JP4623594B2 - Perpendicular magnetic recording medium - Google Patents

Description

  The present invention relates to a magnetic recording medium, and more particularly to a perpendicular magnetic recording medium used in various magnetic recording devices including an external storage device of a computer.

  In recent years, magnetic recording is shifting from an in-plane recording method to a perpendicular magnetic recording method with an increase in recording density. In the perpendicular magnetic recording system, the recording magnetization is perpendicular to the in-plane direction of the recording medium. A perpendicular magnetic recording medium (or perpendicular medium for short) used for perpendicular magnetic recording is mainly composed of a magnetic recording layer of a hard magnetic material, an underlayer for orienting the recording magnetization of the magnetic recording layer in the vertical direction, and a magnetic recording layer. It is composed of a protective layer for protecting the surface, and a backing layer of a soft magnetic material that plays a role of concentrating the magnetic flux generated by the magnetic head used for recording on the recording layer. Since recording is possible without a backing layer, the structure may be omitted.

  As the fine structure of the magnetic recording layer, a structure in which each ferromagnetic particle is magnetically separated and a structure in which a ferromagnetic crystal particle is surrounded by a nonmagnetic grain boundary component is generally used. It is done. In-plane magnetic recording media that are generally used today (abbreviated to in-plane media) use ferromagnetic materials containing at least Co and Cr, such as CoPtCr, CoPtCrTa, and CoPtCrB, as the magnetic recording layer material. Such a structure is realized by segregating Cr and lowering the concentration of Co, the magnetic element, relative to the crystal grains.

These materials can also be used as magnetic recording layer materials for perpendicular media by controlling the crystal orientation using an underlayer or the like and directing the easy axis of magnetization in the vertical direction, as in Patent Document 1, for example. is there. On the other hand, in addition to the materials used in the in-plane medium, CoPtCr—SiO ₂ disclosed in Patent Document 2 and [Co / Pt] n-SiO ₂ has been proposed. These are greatly different from the general in-plane medium materials listed above in that oxides and nitrides are employed as nonmagnetic grain boundary components.

  The characteristic required for magnetic recording media is how many signals can be written, that is, high recording density. To achieve this, the magnetic particles in the magnetic recording layer are made finer, the magnetic particles magnetically Reducing the interaction is effective. However, if the particles are further miniaturized, the thermal stability deteriorates due to so-called thermal fluctuation, so that it is necessary to increase the perpendicular magnetic anisotropy energy Ku of the magnetic particles.

According to Non-Patent Document 1, in a vertical medium, CoPtCr—SiO ₂ to which an oxide is added is more effective in intergranular interaction than CoPtCrB, which is a material used in a conventional in-plane medium. It has been reported that it is excellent in both reduction and high Ku value characteristics. For this reason, it is considered that a hard magnetic material containing oxide or nitride as a nonmagnetic grain boundary component is more advantageous for increasing the recording density of a perpendicular medium.

  On the other hand, in the HDD, it is known that the head magnetic field strength required for recording is proportional to the Ku value. Therefore, when the Ku value is increased, the magnetic field intensity also increases, and it becomes difficult to perform saturation recording in which the magnetization is completely directed in one direction. Further, if the degree is significant, recording is impossible. Problems arise. Further, as the particle (particle size) is further refined, the demagnetizing field applied to the particle is reduced, which also increases the magnetization reversal field. That is, the refinement of the magnetic particles and the increase in the Ku value for increasing the recording density are in a trade-off relationship of deteriorating the writing performance of the magnetic recording medium. From the above background, there is a need for a method for improving the signal quality and stability of a magnetic recording medium while maintaining the writing performance.

  To solve this problem, for example, Patent Document 4 proposes a structure in which ferromagnetic particles having a large Ku value and soft magnetic particles having a very small Ku value are stacked and directly coupled, and the Ku value is very small. The reversal magnetic field is lowered by the effect of the soft magnetic layer, and the writing performance is successfully improved. Further, in Non-Patent Document 2, the switching magnetic field is further reduced by changing (weakening) the exchange coupling force between the particles with a large difference in Ku value as in Patent Document 4 Simulation results have been reported that can be achieved.

  The present inventors also made a theoretical calculation by laminating two layers having different Ku values, and changing the exchange coupling force of both layers. When the exchange coupling force was moderately weakened, the layers were directly coupled (very exchangeable). As a result, the reversal magnetic field can be reduced as compared with the case of high coupling force. This is because both layers do not cause magnetization reversal at the same time, a layer with a small Ku value first undergoes magnetization reversal, and a layer with a large Ku value that is weakly exchange-coupled accordingly starts magnetization reversal. This is because the reversal magnetic field is lower than when both layers are directly coupled (of course, compared with a single layer having a large Ku value). When the exchange coupling force is set to a value that can minimize the reversal magnetic field, the energy barrier, which is an indicator of thermal stability, slightly decreases, but the effect of reducing the reversal magnetic field is more significant. This magnetic recording layer is considered to be suitable for a perpendicular magnetic recording medium having both writing performance and high density performance.

  The key to actually realizing a magnetic recording medium having the above-described configuration is a method for controlling the exchange coupling force of both layers. As one method, a nonmagnetic layer is provided between both layers. A method of inserting can be considered. As a medium having a magnetic recording layer having a structure in which a nonmagnetic layer is inserted between two magnetic layers, the purpose of which has been proposed in, for example, Patent Document 5 is different. In Patent Document 5, when the thickness of each magnetic layer is a relatively large magnetic layer thickness of about several tens of nanometers, the epitaxial growth of the upper layer is not hindered in order to reduce the magnetic interaction in the thickness direction. A non-magnetic intermediate layer is selected and inserted. On the other hand, in Patent Document 6, the magnetic recording layer is divided by an amorphous intermediate layer, and the epitaxial growth is interrupted to maintain the magnetization reversal volume that maintains the thermal stability, while maintaining the magnetic recording medium noise. We propose a method to reduce this.

