JP5128930B2 - Perpendicular magnetic recording medium and manufacturing method thereof - Google Patents

Description

  The present invention relates to a perpendicular magnetic recording medium that realizes high-density magnetic recording and a manufacturing method thereof.

  Patent Document 1 proposes a magnetic recording medium in which a heat insulating layer is formed between a base and a magnetic recording layer for the purpose of heating the magnetic recording layer while minimizing the influence of heat on the base. Yes. Patent Document 3 proposes a magnetic disk in which a magnetic film is formed on the surface of a disk formed of a material having low thermal conductivity. In Patent Document 4, a nonmagnetic underlayer and a ferromagnetic layer are laminated on a nonmagnetic substrate, and the nonmagnetic underlayer has a thermal conductivity of 30 W / (m · k) or less in a temperature range of 20 ° C. to 300 ° C. There has been proposed a magnetic recording medium which is made of a material having the above structure and the ferromagnetic layer is made of a ferromagnetic metal containing Cr. In any of these magnetic recording media, in order to confine heat in the recording layer, a layer having a lower thermal conductivity than the recording layer is provided below the recording layer.

On the other hand, Patent Document 2 includes a region of low thermal conductivity material that extends at least partially through the thickness of the thin film, and a region of high thermal conductivity material that separates the region of low thermal conductivity material, There has been proposed a thin film constructed and arranged such that these regions are regions of higher thermal conductivity than regions of low thermal conductivity and thermal conduction through the film thickness is greater. Further, Patent Document 5, Cu in order to increase the ordering of the L1 ₀ structure, Au, Zn, perpendicular magnetic recording medium of the FePt alloy utilized with the addition of Sn and Pd have been proposed. Alternatively, a perpendicular magnetic recording medium in which the degree of ordering of the CoPt and FePd alloys is improved instead of the FePt alloy has been proposed. In Patent Document 6, a first underlayer, a second underlayer, and a third underlayer on a substrate, and a magnetic layer on the third underlayer, the first underlayer is amorphous. The second underlayer has a single element of W or an alloy containing W, and the third underlayer has an alloy of a body-centered cubic structure containing Cr as a main component and Ti or B. A magnetic recording medium has been proposed in which the magnetic layer is an alloy layer having a hexagonal close-packed structure mainly composed of one or more Co layers.

  Patent Document 7 shows an example of a heat-assisted recording method. Patent Document 8 exemplifies a method of locally heating, such as using a near-field heater. Further, as described in Patent Document 9, a magnetic head having a thin film magnetic head element formed with a thin film resistor in which a magnetic pole tip is protruded by thermal expansion by energizing and generating heat as necessary, When a magnetic head reads / writes from / to a magnetic disk, a thin film resistor is formed by causing the tip of the magnetic pole to thermally expand by being energized to generate heat. It has been proposed that the gap between the magnetic disk surface and the magnetic disk surface be reduced by the protrusion of the magnetic pole tip. Patent Document 10 also proposes a head for a heat-assisted recording apparatus in which a magnetic pole is arranged on the upper part of a scatterer for generating near-field light at the bottom of a slider.

Japanese Unexamined Patent Publication No. 7-65357 JP 2006-196151 A JP 59-165243 JP-A-63-249925 Japanese Patent No. 3730518 JP 2005-190512 A US2006 / 0154110A1 US2002 / 0101673A1 JP-A-5-20635 JP 2007-128573 A

  Corresponding to the increase in surface recording density, it is necessary to refine the crystal grain size used for the recording layer. However, when the crystal grain size of the recording layer is reduced, the instability of the recording magnetization due to thermal fluctuation becomes remarkable. As countermeasures, (1) improvement in crystallinity of the recording layer, (2) reduction in crystal grain size dispersion, (3) use of a recording material having a large magnetic anisotropy, and (4) lamination of magnetic layers having different writing performances Proposal has been proposed. In particular, when using a recording material having a large magnetic anisotropy, it has been proposed to improve the writing performance by heating the recording layer to reduce the coercive force.

However, in a magnetic recording medium using a ferromagnetic material of an intermetallic compound, a metal having a composition that is expected to have an L1 ₀ structure at a stage where ordering has progressed by repeating writing by heating. A sufficient measure has not been taken about the possibility that the writing performance may be deteriorated due to an increase in the degree of order of the intermetallic compound and consequently an increase in magnetic anisotropy. In addition, no magnetic recording medium has been proposed in which a perpendicular magnetic recording medium using a soft magnetic underlayer considers thermal conductivity and simultaneously improves writing performance. In consideration of the role of the soft magnetic underlayer in magnetic recording, a magnetic recording medium with a high crystallinity and thin low thermal conductivity layer that can close the gap between the soft magnetic underlayer and the recording layer has not been proposed. It was.

  From such a background, the problem to be solved by the present invention is to efficiently heat a magnetic recording medium with a small amount of energy consumption in consideration of thermal conductivity when magnetically writing to the magnetic recording medium. An object of the present invention is to improve the writing performance over a long period of time even if the degree of order of the ordered alloy used in the recording layer changes.

In the perpendicular magnetic recording medium of the present invention, a soft magnetic underlayer is formed on a rigid substrate directly or via an adhesive layer, and the soft magnetic underlayer and oxide are formed on the soft magnetic underlayer via a nonmagnetic intermediate layer. After the formation of the low thermal conductivity intermediate layer, the crystal grain size control layer is formed directly or via the crystal orientation control layer, and at the stage where ordering progresses directly or via the crystal orientation control and low thermal conductivity intermediate layer. A granular recording layer mainly composed of an Fe—Pt alloy or a Co—Pt alloy having a composition expected to have an L1 ₀ structure, a cap layer made of an Fe—Pt alloy or a Co—Pt alloy, a protective layer, and The lubricating layer is formed in this order. As the adhesive layer, not only an Al—Ti alloy but also a Cr—Ti alloy can be used. As the crystal grain size control layer, a Cr-MB alloy layer to which at least one element selected from the group M consisting of Ti, Mo, and W is added can be used. Moreover, after forming a Cr-MB alloy layer as a crystal grain size control layer, an MgO layer can also be provided as a crystal orientation control and low thermal conduction intermediate layer.

