JP2007273000A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having a structure capable of executing high-density recording, and improving stability against thermal fluctuation. <P>SOLUTION: A texture in peripheral direction is disposed on a nonmagnetic substrate 11, and an adhesive layer 12 comprising a nonmagnetic amorphous layer is formed in the upper layer of the nonmagnetic substrate 11. Thus, Mrt-OR larger than 1.6 is achieved, and stability against thermal fluctuation of a magnetic recording disk is improved without applying an AFC structure. As Mrt is set to ≥0.350 memu/cm<SP>2</SP>in a circumferential direction, stability against thermal fluctuation is reduced to a non-problem level for a practical purpose, and a high recording density of ≥65Gbit/inch<SP>2</SP>is achieved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a longitudinal recording (in-plane recording) type magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium capable of suitably performing longitudinal recording without employing an AFC (Anti-Ferromagnetic Coupling) structure in a magnetic layer.

  In recent years, magnetic recording media for recording and reproducing information have urgently required higher recording density in order to improve recording capacity. In order to achieve high density recording in a longitudinal recording (in-plane recording) magnetic recording medium, the product of the residual magnetization (Mr) of the magnetic layer constituting the magnetic recording layer and the film thickness (t) of the magnetic layer ( Mrt) should be made as small as possible and the coercive force should be increased to the maximum at which the magnetic head can read and write. In addition, in order to achieve high-density recording and to reduce noise generated from the magnetization transition region, it is also necessary to reduce the size of the magnetic particles constituting the magnetic layer, isolate them, and make them uniform. is there.

  However, if the particle size of the magnetic particles constituting the magnetic layer is too small, a “thermal fluctuation problem” occurs. The thermal fluctuation problem is that when the particle size of the magnetic particles constituting the magnetic layer is excessively reduced, the magnetic energy differs from the thermal energy Et (Et = k × T (k: Boltzmann constant, T: temperature)) of the magnetic particles. The isotropic energy Ep (Ep = Ku × V (Ku: magnetic anisotropy energy density, V: volume of magnetic particles constituting the magnetic layer)) is reduced, and this causes magnetization of the magnetic particles in the magnetic layer. Are reversed by heat and cancel each other, and the magnetization is reduced as a whole. As a result, the recording transition width increases, and the time reduction of the output of the magnetic head is accelerated.

  Conventionally, as a countermeasure against this thermal fluctuation problem, a method of improving the magnetic anisotropic energy density Ku of magnetic particles by adding Pt to the magnetic layer is known.

  As another method, a method of securing and improving thermal stability by adopting an AFC structure as a configuration of the magnetic layer is also known (see Patent Document 1).

The AFC structure is a structure in which a first magnetic layer, a nonmagnetic layer (for example, Ru layer), and a second magnetic layer are laminated in this order in the magnetic layer. If this AFC structure is adopted, Since the two magnetic layers through the non-magnetic layer interact antiferromagnetically with each other, durability against heat is improved, so that stability against thermal fluctuation can be improved.
Japanese Patent Laid-Open No. 2001-56924

  However, in the method of adding Pt to the magnetic layer, the magnetic anisotropy energy density Ku can be increased as the added Pt is increased. However, when Pt is added excessively, noise generated in the magnetic recording medium is increased. There is a problem that increases.

  In the method employing the AFC structure, the nonmagnetic layer sandwiched between the first magnetic layer and the second magnetic layer must be formed with a precision of 1 nm or less, and the configuration of the magnetic layer is also the first. Since the magnetic layer, the nonmagnetic layer, and the second magnetic layer must be multilayered, there is a problem that the film forming process becomes complicated.

  In view of the above problems, an object of the present invention is to provide a magnetic recording medium capable of high-density recording and having high stability against thermal fluctuations without employing an AFC structure.

In order to solve the above problems, in the present invention, in a magnetic recording medium in which at least an underlayer, a magnetic layer, a protective layer, and a lubricating layer are laminated in this order on a nonmagnetic substrate, the nonmagnetic substrate and the underlayer An adhesion layer made of a nonmagnetic amorphous layer is formed between the two layers, and Mrt obtained by the product of the remanent magnetization of the magnetic layer and its film thickness is larger than 0.350 memu / cm ^{2 in the} circumferential direction, Mrt-OR (magnetic anisotropy ratio / Mrt orientation ratio) obtained by the ratio of Mrt in the circumferential direction to Mrt is larger than 1.6.

