JP2006107625A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of developing a high vertical coercive force by decreasing the magnetic coupling between magnetic particles. <P>SOLUTION: The magnetic recording medium is characterized in to include a recording layer comprising a ferromagnetic body expressed in general formula: [(Co<SB>1-m</SB>Pt<SB>m</SB>)<SB>1-n</SB>Cr<SB>n</SB>]<SB>100-x-y</SB>Ta<SB>x</SB>O<SB>y</SB>, wherein m, n are atomic ratios, m is ≥0.2 and ≤0.4, n is ≥0 and ≤0.1, y is ≥16 at.% and ≤26 at.%, and y/x ≥1.7 and ≤2.3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium mounted on various recording devices such as a computer and a video recorder.

As a technique for further increasing the magnetic recording density, a perpendicular magnetic recording system has attracted attention. As a recording medium used for perpendicular magnetic recording, a medium using a recording layer having a granular structure in which SiO ₂ surrounds Co—Pt—Cr crystal grains is disclosed (see Patent Document 1). This medium has a low noise characteristic because the magnetic interaction between the magnetic particles is reduced if each crystal grain of the ferromagnetic Co—Pt—Cr is completely divided by SiO ₂ . Is expected to be obtained. In addition, it is considered that the high magnetocrystalline anisotropy of the Co—Pt—Cr crystal with the c-axis oriented in the direction perpendicular to the film surface exhibits a high perpendicular coercive force by reducing the magnetic interaction between magnetic particles. It has been.
JP 2003-178413 A

As a method for producing the recording layer, sputtering using a material in which a Co—Pt—Cr alloy and SiO ₂ are mixed has been reported. When a film is formed using a target made of a mixed material of metal and oxide, a film having a granular structure in which the metal particles surround the oxide can be obtained.

However, since the inclination parameter α (defined as α = 4π (dM / dH)) of the MH loop in the vertical direction of the obtained film is about 2, a large magnetic coupling between the particles Seems to remain. Moreover, the possibility that the constituent elements of the oxide are mixed in the metal particles cannot be denied. When Si is mixed into magnetic particles in a film formed using a target made of a material in which a Co—Pt—Cr alloy and SiO ₂ are mixed as described above, the perpendicular coercive force of the film is greatly reduced. It is thought to let you. When it is assumed that mixing of oxide elements into the magnetic particles is unavoidable, it is necessary to minimize the degree of deterioration of the perpendicular coercive force of the film to be formed.

  An object of the present invention is to provide a magnetic recording medium that can exhibit a high perpendicular coercive force by reducing the magnetic coupling between magnetic particles.

The magnetic recording medium according to the present invention has the following general formula [(Co _1-m Pt _m ) _1-n Cr _n ] _100-xy Ta _x O _y
(Where m and n are atomic ratios, m is from 0.2 to 0.4, n is from 0 to 0.1, y is from 16 at.% To 26 at.%, Y / x is 1.7. The above is 2.3 or less)
It has the recording layer which consists of a ferromagnetic material represented by these.

  In the present invention, the recording layer preferably has perpendicular magnetic anisotropy. In the present invention, the recording layer is preferably formed under an Ar gas pressure atmosphere of 6 Pa or more and 16 Pa or less.

  The magnetic recording medium of the present invention can reduce the magnetic coupling between magnetic particles and can exhibit a high perpendicular coercive force.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing an example of a magnetic recording medium according to the present invention. The substrate 1 has a structure in which a base layer 2, a Co—Pt alloy crystal grain, a recording layer 3 made of Ta ₂ O ₅ surrounding the base layer 2, and a protective layer 4 are sequentially formed.

  As the substrate 1, any material may be used as long as it has a mechanical strength that is not easily broken and has a smooth surface. Examples thereof include glass, metal, and plastic. The underlayer 2 may not be provided and may have a multilayer structure. For example, a soft magnetic layer such as Ni—Fe used as an auxiliary during recording, or a nonmagnetic film such as Pt or Ru for ensuring the crystal orientation of the recording layer can be used. The thickness of the underlayer 2 is not particularly limited.

  The protective layer 4 may not be provided and may have a multilayer structure. For example, a hard film such as carbon or TiN, and a liquid or solid lubricant may be used on the outermost surface. However, since it is preferable from the viewpoint of recording characteristics that the distance from the tip of the magnetic head to the surface of the recording layer is as small as possible, these thicknesses are preferably as thin as possible.

