Patent Application
20080020242
The foregoing advantages and features of the invention will become apparent upon reference to the following detailed description and the accompanying drawings, of which:
The present invention will be described below with reference to the drawings.
Any substrate that is used in a typical magnetic recording medium may be employed as non-magnetic substrate 1 of the present invention, and specific examples thereof include an NiP-plated aluminum alloy substrate, a reinforced glass substrate, and a crystallized glass substrate.
Non-magnetic underlayer 5 used in the present invention is provided to control the crystalline orientation and grain size of magnetic recording layer 6, and Ru or an alloy containing Ru may be used as the metal of the non-magnetic underlayer.
A ferromagnetic material of an alloy containing at least Co and Cr is preferably used as magnetic recording layer 6 of the present invention. In the alloy, the c axis of the hexagonal close-packed structure is preferably oriented in a perpendicular direction to the film surface.
Protective film 7 may be formed from any material having the required mechanical strength, heat resistance, oxidation resistance, corrosion resistance, and so on, and when a conventionally used material is employed, there are no particular limitations on the material composition thereof. However, a thin film having carbon as a main constituent, for example, can be used favorably. A perfluoropolyether type lubricant, for example, may be used favorably as liquid lubrication layer 8.
A crystalline alloy such as an NiFe-based alloy, a sendust (FeSiAl) alloy, or a FeCo alloy having a large saturation magnetic flux density, or a non-crystalline Co alloy such as CoZrNb, CoTaZr, or the like, for example, may be used as soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 serving as constitutional elements of soft magnetic backing layer 9. The optimum film thickness values of soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 vary according to the structure and characteristics of the magnetic head used for recording, but in consideration of productivity, these values are each preferably set between 10 and 500 nm.
The easy magnetization axes of soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 must be coupled parallel to the substrate surface and oriented 180° from each other. The reason for this is that when the magnetizations of soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 sandwiching non-magnetic metal layer 3 are coupled in anti-parallel and anti-ferromagnetically, the orientation of the magnetizations does not vary even if an external magnetic field equal to or lower than the coupling strength thereof is applied. In other words, a domain wall is not generated in the soft magnetic layer, and the generation of spike noise can be suppressed.
A material having any metal of Cu, Ru, Rh, Pd, and Re or an alloy thereof as a main constituent may be used as non-magnetic metal layer 3. The film thickness of non-magnetic metal layer 3 must be selected appropriately such that the easy magnetization axes of soft magnetic lower layer 2 and soft magnetic upper backing layer 4 are oriented parallel to the substrate surface and in 180° opposing directions, and such that a powerful coupling strength is obtained. To obtain a high level of resistance to an external magnetic field, however, the film thickness of non-magnetic metal layer 3 is preferably set between 0.1 and 5 nm. The reason for this is as follows.
As the film thickness of non-magnetic metal layer 3 increases gradually from 0 nm, a coupling whereby the easy magnetization axes of soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 are parallel to the substrate and oriented in the same direction (ferromagnetic coupling) and a coupling whereby the easy magnetization axes are parallel to the substrate surface and oriented in 180° opposing directions (anti-ferromagnetic coupling) appear alternately. For example, when Ru is used as non-magnetic metal layer 3, soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 are coupled ferromagnetically within an Ru film thickness range of 0 to 0.3 nm, and are coupled anti-ferromagnetically within a range of 0.3 to 1.2 nm. When the film thickness is increased further, soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 are coupled ferromagnetically within a range of 1.2 to 1.8 nm, and coupled anti-ferromagnetically within a range of 1.8 to 3.0 nm.
The film thickness ranges in which ferromagnetic coupling is achieved and the film thickness ranges in which anti-ferromagnetic coupling is achieved differ according to the metal in use, and therefore, in consideration of cases employing various different metals, the film thickness for exhibiting anti-ferromagnetic coupling is preferably set at no less than 0.1 nm.
The coupling strength of soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4 decreases as the film thickness of non-magnetic metal layer 3 increases. As the coupling strength increases, the resistance to an external magnetic field increases, and although this characteristic varies according to the type of metal used for non-magnetic metal layer 3, the film thickness of non-magnetic metal layer 3 is preferably set at no more than 5 nm in order to secure sufficient resistance to a floating magnetic field in a hard disk drive.
Non-magnetic metal layer 3 is subjected to surface exposure processing using a nitrogen-containing gas containing 0.1 to 100 at % nitrogen. When soft magnetic backing layer 9 has a non-magnetic metal layer whose surface has been subjected to surface exposure processing using a nitrogen-containing gas containing 0.1 to 100 at % nitrogen between soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4, an improvement in the anisotropic magnetic field Hk of approximately 200 Oe to 300 Oe can be seen in comparison with the Hk value of a soft magnetic backing layer having a non-magnetic metal layer that has not been subjected to this surface processing between soft magnetic lower backing layer 2 and soft magnetic upper backing layer 4. When the nitrogen concentration of the nitrogen-containing gas is less than 0.1 at %, the improvement in Hk is insufficient. An inert gas such as Ar may be used as a gas component other than nitrogen when the nitrogen-containing gas is not 100 at % nitrogen. When the nitrogen-containing gas contains oxygen in addition to nitrogen and an inert gas, the Hk improving effect of the nitrogen is not inhibited significantly provided the amount of oxygen is less than 2 at %, and therefore the nitrogen-containing gas may contain oxygen.
