WO2010026669A1

WO2010026669A1 - Magnetic recording medium and storage apparatus

Info

Publication number: WO2010026669A1
Application number: PCT/JP2008/066488
Authority: WO
Inventors: Antony Ajan
Original assignee: Fujitsu Limited
Priority date: 2008-09-05
Filing date: 2008-09-05
Publication date: 2010-03-11

Abstract

A magnetic recording medium has an intermediate layer including a first layer made of a PdW alloy, and a recording layer disposed above the intermediate layer. The intermediate layer imparts crystallographic texture growth in the recording layer so that an axis of easy magnetization of the recording layer is dominantly perpendicular to the film plane.

Description

DESCRIPTION

MAGNETIC RECORDING MEDIUM AND STORAGE APPARATUS

TECHNICAL FIELD

The present invention generally relates to magnetic recording media and storage apparatuses, and more particularly to a perpendicular magnetic recording medium or a patterned medium, such as a discrete track patterned medium or a bit patterned medium, and to a storage apparatus provided with such a magnetic recording medium.

BACKGROUND ART Perpendicular magnetic recording media and patterned media can realize high-density recording. For this reason, the perpendicular magnetic recording media are used for hard disk drives for high-end to personal mobile computing, gaming and recreation applications.

One of the main concerns in future perpendicular magnetic recording media and patterned media development is to reduce the medium noise and increase the writability of high anisotropy media at a reduced cost. One of the costliest materials that is currently used in perpendicular magnetic recording media is Ru which is used as an intermediate layer between a magnetic layer and a soft magnetic underlayer or seed layer. For example, the magnetic layer is made of a CoPt alloy.

The intermediate layer made of Ru or a Ru alloy needs to be thicker to reduce the medium noise. Normally, a double Ru layer structure is used for the intermediate layer. A first Ru layer which is located closer to the seed layer is deposited at a relatively low sputtering pressure, and a second layer which is located closer to the magnetic layer is deposited at a relatively high sputtering pressure. The seed layer is made of a metal or an alloy having a (111) crystallographic texture, for example, in order to impart a good Ru (0002) crystallographic texture in the intermediate layer. A good Ru (0002) texture is further useful to grow a good CoPt (0002) texture in the magnetic layer with its axis of easy magnetization (c-axis) perpendicular to the film plane. In the perpendicular magnetic recording medium, the thickness ratio for the first and second Ru layers forming the intermediate layer is typically 1:0.5 to 1:0.6. However, the total thickness of the intermediate layer needs to be at least 20 nm to 30 nm, that is, thick, in order to obtain a good crystallographic texture for the CoPt (0002) grains in the magnetic layer and to obtain a relatively high anisotropy. This thick Ru- based intermediate layer increases the overall cost of the perpendicular magnetic recording medium.

On the other hand, for patterned media, such as discrete track patterned medium and bit patterned media, relatively large grains are required for the intermediate layer and also for the magnetic layer. This is because the grain size of patterned media is determined by the pattern itself, and multiple grains within a single pattern leads to lower thermal stability of the bit.

For example, a Japanese Laid-Open Patent Application No .2004-327006 proposes a perpendicular magnetic recording medium having a first underlayer, a second underlayer, and a magnetic layer that are successively stacked. Pt, Pd or an alloy of Pt or Pd is used for the first underlayer, and Ru or an Ru alloy is used for the second underlayer.

DISCLOSURE OF THE INVENTION Accordingly, it is a general object of the present invention to provide a novel and useful magnetic recording medium and storage apparatus, in which the problems described above are suppressed. Another and more specific object of the present invention is to provide a magnetic recording medium and a storage apparatus, which can reduce the cost without sacrificing the performance of the magnetic recording medium. According to one aspect of the present invention, a magnetic recording medium is provided comprising an intermediate layer including a first layer made of a PdW alloy, and a recording layer disposed above the intermediate layer and having a film plane, wherein the intermediate layer imparts crystallographic texture growth in the recording layer so that an axis of easy magnetization of the recording layer is perpendicular to the film plane. According to the magnetic recording medium in accordance with this aspect of the present invention, it is possible to reduce the cost of the magnetic recording medium without sacrificing the performance of the magnetic recording medium.

