JP5348527B2 - Perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a close-contact layer which does not increase particles even for a long-time use, and to provide a vertical magnetic recording medium which causes less defects. <P>SOLUTION: In the vertical magnetic recording medium, an amorphous thin film containing a metal boride such as CrB, which has a composition around an eutectic point of a metal and boron, is used in a close-contact layer to obtain the close-contact layer which does not increase particles even for a long-time use. The close-contact layer contributes to improvement in yield rate of vertical magnetic recording media. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a magnetic recording medium, and more particularly to a perpendicular magnetic recording medium having a high recording density.

  As the recording density of magnetic recording increases, the recording method is switched from the in-plane recording method to the perpendicular recording method. In the perpendicular recording system, a combination of a double-layered perpendicular magnetic recording medium in which a soft magnetic underlayer and a perpendicular magnetic recording layer are combined with a single pole type head is effective in realizing a high recording density. However, since the thickness of the soft magnetic underlayer is as thick as several tens to several hundreds of nanometers, the surface flatness is lowered, which adversely affects the formation of the perpendicular magnetic recording layer and the flying property of the head. Is large, the adhesion to the substrate may be reduced. Furthermore, due to electrochemical elution of alkali metals from non-magnetic substrate materials, "deterioration of magnetic properties of recording media", "defect adhesion to substrate surface", "surface defects and / or recording skip problems", etc. Problems have been pointed out.

  As means for solving such a problem, a magnetic recording medium in which an adhesion layer for improving adhesion is formed between a substrate and a soft magnetic underlayer has been proposed (see, for example, Patent Documents 1 and 2).

  Further, the adhesion layer used for the perpendicular magnetic recording medium needs to be amorphous in order to ensure the flatness of the surface, and to have good adhesion to the substrate and the magnetic layer. Therefore, as such an adhesion layer material, Cr having high adhesion, and CrTi, CrTa and the like which are made amorphous by adding Ti or Ta to Cr are used (see, for example, Patent Document 3).

  In addition, the adhesion layer is made of non-magnetic amorphous material in order to improve the adhesion to the glass substrate and to prevent the diffusion of contaminating elements such as alkali metals contained in the glass substrate to prevent the deterioration of magnetic properties. Has been proposed (see, for example, Patent Documents 4 and 5).

JP 2003-162860 A JP 2006-114162 A JP 2008-10088 A JP 2006-114182 A JP 2005-196874 A

  However, when using these materials, in order to suppress alkali elution from the substrate, a film thickness of a certain degree (5 nm) or more is required. There is a problem that particles gradually increase in the adhesion layer, increasing the occurrence of defects in the recording medium.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a perpendicular magnetic recording medium with few defects by providing an adhesion layer in which particles do not increase even when used for a long period of time.

  As a result of intensive studies, the present inventors have found that metal borides are used as a material for an adhesion layer that is made amorphous without using expensive metals such as Ti and Ta, and does not increase particles even when used for a long period of time. Clarified what is desirable.

  In view of the above knowledge, the present invention provides a perpendicular magnetic recording medium in which at least an adhesion layer, a soft magnetic backing layer, an intermediate layer, and a magnetic layer are sequentially laminated on a nonmagnetic substrate, wherein the adhesion layer comprises a metal element and boron. A perpendicular magnetic recording medium is provided which is a metal boride having a composition near the eutectic point.

  In the present invention, the metal boride is preferably CrB having a B content of 5 to 20 atomic%. In the present invention, the thickness of the adhesion layer is preferably 2 to 20 nm.

  In the perpendicular magnetic recording medium of the present invention, the magnetic layer may contain Co as a main component, and may further contain Pt, Cr, and O.

  According to the present invention, in a perpendicular magnetic recording medium, by using an amorphous thin film containing a metal boride having a composition near the eutectic point of a metal such as CrB and boron in the adhesion layer, particles can be used for a long time. Thus, an adhesion layer that does not increase is obtained, which can contribute to improvement of the yield rate of perpendicular magnetic recording media.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The following embodiment is merely an example of the present invention, and those skilled in the art can change the design as appropriate.

