JP4405436B2 - Negative anisotropic exchange coupled magnetic recording medium and magnetic recording / reproducing apparatus - Google Patents

Description

  The present invention relates to a negative anisotropic exchange coupled magnetic recording medium and a magnetic recording / reproducing apparatus.

  In recent years, as the processing speed of computers has improved, magnetic recording / reproducing apparatuses such as hard disk drives (HDDs) that record and reproduce information signals have increased recording speed and increased recording density. It is requested. The current HDD employs a so-called in-plane magnetic recording method in which the direction of magnetization is in the in-plane direction of the medium. However, considering the higher recording density of HDD, the so-called perpendicular magnetic recording method in which the magnetization direction is in the normal direction of the medium has a smaller demagnetizing field near the magnetization reversal boundary and sharp reversal. This is advantageous because magnetization can be obtained.

  Furthermore, regarding the thermal fluctuation that has become a problem in recent magnetic recording media, the thickness of the magnetic recording layer of the medium can be set larger in the perpendicular magnetic recording method than in the in-plane magnetic recording medium method. The degradation of the recorded signal can be kept low.

  As the perpendicular magnetic recording layer, a CoCr alloy-based magnetic film including a CoCrPt alloy having an irregular hexagonal crystal structure has been mainly studied. In addition, in order to cope with the above-described problem of thermal fluctuation, research on materials having a larger magnetic anisotropy (Ku) is also in progress.

  However, Ku has a positive correlation with the coercive force (Hc). When magnetic recording is performed on a material having a large Ku, a larger recording magnetic field is required. For this reason, in a perpendicular magnetic recording medium, Ku is often set to a value close to the upper limit of the recording capacity of the head.

  Here, if Hc can be lowered while keeping Ku large, a perpendicular magnetic recording medium having good resistance to thermal fluctuation can be obtained. Further, even if the perpendicular magnetic recording medium has the same resistance to thermal fluctuation, the head design margin can be increased, so that it is easy to design an HDD employing the perpendicular magnetic recording system.

  For this reason, recently, a perpendicular magnetic recording medium (hereinafter referred to as a tilted medium) in which the easy magnetization direction of the magnetic recording layer is inclined with respect to the normal direction of the medium has been proposed. (For example, see Patent Documents 1 and 2 and Non-Patent Document 1). That is, in contrast to the conventional perpendicular magnetic recording medium, the crystal plane of the magnetic crystal grains is oriented so that the easy axis direction of the magnetic recording layer faces the normal direction of the medium. Ted media is characterized in that the crystal planes of magnetic crystal grains are oriented so that the easy axis direction of the magnetic recording layer is inclined with respect to the normal direction of the medium.

  Note that Non-Patent Document 1 reports that Hc is low because the magnetic field application direction, which is the normal direction of the medium, and the easy axis direction have a certain angle. Theoretically, when the crossing angle between the magnetic field application direction and the easy magnetization axis direction is 45 °, the smallest Hc (about half that of 0 °) can be obtained.

  By the way, in order to orient the easy axis of magnetization of the magnetic recording layer obliquely with respect to the normal direction of the medium, it is sufficient to use an underlayer that allows growth of magnetic crystal grains having such an orientation relationship. However, in the CoCrPt alloy-based magnetic film currently in practical use, such a base has not been studied much.

  Furthermore, in order to obtain a practical tilted media, a so-called granular structure in which magnetic crystal particles are divided by a non-magnetic material is necessary. However, in the above-described CoCrPt alloy-based magnetic film, there has been little research on a method of forming a granular structure in which magnetic crystal grains are oriented obliquely with respect to the normal direction of the medium in the direction of easy magnetization (C axis). .

  As described above, there are many problems to be solved at the time of forming a thin film in order to realize the tilted media with the current alloy magnetic material. In such a tilted media, the magnetic crystal particles are inclined, so that the output is reduced. Further, since the C axis grows obliquely with respect to a certain direction for a certain magnetic crystal particle, if this direction is random, the magnetization transition region is the same as in the conventional in-plane magnetic recording system. This causes a problem of demagnetizing field.

  In tilted media, the magnetization vector is oriented in a different direction for each magnetic particle. Therefore, when the magnetic recording layer is a patterned medium that is processed into recording information or a recording track shape, the magnetic characteristics of each pattern vary. Will become bigger. However, a base for aligning magnetic particles in the circumferential direction and obliquely has not been developed at present.

  On the other hand, as another method for realizing tilted media, a composite media (composite media) in which isolated soft magnetic particles are similarly exchange-coupled to magnetically isolated hard magnetic particles in the above-described granular structure has been proposed. (For example, see Non-Patent Document 2). That is, in this composite media, the magnetization of the entire magnetic particle is oriented in the vertical direction when no magnetic field is applied, but when the recording magnetic field is applied, the soft magnetic layer part is reversed first, The magnetization of the exchange-coupled hard magnetic layer is tilted, resulting in a tilted media.

  In the case of this composite medium, it is not necessary to form the easy axis of magnetization of the hard magnetic layer at an angle, so there is no problem of the orientation control of the magnetic crystal grains described above. However, a method for forming a soft magnetic layer having a granular structure and a method for realizing a good crystal orientation even on soft magnetic particles (or C axis direction control in the case of a CoCrPt alloy-based soft magnetic film) have been established. However, the problem in producing the medium still remains.

Furthermore, in the composite media, it is necessary to increase the thickness of the soft magnetic layer in order to realize the above-described magnetic operation. However, in this case, since the magnetization of each magnetic particle becomes large, there arises a problem that the recording pattern is easily recorded and the stability of the magnetization changes due to magnetostatic coupling between the magnetic particles. Furthermore, the material margin for performing the assumed magnetic operation is also narrowed. That is, it becomes difficult to design the magnetic characteristics, film thickness, exchange coupling strength, and the like of the hard magnetic layer and the soft magnetic layer.
JP-A-8-129736 Japanese Patent No. 3235033 IEEE Transaction on Magnetics, vol.38, pp.3675-3683 IEEE Transaction on Magnetics, vol.41, pp.537

As described above, in order to realize a tilted medium with a high Ku and a high Hc and reduced Hc, it is difficult to magnetically divide the soft magnetic portion, and saturation magnetization ( Ms) becomes large, and the margin for media design becomes narrow.
Accordingly, the present invention has been made to solve the above-described problems, and provides a tilted media type perpendicular magnetic recording medium that is easy to manufacture and easy to design, and a magnetic recording / reproducing apparatus using the same. For the purpose.

