Patent Application
20120026628
The present invention relates to magnetic heads for data recording, and more particularly to a perpendicular magnetic write head that has a magnetic trailing wrap-around shield for improving bit error rate and reducing adjacent track interference and far track interference.
The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A giant magnetoresistive (GMR) or tunnel junction magnetoresistive (TMR) sensor senses magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, or barrier layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer. First and second leads are connected to the sensor for conducting a sense current there-through. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
In a perpendicular magnetic recording system, the magnetic media has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from the write pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer. The resulting magnetic flux then travels through the soft underlayer, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the write pole when it passes back through the magnetically hard top layer on its way back to the return pole.
As perpendicular magnetic write heads become smaller, problems regarding adjacent track interference (ATI) and far track interference (FTI) appear. This has been found to be particularly problematic in certain regions within the trailing wrap-around magnetic shield where magnetic hot spots form. Therefore, there is a need for a perpendicular magnetic head design that can minimize such adjacent track interference and FTI, while maintaining excellent magnetic performance. These magnetic hot spots are usually “leaking” localized magnetic field during writing due to concentrations of magnetic domain structures. The leaking field can actually erase the magnetic media underneath, causing errors in these adjacent or far removed tracks.
The present invention provides a perpendicular magnetic write head having improved Bit Error Rate (BER), reduced Adjacent Track Interference (ATI) and Far Track Interference (FTI). The write head includes a write pole and a trailing shield or trailing wrap-around magnetic shield. A permanent magnetic is located at either outer side of the shield. These magnets are magnetized to have magnetizations that are oriented in the same direction, in a direction that is perpendicular to the track direction and parallel with the air bearing surface.
The permanent magnets create a cross-track field that reduces the formation of magnetic hot spots near the write pole, thereby preventing such hotspots from inadvertently erasing the media in adjacent or far away data tracks. The cross track magnetic field accomplishes this by generating magnetic domain formation that has less magnetic field leakage away from the write pole. This cross track field also advantageously increases field gradient, thereby improving the write head's ability to write to a magnetic media.
These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout.
For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale.
The following description is of the best embodiments presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein.
Referring now to
At least one slider 113 is positioned near the magnetic disk 112, each slider 113 supporting one or more magnetic head assemblies 121. As the magnetic disk rotates, the slider 113 moves radially in and out over the disk surface 122 so that the magnetic head assembly 121 may access different tracks of the magnetic disk where desired data are written. Each slider 113 is attached to an actuator arm 119 by way of a suspension 115. The suspension 115 provides a slight spring force which biases slider 113 against the disk surface 122. Each actuator arm 119 is attached to an actuator means 127. The actuator means 127 as shown in
During operation of the disk storage system, the rotation of the magnetic disk 112 generates an air bearing between the slider 113 and the disk surface 122 which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension 115 and supports slider 113 off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk storage system are controlled in operation by control signals generated by control unit 129, such as access control signals and internal clock signals. Typically, the control unit 129 comprises logic control circuits, storage means and a microprocessor. The control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123 and head position and seek control signals on line 128. The control signals on line 128 provide the desired current profiles to optimally move and position slider 113 to the desired data track on disk 112. Write and read signals are communicated to and from write and read heads 121 by way of recording channel 125.
With reference to
An electrically conductive, non-magnetic write coil 318 passes between the write pole 304 and return pole 306 and may also pass above the write pole 304. The write coil 318 can sit on top of a non-magnetic, electrically insulating material 322 and is also embedded in a non-magnetic, electrically insulating material 320 such as alumina and or hard baked photoresist.
During operation, an electrical current flowing through the coil 318 induces a magnetic field that results in a magnetic flux flowing through the write pole 304. This causes a magnetic field to be emitted from the write pole 304 toward a magnetic medium such as the magnetic medium 122 shown in
In order to increase the write field gradient (and thereby facilitate magnetic switching), the write head 302 also includes a magnetic trailing shield 312. This trailing shield 312 is separated from the write pole 304 by a non-magnetic trailing gap layer 402. The write pole 312 may also be connected with a trailing return pole 316 that connects the trailing shield 312 with the back portion of the write head 302, such as the back portion of the shaping layer 310.
Also, as can be seen, the write head 302 includes first and second hard magnets 406, 408 located at first and second outer sides of the wrap-around trailing magnetic shield 312. These hard magnets 406, 408 are magnetized to have a magnetization (indicated by arrows 410, 412) that are oriented in the same direction perpendicular with data track direction (as indicated by line DT), and parallel with the air bearing surface ABS. Although the arrows are shown in
These hot spots arise from the formation of magnetic domains in the trailing shield. A problem presented by the presence of such magnetic hot spots is that the magnetic flux concentrations at the location of these hot spots 502, 504, 602, 604 can magnetize the magnetic media. While adjacent track interference in a single write pass may not be a problem, after several write passes on a data track of interest data tracks that are one or several data tracks away from the intended track may become damaged by the presence of these stray magnetic fields.
With reference again to
Another benefit provided by the presence of the cross track magnetic field is that magnetic switching is made easier through an increase in field gradient. This effect is similar to the field gradient increase provided by the trailing portion of the shield 312 across the trailing gap 418.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
