Multitrack magnetic head having magnetically coupled transducer elements

Elongate magneto-resistive elements (3) spaced apart on a substrate (9) incorporated in a magnetic circuit constituted by a magnetic yoke (5, 7, 9) which is provided with pole faces (19, 21) for the purpose of co-operating with the registration medium, while each magneto-resistive element is provided with two contacts (3A) for connection to a measuring current source. To improve the stability of the magneto-resistive elements, the magnetic head has strip-shaped coupling elements (17) which magnetically couple the magneto-resistive elements and keep them electrically separated from each other.

BACKGROUND OF THE INVENTION 
The invention relates to a magnetic head for detecting magnetic fields 
representing information on a relatively movable magnetic registration 
medium the magnetic head, includes a substrate on which a number of 
juxtaposed elongated magneto-resistive elements are provided which are 
each incorporated in a magnetic circuit constituted by a magnetic yoke 
which is provided with pole faces for the purpose of co-operating with the 
registration medium. Each magneto-resistive element is provided on two 
oppositely located edge portions with contacts for connection to a 
measuring current source. 
A multitrack magnetic head of this type is known from British Patent No. 
2,064,849 The known magnetic head has a number of spatially separated 
transducer elements of the magneto-resistive type and a plane surface for 
magnetic flux coupling of the transducer elements with a magnetic medium. 
To this end a layerwise formed pattern defining a number of 
magneto-resistive elements is provided on a common substrate, whilst the 
magneto-resistive elements are connected to contact faces by means of 
connection conductors. The magneto-resistive elements co-operate with 
discrete magnetic layers of the pattern formed from a number of discrete 
magnetic layers for defining the transducer elements. 
As is known from Philips Technical Review 37, pages 42-50, 1977, no. 2/3, 
the elongated magneto-resistive elements will preferably have such a 
magnetic anisotropy that the magnetically preferred direction coincides 
with the longitudinal axis of the magneto-resistive element. For the 
purpose of linearising the magnetic head one or more oblique conducting 
strips may be provided on one of the plane surfaces of the separate 
magneto-resistive elements, preferably at an angle of 45.degree. with the 
longitudinal axis of the magneto-resistive element. These strips function 
as equipotential strips so that the direction of the current in the 
magneto-resistive elements constitutes an angle with the magnetically 
preferred direction. 
Magnetic heads of the type described above are suitable for use in devices 
for industrial application with magnetic discs, drums or tapes as well as 
in consumer electronics, such as digital and analogue audio recorders. 
It has been found that the known multitrack magnetic head is less suitable 
for detecting magnetic media which are provided with a number of 
juxtaposed very narrow tracks. This is related to the fact that as the 
track width is smaller, the length of the magneto-resistive elements must 
also be taken to be smaller in connection with the track density, thus 
creating a more unfavourable length/width ratio regarding the magnetic 
shape anisotropy of the magneto-resistive elements. This means that 
instabilities in the magneto-resistive elements may be produced during 
operation of the magnetic head, with domain walls being displaced in an 
unpredictable way and with troublesome noise phenomena occurring. 
SUMMARY OF THE INVENTION 
It is an object of the invention to improve the magnetic head described so 
that the magnetic head can be used without any instability problems for 
reading a magnetic registration medium having a great track density and 
whose tracks only have a small track width. Another object is to provide a 
magnetic head having a long lifetime. 
To achieve the above objects the magnetic head is provided with 
strip-shaped coupling elements of a magnetically permeable material for 
coupling the magneto-resistive elements in a soft magnetic manner and 
keeping them electrically separated. Each coupling element bridges the 
distance between two adjacent magneto-resistive elements and covers the 
facing edge portions of the magneto-resistive elements. 
By magnetically connecting the magneto-resistive elements, a composite 
element of great length having a very favourable magnetic shape anisotropy 
so that an optimum stability of the separate magneto-resistive elements is 
ensured. The electrical decoupling of the separate magneto-resistive 
elements provides a better channel separation and therefore reduces the 
risk of crosstalk between the separate magneto-resistive elements. Each 
magneto-resistive element may be connected to a separate amplifier for 
further pressing the detected information, which gives the magnetic head 
more possibilities of use than with the use of differential amplifiers, 
certainly in applications in which not all magneto-resistive elements have 
to be utilised. If the magneto-resistive elements were not electrically 
isolated from each other, series-arranged differential amplifiers would 
have to be used, which has the drawback that the lifetime of the magnetic 
head ends if one of the magneto-resistive elements becomes defective. 
The magneto-resistive elements and the coupling elements will be preferably 
manufactured from the same soft magnetic material, for example, an 
Ni-Fe-based alloy. It has been found that it is favourable to provide the 
coupling elements with extremities which are rounded off. In fact, the 
occurrence of domain walls which are stuck in the vicinity of straight 
corners, also referred to as "pinning points" can be prevented thereby. 
Pinning points may give rise to distortion and noise of the output signals 
of the magnetic head. For the same reason the edge portions of the 
magneto-resistive elements will also be preferably rounded off. 
It is to be noted that a magnetic head with magneto& resistive sensors is 
described in U.S. Pat. No. 3,887,944 in which for the purpose of avoiding 
crosstalk a flux coupling between adjacent sensors is prevented by forming 
the magnetic sensors on a strip of a magneto-resistive material, whilst 
the sensors are mutually magnetically decoupled by local deactivation of 
parts of the strip. Otherwise this known magnetic head is of a type whose 
sensors are in direct contact with the magnetic medium to be read. 
For the sake of completeness reference is made to JP No. 56-156922 in which 
a magnetic head with a magnetic reluctance effect is shown in which a soft 
magnetic material is provided in the vicinity of magnetic reluctance 
elements for the purpose of adjusting a bias field. This known magnetic 
head is of a completely different type than the magnetic head according to 
the invention. 
The magnetic head can have insulation layers of an electrically insulating 
material, which layers are provided at the area of the edge portions 
between the magneto-resistive elements and the coupling elements. In that 
case it is favourable to manufacture the magnetic head by means of a 
thin-film technique, whilst the insulation layer preferably consisting of 
quartz can be selectively structured with respect to the other parts of 
the magnetic head.

