Role Of Anisotropy Research Articles

Micromagnetic simulations of current-induced magnetization switching in Co∕Cu∕Co nanopillars

We studied the current-induced magnetic switching in Co∕Cu∕Co nanopillars with an in-plane magnetization traversed by a perpendicular-to-plane spin-polarized current. The Landau-Lifshitz-Gilbert equation incorporating the spin transfer torque (STT) effect was employed. Magnetization switching was found to take place when the current density exceeds a threshold. It is accompanied by drastic oscillations near the magnetic reversal point. The switching time depends on the applied current density. The magnetization can also be switched by a sufficiently long square pulsed current. The roles of anisotropy, exchange, and demagnetization energies in the magnetization switching process of nanopillars are discussed. It is shown that the switching is mainly determined by the competition between STT and the Gilbert damping torque.

Problem of super-high- Tc superconductivity

A possibility of a general path for the search of “super-high- T c” (SHT) materials is discussed. The approach is based on the idea of enhancement of the basic parameters, entering the BCS formula for T c: the electron–phonon interaction constant, the density of states and the energy of mediating quasiparticles. The known examples of materials with a relatively high- T c are examined. The author’s idea of finding a substance forming a “crystalline excitonium” phase (1978) is presented. Since the BCS formula represents only an isotropic model, the role of anisotropy is analyzed within the author’s model for high- T c layered cuprates. The main conclusion is, that anisotropy of the spectrum and a long-ranged interaction widens the options for obtaining SHT.

LARGE DYNAMICAL SYMMETRY OF QUASI-SPHERICAL GRAVITATIONAL COLLAPSE WITH RADIAL AND TANGENTIAL PRESSURES AND ANISOTROPY AND INHOMOGENEITY OF SPACE–TIME

A detailed study of higher-dimensional quasi-spherical gravitational collapse with radial and tangential stresses has been done and the role of initial data, anisotropy and inhomogeneity has been investigated in determining the end state of collapse. By linear scaling the initial data set and the area radius, it is found that the dynamics of quasi-spherical collapse remains invariant. In other words, the linear transformation identifies an equivalence class of data sets for which physical parameters like density, pressures (radial and tangential), shear remain invariant and the final state of collapse is identical (black hole or naked singularity). Finally, the role of anisotropy and inhomogeneity has been studied by proving some propositions.

Anisotropy-Induced Effects in the Dynamics of an Ion Confined in a Two-Dimensional Paul Trap

We investigate the role of anisotropy in the dynamics of a single trapped ion interacting with two orthogonal laser beams, considering how it modifies a scheme for the generation of Schrödinger cat states and the so called parity effect in two-dimensional isotropic Paul traps. We find that anisotropy gives rise to a richer class for the generated states and to a larger number of observables sensitive to the parity of the number of excitation of the vibrational motion of the ion.

A Critical Review of the Mechanics of Polycrystalline Polar Ice

We review the developments of the constitutive theories of polar ice both from a viewpoint of mechanics as well as materials science, as it was studied during the last approximately 50 years. First proposals were based on the postulation of ice as a very viscous, non-Newtonian and heat conducting fluid. Today's understanding of polar ice sees it as a creeping polycrystal with induced anisotropy and a nontrivial grain-size distribution, both evolving in time. Phenomena related to recrystallization, namely grain rotation, grain-size redistribution by normal and abnormal grain growth, nucleation, polygonization and grain boundary migration have also to be accounted for to obtain a stress constitutive law that may reliably predict ice flow in large ice masses. The main topics on which we focus our efforts are the role of anisotropy and its evolution. We review the models that take into account the microscopic as well as the macroscopic point of view. Numerical models are also considered. A novel graphical method is proposed for the comprehension of the rules that drive the rotation of the crystallites in a polycrystal, not only for the simple cases of compression and extension but also for the simple shear mode of deformation. Particular emphasis is given to the constitutive theories related to recrystallization phenomena, for which the paper can be considered an introductory overview. The research methods on which all proposed laws are based borrow concepts from the mechanics of solids and materials science but belong also to the class of anisotropic fluids. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonlinear current response of one- and two-band superconductors

We have calculated the nonlinear current of a number of single band s-wave electron-phonon superconductors. Among issues considered were those of dimensionality, strong electron-phonon coupling, impurities, and comparison with BCS. For the case of two bands, particular attention is paid to the role of anisotropy, the integration effects of the off-diagonal electron-phonon interaction, as well as inter- and intraband impurities. For the specific case of MgB2, we present results based on the known microscopic parameters of band theory.