  By the way, when a thick magnetic layer as described in Patent Document 5 is applied, the spacing between the soft magnetic underlayer and the magnetic head must be increased, which is disadvantageous in terms of writing performance. It is. Patent Document 5 does not describe the case where an oxide is included as the magnetic recording layer material. The presence of oxides (ie, elemental oxygen) can have a significant impact on the bonding interface, and layers inserted between such magnetic layers should be fully considered. Conceivable.

  Further, in Patent Document 6, since the easy axes of the upper and lower layers are different, there is a demerit that the signal output of the vertical component is smaller than in the case of the same in the vertical direction, and the epitaxial growth is interrupted in the amorphous layer. Therefore, the separation structure of the magnetic particles and nonmagnetic components of the magnetic layer formed immediately above the amorphous layer is disturbed, that is, it is difficult to consistently grow the magnetic particles in the film thickness direction. Met.

  As described above, many problems to be solved remain in realizing a perpendicular magnetic recording medium having good writing performance, high signal quality (that is, high recording resolution) and stability.

Patent Documents 7 and 8 also provide a perpendicular magnetic recording medium in which a coupling layer or an intermediate layer is provided between two magnetic recording magnetic layers, and the magnetic recording magnetic layers are ferromagnetically coupled or antiferromagnetic exchange coupled. However, for the convenience of explanation, details of Patent Document 7 and Patent Document 8 will be described later.
JP 2002-358615 A JP 2003-178812 A JP-A-2005-7401 JP 2005-222675 A JP-A-7-176027 JP 2003-157516 A JP 2006-48900 A JP 2004-39033 A T. Oikawa et al., “Microstructure and Magnetic Properties of CoPtCr-SiO2 Perpendicular Recording Media”, IEEE TRANSACTIONS ON MAGNETICS, VOL.38, NO.5, SEPTEMBER 2002, p.1976-1978 RHVictora et al., "Exchange Coupled Composite Media for Perpendicular Magnetic Recording", IEEE TRANSACTIONS ON MAGNETICS, VOL.41, NO.10, OCTOBER 2005, p.2828-2833

  The present invention has been made in view of the above points, and an object of the present invention is to provide a perpendicular magnetic recording medium excellent in high recording resolution, high signal stability, high writing performance, and uniform characteristics. .

The above-mentioned subject is achieved by the following. That is, according to the present invention, in a perpendicular magnetic recording medium in which at least an underlayer, a magnetic recording layer, and a protective layer are sequentially laminated on a nonmagnetic substrate, the magnetic recording layer includes the first magnetic layer and the exchange coupling control. The first magnetic layer and the second magnetic layer have different perpendicular magnetic anisotropy constants (Ku), and include at least a structure in which the first magnetic layer and the second magnetic layer are sequentially stacked. includes the larger the nonmagnetic oxide of at least Ku value, and the exchange coupling control layer is made of Pt-SiO ₂ or NiFeCr-SiO _2, the thickness thereof and wherein to Rukoto and less than 2nm (Claim 1).

Further, as an embodiment of the invention of claim 1, the inventions of claims 2 to 7 below are preferable. That is, in the perpendicular magnetic recording medium according to claim 1, Ku value of one magnetic layer before Symbol first magnetic layer and the second magnetic layer is at least 1 × 10 ⁶ erg / cm ³ or more, The Ku value of the other magnetic layer is 1 × 10 ⁵ erg / cm ³ or less (claim 2 ).

3. The perpendicular magnetic recording medium according to claim 1, wherein crystal grains in the magnetic recording layer penetrate through the first magnetic layer, the exchange coupling control layer, and the second magnetic layer to form an underlayer interface. have grown structures columnar from, and each particle of the columnar shall formed by magnetically separated by non-magnetic components (claim 3).

The perpendicular magnetic recording medium according to any one of claims 1 to 3 , wherein the oxide contained in the magnetic recording layer is at least one element selected from Si, Ti, Cr, and Co. (Claim 4 ).

Further, in a perpendicular magnetic recording medium according to any one of the claims 1 to 4, wherein the crystal grains of the first magnetic layer and the second magnetic layer is a hexagonal close-packed structure crystal structure (hcp structure) Alternatively, it has a crystal structure mainly composed of a crystal structure (fcc) having a face-centered cubic lattice structure (claim 5 ).

Further, in the perpendicular magnetic recording medium according to any one of claims 1 to 5 , the saturation magnetization of the magnetic layer having a large Ku value is Msh, and the saturation magnetization of the other magnetic layer having a small Ku value is Msl. Then, Msh <Msl is satisfied (claim 6 ).

Further, in a perpendicular magnetic recording medium according to any one of the claims 1 to 6, the saturation magnetization Msl of small magnetic layer of the Ku value is equal to or is at least 800 emu / cc or more (claim 7 ).

  Next, the operational effects of the present invention will be described generally. Details will be described later. By applying a magnetic layer material having a large Ku value and containing at least an oxide as the nonmagnetic component of the magnetic recording layer, it is possible to have a potential excellent in signal quality and stability. Further, by combining with a layer having a very low Ku value and inserting an exchange coupling control layer between both layers, it becomes possible to have good writing performance.

  At this time, the exchange coupling control layer also includes an oxide similar to that of the magnetic layer so that the crystal particles are surrounded by the oxide, so that the magnetic layer immediately above reflects the structure. A structure in which magnetic grain boundary components are separated can be formed. As the crystalline metal at this time, Pt or Pd, or an alloy containing Pt or Pd as a main component can be used.