Granular recording layer mainly composed of composed Fe-Pt alloy composition is expected to take an L1 ₀ structure at the stage of progress in ordering may contain Cu. These Fe—Pt alloys or Fe—Cu—Pt alloys are composed of a composition that is expected to have an L1 ₀ structure at the stage of regularization, and in addition to the composition constituting these intermetallic compounds, SiO 2 ₂ or at least one oxide selected from TiO ₂ and Ta oxides is added to form a granular recording layer.

Or granular recording layer may take the L1 ₀ structure ordered has advanced stage as a main component composed of Co-Pt alloy composition to be expected, which was added to replace the Ni against Co It may be. These Co—Pt alloys or Co—Ni—Pt alloys are composed of a composition that is expected to have an L1 ₀ structure at a stage where ordering has progressed, and SiO 2 is further added to the composition constituting these intermetallic compounds. ₂ or at least one oxide selected from TiO ₂ and Ta oxides is added to form a granular recording layer.

  The crystal orientation control layer can be a W-Co alloy. As a composition of W-Co alloy, as described in JP-A-2005-190512, for example, W-30 at.% Co and W-40 at.

A soft magnetic underlayer is formed on a rigid substrate via an adhesive layer or directly on the substrate, and a soft magnetic underlayer is formed on the soft magnetic underlayer via a nonmagnetic intermediate layer. After heating the substrate in the vacuum process, a low thermal conductivity intermediate layer made of oxide, a crystal orientation control layer, and a crystal grain size control layer are formed in this order, and the crystal is controlled through the crystal orientation control and low thermal conductivity intermediate layer or directly. A granular recording layer mainly composed of an Fe—Pt alloy or a Co—Pt alloy having a composition that is expected to have an L1 ₀ structure at the stage of progress of ordering on the grain size control layer, Fe—Pt The perpendicular magnetic recording medium of the present invention can be manufactured by forming a cap layer and a protective layer made of an alloy or a Co—Pt alloy, followed by heat treatment, and then forming a lubricating layer. The Pt composition of the Fe—Pt alloy or Co—Pt alloy used for the cap layer may be 40 at.% To 60 at.%. Since the crystallinity changes when the Pt addition concentration is reduced too much, any composition having an fcc structure or an fct structure may be used.

  According to the present invention, it is possible to provide a perpendicular magnetic recording medium that can reduce power consumption and heat the magnetic recording medium, and at the same time has excellent writing performance.

  In the present invention, in a perpendicular magnetic recording medium using a soft magnetic underlayer, a recording layer is heteroepitaxially grown on the crystal orientation control layer in order to reduce the distance between the soft magnetic underlayer and the recording layer. The distance between the recording layers was optimized. At the same time, by reducing the thermal conductivity using the crystalline low thermal conductivity intermediate layer, the coercive force of the recording layer can be reduced without heating to the soft magnetic underlayer, and the magnetization can be reversed with low power consumption.

  Forming a soft magnetic underlayer on a rigid substrate via an adhesive layer is preferable because mechanical reliability is improved. When the thickness of the soft magnetic underlayer is about 30 nm or less, the adhesive stress is not necessarily provided because the film stress is small. When an oxide film is formed on a soft magnetic underlayer, the thermal conductivity of the oxide film is about 1 W / (m · K), which is smaller than that of a metal film. Therefore, the recording layer is heated without heating the soft magnetic underlayer during recording. It becomes easy to do. Furthermore, it consists of a Cr-MB alloy layer to which at least one element selected from the group M consisting of Ti, Mo, and W is directly added on the low thermal conductivity intermediate layer made of oxide via a crystal orientation control layer. When the crystal grain size control layer is formed, as shown in FIG. 1, the (100) plane of the alloy intermediate layer having a body-centered cubic structure grows parallel to the substrate surface. The arrow in FIG. 1 corresponds to the a-axis of the body-centered cubic structure. As a result, the (001) plane of the portion having the fcc or fct structure in the granular recording layer formed on the crystal grain size control layer is heteroepitaxially grown parallel to the substrate surface as shown in FIG. The arrow in FIG. 2 corresponds to the a-axis of the fcc or fct structure.

By adjusting the M concentration contained in the Cr-MB alloy film of the grain size control layer having a body-centered cubic structure, the length of √2 times the a-axis length of the body-centered cubic structure is L1 of the granular recording layer. If the lattice constant is controlled as shown in FIG. 3 so as to be longer than the a-axis length of the _0-order alloy structure, the (100) plane of the fct structure in the granular recording layer is less likely to be heteroepitaxially grown parallel to the substrate surface. The heat treatment after forming the recording layer is expected to improve the degree of ordering of the alloy and promote grain boundary segregation by using the strain relief as a driving force.

  The ordered alloy CoPt has an a-axis lattice constant of 0.38 nm and a c-axis lattice constant of 0.368 nm, whereas FePt has a = 0.385 nm and c = 0.371 nm. Therefore, if a crystal grain size control layer having a bcc structure of 0.272, 0.269 nm or more is formed for each recording layer alloy, (001) of the portion having the fcc or fct structure in the granular recording layer. It becomes easy to orient the surface as shown in FIG.

