JP2012033247A - Target, method for manufacturing target, and method for manufacturing magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a target capable of forming a magnetic layer which has superior electromagnetic conversion characteristics and can respond to higher recording density by miniaturizing magnetic grains to be formed and increasing a grain boundary width of the magnetic grains in forming a perpendicular magnetic layer having a granular structure by a sputtering method.SOLUTION: A target used for forming a Co series magnetic layer of a magnetic recording medium by a sputtering method contains 5 mol% or more of Cr or Cr alloy, 5 mol% or more of CoO, and 3 mol% to 20 mol% of oxides having a melting point of 800°C or less in total, and the porosity thereof is 7% or less. Moreover, the target contains one kind selected from a group consisting of SiO, TiO, TiO, ZrO, CrO, TaO, NbO, AlO, and CeO.

Description

  The present invention relates to a target used for sputtering a magnetic layer constituting a magnetic recording medium.

  A hard disk drive (HDD), which is a kind of magnetic recording / reproducing apparatus, has an increasing recording density of 50% or more per year and is said to continue to increase in the future. Accordingly, development of a magnetic recording medium suitable for increasing the recording density has been advanced.

  A magnetic recording / reproducing apparatus currently on the market is equipped with a so-called perpendicular magnetic recording medium in which an easy axis of magnetization in a magnetic film is oriented vertically. Even when the recording density of the perpendicular magnetic recording medium is increased, the influence of the demagnetizing field in the boundary region between the recording bits is small and a clear bit boundary is formed, so that an increase in noise can be suppressed. In addition, the perpendicular magnetic recording medium has excellent thermal fluctuation characteristics because it requires only a small reduction in the recording bit volume accompanying an increase in recording density.

  In addition, in order to improve the recording / reproducing characteristics of the perpendicular magnetic recording medium, an orientation control layer is used, a multilayer magnetic layer is formed by a sputtering method, and crystal grains of each magnetic layer are formed into continuous columnar crystals. It has been proposed to improve the vertical orientation of the magnetic layer (see Patent Document 1).

  In many cases, a perpendicular magnetic recording medium uses a granular magnetic layer. The magnetic layer with a granular structure has a structure in which a magnetic particle is covered with a non-magnetic material, and the magnetic interaction between the magnetic particles is reduced by the non-magnetic material so that the magnetic particles are magnetically separated. Can be reduced.

  An oxide is mainly used for the nonmagnetic material forming the granular structure. As the oxide, Ti, Si, Cr, Ta, W, Nb, or the like that forms a more stable oxide and can be reliably segregated between the magnetic particles while being in the oxide is used. For example, in Patent Document 2, as a sputtering target for forming a granular magnetic layer, a Co alloy, Ti oxide and Si oxide for forming a first oxide, and Co oxide for forming a second oxide are disclosed. It is described that the thing containing is used.

Here, in the magnetic layer having a granular structure, Cr may be contained in both the magnetic particles and the nonmagnetic material covering the magnetic particles. For example, the nonmagnetic material contains Cr ₂ O ₃ and the magnetic particles contain, for example, a CoCrPt-based magnetic alloy.

  When the content of Cr in the magnetic layer having the granular structure is less than 5 atomic%, the thickness of the grain boundary layer formed between the magnetic particles is reduced by Cr segregation, so that the magnetic inter-particle spacing between the magnetic particles is reduced. The interaction increases, and the particle size of the magnetic particles themselves tends to enlarge. As a result, noise during recording and reproduction increases, and a signal / noise ratio (S / N) suitable for higher density recording cannot be obtained. On the other hand, if the Cr content exceeds 28 atomic%, the proportion of Cr not segregating in the grain boundary layer and remaining inside the magnetic particles increases. As a result, the coercive force in the vertical direction and the ratio (Mr / Ms) between the residual magnetization (Mr) and the saturation magnetization (Ms) are likely to be lowered. Furthermore, the crystal orientation of the magnetic particles is impaired, and the ratio (Hc-v) / (Hc-i) of the coercive force (Hc-v) in the vertical direction and the coercive force (Hc-i) in the in-plane direction is small. There is a risk of becoming. (See Patent Document 3)

JP 2004-310910 A JP 2009-238357 A JP 2006-351055 A

  As described above, the magnetic layer having a granular structure is used in the perpendicular magnetic recording medium, so that it is possible to reduce the magnetic interaction between the magnetic particles and reduce the medium noise. There is a constant demand for higher recording density, and there is a need for a magnetic recording medium capable of higher recording density than ever. Therefore, there is a need for a magnetic layer having a granular structure in which the magnetic particles are made finer than before and the width of the nonmagnetic material covering the magnetic particles (the grain boundary width of the magnetic particles) is increased.

  The present invention has been proposed in view of the above circumstances. When a magnetic layer having a granular structure is formed by a sputtering method, the magnetic particles to be formed are made finer, and the grain boundary width of the magnetic particles is increased. Another object of the present invention is to provide a target capable of forming a magnetic layer excellent in electromagnetic conversion characteristics that can cope with higher recording density.

  In order to solve the above-mentioned problems, the present inventor has intensively studied a method for forming a magnetic layer having a granular structure as described below.