According to another aspect of the present invention, a storage apparatus is provided comprising at least one magnetic recording medium having the structure described above, and a head configured to record information on and reproduce information from the at least one magnetic recording medium. According to the storage apparatus in accordance with this aspect of the present invention, it is possible to reduce the cost of the storage apparatus as a whole without sacrificing the performance of the storage apparatus . Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross sectional view showing a portion of a magnetic recording medium in a first embodiment of the present invention;

FIG. 2 is a cross sectional view showing a portion of a magnetic recording medium in a second embodiment of the present invention; FIG. 3 is a cross sectional view showing a portion of a magnetic recording medium of a comparison example;

FIG. 4 is a diagram showing magnetic properties of the magnetic recording medium in the first embodiment and the magnetic recording medium of the comparison example;

FIG. 5 is a diagram showing magnetic properties of the magnetic recording medium in the first embodiment for a case where a seed layer is provided and a case where no seed layer is provided;

FIG. 6 is a diagram for explaining parameter definitions;

FIG. 7 is a diagram showing a portion of FIG. 6 on an enlarged scale; FIG. 8 is a diagram showing magnetic properties of the magnetic recording medium in the second embodiment and the magnetic recording medium of the comparison example;

FIG. 9 is a diagram showing X-ray diffraction patterns of the magnetic recording media in the first and second embodiments and the magnetic recording medium of the comparison example;

FIG. 10 is a diagram showing error rates of the magnetic recording media in the first and second embodiments and the magnetic recording medium of the comparison example;

FIG. 11 is a diagram for explaining lattice changes in an intermediate layer due to materials used;

FIG. 12 is a diagram showing a W dependence of Kerr rotation angle of the magnetic recording medium of the first embodiment;

FIG. 13 is a diagram showing a W dependence of coercivity Hc and saturation field Hs of the magnetic recording medium of the first embodiment ; FIG. 14 is a diagram showing an intermediate layer thickness dependence of a slope α of the magnetic recording medium of the first embodiment;

FIG. 15 is a diagram showing an intermediate layer thickness dependence of coercivity Hc of the magnetic recording medium of the first embodiment;

FIG. 16 is a diagram showing an intermediate layer thickness dependence of distribution ΔHs of the magnetic recording medium of the first embodiment;

FIG. 17 is a diagram showing an intermediate layer thickness dependence of coercivity Hc of the magnetic recording medium of the second embodiment;

FIG. 18 is a diagram showing an intermediate layer thickness dependence of distribution ΔHs of the magnetic recording medium of the second embodiment; FIG. 19 is a cross sectional view showing an internal structure of a portion of a storage apparatus; and

FIG. 20 is a plan view showing a portion of the storage apparatus shown in FIG. 19.

BEST MODE OF CARRYING OUT THE INVENTION

In one embodiment of the present invention, a PdW alloy, which is a relatively inexpensive material when compared to Ru or a Ru alloy, is used to form an intermediate layer of a magnetic recording medium. The PdW alloy has a grain size similar to the grain size of the Ru or the Ru alloy, and gives the magnetic properties of CoPt alloy similar to the magnetic properties when Ru or the Ru alloy is used. The intermediate layer may be formed solely of a PdW alloy layer or, a combination of the PdW alloy layer and a relatively thin Ru or Ru alloy layer which is less than 10 nm thick, in order to minimize the cost of the magnetic recording medium.

The PdW alloy intermediate layer is particularly suited for use in perpendicular magnetic recording media and patterned media, such as discrete track patterned media and bit patterned media.

FIG. 1 is a cross sectional view showing a portion of a magnetic recording medium in a first embodiment of the present invention. A magnetic recording medium 11-1 has a substrate 21, and layers 22 through 29 which are successively stacked on the substrate 21 as shown in FIG. 1. The stacked layers 22 through 29 include the first soft magnetic underlayer 22, the spacer layer 23, the second soft magnetic underlayer 24, the seed layer 25, the intermediate layer 26, the recording layer 27, the protective layer 28 and the lubricant layer 29. Each of the seed layer 25, the intermediate layer 26 and the recording layer 27 may have a single-layer structure which is made up of a single layer or, a multi-layer structure made up of a plurality of layers .

The substrate 21 may be made of glass, Al, Si, TiC or the like. The stacked layers 22 through 29 may be formed on a smooth surface of the substrate 21 or a pre-patterned surface of the substrate 21 or, a patterning for the patterned medium may be made during or after the stacked layers 22 through 27 are formed on the substrate 21.

The first and second soft magnetic underlayers 22 and 24 are anti-parallel coupled via the spacer layer 23 such that the effective magnetization is zero at remanence. Each of the first and second soft magnetic underlayers 22 and 24 may be made of ferromagnetic alloys such as Fe alloys, Co alloys and Ni alloys. The ferromagnetic alloys may further include additives such as Cr, B, Cu, Ti, V, Nb, Zr, Pt, Pd and Ta in order to improve the amorphous nature, corrosion resistance, reduction in stress in the layer or, tuning of magnetic properties. Each of the first and second soft magnetic underlayers 22 and 24 may be 5 nm to 25 nm thick, for example.

