Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-07-03
2004-10-19
Ometz, David (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S125330
Reexamination Certificate
active
06807031
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of electronic data storage and retrieval systems. In particular, the present invention relates to a novel lamination of materials which provides a single domain state shield for a magnetoresistive element of a transducing head and/or a single domain state pole of a perpendicular writer of a transducing head.
In an electronic data storage and retrieval system, a transducing head typically includes a writer for storing magnetically-encoded information on a magnetic disc and a reader for retrieving that magnetically-encoded information from the magnetic disc. The writer is formed of several layers, including at least two magnetic layers that function as a writer core, or magnetic poles. The reader is also formed of several layers, including at least two magnetic layers that function as shields for a read element of the reader.
Within a typical shield of a reader exist a plurality of magnetic domains separated from each other by a plurality of magnetic domain walls. The shields of a reader exert stray magnetic fields on the read element. These stray fields are accounted for when the read element is biased. As the domain walls move, however, these stray magnetic fields change, thus changing the bias point of the read element, as well as the response of the read element to signals emanating from the rotating disc. The overall result is noise during the read operation.
To avoid the problems associated with domain wall movement, the ideal shield structure would have no domain walls. A reduction of domain wall density (or an elimination of domains) from magnetic thin film structures can be achieved by use of a lamination consisting of alternating ferromagnetic films and nonmagnetic spacer films. By equating the thickness·magnetic moment product of each of the ferromagnetic films, a coupling will occur between those films, providing an alternate flux closure path that prevents domain wall formation. Although such structures have greatly reduced demagnetization fields over unlaminated single layer structures, they often feature undesirable edge-closure walls. Additionally, these structures require a very high level of control over layer thicknesses.
Others have proposed that antiferromagnetic layers can be used to bias the shields of a reader, thus resulting in a controlled domain structure. Hard bias or antiferromagnetic layers may be exchange coupled to large sheet films of soft ferromagnetic layers to bias those sheet films into a saturated state. Achievement of a single domain state in the soft ferromagnetic film is dependent upon the exchange field and soft film thickness. The use of such a structure as a shield for a read element, however, is unfeasible since the demagnetization fields associated with structures of the requisite dimensions would be so large as to overcome any induced bias. This would result in a multi-domain structure.
Perpendicular writers currently are being pursued as an option for increasing a real bit density of magnetic media. One difficulty, however, with perpendicular writers is the existence of magnetic domains within a top pole of the writer. Even with no current flowing through a set of coils that wrap about the poles of the writer, remnant magnetic state domain configurations in a pole tip region of the writer top pole may produce stray magnetic fields sufficient to cause degradation of recorded data. Additionally, the temporal decay to a remnant state (after the write current is turned off) may cause a time-dependent erasure of data recorded on the media. Control of such domain structures in the writer top pole is believed to be crucial for the elimination of this remnant erasure.
Thus, a single domain state magnetic layer is needed for use as a shield of a reader and/or for a pole of a writer.
BRIEF SUMMARY OF THE INVENTION
A transducing head has an air bearing surface; a first, a second, and a third magnetic layer; a magnetoresistive sensor; and conductive coils. The second magnetic layer is substantially parallel to the first magnetic layer. The third magnetic layer is separated at the air bearing surface from the second magnetic layer by a gap and is connected to the second magnetic layer opposite the air bearing surface. The magnetoresistive sensor is positioned between the first and the second magnetic layers. The conductive coils are positioned at least in part between the second and the third magnetic layers.
At least one of the first, the second and the third magnetic layers is formed of a thin film structure having a first and a second ferromagnetic layer, a nonmagnetic spacer layer, and a bias layer. The spacer layer is positioned between the first and the second ferromagnetic layers. The bias layer is positioned adjacent the first ferromagnetic layer. The second ferromagnetic layer has a thickness-magnetic moment product substantially equal to a thickness-magnetic moment product of the first ferromagnetic layer. An easy axis of the second ferromagnetic layer is substantially parallel to an easy axis of the first ferromagnetic layer.
In an alternate embodiment of the present invention, at least one of the first, the second and the third magnetic layers is formed of a plurality of thin film structures as described above and a plurality of structure spacer layers interspersed between each of the plurality of thin film structures. In this alternate embodiment, the plurality of thin film structures is arranged to alternate the biased ferromagnetic layers and the unbiased ferromagnetic layers of the plurality of thin film structures.
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Brinkley Gavin
Macken Declan
Plumer Martin Louis
Pokhil Taras Grigoryevich
Shukh Alexandar Mikhailovich
Kinney & Lange , P.A.
Ometz David
Seagate Technology LLC
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