CA1137627A

CA1137627A - Magnetoresistive head

Info

Publication number: CA1137627A
Application number: CA000325893A
Authority: CA
Inventors: Wilhelmus J. Van Gestel; Lambertus Postma
Original assignee: Individual
Current assignee: Koninklijke Philips NV
Priority date: 1978-04-25
Filing date: 1979-04-19
Publication date: 1982-12-14
Also published as: JPS5749965B2; FR2424602A1; GB2019638A; FR2424602B1; JPS54143612A; DE2916283C2; GB2019638B; DE2916283A1

Abstract

ABSTRACT:
A magnetic head having an elongate magneto-resistive element bearing a pattern of equipotential strips extending obliquely to its longitudinal axis for adjusting a suitable workpoint. With its edge extending parallel to the longitudinal axis, the ele-ment bears on components of magnetically permeable material one of which, in operation, is in direct flux coupling with a magnetic recording medium and the other of which is in flux coupling with the recording medium via a further element of magnetically permeable mater-ial, in particular ferrite.

Description

~13~627 The invention relates to a magnetic head for detecting information-representing magnetic fields on a magnetic recording medium movable relatively with res-pect to the magnetic head, the head comprising an elongate magnetoresistive element which at two oppos-itely located ends comprises contacts for the connection to a source of measuring current, which element shows such a magnetic anisotropy that the easy direction of magnetisation is parallel to the longitudinal axis of the element and which comprises at least one electric-ally readily conductive strip which is provided obliquely on a surface of the element at an angle of at least 30 and at most 60 with the longitudinal axis of the ele-ment.
The invention relates to magnetic reading heads destined in particular, but not exclusively, for detecting magnetic fields in magnetic recording media, for example, magnetic tapes or disks.
A magnetic head of the kind mentioned in the preamble is known from Philips Technical Review 37, pp. 42 - 50, 1977, No. 2/3. In the known head, one or more oblique conductive strips are provided on one of the surfaces of the magnetoresistive element, prefer-ably at an angle of 45 with the longitudinal axis of the element. These strips serve as equipotential strips so that the direction of the current in the element which is at right angles to the equipotential strips encloses an angle with the easy direction of magnetisation, pre-ferably an angle of 45. In this manner the operation of the known magnetic head is linearized: the relative resistance variation of the magnetoresistive element ( ~RR) as a function of the transversal external magnetic field (H), which is presented by a magnetic recording medium to be read is then represented as a matter of fact by a substantially linear odd function.
Although -the known head has the advantage of a simple linearisation, it has the disadvantage, however, .
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that a certain deviation from the linear characteristic occurs as a result of the condition that near the edges of the magnetoresistive element extending in the longitudinal direction the angle at which the current flows with res-pect to the longitudinal axis varies until the anglebecomes 0 at the boundary of the element. The result of this is that in fact the playback characteristic of the known magnetic head is not represented by an odd function but by the sum of an odd function and an even function.
It is the object of the invention to provide a magnetic head of the kind mentioned in the preamble which does not exhibit the above-mentioned disadvantage.
For that purpose the magnetic head according to the invention is characterized in that it comprises two components of a magnetically permeable material located in line with each other, between which components a gap is present, the magnetoresistive element bridging said gap, the facing ends of the components of magnetically perme-able material covering the edge zone of the magnetoresis-tive element extending parallel to the longitudinal axis, the end of a first of the components of magnetically permeable material remote from the magnetoresistive ele-ment being destined to cooperate with a magentic recording medium~
In this manner it is ensured that the edge zones of the magnetoresistive element extending parallel to the longitudinal axis are shortcircuited magnetically by the magnetically permeable components. Since now substant-ially no magnetic flux originating from the recording medium flows through the edge zones, the contribution of their resistance variation to the overall resistance variations of the element is very small and hence also the non-linearity caused by the edge zones so that the play-back characteristic has a much more linear variation than that of the known magnetic head.
A geometric arrangement of a magnetoresistive element as a bridge of a gap between two magnetically permeable elements is known per se from United States 0~`
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Patent Specification ~o. 3,921f217. However, the magneto-resistive e]ement disclosed in this Patent Specification is not of the kind to which the invention relates, but of a magnetically biased type in which it is necessary to apply a permanent magnetic field for the linearisation of the playback characteristic of the magnetoresistive ele-ment so as to displace the work-point to a linear area of the curve resistance/magnetic field. However, in a mag-netic field having such a magnetoresistive element the problem for which the invention provides a solution does not occur.
Although the distortion of a current-biased magnetoresistive element with magnetically shortcircuited edge zones according to the invention is already consider-ably less than of a similar element the edge zones of which are not magnetically shortcircuited, some distortion may nevertheless remain. This appears to be due to the condition that the magnetoresistive head according to the invention is supersensitive to long-wavelength signals.
This disadvantage is avoided by a preferred embodiment of the magnetoresistive head according to the invention which is characterized in that the magnetoresis-tive head furthermore comprises a comparatively thick ele-ment of magnetically permeable material which is situated on one side of the element and which is coupled ma~netic-ally to a second of the components of magnetically perme-able material.
As a result of the coupling of such a magnetic element to the flux conductor remote from the recording medium, the magnetic flux which has been "sucked up" by the flux conductor placed near the recording medium can be returned to the recording mediumf which increases the sensitivity of the element to short-wavelength signals.
As a result of this, the overall sensitivity can be reduced, so that the element is then no longer supers~nsi-tive to long wavelengths.
Dependent on what kind of material is chosen for the comparatively thick element of magnetically permeable , .
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material, a good result is not always achieved. When com-paratively small measuring currents (order 10 mA) are used which have the advantage that the (temperature) noise then is smaller than in the case in which comparatively large measuring currents are used, it has been found that the choice of alloys of the nickel-iron type for the compara-tively thick element results in the fact that the gain obtained as regards distortion is partially lost. This is ascribed to the occurrence of one or a few localized domain walls in an element which is manufactured from nickel-iron.
These domain walls can influence the magnetisation of the magnetoresistive element in such a manner that it is no longer related to the direction of the (weak) measuring current.
According to a preferred embodiment of the magnetic head of the invention, the comparatively thick element of magnetically permeable material consists of ferrite. So many arbitrarily orlented domain walls are present in an element of ferrite that they have met no influence on the magnetoresistive element so that when using an element of ferrite, a small measuring current is sufficient to maintain the direction of the magnetisation in a desired direction~
The edge areas of the magnetoresistive element ~5 covered by the ends of the components of magnetically permeable material should preferably correspond at least substantially to the areas of the element in which, when a measuring current flows through it, the direction of the current lines is not uniform.
For that purpose, the further preferred embodi-ment of the magnetic head of the invention is character-ized in that the covering zones have a substantially con-stant width throughout the length of the element, said width being at least equal to _ cos (~ ), where ~ is the angle which the conductive strips enclose with the longi-tudinal direction of the magnetoresistive element, and _ is the distance between the strips mutually.
Herewith it is achieved that the edge zones are ~3~6~7 covered entirely, which maximally reduces their non-linear contribution to the resistance variation.
Still a further preferred embodiment of the mag-netic head of the invention is characterized in that the thickness of the magnetically permeable component which is destined to cooperate with the recording medium is larger than that of the magnetoresistive element.
This makes it possible, with magnetic losses remaining the same, to enlarge the height of the said com-ponent so that detrition due to the frictional contactwith the recording medium has a smaller influence on the behaviour of the magnetic head.
The magnetic head of the invention also obviates a further disadvantage of the known magnetic head. In the known magnetic head, the covering of the magnetoresistive element with the conductive pattern of strips (in areas where conductive material is present on the magnetoresis-tive strip, the underlying magnetoresistive material is shortcircuited) has for its result that the track width is not exactly defined. In the magnetic head of the inven-tion, the first of the magnetically permeable components "sucks up" the flux of the recording medium and couples it to the magnetoresistive element, so that the wid-th of the relevant component exactly defines the track width.
The invention will be described in greater detail, by way of example, with reference to the accom-panying drawing.
Fig. 1 is a cross-sectional view, and Fig. 2 is a longitudinal sectional view of a magnetic head having a magnetoresistive element which is provided with oblique equipotential strips and elements conducting magnetic flux.
Fig. 3 shows a part of Fig. 2 in greater detail.
Fig. 4 shows diagrammatically the variation of the current lines at the edge of a magnetoresistive ele-ment on which oblique equipotential strips have been pro-vided.
Fig. 1 shows a magnetic head l which serves to ~3~