  By using such a metal or alloy, the exchange coupling force with the upper and lower layers can be easily controlled for each particle. This is because Pt or Pd is superior in oxidation resistance compared to other nonmagnetic elements, and is non-magnetic by itself but has a large amount of polarization caused by lamination with a magnetic material such as Co. It is thought to be caused by. That is, the exchange coupling force between the upper and lower layers can be stably maintained in a wider range of film thickness than that of other nonmagnetic elements of 1.5 nm or more that can ensure sufficient film thickness uniformity.

  In addition, an alloy of an element selected from Co, Ni, and Fe and a nonmagnetic metal can be preferably used. The metal or alloy easily forms a separated structure of crystal particles and oxide as described above. That is, a good coupling interface can be formed between crystal grains of the magnetic layer and the exchange coupling control layer. Another advantage is that the exchange coupling force can be controlled by the composition ratio with the nonmagnetic element. When the crystal grains are a single nonmagnetic element or an alloy of nonmagnetic elements, the exchange coupling force is controlled only by the film thickness. For example, when the exchange coupling force is optimal at a relatively thin film thickness of 0.5 nm or less, the distribution of bonding force between particles due to the film thickness distribution becomes large. According to the present invention, the exchange coupling force can be controlled even at a relatively thick film thickness of 0.5 to 2.0 nm, which can ensure sufficient film thickness uniformity.

  Further, Pt or Pd has an fcc crystal structure, and an alloy of an element selected from Co, Ni and Fe and a nonmagnetic metal can also be obtained by increasing the composition ratio of Co or Ni to increase the crystal structure of hcp or fcc. The fcc (111) or hcp (002) of the exchange coupling control layer can be epitaxially grown on the hcp (002) or fcc (111) of the magnetic layer.

  As described above, it is possible to realize a perpendicular magnetic recording medium excellent in high recording resolution, high signal stability, high writing performance, and characteristic uniformity.

  Patent Document 7 discloses a perpendicular magnetic recording medium in which a coupling layer is provided between two magnetic recording magnetic layers having different Ku values, and the magnetic recording layer magnetic layers are ferromagnetically exchange coupled. However, as in the present invention, there is no description about the exchange coupling control layer mainly containing at least Pt or Pd, and there is no description about the case where the coupling layer contains an oxide.

  Further, Patent Document 8 discloses a perpendicular magnetic recording medium in which an intermediate layer is provided between two magnetic recording magnetic layers, and the magnetic recording magnetic layers are antiferromagnetic exchange coupled, and the intermediate layer (M1) is also disclosed. Non-magnetic metal materials such as Ru, Re, Rh, Ir, Tc, Au, Ag, Cu, Si, Fe, Ni, Pt, Pd, Cr, Mn, and Al are disclosed as materials (Patent Literature) 8 paragraphs [0052] to [0054]). However, the Pt or Pd described in Patent Document 8 is merely listed as an example of a nonmagnetic metal material, and there is no description regarding the technical significance of the Pt or Pd of the present invention. In addition, Patent Document 8 has no description relating to other constituent requirements and operational effects of the present invention, including two magnetic recording magnetic layers and oxides having different Ku values.

  According to the present invention, as one magnetic layer material in the magnetic recording layer, at least a material having a large Ku value and excellent magnetic separation and having an oxide as a nonmagnetic grain boundary component is used. It is possible to provide a perpendicular magnetic recording medium that employs a structure in which another magnetic layer made of a material having a very low Ku value is disposed above and below, and in which exchange coupling between both layers is appropriately controlled. Thus, a perpendicular magnetic recording medium excellent in high recording resolution, high signal stability, high writing performance, and characteristic uniformity can be provided.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a perpendicular magnetic recording medium according to an embodiment of the present invention, showing a configuration example of a so-called double-layer perpendicular medium having a soft magnetic backing layer. In the perpendicular magnetic recording medium, a soft magnetic backing layer 2, a seed layer 3, an underlayer 4, a magnetic recording layer 5, and a protective layer 6 are sequentially laminated on a nonmagnetic substrate 1, and further a liquid is placed on the protective layer 6. The lubricating layer 7 is formed and configured. In the present invention, the magnetic recording layer 5 is characterized. As shown in the figure, the magnetic recording layer 5 includes at least a magnetic layer (1) 5-1, an exchange coupling control layer 5-2, and a magnetic layer (2) 5-3, and the exchange coupling control layer 5-2 includes It has a structure inserted between the magnetic layer (1) 5-1 and the magnetic layer (2) 5-3.

  In the perpendicular magnetic recording medium of the present invention, as the non-magnetic substrate (non-magnetic substrate) 1, an Al alloy plated with NiP, chemically strengthened glass, crystallized glass, or the like used for a normal magnetic recording medium is used. it can. When the substrate heating temperature is suppressed to 100 ° C. or less, a plastic substrate made of a resin such as polycarbonate or polyolefin can be used. In addition, a Si substrate can also be used.

  The soft magnetic backing layer 2 is preferably formed to improve the recording / reproducing characteristics by controlling the magnetic flux from the magnetic head used for magnetic recording, and the soft magnetic backing layer can be omitted. As the soft magnetic backing layer, crystalline NiFe alloy, Sendust (FeSiAl) alloy, CoFe alloy, etc., microcrystalline FeTaC, CoFeNi, CoNiP, or the like can be used. In order to improve the recording capability, it is preferable that the soft magnetic underlayer has a larger saturation magnetization. Therefore, in the case of a crystalline NiFe alloy or CoFe alloy, it is preferable to contain 20% or more of Fe. Further, by using an amorphous Co alloy such as CoNbZr or CoTaZr, better electromagnetic conversion characteristics can be obtained. In order to obtain a large saturation magnetization as described above, the Co content is preferably 80% or more.

