Laminated antiferromagnetically coupled media for data storage

Details Laminated antiferromagnetically coupled media for data storage Laminated antiferromagnetically coupled media for data storage

2002-06-18

2004-09-21

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

All metal or with adjacent metals

Having magnetic properties, or preformed fiber orientation...

C428S622000, C428S668000, C428S678000, C428S065100, C428S213000, C428S336000, C428S690000, C428S690000

Reexamination Certificate

active

06794057

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of data storage devices, such as hard disk drives with thin film magnetic disks. More particularly, the present invention relates to a configuration of, and a method for fabricating, a thin film medium, which can be used for magnetic recording applications requiring ultra high density storage of data.
2. Description of the Relevant Art
The magnetic thin film media in a background art hard disk drive consists of a substrate (Glass, Al alloy etc.), an underlayer of Cr or Cr alloy, a magnetic layer of Co-alloy, and a protective overcoat of carbon and lubricant. The data bits are stored as the transition of magnetization of a group of tiny magnetic grains. The signal to noise ratio (SNR) is roughly proportional to the number of grains.
In accordance with the background art, the way to increase an area density of stored data in a magnetic recording medium is to reduce the grain size and thickness. The reduction of grain size leads to sharper transitions and a larger SNR. The reduction of the remnant moment-thickness product (M
r
&dgr;) leads to reduced demagnetizing fields and lower noise.
Unfortunately, the reductions in grain size and thickness lead to a reduction in the available energy (K
u
V) to store written bits (where K
u
is the anisotropy constant, and V is the volume of the grain). At room temperature, the presence of thermal energy increases the possibility of magnetization decay, if K
u
V is small. The ratio, K
u
V/k
B
T, should be about 60, if the data bits are to remain thermally stable. In the conventional single layered magnetic media, this limiting value is achieved at a recording density of 40 Gb/in
2
.
To surpass this limit value, alternative techniques and/or materials have been proposed. Utilization of antiferromagnetic underlayers is one of the ways proposed to overcome the thermal instability issue. U.S. Pat. No. 6,020,060, issued to Yoshida et al., discloses using a bcc structured antiferromagnetic layer.
Further, Abarra et al. and Fullerton et al. have proposed in journals and conferences, the addition of one or two stabilizing layers made of a magnetic material, coupled antiferromagnetically to the magnetic recording layer. See E. N. Abarra, H. Sato, A. Inomata, I. Okamoto, and Y. Mizoshita, AA-06, presented at the Intermag 2000 Conference, Toronto, April 2000. Also see, E. N. Abarra, A. Inomata, H. Sato, I. Okamoto, and Y. Mizoshita, “Longitudinal magnetic reording media with thermal stabilization layers,” Applied Physics Letters, Vol. 77, No. 16, 2000, pp. 2581. Also see, Eric E. Fullerton, D. T. Margulies, M. E. Schabes, M. Carey, B. Gurney, A. Moser, M. Best, G. Zeltzer, K. Rubin, H. Rosen, and M. Doerner, “Antiferromagnetically coupled magnetic media layers for thermally stable high-density recording,” Applied Physics Letters, Vol. 77, No. 23, 2000, pp.3806.
According to the configuration proposed by Abarra et al., two stabilizing ferromagnetic layers are deposited below the main recording layer to improve the thermal stability. Thermal stability is increased because of the increase of grain volume, as well as, due to the antiferromagnetic coupling at two interfaces. Unfortunately, the M
r
&dgr; is not greatly reduced, because the moment of two ferromagnetic layers is reduced by the moment of only one ferromagnetic layer. Therefore, the total M
r
&dgr; remains relatively large.
According to the configuration proposed by Fullerton et al., only one stabilizing layer is deposited below the main recording layer. In this configuration, the M
r
&dgr; reduction is larger than the configuration of Abarra et al. However, the increase of thermal stability is not very large, because the increase in the grain volume is not large, and also there is only one antiferromagnetically coupled interface.
