SPUTTERING TARGET FOR MAGNETIC RECORDING MEDIUM

Abstract

For a further high capacity, provided is a sputtering target for a magnetic recording medium that can form a magnetic thin film having enhanced uniaxial magnetic anisotropy, reduced intergranular exchange coupling, and improved thermal stability and SNR (signal-to-noise ratio).

The sputtering target for a magnetic recording medium, comprises: a metal phase containing Pt and at least one or more selected from Cu and Ni, with the balance being Co and incidental impurities; and an oxide phase containing at least B.sub.2O.sub.3.

Claims

1. A sputtering target for a magnetic recording medium, comprising: a metal phase containing Pt and at least one or more selected from Cu and Ni, with the balance being Co and incidental impurities; and an oxide phase containing at least B.sub.2O.sub.3.

2. The sputtering target for a magnetic recording medium according to claim 1, containing, based on total metal phase components of the sputtering target for a magnetic recording medium, 1 mol % or more and 30 mol % or less of Pt and 0.5 mol % or more and 15 mol % or less of at least one or more selected from Cu and Ni; and comprising, based on the sputtering target for a magnetic recording medium as a whole, 25 vol % or more and 40 vol % or less of the oxide phase.

3. A sputtering target for a magnetic recording medium, comprising: a metal phase containing Pt, at least one or more selected from Cu and Ni, and at least one or more selected from Cr, Ru, and B, with the balance being Co and incidental impurities; and an oxide phase containing at least B.sub.2O.sub.3.

4. The sputtering target for a magnetic recording medium according to claim 3, containing, based on total metal phase components of the sputtering target for a magnetic recording medium, 1 mol % or more and 30 mol % or less of Pt, 0.5 mol % or more and 15 mol % or less of at least one or more selected from Cu and Ni, and more than 0.5 mol % and 30 mol % or less of at least one or more selected from Cr, Ru, and B; and comprising, based on the sputtering target for a magnetic recording medium as a whole, 25 vol % or more and 40 vol % or less of the oxide phase.

5. The sputtering target for a magnetic recording medium according to claim 1, wherein the oxide phase further contains one or more oxides selected from TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, MnO, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4, NiO, ZnO, Y.sub.2O.sub.3, MoO.sub.2, WO.sub.3, La.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and ZrO.sub.2.

6. The sputtering target for a magnetic recording medium according to claim 2, wherein the oxide phase further contains one or more oxides selected from TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, MnO, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4, NiO, ZnO, Y.sub.2O.sub.3, MoO.sub.2, WO.sub.3, La.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and ZrO.sub.2.

7. The sputtering target for a magnetic recording medium according to claim 3, wherein the oxide phase further contains one or more oxides selected from TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, MnO, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4, NiO, ZnO, Y.sub.2O.sub.3, MoO.sub.2, WO.sub.3, La.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and ZrO.sub.2.

8. The sputtering target for a magnetic recording medium according to claim 4, wherein the oxide phase further contains one or more oxides selected from TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, MnO, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4, NiO, ZnO, Y.sub.2O.sub.3, MoO.sub.2, WO.sub.3, La.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and ZrO.sub.2.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is SEM photograph (accelerating voltage of 15 keV) of a cross-section in the thickness direction of a sintered test piece in Example 1.

[0028] FIG. 2 is EDS maps of FIG. 1 (×3,000).

[0029] FIG. 3 is a magnetization curve for a granular medium of Example 1.

[0030] FIG. 4 is SEM photograph (accelerating voltage of 15 keV) of a cross-section in the thickness direction of a sintered test piece in Example 2.

[0031] FIG. 5 is EDS maps of FIG. 4 (×3,000).

[0032] FIG. 6 is XRD profiles in the direction perpendicular to a film surface for magnetic films of Examples 1 and 2 and Comparative Example 1.

[0033] FIG. 7 is TEM images of the magnetic films of Examples 1 and 2 and Comparative Example 1.

[0034] FIG. 8 is a graph showing measured results of M.sub.s for the magnetic films of Examples 1 and 2 and Comparative Example 1.

[0035] FIG. 9 is a graph showing measured results of H.sub.c for the magnetic films of Examples 1 and 2 and Comparative Example 1.

[0036] FIG. 10 is a graph showing measured results of H.sub.n for the magnetic films of Examples 1 and 2 and Comparative Example 1.

[0037] FIG. 11 is a graph showing a for the magnetic films of Examples 1 and 2 and Comparative Example 1.

[0038] FIG. 12 is a graph showing measured results of K.sub.u.sup.Grain for the magnetic films of Examples 1 and 2 and Comparative Example 1.

[0039] FIG. 13 is a graph showing measured results of M.sub.s for magnetic films of Examples 2 and 3.

[0040] FIG. 14 is a graph showing measured results of He for the magnetic films of Examples 2 and 3.

[0041] FIG. 15 is a graph showing measured results of H.sub.n for the magnetic films of Examples 2 and 3 FIG. 16 is a graph showing a for the magnetic films of Examples 2 and 3.

[0042] FIG. 17 is a graph showing measured results of K.sub.u.sup.Grain for the magnetic films of Examples 2 and 3 and Comparative Example 1.