  As the M concentration contained in the Cr-M alloy increases, the crystal grain size increases. When B is added to the Cr-M alloy, the crystal grains can be refined. When the additive concentration of B is 10 at.% Or more, the effect of refining crystal grains becomes too large. Therefore, the effective concentration range of B is 2 at.% To 8 at.%, More preferably 4 at.% Or more. It is preferable to add 8 at.% Or less of B. By providing a crystal orientation control and low thermal conductivity intermediate layer made of MgO on the crystal grain size control layer made of this Cr-MB alloy, the crystal orientation is improved, and at the same time, heat insulation from the recording layer to the substrate side. Can also be increased.

The Fe-Pt alloy in forming the granular recording layer mainly, the addition of Fe to replace with Cu, since easily forming an L1 ₀ ordered structure preferred. The Co-Pt alloy in forming the granular recording layer mainly composed, even if Co is added to replace at Ni, since easily forming an L1 ₀ ordered structure preferred. To granulate the recording layer, Ta oxide or a mixture thereof can be added in addition to SiO ₂ and TiO ₂ .

Rules of the L1 ₀ ordered alloy immediately after the formation of the magnetic recording medium is not necessarily high. However, as heating recording is repeated, the regularity gradually improves and the coercive force increases. Even if the coercive force of the granular recording layer is increased, no problem occurs in writing performance by forming a cap layer on the granular recording layer that triggers magnetization reversal.

The material that can be used as the cap layer may be any material that has a smaller anisotropic magnetic field than the granular recording layer. For example, a cap layer made of an Fe-Pt alloy in which Fe having a low degree of order or an fct structure in which Fe is not substituted with Cu or a Co-Pt alloy in which Co is not substituted with Ni can be used. As a protective layer to be provided after the cap layer is formed, in addition to a protective layer mainly composed of carbon containing nitrogen or hydrogen, it is also possible to form a protective layer mainly composed of silicon nitride from the viewpoint of ease of heating. To preferred. After forming the protective layer, and was heat-treated, by subsequently forming a lubricant layer, it is possible to L1 ₀ structure of the granular recording layer improves the degree of order of the alloy portion expected.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 4 is a cross-sectional view showing the configuration of the magnetic recording medium according to the embodiment. This magnetic recording medium includes an adhesive layer 12, a soft magnetic underlayer 141, a nonmagnetic layer 142, a soft magnetic underlayer 143, a low thermal conductive intermediate layer 144 made of an oxide, a crystal grain size control layer 18, a granular recording on a substrate 10. It has a layer 20, a cap layer 22, a protective layer 24 and a lubricating layer 26.

Next, a method for manufacturing a magnetic recording medium will be described. A chemically strengthened glass substrate having a thickness of 0.508 mm and an outer diameter of 48 mm was used as the substrate 10. All chambers were evacuated to a vacuum of 2 × 10 ⁻⁵ Pa or less using an in-line single-wafer DC / RF magnetron sputtering apparatus. Thereafter, the carrier on which the substrate 10 was placed was moved to each process chamber, the granular recording layer 20 was removed, the discharge Ar gas pressure was 0.7 Pa, and the following thin film was formed by DC magnetron sputtering. The method for forming the thin film is not limited to DC magnetron sputtering. In particular, the granular recording layer 20 was formed using a high-frequency magnetron sputtering method in order to increase the expected crystallinity of the ordered alloy. It is also possible to apply a DC pulse sputtering method or a bias voltage when forming a thin film containing an oxide.

  In this example, a substrate obtained by chemically strengthening the substrate surface made of borosilicate glass or aluminosilicate glass was used as the glass substrate 10 after being washed and dried. Instead of a chemically strengthened glass substrate, a substrate whose surface is polished after Ni-P plating on an aluminum alloy substrate, or a rigid substrate made of Si or Ti alloy can also be used. The outer diameter of the substrate is not limited to 48 mm, and can be selected from 65 mm, 84 mm, and the like. The thickness of the substrate can also be selected as long as the rigidity is maintained, and can be selected from 0.635 mm, 0.8 mm, or the like. A 50 at.% Al-50 at.% Ti alloy film having a thickness of 5 nm was formed as the adhesive layer 12.

  A 51 at.% Fe-34 at.% Co-10 at.% Ta-5 at.% Zr alloy film with a thickness of 20 nm is formed as the soft magnetic underlayer 141, and a Ru film with a thickness of 0.7 nm is formed as the nonmagnetic layer 142. Thereafter, a 51 at.% Fe-34 at.% Co-10 at.% Ta-5 at.% Zr alloy film having a thickness of 20 nm was formed as the soft magnetic underlayer 143. The composition of the soft magnetic underlayers 141 and 143 is not limited to the above composition, but when the total concentration of added elements of Ta and Zr is 5 at.%, An oxidation process within 5 seconds when the substrate is heated to 300 ° C. Thus, the low thermal conductive intermediate layer 144 made of an oxide can be formed. When the total concentration of the added elements of Ta and Zr was 20 at.%, The write characteristics were improved by making the soft magnetic underlayers 141 and 143 thicker than 20 nm, respectively. For example, 48 at.% Fe-37 at.% Co is used instead of the 51 at.% Fe-34 at.% Co-10 at.% Ta-5 at.% Zr alloy while the concentration of the additive element of Ta and Zr is fixed at 15 at. It is also possible to change to a -10 at.% Ta-5 at.% Zr alloy. From the measurement result of the reflection curve by X-ray diffraction, it is considered that all of these Fe—Co—Ta—Zr alloy films are microcrystalline or amorphous.

