Multilayer-based magnetic media with hard ferromagnetic,...

Details Multilayer-based magnetic media with hard ferromagnetic,... Multilayer-based magnetic media with hard ferromagnetic,...

2001-09-04

2004-06-22

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S336000, C428S690000, C428S690000

Reexamination Certificate

active

06753072

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to multilayer magnetic superlattice-based, perpendicular magnetic recording media which have improved thermal stability and very high perpendicular magnetic coercivities which can exceed about 6,500 Oe. The invention finds particular utility in the manufacture of very high areal recording density magnetic data/information storage and retrieval media such as hard disks and hybrid recording devices and systems including such media in combination with magnetoresistive read heads and inductive write heads.
BACKGROUND OF THE INVENTION
Magnetic recording media and devices incorporating same are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes, typically in disk form. Conventional magnetic thin-film media, wherein a fine-grained polycrystalline magnetic alloy layer serves as the active recording medium layer, are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation of the magnetic domains of the grains of magnetic material.
Efforts are continually being made with the aim of increasing the areal recording density, i.e., the bit density, or bits/unit area, of the magnetic media. However, severe difficulties, such as thermal instability, are encountered when the bit density of longitudinal media is increased above about 20-50 Gb/in
2
in order to form ultra-high recording density media, when the necessary reduction in grain size exceeds the superparamagnetic limit. Such thermal instability can, inter alia, cause undesirable decay of the output signal of hard disk drives, and in extreme instances, result in total data loss and collapse of the magnetic bits. In this regard, the perpendicular recording media have been found superior to the more common longitudinal media in achieving very high bit densities.
As indicated above, much effort has been directed toward enhancing the density of data storage by both types of magnetic media, as well as toward increasing the stability of the stored data and the ease with which the stored data can be read. For example, it is desirable to develop magnetic media having large magnetic coercivities, H
c
, since the magnetic moments of such materials require large magnetic fields for reorientation, i.e., switching between digital 1 and 0. Thus, when the magnetic medium has a large coercivity H
c
, exposure of the magnetic medium to stray magnetic fields, such as are generated during writing operations, is less likely to corrupt data stored at adjacent locations.
The density with which data can be stored within a magnetic thin-film medium for perpendicular recording is related to the perpendicular anisotropy (“Ku” or “K
1
1
”) of the material, which reflects the tendency for the magnetic moments to align in the out-of-plane direction. Thin-film magnetic media having high perpendicular anisotropy have their magnetic moments aligned preferentially perpendicular to the plane of the thin film. This reduces the transition length between the magnetic moments with opposite direction, thereby allowing a larger number of magnetic bits (domains) to be packed into a unit area of the film and increasing the areal density with which data can be stored.
A large perpendicular anisotropy is also reflected in a larger value of the magnetic coercivity H
c
, since the preferential out-of-plane alignment of the magnetic moments raises the energy barrier for the nucleation of a reverse magnetization domain, and similarly, makes it harder to reverse the orientation of the magnetic domains by 180° rotation. Further, the magnetic remanence of a medium, which measures the tendency of the magnetic moments of the medium to remain aligned once the magnetic field is shut off following saturation, also increases with increasing K
1
.
While perpendicular media have been fabricated utilizing a single perpendicularly oriented magnetic recording layer, a promising new class of materials for use as the active recording layer of perpendicular magnetic media includes multilayer magnetic “superlattice” structures comprised of a stacked plurality of very thin magnetic
on-magnetic layer pairs, for example, cobalt/platinum (Co/Pt)
n
and cobalt/palladium (Co/Pd)
n
multilayer stacks. As schematically illustrated in the cross-sectional view of
FIG. 1
, such multilayer stacks or superlattice structures
10
comprise n pairs of alternating discrete layers of Co or Co-based materials (designated by the letter A in the drawing) and Pt or Pd (designated by the letter B in the drawing), where n is an integer between about 5 and about 50. Superlattice
10
is typically formed by suitable thin film deposition techniques, e.g., sputtering, and can exhibit perpendicular magnetic isotropy arising from metastable chemical modulation in the direction normal to the underlying substrate S on which superlattice
10
is formed. Compared to media with a single layer of conventional cobalt-chromium (Co-Cr) magnetic alloys utilized in magnetic data storage/retrieval disk applications, such (Co/Pt)
n
and (Co/Pd)
n
, multilayer magnetic superlattice structures offer a number of performance advantages. For example, a sputtered (Co/Pt)
n
multilayer stack or superlattice
10
suitable for use as a magnetic recording layer of a perpendicular medium can comprise n Co/Pt or Co/Pd layer pairs, where n=about 5 to about 50, e.g., 20, and wherein each Co/Pt layer pair consists of an about 3 Å thick Co layer adjacent to an about 10 Å thick Pt or Pd layer, for a total of 40 separate (or discrete) layers, and are characterized by having a large perpendicular anisotropy, high coercivity H
c
, and a high squareness ratio of a magnetic hysteresis (M-H) loop measured in the perpendicular direction. By way of illustration, (Co/Pt)
n
and (Co/Pd)
n
multilayer magnetic superlattices, wherein n=about 10 to about 30 and the layer pairs have thicknesses as indicated above and fabricated, e.g., by means of techniques disclosed in U.S. Pat. No. 5,750,270, the entire disclosure of which is incorporated herein by reference, have stable magnetic domains with a narrow domain wall width, the stability of the Co/Pt and Co/Pd domains being enhanced by a strong domain wall pinning effect. Thus, (Co/Pt)
n
and (Co/Pd)
n
multilayer superlattice structures for use in the fabrication of magneto-optical (“MO”) recording media, perpendicular recording media, and/or magnetoresistance (“MR”) recording media exhibit perpendicular anisotropies exceeding about 2×10
6
erg/cm
3
; coercivities as high as about 5,000 Oe; squareness ratios (S) of a M-H loop, measured in the perpendicular direction, of from about 0.85 to about 1.0, and carrier-to-noise ratios (“CNR”) of from about 30 dB to about 60 dB.
Multilayer superlattice-based structures provide a number of additional advantages vis-à-vis conventional thin-film magnetic media. For example, by virtue of their small magnetic domain diameters, they can advantageously support high areal recording densities (e.g., ~100-600 Gb/in
2
at domain diameters<20 nm); they can be configured either in MR or MO type drives or employed in the form of “hybrid” recording devices including magnetoresistive or giant magnetoresistive (“GMR”) read heads (see below) and inductive write heads; and the read-back signal can be differentiated, whereby the sharp rise-time of the differentiated signal further facilitates high areal density recording.
A key advance in magnetic recording technology which has brought about very significant increases in the data storage densities of magnetic disks has been the development of extremely sensitive magnetic read/write devices which utilize separate magnetoresistive read heads and inductive write heads. The magnetoresistive effect, wherein a change in electrical resistance is exhibited in the presence of a magnetic field, has long been known; however, utilization of the effect in practical MR devices was limited by the very small magnetoresistive response of the available materials. The dev

Affiliated with

Also associated with

Rating

Multilayer-based magnetic media with hard ferromagnetic,... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multilayer-based magnetic media with hard ferromagnetic,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multilayer-based magnetic media with hard ferromagnetic,... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3342746