Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Utility Patent
1999-03-17
2001-01-02
Klimowicz, William (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Utility Patent
active
06169646
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of electronic data storage and retrieval. In particular, the present invention relates to a shield design in a magnetoresistive reader that reduces magnetic interactions between a magnetic read head shield and a magnetic read element by controlling domain wall movement within the shield.
Magnetoresistive (MR) read heads utilize an MR element positioned between a top and a bottom shield to read magnetically-encoded information from a magnetic medium, such as a disc, by detecting magnetic flux stored on the magnetic medium. The read element may be either an anisotropic magnetoresistive (AMR) element or a giant magnetoresistive (GMR) stack. An AMR element is typically fabricated from iron, nickel, or cobalt-based soft ferromagnetic alloys; whereas a GMR stack is a multi-layered structure generally having two separate layers formed from iron, nickel, or cobalt-based soft ferromagnetic alloys separated by a spacer layer formed from nonmagnetic materials, such as copper, silver, or gold.
The read element, which is magnetized along its easy axis, is mounted on the read head such that its easy axis is transverse to the direction of disc rotation and parallel to the plane of the disc. Magnetic flux from the disc surface causes rotation of the magnetization vector of the read element, which in turn causes a change in electrical resistivity of the read element. The change in resistivity of the read element can be detected by passing a sense current through the read element and measuring a voltage across the read element. This voltage information can then be converted into an appropriate format to be manipulated as necessary by external circuitry.
A response curve of the read element 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, of which it is preferred that the read element operate along the linear portions. To force the read element to operate along the linear portions, the read element is magnetically biased at a biasing point that is located along the linear portion of the response curve.
During a read operation, the top and bottom shields ensure that the read element reads only the information stored directly beneath it on a specific track of the magnetic medium or disc by absorbing any stray magnetic fields emanating from adjacent tracks and transitions.
Accordingly, the bottom shield is typically formed of materials having a relatively high permeability. Sendust (85% iron, 9.6% silicon, and 5.4% aluminum) is the generally preferred material for prior art bottom shields because of its near-zero magnetostriction and mechanical hardness. Sendust-shielded read elements can be machined easily to form sliders with minimal smearing across the read element. Smearing across the read element may result in electrical shorts between the read element and the top or bottom shield.
Although sendust is the generally preferred material for use as the bottom shield in read heads, its near-zero magnetocrystalline anisotropy can result in noise in the read element. Within a typical shield exists a plurality of magnetic domains separated from each other by a plurality of magnetic domain walls. Each domain has a magnetization that is oriented in a direction different than the magnetization of all adjacent domains. Because of the near-zero magnetocrystalline anisotropy of a sendust-formed shield, the domain walls within a sendust-formed shield are totally random, although the shape of the shield may somewhat control the location of the domain walls. In addition, the application of an external magnetic field, either during manufacture or from an adjacent track or transition of the magnetic storage medium during operation, to the bottom shield can cause the magnetization of each of the domains within that shield to rotate, thereby causing the domains to move. Thus, the domain walls are relocated due to the external magnetic field. Furthermore, because of the random nature of the domain wall location, the domain walls generally do not return to their original location after the external magnetic field is removed.
The bottom shield exerts 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.
It has been found that the introduction of anisotropy into a shield will result in more predictable domain wall locations within the shield; however, it has also been found that the controlled introduction of anisotropy into a material having near-zero magnetocrystalline anisotropy, such as sendust, is virtually impossible. There is therefore a need for a shield design having the advantages of a sendust-formed shield with a shield having magnetocrystalline anisotropy to reduce noise in the read element by reducing domain wall movement within the shield.
BRIEF SUMMARY OF THE INVENTION
The present invention is a shield having substantial magnetocrystalline anisotropy for a read element in a recording head. A layer of iron—silicon—aluminum alloy is positioned upon a seedlayer of amorphous alloy to form the shield. Percentage weights of iron, silicon, and aluminum in the iron—silicon—aluminum alloy are each selected so that the alloy has both near-zero magnetostriction and distinct magnetocrystalline anisotropy. Use of the amorphous alloy seedlayer results in greater overall magnetocrystalline anisotropy in the shield.
In a preferred embodiment of the iron—silicon—aluminum alloy layer, the percentage weight of iron is in the range of from about 81% to about 93%, the percentage weight of silicon is in the range of from about 6% to about 10%, and the percentage weight of aluminum is in the range of from about 0% to about 13%. Most preferably, the percentage weights of iron, silicon, and aluminum in the iron—silicon—aluminum alloy layer are, respectively, about 89 percent, about 7.5 percent, and about 3.5 percent.
In a preferred embodiment of the seedlayer, the seedlayer is formed of a cobalt-amorphous family alloy or nickel. More preferably, the seedlayer is formed of a cobalt—zirconium—tantalum alloy. A preferred embodiment in which the seedlayer is formed of cobalt—zirconium—tantalum alloy preferably has a percentage weight of cobalt in the seedlayer in the range of about 70 percent to about 90 percent, and a percentage weight of zirconium in the seedlayer substantially equal to a percentage weight of tantalum in the seedlayer. Most preferably, the percentage weight of cobalt in the seedlayer is about 90 percent and the percentage weights of zirconium and tantalum in the seedlayer are each about 5 percent.
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“On the New Alloy ‘Sendust’ and Ternary Alloys Containing Fe-Si-Ai, and the Magnetic and Electrical Properties” by H. Masumoto et
Duddy Kevin J.
Macken Declan
Kinney & Lange , P.A.
Klimowicz William
Seagate Technology Inc.
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