Terence John Nelson

Implantability of small bubble diameter garnet films

Measurements of anisotropy in implanted bubble films indicate that in addition to straining the lattice, implantation also has the effect of suppressing the growth‐induced anisotropy. After annealing at 1000 °C, most of the as‐grown anisotropy is restored, which points to oxygen defects as the most likely mechanism for the effect. The Curie temperature has been found to be lowered by as much as 70 °C by implantation at a typical device dose, and the anisotropy of the implanted layer varies quite rapidly with temperature at elevated temperatures. The results indicate that with proper choice of material parameters and implantation conditions safisfactory bubble propagation can be obtained in high density small bubble diameter devices based on ion‐implanted propagation patterns over a wide temperature range.

Bubble rectifiers and reverse rotation transfer gates based on gaps in ion implanted propagation patterns

Gaps between unimplanted disks in ion implanted propagation patterns (I2P2’s) can allow bubbles to pass through in one direction and not in the opposite direction. These ’’bubble rectifiers’’ have been shown to perform a merge function. In a major‐minor I2P2 bubble memory, a horizontal major line with a gap for each minor loop has been designed. Bubbles transferred out of minor loops down to this major line pass through the gaps and then propagate on the lower side past all the gaps to a detector, preserving the order of data tranferred in at the upper ends of the minor loops. For propagation on these multi‐gapped lines, good bias field margins, somewhat lower than those for minor loop propagation, have been achieved with 2 μm gaps in 8 μm patterns and 1 μm gaps in 4 μm patterns. Using appropriately oriented gaps, bubbles can be transferred from one propagation track to another by temporary reversal of the drive field rotation direction. A family of reverse rotation transfer gates has been designed which ...

NDRO detector for ion‐implanted bubble devices

We report on the design and characterization of a nondestructive readout detector for ion‐implanted bubble devices. Detection takes place, according to this design, as in previously reported destructive readout detectors in ion‐implanted devices.1 The bubble to be detected is stretched into a strip along a magnetoresistive permalloy bar by a current pulse in a hairpin conductor. In our design, however, a second hairpin conductor is added, coplanar with the first one, and a current pulse in this second conductor stretches the end of the bubble to a second propagate track. Finally, a collapse pulse is applied to the first conductor forcing the bubble strip off the permalloy bar. The detector has been produced on 8‐μm period circuits using previously reported implant conditions and processing.1 It has been operated at 50 KHz with bias margin ranges typically 20 Oe at 40 Oe rotating field. An error rate at one bias of <5×10−9 has been demonstrated.

Preparation and properties of V‐substituted garnet films for ion‐implanted 1.0‐micron bubble devices with improved high‐temperature propagation

The growth and properties of films of a novel composition, (SmLuCa)3 (FeVSi)5O12, for 4‐μm period Ion‐Implanted Propagation Pattern devices, are described. The use of vanadium substitution to lower 4πMs yields films with high Curie temperatures (Tc =512–524 °K). Small amounts of silicon are added for lattice matching of the films to the substrate and also to increase the Q value. The presence of vanadium in films was also found to substantially increase the Faraday rotation. The bubble size in these films is nearly constant in the temperature range of −50° to +150 °C. The films also have a high mobility and low dynamic coercivity. Preliminary results of bubble propagation in these films in the temperature range −50° to +160 °C are described. It is expected that because of a combination of the desirable magnetic properties, these films will find a widespread use in bubble devices requiring operations to higher temperatures.

High Curie temperature drive layer materials for ion-implanted magnetic bubble devices

Ion implantation of bubble garnets can lower the Curie temperature by 70 °C or more, thus limiting high temperature operation of devices with ion‐implanted propagation patterns. Therefore, we made double‐layer materials with a conventional 2‐μm bubble storage layer capped by an ion‐implantable drive layer of high Curie temperature, high magnetostriction material. Contiguous disk test patterns were implanted with varying doses of a typical triple implant. Quality of propagation was judged by quasistatic tests on 8‐μm period major and minor loops. Variations of magnetization, uniaxial anisotropy, implant dose, and magnetostriction were investigated to ensure optimum flux matching, good charged wall coupling, and wide operating margins. The most successful drive layer compositions were in the systems (SmDyLuCa)3 (FeSi)5O12 and (BiGdTmCa)3(FeSi)5O12 and had Curie temperatures 25–44 °C higher than the storage layers.

Magnetization distributions in ion‐implanted bubble garnet films

We solved coupled differential equations that govern the magnetization in the storage layer and the drive layer in an ion‐implanted magnetic bubble film. We treat specific numerical cases with film properties and applied fields typical of 8‐μm period bubble devices based on ion‐implanted propagation patterns. The transition field region is approximately 0.07 μm wide, which is twice as large as one previous approximate theory predicts, but which agrees well with another approximate model. We also compute the magnetization direction in the layer as a function of the drive field direction and compare our results (a) with an approximate analytical method which assumes that the polar angle θ is nearly constant and (b) with another numerical study which neglected effects of coupling to the storage layer. Our results are in agreement with the latter, but the variation of polar angle with drive field direction is quite small (∼0.5°) compared to the estimate (∼6°) of the former.