Patent Application
20100328817
A magnetic recording head generally includes two portions, a writer portion for saving magnetically encoded information on a magnetic disc and a reader portion for later retrieval from the disc. The reader portion typically includes a bottom shield, a top shield, and a sensor. The sensor is typically a magnetoresistive, giant magnetoresistive, or tunneling magnetoresistive sensor positioned between the bottom and top shields. Magnetic flux from data previously encoded on the surface of the disc causes rotation of the magnetization vector of a sensing layer of the sensor. Rotation in the sensing layer causes a change in electrical resistivity of the sensor that can be detected by passing a current through the sensor and measuring a voltage across the sensor. External circuitry then converts the voltage measurements into an appropriate format and manipulates them as necessary to recover the data encoded on the disc for use in a digital device or processor.
The writer portion of the magnetic recording head typically includes magnetic poles that are separated from each other at an air bearing surface (ABS) of the writer by a nonmagnetic gap layer. The poles are magnetically connected to each other at a region distal from the ABS by a back gap closure. Positioned on one of the poles or the back gap closure are one or more layers of conductive coils, each encapsulated by one or more insulating layers. The ABS is the surface of the magnetic head immediately adjacent the magnetic media or disc. The writer portion and the reader portion may be arranged in a merged configuration in which the bottom pole of the writer portion also serves as the top shield of the reader portion.
To write data to the magnetic media, electrical current is passed through the conductive coils, thereby inducing a magnetic field. In perpendicular recording, the field passes through one pole, the main or write pole, through a recordable surface layer of the disc and into a magnetically soft sublayer. During this process, the magnetic poles in each recordable sector are aligned perpendicular to the disc surface and the main write pole. The field then returns through both disc layers into a second pole, known as the return pole.
By reversing the polarity of the current through the coils, the induced magnetic field is also reversed, causing the magnetic field created in each sector to have a similar alignment as the write head at the time of writing. However, when current is removed from the coils, the applied magnetic field changes state and the main pole goes into a remanent state. Sometimes, the magnetization in the remanent state is oriented outside the ABS plane. A remanent state with a substantial perpendicular component can be a serious limitation in perpendicular recording, because perpendicular remanence mimics the magnetization field created by normal operation of the write head. This can cause a brief or long term erasure of data after the write sequence especially when the drive has begun to seek its next target on the disc.
Geometry of the main pole plays a substantial role in determining the remanent state. Writer main pole geometries are defined by a transverse width and vertical length at the ABS and by a height above the ABS. The transverse width dimension at the ABS is significantly less than the vertical length dimension and defines the track width. The height, defined as the distance from the ABS to the breakpoint where the pole broadens into the main pole body, is typically at least as long as the pole length. A suggested source of perpendicular remanence is the shape anisotropy of the pole favoring magnetization along the pole height. When the height/width ratio is large, this geometry can be a source of a perpendicular remanent state following writing, when magnetization remains out of the ABS plane.
A common solution to the problem of perpendicular remanence is to laminate the main pole with planar magnetic and nonmagnetic layers parallel to the ABS plane. When the pole laminations are thin enough and their width is large enough, the demagnetization energy tends to favor a magnetic state with remanence parallel to the ABS and to the transverse width direction. Lamination parallel to the ABS can reduce or eliminate the erasure problems for modern pole widths near and above 100 nm. However, this comes with a significant cost of dilution of the pole average magnetization by including a relatively high proportion of nonmagnetic spacer layers. Loss of average magnetization reduces the maximum write field and therefore the writeability and areal density capability of the writer. With diminishing pole width and increasing pole heights, the geometric factors that tend to cause perpendicular remanence become stronger. At the same time, the net impact of magnetic dilution becomes more severe because the required number of laminations increases as the width decreases, causing even greater dilution of the average magnetization.
A magnetic writer includes a write pole with a magnetic easy-axis parallel to the downtrack direction (i.e. the write pole length). The easy-axis anisotropy can be achieved by engineering the intrinsic and extrinsic shape anisotropies. One method to accomplish this is to fabricate a multilayer write pole with alternating planar magnetic and nonmagnetic layers parallel to a vertical length dimension of the pole (the write pole length) and perpendicular to the ABS. Magnetic anisotropy (i.e. the easy axis) in each magnetic layer is parallel to the vertical length dimension of the write pole and parallel to the ABS.
The write pole tip may be formed by defining a shape of the write pole tip, and depositing alternating magnetic layers and nonmagnetic layers so that the magnetic layers are oriented substantially parallel to a length dimension and substantially perpendicular to the ABS, with each magnetic layer having an easy axis and magnetization substantially parallel to the length dimension and the ABS.
The ideal magnetic orientation for a write pole is for the remanence to be parallel to the air bearing surface (ABS) with no perpendicular component of the magnetic field. A number of factors affect magnetic orientation in main write poles. Perhaps the largest effect is due to shape anisotropy where the demagnetization energy is minimized in specific magnetic orientations related to the shape of the pole. A prime example of shape anisotropy in pole structures is the confinement of alternating magnetic vectors to each layer in multilayer magnetic structures. Crystalline anisotropy also affects magnetization orientation, in that the crystalline anisotropy energy is lowest in specific crystallographic directions in a magnetic material. Stress also affects magnetization orientation. The easy axis of magnetization will prefer to orient along the principal directions of tensile stress in a solid with an internal stress field. As another example, the interface anisotropy energy is lowest when magnetization is directed along internal interfaces in structures. Thus, there are a number of ways to control remanent magnetization in write poles.
