JP2006302426A - Perpendicular magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium compatibly attaining thermal stability and reduction of a magnetic cluster size. <P>SOLUTION: In the perpendicular magnetic recording medium provided with a non-magnetic substrate, a non-magnetic intermediate layer and a magnetic recording layer in this order, the magnetic recording layer has a granular structure containing Co, Cr, Pt, Si and O, the diameter of magnetic crystal grains is substantially fixed in the film thickness direction and a region on the interface side between the non-magnetic intermediate layer and the magnetic recording layer has an oxygen content more than that of a region on the surface side of the magnetic recording medium. Preferably, a soft magnetic backing layer and an underlayer are further provided and the underlayer contains Ni and Fe and has a crystal structure comprising a face-centered cubic lattice and soft magnetism. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium mounted on various magnetic recording apparatuses and a manufacturing method thereof. In particular, the present invention relates to a perpendicular magnetic recording medium mounted on a fixed magnetic disk device used as an external storage device such as a computer or AV equipment, and a method for manufacturing the same.

Since 1997, the recording density of HDDs has increased rapidly at an annual rate of 60-100%. Although the momentum is decreasing recently, it is predicted that it will continue to increase at a rate of 30-60% every year. As a result of such remarkable growth, the in-plane recording method used so far is approaching its limit due to the problem of thermal fluctuation. Thermal fluctuation is a phenomenon in which a recorded signal cannot be held stably. In the in-plane recording method, thermal fluctuation increases as the recording density increases. Under such circumstances, development of a perpendicular recording system having characteristics opposite to the in-plane recording system, that is, a characteristic that the bit stability increases with an increase in recording density, has been activated.
A perpendicular magnetic recording medium mainly includes a magnetic recording layer of a hard magnetic material, an underlayer for orienting the magnetic recording layer in a desired direction, a protective layer for protecting the surface of the magnetic recording layer, and recording on the recording layer It is composed of a backing layer of a soft magnetic material that plays a role of concentrating the magnetic flux generated by the magnetic head used in the above.

In order to improve the basic characteristics of the medium, it is necessary to improve the output-noise ratio (SNR). In particular, low noise is a very important factor in increasing the density of media, and various efforts have been made to reduce noise. Above all, promoting the segregation of nonmagnetic substances to the grain boundaries in the magnetic recording layer reduces the exchange interaction between magnetic crystal grains and leads to a reduction in medium noise by reducing the magnetization reversal unit. Materials and processes to promote segregation have been studied.
As magnetic recording layer materials for perpendicular magnetic recording media, alloy materials such as CoCrPt and CoCrTa have been studied so far. In these alloy materials, Cr, which is a non-magnetic material, segregates at the magnetic crystal grain boundaries, so that individual magnetic crystal grains are magnetically separated, and have characteristics necessary for a magnetic recording medium such as high coercive force (Hc). To express. Such segregation of Cr to the magnetic crystal grain boundary has been promoted in the in-plane medium by devising a film forming process such as heating or applying a substrate bias. However, unlike the in-plane medium, the perpendicular magnetic recording medium has a problem in that even when heating or applying a substrate bias is applied, the amount of Cr segregation is small, which causes the medium noise to increase.

As a solution to this problem, a CoPtCrO magnetic recording layer (see, for example, Non-Patent Document 1) or CoPtCr—SiO ₂ that promotes magnetic separation of magnetic crystal grains by segregating oxides to magnetic crystal grain boundaries. A granular medium using a magnetic recording layer (for example, see Non-Patent Document 2) has been proposed. For example, in a CoPtCr—SiO ₂ granular film, the CoPtCr magnetic crystal grains are segregated so as to surround the SiO ₂ , whereby the individual CoPtCr magnetic crystal grains are magnetically separated. As described above, the granular film is characterized in that it does not use phase separation (magnetic phase separation) of the alloy material but adds an amorphous material that is not easily dissolved in the alloy material, such as oxide or nitride. In the above-mentioned documents, it has been confirmed that granular noise can reduce medium noise as compared with a perpendicular magnetic recording medium using a conventional CoCr alloy material as a magnetic recording layer, and is expected as a promising method in the future.
JP 2002-358617 A JP 2003-123239 A Japanese Patent Laid-Open No. 8-63732 JP 2001-202611 A S. Oikawa, A.A. Takeo, T .; Hikosaka, and Y.J. Tanaka, “High performance CoPtCrO single layered pendular media with no recording demonification,” IEEE Trans. Magn. , Vol. 36, pp. 2393-2395, 2000. T. T. et al. Oikawa, M .; Nakamura, H .; Uwazumi, T .; Shimatsu, H .; Muraoka, and Y.M. Nakamura, “Microstructure and Magnetic Properties of CoPtCr—SiO 2 Perpendicular Recording Media,” IEEE Trans. Magn. , Vol. 38, pp. 1976-1978, 2002 J. et al. Chen, H.C. Saito, S .; Ishio and K.K. Kobayashi, “Magnetic cluster and medium noise in CoCrTa / Cr longitudinal film medium by magnetic force microscopy,” J. Am. App. Phys. , Vol. 85, pp. 1037-1042, 1999 Toshiji Takeno, Yasushi Sakai, Kazuo Tsujimoto, Tadaaki Oikawa, Sadayuki Watanabe, Hiroyuki Uezumi, Takehito Shimazu, Hiroaki Muraoka, Yoshihisa Nakamura, "CoPtCr-SiO2 granular perpendicular magnetic recording media", Journal of Applied Magnetics Society of Japan, vol. 27, pp. 940-942, 2003