DETAILED DESCRIPTION OF THE INVENTION 
The inventive multitrack magnetic head 1 shown in 0 the drawing is used to 
detect magnetic fields originating from a multitrack magnetic registration 
medium such as a magnetic tape which is moved along the magnetic head in 
the direction of the arrow A shown. Detection takes place by measuring the 
relative resistance changes of magneto-resistive elements 3 integrated in 
the magnetic head which receive magnetic flux via magnetically permeable 
parts 5, commonly referred to as flux collect guides, whilst magnetically 
permeable parts 7, commonly referred to as flux return guides are used to 
return the magnetic flux. 
The magnetic head according to the invention may be manufactured as a 
multilayer thin-film structure provided on a substrate. Standard 
sputtering and photo-etching techniques can be used to realise the 
multilayer structure. The starting material may be a ferrite magnetic 
substrate 9 on which a first insulation layer 11 of electrically 
insulating material such as SiO.sub.2 is provided. 
The structure further comprises a number of spatially separated layers of a 
magneto-resistive material such as Ni.sub.20 Fe.sub.80 constituting the 
said elongated magneto-resistive elements 3. Electric conductors 13 of, 
for example, Au which are present to connect the magneto-resistive 
elements 3 to a current source are electrically connected to the 
magneto-resistive elements 3 at the area of contact faces 3A. A second 
electric insulation layer 15 of quartz is provided on the 
magneto-resistive elements, which layer also extends at least in part 
across the first insulation layer 11. The magneto-resistive elements 3 are 
magnetically interconnected by means of layers of a soft magnetic material 
such as an NiFe alloy-based layer, for example, Ni.sub.20 Fe.sub.80 
further referred to as coupling elements 17 deposited on the electric 
insulation layer 15 which has a thickness of, for example, 0.15.mu.m. The 
strip-shaped coupling elements 17, which have a thickness of, for example, 
0.06 .mu.m, have a length which is larger than the axial distance between 
the magneto-resistive elements so that the coupling elements 17 cover edge 
portions 3B of the magneto-resistive elements. The flux guides 5 and 7 
already referred to which are constituted by layers of a material having a 
high magnetic permeability, for example, an NiFe alloy are pairwise spaced 
and cover edge zones 3C and 3D on one side of the magneto-resistive 
elements 3. The insulating layers 11 and 15 have holes, which are not 
visible in the drawing, at the area of the flux return guides 7 for the 
purpose of magnetically coupling the parts 7 to the magnetic substrate 9. 
The parts 5, the parts 7 and the substrate 9 together constitute a 
magnetic yoke having a number of pairs of pole faces 19 and 21 
corresponding to the number of magneto-resistive elements, the pole faces 
19 being provided on the parts 5 and the pole faces 21 being provided on 
the substrate 9. A protective layer 23 of an electrically insulating 
material may be provided on the coupling elements 17. For the sake of 
clarity the insulating layers 1, 15 and 23 are not shown in FIG. 1. 
The invention is of course not limited to the embodiment shown and 
described. For example, it is not always necessary to provide the coupling 
elements 17 with extremities 17A which are rounded off. In addition the 
separate magneto-resistive elements 3 may be provided with oblique 
conducting strips for the purpose of linearisation, more specifically in a 
manner as extensively described in the aforementioned Philips Technical 
Review 37, pp. 42-50, 1977, no. 2/3.