Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-02-28
2003-09-16
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324200
Reexamination Certificate
active
06621666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetoresistive-effect element comprising a magnetoresistive-effect thin film, a pair of hard magnetic layers formed respectively at opposite ends of the magnetoresistive-effect thin film and electrode layers formed respectively at the sides of the oppositely disposed main surfaces of the magnetoresistive-effect thin film.
2. Related Background Art
Magnetoresistive-effect magnetic heads (to be referred to as MR head hereinafter) adapted to read information signals recorded on a magnetic recording medium, utilizing the magnetoresistive-effect of magnetoresistive-effect thin film (to be referred to as MR thin film hereinafter), are widely used in many high density magnetic recording/reproduction apparatus including hard disk apparatus and magnetic tape apparatus.
Of MR heads, so called shield type MR heads comprising a magnetoresistive-effect element (to be referred to as MR element hereinafter) sandwiched by a pair of magnetic shield member have been finding practical applications.
Various different types of MR thin film are known to date, including one showing the anisotropic magnetoresistive-effect (AMR), one showing the giant magnetoresistive-effect (GMR) and one showing the tunnelling magnetoresistive-effect (TMR).
Of such known various types of MR thin films, MR thin film that utilizes the tunnelling magnetoresistive-effect (to be referred to as TMR thin film hereinafter) comprises a magnetization fixing layer made of an anti-ferromagnetic material, a pin layer made of a ferromagnetic material a tunnel barrier layer made of a nonmagnetic nonconductive material and a free layer made of a ferromagnetic material, said layers being laid sequentially one on the other.
When a sense current is made to flow substantially perpendicularly relative to the TMR thin film, a tunnelling current flows in the tunnel barrier layer and the flow is directed toward from one of the ferromagnetic layer to the other ferromagnetic layer. This phenomenon is referred to as tunnelling junction type magnetoresistive-effect. In an MR element that utilizes TMR thin film (to be referred to as TMR element hereinafter), the magnetization of the free layer changes as a function of the external magnetic field to consequently change the conductance of the tunnelling current. The external magnetic field is detected by observing the conductance of the tunnelling current.
The change in the conductance-of the tunnelling-current is dependent on the relative angle of the two ferromagnetic layers as viewed in the direction of magnetization. In the case of TMR thin film, theoretically the magnetic reluctance ratio of the two ferromagnetic layers can be determined from their respective polarizabilities of magnetization. Thus, TMR elements are attracting attention from the viewpoint of using them for MR heads.
So-called spin valve film is a type of MR thin film utilizing the giant magnetoresistive-effect (to be referred to as GMR thin film hereinafter) and comprises a magnetization fixing layer made of an anti-ferromagnetic material, a pin layer made of a ferromagnetic material, an intermediate layer made of a nonmagnetic nonconductive material and a free layer made of a ferromagnetic material, said layers being laid sequentially one on the other.
When an external magnetic field is applied to a GMR element, the magnetization of the free layer is defined as a function of the direction and the intensity of the applied external magnetic field. The electric resistance of the spin valve layer is maximized when the direction of magnetization of the pin layer and that of the free layer are differentiated from each other by 180° and minimized when they are made same relative to each other. Therefore, the pin valve film changes its electric resistance as a function of the external magnetic field applied to it. Thus, the external magnetic field can be detected by observing the change in the electric resistance.
Meanwhile, for the MR head, it is important to control the magnetic domains and make the free layer of the MR thin film have a single magnetic domain in order to suppress the Barkhausen noise.
An MR head
100
utilizing the anisotropic magnetoresistive-effect or the giant magnetoresistive-effect comprises a lower magnetic shield layer
102
a
and a lower gap layer
103
a
laid sequentially on a substrate
101
. Then, an MR thin film
104
is formed on the lower gap layer
103
a
and a pair of bias layer
105
,
105
are formed respectively at opposite ends of the MR thin film
104
. An upper gap layer
103
b
and an upper magnetic shield layer
102
b
are formed on the MR thin film
104
and the bias layers
105
,
105
.
The free layer of the MR thin film
104
is made to have a single magnetic domain by arranging a pair of bias layers
105
,
105
to be used to apply a bias magnetic field to the MR thin film
104
respectively at opposite ends of the MR thin film
104
. The bias layers
105
,
105
are made of a hard magnetic material that is electrically conductive such as CoPt.
An MR head using a TMR thin film (to be referred to as TMR head hereinafter) comprises a lower magnetic shield layer, a lower gap layer, a TMR thin film, an upper gap layer, an upper magnetic shield layer that are laid sequentially on a substrate. The lower magnetic shield layer, the lower gap layer, the upper gap layer and the upper magnetic shield layer are designed to operate as electrodes.
Then, a sense current is made to flow substantially perpendicularly relative to the film surface of the TMR thin film and the conductance of the tunnelling current that flows through the tunnel barrier layer of the TMR thin film is observed to read the magnetic signal applied to it.
The above described bias layers
105
,
105
are made of a hard magnetic material that is electrically conductive such as Co.Pt. Therefore, when bias layers are arranged respectively at opposite ends of the TMR head, the sense current can be diverted into the bias layers to make it difficult to read the magnetic signal applied to it. Because of this reason, in the case of a TMR head, it is not appropriate to control magnetic domains by arranging bias layers respectively at opposite ends of the MR thin film.
In recent years, a GMR head adapted to a so-called CPP (current perpendicular to the plane—to be referred to as CPP-GMR head hereinafter) and formed by arranging a gap layer and a shield layer that are designed to operate as electrode layer as shown in
FIGS. 2 and 3
has been proposed as MR head using GMR thin film.
A CPP-GMR head comprises a lower magnetic shield layer, a lower gap layer, a GMR thin film, an upper gap layer and an upper magnetic shield layer that are laid sequentially on a substrate, of which the lower magnetic shield layer, the lower gap layer, the upper gap layer and the upper magnetic shield layer are designed to operate as electrode layers.
Then, a sense current is made to flow substantially perpendicularly relative to the film surface of the GMR thin film and the conductance of the electric current that flows through the intermediate layer of the GMR thin film is observed to read the magnetic signal applied to it.
As pointed out above, a CPP-GMR head is so designed as to make a sense current flow perpendicularly relative to the GMR thin film. Then, the rate of change of the electric current in the CPP-GMR head is larger when it is made to flow perpendicularly relative to the GMR thin film than when it is made to flow in parallel with the GMR thin film. Additionally, since the electrode layers are made to operate as shield layers, it is no longer necessary to electrically insulate the electrode layers and the shield layers if the gap is made narrow and the manufacturing process can be simplified. For theses reasons, CPP-GMR beads have been attracting attention and are getting popularity as magnetic heads.
However, as in the case of a TMR head, when bias layers are arranged respectively at opposite ends of the GMR head, the sense current can be diverted into the bias lay
Ikarashi Minoru
Kano Hiroshi
Miyauchi Teiichi
Mizuguchi Tetsuya
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