detect magnetic fields originating from a magnetic record-ing medium 2 moving past the head 1 in the direction of the arrow 14. The detection of said fields occurs by measuring the relative resistance variation of a magneto resistive element 3 to which magnetic flux is supplied via a magnetically permeable component 6 (so-called flux con-ductor) on (or below) which it engages with one edge, while the magnetic flux is returned to the recording med-ium vla a magnetically permeable component 7 on which it engages with the other edge, and a magnetic element 4 which is coupled thereto and preferably consists of ferrite.
IE desired, the magnetic head according to the invention may comprise a ferrite shield 5 which together with the element 4 ensures a complete screening of the magnetoresistive element 3 from :Long-wave information.
The components 6 and 7 are of a high magnetic permeability material, for example, a nickel-:iron alloy, and are accom-modated so that the component 6 ~aces the recording medium 2 and the component 7 is coupled to the magnetic shields 4 and 5.
As shown in Fig. 2, the components 6 and 7 may be longer than the magnetoresistive element 3 and they cover edge zones 8 and 9 on one side thereof, while on the other side contacts 10 and 11 which are connected to a source of measuring current 15, and electrically readily conductive strips 12 which are at an angle between 30 and 60, preferably 45, with the longitudinal axis of the element 3, are provided. These strips force the current to flow between the strips obliquely with respect to the longitudinal axis, so that the element 3 as it were has an electric bias. The current i in the strips flows in the longitudinal direction of the strips and as a result oE
this produces in the magnetoresistive material a small magnetic field which is capable of maintaining the magnet-isation M in the desired direction.
The covering zones perferably extend entirely over the regions of the magnetoresistive element 3 in ~' ~L~L3762~

