Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
2002-07-02
2004-07-06
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C428S637000, C428S666000, C428S667000, C428S668000, C428S669000, C428S678000, C428S141000, C428S213000, C428S409000, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06759138
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a magnetic recording medium for use with a magnetic disk apparatus for carrying out information recording and reproducing operations.
In order to achieve an increase in recording density of a HDD (hard disk drive), a decrease in medium noise is indispensable. In the past, the decrease in medium noise is achieved by improving a film structure or a film material of a magnetic recording medium in order to reduce a product Mr·t of the magnetic disk, with the help of uninterrupted improvement in output characteristics of a magnetic head. The product Mr·t is a product of residual magnetization (Mr) of a magnetic layer of the magnetic disk and a film thickness (t) of the magnetic layer of the magnetic disk.
The reduction in Mr·t is extremely effective in improving R/W (read/write) characteristics but simultaneously causes a problem of a thermal decay characteristic. The decrease in Mr·t, i.e., the decrease in film thickness of a magnetic layer brings about miniaturization of the grain size of the magnetic layer, resulting in reduction of the medium noise. However, miniaturized crystal grains no longer have a coercive force (Hc) sufficient to hold recorded magnetization as a recorded signal. This results in a phenomenon that the recorded signal is attenuated. This phenomenon is called thermal decay.
In order to prevent the phenomenon (thermal decay) that the recording signal is attenuated, various film structures have been proposed. Attention is recently attracted to one of the film structures which is called an AFC (Anti-Ferro-Coupled-film) structure (see Japanese Unexamined Patent Publication No. 56923/2001 (JP 2001-56293 A)).
A magnetic recording medium disclosed in Japanese Unexamined Patent Publication No. 56923/2001 has a multilayer structure in which a magnetic layer is divided by a nonmagnetic separation layer (Ru, Rh, Ir, or the like) into upper and lower magnetic layers. Specifically, the magnetic layer is divided by the nonmagnetic separation layer into a plurality of magnetic layers having magnetizing directions parallel to one another. Thus, the thermal decay characteristic is improved.
However, a film using the AFC structure is increased in magnetic layer thickness in total due to its structure although the thermal decay characteristic is excellent. The increase in magnetic layer thickness results in a decrease in coercive force squareness ratio (S*). In addition, the pulse width (PW) and the overwrite characteristic are deteriorated. The increase in magnetic layer thickness also results in an increase in grain size of the magnetic layer so that the medium noise (S/N ratio) is deteriorated. Thus, such recording/reproducing characteristics do not fully satisfy recent demands in an increase in recording density.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a magnetic recording medium which is excellent in thermal decay characteristic and in recording/reproducing characteristics such as a coercive force squareness ratio (S*), a pulse width, an overwrite characteristic, and medium noise (S/N ratio).
Magnetic recording media according to this invention are as follows.
1) A magnetic recording medium comprising a base body, a first magnetic layer formed on the base body, a second magnetic layer, and a spacer layer formed between the first and the second magnetic layers, each of the first and the second magnetic layers being of a ferromagnetic material, the spacer layer being for inducing antiferromagnetic exchange interaction between the first and the second magnetic layers, the first magnetic layer being for controlling the antiferromagnetic exchange interaction, the second magnetic layer comprising a primary layer and a secondary layer located nearer to the base body than the primary layer, the primary layer having a primary anisotropic magnetic field, the secondary layer having a secondary anisotropic magnetic field which is smaller than the primary anisotropic magnetic field.
2) A magnetic recording medium as mentioned in the paragraph 1), wherein the secondary layer has a thickness smaller than that of the primary layer.
3) A magnetic recording medium as mentioned in the paragraph 1), wherein the secondary layer has a saturated magnetic flux density smaller than that of the primary layer.
4) A magnetic recording medium as mentioned in the paragraph 1), wherein the spacer layer has a surface roughness Rmax of 6 nm or less and another surface roughness Ra of 0.6 nm or less, where Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point and where Ra is representative of a center-line-mean roughness.
5) A magnetic recording medium as mentioned in the paragraph 1), wherein the spacer layer is made of a material comprising Ru. 6) A magnetic recording medium as mentioned in the paragraph 1), wherein the base body comprises a substrate and an underlying layer formed between the substrate and the first magnetic layer. 7) A magnetic recording medium as mentioned in the paragraph 6), wherein the underlying layer comprises an intermediate layer having an hcp (hexagonal close-packed) structure.
8) A magnetic recording medium as mentioned in the paragraph 7), wherein the intermediate layer is formed so that crystal matching or alignment with the primary magnetic layer is improved away from the substrate towards the primary magnetic layer.
9) A magnetic recording medium as mentioned in the paragraph 7), wherein the intermediate layer comprises a plurality of layers.
10) A magnetic recording medium as mentioned in the paragraph 9), wherein one layer of the plurality of layers of the intermediate layer, that is nearest to the first magnetic layer, is made of a ferromagnetic material.
11) A magnetic recording medium as mentioned in the paragraph 6), wherein the substrate is a glass substrate.
12) A magnetic recording medium as mentioned in the paragraph 6), wherein the base body further comprises a precoat layer formed between the substrate and the underlying layer for controlling crystal grains of the first and the second magnetic layers.
13) A magnetic recording medium as mentioned in the paragraph 12), wherein the precoat layer is made of an alloy comprising Cr and Ta.
As described above, the second magnetic layer comprises a plurality of layers including the primary and the secondary layers. In this case, as compared with the case where the second magnetic layer comprises a single layer, a thermal decay characteristic is improved and, simultaneously, a coercive force squareness ratio (S*) and a pulse width (PW) are improved.
As described above, the secondary layer located nearer to the base body than the primary layer has a thickness smaller than that of the primary layer. With this structure, the primary layer relatively thick and located farther from the base body mainly has magnetic recording/reproducing functions while the secondary layer relatively thin and located nearer to the base body has a function of preventing the disturbance in crystal orientation in case where the primary layer is directly formed on the spacer layer.
Specifically, the primary layer having a thickness suitable for magnetic recording/reproducing operations and the spacer layer are not always have lattice constants approximate to each other. Therefore, by providing an additional layer (namely, the secondary layer) having a lattice constant approximate to those of the spacer layer and the primary layer suitable for the magnetic recording/reproducing operations, the difference in lattice constant between the above-mentioned layers can be reduced. The additional layer (the secondary layer) is mainly intended to approximate (match) the lattice constants. Therefore, the additional layer (the secondary layer) is preferably thin. By matching the lattice constants, the disturbance in crystal orientation is suppressed as compared with the case where the primary layer is directly formed on the spacer layer. As a result, the coercive force squareness ratio (S*) and the pulse widt
Ayama Kenji
Moroishi Keiji
Tomiyasu Hiroshi
Umezawa Teiichiro
Bernatz Kevin M
Hoya Corporation
Sughrue & Mion, PLLC
Zacharia Ramsey
LandOfFree
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