The recording layer 3 is a film having a granular structure composed of Co—Pt alloy crystal grains and Ta ₂ O ₅ grain boundaries surrounding the crystal grains. Although it is difficult to know the state of crystal grains and grain boundaries and the details of each elemental composition separately, the element composition of the entire layer is that O is 16 at. % Or more and 26 at. %, The ratio of O to Ta is 1.7 to 2.3 in terms of atomic ratio, and the total of Co and Pt is 90 at. % Or more and Cr is 10 at. %, And the ratio of Pt in the total of Co and Pt needs to be 0.2 or more and 0.4 or less in terms of atomic ratio.

  O is 16 at. If it is less than%, the absolute amount of oxide is insufficient to form a nonmagnetic grain boundary between crystal grains, and O is 26 at. When it exceeds%, it becomes difficult to maintain the crystal orientation of the crystal grains.

  If all of O and Ta in the film form a Ta oxide and do not exist in other forms, the ratio of O and Ta is 2.5 in atomic ratio. When the ratio of O to Ta in the film is less than 1.7, a significant portion of Ta atoms enter the CoPt alloy magnetic particles in a metallic state, and deteriorate the magnetic properties of the recording layer.

  In order to increase the ratio of O to Ta in the film, there is a method of increasing the Ar gas pressure at the time of film formation or mixing oxygen gas with Ar gas, but the Ar gas pressure at the time of film formation is extremely high. In other cases, it is difficult to maintain the crystal orientation of the crystal grains of the CoPt alloy.

  Further, among all elements except Ta and O, that is, elements considered to constitute crystal grains, the total of Co and Pt is 90 at. If it is less than%, the perpendicular magnetic anisotropy deteriorates. However, for the purpose of reducing noise, etc., a total of 10 at. %, Elements other than Co and Pt, such as Cr, can be added.

  Further, in the CoPt-based alloy, a high coercive force can be obtained when the atomic ratio of Pt is in the range of 0.2 to 0.4 in the total of Co and Pt. In any case, the coercive force deteriorates. Therefore, in the total of Co and Pt in the film, the ratio of Pt needs to be 0.2 or more and 0.4 or less in terms of atomic ratio.

[Preliminary study]
For a CoPt alloy, the Pt ratio is set to 0 at. % To 53.5 at. A CoPt alloy film having a thickness of about 30 nm and varied in the range of% was fabricated, and its perpendicular coercive force was examined. The results are shown in FIG. A high coercive force of 2.5 Oe or more can be obtained when the Pt ratio is in the range of 0.2 to 0.4, but the perpendicular coercive force deteriorates when the Pt ratio is smaller or larger than this range. I understand.

  Hereinafter, the present invention will be specifically described based on examples.

[Example 1]
In this example, the magnetic recording medium shown in FIG. 3 was produced. A 2.5-inch glass disk is used as the substrate 11, a carbon film 12 having a thickness of about 2 nm at an Ar gas pressure of 1 Pa, a Pt film 13 having a thickness of about 5 nm at an Ar gas pressure of 0.07 Pa, and a thickness at an Ar gas pressure of 3 Pa. A Ru film 14 having a thickness of about 15 nm was sequentially formed as an underlayer. Subsequently, using a target with a volume ratio of Co ₈₀ Pt ₂₀ (at.%) Of 70% and a volume ratio of Ta ₂ O ₅ of 30%, the thickness is increased by DC magnetron sputtering at an Ar gas pressure of 1 to 20 Pa. A recording layer 15 having a thickness of about 15 nm was formed. The substrate is not heated in the formation of all layers.

  The elemental composition in the recording layer of the medium was measured by photoelectron spectroscopy after sputter etching of the surface 5 nm, and the perpendicular coercive force was measured by a sample vibration type magnetometer. FIG. 4 shows the amounts of Ta and O elements in the film with respect to the Ar gas pressure when the recording layer is formed. It can be seen that the amount of elements in the film is changed by changing the Ar gas pressure when the recording layer is formed. The amount of Ta is not greatly changed and is 8 to 12 at. %, The amount of O greatly increases as the Ar gas pressure increases. FIG. 6 shows changes in the value of the perpendicular coercive force Hc with respect to the amount of O in the film. O amount is 16 to 26 at. In the% range, a high perpendicular coercive force of 3 kOe or more was developed. FIG. 6 shows changes in the value of the perpendicular coercive force Hc with respect to the atomic ratio of O and Ta in the film. It can be seen that a high perpendicular coercive force of 3 kOe or higher appears in the range of 1.7 to 2.3. In the sample showing the maximum Hc, the slope parameter α of the MH loop in the vertical direction of the film was as small as 1.3.

