JP2007265620A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of sufficiently coping with a writing signal with higher frequency than ever before. <P>SOLUTION: A polycrystaline structure film 22 is formed on the surface of a substrate 21. The second magnetic layers 29 of the polycrystaline structure film 22 have a larger saturation magnetic flux density compared with a first magnetic layer 31, so that larger residual magnetization is secured in the magnetic recording layer of a layered body compared with a case where the magnetic recording layer is provided only with the first magnetic layer 31. Even when the film thickness of the whole layered body is reduced, a sufficiently large tBr (the product of the film thickness with the residual magnetization) is secured. A sufficiently large reproduction output is secured. A magnetic crystal grain is made to be the micro grain in the first and second magnetic layers 29, 31 with the reduction of the film thickness. A recording and reproducing resolution characteristic is raised. Magnetic information is written with the sufficiently higher frequency and also sufficient coercivity is secured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium such as a magnetic disk incorporated in a hard disk drive (HDD).

  Generally, in a magnetic disk, a recording magnetic layer is laminated on the surface of a substrate. Such a magnetic layer is composed of magnetic crystal grains formed based on Co atoms. As is well known, Cr atoms are segregated along the grain boundaries in the magnetic layer. As a result, Cr nonmagnetic walls are formed between the magnetic crystal grains. Cr nonmagnetic walls suppress the interaction between magnetic crystal grains. When the interaction between the magnetic crystal grains is suppressed in this way, noise is reduced when reading magnetic information.

  In order to improve the recording density, it is required to reduce the size of magnetic crystal grains in the magnetic layer. In general, it is widely known that miniaturization of magnetic crystal grains can be realized if the thickness of the magnetic layer is sufficiently reduced. However, when the thickness of the magnetic layer decreases, the strength of the magnetic field leaking from the magnetic layer decreases with a decrease in tBr (product of the film thickness and residual magnetization). Therefore, a sufficiently large reproduction output cannot be ensured. In addition, a decrease in the thickness of the magnetic layer causes a decrease in the coercive force Hc. If the coercive force Hc is excessively reduced, the magnetic information recorded on the magnetic layer is easily destroyed due to thermal disturbance or the like.

  The present invention has been made in view of the above circumstances, and can sufficiently cope with a write signal having a higher frequency than ever, and sufficiently reduce the thickness of the magnetic layer without decreasing the coercive force. An object of the present invention is to provide a magnetic recording medium that can be realized.

  In order to achieve the above object, according to the present invention, a first magnetic layer having a first saturation magnetic flux density and a second saturation magnetic flux density that is laminated on the first magnetic layer and is larger than the first saturation magnetic flux density. And a second magnetic layer having a magnetic recording medium.

  In such a magnetic recording medium, the magnetic recording layer is formed of a laminate of the first magnetic layer and the second magnetic layer. Since the second magnetic layer has a larger saturation magnetic flux density than the first magnetic layer, a large remanent magnetization is generated in the magnetic recording layer of the laminate as compared with the case where the first magnetic layer is provided alone. Can be secured. Therefore, even if the film thickness of the entire laminate is reduced, a sufficiently large tBr (product of film thickness and residual magnetization) can be ensured. A sufficiently large reproduction output can be ensured.

  In addition, a sufficient coercive force can be ensured in such a laminate of the first and second magnetic layers. A decrease in coercive force can be avoided despite a decrease in film thickness. As a result, the magnetic information recorded in the first and second magnetic layers can be reliably held in the recording magnetic layer.

  The first magnetic layer may include, for example, magnetic crystal grains formed based on Co atoms and Cr nonmagnetic walls formed between the magnetic crystal grains. Similarly, the second magnetic layer only needs to include magnetic crystal grains formed based on Co atoms and Cr nonmagnetic walls formed between the magnetic crystal grains. At this time, the content of Cr atoms contained in the second magnetic layer may be set smaller than that of Cr atoms contained in the first magnetic layer. However, the saturation magnetic flux density of the second magnetic layer is required to be secured to 0.5 [T] or more.

  As described above, if the thickness of the first and second magnetic layers is reduced while ensuring a sufficiently large tBr, the magnetic crystal grains can be miniaturized in the first and second magnetic layers. it can. The recording / reproducing resolution characteristic is enhanced. Magnetic information can be written to the first and second magnetic layers at a sufficiently high frequency. If the frequency of the write signal is increased in this way, the recording density of the magnetic recording medium can be increased.

