Generator/shift register/detector for cross-tie wall memory system

Disclosed is a cross-tie wall memory system for the generating, propagating and detecting of binary data represented by the presence or absence of cross-tie, Bloch-line pairs along a cross-tie wall in a thin magnetic data track. The system includes a three-level shift register structure comprised of the following layers: first and second substantially similar, serrated-edged current conductive striplines and a serrated-edged thin magnetic layer data track. The shift register is terminated on one end by a cross-tie, Bloch-line pair generator and on the other end by a cross-tie detector. A data word is stored in the data track between the generator and the detector and is shifted through the detector for readout of the stored data word. The first and second serrated-edged striplines are formed of alternate wide-narrow portions with the wide portion of one stripline oriented above/below the narrow portion of the other stripline. Current signals alternatively coupled to the first and second striplines generate drive fields of differing intensities in the plane of the inductively coupled data track for propagating the cross-tie, Bloch-line pairs therealong.

BACKGROUND OF THE INVENTION 
The propagation of inverted Neel wall sections in a serial access memory 
system was proposed by L. J. Schwee in the publication "Proposal On 
Cross-tie Wall and Bloch-line Propagation In Thin Magnetic Films," IEEE 
Transactions on Magnetics, MAG 8, No. 3, pages 405-407, September 1972. 
Such a memory system utilizes a ferromagnetic film of approximately 81% 
Ni-19% Fe approximately 350 Angstroms (A) thick in which cross-tie walls 
can be changed to Neel walls and Neel walls can be changed to cross-tie 
walls by applying appropriate fields. Associated with the cross-tie wall 
is a section of inverted Neel wall that is bounded by a cross-tie wall on 
one end and a Bloch-line on the other end. 
In such a cross-tie wall memory system, information is entered at one end 
of the serial access memory system by the generation of an inverted Neel 
wall section, formed by a cross-tie on one side and a Bloch-line on the 
other, that is representative of a stored binary 1 or of a non-inverted 
Neel wall section (i.e., the absence of a cross-tie and Bloch-line pair) 
that is representative of a stored binary 0. Such information is moved or 
propagated along the cross-tie wall by the successive generation (and then 
the selective annihilation) of inverted Neel wall sections at successive 
memory cells along the cross-tie wall. In the D. S. Lo, et al, U.S. Pat. 
No. 3,906,466 there is disclosed a propagation circuit for the transfer of 
inverted Neel wall sections at successive memory cells along the cross-tie 
wall. In the L. J. Schwee U.S. Pat. No. 3,868,659 and in the publication 
"Cross-tie Memory Simplified by the Use of Serrated Strips," L. J. Schwee, 
et al, AIP Conference Proceedings, No. 29, 21st Annual Conference on 
Magnetism and Magnetic Materials, 1975, published April 1976, pages 
624-625, and in the publication "Cross-Tie/Bloch-Line Detection," G. J. 
Cosimini, et al, AIP Conference Proceedings, No. 3, 23rd Annual Conference 
on Magnetism and Magnetic Materials, 1978, published March 1978, pages 
1828-1830, there have been published some more recent results of the 
further development of cross-tie wall memory systems. 
In prior art cross-tie wall memory systems, the magnetic film that 
functions as the storage medium has the property of uniaxial anisotropy 
provided by its easy axis induced magnetic fields, which easy axis is 
generated in the magnetic film during its formation in the vapor 
deposition process. This easy axis provides a magnetic field induced 
anisotropy which constrains the generation of the cross-tie wall along and 
parallel to the easy axis. In the above L. J. Schwee, et al, AIP 
publication there are proposed serrated strips of Permalloy film, about 
350 Angstroms (A) in thickness and 10 microns (.mu.m) in width, which 
serrated strips are etched from a planar layer of the magnetic material so 
that the strips are aligned along the easy axis of the film. After an 
external magnetic field is applied normal to the strip length, i.e., 
transverse the easy axis of the film, the magnetization along the opposing 
serrated edges rotates back to the nearest direction that is parallel to 
the edge. This generates two large domains that are separated by a Neel or 
cross-tie wall that is formed along the centerline of the strip. 
Cross-ties are energetically more stable at the necks of the serrated 
edges while Bloch-lines are energetically more stable in the potential 
wells between adjacent necks. 
This serrated strip configuration, because of the contour of the opposing 
edges of the strip, provides the means whereby the cross-tie, Bloch-line 
pairs are structured at predetermined memory sections along the strip. 