DESCRIPTION OF EMBODIMENTS

[0043] Hereinafter, the present invention will be described in detail by reference to the accompanying drawings. However, the present invention is not limited thereto. Herein, a sputtering target for a magnetic recording medium is simply referred to as a sputtering target or a target in some cases.

(1) First Embodiment

[0044] A sputtering target for magnetic recording medium according to the first embodiment of the present invention is characterized by comprising: a metal phase containing Pt and at least one or more selected from Cu and Ni, with the balance being Co and incidental impurities; and an oxide phase containing at least B.sub.2O.sub.3.

[0045] The target of the first embodiment preferably contains, in the metal phase, 1 mol % or more and 30 mol % or less of Pt and 0.5 mol % or more and 15 mol % or less of at least one or more selected from Cu and Ni, with the balance being Co and incidental impurities; and preferably comprises, based on the sputtering target for a magnetic recording medium as a whole, 25 vol % or more and 40 vol % or less of the oxide phase containing at least B.sub.2O.sub.3.

[0046] Co, Pt, and one or more selected from Cu and Ni are constituents of magnetic grains (tiny magnets) in the granular structure of a magnetic thin film to be formed by sputtering. Hereinafter, one or more selected from Cu and Ni are abbreviated to “X” in the present specification, and magnetic grains contained in a magnetic thin film of a magnetic recording medium formed by using the target of the first embodiment are also referred to as “CoPtX alloy grains.”

[0047] Co is a ferromagnetic metal element and plays a central role in the formation of magnetic grains (tiny magnets) in the granular structure of a magnetic thin film. From a viewpoint of increasing the magnetocrystalline anisotropy constant K.sub.u of CoPtX alloy grains (magnetic grains) in a magnetic thin film to be obtained by sputtering as well as maintaining the magnetism of the CoPtX alloy grains (magnetic grains) in the obtained magnetic thin film, the Co content ratio in the sputtering target according to the first embodiment is preferably set to 25 mol % or more and 98.5 mol % or less based on the total metal components.

[0048] Pt acts, by alloying with Co and X within a predetermined compositional range, to reduce the magnetic moment of the resulting alloy and plays a role in adjusting the intensity of the magnetism of magnetic grains. From a viewpoint of increasing the magnetocrystalline anisotropy constant K.sub.u of CoPtX alloy grains (magnetic grains) in a magnetic thin film to be obtained by sputtering as well as adjusting the magnetism of the CoPtX alloy grains (magnetic grains) in the obtained magnetic thin film, the Pt content ratio in the sputtering target according to the first embodiment is preferably set to 1 mol % or more and 30 mol % or less based on the total metal components.

[0049] Cu acts to enhance the separation of CoPtX alloy grains (magnetic grains) by the oxide phase in a magnetic thin film and thus can reduce intergranular exchange coupling. Here, a magnetic thin film formed by sputtering using a CoPtCu—B.sub.2O.sub.3 target will be compared with a magnetic thin film formed by sputtering using a CoPt—B.sub.2O.sub.3 target. In the former, the B.sub.2O.sub.3 oxide phase exists deeper in the depth direction than the latter as partition walls between the neighboring CoPtCu alloy grains (FIG. 7: TEM images) and the magnetization curve has a smaller slope α at the intersection with the horizontal axis (applied magnetic field) than the latter (FIG. 11). Accordingly, it can be confirmed that the separation of magnetic grains is enhanced. Meanwhile, the former has the magnetocrystalline anisotropy constant K.sub.u.sup.Grain per unit grain comparable to the latter (FIG. 12). Accordingly, it can be confirmed that the magnetic thin film exhibits satisfactory uniaxial magnetic anisotropy.

[0050] Ni acts to enhance uniaxial magnetic anisotropy of a magnetic thin film and thus can increase the magnetocrystalline anisotropy constant K.sub.u. Here, a magnetic thin film formed by sputtering using a CoPtNi—B.sub.2O.sub.3 target will be compared with a magnetic thin film formed by sputtering using a CoPt—B.sub.2O.sub.3 target. In the former, the B.sub.2O.sub.3 oxide phase exists deeper in the depth direction than the latter as partition walls between the neighboring CoPtNi alloy grains (FIG. 7: TEM images) and the magnetization curve has a slope α at the intersection with the horizontal axis (applied magnetic field) comparable to the latter (FIG. 11). Accordingly, it can be confirmed that the separation of magnetic grains is satisfactory. Meanwhile, the former has a higher magnetocrystalline anisotropy constant K.sub.u.sup.Grain per unit grain than the latter (FIG. 12). Accordingly, it can be confirmed that the uniaxial magnetic anisotropy of the magnetic thin film is enhanced.

[0051] The content ratio of X in the sputtering target according to the first embodiment is preferably set to 0.5 mol % or more and 15 mol % or less based on the total metal phase components. Cu and Ni may be each alone or in combination contained as the metal phase components of the sputtering target. In particular, using Cu and Ni in combination is preferable since it is possible to reduce intergranular exchange coupling and enhance uniaxial magnetic anisotropy.

[0052] The oxide phase constitutes a nonmagnetic matrix that partitions magnetic grains (tiny magnets) in the granular structure of a magnetic thin film. The oxide phase of the sputtering target according to the first embodiment contains at least B.sub.2O.sub.3. As other oxides, one or more selected from TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, MnO, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4, NiO, ZnO, Y.sub.2O.sub.3, MoO.sub.2, WO.sub.3, La.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3. Lu.sub.2O.sub.3, and ZrO.sub.2 may be contained.