Any suitable material may be used for the spacer layer 23 in order to cause the anti-parallel coupling of the first and second soft magnetic underlayers 22 and 24. The thickness of the spacer layer 23 may be adjusted to obtain first, second or third anti-parallel coupling peaks. The spacer layer 23 may be made of Ru, but a myriad of transition metals including Cr, Cu and rare earth metals such as Rh and Re may be used for the spacer layer 23 in order to obtain the anti-parallel coupling of the first and second soft magnetic underlayers 22 and 24. The spacer layer 23 may be 0.3 nm to 3 nm thick, for example.

The seed layer 25 may be made of a material selected from a group consisting of Ni, Fe, Pt, Pd, Cr, B, Mo, V, W, C and an alloy of at least one of such elements, with a (111) crystallographic texture. However, similar magnetic properties and high performance can be obtained with or without the seed layer 25, as will be described later in the specification. Hence, the seed layer 25 may be 0 run to 10 nm thick, for example.

The intermediate layer 26 separates the second soft magnetic underlayer 25 and the recording layer 27. The intermediate layer 26 is made of PdW or a PdW alloy. The PdW alloy may be a PdW_xY alloy, where x is in a range of 5 at . % to 70 at.%, and Y is an additive for improving a distribution of c-axis alignment of the recording layer 27. The additive Y is selected from a group consisting of Co, Cr, C, Ti, Si, Ta, B, Ru, SiO₂, TiO₂, TaO₂, Ta₂O₅, W, Nb, V and Mo and is greater than 0 at.% but less than 20 at.%. During deposition of the intermediate layer 26, an additional gas other than Ar, such as N₂ or O₂ or CO₂, may be used. The intermediate layer 26 may be 2 nm to 25 nm thick, for example.

The recording layer 27 may be made of a magnetic material selected from a group consisting of Co, Pt and an alloy of at least one of such elements. The material used for the recording layer 27 may additionally include an additive selected from a group consisting of Cr, B, SiO₂,- TiO₂, CrO₂, CrO, CoO, Cu, Ti and Nb. In addition, the recording layer 27 may be made of a granular material, and formed by a CoPt granular layer, for example. The recording layer 27 may have a single-layer structure which is made up of a single magnetic layer or, a multi-layer structure which is made up of multiple magnetic layers. The multi-layer structure may be employed for the recording layer 27 in order to obtain high anisotropy, good grain segregation and good writability. The total thickness of the recording layer 27 may be 8 nm to 20 nm, for example. The protection layer 28 may be made of any suitable material capable of protecting the surface portion of the magnetic recording medium 11-1, namely, the recording layer 27. For example, the protection layer 28 may be made of C or Diamond-Like Carbon (DLC) . The protection layer 28 may be 1 nm to 5 nm thick, for example.

The lubricant layer 29 may be made of any suitable material capable of providing the necessary lubrication between the surface portion of the magnetic recording medium 11-1 and a recording and reproducing head (not shown) which will be described later in the specification. For example, the lubricant layer 29 may be made of an organic lubricant.

FIG. 2 is a cross sectional view showing a portion of a magnetic recording medium in a second embodiment of the present invention. In FIG. 2, those parts that are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted. A magnetic recording medium 11-2 shown in FIG. 2 has an intermediate layer 26 which is made up of a first intermediate layer 26-1 and a second intermediate layer 26-2.

The first intermediate layer 26-1 may be made of a PdW alloy similar to that used for the intermediate layer 26 shown in FIG. 1. The first intermediate layer 26-1 may be 2 nm to 25 nm thick, for example. On the other hand, the second intermediate layer 26-1 may be made of Ru and may be 0.5 nm to 10 nm thick, for example. By using an Ru layer in which the granularity is visible, it is possible to control the grain size and promote the Ru (0002) crystallographic texture in the second intermediate layer 26-2.

FIG. 3 is a cross sectional view showing a portion of a magnetic recording medium of a comparison example. In FIG. 3, those parts that are the same as those corresponding parts in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted. A magnetic recording medium 31 shown in FIG. 3 has an intermediate layer 36 which is made up of a first intermediate layer 36-1 and a second intermediate layer 36-2. Each of the first and second intermediate layers 36-1 and 36-2 is made of Ru or an Ru alloy. The first intermediate layer 36-1 is 10 nm to 20 nm thick, and the second intermediate layer 36-2 is 5 nm to 15 nm thick, so that the total thickness of the intermediate layer 36 is at least 20 nm to 30 nm.