  As the non-magnetic layer 142, Ru-50at.% Fe alloy, Ru-40at.% Cr alloy, Ru-30at.% Co alloy or the like can be used as an alloy containing Ru or Ru as a main component. The film thickness can be changed within a range in which the soft magnetic underlayers 141 and 143 can be antiferromagnetically coupled. Furthermore, reproduction noise can be reduced if the residual magnetizations of the soft magnetic underlayers 141 and 143 are equally antiparallel using this antiferromagnetic coupling. After forming the soft magnetic underlayer 143, the substrate was heated to 300 ° C., and Ar gas containing 1 vol.% Oxygen was exposed for 5 seconds to form a low thermal conductive intermediate layer 144 made of oxide.

After forming the low thermal conductivity intermediate layer 144 made of an oxide, a Cr-18 at.% Ti-4 at.% B alloy film was formed as a crystal grain size control layer 18 from 3 nm to 10 nm. Further, a 92 mol% (50 at.% Fe-50 at.% Pt) -8 mol% SiO ₂ film having a thickness of 12 nm was formed as the granular recording layer 20. The Ar gas pressure for discharge when forming the granular recording layer 20 was 2 Pa.

  Reflection diffraction curves using copper characteristic X-rays were measured for these samples. As a result, it was confirmed that the 200 diffraction intensity derived from the bcc structure increases as the thickness of the Cr—Ti—B alloy film increases. Along with this increase in the diffraction intensity, an increase in the 002 diffraction intensity derived from the fcc structure or the fct structure considered to be caused by the granular recording layer and an increase in the 001 diffraction intensity derived from the fct structure were observed. From this, it was confirmed that this medium was a perpendicular magnetic recording medium in which the easy axis of magnetization of the recording layer was oriented in the direction perpendicular to the film surface.

  After forming the granular recording layer 20, a cap layer 22 made of a 60 at.% Fe-40 at.% Pt alloy was formed to 3 to 12 nm, and a protective layer 24 containing nitrogen or hydrogen and containing carbon as a main component was formed to 3 nm. Furthermore, after maintaining at 300 ° C. for 1 hour in an inert atmosphere substituted with nitrogen, the pressure was returned to atmospheric pressure to form a lubricating layer 26 containing fluorine as a main component.

  After confirming the mechanical flying characteristics, the electromagnetic conversion characteristics of the magnetic recording medium were measured using a TMR head having a shield gap length of 35 nm recorded with a writing pole having a geometric track width PW of 105 nm. FIG. 5 is a cross-sectional view centered on a recording head in which a single magnetic pole head and a scatterer for generating near-field light are combined. A scatterer 34 for generating near-field light was formed on the surface of the slider 32, and a magnetic pole 36 was formed thereon. Light was generated using a semiconductor laser 38 having a wavelength of 785 nm, and the light generated from the semiconductor laser 38 was guided to the scatterer 34 using a waveguide composed of a core portion 40 and a cladding portion 42. The core portion 40 of the waveguide is surrounded by a clad portion 42. A magnetic field generated using the thin film coil 44 was guided near the scatterer 34 by the main magnetic pole 46. The main magnetic pole 46 and the thin film coil 44 are arranged on the outflow end 48 side with respect to the waveguide. The magnetic pole 36 and the main magnetic pole 46 on the upper part of the scatterer 34 are coupled using the magnetic pole 50. An auxiliary magnetic pole 52 for forming a closed magnetic circuit is formed on the opposite side of the thin film coil 44 via the magnetic pole 51. A coil 44 is linked to a magnetic circuit formed by the magnetic pole 36, the magnetic pole 50, the main magnetic pole 46, the magnetic pole 51, and the auxiliary magnetic pole 52 on the scatterer 34. A magnetic reproducing element 54 for reproducing a recording signal is formed beside the waveguide. A shield 56 for shielding a magnetic field from the surroundings is formed around the magnetic reproducing element 54. This reproducing element may be placed beside the auxiliary magnetic pole 52 (on the outflow end 48 side), but in this embodiment, the reproducing element is arranged as shown in FIG. 5 and a TMR element is used as the magnetic reproducing element 54. A thin film resistor 58 was formed in which the reproducing element 54 was thermally expanded and protruded by energizing and generating heat as necessary.

  During recording, light was generated and heated using a semiconductor laser 38 having a wavelength of 785 nm with 120 mW. The electromagnetic conversion characteristics were evaluated under the condition that the thin film resistor 58 was energized with 60 mW without using the semiconductor laser 38 during reproduction.

  The magnetic recording medium was rotated at 90 / s (= 5400 pm), and the skew angle of the head was 0 degree with a radius of 21 mm. Overwrite characteristic (O / W) is demagnetized at 47.2 kFC / mm (= 1200 kFCI), then a 35.4 kFC / mm (= 900 kFCI) signal is written, and a 7.01 kFC / mm (= 178 kFCI) signal is superimposed. Writing was performed and the unerased remainder of the 35.4 kFC / mm signal was evaluated. When performing read / write on the magnetic recording medium, the thin film resistor 58 was heated by energizing 60 mW, and the electromagnetic conversion characteristics were measured. The time-dependent change with respect to the number of writings was measured on the same track by heating in parallel.

  As a result, even after overwriting 10,000 times with respect to the overwrite characteristic in the initial stage of heating, the overwrite characteristic is within an error range of ± 0.2 dB, and even if the degree of ordering of the ordered alloy changes temporarily, it is long. It became clear that there was no problem in writing performance over the period. When the cap layer 22 was formed to have a thickness of 4 nm or more, the overwrite characteristics were improved as shown in FIG.

