JP5620118B2 - Perpendicular magnetic recording medium - Google Patents

Description

  The present invention relates to a perpendicular magnetic recording medium mounted on a perpendicular magnetic recording type HDD (hard disk drive) or the like.

  Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of HDDs using magnetic recording technology continues to increase at an annual rate of about 100%. Recently, a 2.5-inch diameter magnetic recording medium used for HDDs or the like has been required to have an information recording capacity exceeding 200 GBytes per sheet. In order to meet such a demand, one square is required. It is required to realize an information recording density exceeding 400 GB per inch.

  In recent years, a perpendicular magnetic recording system has been proposed in order to achieve a high recording density in a magnetic recording medium used for an HDD or the like. The perpendicular magnetic recording medium used for the perpendicular magnetic recording system is adjusted so that the easy axis of magnetization of the magnetic recording layer is oriented in the direction perpendicular to the substrate surface. Compared to the conventional in-plane recording method, the perpendicular magnetic recording method can suppress the so-called thermal fluctuation phenomenon in which the thermal stability of the recording signal is lost due to the superparamagnetic phenomenon, and the recording signal disappears. Suitable for higher recording density.

As a magnetic recording medium used in the perpendicular magnetic recording system, a CoCrPt—SiO ₂ perpendicular magnetic recording medium (see Non-Patent Document 1) has been proposed because it exhibits high thermal stability and good recording characteristics. This is a granular structure in which a nonmagnetic grain boundary portion in which SiO ₂ is segregated is formed between magnetic grains in which Co hcp structure (hexagonal close-packed crystal lattice) crystals are continuously grown in a columnar shape in a magnetic recording layer. The magnetic particles are made finer and the coercive force Hc is improved. It is known that an oxide is used for a nonmagnetic grain boundary (a nonmagnetic portion between magnetic grains). For example, any one of SiO ₂ , Cr ₂ O ₃ , TiO, TiO ₂ , and Ta ₂ O ₅ is used. Has been proposed (Patent Document 1).

  By the way, as important factors for increasing the recording density, improvement of the magnetostatic characteristics such as the above-mentioned coercive force Hc and the reverse domain nucleation magnetic field Hn, overwriting characteristics (OW characteristics) and SNR (Signal Noise Ratio). There is an improvement in electromagnetic conversion characteristics such as narrowing of the track width.

  In particular, there is a technique for providing an auxiliary recording layer above or below the magnetic recording layer in order to improve the OW characteristics. The auxiliary recording layer is a magnetic layer substantially magnetically continuous in the in-plane direction of the main surface of the substrate, and exerts a magnetic interaction with the magnetic recording layer to improve the reverse domain nucleation magnetic field Hn. The characteristics are improved.

JP 2006-024346 A

T. Oikawa et.al., IEEE Trans. Magn, vol.38, 1976-1978 (2002)

  However, when the auxiliary recording layer is provided, so-called “writing blur” occurs in exchange for the improvement of the OW characteristics, and the track width increases. In addition, writing blur affects adjacent recording bits and tracks, and degrades the signal quality of adjacent tracks. That is, the auxiliary recording layer originally aims to improve the surface recording density by lowering the coercive force Hc and improving the SNR and improving the linear recording density. Thus, the presence of the auxiliary recording layer leads to the adjacent track. The effect lowers the track density and causes a reduction in surface recording density.

  On the other hand, if the auxiliary recording layer is made thin to avoid writing blur, the recording itself becomes difficult (deterioration of OW characteristics) and noise increases.

  For these reasons, it is necessary to form the auxiliary recording layer in an appropriate film thickness. However, the behavior of the auxiliary recording layer is very sensitive to the film thickness, and even if it slightly deviates from the ideal value, the writing blur increases or the OW characteristics deteriorate. That is, there is a trade-off between writing blur and OW characteristics in the auxiliary recording layer, and it is difficult to stably obtain a desired balance.

  In view of such a problem, the present invention achieves both the track width and the SNR by reducing the track width and improving the SNR while maintaining the film thickness of the auxiliary recording layer and maintaining a good OW characteristic. Therefore, an object of the present invention is to provide a perpendicular magnetic recording medium capable of achieving high recording density.

  In order to solve the above-mentioned problems, the inventor diligently studied and made the auxiliary recording layer a two-layer structure, and made one layer closer to the magnetic recording layer a layer having a granular structure. The present invention has been completed with the idea of acting as a layer (magnetization direction fixed layer).

  That is, in order to solve the above problems, a typical configuration of the perpendicular magnetic recording medium according to the present invention is a nonmagnetic grain boundary portion between magnetic particles made of CoCrPt continuously grown in a columnar shape on a substrate. In a perpendicular magnetic recording medium having a granular structure having a magnetic structure for recording a signal and an auxiliary recording layer in this order, the auxiliary recording layer is magnetically substantially in the in-plane direction of the main surface of the substrate. A non-granular auxiliary recording layer which is a continuous magnetic layer; and a granular auxiliary recording layer which is provided under the non-granular auxiliary recording layer and has a higher coercive force than the non-granular auxiliary recording layer and has a granular structure. It is characterized by that.