The present invention provides the following means.
(1) A substrate, a base layer formed on the substrate, a magnetic recording layer formed on the base layer, and a protective layer formed on the magnetic recording layer, the magnetic recording layer comprising: The main recording layer is composed of a main recording layer and an auxiliary layer exchange-coupled to each other, and the main recording layer has magnetic particles and a nonmagnetic material surrounding the magnetic particles and has perpendicular magnetic anisotropy. And the auxiliary layer is made of a material having negative magnetocrystalline anisotropy and has anisotropy in which the medium surface becomes an easily magnetized surface. Medium.
(2) The magnetic recording layer has a region in which a magnetic portion and a nonmagnetic portion are divided in a medium in-plane direction, and the magnetic portion and the nonmagnetic portion are arranged along the circumferential direction of the medium. The negative anisotropy exchange coupled magnetic recording medium as described in (1) above.
(3) The negative anisotropy exchange coupled magnetic recording as described in (1) or (2) above, wherein the absolute value of the magnetocrystalline anisotropy of the auxiliary layer is 10 ⁵ erg / cc or more. Medium.
(4) The negative anisotropic exchange coupling type magnetic recording medium according to any one of (1) to (3), wherein the auxiliary layer has a thickness of 1 nm or more.
(5) The negative anisotropic exchange coupling according to any one of (1) to (4), wherein the auxiliary layer has a thickness equal to or less than half of the thickness of the main recording layer. Type magnetic recording medium.
(6) The auxiliary layer according to any one of (1) to (5) above, wherein the auxiliary layer includes at least one kind or an alloy selected from CoIr, CoFe, MnSb, FeC, and Fe ₃ Pt. The negative anisotropic exchange coupling type magnetic recording medium according to any one of the above.
(7) The negative difference according to any one of (1) to (6), wherein the auxiliary layer is CoIr and the content of Ir is 5 to 40 atomic%. An isotropic exchange coupled magnetic recording medium.
(8) The above-mentioned (1) to (7), characterized in that a crystalline base film in which a hexagonal close-packed lattice plane or a tetragonal lattice plane is oriented in a plane parallel to the substrate is provided below the auxiliary layer. The negative anisotropic exchange coupled magnetic recording medium according to any one of the above.
(9) The negative anisotropic exchange coupled magnetic recording medium according to any one of (1) to (8) above, and signal recording on the negative anisotropic exchange coupled magnetic recording medium, and A magnetic recording / reproducing apparatus comprising a magnetic head for performing reproduction.
(10) The magnetic recording / reproducing apparatus according to (9), wherein the magnetic head is a single pole type magnetic head.

  As described above, according to the present invention, an auxiliary recording layer having negative magnetocrystalline anisotropy is exchange-coupled to a main recording layer having a granular structure, thereby making it easy to manufacture and design a medium. A ted media type perpendicular magnetic recording medium and a magnetic recording / reproducing apparatus using the same can be provided.

  Hereinafter, a negative anisotropic exchange coupling type magnetic recording medium and a magnetic recording / reproducing apparatus to which the present invention is applied will be described in detail with reference to the drawings. In the drawings used in the following description, in order to make the features easy to understand, the portions that become the features may be shown in an enlarged manner for convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent.

First, a magnetic recording medium to which the present invention is applied will be described.
A magnetic recording medium to which the present invention is applied is a magnetic disk 1 used in a magnetic recording / reproducing apparatus such as a hard disk drive (HDD) as shown in FIG. As shown in FIG. 2, the magnetic disk 1 includes a substrate 11, an underlayer 12 formed on the substrate 11, a magnetic recording layer 13 formed on the underlayer 12, and the magnetic recording layer 13. And at least a protective layer 14 formed thereon.

  As the substrate 11, for example, a nonmagnetic substrate made of glass, Al alloy, ceramic, carbon, Si single crystal having an oxidized surface, or the like can be used. Examples of the glass include amorphous glass and crystallized glass. Examples of amorphous glass include general-purpose soda lime glass and aluminosilicate glass. Examples of crystallized glass include lithium-based crystallized glass. Examples of the ceramic include general-purpose aluminum oxide, a sintered body mainly composed of aluminum nitride, silicon nitride, and the like, and fiber reinforced products thereof. Moreover, what formed the NiP layer on the surface of the board | substrate 1, such as the said metal substrate and a nonmetallic substrate, using the plating method or the sputtering method, for example can also be used. Examples of the size of the substrate 1 include various types known so far, such as 3.5 inches, 2.5 inches, 1.8 inches, 1 inch, 0.85 inches, and 0.8 inches. it can.

  The underlayer 12 is for the purpose of controlling the crystal of the magnetic recording layer 13, controlling the particle size, improving adhesion, and the like. The underlayer 12 is used in a normal magnetic recording medium. For example, a metal, a dielectric, or a mixture thereof can be used. The underlayer 12 may be composed of a plurality of layers in order to efficiently achieve the above object. Furthermore, the surface of the layer constituting the underlayer 12 may be modified by ion irradiation or gas exposure.

  The underlayer 12 can also be made of a magnetic material. When a soft magnetic material having a high magnetic permeability is provided as a backing layer (SUL) between the substrate 11 and the magnetic recording layer 13, a so-called perpendicular two-layer medium can be obtained. The SUL in this perpendicular two-layer medium plays a part of the function of the magnetic head for magnetizing the perpendicular magnetic recording layer. For example, the recording magnetic field from the single-pole head is returned to the magnetic head side through the horizontal direction. It has a function to make it. Further, since a steep and sufficient vertical magnetic field can be applied to the magnetic recording layer 13, the recording / reproducing efficiency can be improved.

  SUL includes materials containing Fe, Ni, and Co, for example, FeCo alloys such as FeCo and FeCoV, FeNi alloys such as FeNi, FeNiMo, and FeNiSi, FeAl alloys such as FeAl, FeAlSi, FeAlSiCr, FeAlSiTiRu, and FeAlO. Examples thereof include alloys or FeSi alloys, FeTa alloys such as FeTa, FeTaC, and FeTaN, and FeZr alloys such as FeZrN. In addition, a material having a granular structure in which fine crystal grains such as FeAlO containing 60 at% or more of Fe, FeMgO, FeTaN, and FeZrN, or fine crystal particles are dispersed in a matrix can be used for SUL.

