Dynamic magnetic information storage or retrieval – Head – Head accessory
Reexamination Certificate
1998-08-13
2001-04-24
Letscher, George J. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Head accessory
C360S322000
Reexamination Certificate
active
06222702
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 of a magnetoresistive reader that eliminates magnetic interactions between a magnetic read head shield and a magnetic read element by preventing displacement of domain walls within the shield.
A magnetic read head retrieves magnetically-encoded information that is stored on a magnetic medium or disc. The magnetic read head is typically formed of several layers that include a top shield, a bottom shield, and a read element or sensor positioned between the top and bottom shield. The read element is fabricated from a magnetoresistive composition, typically a ferromagnetic material such as Nickel-Iron (NiFe). The read element is magnetized along an easy axis of low coercivity. The read element is mounted on the read head such that the 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. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
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. Within the bottom shield exists a plurality of magnetic domains. The magnetic domains are separate by one of a plurality of a magnetic domain walls. Each domain has a magnetization that is oriented in a direction different than the magnetization of all adjacent domains. 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 a shield can cause the magnetization of each of the domains within that shield to rotate, thereby causing the domains to move, grow, or shrink. Thus, the domain walls are relocated due to the external magnetic field. The movement of a domain wall through a portion of the shield that is directly adjacent the read element results in Barkhausen noise, which is a local perturbation of the magnetic structure within the read element producing an unwanted change in the resistance of the read element. Until recently, Barkhausen noise induced by domain wall movement has been negligible. However, as storage densities on magnetic media and discs have increased, the read element has necessarily become smaller, more sensitive, and more susceptible to Barkhausen noise created by domain wall movement. Therefore, there is a need for a shield design that elites Barkhausen noise by minimizing domain wall movement within the particular shield.
BRIEF SUMMARY OF THE INVENTION
The present invention is a shield design that eliminates Barkhausen noise by preventing domain wall movement within a particular shield. The shield design includes first and second triangular shaped closure magnetic domains positioned approximate a top surface of the shield such that a first surface of each of the first and second magnetic domains are formed by a portion of a first side of the shield and a second side of the shield, respectively. The shield also includes third and fourth triangular shaped closure magnetic domains positioned approximate the bottom surface of the shield. A first surface of a third and fourth magnetic domains are formed by a portion of the first side and the second side of the shield, respectively. A first magnetic domain wall is positioned between the first and second triangular shaped closure magnetic domains, while a second magnetic domain wall is positioned between the third and fourth triangular shaped closure magnetic domains.
In one preferred embodiment, the first magnetic domain wall intersects both an intersection point of the first triangular shaped closure magnetic domain and an intersection point of the second triangular shaped closure magnetic domain. Likewise, a second magnetic domain wall intersects both an intersection point of the third triangular shaped closure magnetic domain and an intersection point of the fourth triangular shaped closure magnetic domain. Both the first and the second magnetic domain walls are positioned parallel to an air bearing surface of the shield. The first, second, third, and fourth triangular shaped closure magnetic domains each equal an equilibrium domain, the equilibrium domain being an average width of a magnetic domain in a demagnetized sample shield that has a total magnetic moment equal to zero.
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Johnston Alan Biggar
Macken Declan
Mowry Gregory Stephen
Tolman Charles Henry
Kinney & Lange , P.A.
Letscher George J.
Seagate Technology Inc.
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