinsic coercive forces at low temperatures. The thermomagnetic history effects studied on several of these alloys have been interpreted in terms of a thermally activated magnetization process. The magnetic ordering temperatures of the seriesR69Co31scale to the deGennes factor (g−1)2J(J+1) only approximatley. The systematic deviations suggest that the indirect magnetic coupling between the localized 4 fmoments involves a term proportional to Si⋅Ljin addition to the main term, proportional to Si⋅Sj.

ISSN:0021-8979    

DOI:10.1063/1.327944

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper discusses the problem of electron paramagnetic resonance (EPR) line shape of localized magnetic ions in conductors which exhibit a strong dependence of their electrical properties on the applied magnetic field. Semimetals and narrow‐gap semiconductors with highly mobile charge carriers are specifically considered. When specimens (in the form of a plane‐parallel slab) are much thinner than both the skin depth and the internal wavelength, the EPR line shape is Lorentzian, determined by the dissipative part of the dynamic magnetic susceptibility of the localized paramagnetic ions. When the specimens are thicker than the skin depth, a variety of line shapes is predicted, determined not by the value of the conductivity as such, but rather by the loss tangent (i.e., the ratio of the dissipative‐to‐dispersive components of the conductivity). This ratio, in turn, depends on the type of free carriers present (electrons or holes), carrier concentration, carrier mobility, as well as sample temperature and the value of the magnetic field at which EPR occurs. When the specimens are thicker than the internal wavelength, but thinner than the skin depth (a condition frequently satisfied in narrow‐gap semiconductors and semimetals), Fabry‐Perot–like geometrical resonances arise, which again profoundly affect the line shape. Specific ranges of the loss tangent, characteristic of narrow‐gap semiconductors and semimetals, are discussed analytically and illustrated by numerical calculations. Where available, EPR data involving transmission experiments in Hg1−xMnxTe are presented.

ISSN:0021-8979    

DOI:10.1063/1.327945

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The Curie temperatures of 25 amorphous alloy systems involving a binary metal together with metalloids have been fitted to phenomenological equations based on a localized band model involving only one adjustable parameter to describe the variation of Curie temperature with metal composition.

ISSN:0021-8979    

DOI:10.1063/1.327946

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The permittivity and attenuation of prepared samples of wet snow are measured and curves presented showing the dependence of these quantities on snow wetness and frequency. Equations are given that express the experimentally determined relation between attenuation per unit length and volume‐percent wetness at any frequency between 4 and 12 GHz. Additional equations are given for the calculation of permittivity from the snow density, attenuation per unit length, and frequency. Water retention characteristics of snow are described. Some applications of the techniques, such as runoff forecasting from mountain snowpacks, are proposed.

ISSN:0021-8979    

DOI:10.1063/1.327947

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

On polarization echoes, dipolar field contribution was considered and the role of the effectively stimulated oscillation mode was investigated. The investigated theory was based on the torque rotation model derived by Melcher and Shiren. The model was developed here by considering the particle behavior under the effectively stimulated oscillation field and the rotation caused by the local field of oscillating dipoles of nearest neighborhood, after taking off the second electric field. As theoretical results, the echo signal was derived as anharmonicity in collection of effectively stimulated oscillations of the dipoles with deviated orientations. The deviated angles of particles due to the local dipolar field were selectively redistributed in accordance with the oscillation modes effectively stimulated by the two‐pulse sequence. Experimental results for read out multipulse echoes were explained by the theoretical calculation, not only for time detection including the image echoes, but also for relaxation characteristics along the time axis.

ISSN:0021-8979    

DOI:10.1063/1.327948

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The sensitivity of a new spectroscopic technique, photoacoustic Raman spectroscopy (PARS), has been improved substantially by the use of high‐peak‐power pulsed lasers. The theory for generation of photoacoustic signals from stimulated Raman scattering is outlined, and vibration‐rotation Raman spectra for CO2and CH4are presented. Applications of PARS are discussed, and a comparison is made with other Raman techniques.

ISSN:0021-8979    

DOI:10.1063/1.327949

出版商:AIP    

年代:1980

数据来源: AIP