  FIG. 7 shows the relationship between the write track width (Tw) normalized by the geometric track width (Pw) and the thickness of the cap layer 22. The tendency of increasing the (Tw / Pw) value when the thickness of the cap layer was increased was not dependent on the material of the cap layer. From these results, the thickness of the cap layer is required to be at least about 4 nm, but it is considered that the thickness should be about 5 to 8 nm in consideration of the increase in the track width.

[Comparative Example 1]
After forming the low thermal conductive intermediate layer 144 made of oxide without forming the Cr-18 at.% Ti-4 at.% B alloy film as the crystal grain size control layer 18, 92 mol% (50 at. % Fe-50at.% Pt) -8 mol% The SiO ₂ film was formed to a thickness of 12 nm. All other process conditions were the same as those described in Example 1. The magnetic recording medium was rotated at 90 / s (= 5400 pm), and the overwrite characteristic (O / W) was measured with a radius of 21 mm and a head skew angle of 0 degree. As a result, when light was generated using the semiconductor laser 38 with a wavelength of 785 nm of 120 mW and heated during recording, the O / W was about −11 dB. Even when the input power of the semiconductor laser was increased to 140 mW, the O / W was -15.4 dB.

Further, after forming the soft magnetic underlayer 143, the substrate is heated to 300 ° C., and exposed to Ar gas containing 1 vol.% Oxygen, without being exposed to Cr-18 at.% Ti-4at. A 5% B alloy film was formed. Thereafter, all the other process conditions were the same as those described in Example 1 except that a 92 mol% (50 at.% Fe-50 at.% Pt) -8 mol% SiO ₂ film was directly formed as the granular recording layer 20 to 12 nm. Formed. As a result of measuring the overwrite characteristics (O / W) of this magnetic recording medium, when light was generated using a semiconductor laser 38 having a wavelength of 785 nm of 120 mW and heated during recording, the O / W was about −12.3 dB. Met. Even when the input power of the semiconductor laser was increased to 140 mW, the O / W was -16.5 dB.

  From these results, as described in Example 1, in order to obtain an overwrite characteristic of −23 dB or less by heating at 120 mW, the soft magnetic underlayer 143, the low thermal conductive intermediate layer 144 made of oxide, the crystal grain size control It was found that a magnetic recording medium in which the layer 18, the granular recording layer 20, the cap layer 22, and the protective layer 24 are formed in this order and heat-treated in an inert atmosphere is effective.

After forming the soft magnetic underlayer 143 in Example 1, it was once taken out into the atmosphere, and the following post-process was set with another film forming apparatus. After evacuating to 2 × 10 ⁻⁵ Pa or less, heating to 300 ° C., forming a low thermal conductive intermediate layer 144 made of an oxide layer on the surface of the soft magnetic underlayer 143, and then crystal orientation made of a W-30 at.% Co alloy The property control layer 16 was formed to 3 nm, and its surface was exposed to an oxygen atmosphere diluted with Ar to be controlled and oxidized.

Further, a Cr-18 at.% Ti-4 at.% B alloy film was formed from 3 nm to 10 nm as the crystal grain size control layer 18. Further, as the granular recording layer 20, a (50 at.% Fe-50 at.% Pt) -8 mol% SiO ₂ film was formed to 12 nm. The Ar gas pressure for discharge when forming the granular recording layer 20 was 2 Pa.

  For these samples having the cross-sectional structure shown in FIG. 8, the average crystal grain size of the granular magnetic layer was measured. The average crystal grain size <D> was calculated from a transmission electron microscope (TEM) image. First, a crystal grain image of the recording layer in a direction parallel to the substrate surface was taken with a transmission electron microscope. Next, the obtained photograph was captured by a scanner, the core portion where the contrast of the image was observed was defined as a crystal grain, and the number of pixels present in each crystal grain was calculated. From the conversion of the number of pixels and the scale, the area of each crystal is obtained, the crystal grain size is defined as the diameter of a perfect circle having the same area as the obtained crystal grain area, and the grain diameter Di of each crystal grain is obtained. It was. This calculation was performed for about 300 crystal grains, and the arithmetic average value of the obtained particle diameters was defined as the average crystal grain diameter <D>.

In the Fe—Pt—SiO ₂ film added with 8 mol% SiO ₂ , the average crystal grain size <D> was about 8 nm. In the Fe—Pt—SiO ₂ film added with 10 mol% SiO ₂ , <D> was 6.2 nm. Further, in the Fe—Pt—SiO ₂ film added with 12 mol% SiO ₂ , <D> decreased to 5 nm.

  When the Cr—Ti—B alloy layer having the bcc structure formed as the crystal grain size control layer was thickened, the 200 diffraction intensity derived from the bcc structure increased. Along with the increase in X-ray diffraction intensity by the crystal grain size control layer, an increase in 002 diffraction intensity derived from the fcc structure or fct structure of the recording layer and an increase in 001 diffraction intensity derived from the fct structure were also observed. From the behavior of these X-ray diffraction intensities, it is considered that the crystal grain size control layer having a bcc structure and the recording layer having an fcc structure or fct structure formed thereon have a heteroepitaxial growth relationship.

  After forming the granular recording layer 20, as shown in FIG. 9, a cap layer 22 made of 60 at.% Fe-40 at.% Pt alloy or Co-40 at.% Pt alloy is formed from 3 nm to 10 nm, and contains nitrogen or hydrogen. Then, the protective layer 24 mainly composed of carbon was formed to 2.5 nm. Furthermore, after maintaining at 300 ° C. for 1 hour in an inert atmosphere substituted with nitrogen, the pressure was returned to atmospheric pressure to form a lubricating layer 26 containing fluorine as a main component.