However, because prior art strips have field induced uniaxial anisotropy 
imparted during deposition, such strips cannot be utilized to permit the 
use of nonlinear, i.e., curved, data tracks, which curved data tracks are 
essential to the configuration of cross-tie wall memory systems of large 
capacity or of digital logic function capabilities. In the L. H. Johnson, 
et al, U.S. Pat. No. 4,075,612 there is disclosed a design of the edge 
contour of a film strip of, e.g., Permalloy film of approximately 350 A in 
thickness and approximately 10 .mu.m in width. The edge contours are 
mirror images, one of the other, of asymmetrical, repetitive patterns of 
rounded edge portions. The edge contour of each opposing pair of rounded 
edge portions is substantially in alignment with the natural contour of 
the magnetization that is oriented around a Bloch-line, which Bloch-line 
is positioned along the cross-tie wall that is oriented along the 
geometric centerline of the film strip. The neck or narrowest point of the 
edge contour between adjacent rounded edge portions functions to structure 
the static or rest position of the associated cross-tie of the cross-tie, 
Bloch-line pair. 
In the M. C. Paul, et al, U.S. Pat. No. 4,130,888 there is disclosed a 
cross-tie wall memory system and in particular a data track therefor that 
is formed of a strip of magnetic material having substantially zero 
magnetic field induced anisotropy. The data-track-defining-strip of 
isotropic material utilizes its shape, i.e., its edge contour induced, 
anisotropy to constrain the cross-tie wall within the planar contour and 
along the centerline of the film strip. Accordingly, the cross-tie wall is 
constrained to follow the path defined by the magnetic film strip which 
path may be configured into a major loop, or circular data track, 
configuration for large capacity memory storage. 
In the E. J. Torok U.S. Pat. Nos. 4,080,591 and 4,075,613 there is utilized 
the data-track-defining-strip of isotropic magnetic film of the 
hereinabove referenced M. C. Paul, et al, patent to form a replicator of 
and a logic gate for cross-tie, bloch-line pairs. The replicator is 
utilized as a magnetic switch or gate to selectively transfer cross-tie, 
Bloch-line pairs between merging, overlapping data tracks. This permits 
the configuration of a plurality of continuous data tracks into a 
major-loop, minor-loop configuration for a large capacity memory system. 
The logic gate is utilized as a magnetic switch to selectively perform the 
logic OR function or the logic AND function upon two merging, overlapping 
data tracks. 
SUMMARY OF THE INVENTION 
In the cross-tie wall memory system of the present invention there is 
provided a shift register for shifting cross-tie, Bloch-line pairs 
therealong through a plurality of memory cells consisting of a transfer 
section and a store section. The shift register is terminated on one end 
by a cross-tie, Bloch-line pair generator, for selectively coupling 
cross-tie, Bloch-line pairs into the shift register, and on the other end 
by a detector for detecting when a cross-tie has been entered therein from 
the shift register. 
The generator/shift register/detector assembly is fabricated in three 
superposed layers: a first serrated-edged current conductive stripline; a 
serrated-edged thin magnetic layer that forms the data track along the 
geometric centerline of which is formed and structured the cross-tie wall, 
and a second serrated-edged current conductive stripline. Both the first 
and the second serrated-edged current conductive striplines are of similar 
planar conformation having triangular-shaped, mirror-image edge contours 
of alternating width peaks but of similar valleys or necks therebetween. 
The serrated-edged thin film magnetic layer has a planar conformation 
formed of similar diameter overlapping circular disks. The diameter of the 
disks is less than the width of the associated first and second stripline 
peaks while the overlapping disks form necks at the joins of their 
circumferences for forming points of minimum energy states for the 
cross-ties while the centers of the disks form points of minimum energy 
states for the Bloch-lines. 
The shift register is terminated on one end by a cross-tie, Bloch-line pair 
generator and on the other end by a cross-tie detector. Electronic 
circuitry controls the drive current signals to the first and second 
serrated-edged striplines for generating the necessary fields for the 
propagation of the cross-tie, Bloch-line pairs along the serrated-edged 
data track, to the generator to selectively generate, or not, cross-tie, 
Bloch-line pairs, and to the detector to detect the presence, or not, of a 
cross-tie, all in synchronism.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is an illustration of a portion of a cross-tie wall memory system 
into which the generator 10, shift register 12, and the detector 14 of the 
present invention have been incorporated. 
