GB1578454A - Magneto-resistive magnetic domain detectors - Google Patents

Magneto-resistive magnetic domain detectors Download PDF

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Publication number
GB1578454A
GB1578454A GB1192977A GB1192977A GB1578454A GB 1578454 A GB1578454 A GB 1578454A GB 1192977 A GB1192977 A GB 1192977A GB 1192977 A GB1192977 A GB 1192977A GB 1578454 A GB1578454 A GB 1578454A
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United Kingdom
Prior art keywords
detector
domain
signal
strip
max
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GB1192977A
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Siemens AG
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Siemens AG
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Publication of GB1578454A publication Critical patent/GB1578454A/en
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    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11CSTATIC STORES
    • G11C19/00Digital stores in which the information is moved stepwise, e.g. shift registers
    • G11C19/02Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
    • G11C19/08Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
    • G11C19/0866Detecting magnetic domains

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  • Hall/Mr Elements (AREA)
  • Magnetic Heads (AREA)
  • Measuring Magnetic Variables (AREA)

Description

(54) IMPROVEMENTS IN OR RELATING TO MAGNETO RESISTIVE MAGNETIC DOMAIN DETECTORS (71) We, SIEMENS AKTIEN GESELLSCHAFT, a German Company of Berlin and Munich, German Federal Republic, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to magneto-resistive magnetic domain detectors for reading information from a cylindrical magnetic domain transfer store, and is an improvement in or modification of the invention described and claimed in our United Kingdom Patent Specification No.
1,522,694.
When an external magnetic supporting or holding field of appropriate direction and magnitude is applied to a ferromagnetic, monocrystalline storage layer having uniaxial anisotropy perpendicular to the layer plane, the resultant cylindrical magnetic domain may have a direction opposite to that of the environment and any magnetic holding field, as is described in our Patent Specification No. 1,522,694, hereinafter referred to as the parent specification. As explained in the parent Specification, domains may be moved very rapidly, and are therefore suitable for the production of shift-registers that can be interconnected to form serial stores, for example To operate the store it is necessary for the presence or absence of a cylindrical magnetic domain at a specific point inside the store to be indicated to a detector which converts the magnetic field generated by a cylindrical magnetic domain at the detector location into an electrical signal. Detectors are known which utilise a great variety of physical effects, such as the Faraday effect in magneto-optical reading, the Hall effect, or the change in resistance of ferromagnetic materials in a magnetic field.
Generally speaking the magneto-resistive magnetic domain detector has prevailed, i.e.
detectors utilising the last-named effect, because of their being technologically simple in construction. In this the detector element is constituted by a layer forming a detector strip, in particular one running at right angles to the cylindrical-domain track, which is made of a preferably magnetostriction-free Ni-Fe alloy that is applied on the storage plane, by vapourdeposition for instance.
If the detector strip is not exposed to any magnetic stray field from a cylindrical domain, then at the instant of read-out the magnetisation MD of the detector strip due to the rotating field used to drive the domains runs parallel to the direction of a current iD flowing through the detector when the store is in operation. When a magnetic cylindrical domain passes the detector strip, the stray field of the former turns the magnetisation through an angle 8 out of the current path. This alters the resistance R0 of the detector element by an amount AR. At the detector strip this change in resistance produces a voltage drop.
bU=iD . AR (0); and this can be processed as a read-out signal.
Thus for a given detector current iDs the greater the change in resistance AR of the detector element caused by the cylindrical domain, the higher the read-out signal. The value AR is a function of the change in the specific magneto-resistance of the detector material, which initially increases linearly with the increase in strength of the magnetic field, and then tends towards a saturation value. For the detector strip to be completely saturated by a stray field HD of the cylindrical domain, the strength of this stray field must be greater than the sum of the anisotropic field strength Hk of the detector material, which is normally constituted by a ferro-magnetic Ni-Fe alloy, together with the de-magnetised field Hent of the detector strip.