  A magnetic recording medium having such a configuration can achieve a high Mrt-OR. When Mrt-OR is increased in this way, the magnetic anisotropy is also increased, thereby increasing the magnetic anisotropy energy. Therefore, the stability against thermal fluctuation in the magnetic recording medium can be improved without applying the AFC structure. Thereby, high durability in the magnetic recording medium can be realized.

  In the present invention, the adhesion layer preferably contains at least one element of Ti, Y, Zr, Nb, Mo, Hf, Ta, W, Si, and B as the first additive element.

  In the present invention, it is preferable that the adhesion layer contains at least one element selected from Cr, V, Mn, and Co as the second additive element. Specific examples of the structure of the adhesion layer include CrTi.

  In the present invention, the underlayer has at least one layer containing Cr as a main component and containing at least one element selected from Ti, Zr, Nb, Ta, Mo, W, Mn, and Co. preferable. Specific examples of the underlayer include CoW, CrTi, CrMo, and CrW.

  In the present invention, the magnetic layer has at least two layers of a first magnetic layer and a second magnetic layer, the first magnetic layer is mainly composed of Co, and further includes Cr, Pt, Ta, B It is preferable to contain at least one element of Cu, Cu and C. Specific examples of the first magnetic layer include CoCrTa and CoCrPtB.

  In the present invention, the second magnetic layer preferably contains Co as a main component and further contains at least one element selected from Cr, Pt, Ta, B, Cu, and C. A specific configuration of the second magnetic layer includes CoCrB.

In the present invention, a texture is provided on the nonmagnetic substrate, and an adhesion layer made of an amorphous layer is formed on the upper layer of the nonmagnetic substrate. With this configuration, a high Mrt-OR can be realized. When Mrt-OR is increased in this way, the magnetic anisotropy is also increased, thereby increasing the magnetic anisotropy energy. Therefore, the stability against thermal fluctuation in the magnetic recording medium can be enhanced without applying the AFC structure as in the prior art. Thereby, high durability in the magnetic recording medium can be realized. Further, in the magnetic recording medium to which the present invention is applied, since the circumferential Mrt is configured to be larger than 0.350 memu / cm ² , the attenuation of the signal output caused by the thermal fluctuation is at a level that is practically not problematic. Can be reduced. Furthermore, since the magnetic recording medium to which the present invention is applied is configured such that the circumferential Mrt is larger than 0.350 memu / cm ² , a high recording density of 65 Gbit / inch ² or more can be achieved. .

  A magnetic recording medium to which the present invention is applied will be described below with reference to the drawings.

(Configuration of non-magnetic substrate, magnetic disk and magnetic disk device)
1A and 1B are a plan view and a schematic sectional view showing a magnetic disk to which the present invention is applied, respectively. FIG. 2 is an explanatory diagram showing a main configuration of the magnetic disk device. FIG. 1B shows only what layers are stacked in what order on the main surface 110 of the nonmagnetic substrate 11, and the ratio of the thicknesses of the respective layers is as follows. It does not correspond to an actual magnetic recording disk.

  A magnetic recording disk (magnetic recording medium) 1 shown in FIGS. 1A and 1B is an information recording medium used for a disk drive device, and is a longitudinal recording (in-plane recording) type magnetic recording medium. In the magnetic recording disk 1 of this embodiment, an adhesion layer 12, an underlayer 13, a magnetic layer 14, a protective layer 15, and a lubricating layer 16 are laminated in this order on a main surface 110 of a circular nonmagnetic substrate 11 having a center hole 111. The adhesion layer 12 is provided between the nonmagnetic substrate 11 and the underlayer 13.

