JP2007004920A - Perpendicular magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a medium having a high medium S/N and excellent corrosion resistance and scratch durability. <P>SOLUTION: In a perpendicular magnetic recording medium formed by sequentially layering at least a soft magnetic layer 13, a seed layer 14, an intermediate layer 15, a magnetic recording layer 16 and a protective layer 17 on a substrate 11, the magnetic recording layer 16 has a granular structure constituted of a grain boundary layer containing many columnar particles comprising a CoCrPt alloy and an oxide, the seed layer 14 is constituted of a WCo alloy and the intermediate layer 15 is constituted of Ru or a Ru alloy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium capable of recording a large amount of information, and more particularly to a magnetic recording medium suitable for high-density magnetic recording and a manufacturing method thereof.

  In recent years, there has been a strong demand for an increase in the capacity of a magnetic storage device, for example, a small-sized and large-capacity magnetic disk device is mounted not only in a personal computer but also in household electric appliances, and an improvement in recording density is required. In order to cope with this, development of magnetic heads and magnetic recording media has been energetically performed. However, it has become difficult to improve the recording density using the in-plane magnetic recording method that is currently in practical use. Therefore, perpendicular magnetic recording has been studied as an alternative to in-plane magnetic recording. Perpendicular magnetic recording is considered to be a system that is inherently suitable for high density recording because the adjacent magnetizations do not face each other and the high density recording state is stable. Also, by combining a dual-layer perpendicular magnetic recording medium having a perpendicular recording layer and a soft magnetic underlayer and a single-pole type recording head, the recording efficiency can be increased and the coercive force of the recording film can be increased. It is also possible to do. However, in order to realize high-density recording using the perpendicular magnetic recording method, it is necessary to develop a perpendicular magnetic recording medium that is low noise and resistant to thermal demagnetization.

  As a recording layer of a perpendicular magnetic recording medium, a CoCrPt-based alloy film that has been put to practical use in an in-plane magnetic recording medium has been conventionally studied. In order to obtain low noise characteristics using a CoCrPt-based alloy film, it is necessary to reduce exchange coupling between magnetic crystal grains by using Cr segregation to grain boundaries to reduce the magnetization reversal unit. However, when the amount of Cr is insufficient, the particles are coalesced and enlarged in the formation process of the recording layer, or the exchange coupling between the particles is insufficiently reduced, and low noise characteristics cannot be obtained. On the other hand, when the amount of Cr is increased, the magnetic anisotropy energy of the magnetic particles is lowered due to a large amount of Cr remaining in the particles, and sufficient resistance to thermal demagnetization cannot be obtained.

  In order to overcome such problems and obtain low noise characteristics, for example, as shown in Japanese Patent Application Laid-Open No. 2003-178413, investigation of a granular recording layer in which an oxide is added to a CoCrPt alloy is actively conducted. Has come to be done. When this granular type recording layer is used, the exchange coupling between the magnetic particles is reduced by forming an oxide grain boundary layer so as to surround the magnetic particles, so that the CoCrPt alloy is high regardless of the Cr concentration. A material having magnetic anisotropy energy can be used. In addition, since the oxide grain boundary layer is discontinuous in crystal with the magnetic particles and has a certain thickness, the particles are unlikely to coalesce during the recording layer formation process. Therefore, a granular type perpendicular magnetic recording medium in which an oxide is added to a CoCrPt alloy has attracted attention as a candidate for a perpendicular magnetic recording medium that has low noise and is resistant to thermal demagnetization. The seed layer and the intermediate layer of the perpendicular magnetic recording medium have been widely studied so far. For example, it has been reported in IEEE Transactions on Magnetics, Vol. 38, No. 5, p. 1976 (2002) that Ru is suitable as an intermediate layer of an oxide granular type perpendicular magnetic recording medium. It has been reported in IEEE Transactions on Magnetics, Vol. 38, No. 5, p. 1979 (2002) that the seed layer can improve the crystal orientation of the Ru intermediate layer.

  JP-A-2004-70980 discloses a WCo seed layer in which one or two of Ti, V, Sr, Y, Nb, Mo, Zr, Hf, Ta, Ni and W are combined with Co. A perpendicular magnetic recording medium having a CoCr intermediate layer and improved S / N and thermal fluctuation is disclosed.

  US 2004-0072072 discloses a perpendicular magnetic recording medium having a Ru intermediate layer and a seed layer using CoCrRu, CoCr, W, Ta, Mo, Hf or Ti.

