Magnetic recording medium

Details Magnetic recording medium Magnetic recording medium

2002-09-06

2004-10-12

Rickman, Holly (Department: 1773)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S690000, C428S336000, C428S900000

Reexamination Certificate

active

06803131

ABSTRACT:

CROSS REFERENCES TO RELATED APPLICATIONS
The present document is based on Japanese Priority Document JP 2001-278192, filed in the Japanese Patent Office on Sep. 13, 2001, the entire contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention particularly relates to a high density magnetic recording medium which is applicable to an MR (magneto-resistive) head and a GMR (giant magneto-resistive) head.
2. Description of Related Art
Conventionally, as a magnetic recording medium, a so-called coating type magnetic recording medium is well-known, which is manufactured in such a way that a magnetic coating where a magnetic oxide powder or a magnetic alloy powder is dispersed in an organic binder such as polyvinylchrolide polyvinylacetate co-polymer, polyester resin, polyurethane resin is coated on a non-magnetic base and then dried.
While, according to a need for higher density recording, a magnetic recording medium having a magnetic layer comprising a ferromagnetic thin film where a ferromagnetic material comprising a metal or an alloy such as Co—Ni is directly coated on a non-magnetic base by means of plating or a vacuum thin-film forming process (such as a vacuum deposition process, a sputtering process, an ion plating process, and the like) is used in practice.
Such a magnetic recording medium of a so-called magnetic thin metal film type has several advantages in coercive force, remanent magnetization, squareness ratio, and not only has an excellent electromagnetic transformation performance at a shorter wavelength but also may be formed to have a very thin magnetic layer so that a demagnetization in records and a caliper loss during reproduction may be reduced. Further, since it is not necessary to mix a binder of a non-magnetic material into the magnetic layer, the medium may have a high filling up ratio of a magnetic material so as to obtain a higher magnetization, for example.
Further, in an effort to obtain a larger output by improving an electromagnetic transformation performance in such a kind of magnetic recording medium, a so-called oblique evaporation a magnetic layer is obliquely or tiltedly formed by means a vapor deposition process has been proposed and used in practice in a magnetic tape for a high quality VTR, a digital VTR, a data storage, and the like.
Although the magnetic recording medium of magnetic metal thin-film type has advantages as described above, there is a need for forming fine projections on an outermost surface on the magnetic layer side in order to reduce friction between a recording/reproducing magnetic head and a slide-contact surface of the magnetic recording medium—that is the outermost surface of the magnetic layer side—and to obtain sufficient durability of the magnetic layer.
In particular, according to a need for higher density recording, it is required that the fine projections should have an even and appropriate height in order to reduce a spacing loss and be dispersed in the magnetic layer evenly and in an appropriate density in order to obtain an appropriate electromagnetic transformation performance while maintaining low friction and high durability as well, and the magnetic layer is required to be formed much thinner because of a need for a smaller medium with a larger capacity.
Further, in response to a higher recording density in the magnetic recording medium, it is expected that, as to a magnetic head, a conventional inductive head will be replaced with a more sensitive head such as a magneto-resistive head (MR head) and a giant magneto-resistive head (GMR head).
When a magnetic head of a magneto-resistive effect type such as an MR head and a GMR head is used for a magnetic recording medium of a thin metal film type, the magnetic head provides a higher output than the conventional inductive head and has advantages in that the output does not depend on a relative speed between the medium tape and the head, for example.
However, a conventional metal evaporated tape generates an excessive amount of magnetic flux so that a resistance change in an MR element is out of a linear area. As a result it becomes difficult to obtain a distortion-free characteristic.
Further, a reproducing head has a high sensitivity so that a media noise becomes dominant in a C/N
media
(C/N: carrier to noise ratio), whereby a conventional surface design on the magnetic layer side causes an excessive amount of noises.
In addition, an abrasion of the MR element causes a problem in that a reproduced waveform becomes asymmetrical, for example.
In consideration of the above, as for a magnetic recording medium applicable to a highly sensitive magnetic head such as an MR head and a GMR head, the present inventors have made an effort to provide a magnetic recording medium capable of reducing a media noise and an abrasion in a reproducing MR head or a reproducing GMR head and of having durability as well by optimizing a thickness of the magnetic layer and a magnetic characteristic and further of controlling the fine projections on the surface of the magnetic layer.
SUMMARY OF THE INVENTION
A magnetic recording medium according to the present invention, comprises a magnetic layer, on a main surface of a non-magnetic base, which is formed by means of a thin-film forming technology by vacuum, and the magnetic recording medium is applicable to a reproducing system using a magneto-resistance effect type (magneto-resistive) head (MR head) or a giant magneto-resistance effect type (giant magneto-resistive) head (GMR head). Fine projections are formed at the outermost surface of the magnetic layer side.
Assuming that a height of the fine projections is h and a diameter of the fine projections at a half-height h/2 is &phgr;
h/2
, 99% of the fine projections having a height not less than 10 nm satisfy a relationship expressed by 100 nm≧&phgr;
h/2
≧40 nm, and a relationship between the height h of the fine projections and a density P (a number of fine projections per square mm) of the fine projections is as follows:
for h>25 nm, P is 250,000/mm
2
or less;
for 25 nm≧h>20 nm, P is 300,000/mm
2
or more and 1,250,000/mm
2
or less;
for 20 nm≧h>15 nm, P is 1,000,000/mm
2
or more and 3,750,000/mm
2
or less;
for 15 nm≧h>10 nm, P is 8,000,000/mm
2
or more and 25,000,000/mm
2
or less; and
for 10 nm≧h>5 nm, P is 50,000,000/mm
2
or less.
By controlling the conditions as described above, the present invention provides a magnetic recording medium which reduces noises, obtains a high C/N, reduces abrasion in the reproducing MR head and the reproducing GMR head, and also has good durability.
By controlling fine projections on the surface of the non-magnetic base, a height and a density of fine projections on the magnetic layer, the C/N
media
may be improved, good shuttling durability and corrosion resistance may be provided, and abrasion resistance of the MR head may be improved.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A magnetic recording medium according to the present invention, comprises a magnetic layer having a thickness of 30 nm or more and 80 nm or less on a main surface of a non-magnetic base. The magnetic layer is fabricated by means of a thin-film forming technology by vacuum, and the magnetic recording medium is a magnetic tape applicable to a helical scanning recording/reproducing system using a reproducing MR head or a reproducing GMR head; and fine projections are formed at the outermost surface of the magnetic layer side.
Assuming that the height of the fine projections is h and the diameter of the fine projections at the half-height h/2 is &phgr;
h/2
, 99% of the fine projections having a height not less than 10 nm are controlled to satisfy a relationship as shown in a formula 100 nm≧&phgr;
h/2
≧40 nm, and a relationship between a height h of the fine projections and a density P of the fine projections as follows:
for h>25 nm, P is 250,000/mm
2
or less;
for 25 nm≧h>20 nm, P is 300,000/mm
2
or more and 1,250,000/mm
2
or less;
for 20 nm≧h>15

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