Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-12-05
2004-03-30
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S329000, C428S403000, C428S690000
Reexamination Certificate
active
06713173
ABSTRACT:
This invention relates to a magnetizable device which comprises a magnetic layer composed of domain-separated, nanoscale (e.g. 1-100 nm) ferromagnetic particles. The magnetizable device of the invention may be used as a magnetic storage device having improved data storage characteristics. In particular, the invention relates to magnetic storage media comprising single-domain, domain-separated, uniform, ferromagnetic nanoscale (e.g. 1-100 nm) particles which may be arranged into a regular 2-D packed array useful in the storage of information.
Among the possible pathways to ultrahigh-density (>=1 Gbit/in
2
) magnetic media is the use of nanoscale (1-100 nm) particles. Beyond the standard requirements for magnetic media, a viable particulate media should have a small standard deviation in particle size as well as the particles being exchange decoupled. These requirements are necessary to avoid adverse media noise. Current methods of fabricating nanoscale particles, such as arc-discharge or multiple target ion-beam sputtering, have not fully addressed these two requirements. Moreover, if the uniform particles are arranged into an ordered array, each particle can represent a “bit” of information at a predictable location further increasing the media's efficiency. This invention details methods of producing particulate media that meet these requirements for ultrahigh-density recording. This invention is also an open system which allows for the production of a variety of magnetic materials, such that the media can be tuned for different applications.
In particular this invention details the use of an iron storage protein, ferritin, whose internal cavity is used to produce the nanoscale particles. Ferritin is utilised in iron metabolism throughout living species and its structure is highly conserved among them. It consists of 24 subunits which are arranged to provide a hollow shell roughly 8 nm in diameter. The cavity normally stores 4500 iron(III) atoms in the form of paramagnetic ferrihydrite. However, this ferrihydrite can be removed (a ferritin devoid of ferrihydrite is termed “apoferritin”) and other materials may be incorporated. Examples include ceramics, superparamagnetic magnetite, acetaminophen, and even the sweetener aspartame. To address magnetic media concerns, the invention incorporates ferromagnetically ordered materials.
According to a first aspect of the present invention, there is provided a magnetizable device which comprises a magnetic layer composed of domain-separated, ferromagnetic particles each of which has a largest dimension no greater than 100 nm.
According to a second aspect of the invention, there is provided a magnetic recording medium which includes a magnetizable layer, wherein said magnetizable layer comprises a plurality of ferromagnetic particles each having a largest dimension no greater than 100 nm, and each of which particles represents a separate ferromagnetic domain. The magnetizable layer is preferably supported on a nonmagnetic substrate.
According to a third aspect of the present invention, there is provided a magnetic composition comprising a plurality of ferromagnetic particles each of which is bound to an organic macromolecule, and each of which has a largest dimension no greater than 100 nm. In this aspect of the invention, it is preferred that said organic macromolecule is ferritin from which the normal core ferrihydrite has been removed and replaced by a ferromagnetic particle.
As used herein, the term “ferromagnetic” embraces materials which are either “ferromagnetic” and “ferrimagnetic”. Such usage is common in the electrical engineering art.
The ferromagnetic particles used in the invention should be of a material and size such that they possess ferromagnetic properties at ambient temperatures (e.g 15° C. to 30° C.).
Preferably, the ferromagnetic particles each have a largest dimension no greater than 50 nm, more preferably less than 25 nm and most preferably smaller than 15 nm. The largest dimension of the ferromagnetic particles should not be so small that the particle will lose its ferromagnetic property and become superparamagnetic at the desired operating temperature of the recording medium. Typically, for operation at ambient temperature, this means that the magnetic particles will normally be no smaller than about 3 nm in their largest diameter.
In the magnetizable device of the first aspect of this invention and the magnetic recording medium of the second aspect of this invention, the distance between adjacent ferromagnetic domains is preferably as small as possible to permit the maximum number of discrete domains in a given area, and provide the maximum storage capacity for the recording medium. The actual lower limit will vary for different materials and other conditions such as the temperature at which the recording medium is to be used. The key requirement, however, is that neighbouring domains should not be able to interfere magnetically with each other to the extent that the magnetic alignment of any domain can be altered by neighbouring domains. Typically, the lower limit on the spacing of the domains is about 2 nm. The distance between adjacent domains will be determined by the density of discrete domains required. Typically, however, to take advantage of the miniaturization possibilities provided by the invention, the distance between adjacent domains will be no greater than 10 nm.
Generally the particles will be uniform in size, by which we mean that the particles do not vary in largest diameter by more than about 5%. One of the advantages of the use in the invention of an organic macromolecule which binds a magnetic particle by surrounding it is that this can be used to select particles of a uniform size.
In the case where the particles are spheroidal, it will be the diameter of the particles which must be no greater than 100 nm.
In preferred embodiments of all aspects of this invention, each ferromagnetic particle is encased, or partially encased, within an organic macromolecule. The term macromolecule means a molecule, or assembly of molecules, and may have a molecular weight of up 500 kD, typically less than 500 kD. Ferritin has a molecular weight of 400 kD.
The macromolecule should be capable of binding by encasing or otherwise organising the magnetic particle, and may therefore comprise a suitable cavity capable of containing the particle; a cavity will normally be fully enclosed within the macromolecule. Alternatively, the macromolecule may include a suitable opening which is not fully surrounded, but which nevertheless is capable of receiving and supporting the magnetic particle; for example, the opening may be that defined by an annulus in the macromolecule. For example, suitable macromolecules which may be used in the invention are proteins, for example the protein apoferritin (which is ferritin in which the cavity is empty), flagellar L-P rings, cyclodextrins, self-assembled cyclic peptides. As an alternative to encasing the magnetic particles within the macromolecule, they may be organised on the macromolecule, such as on a bacterial S-layer.
Other materials which may be used in the invention to organise the ferromagnetic particles are inorganic-silica networks such as MCM type materials, dendrimers and micellar type systems.
The presently preferred macromolecule for use in the invention is the apoferritin protein which has a cavity of the order of 8 nm in diameter. The ferri- or ferromagnetic particles to be accommodated within this protein should have a diameter no greater than 8 nm.
The bound particles of this aspect of the present invention with a coating that inhibits aggregation and oxidation, also helping them to be domain-separated.
In the magnetizable device of the first aspect of this invention and the magnetic recording medium of the second aspect of this invention, the particles are preferably arranged in a 2-D ordered array which would yield an ultrahigh-density magnetic media.
The ferromagnetic material may be a metal, such as cobalt, iron, or nickel; a metal alloy, such as
Mayes Eric Leigh
Tyler Malvin Nicolas
Nanomagnetics Limited
Resan Stevan A.
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