  When the present inventors use a material containing CoO as a target when forming a granular Co-based magnetic layer by a sputtering method, the Co-based magnetic particles are made finer, and the grain boundary width of the magnetic particles is increased. It has been found that it is possible to make the image sharper. That is, it was clarified that CoO contained in the target was separated during sputtering, and the separated Co acted to refine and isolate the Co-based magnetic particles, and the other O had the effect of widening the grain boundary width of the magnetic particles. . However, CoO contained in the target is easily separated in the manufacturing process such as firing of the target. In particular, when the target contains metal Cr or Cr alloy, this is combined with oxygen taken from CoO, and the above-mentioned Co-based It was found that the effect of miniaturizing and isolating magnetic particles and widening the grain boundary width of magnetic particles disappeared.

  Therefore, in order to prevent the reaction between CoO and Cr, the present inventor tried firing at a temperature lower than the reaction temperature between CoO and Cr, specifically, 800 ° C. or lower, manufactured a target in which CoO and Cr coexisted, and magnetic An attempt was made to form a magnetic layer of the recording medium. However, when sputter deposition was performed with the obtained target, sputter dust was generated and adhered to the disk, and a magnetic recording medium with high smoothness could not be obtained. As a cause, the inventors found that the target obtained by low-temperature firing had a sintered density as low as about 75% of the true density (theoretical value) (porosity was 25%). It is considered that the plasma discharge becomes unstable and abnormal discharge (spark) occurs in the target part, which generates dust.

  Based on the above findings, the inventor of the present application has conducted further studies, and as a result, by adding an oxide having a melting point of 800 ° C. or less to a Co-based powder mixture, the porosity is reduced at a temperature at which CoO and Cr do not react. The present invention was completed by finding that a target having a low sintering density and a true sintering density can be produced.

That is, the present invention relates to the following.
(1) A target used for forming a Co-based magnetic layer of a magnetic recording medium by sputtering, wherein the target contains 5 mol% or more of Cr or Cr alloy, contains 5 mol% or more of CoO, and has a melting point of 800. A target comprising oxides at or below ° C within a range of 3 mol% to 20 mol% in total and having a porosity of 7% or less.
(2) The target is further selected from the group consisting of SiO ₂ , TiO, TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , and CeO ₂ . The target according to (1), comprising one type.
(3) The target contains Co in a range of 55 mol% to 75 mol%, Cr or Cr alloy in a range of 5 mol% to 28 mol%, and Pt in a range of 5 mol% to 25 mol%. Within a range, including CoO within a range of 5 mol% to 15 mol%, including oxides having a melting point of 800 ° C. or less within a total range of 3 mol% to 15 mol%, SiO ₂ , TiO, TiO ₂ , oxides selected from the group consisting of ZrO ₂ , Cr ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , CeO ₂ are included within a total range of 5 mol% to 25 mol%. The target according to (1) or (2), wherein
(4) The oxide having a melting point of 800 ° C. or lower is at least one selected from boron oxide, vanadium oxide, tellurium oxide, molybdenum oxide, and low-melting glass, any one of (1) to (3) The target according to item 1.
(5) Co in the range of 55 mol% to 75 mol%, Cr or Cr alloy in the range of 5 mol% to 28 mol%, Pt in the range of 5 mol% to 25 mol%, CoO in the range of 5 mol% Within a range of ˜15 mol%, a total of oxides having a melting point of 800 ° C. or less within a range of 3 mol% to 15 mol%, SiO ₂ , TiO, TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , CeO _2, oxides selected from the group consisting of 5 mol% to 25 mol% in total are mixed, pre-molded, and then 430 ° C. A method for producing a target for forming a magnetic layer of a magnetic recording medium, comprising sintering at a porosity of 7% or less within a range of ˜800 ° C.
(6) The target according to (5), wherein the oxide having a melting point of 800 ° C. or lower is at least one selected from boron oxide, vanadium oxide, tellurium oxide, molybdenum oxide, and low-melting glass. Method.
(7) A method for producing a magnetic recording medium, wherein a magnetic layer is formed on a substrate by a sputtering method using the target according to any one of (1) to (4).

  In the present invention, since a low porosity target containing CoO and Cr or Cr alloy can be provided, separation of CoO is promoted at the time of sputtering, and Co-based magnetic particles are refined and a grain boundary width is increased. In addition, the interface can be made sharp. Therefore, it is possible to form a magnetic layer with excellent writing characteristics and low noise. By using a magnetic recording medium including this magnetic layer in a magnetic recording / reproducing apparatus, it is possible to provide an apparatus capable of increasing the recording density.

FIG. 1 shows an example of a magnetic recording medium formed using the target of the present invention. FIG. 2 is an enlarged schematic view for explaining the laminated structure of the orientation control layer and the perpendicular magnetic layer of the magnetic recording medium, and is a sectional view showing a state in which the columnar crystals of each layer are grown perpendicular to the substrate surface. is there. FIG. 3 is an enlarged cross-sectional view showing the laminated structure of the magnetic layers constituting the perpendicular magnetic layer of the magnetic recording medium. FIG. 4 shows an example of a magnetic recording / reproducing apparatus using the magnetic recording medium of the present invention. FIG. 5 is a graph showing the porosity of a target manufactured by adding boron oxide.