[0053] B.sub.2O.sub.3 with a low melting point of 450° C. is slow to be deposited in the film forming process by sputtering. Accordingly, while CoPtX alloy grains grow into columnar grains, B.sub.2O.sub.3 in the liquid state exists between the columnar CoPtX alloy grains. For this reason, B.sub.2O.sub.3 is finally deposited as grain boundaries, which partition the CoPtX alloy grains that have grown into columnar grains, and constitutes a nonmagnetic matrix that partitions magnetic grains (tiny magnets) in the granular structure of a magnetic thin film. It is preferable to increase the oxide content in a magnetic thin film since magnetic grains are reliably and readily partitioned and isolated from each other. In this view, the oxide content in the sputtering target according to the first embodiment is preferably 25 vol % or more, more preferably 28 vol % or more, and further preferably 29 vol % or more. Meanwhile, when the oxide content in a magnetic thin film excessively increases, there is a risk that the oxide is mixed into CoPtX alloy grains (magnetic grains) and adversely affects the crystallinity of the CoPtX alloy grains (magnetic grains) to increase the proportion of structures other than hcp in the CoPtX alloy grains (magnetic grains). Moreover, a reduced number of magnetic grains per unit area in the magnetic thin film makes it difficult to increase the recording density. In this view, the oxide contents in the sputtering target according to the first embodiment is preferably 40 vol % or less, more preferably 35 vol % or less, and further preferably 31 vol % or less.

[0054] In the sputtering target according to the first embodiment, the total content ratio of metal phase components and the total content ratio of oxide phase components based on the entire sputtering target are determined by the intended component composition of a magnetic thin film and thus are not particularly limited. For example, the total content ratio of metal phase components may be set to 89.4 mol % or more and 96.4 mol % or less based on the entire sputtering target, and the total content ratio of oxide phase components may be set to 3.6 mol % or more and 11.6 mol % or less based on the entire sputtering target.

[0055] The microstructure of the sputtering target according to the first embodiment is not particularly limited but is preferably a microstructure in which the metal phase and the oxide phase are mutually and finely dispersed. Such a microstructure is less likely to cause trouble during sputtering, such as nodules or particles.

[0056] The sputtering target according to the first embodiment can be produced as follows, for example.

[0057] A molten CoPt alloy is prepared from metal components each weighed to satisfy a predetermined composition. The molten alloy was gas-atomized to yield CoPt alloy atomized powder. The prepared CoPt alloy atomized powder is classified into a predetermined particle size or less (106 μm or less, for example).

[0058] The prepared CoPt alloy atomized powder is added with X metal powder, B.sub.2O.sub.3 powder, and other oxide powders as necessary (for example, TiO.sub.2 powder, SiO.sub.2 powder, Ta.sub.2O.sub.5 powder, Cr.sub.2O.sub.3 powder, Al.sub.2O.sub.3 powder, ZrO.sub.2 powder, Nb.sub.2O.sub.5 powder, MnO powder, Mn.sub.3O.sub.4 powder, CoO powder, Co.sub.3O.sub.4 powder, NiO powder, ZnO powder, Y.sub.2O.sub.3 powder, MoO.sub.2 powder, WO.sub.3 powder, La.sub.2O.sub.3 powder, CeO.sub.2 powder, Nd.sub.2O.sub.3 powder, Sm.sub.2O.sub.3 powder, Eu.sub.2O.sub.3 powder, Gd.sub.2O.sub.3 powder, Yb.sub.2O.sub.3 powder, and Lu.sub.2O.sub.3 powder) and mixed/dispersed within a ball mill to yield a mixed powder for pressure sintering. Through mixing/dispersing of the CoPt alloy atomized powder, X metal powder, B.sub.2O.sub.3 powder, and other oxide powders as necessary in a ball mill, it is possible to prepare a mixed powder for pressure sintering in which the CoPt alloy atomized powder, X metal powder, B.sub.2O.sub.3 powder, and other oxide powders used as necessary are mutually and finely dispersed.

[0059] From a viewpoint of reliably partitioning and readily isolating magnetic grains from each other by B.sub.2O.sub.3 and other oxides as necessary in a magnetic thin film formed by using a sputtering target to be obtained, from a viewpoint of facilitating the formation of the hcp structure of CoPtX alloy grains (magnetic grains), and from a viewpoint of increasing the recording density, the total volume fraction of B.sub.2O.sub.3 powder and other oxide powders used as necessary is preferably 25 vol % or more and 40 vol % or less, more preferably 28 vol % or more and 35 vol % or less, and further preferably 29 vol % or more and 31 vol % or less based on the entire mixed powder for pressure sintering.

[0060] The prepared mixed powder for pressure sintering is formed to produce a sputtering target through pressure sintering by a vacuum hot press process. Since the mixed powder for pressure sintering has been mixed/dispersed in a ball mill, the CoPt alloy atomized powder. X metal powder, B.sub.2O.sub.3 powder, and other oxide powders used as necessary are mutually and finely dispersed. For this reason, when sputtering is performed using a sputtering target obtained by the present production method, trouble, such as generation of particles or nodules, is less likely to arise. Here, the pressure sintering process for the mixed powder for pressure sintering is not particularly limited, and a process other than the vacuum hot press process, such as the HIP process, may be employed.