  Furthermore, a Co alloy containing Co and at least one selected from Zr, Hf, Nb, Ta, Ti, and Y can be used for SUL. This Co alloy preferably contains 80 at% or more of Co. Further, when such a Co alloy is formed by sputtering, an amorphous layer is easily formed. When such an amorphous layer is formed, the amorphous soft magnetic material has a crystalline magnetic anisotropy. Since there are no crystal defects and no grain boundaries, very good soft magnetism is exhibited. Further, by using this amorphous soft magnetic material, the noise of the medium can be reduced. Suitable examples of the amorphous soft magnetic material include CoZr, CoZrNb, and CoZrTa alloys.

  Under the SUL, in order to improve the crystallinity of the SUL and the adhesion to the substrate 11, an underlayer can be further provided. Ti, Ta, W, Cr, Pt, an alloy containing these, an oxide, a nitride, or the like can be used for the underlayer.

  In addition, an intermediate layer made of a nonmagnetic material may be provided between the SUL and the magnetic recording layer 13 as a part of the plurality of layers constituting the underlayer 12. This intermediate layer is intended to block the exchange coupling interaction between the SUL and the magnetic recording layer 13 and to control the crystallinity of the magnetic recording layer 13. For this intermediate layer, for example, Ru, Re, Pt, Pd, W, Ti, Ta, Cr, Si, an alloy containing these, an oxide, a nitride, or the like can be used.

  In order to prevent spike noise, the SUL may be divided into a plurality of layers and anti-ferromagnetically coupled by inserting, for example, 0.5 to 1.5 nm of Ru between these layers. it can. In addition, a hard magnetic film having in-plane anisotropy such as CoCrPt, SmCo, or FePt, or a pinned layer made of an antiferromagnetic material such as IrMn or PtMn and a soft magnetic layer are exchange coupled. You can also. In this case, in order to control the exchange coupling force, a magnetic film (for example, Co) or a nonmagnetic film (for example, Pt) may be laminated before and after the Ru layer.

  The magnetic recording layer 13 includes an auxiliary layer 15 and a main recording layer 16 formed on the auxiliary layer 15. The main recording layer 16 and the auxiliary layer 15 are exchange-coupled to each other. In order to exchange-couple the main recording layer 16 and the auxiliary layer 15, it is preferable that the main recording layer 16 and the auxiliary layer 15 are in contact with each other. Even when the main recording layer 16 and the auxiliary layer 15 are not in contact with each other, an exchange coupling action is exerted if the distance between them is 2 nm or less. An intermediate layer made of a nonmagnetic material of 2 nm or less can also be provided.

  The magnetic recording layer 13 may be provided with an intermediate layer made of a magnetic material between the main recording layer 16 and the auxiliary layer 15 in order to adjust the exchange coupling force. The magnetic recording layer 13 is not limited to the structure in which the main recording layer 16 is disposed on the auxiliary layer 15 as shown in FIG. 2, for example, and has a structure in which the auxiliary layer 15 is disposed on the main recording layer 16. There may be. In addition, the magnetic recording layer 13 may have a structure in which a plurality of these main recording layers 16 and auxiliary layers 15 are stacked. For example, when the main recording layer 16, the auxiliary layer 15, and the main recording layer 16 are stacked in this order, the exchange coupling force acting on the auxiliary layer 15 can be doubled. The design margin can be increased. Further, the magnetic recording layer 13 may have a structure in which a plurality of magnetic layers and nonmagnetic layers are stacked. For example, by inserting a Ru layer between a plurality of magnetic layers, the linear recording density can be improved using a technique for inducing antiferromagnetic exchange coupling.

  The presence or absence of exchange coupling between the auxiliary layer 15 and the main recording layer 16 can be determined from the hysteresis loop. That is, when the exchange coupling is not performed, the hysteresis loop is a simple superposition of the loops of the respective layers, but when the exchange coupling is performed, the hysteresis is changed. The present invention is characterized in that the coercive force (Hc) inherent in the main recording layer 16 is reduced due to exchange coupling with the auxiliary layer 15. Therefore, the magnetic anisotropy (Ku) of the main recording layer 16 is calculated by torque measurement or the like, and a hysteresis loop showing a smaller Hc than the expected Hc is obtained, whereby the presence of exchange coupling can be confirmed. . Moreover, it can also be judged from the peculiar hysteresis described in detail later.

  The main recording layer 16 is made of a hard magnetic material having perpendicular magnetic anisotropy. That is, the main recording layer 16 is a so-called perpendicular magnetization film composed of magnetic crystal grains whose easy axis of magnetization is mainly oriented in the medium perpendicular direction. The magnetic crystal grains constituting the main recording layer 16 are made of an alloy containing Co as a main component. For example, when made of a CoPt alloy, a large anisotropy can be obtained. In addition to the alloy containing Co, Cr, and Pt, the magnetic crystal grains are at least one selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, and Re. The above elements can be included. By including the above elements, the crystallinity and orientation of the magnetic particles can be improved, the magnetic characteristics can be adjusted, and recording / reproduction characteristics and thermal fluctuation characteristics suitable for higher density recording can be obtained. Further, a so-called magnetic artificial lattice in which a large number of Co and noble metals such as Pt and Pd are stacked may be used. Also, an ordered phase alloy composed of Fe or Co and Pt or Pd can be used. The main recording layer 16 may have a multilayer structure, and it is possible to cope with higher recording density by laminating two or more magnetic films having different magnetic characteristics.

The thickness of the main recording layer 16 is preferably 2 to 60 nm, and more preferably 3 to 30 nm. If the thickness of the main recording layer 16 is less than 2 nm, the reproduction output is too low and the noise component becomes higher. On the other hand, if the thickness of the main recording layer 16 exceeds 60 nm, the reproduction output is too high and the waveform is distorted. Therefore, by setting the thickness of the main recording layer 16 in the above range, a magnetic recording medium suitable for higher recording density can be obtained. The coercive force of the main recording layer 16 is preferably set to 237000 A / m (3 kOe) or more independently in order to prevent deterioration of resistance against thermal fluctuation. The Ku of the main recording layer 16 is preferably 10 ⁶ erg / cc or more.