The present invention relates to a target used for forming a Co-based magnetic layer of a magnetic recording medium by a sputtering method, and this target contains Cr or a Cr alloy, and an oxide having a melting point of 800 ° C. or less containing 5 mol% or more of CoO. It is contained within the range of 3 mol% to 20 mol% in total, and the porosity is 7% or less. Here, the porosity means the ratio of the volume of all pores in the sintered body to the volume of the sintered body. The porosity is expressed by the following equation, and the sintered density can be calculated by a known method using JIS Z 2505 or the like. Further, as a method of directly calculating the porosity, there is a method of observing the cross section of the obtained sintered body, measuring the area of the pores, and calculating the volume of the pores from the area.
Porosity (%) = (1− (sintering density / true density)) × 100

  A target used in the sputtering method is manufactured by mixing a metal powder at a predetermined composition ratio, then compressing and molding the metal powder, and sintering it at a high temperature in an inert gas atmosphere or vacuum. The metal powder is generally produced by a gas atomization method. That is, the raw material is dissolved in an inert gas atmosphere or in a vacuum, and atomized with an inert gas such as argon gas or nitrogen gas. At this time, since the raw material is rapidly solidified directly from the molten state, a spherical powder having a very fine solidified structure and high uniformity in composition and an average particle diameter of several μm can be produced.

In addition to the sintering and hot pressing methods that have been used for a long time, there are hot isostatic pressing (HIP) methods and hot extrusion methods aiming at higher density. . In particular, in the case of a target for magnetic recording media, high homogeneity of the composition distribution and low generation of particles due to the above-described mechanism are required, so high-temperature sintering in a vacuum or an inert atmosphere is necessary. Reaction of CoO and Cr occurs. That is, when the present inventor contains CoO in the target, it is separated during sputtering, the separated Co acts on the refinement of Co-based magnetic particles, and the other O acts to widen the grain boundary width of the magnetic particles. It has been found that the CoO contained in the target reacts with the metal Cr or Cr alloy in the high-temperature sintering process of the target, specifically, forms CoCr ₂ O ₄ , Cr ₂ O _3, etc. During the process, it becomes difficult to separate Co and O, and the above effect is lost.

  Therefore, in the present invention, the powder for producing the target contains Cr or a Cr alloy and CoO in an amount of 5 mol% or more, and a total of 3 mol% to 20 mol% of oxides having a melting point of 800 ° C. or less. It was found that the above-mentioned problems can be solved by making the content within the range and sintering this so that the porosity of the target is 7% or less. This will be described in detail.

  The inventor of the present application conducted an experiment in which powders of CoO and Cr were mixed and sintered in an argon atmosphere in the temperature range of 700 ° C. to 900 ° C., and the results shown in Table 1 were obtained. The sintering time in this experiment was 1 hour. From this result, when sintering the powder containing CoO and Cr powder, the sintering temperature is set to 800 ° C. or lower, so that 73 mol% or more of CoO contained in the powder is contained in the sintered target. Clarified that it can survive.

Further, the inventor made 8 mol% of CoO, 7 mol% of Cr, 7 mol% of SiO ₂ , and 0 to 6 mol% of B ₂ O ₃ (melting point: 430 ° C.) as an oxide having a melting point of 800 ° C. or less. An experiment was conducted in which powders with the balance being 84Co16Pt were mixed and sintered at 800 ° C. for 1 hour. The result is shown in FIG. From this result, it became clear that the porosity of the obtained sintered body can be made 7% or less by containing 3 mol% or more of B ₂ O ₃ . This is because when an oxide having a melting point of 800 ° C. or less is mixed and the target is sintered, this oxide becomes a melt at the time of sintering, which fills the space between other powders by capillary action, It is thought that the rate was lowered.

Further, according to the study of the present inventor, as the oxide having a melting point of 800 ° C. or lower, a substance that has little influence even when mixed in the magnetic layer of the magnetic recording medium can be employed. : 430 ° C.), vanadium oxide (melting point: 690 ° C.), tellurium oxide (melting point: 733 ° C.), molybdenum oxide (melting point: 795 ° C.), low-melting glass (melting point: 800 ° C. or lower) is preferable. Became. Here, as the low melting point glass, in addition to a mixture with Na ₂ O, MgO, CaO, B ₂ O ₅ , P ₂ O _5, etc., which contains SiO _{2 as a} main component, PbO—SiO ₂ —B ₂ O ₃ , PbO -P ₂ O ₅ -SnF ₂ and the like.

In the present invention, SiO ₂ (melting point: 1550 ° C.), TiO (melting point: 1750 ° C.), TiO ₂ (melting point: 1812 ° C.), ZrO, which may be slightly reacted with CoO, although not as much as Cr. ₂ (melting point: 2700 ° C.), Cr ₂ O ₃ (melting point: 2435 ° C.), Ta ₂ O ₅ (melting point: 1468 ° C.), Nb ₂ O ₅ (melting point: 1520 ° C.), Al ₂ O ₃ (melting point: 2046 ° C.) ), CeO ₂ (melting point: 1950 ° C.) is preferably contained in the target. Since these oxides are useful for forming nonmagnetic grain boundaries in a magnetic layer having a granular structure, the target of the present invention contains a magnetic material having excellent electromagnetic characteristics by incorporating these oxides. A layer can be formed.