  Japanese Patent Laid-Open No. 2004-178748 discloses a perpendicular magnetic recording medium in which WCo is used as the second underlayer option, Ru is used as the first underlayer option, and the recording layer is a non-granular heat segregation type. Yes.

IEEE Transactions on Magnetics, Vol.38, No.5, p.1976 (2002) IEEE Transactions on Magnetics, Vol.38, No.5, p.1979 (2002) Journal of Materials Research Vol. 16, pp.1789-1794 (2001) Japanese Patent Laid-Open No. 2004-70980 US2004-0072072 Publication JP 2004-178748 A

  So far, noise characteristics and thermal demagnetization characteristics have been studied for oxide granular type perpendicular magnetic recording media, but sufficient investigation has not been made on corrosion resistance and scratch resistance. Therefore, when an oxide granular type perpendicular magnetic recording medium using a Ta seed layer and a Ru intermediate layer that can obtain a high S / N ratio was subjected to corrosion resistance and scratch resistance tests, the scratch strength was weak and many corrosions were observed. The point was observed and it turned out that there is also a problem in corrosion resistance. Further, when a nonmagnetic CoCr alloy well known as an intermediate layer of a conventional in-plane magnetic recording medium is used for the intermediate layer instead of Ru, the corrosion resistance is improved, but the medium S / N is reduced. It turns out that it falls significantly. In other words, it has been found that the conventionally known combination of the intermediate layer material and the seed layer material has a problem that it is impossible to achieve both high medium S / N, corrosion resistance, and scratch resistance.

  An object of the present invention is to make a conventional magnetic recording medium compatible with a perpendicular magnetic recording medium having a granular recording layer in which an oxide is added to a CoCrPt alloy, by selecting a combination of materials and structures of an intermediate layer and a seed layer. An object of the present invention is to realize a perpendicular magnetic recording medium that has both high medium S / N, corrosion resistance, and scratch resistance, which has been considered difficult, and has high medium S / N and excellent corrosion resistance and scratch resistance.

  To achieve the above object, according to one aspect of the present invention, there is provided a perpendicular magnetic recording medium in which at least a soft magnetic layer, a seed layer, an intermediate layer, a magnetic recording layer, and a protective layer are sequentially stacked on a substrate. The magnetic recording layer has a granular structure composed of a large number of columnar grains made of a CoCrPt alloy and a grain boundary layer containing an oxide, the seed layer is composed of a WCo alloy, and the intermediate layer is composed of Ru or a Ru alloy. The granular type perpendicular magnetic recording medium of the present invention combines a high medium S / N with excellent corrosion resistance and scratch resistance by combining a seed layer made of a WCo alloy and an intermediate layer made of Ru or Ru alloy. According to the analysis of the present inventors, this perpendicular magnetic recording medium is characterized in that the full width at half maximum of the rocking curve of Ru (0002) diffraction measured using an X-ray diffractometer is 5 degrees or less. The Co content of the WCo alloy seed layer is preferably 20 at.% Or more and 60 at.% Or less.

  In order to improve the corrosion resistance of the perpendicular magnetic recording medium, it has been considered that it is effective to use a material having excellent corrosion resistance as a material used for each layer constituting the medium. However, it has been found that even if a material having equivalent corrosion resistance is used, a large difference occurs in the corrosion resistance as a perpendicular magnetic medium. As a result of detailed studies by the present inventors, it has been found that not only the corrosion resistance of each material itself used, but rather the combination of the material of the layer structure constituting the medium affects the corrosion resistance of the perpendicular magnetic medium. . The electrochemical properties and adhesion between materials are considered to be important factors that determine the corrosion resistance. Furthermore, the present inventors have found that not only the adhesion between materials but also the crystallinity is an important factor for improving the scratch resistance of the perpendicular magnetic recording medium. The perpendicular magnetic recording medium of the present invention achieves excellent corrosion resistance and scratch resistance without impairing high medium S / N characteristics by combining a WCo alloy seed layer and a Ru intermediate layer. This is the result of finding that it is important to control the crystal orientation and setting the Co content of the WCo alloy seed layer in an appropriate range.

