1146 IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-17, NO. 1, JANUARY 1981

Tolerant E. I. IL'YASHENKO, S. N. MATVEYEV, N.

Abstract-The paper is concerned with a method for measuring Hb-b, the field of bubble-bubble interaction in the entire operation margins of bubble devices. Measurements of Hb-b are given for asymmetrical chevron, tapir, and half-disk patterns with various code sequences and interelement gaps. In the main part of the operation margin of Hb the dependence Hb-b = f ( f i b ) is shown to be linear for practically all code sequences. The method helps reveal certain features of bubble-bubble interaction in the I-1 pattern.

N INTRODUCTION

UMEROUS researchers have reported measurements of bubble-bubble interaction in T-bar drive and asym-

metrical chevron patterns [ 11 - [ 5 ] . The measurements were made near the upper boundary of the operation margin, or near the bubble collapse area, and the magnitude of interac- tion was determined from distortion of the correct bubble code combination recorded in advance. The distortions were read out by a bubble detector. The operation margins were shown to depend on the code sequence because of the bubble- bubble interaction. This approach did not permit measure- ments in any desired point of the operation margin, and for this reason its utility was limited. This paper describes a method of measuring bubble-bubble interaction in devices which operate with bubbles whose size is just a few microns and provides very readily this value in functioning bubble de- vices with any admissible values of the bias field f i b and the drive field Hdp.

Bubble-bubble interaction is reasonably typical in gap toler- ant propagation circuits [5] and so the investigations were conducted on closed-loop 30-bit registers made of asymmet- rical chevrons, half-disks, and tapirs [6] with structure periods of 20, 21, and 22 pm. All the registers had right 90" turns. The test sample was fabricated on an epitaxial ferro-garnet material with drive and isolating overlays sputtered and pat- terned as for the optoelectric method [ 6 ] . Liquid phase epitaxial (LPE) garnet films were grown on GGG substrates and had the following typical parameters: thickness 15 p m ; stripe width in the demagnetized state 7.6 p m ; mobility (translation method) 200 cm/s . Oe; the mean collapse field Hco, = 106 Oe at 25'C, and the nominal composition Yl.2 Gdl., YBo.3 Bio.4 Fe,., A10.7012 (except in investigation of the I-lpattern). All the measurements described hereinafter were obtained from these garnet films with Hdr = 40 Oe at fre- quency 10 kHz and an ambient temperature of 40'C. In the

Manuscript received March 17,1980; revised August 11, 1980. The authors are with the Institute of Control Sciences, Moscow,

U.S.S.R.

Measuring Bubble-Bubble Interaction in Gap

0018-9464/81/0100-1146$00.75 0 1981 IEEE

Circuits I. KARMATSKIY, AND YE. P. PARINOV

garnet material the nominal bubble dimension d, was some- what increased (7.5 p n ) in comparison with the pattern pe- riod, or h = 3d, in our case. The interaction was therefore expected to be more pronounced than in conventional circuits where h 2 4d,.

THE METHOD AND EXPERIMENTAL The bubble-bubble interaction was measured as the bubble

area changed by the z-component of neighboring bubble stray fields in a certain position of the drive pattern with subsequent comparison of that change with the area of a (single) interac- tion-free bubble which propagates through that position on the drive pattern with the same values of Hb and Hdr. The bubble areas were measured by the optoelectric method with the open photoelectronic multiplier (PEM) photocathode whose output signal is proportional with the bubble area.

By comparing the bubble areas in different positions of the period in the gap tolerant circuits the value of the neighboring bubble stray field z-component (to be referred to hereinafter as Hb-6) is maximal when the bubbles propagate through in- terelement gaps. This is easy to explain. With neighboring bubbles in other positions of the period or under the drive magnetic elements, the most important part of Hb-b, which embraces these elements and is responsible for bubble-bubble interaction, should cross the interelement gaps and so is significantly reduced. For this reason all the measurements were made for that position. Fig. 1 shows a change in the area of an interaction-free bubble (Hb-b = 0 ) in asymmetrical chevron registers for two different interelement gaps, 6 = 3 lun a n d 6 = 5 p m .