  After confirming the mechanical flying characteristics, the same head as in Example 1 was used, and heating was performed using a semiconductor laser 38 having a wavelength of 785 nm of 120 mW during recording. During reproduction, the semiconductor laser 38 was not used, and the electromagnetic conversion characteristics were measured under the condition that the thin film resistor 58 was energized with 60 mW. As a result, when the cap layer 22 was formed to have a thickness of 4 nm or more, the overwrite characteristic was improved from 1 dB to 4 dB as compared with Example 1. On the other hand, the write track width became wider as the cap layer 22 became thicker. This tendency, that is, the tendency that the track width becomes wider as the cap layer becomes thicker was the same even when the material of the cap layer was changed. From these results, the thickness of the cap layer needs to be at least about 4 nm, but it is considered that the thickness should be about 6 to 8 nm in consideration of the increase in the track width.

  In parallel, the time-dependent change with respect to the number of heating writings was measured on the same track. As a result, even after overwriting 10,000 times with respect to the overwrite characteristics in the initial stage of heating, the overwrite characteristics are within an error range of ± 0.2 dB, and even if there is a change in the degree of order of the ordered alloy It was confirmed that there was no problem in writing performance over a period.

  In Example 1, after the soft magnetic underlayer 143 is formed, the substrate is heated to 300 ° C., and Ar gas containing 1 vol.% Oxygen is exposed for 5 seconds to form a low thermal conductive intermediate layer 144 made of oxide. A Cr-18 at.% Ti-4 at.% B alloy film was directly formed as the crystal grain size control layer 18.

On the other hand, in Example 2, after the soft magnetic underlayer 143 was formed, it was once taken out into the atmosphere, evacuated to 2 × 10 ⁻⁵ Pa or less with another film forming apparatus, heated to 300 ° C. After forming the low thermal conductivity intermediate layer 144 made of an oxide layer on the surface of the base layer 143, the crystal orientation control layer 16 made of a W-30 at.% Co alloy is formed to 3 nm, and the surface is exposed to an oxygen atmosphere diluted with Ar. Then, after control and oxidation, by forming a Cr-18 at.% Ti-4 at.% B alloy film as the crystal grain size control layer 18, it becomes possible to increase the crystallinity of the crystal grain size control layer 18. It was. In the case of Example 1, the half-value width of 200 diffraction intensity considered to be caused by the Cr—Ti—B alloy layer having a bcc structure formed so as to have a thickness of 8 nm as the crystal grain size control layer is 5.4 degrees. In contrast, in Example 2, the half width of the 200 diffraction intensity caused by the Cr—Ti—B alloy layer having the same thickness was 3.8 degrees. The improvement in the overwrite characteristics of Example 2 compared to Example 1 is considered to correspond to the decrease in the half-value width of 200 diffraction intensity.

A perpendicular magnetic recording medium whose cross-sectional schematic diagram is shown in FIG. 10 was produced. After forming the soft magnetic underlayer 143 in Example 1, it was heated to 300 ° C. to form a low thermal conductive intermediate layer 144 made of an oxide layer on the surface of the soft magnetic underlayer 143. Thereafter, a W-40 at.% Co alloy film of 4 nm was formed as the crystal orientation control layer 16 and exposed for 4 seconds in an oxygen gas atmosphere diluted 100 times with Ar gas. Further, a Cr-20 at.% Ti-5 at.% B alloy layer was formed with a thickness of 5 nm as the crystal grain size control layer 18, and then an MgO layer was formed with a thickness of 4 nm as the crystal orientation control and low thermal conduction intermediate layer 19 by RF magnetron sputtering. Further, after forming a 90 mol% (50 at.% Fe-50 at.% Pt)-(10 mol% SiO ₂ ) film with a thickness of 11 nm, a cap layer 22 made of a Co-45 at.% Pt alloy is formed with a thickness of 3 nm to 10 nm. Alternatively, the protective layer 24 containing hydrogen and containing carbon as a main component was formed to 3 nm. Furthermore, after maintaining at 300 ° C. for 1 hour in an inert atmosphere purged with nitrogen, the pressure was returned to atmospheric pressure to form a lubricating layer 26 composed mainly of perfluoropolyether.

  After confirming the mechanical flying characteristics, the same head as in Example 1 was used, and during recording, heating was performed using a semiconductor laser 38 with a wavelength of 785 nm of 100 mW. At the time of reproduction, the semiconductor laser 38 was not used, and the electromagnetic conversion characteristics were measured by maintaining the distance between the head protective film and the medium protective layer 24 at 2 nm under the condition that 60 mW was applied to the thin film resistor 58. As a result, when the cap layer 22 was formed to have a thickness of 4 nm or more, the overwrite characteristic was improved by 4 dB or more compared to the case where the cap layer 22 was not formed. On the other hand, when the cap layer 22 is thick, the write track width is widened.

  Even when the input power was reduced from 120 mW (Example 1) to 100 mW (Example 3), an O / W characteristic of −25 dB or less was obtained because the MgO layer was used as the crystal orientation control / low thermal conductivity intermediate layer 19. This is considered to be due to the fact that the temperature of the recording layer is effectively increased easily by forming 4 nm.