[0061] To prepare a mixed powder for pressure sintering, each metal element powder may be used without being limited to the atomized powder. In this case, a mixed powder for pressure sintering can be prepared by mixing/dispersing each metal element powder, B.sub.2O.sub.3 powder, and other oxide powders as necessary in a ball mill.

(2) Second Embodiment

[0062] A sputtering target for magnetic recording medium according to the second embodiment of the present invention is characterized by comprising: a metal phase containing Pt, at least one or more selected from Cu and Ni, and at least one or more selected from Cr, Ru, and B, with the balance being Co and incidental impurities; and an oxide phase containing at least B.sub.2O.sub.3.

[0063] The target of the second embodiment preferably comprises a metal phase containing 1 mol % or more and 30 mol % or less of Pt, more than 0.5 mol % and 30 mol % or less of at least one or more selected from Cr, Ru, and B, and 0.5 mol % or more and 15 mol % or less of at least one or more selected from Cu and Ni, with the balance being Co and incidental impurities; and preferably comprises, based on the sputtering target for a magnetic recording medium as a whole, 25 vol % or more and 40 vol % or less of one or more oxides including at least B.sub.2O.sub.3.

[0064] Co, Pt, one or more selected from Cu and Ni (hereinafter, also referred to as “X”), and one or more selected from Cr, Ru, and B (hereinafter, also referred to as “M”) are constituents of magnetic grains (tiny magnets) in the granular structure of a magnetic thin film to be formed by sputtering. Hereinafter, magnetic grains of the second embodiment are also referred to as “CoPtXM alloy grains” in the present specification.

[0065] Co is a ferromagnetic metal element and plays a central role in the formation of magnetic grains (tiny magnets) in the granular structure of a magnetic thin film. From a viewpoint of increasing the magnetocrystalline anisotropy constant K.sub.u of CoPtXM alloy grains (magnetic grains) in a magnetic thin film to be obtained by sputtering as well as maintaining the magnetism of the CoPtXM alloy grains (magnetic grains) in the obtained magnetic thin film, the Co content ratio in the sputtering target according to the second embodiment is preferably set to 25 mol % or more and 98 mol % or less based on the total metal components.

[0066] Pt acts, by alloying with Co, X, and M within a predetermined compositional range, to reduce the magnetic moment of the resulting alloy and plays a role in adjusting the intensity of the magnetism of magnetic grains. From a viewpoint of increasing the magnetocrystalline anisotropy constant K.sub.u of CoPtXM alloy grains (magnetic grains) in a magnetic thin film to be obtained by sputtering as well as adjusting the magnetism of the CoPtXM alloy grains (magnetic grains) in the obtained magnetic thin film, the Pt content ratio in the sputtering target according to the second embodiment is preferably set to 1 mol % or more and 30 mol % or less based on the total metal phase components.

[0067] At least one or more selected from Cr, Ru, and B act, by alloying with Co within a predetermined compositional range, to reduce the magnetic moment of Co and play a role in adjusting the intensity of the magnetism of magnetic grains. From a viewpoint of increasing the magnetocrystalline anisotropy constant K.sub.u of CoPtXM alloy grains (magnetic grains) in a magnetic thin film to be obtained by sputtering as well as maintaining the magnetism of the CoPtXM alloy grains in the obtained magnetic thin film, the content ratio of at least one or more selected from Cr, Ru, and B in the sputtering target according to the second embodiment is preferably set to more than 0.5 mol % and 30 mol % or less based on the total metal phase components. Cr, Ru, and B may be used alone or in combination and form the metal phase of the sputtering target together with Co and Pt.

[0068] Cu acts to enhance the separation of CoPtXM alloy grains (magnetic grains) by the oxide phase in a magnetic thin film and thus can reduce intergranular exchange coupling.

[0069] Ni acts to enhance uniaxial magnetic anisotropy of a magnetic thin film and thus can increase the magnetocrystalline anisotropy constant K.sub.u.

[0070] The content ratio of X in the sputtering target according to the second embodiment is preferably set to 0.5 mol % or more and 15 mol % or less based on the total metal phase components. Cu and Ni may be each alone or in combination contained as metal phase components of the sputtering target. In particular, using Cu and Ni in combination is preferable since it is possible to reduce intergranular exchange coupling and enhance uniaxial magnetic anisotropy.

[0071] The oxide phase constitutes a nonmagnetic matrix that partitions magnetic grains (tiny magnets) in the granular structure of a magnetic thin film. The oxide phase of the sputtering target according to the second embodiment contains at least B.sub.2O.sub.3. As other oxide components, one or more selected from TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.5, Cr.sub.2O.sub.3, Al.sub.2O.sub.3, Nb.sub.2O.sub.5, MnO, Mn.sub.3O.sub.4, CoO, Co.sub.3O.sub.4, NiO, ZnO, Y.sub.2O.sub.3, MoO.sub.2, WO.sub.3, La.sub.2O.sub.3, CeO.sub.2, Nd.sub.2O.sub.3, Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, and ZrO.sub.2 may be contained.