However, in the CoPtCr—SiO ₂ granular film, the magnetic crystal grains seem to be separated very well at first glance, but actually, the magnetic crystal grains are not reversed independently, but several magnetic crystal grains are simultaneously magnetized. It has recently become clear that this is reversed. That is, even in the case of a CoPtCr—SiO ₂ granular film that looks very well separated, the exchange interaction between magnetic crystal grains is not sufficiently reduced, and thus the medium noise cannot be sufficiently reduced.
In a magnetic recording layer composed of fine magnetic crystal grains, it is known that magnetization reversal does not occur for each magnetic crystal grain, and several magnetic crystal grains are magnetically connected and behave as one magnetization reversal unit. Such a magnetization reversal unit is called a magnetic cluster, and it has been reported that the measured magnetic cluster size and the medium noise correlate well (for example, see Non-Patent Document 3).

The current CoPtCr—SiO ₂ granular film looks very well separated when viewed with a transmission electron microscope (TEM) image or the like, but the surface of the granular medium AC-erased using a magnetic force microscope (MFM) is observed, When the magnetic cluster size is measured by image processing, it has been found that the size is several to 10 times the magnetic crystal grain size. This means that several to 10 or more magnetic crystal grains form one magnetic cluster and are simultaneously reversed in magnetization. The cause of the magnetic cluster size being larger than the magnetic crystal grain size is It is believed that there is an exchange interaction between magnetic crystal grains. However, in the CoPtCr—SiO ₂ granular film in which the separation of magnetic crystal grains looks very good, it has not been clarified so far about which part of the exchange interaction is insufficiently reduced. On the other hand, it has recently been found that the cause of this is the initial growth layer of the magnetic recording layer (see, for example, Non-Patent Document 4).

The present inventors have so far used a soft magnetic permalloy-based material as an underlayer and a Ru or Ru-based alloy as a nonmagnetic intermediate layer, thereby improving the orientation of the magnetic recording layer and the initial growth layer of the magnetic recording layer. It has been reported that reduction, reduction of magnetic crystal grain size, and the like can be achieved (see, for example, Patent Documents 1 and 2). By applying the underlayer and intermediate layer based on these inventions, a magnetic recording layer having good crystallinity and orientation can be obtained, and an initial growth layer in the magnetic recording layer that causes a decrease in magnetic properties and crystal orientation Can be reduced. However, in order to reduce the exchange interaction between the magnetic crystal grains in the initial formation region of the magnetic recording layer, it is not sufficient to improve only the underlayer and the intermediate layer, and improvement of the magnetic recording layer itself has been desired.
On the other hand, as a means for reducing exchange interaction between magnetic crystal grains in the magnetic recording layer, a method of adding O (oxygen) has been proposed. For example, in Patent Document 3, the film is formed by adding O to Co, thereby reducing the magnetic interaction between the magnetic crystal grains, and increasing the amount of O contained in the film surface. It is proposed that the film can prevent corrosion and increase mechanical strength. However, since this method is mainly intended to increase the mechanical strength such as wear resistance on the surface of the magnetic recording layer, the purpose is to reduce the exchange interaction between the magnetic crystal grains in the initial growth stage of the magnetic recording layer. A sufficient effect cannot be obtained. In addition, no consideration is given to the viewpoint of thermal stability.

In Patent Document 4, the amount of oxide added to the magnetic recording layer is changed in the film thickness direction, and the magnetic crystal grain size is changed in the film thickness direction by increasing the amount on the substrate side and decreasing it at the center of the film. A method has been proposed. However, since the change in the magnetic crystal grain size is accompanied by a change in the gap between adjacent magnetic crystal grains, the exchange interaction between the magnetic crystal grains becomes unstable, resulting in an increase in noise and the subgrains of the magnetic crystal grains. Has the problem that thermal stability is reduced.
The present invention has been made in view of such a problem, and an object of the present invention is to reduce the size of the magnetic cluster in the initial growth of the magnetic recording layer without deteriorating the thermal stability of the medium. An object of the present invention is to provide a perpendicular magnetic recording medium that simultaneously realizes improvement of medium performance such as low noise and improvement of SNR and maintenance of thermal stability.