  FIG. 1 is a cross-sectional view showing the configuration of an embodiment of the perpendicular magnetic recording medium of the present invention. The perpendicular magnetic recording medium of the present invention includes a nonmagnetic substrate 1, an adhesion layer 2 formed on the nonmagnetic substrate 1, a soft magnetic backing layer 3 formed on the adhesion layer 2, and a soft magnetic backing layer 3. The intermediate layer 4 is formed on the intermediate layer 4 and the magnetic layer 5 is formed on the intermediate layer 4. Further, the perpendicular magnetic recording medium of the present invention may optionally have a protective layer 6 formed on the magnetic layer 5 as shown in FIG. 1, and further formed on the protective layer 6. The lubricating layer 7 may be included. In FIG. 1, the intermediate layer 4 is shown as one layer, but it is not necessarily one layer, and a layer for controlling the orientation is provided between the soft magnetic backing layer 3 and the intermediate layer 4. It is also possible to provide a plurality.

(Non-magnetic substrate)
The nonmagnetic substrate 1 used in the present invention is made of a nonmagnetic material and can withstand the conditions (solvent, temperature, etc.) used for forming each layer described later. Furthermore, it is preferable that it is excellent in dimensional stability. More specifically, a substrate made of a material such as glass, Al alloy, silicon, or various plastics can be used.

(Adhesion layer)
Next, the adhesion layer 2 is formed on the nonmagnetic substrate 1. The adhesion layer 2 is used for enhancing adhesion between the soft magnetic backing layer 3 formed thereon and the nonmagnetic substrate 1 and further suppressing alkali elution from the nonmagnetic substrate 1.

  In the present invention, as the material of the adhesion layer 2, a metal boride having a composition near the eutectic point of the metal element and boron can be used. The metal boride having a eutectic point includes a compound of boron, such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Hf, Cu, Mo, W, Nb, and Ta. Preferably, it is CrB.

  When CrB is used as the metal boride, the eutectic composition of Cr and B exists at three points of Cr-13.5 at% B, Cr-53.5 at% B, and Cr-83.0 at% B. Preferably has a composition in the vicinity of Cr-13.5 at% B. In the present specification, “a metal boride having a composition near the eutectic point of a metal element and boron” is ± 10%, preferably ± 8%, more preferably ± 5% around the eutectic point. 2 shows a metal boride having a B content of Specifically, the B content of the metal boride of the present invention is preferably 5 to 20 atomic% of the entire metal boride.

  The adhesion layer 2 is formed using any method known in the art, such as sputtering using a metal boride (including DC magnetron sputtering, RF magnetron sputtering, etc.), vacuum deposition, and the like. be able to. The film thickness of the adhesion layer 2 is desirably sufficient to suppress the deterioration of the magnetic characteristics and electromagnetic conversion characteristics of the magnetic recording layer, and in the normal case, it is desirably in the range of 2 to 20 nm.

  In the present invention, by using a thin film containing a metal boride such as CrB having a composition in the vicinity of the eutectic point of metal and boron, an adhesion layer 2 that is amorphized and does not increase in particles even when used for a long period of time is obtained. be able to.

  The detailed reason why a good adhesion layer 2 can be obtained by such a configuration is unknown, but since metal borides generally have a high melting point and are difficult to grow crystals, in addition to easily taking an amorphous structure, in the present invention Since a composition close to the eutectic point of the metal element and boron is selected, it is considered that the alkali barrier performance can be maintained even with a thin film thickness and particles can be reduced.

(Soft magnetic backing layer)
The soft magnetic backing layer 3 is formed on the adhesion layer 2 and is a layer for concentrating the perpendicular magnetic field on the magnetic layer 5. The soft magnetic backing layer 3 is not particularly limited, but preferably includes at least one of Fe, Co, Ni, Ta, and Zr. For example, the soft magnetic backing layer 3 can be formed using various soft magnetic materials such as a Co—Zr alloy, Fe—Co alloy, Fe—B alloy, and ferrite.