  In order to obtain a high medium S / N, it is more preferable to increase the surface unevenness of the intermediate layer on the recording layer side to promote the segregation of oxides on the crystal grain boundaries of the magnetic recording layer. That is, in order to achieve both high medium S / N and excellent corrosion resistance, it is more preferable to use an intermediate layer having good crystal orientation and large surface irregularities. In order to realize such an intermediate layer, in the method for manufacturing a perpendicular magnetic recording medium of the present invention, the intermediate layer is made of Ru or Ru alloy in which a first intermediate layer and a second intermediate layer different in manufacturing method are laminated, It is desirable that the gas pressure when forming the second intermediate layer is higher than the gas pressure when forming the first intermediate layer. Instead of changing the gas pressure when forming the first intermediate layer and the second intermediate layer, the film forming rate may be changed. In that case, the first intermediate layer is formed at a higher film forming rate than the second intermediate layer. Moreover, you may change both a gas pressure and a film forming rate at the time of formation of a 1st intermediate | middle layer and a 2nd intermediate | middle layer.

  According to the present invention, by selecting a combination of an intermediate layer made of Ru or a Ru alloy and a seed layer made of a WCo alloy, a high medium S / N that has been considered difficult to achieve in the prior art. In addition, it is possible to realize an oxide granular type perpendicular magnetic recording medium that achieves both high corrosion resistance and scratch resistance, high medium S / N ratio, and excellent corrosion resistance and scratch resistance.

As an example of the perpendicular magnetic recording medium of the present invention, it was produced using an ANELVA sputtering apparatus (C3010). This sputtering apparatus is composed of 10 process chambers and one substrate introduction chamber, and each chamber is evacuated independently. The exhaust capacity of all the chambers is 6 × 10 ⁻⁶ Pa or less.

  The grain boundary width of the magnetic recording layer crystal grains was determined by observing a bright field image on the plane of the magnetic recording layer with a transmission electron microscope. In the bright field image, the larger the atomic number of the atoms constituting the sample, the larger the electron scattering angle, resulting in darker contrast. In a bright field image of a magnetic recording layer having a granular structure, a crystal grain portion is observed as a dark contrast portion, and a grain boundary portion made of oxide is observed as a bright contrast portion. The width of each grain boundary was obtained by drawing a line connecting the gravity center positions of adjacent crystal grains and obtaining the length of the grain boundary part on the line. The grain boundary width was determined for 100 or more grain boundaries, and these were averaged to obtain the average grain boundary width.

  The recording / reproduction characteristics were evaluated by a spin stand. The head used for the evaluation is a composite magnetic head composed of a reproducing element using a giant magnetoresistance effect with a shield gap length of 55 nm and a track width of 120 nm, and a single-pole writing element with a track width of 170 nm. Reproduction output and noise were measured under conditions of a peripheral speed of 10 m / s, a skew angle of 0 degree, and a magnetic spacing of about 15 nm, and the medium S / N was a solitary wave reproduction output when a signal having a linear recording density of 1970 fr / mm was recorded. It was determined as a ratio to the integrated noise when a signal having a linear recording density of 23620 fr / mm was recorded.

  The corrosion resistance was evaluated according to the following procedure. First, the sample is allowed to stand for 96 hours under conditions of a high temperature and high humidity state at a temperature of 60 ° C. and a relative humidity of 90% RH or higher. Next, the number of corrosion points within a radius of 14 mm to 25 mm was counted using an Optical Surface Analyzer, and ranked as follows. A sample having a count number of less than 50 was evaluated as A, a sample having a count of 50 or more and less than 200 was evaluated as B, a sample having a count of 200 or more and less than 500 was evaluated as C, and a sample having a count number of 500 or more was evaluated as D. In practice, a rank of B or higher is desirable.

  The scratch test was performed by forcibly exciting a diamond needle of 5 μmR with a ceramic actuator and moving the stage at a speed of 30 μm / sec with the stage tilted 5 degrees. Moving the stage to the side gradually increases the load and destroys the sample. This means that the greater the load to be destroyed, the stronger the scratch resistance.

  Hereinafter, specific embodiments to which the present invention is applied will be described with reference to the drawings.

[Experimental Example 1]
FIG. 1 shows the layer structure of the perpendicular magnetic recording medium of this experimental example. A glass substrate having a thickness of 0.635 mm and a diameter of 65 mm (2.5 inch type) is used as the substrate 11, and an adhesion layer 12, a soft magnetic underlayer 13, a seed layer 14, an intermediate layer 15, and a magnetic recording layer are formed by sputtering. 16 and the protective layer 17 were formed in order. Table 1 shows the target, Ar gas pressure, film formation rate, and film thickness used for the production of each layer.