[0072] B.sub.2O.sub.3 with a low melting point of 450° C. is slow to be deposited in the film forming process by sputtering. Accordingly, while CoPtXM alloy grains grow into columnar grains, B.sub.2O.sub.3 in the liquid state exists between the columnar CoPtXM alloy grains. For this reason, B.sub.2O.sub.3 is finally deposited as grain boundaries, which partition CoPtXM alloy grains that have grown into columnar grains, and constitutes a nonmagnetic matrix that partitions magnetic grains (tiny magnets) in the granular structure of a magnetic thin film. It is preferable to increase the oxide content in a magnetic thin film since magnetic grains are reliably and readily partitioned and isolated from each other. In this view, the oxide content in the sputtering target according to the second embodiment is preferably 25 vol % or more, more preferably 28 vol % or more, and further preferably 29 vol % or more. Meanwhile, when the oxide content in the magnetic thin film excessively increases, there is a risk that the oxide is mixed into CoPtXM alloy grains (magnetic grains) and adversely affects the crystallinity of the CoPtXM alloy grains (magnetic grains) to increase the proportion of structures other than hcp in the CoPtXM alloy grains (magnetic grains). Moreover, a reduced number of magnetic grains per unit area in the magnetic thin film makes it difficult to increase the recording density. In this view, the content of the oxide phase in the sputtering target according to the second embodiment is preferably 40 vol % or less, more preferably 35 vol % or less, and further preferably 31 vol % or less.

[0073] In the sputtering target according to the second embodiment, the total content ratio of metal phase components and the total content ratio of oxide phase components based on the entire sputtering target are determined by the intended component composition of a magnetic thin film and thus are not particularly limited. For example, the total content ratio of metal phase components may be set to 88.2 mol % or more and 96.4 mol % or less based on the entire sputtering target, and the total content ratio of oxide phase components may be set to 3.6 mol % or more and 11.8 mol % or less based on the entire sputtering target.

[0074] The microstructure of the sputtering target according to the second embodiment is not particularly limited but is preferably a microstructure in which the metal phase and the oxide phase are mutually and finely dispersed. Such a microstructure is less likely to cause trouble during sputtering, such as nodules or particles.

[0075] The sputtering target according to the second embodiment can be produced as follows, for example.

[0076] A molten CoPtM alloy is prepared from Co, Pt, and one or more (M) selected from Cr, Ru, and B each weighed to satisfy a predetermined composition. The molten alloy was gas-atomized to yield CoPtM alloy atomized powder. The prepared CoPtM alloy atomized powder is classified into a predetermined particle size or less (106 μm or less, for example).

[0077] The prepared CoPtM alloy atomized powder is added with X metal powder, B.sub.2O.sub.3 powder, and other oxide powders as necessary (for example, TiO.sub.2 powder, SiO.sub.2 powder, Ta.sub.2O.sub.5 powder, Cr.sub.2O.sub.3 powder, Al.sub.2O.sub.3 powder, ZrO.sub.2 powder, Nb.sub.2O.sub.5 powder, MnO powder, Mn.sub.3O.sub.4 powder, CoO powder, Co.sub.3O.sub.4 powder, NiO powder, ZnO powder, Y.sub.2O.sub.3 powder, MoO.sub.2 powder, WO.sub.3 powder, La.sub.2O.sub.3 powder, CeO.sub.2 powder, Nd.sub.2O.sub.3 powder, Sm.sub.2O.sub.3 powder, Eu.sub.2O.sub.3 powder, Gd.sub.2O.sub.3 powder, Yb.sub.2O.sub.3 powder, and Lu.sub.2O.sub.3 powder) and mixed/dispersed in a ball mill to yield a mixed powder for pressure sintering. Through mixing/dispersing of the CoPtM alloy atomized powder, X metal powder, B.sub.2O.sub.3 powder, and other oxide powders as necessary in a ball mill, it is possible to prepare a mixed powder for pressure sintering in which the CoPtM alloy atomized powder, X metal powder, B.sub.2O.sub.3 powder, and other oxide powders used as necessary are mutually and finely dispersed.

[0078] From a viewpoint of reliably partitioning and readily isolating magnetic grains from each other by B.sub.2O.sub.3 and other oxides as necessary in a magnetic thin film formed by using a sputtering target to be obtained, from a viewpoint of facilitating the formation of the hcp structure of CoPtXM alloy grains (magnetic grains), and from a viewpoint of increasing the recording density, the total volume fraction of B.sub.2O.sub.3 powder and other oxide powders used as necessary is preferably 25 vol % or more and 40 vol % or less, more preferably 28 vol % or more and 35 vol % or less, and further preferably 29 vol % or more and 31 vol % or less based on the entire mixed powder for pressure sintering.

[0079] The prepared mixed powder for pressure sintering is formed to produce a sputtering target through pressure sintering by a vacuum hot press process, for example. Since the mixed powder for pressure sintering has been mixed/dispersed in a ball mill, the CoPtM alloy atomized powder, X metal powder, B.sub.2O.sub.3 powder, and other oxide powders used as necessary are mutually and finely dispersed. For this reason, when sputtering is performed by using a sputtering target obtained by the present production method, trouble, such as generation of particles or nodules, is less likely to arise. Here, the pressure sintering process for the mixed powder for pressure sintering is not particularly limited, and a process other than the vacuum hot press process, such as the HIP process, may be employed.