  In other words, a typical configuration of the perpendicular magnetic recording medium according to the present invention is that a nonmagnetic grain boundary is formed between magnetic grains made of an alloy containing CoCrPt continuously grown in a columnar shape on a substrate. In the perpendicular magnetic recording medium comprising the magnetic recording layer having the granular structure and the auxiliary recording layer containing CoPt in this order, the auxiliary recording layer is a magnetic layer substantially magnetically continuous in the in-plane direction of the substrate main surface. A non-granular auxiliary recording layer, and a granular auxiliary recording layer which is provided immediately below and in contact with the non-granular auxiliary recording layer and has the same material and structure as the magnetic recording layer.

  According to the above configuration, the granular auxiliary recording layer having a high coercive force acts as a pinned layer of the non-granular auxiliary recording layer. Therefore, normally, if the auxiliary recording layer is thickened, writing bleeding increases. However, even if a thick auxiliary recording layer is provided, the track width can be narrowed (reducing writing bleeding) and the SNR is improved. In this way, both the track width and the SNR can be achieved.

  In the granular auxiliary recording layer, it is preferable that at% of Cr is small and at% of CoPt is large as compared with the magnetic recording layer. In other words, it is preferable that the magnetic grains of the granular auxiliary recording layer have a Cr at% equivalent or lower and a Pt at% higher or lower than the magnetic grains of the magnetic recording layer. According to such a composition, it is considered that the magnetic anisotropy Ku of the granular auxiliary recording layer is higher than that of the magnetic recording layer, and ideally acts as a pinned layer of the non-granular auxiliary recording layer.

  The difference (A−B) between the Cr concentration (A) of the magnetic recording layer and the Cr concentration (B) of the granular auxiliary recording layer is preferably 1 at% or more and 4 at% or less. In other words, the difference (A−B) between the Cr concentration (A) of the magnetic grains of the magnetic recording layer and the Cr concentration (B) of the magnetic grains of the granular auxiliary recording layer is 1 at% or more and 4 at% or less. There should be. That is, in the metal layer, the Cr concentration difference (A−B) is preferably 1 at% or more and 4 at% or less.

  The granular auxiliary recording layer is preferably thinner than the non-granular auxiliary recording layer. If the thickness of the non-granular auxiliary recording layer is reduced, the OW characteristics are degraded and writing becomes difficult. Accordingly, the non-granular auxiliary recording layer is made thick so that the thin granular auxiliary recording layer acts as a pinned layer of the non-granular auxiliary recording layer while ensuring the OW characteristics by increasing the thickness of the non-granular auxiliary recording layer. For example, the granular auxiliary recording layer may have a thickness of 0.5 nm to 5.0 nm, and the non-granular auxiliary recording layer may have a thickness of 4.0 to 8.0 nm.

  It is preferable to provide a nonmagnetic dividing layer between the magnetic recording layer and the auxiliary recording layer so that the strength of the ferromagnetic coupling between the magnetic recording layer and the auxiliary recording layer can be adjusted. Thereby, the strength of the magnetic interaction (ferromagnetic exchange coupling) can be adjusted by magnetically separating the magnetic recording layer and the granular auxiliary recording layer. Therefore, the granular auxiliary recording layer and the non-granular auxiliary recording layer are preferentially subjected to magnetization reversal as one group preferentially over the magnetic recording layer, and the role as the auxiliary recording layer can be more clearly performed.

  The magnetic recording layer is preferably formed of a plurality of layers. Thereby, it can suppress that it enlarges as a magnetic particle is formed into a film, and can make the particle size from a lower layer to an upper layer uniform. Note that the stacked films may be made of the same material or different materials.

  According to the present invention, while maintaining the film thickness of the auxiliary recording layer and maintaining the OW characteristics in a good state, the track width is narrowed to improve the SNR, thereby achieving both the track width and the SNR. A perpendicular magnetic recording medium capable of achieving a high recording density can be provided.

It is a figure explaining the structure of the perpendicular magnetic recording medium concerning this embodiment. It is a figure explaining the layer structure from the main recording layer of FIG. 1 to an auxiliary recording layer. It is a figure which compares the track width and SNR of the Example which changed the film thickness of the granular auxiliary recording layer and the non-granular auxiliary recording layer variously, and the comparative example which has only a non-granular auxiliary recording layer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.
(Embodiment)

[Perpendicular magnetic recording medium]
FIG. 1 is a diagram for explaining the configuration of a perpendicular magnetic recording medium 100 according to the present embodiment. A perpendicular magnetic recording medium 100 shown in FIG. 1 includes a disk substrate 110, an adhesion layer (adhesion layer) 112, a first soft magnetic layer 114a, a spacer layer 114b, a second soft magnetic layer 114c, and a pre-underlayer 116 (nonmagnetic layer). , First under layer 118a, second under layer 118b, nonmagnetic granular layer 120, lower recording layer 122a, intervening layer 122b, first main recording layer 122c, second main recording layer 122d, dividing layer 124, granular auxiliary recording layer 126a, a non-granular auxiliary recording layer 126b, a medium protective layer 128, and a lubricating layer 130. The first soft magnetic layer 114a, the spacer layer 114b, and the second soft magnetic layer 114c together constitute the soft magnetic layer 114. The first base layer 118a and the second base layer 118b together constitute the base layer 118. The lower recording layer 122a, the intervening layer 122b, the first main recording layer 122c, and the second main recording layer 122d together constitute the magnetic recording layer 122. The granular auxiliary recording layer 126a and the non-granular auxiliary recording layer 126b together form an auxiliary recording layer 126.