  The optimum value of the thickness of the soft magnetic backing layer 2 varies depending on the structure and characteristics of the magnetic head used for magnetic recording. However, when it is formed by continuous film formation with other layers, the balance with productivity is required. It is desirable that it is 10 nm or more and 500 nm or less. This is not the case when the non-magnetic substrate is previously formed by plating or the like before forming the other layers, and the thickness can be increased to several hundred nm to several μm. Since the saturation magnetization of the soft magnetic underlayer 2 is large, there is a possibility that noise is generated when the magnetic domain is disturbed. Therefore, a magnetic domain control layer can be provided.

  The seed layer 3 is a layer that is preferably formed immediately below the underlayer in order to improve the orientation of the underlayer 4 or to reduce the particle size, and the seed layer 3 can be omitted. The seed layer 3 can be made of a nonmagnetic material or a soft magnetic material, but from the viewpoint of recording capability, it is desirable to reduce the distance between the magnetic head and the soft magnetic layer. Therefore, a soft magnetic material is preferably used so that the seed layer 3 functions in the same manner as the soft magnetic backing layer, and it is desirable to make it as thin as possible when using a nonmagnetic material.

  As a material for the seed layer 3 exhibiting soft magnetic properties, Ni-based alloys such as NiFe, NiFeNb, NiFeSi, NiFeB, and NiFeCr can be used. Also, Co alone, Co-based alloys such as CoB, CoSi, CoNi, CoFe, CoNiFe, CoNiFeSi, or the like can be used. The crystal structure is preferably an hcp or fcc structure. In the case where Fe is contained, if the content is large, a bcc structure is likely to be formed. Therefore, the Fe content is preferably 20% or less. As a material for the seed layer 3 exhibiting nonmagnetic properties, Ni-based alloy such as NiP, Co-based alloy such as CoCr, Pt, Ta, Ti, or the like can be used.

  The underlayer 4 is a layer that is preferably formed immediately below the magnetic recording layer 5 in order to suitably control the crystal orientation, crystal grain size, grain size distribution, and grain boundary segregation of the magnetic recording layer 5. The crystal structure can be appropriately changed by the magnetic recording layer 5. When the magnetic recording layer 5 has an hcp or fcc structure, it is preferable that the underlayer also has an hcp or fcc crystal structure. As the material of the underlayer 4, Ru, Rh, Os, Ir, Pt or the like is preferably used. An alloy containing Ru, Rh, Os, Ir, or Pt as a main component is also used. Further, in order to break the magnetic interaction between the magnetic recording layer 5 and the soft magnetic backing layer 2, the underlayer 4 is preferably nonmagnetic. In order to reduce the magnetic spacing between the magnetic head and the soft magnetic backing layer 2, the film thickness is preferably thin, and a film thickness of 3 to 30 nm is preferably used.

  The magnetic recording layer 5 includes at least a structure in which the magnetic layer (1) 5-1, the exchange coupling control layer 5-2, and the magnetic layer (2) 5-3 are sequentially stacked. The magnetic layer (1) 5-1 having a large Ku value and the magnetic layer (2) 5-3 having a small Ku value are magnetically weakly coupled via the exchange coupling control layer 5-2, and the magnetic layer (1 ) The exchange coupling force between 5-1 and the magnetic layer (2) 5-3 is controlled by the exchange coupling control layer 5-2.

The magnetic layer (1) 5-1 having a large Ku value is a layer that bears the Ku value of the entire magnetic recording layer 5, and a material having as large a Ku value as possible is preferable. The Ku value is preferably at least 1 × 10 ⁶ erg / cm ³ or more. As a material having an easy axis of magnetization perpendicular to the substrate surface and exhibiting such performance, a material in which ferromagnetic particles are separated by a nonmagnetic grain boundary component of an oxide is used. For example, a material obtained by adding an oxide to a ferromagnetic material containing at least CoPt, such as CoPtCr—SiO ₂ or CoPt—SiO ₂ , is preferably used. In addition, a multilayer multilayer film in which Co and Pt containing an oxide in at least one of them are laminated many times with a thin film of 2 nm or less can be used. In any case, it is preferable to have a crystal structure mainly composed of a hexagonal close-packed structure (hcp structure) or a face-centered cubic lattice structure (fcc). The film thickness (total film thickness in the case of a multilayered multilayer film) is preferably made as thin as possible within a range in which the required Ku value can be ensured in terms of magnetic spacing, and is preferably 20 nm or less, more preferably 5 to 10 nm. To do.

  The exchange coupling control layer 5-2 includes a crystalline metal or alloy and an oxide. As the material of the crystalline metal or alloy, Pt or Pd or an alloy thereof is used. As the crystalline alloy, an alloy of an element selected from Co, Ni, and Fe and a nonmagnetic metal can also be used. The crystal structure of the crystalline part can be an fcp structure or an fcc structure. The oxide serves as a grain boundary component of the exchange coupling control layer, and is preferably added to promote continuous grain growth from the lower magnetic layer (1) 5-1.

  The strength of the exchange coupling force between the upper and lower magnetic layers (1) 5-1 and (2) 5-3 is most easily controlled by changing the film thickness of the exchange coupling control layer 5-2. be able to. If the film thickness is too thin, the uniformity may be impaired, and if it is too thick, the upper and lower layers are disconnected and the desired effect is not achieved. Therefore, the practical film thickness is preferably about 0.5 nm to 2.0 nm.

  In addition to the film thickness, the bonding force can be controlled by the alloy composition. In the case of an alloy containing Pt or Pd, for example, a method can be used in which the film thickness is 1.0 nm that can ensure uniformity, and another nonmagnetic element is added to Pt or Pd. The addition of the magnetic element seems to be unfavorable because it also works in the direction of strengthening the interaction between particles together with the exchange coupling force of the upper and lower layers, but in the present invention, the exchange coupling control layer contains an oxide, Since the interaction between particles can be made sufficiently small, application is possible.

