Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-08-02
2001-11-13
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S327000, C360S324100, C360S316000
Reexamination Certificate
active
06317302
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thin-film magnetic read head device comprising an end face extending in a first direction, in which a magnetic information carrier is movable with respect to the magnetic head device, and in a second direction, perpendicular to said first direction, the magnetic head device further comprising a multilayer structure with at least two soft-magnetic layers separated by a magnetic insulation layer and with at least one exchange biasing layer cooperating with one of said soft-magnetic layers, which multilayer structure extends in the second direction and in a third direction, perpendicular to the first and the second direction, and forms at least one flux path in the first and the third direction.
Such a thin-film magnetic read head device is known from Koshkawa et al, Flux-Guided MR Head for Very Low Flying Height, IEEE Trans. Magn. 30 (1994), pp. 3840-3842. In this article, particularly on page 3840 and
FIG. 2
, a shielded read head is described and illustrated with an interrupted wing-like exchange biasing layer, the interruption determining the read width. The wing-like embodiment of the exchange biasing layer is applied for stabilizing a magnetoresistive element by boundary control stabilization and for determining the read width. As a consequence of the structuring, i.e. the interruption, of the exchange biasing layer, this magnetic read head device is not appropriate to realize read widths below about 1 &mgr;m.
In former yoke-type magnetic read heads, the dimension in the second direction of the flux guide in front of a magnetoresistive element usually determined the read width. A multichannel magnetic read head device was obtained by an arrangement in the second direction of flux guides and magnetoresistive elements cooperating therewith. However, for read widths below about 20 &mgr;m, multidomain states were likely to occur in the front flux guide, resulting in Barkhausen noise. Therefore an improvement was proposed in EP application No. 96203031.8.
In order to obtain a multichannel magnetic read head device, this document describes a number of flux-guiding elements and a number of magnetoresistive elements, cooperating with said flux-guiding elements, which elements form a number of parallel flux paths in the first and the third direction, the number corresponding to the number of magnetic channels of the magnetic read head device. A channel separation, i.e. a separation of the parallel flux paths, is obtained by a magnetically anisotropic structure, the magnetic permeability thereof in the second direction being small in comparison with the magnetic permeability in the third direction.
By application of the embodiments, described in EP application No. 96203031.8, the read widths are controlled by the anisotropy in combination with the distance between the contacts on the magnetoresistive elements. This method allows use of front flux guides with a width larger than the read width and thereby retains a single domain configuration also for smaller track widths. This is a viable method for track widths down to about 5 &mgr;m. For track widths of a few microns and less, this method appears to be no longer sufficient due to limitations in the soft-magnetic material properties.
In shielded magnetic read heads with the magnetoresistive elements extending to the head surface, the read width was determined by the spacing between the contacts on the magnetoresistive element or, in the case of a multichannel head, magnetoresistive elements. By careful structuring of the metallization layer and the biasing layers in the shielded heads read widths down to about 1 &mgr;m could be obtained. However, structuring methods based on optical lithography will probably not have a sufficient accuracy for read widths below this value.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a thin-film magnetic read head device, in which a track width below about 1 &mgr;m will be possible.
Therefore, in accordance with the invention, there is provided a thin-film magnetic read head device as described in the opening paragraph, which is characterized in that the exchange coupling between one of the soft-magnetic layers and the exchange biasing layer is at least partly reduced locally in at least the second direction, and in that the exchange biasing layer extends uninterruptedly in the region of said local reductions. This device achieves the object defined.
In the following, the expression “reduced” means “interrupted or at least substantially reduced”, while the expression “reduction” means “interruption of or at least substantial reduction”. A locally reduced exchange coupling between one of the soft-magnetic layers and the exchange biasing layer may be important to control the read width as well as the flux-guiding efficiency. Although in known magnetoresistive elements, like giant magnetoresistive elements or spin tunnel junction type magnetoresistive elements, a type of exchange biasing layers may be provided to pin the direction of magnetization in an adjacent magnetic layer, an exchange biasing layer of such a type is excluded from the term exchange biasing layer in the sense of the present invention in which the coupling between the exchange biasing layer and the adjacent soft-magnetic layer is locally reduced to control the read width or to improve the flux-guiding efficiency.
The present invention can be applied in shielded type magnetic heads as well as in yoke-type magnetic read heads. In both cases, a small-sized read width for a magnetic read head device will be obtained by applying the idea of local reduction of the coupling between an uninterrupted exchange biasing layer and a soft-magnetic layer.
The exchange biasing layer may not only be provided on one of the soft-magnetic layers, but may also be constituted by or be part of the magnetic insulation layer. In a configuration with two exchange biasing layers, both situations may occur.
The reduction can be achieved by the introduction of a specific interface layer structure, particularly only a few monolayers, of non-magnetic material between the exchange biasing layer and the soft-magnetic layer. In accordance with said specific structure, the thickness and/or the composition or microstructure of the interface layer between the exchange biasing layer and the soft-magnetic adjacent layer is locally modified, e.g. by in situ focused ion beam etching or implantation.
For converting the read information into an electric signal, there is provided at least one magnetoresistive element which may comprise at least one of said soft-magnetic layers and said exchange biasing layer, the exchange biasing between these layers at least being partly reduced locally to control the read width. The at least one magnetoresistive element may also be magnetically coupled with or comprise the soft-magnetic layer which is locally coupled with the exchange biasing layer to control the read width. In the latter case, the soft-magnetic layer to which the magnetoresistive element is magnetically coupled may be interrupted in the third direction, while the exchange coupling of the part of said interrupted soft-magnetic layer which is most near the end face and the exchange biasing layer is locally reduced to control the read width. In that case, an exchange biasing layer may be provided between the magnetoresistive element and the soft-magnetic layer to which the magnetoresistive element is coupled, with the exchange biasing being decoupled in the contact region of the magnetoresistive element with the latter exchange biasing layer to control the flux-guiding to said magnetoresistive element.
The magnetoresistive element may be of an anisotropic (AMR), a giant (GMR) or a spin tunnel junction (STJ-MR) type.
In a particular embodiment, the magnetic read head device is a multichannel magnetic head device with the soft-magnetic layers and a number of magnetoresistive elements forming a corresponding number of parallel flux paths in the first and the third direction, this number corres
Adelerhof Derk J.
Coehoorn Reinder
Van Kesteren Hans W.
Evans Jefferson
Treacy David R.
U.S. Philips Corporation
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