Magnetic recording medium and magnetic storage

Details Magnetic recording medium and magnetic storage Magnetic recording medium and magnetic storage

2000-10-03

2003-04-08

Rickman, Holly C. (Department: 1773)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S690000, C428S900000

Reexamination Certificate

active

06544672

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium improved to be suitable for high density magnetic recording by reducing noise generated from the magnetic recording medium and to a magnetic storage device using the same.
Studies have been made on a magnetic recording medium formed of a continuous magnetic thin film for realizing high density magnetic recording. Specifically, such a magnetic recording medium is prepared by a method wherein a thin film made of a ferromagnetic metal, Co or Co-based alloy is formed on a substrate made of a nonmagnetic material such as aluminum or glass coated with a plastic film or NiP film by radio frequency sputtering, ion beam sputtering, vacuum evaporation, electric plating or chemical plating. In the magnetic recording medium thus prepared, a microstructure of a magnetic thin film is closely related to magnetic properties. As a result, various attempts have been made to improve a magnetic layer constituting a magnetic recording medium for enhancing magnetic recording density and reproduced output.
For a longitudinal magnetic recording medium, it has been conceived that an easy magnetization axis thereof is desirable to be parallel to a substrate. On the other hand, various methods have been known to provide an underlayer between a substrate and a magnetic layer for ensuring longitudinal magnetic anisotropy. For example, U.S. Pat. No. 4,654,276 discloses a method in which a layer made of W, Mo, Nb or V is used as an underlayer for a Co—Pt magnetic layer. U.S. Pat. No. 4,652,499 discloses a method in which a V—Cr or Fe—Cr alloy material is used as an underlayer. Japanese Patent Laid-open No. Sho 63-106917 discloses a method in which a nonmagnetic layer made of Cr, Ho, Ti or Ta as an underlayer for a magnetic layer made of Co, Ni, Cr or Pt. U.S. Pat. No. 4,789,598 discloses a method in which Cr or a Cr—V alloy is effective as an underlayer for a Co—Pt—Cr layer.
When a Co-based alloy magnetic layer is formed on a substrate through an underlayer made of Cr or a Cr alloy by sputtering, the underlayer is first oriented in (100) or (110). In this case, when the Co-based alloy magnetic layer is formed on the (100) orientated layer, the easy magnetization axis thereof is parallel to the substrate; while when the Co-based alloy magnetic layer is formed on the (110) oriented layer, the easy magnetization axis thereof is substantially in parallel to the substrate, more specifically, it is inclined at about 30° relative to the surface of the substrate.
For improvement in an areal density of magnetic recording, it is required to reduce noise generated from a magnetic recording medium as well as to enhance resolution of magnetic recording. In particular, when a reproducing magnetic head of a magneto-resistance (MR) type being high in read-out sensitivity, it becomes important to reduce noise of a magnetic recording medium. The prior art magnetic recording medium of a type in which the easy magnetization axis thereof is oriented in the longitudinal direction has a disadvantage that it can improve resolution of magnetic recording; however, it has a difficulty in reducing noise thereof. In particular, for an areal recording density of magnetic recording increased to 1 Gb/in
2
or more, the prior art magnetic recording medium is very difficult to reduce noise thereof.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic recording medium suitable for high density magnetic recording and a magnetic storage device using the same.
The present inventors have experimentally studied magnetic recording media suitable for high density magnetic recording and found that the above-described object can be achieved by the following methods.
Specifically, it was revealed that a magnetic recording medium being low in degree of orientation or being isotropic (containing a perpendicular magnetization component) is superior in noise reduction to a magnetic recording medium with the easy magnetization axis thereof oriented in the longitudinal direction. Such a magnetic recording medium is required to satisfy the following requirement:
−0.5
≦{Hc
(1)−
Hc
(
P
)}/
Hc
(1)≦0.3
where Hc(1) is a coercivity measured in the longitudinal direction, and Hc(p) is a coercivity measured in the perpendicular direction.
In this requirement, to realize high density magnetic recording having an areal recording density of 1 Gb/in
2
or more, the corecivity Hc(1) is required to be 2 kOe or more and a product of a remanent magnetization Br and a layer thickness “t” is required to be within the range of from 20 to 100 G×&mgr;m. When Hc(1) is less than 2 kOe or Br×t is more than 100 G×&mgr;m, resolution of magnetic recording fails to be enhanced. On the other hand, when Br×t is less than 20 G×&mgr;m, a sufficient signal output cannot be obtained upon reproduction of a recording signal by the magnetic head, the magnetic recording medium is difficult to be operated as a magnetic storage device.
To obtain a magnetic recording medium capable of satisfying the above-described requirement, the magnetic recording medium is required to ensure a high coercivity Hc(1) while thinning the thickness of a magnetic layer to 20 nm or less. In general, for a magnetic layer having a thickness of 20 nm or less, it is difficult to ensure a high coercivity. Consequently, to ensure a high coercivity of a magnetic recording medium using a magnetic layer having a thickness of 20 nm or less, a magnetic anisotropy energy Ku of the magnetic layer is required to be 3×10
6
erg/cm
3
or more.
To obtain a high coercivity Hc(1) in a magnetic recording medium using a magnetic layer being thin in thickness, it is effective that the magnetic layer is of a laminated structure. Specifically, in the case where the thickness of a magnetic layer is limited for reducing the value of Br×t to 100 G×&mgr;m or less, the coercivity Hc(1) can be increased using the magnetic layer of a laminated structure in which two kinds or more magnetic layers different in composition are directly laminated, as compared with a single magnetic layer. While being not clear, the reason for this is conceived that stress and strain are generated at each interface between the magnetic layers because of a slight difference in lattice constant therebetween, thus contributing to improvement in corecivity. In this case, nonmagnetic elements of alloy components constituting the magnetic layers are collected at the interface between the magnetic layers. As a result, magnetic coupling between a plurality of the magnetic layers is weakened, causing an effect in reducing noise generated from the magnetic recording medium.
To positively weaken magnetic coupling between a plurality of magnetic layers, it is effective to insert a nonmagnetic layer at each interface between two kinds or more of the magnetic layers different in composition.
Another method may be also adopted to form a nonmagnetic material between crystal grains of a magnetic thin layer, wherein a magnetic layer is formed by sputtering, using an alloy target made of a Co—Cr, Co—Pt, Co—Cr—Ta, or Co—Cr—Pt alloy placed with pellets of a nonmagnetic material such as SiO
2
, ZrO
2
, TiB
2
, ZrB
2
, MoSi
2
, LaB
6
, SiC, B
4
C, or B
6
Si. In this method, an average grain diameter of magnetic crystals constituting the magnetic thin layer becomes smaller and also a thin layer made of nonmagnetic material is interposed between the crystal grains of the magnetic thin layer. In the magnetic recording medium having such a structure, the magnetic coupling force between magnetic crystal grains can be reduced, and thereby noise of the medium can be reduced. To realize a high density magnetic recording having an areal recording density of 1 Gb/in
2
or more, the average grain diameter of magnetic crystals of a magnetic layer is desirable to be within the range of from 5 to 15 nm.
As a magnetic head in combination with such a magnetic record

Affiliated with

Also associated with

Rating

Magnetic recording medium and magnetic storage does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Magnetic recording medium and magnetic storage, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic recording medium and magnetic storage will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3097812