  In the case of an alloy of an element selected from Co, Ni, and Fe and a nonmagnetic metal, the exchange coupling force can be similarly controlled by controlling the composition. For example, when Cr is applied as the nonmagnetic element, CoCr, NiFeCr, CoNiFeCr, and the like are given as examples, and the binding force can be controlled by changing the ratio of Cr to the magnetic elements Co, Ni, and Fe. .

Since the magnetic layer (2) 5-3 having a small Ku value mainly plays a role of reducing the magnetization reversal magnetic field, a material having a Ku value as small as possible is preferable. The Ku value is preferably 1 × 10 ⁵ erg / cm ³ or less. Mainly, a material that exhibits a soft magnetic property with a single layer, such as Co, NiFe, and CoNiFe, is preferably used. Since these materials have a very large saturation magnetization Ms, the interaction between particles is large. Therefore, like the magnetic layer (1) 5-1, it is preferable to add a material that becomes a nonmagnetic grain boundary component. As the nonmagnetic grain boundary component, an oxide is preferably used as in the magnetic layer (1) 5-1.

  In order to effectively reduce the magnetization reversal field of the entire magnetic recording layer 5 by increasing its own demagnetizing field, the magnetic layer (2) 5-3 has Ms higher than that of the magnetic layer (1) 5-1. Large and thin films are preferred. That is, when the saturation magnetization of the magnetic layer (1) 5-1 having a large Ku value is Msh and the saturation magnetization of the other magnetic layer (2) 5-3 having a small Ku value is Msl, Msh <Msl. Msl is more preferably 800 emu / cc or more. The film thickness is preferably 10 nm or less, more preferably 5 nm or less.

  When the magnetic layer (1) 5-1, the exchange coupling control layer 5-2, and the magnetic layer (2) 5-3 are viewed comprehensively, one crystal grain that is the minimum unit of magnetization reversal is the magnetic layer (1 ) 5-1 through the exchange coupling control layer 5-2 and the magnetic layer (2) 5-3, and has a structure in which the pillar-shaped magnetic particles are separated from each other by a non-magnetic component. It is preferable that it is a structure. With such a structure, the interaction between particles is reduced, and the magnetization directions of the magnetic layer (1) 5-1 and the magnetic layer (2) 5-3 with respect to the film surface in the residual magnetization state after recording. Can match in the vertical direction.

  The protective layer 5 can be a conventionally used protective film, for example, a protective film mainly composed of carbon. Instead of a single layer, for example, a double-layer carbon having different properties, a metal film and a carbon film, or a laminated film of an oxide film and carbon can be used. For the liquid lubricant layer 7, for example, a perfluoropolyether lubricant can be used.

Next, based on FIGS. 2-7, the Example of this invention is described with a comparative example. These examples are merely representative examples for suitably explaining the magnetic recording medium of the present invention, and are not limited thereto. In the following description, the pressure is expressed in units of Torr. However, when this is converted into Pa (Pascal) which is an SI unit, it may be converted by 1 Torr = 133 Pa. Furthermore, although the perpendicular magnetic anisotropy energy Ku value (previously described) is expressed in units of erg / cm ³ , when this is converted to SI unit J / m ³ , 1 erg / cm ³ (erg / may be converted by ^{cc) = 0.1 J / m 3} . Further, when the saturation magnetization unit emu / cc is converted to the SI unit, it may be converted by 1 emu / cc = 0.0005125 Wb / m ² .

Example 1
A disc-shaped glass substrate having a smooth surface is used as the non-magnetic substrate 1, and after cleaning, this is introduced into a sputtering apparatus, and a Ta target is used to form 5 nm of Ta under an Ar gas pressure of 2.3 mTorr. Using a Pt target, 10 nm of Pt was formed under an Ar gas pressure of 2.3 mTorr, and a Ta / Pt seed layer 3 was formed. Subsequently, a Ru underlayer 4 was formed to a thickness of 20 nm under an Ar gas pressure of 11.3 mTorr using a Ru target.

Then, under an Ar gas pressure of 30 mTorr, 0.6 nm of Pt with Pt target, Co ₉₃ - the Co with (SiO _{2) 7} targets, by stacking 9 times alternately, [Co-SiO ₂ / A magnetic layer (1) 5-1 of a Pt] multilayer laminated film was formed. Subsequently, the Pt—SiO ₂ exchange coupling control layer 5-2 was formed under an Ar gas pressure of 2.3 mTorr using a Pt ₉₃ — (SiO ₂ ) ₇ target. When the thickness was changed to 4.0 nm and the film thickness was 2 nm or more, it was described later as a reference example .

Subsequently, under the Ar gas pressure of 2.3 mTorr, a Co—SiO ₂ magnetic layer (2) 5-3 was formed to 2 nm using a Co ₈₈ — (SiO ₂ ) ₁₂ target. As described above, [Co—SiO ₂ / Pt] × 9 / Pt—SiO ₂ / Co— composed of the magnetic layer (1) 5-1 / exchange coupling control layer 5-2 / magnetic layer (2) 5-3. A SiO ₂ magnetic recording layer 5 was formed. The layers formed so far were formed by the RF magnetron sputtering method for the target material containing SiO ₂ and the DC magnetron sputtering method for all other layers. Next, the protective layer 6 made of carbon was formed with a thickness of 4 nm by the CVD method and then taken out from the vacuum apparatus. Thereafter, a liquid lubricating layer 7 made of perfluoropolyether was formed to a thickness of 2 nm by a dipping method to obtain a magnetic recording medium.

(Comparative Example 1)
Except that the Pt—SiO ₂ film of the exchange coupling control layer 5-2 was not formed and the magnetic recording layer 5 was [Co—SiO ₂ / Pt] × 9 / Co—SiO ₂ , everything was the same as in Example 1. Thus, a perpendicular magnetic recording medium was obtained.