  The nonmagnetic substrate 11 is made of a glass substrate such as aluminosilicate glass, for example, and a circumferential texture is formed on the main surface 110 of the nonmagnetic substrate 11. In the nonmagnetic substrate 11, the inner end portion 112 and the outer end portion 113 are each chamfered. However, the chamfered portion is not shown in FIG. Such a non-magnetic substrate 11 is obtained by, for example, obtaining a glass substrate made of aluminosilicate glass from a molten glass by direct pressing using an upper die, a lower die, and a barrel die, and a shape processing step, an abrasive slurry, etc. It is obtained by applying a polishing process using a chemical, a chemical strengthening process, a texture process using a diamond slurry, or the like. As the chemical strengthening treatment, a chemical strengthening treatment method by ion exchange that performs chemical strengthening by replacing some ions contained in the surface layer of the glass substrate with ions in a chemical strengthening treatment liquid having an ion radius larger than the ions, Examples thereof include a chemical strengthening treatment method by dealkalization treatment in which chemical strengthening is performed by removing alkali ions contained in the surface layer of the glass substrate. As the texture processing, a tape made of polyester fiber cloth or the like is pressed against the surface of the substrate, a polishing slurry is interposed between the surface of the substrate and the tape, and the nonmagnetic substrate is rotated in the circumferential direction of the substrate. A tape texture method for forming a texture (polishing marks) over the entire surface can be mentioned.

  Hereinafter, the configuration of the magnetic recording disk 1 will be described in more detail while explaining a method of manufacturing the magnetic recording disk 1 by sequentially forming a plurality of layers on the nonmagnetic substrate 11 that has been subjected to the processing described above.

  In order to manufacture the magnetic recording disk 1 of this embodiment, first, the adhesion layer 12 is formed on the main surface 110 of the nonmagnetic substrate 11 by using a vapor phase film forming method such as sputtering. The adhesion layer 12 is a nonmagnetic amorphous layer made of, for example, a CrTi alloy, and improves adhesion with the nonmagnetic substrate 11 and suppresses the diffusion of contaminant elements such as alkali metals contained in the nonmagnetic substrate 11. It is formed to prevent the deterioration of magnetic properties. Here, the nonmagnetic amorphous layer also used as the adhesion layer 12 contains Ti, Y, Zr, Nb, Mo, Hf, Ta, W, Si, or B as the first additive element, As an additive element, a layer containing Cr, V, Mn, or Co can be used.

  Next, the base layer 13 is formed on the upper layer of the adhesion layer 12 by using a vapor deposition method such as sputtering. Such an underlayer 13 is formed in order to improve the crystal structure of the magnetic layer 14. The underlayer 13 preferably has at least one layer containing Cr as a main component and containing at least one element selected from Ti, Zr, Nb, Ta, Mo, W, Mn, and Co. In this embodiment, the first underlayer is made of a CoW alloy, the second underlayer is made of a CrMn alloy, and the third underlayer is made of a CrMoTi alloy. The surface of the first underlayer made of CoW alloy is subjected to oxygen exposure treatment.

  Next, the magnetic layer 14 is formed on the upper layer of the underlayer 13 by using a vapor deposition method such as sputtering. In this embodiment, the magnetic layer 14 has a configuration in which a first magnetic layer and a second magnetic layer are laminated in this order. The first magnetic layer is mainly composed of Co, and further includes Cr, It is composed of a layer containing at least one element of Pt, Ta, B, Cu, and C, and the second magnetic layer is mainly composed of Co, and further includes Cr, Pt, Ta, B, Cu, and C. It is comprised by the layer containing at least 1 sort (s) of element. In this embodiment, the first magnetic layer is made of a CoCrTa alloy, and the second magnetic layer is made of a CoCrB alloy.

  Next, the protective layer 15 is formed on the upper layer of the magnetic layer 14 by using a vapor deposition method such as sputtering or plasma CVD. The protective layer 15 is made of, for example, diamond-like carbon, and has a function of improving the wear resistance and protecting the magnetic layer 14.

  Next, the lubricating layer 16 is formed on the protective layer 15 by an immersion film forming method. The lubrication layer 16 is composed of a perfluoropolyether layer or the like, and has a function of mitigating impact when coming into contact with the magnetic head.

  Among the magnetic disk devices including the magnetic recording disk 1 configured as described above, for example, the hard disk drive device 100 adopting the LUL (load / unload) method shown in FIG. A recording disk 1, a drive mechanism 3 having a spindle motor that supports and rotates these magnetic recording disks 1, and a head element (not shown) for recording and reproducing information to and from the magnetic recording disk 1 are held. The slider 2 includes a head suspension assembly 4 that supports the slider 2 so as to be movable with respect to the magnetic recording disk 1. 2 employs a LUL (load / unload) method, and the slider 2 is positioned near the outside of the magnetic recording disk 1 when the magnetic recording disk 1 is stopped. After the magnetic recording disk 1 is rotated, the slider 2 is moved onto the disk surface by a guide mechanism (not shown) to perform recording and reproduction. A predetermined load is applied to the slider 2 toward the magnetic recording disk 1 by a gimbal spring (not shown) provided at the tip of the head suspension assembly 4.