  The soft magnetic backing layer 3 can also be configured as a single layer film having a specific composition. In addition, a plurality of magnetic films are formed so as to stabilize the magnetization recorded in the magnetic layer 5 and increase the magnetization intensity leaking from the medium surface, thereby increasing the recording efficiency of the recording head and, as a result, reducing the noise of the recording medium. It is also possible to form a laminated film in which is bonded ferromagnetically or antiferromagnetically. The soft magnetic backing layer 3 usually has a thickness of 10 nm to 100 nm.

(Middle layer)
The intermediate layer 4 can be formed using a hexagonal metal such as Ru, Re, Os, or an alloy containing these. This is because these materials are the same hexagonal metal as the Co alloy used for the magnetic layer 5 formed thereon, and have a lattice constant close to that of the Co alloy. The intermediate layer 4 can also adjust the magnetic exchange interaction between the magnetic layer 5 and the soft magnetic backing layer 3.

  An orientation control layer (not shown) for efficiently orienting the intermediate layer may be provided between the soft magnetic backing layer 3 and the intermediate layer 4 as necessary. Such a material is preferably a non-magnetic Co alloy or Ni alloy, and these have the effect of reducing variations in crystal grain size.

(Magnetic layer)
The magnetic layer 5 formed on the intermediate layer 4 only needs to be a perpendicular magnetic film made of an alloy containing Co as a main component. Can also be used. The main component means a component having the largest content (atomic%) among the components constituting the magnetic layer 5. Preferably, the magnetic layer 5 contains 50 to 90 atomic%, more preferably 60 to 80 atomic% of Co. Here, the magnetic layer 5 preferably further contains Pt, Cr, and O in addition to Co. By adopting such a configuration, it is possible to provide a magnetic layer with good crystallinity that inherits the crystal grain size and segregation structure of the intermediate layer.

  The magnetic layer 5 may be a single layer. The magnetic layer 5 may be composed of a plurality of layers, for example, a first magnetic layer and a second magnetic layer, and a coupling control layer (not shown) between the first magnetic layer and the second magnetic layer. ). Both the first magnetic layer and the second magnetic layer can use the above materials as they are. By making the magnetic layer 5 have a two-layer structure, the crystal grain size and grain boundary layer thickness controlled by the coupling control layer can be maintained up to the top of the magnetic layer, and a magnetic layer having good magnetic separation can be produced. it can.

  The coupling control layer is a layer provided to adjust the exchange coupling between the first magnetic layer and the second magnetic layer. This makes it easier to control the magnetic characteristics of the magnetic layer and optimizes the electromagnetic conversion characteristics. Can be kept in. As the material that can be used for the integrated control layer, any hexagonal nonmagnetic metal can be used. Specifically, it is preferable to use Ru, Re, Os, or an alloy containing these as a main component.

  About the film forming method of each above-mentioned layer, it implements using arbitrary methods known in the said technique other than sputtering method (including DC magnetron sputtering method, RF magnetron sputtering method, etc.), such as a vapor deposition method and a coating method. be able to. From the viewpoint of controllability and the like, it is preferable to use a direct current magnetron sputtering method.

(Protective layer and lubricating layer)
Optionally, a protective layer 6 may be formed on the magnetic layer 5. The protective layer 6 is a layer for protecting each constituent layer below the magnetic layer 5 underneath. The protective layer 6 can be formed using carbon (C) (amorphous carbon or the like) or various thin film materials known as materials for a magnetic recording medium protective film. The protective layer 6 can be generally formed by using a sputtering method (including a direct current magnetron sputtering method, an RF magnetron sputtering method, etc.), a vacuum deposition method, a CVD method, or the like.

  Further, the lubricating layer 7 may be formed on the protective layer 6. The lubrication layer 7 is a layer for providing lubrication when the recording / reading head is in contact with the magnetic recording medium. For example, the lubrication layer 7 is a perfluoropolyether liquid lubricant or known in the art. Can be formed using a variety of liquid lubricant materials. The lubricating layer using the liquid lubricant can be formed by using any coating method known in the art such as a dip coating method and a spin coating method.

