Patent Application
20070297081
Magnetic writer 10 is carried over the surface of magnetic medium 14, which is moved relative to magnetic writer 10 as indicated by arrow A such that write pole 20 is the trailing pole and is used to physically write data to magnetic medium 14. Conductive coils 24 surround back via 26 such that, when a write current is caused to flow through conductive coils 24, the magnetomotive force in the coils magnetizes write pole 20 and return pole 28. This causes a write field to be generated at pole tip 34 of main portion 30, which is used to write data to magnetic medium 14. The direction of the write field at pole tip 34, which is related to the state of the data written to magnetic medium 14 is related, is controllable based on the direction that the write current that flows through conductive coils 24.
Magnetic writer 10 is shown merely for purposes of illustrating a construction that may be used in conjunction with the current assisted recording of the present invention, and variations on the design may be made. For example, while write pole 20 includes main portion 30 and yoke portion 32, write pole 20 can also be comprised of a single layer of magnetic material. Also, magnetic writer 10 may include no return pole, or may include multiple return poles, such as a configuration including a leading return pole that is coupled to yoke portion 32 through a leading back gap closer and a trailing return pole that is coupled to main portion 30 through a trailing back gap closer. In addition, magnetic writer 10 is configured for writing data perpendicularly to magnetic medium 14, but magnetic writer 10 and magnetic medium 14 may also be configured to write data longitudinally. Furthermore, a magnetic reader may be provided adjacent to and carried over magnetic medium 14 on the same device as magnetic writer 10.
Magnetic medium 14 includes substrate 36, soft underlayer (SUL) 38, and medium layer 40. SUL 38 is disposed between substrate 36 and medium layer 40. Magnetic medium 14 is positioned proximate to magnetic writer 10 such that the surface of medium layer 40 opposite SUL 38 faces write pole 20. In some embodiments, substrate 36 is comprised of a non-magnetic material, such as aluminum and aluminum based alloys, SUL 38 is comprised of a magnetically soft (i.e., high permeability) material, and medium layer 40 is comprised of a granular material having a high perpendicular anisotropy and high coercivity.
SUL 38 is located below medium layer 40 of magnetic medium 14 and enhances the amplitude of the write field produced by the write pole 20. The image of the write field is produced in SUL 38 to enhance the field strength produced in magnetic medium 14. As the write field from write pole 20 (and in particular, pole tip 34) passes through medium layer 40, medium layer 40 is magnetized perpendicular to the medium plane to store data based on the write field direction. The flux density that diverges from pole tip 34 into SUL 38 returns through return pole 28. Return pole 28 is located a sufficient distance from write pole 20 such that the material of return pole 28 does not affect the magnetic flux of write pole 20.
In magnetic medium 14, medium layer 40 may be made of a material having a very high magnetic anisotropy at ambient temperatures to prevent magnetic instabilities caused by thermal energy at high areal densities. In order to facilitate writing to magnetic medium 14, medium layer 40 may be locally heated to reduce the coercivity of medium layer 40 so that the write field generated by write pole 20 can more easily direct the magnetization of the medium layer 40 during the temporary magnetic softening of the medium layer 40 caused by the heating. In order to accomplish this, current assist electrode 12 is provided proximate to write pole 20 and magnetic medium 14. As will be described in more detail herein, current assist electrode 12 is operable to provide a potential difference between current assist electrode 12 and magnetic medium 14. This potential difference results in localized Joule heating of the medium under current assist electrode 12 to temperatures that approach the Curie temperature of medium layer 40.
Magnetic medium 14 is shown merely for purposes of illustrations, and variations on the configuration of magnetic medium 14 can be made. For example, magnetic medium 14 may include a thermal barrier layer disposed between the SUL 38 and medium layer 40 and/or between substrate 36 and SUL 38 to provide a good thermal path for heat caused by the Joule heating to be distributed and dissipated. Also, while SUL 38 and medium layer 40 are shown as single layer structures, SUL 38 and medium layer 40 may also be formed as multilayer structures. In addition, magnetic medium 14 may be formed without SUL 38, or a thermal conductivity layer may be provided in place of SUL 38. Furthermore, magnetic medium 14 may be configured for use in conjunction with a longitudinal or oblique/tilted recording systems, and magnetic writer 10 may be configured for use with other types of media, including composite media, continuous/granular coupled (CGC) media, discrete track media, and bit-patterned media.