  As the disk substrate 110, a glass disk obtained by forming amorphous aluminosilicate glass into a disk shape by direct pressing can be used. The type, size, thickness, etc. of the glass disk are not particularly limited. Examples of the material of the glass disk include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or glass ceramic such as crystallized glass. It is done. The glass disk is subjected to grinding, polishing, and chemical strengthening sequentially to obtain a smooth non-magnetic disk base 110 made of a chemically strengthened glass disk.

  On the disk substrate 110, a film is sequentially formed from the adhesion layer 112 to the auxiliary recording layer 126 by a DC magnetron sputtering method, and the medium protective layer 128 can be formed by a CVD method. Thereafter, the lubricating layer 130 can be formed by a dip coating method. Note that it is also preferable to use an in-line film forming method in terms of high productivity. Hereinafter, the configuration of each layer will be described.

  The adhesion layer 112 is formed in contact with the disk substrate 110, has a function of increasing the peel strength between the soft magnetic layer 114 formed on the disk substrate 110 and the disk substrate 110, and a crystal of each layer formed on the soft magnetic layer 114. It has a function to make grains finer and uniform. When the disk substrate 110 is made of amorphous glass, the adhesion layer 112 is preferably an amorphous (amorphous) alloy film so as to correspond to the amorphous glass surface.

  The adhesion layer 112 can be selected from, for example, a CrTi amorphous layer, a CoW amorphous layer, a CrW amorphous layer, a CrTa amorphous layer, and a CrNb amorphous layer. The adhesion layer 112 may be a single layer made of a single material, or may be formed by laminating a plurality of layers. For example, a CoW layer or a CrW layer may be formed on the CrTi layer. These adhesion layers 112 are preferably formed by sputtering with a material containing carbon dioxide, carbon monoxide, nitrogen, or oxygen, or the surface layer is exposed with these gases.

  The soft magnetic layer 114 is a layer that temporarily forms a magnetic path during recording in order to pass magnetic flux in a direction perpendicular to the recording layer in the perpendicular magnetic recording method. The soft magnetic layer 114 can be configured to include AFC (Anti Ferro magnetic exchange Coupling) by interposing a nonmagnetic spacer layer 114b between the first soft magnetic layer 114a and the second soft magnetic layer 114c. As a result, the magnetization direction of the soft magnetic layer 114 can be aligned along the magnetic path (magnetic circuit) with high accuracy, and the vertical component of the magnetization direction is extremely reduced, so that noise generated from the soft magnetic layer 114 is reduced. Can do. The composition of the first soft magnetic layer 114a and the second soft magnetic layer 114c includes a cobalt-based alloy such as CoTaZr, a Co—Fe-based alloy such as CoCrFeB and CoFeTaZr, and a Ni like a [Ni—Fe / Sn] n multilayer structure. A Fe alloy or the like can be used.

  The pre-underlayer (orientation control layer) 116 is a nonmagnetic layer, that is, a nonmagnetic alloy layer, and has a function of protecting the soft magnetic layer 114 and a function of promoting the alignment of crystal grain orientations of the underlayer 118. Specifically, the material of the front ground layer 116 can be selected from Ni, Cu, Pt, Pd, Zr, Ta, Hf, and Nb. Furthermore, it is good also as an alloy which contains these metals as a main component and contains any one or more additional elements of Ti, V, Ta, Cr, Mo, and W. For example, NiW, NiCr, NiTa alloy, CuW alloy, and CuCr alloy can be suitably selected. Further, it may be formed as a plurality of layers.

  Thereby, the roughness of each interface in the plurality of layers formed on the soft magnetic layer 114 is improved, and the crystal orientation of these layers can be improved. Therefore, it is possible to improve the SNR and achieve a high recording density.

  The underlayer 118 has an hcp structure, and has a function of growing a Co hcp crystal of the magnetic recording layer 122 as a granular structure. Therefore, the higher the crystal orientation of the underlayer 118, that is, the more the (0001) plane of the crystal of the underlayer 118 is parallel to the main surface of the disk substrate 110, the more the orientation of the magnetic recording layer 122 is improved. Can do. In order to impart further separability, it is preferable that the Ar pressure during film formation is divided into a lower layer having a low pressure and an upper layer having a high pressure. Ru is a typical material for the underlayer 118, but in addition, it can be selected from Re, Pt, RuCr, and RuCo. Since Ru has an hcp structure and crystal atomic spacing is close to Co, the magnetic recording layer 122 containing Co as a main component can be well oriented. Further, an oxide may be added.

  When the underlayer 118 is made of Ru, a two-layer structure made of Ru can be obtained by changing the gas pressure during sputtering. Specifically, when forming the first underlayer 118a on the lower layer side, the Ar gas pressure is set to a predetermined pressure, that is, a low pressure, and when forming the second underlayer 118b on the upper layer side, the first lower layer 118b on the lower layer side is formed. The gas pressure of Ar is set higher than when forming the first underlayer 118a, that is, the pressure is increased. Thereby, the crystal orientation of the magnetic recording layer 122 can be improved by the first underlayer 118a, and the grain size of the magnetic particles of the magnetic recording layer 122 can be reduced by the second underlayer 118b.

  Further, when the gas pressure is increased, the mean free path of the plasma ions to be sputtered is shortened, so that the film formation rate is slow and the film becomes rough, so that separation and refinement of Ru crystal particles can be promoted, Co crystal grains can also be made finer.

