The present invention relates to a magneto-resistive element and more specifically to a structure of a bias application layer for applying a bias magnetic field to a sensing layer whose magnetization rotates in response to an external magnetic field.
Magnetization of the pinned-magnetic layer 12 is fixed in a constant direction by the anti-ferro-magnetic layer 13. The magnetizing angle of the free-magnetic layer 11 changes in response to a medium magnetic field. The non-magnetic layer 14 is formed of a conductive material such as Cu or the like.
The magnetization of the free-magnetic layer is difficult to rotate in the bias direction at both end portions by a self-demagnetizing field. Accordingly, a response to the medium magnetic field also generates hysteresis, likely resulting in the generation of Barkhausen noise. Therefore, on both sides of the element 10, a ferro-magnetic layer 15a, 15b such as CoCrPt or the like is allocated as a bias application layer via an underlayer 16a, 16b such as Cr or the like. This bias magnetic field stabilizes magnetization of the free-magnetic layer to prevent generation of Barkhausen noise.
In recent years, a read head is required that can read narrower gaps and narrower tracks in higher density magnetic recording medium. However, realization of such narrower gaps and narrower tracks makes effective application of a bias magnetic field to the magnetoresistive element difficult. Therefore, still higher coercive force and residual magnetic flux density of the ferro-magnetic layer are required.
Japanese Unexamined Patent Publication No. 1997-282612 discloses a bias magnetic field application layer formed of a soft-magnetic layer and a hard-magnetic layer. Moreover, Japanese Unexamined Patent Publication No. 2005-38508 discloses a bias magnetic field application layer formed of a hard-magnetic layer, a ferro-magnetic layer, and an underlayer. However, these technologies are characterized in that higher coercive force and residual magnetic flux density are attained by laminating multilayers of the soft-magnetic layer and hard-magnetic layer.
However, as the coercive force of the ferro-magnetic layer and the residual magnetic flux density are increased, the exchange coupling force of magnetization is also increased, and moreover, a grain size of the ferro-magnetic layer is also increased. Since element size is reduced to 200 nm×200 nm, or less, due to higher recording density of the magnetic recording apparatus, the amount of grains in the ferro-magnetic layer 15a, 15b in the element height direction becomes 10 or less.
Accordingly, it is an object of the present invention to apply a more uniform bias magnetic field to the sensing layer while the coercive force and residual magnetic flux density of the ferromagnetic layer are maintained at higher values.
In accordance with an aspect of an embodiment, a magnetoresistive element includes a sensing layer in which magnetization rotates in response to an external magnetic field, a bias application layer for applying a bias magnetic field to said sensing layer via an underlayer, and a magnetic layer is positioned between said underlayer and said bias application layer, wherein a crystal grain size of said magnetic layer is smaller than a crystal grain size of said bias application layer.
The present invention will be explained with reference to the accompanying drawings.
The preferred embodiment of the present invention will be explained in detail with reference to the accompanying drawings.
The lower shield layer 1 is formed of a soft-magnetic material such as NiFe, FeCo, FeCoNi, or the like, in a thickness of between about 1 to about 4 μm, for example, 3 μm. Thereafter, a non-magnetic insulating layer of Al2O3, AlN, SiO2, or the like, is formed over the lower shield layer 1 as the lower gap layer 18 in thickness of between about 5 to about 25 nm.
The MR element 10 can be, for example, a giant magnetoresistive (GMR) film and a tunnel magnetoresistive film. This embodiment discloses the giant magnetoresistive (GMR) film composed of a free-magnetic layer 11 as the sensing layer, a pinned-magnetic layer 12, and an anti-ferro-magnetic layer 13 for fixing magnetization of the pinned-magnetic layer.
The MR element 10 is formed by sequentially laminating an underlayer (not illustrated), the anti-ferro-magnetic layer 13, pinned-magnetic layer 12, non-magnetic layer 14, free-magnetic layer 11 and a protection layer (not illustrated) on a lower gap layer 18. The magnetization of the free-magnetic layer 11 rotates in response to a magnetic field of medium. Meanwhile, the pinned-magnetic layer 12 is fixed in a constant direction through exchange coupling with the anti-ferro-magnetic layer 13 and does not respond to the magnetic field of the medium. Moreover, the free-magnetic layer 11 is magnetized in a bias direction that is almost orthogonal to the magnetizing direction of the pinned-magnetic layer 12.