In particular, the present invention includes Co in the range of 55 mol% to 75 mol%, includes Cr and Cr alloy in the range of 5 mol% to 28 mol%, includes Pt in the range of 5 mol% to 25 mol%, CoO is included in the range of 5 mol% to 15 mol%, boron oxide is included in the range of 3 mol% to 15 mol%, SiO ₂ , TiO, TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , Ta ₂ O ₅ , CoCrPtB system with excellent electromagnetic conversion characteristics by using a target containing oxides selected from the group consisting of Nb ₂ O ₅ , Al ₂ O ₃ , and CeO ₂ within a total range of 5 mol% to 25 mol% It is preferable that the granular magnetic layer can be formed by sputtering.

Specific examples of the good CoCrPtB-based granular magnetic layer of the electromagnetic conversion _{characteristics, CoCrPtB-SiO 2, CoCrPtB-} TiO, CoCrPtB-TiO-SiO 2, CoCrPtB-TiO-SiO 2 -TiO 2, CoCrPtB-SiO 2 -TiO such as _{2, CoCrPtB-ZrO 2, CoCrPtB} -Cr 2 O 3, CoCrPtB-Nb 2 O 5, CoCrPtB-Al 2 O 3 can be exemplified.

  Hereinafter, a method of manufacturing a magnetic recording medium using the target of the present invention and a magnetic recording / reproducing apparatus incorporating the magnetic recording medium manufactured thereby will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

(Manufacture of magnetic recording media)
The magnetic recording medium using the target of the present invention can be manufactured, for example, on a non-magnetic substrate, a soft magnetic underlayer, an orientation control layer for controlling the orientation of the layer immediately above, and the easy axis of the non-magnetic layer. A perpendicular magnetic layer oriented mainly perpendicular to the substrate is formed by sputtering.

  FIG. 1 shows an example of a magnetic recording medium manufactured according to the present invention. Hereinafter, the magnetic recording medium shown in FIG. 1 will be described as an example of the magnetic recording medium of the present invention. In the magnetic recording medium shown in FIG. 1, a soft magnetic underlayer 2, an orientation control layer 3, a perpendicular magnetic layer 4, a protective layer 5, and a lubricating layer 6 are sequentially laminated on a nonmagnetic substrate 1. It has a structure. Among these, the soft magnetic underlayer 2 and the orientation control layer 3 constitute an underlayer.

"Non-magnetic substrate"
As the nonmagnetic substrate 1, a metal substrate made of a metal material such as aluminum or an aluminum alloy may be used, or a nonmetal substrate made of a nonmetal material such as glass, ceramic, silicon, silicon carbide, or carbon is used. Also good. Further, as the nonmagnetic substrate 1, a substrate in which a NiP layer or a NiP alloy layer is formed on the surface of the metal substrate or the nonmetal substrate by using, for example, a plating method or a sputtering method may be used.

  As the glass substrate, for example, amorphous glass or crystallized glass can be used, and as the amorphous glass, for example, general-purpose soda lime glass or aluminosilicate glass can be used. In addition, as the crystallized glass, for example, lithium-based crystallized glass can be used. As the ceramic substrate, for example, general-purpose aluminum oxide, a sintered body mainly composed of aluminum nitride, silicon nitride, or the like, or a fiber reinforced material thereof can be used.

"Soft magnetic underlayer"
A soft magnetic underlayer 2 is formed on the nonmagnetic substrate. The method for forming the soft magnetic underlayer 2 is not particularly limited, and for example, a sputtering method can be used.

  The soft magnetic underlayer 2 increases the component of the magnetic flux generated from the magnetic head in the direction perpendicular to the substrate surface, and further strengthens the direction of magnetization of the perpendicular magnetic layer 4 on which information is recorded to be perpendicular to the nonmagnetic substrate 1. It is provided to fix in any direction. This effect becomes more conspicuous particularly when a single pole head for perpendicular recording is used as a magnetic head for recording and reproduction.

  As the soft magnetic underlayer 2, for example, a soft magnetic material containing Fe, Ni, Co, or the like can be used. Specific examples of soft magnetic materials include CoFe alloys (CoFeTaZr, CoFeZrNb, etc.), FeCo alloys (FeCo, FeCoV, etc.), FeNi alloys (FeNi, FeNiMo, FeNiCr, FeNiSi, etc.), FeAl alloys (FeAl, etc.). FeAlSi, FeAlSiCr, FeAlSiTiRu, FeAlO, etc.), FeCr alloys (FeCr, FeCrTi, FeCrCu, etc.), FeTa alloys (FeTa, FeTaC, FeTaN, etc.), FeMg alloys (FeMgO, etc.), FeZr alloys (FeZrN, etc.) , FeC alloys, FeN alloys, FeSi alloys, FeP alloys, FeNb alloys, FeHf alloys, FeB alloys and the like.

`` Orientation control layer ''
An orientation control layer 3 is formed on the soft magnetic underlayer 2. The orientation control layer 3 is to refine the crystal grains of the perpendicular magnetic layer 4 and improve the recording / reproducing characteristics. As shown in FIG. 1, the orientation control layer 3 of the present embodiment is arranged on the first orientation control layer 3a arranged on the soft magnetic underlayer 2 side and on the perpendicular magnetic layer 4 side of the first orientation control layer 3a. And a second orientation control layer 3b.