  As schematically shown in FIG. 3, the main recording layer 16 has a so-called granular structure composed of magnetic particles 17 and a nonmagnetic material 18 surrounding the magnetic particles 17. In this granular structure, each magnetic particle 17 is completely divided. However, if there is no problem in magnetic recording, it may not be partially cut. In FIG. 3, the auxiliary layer 15 also has a granular structure. However, the auxiliary layer 15 may have a granular structure or a continuous film, and a structure including both of them (for example, the upper half). May be a granular structure).

The auxiliary layer 15 is made of a magnetic material having negative magnetocrystalline anisotropy (Ku) in which the easy magnetization surface (C surface) is oriented parallel to the medium surface. That is, the difficult axis (C axis) of the auxiliary layer 15 is perpendicular to the in-plane direction of the medium. At this time, since the easy axis of magnetization is not in a specific in-plane direction in the magnetic crystal grains constituting the auxiliary layer 15, the magnetization direction can be taken in any direction in the plane. In the present invention, since the easy magnetization axis cannot be defined in a specific direction in the film surface, the surface on which the easy magnetization axis exists is defined as “easy magnetization surface”. This is because a magnetic material having positive magnetocrystalline anisotropy (Ku) having an easy axis of magnetization in the in-plane direction of the medium, such as a CoCr-based alloy having a C-axis in the in-plane direction used for a longitudinal medium, or four directions This is different from an fcc crystal having an easy magnetization axis. Examples of the material exhibiting such characteristics include CoIr, CoFe, MnSb, FeC, and Fe ₃ Pt.

The magnetic recording medium to which the present invention is applied realizes a tilted media by exchange coupling the auxiliary layer 15 with the main recording layer 16, but in order to exhibit the performance as this tilted media, The absolute value of Ku of the auxiliary layer 15 is preferably 10 ⁵ erg / cc or more.

Specifically, the exchange-coupled main recording layer 16 and auxiliary layer 15 are integrated and subjected to thermal fluctuations, and therefore the overall thermal fluctuation resistance is reduced unless Ku of the auxiliary layer 15 is also large. For example, in the case of the composite media described in Non-Patent Document 2, since the soft magnetic material whose Ku of the auxiliary layer can be regarded as 0 is used, the thermal recording resistance must be borne only by the main recording layer. Therefore, the total thickness of the main recording layer and the auxiliary layer is increased. This is not preferable for a perpendicular magnetic recording medium in which the distance between the SUL and the recording head must be shortened. At this time, the direction of the easy axis of anisotropy is orthogonal between the auxiliary layer 15 and the main recording layer 16, but the direction is not related to thermal fluctuation resistance. This is because when the auxiliary layer 15 has a large Ku, the fine structure of the magnetization is determined at the point where the energy of the two is balanced, but the structure thus determined itself has a thermal fluctuation resistance that is an intermediate value between the two Kus. It is. From such a viewpoint, the absolute value of Ku of the auxiliary layer 15 is preferably 10 ⁵ erg / cc or more, and more preferably 1 Merg / cc or more.

Examples of the material for the auxiliary layer 15 that satisfies such conditions include the above-described CoIr, CoFe, MnSb, FeC, Fe ₃ Pt, and the like. Among these, CoIr has the same hexagonal close-packed (hcp) structure as the CoCrPt alloy used in the current magnetic recording medium for HDDs, and has a lattice constant close to each other. There are advantages. Therefore, when a CoCrPt film is formed on C-axis oriented CoIr, the CoCrPt is also C-axis oriented. In this case, the easy magnetization surface of CoIr serving as the auxiliary layer 15 is a film surface, and the easy magnetization axis of CoCrPt serving as the main recording layer 16 is perpendicular to the film surface.

  On the other hand, if C-axis oriented CoCrPt can be obtained by using the underlayer used in the current magnetic recording medium for HDD, conversely, the C-axis of CoIr formed on CoCrPt is oriented perpendicularly to the film surface. Can be made. That is, also in this case, the easy magnetization surface of CoIr serving as the auxiliary layer 15 is a film surface, and the easy magnetization axis of CoCrPt serving as the main recording layer 16 is perpendicular to the film surface.

  Specifically, in order to align CoIr serving as the auxiliary layer 15 in the C axis, a crystal in which a hexagonal close-packed lattice plane or a tetragonal lattice plane is aligned in a plane parallel to the substrate 11 below the auxiliary layer 15. A quality base film (base layer 12) may be disposed. That is, by using a crystalline base film in which a hexagonal close-packed lattice plane or a tetragonal lattice plane is aligned in a plane parallel to the substrate 11, a thin film in which the C axis of CoIr is aligned in the in-plane perpendicular direction of the medium is obtained. be able to.

  In the case of the CoCr alloy-based main recording layer 16 or the CoIr-based auxiliary layer 15, the underlying layer 12 for vertically aligning the auxiliary layer 15 has a hexagonal close-packed (hcp) structure or a face-centered cubic (fcc). For example, Ru, Pt, Pd, NiCr, NiFeCr, Mg, or the like having a structure can be used.

  As described above, in the magnetic recording medium to which the present invention is applied, CoCrPt is laminated on CoIr, CoIr is laminated on CoCrPt, or these CoIr and CoCrPt are laminated repeatedly. The easy magnetization surface of CoIr serving as the auxiliary layer 15 can be a film surface, and the easy magnetization axis of CoCrPt serving as the main recording layer 16 can be perpendicular to the film surface.

Furthermore, in the magnetic recording medium to which the present invention is applied, the saturation magnetization (Ms) of this CoIr can be adjusted by adjusting the content of Ir contained in CoIr serving as the auxiliary layer 15. Specifically, when the content of Ir contained in CoIr is 5 to 40 at%, the Ku value of the auxiliary layer 15 described above is negative and the absolute value is 10 ⁵ erg / cc or more. be able to.

  Furthermore, the thickness of the auxiliary layer 15 is preferably 0.5 nm or more, and more preferably 1 nm or more. This is because if the thickness of the auxiliary layer 15 is less than 0.5 nm, the effect as a tilted medium is reduced and it is difficult to ensure uniformity over the entire surface of the medium.

