Formation Of Charged Walls Research Articles

Stress/strain distribution around implantation boundaries

Abstract Ion implantation in ferrimagnetic garnet epilayers containing bubbles suppresses hard bubbles and defines the propagation tracks for moving bubbles. It has been recognized that the existence of a strain/stress gradient in the vicinity of an implantation boundary is responsible for the formation of charged walls to which bubbles are attached. Two elastic models describing the stress/strain distribution around an implantation boundary are presented. They rely on densities of defects, infinitesimal dislocations and point defects in the continuum approximation, Assuming a ribbon geometry reduces the elastic problem to a plane-strain one. Very compact expressions can be deduced from the point-defect model if the half-space is restricted to a plane. The dislocation model indicates that most of the elastic strain/stress is due to the lateral thrust exerted by the implanted ribbon on the surrounding elastic medium.

The effects of stress relaxation and anisotropic magnetostriction on charged walls in ion implanted garnets

This paper reviews present understanding and presents new data on the effects of ion implantation on garnet materials and on the mechanisms giving rise to charged walls at boundaries between implanted and unimplanted regions. It is shown that uniaxial anisotropy parallel to pattern boundaries, which is due to stress relaxation normal to pattern edges, is necessary for the formation of charged walls. Furthermore. it is shown that, whereas early reseachers ascribed the three-fold symmetric behavior of charged walls in the ion implanted layers of

Modeling of transfer gates in ion-implanted bubble devices

In-plane domain structures of rudimentary transfer gates for 2μm bubble devices are calculated by numerical minimization of energy. Results are compared with failure mechanisms observed through high speed optical sampling techniques. Insights into the formation of charged walls are obtained in addition to general design rules for such gates. A uniaxial anisotropy term along the pattern edge was found necessary for the general formation of charged walls, as was previously suggested. The need for this term is especially apparent when the applied field is directed along an easy magnetization direction, a condition that occurs in the model transfer gates. The experimental study shows that small local radii of curvature for both the major and minor loop elements result in lower minimum drive fields. Also, positioning the major loop cusp far from the minor loop element reduces the loss of low bias margin that results from strip-out.

Strain profiles in ion-implanted bubble devices investigated by transmission electron diffraction

Selected area electron diffraction has been used to obtain strain profiles around unimplanted disks in thin (<2000 Å) films of (111) oriented garnets. Measurements of in-plane lattice constant were made as a function of position in (SmYGdTm)3Ga0.4Fe4.6O12 films implanted with oxygen (120 KeV, 1×1014/cm2) and helium (80 KeV, 4×1015/cm2). In most cases the data show a relaxation of stress normal to and near to the implanted boundary. These results are consistent with models suggesting that stress relaxation normal to an implanted boundary is critical to the formation of charged walls. In addition, effects of the nonuniform stress field on the local anisotropy in the underlying bubble layer of an ion-implanted contiguous disk device are considered. It is shown that under the edge of an implanted region, there is a tensile stress perpendicular to the film plane which reduces the perpendicular anisotropy, causing reduced bubble-nucleation thresholds in bubble materials with large negative values of λ111.

Magnetization reversal in narrow strips of NiFe thin films

The magnetization reversal in 2-30μm wide 60nm thick NiFe strips takes place basically by the same process in single layers and closely coupled bilayers as shown by Lorentz microscopy. At remnance after saturation very narrow domains of reverse magnetization exist along the long edges and closure domains are formed at the ends. Under application of a reversing field the center of the strip is sectioned into transverse domains by rotation with opposite sense of adjoining blocks. In single layers with low coercivity [H c ] the formation of charged walls is thought to retard switching, while in high H c films reversal takes place by sweep of the closure domains from the ends through the strip. Closely coupled bilayers enhance rotation of blocks and the movement across the strip of the reverse domains from the long edges.

Critical curves for determining magnetization directions in implanted garnet films

Critical curves have been calculated for the graphical determination of the magnetization direction as function of applied magnetic field in ion-implanted garnet films having cubic anisotropy. Up to three stable magnetization directions may exist when the applied field is inside the critical curves. This leads to the formation of charged walls. The hard magnetization directions are found to be favorable directions for charged walls and the easy magnetization directions are unfavorable. The complex domain-wall patterns revealed by Ferrofluid techniques in 1-μm magnetic bubble devices are explained by using the calculated critical curve. Futhermore, critical curves for several different symmetries have also calculated to correspond to different crystallographic orientations and garnet material parameters.