  Here, as the head element held by the slider 2, for example, a tunneling magnetoresistance (TMR) element is used. For example, the TMR element has aluminum oxide or magnesium oxide as a tunnel barrier. Is used and has a low resistance and a large magnetoresistance ratio.

(Main effect of this form)
Hereinafter, main effects of this embodiment will be described with reference to FIG. FIG. 3 is a graph showing a relationship between Mrt and thermal fluctuation characteristics in the circumferential direction of the magnetic layer in the magnetic recording disk. In addition, the value of Mrt in FIG. 3 and the values of Mrt in Tables 1 and 2 described later were measured using an M2 Automated Disk Media Measurement and Mapping System manufactured by Digital Measurement Systems.

  In this embodiment, a circumferential texture is provided on a nonmagnetic substrate 11 made of a glass substrate, and an adhesion layer 12 made of a nonmagnetic amorphous layer is formed between the nonmagnetic substrate 11 and the underlayer 13. Further, the surface of the first underlayer constituting the underlayer 13 is subjected to oxygen exposure treatment. For this reason, it is possible to realize high Mrt-OR (magnetic anisotropy ratio), specifically, Mrt-OR which is larger than 1.60. Here, Mrt-OR is the ratio of the Mrt in the circumferential direction of the magnetic recording disk 1 (the product of the residual magnetization (Mr) and the film thickness (t) in the magnetic layer 14) to the Mrt value in the radial direction (circle). Mrt in the circumferential direction / Mrt in the radial direction) The higher the value of Mrt-OR, the easier the magnetic recording disk 1 is magnetized in the circumferential direction. When Mrt-OR is increased in this way, the magnetic anisotropy is also increased, thereby increasing the magnetic anisotropy energy. Therefore, the stability against thermal fluctuation in the magnetic recording disk 1 can be improved without applying the AFC structure as in the prior art. Thereby, high durability in the magnetic recording disk 1 can be realized.

Further, in the magnetic recording disk 1 to which the present invention is applied, since the circumferential Mrt is configured to be larger than 0.350 memu / cm ^{2, the} stability against thermal fluctuation can be suppressed to a practically satisfactory level. it can. That is, in the magnetic recording disk 1 to which the present invention is applied, there is a correlation shown in FIG. 3 between the Mrt in the circumferential direction of the magnetic layer and the thermal fluctuation characteristic (attenuation of signal output). Since the magnetic recording disk 1 is configured so that the circumferential direction Mrt is larger than 0.350 memu / cm ² , the attenuation of the signal output due to thermal fluctuation is suppressed to 0.100 dB / decade or less which is practically no problem. Can do.

Further, in the magnetic recording disk 1 to which this embodiment is applied, since the Mrt in the circumferential direction of the magnetic layer 14 is configured to be larger than 0.350 memu / cm ^{2, the} recording density is increased to 65 Gbit / inch ² or more. Can be achieved. Therefore, it is suitable for mounting on an HDD apparatus having a TMR type magnetic head.

  An embodiment of the magnetic recording disk 1 to which the present invention is applied will be described with reference to Tables 1 and 2. Table 1 shows the configurations of the first magnetic layer of the magnetic recording disks according to Examples 1 and 2 of the present invention and the comparative example having the AFC structure, Mrt in the circumferential direction (product of residual magnetization and film thickness), Mrt-OR (magnetic anisotropy ratio) and thermal fluctuation characteristics are shown. Table 2 shows the configuration of the first magnetic layer of the magnetic recording disks according to Examples 3 to 7 to which the present invention is applied, and the Mrt, Mrt-OR, and SNR (signal-to-noise ratio) in the circumferential direction.

  The other configuration of the magnetic recording disk used in the example is as described with reference to FIG. 1. The adhesion layer 12 made of a CrTi alloy (nonmagnetic amorphous layer) is applied to a textured glass substrate. A magnetic layer 14 (magnetic recording layer) composed of a base layer 13 made of a CoW alloy, a CrMn alloy, and a CrMoTi alloy, a first magnetic layer and a second magnetic layer made of a CoCrB alloy shown in Table 1, diamond-like A protective layer 15 made of carbon and a lubricating layer 16 made of a perfluoropolyether layer are laminated in this order.

