Characterization of magnetic materials and circuits for bubble mass memories

Epitaxial garnet films containing many different mixtures of the rare earths have been prepared for materials and device characterization. In addition, several different types of circuits for propagating and manipulating bubble domains have been proposed and demonstrated. This paper reviews some of the recent progress in characterizing these circuits and materials with respect to mass memory applications. The approach under consideration utilizes a rotating magnetic field for bubble propagation and pulsed-current conductors for certain control functions, such as bubble generation, bubble annihilation, and bubble transfer from one propagation loop to another. The detection function is done with magnetoresistive elements. Operation at frequencies of at least 100 kHz is desired and has been obtained separately for each of the required functions, using particular combinations of circuits and materials. More detailed characterizations of the materials, the circuits, and their combinations are presently in progress in order to achieve all required functions simultaneously with a single material-circuit combination.     

The design of single crystal materials for magnetic bubble domain applications

The criteria for the existence of stable magnetic bubble domains and their potential in data storage applications are outlined. The development of single crystal materials capable of supporting such domains is reviewed. Particular emphasis is given to both the static and dynamic properties of bubble domains and to how, by careful materials design and preparation, the optimum balance of these properties can be attained.     

单泡声致发光现象 - 气泡运动的Mie散射测量

单泡声致发光现象时间和空间的高重复性,为实验研究气泡动力学特性提供了可能。文章利用Dave倒推算法,计算气泡Mie散射光强随散射角和气泡半径的变化,并选择了散射角80°为实验测量位置。利用R P方程理论计算的R(t)曲线与Mie散射实测结果相拟合,定量研究了气泡平衡半径、压缩比及崩溃阶段气泡的能量转换,结果表明,随激励声压的增大,气泡所吸收的声能可能绝大部分转换成激波及热能,使泡内温度上升。     

Characterisation of bubble materials

The rapid development of magnetic bubble technology has required growth to exacting specifications of a large number of magnetic films of garnets and some amorphous binary and ternary alloys of rare-earth and transition metals. The characterisation of these films is an essential part in the search for newer materials which hold out promise for better device performance and cost viability. Many methods of films characterisation have been reported from time to time. By and large, these methods can be divided into two groups: one, bulk measurements made on the film and two, measurements made on the domains. We have attempted to collate and briefly introduce various techniques to characterise magnetic bubble materials in this review.     

气泡在剪切作用下的运动特性研究

采用基于自由能模型的格子Boltzmann方法,考虑到毛细管数和气液黏性比的影响,模拟了气泡在剪切作用下的动力特性.结果表明,无论气泡半径大小,总是其长轴被拉伸,中轴和短轴被压缩,且中轴的长度总大于短轴的长度.随着毛细管数的增加或气液黏性比的增大,气泡变形和偏转程度越剧烈.     

Characterization of magnetic bubble generators

Two types of magnetic bubble generators suitable for a field-access bubble memory have been tested at 1.00 kHz bit rate at in-plane rotating fields above 15 Oe. The bias field margins of the generators at 30 Oe rotating field are equal to or greater than those of loop propagation. Both designs are based on the principle of stretching and cutting seed bubbles circulating around a Permalloy disk. Functions of stretching, cutting and transferring in the generator sequence are accomplished either with Permalloy elements or pulsed current conductors. The operating conditions of the generators in terms of current pulse amplitudes, widths and phase angles are presented. Among the two designs, namely Permalloy-stretch and conductor-stretch generators, the latter has a wider phase-angle margin.     

Steady motion of a gas bubble in a liquid

A method is proposed for calculating the velocity of a gas bubble during a steady lift in a liquid, on the assumption that the bubble transmits to the medium an array of weak waves.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 4, pp. 656–662, October, 1973.     

Slow motion of a bubble in a viscoelastic fluid

Summary The motion of a deformed spherical body in a fluid medium is significantly different from the motion of an undeformed spherical body in the same medium. It is shown in this work that a bubble moving in a viscoelastic fluid takes the shaper=a+U ₀₀/a( ₁– ₂)(180R ³+240R ²+816R+672)P ₂(cos)/960(1+R)³ and so one must expect the dynamics of a bubble moving in a non-Newtonian fluid to be significantly different from that of a bubble moving in a purely viscous fluid.     

Optical operation of a magnetic bubble

A magnetic bubble domain is generated on liquid-phase epitaxial (LPE) garnet film by focusing laser light. It is possible to write with only a few milliwatts light power on a thin film with a low anisotropy field. Because the Bi-containing LPE films used have a high Faraday rotation angle, a written bit or bubble can be read out with a high contrast ratio. Because of its low coercivity, the bubble moves along the temperature gradient to the region heated by the light beam and is then stabilized at a corner of a square formed on the film by etching or ion-implantation. Erasure is possible selectively or all together by increasing the bias field. These optical operations of a magnetic bubble are discussed in connection with the material parameters.     

A practical magnetic bubble AND-OR gate

The design and operation of a magnetic bubble AND-OR gate are reported. Operation at 100 kHz in a 25 Oe rotating field with 28.2 μm circuit periodicity was achieved with about 50 percent of the free bubble bias field margins. A transfer pulse is used to divert bubbles from a propagation path which delivers the AND output tO one which delivers the OR output. The transfer is defeated by the presence of a bubble in the appropriate cycle of the OR path. The AND bubble is then delayed by one cycle instead of being transferred. This frastrated transfer strategy was devised to circumvent the restrictive bias field limitations in the operation of previous logic circuits.     