The processing time of the surface exposure processing using the nitrogen-containing gas is preferably set between 0.1 and 10 seconds. Below 0.1 seconds, the surface exposure processing effect is insufficient, and above 10 seconds, no further improvements in the processing effect are obtained, and the cost of the gas used increases. Furthermore, the atmosphere of the surface exposure processing is preferably set in a pressure range of 3 to 120 mTorr.
The backing layer, underlayer, magnetic recording layer, and protective film are formed by a vapor deposition method. Examples of vapor deposition methods include physical vapor deposition and chemical vapor deposition (CVD), and examples of physical vapor deposition methods include sputtering and vacuum deposition. In other words, sputtering, vacuum deposition, and CVD may be cited as vapor deposition methods. DC (direct current) magnetron sputtering and RF (radio frequency) magnetron sputtering may be cited as sputtering methods.
When a plurality of layers are to be formed using vapor deposition, all of the layers may be formed by the same vapor deposition method, or a different vapor deposition method may be selected for each layer to be formed. In other words, any of sputtering, vacuum deposition, and CVD, or a combination of two or more thereof, may be employed as the vapor deposition method.
Next, a manufacturing method of the perpendicular magnetic recording medium according to the present invention will be described.
First, the manufacturing method of the present invention comprises a process for forming soft magnetic backing layer 9, in which soft magnetic lower backing layer 2 and non-magnetic metal layer 3 are formed in order on non-magnetic substrate 1 using a vapor deposition method, the surface of the formed non-magnetic metal layer 3 is subjected to surface exposure processing using a nitrogen-containing gas containing 0.1 to 100 at % nitrogen, and soft magnetic upper backing layer 4 is then formed on non-magnetic metal layer 3 using a vapor deposition method. The materials used for forming non-magnetic substrate 1, soft magnetic lower backing layer 2, non-magnetic metal layer 3, and soft magnetic upper backing layer 4 are as noted above in the description of the perpendicular magnetic recording medium.
In this manufacturing method, the film thickness of the soft magnetic lower backing layer is preferably between 10 and 500 nm, the film thickness of the non-magnetic metal layer is preferably between 0.1 and 5 nm, and the film thickness of the soft magnetic upper backing layer is preferably between 10 and 500 nm. The reasons for this are as noted above in the description of the perpendicular magnetic recording medium.
Further, the manufacturing method of the present invention comprises a process for forming non-magnetic underlayer 5 on soft magnetic backing layer 9 formed in the manner described above using a vapor deposition method. The materials used for forming non-magnetic underlayer 5 are as noted above in the description of the perpendicular magnetic recording medium.
The manufacturing method of the present invention further comprises a process for forming magnetic recording layer 6 on non-magnetic underlayer 5 formed in the manner described above using a vapor deposition method. The materials used for forming magnetic recording layer 6 are as noted above in the description of the perpendicular magnetic recording medium. The manufacturing method of the present invention further comprises a process for forming protective film 7 on magnetic recording layer 6 formed in the manner described above using a vapor deposition method. The vapor deposition methods employed in the manufacturing method of the present invention are as noted above in the description of the perpendicular magnetic recording medium.
The manufacturing method of the present invention may include a process for providing liquid lubricant layer 8 on protective film 7 formed in the manner described above. The aforementioned lubricant may be used as a lubricant, and a dip-coat method or spin coat method, for example, may be employed to form the liquid lubricant layer.
The perpendicular magnetic recording medium and manufacturing method thereof according to the present invention will be described in further detail below using experimental examples.
A chemically strengthened glass substrate having a smooth surface (N-5 glass substrate, manufactured by HOYA) was used as non-magnetic substrate 1. After being washed, the substrate was introduced into a sputtering apparatus, and using a Co85Zr10Nb5 target, CoZrNb amorphous soft magnetic lower backing layer 2 was deposited at 110 nm using a DC magnetron sputtering method. Next, using a Ru target, Ru non-magnetic metal layer 3 was deposited at 0.8 nm using a DC magnetron sputtering method.
Next, using Ar gas containing 10 at % nitrogen gas (Ar-10% N2 gas), the surface of Ru non-magnetic metal layer 3 was subjected to nitrogen exposure processing for 3 seconds in an atmosphere of 10 mTorr. Then, again using a Co85Zr10Nb5 target, CoZrNb amorphous soft magnetic upper backing layer 4 was deposited at 90 nm using a DC magnetron sputtering method. Next, using a carbon target, protective film 7 made of carbon was deposited at 10 nm using a DC magnetron sputtering method, whereupon the structure was removed from the sputtering apparatus. Next, 2 nm thick liquid lubrication layer 8 of perfluoropolyether was formed using a dip-coat method, and thus a partial model body of a disk-shaped perpendicular magnetic recording medium having neither a non-magnetic underlayer nor a magnetic recording layer was created.