  The first orientation control layer 3 a is for increasing the nucleation density of the orientation control layer 3, and includes a crystal serving as a columnar crystal nucleus constituting the orientation control layer 3. In the first orientation control layer 3a of the present embodiment, as shown in FIG. 2, a dome-shaped convex portion is formed on the top of the columnar crystal S1 formed by growing a crystal serving as a nucleus.

"Perpendicular magnetic layer"
The perpendicular magnetic layer of the present invention has a granular magnetic layer formed by at least one sputtering process using the target of the present invention, and the granular magnetic layer includes a plurality of magnetic particles including a Co alloy and the plurality of magnetic particles. It is comprised from the oxide which isolate | separates the magnetic particle. Since the granular magnetic layer is formed using a target containing cobalt oxide, the magnetic particles are miniaturized and isolated, and the grain boundaries of the magnetic particles are expanded.

The perpendicular magnetic layer formed in the present invention will be described with reference to FIG. The perpendicular magnetic layer 4 of the present invention is formed on the second orientation control layer 3b, for example. As shown in FIG. 1, the perpendicular magnetic layer 4 includes, for example, a first magnetic layer 4a, a second magnetic layer 7a, a third magnetic layer 4b, a fourth magnetic layer 7b, and a first magnetic layer 4 from the nonmagnetic substrate 1 side. 5 magnetic layers 4c. Among these, at least one of the first magnetic layer 4a, the second magnetic layer 7a, the third magnetic layer 4b, and the fourth magnetic layer 7b contains 5 mol% or more of Cr and CoO, and 3% of boron oxide. It is preferable to form a film using a target that is included in the range of mol% to 20 mol% and has a porosity of 7% or less. For example, CoPt—SiO ₂ (first magnetic layer 4a), CoCrPtB—SiO ₂ (Second magnetic layer 7a), CoPt—SiO ₂ (third magnetic layer 4b), and CoCrPtB—SiO ₂ (fourth magnetic layer 7b). In the case of this laminated structure, the second magnetic layer 7a and the fourth magnetic layer 7b are layers formed using the target of the present invention. In these two magnetic layers, a refined Co-based magnetic particle and a nonmagnetic oxide that increases the grain boundary width of the magnetic particle are formed. A preferred configuration of the fifth magnetic layer 4c will be described later.

  Crystal grains constituting each of the magnetic layers 4a, 4b, 7a, and 7b are formed on the orientation control layer 3 as columnar crystals that are continuous with the columnar crystals of the first orientation control layer 3a and the second orientation control layer 3b of the orientation control layer 3. Epitaxially grown.

  FIG. 3 is an enlarged cross-sectional view showing the laminated structure of the magnetic layers constituting the perpendicular magnetic layer. As shown in FIG. 3, the magnetic layer constituting the perpendicular magnetic layer 4 is a granular magnetic layer, and includes magnetic particles (crystal particles having magnetism) 42 including Co, Cr, Pt, and the like, and an oxide 41. It is preferable that it contains.

As the oxide 41, for example, an oxide such as Si, Ta, Al, Ti, Mg, Co, and Ce is preferably used. Among _them, it can be suitably used such as TiO 2, SiO _2. The magnetic layer is preferably made of a composite oxide to which two or more kinds of oxides are added. Among them, particularly, SiO ₂ —TiO ₂ can be preferably used.

  The magnetic particles 42 are preferably dispersed in the magnetic layer. The magnetic particles 42 preferably have a columnar structure that vertically penetrates the magnetic layers 4a, 4b, 7a, 7b and the magnetic layer 4c. By having such a structure, the orientation and crystallinity of the magnetic layer become favorable, and as a result, a signal / noise ratio (S / N ratio) suitable for high-density recording can be obtained.

In order to obtain the perpendicular magnetic layer 4 having the magnetic particles 42 having the columnar structure, the content of the oxide 41 contained in the magnetic layer and the film formation conditions of the magnetic layer are important. The content of the oxide 41 contained in the magnetic layer is 3 mol% or more and 18 mol% or less with respect to the total mol calculated by using, for example, an alloy such as Co or Pt constituting the magnetic particle 42 as one compound. It is preferably 6 mol% or more and 13 mol% or less.

The content of the oxide 41 in the magnetic layer is preferably within the above range because the oxide 41 is deposited around the magnetic particles 42 when the magnetic layer is formed, and the magnetic particles 42 can be isolated and refined. It is to become. On the other hand, when the content of the oxide 41 exceeds the above range, the oxide 41 remains in the magnetic particles 42, and the orientation and crystallinity of the magnetic particles 42 are impaired. This is not preferable because the product 41 is deposited and the columnar structure in which the magnetic particles 42 penetrate the magnetic layers 4a to 4c vertically is not formed. In addition, when the content of the oxide 41 is less than the above range, separation and refinement of the magnetic particles 42 are insufficient, resulting in an increase in noise during recording and reproduction, and a signal / This is not preferable because the noise ratio (S / N ratio) cannot be obtained.
The Pt content in the magnetic layer is preferably 5 atomic% or more and 25 atomic% or less.