First, as shown in Table 1, Mrt, which is the product of the remanent magnetization (Mr) and the film thickness (t) in the magnetic layer 14, is 0.436 memu in the circumferential direction in each of Example 1 and Example 2. / Cm ² , 0.467 memu / cm ² , and in Comparative Example 1 (having an AFC structure), it was 0.449 memu / cm ² . Moreover, all Mrt-OR in Example 1 and Example 2 was larger than 1.60. Further, the attenuation of the signal output indicating the thermal fluctuation characteristics is −0.078 dB / decade and −0.069 dB / decade in Example 1 and Example 2, respectively, and −0.078 dB in Comparative Example 1. / Decade.

  As described above, the magnetic recording disks according to Examples 1 and 2 of the present invention have substantially the same Mrt value as that of the conventional magnetic recording disk having the AFC structure, and the magnetic fluctuation characteristics have the AFC structure. It can be seen that it exhibits substantially the same characteristics as the recording disk. Therefore, the magnetic recording disk according to the embodiment of the present invention can perform high density recording substantially the same as the magnetic recording disk having the AFC structure, and can improve the stability against thermal fluctuation without using the AFC structure. It is understood that is possible. The reason why the magnetic recording disk to which the present invention is applied has high stability against thermal fluctuation is that the magnetic anisotropy energy in the magnetic recording disk is increased by making Mrt-OR larger than 1.6. it is conceivable that.

Next, as shown in Table 2, all Mrts in Examples 3 to 7 were larger than 0.350 memu / cm ^{2 in the} circumferential direction, and all Mrt-ORs were larger than 1.60. Moreover, all SNR in Examples 3-7 was 20.0 vicinity. Therefore, it can be seen that the magnetic recording disk to which the present invention is applied can perform high-density recording, and can obtain good electromagnetic conversion characteristics with an SNR value of around 20.0. The reason why the magnetic recording disk to which the present invention is applied has good electromagnetic conversion characteristics is that the magnetic anisotropy in the circumferential direction of the magnetic recording disk is improved by making Mrt-OR larger than 1.6. It is considered that better electromagnetic conversion characteristics can be obtained.

(a), (b) is the top view and schematic sectional drawing which respectively show the magnetic recording disk to which this invention is applied. It is explanatory drawing which shows the principal part structure of a magnetic disc apparatus. It is a graph which shows the relationship between Mrt and the thermal fluctuation characteristic in the circumferential direction of the magnetic layer in a magnetic recording disk.

Explanation of symbols

1 Magnetic recording disk (magnetic recording medium)
11 Nonmagnetic substrate 12 Adhesion layer 13 Underlayer 14 Magnetic layer 15 Protective layer 16 Lubrication layer

Claims (6)

In a magnetic recording medium in which at least an underlayer, a magnetic layer, a protective layer, and a lubricating layer are laminated in this order on a nonmagnetic substrate,
An adhesion layer made of a nonmagnetic amorphous layer is formed between the nonmagnetic substrate and the underlayer,
The Mrt obtained by the product of the remanent magnetization of the magnetic layer and its film thickness is greater than 0.350 memu / cm ^{2 in the} circumferential direction, and the Mrt-OR obtained by the ratio of the Mrt in the circumferential direction to the Mrt in the radial direction is A magnetic recording medium characterized by being larger than 1.6.   The adhesion layer contains at least one element of Ti, Y, Zr, Nb, Mo, Hf, Ta, W, Si, and B as the first additive element. 2. A magnetic recording medium according to 1.   The magnetic recording medium according to claim 2, wherein the adhesion layer contains at least one element of Cr, V, Mn, and Co as a second additive element.   The underlayer has at least one layer containing Cr as a main component and containing at least one element selected from Ti, Zr, Nb, Ta, Mo, W, Mn, and Co. Item 4. The magnetic recording medium according to any one of Items 1 to 3. The magnetic layer has at least two layers of a first magnetic layer and a second magnetic layer,
5. The first magnetic layer according to claim 1, wherein the first magnetic layer contains Co as a main component and further contains at least one element selected from Cr, Pt, Ta, B, Cu, and C. 2. A magnetic recording medium according to 1.   6. The magnetic recording according to claim 5, wherein the second magnetic layer contains Co as a main component and further contains at least one element selected from Cr, Pt, Ta, B, Cu, and C. Medium.

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