First, NiTa as an adhesion layer is 30 nm on the substrate 11, CoTaZr as the first soft magnetic layer 131 is 50 nm, Ru as the nonmagnetic layer 132 is 0.8 nm, and CoTaZr as the second soft magnetic layer 133. Were formed in order of 50 nm, and the substrate was cooled in a magnetic field to 80 ° C. or lower to form the soft magnetic underlayer 13. Here, the first soft magnetic layer 131 and the second soft magnetic underlayer 133 are antiferromagnetically coupled via the Ru nonmagnetic layer 132. Further, 1 nm of WCo as the seed layer 14, 18 nm of Ru as the intermediate layer 15, 16 nm of CoCrPt—SiO ₂ as the recording layer 16, and 5 nm of carbon as the protective layer 17 were formed. Thereafter, a lubricant obtained by diluting a perfluoroalkyl polyether material with a fluorocarbon material was applied, and the surface was burnished to produce a perpendicular recording medium of this example. Ar was used as the sputtering gas, and oxygen was added at a partial pressure of 20 mPa when forming the magnetic recording layer. When forming the protective layer 17, nitrogen was added at a partial pressure of 50 mPa with respect to an Ar pressure of 0.6 Pa during film formation.

  In order to investigate the effect of the combination of the intermediate layer and the seed layer on the recording / reproducing characteristics and the corrosion resistance, various samples having different seed layer and intermediate layer materials were prepared. In any sample, the film thickness and film forming conditions of the seed layer and the intermediate layer are constant, and the other configurations are the same as those in the above experimental example. Table 2 shows the evaluation results of the grain boundary width and the corrosion resistance of the magnetic recording layer obtained using the seed layer and intermediate layer materials of the prepared sample, the medium S / N, and the transmission electron microscope.

  First, paying attention to the medium S / N, the samples 1-6 to 1-10 using Ru as the intermediate layer are higher than the samples S1-1 to 1-5 using the CoCr alloy as the intermediate layer. N (17 dB or more) is obtained. The crystal grain boundary width of the magnetic recording layer of Sample 1-2 was determined to be 0.4 nm using a transmission electron microscope. On the other hand, the grain boundary width of Sample 1-7 from which the highest medium S / N was obtained was 1.1 nm, and the grain boundary width was significantly increased as compared with Sample 1-2. When the grain boundary width was determined for other samples, the grain boundary width was 0.5 nm or less for all samples having a low medium S / N (for example, 13 dB or less). Thus, in a perpendicular magnetic recording medium having a granular magnetic recording layer in which an oxide is added to a CoCrPt alloy, in order to obtain a high medium S / N (for example, 17 dB or more), the grain boundary of the oxide It is more preferable to increase the width, and it can be seen that Ru is suitable as an intermediate layer for realizing this.

  Next, attention is focused on the results of the corrosion resistance evaluation. Regarding samples 1-1 to 1-5 using CoCr alloy as the intermediate layer, when NiFe and W were used for the seed layer, the corrosion resistance was not good (rank C). Corrosion resistance (rank B) is shown. However, as described above, in any case, the medium S / N is low (13 dB or less), so that it is incompatible with the corrosion resistance. On the other hand, in the combination with the Ru intermediate layer in which a high medium S / N (17 dB or more) is obtained, the variation in the corrosion resistance rank depending on the material of the seed layer is large. In particular, Samples 1-7 and 1-8 using Ta or NiFe for the seed layer have a very low corrosion resistance of D rank even though a high medium S / N is obtained. From Sample 1-7, the Ta seed layer is very effective in improving the crystal orientation of the Ru intermediate layer and obtaining a high medium S / N, but there is a problem in corrosion resistance when combined with the Ru intermediate layer. I found out. On the other hand, when W or WCo is used as a seed layer, it shows relatively good corrosion resistance. In particular, in Sample 1-10, a medium having a high density of 17 dB or more is obtained by combining the WCo seed layer and the Ru intermediate layer. While maintaining S / N, excellent corrosion resistance higher than rank B could be obtained.

  In this experimental example, a magnetic recording layer in which 17.5 vol.% Of Si oxide was added to a Co-13Cr-14Pt (at.%) Alloy was used, but the addition amount of Si oxide was 15 vol.% And 20 vol. This is also the case when using Co-15Cr-14Pt (at.%), Co-19Cr-14Pt (at.%), Or Co-17Cr-16Pt (at.%) With different compositions of CoCrPt alloys. The same tendency as in the experimental example was obtained. Moreover, as a result of examining various materials as oxides added to the magnetic recording layer, the same tendency as in this experimental example was observed in Al oxide, Ti oxide, Ta oxide, and B oxide in addition to Si oxide. It was. The effect of the present invention is remarkably exhibited when a material suitable for forming a crystal grain boundary having a width of 1 nm or more is added to the magnetic recording layer, since oxides are easily generated stably.

