Dynamic magnetic information storage or retrieval – General recording or reproducing – Thermomagnetic recording or transducers
Reexamination Certificate
2000-03-31
2004-08-03
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Thermomagnetic recording or transducers
C369S044230
Reexamination Certificate
active
06771445
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a novel assembly and method suitable for thermo-magnetic writing/reading of data.
INTRODUCTION TO THE INVENTION
The significance and novelty of the present invention and its discoveries, with respect to thermo-magnetic writing/reading, may be discerned by first referencing and setting in apposition a disparate and important recording technology, namely, classical thermo-magnetic recording utilizing a focused laser beam.
In particular, classical 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 at least twofold evaluation of the capabilities of classical thermo-magnetic recording utilizing a focused laser beam.
In particular, we first note that this classical technique enables one to write magnetic bits with dimensions only 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 classical thermo-magnetic recording utilizing a focused laser beam, is fundamentally limited.
Second, we note that even for traditional techniques on longitudinal recording media which use exclusively a magnetic field without any heating, the concept for nanoscale heating may be very important in the future. In order to obtain stable magnetic bits, the magnetic material has to become harder and harder as the bit size decreases. Specifically, thermal stability of magnetic media is described by the thermal reversal energy, which is for an ideal material the product of the magnetic anisotropy (Ku) of the material and the volume (V) of each magnetic ‘grain”. A material is considered to be thermally stable if the KuV/kT>40, where kT is the thermal energy at ambient temperature. As the bit size decreases, materials with higher Ku are needed as a recording media. Although these materials are available, they cannot be used in the traditional way, because the magnetic field from a head is not sufficient to switch them. Improvements on the field strengths of a magnetic head cannot be foreseen. Hence, the only practical way of recording on these films is to thermally assist the writing process by heating locally.
The discoveries of the present invention, in sharp contrast to the inherent and fundamental limitations of classical focused laser beam techniques, include a novel assembly 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 electromagnetic coupling between an antenna and a magnetic thin film media. In this novel methodology, heat may be developed by way of the electromagnetic coupling and directly and locally deposited onto the magnetic thin film media or surface on a submicroscopic scale. Preferably, a novel nanoscale antenna or probe guides electromagnetic energy and amplifies and focuses it onto the thermo-magnetic media, typically 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 antenna, 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 classical 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 electromagnetic coupling between an antenna and a magnetic thin film media. The direct electromagnetic coupling can subsume far-field and preferably 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 the antenna, which can be easily less than 10,000 A°, e.g., 100 A°. Consequently, the magnetic bits written with this coupling can be significantly smaller than the magnetic bits written by conventional or classical techniques; for example, the preferred 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 basically limited by the thermal diffusion length l=(&kgr;xt)
0.5
1
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 &kgr;=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 assembly for writing/reading high-density data on a recording media as a series of tags comprising a magnetic information bit pattern, the assembly comprising:
1) an antenna positionable near the media;
2) a source of electromagnetic radiation for producing an incident wave at least a portion of which can be coupled to the antenna; and
3) means for coordinating a mutual positioning of the source of the electromagnetic radiation and the antenna, so that the antenna can generate a highly localized electromagnetic field in the vicinity of the media for inducing localized heating of the media; the assembly capable of writing/erasing said high-density data by using an information signal for modulating the localized electromagnetic field generated in the vicinity of the media;
the assembly capable of reading by coordinating the mutual positioning of the antenna and the media.
In a second aspect of the present invention, we disclose a novel method for writing/erasing high-density data on a recording media as a series of tags comprising a magnetic information bit pattern, the method comprising the steps of:
1) positioning an antenna near the media;
2) generating an incident electromagnetic wave for coupling to the antenna;
3) coordinating a mutual positioning of the incident electromagnetic wave and the antenna for generating a highly localized electromagnetic fie
Hamann Hendrik F.
Martin Yves
Wickramasinghe Hemantha Kumar
Colon Rocio
Hitachi Global Storage Technologies - Netherlands B.V.
Hudspeth David
McGinn & Gibb PLLC
Millett, Esq. Douglas A.
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