(Comparative Example 2)
Perpendicular magnetic recording was performed in the same manner as in Comparative Example 1 except that the Co—SiO ₂ film of the magnetic layer (2) 5-3 was not formed and the magnetic recording layer 5 was [Co—SiO ₂ / Pt] × 9. The medium.

(Comparative Example 3)
A perpendicular magnetic recording medium is the same as in Example 1 except that the Cr—SiO ₂ exchange coupling control layer 5-2 is formed under the Ar gas pressure of 2.3 mTorr using a Cr ₉₃ — (SiO ₂ ) ₇ target. It was.

(Comparative Example 4)
Perpendicular magnetic recording medium in the same manner as in Example 1 except that the Ru—SiO ₂ exchange coupling control layer 5-2 was formed under an Ar gas pressure of 2.3 mTorr using a Ru ₉₃ — (SiO ₂ ) ₇ target. It was.

(Example 2)
Two layers were formed in the same manner as in Example 1 except that a Co ₈₈ Nb ₇ Zr ₅ target was used and a CoNbZr soft magnetic backing layer 2 was formed to 100 nm under an Ar gas pressure of 2.3 mTorr before the Ta layer was formed. A perpendicular magnetic recording medium was obtained.

(Comparative Example 5)
Except that the Pt—SiO ₂ film of the exchange coupling control layer 5-2 was not formed and the magnetic recording layer 5 was [Co—SiO ₂ / Pt] × 9 / Co—SiO ₂ , everything was the same as in Example 2. Thus, a two-layer perpendicular magnetic recording medium was obtained.

(Comparative Example 6)
Two layers perpendicular to each other in the same manner as in Comparative Example 5 except that the magnetic layer (2) 5-3 is not formed of Co—SiO ₂ and the magnetic recording layer 5 is [Co—SiO ₂ / Pt] × 9. A magnetic recording medium was obtained.

(Example 3)
_{{(Ni 80 Fe 20) 75} Cr 25} 93 - All the embodiments except for forming the _{{SiO 2} 7 NiFeCr-SiO} 2 exchange coupling control layer 5-2 in an Ar gas pressure 2.3mTorr under using a target A perpendicular magnetic recording medium was obtained in the same manner as in Example 1.

Example 4
_{{(Ni 80 Fe 20) 60} Cr 40} 93 - All the embodiments except for forming the _{{SiO 2} 7 NiFeCr-SiO} 2 exchange coupling control layer 5-2 in an Ar gas pressure 2.3mTorr under using a target A perpendicular magnetic recording medium was obtained in the same manner as in Example 1.

  Next, the performance evaluation results of the perpendicular medium of this example will be described.

First, as a preliminary study, the magnetic anisotropy of the [Co ₉₃ — (SiO ₂ ) ₇ / Pt] × 9 layer (hereinafter simply referred to as a [Co—SiO ₂ / Pt] layer) of Comparative Example 2 was measured as a torque meter. And Ku = 6.3 × 10 ⁶ erg / cc (average Ms of film = 360 emu / cc). Moreover, when the sample in which the [Co—SiO ₂ / Pt] layer of Comparative Example 2 was replaced with 2 nm of Co ₈₈ — (SiO ₂ ) ₁₂ layers (hereinafter simply referred to as “Co—SiO ₂ layer”) was measured, Ku = 1.2 × 10 ⁴ erg / cc (Ms of membrane average = 1000 emu / cc). That is, the high Ku value [Co—SiO ₂ / Pt] magnetic layer and the low Ku value Co—SiO ₂ magnetic layer used in Example 1 and Comparative Example 1 have a large magnetic anisotropy of two orders of magnitude or more. I found that there is a difference.

  Next, the magnetic characteristics of Example 1 and Comparative Examples 1 to 3 were evaluated. A VSM measuring device was used for magnetic property evaluation. “Magnetic curve” measurement, which measures magnetization while applying a magnetic field of +20 kOe → −20 kOe → + 20 kOe, and once saturates the magnetization in one direction by applying −20 kOe, then measures the magnetization with a magnetic field of 0 → sets a certain magnetic field After the increase to the value, two types of evaluations were performed: “residual magnetization curve” measurement in which the measurement was repeated while the magnetic field was returned to 0, and this measurement was repeated while increasing the magnetic field setting value to +20 kOe.

Respectively in FIGS 3, Comparative Example 2, shows the magnetization curves and residual magnetization curves of Comparative Example 1, the film thickness of the Pt-SiO ₂ exchange coupling control layer in Example 1 in FIG. 4, 1. Shows the magnetization curves and residual magnetization curve when an 5n m. 5 and 6 show as reference examples 1 and 2 a magnetization curve and a residual magnetization curve when the film thickness of the exchange coupling control layer is 2.5 nm and 4.0 nm, respectively. 2 and 3, when Comparative Example 2 and Comparative Example 1 are compared, Comparative Example 1 (Pt—SiO ₂ = 0 nm) provided with a Co—SiO ₂ layer is compared with Comparative Example 2. The coercive force Hc is greatly reduced, and the magnetic field Hs at which the magnetization is saturated is also reduced. This is because a Co—SiO ₂ layer having a low Ku value is stacked, but the [Co—SiO ₂ / Pt] layer and the Co—SiO ₂ layer are strongly coupled to cause magnetization reversal as a whole. it is conceivable that.

In FIG. 4 where the film thickness of the exchange coupling control layer (Pt—SiO ₂ layer) of Example 1 is 1.5 nm, Hc and Hs are further reduced, and the slopes of the magnetization curve and the residual magnetization curve become steep. With this film thickness, Hc and Hs are reduced because the exchange coupling force between the two magnetic layers is reduced. First, after the magnetization reversal of the Co—SiO ₂ layer occurs, the magnetization of the [Co—SiO ₂ / Pt] layer This is probably because reversal occurs. Note that the steep inclination of the magnetization curve is attributed to the fact that the demagnetizing field energy exerted on itself is large because the upper layer Co—SiO ₂ is as thin as 2 nm and Ms is large. It is done. It can be seen from the figures described later that the effects of the present invention are most effectively generated when the film thickness is 1.5 nm.

