Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1990-07-09
1993-07-20
Thibodeau, Paul
Stock material or miscellaneous articles
Composite
Of inorganic material
428403, 428900, 252 6254, 360 17, 360 59, G11B 500
Patent
active
052292193
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a magnetic powder, a method for preparing the magnetic powder, a magnetic recording medium using the magnetic powder, and a magnetic recording method using the medium.
BACKGROUND OF THE INVENTION
Known contact duplication for magnetic tape is a thermal duplication method (see the Japan Electronic Communications Society, 1971 National Meeting, S9-7 and IEEE Transaction on Magnetics, Vol. MAG-20, No. 1, January 1984, p19-23, for example).
The thermal duplication method is to duplicate signals through thermal duplication by using a master tape in the form of a .gamma.-Fe.sub.2 O.sub.3 tape or the like, and moving the master tape and a CrO.sub.2 tape in mutual contact at a high speed, while heating at about 150.degree. C.
However, since the prior art CrO.sub.2 tape has no flat frequency response to duplication signals, the master tape must be recorded with emphasis.
Also, the CrO.sub.2 tape is inconvenient to handle in that it can be erased with conventional magnetic heads because CrO.sub.2 particles have a coercive force Hc as low as 0.4 to 0.7 kOe.
In turn, known high coercive force materials having a low Curie point include magnetic alloy particles such as MnBi.
In order to provide a high coercive force, these alloy materials, however, must have a Curie point of about 300.degree. C. or higher, which requires a higher heating temperature with the risk that the substrate can be thermally deformed and an output with deteriorated waveform will result.
Because of a low squareness ratio and a broad thermal demagnetization curve, the output varies with the varying temperature of the heating head. In addition, noises frequently occur and an output S/N ratio is low.
In addition, corrosion resistance and weathering resistance are insufficient.
DISCLOSURE OF THE INVENTION
A first object of the present invention is to provide a magnetic recording medium which requires a low heating temperature, is easy for thermomagnetic duplication recording and thermomagnetic recording, exhibits a flat frequency response upon such recording, is not easily erasable once recorded, produces outputs which least vary with variations in heating temperature and have an improved S/N ratio, and has improved corrosion resistance and weathering resistance, and excellent input/output properties as well as a magnetic recording method using the medium.
A second object of the present invention is to provide a magnetic powder offering better results in implementing such a magnetic recording medium and a method for preparing the powder.
These objects are accomplished by the present invention as defined below.
In a first form of the present invention, there is provided a magnetic powder characterized by comprising particles having a composition of the following formula: Ba, Sr, Pb, and Ca, those particles having a particle size of from 0.5d to 1.5o is at least 65% of the entire particles.
The magnetic powder is preferably obtained by mechanically milling a corresponding sintered material.
In a second form of the present invention, there is provided a magnetic powder characterized by comprising particles having a composition of the following formula: Ba, Sr, Pb, and Ca, the Fe content in the particle interior.
Preferably, the particles have an average particle size d, and the number of those particles having a particle size of from 0.5d to 1.5d is at least 65% of the entire particles.
Also, the magnetic powder is preferably obtained by mechanically milling a corresponding sintered material.
In a third form of the present invention, there is provided a method for preparing a magnetic powder having a composition of the following formula: Ba, Sr, Pb, and Ca, feed gas into a milling chamber; injecting the feed gas as a high velocity gas flow into the chamber through a gas injection nozzle; and milling the feed powder in the high velocity gas flow in the chamber, or milling the feed powder by forcedly impinging it against an impact plate, thereby obtaining the powder.
In the preferred method for prepar
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Kohmoto Osamu
Makimura Atsushi
Mimura Shohei
Moro Hideharu
Satoh Shigeo
Resan Stevan A.
TDK Corporation
Thibodeau Paul
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