  Examples of the present invention will be described below. However, the following examples do not limit the present invention at all, and various modifications can be made by those skilled in the art without departing from the gist of the present invention.

  Using the configuration shown in FIG. 1, Examples 1 to 5 and Comparative Examples 1 to 4 in which the material and film thickness of the adhesion layer 2 were changed were produced.

(Examples 1-5)
As the nonmagnetic substrate 1, a glass substrate that satisfies the standard specifications of a 2.5 inch magnetic disk was used. Each layer was formed on the nonmagnetic substrate 1. First, CrB adhesion layers 2 were formed on the nonmagnetic substrate 1 by sputtering using a Cr-13 at% B alloy target with a film thickness of 2, 6, 10, 14, and 18 nm, respectively. In addition, the sputtering method in a present Example was implemented using the direct-current magnetron sputtering apparatus unless otherwise indicated.

  Thereafter, a CoZrNb alloy target and a Ru target are sputtered to form a three-layer film (CoZrNb / Ru / CoZrNb) having a CoZrNb layer about 20 nm above and below with a Ru layer having a thickness of 1 nm sandwiched between them. The backing layer 3 was used.

  Next, a NiW film having a thickness of 10 nm was formed as an orientation control layer by sputtering in an Ar atmosphere containing a small amount of nitrogen, and a Ru intermediate layer 4 having a thickness of 14 nm was formed thereon by sputtering.

Further, on the intermediate layer 4, a first magnetic layer and a second magnetic layer were produced with Ru as a coupling control layer, and the magnetic layer 5 was obtained. Specifically, the first magnetic layer in contact with the intermediate layer 4 was produced by sputtering a CoPtCr—SiO ₂ mixed target in an Ar atmosphere containing a small amount of O ₂ to form a CoPtCrSiO film. Next, after a Ru coupling control layer was formed thereon, a CoPtCrB alloy target was sputtered as a second magnetic layer to form a CoPtCrB film. In this way, a perpendicular magnetic recording layer (magnetic layer 5) having a laminated structure (CoPtCrSiO / Ru / CoPtCrB) composed of a CoPtCrSiO first magnetic layer, a Ru coupling control layer, and a CoPtCrB second magnetic layer was formed.

  Thereafter, a carbon protective layer 6 having a thickness of 3 nm was formed by a CVD method, and a liquid lubricating layer 7 made of perfluoropolyether was formed by a dip method at a thickness of 2 nm.

  The perpendicular magnetic recording media manufactured as described above were designated as Examples 1 to 5, respectively.

(Comparative Examples 1-3)
Perpendicular magnetic recording media of Comparative Examples 1 to 3 were produced in the same manner as in Examples 1 to 5, except that 2 nm, 6 nm and 10 nm thick CrTi films were produced as the adhesion layer 2.

(Comparative Example 4)
A perpendicular magnetic recording medium of Comparative Example 4 was produced in the same manner as in Examples 1 to 5 except that a 6 nm thick Cr-40 at% B film was produced as the adhesion layer 2.

(Evaluation Test 1)
The magnetic layer of the perpendicular magnetic recording medium produced in each example and comparative example had a coercive force of 397.9 kA / m (5 kOe). Next, for each example and comparative example, the corrosion resistance, alkali barrier performance, and SNR of the perpendicular magnetic recording medium were evaluated. The measurement results are shown in Table 1.

Corrosion resistance is evaluated by using an ICP plasma emission spectrophotometer for the presence or absence of Co elution in the nitric acid droplet after being left for 1 hour in a state where the nitric acid droplet is dropped on a recording medium left for 48 hours under high temperature and high humidity. did. Table 1 shows the elution amount of Co. Here, the standard of corrosion resistance as a medium is that the Co elution amount is 0.02 ng / cm ² or less.

  The alkali barrier performance was evaluated as “◯” by observing the surface state of the medium after being left for 500 hours under high temperature and high humidity using an optical surface inspection apparatus, and that no white clouding occurred on the outer peripheral portion.