  According to the inventor's verification, it is desirable that the thickness of the second magnetic layer be set in the range of 0.5 to 3.0 nm. In the second magnetic layer, since the content of nonmagnetic atoms such as Cr is smaller than that in the first magnetic layer, a sufficient nonmagnetic wall cannot be formed between the magnetic crystal grains. In the second magnetic layer, the magnetic interaction between the magnetic crystal grains cannot be sufficiently cut off. When the thickness of the second magnetic layer exceeds 3.0 nm, the characteristics of the second magnetic layer are greatly affected in the laminated body of the first and second magnetic layers as compared with the characteristics of the first magnetic layer. Noise cannot be sufficiently reduced when reading magnetic information.

  In addition, the first magnetic layer may be laminated on the base magnetic layer. For example, the base magnetic layer may include magnetic crystal grains formed based on Co atoms and Cr nonmagnetic walls formed between the magnetic crystal grains. According to such a function of the under magnetic layer, the easy axis of magnetization can be well established in the so-called in-plane direction in the first magnetic layer. However, it is desirable that the thickness of the under magnetic layer be set in the range of 0.1 to 3.5 nm. According to the verification by the present inventor, when the thickness of the underlying magnetic layer deviates from this range, noise cannot be sufficiently reduced when reading magnetic information.

  Furthermore, the under magnetic layer may be laminated on the nonmagnetic under layer. This nonmagnetic underlayer may contain nonmagnetic atoms such as Cr. When a Cr layer is used for the nonmagnetic underlayer, the film thickness of the nonmagnetic underlayer may be set to about 0.5 to 7.0 nm, for example.

  The magnetic recording medium as described above can include various magnetic recording media in addition to a magnetic disk incorporated in, for example, a hard disk drive (HDD).

  As described above, according to the present invention, the magnetic recording medium can sufficiently cope with a write signal having a higher frequency than ever before. As a result, the recording density of the magnetic recording medium can be increased.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 schematically shows an internal structure of a hard disk drive (HDD) 11 as a specific example of a magnetic recording medium drive. The HDD 11 includes, for example, a box-shaped housing body 12 that partitions a flat rectangular parallelepiped internal space. In the accommodation space, one or more magnetic disks 13 as recording media are accommodated. The magnetic disk 13 is mounted on the rotation shaft of the spindle motor 14. The spindle motor 14 can rotate the magnetic disk 13 at a high speed such as 7200 rpm or 10000 rpm. A lid body, that is, a cover (not shown) that seals the housing space with the housing body 12 is coupled to the housing body 12.

  The head actuator 15 is further accommodated in the accommodation space. The head actuator 15 includes an actuator block 17 that is rotatably supported by a support shaft 16 extending in the vertical direction. A rigid actuator arm 18 extending in the horizontal direction from the support shaft 16 is defined in the actuator block 17. The actuator arm 18 is disposed for each of the front and back surfaces of the magnetic disk 13. The actuator block 17 may be formed from aluminum based on casting, for example.

  A head suspension 19 is attached to the tip of the actuator arm 18. The head suspension 19 extends forward from the tip of the actuator arm 18. As is well known, a flying head slider 21 is supported at the front end of the head suspension 19. Thus, the flying head slider 21 is connected to the actuator block 17. The flying head slider 21 is opposed to the surface of the magnetic disk 13.

  A so-called magnetic head, that is, an electromagnetic transducer (not shown) is mounted on the flying head slider 21. This electromagnetic conversion element is, for example, a read element such as a giant magnetoresistive element (GMR) or a tunnel junction magnetoresistive element (TMR) that reads information from the magnetic disk 13 by using a resistance change of a spin valve film or a tunnel junction film. (Not shown) and a writing element (not shown) such as a thin film magnetic head for writing information on the magnetic disk 13 using a magnetic field generated by a thin film coil pattern.

  A pressing force is applied to the flying head slider 21 from the head suspension 19 toward the surface of the magnetic disk 13. Buoyancy acts on the flying head slider 21 by the action of airflow generated on the surface of the magnetic disk 13 based on the rotation of the magnetic disk 13. Due to the balance between the pressing force of the head suspension 19 and the buoyancy, the flying head slider 21 can continue to fly with relatively high rigidity during the rotation of the magnetic disk 13.