FIG. 4 is a diagram showing magnetic properties of the magnetic recording medium 11-1 in the first embodiment and the magnetic recording medium 31 of the comparison example. In FIG. 4, "IML structure" indicates the intermediate layer structure, cmp indicates the comparison example, and Embl-1, Embl-2 and Embl-3 respectively indicate samples of the first embodiment. "RuI ( 14 ) /Ru2 ( 8 ) " indicates that the first intermediate layer 36-1 is made of Ru which is 14 nm thick, and the second intermediate layer 36-2 is made of Ru which is 8 nm thick. "PdW40(20)" indicates that the intermediate layer 26 is made of PdW with W = 40 at . % and thickness of 20 nm, "PdW30(20)" indicates that the intermediate layer 26 is made of PdW with W = 30 at.% and thickness of 20 nm, and "PdW20(20)" indicates that the intermediate layer 26 is made of PdW with W = 20 at.% and thickness of 20 nm. In the comparison example cmp and each of the samples Embl-1, Embl-2 and Embl-3 of the first embodiment, the recording layer 27 has a two-layer structure made up of a CoCrPt-TiO₂ granular layer which is 11 nm thick and is provided on the intermediate layer 26 or 36, and CoCrPtB layer which is 7 nm thick and is provided on the CoCrPt-TiO₂ granular layer. The magnetic properties shown in FIG. 4 includes the squareness ratio SQ, the coercivity Hc, the slope α, the nucleation field Hn, the distribution ΔHs, and the saturation field Hs. The distribution ΔHs is the difference between the saturation field Hs and a minimum value of the field at which magnetization is saturated in a hysteresis loop (magnetization-field curve) .

It was confirmed from FIG. 4 that the magnetic properties of the samples Embl-1 through Embl-3 are basically the same as that of the comparison example Cmp, however, the cost of the samples Embl-1 through Embl-3 is much smaller compared to the comparison example Cmp which uses 2 Ru layers 36-1 and 36-2 for the intermediate layer 36.

FIG. 5 is a diagram showing magnetic properties SQ, Hc, α, Hn, ΔHs and Hs of the magnetic recording medium 11-1 in the first embodiment for a case where the seed layer 25 is provided and a case where no seed layer is provided. In FIG. 5, "IML structure" indicates the intermediate layer structure, and Embl-11 and Embl-12 respectively indicate samples of the first embodiment with and without the seed layer 25. "NiW (8 ) /PdW40 ( 17 ) " indicates that the seed layer 25 is made of NiW and is 8 nm thick, and the intermediate layer 26 is made of PdW with W = 40 at . % and thickness of 17 nm. "NiW(O) /PdW40 (17) " indicates that no seed layer 25 is provided, and the intermediate layer 26 is made of PdW with W = 40 at . % and thickness of 17 nm.

In each of the samples Embl-11 and Embl-12 of the first embodiment, the recording layer 27 has a two-layer structure made up of a CoCrPt-TiO₂ granular layer which is 11 nm thick and is provided on the intermediate layer 26 or 36, and CoCrPtB layer which is 7 nm thick and is provided on the CoCrPt-TiO₂ granular layer.

It was confirmed from FIG. 5 that the magnetic properties of the samples Embl-11 and Embl- 12 are similar. Hence, the cost of the sample Embl- 12 which does not have the seed layer 25 can further be reduced compared to the sample Embl-11 which has the seed layer 25 but does not use Ru for the intermediate layer 26. Because the writing capability of the magnetic recording medium 11-1 increases with a thinner intermediate layer portion which is made up of the total thickness of the seed layer 25 and the intermediate layer 26, the sample Embl-12 without the seed layer 25 further improves the writing capability. However, in order to enhance the magnetic and read-write properties of the magnetic recording medium 11-1, a single or multiple seed layer structure may be used without departing from the above mentioned intermediate alloy structure. Moreover, the PdW alloy may be deposited, as the intermediate layer 26, either as a single or multiple layer structure with various composition ratios and process parameters across the layers .

FIG. 6 is a diagram for explaining parameter definitions, and FIG. 7 is a diagram showing a portion of FIG. 6 on an enlarged scale. In FIGS. 6 and 7, the ordinate indicates the angle θk (degrees) between the applied field H (kθe) and the anisotropy axis of the recording layer 27, and the abscissa indicates the applied field H (kθe) . The applied field H is the field applied on the magnetic recording medium 11-1 or 31. In FIGS. 6 and 7, -HnI and Hn2 indicate the nucleation field Hn at respective sides of the hysteresis loop, and HcI and -Hc2 indicate the coercivity Hc at respective sides of the hysteresis loop. Further, ΔHsl indicates the distribution ΔHs (that is, the difference between the saturation field Hs and the minimum value of the field at which magnetization is saturated on one side of the hysteresis loop. The slope α is taken near the coercivity HcI or Hc2. In FIG. 6, points C and C and B and B' are used to calculate the slope α, with the center as Hc2 and HcI respectively. Points A and A' are remanent magnetizations of the hysterisis loop if SQ = 1 and R and R' are the actual remanence points of the hysterisis loop. In FIG. 7 , the definition of ΔHs, which gives the distribution of magnetic properties in the magnetic recording medium is shown. The distribution ΔHs is estimated from the actual saturation of the M-H loop and the estimated saturation points (Sl) if there is no distribution.