Static characterization of magnetic bubble films

A.C. susceptibility and optical interference are combined to determine the material length, saturation magnetization and thickness of garnet bubble films on GGG substrates. These measurements have been automated to provide precisions of better than 1% and throughputs of more than sixty wafers per hour. Derived values of material length and saturation magnetization agree to better than ±3% with those from visual measurements of stripe width and bubble collapse field for a single film composition. Disagreement between results from two film compositions possibly points up a fundamental difference between the measurement techniques.     

Planar processing for magnetic bubble devices

A two-mask level, conductor first thin film process is described for fabrication of magnetic bubble devices. The process permits a stepless permalloy level over a conductor that may be two to three times as thick as conventional processing The planar process is attained by anodizing a thick aluminum alloy film in all regions where no conductor is needed. The process described solves problems in conventional processing caused by thin conductor metalization and permalloy step coverage. Replication, nucleation, and annihilation devices made with this process promise superior performance.     

Request queueing for magnetic bubble memories

The improvements in request throughput that result from the use of the shortest seek time first (SSTF) request, scheduling algorithm for major/minor loop organized magnetic bubble memories are considered. For the satisfaction of read requests the bubble memory can be considered as equivalent to a file drum with fixed block size. Bubble memories are considered with 64 kbits per chip running at a 5.6 μs stepping rate and serving 750 to 830 read requests pet second (as opposed to ≤ 419 requests per second without queueing) with both uniform and Poisson arrival rates. A priority interrupt algorithm is implemented that assures that all requests are served in ≤ 60ms, while average service times are 10 to 20 ms. Results of simulation runs, corresponding to the various cases of interest, are presented. It is concluded that request queueing with the appropriate scheduling algorithm is a practical way of improving bubble memory performance.     

Logic functions for magnetic bubble devices

An analysis has been made of the number and types of logical functions which can be performed using the interaction of circular magnetic domains in rare earth iron oxides. Multiple logic functions are found to be produced simultaneously at any logical area. These conjunctive output sets have been categorized. Several conjunctive logic gates have been designed, fabricated, and tested successfully in Sm0.55Tb0.45FeO3using Permalloy overlays. Utilizing a circuit in which AND/OR logic gates are coupled to a dynamic memory bank, the total correlation of two data streams has been performed. It is shown how this multiply accessed dynamic memory serves to establish the correlation threshold.     

On the theory of bubble domain motion in propagation circuits

The stability conditions for a bubble domain in the fields of magnetostatic traps are analyzed. For this purpose the quasi-stationary equations of bubble motion are derived which take into account field nonuniformity across the bubble diameter. The contribution of the Permalloy overlay is considered qualitatively. The conditions of static and dynamic stability of trapped bubbles are studied and the stability role in the operating margin development is analyzed.     

LPE growth reproducibility of garnet bubble materials

The problem of growth reproducibility in liquid phase epitaxy of bubble garnet films is analysed. Deviations of the optimum growth temperature are considered to be the main cause of non-reproducibility of the film properties. An expression is derived for the growth temperature sensitivity of the bubble collapse field of grown films. Evaluation of this expression shows that the sensitivity can be minimized if the growth temperature derivative of the magnetization can be adjusted in a controlled way, preferably in the range of 3 to 6 Gauss/°C. This derivative is determined for several melts of the usual CaGe:YIG-type. It is found to be almost independent of the melt composition and always larger than 5 Gauss/°C. Thus growth reproducibility can be improved to a rather limited extent for such CaGe:YIG-type melts.     

New bubble materials with high peak velocity

Peak velocities higher than 40000 cm s^-1and domain wall mobilities of the order of 1500 cm s^-1Oe^-1were measured by the dynamic bubble collapse method in garnet films having an orthorhombic anisotropy. The orthorhombic anisotropy was realized by growing garnet films with positive magnetostriction constants under strong compression on     

A magnetic bubble passive time-slot interchanging gate

The design and operation of a magnetic bubble logic gate, able to perform the basic retardation operations for a magnetic bubble PCM time-slot interchanger,are reported. With this design no external current pulses are needed to perform those functions. With a 32 µ circuit periodicity and using (SmY)3(GaFe)5O12, bias field marginsashigh as 11.5% for the passive logic function are reported in a 25 Oe rotating field. Because no precautions are taken againsthard bubbles the unsuspicious range of frequency is limited to 20 kHz. Nearly no difference is seen in operating margins between low andhigh frequencies. Design rules are given that canlead to other bubble-to-bubble logic circuits with high operating margins.     

Analysis of rotating fields in magnetic bubble drive coils

Closed-form normalized expressions for the field components inside a single-layer rectangular solenoid are derived from a model in which the solenoid is approximated by finite length current sheets of infinitesimal thickness. The equations are extended by superposition to include the case of a multi-layered solenoid, and the effects of nearby magnetic materials are included by employing the method of images. Computer generated field plots compare favorably with measured data.     

Bloch line propagation with Co-Pt bit patterns in stripe domainsconfined by grooves

Bloch Line (BL) pair propagation using a field-access scheme has been investigated in the straight pair of stripe domains stabilized around completely etched grooves. Potential wells to define the bit position for the BL pairs were produced by the stray field from Co-Pt thin-film patterns with high coercivity. By applying a series of asymmetric triangular bias pulsed fields, a BL pair was propagated at 500 kHz with a 14% bias field margin. At 1 MHz, however, the bias field margin was only 7%. This reduction was due to the long relaxation time of the domain walls. The drive field margins depended on the orientation of the propagation direction relative to the magnetized direction of the Co-Pt bit patterns. This dependence became small when the in-plane bias field was decreased