Dynamic magnetic information storage or retrieval – Head – Read only detector using light for reading magnetically...
Reexamination Certificate
2001-11-14
2003-03-18
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Read only detector using light for reading magnetically...
Reexamination Certificate
active
06535351
ABSTRACT:
TECHNICAL FIELD
The invention relates to magnetic data storage and, in particular, magneto-optic read heads for magnetic media.
BACKGROUND
Magnetic storage media, which include magnetic tape and magnetic disks, are commonly used for storage and retrieval of data. The data is typically encoded in magnetizations on the recording surface of the magnetic media. A typical magnetic recording medium includes a thin layer of ferromagnetic material, such as gamma ferric oxide, supported by a non-magnetic substrate. The ferromagnetic material is a material that can be permanently magnetized by the application of an external magnetic field. The ferromagnetic material typically includes magnetic particles mixed with a binder material that can attach to the non-magnetic substrate. The ferromagnetic material is typically applied to the non-magnetic substrate in a coating process. Alternatively, metal evaporation techniques or sputtering techniques can be used to apply the ferromagnetic material on the non-magnetic substrate.
Magneto-optic read techniques have been developed for readout of data stored on magnetic media. Magneto-optic read techniques take advantage of both electromagnetic principles and optics to facilitate data readout. A magneto-optic read head has a simple magnetic structure that includes two magnetic poles separated by a non-magnetic layer (gap). The read head can capture fringing magnetic fields produced by the magnetic particles that are encoded with data on the surface of the magnetic media. Light is reflected off one of the magnetic poles of the read head, typically near the edge of the pole, and detected by a light detector such as a linear charged coupled device (CCD). When the light is reflected, a polarization rotation occurs, sometimes referred to as the longitudinal Kerr effect. The polarization rotation is proportional to the pole magnetization in the read head. Thus, the polarization of the detected light can be interpreted to facilitate readout of the data magnetically encoded in the surface of the magnetic media.
Migration of magnetic tape technology to higher and higher recording densities require narrower track widths on the magnetic tape. Magneto-optic read heads can mitigate media dimensional instability and can improve track following capabilities to facilitate narrower track widths, and thus accommodate higher data storage densities on magnetic tape. However, magnetic cross-talk in the magneto-optic read head may limit track density. In other words, as data tracks on the magnetic media are spaced closer and closer together, the magnetic flux captured in the magneto-optic read head can overlap for adjacent tracks. This magnetic cross-talk can undermine the ability to effectively read the data stored on the magnetic media. For this reason, track width reduction presents a significant challenge to magneto-optic read head technologies.
SUMMARY
In general, the invention is directed toward a magneto-optic read head formed to suppress magnetic exchange coupling at regular intervals along a lateral direction of the read head. For example, in the region of the magneto-optic read head where light is reflected, i.e., the optical scanning region, the read head can be formed with a series of ferromagnetic exchange breaks that reduce lateral permeability of magnetic fields, and hence reduce lateral flux through the read head. In this manner, the effective resolution of the read head can be increased, thereby facilitating readout of data stored on narrower data tracks.
The inventive read head can significantly reduce magnetic cross-talk in the optical scanning region. The cross-talk can be reduced, for example, by forming the series of ferromagnetic exchange breaks that reduce lateral permeability in the optical scanning region. Thus, the magnetic flux associated with adjacent tracks does not substantially permeate across the ferromagnetic exchange breaks in the optical scanning region. In other words, the presence of ferromagnetic exchange breaks in the optical scanning region ensures that the magnetic fields for the data regions in one track do not corrupt the readout of data regions in adjacent tracks. In some embodiments, the ferromagnetic exchange breaks are defined by the absence of magnetic material, which can be etched away to define the ferromagnetic exchange breaks. In other embodiments, the ferromagnetic exchange breaks can be formed by doping lines through the magnetic material, for example, by using ion implantation methods.
The ferromagnetic exchange breaks may be formed only in the optical scanning region. The other regions of the magneto-optic read head, including the other regions on a magnetic film, may not include the ferromagnetic exchange breaks. Such a configuration can decrease the total reluctance through the read head, while also reducing cross-talk in the optical scanning region. Decreasing the reluctance through the read head, in turn, can improve the ability to read the data by increasing magnetic field strength throughout the read head.
The ferromagnetic exchange breaks may be spaced at intervals less than one-half of a track width associated with a recorded media to be read by the magneto-optic read head to effectively over-sample the data. This over-sampling can ensure that all of the relevant data is captured even if the read head moves laterally relative to the magnetic media. In particular, over-sampling ensures that all of the data is captured as long as the head is positioned somewhere over the data tracks. The captured data can then be resolved by signal processing algorithms or techniques. In particular, by spacing the ferromagnetic exchange breaks at intervals less than one-half of the track width, crosstalk can be reduced or eliminated. In that case, at least one flux guide, which separates the ferromagnetic exchange breaks, would be dedicated to each track.
In one embodiment, the invention is directed toward a magneto-optic read head. For example, the magneto-optic read head may include a first magnetic layer and a second magnetic layer separated by a non-magnetic layer. The first magnetic layer may be a magnetic film that includes an optical scanning region formed with a series of ferromagnetic exchange breaks. In some embodiments, the series of ferromagnetic exchange breaks are formed by etching or doping lines through the optical scanning region. The ferromagnetic exchange breaks can reduce lateral permeability of magnetic flux through the first magnetic layer. The series of ferromagnetic exchange breaks can be spaced at intervals less than one-half of a track width associated with a recorded medium to be read by the magneto-optic read head. The magneto-optic read head may include the ferromagnetic exchange breaks only in the optical scanning region.
In another embodiment, the invention may comprise a magneto-optic read system that includes the magneto-optic read head as described above. In addition, the system may include a light source that illuminates the optical scanning region of the read head, and a light detector that detects light reflected off the optical scanning region. For example, the reflected light can be detected and interpreted to facilitate data readout.
In other embodiments, the invention is directed toward one or more methods. For example, a method may include positioning a magneto-optic read head in proximity to a magnetic data storage medium. The magneto-optic read head may include one or more of the features outlined above. After positioning the read head, the optical scanning region of the read head can be illuminated. Light reflected by the optical scanning region can then be detected to facilitate data readout. In particular, light polarization may be detected, and then interpreted and used to generate a readout signal indicative of data stored on the magnetic data storage medium.
In still another embodiment, a method of creating a magneto-optic read head includes depositing a magnetic material to create a thick layer of magnetic material and depositing a non-magnetic material on the thick layer o
Stubbs Daniel P.
Yip Yung
Imation Corp.
Tupper Robert S.
Watko Julie Anne
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