[0080] To prepare a mixed powder for pressure sintering, each metal element powder may be used without being limited to the atomized powder. In this case, a mixed powder for pressure sintering can be prepared by mixing/dispersing each metal element powder, B powder as necessary. B.sub.2O.sub.3 powder, and other oxide powders as necessary in a ball mill.

EXAMPLES

[0081] Hereinafter, the present invention will be described further by means of Examples and Comparative Examples. In any of the Examples and the Comparative Examples, the total oxide content in a sputtering target was set to 30 vol %.

Example 1

[0082] The composition of the entire target prepared as Example 1 is (75Co-20Pt-5Ni)-30 vol % B.sub.2O.sub.3 (atomic ratio for metal components), which is expressed by the molar ratio as 92.55(75Co-20Pt-5Ni)-7.45B.sub.2O.sub.3.

[0083] To produce the target according to Example 1, 50Co-50Pt alloy atomized powder and 100Co atomized powder were prepared first. Specifically, for the alloy atomized powder, each metal was weighed to satisfy the composition of 50 at % of Co and 50 at % of Pt. Both 50Co-50Pt alloy atomized powder and 100Co atomized powder were prepared by heating metal(s) to 1,500° C. or higher to form a molten alloy or a molten metal, followed by gas atomization.

[0084] The prepared 50Co-50Pt alloy atomized powder and 100Co atomized powder were classified through a 150 mesh sieve to obtain 50Co-50Pt alloy atomized powder and 100Co atomized powder each having a particle size of 106 μm or less.

[0085] To satisfy the composition of (75Co-20Pt-5Ni)-30 vol % B.sub.2O.sub.3, Ni powder and B.sub.2O.sub.3 powder were added to the classified 50Co-50Pt alloy atomized powder and 100Co atomized powder and mixed/dispersed in a ball mill to yield a mixed powder for pressure sintering.

[0086] The obtained mixed powder for pressure sintering was hot-pressed at a sintering temperature of 710° C. and a sintering pressure of 24.5 MPa for a sintering time of 30 minutes in an atmosphere of a vacuum condition of 5×10.sup.−2 Pa or less to yield a sintered test piece (030 mm). The prepared sintered test piece had a relative density of 100.4% and a calculated density of 9.04 g/cm.sup.3. The cross-section in the thickness direction of the obtained sintered test piece was mirror-polished and observed under a scanning electron microscope (SEM: JCM-6000Plus from JEOL Ltd.) at an accelerating voltage of 15 keV. The results are shown in FIG. 1. Moreover, compositional analysis of the cross-sectional structure was performed by an energy dispersive X-ray spectrometer (EDS) attached to the SEM. The results are shown in FIG. 2. From these results, the metal phase (75Co-20Pt-5Ni alloy phase) and the oxide phase (B.sub.2O.sub.3) were confirmed to be finely dispersed. The ICP analysis results of the obtained sintered test piece are shown in Table 3. Next, the prepared mixed powder for pressure sintering was hot-pressed at a sintering temperature of 920° C. and a sintering pressure of 24.5 MPa for a sintering time of 60 minutes in an atmosphere of a vacuum condition of 5×10.sup.−2 Pa or less to produce a target (0153.0×1.0 mm+ø161.0×4.0 mm). The produced target had a relative density of 96.0%.

[0087] Sputtering was performed by using the prepared target in a DC sputtering apparatus (C 3010 from Canon Anelva Corporation) to form a magnetic thin film of (75Co-20Pt-5Ni)-30 vol % B.sub.2O.sub.3 on a glass substrate, thereby preparing a sample for magnetic characteristics measurement and a sample for structure observation. These samples have a layered structure of Ta (5 nm, 0.6 Pa)/Ni.sub.90W.sub.10(6 nm, 0.6 Pa)/Ru (10 nm, 0.6 Pa)/Ru (10 nm, 8 Pa)/CoPt alloy-oxide (8 nm, 4 Pa)/C (7 nm, 0.6 Pa) in this order from the side closer to the glass substrate. The numbers in the left side within the parentheses represent thickness, and the numbers in the right side represent pressure of Ar atmosphere during sputtering. The magnetic thin film formed by using the target prepared in Example 1 is CoPtNi alloy-oxide (B.sub.2O.sub.3) and is a magnetic thin film as a recording layer of a perpendicular magnetic recording medium. Here, the magnetic thin film was formed at room temperature without elevating the temperature of the substrate.

[0088] For measuring the magnetic characteristics of the obtained sample for magnetic characteristics measurement, a vibrating sample magnetometer (VSM: TM-VSM211483-HGC from Tamagawa Co., Ltd.), a torque magnetometer (TM-TR2050-HGC from Tamagawa Co., Ltd.), and a polar Kerr effect measurement apparatus (MOKE: BH-810CPM-CPC from Neoark Corporation) were used.

[0089] FIG. 3 shows an exemplary magnetization curve for a granular medium of the sample for magnetic characteristics measurement in Example 1. In FIG. 3, the horizontal axis represents the intensity of applied magnetic field and the vertical axis represents the intensity of magnetization per unit volume.

[0090] From the measured results of the magnetization curve for the granular medium of the sample for magnetic characteristics measurement, the saturation magnetization (M.sub.s), coercivity (H), and slope (α) at the intersection with the horizontal axis were obtained. Moreover, the magnetocrystalline anisotropy constant (K.sub.u) was measured by using the torque magnetometer. These values, together with the results for other Examples and Comparative Examples, are shown in Table 1 and FIGS. 8 to 12.