  Furthermore, the thickness of the auxiliary layer 15 is preferably less than or equal to half the thickness of the main recording layer 16. This is because when the thickness of the auxiliary layer 15 exceeds half of the thickness of the main recording layer 16, the main component of magnetization becomes in-plane and the signal intensity decreases.

  The protective layer 14 prevents corrosion of the magnetic recording layer 3 and prevents damage to the medium surface when the magnetic head comes into contact with the magnetic recording medium. Examples of the protective layer 14 include those containing hard materials such as C, Si—O, Zr—O, Si—N, and the like. The thickness of the protective layer 14 is preferably 0.5 to 10 nm. As a result, the distance between the magnetic head and the magnetic recording layer 13 can be reduced, and the recording density can be increased. In addition, the magnetic recording medium to which the present invention is applied may have a structure in which a lubricating layer (not shown) is provided on the protective layer 14. Examples of the lubricant used in the lubricating layer include conventionally known materials such as perfluoropolyether, fluorinated alcohol, and fluorinated carboxylic acid.

  In the magnetic recording medium to which the present invention is applied, a tilted medium in which the Hc of a perpendicular magnetic recording medium having a high Ku and a high Hc is reduced can be realized by having the above-described structure.

  Here, the principle of obtaining the effect of reducing Hc in the present invention will be described with reference to FIG. 4 schematically shows the state of magnetization in the cross-sectional direction of the auxiliary layer 15 and the main recording layer 16. In FIG. 4, the white arrow indicates the direction of the external magnetic field, and white The length of the arrow indicates the magnitude of the external magnetic field, and the black arrow indicates the magnetization direction of each layer.

First, as shown in FIG. 4A, when there is no external magnetic field, the magnetizations of the auxiliary layer 15 and the main recording layer 16 are generally in one direction (upward in FIG. 4A). That is, when the magnetic anisotropy energy of the main recording layer 16 is larger than that of the auxiliary layer 15, the magnetization of the auxiliary layer 15 also faces the vertical direction. However, in practice, a twisted structure of magnetization may occur inside the auxiliary layer 15.
Next, as shown in FIG. 4B, when a small reversal magnetic field is applied, the magnetization of the auxiliary layer 15 starts to face in the in-plane direction, and the exchange coupling interaction with the auxiliary layer 15 causes the main recording layer 16 to Magnetization also begins to tilt.
Next, as shown in FIG. 4C, immediately before the main recording layer 16 is reversed as the reversal magnetic field increases, the magnetization of the auxiliary layer 15 is directed in the in-plane direction, and the magnetization of the main recording layer 16 is about 45 °. It becomes. As a result, as in the 45 ° recording method, the magnetization can be reversed with a smaller external magnetic field than in the case of the main recording layer 16 alone.

In the magnetic recording medium to which the present invention is applied, the magnetic recording layer 13 is divided into a magnetic portion and a nonmagnetic portion in the medium in-plane direction, and the magnetic portion and the nonmagnetic portion are along the circumferential direction of the medium. It is characterized by having an arrayed region.
Such a magnetic recording medium is called a patterned medium. For example, the magnetic recording layer 13 is divided into a magnetic part and a non-magnetic part by an uneven pattern 20 as shown by a surrounded part A in FIG. . Specifically, as shown in an enlarged view in FIG. 5, the surface of the magnetic recording medium 1 is a servo signal area 22 for tracking and data access control such as a burst signal, an address, and a preamble, and data for writing data. A track area 21 exists. These regions 21 and 22 are regions divided into a magnetic portion and a non-magnetic portion by the pattern 20, and the pattern 20 is processed into a desired shape after the magnetic recording layer 13 is formed. Alternatively, the thin film may be modified, or the magnetic recording layer 13 may be deposited by a normal thin film forming process on the substrate 11 processed into a desired shape. Further, the data track area 21 may be a track divided in units of 1 bit or a plurality of bits as shown in FIG. 6 in addition to the continuous track as shown in FIG.

  The magnetic recording medium shown in FIG. 5 is also called a discrete track medium, and the magnetic recording medium shown in FIG. 6 is sometimes called a patterned medium in a narrow sense. In the discrete track medium, the linear recording density is determined by the magnetization transition width formed on the medium by the head as in the present. On the other hand, in the patterned medium shown in FIG. 6, the linear recording density is determined by the processed shape. In general, the patterned medium shown in FIG. 6 can increase the recording density.

  Further, as shown in FIG. 7, the patterned medium includes a substrate processing mold in which the substrate 11 is subjected to pattern processing for dividing the servo signal area 21 and the data track area 22, and magnetic recording as shown in FIG. There is a magnetic material processing mold in which the layer 13 is subjected to a pattern processing that is divided into a servo signal region 21 and a data track region 22. In the case of the magnetic material processing type shown in FIG. 8, it is only necessary to obtain a signal in accordance with the processing shape from the magnetic recording layer 13, so that the processing may extend to the underlying layer 12 and the substrate 11 therebelow. Absent. Further, the magnetic recording layer 13 may have a shallow structure in which a part of the magnetic material remains (for example, only the main recording layer 16 is processed).

  The present invention can be applied to any of the patterned media shown in FIGS. 5 to 8, and an effect of reducing Hc can be obtained in a patterned region. Therefore, the patterned area may exist on the entire surface of the medium or may exist only on a part thereof. Moreover, the patterned area | region may exist continuously in the circumferential direction, or may exist intermittently in the circumferential direction.

Next, a magnetic recording / reproducing apparatus to which the present invention is applied will be described.
A magnetic recording / reproducing apparatus to which the present invention is applied is, for example, a hard disk drive (HDD) 30 shown in FIG. The HDD 30 records and reproduces various data by a perpendicular magnetic recording system. The HDD 30 is attached to a spindle motor (not shown) in a housing 31 and is driven to rotate. A magnetic head 32 that records and reproduces signals to and from the magnetic disk 1, a head suspension assembly 33 that mounts the magnetic head 32, an actuator 34 that drives the head suspension assembly 33, and a circuit board that controls each part 35.