On the role of anisotropy of membrane constituents in budding of a multicomponent membrane

On the role of anisotropy of membrane constituents in budding of a multicomponent membrane

QUASI-SPHERICAL GRAVITATIONAL COLLAPSE AND THE ROLE OF INITIAL DATA, ANISOTROPY AND INHOMOGENEITY

In this paper, the role of anisotropy and inhomogeneity has been studied in quasi-spherical gravitational collapse. Also the role of initial data has been investigated in characterizing the final state of collapse. Finally, a linear transformation on the initial data set has been presented and its impact has been discussed.

Role of anisotropy in the elastoplastic response of a polygonal packing

We study the effect of the anisotropy induced by loading on the elastoplastic response of a two dimensional discrete element model granular material. The anisotropy of the contact network leads to a breakdown of the linear isotropic elasticity. We report on a linear dependence of the Young moduli and Poisson ratios on the fabric coefficients, measuring the anisotropy of the contact network. The resulting nonassociated plastic flow rule and the linear relationship between dilatancy and stress ratio are discussed in terms of several existing models. We propose a paradigm for understanding soil plasticity, based on the correlation between the plastic flow rule and the induced anisotropy on the subnetwork of sliding contacts.

Parametric modelling of magnetic fine particle systems: the role of single domain particle size distributions and magnetic anisotropy

We demonstrate the effects and role of anisotropy and particle size distributions upon the values of constitutive parameters determined from experimental M(H) loops of single domain nanoparticle systems. We employ experimental and magnetic material parameters as inputs to a numerical programme run from a graphical user interface (GUI) to permit modelling and interpretation of experimental data and assessment of the stability of the constitutive parameters so derived and characterisation of the departures observed from pure Langevin behaviour.

The role of anisotropy in the thermoelectric detection of holes in metals

In this paper we demonstrate that the presence of thermoelectric anisotropy, no matter how small, can be exploited to unmask the presence of cracks and holes in metals. This is in direct contrast with situations involving isotropic metals where such detection is not possible. Although such a phenomenon will occur for all types and shapes of cracks and holes, for simplicity we shall demonstrate our theoretical and numerical modeling on the more mathematically tractable case of a cylindrical hole aligned along an axis of symmetry of an anisotropic metal medium.

Different roles of anisotropy and disorder on the vortex matter of Bi 2Sr 2CaCu 2O 8+ δ single crystal

The oxygen doped and Pb-substituted single crystalline Bi 2Sr 2CaCu 2O 8+ δ samples having T c,on and anisotropy ( γ 2) ranging respectively from 65 to 93 K and from 773 to 49,715 have been studied in the basis of magneto-resistance and magnetization data. It is found that the lowering of anisotropy due to higher oxygen content or Pb substitution is responsible for the reduction of magnetic field-induced transitional broadening and a shift of H irr( T) and H g( T) to higher temperatures and magnetic field. Meanwhile, the increasing disorder manifested by decreasing T c also leads to the extended range of appearance for the second magnetization peak (SMP) and enlarged critical glassy region. It is shown that decreasing anisotropy does not necessarily lead to the lowering of T c in contrast to the monotonic dependence of T c on the disorder measured in the temperature range of SMP effect. Additionally, a remarkable monotonic correlation between T c and the glassy exponent s has been established.

Role of anisotropy in noncontacting thermoelectric materials characterization

Inclusions and other types of imperfections in metals can be nondestructively detected by noncontacting magnetic measurements that sense the thermoelectric currents that appear when the specimen is subjected to directional heating and cooling. The detectability of small imperfections is ultimately limited by the intrinsic thermoelectric anisotropy and inhomogeneity of the material to be inspected. This article presents an analytical method for calculating the magnetic field produced by thermoelectric currents in anisotropic materials under two-dimensional directional heating and cooling. Experimental results from a textured Ti–6Al–4V titanium-alloy plate are shown to be in very good agreement with the predictions of this model. The described analytical method can be used to optimize thermoelectric inspection procedures and to evaluate the macroscopic texture of metals from their characteristic magnetic signatures.

On the theory of wave propagation in anisotropic plates

A theoretical framework is developed which describes wave propagation in infinite homogeneous elastic plates of unrestricted anisotropy. The approach exploits the propagator matrix which is the exponential of the fundamental elasticity matrix underlying Stroh9s formalism of anisotropic elastodynamics. The matrices of plate impedance and admittance are introduced, and their analytical properties are established, which appear fruitful for computing and analysing the plate wave spectra. On this basis, the dispersion equation can be cast into the form of a real equation involving the monotonic function, whose zeros and poles are the wave velocities in a given plate subjected to different boundary conditions (traction–free or clamped faces). It is proved that three fundamental wave branches exist for any orientation of wave propagation in an anisotropic plate with traction–free faces, and that those branches are missing if one or both faces are clamped. The intrinsic symmetry of the wave motion in an arbitrary plate is revealed. The general formalism is applied to elaborate the long–wavelength low–frequency approximation for a (thin) free plate of unrestricted anisotropy. The frequency–dispersive wave velocities, displacements and tractions at the onset of the fundamental wave branches are derived explicitly. The conditions for the extreme velocity values and some other useful universal connections are determined for an arbitrary thin plate, and exemplified for specific anisotropy cases.