If the Pt content is less than 5 atomic%, the magnetic anisotropy constant Ku necessary for the perpendicular magnetic layer 4 to obtain thermal fluctuation characteristics suitable for high-density recording cannot be obtained. When the content of Pt exceeds 25 atomic%, a stacking fault occurs inside the magnetic particle 42, and as a result, the magnetic anisotropy constant Ku decreases. In addition, when the Pt content exceeds the above range, an fcc structure layer is formed in the magnetic particles 42, and the crystallinity and orientation may be impaired.
Therefore, in order to obtain thermal fluctuation characteristics and recording / reproduction characteristics suitable for high-density recording, it is preferable to set the content of Pt in the magnetic layer within the above range.

In addition to Co, Cr, Pt, the magnetic particles 42 of the magnetic layer contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re. It may be included. Among these, B is also supplied from a decomposition product of boron oxide contained in the target. By including the above elements, the miniaturization of the magnetic particles 42 can be promoted or the crystallinity and orientation can be improved, and recording / reproduction characteristics and thermal fluctuation characteristics suitable for higher density recording can be obtained.

  The total content of Co and Pt other than the above elements contained in the magnetic particles 42 is preferably 10 atomic% or less. When the total content of the above elements exceeds 10 atomic%, a phase other than the hcp phase is formed in the magnetic particles 42, so that the crystallinity and orientation of the magnetic particles 42 are disturbed, and as a result suitable for high-density recording. Further, the recording / reproducing characteristics and the thermal fluctuation characteristics cannot be obtained, which is not preferable.

  The magnetic layer 4c constituting the perpendicular magnetic layer 4 is not a layer formed using the target of the present invention, but includes magnetic particles (crystal particles having magnetism) 42 containing Co, as shown in FIG. It is preferable that the oxide 41 is not included. The magnetic particles 42 in the magnetic layer 4c are preferably grown epitaxially in a columnar shape from the magnetic particles 42 in the magnetic layer 4a. In this case, the magnetic particles 42 of the magnetic layers 4a to 4c are preferably epitaxially grown in a columnar shape in a one-to-one correspondence in each layer. Further, since the magnetic particles 42 of the magnetic layer 4b are epitaxially grown from the magnetic particles 42 in the magnetic layer 4a, the magnetic particles 42 of the magnetic layer 4b are miniaturized and the crystallinity and orientation are further improved. .

  The content of Cr in the magnetic layer 4c is preferably 10 atomic percent or more and 24 atomic percent or less. By setting the Cr content in the above range, it is possible to sufficiently ensure output during data reproduction and to obtain better thermal fluctuation characteristics. On the other hand, when the content of Cr exceeds the above range, the magnetization of the magnetic layer 4c becomes too small, which is not preferable. When the Cr content is less than the above range, the magnetic particles 42 are not sufficiently separated and refined, noise during recording / reproduction increases, and a signal / noise ratio (S) suitable for high-density recording (S / N ratio) is not obtained.

  The perpendicular coercive force (Hc) of the perpendicular magnetic layer 4 is preferably 3000 [Oe] or more. When the coercive force is less than 3000 [Oe], the recording / reproducing characteristics, particularly the frequency characteristics, are deteriorated, and the thermal fluctuation characteristics are also deteriorated, which is not preferable as a high-density recording medium. The reverse magnetic domain nucleation magnetic field (-Hn) of the perpendicular magnetic layer 4 is preferably 1500 [Oe] or more. When the reverse domain nucleation magnetic field (-Hn) is less than 1500 [Oe], the thermal fluctuation resistance is poor, which is not preferable.

  The average particle size of the magnetic particles 42 constituting the perpendicular magnetic layer 4 is preferably in the range of 3 to 12 nm, and the grain boundary width is preferably in the range of 0.5 to 4 nm. Particularly in the present invention, the average particle size is 6 nm or less. The grain boundary width of the Co-based magnetic particles can be 1.5 nm or more, and the interface of the magnetic particles can be made clear (sharp). As described above, in the present invention, when the granular magnetic layer is formed, the target containing CoO is used. Therefore, the separation of CoO is promoted, the Co-based magnetic particles are refined, isolated, and the grain boundary width is increased. And the interface can be sharpened. The average particle size, grain boundary width, and sharpness of the magnetic particle interface of the magnetic particles 42 can be obtained by, for example, observing the perpendicular magnetic layer 4 with a TEM (transmission electron microscope) and image-processing the observed image. .

"Protective layer"
A protective layer 5 is formed on the perpendicular magnetic layer 4. The protective layer 5 prevents corrosion of the perpendicular magnetic layer 4 and prevents damage to the medium surface when the magnetic head comes into contact with the magnetic recording medium. As the protective layer 5, a conventionally known material can be used. For example, a material containing C, SiO ₂ , or ZrO ₂ can be used. The thickness of the protective layer 5 is preferably 1 to 10 nm from the viewpoint of high recording density because the distance between the magnetic head and the magnetic recording medium can be reduced. The protective layer 5 is formed using, for example, a CVD (chemical vapor deposition) method.

