Dynamic magnetic information storage or retrieval – General recording or reproducing – Thermomagnetic recording or transducers
Reexamination Certificate
1999-09-30
2003-03-11
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Thermomagnetic recording or transducers
C369S013010, C369S013110, C369S013200, C346S074400, C219S209000, C219S540000
Reexamination Certificate
active
06532125
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to novel apparatus and method suitable for magnetic-thermal recording.
INTRODUCTION TO THE INVENTION
The significance and novelty of the present invention and its discoveries, with respect to magnetic-thermal recording, may be discerned by first referencing and setting in apposition a disparate and important recording technology, namely, thermo-magnetic recording utilizing a focused laser beam.
In particular, thermo-magnetic recording employing a focused laser beam contemplates using the focused laser beam for creating a hot spot on a thermo-magnetic material. The thermo-magnetic material, in turn, typically comprises a thin film magnetic media, which, at ambient temperature, has a high magnetic coercivity and is non-responsive to an externally applied magnetic field. However, as the focused laser beam raises the local temperature of the thin film magnetic media, the hot spot can become magnetically soft (i.e., its coercivity decreases), and eventually, at a critical point (the Curie temperature), the coercivity becomes zero. At a certain temperature, the field of the externally applied electromagnet can overcome the media's resistance to reversal, thereby switching its magnetization. Turning the laser off can bring the temperature back to normal (ambient temperature), but the reverse-magnetized domain remains frozen in the film. Recording may be realized by laser power modulation (LPM) or magnetic field modulation (MFM).
SUMMARY OF THE INVENTION
Our work includes an evaluation of the capabilities of thermo-magnetic recording utilizing a focused laser beam. In particular, we note that this technique enables one to write magnetic bits with dimensions in the micrometer range. A minimum size of these written bits can be determined by the focal spot of the laser beam (approximately 1 micrometer). However, since the minimum focal spot may be determined by the diffraction limit
(
approximately
(
wavelength
2
)
)
,
the storage capability of thermo-magnetic recording utilizing a focused laser beam, is fundamentally limited.
The discoveries of the present invention, in sharp contrast to the inherent and fundamental limitations of focused laser beam techniques, include novel apparatus and methodology which can qualitatively and advantageously transcend focused laser beam diffraction limited constraints.
In overview, the discoveries and advantages of the present invention can work to circumvent the severe diffraction limited constraints, by using direct thermal coupling between a heater and a magnetic thin film media. In this novel methodology, heat may be deposited onto the magnetic thin film media or surface on a submicroscopic scale. Preferably, a novel nanoscale feature or probe guides the thermal energy and focuses it onto the thermo-magnetic media in the presence of a magnetic bias field. Since the area of the local heating on the surface may be determined approximately by the dimensions of the probe, magnetic bits may be written which are substantially below 0.1 micrometer, i.e., far below the diffraction limit. Consequently, the discoveries of the present invention, in contrast to prior art diffraction limited techniques, can realize significant improvements in data storage densities (approximately by a factor of 10 or larger). Moreover, since the writing speed is governed by thermal diffusion, very high and competitive writing speeds of approximately greater than 100 MHz, can be achieved.
These important aspects relating to the discoveries of the present invention, are usefully restated and reinforced by the following considerations.
In general, the present invention focuses on high density as well as high speed data recording.
With respect to high density, we note the following: The present invention uses the idea of direct thermal coupling between a heater and a magnetic thin film media. The direct thermal coupling can subsume far-field or near-field effects (see below), in order to heat the thin film media, preferably on a very local scale. This scale, in turn, can be made to correlate to the dimensions of a heater probe, which can be easily less than 10,000 A°, e.g., 100 A°. Consequently, the magnetic bits written with thermal coupling can be significantly smaller than the magnetic bits written by conventional techniques; for example, thermal near-field coupling can translate into data storage densities of approximately greater than 100 Gbit/inch
2
, for example, 400 Gbit/inch
2
.
With respect to high speed data recording, the writing speed realized by this invention can be very high, because it is only limited by the thermal diffusion length l=(&kgr;×t)
0.5
, where &kgr; is the thermal diffusivity and t is the time after the arrival of a heating pulse. Specifically, the heat in a good thermal conductor (approximately &eegr;=2·10
−5
m
2
/s) can diffuse a distance of 0.45 micrometer in only approximately 10 ns corresponding to data recording rates of 100 MHz (C. A. Paddock et al., J. Appl. Phys. 60, 285 (1986)). It should be pointed out that the heat diffusion speed increases considering a three-dimensional heat flow, which promises even higher data recording rates.
Accordingly, pursuant to a first aspect of the present invention, we disclose a novel apparatus for writing/erasing high-density data on a digital recording media as a series of tags comprising a magnetic information bit pattern, the apparatus comprising:
1) a source of thermal radiation for generating an incident wave to the media;
2) means for applying a magnetic bias field on the digital recording media; and
3) means for coordinating a mutual positioning of the incident wave and the media for inducing a direct thermal coupling therebetween; the apparatus capable of writing/erasing said high-density data by at least one of the following actions;
i) using an information signal for modulating the magnetic bias field;
ii) using an information signal for modulating the power of the incident thermal wave to the media.
In a second aspect of the present invention, we disclose a novel method for writing/erasing high-density data on a digital recording media as a series of tags comprising a magnetic information bit pattern, the method comprising the steps of:
1) generating and directing an incident thermal wave to the media;
2) applying a magnetic bias field on the digital recording media;
3) coordinating a mutual positioning of the incident wave and the media for inducing a direct thermal coupling therebetween; and
4) writing/erasing said high-density data by at least one of the following actions:
i) using an information signal for modulating the magnetic bias field;
ii) using an information signal for modulating the power of the incident wave to the media.
In a third aspect of the present invention, we disclose a novel thermal near-field heater that may be advantageously employed in the above disclosed novel apparatus, and for realizing the above disclosed novel method, especially in a near-field mode.
The novel thermal near-field heater comprises:
1) a heating plate that can operate as a heat source; and
2) a heat sink attached to the heating plate;
the heater capable of developing a thermal coupling with a media, wherein at least one portion of the coupling is in the thermal near-field.
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Hamann Hendrik F.
Martin Yves
Wickramasinghe Hemantha Kumar
Davidson Dan I.
Hudspeth David
International Business Machines - Corporation
Kaufman, Esq. Stephen C.
McGinn & Gibb PLLC
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