Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-09-14
2004-10-05
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06801409
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to a shield for use with a magnetoresistive (MR) read head that absorbs strayed magnetic fields that could affect the operation of a read element of the MR read head. More particularly, the present invention relates to a patterned shield of an MR read head having a magnetic domain configuration that is highly stable against exposure to large and non-uniform magnetic fields.
Disc drives are the primary devices employed for mass storage of computer programs and data used in computer systems. Disc drives typically use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. An MR head is adapted to write information to and read information from the data tracks. The MR head is carried by a slider which is connected to an actuator mechanism. The actuator mechanism moves the slider from track-to-track across the surface of the disc under control of electronic circuitry. The actuator mechanism includes a suspension assembly that applies a load force to the slider that urges the slider toward the disc. As the disc rotates, air is dragged and compressed under bearing surfaces of the slider creating a hydrodynamic lifting force that counteracts the load force and causes the slider to lift and “fly” in close proximity to the disc surface. A gimbaled attachment between the slider and the suspension assembly allows the slider to pitch and roll to follow the topography of the disc.
Typical MR heads include both read and write head portions. The read head includes a read element that is adapted to read magnetic flux transitions recorded to the disc in circular tracks which represent bits of data. The magnetic flux from the disc surface causes a change in the electrical resistivity of the read element, which can be detected by passing a sense current through the read element and measuring a voltage across the read element. The voltage measurement can then be decoded to determine the recorded data. The write head includes an inductive write element for generating a magnetic field that aligns the magnetic moments that are recorded to the disc surface to represent bits of data.
In high density disc drives the bits are closely spaced linearly along each circular track. In order for the read head to play back the closely spaced bits, the read element must be shielded from magnetic flux emanating upstream and downstream from the bit being read and from adjacent tracks. This is generally accomplished by positioning the read element between top and bottom shields. During a read operation, the shields ensure that the read element reads only the information stored directly beneath it on a specific track of the magnetic disc by absorbing the stray magnetic fields emanating from the surroundings.
As mentioned above, the read element of the read head has a resistance that varies in response to magnetic flux emanating from the dics surface. To illustrate the behavior of the read element, a response curve of the read element is generated that compares the voltage across the read element to the magnetic flux received from the disc by the read element. This response curve has both linear and non-linear portions and is dependent on stray magnetic fields produced, for example, by the bottom shield. It is preferred that the read element operate along the linear portions. This is accomplished by magnetically biasing the read element to operate at a biasing point that is located along the linear portion of the response curve. The stray fields produced, for example, by the bottom shield are accounted for when the read element is initially biased.
The top and bottom shields typically each include a ferromagnetic (FM) layer having a domain configuration that is defined by a plurality of magnetic domains that are contained within domain walls. Each magnetic domain has a magnetization that is oriented in a direction that is different than the magnetization of all adjacent domains. When exposed to a magnetic field, either during manufacture or operation of the disc drive, the magnetization of the magnetic domains within that shield change, thereby potentially causing the magnetic domains to move, grow, or shrink. If the magnetic field is sufficiently large, the shield's exposure to it can cause a random change in the domain configuration of the shield by relocating the domain walls in response to the shift in the magnetic domains.
As storage densities on magnetic discs have increased, the read element has become smaller and more sensitive to shifts in the domain configuration of the shields. Thus, when the shield is subjected to a large applied field, such as by the write element during write operations, the domain configuration of the shields move and then return to a different random arrangement. Unfortunately, when the domain configurations of the shields move, the stray magnetic fields produced by the shields change, thus changing the bias point of the read element as well as the response of the read element to signals emanating from the magnetic disc. The result is undesirable noise during read operations.
Therefore, it is desirable that the domain configurations of the shields be extremely stable. This relates to the tendency of the domain configuration to return to the same domain configuration even after the application and removal of a strong magnetic field. Accordingly, a stable domain configuration would only temporarily shift in position when a magnetic field is applied, and then return to the same domain configuration once it is removed. Unfortunately, prior art shields are not sufficiently stable to resist this domain configuration shift caused by application of a strong magnetic field.
Two proposals for increasing domain configuration stability in a shield are disclosed in U.S. Pat. Nos. 5,515,221 and 5,621,592, which issued to Gill et al. on May 7, 1996 and Apr. 15, 1997, respectively. The patents disclose a multi-layer magnetic structure that can be used to form a shield in an MR read head. The multi-layer structure includes an anti-ferromagnetic layer and a ferromagnetic layer. The anti-ferromagnetic layer is annealed in a magnetic field that increases the uniaxial and uni-directional anisotropy of the ferromagnetic layer and provides exchange pinning of the ferromagnetic layer which motivates the domain configuration of the ferromagnetic layer to return to a stable state even after application of an external magnetic field. Unfortunately, when the multi-layered magnetic structure is processed (e.g., milled, lapped, etc.) the pinned domain configuration of the ferromagnetic layer may no longer be in an ideal stable state. In other words, the domain configuration of the ferromagnetic layer would shift in the event that the anti-ferromagnetic layer was removed even when in a zero magnetic field environment. Due to this instability, the application of an external magnetic field to the shield formed of the multi-layer magnetic structure of the Gill patents can result in an undesirable random shift to the domain configuration of the ferromagnetic layer. As a result, an MR head utilizing the shield material disclosed in the Gill patents can still encounter problems associated with shield instability.
The domain configuration instability problems described above will be exacerbated as the read elements of the MR read head are formed smaller and made more sensitive in order to meet the ever increasing demands for higher data areal density recordings. Accordingly, there is a continued need to improve domain configuration stability of shields used in MR heads.
SUMMARY OF THE INVENTION
Aspects of the present invention are directed toward a disc drive storage system and a read head for use in a disc drive storage system. More particularly, the present invention is directed toward a shield for use in the disc drive storage system and read head. Additionally, the present invention is directed toward a method of forming the shield. The shield includes a ferro
Han Dehua
Inturi Venkateswara R.
Kief Mark T.
Michel Richard P.
Vas'ko Vladyslav A.
Letscher George J.
Seagate Technology LLC
Westman Champlin & Kelly
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