[Example 2]
After carbon, Pt, and Ru underlayers were formed on a glass disk substrate in the same manner as in Example 1, a Cr chip was placed on the surface of the target used in Example 1, and DC magnetron sputtering was used. A recording layer having a thickness of about 15 nm was formed at an Ar gas pressure of 5 Pa. The elemental composition in this film is Co48.4 at. %, Pt 13.6 at. %, Cr 3.8 at. %, Ta8.3 at. %, O25.9 at. %, And the ratio of Cr in the elements other than Ta and O is 5.8 at. %Met. The Hc of this film was 2688 Oe.

  By adding Cr in addition to Co and Pt as metal elements to the recording layer, Hc was reduced, but the value of 2.5 kOe or more was maintained, and elements other than Co and Pt were used as constituent elements of the crystal grains. It can be seen that good magnetic properties can be maintained even when added in a small amount.

[Comparative Example 1]
After carbon, Pt, and Ru underlayers were formed on a glass disk substrate in the same manner as in Example 1, the volume ratio of Co ₈₀ Pt ₂₀ (at.%) Was 70% and the volume ratio of SiO ₂ was Using a 30% target, a recording layer having a thickness of about 15 nm was formed at an Ar gas pressure of 3 to 10 Pa. The perpendicular coercive force changed depending on the film-forming Ar gas pressure, and a maximum value (a value close to the disclosure of Reference 1) was obtained at 7 Pa. The sample showing the maximum Hc had a value of the slope parameter α of the MH loop of 2.0, which was larger than that of Example 1.

[Comparative Example 2]
After carbon, Pt, and Ru underlayers were formed on a glass disk substrate in the same manner as in Example 1, a Cr ₂ O ₃ chip was placed on the target surface of Co ₈₀ Pt ₂₀ (at.%). A recording layer having a thickness of about 15 nm was formed at a Ar gas pressure of 3 to 10 Pa by a DC magnetron sputtering method. The perpendicular coercive force changed depending on the film-forming Ar gas pressure, and Hc was maximized at 5 Pa. The sample showing the maximum Hc had a MH loop slope parameter α of 1.9, which was larger than Example 1.
In FIG. 7, the evaluation result of Example 1, the comparative example 1, and the comparative example 2 is shown collectively.

As described above, a medium using Ta ₂ O ₅ as an oxide constituting the recording layer can be used as an oxide constituting the recording layer by adjusting Ta and O in the film to an appropriate amount according to the film forming conditions. Compared with the medium using SiO ₂ or Cr ₂ O ₃ , a high perpendicular coercive force and a small MH loop slope parameter α were shown. This suggests that the medium using Ta ₂ O ₅ oxide has a smaller magnetic interaction between the magnetic particles than the medium using SiO ₂ or Cr ₂ O ₃ . In the recording layer, Cr 3.8 at. % (5.8 at.% In the elements excluding Ta and O) also showed a high perpendicular coercive force of 2.5 kOe or more.

1 is a cross-sectional view showing an example of a magnetic recording medium according to the present invention. The figure which shows the change of the perpendicular coercive force of a film | membrane with respect to the atomic ratio of Pt in a CoPt alloy film. Sectional drawing which shows the magnetic recording medium produced in the Example. FIG. 4 is a diagram showing the element amounts of Ta and O in the film with respect to the Ar gas pressure when forming the recording layer for the magnetic recording medium of Example 1. The figure which shows the change of the value of the perpendicular coercive force Hc with respect to the amount of O in a film | membrane about the magnetic recording medium of Example 1. FIG. FIG. 4 is a graph showing changes in the value of the perpendicular coercive force Hc with respect to the atomic ratio of O and Ta in the film for the magnetic recording medium of Example 1. The figure which shows collectively the evaluation result of Example 1, the comparative example 1, and the comparative example 2. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Underlayer, 3 ... Recording layer, 4 ... Protective layer, 11 ... Substrate, 12 ... Carbon film, 13 ... Pt film, 14 ... Ru film, 15 ... Recording layer.

Claims (3)

The following general formula [(Co _1-m Pt _m ) _1-n Cr _n ] _100-xy Ta _x O _y
(Where m and n are atomic ratios, m is from 0.2 to 0.4, n is from 0 to 0.1, y is from 16 at.% To 26 at.%, Y / x is 1.7. The above is 2.3 or less)
A magnetic recording medium comprising a recording layer made of a ferromagnetic material represented by:   The magnetic recording medium according to claim 1, wherein the recording layer has perpendicular magnetic anisotropy.   The magnetic recording medium according to claim 1, wherein the recording layer is formed under an Ar gas pressure atmosphere of 6 Pa to 16 Pa.

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