  Among these, the magnetic head 32 is a composite head in which the recording head and the reproducing head are mounted on a common slider mechanism. In the magnetic recording medium to which the present invention is applied, the effect of reducing Hc can be obtained as described above. However, since the effect is large when the direction of the recording magnetic field is the vertical direction of the medium, the recording head is a single pole type. It is preferable to use a magnetic head. In addition, a so-called shielded pole structure in which a shield is provided on a single magnetic pole type magnetic head can be used. On the other hand, perpendicular magnetic recording can also be performed using a ring-type magnetic head used in a longitudinal medium. As the reproducing head, a shield type MR reproducing element using a GMR film, a TMR film or the like can be used.

  The head suspension assembly 33 supports the magnetic head 32 so as to face the recording surface of the magnetic disk 1, and includes a suspension 34 having the slider mechanism attached to the tip thereof and an arm 35 that supports the base end of the suspension 34. And. The actuator 34 positions the magnetic head 32 at an arbitrary radial position of the magnetic disk 1 via the head suspension assembly 33 by a voice coil motor (VCM). The circuit board 35 includes a head IC, and performs head drive control by the actuator 34 and data write or read control by the magnetic head 32.

Hereinafter, the effects of the present invention will be clarified by examples.
Example 1
In Example 1, first, it was examined by LLG simulation that the above-described effect of reducing Hc of the present invention can occur in a practical range. The simulation result is shown in FIG.
In this simulation, the calculation was performed on the assumption that Ku of the magnetic characteristics of the main recording layer was 6 Merg / cc and Ms was 500 emu / cc. This is a value close to the characteristics of CoCrPt used for the magnetic recording layer of the perpendicular magnetic recording medium. On the other hand, of the magnetic characteristics of the auxiliary layer, the calculation was performed assuming that Ku is −4 Merg / cc and Ms is 1000 emu / cc. This is a value close to the characteristic of CoIr. The exchange coupling constant was calculated on the assumption that the grain size and the main recording layer and the auxiliary layer were 0.5 μerg / cm. The mesh size was 1 nm cube, and the calculation was performed as a model simulating a cylinder having a diameter of 8 nm and a height of 18 nm.

  From the results shown in FIG. 10, the dotted line is a hysteresis loop in the case where a cylinder having a height of 18 nm is formed only by the main recording layer, and Hc is about 20 kOe. On the other hand, the solid line is the hysteresis when the main recording layer is 12 nm and the auxiliary layer is 6 nm, and Hc (the value of the external magnetic field H at which M = 0) is less than half. Further, the value of M (residual magnetization: Mr) at H = 0 is smaller than the saturation value (saturation magnetization: Ms). This is presumably because magnetization in the in-plane direction was present without the magnetization being completely aligned with the main recording layer inside the auxiliary layer. Further, the curve portion from when H = 0 to the point where the magnetization changes abruptly in the vicinity of Hc indicates that the magnetization component in the in-plane direction gradually increases as the switching magnetic field increases. And this part is reversibly rotated in magnetization, and returns to the value of Mr when the external magnetic field is returned to zero. Moreover, the rapid change in Hc is irreversible, and becomes -Mr when the external magnetic field is returned to zero. Therefore, the magnetic field that causes magnetization reversal is Hc. This phenomenon occurs as long as the Ku of the auxiliary layer is negative and the easy magnetization surface is the film surface.

Next, a simulation was performed by changing the thicknesses of the main recording layer and the auxiliary layer under the above conditions. The simulation result is shown in FIG.
In this simulation, the calculation was performed with the total thickness of the main recording layer and the auxiliary layer kept constant at 18 nm. The calculation was also performed when Ms of the auxiliary layer was 600 emu / cc. In FIG. 11, the horizontal axis indicates the thickness of the auxiliary layer, and the vertical axis indicates the coercive force Hc and the squareness ratio S (Mr / Ms).

  From the results shown in FIG. 11, it can be seen that there is an effect of almost halving Hc even if the thickness of the auxiliary layer is 1 nm. Further, since the S becomes smaller as the auxiliary layer becomes thicker, the thinner the auxiliary layer is preferable from the viewpoint of the reproduction signal intensity. Thus, if the thickness of the auxiliary layer is small, the change in total thermal fluctuation resistance is reduced. Further, the obstruction of the flow of magnetic flux passing in the order of the magnetic pole head, the main recording layer, the auxiliary layer, the intermediate underlayer, and the SUL is reduced.

  This result is the same both when the main recording layer is formed on the auxiliary layer and when the auxiliary layer is formed on the main recording layer. In addition, an auxiliary layer can be inserted between the main recording layers. In this case, since the exchange coupling interaction acting on the auxiliary layer is doubled, the value of S can be made closer to 1.

Next, the angle dependence of the magnetic recording medium to which the present invention was applied was examined by simulation. The simulation result is shown in FIG.
In this simulation, calculation was performed assuming that Ku of 6 Merg / cc, Ms of 500 emu / cc, and a thickness of 12 nm among the magnetic characteristics of the main recording layer. On the other hand, among the magnetic properties of the auxiliary layer, calculation was performed assuming that Ku is −4 Merg / cc, Ms is 1000 emu / cc, and the thickness is 6 nm.

  When the main recording layer is a single layer, if the magnetization reversal follows the so-called SW model, the angle dependency of Hc becomes a downwardly convex curve having a minimum value of 45 °. However, the magnetic recording medium to which the present invention is applied shows a different angle dependency of Hc. That is, from the results shown in FIG. 12, Hc is almost the same value from 0 ° to 45 °. This is presumably because the magnetization structure has a portion having an angle that is not always zero with respect to the magnetic field.

  This can be realized with the same granular structure as the magnetic recording medium used in the current HDD, but can also be realized with the patterned medium described above. That is, the effect of the present invention is that the magnetic recording layer is divided into a magnetic part and a nonmagnetic part in the in-plane direction, and the pattern has a region in which the magnetic part and the nonmagnetic part are arranged along the circumferential direction of the substrate. It can also be obtained by a medium. In addition, recording density in the bit direction can be improved by using a patterned medium instead of a granular medium. Note that which medium is used may be selected as appropriate from the viewpoint of what HDD system is to be manufactured or manufacturing cost.