Further, in the case of Reference Example 1 in which Pt—SiO ₂ = 2.5 nm in FIG. 5 in which the film thickness was increased, the shape of the magnetization curve changed, and H≈ ± 3 kOe and H≈ ± 6 kOe vicinity. This is probably because two-stage magnetization reversal is performed, and in this case, the exchange coupling force between the two magnetic layers is too weak. In the case of FIG. 5, the locus of the remanent magnetization curve does not coincide with the magnetization curve and shows a one-step curve. This is because, when a magnetic field is applied, Co—SiO ₂ having a small Ku value is reversed according to the magnetic field, but [Co—SiO ₂ / Pt] having a large Ku value is not reversed. And in the residual magnetization state where no magnetic field is applied, the coupling force between the layers remains although it is weak, so that Co—SiO ₂ is in the same direction (returns) as the magnetization of [Co—SiO ₂ / Pt]. Is shown.

In the case of Reference Example 2 in which Pt—SiO ₂ in FIG. 6 is 4.0 nm, the magnetization curve and the remanent magnetization curve coincide with each other, and it can be seen from the shape that the magnetization reversal is performed in two stages. That is, exchange coupling between the _{Co-SiO 2 [Co-SiO} 2 / Pt] layer is completely cut, each layer independently reversed, it can be seen that also retain its state residual magnetization state.

Next, FIG. 7 will be described. FIG. 7 shows the dependence of the coercive force Hc obtained from the magnetization curve and the residual coercive force Hr obtained from the residual magnetization curve on the exchange coupling control layer thickness (Pt—SiO ₂ film thickness). When the exchange coupling control layer thickness (Pt—SiO ₂ thickness) is between 0.2 and 1.8 nm, Hc and Hr are reduced as compared with the case of Pt—SiO ₂ = 0.0 nm. The effect of the present invention is shown. When the film thickness is 2 nm or more, Hc and Hr do not coincide with each other, indicating that the exchange coupling force of both layers is too weak to show an effect.

When the same measurement was performed in Comparative Example 3 in which the exchange coupling control layer was Cr—SiO ₂ and Comparative Example 4 in which Ru—SiO ₂ was used, the film thickness was 0.5 nm or more in any exchange coupling control layer. Hc and Hr did not match. That is, when the film thickness is 0.5 nm, a portion where the bonding force is already weakened or completely cut is generated. Compared with these, in the case of Pt—SiO ₂ , as is apparent from FIG. 7, it can be seen that there is an effect that the exchange coupling force can be maintained in a relatively wide range of film thickness of less than 2.0 nm. .

  Next, in order to clarify the practical effect of the present invention, the electromagnetic conversion characteristics of Example 2, Comparative Example 5 and Comparative Example 6 were measured. Sample Example 2, Comparative Example 5, and Comparative Example 6 to be compared here have the same soft magnetism as Example 1, Comparative Example 1, and Comparative Example 2 described above so that the recording / reproducing characteristics can be sufficiently exhibited. It has a structure with a backing layer. Since CoNbZr applied as a soft magnetic underlayer has an amorphous structure, it does not affect the crystal orientation and microstructure of the upper layer, and the change in the magnetization curve and magnetic characteristics of the magnetic recording layer confirmed by the Kerr effect measurement device This was consistent with that described in Example 1, Comparative Example 1, and Comparative Example 2. The electromagnetic conversion characteristics were evaluated using a GMR head with a spin stand tester. A head having a recording track width of 180 nm and a reproducing track width of 140 nm was used.

  Table 1 shows the results of evaluating the electromagnetic conversion characteristics of Example 2, Comparative Example 5, and Comparative Example 6.

Table 1 collectively shows SNR (signal-to-noise ratio), overlay OW (Over Write) characteristics, and signal output degradation degree (Decay) characteristics. SNR is a value at a linear recording density of 600 kFCI, and is an indicator of signal quality, that is, recording density. OW is a value obtained by superimposing a 70 kFCI signal on a signal having a linear recording density of 500 kFCI, and serves as an index of the ease of writing on the medium. Decay is a measure of signal stability measured by measuring the change over time of the signal output written at a recording density of 50 kFCI. The thickness of the exchange coupling control layer in Example 2 of Table 1 (Pt-SiO ₂ layer) was set to the thickness equivalent to 1.5nm was good in Example 1.

From Table 1, it can be seen that Comparative Example 6, which has only a [Co—SiO ₂ / Pt] layer with a large Ku value, is a medium with very poor OW and poor writing performance. Therefore, it is understood that unsaturated recording in which the magnetization is not sufficiently saturated occurs, the SNR is deteriorated, and is significantly inferior to those of other comparative examples 5 and 2. In the case of the comparative example 5 having the configuration of [Co—SiO ₂ / Pt] / Co—SiO ₂ without an exchange coupling control layer, the effect of reducing Hc by providing the Co—SiO ₂ layer having a small Ku value as described above. OW is significantly improved as compared with Comparative Example 6. Further, since saturation recording becomes possible, the SNR is also superior to that of Comparative Example 6.

  And in Example 5 which is the structure which inserted the exchange coupling control layer in the comparative example 6, 5 dBOW is further improved compared with the comparative example 5. FIG. This is the effect of moderately weakening the exchange coupling force of the upper and lower layers. Also, the SNR was a good value of 1.6 dB. This is considered to be due to a reduction in transition noise between bits due to an increase in the slope of the magnetization curve due to a change in magnetic characteristics.

Moreover, Decay is 0 in any sample, and even when the exchange coupling force is weakened in Example 2, it is clear that the signal output does not change with time, and the bit can be held stably. In the examination of the magnetic characteristics of Example 1, when the coupling force was weakened too much or when the Pt—SiO ₂ film thickness was 2 nm or more, the OW was not improved and the effect of improving the writing ability was observed. I couldn't.