  Next, for the seed layers of Samples 1-7 to 1-10, the peel strength at the interface with the Ru intermediate layer and the interface with the CoTaZr soft magnetic layer was calculated using molecular dynamics simulation. Table 3 shows the calculation results and the actual measurement results. In the calculation, the soft magnetic layer is Co-3Ta-5Zr (at.%), And the composition of the seed layer is exemplified in Table 3. The calculation was performed by the method disclosed in Journal of Materials Research Vol. 16, pp.1789-1794 (2001).

  When Ta was used for the seed layer (Sample 1-7), it was found that the peel energy was small and the scratch breakdown load was as weak as 85 mV at either the interface with the Ru intermediate layer or the interface with the CoTaZr soft magnetic layer. When WCo was used for the seed layer (sample 1-10), the peel energy was the largest, and the scratch breaking load increased nearly twice as much as that of Ta. From this result, it is considered that the use of the WCo seed layer increased the peel strength at the interface between the CoTaZr soft magnetic layer and the Ru intermediate layer and improved the scratch resistance. The scratch resistance required in the present invention requires a scratch breaking load of 150 mV or more, and more preferably 160 mV or more. In addition, the W seed layer (comparison between samples 1-8 and 1-9 in Table 2), which has characteristics superior to the NiFe seed layer in corrosion resistance, is inferior to the NiFe seed layer in scratch resistance (Sample 1 in Table 3). 8 and 1-9), as is clear from the above, in order to achieve excellent corrosion resistance and high scratch resistance at the same time, an optimal combination of the seed layer and the intermediate layer is important. As a result of examining the combination of materials in detail, it was found that the combination of the WCo alloy seed layer and the Ru intermediate layer is more preferable.

  In this experimental example, Co-3Ta-5Zr (at.%) Was used for the soft magnetic layer. For example, Co-5Ta-5Zr (at.%), Co-5Nb-5Zr (at.%), And Co having different compositions were used. The same tendency was obtained when other Co-based amorphous alloys such as -5Ta-5Hf (at.%) Were used.

[Experimental example 2]
The perpendicular magnetic recording medium of this experimental example was manufactured with the same film configuration and film forming conditions as those of Sample 1-10 of Experimental example 1 except for the material of the seed layer. In this experimental example, the WCo alloy composition of the seed layer was changed. FIG. 2A shows the relationship between the WCo alloy composition of the seed layer and the count of corrosion points, and FIG. 2B shows the relationship between the WCo alloy composition of the seed layer and the medium S / N. When the WCo alloy contains 20 at.% To 70 at.% Co, excellent corrosion resistance of rank B or higher was obtained, and when the WCo alloy contained 60 at.% Or less, high medium S / N (17 dB or more) was obtained. . The same tendency was obtained when Ru-5Ti (at.%), Ru-10Co (at.%), Or Ru-15SiO ₂ (Vol.%) Was used as the intermediate layer instead of Ru.

  From the above results, in order to realize a high medium S / N and excellent corrosion resistance by combining the WCo seed layer with the Ru or Ru alloy intermediate layer, the WCo alloy of the seed layer has a Co content of 20 at.% To 60 at.%. It is desirable to contain.

[Experimental Example 3]
FIG. 3 shows the layer structure of the perpendicular magnetic recording medium of this experimental example. In this experimental example, the intermediate layer 35 has a laminated structure of a first intermediate layer 351 and a second intermediate layer 352. The film configuration and film forming conditions other than the intermediate layer 35 are the same as those of Sample 1-10 of Experimental Example 1. In this experimental example, the film forming conditions (Ar gas pressure and film forming rate) of the intermediate layer 35 were changed, and the film thicknesses of the first intermediate layer 351 and the second intermediate layer 352 were 8 nm, respectively.

Table 4 shows the film forming conditions of the intermediate layer of each sample, the full width at half maximum Δθ ₅₀ of the rocking curve of Ru (0002) diffraction measured using an X-ray diffractometer, the corrosion resistance evaluation results, and the scratch fracture load.