  Further, a small amount of oxygen may be contained in Ru of the base layer 118. As a result, the separation and refinement of the Ru crystal grains can be further promoted, and the magnetic recording layer 122 can be further isolated and refined. Therefore, in the present embodiment, oxygen is included in the second underlayer formed immediately below the magnetic recording layer in the underlayer 118 constituted by two layers. That is, the second underlayer is made of RuO. Thereby, said advantage can be acquired most effectively. Note that oxygen may be contained by reactive sputtering, but it is preferable to use a target containing oxygen at the time of sputtering film formation.

  The nonmagnetic granular layer 120 is a nonmagnetic layer having a granular structure. A nonmagnetic granular layer 120 is formed on the hcp crystal structure of the underlayer 118, and a granular layer of the lower recording layer 122a (that is, the entire magnetic recording layer 122) is grown thereon, thereby initial growth of the magnetic granular layer. It has an action of separating from the stage (rise). Thereby, isolation of the magnetic particles of the magnetic recording layer 122 can be promoted. The composition of the nonmagnetic granular layer 120 can be a granular structure by forming a grain boundary by segregating a nonmagnetic substance between nonmagnetic crystal grains made of a Co-based alloy.

In the present embodiment, CoCr—SiO ₂ is used for the nonmagnetic granular layer 120. As a result, SiO ₂ (nonmagnetic substance) segregates between Co-based alloys (nonmagnetic crystal grains) to form grain boundaries, and the nonmagnetic granular layer 120 has a granular structure. Note that CoCr—SiO ₂ is an example, and the present invention is not limited to this. In addition, CoCrRu—SiO ₂ can be preferably used, and Rh (rhodium), Pd (palladium), Ag (silver), Os (osmium), Ir (iridium), Au (gold) can be used instead of Ru. Can also be used. A non-magnetic substance is a substance that can form a grain boundary around magnetic particles so that exchange interaction between magnetic particles (magnetic grains) is suppressed or blocked, and cobalt (Co). Any non-magnetic substance that does not dissolve in solution can be used. Examples thereof include silicon oxide (SiOx), chromium (Cr), chromium oxide (Cr ₂ O ₃ ), titanium oxide (TiO ₂ ), zircon oxide (ZrO ₂ ), and tantalum oxide (Ta ₂ O ₅ ).

  In this embodiment, the nonmagnetic granular layer 120 is provided on the underlayer 188 (second underlayer 188b). However, the present invention is not limited to this. The recording medium 100 can also be configured.

  The magnetic recording layer 122 has a columnar granular structure in which a nonmagnetic substance is segregated around a magnetic particle of a hard magnetic material selected from a Co alloy, an Fe alloy, and a Ni alloy to form a grain boundary. (Granular magnetic recording layer). By providing the nonmagnetic granular layer 120, the magnetic particles can be epitaxially grown continuously from the granular structure. In this embodiment, the magnetic recording layer 122 includes a lower recording layer 122a, an intervening layer 122b, a first main recording layer 122c, and a second main recording layer 122d. Thereby, small crystal grains of the first main recording layer 122c and the second main recording layer 122d continue to grow from the crystal grains (magnetic particles) of the lower recording layer 122a, and the main recording layer can be miniaturized. SNR can be improved.

In this embodiment, CoCrPt—Cr ₂ O ₅ —SiO ₂ is used for the lower recording layer 122a. In CoCrPt—Cr ₂ O ₅ —SiO ₂ , Cr ₂ O ₅ and SiO ₂ (oxide), which are nonmagnetic substances, segregate around magnetic particles (grains) made of CoCrPt to form grain boundaries, and magnetic A granular structure is formed in which particles grow in a columnar shape. The magnetic particles were epitaxially grown continuously from the granular structure of the nonmagnetic granular layer 120.

  The intervening layer 122b is a nonmagnetic thin film, and by interposing it between the lower recording layer 122a and the first main recording layer 122c, the magnetic continuity between them can be divided and adjusted. At this time, by setting the thickness of the intervening layer 122b to a predetermined thickness (0.2 to 0.9 nm), antiferromagnetic exchange coupling (AFC) is established between the lower recording layer 122a and the first main recording layer 122c. ) Is considered to occur. As a result, magnetization is attracted between the upper and lower layers of the intervening layer 122b and acts to fix the magnetization directions to each other, so that fluctuations in the magnetization axis can be reduced and noise can be reduced.

  The intervening layer 122b is preferably composed of Ru or a Ru compound. This is because Ru has an atomic interval close to that of Co constituting the magnetic particles, and thus it is difficult to inhibit the epitaxial growth of Co crystal particles even if it is interposed between the magnetic recording layers 122. In addition, even if the intervening layer 122b is extremely thin, it is difficult to inhibit the epitaxial growth.

  Here, the lower recording layer 122a is a magnet that is continuous with the first main recording layer 122c and the second main recording layer 122d without the intervening layer 122b. Become. Further, by reducing the film thickness of the lower recording layer 122a, the aspect ratio of the granular magnetic particles is shortened (in the perpendicular magnetic recording medium, the film thickness direction corresponds to the longitudinal direction of the easy axis of magnetization). The demagnetizing field generated inside becomes stronger. For this reason, although the lower recording layer 122a is hard magnetic, the magnetic moment to be exposed to the outside becomes small and it is difficult to be picked up by the magnetic head. That is, by adjusting the film thickness of the lower recording layer 122a, the magnetic moment (magnet strength) is such that the magnetic flux does not easily reach the magnetic head and has a magnetic interaction with the first main recording layer 122c. ), A magnetic recording layer with low noise while exhibiting a high coercive force can be obtained.

