Magnetic recording head including background magnetic field generator

A perpendicular recording head (10) for use with magnetic recording media (30) includes a main pole (14) and a magnetic field source which is positioned sufficiently close to the main pole tip to generate a background magnetic field in the recording media. A conductive magnetizing coil (20) surrounding the main pole is preferably used as the magnetic field source. The background magnetic field generated by the magnetizing coil effectively reduces the coercivity of the magnetic recording media in the region affected by the background field. The recording head enables writing on high coercivity/high anisotropy magnetic media, thereby achieving extremely high recording densities.

FIELD OF THE INVENTION

The present invention relates to recording heads for use with magnetic storage media, and more particularly relates to a perpendicular recording head which generates a background magnetic field in the magnetic media.

BACKGROUND INFORMATION

In order to increase the data storage density of hard disk drives, the use of magnetic media having increased magnetic anisotropy has been proposed. However, highly anisotropic media exhibit extremely high coercivities, e.g., well over 5,000 Oe. Conventional perpendicular magnetic recording heads are not capable of recording on media having such high coercivities.

The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.

SUMMARY OF THE INVENTION

The present invention provides a magnetic recording head for use with magnetic recording media having a magnetic field generating coil configured and positioned to generate a background magnetic field in the magnetic recording media.

The magnetic recording head preferably comprises a perpendicular configuration. In accordance with the present invention, the perpendicular recording head generates a supplemental magnetic field which increases the magnetic recording field in comparison with conventional perpendicular recording heads. Although not limited to such use, perpendicular recording heads of the present invention are particularly useful for computer hard disk drives.

A typical perpendicular recording head includes a main pole, an opposing pole magnetically coupled to the main pole, and an electrically conductive magnetizing coil surrounding the main pole. The bottom of the opposing pole will typically have a surface area greatly exceeding the surface area of the tip of the main pole. In a preferred embodiment, electrical current flowing through the magnetizing coil creates a flux through the main pole tip and also generates the background magnetic field in the recording media.

A typical magnetic recording medium for use in conjunction with the present perpendicular recording head includes an upper layer having multiple magnetically permeable tracks separated by nonmagnetic transitions, and a magnetically permeable lower level. The lower level is magnetically soft relative to the tracks.

To write to the magnetic recording medium, the recording head is separated from the magnetic recording medium by a distance known as the flying height. The magnetic recording medium is moved past the recording head so that the recording head follows the tracks of the magnetic recording medium, with the magnetic recording medium first passing under the opposing pole and then passing under the main pole. Current is passed through the coil to create magnetic flux within the main pole. The magnetic flux will pass from the main pole tip through the track, into the lower layer, and across to the opposing pole. In addition to the magnetic field generated at the main pole tip, a supplemental magnetic field is generated in accordance with the present invention. The combined magnetic flux from the pole tip and from the coil causes the magnetic fields in the tracks to align with the magnetic flux of the recording head. Changing the direction of electric current changes the direction of the flux created by the recording head and therefore the magnetic fields within the magnetic recording medium.

An aspect of the present invention is to provide a perpendicular recording head including a main pole having a tip, and an electrically conductive magnetizing coil positioned sufficiently close the main pole tip to generate a background magnetic field in the magnetic recording medium when current is passed through the magnetizing coil.

Another aspect of the present invention is to provide a magnetic recording apparatus comprising a magnetic recording medium and a recording head. The magnetic recording medium includes an upper layer having a plurality of data storage tracks, and a lower layer being magnetically soft relative to the data storage tracks. The recording head includes a main pole having a tip, and an electrically conductive magnetizing coil positioned sufficiently close the main pole tip to generate a background magnetic field in the magnetic recording medium when the recording head is positioned at a flying height above the magnetic recording medium and current is passed through the magnetizing coil.

A further aspect of the present invention is to provide a method of storing data on a magnetic storage medium. The method includes the steps of providing a magnetically permeable main pole, providing a magnetic storage medium adjacent the main pole, directing magnetic flux from the main pole toward the magnetic storage medium, and additionally generating a background magnetic field in the magnetic storage medium.

DETAILED DESCRIPTION

The preferred embodiment of the present invention provides a perpendicular recording head for use with magnetic recording media. As used herein, “recording head” means a head adapted for read and/or write operations.