Role of anisotropy in turbulent mixing noise

Role of anisotropy in turbulent mixing noise

The effect of excess neodymia on the grain growth of Nd1+xBa2−xCu3Oy solid solutions

The grain growth of dense, fine-grained Nd1+xBa2−xCu3Oy (x = 0.1−0.4) specimens has been examined in pure O2(g) at 938 °C and 967 °C. No detectable change in average grain size was observed for Nd1.4Ba1.6Cu3Oy within 72 h at 967 °C; however, a significant increase in average grain size developed between 18 and 24 h at 967 °C for Nd1.3Ba1.7Cu3Oy, and within 8−12 h at ≤967 °C for Nd1.2Ba1.8Cu3Oy and Nd1.1Ba1.9Cu3Oy. Microstructural analyses revealed that sudden changes in average grain size coincided with the formation of relatively large (abnormal) grains. A broadening of the grain size distribution was also observed. TEM analyses revealed that grain boundaries were free of second phases. The possible role of anisotropy in grain boundary energy and/or mobility on grain growth is discussed.

CLINICAL IMPLEMENTATION OF ULTRASONIC QUANTITATIVE NONDESTRUCTIVE EVALUATION OF THE HEART: A REVIEW

Diagnostic ultrasonic characterization of the heart is designed to assess the state of the myocardium with ultrasonic parameters that relate to structural or functional components of cardiac muscle. The potential cross fertilization of ideas and methods between those borne out of research in quantitative nondestructive evaluation of materials and those borne out of research in diagnostic medical applications in the area of ultrasonics represents an attractive goal. In this paper we describe our approach to tissue characterization of the heart based on quantitative ultrasonic imaging. We discuss methods of ultrasonic tissue characterization applied in laboratory and clinical investigations. Specific examples of the application of clinical quantitative tissue characterization include measurements of the hearts of patients with remote myocardial infarction, dilated cardiomyopathy, acute myocardial ischemia, and hearts of patients with diabetes. The role of anisotropy in quantitative tissue characterization and its effect on measurements obtained from specific standard echocardiographic views are reviewed.

Role of anisotropy of the coupling constant in a superconductor model with singularities near the Fermi surface

The role of anisotropy of the coupling constant in the influence of nonmagnetic impurities on the behavior of the superconducting transition temperature Tc is investigated in the high-temperature superconductor (HTSC) model, where high values of Tc result from an increase in the density of states near the Fermi surface. It is shown that this model is more sensitive to impurities than the BCS model; Anderson compensation does not occur in the HTSC model, even for identical distributions of the densities of states in the superconducting and impurity channels, and the impurity contributions are no longer linear with respect to the impurity concentration in the vicinity of Tc. Anisotropy of the superconducting gap Δ and the possibility of its disappearance at certain points on the Fermi surface due to various types of pairing are manifested in the stability of the superconducting phase against the influence of impurities.

Crossover from fractal to non-fractal flux penetration in vicinal Tl2Ba2CuO6+δ thin films

The role of anisotropy on magnetic flux penetration and critical current density jc in c-axis epitaxial Tl2Ba2CuO6+δ (Tl2201) films is investigated by magneto-optics. Thin films of Tl2201 are deposited by a sputtering technique on vicinal (001) SrTiO3 substrates with miscut angles of 0.5 and 2.5 degrees and patterned into various shapes. Circular samples are used to determine the current anisotropy axis, whereas square samples allow to evaluate the amplitude of this anisotropy. A cross-over from fractal to uniform anisotropic flux penetration is observed with increasing miscut angle.

Magnetic nanoparticles and magnetocrystalline anisotropy

The size dependent properties of monodomain ferromagnets are described. Following an introduction to the technical magnetics parameters used to describe bulk ferromagnets, the size dependence of these parameters is described. Bulk ferromagnetic materials are generally described as either hard or soft, depending on the value of their magnetocrystalline anisotropy. The role of anisotropy in monodomain ferromagnets is investigated through examination of two case studies: the high anisotropy alloy SmCo 5, and a series of Fe xCo 1−x alloys with very low anisotropy. Both dipolar and exchange interactions between particles are discussed, and the connection is made between isolated fine particles and compacted nanocrystalline materials.