In order to solve the above-described problem, the perpendicular magnetic recording medium of the present invention is a perpendicular magnetic recording medium including a nonmagnetic substrate, a nonmagnetic intermediate layer, and a magnetic recording layer in this order. , Cr, Pt, Si and O, and a structure in which a non-magnetic grain boundary containing oxygen surrounds the magnetic crystal grains, and the magnetic crystal grain size is substantially constant in the film thickness direction. A region having more oxygen than the surface side of the magnetic recording layer is provided on the interface side with the magnetic intermediate layer.
It is preferable that the amount of oxygen contained in the magnetic recording layer continuously decreases from the interface side with the nonmagnetic intermediate layer toward the surface side of the magnetic recording layer.
Moreover, it is preferable to provide a soft magnetic backing layer between the nonmagnetic substrate and the nonmagnetic intermediate layer.
In addition, it is preferable to provide a soft magnetic underlayer containing Ni and Fe, having a crystal structure of a face-centered cubic lattice, and having soft magnetism between the soft magnetic backing layer and the nonmagnetic intermediate layer.

A method for producing the perpendicular magnetic recording medium is characterized in that the sputtering gas contains oxygen, and the oxygen concentration in the first half of the film formation is higher than the oxygen concentration in the second half of the film formation. To do.
It is preferable to perform sputtering film formation while continuously reducing the oxygen concentration during film formation.
Further, in the method for manufacturing the perpendicular magnetic recording medium, the substrate is exposed to a sputtering gas containing oxygen for 0.4 second or more and 1.5 seconds or less in a chamber for forming a magnetic thin film, Sputtering is started.

  Constructing or manufacturing a perpendicular magnetic recording medium as described above promotes the segregation of oxides to the magnetic grain boundaries in the initial growth layer without reducing uniaxial anisotropy or forming subgrains. It becomes possible. As a result, the magnetic cluster size of the magnetic recording layer can be reduced without degrading the thermal stability, and it is possible to improve the media performance such as low noise and SNR, and the density of the perpendicular magnetic recording medium is increased. Achieved.

First, the principle of the present invention will be described.
FIG. 2 is a schematic diagram for explaining the details of the magnetic recording layer 5, FIG. 2a is a plan view seen from the top of the magnetic recording layer 5, and FIG. 2b is a schematic sectional view. The magnetic recording layer 5 is formed by forming an initial growth layer 51 and subsequently growing a bulk layer 52. Further, the magnetic crystal grains 10 are surrounded by a nonmagnetic grain boundary 11 to form a so-called granular type magnetic recording layer.
Recording / reproducing performance is improved by configuring the magnetic crystal grains 10 to have a substantially constant grain size in the film thickness direction. This is for the following two reasons. First, when the magnetic crystal grain size fluctuates, the magnetic interaction between the magnetic crystal grains becomes unstable, and recording and reproduction noise increases. For example, when the magnetic crystal grain size is increased in a part of the film thickness direction in a certain magnetic crystal grain, the distance between adjacent magnetic crystal grains is shortened and the magnetic interaction is increased. That is, as a result, the magnetic cluster size increases. Secondly, conversely, when the magnetic crystal grain size is reduced in a part of the film thickness direction, subgrains are generated and thermal stability is lowered.

On the other hand, as a result of investigations by the inventors, it has been found that the following difficulties arise in order to keep the magnetic crystal grain size constant. When using a magnetic recording layer containing oxygen or oxide, the degree of segregation of the oxide to the nonmagnetic grain boundary differs between the initial growth stage and the growth stage, and segregation of the oxide to the nonmagnetic grain boundary occurs in the early growth stage. hard. Therefore, it is difficult to keep the magnetic crystal grain size constant at the same oxide concentration.
Further, as shown in FIG. 2, a recess 20 is formed on the interface side of the nonmagnetic intermediate layer 4 with the magnetic recording layer 5. This is because the crystal grain boundary on the surface of the nonmagnetic intermediate layer has a concave shape because the crystal grains constituting the nonmagnetic intermediate layer have a tapered shape. The magnetic crystal grains of the magnetic recording layer are epitaxially grown on the crystal grains of the nonmagnetic intermediate layer, and the nonmagnetic grain boundaries of the magnetic recording layer are formed on the crystal grain boundaries of the nonmagnetic intermediate layer. Therefore, at the initial stage of growth of the magnetic recording layer, the oxide needs to be formed also in the concave portion at the interface of the nonmagnetic intermediate layer, and it is necessary to add a sufficient amount of oxide to fill the concave portion.