FIG. 2 is an illustration of a cross-section of the memory plane of FIG. 1 
taken along line 2--2 thereof for the purpose of illustrating the stacked, 
superposed elements of FIG. 1. The memory system of FIG. 1 includes a 
non-magnetizable, e.g., glass or silicon, substrate member 16 having the 
following active members arranged in a stacked, superposed integral 
assembly: conductive, e.g., gold, serrated-edged stripline 18; 
magnetizable, e.g., NiFe, serrated-edged data track 20; and conductive, 
e.g., gold, serrated-edged stripline 22. Not illustrated in FIG. 1 or FIG. 
2 are: a thin adhesive layer of, e.g., chromium, that may be affixed to 
the top and/or the bottom surfaces of the metallic layers for ensuring an 
integral assembly of the metallic layers with the adjacent metallic or 
insulating layers. Illustrated in FIG. 2 is a thin, smoothing and 
insulating layer 24 of, e.g., SiO. Between the current-conducting 
striplines 18 and 22, and superposed this entire assembly and affixed to 
the top surface thereof, there may be provided an additional, e.g., SiO, 
sealing and insulating layer 26. 
As is well known, data track 20 when effected by the proper drive fields 
establishes a cross-tie wall 30 along its geometric centerline which is 
substantially aligned with its longitudinal axis, identified as line 32 of 
FIG. 1. Preferably the film strip is isotropic, i.e., has substantially 
zero magnetic field induced anisotropy, and utilizes its shape, i.e., its 
edge contour, to constrain the cross-tie wall within the planar contour of 
and along the longitudinal axis 32. In the present invention, as 
illustrated in FIG. 1, data track 20 has a planar conformation that is 
defined by a series of overlapping circular disks, the joins of their 
circumferences forming necks that generate minimum energy states for the 
cross-ties while the centers of the disks form minimum energy states for 
the Bloch-lines. 
In the present invention, as illustrated in the embodiment of FIG. 1, 
striplines 18 and 22 are configured into similar serrated-edged drive 
lines, the serrated-edged contours of which are comprised of alternating 
triangular-shaped portions, in which the height of the wide triangular 
portion is approximately twice the height of the narrow triangular 
portion. The necks between the triangular-shaped portions of striplines 18 
and 22 are substantially centered about and in line with the narrow 
portions or necks of data track 20. For purposes of the present invention, 
the alternate, every other, narrow portions or necks of data track 20 and 
the associated narrow portions or necks of striplines 18 and 22, beginning 
at generator segment 10c of generator 10, are defined as a store segment, 
while the other alternate narrow portions or necks of data track 20 and 
the associated narrow portions or necks of striplines 18 and 22 are 
defined as a transfer segment--see the D. S. Lo, et al, U.S. Pat. No. 
3,906,466--both combining to comprise a memory cell, a plurality of which 
are aligned along the shift register 12 formed of data track 20 and 
striplines 18 and 22 of FIG. 1. Thus, generator 10 of FIG. 1 is centered 
about a store segment while detector 14 is centered about a transfer 
segment. 
With particular reference to FIG. 3, there is presented a cross-sectional 
view of FIG. 1 taken along line 3--3 in the area of gap 15. FIG. 3 
illustrates that this stacked, superposed relationship includes the 
following listed successive layers, with the adhesive layers not 
illustrated for clarity: 
glass substrate 16--0.50 mm thick 
chromium adhesive layer--100 A thick 
gold stripline 18--1500 A thick 
chromium adhesive layer--100 A thick 
SiO insulative layer 24--12,500 A thick 
Permalloy data track 20--approximately 81% Ni-19% Fe, 350 A thick 
chromium adhesive layer--100 A thick 
gold detector arms 14a, 14b--1000 A thick 
chromium adhesive layer--100 A thick 
SiO insulative layer 28--12,500 A thick 
chromium adhesive layer--100 A thick 
gold stripline 22--1000 A thick 
SiO sealing layer 26--12,500 A thick. 
With reference back to FIG. 1, there is illustrated a shift register 12, 
comprised of serrated-edged stripline 18, serrated-edged data track 20 and 
serrated-edged stripline 22. Shift register 12 is terminated at one end by 
generator 10, comprised of conductive element 10a extending across shift 
register 12, followed by a narrow portion 10c, in which the cross-tie of 
the cross-tie, Bloch-line pair is generated, and a terminating wide end 
portion 10b. Shift register 12 is terminated on the other end by detector 
14, consisting of conductive elements 14a and 14b extending across shift 
register 12. Following element 14b and separated therefrom, conductive 
element 14a forms the other electrode, with element 14b of detector 14, 
across which separation or gap 15 the presence or absence of the cross-tie 
is detected magneto-resistively. 