  The SNR was evaluated by a method of writing a signal using a single magnetic pole head and reading a signal using a GMR head. SNR is the signal-to-noise ratio at a linear recording density of 716 kFCI. S is a peak value in magnetization reversal of an isolated waveform of 716 kFCI, that is, a value obtained by halving the difference between the maximum value and the minimum value. N is an rms value (root mean square-inches) at 60 kFCI.

  As a result, it was found that the recording media of Examples 1 to 5 of the present invention were able to maintain the same performance as that of the conventional CrTi adhesion layer in the SNR.

  Further, in terms of corrosion resistance, all CrB films are within the standard, but in the case of conventional CrTi, a value slightly exceeding the standard is shown under a thick condition of 10 nm (Comparative Example 3). From the results of AFM measurement, it is known that CrB has good flatness when a film thicker than CrTi is applied. Therefore, it is considered that the corrosion resistance of CrB is within the standard even if it is a thick film.

  Furthermore, the alkali barrier performance is out of the standard when the conventional CrTi adhesion layer is as thin as 2 nm, whereas when the CrB adhesion layer of this example is used, there is no problem even in the case of 2 nm, and sufficient durability. have. Further, even in Comparative Example 4 in which the composition near the eutectic point was not used, the alkali barrier performance was out of specification. This is because grain boundaries are likely to occur when not near the eutectic point, which is considered to reduce the alkali barrier performance.

  Thus, it was found that the CrB adhesion layer of the present invention is superior to the conventional CrTi adhesion layer. This thinning of the adhesion layer suggests that the generation of particles can be reduced even when used for a long period of time, leading to a reduction in the number of recording media on which defects are indirectly generated.

(Evaluation test 2)
Further, for Example 2 and Comparative Example 2, the change in the number of defects when each recording medium was continuously produced with the same sputtering apparatus was evaluated. Specifically, 30000 recording media were continuously produced in the same sputtering apparatus. Then, the production of the recording medium was continued, and 100 samples were taken out. Next, for each of the recording media taken out, a portion where the uniformity of the film on the surface was not maintained (a scratch such as a chip, a bulge, or a dent) was counted as a defect, and the average was calculated. The same evaluation was repeated when 60000 pieces were produced and when 90000 pieces were produced. The results are shown in Table 2.

  In the comparative example, the number of recording media in which defects have occurred has increased since 60000 were produced. On the other hand, when the CrB adhesion layer of this example was used, the number of defects was increased even when the number of manufactured media increased. The number of generated recording media hardly increased. That is, even when the film thickness is the same as that of the conventional CrTi adhesion layer, the occurrence of defects in the recording medium can be reduced by using the adhesion layer of the present invention having a composition close to the eutectic point of the metal element and boron. did it.

It is a figure which shows the cross-sectional structure of the perpendicular magnetic recording medium of this invention.

Explanation of symbols

1 Nonmagnetic substrate 2 Adhesion layer 3 Soft magnetic backing layer 4 Intermediate layer 5 Magnetic layer 6 Protective layer 7 Lubricating layer

Claims (4)

A perpendicular magnetic recording medium in which at least an adhesion layer, a soft magnetic backing layer, an intermediate layer, and a magnetic layer are sequentially laminated on a nonmagnetic substrate,
The adhesion layer is a metal boride having a composition near the eutectic point of the metal element and boron;
The soft magnetic backing layer, possess Co-Zr-based alloy, Fe-Co-based alloy, at least one of the soft magnetic material is selected from among Fe-B based alloy and ferrite,
A perpendicular magnetic recording medium, wherein the metal boride is CrB and the B content is in the range of 5 to 20 atomic% . The perpendicular magnetic recording medium according to claim 1, wherein the adhesion layer has a thickness in a range of 2 to 20 nm. The magnetic layer, a perpendicular magnetic recording medium according to claim 1 or 2, characterized in that a main component Co. The perpendicular magnetic recording medium according to claim 3 , wherein the magnetic layer further contains Pt, Cr, and O.

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