Now if, without changing the position of the PEM cathode and with a certain chosen value of the bias field H b l , three subsequent bubbles are written in the register (code - 000111000 + e ) , then an oscillogram of the PEM output, or changes in the area of the three bubbles, is recorded. Fig. 2 represents the case of 6 = 5 pm. Reduction in the area of the middle bubble AS is seen to be the largest. Let us determine Hb-b which affects it. For this the value of S2 is represented on the Y-line as a function S =f(Hb), and the associated value of the bias field Hb2 is found. Since Hb2 is the value of the bias field with which the interaction-free bubble area is S 2 , the difference Hb2 - f f b l is the additional field which is responsible for the reduction in the bubble area.

Taking now a new value, Hb3, and performing the above graphics for it gives a new value of Hb-b. In this way the char- acteristic Hb-b =f (Hb) is obtained for the entire operating range of Hb with a specified value of Hdr. Also, Hb can be

IL'YASHENKO et 01.: BUBBLE-BUBBLE INTERACTIONS 1147

0 4 d i v

105 110 11s 120 Hb,02

Fig. 1. Plots of S = f ( H b ) for asymmetrical chevron drive overlays with interelement gaps 6 = 3 pm and 6 = 5 pm. The case of an in- teraction-free bubble in the registers. The PEM photocathode posi- tion with respect to the image of the drive pattern is shown on top in the right.

gap posit ion photocathode of PE;M

1 0 0 0 1 1 I

Fig. 2. Oscillogram of PEM output showing variations in the areas of three bubbles propagating through an interelement gap with an asym- metrical chevron drive overlay and a gap 6 = 5 pm. The PEM photo- cathode position with respect to the image of the drive pattern is shown in the right.

102 105 I10 115 120 Fig. 3. Hb-b = f ( H b ) plot for an asymmetrical chevron and two dif-

ferent code sequences, interelement gaps being 6 = 3 pm and 6 = 5 pm.

maintained constant and Hdr changed; then in the above pro- cedure Hb-& =f(H&) can be found.

Figs. 3 and 4 show the dependencies Hb-b = f (Hb) for asym- metrical chevrons and tapirs with different 6 and two different code combinations. For half-disk structures with short dis- tances between neighboring tracks used in many bubble de- vices, the dependence Hb-b = f ( H b ) for four code sequences is shown in Fig. 5. In all cases the Hb-b is measured for the bubble which collapses the first (underlined in the figures).

DISCUSSION OF INTERACTIONS Analysis of the dependencies Hb-b =f(Hb) shown in Figs.

3-5 reveals that in the main operating range of Hb there is a

/-lb-b.Oe 12

t

, !05 110 115 120 Fig. 4. Hb-b = f ( H b ) plot for a tapir drive pattern and two different

code sequences with interelement gaps being 6 = 3 pm and 6 = 5 pm.

l l l ~ l l l ~ l l l l l D l l

A 0 0 0 1 ~ 0 0 0

H b - 4 + 0 0 0 1 1 ~ 1 1 0 0 0 o e

.- m8"'$J*~j-9+p 7

.. . y 0 0 0 1 ~ 1 0 0 0 8 - $\ ..j..-& W

6

-- 5 -- $A

A+ \$e+ ' .- 'A\A

A 'Y

.A

3 .. \A A

L A . * &..+- ,.--,.-- +- -/-_. -f -__-

0 92 9 4 9 6 9 8 l o o !-I, Oe >

Fig. 5 . Hb-b = f ( H b ) plots for a half-disk drive pattern and four dif- ferent code sequences; 6 = 3 pm, A = 10 pm.

practically linear dependence of the bubble-bubble interac- tion field Hb-b and the bias field Hb for all code sequences. The linearity is disturbed only in the neighborhood of the elliptical bubble instability and collapse fields. Comparison of Hb-b =f (Hb) , Figs. 3 and 4, for various interelement gaps of the asymmetrical chevron and tapir patterns indicates that with identical code sequences Hb-b decreases when the gap 6 increases. However, the reduction of Hbab amounts to tenths of one Oersted, or a small fraction ofHb-b (<0.1 Hb-&) when the gap increases 1.7 times. From the plots of Figs. 3 and 4 it also follows that with change of the code sequence from three subsequent bubbles fed into the register until it is completely filled, Hb-b increases insignificantly; in the entire operating range it grows by 2 Oe. If, however, there is one bubble nearby (code * 1 0001 1000 - * , Fig. S), then Hb-b is approxi- mately half that in the case of two bubbles nearby.