First, paying attention to the results of the corrosion resistance, a difference appeared in the evaluation results of the corrosion resistance in spite of using the same combination of the Ru intermediate layer and the WCo seed layer. When samples 2-1 and 2-2 in which the first intermediate layer 351 and the second intermediate layer 352 are produced under the same film forming conditions are compared, the Δθ ₅₀ is small, and the crystal orientation of the Ru intermediate layer is good. Higher corrosion resistance is obtained. Samples 2-4, 2-5, and 2-6, in which the first intermediate layer 351 is formed at a lower gas pressure or higher film formation rate than the second intermediate layer 352, show high rank A corrosion resistance. It was found that the corrosion resistance was further improved by forming the intermediate layer Ru in a two-layer structure and forming the first intermediate layer at a lower gas pressure or higher film formation rate than the second intermediate layer, and the effects of the present invention appeared remarkably. .

Next, as a result of investigating the relationship with the corrosion resistance by paying attention to the full width at half maximum Δθ ₅₀ of the rocking curve of Ru (0002) diffraction, samples 2-1 and 2-4 showing high crystal orientation with Δθ ₅₀ of 5 degrees or less, With respect to 2-5 and 2-6, very excellent corrosion resistance of A rank was obtained. That is, it was found that not only the combination of film materials but also the crystal orientation of the Ru intermediate layer is important for improving the corrosion resistance. When the medium S / N of the sample of this experimental example was examined, all the required medium S / N (17 dB) standards were satisfied. The media S / N of samples 2-1 and 2-2 are 17.1 dB and 17.3 dB, respectively. The media S / N is higher than that of sample 2-3, and sample 2-4 is 17.8 dB. I found it expensive. This is presumably because the intermediate layer formed at a low gas pressure is less prone to surface irregularities and segregation to the crystal grain boundaries of the magnetic recording layer is unlikely to occur. In order to achieve both high medium S / N and excellent corrosion resistance, it is more preferable that the intermediate layer in contact with the seed layer has a high crystal orientation and the intermediate layer in contact with the recording layer has a large surface irregularity.

  In order to realize an intermediate layer having such characteristics, first, the intermediate layer is composed of a first intermediate layer 351 and a second intermediate layer 352 that are manufactured differently, and, as in Sample 2-4, It was found that the intermediate layer 351 is more preferably a film formed in a low gas pressure atmosphere and exhibiting high crystal orientation.

  In Sample 2-5, the film forming rate was changed instead of changing the gas pressure when the first intermediate layer 351 and the second intermediate layer 352 were formed. When the film is formed at a low film formation rate, the same effect as that formed in a high gas pressure atmosphere can be obtained, and surface irregularities are easily formed and the crystal orientation is deteriorated. On the other hand, when the film is formed at a high film formation rate, the same effect as that formed in a low gas pressure atmosphere can be obtained, and the crystal orientation is improved although the surface unevenness is hardly formed. In Sample 2-5, the first intermediate layer 351 was formed at a high film formation rate, and the second intermediate layer 352 was formed at a low film formation rate. Similarly to Sample 2-4, Sample 2-5 was able to achieve both high medium S / N (17.9 dB) and excellent A-rank corrosion resistance.

  In Sample 2-6, the second intermediate layer 352 was formed in a gas pressure atmosphere higher than that of the first intermediate layer 351 and at a low film formation rate. Sample 2-6 also exhibited medium S / N (18.0 dB) and A rank corrosion resistance equivalent to sample 2-4.

  Moreover, when the scratch fracture strength of these samples was measured, it was found that Samples 2-4, 2-5, and 2-6, which had good crystal orientation, were particularly excellent in scratch resistance.

[Experimental Example 4]
The perpendicular magnetic recording medium of this experimental example was manufactured with the same film configuration and film forming conditions as those of sample 2-4 of experimental example 3. In this example, five types of samples 3-1 to 3-5 were prepared by changing the thickness of the WCo seed layer in the range of 1 nm to 8 nm, and the influence on the medium S / N, scratch resistance, and corrosion resistance was examined. The results are shown in Table 5.

  FIG. 4A shows the relationship between the thickness of the WCo seed layer and the corrosion point, and FIG. 4B shows the relationship with the scratch breaking load. Here, the Co content of the WCo seed layer is 25 at.%, And the medium of this experimental example has excellent corrosion resistance of A rank at any film thickness, and the corrosion point decreases as the film thickness increases. It was found that the corrosion resistance was further improved. Similarly, the scratch breaking load increased with an increase in the thickness of the WCo seed layer. That is, it has been found that increasing the thickness of the WCo seed layer is effective in improving the corrosion resistance and scratch resistance. Next, the relationship between the thickness of the WCo seed layer and the medium S / N was examined. The result is shown in FIG.