Finally, the effects of the exchange coupling control layer material were compared. Example 1 (Pt-SiO _2), Example _{3 ({(NiFe) 75 Cr} 25} -SiO 2), Example _{4 ({(NiFe) 60 Cr} 40} -SiO 2), Comparative Example 3 (Cr- The dependence of the coercivity of SiO ₂ ) on the exchange coupling control layer thickness was measured. As a result, Example 1, Example 3, and Example 4 have film thicknesses of 1.5 nm, 1.0 nm, and 1.5 nm, respectively, and the coercive force has a minimum value. The change rates of the coercive force with respect to the case without the control layer were −12%, −18%, and −7%, respectively. That is, in Example 3 and Example 4 in which an alloy of Ni, Fe, and Cr is crystalline, the same effect as in Example 1 that is Pt—SiO ₂ is observed, and the bonding force at the interface is moderately increased. It turns out that it can control. Also, the composition ratio of NiFe and Cr is different between Example 3 and Example 4. In this example, the amount of Cr is relatively small in Example 4, and the rate of decrease in coercive force is large. Even in the composition ratio of NiFe and Cr, bonding is achieved. It can be seen that the force can be controlled.

On the other hand, in Comparative Example 3, the coercive force does not decrease, the coercive force increases monotonously with increasing film thickness, and the desired effect cannot be obtained. This, Cr will be overall exchange coupling control layer 5-2 influence being oxidized becomes an oxide film layer by oxygen is contained in the SiO ₂ was added, greatly reduces the binding strength of the interface between the magnetic layer, bond Is presumed to be completely divided . This means that the coupling control with the film thickness is difficult. From the above, the effect of applying a nonmagnetic alloy with at least one element selected from Co, Ni, and Fe as the crystalline material of the exchange coupling control layer containing an oxide has been clarified.

1 is a schematic cross-sectional view of a perpendicular magnetic recording medium according to an embodiment of the present invention. The figure which shows the magnetization curve and the residual magnetization curve of the comparative example 2 with respect to the Example of this invention. The figure which shows the magnetization curve and the remanent magnetization curve of the comparative example 1 with respect to the Example of this invention. The figure which shows the magnetization curve in the case of the exchange coupling control layer film thickness of 1.5 nm of Example 1 of this invention, and a remanent magnetization curve. The figure which shows the magnetization curve and remanent magnetization curve in the case of the exchange coupling control layer film thickness of 2.5 nm of the reference example 1 of this invention. The figure which shows the magnetization curve in the case of the exchange coupling control layer film thickness of 4.0 nm of the reference example 2 of this invention, and a residual magnetization curve. Involved in an embodiment of the present invention, the residual coercivity Hr calculated from the coercive force Hc and the residual magnetization curve obtained from the magnetization curve, shows the exchange coupling control thickness (Pt-SiO ₂ film thickness nm) dependence.

  1: nonmagnetic substrate, 2: soft magnetic backing layer, 3: seed layer, 4: underlayer, 5: magnetic recording layer, 5-1: magnetic layer (1), 5-2: exchange coupling control layer, 5- 3: Magnetic layer (2), 6: Protective layer, 7: Liquid lubricating layer.

Claims (7)

In a perpendicular magnetic recording medium in which at least an underlayer, a magnetic recording layer, and a protective layer are sequentially laminated on a nonmagnetic substrate, the magnetic recording layer includes a first magnetic layer, an exchange coupling control layer, and a second magnetic layer. The first magnetic layer and the second magnetic layer include at least a sequentially laminated structure, and the perpendicular magnetic anisotropy constant (Ku) of the first magnetic layer is different from that of the magnetic layer. comprises an oxide of a non-magnetic, and the exchange coupling control layer, Pt-SiO ₂ or consists NiFeCr-SiO _2, the perpendicular magnetic recording medium has a film thickness, wherein to Rukoto and less than 2 nm. 2. The perpendicular magnetic recording medium according to claim 1 , wherein the Ku value of one magnetic layer of the first magnetic layer and the second magnetic layer is at least 1 × 10 ⁶ erg / cm ³ or more and the other magnetic layer is magnetic. A perpendicular magnetic recording medium, wherein the Ku value of the layer is 1 × 10 ⁵ erg / cm ³ or less. 3. The perpendicular magnetic recording medium according to claim 1, wherein crystal grains in the magnetic recording layer pass through the first magnetic layer, the exchange coupling control layer, and the second magnetic layer, and form a columnar shape from the underlayer interface. A perpendicular magnetic recording medium having a grown structure and each of its columnar grains magnetically separated by a nonmagnetic component. The perpendicular magnetic recording medium according to any one of claims 1 to 3, oxide contained in the magnetic recording layer, Si, Ti, Cr, an oxide of at least one element selected from among Co A perpendicular magnetic recording medium characterized by the above. The perpendicular magnetic recording medium according to any one of claims 1 to 4, the crystal grains of the first magnetic layer and the second magnetic layer, the crystal structure (hcp structure) having a hexagonal close-packed structure or a face-centered A perpendicular magnetic recording medium having a crystal structure mainly composed of a crystal structure (fcc) having a cubic lattice structure. The perpendicular magnetic recording medium according to any one of claims 1 to 5 , wherein the saturation magnetization of the magnetic layer having a large Ku value is Msh, and the saturation magnetization of the other magnetic layer having a small Ku value is Msl. A perpendicular magnetic recording medium, wherein Msh <Msl. The perpendicular magnetic recording medium according to any one of claims 1 to 6, the perpendicular magnetic recording medium, wherein the saturation magnetization Msl of small magnetic layer of the Ku value is at least 800 emu / cc or more.

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