  A power source 22 such as a voice coil motor (VCM) is connected to the actuator block 17. The actuator block 17 can rotate around the support shaft 16 by the action of the power source 22. Based on the rotation of the actuator block 16, the swing of the actuator arm 17 and the head suspension 19 is realized. When the actuator arm 18 swings around the support shaft 16 while the flying head slider 21 is flying, the flying head slider 21 can cross the surface of the magnetic disk 13 in the radial direction. As is well known, when a plurality of magnetic disks 13 are incorporated in the housing body 12, two actuator arms 18, that is, two head suspensions 19, are arranged between adjacent magnetic disks 13.

  FIG. 2 shows the cross-sectional structure of the magnetic disk 13 in detail. The magnetic disk 13 includes a substrate 21 as a support and a polycrystalline structure film 22 spreading on the front and back surfaces of the substrate 21. The substrate 21 may be composed of, for example, a disk-shaped Al main body 23 and NiP films 24 spreading on the front and back surfaces of the Al main body 23. However, a glass substrate may be used for the substrate 21. Magnetic information is recorded in the polycrystalline structure film 22. The surface of the polycrystalline structure film 22 is covered with a carbon protective film 25 such as diamond-like carbon and a lubricating film 26.

  The polycrystalline structure film 22 includes a base crystal layer 27 extending on the surface of the substrate 21. The base crystal layer 27 includes a first nonmagnetic base layer 27a formed on the surface of the NiP film 24 and a second nonmagnetic base layer 27b formed on the surface of the first nonmagnetic base layer 27a. Prepare. The first and second nonmagnetic underlayers 27a and 27b may be made of a nonmagnetic material such as Cr. However, Mo or W having a lattice constant larger than that of Cr is added to the second nonmagnetic underlayer 27b.

  The under magnetic layer 28 spreads on the surface of the second nonmagnetic under layer 27b. The under magnetic layer 28 may be made of a Co-type alloy having an hcp structure (hexagonal fine structure) such as a CoCrTa alloy. The under magnetic layer 28 may be added with at least one of Cr, Ta, Mo, Mn, Re, and Ru. In the under magnetic layer 28, magnetic crystal grains are formed based on Co atoms. A Cr nonmagnetic wall is formed between the magnetic crystal grains. Cr nonmagnetic walls can break the magnetic interaction between magnetic grains. The thickness of the under magnetic layer 28 may be set in the range of, for example, 0.1 to 3.5 nm.

  A first magnetic layer 29 spreads on the surface of the underlying magnetic layer 28. The first magnetic layer 29 may be composed of, for example, CoCrPtB alloy laminates 29a and 29b. At this time, for example, the lower CoCrPtB layer 29a only needs to contain Pt with a larger content than the upper CoCrPtB layer 29b, and the upper CoCrPtB layer 29b contains Cr with a smaller content than the lower CoCrPtB layer 29a. It only has to be done. In the first magnetic layer 29, magnetic crystal grains are formed based on Co atoms. A Cr nonmagnetic wall is formed between the magnetic crystal grains. Cr nonmagnetic walls can break the magnetic interaction between magnetic grains. In addition, the first magnetic layer 29 may be composed of a single-layer Co-based alloy.

  The second magnetic layer 31 spreads on the surface of the first magnetic layer 29. The second magnetic layer 31 may be made of a Co-based alloy having an hcp structure such as a CoCrTa alloy. In the second magnetic layer 31, magnetic crystal grains are formed based on Co atoms. A Cr nonmagnetic wall is formed between the magnetic crystal grains. Cr nonmagnetic walls can break the magnetic interaction between magnetic grains. The film thickness of the second magnetic layer 31 may be set in the range of 0.5 to 3.0 nm, for example. Here, the second magnetic layer 31 is given a higher saturation magnetic flux density Bs than the first magnetic layer 29 described above. In realizing the saturation magnetic flux density Bs, the second magnetic layer 31 may contain Cr atoms with a smaller content (atomic%) than the first magnetic layer 29. The second magnetic layer 31 only needs to have a saturation magnetic flux density Bs of 0.5 [T] or more.

  In the polycrystalline structure film 22 as described above, a magnetic recording layer is formed by a laminated body of the first and second magnetic layers 29 and 31. Since the second magnetic layer 31 has a larger saturation magnetic flux density Bs than that of the first magnetic layer 29, a larger remanent magnetization Br than that in the case where the magnetic recording layer is provided by the first magnetic layer 29 alone has a larger stack magnetization. It can be secured in the magnetic recording layer. Therefore, even if the film thickness of the entire laminate is reduced, a sufficiently large tBr (product of film thickness and residual magnetization) can be ensured. A sufficiently large reproduction output can be ensured.