The present invention has been developed in order to overcome certain problems with conventional hard disk drive systems. Granular magnetic recording media used in such systems is subject to superparamagnetic instabilities when the anisotropy energy of the grains (Ku×V, where V is the grain volume) becomes comparable to the energy of thermal fluctuations, kT. Improvements in recording densities requires continuous refinement of the grain size. Higher anisotropy materials are desirable in order to keep the media thermally stable. As an example, the L10 phase of Co50Pt50has an anisotropy energy Ku=4×106J/m3(compare with Ku=˜105J/m3for CoCr media). Such high anisotropy reduces the critical size at which grains become thermally unstable to less than 1 nm. Utilizing these materials for recording media can potentially extend the recording densities well beyond 100 Gbit/in2. However, a major obstacle preventing utilization of high anisotropy media is that such media exhibit exceptionally high coercivities, e.g., in excess of 5,000 Oe.

The magnitude of the fields generated by conventional perpendicular recording heads is limited by the saturation moment of the yoke material.FIG. 1is a graph illustrating the dependence of magnet field strength on the distance from the pole tip or air-bearing surface (ABS) for a conventional single-pole perpendicular head utilizing FeAlN (saturation moment of 2Tesla) as the pole material. At distances greater than 15 nm from the ABS, the field drops below 5,000 Oe. This arrangement is therefore not sufficient for recording on media with coercivities of 5,000 Oe and higher.

FIG. 2schematically illustrates a single pole perpendicular recording head10in accordance with an embodiment of the present invention. The perpendicular recording head10includes a yoke12made of magnetically permeable material such as NiFe, CoZrNb, CoZrTa, CoNiFe, FaAlN, FeTaN, CoFe, CoFeB or any other soft magnetic materials, including multiple layers or laminates of such materials. A main pole14extends from the yoke12and includes a main pole tip16. The main pole14may be made of any suitable magnetically permeable material such as NiFe, FeAlN, FeTaN, CoFe, CoFeB, CoFeN or any other soft magnetic materials, including multiple layers of such materials. An opposing pole18is magnetically coupled to the main pole14. In accordance with the present invention, an electrically conductive magnetizing coil20surrounds the yoke12and main pole14. As shown inFIG. 2, the magnetizing coil20is located close to the main pole tip16. Electrical current is supplied to the coil20through electrical connections22. The magnetizing coil20may be made of any suitable electrically conductive material, such as Cu, Ag, Au or any other high conductivity materials or alloys.

As shown inFIG. 2, the perpendicular recording head10is positioned above a magnetic storage media including a hard magnetic recording layer30and a soft magnetic underlayer32. A protective overcoat33such as diamond-like carbon is applied over the recording layer30. During recording operations, the magnetic media moves in the direction of the arrow shown in FIG.2.

The recording layer30may be made of any suitable hard magnetic material such as CoCrPt, CoCrPtTa, CoCrPtB, CoCrPtTaNb or other high anisotropy hexagonal Co-containing alloys. The recording layer30may also be made of CoPt, FePt, CoPd, FePd or other high anisotropy L10 materials. High anisotropy materials such as Co/Pd, CoB/Pd, CoCr/Pd, CoCrPt/Pd, CoCrPd/Pt, CoB/Pt, Co/Pt, CoCr/Pt, Fe/Pd and Fe/Pt may also be used as the recording layer30. Furthermore, high anisotropy ferrites such as Ba ferrite may be used as the recording layer30. Preferred materials for the recording layer30include L10 materials such as CoPt, FePt, CoPd and FePd, and multilayers of Co/Pt and Co/Pd. The recording layer may have a relatively high anisotropy energy Ku, e.g., greater than about 106J/m3. For example, recording layers having anisotropy energy Kulevels of from about 106to about 108μm3may be used. The recording layer may also have a relatively high coercivity above 5,000 Oe, e.g., above 8,000 or 10,000 Oe. The underlayer32may be made of any suitable soft magnetic material, such as FeAlN, FeTaN, CoFe, CoFeB, CoFeN or other high moment soft magnetic materials or soft magnetic films comprising multiple layers of such materials.

