Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2002-09-17
2004-10-12
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C360S059000
Reexamination Certificate
active
06804175
ABSTRACT:
The invention relates to a storage medium for thermally-assisted magnetic recording including a recording layer having substantially parallel tracks for recording information. The invention also relates to a method for recording information on a storage medium and an apparatus for carrying out the method.
In the near future, both longitudinal magnetic and (magneto) optical recording will be hampered in their growth to higher densities and data rates. In conventional magnetic recording superparamagnetism will finally limit the stable and low-medium-noise recording of information, while in magneto-optical recording the bit size and read data rate are limited by the optical resolution and the limited Kerr rotation and allowable laser power during reading, respectively. It is generally believed that the limits of conventional magnetic disk recording of about 50-100 Gb/in
2
will be reached in a few years from now, because the present areal density in the most advanced products is already near 10 Gb/in
2
and the present annual growth rate is over 60%.
Limiting areal densities, D
a
, of 50-100 Gb/in
2
(1 Gb/in
2
=1 Giga bit per square inch=1.6 bit/&mgr;m
2
) for conventional longitudinal recording were estimated by Bertram et al.
1
, based on the calculated SNR of granular media, SNR
med
, with 10-year data life time and recordable with high-saturation write heads. For future improvements in densities a drastic reduction of the grain size is necessary to maintain a sufficient SNR
med
. Particle-size reduction, however, reduces the stability of the stored information strongly, unless the anisotropy field, H
k
, of the particles is drastically increased. A medium with a high H
k
has a higher coercivity field, H
c
, and it is more difficult or even impossible to record on such media with conventional write heads or even the best write heads presently available with iron or cobalt-rich flux guides.
The areal density may be further increased using hybrid recording. Hybrid recording is a form of thermally-assisted magnetic recording. Both hybrid recording and magneto-optical recording use a magnetic field to change locally the magnetisation of the recording layer and a radiation beam to heat the recording layer. In general, the radiation beam has a wavelength in or near the visible part of the spectrum. In hybrid recording the bits are recorded along a track of a recording layer in the form of magnetisation transitions by reversing a magnetic field at the position of the recording layer, wherein the position of the transition along the track is determined by the reversals of the magnetic field. In contrast, the position of the magnetisation reversals when using magneto-optical recording is determined by the change in power of the radiation beam used to heat the recording layer. In other words, the position of the transition is fixed by a decrease of the magnetic field in hybrid recording and by a decrease in temperature in magneto-optical recording. The sharpness of the magnetisation transition in hybrid recording is determined by the magnetic field gradient in the recording layer during the recording process, whereas in magneto-optical recording it is determined by the temperature gradient in the recording layer during the recording process. In general the thermal profile in the recording layer caused by the radiation beam is larger than the distribution of the magnetic field in the recording layer in hybrid recording and smaller in magneto-optical recording.
The increase in density is limited by the stability of the recorded bits. In order to increase the stability of the recorded information on extremely small grains, writing in hybrid recording is carried out at an elevated temperature on a medium with a very high coercivity at room temperature, using write heads with high-saturation flux guides and an integrated light path added to it. Local heating of the medium by laser light through a light path during writing reduces the coercivity of the medium temporarily to a value that makes recording with high-saturation write heads possible. With hybrid recording, a smaller transition width and higher density or a better signal-to-noise ratio can be obtained than those achievable by conventional magnetic and magneto-optical recording.
Hybrid recording media are known from inter alia the article by H. Katayama, S. Sawamura, Y. Ogimoto, J. Nakajima. K. Kojima and K. Ohta, published in Proc. of MORIS'99, J. Magn. Soc. Jpn. 23, Suppl. S1, 233 (1999). A disadvantage of these media is that the storage life of the recorded data is shorter than what is determined from the storage temperature and the stability of the magnetic transitions on the recording layer.
It is an object of the invention to provide a hybrid recording medium having a storage life of the recorded data than the known recording media.
The object of the invention is achieved if the storage medium of the preamble is characterised in that the recording layer includes a series of recording regions, each region comprising a plurality of tracks having a pitch p for magnetically recording information, and extending a distance ½ p beyond a centre line of the outermost track of the region, and in that neighbouring regions are separated by magnetically non-recording areas having a width substantially equal to or larger than the pitch p. The invention is based on the insight, that the relatively short storage life of the known storage media for thermally-assisted magnetic recording is caused by the spatial extent of the thermal profile of the known recording heads. Since the profile extends over the tracks neighbouring the one being recorded, the neighbouring tracks are subject to short periods of increased temperature. The stability of the recorded data is limited by the total heating time during and after recording. Hence, recording of a track reduces the life of the data recorded in the neighbouring tracks. Repetitive recording of parts of the medium that are very close to each other will decrease the storage life of the data. When this recording is more or less randomly organised, the maximum writing time is more or less undetermined, and no specific maximum writing time can be guaranteed. Therefore, a special data write architecture is preferred to avoid heating much longer than the unavoidable heating time due to writing the tracks once. The storage medium according to the invention solves this problem by dividing the recording layer into regions separated from one another by non-recording areas. If the regions are written in a single session, the tracks in the region have been heated only during the unavoidable heating time. The neighbouring regions have not been heated at all, because of the non-recording areas. The regions can be written in a random fashion without endangering the data recorded in neighbouring regions.
The width of the non-recording areas should be at least equal to half the width of the thermal profile in the recording layer. For a small radiation distribution the distance between the centre lines of the closest tracks of neighbouring regions should be equal to or larger than twice the pitch of the tracks within a region. For larger thermal profiles, the distance should be at least three times the pitch.
A second aspect of the invention relates to an apparatus for thermally-assisted magnetic recording of information in the form of magnetisation transitions in tracks of a recording layer of a storage medium, the apparatus including a recording head for forming a radiation field and a magnetic field at the location of the recording layer, the radiation field forming a thermal profile larger than a distribution of the magnetic field in the recording layer, a control unit for controlling the radiation field and the magnetic field such that the position along the track of the magnetisation transitions are determined by reversals of the magnetic field. The size of the thermal profile for the purpose of comparison with the distribution of the magnetic field is the area where the temperature i
Luitjens Steven Broeils
Ruigrok Jacobus Josephus Maria
Belk Michael E.
Dinh Tan
Koninklijke Philips Electronics , N.V.
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