  If the thickness of the first and second magnetic layers 29 and 31 is reduced while a sufficiently large tBr is secured in this way, the magnetic crystal grains can be miniaturized in the first and second magnetic layers 29 and 31. Can. The recording / reproducing resolution characteristic is enhanced. Magnetic information can be written to the first and second magnetic layers 29 and 31 at a sufficiently high frequency. If the frequency of the write signal is increased in this way, the recording density of the magnetic disk 13 can be increased. The recording / reproducing resolution Res is expressed by the following equation.

ここで、ＶＦ２、ＶＦ８は記録磁性層から読み出される再生出力の大きさを示す。ＶＦ２の検出にあたって記録磁性層には最高周波数の２分の１の周波数で磁気情報は書き込まれる。ＶＦ８の検出にあたって記録磁性層には最高周波数の８分の１の周波数で磁気情報は書き込まれる。最高周波数は任意の周波数に設定されればよい。広く知られるように、記録磁性層の記録再生分解能Ｒｅｓの値が大きいほど、高い周波数で書き込まれる磁気情報の再生出力は増大する。それだけ磁気ディスク１３には高い周波数で磁気情報は書き込まれることができる。

Here, VF2 and VF8 indicate the magnitudes of reproduction outputs read from the recording magnetic layer. In detecting VF2, magnetic information is written in the recording magnetic layer at a frequency that is half the maximum frequency. When detecting VF8, magnetic information is written in the recording magnetic layer at a frequency of 1/8 of the maximum frequency. The highest frequency may be set to an arbitrary frequency. As is widely known, the reproduction output of magnetic information written at a higher frequency increases as the value of the recording / reproducing resolution Res of the recording magnetic layer increases. Accordingly, magnetic information can be written on the magnetic disk 13 at a high frequency.

  In addition, a sufficient coercive force Hc can be ensured in the laminated body of the first and second magnetic layers 29 and 31. Despite the decrease in film thickness, the decrease in coercive force Hc can be avoided. As a result, the magnetic information recorded in the first and second magnetic layers 29 and 31 can be reliably held in the recording magnetic layer.

  Next, a method for manufacturing the magnetic disk 13 will be briefly described. First, a disk-shaped substrate 21 is prepared. A NiP film 24 is laminated in advance on the surface of the substrate 21. In forming the NiP film 24, for example, an electroless plating method is used. The substrate 21 is mounted on, for example, a sputtering apparatus. In this sputtering apparatus, a polycrystalline structure film 22 is formed on the surface of the substrate 21. Details of the forming method will be described later. Thereafter, a carbon protective film 25 and a lubricating film 26 are formed on the surface of the polycrystalline structure film 22. The carbon protective film 25 may be formed by lamination based on, for example, a CVD method (chemical vapor deposition method).

In the sputtering apparatus, the polycrystalline structure film 22 is formed based on a so-called DC magnetron sputtering method. Ar gas is introduced into the chamber of the sputtering apparatus for film formation. The inside of the chamber is held under a pressure of 0.67 [Pa], for example. Prior to the introduction of Ar gas, a vacuum environment of about 4.0 × 10 ⁻⁵ [Pa] is established in the chamber.

  Prior to film formation, the substrate 21 is heated to about 220 degrees Celsius. Impurities adhering to the surface of the substrate 21 are removed by heating. Here, the substrate 21 is desirably heated to at least 200 degrees Celsius. However, if it exceeds 270 degrees Celsius, magnetization is established in the NiP film 24 due to crystallization of the NiP film 24. Therefore, the temperature of the substrate 21 is kept below 270 degrees Celsius.

  As shown in FIG. 3, a first nonmagnetic underlayer 27 a is formed on the surface of the substrate 21. A Cr target is used for film formation. Cr atoms 33 are deposited on the surface of the substrate 21. The Cr atoms 33 form crystal grains on the substrate 21. Since the substrate 21 is maintained at a high temperature, the crystal orientation is aligned in a predetermined direction in the Cr layer 34 formed on the substrate 21. For example, the Cr layer 34 is formed to a thickness of about 5.0 nm.

  Subsequently, as shown in FIG. 4, a second nonmagnetic underlayer 27 b is formed on the surface of the Cr layer 34. A CrMo target is used for film formation. Mo is added to the CrMo target at a predetermined content. Thus, a CrMo alloy layer 35 is formed on the surface of the Cr layer 34. Epitaxial growth is established in the CrMo alloy layer 35 based on the Cr layer 34 described above. The CrMo alloy layer 35 is formed to a thickness of about 2.0 nm.