In consideration of the above, by providing a region with more oxygen or oxide on the interface side of the magnetic recording layer 5 with the nonmagnetic intermediate layer 4 than on the surface side of the magnetic recording layer 5, good crystallinity and orientation It can be seen that the magnetic cluster size in the initial growth layer of the magnetic recording layer can be reduced while maintaining the above. In addition, it is possible to promote the segregation of oxide to the magnetic grain boundary in the initial growth layer without causing a decrease in uniaxial anisotropy or formation of subgrains, and magnetic recording without reducing thermal stability. The magnetic cluster size of the layer can be reduced.
When simply increasing the amount of oxygen or oxide contained in the magnetic recording layer for the purpose of improving the performance of the initial growth layer, the upper layer excluding the initial growth layer becomes excessive in oxygen and the uniaxial anisotropy decreases. In other words, fine and non-oriented subgrains are formed, and the thermal stability is lowered.

Here, the magnetic crystal grain size is substantially constant means that a change in magnetic interaction due to a change in the gap between adjacent magnetic crystal grains does not cause a practical problem. The change in crystal grain size is approximately within 10%.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining a configuration example of a perpendicular recording medium according to the present invention. On the nonmagnetic substrate 1, a soft magnetic backing layer 2, an underlayer 3, a nonmagnetic intermediate layer 4, a magnetic recording layer 5, a protective layer 6, and a liquid lubricating layer 7 are formed.
The nonmagnetic substrate 1 may be various substrates having a smooth surface. For example, an Al alloy plated with NiP, tempered glass, crystallized glass or the like used for a magnetic recording medium can be used.
The soft magnetic underlayer 2 is a layer that is preferably provided in order to efficiently concentrate the magnetic flux of the magnetic head responsible for recording / reproducing, and can be omitted. As the material, crystalline FeTaC, Sendust (FeSiAl) alloy, etc., or amorphous Co alloy such as CoZrNb, CoTaZr, etc. can be used. The optimum value of the film thickness of the soft magnetic underlayer 2 varies depending on the structure and characteristics of the magnetic head used for recording, but is preferably about 10 nm to 500 nm in view of productivity.

The underlayer 3 is a layer that is preferably provided to improve the crystallinity, orientation, and the like of the nonmagnetic intermediate layer 4 formed thereon, and can be omitted. When the underlayer 3 is provided, it is preferable to use a soft magnetic material containing Ni and Fe and having an fcc structure. For example, NiFeNb, NiFeB, NiFeSi, CoNiFe, CoNiFeSi, CoNiFeNb, etc. can be used. Since this underlayer functions in the same way as the soft magnetic underlayer, there is no particular problem in terms of function as a thick film, but the magnetic crystal grain size increases as the film thickness increases. The film thickness is preferably 30 nm or less. Especially preferably, they are 1 nm or more and 15 nm or less.
The nonmagnetic intermediate layer 4 is made of a material selected from Ru, Re, Pd, Ir, Pt or Rh, or an alloy whose main component is a material selected from Ru, Re, Pd, Ir, Pt or Rh. It is preferable to form. The film thickness of the nonmagnetic intermediate layer should be as thin as possible within a range that does not deteriorate the magnetic characteristics and electromagnetic conversion characteristics of the magnetic recording layer, and is required to realize high-density recording, and should be 20 nm or less. preferable. Especially preferably, they are 1 nm or more and 10 nm or less.

The magnetic recording layer 5 is made of an alloy ferromagnetic material containing at least Co, Cr, Pt, Si, and O, and it is perpendicular that the c-axis of the hexagonal close-packed structure is oriented in a direction perpendicular to the film surface. Necessary for use as a magnetic recording medium. The magnetic crystal grain size is substantially constant in the thickness direction of the magnetic recording layer. Examples of the material include, but are not limited to, granular materials such as CoCrPt—SiO ₂ , CoCrPtSiO, CoCrPtSiBO, and CoCrPt—SiO ₂ —Al ₂ O ₃ . The thickness of the magnetic recording layer 5 is not particularly limited, but is preferably 30 nm or less, and more preferably 15 nm or less, from the viewpoint of productivity and high density recording. The amount of oxygen contained in the magnetic recording layer 5 is not constant in the film thickness direction, and is configured to have a region with more oxygen on the interface side with the nonmagnetic intermediate layer 4 than on the surface side of the magnetic recording layer. Further, the amount of oxygen contained in the magnetic recording layer 5 may be formed so as to gradually decrease from the interface side with the nonmagnetic intermediate layer 4 toward the surface side. The amount of oxygen is set from the viewpoint of the crystallinity and orientation of the magnetic alloy contained in the magnetic recording layer and the magnetic crystal grain size considering thermal fluctuation. When the amount of oxygen is defined by the volume fraction of the oxide, the volume fraction of the oxide contained in the magnetic recording layer in the initial growth layer 51 is preferably 30 vol% or more and 50 vol% or less. The volume fraction is preferably 35 vol% or less. The film thickness of the initial growth layer 51 is 2 nm to 6 nm.

