Field Dependence Of Coefficient Research Articles

Irreversible response in spin-glasses: An experimental study in amorphous Fe-Mn

The equilibrium and nonequilibrium susceptibilities ${\ensuremath{\chi}}_{\mathrm{e}}$ and ${\ensuremath{\chi}}_{\mathrm{ne}}$ of the spin-glass ${({\mathrm{Fe}}_{0.64}{\mathrm{Mn}}_{0.36})}_{75}$${\mathrm{P}}_{16}$${\mathrm{B}}_{6}$${\mathrm{Al}}_{3}$ have been measured as functions of temperature ($4.2l~Tl~80$ K) and a cooling field ($8 \mathrm{Oe}l~Hl~2 \mathrm{kOe}$). A phase transition occurs at a temperature ${T}_{c}(H)$ below which the irreversible response $\ensuremath{\Delta}(T)\ensuremath{\propto}T({\ensuremath{\chi}}_{\mathrm{e}}\ensuremath{-}{\ensuremath{\chi}}_{\mathrm{ne}})$ appears. ${T}_{c}(H)$ decreases from the freezing temperature (${T}_{f}=41.6$ K) as ${H}^{0.75\ifmmode\pm\else\textpm\fi{}0.1}$. For small $\ensuremath{\tau}\ensuremath{\equiv}1\ensuremath{-}\frac{T}{{T}_{c}(H)}$, $\ensuremath{\Delta}$ behaves as $A\ensuremath{\tau}+B{\ensuremath{\tau}}^{2}$ with field-dependent coefficients $A$ and $B$ and $A(H=0)=0$. The results are compared with the predictions of the mean-field theory of spin-glasses.

Electroabsorption in ZnSe cubic crystals

Abstract An experimental study of electroabsorption in ZnSe crystals has been made using several techniques: first with a direct field applied, secondly with an alternating field and thirdly with a direct field modulated by an alternating component. Each method gives a field-dependent absorption coefficient x = x0 + CFn, n being about 2·3. The results are compared with theoretical models proposed by various authors.

Analytic modeling of transit-time device drift regions with field-dependent transport coefficients

An iterative procedure for obtaining two-carrier d.c. solutions in regions of rapidly varying carrier concentration is presented. The procedure uses an analytic solution for the carrier concentrations in a region of linear spatial electric field variation. Field-dependent diffusion and field-dependent velocities are assumed. A single-carrier small-signal model for a drift region with a spatially varying field and field-dependent transport properties is presented. When applied to a BARITT device, results consistent with published experimental data are obtained. The importance of momentum relaxation effects in Si BARITT drift regions is discussed.

Kinetics of permeability changes induced by electric impulses in chromaffin granules.

Electric field pulses, ranging in intensity from 20 to 50 kV/cm and in duration from 10 to 40 micronsec, caused a transient increase in the membrane permeability of chromaffin granules from the bovine adrenal medulla, that led to partial release of granule soluble constituents. This transient permeability change was long-lived, as compared to the pulse duration, and the main part of material efflux occurred after the termination of the pulse. During the latter phase the temporarily increased permeability decayed to its original value, in the absence of the electric field. This indicated that the structural perturbation induced in the membrane was transient and apparently reversible. The release event was characterized by a field-dependent permeability coefficient ranging from 2x10(-4) cm/sec at 30 kV/cm to 3x10(-3) cm/sec at 50 kV/cm. The resealing process of the membrane could be described by two relaxation times, both of which decreased with increasing field strength. Tau1 varied from about 3.0 msec at 30 kV/cm to less than 2.0 msec at 50 kV/cm, while tau2 varied from about 100 to about 40 msec in the same interval of field strength. The distribution in the degree of filling of granules that had been partially depleted by an electric field pulse indicated that the population could be considered homogeneous with respect to release.

The viscomagnetic effect in polar gases

The magnetic field effect on the viscosity has been measured for several polyatomic gases with the emphasis on symmetric top molecules with strong electric dipoles. Theoretical expressions are given for the field dependent viscosity coefficients for various types of angular momentum polarizations, both for linear and symmetric top molecules. For CO2, OCS, N2O, SF6, CH3F, CHF3, PF3 and NF3 a decrease of the viscosity in a magnetic field was observed, which can be well described on the basis of a single angular momentum tensor polarization of the type . For NH3 and ND3, however, an increase in the viscosity was observed. In this case, a single polarization of the type J is involved. For HCl, DCl, AsH3 and PH3, no effects could be observed (|Δη/η|⩽2×10−5). No simple correlation is found between the magnitude of the effect and the strength of the molecular electric dipole moment. The experimental results are expressed in terms of effevtive cross sections.

Five different modes of high-field domains due to field-dependent carrier diffusion

Five different modes of high-field domains due to the field-dependent diffusion coefficient in a material with negative differential mobility (NDM) are discussed. Two of them are periodically traveling domain modes whose traveling directions are opposite each other. The remainder are trapped domain modes and are classified by the positions where the domains are trapped. For a bulk-effect device operated in the trapped domain mode, the static negative resistance (SNR) appears in its current-voltage characteristic.

Propagation of a Strong Circularly Polarized Electromagnetic Wave through Afterglow Plasmas near the Electron Cyclotron Frequency

We seek to explain the experimental observation of enhanced transmission of a strong right-hand circular wave near cyclotron resonance in an afterglow helium slab plasma occurring at earlier times than for a corresponding weak electromagnetic field. A strong field heats the electrons and alters the collision frequency and the velocity distribution function. For our experimental conditions, electron–electron relaxation processes can influence the distribution function. Furthermore, because of the field dependent absorption coefficient, the temperature and field strength can vary within the plasma slab. Although the collision frequency increase with temperature predicts an earlier time for stronger-field transmission at cyclotron resonance, none of the above processes is sufficient to explain the experimentally observed large spread in times of transmission for various electric field strengths. The explanation is ascribed to the fact that the electron density decay constant due to diffusion also increases with temperature, so that the electron density decay rates vary with electric field resulting in a larger spread in times of transmission. Experimental results from double probes, although operating under low sensitivity, suggest a decrease in density near the front edge of the plasma subject to strong fields.

On the Pressure Dependence of the Transport Properties of Dilute Polyatomic Gases

Abstract It is shown that the transport coefficients of dilute polyatomic gases in the ordinary Navier-Stokes regime contain an extra pressure dependence when the internal state Hamiltonian does not commute with the nonequilibrium distribution function-density matrix for the gas. As a specific example, the pressure dependence of the shear viscosity of a gas of paramagnetic 2Σ molecules is considered. Furthermore, the pressure dependence of the Senftleben and Senftleben-Beenakker effects is discussed and examples are given of the different types of molecules for which pressure dependence in the field-free as well as in the field-dependent transport coefficients may be expected.

Space-charge wave instability in a semiconductor exhibiting field-dependent diffusion coefficient and saturated drift velocity

It is shown that, in a semiconductor biased in the saturation region, the combination of a field-dependent diffusion coefficient with a gradient in the steady-state electric-field distribution may lead to space-charge wave amplification.

Instrumentation for Fermi Surface Measurements Using Ultrasonics

Three methods are described for enhancing specific oscillatory components of the magnetic field dependent attenuation coefficient of sound found in pure metals at liquid He temperatures. These oscillations are related to Fermi surface properties. Instrumentation suitable for these methods is described in detail. Some data taken with these techniques are shown. In addition, a description of the ultrasonic technique used is included.