Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-02-15
2004-03-09
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06704177
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magneto resistive effect head for reading a record from a recording medium by using the magneto-resistive effect.
2. Description of the Prior Art
Usually, a magnetic head provided in a hard disk drive (HDD) includes: a writing head for writing information as a magnetization signal onto a recording medium (hard disk); and a reproducing head for reading the signal recorded as a magnetization signal on the recording medium. Since the reproducing head is constructed by a stack including a plurality of magnetic thin films and non-magnetic thin films and reads the signal by using the magneto-resistive effect, it is called a magneto-resistive effect head. There are a few kinds of stacking structures of the magneto-resistive effect head and they are classified into an AMR head, a GMR head, a TMR head, and the like in accordance with a principle of magneto-resistance which is used. An input magnetized field entered from the recording medium into the reproducing head is extracted as a voltage change by using an AMR (Anisotropy Magneto-Resistive effect), a GMR (Giant Magneto-Resistive effect), or a TMR (Tunneling Magneto-Resistive effect).
In the stack layer of the reproducing head, a magnetic layer whose magnetization is rotated by receiving the input field from the recording medium is called a free layer. To suppress various noises such as a Barkhausen noise and the like or to control an asymmetry output, it is important to convert the free layer into a single domain in a track width direction. If the free layer has a magnetic domain without being converted into the single domain, the free layer receives the input magnetized field from the recording medium, so that a domain wall movement occurs and becomes a cause of the noise.
As a method of the magnetic domain control for converting the free layer into the single domain, for example, as disclosed in JP-A-3-125311, there is a method whereby magnetic domain control layers including magnet layers are arranged at both ends of the free layer, and a magnetic field which is caused in the track width direction from the magnet layers is used.
FIG. 8
shows a schematic diagram which is obtained when a magneto-resistive head subjected to the magnetic domain control by such a method is seen from an air bearing surface. A free layer
2
is formed via a spacer
3
over a soft magnetic layer (called a pinned layer)
4
and magnetization of the soft magnetic layer
4
has been fixed by an antiferromagnetic layer
5
. A cap layer
1
is formed on the free layer
2
. A width of free layer
2
is called a track width Twr. Both ends of the stack of the antiferromagnetic layer
5
are shaved from the cap layer
1
by ion milling or the like, so that a device has a trapezoidal shape when it is seen from the air bearing surface as shown in
FIG. 8. A
structure of the head of
FIG. 8
is characterized in that magnetic domain control layers
7
including magnet layers are arranged to both ends of the device via seed layers
6
. According to such a structure, a magnetization distribution of the free layer
2
is controlled by using a magnetic field which is developed from the magnetic domain control layers
7
and the free layer is converted into the single domain.
As another method of the magnetic domain control, for example, as shown in U.S. Pat. No. 4,663,685, there is a method whereby antiferromagnetic films are stacked on both ends of a free layer and an exchange coupling between the antiferromagnetic film and the free layer is used.
FIG. 9
shows a schematic diagram which is obtained when a magneto-resistive effect head subjected to the magnetic domain control by such a method is seen from an air bearing surface. A structure of the head of
FIG. 9
is characterized in that the free layer
2
is formed via the spacer
3
over the soft magnetic layer (called a pinned layer)
4
whose magnetization has been fixed by the antiferromagnetic layer
5
, and antiferromagnetic films
12
are stacked at both ends of an upper portion of the free layer
2
.
A magnetic domain control is performed by an exchange interaction which acts between the antiferromagnetic film
12
and free layer
2
. The free layer
2
is formed so as to be wider than the width of track written on the recording medium and has a shape such that end regions are fixed. According to such a structure, therefore, a record is read by a portion Tw (of the free layer
2
) between the antiferromagnetic films
12
(such a portion is called a sensing region). A lead layer
10
is stacked over the upper surface of the antiferromagnetic film
12
via a seed layer
11
. It is not always necessary to form the seed layer
11
.
As shown in JP-A-11-203634, there is also a method of stacking an antiferromagnetic layer having a uniform thickness onto the whole surface of a free layer, or the like. However, since a track width of the present head is very narrow, there is a fear that, if the whole surface of the free layer is fixed by a uniform magnetic field, sensitivity deteriorates and a magnetic domain control field of a track end portion where the magnetic domain control is particularly necessary is contrarily insufficient. As shown in JP-A-2001-84527, a method whereby a magnetic domain control layer is constructed by a stack layer of a layer of high coercivity and at least one of a ferromagnetic layer and an antiferromagnetic film has also been proposed.
Each of the above magnetic domain control structures has the following problems. According to the magnetic domain control system as shown in
FIG. 8
such that the magnetic domain control layers comprising the magnet layers are arranged on both sides of the free layer, since a magnetic field which is developed at an interface where the magnetic domain control layer and the free layer are come into contact with each other is too strong, a region (dead region) where the magnetization of the free layer is hard to be rotated with respect to the medium field is caused. To reduce the dead region, it is sufficient to weaken a magnetic domain control force by simply thinning the thickness of magnet layer or by another method. In case of using such a method, however, since an inconvenience such that the Barkhausen noise or an output signal instability is contrarily caused, asymmetry of an output increases, or the like occurs, the magnetic domain control force of a certain extent is necessary.
When a recording density of the recording medium is large and the track width Twr which is defined by the width of free layer is wide, since a ratio of the dead region which occupies the track width Twr is small, such an influence does not cause a large problem. However, the track width Twr is decreasing more and more in accordance with a recent extreme increase in recording density. Therefore, the ratio of the dead region which occupies the track width Twr is increasing. Unless some countermeasures are taken, it is very difficult to assure enough sensitivity of the head without deteriorating characteristics of noises or the like.
As one of the countermeasures, a method whereby an interval between leads is set to be smaller than the interval of the track width Twr and the portion of the dead region of low sensitivity is not used for reading, thereby enabling a high reproduction output to be obtained has been proposed in, for example, JP-A-9-282618 or U.S. Pat. No. 5,739,990. However, according to such a method, there is a problem such that since a magnetic domain control force which is applied to the end portion of the free layer locating under the lead is weak, a side reading increases.
According to the magnetic domain control method as shown in
FIG. 9
whereby the antiferromagnetic film is arranged, since the coupling field acts only on the portion where the antiferromagnetic film and the free layer are in contact with each other, the problem of the dead region as mentioned above does not occur. It is advantageous for realization of a narrow track. However, the exchange coupling field between
Morinaga Akira
Ohtsu Takayoshi
Evans Jefferson
Hitachi , Ltd.
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