FIG. 3is an enlarged view of a portion of the perpendicular recording head10ofFIG. 2, showing dimensional details of the yoke12, main pole14and magnetizing coil20. The magnetizing coil20has a radial dimension R measured from the center of the yoke12or the longitudinal axis of the main pole14. The coil20is located at a distance D from the main pole tip16, measured in a direction parallel with the longitudinal axis of the main pole14(normal to the surface of the recording layer30). The main pole tip16is located at a flying height H above the upper surface of the protective layer33. The main pole tip16preferably forms part of the air bearing surface of the recording head10. The magnetizing coil20is positioned at a distance Z from the upper surface of the recording layer30, measured in a direction parallel with the longitudinal axis of the main pole14. The distance Z is equal to the sum of the distances D and H, plus the thickness of the protective layer33. As further shown inFIG. 3, the yoke12has a thickness Tywhich is preferably larger than the thickness Tpof the main pole14.

The dimensions R, D, H, Z, Tyand Tpare preferably selected in accordance with the present invention to produce a sufficient background magnetic field in the recording layer30when current flows through the coil20. For many perpendicular recording head configurations, R preferably ranges from about 0.1 to about 5 micron, D ranges from about 0.1 to about 5 micron, H ranges from zero to about 0.1 micron, and Z ranges from about 0.1 to about 5 micron. The yoke thickness Tymay typically be from about 0.1 to about 5 micron, preferably from about 0.1 to about 1 micron. The main pole thickness Tpmay be from about 0.01 to about 0.5 micron, preferably from about 0.01 to about 0.1 micron.

In accordance with the present invention, the ratio of the coil radial dimension R to the distance D is preferably controlled in order to generate the desired background magnetic field in the recording layer30, as more fully described below. The ratio of R:D typically ranges from about 1:1 to about 10:1, preferably from about 1:1 to about 5:1. The ratio of the yoke thickness Tyto the pole thickness Tpis also controlled. The ratio of Ty:Tppreferably ranges from about 1:1 to about 10:1. More preferably, the ratio of Ty:Tpranges from about 2:1 to about 5:1.

Although the magnetizing coil20shown inFIGS. 2 and 3comprises a single circular winding, multiple windings and/or other coil shapes may be used. For example, the coil20may alternatively be square, rectangular, helical, straight, etc. Similarly, the cross-sectional shapes of the yoke12and main pole14may be round, square, rectangular, or the like. The magnetizing coil20preferably surrounds the yoke12and main pole14as shown inFIGS. 2 and 3. However, the coil could be located at a different position on the head10as long as a sufficient background magnetic field is generated. Furthermore, although not preferred, a permanent magnet could be used in place of, or in addition to, the coil20.

FIGS. 4 and 5schematically illustrate alternative coil configurations in accordance with the present invention. In the embodiment shown inFIG. 4, an electrically conductive magnetizing coil24surrounds and is positioned directly adjacent the outer surface of the yoke12. In the embodiment shown inFIG. 5, an electrically conductive magnetizing coil26surrounds and is embedded in a recess28which extends around the outer surface of the yoke12. InFIGS. 4 and 5, each of the magnetizing coils24and26is shown as a single winding around the yoke12. Alternatively, multiple coil windings may be used. Although the magnetizing coils24and26shown inFIGS. 4 and 5have square cross sections, any other suitable sectional shape may be used, such as rectangular, circular, etc. The cross-sectional thickness of the magnetizing coils20,24and26typically ranges from about 0.01 to about 5 micron, preferably from about 0.1 to 2 micron.

In the embodiments shown inFIGS. 2-5, the pole tip16comprises a flat surface. Alternatively, the present design can be combined with a perpendicular head having a concave pole tip design, such as the concave pole tips described in U.S. patent application Ser. No. 09/665,598, filed Sep. 19, 2000 entitled Perpendicular Recording Head Including Concave Tip, which is incorporated herein by reference.

In accordance with the present invention, the amount of electrical current supplied to the magnetizing coil20is controlled in order to generate the desired background magnetic field strength at the recording layer30, the background magnetic field is typically greater than 100 Gauss, preferably greater than 1,000 or 2,000 Gauss. Depending upon the magnetic properties of the recording layer30, the background magnetic field may typically range from about 100 to about 20,000 Gauss, preferably from about 1,000 to about 15,000 Gauss, and more preferably from about 5,000 to about 10,000 Gauss at the recording layer30. The background magnetic field effectively decreases the coercivity of the recording layer30. The coercivity of the recording layer30may be defined as Hc, and the background magnetic field effectively decreases the coercivity Hcto a lower value defined as Hb. The ratio of Hb:Hcpreferably ranges from about 1:10 to about 9:10, more preferably from about 3:10 to about 8:10. In a particularly preferred embodiment, the ratio of Hb:Hcis about 5:10.

