Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-05-25
2001-01-23
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S900000, C360S112000, C324S252000
Reexamination Certificate
active
06177208
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording system used for an auxiliary recording system of computers and the like and a magnetic recording medium used for the magnetic recording system. More particularly, it relates to a magnetic recording system having a high recording density of 1 gigabit per 1 square inch or more and a magnetic recording medium suitable for realizing the high recording density.
JP-A-5-73880 discloses a magnetic recording medium which comprises a CoCrPt magnetic layer containing silicon oxide, zirconium oxide, tantalum oxide, silicon nitride, boron nitride, titanium nitride or aluminum nitride.
JP-A-5-197944 discloses a magnetic recording medium which comprises a CoNiPtMO magnetic layer or CoCrPtMO magnetic layer (M is at least one element selected from Si, B, Zr, Al, Y, P, Ti, Sn and In).
In the above conventional magnetic recording media, coercivity is increased and medium noise is decreased by adding oxides or nitrides to the magnetic layer of the media.
However, according to the investigation by the inventors, the above conventional magnetic recording media suffer from the problems that decrease of medium noise in the high linear recording density area of higher than 150 kFCI (Flux Change per Inch) is insufficient and it is difficult to realize a high recording density of at least 1 gigabit per square inch.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to solve the above technical problems and to provide a magnetic recording system which makes it possible to attain a high recording density of at least 1 gigabit per 1 square inch, and a magnetic recording medium suitable for realizing the high recording density.
In the first aspect, the present invention provides a magnetic recording system having a magnetic recording medium and a magnetic recording head which carries out writing in and reading back from the magnetic recording medium, said magnetic recording medium comprising a substrate and a magnetic layer formed on the substrate directly or indirectly with an underlayer intervening between the magnetic layer and the substrate, characterized in that the magnetic layer of the magnetic recording medium comprises a mixture of at least one non-magnetic compound selected from the group consisting of oxides represented by the formula MOx (wherein M represents at least one element selected from Si, Al, Ta, Y and Ti, and x represents a numerical value of from about 1 to about 2.5) and a magnetic material of an alloy comprising Co and Pt as main components, the molar ratio of Pt to Co in the magnetic layer is 0.6-1.2 and the molar ratio of the non-magnetic compound to Co is 0.1-2.8, and the magnetic recording head includes a magnetoresistive read back magnetic recording head.
In the second aspect, the present invention provides the magnetic recording system having the above construction, characterized in that the magnetoresistive read back magnetic recording head has two shield layers and a magnetoresistive sensor formed between the shield layers and the distance between the two shield layers is 0.35 &mgr;m or less.
In the third aspect, the present invention provides the magnetic recording system having the above construction, characterized in that the product (Br·t) of a residual magnetic flux density, Br, measured by applying a magnetic field in the relative running direction of the magnetic recording head in respect to the magnetic recording medium at the time of recording and a thickness, t, of the magnetic layer of the magnetic recording medium is 10-100 gauss·micron.
In the fourth aspect, the present invention provides the magnetic recording system having the above construction, characterized in that the coercivity of the magnetic recording medium measured by applying a magnetic field in the relative running direction of the magnetic recording head in respect to t he magnetic recording medium at the time of recording is 2.4 kOe or more.
In the fifth aspect, the present invention provides the magnetic recording system having the above construction, characterized in that the magnetoresistive read back magnetic recording head has a magnetoresistive sensor which includes a plurality of magnetic layers and non-magnetic layers provided between the magnetic layers, said magnetic layers causing a great change in resistivity due to a relative change of mutual magnetization directions by an external magnetic field.
In the sixth aspect, the present invention provides the above-mentioned magnetic recording system of the first aspect, characterized in that the non-magnetic compound in the magnetic layer of the magnetic recording medium is not an oxide, but a nitride represented by the formula LNy (wherein L represents at least one element selected from Si, B and Al and y represents a numerical value of from about 1 to about 1.3).
The inventions of the second to fifth aspects can also be applied to the invention of the sixth aspect.
It is further preferred in the invention of the first or sixth aspect that the molar ratio of the non-magnetic compound to Co in the magnetic layer of the magnetic recording medium is 0.5-2.4.
In the seventh aspect, the present invention provides a magnetic recording medium comprising a substrate and a magnetic layer formed on the substrate directly or indirectly with an underlayer intervening between the magnetic layer and the substrate, characterized in that the magnetic layer of the magnetic recording medium comprises a mixture of at least one non-magnetic compound selected from the group consisting of oxides represented by the formula MOx (wherein M represents at least one element selected from Si, Al, Ta, Y and Ti, and x represents a numerical value of from about 1 to about 2.5) and a magnetic material of an alloy comprising Co and Pt as main components, the molar ratio of Pt to Co in the magnetic layer is 0.6-1.2 and the molar ratio of the non-magnetic compound to Co is 0.1-2.8.
In the eighth aspect, the present invention provides the magnetic recording medium of the seventh aspect, characterized in that the non-magnetic compound in the magnetic layer of the magnetic recording medium is not an oxide, but a nitride represented by the formula LNy (wherein L represents at least one element selected from Si, B and Al and y represents a numerical value of from about 1 to about 1.3).
It is further preferred in the invention of the seventh or eighth aspect that the molar ratio of the non-magnetic compound to Co in the magnetic layer of the magnetic recording medium is 0.5-2.4.
The inventors have prepared various magnetic recording media by changing the composition of the magnetic layer to search for the composition of the magnetic layer which is optimum when the medium is combined with a magnetic recording head. Furthermore, they have changed the magnetic recording heads to search for magnetic recording heads having the structure which is optimum when the magnetic recording head is combined with the magnetic recording medium. As a result, the magnetic recording systems and magnetic recording media of the present invention have been accomplished.
In the magnetic recording system of the first aspect, the magnetic layer of the magnetic recording medium is composed of a mixture of at least one non-magnetic compound selected from the group consisting of oxides and nitrides and a magnetic material of an alloy comprising Co and Pt as main components, the molar ratio of Pt to Co in the magnetic layer is limited to 0.6-1.2, and, furthermore, a magnetoresistive read back recording head is employed.
When Co and Pt are used as the main components of the magnetic material and the molar ratio of them is limited and the magnetic recording medium is combined with a magnetoresistive head, the medium S/N can be increased to about 2.0 or more. The medium S/N is a ratio of output to medium noise (a value obtained by excluding the noise of system from the total noise). Thus, the medium noise in a high linear recording density area of at least 150 kFCI can be sufficiently reduced, a high recor
Futamoto Masaaki
Hosoe Yuzuru
Igarashi Masukazu
Inaba Nobuyuki
Mangyo Emi
Hitachi , Ltd.
Kiliman Leszek
Mattingly Stanger & Malur, P.C.
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