  In FIG. 5, for comparison with the WCo seed layer, a medium in which a W-based alloy other than WCo such as W, WAl, WCr, WNi or the like is used for the seed layer is manufactured, and the seed layer thickness and The relationship with the medium S / N is also illustrated. In addition, all the media produced for comparison have the same layer configuration other than the seed layer, their composition, film thickness, and film forming conditions as in Sample 2-4 of Experimental Example 3. As shown in FIG. 5, the medium using WCo for the seed layer (shown by ◆) can obtain a high medium S / N up to a film thickness of 8 nm, regardless of the increase in film thickness. The above characteristics were obtained. However, when the film thickness is 10 nm or more, the medium S / N deteriorates. This is considered to be caused by a decrease in recording efficiency due to an increase in the thickness of the WCo seed layer. In general, the W-based seed layer is said to be superior in terms of the medium S / N. In the W-based seed layers of W, WAl, WCr, WNi and the like of the comparative examples illustrated in Table 6, a Ru intermediate layer In combination with the above, medium S / N characteristics (15 dB or more) are obtained to some extent in the extremely thin range of 1 nm to 3 nm. However, no matter how it is combined with the Ru intermediate layer, as shown in FIG. 5, the medium S / N decreases as the film thickness of any W-based seed layer other than WCo increases. In particular, W (shown by ●) and WAl (shown by ▲) deteriorate the medium S / N by nearly 1 dB only by increasing the film thickness from 1 nm to 2 nm. In other words, the W alloy-based seed layer is too dependent on the film thickness of the medium S / N, so the film thickness cannot be increased in order to increase the corrosion resistance and scratch resistance, and the high medium S / N and excellent corrosion resistance and scratch can be obtained. It was impossible to balance proof stress.

Table 6 shows the medium S / N, the corrosion resistance rank, and the full width at half maximum Δθ ₅₀ of the rocking curve of Ru (0002) diffraction when the film thickness of the seed layer is 3 nm. It was found that the comparative example seed layer had a larger Δθ ₅₀ than the WCo seed layer of this example. It is considered that the W, WAl, WCr, and WNi seed layers have large surface irregularities and the crystal orientation of the intermediate layer Ru is deteriorated, and therefore the medium S / N is deteriorated.

  From these results, it was found that the combination of the WCo alloy seed layer and the Ru intermediate layer is most desirable in order to achieve both good medium S / N and excellent corrosion resistance and scratch resistance. In particular, in an oxide granular type perpendicular magnetic recording medium composed of a large number of columnar particles made of a CoCrPt alloy and a grain boundary layer containing an oxide, the combination of the WCo alloy seed layer and the Ru intermediate layer is the best, and the combination effect Demonstrate. In general, it has been said that the W-based seed layer is superior in terms of the medium S / N. However, since the film thickness dependency of the medium S / N is too large, the seed layer cannot be made thick. It was. That is, if the film thickness is increased in order to increase the corrosion resistance and scratch resistance, the medium S / N is greatly deteriorated, and it is impossible to achieve both high medium S / N and excellent corrosion resistance and scratch resistance. However, the present invention has been made as a result of finding that the WCo seed layer can maintain a high medium S / N regardless of the increase in film thickness. By combining the WCo alloy seed layer and the Ru intermediate layer, a high medium can be obtained. It achieves excellent corrosion resistance and scratch resistance without impairing the S / N characteristics. Furthermore, in order to control the crystal orientation of the Ru intermediate layer, the Co content of the WCo alloy seed layer is set to an appropriate range.

The figure which shows the structure of the perpendicular magnetic recording medium described in Experimental example 1 and Experimental example 2 of this invention. The figure which shows the relationship between Co content in a WCo seed layer, the number of corrosion points, and medium S / N. The figure which shows the structure of the perpendicular magnetic recording medium described in Experimental example 3 and Experimental example 4 of this invention. The figure which shows the relationship between the film thickness in a WCo seed layer, the number of corrosion points, and a scratch fracture load. The figure which shows the film thickness of a seed layer, and medium S / N relationship.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 31 ... Substrate, 12, 32 ... Adhesion layer, 13, 33 ... Soft magnetic underlayer, 14, 34 ... Seed layer, 15, 35 ... Intermediate layer, 16, 36 ... Magnetic recording layer, 17, 37 ... Protection Layer, 131,331 ... first soft magnetic layer, 132,332 ... nonmagnetic layer, 133,333 ... second soft magnetic layer, 351 ... first intermediate layer, 352 ... second intermediate layer

Claims (17)