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which the direction of the current lines is not uniform.
Fig. 3 shows in more detail the width _ of one of said regions, in which r can be derived in the following man-ner:
When, for example, d is the intermediate space between two conductive equipotential strips and ~ is the slope of these same strips with respect to the longitud-inal direction of the magnetoresistive element, a simple trigonometric calculation gives:
r = d.cos (~ ).
The covering width should be at least equally large as the edge zone of the magnetoresistive element where the current lines do not extend uniformly, as is shown in Fig. 4. The current lines are tracks which extend at right angles to the equipotential strips but -the discontinuity at the edge interferes with the uniform variation of these lines over a given distance. This dis-tance is obtained by projecting a point A which forms the base of a first equipotential strip, on an adjacent equi-potential strip, which gives a point H.
In the zone which lies between a line through ~Iand the edge the current lines show a varying angle with the longitudinal axis of the element. (The easy direction of magnetisation of the magnetoresistive element is par-allel to the longitudinal axis).
In the magnetic head of the invention the edgezones are made inactive as it were, so that it is possible to very closely approach the ideal response characteristic.
Additional advantages resulting from the use of the magnetic flux conductors 6 and 7 are that the magneto-resistive element does not experience any mechanical detrition because it is not placed in direct contact with the moving magnetic recording medium, while temperature fluctuations influencing the resistance and hence causing noise occur to a smaller extent.
Moreover, the width of the track which is read is better defined as a result of the use of the magnetic flux conductor 6 having a width equal to the track width.

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The thickness of 6 is considerably larger than that of 3.
The magnet.ic head of the invention is well suit-able for a construction in thin layers via suitable masks, which results in the following multilayer structure which includes a ferrite substrate or a substrate carrying a ferrite top layer, on which are provided successively:
- a first insulation layer of quartz, - a magnetoresistive layer - one or more strips of electrically conduct-ive material extending obliquely to a side of the magnetoresistive layer - a second insulation layer of quartz - a layer of nickel-iron in two parts separated by an intermediate space which e~poses the central portion of the magnetoresistive layer, one of the two parts contacting the ferrite via a through hole in the first insulation layer.
It will be apparent that many variations are possible to those skilled in the art without departing from the scope of the invention, for example the sequence of ma~netoresistive layer with oblique strips and nickel-iron layer may be reversed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A magnetic head for detecting information-representing magnetic fields on a magnetic recording medium movable relatively with respect to the magnetic head, the head comprising an elongate magnetoresistive element which is provided on two oppositely located ends with contacts for the connection to a source of measuring current, which element has such a magnetic anisotropy that the easy direction of magnetisation is parallel to the longitudinal axis of the element, and comprising at least one electrically readily conductive strip which is provided obliquely on a surface of the element at an angle of at least 30° and at most 60°
with the longitudinal axis of the element, character-ized in that the magnetic head comprises two components of magnetically permeable material located in line with each other, between which components a gap is present, the magnetoresistive element spanning said gap, the facing ends of the components of magnetically permeable material covering the edge zones of the magnetoresistive element extending parallel to the longitudinal axis, one end of the first one of the components of magnetic-ally permeable material. remote from the magnetoresistive element being destined to cooperate with a magnetic recording medium.

2. A magnetic head as claimed in Claim l, charac-terized in that it further includes a comparatively thick element of magnetically permeable material which is posi-tioned in substantially parallel relationship to the two components of magnetically permeable material and is coupled magnetically to the second one of the components of magnetically permeable material.

3. A magnetic head as claimed in Claim 2, charac-terized in that the comparatively thick element of magnet-ically permeable material consists of ferrite.

4. A magnetic head as claimed in Claim 3, charac-terized in that it is in the form of a multilayer structure which includes a ferrite substrate or a substrate carrying a top-layer of ferrite on which are provided successively;
- a first insulation layer of quartz - a magnetoresistive layer - one or more strips of electrically conductive material extending obliquely to a side of the magnetoresistive layer - a second insulation layer of quartz - a layer of nickel-iron in two parts separated by an intermediate space which exposes the central portion of the magnetoresistive layer, one of the two parts contacting the ferrite via a through hole in the first insulation layer.

5. A magnetic head as claimed in Claim 1, charac-terized in that the thickness of the first one of the com-ponents of magnetically permeable material is larger than that of the magnetoresistive element.

6. A magnetic head as claimed in Claim 1, 2 or 5, characterized in that the covering zones have a width which is substantially constant throughout the length of the ele-ment, said width being at least equal to d.cos (?), where ? is the angle which the conductive strips enclose with the longitudinal direction of the magnetoresistive element and d is the distance between the strips mutually.