Sl (Δ, SxI) gives the coordinates of the point Sl. In other words, in this specification, the definitions used for the magnetic properties are made using the standard M-H hysteresis loop. FIG. 8 is a diagram showing magnetic properties SQ, Hc, α, Hn, ΔHs and Hs of the magnetic recording medium 11-2 in the second embodiment and the magnetic recording medium 31 of the comparison example. In FIG. 8, "IML structure" indicates the intermediate layer structure, cmp indicates the comparison example, and Emb2-1, Emb2-2 and Emb2-3 respectively indicate samples of the second embodiment. "RuI ( 14 ) /Ru2 ( 8 ) " indicates that the first intermediate layer 36-1 is made of Ru which is 14 nm thick, and the second intermediate layer 36-2 is made of Ru which is 8 nm thick. "PdW40(10)/ Ru(7)" indicates that the first intermediate layer 26-1 is made of PdW with W = 40 at . % and thickness of 10 nm and the second intermediate layer 26-2 is made of Ru which is 7 nm thick, "PdW30 ( 10 ) /Ru (7 ) " indicates that the first intermediate layer 26-1 is made of PdW with W = 30 at . % and thickness of 10 nm and the second intermediate layer 26-2 is made of Ru which is 7 run thick, and "PdW20 ( 10) /Ru (7 ) " indicates that the first intermediate layer 26-1 is made of PdW with W = 20 at.% and thickness of 10 nm and the second intermediate layer 26-2 is made of Ru which is 7 nm thick.

In the comparison example cmp and each of the samples Emb2-1, Emb2-2 and Emb2-3 of the second embodiment, the recording layer 27 has a two-layer structure made up of a CoCrPt-TiC>₂ granular layer which is 11 nm thick and is provided on the intermediate layer 26 or 36, and CoCrPtB layer which is 7 nm thick and is provided on the CoCrPt-TiO₂ granular layer. It was confirmed from FIG. 8 that the magnetic properties of the samples Emb2-1 through Emb2-3 are basically the same as that of the comparison example Cmp, however, the cost of the samples Emb2-1 through Emb2-3 is much smaller compared to the comparison example Cmp which uses 2 Ru layers 36-1 and 36-2 for the intermediate layer 36. Moreover, in the case of the samples Emb2-1 through Emb2-3, the distribution of c-axis alignment of the recording layer 27 is slightly improved compared to the samples Embl-1 through Embl-3, which may result in basically the same read-write performance as that of the comparison example Cmp.

FIG. 9 is a diagram showing X-ray diffraction patterns of the magnetic recording media in the first and second embodiments and the magnetic recording medium of the comparison example. In FIG. 9, the ordinate indicates the X-ray diffraction intensity in arbitrary units (A.U.), and the abscissa indicates 2Θ (degrees). The X-ray diffraction pattern of the magnetic recording medium 11-1 in the first embodiment (sample Embl-1) with "PdW40(20)" indicating that the intermediate layer 26 is made of PdW with W = 40 at . % and thickness of 20 nm, is indicated by I. The X-ray diffraction pattern of the magnetic recording medium 11-2 in the second embodiment (sample) with "PdW40 (8 ) /Ru (7.5) " indicating that the first intermediate layer 26-1 is made of PdW with W = 40 at . % and thickness of 7.5 nm, and the second intermediate layer 26-2 is made of Ru which is 7.5 nm thick, is indicated by II. The X- ray diffraction pattern of the magnetic recording medium 31 (comparison example Cmp) is indicated by III.

It was confirmed from FIG. 9, the

CoPt (0002) crystallographic growth of the recording layer 27 is similar for each of the cases I, II and III.