In accordance with a further aspect of the present invention, the level of the background magnetic field Hbis controlled in relation to the strength of the magnetic field Hpgenerated at the main pole tip16. Preferably, the ratio of Hb:Hpis from about 1:10 to about 10:1, more preferably from about 4:10 to about 3:1. As a particular example, a recording layer having a coercivity of 10,000 Oe may be written on with a recording head of the present invention which generates a pole tip coercivity Hpof 5,000 Oe and a background coercivity Hbof 8,000 Oe. Thus, while the magnetic flux generated from the pole tip would not be sufficient to write on the recording layer alone, the background magnetic field is sufficient to effectively reduce the dynamic coercivity of the recording layer, thereby enabling writing on the recording layer.

As long as the pole tip is not completely saturated, the magnetic flux is mainly concentrated within the pole tip. A standard way of operating a single pole head is to choose a current value SAT that causes complete saturation of the pole tip. The fields generated by the saturated pole are localized and their gradients within the recording layer determine the minimum bit cell size. If the current in the coil is further increased by ΔI (ΔI=I-ISAT), the extra flux generated will no longer be confined to the pole tip. The magnitude of the additional field AB will be proportional to ΔI. The field flux will be spread over a significantly larger region within the recording layer, the size of which is determined by the diameter of the coil due to the relative proximity of the coil to the recording layer. The magnitude of ΔB can be fine-tuned by the current in the coil. For a single turn coil the magnitude of ΔB is given by:Δ⁢⁢B=μ0⁢Δ⁢⁢I2⁢R2(R2+z2)3/2,
where R is the radius of the coil and z is the distance from the coil to the hard layer. For R=0.2 μm and z=0.1 μm, background fields in excess of 1Tesla (10,000 Oe) can be generated with currents as small as 400 mA with a resolution of about 25 Oe/mA if a single turn coil is used.

The presence of the additional background field AB effectively reduces coercivity of the recording layer. It enables writing on high coercivity media using heads based on available soft materials. Because of high data rates, the dynamic coercivity will be affected by the introduction of such background field because the dynamic coercivity is significantly higher than the static coercivity.

FIG. 6illustrates magnetic field simulation results using a boundary element solver, Amperes, for different values of coil current. The field profiles at I=50 mA (=ISAT) and I=200 mA (ΔI=150 mA) are given. The additional 150 mA of current on top of the saturation current ISATgenerates a background field of 4,000 Oe. This background field would not be high enough to erase the previously recorded bit pattern, but it effectively increases the write field of the pole tip, i.e., decreases the effective media coercivity.

A test was conducted to confirm the performance of the present design.FIG. 7schematically illustrates the test. A conventional perpendicular writer34having a magnetic coil35placed far from the pole tip36or the air bearing surface of the writer was used in combination with an external field source38(a strong rare earth-based permanent magnet that could generate stray fields in excess of 2,000 Oe) to simulate a background field from a coil if the coil was placed in close proximity to the ABS. The recording tests were conducted on a multilayer perpendicular media30comprised of twenty layers of Co/Pd on a soft underlayer of FeAlN, having a coercivity in excess of 8,000 Oe. First, the media was DC saturated (DC erased) in a strong magnetic field generated using a large electromagnet. As expected, due to demagnetizing fields, no stray field emanates from the DC saturated media, resulting in zero signal read-out. Next, recording with a conventional perpendicular writer was attempted, which failed due to insufficient magnitude of the recording field. The recording failure was confirmed by the absence of the read-out signal. Finally, a small permanent magnet was placed above the recording head in close proximity to the media, as schematically illustrated inFIG. 7, and another recording attempt was performed. The result was a well-recorded bit pattern with the playback shown in FIG.8. The results shown inFIG. 8demonstrate that the anisotropy of the recording media is effectively temporarily lowered by the application of the background magnetic field.

The present recording system effectively reduces the coercivity of the media. This is accomplished by generating a background field utilizing a magnetizing coil which is placed in proximity to the recording layer. This recording system enables writing on high coercivity/high anisotropy media that can support very high recording densities, e.g., in excess of 100 Gbit/in2. High recording densities can therefore be achieved without the necessity of major changes in the recording process.