  As a method of changing the amount of oxygen added to the magnetic recording layer, a method of preparing a plurality of sputtering targets having different compositions, a method of changing the composition of the sputtering gas during film formation, or the like can be used. The latter is preferable in view of productivity. More specifically, in the sputtering method, it is preferable to use a sputtering gas containing oxygen and to make the oxygen concentration in the first half of the film formation higher than the oxygen concentration in the second half of the film formation. Similarly, it is also preferable to form a film using a sputtering gas containing oxygen and continuously reducing the oxygen concentration during the film formation. Further, in a chamber for forming the magnetic recording layer, the substrate immediately before the magnetic recording layer is formed is exposed to a sputtering gas containing oxygen for 0.4 seconds or more and 1.5 seconds or less, and then the magnetic recording layer is sputtered. By starting, the amount of oxygen in the initial growth layer can be increased.

For example, a thin film mainly composed of carbon is used for the protective layer 6. In addition, various thin film materials generally used as a protective layer of a magnetic recording medium may be used.
For the liquid lubricant layer 7, for example, a perfluoropolyether lubricant can be used. In addition, various lubricating materials that are generally used as liquid lubricating layer materials for magnetic recording media may be used.
Each layer laminated on the non-magnetic substrate can be formed by various film forming techniques usually used in the field of magnetic recording media. For example, a DC magnetron sputtering method, an RF magnetron sputtering method, or a vacuum deposition method can be used to form each layer except the liquid lubricant layer. In addition, for example, a dipping method or a spin coating method can be used for forming the liquid lubricating layer. However, it is not limited to these.

  The perpendicular magnetic recording medium of the present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples, and it goes without saying that various changes can be made without departing from the scope of the present invention.

A chemically tempered glass substrate (N-5 glass substrate manufactured by HOYA) having a smooth surface is used as the non-magnetic substrate 1, and this is introduced into the sputtering apparatus after cleaning. Co3Zr5Nb Zr is 3 atomic%, Nb is 5 atomic%, and the remainder is Co. The same applies hereinafter.) Using a target, the CoZrNb amorphous soft magnetic underlayer 2 is formed to a thickness of 160 nm. To form a film. Next, a CoNiFeSi underlayer 3 was formed to a thickness of 6 nm using a Co35Ni4Fe1Si target. Subsequently, a Ru nonmagnetic intermediate layer 4 was formed to a thickness of 10 nm under an Ar gas pressure of 4.0 Pa using a Ru target. Subsequently, a CoCrPt—SiO ₂ magnetic recording layer 5 was formed to a thickness of 10 nm under a gas pressure of 5.3 Pa using a 92 mol% (Co12Cr14Pt) -8 mol% (SiO ₂ ) target. At this time, a sputtering gas containing 3.8% by volume of oxygen in Ar was used for the first half of 5 nm, and a sputtering gas containing 2.3% by volume of oxygen in Ar was used for the latter 5 nm. In addition, a substrate bias of −200 V was applied when forming the magnetic recording layer. Finally, a protective layer 6 made of carbon was formed with a film thickness of 3.5 nm using a CVD apparatus, and then taken out from the vacuum apparatus. All of these films except for the Ru nonmagnetic intermediate layer and the CoCrPt—SiO ₂ magnetic recording layer were formed under an Ar gas pressure of 0.67 Pa, and the CoCrPt—SiO ₂ magnetic recording layer was formed by a pulsed DC magnetron sputtering method. Was formed by DC magnetron sputtering. Thereafter, a liquid lubricating layer 7 made of perfluoropolyether was formed by a dipping method with a film thickness of 2 nm to obtain a perpendicular magnetic recording medium.

A 90 mol% (Co12Cr14Pt) -10 mol% (SiO ₂ ) target was used as the magnetic recording layer 5, and the CoCrPt—SiO ₂ magnetic recording layer 5 was formed by pulsed DC magnetron sputtering at a thickness of 10 nm under a gas pressure of 5.3 Pa. A film was formed. A mixed gas of Ar and oxygen is used for sputtering, the oxygen in the gas is set to 3.8% by volume at the start of sputtering, the oxygen flow rate is linearly reduced during sputtering, and the oxygen flow rate is zero at the end of sputtering (only Ar) It adjusted so that it might become. A perpendicular magnetic recording medium was fabricated in exactly the same manner as in Example 1 except for the magnetic film.