The free-magnetic layer 11 uses a soft-magnetic material such as NiFe, CoFe, or the like, in a thickness of between about 3 to about 5 nm, while the pinned-magnetic layer 12 uses a soft-magnetic material such as CoFe, or the like, in a thickness of between about 2 to about 3 nm, and the anti-ferro-magnetic layer 13 uses an anti-ferro-magnetic material such as PdPtMn, IrMn, NiO, and FeMn, or the like, in a thickness of between about 10 to about 30 nm. The non-magnetic layer 14 uses a non-magnetic material such as Cu, Ru, Ir, or the like, in a thickness of between about 1 to about 2 nm. However, in the tunnel magnetoresistive film, the non-magnetic layer 14 uses an insulating material such as Al2O3, MgO, or the like, in the thickness of about 0.5 nm. The protection layer (not illustrated) uses Ta, Al2O3 in a thickness of between about 10 to about 20 nm. The pinned-magnetic layer 12 could also be a double-layer structure such as CoFe/Ru/CoFe, which includes an intermediate layer such as Ru.
The ferro-magnetic layer 15a, 15b is allocated via the underlayer 16a, 16b on both sides of the bias direction to hold the magnetoresistive film. Thus, ferro-magnetic layer 15a, 15b acts as the bias application layer. A soft-magnetic layer is allocated as a magnetic layer 22a, 22b between the underlayer 16a, 16b and the ferro-magnetic layer 15a, 15b.
As the ferro-magnetic layer 15a, 15b, a ferro-magnetic material such as CoPt, CoCrPt in a thickness of between about 10 nm to about 30 nm is used. Moreover, as the underlayer 16a, 16b, a non-magnetic layer such as Cr, Ti, and W in a thickness of between about 1 to about 2 nm is used and magnetization of the ferro-magnetic layer 15a, 15b is oriented within the film surface. Here, as the magnetic layer 22a, 22b, a metal material including at least any of Fe, Co, and Ni is used as the soft-magnetic layer.
Moreover, the ferro-magnetic layer 15a, 15b is magnetized in the bias direction. In this case, the magnetic layer 22a, 22b preferably has a coercive force of approximately 500 Oe, or less, for magnetization of the magnetic layer 22a, 22b in the bias direction. In addition, the magnetic layer 22a, 22b preferably also has a saturated magnetic flux density of about 5000 G, or more, for application of sufficient bias magnetic field to the free-magnetic layer 11. The reason is that the crystal grain size becomes smaller in the condition explained above.
Next, the magnetic recording apparatus mounting the magnetic head explained in this embodiment will be explained briefly.
The slider 30 is mounted to the suspension 26 at the lower part thereof to constitute a head suspension assembly. When the magnetic disk 24 rotates at a high velocity, air is drawn into a gap between the slider 30 and the magnetic disk 24, and the air pressure generated in this case levitates the slider 30. The magnetic head mounted to the front end part of slider 30 is connected electrically to the detecting circuit via the insulated conductive lead wire 28 on the suspension 26 and actuator arm 25.
According to the preferred embodiment of magnetoresistive element of the present invention, it is possible, even when the element size is set to 200 nm×200 nm or less, to provide the magnetoresistive element which is controlled in generation of the Barkhausen noise, the magnetic head and the magnetic recording apparatus provided with the relevant magnetoresistive element.
The magnetoresistive element, magnetic head, and magnetic recording apparatus of the present invention may be applied in common to the magnetoresistive element, magnetic head, and magnetic recording apparatus comprising the soft-magnetic layer (free-magnetic layer) which can freely change in the magnetizing direction in response to the medium magnetic field, for example the spin valve element and tunnel resistive element or the like.
Moreover, the magnetoresistive element of the present invention may be used not only in a magnetic head for reading a magnetic field of a medium, but also in a magnetic device such as MRAM. In addition, the magnetoresistive element of the present invention may also be used as the magnetoresistive element provided in the read head in regard not only to the in-plane recording type magnetic head shown in
Number | Date | Country | Kind |
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2006-319553 | Nov 2006 | JP | national |