Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
I'~IN. 7ll69
KO~ K~S/
5-2-1975
lOSSlSS
"~lagnetoresistive magnetic head".
T~le invention relates to a magnetic head for
detecting information-representing magnetic fields on a
magnetic recording medium and comprising an elongate
magnètoresistive element of a magneticàlly anisotropic
material which at its ends has contacts for the connection
to a current or voltage source.
Such a magnetic head is known, for example,
from the United States Patent Specification 3,493,694.
The operation of said so-called magneto-
resistive head is based on the use of a strip-shaped
element of a ferro-magnetic, metallic magnetically
anisotropic material, for example Ni-Fe, which is
arranged with one of its edges in the immediate proximity
of, or in contact with, a magnetic recording medium. The
field of the recording medium produces variations in
the magnetisation of the element and modulates the
resistance thereof v the magnetoresistance effect.
This means that when the recording medium passes the
head, the information-representing magnetic fields
present on the medium rotate the spin system of the
magnetoresistive element so that the resistance varies.
In this manner the o~tput signal of an external circuit
which is connected to the element assumes the form of
current or voltage fluctuations which represent the
information stored in the recording medium.
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P]IN. 7469
5-2-1975
1055155
Since the variation of the resistance of a
magnetoresistive element under the influence of a
magnetic field is quadratic, it is usual to optimize
the operation in the case of analog recordin~ by
linearizing th~ head.
~or that purpose, according to the already
mentioned United States Patent Specification, a
transverse magnetic bias field is applied through
e~ternal means to an elongate element the easy axis of
magnetization Or which coincides with the longitudinal
direction of the element. Under the influence of said
field~ the direction of magnetisation of the element
which without a field coincides with the easy axis of
magnetization is rotated through a certain angle. The
strength of the bias field should be such that the
direction of magnetization encloses an angle of 45 with
the longitudinal direction of the element which is
also the direction of current passage through the
element. The drawback of the use of the transverse
20 , magnetic bias field is that the possibility exists that
- the information on the recording medium is erased by it,
while it is difficult to adjust the strength~of the
field at the correct value.
It is known from the published German Patent
Application 2, 121,443 to linearize the magnetoresistive
head by means of internal means in contrast with the
above described external biassing technique. ~or this
~ 3 --
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purpose, the easy axis of magnetization is given a fixedly adjusted
angle relative to the longitudinal direction of the element (the
direction of current passage) by means of a tempering process or via
the magnetostrictice properties. Since the characteristic of each
magnetoresistive element is different, it is very difficult to obtain the
same results in all the cases in the described manner.
It is the object of the invention to provide a magnetic head of
the present type which does not exhibit the above drawbacks.
In accordance with this invention there is provided a magnetic
head for detecting information representing magnetic fields on a magnetic
recording medium and comprising an elongate magneto-resistive element of
a magnetically anisotropic material which at its ends has contacts for the
connection to a current or voltage source, the easy axis of magnetization
thereof coinciding with the longitudinal axis of the element and said
head further including means to force the current to travel at an angle
of minimum 15 and maximum 75 with the longitudinal axis of said element,
said means including at least one readily conductive equipotential strip
intermediate said contacts in oblique relationship to said axis.
The advantages of the magnetic head according to the invention ~-
are evident.
1. In order to realise the desired angle between the direction of
current and the direction of magnetisation, no transverse magnetic bias
field is necessary. Hence there are no undesired erasing effects.
2. m e angle between the direction of current and the easy axis
of magnetization (the direction of magnetization in the rest condition)
can be fixed with
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I'lIN. 7ll G'3
5-2-1975
1055155:
with external means.
~lthough it is possible to enforce the desired
current direction by provi,ding slots in the element
whicll extend at an angle relative to the longitudinal
direction and alternatèly debouch in ~he upper side and
in thè lower side, a preferred embodiment of the
magnetic head according to the invention is characterized
in that at least one readily conducting equipotential
strip is provided between the contacts transversely
across at least one side face of the magnetoresistive
element at an angle of minimum 15 and maximum 75 with
the longitudinal direction thereof. The advantage is
that when the element wears off during use, the good
operation is not lost, which would be the case indeed in
a construction wi~h slots, while the magnetic material
itself need not be changed either. Moreover the
equipote~tial strip (however, the el~ment preferably
has a number of mutually parallel equipotential strips)
can be provided via the same mask with which the current
contacts are provided on the element. ln a construction
with slots on the contrary an extra etching step is
necessary.
A further preferred embodiment of thé
magnetic head according to the invention is characterized
in that magnetic means are; present to generate a magnetic
auxi~iary field having a direction which coincides with
the longitudinal direction of the magnetoresistive
.
~'~IN. 7~1 fi
5-2-1~75
1055155
element. It proves possible to obtain an optimum
linearisation with such a longitudinal auxiliary field
which preferably has a strength wllich is of the order
of magnitude of the coercive strength of the material of
the magnetoresistive element. The str~ength of said
field, however, is so small that no danger of erasing of
the recording medium exists.
The invention ~ill be described in greater
detail, by way of example, with reference to the drawing.