In the present embodiment, the first main recording layer 122c is made of CoCrPt—SiO ₂ —TiO ₂ . As a result, also in the first main recording layer 122c, nonmagnetic materials such as SiO ₂ and TiO ₂ (composite oxide) are segregated around the magnetic grains (grains) made of CoCrPt to form grain boundaries, and the magnetic grains Formed a granular structure with columnar growth.

In the present embodiment, the second main recording layer 122d is continuous with the first main recording layer 122c, but the composition and film thickness are different. The second main recording layer 122d is made of CoCrPt—SiO ₂ —TiO ₂ —Co ₃ O ₄ . As a result, also in the second main recording layer 122d, nonmagnetic materials such as SiO ₂ , TiO ₂ , and Co ₃ O ₄ (composite oxide) are segregated around the magnetic grains (grains) made of CoCrPt to form grain boundaries. As a result, a granular structure in which magnetic grains were grown in a columnar shape was formed.

  As described above, in the present embodiment, the second main recording layer 122d includes more oxide than the first main recording layer 122c. Thereby, separation of crystal grains can be promoted stepwise from the first main recording layer 122c to the second main recording layer 122d.

Further, as described above, the second main recording layer 122d contains Co oxide. When SiO ₂ or TiO ₂ is mixed as an oxide, there is a fact that oxygen deficiency occurs, Si ions or Ti ions are mixed into the magnetic particles, the crystal orientation is disturbed, and the holding force Hc is reduced. Therefore, by containing Co oxide, it can function as an oxygen carrier for compensating for this oxygen deficiency. Co ₃ O ₄ is exemplified as the Co oxide, but CoO may be used.

Co oxide has Gibbs liberalization energy ΔG larger than that of SiO ₂ or TiO ₂ , and Co ions and oxygen ions are easily separated. Therefore, oxygen is preferentially separated from the Co oxide, and oxygen vacancies generated in SiO ₂ and TiO ₂ are compensated to complete Si and Ti ions as oxides, which can be precipitated at grain boundaries. Thereby, it can prevent that foreign materials, such as Si and Ti, mix in a magnetic particle, and can prevent disordering the crystallinity of a magnetic particle by the mixing. At this time, surplus Co ions are considered to be mixed in the magnetic particles, but since the magnetic particles are a Co alloy in the first place, the magnetic properties are not impaired. Accordingly, the crystallinity and crystal orientation of the magnetic particles are improved, and the coercive force Hc can be increased. Further, since the saturation magnetization Ms is improved, there is an advantage that the overwrite characteristic is also improved.

  However, when Co oxide is mixed in the magnetic recording layer, there is a problem that the SNR is lowered. Therefore, by providing the first main recording layer 122c not mixed with Co oxide as described above, a high SNR is secured in the first main recording layer 122c, while a high holding force Hc and overload are achieved in the second main recording layer 122d. Light characteristics can be obtained. The second main recording layer 122d is preferably thicker than the first main recording layer 122c. As a preferred example, the first main recording layer 122c is 4 nm and the second main recording layer 122d is 6 nm. be able to.

The materials used for the lower recording layer 122a, the first main recording layer 122c, and the second main recording layer 122d described above are merely examples, and the present invention is not limited thereto. Examples of nonmagnetic substances for forming grain boundaries include silicon oxide (SiO _x ), chromium (Cr), chromium oxide (Cr _X O _Y ), titanium oxide (TiO ₂ ), zircon oxide (ZrO ₂ ), and oxidation. Examples of the oxide include tantalum (Ta ₂ O ₅ ), iron oxide (Fe ₂ O ₃ ), and boron oxide (B ₂ O ₃ ). Further, nitrides such as _BN, a carbide such as B 4 _{C 3} can also be suitably used.

Furthermore, in the present embodiment, two types of nonmagnetic substances (oxides) are used in the lower recording layer 122a and the first main recording layer 122c, and three types of nonmagnetic substances (oxides) are used in the second main recording layer 122d. Absent. For example, in any or all of the lower recording layer 122a to the second main recording layer 122d, one type of nonmagnetic material may be used, or two or more types of nonmagnetic materials may be used in combination. . Although there is no limitation on the kind of nonmagnetic substance contained at this time, it is particularly preferable to contain SiO ₂ and TiO ₂ as in this embodiment. Therefore, unlike the present embodiment, when the second main recording layer 122d is composed of only one layer from the lower recording layer 122a (when the intervening layer 122b is not provided), the magnetic recording layer is CoCrPt—SiO ₂ —TiO _{2. 2} is preferable.

  The dividing layer 124 is a nonmagnetic layer provided between the magnetic recording layer 122 (second main recording layer 122 d) and the auxiliary recording layer 126. By providing the dividing layer 124, the strength of the ferromagnetic exchange coupling between the magnetic recording layer 122 and the auxiliary recording layer 126 can be adjusted. The thickness of the dividing layer 124 is preferably in the range of 0.1 to 1.0 nm.

