S. Konishi

Chip organization of Bloch line memory

A detailed and practical chip organization of Bloch line memory is proposed on the basis of preliminary experiments and computer simulations. The major line - minor loop organization is composed of two levels zigzag conductors to propagate bubbles (major line) and stripe domain walls surrounding grooved region where the epitaxial garnet layer is completely etched (minor loops). The garnet film thickness is chosen as one half of the usual bubble memory chip, which reduces the magneto-static attractive force between bubbles and between Bloch line pairs, and is preferable for Bloch line potential well generation to define bit position. New practical methods for VBL read-write operation are established by simulations and experiments.

Bloch line memory, an approach to gigabit memory

The Bloch line memory is intended as a post-bubble memory hopefully to realize Gigabit density. However, there remain many uncertainties for this new technology. This paper presents the recent activities in our laboratory such as the stripe domain collapse observation using a high speed photography technique to demonstrate the wall-wall interaction, the stripe domain chopping experiment to convert the presence of a Bloch line to the presence of a bubble, and computer simulation of these phenomina and the propagation of Bloch lines in a stripe domain wall. The importance of potential wells for Bloch line and domain wall is emphasized for successful bit by bit propagation.

New bubble garnet films with orthorhombic magnetic anisotropy and high mobility: (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG

New orthorhombic magnetic anisotropy garnet liquid phase epitaxial films with high mobility and low coercivity, (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG, have been successfully obtained. There are no hard bubbles, and wall states are either S = 0, 1, or −1. For 2 μm bubble material (YBi)3(FeGa)5O12/(110)GGG, mobility is μw = 85 m/s Oe and saturation velocity is Vs ≃130 m/s. For 6 μm bubble material (YTmBi)3(FeGa)5O12/(110)GGG, μw = 23 m/s Oe and Vs ≃130 m/s are observed. Vs ≃130 m/s for 2 μm bubble material assures bubble transfer at more than 10 MHz in a current access dual conductor device and utilization of the material for a magneto‐optic readout head. Orthorhombic anisotropy for these materials is mostly growth induced. Growth‐induced perpendicular anisotropies are not observed for eight other garnet systems on the (110)‐GGG. Growth‐induced orthorhombic anisotropy energy for Bi containing garnets is discussed using Gyorgy’s phenomenological parameters, A and B, compared with growth‐induced an...

A three-dimensional computer model of domain wall motion in magnetic bubble materials

The existing equations of motion for a domain wall, as initially proposed by Slonczewski, are modified to permit treatment of a curved wall, with associated magnetization structure, in three-dimensions. The equations are solved numerically, by the so-called explicit method, to investigate dynamic wall conversion in the case of a translating bubble. A comparatively large grid matrix of 3552 points is used to define a bubble of radius 3 μm. To reduce the otherwise enormous computation time required by such a matrix (a) the Dufort-Frankel scheme for the 2nd order spatial partial differentials was modified to permit a feasible time step, and (b) a combination of analytical and numerical methods in the demagnetizing and stray field calculation were employed. The principle of the numerical solution is given, and examples of bubble transport are included to illustrate the capability of the method.

Dynamic behavior of plane wall in bubble garnet films (computer simulation)

The equations of motion of a nearly plane wall are solved numerically by using the finite difference method. The simulation model is extended to include the influence of the wall bowing. Steady state wall motion for a wide range of drive field, the dependence of peak wall velocity on film thickness and the low damping influence for wall velocity are obtained.

Domain wall velocity in orthoferrites

The domain wall velocity in YFeO3 and TbFeO3 single‐crystal platelets is measured by the bubble‐collapse method. Though weak knees like saturation occur at 4800, 8000, and 14 000 m/sec, the wall velocity in YFeO3 increases nearly linearly with increasing drive field up to 25 000 m/sec at a drive field of 370 Oe. The velocity in TbFeO3 increases linearly up to 3000 m/sec (600 Oe). A mechanism quite different from that in garnet films appears to be operative in orthoferrites.

Computer simulation of vertical Bloch line propagation around stripe domain head

Vertical Bloch line pair propagation at the stripe domain head is studied by computer simulation. Several numerical techniques in the calculation are adopted to save computation time. The time step and the grid points interval are varied through the iterative computation. The side wall of the stripe domain is assumed to be straight to simulate a long domain with small number of grid points. Simulation results reveal that a thickness step inside the stripe domain is effective to control the wall motion. A half of the film thickness is chosen for the step depth. The VBL pairs at the stripe head can be propagated one bit period by applying a collapse bias pulse.

Discrimination and state stability of S=1 and 0 bubbles in a field access racetrack

Discrimination of S=1 and 0 bubbles using dynamic bubble collapse and a state‐stability test under quasistatic translation were tried for a YY‐pattern racetrack on a 3‐μm bubble film with a YIG capping layer. The bias‐field margin for collapse discrimination was 5 Oe. These two states were stable for 140–160 Oe of bias field and for 25–50 Oe of rotating in‐plane field.

Transient and steady‐state domain‐wall velocities in a garnet film

The transient and steady‐state domain‐wall velocities are measured by a refined collapse method in a bubble garnet film. The usual average velocity as a function of pulse width shows very large velocity for short pulse width and relaxation to the steady state. The instantaneous velocity defined simply from the increments of wall displacement distance and pulse width shows that the velocity is nearly steady over about 10 ns. The steady‐state velocity below the drive field of 500 Oe includes both a velocity component independent of drive field and a component increasing linearly with field. The former mode is not operative above 900 Oe. These are discussed from the theoretical predictions, together with the wall velocity in hard bubbles.

Discrimination of domain wall states by bubble collapse time

The discrimination of bubble states by dynamic bubble collapse was studied for 5 and 3 μm bubble films. We obtained bias field margin of 6 Oe for the 5 μm bubble film (S=1H and S=0), and about 10 Oe for 3 μm bubble films (S=1H and S= (120)). The discrimination was also tried for 3 μm bubble YY‐propagation pattern chips, for which we got about 8 Oe of bias field margin. Demonstrated was this collapse discrimination for ’’1111...’’ ’’0000...’’, and ’’1010...’’ bubble patterns utilizing an on‐chip bubble annihilator.