An increase in the change in resistance can be brought about by making the detector strip as long as possible, but this is only justifiable if the entire length of the detector strip is affected by the stray field of the cylindrical domain, for which reason the cylindrial domain may be extended in stages to the given length of the detector strip, i.e.
it may be elongated into a long strip domain, by a so-called domain stretcher, generally a suitable layer-type pattern formed by a non magneto-strictive ferro-magnetic nickel iron alloy, which is applied to cause a significant extension of the stray field of the cylindrical domain that is to be detected.
Our United Kingdom Patent Specification No. 1,522,694 describes and claims a magneto-resistive domain detector for reading out information stored in a cylindrical magnetic domain transfer store, comprising a layer type detector strip extending generally perpendicular to the propagation path of the cylindrical domains, said strip being made of magneto-resistive material and a domain stretcher electrically decoupled from said detector strip.
Figure 1 of the drawings forming part of this present specification illustrates a known pattern for a domain stretcher with a detector strip 1 sitting between chevrons 2 disposed symmetrically with respect to the detector strip, each of the chevron banks 2 being formed with the same number of chevron elements 3 each exhibiting a 900 bend, and each overlapping the detector strip in zones 4. As is explained in the parent specification, these earlier constructions were such that the chevrons and the detector strip were in electrical contact at the overlapping zones. Further banks of chevrons disposed parallel to the chevron banks shown are located in the direction of the cylindrical domain track, which is not illustrated but merely indicated by an arrow A.
With such known magneto-resistive magnetic domain detectors the saturation value for the relative change in magnetoresistance of the detector element lies below the value for the detector material, so that the magneto-resistive properties of the detector material are only partially exploited for the signal detection and consequently only read-out signals of relatively limited magnitude can be obtained.
An object of the parent British patent application was to provide a magnetoresistive magnetic domain detector of a construction capable of providing improved read-out signals, in comparison with the then known magneto-resistive domain detectors, the change in resistance of the detector strip that is brought about the stray field of the cylindrical domains being increased.
The proposal in the parent specification is based on the knowledge that the aforementioned disadvantage is caused by the magnetic elements of the domain stretcher overlapping the detector strip, and as stated above, the parent specification proposes a construction in which the detector strip is electrically decoupled from the domain stretcher, for example by arranging that each extremity of the domain stretchers facing the detector strip is disposed at a distance from the detector strip, i.e. a space is left between the boundary line of each element near to the detector strip. If part of the domain stretcher overlaps the detector strip, electrical decoupling can be effected by means of an intermediate insulating coating, e.g. an SiO2 coating, for example.
With a domain detector formed in this way the read-out signal occurs when the magnetisation MD of the detector material lies parallel to the path of the detector current iD, since Mn changes in direction in synchronisation with the rotary field used to move the cylindrical domains.
One object of the present invention is to provide a further improved construction of domain detector that has a still higher signal sensitivity and a better signal to noise ratio.
The invention consists in a magnetoresistive domain detector as claimed in our United Kingdom Patent Specification No.
1,522,694, in which the detector strip has a longitudinal median axis, and said domain stretcher forms part of an arrangement of mutually similar chevron banks, one along each side of said detector strip, said arrangement having an axis of symmetry that lies parallel to but off-set from said median axis.
Since the magneto-resistance is a function of cos2 0, where fl is the angle between the magnetisation Mn and the detector current i,, the highest signal sensitivity level is obtained when the paths of magnetisation and detector current form an angle of 45".
This condition, which is essential if optimum signal sensitivity is to be obtained, is satisfied by the asymmetrical arrangement of domain stretcher and detector strip proposed in accordance with the invention.
Advantageously, the domain detector has at least one of the two chevron banks alongside the detector strip partly overlapping the strip but electrically decoupled therefrom by an intermediate insulating layer.