A 90 mol% (Co12Cr14Pt) -10 mol% (SiO ₂ ) target was used as the magnetic recording layer, and the CoCrPt—SiO ₂ magnetic recording layer 5 was formed by pulsed DC magnetron sputtering at a thickness of 10 nm under a gas pressure of 5.3 Pa. Filmed. In the magnetic recording layer deposition process, the substrate on which the nonmagnetic intermediate layer has been deposited is exposed to Ar gas containing 5% by volume of oxygen gas for 0.8 seconds before the start of sputtering, and simultaneously with the start of deposition. The supply of oxygen gas was stopped by setting the flow rate of oxygen gas to zero. A perpendicular magnetic recording medium was fabricated in exactly the same manner as in Example 1 except for the magnetic recording layer.
(Comparative Example 1)
A perpendicular magnetic recording medium was fabricated in exactly the same manner as in Example 1 except that a 92 mol% (Co12Cr14Pt) -8 mol% (SiO ₂ ) target was used as the magnetic recording layer and sputtering was performed in pure Ar gas.
(Comparative Example 2)
Other than using a 92 mol% (Co12Cr14Pt) -8 mol% (SiO ₂ ) target as the magnetic recording layer and fixing the oxygen concentration contained in the sputtering gas composed of oxygen and Ar to 3.8% by volume. A perpendicular magnetic recording medium was fabricated in exactly the same manner as in Example 1.
(Comparative Example 3)
Other than using a 92 mol% (Co12Cr14Pt) -8 mol% (SiO ₂ ) target as the magnetic recording layer and fixing the oxygen concentration contained in the sputtering gas composed of oxygen and Ar to 2.3 vol%. A perpendicular magnetic recording medium was fabricated in exactly the same manner as in Example 1.
(Comparative Example 4)
Using 92 mol% as a magnetic recording layer (Co12Cr14Pt) -8 mol% (SiO ₂₎ target, for the first half 5nm min, using a sputtering gas containing oxygen 2.3 vol% in Ar, the second half of 5nm is A perpendicular magnetic recording medium was fabricated in the same manner as in Example 1 except that a sputtering gas containing 3.8% by volume of oxygen in Ar was used.

For the perpendicular magnetic recording media of Examples 1 to 3 and Comparative Examples 1 to 4 obtained as described above, the coercive force _Hc and the squareness ratio S were measured using a Kerr effect measuring apparatus. Further, medium noise, SNR (signal-to-noise ratio), and Decay (deterioration rate of recorded signal) were measured and compared using a read / write tester (hereinafter referred to as R / W characteristics). Further, by using an X-ray diffraction (XRD) apparatus, crystallinity was evaluated from the θ-2θ peak intensity, and orientation dispersion was evaluated from a rocking curve.
In addition to these evaluation items, the magnetic cluster size (D _cluster ) of each medium was evaluated using a magnetic force microscope (MFM). An example of the evaluation is shown in FIG. The evaluation method is as follows. First, the medium to be evaluated is AC demagnetized and the surface thereof is observed with MFM. Next, the inversion unit is approximated by a circle from the obtained image. Finally, the approximate circle diameter was extracted to create a histogram, and the average value was defined as D _cluster . The D _cluster of each medium evaluated in this way was compared.

Table 1 shows H _c , squareness ratio S, SNR at a linear recording density of 372 kfci, normalized noise, and Decay at a linear recording density of 31 kfci of the perpendicular magnetic recording media according to Examples 1 to 3 and Comparative Examples 1 to 4. Further, the intensity of the Co (002) peak by XRD I _{Co (002)} (represented by cps which is the number of counts per unit time), the rocking curve half-value width Δθ _{50 of} the Co (002) peak, D _cluster measured using MFM. Also shown.
Example 1 and Comparative Example 1 will be compared and discussed. Comparative Example 1 is a conventional example in which sputtering was performed only with Ar without adding oxygen to the sputtering gas when forming the magnetic recording layer. That is, in the magnetic recording layer of the medium of Comparative Example 1, the oxide (or oxygen) concentration is determined by the target composition and is constant in the film thickness direction. From Table 1, the medium of Example 1 has a squareness ratio S and Decay that are substantially the same as the medium of Comparative Example 1, but Hc is about 13% and SNR is about 2.7 dB higher. Since the intensity of the Co (002) peak and Δθ ₅₀ are slightly better in the medium of Comparative Example 1, it is considered that there is no problem with the medium of Comparative Example 1 regarding the crystallinity and orientation of the magnetic recording layer. On the other hand, D _cluster shows that the medium of Comparative Example 1 is nearly twice as large as the medium of Example 1. Thus, in the medium of Example 1, it is considered that low noise and high SNR were achieved by reducing D _cluster as compared with Comparative Example 1 which is a conventional medium.