With particular reference to FIG. 4 and FIGS. 7a through 7i, there are 
presented illustrations of a timing diagram and the resultant generation, 
propagation and detection of cross-tie, Bloch-line pairs in the cross-tie 
wall memory system of FIG. 1. 
The propagation of the cross-tie, Bloch-line pairs along data track 20 
under the influence of the drive fields provided by the coupling of the 
proper current drive signals to stripline 18 and stripline 22 is in the 
well-known two-step manner. This requires a store-transfer sequence of the 
propagation of the cross-tie and the Bloch-line within a memory cell--see 
the D. S. Lo, et al, U.S. Pat. No. 3,906,466. In this method of 
propagation, the cross-tie wall is initially formed along the geometric 
centerline of the data track by an in-plane field normal to the 
longitudinal axis of the data track. The circular serrated edges of the 
data track, when the in-plane field is removed, cause the magnetization M 
within the data track to collapse forming two anti-parallel magnetic 
domains on opposite sides of the cross-tie wall. 
The combination of the pattern of the circular, serrated edges of the data 
track and the triangular, serrated edges of the propagate drive lines, 
i.e., the wide-narrow edge pattern of striplines 18 and 22, establishes or 
structures the memory cells along the data track. To propagate the 
cross-tie, Bloch-line pairs in the well-known manner, each memory cell is 
required to include a store segment and a transfer segment, the order or 
names of which are purely arbitrary. These two segments are required due 
to the mechanism whereby cross-tie, Bloch-line pairs are propagated along 
a data track. 
Initially, a cross-tie, Bloch-line pair is established in a first store 
segment defined by the length of one serrated edge along the data track in 
which the cross-tie is oriented between the necks formed by the narrow 
width or portion of the data track, and the associated Bloch-line is 
oriented between the two adjacent narrow portions and on the downstream 
side of the associated cross-tie. Next, a drive field separates the 
Bloch-line from the associated cross-tie, "pushing" the Bloch-line 
downstream into the adjacent transfer segment leaving the associated 
cross-tie in its initial position. Next, a nucleate drive field generates 
a cross-tie, Bloch-line pair between the separated cross-tie and 
Bloch-line. Next, an annihilate drive field annihilates the cross-tie, 
Bloch-line pair that is resident in the store segment effectively 
transferring the initial cross-tie, Bloch-line pair from the store segment 
into the downstream transfer segment. This sequence is repeated so that 
after two consecutive push-nucleate-annihilate cycles the cross-tie, 
Bloch-line pair has been propagated from a store segment, through a 
transfer segment of the same memory cell and into the store segment of the 
next adjacent downstream memory cell. 
In the illustrated embodiment of FIG. 1, the narrow portions or necks of 
striplines 18 and 22 formed by their adjacent triangular serrated-edges 
and the narrow portions or necks of data track 20 formed by its adjacent 
overlapping circular-disk forming serrated-edges define the minimum energy 
states for the propagating cross-ties while the centers of the overlapping 
circular disks define the minimum energy states for the propagating 
Bloch-lines. 
With respect to FIGS. 5 and 6 there are illustrated the magnetization 
orientation within data track 20 and in particular with respect to a 
cross-tie 40, Bloch-line 42 pair and the orientation and effect of the 
drive fields generated by a drive current signal coupled to one of the 
striplines 18 or 22. In FIG. 5, data track 20 is shown as having a 
cross-tie wall 30 established along its longitudinal axis 32. Cross-tie 
wall 30 separates two anti-parallel magnetic domains in data track 20: a 
magnetic domain above cross-tie wall 30 that is oriented to the right as 
indicated by arrows 44; and a magnetic domain below cross-tie wall 30 that 
is oriented to the left as indicated by arrows 46. The magnetization 
within cross-tie wall 30 is indicated by the upwardly directed arrows 48 
while the magnetization about Bloch-line 42 is indicated by the circularly 
directed arrows 50 providing between cross-tie 40 and Bloch-line 42 the 
inverted Neel wall section as indicated by the downwardly directed arrows 
50 therebetween. 