  Subsequently, as shown in FIG. 5, a base magnetic layer 28 is formed on the surface of the CrMo alloy layer 35. A CoCrTa target is used for film formation. A CoCrTa alloy layer 36 is formed on the surface of the CrMo alloy layer 35. Epitaxial growth is established in the CoCrTa alloy layer 36 based on the CrMo layer 35 described above. The film thickness of the CoCrTa alloy layer 36 may be set in the range of about 0.1 to 3.5 nm.

  Subsequently, as shown in FIG. 6, the first magnetic layer 29 and the second magnetic layer 31 are successively formed on the surface of the CoCrTa alloy layer 36. A CoCrPtB target is used for forming the first magnetic layer 29. Similarly, a CoCrTa target is used in forming the second magnetic layer 31. At this time, in the CoCrTa target, the Cr content (atomic%) is suppressed as compared with the CoCrPtB target. CoCrPtB alloy layers 37 and 38 are successively formed on the surface of the CoCrTa alloy layer 36. In each CoCrPtB alloy layer 37, 38, magnetic crystal grains are established based on epitaxial growth. With the above-described action of the Cr layer 34, the easy axis of magnetization is well established in the in-plane direction in the CoCrPtB alloy layers 37 and 38. Since the substrate 21 is maintained at a high temperature, Cr atoms 39 are segregated between the magnetic crystal grains. Cr atoms 39 create nonmagnetic walls. A CoCrTa alloy layer 41 is formed on the surface of the CoCrPtB alloy layer 38. In the CoCrTa alloy layer 41, a saturation magnetic flux density Bs of about 0.5 [T] may be ensured. The film thickness t of the laminated body of the first and second magnetic layers 29 and 31 may be set with tBr = 5.5 [nTm] as a guide.

  The inventor has verified the magnetic characteristics of the polycrystalline structure film 22 manufactured as described above. The film thickness of the first nonmagnetic underlayer 27a, that is, the Cr layer 34 was set to 5.0 nm. The film thickness of the second nonmagnetic underlayer 27b, that is, the CrMo alloy layer 35 was set to 2.0 nm. The saturation magnetic flux density Bs of the second magnetic layer 31, that is, the CoCrTa alloy layer 41 was set to 0.5 [T]. In this setting, the content (atomic%) of Cr atoms contained in the second magnetic layer 31 was adjusted. In the laminated body of the first and second magnetic layers 29 and 31, tBr was set to 5.5 [nTm].

  The inventor measured the recording / reproducing resolution Res of the polycrystalline structure film 22. A GMR (giant magnetoresistive) head was used for the measurement. At this time, the film thickness of the under magnetic layer 28, that is, the CoCrTa alloy layer 36 was changed to 1.0 nm, 2.0 nm, and 3.0 nm. Similarly, in the prepared comparative example, the formation of the base magnetic layer 28 was omitted. As is apparent from FIG. 7, the maximum recording / reproduction resolution Res was recorded when the thickness of the under magnetic layer 28 was around 2.0 nm. It was confirmed that when the film thickness of the under magnetic layer 28 was set in the range of 0.1 to 3.5 nm, the recording / reproducing resolution Res could be sufficiently increased.

  Similarly, the inventor measured the recording / reproducing resolution Res of the polycrystalline structure film 22. Here, the thickness of the under magnetic layer 28 was fixed at 2.0 nm. On the other hand, the thickness of the second magnetic layer 31, that is, the CoCrTa alloy layer 41 was changed to 0.5 nm, 1.0 nm, 1.5 nm, 2.0 nm, and 4.0 nm. With the change in the thickness of the second magnetic layer 31, the thickness of the first magnetic layer 29 was adjusted. In the adjustment, tBr was set to 5.5 [nTm] in the laminated body of the first and second magnetic layers 29 and 31. In the prepared comparative example, the formation of the second magnetic layer 31 was omitted. As is clear from FIG. 8, the maximum recording / reproduction resolution Res was recorded when the thickness of the second magnetic layer 31 was around 2.0 to 2.5 nm. It was confirmed that when the film thickness of the second magnetic layer 31 was set in the range of 0.5 to 3.0 nm, the recording / reproducing resolution Res could be sufficiently increased.