[0091] Further, for assessing the structure (assessing particle size and so forth of magnetic grains) of the obtained sample for structure observation, an X-ray diffractometer (XRD: SmartLab from Rigaku Corporation) and a transmission electron microscope (TEM: H-9500 from Hitachi High-Tech Corporation) were used. The XRD profile in the direction perpendicular to the film surface is shown in FIG. 6 and Table 2, and the TEM image is shown in FIG. 7.

Example 2

[0092] The composition of the entire target prepared in Example 2 is (75Co-20Pt-5Cu)-30 vol % B.sub.2O.sub.3 (atomic ratio for metal components), which is expressed by the molar ratio as 92.52(75Co-20Pt-5Cu)-7.48B.sub.2O.sub.3. A sample for magnetic characteristics measurement and a sample for structure observation were prepared and observed in the same manner as Example 1 except for changing the target composition from Example 1. The results are shown in FIGS. 4 and 5. The Cu powder used had an average particle size of 3 μm or less. A sintered test piece (ø30 mm) was prepared by hot pressing at a sintering temperature of 720° C. and a sintering pressure of 24.5 MPa for a sintering time of 30 minutes in an atmosphere of a vacuum condition of 5×10.sup.−2 Pa or less. The prepared sintered test piece had a relative density of 99.8% and a calculated density of 9.03 g/cm.sup.3. The cross-section in the thickness direction of the obtained sintered test piece was observed under a metallurgical microscope, and the metal phase (75Co-20Pt-5Cu alloy phase) and the oxide phase (B.sub.2O.sub.3) were confirmed to be finely dispersed. The ICP analysis results of the obtained sintered test piece are shown in Table 3.

[0093] Next, a prepared mixed powder for pressure sintering was hot-pressed at a sintering temperature of 920° C. and a sintering pressure of 24.5 MPa for a sintering time of 60 minutes in an atmosphere of a vacuum condition of 5×10.sup.−2 Pa or less to produce a target (ø153.0×1.0 mm+ø161.0×4.0 mm). The produced target had a relative density of 100.1%.

[0094] Later, magnetic characteristics assessment and structure observation for films were performed in the same manner as Example 1. The measured results of the magnetic characteristics, together with the target composition, are shown in Table 1 and FIGS. 8 to 12. Moreover, the XRD profile in the direction perpendicular to the film surface obtained by structure observation is shown in FIG. 6 and Table 2, and the TEM image is shown in FIG. 7.

Comparative Example 1

[0095] A sintered test piece and a target were prepared as well as a magnetic thin film was formed and assessed in the same manner as Examples 1 and 2 except for changing the composition of the entire target to (80Co-20Pt)-30 vol % B.sub.2O.sub.3 (atomic ratio for metal components). The measured results of the magnetic characteristics, together with the target composition, are shown in Table 1 and FIGS. 8 to 12. The XRD profile in the direction perpendicular to the film surface obtained by structure observation is shown in FIG. 6, and the CoPt(002) peak position (2θ) and c-axis lattice constant read from the XRD profile are shown in Table 2. The TEM image is shown in FIG. 7, and the ICP analysis results of the obtained sintered test piece are shown in Table 3.

[0096] The symbols in Table 1 mean the following.

t.sub.Mag1: thickness of magnetic layer in layered film
M.sub.s.sup.Grain: saturation magnetization solely for magnetic grains of magnetic layer in layered film
H.sub.c: coercivity measured by Kerr effect
H.sub.n: nucleation field measured by Kerr effect
α: slope at intersection with horizontal axis (applied magnetic field) of magnetization curve measured by Kerr effect
H.sub.c−H.sub.n: difference between coercivity and nucleation field measured by Kerr effect
K.sub.u.sup.Grain: magnetocrystalline anisotropy constant solely for magnetic grains of magnetic layer in layered film

TABLE-US-00001 TABLE 1 Measured results of magnetic characteristics t.sub.Mag, 1 M.sub.s.sup.Grain H.sub.c H.sub.n H.sub.c − H.sub.n K.sub.u.sup.Grain X (nm) (emu/cm.sup.3) (kOe) (kOe) α (kOe) (*10.sup.6 erg/cm.sup.3) Co 16 1215.72 10.62 2.96 1.40 7.66 12 1247.06 9.49 2.22 1.51 7 27 8 1220.75 6.74 0.39 1.69 6.35 11.93 4 1269.67 1.41 −1.75 3.53 3.16 Cu 16 1201.56 9.87 1.08 1.20 8.79 12 1197.03 8.38 −0.26 1.22 8.64 8 1191.72 5.37 −1.45 1.54 6.82 11.89 4 1200.49 0.63 −3.64 2.47 4.27 Ni 16 1238.27 9.96 2.38 1.44 7.58 12 1264.09 8.91 0.75 1.36 8.16 8 1305.88 6.15 −0.47 1.74 6.62 13.43 4 1340.90 1.21 −2.68 3.03 3.89

TABLE-US-00002 TABLE 2 CoPt(002) peak position and C-axis lattice constant CoPt(002) peak C-axis lattice X position (°) constant (Å) Cu 42.91 4.212 Ni 42.94 4.209 Co 42.97 4.206

