Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-06-26
2003-09-23
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S611000, C428S667000, C428S680000, C428S900000
Reexamination Certificate
active
06623874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a longitudinal magnetic recording medium with noise suppressed and stability improved, and more particularly to a magnetic recording apparatus having a high recording density which is arranged to use the longitudinal magnetic recording medium.
2. Description of the Related Art
In recent days, a request has been increasingly elevated for enlarging a volume of a magnetic disk drive. Accordingly, the magnetic head has been requested to have a far higher efficiency and the recording medium has been requested to have a far higher coercivity and lower noise.
The magnetic head is used of a composite head that includes both an inductive head for recording data and a spin-valve type head for reading back data. The spin-valve type head is a read-back head that is composed of a magnetoresistive sensor having a plurality of conductive magnetic layers whose directions of magnetization are relatively changed by the outside magnetic field so that a large resistance change may be brought about and conductive non-magnetic layers located between the adjacent conductive magnetic layers.
The magnetic recording medium is composed of a first underlayer called a seed layer formed on a substrate, a second underlayer composed of a Cr alloy having a body-centered cubic structure (bcc structure), a magnetic layer composed of a Co alloy having a hexagonal closed packed structure, and a carbon protective layer. In order to obtain a strong in-plane magnetic anisotropy (high in-plane coercivity), it is preferable that the longitudinal magnetic recording medium has a c-axis, that is, an axis of easy magnetization of the magnetic layer is oriented into the in-plane direction. Hence, the Co alloy of the magnetic layer has an orientation in which the (11.0) plane is positioned in parallel to the substrate plane (called the (11.0) orientation) or another orientation in which the (10.0) plane is positioned in parallel to the substrate plane (called the (10.0) orientation). It is known that the crystal lattice of the magnetic layer may be controlled by the seed layer. Further, it has been reported that the former orientation can be obtained by using Ta (see JP-A-4-188427) or MgO (see Appl. Phys, Lett., vol. 67, pp. 3638-3640, December (1993)) for the seed layer and the latter orientation can be obtained by using an NiAl alloy having a B
2
crystal structure (see IEEE Trans. Magns., vol 30, pp. 3951 to 3953 (1994)) for the seed layer.
In order to further enhance the orientation of the magnetic layer, it has been studied that a non-magnetic Co alloy having a hcp structure is formed as a third underlayer between the second underlayer composed of a Cr alloy and the magnetic layer composed of a Co alloy. This study is tried as remarking the fact that the crystal of the magnetic layer is grown on the Co alloy underlayer having the same hcp structure as that of the magnetic layer more microfine than on the Cr alloy underlayer having a bcc structure. As this type of example, the CoCr alloy (see JP-A-10-79113 or JP-A-10-233014) or the CoCrRu alloy (see JP-A-2000-113445) has been reported.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a magnetic recording medium having a longitudinal recording density of 30 megabits or more per one square millimeter, which has a low noise and high coercivity, and is sufficiently stable for thermal fluctuation.
The inventors tried the following experiment. A non-magnetic alloy layer composed of a Co-40 at. % Ru alloy having a hexagonal closed packed structure (hcp structure) was laid between the magnetic layer and the Cr alloy underlayer. Then, the change of the characteristic was studied. As a result, when the Cr alloy underlayer has (100) orientation and the average grain size of the underlayer is as small as 20 to 25 nm or less, it was found that the characteristics such as the coercivity and reduction of noise are remarkably improved.
The magnetic recording medium of the first object has the following structure. That is, an amorphous first underlayer, a second underlayer of a body-centered cubic structure having Cr as a main component, a third underlayer of a hexagonal closed packed structure having Co as a main component, a magnetic layer of a hexagonal closed pack structure, and a carbon protective film, all of which are formed on the non-magnetic substrate vertically in this describing sequence. Then, a lubricant agent is coated on the carbon protective film. Herein, the term “amorphous” means that no obvious diffraction peak indicates that except a hollow pattern appears in the X-ray diffraction spectrum or the average grain size obtained from a lattice image imaged by a high resolution electronic microscope is 5 nm or less.
In order to keep the second underlayer of the body-centered cubic structure having Cr as a main component in the (100) orientation and make the average grain size smaller, it is preferable to form the first underlayer of the following amorphous alloy, in which alloy Cr is used as a main component and at least one element selected from the first element group consisting of Cr, V and Mn constitutes 30 at. % to 60 at. % and at least one element selected from the second element group consisting of Zr, Hf, Ta, Nb, Ti, W, Mo, B and Si constitutes 3 at. % to 30 at. %. If the total sum of the addition of the first element group is 30 at. % or less, the magnetization is not sufficiently cancelled, while if the total sum of the addition of the second element group is 60 at. % or more, undesirably, it is difficult to implement the amorphousness. Further, if the total sum of the addition of the second element group ranges from 3 at. % to 30 at. %, undesirably, the amorphousness cannot be implemented. The use of the amorphous Co alloy on the first underlayer makes it possible to become the grain size of the magnetic layer smaller, which is preferable to obtaining the medium with reduced noise.
As another method, it is possible to use, as the first underlayer, the following amorphous alloy in which Ni is used as a main component, at least one element selected from the foregoing first element group constitutes 50 at. % or less, and at least one element selected from the third element group consisting of Zr, Ta, Ti, W, Mo, B and Si constitutes 3 at. % to 60 at. %. In this case, since the magnetic layer has an especially strong (11.0) orientation, this amorphous alloy is preferable to obtaining a medium with high coercivity. If the addition of the element selected from the third element group causes the underlayer of the Ni alloy to be sufficiently non-magnetized, no addition of the first element group is required. If non-magnetization is not sufficient, it is necessary to add at least one element of the first element group. In order to prevent the underlayer of the Ni alloy from being crystallized, it is preferable to suppress the total sum of the addition to 50 at. % or less. Further, it is preferable to suppress the total sum of the addition of the third element group to 3 at. % to 60 at. % for the purpose of preventing the underlayer from being crystallized.
The alloy used for making the first underlayer is not limited only if it is amorphous and has a microfine crystal structure having an average crystal grain size of 5 nm or less. It was assured that the same effect in improving the characteristics as the above can be obtained by using amorphous a Cr-15 at. % Ti or Nb-15 at. % Si alloy for the first underlayer. Though it is preferable that the first underlayer is non-magnetic, if Br
1
·t
1
(a product of residual magnetic flux density Br
1
and a film thickness t
1
of the first underlayer) is 20% or less of Br·tmag (a product of residual magnetic flux density Br and a film thickness tmag of the magnetic layer), no substantial problem takes place even if some magnetization is left.
Further, after forming the first underlayer, by exposing the first underlayer in a mixed gas atmosphere having argon as its main component where oxygen constitutes 1 to 10%
Inagaki Jo
Kanbe Tetsuya
Matsuda Yoshibumi
Sakamoto Koji
Yahisa Yotsuo
Mattingly Stanger & Malur, P.C.
Rickman Holly
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