  In the present embodiment, the dividing layer 124 can be formed of a thin film containing Ru, a Ru compound, Ru and oxygen, or Ru and an oxide. This can also reduce noise caused by the auxiliary recording layer 126. When the dividing layer 124 is formed, oxygen contained in the dividing layer 124 is segregated on the oxide of the magnetic recording layer 122, and Ru is segregated on the magnetic particles. This is because the crystal structure of the auxiliary recording layer 126 can be inherited to Co.

Various oxides are conceivable as Ru contained in the dividing layer 124, and electromagnetic conversion characteristics (SNR) can be improved by using an alloy or oxide of W, Ti, Ru in particular. For example, the dividing layer 124 may include RuCr, RuCo, RuO, RuWO ₃ , RuTiO ₂ , RuCr, RuCo, or the like containing an oxide. Among them, RuCr, RuCo, RuWO ₃ can obtain a high effect.

Regarding RuWO _3, it is considered that oxygen contained in Ru is dissociated during sputtering, and the dissociated oxygen also exhibits the effect of oxygen addition. That is, the use of WO ₃ is preferable because it can have both the effect of adding oxygen and the effect of adding oxide. Moreover, in this embodiment, since the oxide is contained in the upper and lower layers of a dividing fault, it is guessed that it is also due to the high material affinity at the time of lamination | stacking. Other examples of the oxide include silicon oxide (SiO _x ), chromium (Cr), chromium oxide (Cr _X O _Y ), titanium oxide (TiO ₂ ), zircon oxide (ZrO ₂ ), and tantalum oxide (Ta ₂ O). ₅ ), oxides such as iron oxide (Fe ₂ O ₃ ) and boron oxide (B ₂ O ₃ ). Further, nitrides such as _BN, a carbide such as B 4 _{C 3} can also be suitably used. In addition, about RuCr and RuCo, since Cr and Co are contained in the upper and lower layers, it is considered that the affinity becomes high and good characteristics are exhibited.

  In the present embodiment, the auxiliary recording layer 126 is composed of two layers, a granular auxiliary recording layer 126a and a non-granular auxiliary recording layer 126b. First, the non-granular auxiliary recording layer 126b will be described. The non-granular auxiliary recording layer 126b is a magnetic layer that is substantially magnetically continuous in the in-plane direction of the main surface of the substrate. The non-granular auxiliary recording layer 126b needs to be adjacent or close to the magnetic recording layer 122 so as to have a magnetic interaction. As a material of the non-granular auxiliary recording layer 126b, for example, CoCrPt, CoCrPtB, or a small amount of oxides can be contained in these. The non-granular auxiliary recording layer 126b is intended to adjust the reverse magnetic domain nucleation magnetic field Hn and the coercive force Hc, thereby improving the heat-resistant fluctuation characteristics, the OW characteristics, and the SNR. In order to achieve this object, it is desirable that the non-granular auxiliary recording layer 126b has high perpendicular magnetic anisotropy Ku and saturation magnetization Ms.

  Note that “magnetically continuous” means that magnetism is continuous. “Substantially continuous” means that the magnetism may be discontinuous due to grain boundaries of crystal grains, etc., instead of a single magnet when observed over the entire non-granular auxiliary recording layer 126b. . The grain boundaries are not limited to crystal discontinuities, and Cr may be segregated, and further, a minute amount of oxide may be contained and segregated. However, even when a grain boundary containing an oxide is formed in the non-granular auxiliary recording layer 126b, it is preferable that the area is smaller than the grain boundary of the magnetic recording layer 122 (the content of the oxide is small). Although the function and operation of the non-granular auxiliary recording layer 126b are not necessarily clear, Hn and Hc can be adjusted by having a magnetic interaction (perform exchange coupling) with the granular magnetic particles of the magnetic recording layer 122. It is considered that the heat fluctuation characteristics and SNR are improved. In addition, since the crystal particles (crystal particles having magnetic interaction) connected to the granular magnetic particles have a larger area than the cross-section of the granular magnetic particles, the magnetization is easily reversed by receiving a large amount of magnetic flux from the magnetic head. It is thought to improve the characteristics.

  FIG. 2 is a diagram for explaining the layer structure from the main recording layer to the auxiliary recording layer. In the present embodiment, a granular auxiliary recording layer 126a having a granular structure is provided below the non-granular auxiliary recording layer 126b, which has a higher coercive force than the non-granular auxiliary recording layer 126b. In FIG. 2, the shaded area is granular magnetic particles. The granular auxiliary recording layer 126a is magnetically separated from the second main recording layer 122d by the dividing layer 124, and the magnetization direction can be reversed separately from the second main recording layer 122d. Then, magnetic interaction is exerted on the non-granular auxiliary recording layer 126b so that the magnetization direction of the auxiliary recording layer 126 is hardly reversed. Since the dividing layer 124 is extremely thin (about 0.7 nm), the granular auxiliary recording layer 126a inherits the granular structure of the second main recording layer 122d and grows.

  According to the above configuration, the granular auxiliary recording layer 126a having a high coercive force acts as a pinned layer of the non-granular auxiliary recording layer 126b. Therefore, normally, if the auxiliary recording layer 126 is thickened, writing blur increases. However, even if the thick auxiliary recording layer 126 is provided, the track width can be narrowed (reducing writing blur) and the SNR is improved. In this way, both the track width and the SNR can be achieved.

  The granular auxiliary recording layer 126a has a smaller at% of Cr and a larger at% of CoPt than the first main recording layer 122c and the second main recording layer 122d. According to such a composition, the coercive force of the granular auxiliary recording layer 126a is higher than that of the first main recording layer 122c and the second main recording layer 122d, and ideally acts as a pinned layer of the non-granular auxiliary recording layer 126b. .

