Dynamic magnetic information storage or retrieval – Head – Hall effect
Patent
1997-03-12
1999-06-08
Cao, Allen T.
Dynamic magnetic information storage or retrieval
Head
Hall effect
G11B 5127
Patent
active
059108690
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a planar magnetic head having a longitudinal multilayer magnetoresistance. It is used in magnetic recording. The head according to the invention can be read only and constitute a sensor, or can be of the read and write type.
PRIOR ART
The invention essentially applies to so-called horizontal, thin film heads, as is shown in the attached FIG. 1. FIG. 1 shows in section a head having an e.g. silicon semiconductor substrate 10, in which has been etched a recess 12. In said recess has e.g. been electrolytically formed a lower magnetic layer 14, which has been extended by two vertical contact pieces 16.sub.1, 16.sub.2. A conductor winding 18 surrounds the contact pieces and is embedded in an insulating layer 20. The magnetic circuit is completed by an upper magnetic layer subdivided into two pole pieces 22.sub.1, 22.sub.2 kept apart by an amagnetic spacer 24 forming a head gap.
A magnetoresistant element MR, made from a monolithic material (e.g. Fe--Ni) is placed beneath the amagnetic spacer 24. The head moves in front of a magnetic support 30, where the informations to be read or written are recorded. Such a head is described in FR-A-2 657 189.
The operation of said head is as follows. On writing, the current flowing in the winding 18 creates a magnetic field and consequently an induction in the magnetic circuit. The field lines open out around the spacer 24 and induce a magnetization in the support 30.
On reading, a magnetic information recorded on a track of the support 30 produces a magnetic reading field and consequently an induction in the magnetic circuit. This induction is partly closed again across the magnetoresistant element MR. This leads to a magnetization in said element, which will bring about a resistance variation therein. Not shown means make it possible to measure said resistance variation and thus supply again the information recorded on the support.
Although satisfactory in certain respects, such heads suffer from a disadvantage when the track width to be read is small. For a width of a few micrometers (e.g. 2 .mu.m), the length of the magnetoresisitance (counted in the transverse direction, i.e. perpendicular to the track) is a few microns (e.g. 3 .mu.m), which is of the same order of magnitude as the width of the magnetoresistance (2 to 3 .mu.m). The magnetoresistance has a substantially square shape with very small dimensions. It is then very difficult to obtain a resistance adapted to the detection circuit and which is generally approximately 50 ohms, which would require a much thinner layer in order to be usable.
JP-B-286 413 describes an identical device with only two substantially planar pole pieces separated by a head gap. A magnetoresistant element is placed just beneath the head gap, everything resting on a substrate. This magnetoresistant element operates in the transverse mode, as in the head described in the aforementioned FR-A-2 657 189.
Other magnetic heads are known, such as those described in EP 475 397. In such heads, there are auxiliary head gaps in the magnetic circuit, apart from the main head gap. The magnetoresistant element is not placed just below the main head gap, but instead extends from one auxiliary head gap to the other. This magnetoresistant element is also in contact with the pole pieces.
Therefore, the magnetoresistant element is very remote from the main head gap. Moreover, as said element is in contact with the pole pieces, it forms a true second magnetic circuit.
The present invent ion aims at obviating this disadvantage.
DESCRIPTION OF THE INVENTION
The invention retains the arrangement consisting of placing the magnetoresistant element just below the head gap. However, the invention proposes using on the one hand as the magnetoresistant element a magnetoresistance of a particular type, namely of the multilayer and no longer monolithic type and on the other hand making said magnetoresistance operate in the longitudinal mode and no longer in the transverse mode.
It is known that multilayer magnetore
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patent: 5301079 (1994-04-01), Cain et al.
patent: 5648884 (1997-07-01), Lazzari
IEEE Transactions on Magnetics 25(5), 3689-3691 (1089), Chapman, D.W., et al "A New Horizontal MR Head Structure".
Patent Abstracts of Japan 13(85) Feb. 27, 1989.
Patent Abstracts of Japan 16(117), Mar. 24, 1992.
Cao Allen T.
Commissariat a l''Energie Atomique
Meller Michael N.
Silmag
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