The formation of a granular recording layer made of the following alloy instead of forming a 90 mol% (50 at.% Fe-50 at.% Pt) -10 mol% SiO ₂ film at the time of forming the granular recording layer described in Example 3 A magnetic recording medium was formed in the same manner as in Example 3 except for the above.
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-12 mol% SiO ₂
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-10 mol% SiO ₂ -2 mol% TiO ₂
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-8 mol% SiO ₂ -4 mol% TiO ₂
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-6 mol% SiO ₂ -6 mol% TiO ₂
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-4 mol% SiO ₂ -8 mol% TiO ₂
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-12 mol% TiO ₂
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-12 mol% Ta ₂ O ₅
88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-6 mol% SiO ₂ -6 mol% Ta ₂ O ₅
92 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-8 mol% TiO ₂
92 mol% [(50 at.% Fe-5 at.% Cu-45 at.% Pt)]-8 mol% TiO ₂
92 mol% [(50 at.% Fe-0 at.% Cu-50 at.% Pt)]-8 mol% TiO ₂

After the granular recording layer 20 was formed, a cap layer 22 made of an Fe-40 at.% Pt alloy was formed to a thickness of 3 to 10 nm. Further, a protective layer 24 containing nitrogen or hydrogen and containing carbon as a main component was formed to 3.3 nm. Furthermore, after maintaining at 300 ° C. for 1 hour in an inert atmosphere substituted with nitrogen, the pressure was returned to atmospheric pressure to form a lubricating layer 26 containing fluorine as a main component.

  After confirming the mechanical flying characteristics, the same head as in Example 1 was used, and during recording, heating was performed using a semiconductor laser 38 with a wavelength of 785 nm of 100 mW. During reproduction, the semiconductor laser 38 was not used, and the electromagnetic conversion characteristics were measured under the condition that the thin film resistor 58 was energized with 60 mW.

As a result, when the cap layer 22 was formed to have a thickness of 4 nm or more, the overwrite characteristic was improved by 4 dB or more as compared with the case where the cap layer 22 was not formed. When the cap layer 22 was thicker, the write track width was widened. Composition of 88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-xmol% SiO _2- (12-x) mol% TiO ₂ when a 4 nm thick cap layer is formed FIG. 11 shows the relationship between and the overwrite characteristics. When the added concentration of TiO ₂ was increased, the overwrite characteristics deteriorated by about 3 dB.

In the case where a cap layer having a thickness of 4 nm was formed, the granular recording layer was 88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-x mol% SiO _2- (12-x) mol% TiO ₂ . FIG. 12 shows the relationship of So / Nd logarithmically expressing the ratio of composition, medium noise Nd, and reproduction signal output So. With 88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-6 mol% SiO ₂ -6 mol% TiO ₂ , good So / Nd was obtained although the deterioration of the overwrite characteristics was small. .

88 mol% [(45 at.% Fe-5 at.% Cu-50 at.% Pt)]-12 mol% SiO ₂ granular recording layer and 88 mol% [(45 at.% Fe-5 at.% Cu-50 at.%) Pt)] - 12mol% TiO ₂ results comparing the granular recording layer, a TiO ₂ becomes clear grain boundary mainly in granular recording layer with the addition of TiO _2, compared with the granular recording layer with the addition of SiO ₂ relative In particular, the grain boundary width was wide. From this result, in the medium having a high concentration of TiO ₂ , the magnetic particles are easily magnetically isolated, the medium noise Nd is reduced, the So / Nd is improved as compared with the medium having a high concentration of SiO ₂ , and TiO ₂ and SiO ₂ are reduced. It has been clarified that there is a composition that can achieve both overwrite characteristics and So / Nd in a composition range containing ₂ at the same time.

[Comparative Example 2]
Instead of forming a 90 mol% (50 at.% Fe-50 at.% Pt) -10 mol% SiO ₂ film of 11 nm during the formation of the granular recording layer described in Example 3, 92 mol% [(45 at.% Fe-5 at.% Zn— 50 at.% Pt)]-8 mol% SiO ₂ film was formed. As a result of X-ray fluorescence analysis of the granular film formed in the initial stage and the granular film manufactured the next day, the composition of Zn contained in the granular recording layer was lowered. From this result, it was clarified that when the alloy target for forming the granular film is held in a vacuum, it is necessary to manage the change in the Zn concentration in consideration of the composition variation at the time of mass production and the stability of the magnetic characteristics. .

As granular recording layer 20 in Example 1, (50at.% Fe- 50at.% Pt) instead -8 mol% SiO ₂ film (50at.% Co-50at. % Pt) -10mol% SiO 2 film or (40 at. % Co-10 at.% Ni-50 at.% Pt) -10 mol% SiO ₂ film was formed to a thickness of 12 nm. The Ar gas pressure for discharge when forming the granular recording layer 20 was 2.5 Pa. After the granular recording layer 20 is formed, a cap layer 22 made of 50 at.% Co-50 at.% Pt alloy or 50 at.% Ni-50 at.% Fe alloy is formed from 3 nm to 12 nm, and a protective layer mainly composed of silicon nitride. 24 was formed to 2 nm. Furthermore, after maintaining at 300 ° C. for 1 hour in an inert atmosphere substituted with nitrogen, the pressure was returned to atmospheric pressure to form a lubricating layer 26 containing fluorine as a main component.

  After confirming the mechanical flying characteristics, the same head as in Example 1 was used, and during recording, heating was performed using a semiconductor laser 38 with a wavelength of 785 nm of 100 mW. During reproduction, the semiconductor laser 38 was not used, and the electromagnetic conversion characteristics were measured under the condition that the thin film resistor 58 was energized with 60 mW. As a result, when the cap layer 22 was formed to have a thickness of 4 nm or more, the overwrite characteristics were improved to −25 dB or less. In particular, when a 50 at.% Ni-50 at.% Fe alloy is used, when the thickness of the cap layer 22 is about 4 nm to 6 nm, the overwrite characteristic is −30 dB or less and is normalized by the geometric track width. The ratio of the write track width was also in the range of 1.2 to 1.3, and the improvement was remarkable.

  On the other hand, the write track width increased as the cap layer 22 increased from 4 nm to 12 nm. This tendency did not depend on the material of the cap layer. From these results, it is clear that the thickness of the cap layer needs to be at least about 4 nm, but considering the widening of the track width, it is sufficient to form the cap layer about 8 nm even if it is thick.