Hb-b decreases still further (to tenths of one Oersted) with codes 010101 * * or 001010001 * . + , or when there are no two successive bubbles. Computations show that the z-component of the stray field for an 8-pm bubble is 1.1 Oe at a distance of 20 pn for this material. Therefore for a code 00011000, Fig. 5 , the drive magnetic element, which is be- tween the bubbles, increases the z-component of the bubble stray field approximately fourfold.

1148 IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-17, NO. 1 , JANUARY 1981

/ -

1

r, n . . smaller than 6 pm. In our experiment an 1-1 closed register was investigated where the code recorded was. . * 001000100 . . The interaction of the adjacent bubbles was practically zero. But this sequence enabled observing simultaneously by the optoelectric method the output signal, which is propor- tional to the area of the bubble free of interacting with the bubble of the neighboring track and the output signal propor-

I tional with the area of the bubble which interacts with the bubble of the neighboring track across the I-element. Fig. 6 shows that oscillogram. An estimate by the above method yields Hb-b zz 2 Oe. This fits the experimental data for 6 pm

t - in [7].

ACKNOWLEDGMENT Fig. 6. Oscillogram of PEM output signals which show the areas of two

bubbles propagating through a gap in a 1-1 pattern. The bubble of a The authors wish to thank Drs. I. G. Avaeva and v. smaller dimension (the first one) is affected by the stray field of the Kravchenko for samples of garnet films. bubble in the Z-shaped element of the neighboring track. The garnet film is (Y,, Gd, Yb, Bi)3 (Fe, A1)5012, thickness 15 pm, the stripe width in the demagnetized state w = 14 pm, mobility = 200 cm/ REFERENCES sec * Oe, the collapse field HCo1 = 62 Oe, and Hdr = 40 Oe. [ l ] P. W. Shumate, P. C. Michaelis, and R. J . Peirce, in AZP Conf:

It is interesting to note that in the 1-1 pattern with two gaps [21 w. D. Doyle, w. E. Flannery, and J- A. Coleman, in AIi‘ COnf:

per bit the interaction between neighboring is found [3] H. Callen, W. D. Doyle, and J . S. Seitchk, J. Appl. Phys., vol. 46,

Boc., V O ~ . 18, pp. 140-151,1974.

Boc., V O ~ . 18, pp. 152-156, 1974.

to be much weaker. In such patterns, however, a major part pp. 4970-4975,1975. of Hb-b is represented by a component caused by the stray [41 s. Orihara, S . Iwasa, T. Majima, K. Nogiwa, and K. Yamagishi,

field of the bubble from the neighboring track, a component “Diagnostic testing of a 10-kbit bubble memory chip,” IEEE Trans. Magn., vol. MAG-11, pp. 1685-1688, Nov., 1975.

which magnetized the opposing part of the I-shaped element. [5] F. Hagedorn, J. Appl. Phys., vol. 50, pp. 2228-2230,1979.

the operation margin of the 1-1 in comparison with the T-1 pattern, especially for a propagation structure with bubbles [7] S . Igarashi, et al., AIP Con5 Proc., vol. 29, pp. 48-50,1976.

This phenomenon has been found to be felt as reduction of [61 E. I. Il’yashenko, e t al., ’‘OPtoeleCtri~l study of bubble ProPaga- tion in field access devices,”IEEE Trans. Magn., vol. MAG-15, pp. 1120-1123, July, 1979.

The Numerical Solution of Steady-State Skin Effect Problems-An Integrodifferential Approach

~ b s f r 0 c t - h entirely new formulation of the classical steady-state INTRODUCTION skin effect problem is presented. The magnetic vector potential is ob- tained directly from the projective solution of a single integrodiffer- HE SKIN EFFECT problem is the magnetodynamic entia1 equation. In this new form of the steady-state diffusion equation, problem of finding the total current density distribution T the known measurable total current in conductors replaces the usual in an arbitrary system of current carrying conductors. a s - unknown source current density vector. The validity and Correctness placement effects are considered negligible. When the excita- of the new formulation are demonstrated by a simple, easily verifiable example based on finite element discretization.

tions are time harmonic and all transients have disappeared, one is dealing with a steady-state skin effect problem.

Manuscript received June 26, 1980; revised August 11,1980. The total current density distribution in a conductor deter-

The author is with Research and Development, mines its dynamic impedance which is of major concern to Electric Company, Schenectady, NY 12301. designers of many electrical devices and systems operating

0018-9464/81/0100-1148$00.75 0 1981 IEEE