  Furthermore, the inventor measured the coercive force Hc of the polycrystalline structure film 22 while changing the film thickness of the second magnetic layer 31 in the same manner as described above. A VSM (vibrating sample magnetometer) was used for the measurement. As is clear from FIG. 9, it was confirmed that a constant coercive force Hc was ensured regardless of the thickness of the second magnetic layer 31. That is, it was confirmed that a sufficient coercive force Hc was ensured even when the thickness of the stacked body of the first and second magnetic layers 29 and 31 was reduced as the thickness of the second magnetic layer 31 was increased.

  (Supplementary Note 1) A first magnetic layer having a first saturation magnetic flux density and a second magnetic layer laminated on the first magnetic layer and having a second saturation magnetic flux density greater than the first saturation magnetic flux density. A magnetic recording medium characterized by the above.

  (Supplementary note 2) The magnetic recording medium according to supplementary note 1, wherein the second saturation magnetic flux density is set to 0.5 [T] or more.

  (Supplementary Note 3) In the magnetic recording medium according to Supplementary Note 1 or 2, the first magnetic layer includes magnetic crystal grains formed based on Co atoms, and Cr nonmagnetic walls formed between the magnetic crystal grains. A magnetic recording medium comprising:

  (Supplementary note 4) In the magnetic recording medium according to supplementary note 3, the second magnetic layer includes magnetic crystal grains formed based on Co atoms and Cr nonmagnetic walls formed between the magnetic crystal grains. The content of Cr atoms contained in the second magnetic layer is set smaller than that of Cr atoms contained in the first magnetic layer.

  (Additional remark 5) The magnetic recording medium in any one of additional remarks 1-4 WHEREIN: The film thickness of a said 2nd magnetic layer is set in 0.5-3.0 nm, The magnetic recording medium characterized by the above-mentioned.

  (Supplementary note 6) In the magnetic recording medium according to supplementary note 1, the first magnetic layer is stacked on a base magnetic layer, and the base magnetic layer includes magnetic crystal grains formed on the basis of Co atoms and magnetic crystal grains. A magnetic recording medium comprising a Cr nonmagnetic wall formed between the two.

  (Additional remark 7) The magnetic recording medium of Additional remark 6 WHEREIN: The film thickness of the said base magnetic layer is set in the range of 0.1-3.5 nm, The magnetic recording medium characterized by the above-mentioned.

  (Supplementary note 8) The magnetic recording medium according to supplementary note 6 or 7, wherein the under magnetic layer is laminated on a nonmagnetic under layer.

It is a top view which shows roughly the internal structure of one specific example, ie, a hard-disk drive (HDD), of a magnetic-recording-medium drive device. 1 is an enlarged vertical sectional view showing in detail a structure of a magnetic disk according to an embodiment of the present invention. It is a perpendicular | vertical fragmentary sectional view of the board | substrate which shows the film-forming process of a 1st nonmagnetic base layer roughly. It is a perpendicular | vertical fragmentary sectional view of the board | substrate which shows the film-forming process of a 2nd nonmagnetic base layer roughly. It is a perpendicular | vertical fragmentary sectional view of the board | substrate which shows the film-forming process of a base magnetic layer roughly. FIG. 4 is a vertical partial cross-sectional view of a substrate schematically showing a film forming process of first and second magnetic layers. It is a graph which shows the relationship between the film thickness of a base magnetic layer, and recording / reproducing resolution. It is a graph which shows the relationship between the film thickness of a 2nd magnetic layer, and recording / reproducing resolution. It is a graph which shows the relationship between the film thickness of a 2nd magnetic layer, and a coercive force.

Explanation of symbols

  13 Magnetic disk as magnetic recording medium, 29 1st magnetic layer, 31 2nd magnetic layer.

Claims (4)

  A first magnetic layer having a first saturation magnetic flux density, and a second magnetic layer laminated on the first magnetic layer and having a second saturation magnetic flux density greater than the first saturation magnetic flux density. Magnetic recording medium.   The magnetic recording medium according to claim 1, wherein the first magnetic layer includes magnetic crystal grains formed based on Co atoms and Cr nonmagnetic walls formed between the magnetic crystal grains. Magnetic recording medium.   3. The magnetic recording medium according to claim 2, wherein the second magnetic layer includes magnetic crystal grains formed based on Co atoms, and Cr nonmagnetic walls formed between the magnetic crystal grains. A magnetic recording medium, wherein the content of Cr atoms contained in the magnetic layer is set smaller than that of Cr atoms contained in the first magnetic layer.   4. The magnetic recording medium according to claim 1, wherein the thickness of the second magnetic layer is set in a range of 0.5 to 3.0 nm.

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