As indicated in FIG. 5 the narrow portion 10c of generator 10, at the 
narrow portions or widths across striplines 18 and 22 and data track 20, 
defines the store segment of the initial memory cell along shift register 
12 while the next adjacent downstream narrow portion of data track 20 
defines the associated transfer segment. Also illustrated is that the gap 
15 of detector 14 is positioned or centered about the transfer segment of 
the last memory cell along shift register 12. FIG. 5 also illustrates that 
data track 20 is formed by a series of overlapping circular disks 52 that 
at the joins 53 of their overlapping circumferences form the positions 
along data track 20 of minimum energy states for the propagating 
cross-ties while the centers of the circular disks 52 form the positions 
along data track 20 of minimum energy states for the propagating 
Bloch-lines. This configuration of data track 20 is somewhat similar to 
the serrated-edged data track of the L. H. Johnson, et al, U.S. Pat. No. 
4,075,612. 
In U.S. Pat. No. 4,075,612 there is illustrated the serrated-edged magnetic 
data track of the L. J. Schwee, et al, Publication "Cross-tie Memory 
Simplified by the Use of Serrated Strips," AIP Conference Proceedings, No. 
29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975, 
published April 1976, pages 624-625. In the present invention conductive 
striplines 18 and 22 have similar serrated-edge conformation; however, the 
serrated-edge conformation in striplines 18 and 22 is used to provide a 
shaped magnetic field of a controllable but variable intensity along the 
stripline length, acting upon the data track for propagation as well as 
for generating the cross-tie wall in the data track, not just to generate 
the cross-tie wall in the data track upon the collapse of the externally 
applied field, as does the serrated data track of Schwee, et al. 
With respect to FIG. 6 there are illustrated the various magnetic field 
intensities and orientations in the plane of data track 20, due to a drive 
current signal being coupled to stripline 18. Note that in the illustrated 
embodiment striplines 18 and 22 have identically dimensioned conformations 
and are superposed along their longitudinal axes but are shifted one 
serrated-edge pattern along such longitudinal axes. As illustrated in 
FIGS. 1, 5 and 6, stripline 18 (and 22) is comprised of mirror-imaged 
serrated-edge patterns formed of triangular-shaped sections. Alternate 
triangular-shaped sections along stripline 18 are formed of triangles of a 
first lower height while the other alternate triangular-shaped sections 
along stripline 18 are formed of triangles of a second higher height. As 
the joins of the adjacent triangles are at the same distance from the 
centerline of stripline 18 and the apex of the different height triangles 
are at the same distance along the longitudinal axis of the stripline, the 
outside edges of the different height triangles are at different angles to 
the longitudinal axis of the stripline. These different angles and 
different heights, when stripline 18 is coupled by the appropriate drive 
current signal, generate drive fields, in the plane of data track 20, of 
different intensities and orientations. 
In the larger area spanned by the larger-width triangles of stripline 18 
there is generated a drive field H.sub.2 while in the smaller area spanned 
by the smaller-width triangles of stripline 18 there is generated a drive 
field H.sub.1 in which the relative field intensity of drive field H.sub.1 
is greater than that of drive field H.sub.2 ; 
EQU H.sub.1 &gt;H.sub.2. 
This difference in relative drive field intensities in the transfer segment 
and store segment of the memory cells along shift register 12 is essential 
to the operation of the cross-tie memory system of the present invention. 
By alternatively selectively coupling the appropriate drive current 
signals to stripline 18 and then to stripline 22 the relative field 
intensities in the store segment and the transfer segment of each memory 
cell along shift register 12 are made alternatively relatively more 
intense and less intense, i.e., stronger and weaker, as a function of the 
driving stripline 18 or 22. This permits the two-step 
push-nucleate-annihilate sequence of operation using the shaped drive 
fields provided by the shaped-edged striplines 18 and 22. 
With respect to FIG. 6, the relatively stronger Push drive field H.sub.1 
and the relatively weaker Push drive field H.sub.2 --field H.sub.1 being 
directed between cross-tie 40 and Bloch-line 42 and field H.sub.2 being 
directed outside of the cross-tie 40, Bloch-line 42 pair--provide the 
necessary relative field intensity variations along the cross-tie wall 30 
(and longitudinal axis 32) of data track 20 of shift register 12 to 
produce the necessary downstream propagation of the Bloch-line during the 
Push cycle to enable the following Nucleate and Annihilate cycles to 
provide the desired two-step propagation sequence of operation. 