  Instead of forming a Cr-20 at.% Ti-5 at.% B alloy layer of 5 nm as the grain size control layer 18 in Example 3, a Cr-16 at.% Mo-4 at.% B alloy layer, Cr-30 at.% Mo-4at.% B alloy layer, Cr-30at.% Mo-8at.% B alloy layer, Cr-30at.% Mo-10at.% B alloy layer, Cr-15at.% W-4at.% B alloy layer , Cr-25 at.% W-4 at.% B alloy layer, Cr-25 at.% W-8 at.% B alloy layer, Cr-25 at.% W-10 at. A recording medium was produced. FIG. 13 shows the concentration dependency of the coercive force measured at room temperature in the vertical direction in the crystal grain size control layer. When the B addition concentration contained in the grain size control layer using Cr-30 at.% Mo-B alloy and Cr-25 at.% WB alloy is increased from 8 at.% To 10 at. Magnetic force decreased. From this result, the upper limit of the B addition concentration is preferably about 8 at.

  The magnetic recording medium of the present invention can be used as a heat-assisted magnetic recording medium.

The conceptual diagram of the atomic arrangement | sequence of the (100) plane of the crystal grain diameter control layer which takes a body centered cubic structure. Conceptual diagram except among grain boundaries of the granular recording layer takes a face-centered cubic structure or L1 ₀ structure (100) plane of the atomic arrangement. The conceptual diagram of the atomic arrangement of a crystal grain diameter control layer and a granular recording layer. 1 is a cross-sectional configuration diagram of a magnetic recording medium according to the present invention. The conceptual diagram of a heat assistance record. The figure which shows the relationship between an overwrite characteristic and the thickness of a cap layer. The figure which shows the relationship between the write track width normalized by the geometric track width, and the thickness of the cap layer. The cross-sectional block diagram of the sample for measuring an average crystal grain diameter. 1 is a cross-sectional configuration diagram of a magnetic recording medium according to the present invention. 1 is a cross-sectional configuration diagram of a magnetic recording medium according to the present invention. The figure which shows the relationship between the composition of a granular recording layer, and an overwrite characteristic. The figure which shows the composition of a granular recording layer, and the relationship of So / Nd. The figure which shows the relationship between the B addition density | concentration contained in a crystal grain diameter control layer, and the perpendicular coercive force of the magnetic-recording medium measured at room temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Substrate 12 ... Adhesion layer 14 ... Soft magnetic underlayer 141 ... Soft magnetic underlayer 142 ... Nonmagnetic layer 143 ... Soft magnetic underlayer 144 ... Low thermal conduction intermediate layer 16 ... Crystal orientation control layer 18 ... Crystal grain size control layer DESCRIPTION OF SYMBOLS 19 ... Crystal orientation control and low thermal conductive intermediate layer 20 ... Granular recording layer 22 ... Cap layer 24 ... Protective layer 26 ... Lubricating layer 30 ... Magnetic recording medium 32 ... Slider 34 ... Scattering body 36 for generating near-field light ... Magnetic pole 38 ... Semiconductor laser 40 ... Waveguide core part 42 ... Waveguide clad part 44 ... Thin film coil 46 for magnetic field generation ... Main magnetic pole 48 ... Outflow end 50, 51 ... Magnetic pole 52 ... Auxiliary magnetic pole 54 ... Magnetic reproducing element 56 ... Shield 58 ... Thin film resistors

Claims (5)

A first soft magnetic underlayer formed directly or via an adhesive layer on a rigid substrate;
A second soft magnetic underlayer formed on the first soft magnetic underlayer via a nonmagnetic intermediate layer;
A low thermal conductivity intermediate layer made of an oxide formed on the second soft magnetic underlayer;
A crystal grain size control layer formed on the low thermal conductivity intermediate layer directly or via a crystal orientation control layer;
Mainly composed of crystal grain size was formed through the MgO layer to control layer, Fe-Pt alloy or Co-Pt alloy consisting of a composition which is expected to take an L1 ₀ structure at the stage of progress in ordering A granular recording layer, and
A cap layer made of Fe-Pt alloy or Co-Pt alloy formed on the granular recording layer;
A perpendicular magnetic recording medium comprising: a protective layer formed on the cap layer.   2. The perpendicular magnetic recording medium according to claim 1, wherein a Cr-MB alloy layer to which at least one element selected from the group M consisting of Ti, Mo, and W is added is provided as the crystal grain size control layer. A perpendicular magnetic recording medium.   2. The perpendicular magnetic recording medium according to claim 1, wherein the granular recording layer containing the Fe-Pt alloy as a main component contains Cu.   2. The perpendicular magnetic recording medium according to claim 1, wherein the crystal orientation control layer is made of a W-Co alloy. A soft magnetic underlayer is formed on a rigid substrate via an adhesive layer or directly on the substrate, and the substrate on which the soft magnetic underlayer is formed on the soft magnetic underlayer via a nonmagnetic intermediate layer is taken out into the atmosphere, after heating the substrate in a separate vacuum process, the low thermal conductive intermediate layer made of oxide, the crystal orientation system layer, the crystal grain diameter control layer are formed in this order, the crystal grain diameter control layer through the MgO layer, granular recording layer mainly composed of composed Fe-Pt alloy or Co-Pt alloy composition is expected to take an L1 ₀ structure at the stage of progress in ordering from Fe-Pt alloy or Co-Pt alloy A method of manufacturing a perpendicular magnetic recording medium, comprising: forming a cap layer and a protective layer, followed by heat treatment, and then forming a lubricating layer.

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