The invention will now be described with reference to the drawings, in which: Figure 1 schematically illustrates a known domain detector, as already discussed; Figure 2 schematically illustrates one exemplary embodiment of a domain detector in accordance with the invention; Figure 3 is a first explanatory graph of the domain detector constructed in accordance with the invention; and Figure 4 is a second explanatory graph.
In the exemplary embodiment shown in Figure 2, an axis of symmetry of an arrangement 5 of chevron banks 2 is offset parallel to a detector strip 1 that has a longitudinal median axis, and that bank 2 that is shown on the left hand side of the drawing partly overlaps the detector strip 1, but its ends are electrically decoupled from the detector strip by means of an intermediate insulating layer coating (not shown) e.g. an SiO2 coating.
Figure 3 graphically illustrates the magnitude variations between a readout signal Usiq from a known detector as described with reference to Figure 1 and of the Figure 2 embodiment of the invention, plotted against detector current i,, for detectors 285 microns long and 6.5 microns wide. Curve 1' relates to the known arrangement of Figure 1 and curve 2' the readout signal for the embodiment of the invention shown in Figure 2. The respective signal sensitivities for Figures 1 and 2 are 1.3 mV/mA and 2 mV/mA i.e. a 50% improvement in signal sensitivity is obtained by displacing the axis of symmetry of the domain stretcher relative to the longitudinal median axis of the detector strip.
In addition to the absolute level of the readout signal, the signal-to-noise ratio is a particularly important factor for satisfactory recognition between the binary "1" state at which a cylindrical domain passes the detector, and the binary "0" state at which no domain is passing the domain detector.
When the readout signal is processed electronically, this is only evaluated for a fraction of the time between two successive signals. Thus a distinction must be made between the signal-noise ratio (S/N)max related to the maximum noise signal, and the signal-noise ratio (S/N)wjndoW which relates to the noise signal occurring in the time defined as the evaluation window. In the case of the known symmetrical domain detector shown in Figure 1 (S/N)maX is equal to (S/N)WjndoW since both the readout signal and maximum noise signal occur at approximately the same time within a readout cycle. The asymmetrical arrangement of a domain detector constructed in accordance with the invention such as that shown in Figure 2, has the result that the readout signal is positively displaced on the time axis within a readout cycle whilst the position of the maximum noise signal is unaffected, so in this case (S/N)max is less than (S/N)window The graph shown in Figure 4 plots the magnitudes (S/N)max and (S/N)w,ndoW for the domain detectors shown in Figures 1 and 2 respectively as functions of the detector current i,, and (S/N)max is equal to (S/N)windoW for the known domain detector shown in Figure 1 (see curve 1"). The socalled evaluation window chosen in this case was a time interval of a value equal, in relation to the signal maximum, to about 20% of a readout cycle. It can be seen, as expected, that in the case of the exemplary domain detector embodiment constructed in accordance with the invention, as shown in Figure 2 (S/N)wjndoW (see curve 2") is considerably greater than (S/N)max (see curve 2"'). The difference in (S/N)max of the two domain detectors is caused by the different signal sensitivity. For a typical detector current for store operation of 3 mA the improvement in the value of (S/N)window that can be obtained with a domain detector constructed as shown in Figure 2 is about 400%.
WHAT WE CLAIM IS: 1. A magneto-resistive domain detector as claimed in our United Kingdom Patent Specification No. 1,522,694, in which the detector strip has a longitudinal median axis, and said domain stretcher forms part of an arrangement of mutually similar chevron banks, one along each side of said detector strip, said arrangement having an axis of symmetry parallel to but off-set from said median axis.
2. A domain detector as claimed in Claim 1, in which at least one of the two chevron banks alongside the detector strip partly overlaps said strip but is electrically decoupled therefrom by an intermediate insulating layer.
3. A magneto-resistive domain detector substantially as described with reference to Figure 2 of the drawings forming part of this specification.