  In this embodiment, the difference (A−B) between the Cr concentration (A) of the magnetic recording layer 122 and the Cr concentration (B) of the granular auxiliary recording layer 126a is 1 at% or more and 4 at% or less. Compared to the first main recording layer 122c and the second main recording layer 122d, the at% of Cr is reduced and the at% of CoPt is increased to increase the coercive force.

  In the present embodiment, the granular auxiliary recording layer 126a is thinner than the non-granular auxiliary recording layer 126b. If the thickness of the non-granular auxiliary recording layer 126b is reduced, recording itself becomes impossible. Therefore, while maintaining the thickness and maintaining the OW characteristics, the granular auxiliary recording functioning as a pinned layer of the non-granular auxiliary recording layer 126b. This is to prevent the layer 126a from bleeding. In the present embodiment, the granular auxiliary recording layer may have a thickness of 0.5 nm to 5.0 nm, and the non-granular auxiliary recording layer may have a thickness of 4.0 to 8.0 nm.

  The medium protective layer 128 can be formed by depositing carbon by a CVD method while maintaining a vacuum. The medium protective layer 128 is a layer for protecting the perpendicular magnetic recording medium 100 from the impact of the magnetic head. In general, carbon deposited by the CVD method has improved film hardness compared to that deposited by the sputtering method, so that the perpendicular magnetic recording medium 100 can be more effectively protected against the impact from the magnetic head.

  The lubricating layer 130 can be formed of PFPE (perfluoropolyether) by dip coating. PFPE has a long chain molecular structure and binds with high affinity to N atoms on the surface of the medium protective layer 128. Due to the action of the lubricating layer 130, even if the magnetic head comes into contact with the surface of the perpendicular magnetic recording medium 100, the medium protective layer 128 can be prevented from being damaged or lost.

  Through the above manufacturing process, the perpendicular magnetic recording medium 100 was obtained. Next, examples of the present embodiment will be described.

(Example)
On the disk substrate 110, a film was formed in order from the adhesion layer 112 to the auxiliary recording layer 126 in an Ar atmosphere by a DC magnetron sputtering method using a film forming apparatus that was evacuated. Note that the pressure during sputtering film formation was 0.6 Pa unless otherwise specified. The adhesion layer 112 was formed to a thickness of 10 nm using a Cr-50Ti target. The soft magnetic layer 114 is formed with a thickness of 20 nm using a 92 (Co-40Fe) -3Ta-5Zr target for the first soft magnetic layer 114a and the second soft magnetic layer 114c, and the Ru layer is used for the spacer layer 114b. A 0.7 nm film was formed. The pre-underlayer 116 was formed to a thickness of 5 nm using a Ni-5W target. The first underlayer 118a was formed to a thickness of 10 nm using a Ru target at 0.6 Pa. The second underlayer 118b was formed to a thickness of 10 nm at 5.0 Pa using a Ru target. Nonmagnetic granular layer 120 was 1nm deposited at 4Pa using a 88 (Co-40Cr) -12SiO ₂ target. The lower recording layer 122a was 2.0nm formed at 4Pa using a target of (Co-12Cr-16Pt) -2.5 (Cr 2 O 5) -2.5 (SiO 2). The intervening layer 122b was formed to 0.4 nm using a Ru target. The first main recording layer 122c was formed to 4 nm at 4 Pa using a target of 90 (Co-12Cr-16Pt) -5 (SiO ₂ ) -5 (TiO ₂ ). The second main recording layer 122d is formed with a thickness of 6 nm at ₄ Pa using a target of 90 (Co-12Cr-16Pt) -4.5 (SiO ₂ ) -4.5 (TiO ₂ ) -1 (Co ₃ O ₄ ). did. The dividing layer 124 was formed with a thickness of 0.5 nm using a Ru-10 (WO ₃ ) target. The granular auxiliary recording layer 126a was formed to a predetermined thickness at 4 Pa using a target of 90 (Co—Cr—Pt) -5 (SiO ₂ ) -5 (TiO ₂ ). The detailed composition and film thickness of Co—Cr—Pt were set to values described later. The non-granular auxiliary recording layer 126b was formed to 6.4 nm using a Co-18Cr-15Pt-5B target. The medium protective layer 128 was formed using C ₂ H ₄ by the CVD method, and the lubricating layer 130 was formed using PFPE by the dip coating method.

  FIG. 3 is a diagram comparing the track width and SNR of Examples 1 to 16 in which the film thickness of the granular auxiliary recording layer 126a is variously changed and Comparative Examples 1 and 2, and FIG. Data, FIG. 3 (b) is a graph plotting it.

  In this example and the comparative example, at% of Co: Cr: Pt in the metal phase (main phase) of the main recording layer was 72Co-12Cr-16Pt, and the CoCrPt metal phase of the granular auxiliary recording layer 126a. The composition and film thickness were changed. The number of moles of oxide in the main recording layer and the granular auxiliary recording layer is the same.