U.S. Pat. No. 6,077,586, issued to Bian et al., discloses a structure similar to that of Fullerton et al. However, the structure of Bian et al. is not based on antiferromagnetic coupling, because Bian et al.'s spacer layer is more than 1 nm in thickness.
FIG. 1
is a cross sectional view showing a configuration of a thin film magnetic disk, in accordance with a first embodiment of the background art. The configuration of
FIG. 1
is used by the Fujitsu corporation. The configuration includes a first ferromagnetic layer L
1
having a first thickness t1, a second ferromagnetic layer L
2
having a second thickness t2, and a third ferromagnetic layer L
3
having a third thickness t3. The first layer L
1
is the main recording layer. Non-ferromagnetic spacer layers separate the second ferromagnetic layer L
2
from the first and third ferromagnetic layers L
1
and L
3
. An intermediate layer, underlayer and substrate reside beside the first ferromagnetic layer L
1
. Further, an overcoat and lubricate reside beside the third ferromagnetic layer L
3
. In this configuration, M
r
is defined as the remnant moment. Even if full cancellation of moments between the layers L
1
, L
2
, L
3
, at remanence is assumed, the total M
r
&dgr; is given by Mr (t1−t2+t3).
FIG. 2
is a cross sectional view showing a configuration of a thin film magnetic disk, in accordance with a second embodiment of the background art. The configuration of
FIG. 2
is used by the IBM corporation. The configuration includes a first ferromagnetic layer L
1
and a second ferromagnetic layer L
2
. The first ferromagnetic layer L
1
has a thickness of t1, and the second ferromagnetic layer L
2
has a thickness of t2. A non-ferromagnetic spacer layer reside between the first and second ferromagnetic layers L
1
and L
2
. Again, the thin film magnetic disk includes a substrate, an underlayer, an intermediate layer, an overcoat and a lubricant, as discribed in conjunction with FIG.
1
. In this configuration, the total M
r
&dgr; is given by Mr (t1−t2), if full cancellation of the moments between the layers at remanence is assumed. Thus, in the configurations of
FIGS. 1 and 2
, the reduction of the M
r
&dgr; comes from only one stabilizing layer, namely layer L
2
.
SUMMARY OF THE INVENTION
In the background art, a reduction in M
r
&dgr; comes from only one of the stabilizing layers, namely the layer L
2
in
FIGS. 1 and 2
. The present invention appreciates that if the reduction of M
r
&dgr; comes from two stabilizing layers, the recording media will be less noisy, i.e. a higher SNR can be achieved. Also, the present invention appreciates that if there are two or more anti-ferromagnetically coupled interfaces, the data will be more thermally stable. Therefore, the total number of ferromagnetic layers is three or more. The present invention proves a thin film magnetic media for storing data having a relatively increased thermal stability and a relatively reduced M
r
&dgr; in comparison to the background art configurations.
Another object of the present invention is to provide a fabrication method for a high-density longitudinal magnetic recording medium, which can support an ultra high recording area density relative to the background art configurations.
Yet another object of the present invention is to provide a medium having magnetic layers disposed adjacent to non-ferromagnetic spacer layers, such as Ru. The antiparallel coupling between the layers cause a reduction in the M
r
&dgr;. In such a configuration, the M
r
&dgr; reduction comes from two layers. Such a media is suitable for very high-density recording.
It is a further object of the present invention to provide a magnetic recording medium with three ferromagnetic layers. Two non-ferromagnetic spacer layers separate the three ferromagnetic layers from each other. Out of the three ferromagnetic layers, the middle layer is thicker than the other two layers and is the main recording layer. The M
r
&dgr; reduction comes from the top and bottom ferromagnetic layers and so, the M
r
&dgr; reduction is larger. Because of two antiferromagnetically-coupled interfaces and a larger grain volume the thermal stability is also larger.
Other objects and further sco

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