(Example 2)
In Example 2, based on the result of Example 1, the following 1.5-inch hard disk magnetic disk was manufactured. Specifically, first, a nonmagnetic glass substrate (TS-10SX made by OHARA) was prepared, and this substrate was introduced into a vacuum chamber of a sputtering apparatus (C-3010 made by ANELVA), and then 1 × 10 ⁻ Under a reduced pressure of ⁶ Pa or less, on the substrate, the soft magnetic underlayer made of CoZrNb is 100 nm, the seed layer made of Ta is 5 nm, the underlayer made of Pt is 10 nm, the underlayer made of Ru is 10 nm, A main recording layer made of CoCrPt and SiO ₂ was sequentially laminated with t ₁ nm, an auxiliary layer (18-t ₁ ) nm, and a protective layer made of C with 4 nm. And after taking out the board | substrate with which these laminated films were formed from the vacuum chamber, perfluoropolyether (PFPE) was apply | coated by the dip method with the thickness of 1.3 nm as a lubricant on the surface of the protective layer. Since the main recording layer and the auxiliary layer were continuously formed in a vacuum state, an interface layer such as a surface oxide film was not formed, and a good exchange coupling state was obtained at the interface between the two. For the main recording layer, a target composition having a ((Co ₉₀ Cr ₁₀ ) ₈₀ Pt ₂₀ ) _90- (SiO ₂ ) ₁₀ ) was used. In addition, the number in () represents each composition ratio, and a unit is atomic%.

  Next, the prepared magnetic recording medium was sliced so that only the auxiliary layer and the main recording layer were observed as much as possible, and the surface of the obtained sample was observed with a transmission electron microscope (TEM). 3 was found to be a granular structure composed of magnetic particles as shown in FIG. 3 and a nonmagnetic material surrounding the magnetic particles. The thickness of the sample is about 10 nm. Further, when the EDX measurement was performed sequentially, it was confirmed that the signal from the underlying Ru was low.

Further, the non-magnetic part is mainly composed of SiO _{2. When} EDX analysis of this part was performed, peaks of Co and Cr were also confirmed. In the EDX analysis, since the constituent elements of the main recording layer and the auxiliary layer were detected, it is considered that the auxiliary layer and the main recording layer overlap each other in the magnetic particle portion. For this reason, when the cross section of the sample was observed with the transmission electron microscope (TEM), it turned out that it is a cross-sectional structure as shown in the said FIG. The auxiliary layer is considered to have a granular structure due to diffusion of an element such as Si from the main recording layer, although no element for dividing particles is added. Further, during the formation of the auxiliary layer, CoIr is easily deposited on CoCrPt, which is a similar alloy, and a base material mainly composed of SiO ₂ is an oxide such as Co—O that is inevitably generated during the film formation. One of the reasons for this granular structure is that it easily deposits on the surface.

Further, when the thickness t ₁ of the main recording layer was 18 nm, that is, when there was no auxiliary layer, Hc was 5.4 kOe. Next, when Co ₈₀ Ir ₂₀ was used for the auxiliary layer and samples with a main recording layer thickness t ₁ of 17 nm, 15 nm, 9 nm, and 3 nm were prepared, hysteresis similar to FIG. 10 was obtained for all samples. It was. Furthermore, when Hc at the position where the magnetization of each sample changed sharply was estimated to be 3.9 kOe, 3.5 kOe, 2.8 kOe, and 2.5 kOe, respectively, the effect of reducing Hc was confirmed. Incidentally, unlike the simulation result, the Hc in the application of the present invention is not halved, mainly when the thickness t ₁ of the recording layer is 18 nm, the perpendicular magnetic anisotropy is completely oriented perpendicular to the film surface However, it is considered that the angle has a dispersion of about 5 °, the intensity has a dispersion of about 10%, or both.

By the way, when the value of Ku of CoIr was estimated by torque measurement, it was found to be about -4 Merg / cc. A main recording layer having a thickness t ₁ of 3 nm is difficult to be used as a magnetic recording medium as it is because the residual magnetization Mr is small.

Next, samples were prepared in which the thickness t ₁ of the main recording layer was 9 nm and the auxiliary layer material was CoFe, MnSb, FeC, Fe ₃ Pt, and each sample had Hc of 3 to 4 kOe, which reduced Hc. The effect to do was obtained.

  Next, a magnetic recording / reproducing apparatus as shown in FIG. 9 was produced using a magnetic recording medium having CoIr as an auxiliary layer. In this magnetic recording / reproducing apparatus, a ring head generally used for a longitudinal medium is used as a recording head, the rotational speed of the disk is 4500 rpm, and the recording frequency is a single frequency of 50 MHz. As a result, only samples with Hc of less than 3 kOe could be recorded, and with other samples, sufficient recording could not be performed, so that obvious waveform disturbance was observed on the oscilloscope.

Next, a magnetic recording / reproducing apparatus having a single magnetic pole head as a recording head was manufactured and the same recording operation as that described above was performed. As a result, sufficient recording was performed with samples having a main recording layer thickness t ₁ of 17 nm, 15 nm, and 9 nm. However, in the sample with the main recording layer thickness t ₁ of 18 nm, sufficient recording could not be performed, and thus waveform disturbance was observed on the oscilloscope.

(Example 3)
In Example 3, a base layer made of Ti is 7 nm, a base layer made of Ru is 3 nm, an auxiliary layer made of CoIr and SiO ₂ is 5 nm, and a protective layer made of C is 4 nm on the substrate in order. A magnetic recording medium similar to that of Example 2 was prepared except that the layers were stacked. Note that the film formation of CoIr—SiO ₂ is performed by ternary simultaneous sputtering of a Co—SiO ₂ target, a Co target, and an Ir target.

In Example 3, first, the value of Ku when the atomic composition ratio of Ir was changed so that the volume ratio of SiO ₂ was 10% was measured. The measurement results are shown in FIG. From the measurement shown in FIG. 13, it can be seen that Ku is negative when Ir is in the range of 5 to 40 at%, although there is a difference depending on the pressure during film formation (Ar is used as the sputtering gas).

Next, a magnetic recording / reproducing apparatus as shown in FIG. 9 was produced using the magnetic recording medium having CoIr as an auxiliary layer. As a magnetic recording medium, on a glass substrate, a base layer made of Ti is 7 nm, a base layer made of Ru is 3 nm, an auxiliary layer made of CoIr and SiO ₂ is 5 nm, and a main layer made of CoCrPt and SiO ₂ is used. A recording layer having a thickness of 13 nm and a protective layer made of C and a thickness of 4 nm were sequentially stacked. Since this magnetic recording medium does not use a soft magnetic underlayer (SUL), recording with a ring head is possible.