TABLE-US-00003 TABLE 3 Component composition and ICP analysis results Measured values (weight ratio) Metal component ratio Co Pt Ni Cu B (at % ratio) B.sub.2O.sub.3 Composition concentration concentration concentration concentration concentration Co Pt Ni Cu vol. % Comp. Ex. 1 (Co-20Pt)-30 52.03 41.97 1.89 80.4 19.6 0.0 0.0 29.8 vol. % B.sub.2O.sub.3 Ex. 1 (Co-20Pt-5Ni)-30 48.53 42.44 3.04 1.90 75.4 19.9 4.7 0.0 30.0 vol. % B.sub.2O.sub.3 Ex. 2 (Co-20Pt-5Cu)-30 48.56 42.19 3.20 1.94 75.6 19.8 0.0 4.6 30.5 vol. % B.sub.2O.sub.3

[0097] From FIG. 6 and Table 2, it is confirmed that the CoPt(002) peaks of Example 1 (Ni) and Example 2 (Cu) are shifted to lower angles relative to the peak of Comparative Example 1 (Co). Accordingly, at least part of Ni or Cu is considered to replace Co. However, the changes in c-axis lattice constant of the CoPt phase calculated from the peak positions are 0.01 Å or less. In addition, no structural change of the CoPt phase is observed. Meanwhile, no peak shift is observed for Ru and NiW.

[0098] In FIG. 7, it is observed that the gaps between the neighboring magnetic columns extend deeper in the depth direction in the magnetic thin film containing Ni or Cu than in the magnetic thin film (X=Co) containing neither Ni nor Cu. Accordingly, it is confirmed that the separation of magnetic grains is improved by using a target containing Ni or Cu.

[0099] FIG. 8 shows a slight increase in M: for Example 1 (Ni) and a slight decrease in M.sub.s for Example 2 (Cu) relative to Comparative Example 1 (Co). However, these levels do not pose any problem in terms of maintaining the magnetism of CoPtX alloy grains (magnetic grains).

[0100] FIG. 9 reveals that the magnetic thin film containing Ni or Cu has He comparable to or slightly lower than the magnetic thin film (X=Co) containing neither Ni nor Cu. However, a further increase in He can be expected, for example, by optimizing the composition or by using Ni and Cu in combination.

[0101] In FIG. 10, a lowering in He for Example 1 (Ni) and a further lowering in He for Example 2 (Cu) are observed relative to Comparative Example 1 (Co). This suggests improved separation of magnetic grains.

[0102] In FIG. 11, the Ni-containing magnetic thin film has a comparable to the Ni-free magnetic thin film (X=Co) and is thus confirmed to exhibit satisfactory separation of magnetic grains. In addition, the Cu-containing magnetic thin film has a smaller than the Cu-free magnetic thin film and is thus confirmed to exhibit improved separation of magnetic grains.

[0103] In FIG. 12, the Ni-containing magnetic thin film has K, higher than the Ni-free magnetic thin film (X=Co) and is thus confirmed to exhibit improved uniaxial magnetic anisotropy of magnetic grains by addition of Ni. Meanwhile, the Cu-containing magnetic thin film has K.sub.u comparable to the Cu-free magnetic thin film and is thus confirmed to maintain high uniaxial magnetic anisotropy.

Example 3

[0104] A target was prepared in the same manner as Examples 1 and 2 except for changing Cu content in the metal phase to 10 at % and 15 at % in the target of Example 2. A magnetic thin film was formed by using the target and assessed. The measured results of the magnetic characteristics are shown in Table 4 and FIGS. 13 to 17. In FIGS. 13 to 17, the results of Comparative Example 1 and the results of Example 2 are incorporated into 0 at % and 5 at % of Cu contents (at %), respectively.

TABLE-US-00004 TABLE 4 Measured results of magnetic characteristics K.sub.u.sup.Grain Cu contents M.sub.s.sup.Grain H.sub.c H.sub.n H.sub.c − H.sub.n (*10.sup.6 (at %) (emu/cm.sup.3) (emu/cm.sup.3) (kOe) α (kOe) erg/cm.sup.3) 10 1252.62 5.05 −1.69 1.64 6.73 11.83 15 1106.06 2.90 −3.69 1.48 6.58 8.99

[0105] In FIG. 15, it is observed that the Cu-containing magnetic thin films have H.sub.n smaller than the Cu-free magnetic thin film (Comparative Example 1: Cu contents=0 at %). In particular, H.sub.n steeply decreases to −3.69 kOe at Cu content of 15 at %, suggesting remarkably improved separation of magnetic grains.

[0106] FIG. 16 shows a lowering in a for the Cu-containing magnetic thin films relative to the Cu-free magnetic thin film (Comparative Example 1: Cu contents=0 at %) and α of 1.48 at Cu content of 15 at %. Here, a is an indicator of magnetic separation, where α closer to 1 is better.

[0107] In FIG. 17, the Cu-containing magnetic thin films have K.sub.u comparable to the Cu-free magnetic thin film (Comparative Example 1: Cu contents=0 at %). Although a slight lowering is observed at Cu content of 15 at %, the magnetic thin film maintains K.sub.u of about 9×10.sup.6 erg/cm.sup.3 and is thus considered to exhibit satisfactory uniaxial magnetic anisotropy.