  In Examples 1 to 3 (“♦” in the graph), the Co: Cr: Pt at% ratio of the granular auxiliary recording layer 126a is 73Co-11Cr-16Pt, and the film thicknesses are 1.4 nm and 2.6 nm, respectively. 3.6 nm. In Examples 4 to 5 (“■” in the graph), 76Co-8Cr-16Pt was used, and the film thicknesses were 0.7 nm and 1.4 nm, respectively. In Examples 6 to 7 (“（” in the graph), 77Co-7Cr-16Pt was used, and the film thicknesses were 0.7 nm and 1.4 nm, respectively. In Examples 8 to 9 (“●” in the graph), 72Co-12Cr-16Pt was used, and the film thicknesses were 1.4 nm and 2.5 nm, respectively.

In Examples 10 to 12, the Co: Cr: Pt at% ratio of the granular auxiliary recording layer 126a is 73Co-11Cr-16Pt, the film thickness is constant 1.4 nm, and the composition of the dividing layer 124 is set to Example 10. In Ru, in Example 11, it was Ru-50Cr, and in Example 12, it was Ru-50Co. In Examples 13 to 16, the Co: Cr: Pt at% ratio of the granular auxiliary recording layer 126a is 73Co-11Cr-16Pt, and the molar ratio of 73Co-11Cr-16Pt: SiO ₂ : TiO ₂ is set in Example 13. 91: 4.5: 4.5, 92: 4.0: 4.0 in Example 14, 93: 3.5: 3.5 in Example 15, and 89: 5.5 in Example 16. : 5.5.

  In Comparative Examples 1 and 2 (“◯” in the graph), the granular auxiliary recording layer 126a was not formed. In a layer containing an oxide like the granular auxiliary recording layer 126a, the coercive force Hc changes depending on the composition of CoCrPt as the main phase in addition to the amount of oxide. In particular, when the Cr content, which is diamagnetic, is increased, the magnetism of Co is canceled and the coercive force Hc is decreased.

  As shown in FIG. 3A, the granular auxiliary recording layer 126a of Examples 1 to 9 is formed thinner than the non-granular auxiliary recording layer 126b.

  As shown in FIGS. 3A and 3B, when the film thickness is reduced in each material of the granular auxiliary recording layer, the track width increases and the SNR tends to increase. This suggests that, depending on the film thickness of the granular auxiliary recording layer, the track width and the SNR are in a trade-off, so that a high recording density cannot be achieved. On the other hand, in terms of the presence / absence of the granular auxiliary recording layer, it can be seen that the characteristics of Examples 1 to 9 are improved compared to Comparative Examples 1 and 2 even if the trade-off is taken into consideration. It can be seen that both width and SNR are achieved.

Further, when Example 1 and Examples 10 to 12 are compared, even if the composition of the dividing layer 124 is changed from Ru-10 (WO ₃ ) to Ru or other Ru compound, good characteristics almost equivalent to those of Example 1 are obtained. Can be obtained. Furthermore, when Example 1 is compared with Examples 13 to 16, magnetic recording in which both the track width and the SNR are compatible is achieved as in Example 1, even if the molar ratio of the oxide in the granular auxiliary recording layer is changed. It can be seen that a medium is obtained.

  As mentioned above, although the suitable Example of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  The present invention can be used as a perpendicular magnetic recording medium mounted on a perpendicular magnetic recording type HDD or the like.

DESCRIPTION OF SYMBOLS 100 ... Perpendicular magnetic recording medium 110 ... Disk base | substrate 112 ... Adhesion layer 114 ... Soft magnetic layer 114a ... First soft magnetic layer 114b ... Spacer layer 114c ... Second soft magnetic layer 116 ... Pre-underlayer 118 ... Underlayer 118a ... First Underlayer 118b ... second underlayer 120 ... nonmagnetic granular layer 122 ... magnetic recording layer 122a ... lower recording layer 122b ... intervening layer 122c ... first main recording layer 122d ... second main recording layer 124 ... split layer 126 ... auxiliary recording Layer 126a ... Granular auxiliary recording layer 126b ... Non-granular auxiliary recording layer 128 ... Medium protective layer 130 ... Lubrication layer

Claims (5)

A magnetic recording layer having a granular structure in which a nonmagnetic grain boundary portion is formed between magnetic particles made of CoCrPt continuously grown in a columnar shape on a substrate, and an auxiliary recording layer are provided. In the perpendicular magnetic recording medium provided in order,
The auxiliary recording layer is
A non-granular auxiliary recording layer which is a magnetic layer substantially magnetically continuous in the in-plane direction of the main surface of the substrate;
A granular auxiliary recording layer provided under the non-granular auxiliary recording layer, having a higher coercive force than the non-granular auxiliary recording layer and having a granular structure;
Only including,
A perpendicular magnetic recording medium , wherein the magnetic particles of the granular auxiliary recording layer have a smaller at% of Cr and a larger at% of CoPt than the magnetic particles of the magnetic recording layer . And wherein the difference in the Cr concentration of the magnetic particles of Cr concentration (A) and the granular auxiliary recording layer of the magnetic particles in the magnetic recording layer (B) (A-B) is not less than 1 at.%, Or less 4at% The perpendicular magnetic recording medium according to claim 1 .   The perpendicular magnetic recording medium according to claim 1, wherein the granular auxiliary recording layer is thinner than the non-granular auxiliary recording layer. 4. The perpendicular magnetic recording medium according to claim 1 , wherein a nonmagnetic dividing layer is provided between the magnetic recording layer and the auxiliary recording layer. 5. The perpendicular magnetic recording medium according to any one of claims 1 to 4, wherein the magnetic recording layer is formed of a plurality of layers.

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