The medium of Example 1 was subjected to cross-sectional observation using a transmission electron microscope (TEM). When the change of the grain size in the film thickness direction of the magnetic crystal grains of the magnetic recording layer 30 was measured, the change was 8% or less except for the very surface. From this result, it can be said that in the medium produced using the process of Example 1, the crystal grain size of the magnetic recording layer 30 is substantially constant in the film thickness direction. In addition, the concave portion shown in FIG. 2B was observed on the surface of the nonmagnetic intermediate layer, and it was simultaneously observed that the concave portion was filled with oxide. Further, when the cross section of the media of Examples 2 and 3 was similarly observed using a transmission electron microscope (TEM), the magnetic crystal grain size of the magnetic recording layer was substantially constant in the film thickness direction. .
Next, Example 1 and Comparative Example 2 are compared and considered. Comparative Example 2 is an example in which the concentration of oxygen added to the sputtering gas is constant at 3.8% by volume when the magnetic recording layer is formed. That is, in the magnetic recording layer of the medium of Comparative Example 2, the oxide (or oxygen) concentration contained in the magnetic recording layer is different from that of Comparative Example 1, but the oxide (or oxygen) concentration in the film thickness direction is constant. ing. As is clear from Table 1, the medium of Example 1 is superior in terms of Hc, SNR, and normalized noise. The medium of Comparative Example 2 is close to the medium of Example 1 in terms of Hc and SNR, but Decay is large, and the peak intensity of Co (002) is decreased and Δθ ₅₀ is increased. This indicates that the crystallinity is deteriorated and the c-axis orientation dispersion of the magnetic crystal grains is increased. Actually, it was confirmed from the transmission electron microscope (TEM) image that fine non-oriented subgrains were grown from the middle of the film in the medium of Comparative Example 2, and the generation of such subgrains was caused by Decay. It was considered that it affected the deterioration of R / W characteristics such as an increase in R.W. That is, in the medium of Comparative Example 2, the oxygen concentration is appropriate at the initial stage of the magnetic recording layer, which is considered to contribute to the reduction of D _cluster in the initial growth layer. However, since the oxygen concentration is excessive from the middle to the surface, the refinement of the magnetic crystal grain size is excessively promoted, and the uniaxial anisotropy and orientation decrease due to the generation of subgrains, resulting in an increase in decay. It can be considered that it has been lost. In addition, since subgrains are generated at the portion that should become the nonmagnetic grain boundary, the separability of the magnetic crystal grains is lowered, and contrary to the initial growth layer, D _cluster is increased near the surface. It is considered a thing.

Next, Example 1 and Comparative Example 3 will be compared and discussed. Comparative Example 3 is an example in which the concentration of oxygen added to the sputtering gas is constant at 2.3% by volume when the magnetic recording layer is formed. That is, in the magnetic recording layer of the medium of Comparative Example 3, the oxide (or oxygen) concentration contained in the magnetic recording layer is different from Comparative Example 1 or Comparative Example 2, but the oxide (or oxygen) concentration in the film thickness direction. Is constant. Again, as is clear from Table 1, the medium of Example 1 is superior in terms of Hc, SNR, and normalized noise. In the medium of Comparative Example 3, the D _cluster is larger than that of the medium of Example 1 or Comparative Example 2, resulting in an increase in medium noise and a decrease in SNR. In other words, it is considered that the medium of Comparative Example 3 does not have a small D _cluster due to an insufficient amount of oxygen to be added, and various characteristics of the medium are low.
Next, Example 1 and Comparative Example 4 are compared and considered. In Comparative Example 4, as in Example 1, the concentration of oxygen added to the sputtering gas during film formation of the magnetic recording layer was changed during the film formation, but the concentration during the first 5 nm film formation was the same as that of Comparative Example 3. The second embodiment is different from the first embodiment in that the volume is 2.3 volume%, the concentration at the latter half of 5 nm is 3.8 volume%, and the oxygen concentration near the surface is higher than the oxygen concentration at the initial stage of film formation. From Table 1, it can be seen that the characteristics of the medium of Example 1 are superior to those of the medium of Comparative Example 4. Here, further discussion will be made focusing on the fact that the characteristics of the medium of Comparative Example 4 are close to those of the medium of Comparative Example 3. In Comparative Example 4, although the oxygen addition concentration in the latter half at the time of forming the magnetic recording layer is higher than that in Comparative Example 3, there is no great difference in various characteristics. Further, when the D _clusters of the media of Comparative Examples 2 to 4 are compared, they are almost the same in Comparative Examples 3 and 4, whereas in Comparative Example 2, they are 15 to 17% smaller. In other words, D _cluster that greatly affects the R / W characteristics greatly depends on the oxygen concentration in the initial _stage of the magnetic layer deposition, and it is considered that the contribution to the reduction of D _cluster is small even if the oxygen concentration in the latter half is increased.

