The design of a Bloch line memory prototype is presented. The different basic functions are studied experimentally. Two aspects of minor loop initialization are considered: memory clearing and bias field stability. Minor loop stability margins depend on material parameters and the groove design. The propagation of line pairs as well as line clusters is studied. The maximum line displacement is 2 micron per pulse. Bit propagation depends on the fall time of the vertical field pulse. At short fall time pinning points hamper bit propagation. Preliminary results of the input/output gate show that the basic functions such as stripe head stretching, line control and chopping are compatible. The major loop operation, including bubble propagation and stretching, is demonstrated.

In Bloch Line memories understanding of the reading process is fundamental for the operation of the memory. The principle of this function is to discriminate parallel and antiparallel domain walls by chopping at different currents. Many parameters can influence this scheme, namely quasistatic or dynamic conditions, material characteristics, actual wall structure before and during chopping. The goal of this paper is to present a systematic study of these factors in order to give indications for practical devices.

In Bloch line memories magnetic domain walls are used as storage loops for shift registers. A preliminary condition for device operation is to set the domain walls at given positions where they will remain stable. It is then necessary to control the wall state of these domains and to manipulate the domain heads for write and read operation. The authors present structures which have been designed and realized for that goal and the results of device operation for the preliminary step. A simple, reliable procedure for nucleating an array of parallel domains is presented. Grooving the garnet proves efficient in stabilizing the domain walls. The influence of material parameters is discussed as well as the application of this initialization procedure to further studies

Vertical Block line (BL) gyrotropic propagation was studied experimentally. Single BLs nucleated in an as-grown (YSmBi)/sub 3/(FeGa)/sub 5/O/sub 12/ garnet film were viewed directly using the PADO (polarized anisotropic dark-field observation) technique. Gyrotropic force was provided by an asymmetrical triangular-shaped bias field pulse. A short-risetime pulse moved the line of a straight wall in one direction, whereas a large-risetime pulse moved it backward. This gyrotropic propagation phenomenon is reproducible for varying bias field; however, some scatter is observed in BL displacement. Block wall response to the bias field pulses is also considered. The range of effective drive field inducing good gyrotropic propagation is discussed.< >

A new technique for observing domain walls and lines in materials with perpendicular anisotropy is presented. It employs laser light in a laser scan microscope and uses anisotropic diffraction by the wall/line magnetic structure. The contrast obtained can be understood simply and a numerical computation shows good agreement with experimental results. Wall configurations with numerous lines may be obtained when nucleating parallel stripes upon reduction to zero of a saturating in-plane field.

A technique is presented to delineate correctly the position of the storage loops, i.e. domain walls where the Bloch line pairs have to sit for the operation of the memory. To make the loop confinement technique feasible over a wide range of material parameters, bias field values, and technological parameters, a grooving technique is chosen. A model is first described and various stability conditions are studied. Experimental realization of that technique is then presented and illustrated, and the confinement conditions are compared with the predictions of the model.

Magnetization inhomogeneities are observed by optical means in the walls of domains in bubble garnet films with perpendicular magnetization. Specific illumination conditions (scanned laser light, angular selection, dark field imaging) allowed for this achievement. Experiments using known wall states, static in-plane field and pulsed bias field indicate that the magnetic origin of these structures can be assigned to vertical Bloch lines (Neel segments in Bloch walls). A magnetooptical explanation of the observed contrasts is outlined.

Direct observations and Fourier transforms of amorphous networks of magnetic bubbles in ion-implanted garnets and in pure films are shown with evidence for a short coherence size. This is interpretated on the basis of a model of interaction of bubbles via dipolar interactions where only short-range effects are considered because long-range effects are totally screened by the numerous domains included in this range. Moreover these dipolar forces which are proportional to both the magnetizations stabilize the occurrence of different radii of bubbles. These two considerations enable us to understand these amorphous networks as due to short-range interactions and random fields and thence to predict a coherence size of typically 50–300 bubbles in a hexagonal arrangement. Small rotating fields in the phase of the film do not strongly perturb the size distribution of bubbles, i.e., the transverse magnetic field distribution, but induce many local displacements of bubbles. These displacements can be coherent and thus collective if the excitation frequency is associated with a soft mode of this amorphous structure. Thus local cascades of hopping motion as well as collective modes are observed as a function of the excitation frequency. The practical soft modes are localized on the grain boundaries and lead either to a decrease of the coherence size, i.e., melting or to an increase, i.e., recrystallization. Theoretical investigations of the soft mode frequency and localization are given. Experimentally direct and Fourier transform observations as a function of frequency are recorded in a video tape.