~ig. 1 is a simplified perspective view of a
magnetic head according to the invention,
~ig. 2 is a graph showing the resistance
variation~R/R of the magnetoresistive element of the
head shown in ~ig. 1 as a function of a transve~se
external field H.
~ig. 3 is a graph showing the resistance
variation~R/R of a conventional magnetoresistive element.
~ig. 1 shows a magnetoresistive head 1 which
is used in reading the information contents of a magnetic
recording medium 2. The head 1 comprises a magneto- -
resistive element 3 which is oonnected to an external
reading circùit 6 via conductlve contacts ~ and 5. The
elements 3, 4 and 5 are provided on a substrate 7, which
may be glass, by means of methods used in the manufacture
25 . of integrated circuits. In a proto,type of the magnetic
head according to the invention the element 3 consisted
of an ~ e alloy having a th~ckness d of approximately
- 6 -
7~69
5-2-1975
- 1055155
1200 ~, a length 1 of 200 microns and a height h of 10
microns. The contacts 4 and 5 were formed by vapour-
deposited strips of gold. A number of thin gold strips
~, 8', 8", ~"' ... having a thickness of 1 micron and a
width of 5 microns were provided on the element 3 at
mutual distances of 5 microns at an ang~e of 45. Since
gold has a 5 x lower resistivity than the Ni-~e used and
the thickness of the gold strips is approximately 10 x as
~ large as the thickness d of the magnetoresistive
material, the gold strips have a 50 x better conductivity
and serve as "equipotential strips" which force the
current in the Ni-Fe paths between them to travel at an
angle of approximately 45 with the longitudinal
direction. Under the influence of an information-
containing magnetic field on the record~ng medium 2 the
- resistance of each of the said intermediately located
Ni-Fe paths will decrease or increase according as the
direction of magnetisatlon coincides more or less with
the current direction. This means that in principle
20 , linear recording by means of a non-biased magneto-
resistive head is possible.
A longitudinal auxiliary field ~ is generated
by means of a magnet (not shown). The strength of this
auxiliary field in the present case was 6 Oersted, which
corresponds to the coercive field strength of the Ni-Fe
used for the element 3 (5.9 Oersted). This field strength
ifi SO small that erasing of the lnformation on the
1055155
medium 2 need not be feared. This in contrast with the
use of a transverse field for the linearisation in which
field strengths of, for example, 100 Oersted are
necessary. Moreover, when the head 1 is manufactured by
means of methods used in the manufacture of integrated
circuits, it is comparatively simple to provide the
magnet for the longitudinal auxiliary field in the form
of a permanent magnetic layer of the required - low -
field strength which occupies little space. An elegant
solution is also to manufacture the substrate 7 from a
magnetic material and to magnetise it in the desired
direction. In order to illustrate the results obtained
with the above-described prototype, Figure 2 shows the
variation ~RlR of the resistance R of the element 3
under the influence of an external field H. The curve
shown in solid line represents the behaviour of the element
3 when an auxiliary field Hh with a strength of 6 Oersted
is applied in the + x direction and the curve shown in
broken line when an auxiliary field Hh with a strength of
6 Oersted is applied in the - x direction. The ohmic
resistance of the element 3 was 20 Ohm, while a current
of S mA was supplied by the current source 9. The
linearity of the behaviour of the element in the range of
field values between -120 Oersted and ~120 Oersted is
remarkable.
Figure 3 serves for comparison and the curve
in said figure represents the behaviour of the element
3 prior to the provision of conductive strips. (This
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P~ 7~l~9
5-~-1975
1055155
means that actually the behaviour of the conventional
magnetoresistive element is shown). The behaviour is
significantly ]ess linear, whil ~ it furthermore appears
that, in order to obtain a response which is linear as
much as possible, a transverse field of approximately
90 Oersted is to be applied. (operating point W). The
field is so large`that influencing (erasing) of the
recording medium might occur.
~J~
The longitudinal auxiliary foold to be
applied in the magnetic head according to the invention
is considerably smaller, namely approximately equal to
the strength of the coercive field of the material of the
magneto-resistive element (in the present exa~ple 6
Oersted). The coercive field strength of the magneto-
resistive material can be ~ept very small when this is
not deposited direct~on the substrate but on a thin
intermed-iate layer (of, for example, 30 R) of chromium
.r or titanium. Coercive field strengths of 1 Oersted can
~ be realised in this manner. The longitudinal auxiliary
field may then have a correspondingly small strenght. The
behaviour of the element at other field strengths;o`fthe
auxiliary field was also considered. At smaller field
strengths the curves started to show a slightly hysteretic
behaviour while at larger field strengths the slope of
the straight portion of the curve became less steep.
Howe~er, the strength of the auxiliary field is not
very critical since the angle be~tween the current
_ 9 _
'. 7~l6'~
5-2-1975
lOS5155
direction and the anisotropy axis is fixed by the
geometry of the pattern of strips. This means that by
means of the same mask for providing the strips a large
nwnber of magneto-resistive elements can be given the
same adjustment, independently of the exact strength of
the magnets to be used for generating the auxiliary
field.
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