Laminated medium with antiferromagnetic stabilization layers

Details Laminated medium with antiferromagnetic stabilization layers Laminated medium with antiferromagnetic stabilization layers

2001-07-18

2004-07-06

Rickman, Holly (Department: 1773)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S690000, C428S336000, C428S900000, C427S131000, C427S132000

Reexamination Certificate

active

06759149

ABSTRACT:

FIELD OF INVENTION
This invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The invention has particular applicability to high areal density longitudinal magnetic recording media having very low medium noise and high degree of thermal stability, and more particularly, to a laminated medium with antiferromagnetic stabilization layers.
BACKGROUND
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), signal-to-medium noise ratio (SMNR), and thermal stability of the media. In particular, as the SMNR is reduced by decreasing the grain size or reducing exchange coupling between grains, it has been observed that the thermal stability of the media decreases. Therefore, it is extremely difficult to produce a magnetic recording medium satisfying above mentioned demanding requirements.
Magnetic discs and disc drives provide quick access to vast amounts of stored information. Both flexible and rigid discs are available. Data on the discs is stored in circular tracks and divided into segments within the tracks. Disc drives typically employ one or more discs rotated on a central axis. A magnetic head is positioned over the disc surface to either access or add to the stored information. The heads for disc drives are mounted on a movable arm that carries the head in very close proximity to the disc over the various tracks and segments.
FIG. 1
shows the schematic arrangement of a magnetic disk drive
10
using a rotary actuator. A disk or medium
11
is mounted on a spindle
12
and rotated at a predetermined speed. The rotary actuator comprises an arm
15
to which is coupled a suspension
14
. A magnetic head
13
is mounted at the distal end of the suspension
14
. The magnetic head
13
is brought into contact with the recording/reproduction surface of the disk
11
. A voice coil motor
19
as a kind of linear motor is provided to the other end of the arm
15
. The arm
15
is swingably supported by ball bearings (not shown) provided at the upper and lower portions of a pivot portion
17
.
A cross sectional view of a conventional longitudinal recording disk medium is depicted in
FIG. 2. A
longitudinal recording medium typically comprises a non-magnetic substrate
20
having sequentially deposited on each side thereof an underlayer
21
,
21
′, such as chromium (Cr) or Cr-containing, a magnetic layer
22
,
22
′, typically comprising a cobalt (Co)-base alloy, and a protective overcoat
23
,
23
′, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer
21
,
21
′, magnetic layer
22
,
22
′, and protective overcoat
23
,
23
′, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-containing underlayer.
A conventional longitudinal recording disk medium is prepared by-depositing multiple layers of films to make a composite film. In sequential order, the multiple layers typically comprise a non-magnetic substrate, one or more underlayers, one or more magnetic layers, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) alloy magnetic layer is deposited on a chromium or chromium-alloy underlayer.
Conventional methods for manufacturing a longitudinal magnetic recording medium with a glass, glass-ceramic, Al or Al—NiP substrate may also comprise applying a seedlayer between the substrate and underlayer. A conventional seedlayer seeds the nucleation of a particular crystallographic texture of the underlayer. Conventionally, a seedlayer is the first deposited layer on the non-magnetic substrate. The role of this layer is to texture (alignment) the crystallographic orientation of the subsequent Cr-containing underlayer, and might also produce small grain size, which is desired for the purpose of reducing recording noise.
The seedlayer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 Å thick.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Al—Mg) alloy. Such Al—Mg-alloys are typically electrolessly plated with a layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as glass, e.g., an amorphous glass, glass-ceramic material that comprises a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks.
According to the domain theory, a magnetic material is composed of a number of submicroscopic regions called domains. Each domain contains parallel atomic magnetic moments and is always magnetized to saturation (Ms), but the directions of magnetization of different domains are not necessarily parallel. In the absence of an applied magnetic field, adjacent domains may be oriented randomly in any number of several directions, called the directions of easy magnetization, which depend on the geometry of the crystal, stress, etc. The resultant effect of all these various directions of magnetization may be zero, as is the case with an unmagnetized specimen. When a magnetic field is applied, the domains most nearly parallel to the direction of the applied field may grow in size at the expense of the others. This is called boundary displacement of the domains or the domain growth. Domains may also rotate and align parallel to the applied field. When the material reaches the point of saturation magnetization, no further domain growth and rotation would take place on increasing the strength of the magnetic field.
The ease of magnetization or demagnetization of a magnetic material depends on the crystal structure, grain orientation, the state of strain, and the direction of the magnetic field. The magnetization is most easily obtained along the easy axis of magnetization but most difficult along the hard axis of magnetization. A magnetic material is said to posses a magnetic anisotropy when easy and hard axes exist. On the other hand, a magnetic material is said to be isotropic when there are no easy or hard axes. A magnetic material is said to possess a uniaxial anisotropy when the easy axis is oriented along a single crystallographic direction, and to possess multiaxial anisotropy when the easy axis aligns with multiple crystallographic directions.
“Anisotropy energy” is the work against the anisotropy force to turn magnetization vector away from an easy direction. For example, a single crystal of iron, which is made up of a cubic array of iron atoms, tends to magnetize in the directions of the cube edges along which lie the easy axes of magnetization. A single crystal of iron requires about 1.4×10
5
ergs/cm
3
(at room temperature) to move magnetization into the hard axis of magnetization from an easy direction, which is along a cubic body diagonal.
The anisotropy energy U
A
could be expressed in an ascending power series of the direction cosines between the magnetization and the crystal axes. For cubic crystals, the lowest-order terms take the form of Equation (1),
U
A
=K
1
(&agr;
1
2
&agr;
2
2
+&agr;
2
2
&agr;
3
2
+&agr;
3
2
&agr;
1
2
)+
K
2
(&agr;
1
2
&agr;
2
2
&agr;
3
2
)  (1)
where &agr;
1
, &agr;
2
and &agr;
3
are dire

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