Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-11-15
2004-07-20
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S322000
Reexamination Certificate
active
06765767
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to magnetic recording heads, and more particularly, to a read head for detecting magnetically encoded information in magnetic storage media and a related method for making such a read head.
BACKGROUND OF THE INVENTION
Devices utilizing the giant magnetoresistance (GMR) effect have utility as magnetic sensors, especially in read heads used in magnetic disc storage systems. The GMR effect is observed in thin, electrically conductive multi-layer systems having magnetic layers. Magnetic sensors utilizing the GMR effect are frequently referred to as “spin valve” sensors.
A spin valve sensor is typically a sandwiched structure including two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the “pinned layer” because it is magnetically pinned or oriented in a fixed and unchanging direction. A common method of maintaining the magnetic orientation of the pinned layer is through anti-ferromagnetic exchange coupling utilizing a proximate, i.e. adjacent or nearby, anti-ferromagnetic layer, commonly referred to as the “pinning layer.” The other ferromagnetic layer is called the “free” or “unpinned” layer because its magnetization can rotate in response to the presence of external magnetic fields.
The benefits of spin valve sensors result from a large difference in electrical conductivity exhibited by the devices depending on the relative alignment between the magnetizations of the GMR element ferromagnetic layers. In order for antiferromagnetically pinned spin valve sensors to function effectively, a sufficient pinning field from the pinning layer is required to keep the pinned ferromagnetic layer's magnetization unchanged during operation. Various anti-ferromagnetic materials, such as PtMn, NiMn, FeMn, NiO, IrMn, PtPdMn, CrMnPt, RuRhMn, and TbCo, have been used or proposed as antiferromagnetic pinning layers for spin valve sensors. GMR sensors can be used to sense information encoded in magnetic storage media. In operation, a sense current is passed through a GMR stack. The presence of a magnetic field in the storage media adjacent to the sensor changes the resistance of a GMR stack. A resulting change in voltage drop across the GMR stack due to the change of the resistance of the GMR stack can be measured and used to recover magnetically stored information.
These sensors typically comprise a stack of thin sheets of a ferromagnetic alloy, such as NiFe (permalloy), magnetized along an axis of low coercivity. The sheets are usually mounted in the head so that their magnetic axes are transverse to the direction of disc rotation and parallel to the plane of the disc. The magnetic flux from the disc causes rotation of the magnetization vector in at least one of the sheets, which in turn causes a change in resistivity of the stack.
A magnetic sensor for use in a disc drive can include a first shield, a second shield, and a GMR stack located between the first shield and the second shield. A permanent magnet can be located adjacent to the GMR stack to provide a bias magnetic field. For operation of the sensor, a sense current is caused to flow through the GMR stack. As resistance of the GMR stack changes, the voltage across the GMR stack changes. This is used to produce an output voltage.
A schematic of a conventional spin valve head
10
is illustrated in
FIGS. 1A and 1B
. The head
10
, shown as formed on a substrate
11
, includes a top shield
12
and a bottom shield
14
separated by a reproduce gap width, G, which includes leads
15
and
16
and may include the layers of insulation
13
. The head
10
also includes a read sensor
20
positioned between the top and bottom shields
12
and
14
and adjacent the leads
15
and
16
. The read sensor
20
has a track-width dimension, designated as Wt, which is defined by a permanent magnet (not shown) and leads
15
and
16
. The read sensor
20
also includes a stripe height dimension, designated as Hs, along which the flux from the recorded media bit is propagated until it closes in a closed path to the shields
12
and
14
. As illustrated by coordinate system
17
, the X direction refers to a down-track direction and the Z direction refers to a cross-track direction.
Despite the improvements in head sensitivity as a result of, for example, utilizing GMR heads, storage technology trends indicate that heads providing higher sensitivity, higher linear resolution, and higher track-resolution will be required for increased information retrieval capabilities of magnetic recording systems. Linear resolution generally relates to linear density, i.e. how many bits of information may be packed into a given length of magnetic track on the magnetic recording media. Track-resolution generally relates to track density, i.e. a measure of how tightly a plurality of magnetic tracks are packed onto a disc which forms the magnetic recording media. Such improvements have been evolving by reducing the bits aspect ratio of track-width to bit length to values of the order of about one. Therefore, heads with lateral dimensions of the order of the sensor film thickness will become necessary. While head sensitivity has been increased by enhancing the magnetoresistive effect ratio, as described, track-resolution and linear resolution have been improved by lithographically scaling sensor width and scaling magnetoresistive element to shield spacing, respectively. However, such techniques have limitations as the need for higher sensitivity and higher linear and track-resolution increases.
As head dimensions continue to decrease in conjunction with the higher linear and track-resolutions, there is an increased likelihood of non-intended magnetic fields being read by the head. Specifically, the head may sense a magnetic field from tracks adjacent to a magnetic track upon which a read operation is being performed and/or sense an adjacent magnetic domain within the magnetic track upon which a read operation is being performed. Either situation results in a decreased effectiveness of the read head. Spin valve heads, having the need for an insulator between the sensor, the permanent magnet biasing and leads and the shields have a linear resolution always limited by the total thickness of the stack and the insulator. Moreover, the track-width is defined by the permanent magnet and leads. The permanent magnet and the sensor are magnetostatically coupled. The control of magnetostatic coupling, profile of the junction and less than, for example, 100 nm track-widths become a complex problem.
Thus, there is identified a need for improved recording heads which provide for increased recording densities.
SUMMARY OF THE INVENTION
The invention meets the identified need, as well as other needs, as will be more fully understood following a review of the specification and drawings.
In accordance with an aspect of the invention, a read head for use with magnetic recording media having a plurality of magnetic tracks, each of the tracks having a plurality of magnetic domains, wherein the read head comprises a read sensor and first and second magnetic lead shields structured and arranged to shield the read sensor from a magnetic field within magnetic tracks adjacent to the magnetic track upon which a read operation is being performed. The read sensor is formed on a side wall of one of the first and second magnetic lead shields that are part of a set of two shields determining the track-width. The read sensor may be a spin valve, a GMR multilayer or a tunneling magnetoresistive sensor. To illustrate the invention, the read sensor is assumed to use a current perpendicular to the plane defined by the magnetization of the layers.
In accordance with a further aspect of the invention, a read head for use with magnetic recording media having a plurality of magnetic tracks, each of the tracks having a plurality of magnetic domains, wherein the read head comprises a read sensor, first and second magnetic lead shields, and first and second magnetic shields. The first and second magnetic lead sh
Seigler Michael A.
Trindade Isabel G.
Klimowicz William
Lenart, Esq. Robert P.
Pietragallo Bosick & Gordon
Queen, II, Esq. Benjamin T.
Seagate Technology LLC
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