With respect to the timing diagram of FIG. 4, assume that prior to time 
t.sub.0 the generator 10 of FIG. 1 is empty having no cross-tie, 
Bloch-line pair established therein. This is as indicated in FIG. 7a. Now, 
at a time t.sub.0, generator 48 couples a Generate current signal to 
generator 10, via conductive elements 10a, 10b, generating a cross-tie, 
Bloch-line pair in generator 10. This is as illustrated in FIG. 7b. Note 
that generator 48 selectively couples the Generate current signal to 
generator 10 for the generation vel non of a cross-tie, Bloch-line pair 
within generator 10. In the timing diagram of FIG. 4 the generation of the 
cross-tie, Bloch-line pair is indicative of the significant amplitude 
signal representative of the storage of a "1" in the cross-tie wall memory 
system of FIG. 1 while the insignificant signal is indicative of the 
storage of a "0" in the cross-tie wall memory system of FIG. 1. 
Next, at time t.sub.1 with the Generate current signal terminated, 
generator 60 couples a Push current signal to stripline 18 via conductive 
line 18a. The Push current signal flows down stripline 18 to ground. This 
Push current signal "pushes" the Bloch-line in the store segment of the 
memory cell in generator 10 into the next adjacent downstream transfer 
segment thereof--this is as illustrated in FIG. 7c. 
Next, at time t.sub.2, with the Push current signal terminated, generator 
61, via line 18a couples a Nucleate current signal to stripline 18. 
Nucleate current signal flows down stripline 18 to ground. This Nucleate 
current signal generates a new cross-tie, Bloch-line pair between the 
separated cross-tie, Bloch-line pair previously separated at time t.sub.1 
--this is as illustrated in FIG. 7d. 
Next, at time t.sub.3, with the Nucleate current signal terminated, 
generator 62 couples an Annihilate current signal to stripline 18 via line 
18a. The Annihilate current signal flows down stripline 18 to ground. This 
Annihilate current signal annihilates the cross-tie, Bloch-line pair 
resident in the store segment of the memory cell in generator 10--this is 
as illustrated in FIG. 7e. The cross-tie, Bloch-line pair generated in 
generator 10 in the store segment of the memory cell in generator 10 has 
now been propagated downstream into the associated transfer segment. Note 
that at this time a cross-tie, Bloch-line pair if previously, as at time 
t.sub.0, in the store segment immediately upstream of detector 14 would 
now be in the transfer segment of detector 14 as illustrated in FIG. 7f. 
Next, at time t.sub.4, with the Annihilate current signal terminated, 
generator 36 couples a read current signal across conductive elements 14a 
and 14b of detector 14. The resulting readout signal on line 68 as 
detected by sense amplifier 67 and as gated by the Gate Detect signal on 
line 66 is a function of the magneto-resistive effect of the presence or 
absence of a cross-tie in the transfer segment of the memory cell in gap 
15 of detector 14. As under the present assumed conditions, no cross-tie 
is present in the transfer section of the memory cell in detector 14 
between conductive elements 14a and 14b, sense amplifier 67 detects a 
relatively high magneto-resistive condition providing a relatively 
insignificant "0" output signal on line 68. 
Next, at time t.sub.5, with the read current signal from generator 36 
terminated, generator 63 couples a Push current signal to stripline 22 via 
conductive element 22a. The Push current signal flows down stripline 22 to 
ground. This Push current signal "pushes" the Bloch-line in the transfer 
segment of the memory cell in generator 10 into the store segment of the 
next downstream memory cell--this is as illustrated in FIG. 7g. 
Next, at time t.sub.6, with the Push current signal terminated, generator 
64, via line 22a couples a Nucleate current signal to stripline 22. The 
Nucleate current signal flows down stripline 22 to ground. This Nucleate 
current signal generates a new cross-tie, Bloch-line pair between the 
separated cross-tie, Bloch-line pair previously separated at time t.sub.5. 
This is as illustrated in FIG. 7h. 
Next, at time t.sub.7, with the Nucleate current signal terminated, 
generator 65 couples an Annihilate current signal to stripline 22 via line 
22a. The Annihilate current signal flows down stripline 22 to ground. This 
Annihilate current signal annihilates the cross-tie, Bloch-line pair 
presently resident in the transfer segment of the memory cell in detector 
14 leaving the now-propagated cross-tie, Bloch-line pair resident in the 
store segment of the next downstream memory cell from generator 10--this 
is as illustrated in FIG. 7i. 
This push/nucleate/annihilate sequence continues propagating the cross-tie, 
Bloch-line pairs generated by generator 10 through the shift register 12 
and into the detector 14--see FIG. 7f--from whence the information is read 
out in the manner as described above with particular reference to FIG. 4 
at time t.sub.4.