  Then, a magnetic recording medium in which the atomic composition ratio of Ir was changed to 0, 5 at%, 10 at%, 20 at%, 30 at%, 40 at%, and 50 at% was manufactured, and the recording operation was performed under the same conditions as in Example 2 above. As a result, in a magnetic recording medium with an atomic composition ratio of Ir of 0 at% and 50 at%, sufficient recording could not be performed, so that waveform disturbance was observed on an oscilloscope. Of these, the one with 0 at% is an auxiliary layer made only of Co, and therefore, the average saturation magnetization of the whole is increased, and an indefinite magnetic domain structure is formed by magnetostatic interaction. On the other hand, in the case of 50 at%, the Ms of the auxiliary layer is small, so the value of Ku becomes positive, the coercive force is close to the original value of the main recording layer, and it is considered that the ring head can no longer perform recording. For all other magnetic recording media, the effect of reducing Hc could be obtained, and a normal recording operation could be performed even with a ring head.

Example 4
In Example 4, the base layer made of Ti is 7 nm, the main recording layer made of CoCrPt and SiO ₂ is 10 nm, the auxiliary layer is 3 nm, and the main recording layer made of CoCrPt and SiO ₂ is 5 nm on the substrate. A magnetic recording medium similar to that of Example 2 was prepared except that a protective layer made of C and 4 nm were sequentially stacked. When the Hc of this magnetic recording medium was estimated, it was 3.0 kOe, and it was found that the effect of reducing Hc was further obtained and the squareness ratio was improved as compared with the case of Example 2.

Then, using this magnetic recording medium, a magnetic recording / reproducing apparatus as shown in FIG. 9 was produced, and a recording operation under the same conditions as in Example 2 was performed. A single magnetic pole type magnetic head was used as the recording head. As a result, it was found that the signal intensity increased by 10% and the SNR increased by about 2 dB as compared with the case where the thickness t ₁ of the main recording layer of Example 2 was 15 nm. This is presumably because the signal intensity became stronger because the effect of reducing Hc was enhanced and the squareness ratio increased.

1 is a perspective view showing a magnetic recording medium to which the present invention is applied. It is sectional drawing which shows the laminated structure of the magnetic recording medium shown in FIG. It is a schematic diagram which shows the granular structure of the magnetic recording medium shown in FIG. It is a schematic diagram for demonstrating the magnetization reversal process of the magnetic recording medium shown in FIG. FIG. 2 is a plan view of a discrete track medium showing an enlarged encircled portion A in FIG. 1. It is a top view of the patterned medium which expands and shows the enclosure part A in FIG. It is sectional drawing which shows a substrate processing type patterned medium. It is sectional drawing which shows a magnetic body processing type patterned medium. It is a perspective view which shows the magnetic recording / reproducing apparatus to which this invention is applied. It is a graph which shows the hysteresis loop obtained by the simulation of this invention. It is a graph which shows the relationship between the thickness of the auxiliary layer of this invention, a coercive force, and a squareness ratio. It is a graph which shows the relationship between the magnetic field application angle of this invention, and a coercive force. It is a graph which shows the relationship between the atomic composition ratio of Ir and Ku in the auxiliary layer of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Magnetic disk (magnetic recording medium) 11 ... Substrate 12 ... Underlayer 13 ... Magnetic recording layer 14 ... Protective layer 15 ... Auxiliary layer 16 ... Main recording layer 17 ... Magnetic particle 18 ... Nonmagnetic material 20 ... Pattern 21 ... Servo signal Area 22 ... Data track area 30 ... Hard disk drive (magnetic recording / reproducing device) 31 ... Housing 32 ... Magnetic head 33 ... Head suspension assembly 34 ... Actuator 35 ... Circuit board 36 ... Suspension 37 ... Arm

Claims (10)

A substrate, a base layer formed on the substrate, a magnetic recording layer formed on the base layer, and a protective layer formed on the magnetic recording layer,
The magnetic recording layer is composed of a main recording layer and an auxiliary layer exchange-coupled to each other,
The main recording layer has magnetic particles and a nonmagnetic material surrounding the magnetic particles, and has perpendicular magnetic anisotropy,
A negative anisotropy exchange coupled magnetic recording medium characterized in that the auxiliary layer is made of a material having negative magnetocrystalline anisotropy and has an anisotropy in which the medium surface becomes an easily magnetized surface.   The magnetic recording layer is divided into a magnetic part and a nonmagnetic part in a medium in-plane direction, and has a region in which the magnetic part and the nonmagnetic part are arranged along the circumferential direction of the medium. The negative anisotropic exchange coupled magnetic recording medium according to claim 1. The negative anisotropic exchange coupling type magnetic recording medium according to claim 1, wherein the absolute value of the magnetocrystalline anisotropy of the auxiliary layer is 10 ⁵ erg / cc or more.   4. The negative anisotropic exchange coupled magnetic recording medium according to claim 1, wherein the auxiliary layer has a thickness of 1 nm or more. 5.   5. The negative anisotropic exchange coupled magnetic recording medium according to claim 1, wherein a thickness of the auxiliary layer is not more than half of a thickness of the main recording layer. The auxiliary layer, CoIr, CoFe, MnSb, FeC , to any one of claims 1 to 5, characterized in that it comprises at least one or more alloys selected from among _Fe 3 Pt The negative anisotropic exchange coupling type magnetic recording medium described.   The negative anisotropy exchange coupling type according to any one of claims 1 to 6, wherein the auxiliary layer is made of CoIr and has an Ir content of 5 to 40 atomic%. Magnetic recording medium.   8. The crystalline underlayer according to claim 1, further comprising a hexagonal close-packed lattice plane or a tetragonal lattice plane oriented in a plane parallel to the substrate, under the auxiliary layer. 9. The negative anisotropy exchange coupled magnetic recording medium described in the item. The negative anisotropic exchange coupling type magnetic recording medium according to any one of claims 1 to 8,
A magnetic recording / reproducing apparatus comprising: a magnetic head for recording and reproducing signals to and from the negative anisotropic exchange coupled magnetic recording medium.   The magnetic recording / reproducing apparatus according to claim 9, wherein the magnetic head is a single magnetic pole type magnetic head.

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