FIG. 10 is a diagram showing error rates of the magnetic recording media in the first and second embodiments and the magnetic recording medium of the comparison example. In FIG. 10, the ordinate indicates the error rate (VMM*WCW) that is normalized with respect to on-track signal width (WCW: Write Core Width) of the signal across the written track (WCW) , and the abscissa indicates the intermediate layer (IML) structure, where the Viterbi Metric Margin (VMM) is used as the error rate. In this case, VMM and WCW are measured using separate methods. VMM and WCW show nearly a linear relationship, showing higher VMM (worse) at lower WCW. VMM*WCW thus gives a fair comparison of the error rates at same WCW. The hatched leftmost error rate is for the comparison example Cmp. The 3 unshaded error rates on the right respectively are for the samples Embl-1, Embl-2 and Embl-3. The 3 shaded error rates on the right respectively are for samples Emb2-la, Emb2-2a and Emb2-3a similar to the samples Emb2-1, Emb2-2 and Emb2-3 except that the Ru thickness of the second intermediate layer 26-2 is 7 . 5 nm and not 7 nm.

In FIG. 10, the smaller VMM*WCW values are better and indicate better error rates. It was confirmed from FIG. 10 that the samples Embl-1 through Embl-3 are only slightly worse in performance than the comparison example, and that the performance improves significantly for the samples Emb2-la through Emb2-3a which include the thin 7.5 nm Ru second intermediate layer 26-2. The samples Emb2-la through Emb2-3a show better performances than that the comparison example Cmp.

Next, a description will be given of lattice changes in PdCrx, PdCrCx and PdWx alloys, by referring to FIG. 11. FIG. 11 is a diagram for explaining lattice changes in the intermediate layer due to materials used for the intermediate layer. In FIG. 11, the ordinate indicates the lattice parameter (A) , and the abscissa indicates the intermediate layer having various compositions. It may be seen from FIG. 11 that the addition of Cr to Pd continuously reduces the lattice parameter, which indicates that Cr is going inside the lattice of Pd. However, it may be seen that the addition of C to PdCr30 increases the lattice parameter and returns the lattice parameter back to the level of the Pd lattice parameter, which indicates that C and Cr are preferably present at the grain boundaries than inside the Pd grains. It may be seen from FIG. 11 that the addition of W to Pd does not greatly change the lattice parameter from the Pd lattice parameter. However, a slight increase from the Pd lattice parameter was observed when W is added to Pd, which indicates that the lattice becomes slightly larger with the addition of W.

In each of the first and second embodiments, the composition used for the intermediate layer 26 or 26-1 is mainly the PdW alloy. But as described above, the PdW alloy may be the PdW_xY alloy, where the additive Y is added to improve the distribution of c-axis alignment of the recording layer 27. In other words, the additive Y may be added to improve the grain segregation, to obtain smaller grain sizes, and to improve the formation of a more HCP-like granular structure.

The elements described above which may be used as the additive Y are speculation based on the known studies in the field of perpendicular magnetic recording media. For example, the addition of an oxide, such as SiO₂ and TiO₂, as the additive Y, improves the segregation in the recording layer 27, as is well known. Moreover, the addition of Cr in CoPt improves the grain segregation and reduces exchange, as is well known. Similarly, the addition of Cr to Ru improves the grain segregation, as is well known. The use of carbon (C) as the additive Y may also be useful. FIG. 11 also shows the lattice parameters for PdCr30C5 and PdCr30C10 which are used as the additive Y with respect to the PdWxY alloy. It may be seen from FIG. 11 that, as the C content increases in the layer having the PdCr30 composition, the (111) diffraction peak position shifts towards

Pd (111) diffraction. This is a clear evidence that the addition of carbon (C) is causing more Cr to be pulled out of the PdCr lattice and hence the boundary region is more filled with Cr and C. Although the data for all the additives Y are not shown, it may be appreciated by those skilled in the art that the trend is expected to be similar for each of the additives Y described above. However, BCC-like additives such as Cr, Nb and V, are expected to be different since such materials will be more inside the Pd grains than at the grain boundaries . Next, a description will be given of the W composition dependence of the magnetic parameters of the PdWx alloy, by referring to FIGS. 12 and 13. FIG. 12 is a diagram showing the W dependence of Kerr rotation angle of the magnetic recording medium of the first embodiment. In FIG. 12, the ordinate indicates the Kerr Rotation angle in arbitrary units, and the abscissa indicates the magnetic field (Oe) . FIG. 13 is a diagram showing the W dependence of coercivity Hc and saturation field Hs of the magnetic recording medium of the first embodiment. In FIG. 13, the ordinate indicates the coercivity Hc (Oe) and the saturation field Hs (Oe) , and the abscissa indicates the W at.% in PdW. FIG. 12 shows the M-H hysteresis loops for the magnetic recording medium 11-1 where the materials and thicknesses of the layers are as follows .

