Andrew Henry Bobeck

Application of orthoferrites to domain-wall devices

Orthoferrites are of general formula RFeO 3 where R is any rare earth or yttrium. They are usually flux grown as large single crystals and then processed to provide platelets several mils in thickness. A high uniaxial anisotropy gives rise to a single unique easy magnetization direction parallel to the c axis above room temperature in all orthoferrites except SmFeO 3 . A low saturation magnetization results from the canting of a pair of anti-parallel spin systems. Platelets prepared so that the easy axis of magnetization is normal to the planar surface display a serpentine domain pattern made visible by the Faraday effect. Under specific conditions cylindrical domains are observed. These domains, which in Sm 0.55 Tb 0.45 FeO 3 are as small as 0.8 mil in diameter, can be manipulated to perform memory and logic. Three techniques can be used to propagate cylindrical domains. The first uses a sequence of current pulses applied to a conductor array. The second requires an in-plane rotating field acting on a structured Permalloy pattern to generate traveling positive and negative poles. These poles selectively attract and repel a cylindrical domain and thereby control its motion. The movement of an inchworm most closely approximates the propagation mechanism of the third technique. Interacting a pulsating domain with a wedge-like Permalloy pattern results in a unidirectional movement.

LIQUID PHASE EPITAXIAL GROWTH OF UNIAXIAL GARNET FILMS; CIRCUIT DEPOSITION AND BUBBLE PROPAGATION

Magnetically uniaxial epitaxial films of Eu2Er1Ga0.7Fe4.3O12 and Er2Eu1Ga0.7Fe4.3O12 5–20 μm thick have been grown free of cracks from PbO · B2O3 solutions on (110) and (111) Gd3Ga5O12 substrates, respectively. Bubble propagating T‐bar and Y‐bar circuits of nickel‐cobalt‐phosphorus were electrolessly deposited on these films. Operation in excess of 100 steps has been achieved in T‐bar and Y‐bar bubble domain shift registers. Details of the growth procedure, magnetic properties, and circuit preparation are presented.

Magnetic bubble memory chip design

The choice and organization of bubble-circuit functions in the design of a magnetic bubble mass memory chip are discussed with emphasis on factors such as circuit function compatibility and performance, circuit density, and processing simplicity. A specific major-minor organized chip design is described which uses rotating field driven propagation,

Radio‐Frequency Determination of New Growth‐Induced Anisotropy in Garnets for Bubble Devices

-sign transfer gates, all T-bar minor loops, a nucleate generator with chevron merging port, a chevron based replicator/ annihilator and a chevron guard rail expander detector. The overall operating characteristics of chips having 20 510 bits of storage capacity have been measured and a bias field margin of 12 Oe is typically obtained with a 25 Oe, 100 kHz rotating field.

A second look at magnetic bubbles

A new type of magnetocrystalline anisotropy has been observed under {110} faces in several fluxgrown mixed rare‐earth iron garnets. This anisotropy is different in direction and magnitude from that previously reported in similar garnets under {211} faces. In Eu2ErGa0.6Fe4.4O12 with 4πM near 350 G at 300°K, microwave resonance measurements have shown that {110} face material has a large effective uniaxial anisotropy. The [100] in the growth plane is the easy axis, [011] normal to this plane is medium, and [011] parallel to this plane is hard. Using a resonance equation appropriate to the orthorhombic magnetic symmetry and neglecting the relatively small cubic terms, the effective uniaxial anisotropy field is ∼1300 Oe. This anisotropy leads to a new cutting procedure (type 3 cut) for bubble devices: {100} platelets are cut normal to the natural {110} faces. Using 15‐μ‐thick platelets of this type, bubbles ∼8μ in diameter were propagated. The domain wall mobility is ∼170 cm/sec/Oe. These properties are comp...

Characterization and test results for a 272K bubble memory package

Material selection is discussed. The data rate of orthoferrites, garnets, and magnetoplumbite devices, for example, are compared. Also reviewed is the status of propagation circuits. The bubble is examined from the viewpoint of its use as a vehicle to obtain material data. A new method to measure domain-wall mobilities is introduced. This method, which is based on the dynamics of a collapsing bubble, permits measurements to be made over a wide dynamic range.

Magnetic properties of flux grown uniaxial garnets

A magnetic bubble memory package has been designed specifically as a serial data store for use in a voice synthesis system. The memory package contains four 68,121 bit serial shift-register chips for a total capacity of 272,484 bits. One such package, operating at a 24 kHz data rate, can provide 12 seconds of speech. Each 5 mm by 6 mm bubble chip consists of a single 68,121 bit shift register, data replicator, expander active and dummy detector, and nucleate generator. A garnet composition with nominally 3 μm bubbles was selected because its bubble-collapse-field temperature coefficient -0.2%/°C accurately tracks that of Indox over the required 10°C to 60°C temperature range. The nominal in-plane fields are 40 Oe amplitude at a frequency of 48 kHz. The bubble chips and the packages used in this study were fabricated in a Device Capability Line at the Reading Western Electric Facility.

Reversible, Diodeless, Twistor Shift Register

Static and dynamic properties of bubble domains are given for a number of mixed rare earth and related iron garnets that have growth induced noncubic magnetic properties that are of interest and, in some cases, are useful for bubble-domain device applications. Rules for predicting domain alignments related to {211} facets, the various cuts for obtaining useful platelets, and compositional controls for obtaining temperature independent properties are also outlined.

Thin‐Film Surface Bias on Magnetic Bubble Materials

A twistor shift register has been built and operated successfully. The design utilizes interaction effects which exist between magnetized regions on a magnetic wire. Only a single magnetic wire is required for a complete register. The information is stored as magnetically polarized zones which can be moved along the wire by means of a five phase pulse source.No diodes are required. Therefore, drive powers can be greatly decreased since the only threshold consideration is the magnetic material itself. Bi‐directional operation is easily secured. The upper frequency limit has not been established; however, a several hundred kilocycle bit rate should be possible. Physically, the register could be made of no more than magnetic and copper wire. This should make fabrication considerably cheaper than conventional shift registers.

Characteristics of a Detection‐Propagation Structure for Bubble‐Domain Devices

A method of reducing the external magnetic bias field to maintain stable cylindrical domains (magnetic bubbles) in uniaxial orthoferrites or garnets is presented. A thin film of a permanent magnetic material is sputtered onto a platelet inducing an exchange coupling interaction across the interface. This interaction manifests itself as an effective bias field which reduces the external applied field required to stabilize bubbles. So far the largest effective bias obtained has been about 25 Oe, using Co3.2Cu1.3Fe0.5Ce0.25Sm0.75 sputtered onto a 15‐μ‐thick platelet of Sm0.55Tb0.45FeO3. Dynamic properties do not seem to be appreciably altered for low‐speed operation in a T‐bar rotating field device.