Magnetic medium 14 (and in particular substrate 36) is electrically coupled to a first voltage source 44 having a voltage V1 and current assist electrode 12 is electrically coupled to a second voltage source 46 having a voltage V2. During the recording process, voltage sources 44 and 46 are controlled such that voltage V1 is different from voltage V2. When voltages V1 and V2 are different, a current IH is generated between current assist electrode 12 and magnetic medium 14. The separation between current assist electrode 12 and magnetic medium 14 is small enough such that current IH is conducted across this separation by tunneling or field emission. In an alternative embodiment, current assist electrode 12 is disposed closer to magnetic medium 14 by, for example, forming current assist electrode 12 so as to protrude closer to magnetic medium 14 than pole tip 34. Current IH causes localized heating in medium layer 40 under current assist electrode 12. In order to prevent current IH from spreading in medium layer 40 beyond the profile of current assist electrode 12, additional layers that may be included on top of medium layer 40 (e.g., a lubrication layer and an overcoat layer) may be selected to have good conductive and thermal properties. The voltage difference between current assist electrode 12 and magnetic medium 14 may also cause eddy currents to develop in current assist electrode 12. These eddy currents are imaged in magnetic medium 14, which cause medium layer 40 to heat in the region of the imaged eddy currents.
Voltage source 44 may be maintained at a constant or reference voltage (e.g., ground) while voltage source 46 is controlled to provide a voltage difference between current assist electrode 12 and magnetic medium 14. Voltage source 46 may be an alternating current (AC) voltage source that provides a high frequency AC voltage V2 (e.g., up to 200 GHz) to current assist electrode 12. The degree of heating in medium layer 40 below current assist electrode 12 is controllable by adjusting the amplitude and frequency of voltage V2 supplied by voltage source 46. In some embodiments, the AC voltage source has a frequency about equal to a recording frequency of the magnetic writer 10 to about ten times the recording frequency of magnetic writer 10.
The portion of medium layer 40 that is heated due to the potential difference between current assist electrode 12 and magnetic medium 14 is related to the area and shape of current assist electrode 12 at medium layer 40. In order to increase the density of data that is recorded to magnetic medium 14, the surface of current assist electrode 12 that confronts magnetic medium 14 may have an area that is less than the area of pole tip 34 at magnetic medium 14, as is shown in
Magnetic medium 14 (and in particular substrate 36) is electrically coupled to a first voltage source 44 having a voltage V1, similar to the embodiment shown in
Voltage source 44 may be maintained at a constant or reference voltage (e.g., ground) while voltage source 52 is controlled to provide a voltage difference between write pole 20 and magnetic medium 14. Voltage source 52 may be an alternating current (AC) voltage source that provides a high frequency AC voltage V2 to write pole 20. The degree of heating in medium layer 40 below write pole 20 is controllable by adjusting the amplitude and frequency of voltage V2 supplied by voltage source 52.
In summary, the present invention relates an apparatus including a write element for writing to a medium. The apparatus is configured to effectuate an electrical potential difference between a portion of the apparatus and a portion of the medium such that a current flows between the apparatus and the medium to reduce a coercivity of the medium proximate to the write element. The electrical potential difference causes a current to flow between the apparatus and the medium to reduce a coercivity of the medium proximate to the write element. This portion of the medium is heated to close to its Curie temperature, which reduces the write field needed to write to the medium. In one embodiment, the apparatus includes an electrode coupled to a voltage source to effectuate an electrical potential difference between a portion of the apparatus and a portion of the medium. The dimensions of the heated portion of the medium are controllable by adjusting the dimensions of the electrode at the medium confronting surface. Consequently, the portion of the medium that is heated can be made smaller than the write element at the medium confronting surface, which allows for denser recording on the medium. In another embodiment, a voltage source is coupled to the write element, which allows the current to flow from the write element to heat a portion of the medium.
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. For example, while the present invention has been described with regard to perpendicular recording applications, the principles of the present invention are also applicable to longitudinal and oblique/tilted recording applications.