A perpendicular magnetic recording medium in which at least a soft magnetic layer, a seed layer, an intermediate layer, a magnetic recording layer, and a protective layer are sequentially laminated on a substrate,
The seed layer is made of a WCo alloy containing Co at 20 at.% Or more and 60 at.% Or less, the intermediate layer is made of Ru or Ru alloy, and the magnetic recording layer is made of a CoCrPt alloy. A perpendicular magnetic recording medium having a granular structure constituted by layers.   2. The perpendicular magnetic recording medium according to claim 1, wherein a half width of a rocking curve of Ru (0002) diffraction measured using an X-ray diffractometer is 5 degrees or less.   2. The perpendicular magnetic recording medium according to claim 1, wherein the thickness of the seed layer is greater than 0 nm and less than 10 nm, preferably 2 nm or more and 8 nm or less.   2. The perpendicular magnetic recording medium according to claim 1, wherein in the magnetic recording layer, an average width of a grain boundary layer surrounding the columnar grains constituting the magnetic recording layer is 1 nm or more.   5. The perpendicular magnetic recording medium according to claim 4, wherein when the bright field image of the magnetic recording layer is observed with a transmission electron microscope, the columnar particle portion is observed as a dark contrast, and the grain boundary layer portion is bright. A perpendicular magnetic recording medium characterized by being observed as contrast.   2. The perpendicular magnetic recording medium according to claim 1, wherein the medium S / N is 17 dB or more and the scratch breaking load is 150 mV or more.   2. The perpendicular magnetic recording medium according to claim 1, wherein the intermediate layer is formed of a two-layered laminate having different Ar gas pressures or film forming rates.   2. The perpendicular magnetic recording medium according to claim 1, wherein the intermediate layer has a high crystal orientation in a layer in contact with the seed layer, and a layer in contact with the magnetic recording layer has large surface unevenness. recoding media. A perpendicular magnetic recording medium in which at least a soft magnetic layer, a seed layer, an intermediate layer, a magnetic recording layer, and a protective layer are sequentially laminated on a substrate,
The magnetic recording layer has a granular structure composed of columnar particles made of a CoCrPt alloy and a grain boundary layer containing an oxide;
The perpendicular magnetic recording medium characterized in that the seed layer is made of a WCo alloy, the intermediate layer is made of Ru or a Ru alloy, the medium S / N is 17 dB or more, and the scratch breaking load is 150 mV or more. .   10. The perpendicular magnetic recording medium according to claim 9, wherein the seed layer is made of a WCo alloy containing Co at 20 at.% Or more and 60 at.% Or less.   10. The perpendicular magnetic recording medium according to claim 9, wherein a half width of a rocking curve of Ru (0002) diffraction measured using an X-ray diffractometer is 5 degrees or less.   10. The perpendicular magnetic recording medium according to claim 9, wherein when the magnetic recording layer is observed with a transmission electron microscope, the columnar particle portion is observed as a dark contrast, and the grain boundary layer portion is observed as a bright contrast. And the average width of the grain boundary layer surrounding the columnar particles constituting the magnetic recording layer is 1 nm or more.   10. The perpendicular magnetic recording medium according to claim 9, wherein the intermediate layer is formed of a two-layered laminate having different Ar gas pressures or film forming rates.   10. The perpendicular magnetic recording medium according to claim 9, wherein the intermediate layer has a high crystal orientation in a layer in contact with the seed layer, and a layer in contact with the magnetic recording layer has large surface irregularities. Medium. Forming a soft magnetic layer;
Forming a seed layer made of a WCo alloy on the soft magnetic layer;
Forming an intermediate layer made of Ru or a Ru alloy on the seed layer;
And forming a magnetic recording layer having a granular structure composed of columnar particles made of a CoCrPt alloy and a grain boundary layer containing an oxide on the intermediate layer. .   16. The method of manufacturing a perpendicular magnetic recording medium according to claim 15, wherein the step of forming the intermediate layer includes a step of forming a first intermediate layer made of Ru or a Ru alloy by a first gas pressure, and the first intermediate layer. And forming a second intermediate layer made of Ru or a Ru alloy with a second gas pressure higher than the first gas pressure.   16. The method of manufacturing a perpendicular magnetic recording medium according to claim 15, wherein the step of forming the intermediate layer includes a step of forming a first intermediate layer made of Ru or a Ru alloy at a first film formation rate, and the first intermediate layer. Forming a second intermediate layer made of Ru or a Ru alloy at a second film forming rate lower than the first film forming rate on the layer.

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