"Lubrication layer"
A lubricating layer 6 is formed on the protective layer 5. For the lubricating layer 6, it is preferable to use a lubricant such as perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid, or the like. The lubricating layer 6 is formed using, for example, a dipping method.

(Magnetic recording / reproducing device)
FIG. 4 shows an example of a magnetic recording / reproducing apparatus to which the present invention is applied.
This magnetic recording / reproducing apparatus includes a magnetic recording medium 50 having the configuration shown in FIG. 1, a medium driving unit 51 that rotationally drives the magnetic recording medium 50, a magnetic head 52 that records and reproduces information on the magnetic recording medium 50, and A head driving unit 53 that moves the magnetic head 52 relative to the magnetic recording medium 50 and a recording / reproducing signal processing system 54 are provided.

  The recording / reproduction signal processing system 54 can process data input from the outside and send a recording signal to the magnetic head 52, process a reproduction signal from the magnetic head 52, and send the data to the outside. . As the magnetic head 52 used in the magnetic recording / reproducing apparatus to which the present invention is applied, a magnetic head having a GMR element utilizing a giant magnetoresistive effect (GMR) as a reproducing element and suitable for higher recording density is used. it can.

  The magnetic recording / reproducing apparatus shown in FIG. 4 includes the magnetic recording medium 50 shown in FIG. 1 as an example of the magnetic recording medium of the present invention, and a magnetic head 52 that records and reproduces information on the magnetic recording medium 50. Therefore, the magnetic recording medium having a signal / noise ratio (S / N ratio) and recording characteristics (OW) suitable for high-density recording is excellent.

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

(Manufacture of the target of an Example)
A target having a composition made of CoCrPtB—SiO ₂ was produced by the following method.

First, by a gas atomizing method was prepared _{Co16Pt, CoO, Cr, B 2} O 3, a SiO ₂ powder. The average particle size of the powder was about 5 μm. The powder was mixed with 8 mol% CoO, 7 mol% Cr, 7 mol% SiO ₂ and B ₂ O ₃ within a range of 0 to 6 mol%, and the remainder was mixed as Co16Pt. After pre-molding, hot pressing was performed in an argon atmosphere at 800 ° C. and a pressure of 200 kgf / cm ² for 1 hour, and the sintered body was cut into a target shape to produce a target. The porosity of the obtained target is shown in FIG. 5, and a target having a porosity of 7% or less could be produced by containing 3 mol% or more of boron oxide. Separately, when an experiment was made to contain 20 mol% of boron oxide, a porosity of less than 2% was achieved.

(Example)
The magnetic recording media of the examples were manufactured and evaluated by the manufacturing methods shown below. Incidentally, granular magnetic layer of the present example, in the preparation of the target, with porosity of 2% target obtained with B ₂ O ₃ as a 5.5 mole%.

First, a cleaned glass substrate (manufactured by Konica Minolta, 2.5 inch outer diameter) is housed in a film forming chamber of a DC magnetron sputtering apparatus (C-3040, manufactured by Anelva), and the ultimate vacuum is 1 × 10 ^−3. After evacuating the film formation chamber to ⁵ Pa, an adhesion layer having a thickness of 10 nm was formed on the glass substrate using a Cr target.

  On the adhesion layer thus obtained, a target of Co-20Fe-5Zr-5Ta {Fe content 20 atomic%, Zr content 5 atomic%, Ta content 5 atomic%, balance Co} is used. A soft magnetic layer having a layer thickness of 25 nm is formed at a substrate temperature of 100 ° C. or less, a Ru layer is formed thereon with a layer thickness of 0.7 nm, and a soft magnetic layer of Co-20Fe-5Zr-5Ta is further formed. A film having a thickness of 25 nm was formed as a soft magnetic underlayer.

  Next, an orientation control layer was formed on the soft magnetic underlayer by a sputtering method. As the orientation control layer, a first orientation control layer made of Ru arranged on the soft magnetic underlayer side and a second orientation control layer made of Ru arranged on the perpendicular magnetic layer side of the first orientation control layer are sputtered. Formed by. The sputtering gas pressure of the first orientation control layer was 3 Pa, and the sputtering gas pressure of the second orientation control layer was 10 Pa.

Thereafter, a perpendicular magnetic layer having a granular structure using the above target was formed on the orientation control layer. The sputtering gas pressure was set to 2 Pa and the film was formed with a layer thickness of 4 nm. The composition of the formed perpendicular magnetic layer having a granular structure was 92 (Co10Cr14Pt5B) -8 (SiO ₂ ).

  Next, a nonmagnetic layer made of Ru was formed with a layer thickness of 0.3 nm on the magnetic layer having a granular structure.

  Next, a sputtering gas pressure is set to 0.6 Pa on a nonmagnetic layer using a target made of Co20Cr14Pt3B {Cr content 20 atomic%, Pt content 14 atomic%, B content 3 atomic%, balance Co}. The magnetic layer was formed with a layer thickness of 7 nm.

  Next, a protective layer having a thickness of 3.0 nm was formed by a CVD method, and then a lubricating layer made of perfluoropolyether was formed by a dipping method to produce a magnetic recording medium.

  With respect to the magnetic recording medium thus obtained, a signal / noise ratio (S / N ratio) and a recording characteristic (OW) as recording / reproducing characteristics using a read / write analyzer RWA1632 and spin stand S1701MP manufactured by GUZIK, USA. Evaluation was performed.

