摘要:

A decreased laser threshold has been observed for a flashlamp‐pumped Rhodamine B dye laser as the temperature of the solution is reduced. The change in threshold is attributed to an increase in the fluorescence quantum yield and can be characterized by an activation energy of 880 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.1657365

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

After a brief description of the basic characteristics of type‐I and type‐II superconductors, we outline a unified classical thermodynamic treatment. Some applications of thermodynamic formulae to type‐II behavior are then discussed, closing with a consideration of upper‐critical‐field limits and fluctuation super‐conductivity in bulk extreme‐type‐II superconductors.

ISSN:0021-8979    

DOI:10.1063/1.1657366

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Computer‐aided variational calculations were made to examine the stability of various lattice defects in the flux line lattice which exist in the mixed state of Type II superconductors. The stable configurations agreed with the direct experimental observations of Essmann and Tra¨uble, if the dislocations and vacancies were assumed to be associated with pinning centers. The presence of pinning centers can also explain the frequencies with which the various defects are observed. The Peierls potential for dislocations was also calculated, as well as the theoretical shear stress for the perfect lattice.

ISSN:0021-8979    

DOI:10.1063/1.1657367

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Experimental results are presented for wire specimens of high‐purity lead, indium, and thallium which have been plastically deformed at liquid‐helium temperatures and subsequently annealed. The deformation is found to broaden the magnetic transition to the normal state in lead but not in indium or thallium. It is proposed that, for the deformed lead samples in fields larger than the bulk critical field, the superconductivity is confined to small filaments with high defect concentrations. These filaments are restricted to the surface of lightly deformed samples but exist throughout the bulk of heavily deformed samples. It is suggested that the Mendelssohn sponge model is a natural consequence of the Ginzburg‐Landau theory for those inhomogeneous, Type I superconductors which, when homogeneous, have large kappa values. Significant recovery of the strain‐induced resistivity increment is observed below liquid‐nitrogen temperatures for all three metals; at higher temperatures a pronounced recrystallization step is observed in lead but not in indium and thallium. Dislocation‐induced deviations from Kohler's rule were observed in the magneto‐resistivity of lead.

ISSN:0021-8979    

DOI:10.1063/1.1657368

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The conductance of Cr (single crystal)‐Cr oxide‐Pb tunnel junctions was measured as a function of bias voltage for (100) and (110) crystalline directions. Although our results are complicated by the presence of a large background conductance, the data support the existence of an antiferromagnetic energy gap in Cr at 1°K.

ISSN:0021-8979    

DOI:10.1063/1.1657369

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The internal stress distribution theory of magnetomechanical damping is modified and extended to include effects of applied magnetic fields and applied static stresses. The present internal stress distribution function yields Rayleigh behavior at low vibration stress and has a more realistic shape than that of the previous model. The theory, besides giving a qualitative description of the damping behavior as a function of vibration stress, agrees quite well with measurements of the dependence of the damping maximum on applied field and static stress.

ISSN:0021-8979    

DOI:10.1063/1.1657370

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An analysis is given which predicts that initial permeabilities of the order of a million could be obtained from typical permalloy thin films if these films were in the appropriate type of structure. A three‐layered structure, where a permalloy layer is sandwiched between and exchange‐coupled to a pair of highly anisotropic magnetic layers, can be arranged so that having the outer layers magnetized in opposite directions is a stable magnetic configuration. Because of the exchange coupling, this configuration creates a domain wall in the plane of the permalloy layer. The methods of micromagnetics are applied in this paper to obtain a mathematical analysis of such domain walls, giving the functional dependences of the wall shape and position on the external field, layer thicknesses and magnetic parameters. Numerical results show that typical permalloy layers of several microns in thickness could exhibit initial permeabilities of a million in external fields of the order of millioersteds. Inductor applications of this structure are briefly discussed, where it is concluded that such inductors would have a maximum operating frequency of 105to 106Hz.

ISSN:0021-8979    

DOI:10.1063/1.1657371

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The theory given in a previous paper is extended and refined. The restriction of collinear spins is lifted and the idea of local random canting as suggested by Geller is introduced. It is assumed that when a magnetic ion has only one magnetic nearest neighbor, its spin need not be collinear with the total magnetization. The angle by which these spins are canted is treated as an adjustable parameter. This refinement of the theory makes it possible to reproduce in addition to the substitution dependence of the magnetic moments at 0°K, also the substitution dependence of the transition temperatures for a large variety of ferrimagnetic‐substituted garnet systems. All of this agreement is obtained with a single adjustable parameter. When substitution is in the octahedral site, canting occurs in the tetrahedral site, and vice versa. It was found that spins in the ``d'' site having only one nearest magnetic neighbor are canted by about 60° when substitution is performed in the ``a'' site. Very small canting, if any at all, occurs in the ``a'' site when the substitution is in the ``d'' site. In double‐substituted systems there is also no canting in the ``a'' site and the canting angles in the ``d'' site are ∼0° in Mg‐substituted systems, ∼50° in Sc‐substituted systems, and ∼75° in Zr‐substituted systems.

ISSN:0021-8979    

DOI:10.1063/1.1657372

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An expression for the attenuation of a generalized Rayleigh wave has been obtained in terms of a viscosity tensor. The values of the viscosity components for Quartz obtained from measurements on bulk waves have been used to calculate the attenuation of several surface waves on that material. An attenuation of 7.0 dB/cm is predicted at 1 GHz and 300°K for the surface wave propagating in theXdirection on theYsurface. This figure compares favorably with an experimental value of 8.6 dB/cm at the same temperature and frequency. An expression for the attenuation of Rayleigh waves on isotropic media is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.1657373

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Measurement of the heat capacity from 2.13° to 10°K and of the elastic constants at 4.2°K have been made on a single crystal of CsI. The Debye temperature at 0°K, &thgr;0, as calculated from the heat capacity is &thgr;0=127.67°K. Values of the elastic constants at 4.2°K arec11=2.725±0.6%,c44=0.873±0.6%, andc12=0.767±3% in units of 1011dyn/cm2. &thgr;0calculated from the elastic constants at 4.2°K is equal to 129.4°K.

ISSN:0021-8979    

DOI:10.1063/1.1657374

出版商:AIP    

年代:1969

数据来源: AIP