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. Figure 3 is a first explanatory graph of the domain detector constructed in accordance with the invention; and Figure 4 is a second explanatory graph. In the exemplary embodiment shown in Figure 2, an axis of symmetry of an arrangement 5 of chevron banks 2 is offset parallel to a detector strip 1 that has a longitudinal median axis, and that bank 2 that is shown on the left hand side of the drawing partly overlaps the detector strip 1, but its ends are electrically decoupled from the detector strip by means of an intermediate insulating layer coating (not shown) e.g. an SiO2 coating. Figure 3 graphically illustrates the magnitude variations between a readout signal Usiq from a known detector as described with reference to Figure 1 and of the Figure 2 embodiment of the invention, plotted against detector current i,, for detectors 285 microns long and 6.5 microns wide. Curve 1' relates to the known arrangement of Figure 1 and curve 2' the readout signal for the embodiment of the invention shown in Figure 2. The respective signal sensitivities for Figures 1 and 2 are 1.3 mV/mA and 2 mV/mA i.e. a 50% improvement in signal sensitivity is obtained by displacing the axis of symmetry of the domain stretcher relative to the longitudinal median axis of the detector strip. In addition to the absolute level of the readout signal, the signal-to-noise ratio is a particularly important factor for satisfactory recognition between the binary "1" state at which a cylindrical domain passes the detector, and the binary "0" state at which no domain is passing the domain detector. When the readout signal is processed electronically, this is only evaluated for a fraction of the time between two successive signals. Thus a distinction must be made between the signal-noise ratio (S/N)max related to the maximum noise signal, and the signal-noise ratio (S/N)wjndoW which relates to the noise signal occurring in the time defined as the evaluation window. In the case of the known symmetrical domain detector shown in Figure 1 (S/N)maX is equal to (S/N)WjndoW since both the readout signal and maximum noise signal occur at approximately the same time within a readout cycle. The asymmetrical arrangement of a domain detector constructed in accordance with the invention such as that shown in Figure 2, has the result that the readout signal is positively displaced on the time axis within a readout cycle whilst the position of the maximum noise signal is unaffected, so in this case (S/N)max is less than (S/N)window The graph shown in Figure 4 plots the magnitudes (S/N)max and (S/N)w,ndoW for the domain detectors shown in Figures 1 and 2 respectively as functions of the detector current i,, and (S/N)max is equal to (S/N)windoW for the known domain detector shown in Figure 1 (see curve 1"). The socalled evaluation window chosen in this case was a time interval of a value equal, in relation to the signal maximum, to about 20% of a readout cycle. It can be seen, as expected, that in the case of the exemplary domain detector embodiment constructed in accordance with the invention, as shown in Figure 2 (S/N)wjndoW (see curve 2") is considerably greater than (S/N)max (see curve 2"'). The difference in (S/N)max of the two domain detectors is caused by the different signal sensitivity. For a typical detector current for store operation of 3 mA the improvement in the value of (S/N)window that can be obtained with a domain detector constructed as shown in Figure 2 is about 400%. WHAT WE CLAIM IS:
1. A magneto-resistive domain detector as claimed in our United Kingdom Patent Specification No. 1,522,694, in which the detector strip has a longitudinal median axis, and said domain stretcher forms part of an arrangement of mutually similar chevron banks, one along each side of said detector strip, said arrangement having an axis of symmetry parallel to but off-set from said median axis.
2. A domain detector as claimed in Claim 1, in which at least one of the two chevron banks alongside the detector strip partly overlaps said strip but is electrically decoupled therefrom by an intermediate insulating layer.
3. A magneto-resistive domain detector substantially as described with reference to Figure 2 of the drawings forming part of this specification.
GB1192977A 1976-03-22 1977-03-22 Magneto-resistive magnetic domain detectors Expired GB1578454A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19762612090 DE2612090C3 (en) 1976-03-22 1976-03-22 Magnetoresistive domain detector for reading the stored information of a cylinder domain transport memory

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GB1578454A true GB1578454A (en) 1980-11-05

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JP (1) JPS5947378B2 (en)
DE (1) DE2612090C3 (en)
FR (1) FR2345785A1 (en)
GB (1) GB1578454A (en)
NL (1) NL7703044A (en)

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* Cited by examiner, † Cited by third party
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US4432069A (en) * 1981-01-29 1984-02-14 Intel Corporation Multiplexed magnetic bubble detectors

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA959969A (en) * 1972-09-20 1974-12-24 Jeffrey L. Williams Magnetic bubble domain detection device
DE2440997C2 (en) * 1974-08-27 1981-06-25 Siemens AG, 1000 Berlin und 8000 München Magnetoresistive domain detector for reading the stored information of a cylinder domain transport memory

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FR2345785A1 (en) 1977-10-21
JPS5947378B2 (en) 1984-11-19
DE2612090A1 (en) 1977-10-06
JPS52115130A (en) 1977-09-27
NL7703044A (en) 1977-09-26
DE2612090C3 (en) 1981-11-26
DE2612090B2 (en) 1979-10-18
FR2345785B1 (en) 1982-03-05

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