From the above results, it is possible to reduce D _cluster and improve R / W characteristics by appropriately adjusting the oxide (or oxygen) concentration contained in the initial stage of magnetic recording layer growth. When the (or oxygen) concentration is not set lower than the concentration at the initial stage of growth, it has been clarified that the R / W characteristics are deteriorated conversely due to generation of subgrains.
Finally, Examples 2 and 3 are considered. In Example 2, the amount of oxygen contained in the sputtering gas at the time of film formation of the magnetic recording layer is continuously changed so as to be 3.8% by volume at the start and zero at the end of sputtering. In Example 3, the substrate was exposed to a gas containing 5% by volume of oxygen in Ar for 0.8 seconds before the start of sputtering, and then the supply of oxygen was stopped (the flow rate was reduced to zero) simultaneously with the start of film formation. ing. In the process of Example 3, since the oxygen in the atmosphere does not disappear immediately even after the supply of oxygen is cut off, it is considered that the oxygen concentration gradually decreases during sputtering. In any embodiment, the oxygen concentration at the end of film formation is adjusted to be lower than the oxygen concentration at the start of film formation. From Table 1, the medium of Example 2 has superior characteristics than the medium of Example 1. In addition, although the medium of Example 3 is slightly inferior to the medium of Example 1, the performance is sufficiently high as compared with the media of Comparative Examples 1 to 4.

  As described above, although the film formation process is different between Examples 1 to 3, the amount of oxygen contained in the film at the initial stage of film formation of the magnetic recording layer is made higher than the vicinity of the film surface without lowering the thermal stability. It has been found that the magnetic cluster size of the magnetic recording layer can be reduced, and it is possible to improve medium performance such as low noise of the medium and SNR improvement.

FIG. 3 is a schematic cross-sectional view for explaining a configuration example of a perpendicular magnetic recording medium according to the present invention. The schematic diagram for demonstrating the detail of a magnetic-recording layer. It is a figure for demonstrating the measurement result of a magnetic cluster size.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonmagnetic base | substrate 2 Soft magnetic backing layer 3 Underlayer 4 Nonmagnetic intermediate layer 5 Magnetic recording layer 51 Initial growth layer 52 Bulk layer 6 Protective layer 7 Liquid lubrication layer 10 Magnetic crystal grain 11 Nonmagnetic grain boundary 20 Nonmagnetic intermediate layer Recess

Claims (7)

A perpendicular magnetic recording medium comprising a nonmagnetic substrate, a nonmagnetic intermediate layer, and a magnetic recording layer in this order,
The magnetic recording layer contains Co, Cr, Pt, Si, and O, and has a structure in which a nonmagnetic grain boundary containing oxygen surrounds the magnetic crystal grains, and the magnetic crystal grain size is substantially in the film thickness direction. The perpendicular magnetic recording medium is characterized by having a region with more oxygen on the interface side with the nonmagnetic intermediate layer than on the surface side of the magnetic recording layer.   2. The perpendicular magnetic recording medium according to claim 1, wherein the amount of oxygen contained in the magnetic recording layer continuously decreases from the interface side with the nonmagnetic intermediate layer toward the surface side of the magnetic recording layer. .   3. The perpendicular magnetic recording medium according to claim 1, further comprising a soft magnetic backing layer between the nonmagnetic substrate and the nonmagnetic intermediate layer.   The underlayer having a crystal structure including Ni and Fe, having a face-centered cubic lattice, and having soft magnetism is provided between the soft magnetic underlayer and the nonmagnetic intermediate layer. 4. The perpendicular magnetic recording medium according to 3.   5. The method for producing a perpendicular magnetic recording medium according to claim 1, wherein the sputtering gas contains oxygen, and the oxygen concentration in the first half of the film formation is set higher than the oxygen concentration in the second half of the film formation. A method of manufacturing a perpendicular magnetic recording medium, comprising forming a film.   6. The method of manufacturing a perpendicular magnetic recording medium according to claim 5, wherein sputtering film formation is performed while continuously reducing the oxygen concentration during film formation.   5. The method for manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the substrate is placed in a sputtering gas containing oxygen for 0.4 seconds or more and 1.5 seconds in a chamber for forming a magnetic thin film. A method of manufacturing a perpendicular magnetic recording medium, wherein sputtering is started after exposure for the following time.

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