A remanent state parallel to the vertical length direction can be established by engineering the geometry and material properties to insure a minimum energy state for this vertical orientation. Preferably this is accomplished using a very high moment material such as Fe60Co40 with Ms=2.4 T. There are many factors that contribute to the net energy. These are listed in Table 1 in decreasing order of influence.
The net effect depends upon the balancing of the geometry and materials. Roughly these energies are listed in decreasing magnitude. Bulk effects outweigh interface effects which outweigh surface energy effects. Pole shape is a major factor in tailoring the vertical remanence proposed herein. In addition to controlling remanence/erasure, it is critical to maximize write field to enable higher areal densities. For maximum write field, the dilution must be minimized with an ultimate target of zero (i.e. Pole Ms=2.4 T). This implies a “single-lamination”. This can be accomplished by engineering the material magnetic anisotropies listed above and defining a high aspect ratio pole geometry. Vertical remanence can also be reinforced by the addition of bevel and narrow-gap trailing shield structures.
The embodiments disclosed herein describe laminated write poles with remanent magnetizations parallel to the ABS and also to the vertical length direction of the pole tip. The planar laminations are oriented perpendicular to the ABS, thereby eliminating problems associated with prior art poles in which the planar orientations of the laminations are parallel to the ABS.
Write pole 14 is oriented substantially perpendicular to magnetic storage medium 12. Write pole 14 includes pole tip 16, which is magnetically coupled to flux return pole 18 through back gap passage 20. Return pole 18 has a substantially larger area facing magnetic storage medium 12 than the bottom surface of write pole tip 16. For recording, a magnetic field is induced in write pole 14 by an electrically conducting write coil 22. Write pole 14 is separated from return pole 18 by a nonmagnetic gap and is separated from electrically conducting coil 22 by an insulating layer (not shown). The magnetic field passes through storage medium 12 as indicated by arrow 28 and orients the magnetization of regions 30 in track 32 of hard magnetic recording layer 24 either perpendicularly up or down depending on the direction of the current in write coil 22. After the magnetic field passes through hard magnetic recording layer 24, it passes through soft magnetic underlayer (SUL) 26 before it enters return pole 16 and back gap passage 20 to complete the magnetic write circuit.
When transverse pole width W is considerably less than height H, there is a strong potential for magnetic remanence in pole tip 16 to be perpendicular to the ABS, predominantly due to shape anisotropy. This residual magnetic field out of the ABS plane is likely to cause unintended writing or erasure of data during otherwise normal operation. The potential for perpendicular remanence in main pole 14 increases with the aspect ratio (height/width) of pole tip 16. Prior art steps taken to counter the potential for vertical remanence, such as lamination of the main pole parallel to ABS, achieve the desired effect but also have the undesired effect of reducing the strength of the write field due to dilution resulting from the increased volume percentage of nonmagnetic layers. A strong write field precisely targeted to the correct region on the disc is important for performance of the disc drive. As demand grows for smaller pole tips and the resulting increased areal density disc drives, the aspect ratio of pole tip 16 continues to increase. The resulting vertical remanence effects have and will continue to be more problematic.
While pole tip 16 schematically illustrated in
The above mentioned issues with excessive magnetic field dilution resulting from excess nonmagnetic material in pole tip 16A of
Two embodiments whereby laminated write pole tip 16B is formed such that the remanent magnetization is parallel to both vertical direction L as well as to the ABS are described in what follows.
To form the damascene pole structure, as described in
In another embodiment, a multilayer write pole with remanent easy axes parallel to both vertical direction L of the pole tip and the ABS is formed by physical vapor deposition (PVD). The steps to form write pole tip 16B by PVD are schematically listed in
Write pole tip 20B, shown in
Multilayer structure 100 can be formed by physical vapor deposition, ion beam deposition, magnetron sputtering and other deposition methods. Static off-axis deposition of multilayer structure 100 offers an added benefit. By controlling angle θ of the deposition flux, magnetic anisotropy can be induced in magnetic layers 106. Depending on the value of θ, magnetic anisotropy parallel to or perpendicular to the flux direction can occur that can be used to advantage to amplify the shape anisotropy direction imparted by the thin film layers. Preferably, magnetic layer 106 is formed of cobalt iron (CoFe), cobalt nickel iron (CoNiFe), nickel iron (NiFe), cobalt (Co) or other magnetic material. A high moment 1.2 T cobalt-iron alloy is preferred. The thickness of magnetic layer 106 is preferably between about 20 nm to about 300 nm, more preferably between about 120 nm to about 250 nm microns. Spacer layer 108 can be tantalum (Ta), ruthenium (Ru), chromium (Cr), aluminum (Al), copper (Cu) or other nonmagnetic metals. The thickness of nonmagnetic spacer layer 108 is preferably between about 5 nm to about 100 nm, more preferably between about 25 nm to about 50 nm microns.
Micromagnetic simulations of the times to reach equilibrium from the saturated state have been made for two laminated write pole configurations. Write pole configuration A resembled prior art pole 14A and pole tip 16A shown in
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. The implementations described above and other implementations are within the scope of the following claims.