Note that the film thickness of the non-magnetic metal layer was selected such that the Hk value of the soft magnetic backing layer reached a maximum, and to verify the increase or decrease in Hk according to the application of the nitrogen exposure process, the film thickness of the non-magnetic metal layer was made identical in each experimental example, including a comparative experimental example.
In the nitrogen exposure process, exposure was performed for 10 seconds using Ar-0.1% N2 gas. Otherwise, a partial model body of a disk-shaped perpendicular magnetic recording medium having neither a non-magnetic underlayer nor a magnetic recording layer was created in a similar manner to the first experimental example. The Hk value was determined in a similar manner to the first experimental example using the obtained medium. The results are shown in Table 1 together with the results of the first experimental example.
Pure N2 (100%) gas was used in the nitrogen exposure process. Otherwise, a partial model body of a disk-shaped perpendicular magnetic recording medium having neither a non-magnetic underlayer nor a magnetic recording layer was created in a similar manner to the first experimental example. The Hk value was determined in a similar manner to the first experimental example using the obtained medium. The results are shown in Table 1 together with the results of the first experimental example.
In the nitrogen exposure process, Ar-10% N2-2% O2 gas with added oxygen was used. Otherwise, a partial model body of a disk-shaped perpendicular magnetic recording medium having neither a non-magnetic underlayer nor a magnetic recording layer was created in a similar manner to the first experimental example. The Hk value was determined in a similar manner to the first experimental example using the obtained medium. The results are shown in Table 1 together with the results of the first experimental example.
A nitrogen exposure process was not performed. Otherwise, a partial model body of a disk-shaped perpendicular magnetic recording medium having neither a non-magnetic underlayer nor a magnetic recording layer was created in a similar manner to the first experimental example.
Similarly to the first experimental example, CoZrNb amorphous soft magnetic lower backing layer 2 and Ru non-magnetic metal layer 3 were laminated onto non-magnetic substrate 1 constituted by a chemically strengthened glass substrate (N-5 glass substrate, manufactured by HOYA), and the surface of Ru non-magnetic metal layer 3 was subjected to nitrogen exposure processing, whereupon CoZrNb amorphous soft magnetic upper backing layer 4 was deposited. Ta was then deposited at a thickness of 6 nm on soft magnetic backing layer 9 obtained in this manner in a sputtering apparatus using a DC magnetron sputtering method to form non-magnetic underlayer 5, and Co77Cr9Pt10SiO24 was deposited thereon at 20 nm as magnetic recording layer 6. Next, similarly to the first experimental example, carbon protective film 7 was formed on magnetic recording layer 6, whereupon liquid lubrication layer 8 was formed from perfluoropolyether, and thus the disk-shaped perpendicular magnetic recording medium was obtained. The SN ratio of the obtained perpendicular magnetic recording medium is shown in Table 1.
The perpendicular magnetic recording media of the second to fourth examples and the first comparative example were obtained in a similar manner to the first example except that the second to fourth experimental examples and the first comparative experimental example were followed instead of the first experimental example. The SN ratios of the obtained perpendicular magnetic recording media are shown in Table 1.
It can be seen from a comparison of the first experimental example and the comparative experimental example that by performing the nitrogen exposure process, an improvement in Hk of approximately 1.9 times is obtained. In other words, the Hk can be increased using a simple method merely involving nitrogen exposure processing, without the need for complicated and expensive methods.
Further, it can be seen from Table 1 that as the nitrogen concentration of the exposure processing gas for exposing the surface of the non-magnetic metal increases, the Hk of the soft magnetic backing layer improves. For example, the Hk of the perpendicular magnetic recording medium of the third experimental example, in which exposure processing is performed using 100% nitrogen gas, is 791 Oe, which is approximately twice that of the comparative experimental example and the highest value in Table 1. Note that no differences in Hk were found within a nitrogen-containing gas exposure processing time range of 0.1 to 10 seconds. Further, it is evident from the fourth experimental example that even when the nitrogen-containing gas used for exposure processing contains oxygen, a nitrogen-induced Hk improving effect can be exhibited.
It also was found from the first to fourth examples and the first comparative example that as the Hk value of the soft magnetic backing layer increases, a steadily more favorable SN ratio is obtained. For example, in comparison with the first comparative example, in which nitrogen exposure is not performed, the third example, in which 100% nitrogen gas is used, exhibits an improvement of approximately 1.0 dB in the SN ratio.
According to the present invention, an increase in Hk can be achieved using a simple process of subjecting the surface of the non-magnetic metal layer to nitrogen gas exposure, without the need for a special layer configuration, and therefore the present invention incurs substantially no cost increases, is suitable for mass production, and is useful as means for improving the SN ratio of a perpendicular magnetic recording medium.
Thus, a perpendicular magnetic recording medium and manufacturing method thereof has been described according to the present invention. Many modifications and variations may be made to the techniques and structures described and illustrated herein without departing from the spirit and scope of the invention. Accordingly, it should be understood that the media and methods described herein are illustrative only and are not limiting upon the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-198118 | Jul 2006 | JP | national |
