Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-09-18
2002-12-10
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06493197
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magneto-resistance effect type head for detecting an intensity of a magnetic field based on a resistance change corresponding to this intensity and an information reproducing apparatus for reproducing information stored on a storage medium.
BACKGROUND ART
Recently, with prevalence of computers in the society, an enormous amount of information is handled daily. To store such information is there available a magnetic disk. The magnetic disk has its surface made of a magnetic material, which is divided into many minute 1-bit segments, according to a magnetization direction of each 1-bit segment the information can be stored at a high storage density. To reproduce such information is there available a hard disk drive, which has a magnetic head for detecting an intensity of a magnetic field generated by the magnetization of the magnetic disk. The magnetic head sequentially reads out a magnetization direction of each 1-bit segment of the magnetic disk to generate an electric reproduced signal corresponding to the magnetization direction, thus reproducing the information born by use of that magnetization.
The recording density of the information stored on a magnetic disk has been increasing year by year with an accompanying decrease in the area occupied by each 1-bit segment of the magnetic disk. To detect a direction of the magnetization of such a small-area 1-bit segment, it is necessary to use a reproducing magnetic head with a high sensitivity.
As the high-sensitivity reproducing magnetic head is available a magneto-resistance effect type head (hereinafter called MR head) utilizing the magneto-resistance effect of a changing resistance in correspondence with an external magnetic field, especially a spin-valve type MR head well known for its very high sensitivity. This spin-valve type MR head is comprised of a multi-layer film including a soft-magnetism free-magnetic layer which changes in orientation of magnetization corresponding to an external magnetic field, in which the resistance changes greatly with a change in that magnetization orientation. This spin-valve type MR head comes in contact or in near contact with each 1-bit segment of the magnetic disk at a read-out portion of its surface perpendicular to the multi-layer film to thereby detect a magnetic field generated by magnetization of that 1-bit segment, thus generating an electric reproduced signal based on a change in resistance corresponding to that magnetic field.
The free-magnetic layer of the multi-layer film is liable to have a magnetic domain wall occurring at the end, so that if this magnetic domain wall moves due to a change in an external magnetic field, the reproduced signal contains Barkhausen noise. To inhibit the generation of the Barkhausen noise, a magnetic domain-wall control layer made of, e.g., a hard-magnetism ferromagnetic material is arranged as one layer of the multi-layer film, so that the free magnetic layer has the magnetic domain wall fixed due to a static magnetic field and switched connection brought about by that magnetic domain-wall control layer. Although this magnetic domain-wall control layer is preferably thinned in order to realize a small read-out portion fitted to reproduction of information recorded on a magnetic disk at a high recording density, it needs to have a predetermined thickness in order to control the electric domain wall in a stable manner by applying a strong static magnetic field on the free magnetic layer. By utilizing switched connection brought about when the free magnetic layer and the magnetic domain-wall control layer come in direction contact with each other, however, it is possible to compensate for a decrease in the intensity of the static magnetic field caused by the thinning of the layer.
Conventionally, such a spin-valve type MR head with a construction having a very small junction called an abutted junction has been well known that the magnetic domain-wall control layer attached to a tapered layer cross section of the free magnetic layer. That junction has switched connection occurring thereat but can hardly preserve stable connection because it has a small junction area.
Therefore, such a construction has been worked out that is of a so-called vertical-bias underlay type, in which part of the free magnetic layer is stacked on, as covering, the magnetic domain-wall control layer directly or with an underlying layer therebetween. By this construction, when the free magnetic layer is directly stacked on the magnetic domain-wall control layer, an area of the junction between these layers is very large as compared to a junction area of the abutted junction, so that stable switched connection can be preserved always, thus effectively inhibiting the occurrence of the Barkhausen noise.
Generally, however, preferably the free magnetic layer is formed on a predetermined non-magnetic underlying layer so that the existence of the underlying layer assures good crystallinity of the free magnetic layer. Good crystallinity improves the soft-magnetization properties of the free magnetic layer, which in turn improves the sensitivity of the spin-valve type MR head.
The spin-valve type MR head having a vertical-bias underlay type construction in which this free magnetic layer is formed on one pair of magnetic domain-wall control layers with a non-magnetic underlying layer therebetween is disclosed in Japan Patent Publication Hei 10-312515. Although, in this spin-valve type MR head, the non-magnetic underlying layer weakens or eliminates the switched connection between the magnetic domain-wall control layer and the free magnetic layer, this weakness in switched connection can be compensated for by enhancing, in adjustment, the intensity of a static magnetic field of the magnetic domain-wall control layer given to the free magnetic layer.
However, the spin-valve type MR head that has such a vertical-bias underlay type construction that the free magnetic layer is formed on the non-magnetic underlying layer cannot effectuate a feature of the structure held by the spin-valve type MR head that stable switched connection can be obtained by direct junction of the magnetic domain-wall control layer and the free magnetic layer. Therefore, there is desired such a spin-valve type MR head that has good crystallinity as well as high sensitivity, and effectively inhibits the occurrence of the Barkhausen noise by utilizing the feature of the vertical-bias underlay type construction of obtaining stable switched connection between the free magnetic layer and the magnetic domain-wall control layer.
DISCLOSURE OF THE INVENTION
In view of the above, it is an object of the present invention to provide a spin-valve type magneto-resistance effect type head and information reproducing apparatus which can well reproduce information recorded on a recording medium at a high recording density while inhibiting occurrence of the Barkhausen noise.
To the above-mentioned end, a first magneto-resistance effect type head according to the present invention includes:
a magneto-resistance effect element exhibiting a change in resistance in correspondence with an intensity of an external magnetic field, to detect the magnitude of the resistance of the magneto-resistance effect element, thus detecting the intensity of the magnetic field, in such a configuration that:
the magneto-resistance effect element is comprised of a multi-layer film including a free magnetic layer which has a magnetization direction changing in correspondence with the external magnetic field, the magneto-resistance effect type head having:
an insulating layer made of an insulating material;
a non-magnetic underlying layer formed on the insulating layer; and
one pair of magnetic domain-wall control layers formed on the underlying layer in its in-face direction with a predetermined spacing therebetween, for controlling the movement of the magnetic domain wall of the free magnetic layer,
in which the free magnetic layer is formed in such a manner as to have its both ends directly stack
Ito Jun-ichi
Kanai Hitoshi
Kanamine Michiaki
Fujitsu Limited
Greer Burns & Crain Ltd.
Letscher George J.
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