Substrate 21: Glass First Soft Magnetic Underlayer 22: CoCr Alloy Spacer Layer 23: Ru

Second Soft Magnetic Underlayer 24: CoCr Alloy Seed layer 25: Ta, 3 nm thick Intermediate Layer 26: PdWx, 10 nm thick Recording Layer 27: CoCrPt-SiO₂, 11 nm thick Protection Layer 28: C, 3 nm thick

In FIG. 12, A shows the loop for x = 0 at.%, and B shows the loop for x = 40 at.% in the PdWx alloy intermediate layer 26. It may be seen that pure FCC intermediate layers, such as a Pd intermediate layer, will not be able to give the required c-axis orientation for the CoPt (0002) lattice of the recording layer 27. Therefore, the addition of Cr and W or any BCC metal is necessary to make the intermediate layer 26 behave more like a HCP-like structure.

FIG. 12 shows the data of Hc variation for various composition ranges of PdCr and PdW. As may be seen from FIG. 12, for CoPt grown directly on Pd gives almost no coercivity Hc, indicating that CoPt is grown as a FCC-like structure. However, as more W or any BCC metal is added to Pd, the coercivity Hc and the saturation field Hs improve significantly, and makes the magnetic recording medium suited for the high-density recording. Moreover, when W or BCC metal is added to the Pd of the intermediate layer, a very thin Ru layer may be provided on the PdW layer to form the intermediate layer by the PdW and Ru layers, it is possible to further improve the anisotropic magnetic properties.

Next, a description will be given of the thickness range of the PdW alloy forming the intermediate layer 26, by referring to FIGS. 14 through 16. FIGS. 14 through 16 show the data for the magnetic recording medium 11-1 where the materials and thicknesses of the layers are as follows.

Substrate 21: Glass

First Soft Magnetic Underlayer 22: CoCr Alloy Spacer Layer 23: Ru

Second Soft Magnetic underlayer 24: CoCr Alloy Seed layer 25: Ni alloy, 6 nm thick

Intermediate Layer 26: PdWx, t nm thick Recording Layer 27: CoCrPt-SiO₂, 11 nm thick Protection Layer 28: C, 4 nm thick

FIG. 14 is a diagram showing an intermediate layer thickness dependence of the slope α of the magnetic recording medium of the first embodiment, FIG. 15 is a diagram showing an intermediate layer thickness dependence of coercivity Hc of the magnetic recording medium of the first embodiment, and FIG. 16 is diagram showing an intermediate layer thickness dependence of the distribution ΔHs of the magnetic recording medium of the first embodiment. In FIGS. 14, 15 and 16, the abscissa indicates the thickness (nm) of the PdW alloy. The ordinate in FIG. 14 indicates the slope α, the ordinate in FIG. 15 indicates the coercivity Hc (kθe), and the ordinate in FIG. 16 indicates the distribution ΔHs (kθe) .

It may be seen from FIGS. 14 through 16 that, in the case of the magnetic recording medium 11-1, the thickness range of the PdW alloy forming the intermediate layer 26 should be selected in order to reduce the slope α near the Hc value, obtain high coercivity Hc, and reduce the distribution ΔHs. In this case, it was confirmed that the thickness range of 16 nm to 25 nm is preferable for the PdW alloy forming the intermediate layer 26, as indicated by data surrounded by dotted lines in FIGS. 14 through 16. Of course, this thickness range may be varied slightly depending on the additive Y added to the PdW alloy.

Next, a description will be given of the thickness range of the PdW alloy forming the first intermediate layer 26-1 of the intermediate layer 26, by referring to FIGS. 17 and 18. FIGS. 17 and 18 show the data for the magnetic recording medium 11-2 where the materials and thicknesses of the layers are as follows. In this particular case, the recording layer 27 is made up of a first magnetic layer provided on the intermediate layer 26, and a second magnetic layer provided on the first magnetic layer .

Substrate 21: Glass

First Soft Magnetic Underlayer 22: CoCr Alloy Spacer Layer 23: Ru Second Soft Magnetic Underlayer 24: CoCr Alloy Seed layer 25: Ni alloy, 6 nm thick First Intermediate Layer 26-1: PdWx, t nm thick

Second Intermediate Layer 26-2: Ru, 7.5 nm thick

Recording Layer 27: First Magnetic Layer: CoCrPt-SiO₂, 11 nm thick Second Magnetic Layer: CoCrPtB, 8 nm thick Protection Layer 28: C, 4 nm thick

FIG. 17 is a diagram showing an intermediate layer thickness dependence of the coercivity Hc of the magnetic recording medium of the second embodiment, and FIG. 18 is a diagram showing an intermediate layer thickness dependence of the distribution ΔHs of the magnetic recording medium of the second embodiment. In FIGS. 17 and 18, the abscissa indicates the thickness (nm) of the PdW alloy. The ordinate in FIG. 17 indicates the coercivity Hc (kθe), and the ordinate in FIG. 18 indicates the distribution ΔHs (kθe).

