Kind Of Anisotropy Research Articles

Selective resputtering-induced anisotropy in amorphous films

A model will be presented to explain the bias voltage dependence of magnetic anisotropy in sputtered amorphous films of gadolinium cobalt alloys. It has been found that the magnetic anisotropy increases with bias voltage up to a critical bias voltage (∠150 V depending on the sputter gas) then decreases precipitously at higher voltages. The model used to explain this behavior is based on selective resputtering of atoms in different surface sites causing an anisotropic distribution of Gd and Co atoms with respect to the growth direction. For example, a Gd adatom in contact with three surface atom neighbors can have 0, 1, 2, or 3 cobalt neighbors. The sputtering threshold for each type of Gd adatom will be different so those with a low threshold will be selectively removed giving a structural anisotropy. This anisotropic atomic distributions can cause different kinds of anisotropy with respect to the growth direction depending on the type of amorphous film. For example, both easy-axis (GdCo) and hard-axis (GdFe) magnetic anisotropies have been observed. It may be possible to extend this model to other types of anisotropy in amorphous films.

Electronic emission from solid targets bombarded by noble gas ions (10–100 keV): Energetic and spatial distributions

The variation of the Be K ionization cross sections as a function of the ionic incident energy was determined by Auger emission from solid targets. The results obtained with Xe + and Ar + ions show a low energy threshold and a break formation situated at about 50 keV for Ar + ions and 80 keV for Xe + ions. The angular distributions of the secondary electrons emitted from single crystals were studied. They show two kinds of anisotropy. The first one is interpreted in terms of electron diffraction. This angular dependence is observed all over the ionic energy range explored in our measurements. In our geometrical conditions, the second kind of anisotropy only rises from an ionic velocity of about 5×10 5 m/s. It may be due to an electron axial channeling along the close packed directions of the direct lattice.

Influence of Transverse Anisotropy on the Plastic Collapse of Plates and Shells

A modification of Tresca’s yield criterion is discussed for plane stress in anisotropic materials, when the yield stress in the thickness direction is higher than in any direction perpendicular to it. Special consideration is given to the determination of collapse loads for symmetrically loaded plates and shells having this kind of anisotropy. It is found that the carrying capacity significantly increases with the degree of transverse anisotropy represented by a single parameter μ.

Magnetic measurements with the rotating-sample magnetometer

The general features common to all rotating-sample magnetic measurements are described, and the governing equations are given. A number of cases of special interest are discussed in some detail: these include the measurement of magnetization as a function of field and temperature and the measurement of rotational hysteresis, various kinds of anisotropy, and magnetostriction. The concept of the rotating sample magnetometer is not new, but the method has greatly increased in practical value because of the development of the lock-in amplifier. The rotating-sample magnetometer method has many points of similarity to the vibrating-sample magnetometer. It is superior to the vibrating-sample magnetometer for some purposes, notably for anisotropy and magnetostriction measurements, and is generally simpler to construct.

Magnetoresistance of stray-field coupled films

The magnetoresistance effect is used as an experimental tool in the investigation of the mechanism of magnetic coupling in multilayer films with intermediate laminations of electric insulating materials. The analysis of the shape of the hysteresis loops of the magnetoresistance can provide information about the inhomogeneous magnetization of such films. The films consisted of a soft layer of NiFe and a hard layer of Co, separated by approximately 1000 A of SiO. Shifted hysteresis loops, indicating the presence of a unidirectional anisotropy, were observed when the driving field had a small amplitude. However, with increasing drive amplitude these loops became regular, and the existence of a field dependent uniaxial anisotropy was demonstrated. Both kinds of anisotropies are discussed in terms of stray field effects introduced by the initially polarized hard layer. With films whose ferromagnetic layers have nearly perpendicular easy axes, one obtains asymmetric magnetoresistance loops for some orientations of the driving field. These loops were attributed to the inhomogeneous distribution of the magnetization vectors within the laminations of the coupled films. This new method of investigation of the magnetic behavior of coupled films seems to be preferable to other methods when the ferromagnetic layers of the films are very thin.

Magnetic anisotropy in ferromagnetic thin films

Measurements of the induced magnetic anisotropy in thin iron and nickel films were performed by means of the magnetoresistance effect (MRE) in three perpendicular directions, at 120°K and 300°K. Two kinds of induced anisotropies were detected. The first one is independent of the magnetic field H d , which was applied during the deposition of the film. It is related in both materials to an angle of incidence effect, arising from the geometry of the deposition. This anisotropy in thin iron films has a radial symmetry in the plane of the film, and decreases to zero with the growing thickness of the film. In nickel films the same kind of anisotropy was found to exist in a wide range of thicknesses, increasing with the growth of the film, but having a circular symmetry. The second anisotropy, detectable in relatively thick iron films (5000 Å), is aligned with its easy magnetic axis parallel to the field H d . Its magnitude was found to be about 0.1 K 1 at 120°K (K 1 is the first cubic magnetocrystalline anisotropy constant for iron) and decreased at room temperature. The MRE in the transverse-perpendicular direction points to the presence of a preferred orientation described by plane (111) as contact plane with the substrate, and by the [11 2 ] direction in this plane parallel to H d . This preferred orientation also accounts for the magnitude, direction and temperature dependence of the field induced anisotropy. This interpretation is based on a magneto-elastic interaction due to magnetostriction and isotropic tensile stresses in the plane of the film.

LOVE WAVE DISPERSION IN HETEROGENEOUS ANISOTROPIC MEDIA

An analysis is made of Love‐wave propagation in a medium composed of transversely isotropic layers. This is the kind of anisotropy which most commonly occurs at the surface of the earth, and in particular is displayed by bedded sediments. The exact boundary value problem is solved for a simple layer and extended to multilayered media by a generalization of Haskell’s technique. By a suitable redefinition of parameters, it is possible to cast the anisotropic problem into isotropic form so that existing programs, tables, and graphs can be used to determine the structure of layered anisotropic media. It can be shown that the Love‐wave period equation expresses the condition of constructive interference between multireflected SH waves with directionally dependent velocities. Also, it is demonstrated analytically and numerically that a restricted form of the anisotropy considered here is the limit of a finely laminated solid as the laminations become much smaller than a wave length. For long wave lengths, a multilayered structure may be replaced by an equivalent single layer.

Elastic wave propagation in layered anisotropic media

This is an analysis of the dispersive properties of transversely isotropic media. This kind of anisotropy is exhibited by hexagonal crystals, sediments, planar igneous bodies, ice sheets, and rolled metal sheets where the unique axis is perpendicular to the direction of surface wave propagation and the other axes are distributed randomly in the plane of the layers. Period equations are derived for waves of Rayleigh, Stoneley, and Love types, and comparisons are made, in certain cases, with ray theoretical and plane stress solutions. Anisotropy can have a pronounced effect on both the range of existence and the shape of the dispersion curves and can lead to an apparent discrepancy between Love and Rayleigh wave data. Attention is focused in this initial paper on a single solid layer in vacuo (i.e. a free plate) and a solid layer in contact with a fluid halfspace. The single layer solutions are generalized to n-layer media by the use of Haskell matrices.

The twist in a crystal whisker containing a dislocation

Abstract The twist due to a screw dislocation parallel to the axis of an isotropic cylinder of arbitrary cross section can be found from the solution of the ordinary torsion problem for the same cylinder. Some particular cases are worked out. The results are also valid for certain kinds of anisotropy.