  As the magnetic head, a head using a single pole magnetic pole on the writing side and a TMR element on the reading side was used.

  The signal / noise ratio (S / N ratio) was measured at a recording density of 750 kFCI.

  Regarding the recording characteristics (OW), first, a 750 kFCI signal was written, then a 100 kFCI signal was overwritten, a high frequency component was taken out by a frequency filter, and the data writing ability was evaluated by the residual ratio. As a result, the S / N ratio was 14.10 dB and OW was 42.4 dB, which was excellent in electromagnetic conversion characteristics. After the evaluation, the granular magnetic layer was observed by TEM. As a result, the average particle size of the magnetic particles was 5.5 nm, the grain boundary width was 1.6 nm, and the interface of the magnetic particles was clear.

(Manufacture of target of comparative example)
A target having a composition composed of 92 (71Co10Cr14Pt5B) -8 (SiO ₂ ) was produced by the following method.

First, Co, Cr, and Pt powders were manufactured by a gas atomization method. The average particle size of the powder was about 5 μm. B, SiO ₂ powder having an average particle diameter of about 5 μm was added to this powder to give a composition ratio of 92 (71Co10Cr14Pt5B) -8 (SiO ₂ ). After this mixed powder was pre-molded into a mold, 1200 ° C., pressure 200 kgf / Cm ² , hot pressing for 3 hours in a vacuum, and the sintered body was cut into a target shape to produce a target. The porosity of the obtained target was 2%.

(Comparative example)
A magnetic recording medium was manufactured in the same manner as in the example, but the target of the above-mentioned comparative example having a composition of 92 (71Co10Cr14Pt5B) -8 (SiO ₂ ) was used for forming the perpendicular magnetic layer having a granular structure.

  The magnetic conversion characteristics of the obtained magnetic recording medium were inferior to those of the examples, with an S / N ratio of 13.60 dB and an OW of 41.5 dB. After the evaluation, the granular magnetic layer was observed with a TEM. The average particle size of the magnetic particles was 6.1 nm, and the grain boundary width was 1.9 nm.

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic substrate, 2 ... Soft magnetic underlayer, 3 ... Orientation control layer, 3a ... 1st orientation control layer, 3b ... 2nd orientation control layer, 4 ... Perpendicular magnetic layer, 7 ... Perpendicular magnetic layer, 4a ... 1st 1 magnetic layer 7a 2nd magnetic layer 4b 3rd magnetic layer 7b 4th magnetic layer 4c 5th magnetic layer 5 5 protective layer 6 lubrication layer 15 oxidation S1, S2, S3 ... columnar crystals, S1a ... irregular surface, 41 ... oxide, 42 ... magnetic particles, 50 ... magnetic recording medium, 51 ... medium drive unit, 52 ... magnetic head, 53 ... head drive unit, 54 ... Recording / reproduction signal processing system.

Claims (7)

A target used for forming a Co-based magnetic layer of a magnetic recording medium by a sputtering method, wherein the target contains 5 mol% or more of Cr or Cr alloy, contains 5 mol% or more of CoO, and has a melting point of 800 ° C. or less. A target comprising oxides in the range of 3 to 20 mol% in total and having a porosity of 7% or less. The target is selected from the group consisting of SiO ₂ , TiO, TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , and CeO _2. The target according to claim 1, comprising: a target. The target contains Co in the range of 55 mol% to 75 mol%, contains Cr or Cr alloy in the range of 5 mol% to 28 mol%, and Pt in the range of 5 mol% to 25 mol%. CoO is included in the range of 5 mol% to 15 mol%, oxides having a melting point of 800 ° C. or less are included in the total range of 3 mol% to 15 mol%, and SiO ₂ , TiO, TiO ₂ , ZrO ₂ , oxides selected from the group consisting of Cr ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , and CeO ₂ are included within a total range of 5 mol% to 25 mol%. The target according to claim 1 or 2. 4. The oxide according to claim 1, wherein the oxide having a melting point of 800 ° C. or lower is at least one selected from boron oxide, vanadium oxide, tellurium oxide, molybdenum oxide, and low-melting glass. Target. Co in the range of 55 mol% to 75 mol%, Cr or Cr alloy in the range of 5 mol% to 28 mol%, Pt in the range of 5 mol% to 25 mol%, CoO in the range of 5 mol% to 15 mol% %, A total of oxides having a melting point of 800 ° C. or less within a range of 3 mol% to 15 mol%, SiO ₂ , TiO, TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O _{5, Al} 2 _O 3, an oxide selected from the group consisting of CeO ₂ is in the range of 5 mol% to 25 mol% in total powder was after mixing, preformed, then, 430 ° C. to 800 ° C. And manufacturing the target for forming the magnetic layer of the magnetic recording medium, wherein the porosity is 7% or less within the above range. 6. The method for producing a target according to claim 5, wherein the oxide having a melting point of 800 ° C. or lower is at least one selected from boron oxide, vanadium oxide, tellurium oxide, molybdenum oxide, and low-melting glass. A method for producing a magnetic recording medium, comprising forming a magnetic layer on a substrate by sputtering using the target according to claim 1.

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