It may be seen from FIGS. 17 and 18 that, in the case of the magnetic recording medium 11-2, the thickness range of the PdW alloy forming the first intermediate layer 26-1 should be selected in order to reduce the slope α near the Hc value, obtain high coercivity Hc, and reduce the distribution ΔHs. In this case, it was confirmed that the thickness range of 8 nm to 11 nm is preferable for the PdW alloy forming the first intermediate layer 26-1, as indicated by data surrounded by dotted lines in FIGS. 17 and 18. Of course, this thickness range may be varied slightly depending on the additive Y added to the PdW alloy.

Next, a description will be given of a storage apparatus in one embodiment of the present invention, by referring to FIGS. 19 and 20. FIG. 19 is a cross sectional view showing the internal structure of a portion of the storage apparatus, and FIG. 20 is a plan view showing a portion of the storage apparatus shown in FIG. 19.

As shown in FIGS. 19 and 20, the storage apparatus has a housing 113. A motor 114, a hub 115, a plurality of magnetic recording, media 116, a plurality of recording and reproducing heads 117, a plurality of suspensions 118, a plurality of arms 119, and an actuator unit 120 are provided within the housing 113. The magnetic recording media 116 are mounted on the hub 115 which is rotated by the motor 114. Each recording and reproducing head 117 is mounted on the tip end of a corresponding arm 119 via the suspension 118. The arms 119 are moved by the actuator unit 120. The basic structure of this storage apparatus is known, and a detailed description thereof will be omitted in this specification .

Each magnetic recording medium 116 has the structure of any of the embodiments described above in conjunction with FIGS. 1 and 2. Of course, the number of magnetic recording media 116 is not limited to three, and only one, two or four or more magnetic recording media 116 may be provided.

The basic structure of the storage apparatus is not limited to that shown in FIGS. 19 and 20. In addition, the magnetic recording medium used in the storage apparatus is not limited to a magnetic disk, and other magnetic recording media such as magnetic tapes and magnetic cards may be used. Moreover, the magnetic recording medium does not need to be provided within the housing 113 of the storage apparatus, and the magnetic recording medium may be a portable type medium which is loaded into and unloaded from the housing 113.

Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention.

Claims

1. A magnetic recording medium comprising: an intermediate layer including a first layer made of a PdW alloy; and a recording layer disposed above the intermediate layer and having a film plane, wherein the intermediate layer imparts crystallographic texture growth in the recording layer so that an axis of easy magnetization of the recording layer is perpendicular to the film plane.

2. The magnetic recording medium as claimed in claim 1, wherein the recording layer is made of a CoPt alloy, and the intermediate layer imparts a CoPt (0002) crystallographic texture of the recording layer.

3. The magnetic recording medium as claimed in claim 1 or 2, wherein the PdW alloy of the first layer includes 20 at.% to 40 at . % of W.

4. The magnetic recording medium as claimed in claim 3, wherein the first layer has a thickness of 16 nm to 25 nm.

5. The magnetic recording medium as claimed in any of claims 1 to 3, wherein the intermediate layer further includes a second layer disposed on the first layer and made of Ru or an Ru alloy.

6. The magnetic recording medium as claimed in claim 5, wherein the first layer has a thickness of 8 nm to 11 nm.

7. The magnetic recording medium as claimed in claim 5 or 6, wherein the second layer has a granular structure, and the recording layer has a granular structure.

8. The magnetic recording medium as claimed in any of claims 5 to 7, wherein the second layer has a thickness greater than 0 nm but 10 nm or less .

9. The magnetic recording medium as claimed in any of claims 1 to 8, wherein the first layer is made of a PdWxY alloy, where x is 20 at . % to 40 at.%, Y is an additive for improving a distribution of c-axis alignment of the recording layer, the additive Y is selected from a group consisting of Co, Cr, C, Ti, Si, Ta, B, Ru, SiO₂, TiO₂, TaO₂, Ta₂O₅, W, Nb, V and Mo and is greater than 0 at.% but less than 20 at.%.

10. The magnetic recording medium as claimed in any of claims 1 to 9, further comprising: a seed layer made of a material having one of a (111) crystallographic texture, an amorphous structure, a BCC structure and a B2 structure.

11. The magnetic recording medium as claimed in any of claims 1 to 10, forming a medium selected from a group consisting of a perpendicular magnetic recording medium, a discrete track patterned medium and a bit patterned medium.

12. A storage apparatus comprising: at least one magnetic recording medium according to any one of claims 1 to 10. and a head configured to record information on and reproduce information from the at least one magnetic recording medium.