Pt-oxide sputtering target and perpendicular magnetic recording medium

Abstract

Provided are: a magnetic recording medium having a high magnetocrystalline anisotropy constant Ku and coercive force Hc; and a sputtering target used to produce this magnetic recording medium.　This Pt-oxide sputtering target is formed from 60 vol% or more but less than 100 vol% of a Pt-based alloy phase and more than 0 vol% but 40 vol% or less of an oxide, the Pt-oxide sputtering target being characterized in that the Pt-based alloy phase contains 50 to 100 at% of Pt.

Description

[Technical Field]

[0001] The present invention relates to a Pt-oxide sputtering target and a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium as a microwave-assisted magnetic recording medium and a Pt-oxide sputtering target used to form the perpendicular magnetic recording medium by magnetron sputtering. [Background technology]

[0002] In hard disk drives, information signals are recorded on tiny bits of the magnetic recording medium. To further improve the recording density of the magnetic recording medium, it is necessary to reduce the size of the bit that holds a single piece of recorded information while increasing the signal-to-noise ratio, which is an indicator of information quality. Increasing the signal-to-noise ratio requires either increasing the signal strength or reducing the noise.

[0003] In the magnetic disks of hard disk drives, a magnetic thin film consisting of a granular structure of CoPt-based alloy-oxide is used as one of the magnetic recording films responsible for recording information signals (see, for example, Non-Patent Literature 1). This granular structure consists of columnar CoPt-based alloy crystal grains and surrounding oxide crystal grain boundaries. When increasing the recording density of such magnetic recording media, it is necessary to smooth the transition regions between recording bits to reduce noise. To smooth the transition regions between recording bits, miniaturization of the CoPt-based alloy crystal grains contained in the magnetic thin film is essential. Therefore, in order to further improve the recording density of a magnetic thin film consisting of a granular structure of CoPt-based alloy-oxide formed at room temperature, it is necessary to miniaturize the CoPt-based alloy crystal grains contained in the magnetic recording layer (magnetic thin film).

[0004] However, as the grain size of CoPt-based alloy crystals has become finer, a phenomenon known as thermal fluctuation has begun to occur, in which the thermal stability of the recorded signal is impaired due to superparamagnetic phenomena, causing the recorded signal to disappear. This thermal fluctuation phenomenon is a major obstacle to increasing the recording density of magnetic disks.

[0005] To overcome this obstacle, it is necessary to increase the magnetic energy in each CoPt-based alloy crystal grain so that the magnetic energy overcomes the thermal energy. The magnetic energy of each CoPt-based alloy crystal grain is determined by the product v × Ku, which is the volume v of the CoPt-based alloy crystal grain and the crystal magnetic anisotropy constant Ku. Therefore, in order to increase the magnetic energy of the CoPt-based alloy crystal grain, it is essential to increase the crystal magnetic anisotropy constant Ku of the CoPt-based alloy crystal grain (see, for example, Non-Patent Document 2).

[0006] To grow columnar crystal grains of CoPt-based alloy with a large Ku content, it is essential to achieve phase separation between the CoPt-based alloy crystal grains and the grain boundary material. If the phase separation between the CoPt-based alloy crystal grains and the grain boundary material is insufficient and the intergranular interaction between the CoPt-based alloy crystal grains becomes large, the coercivity Hc of the magnetic thin film consisting of a granular structure of CoPt-based alloy-oxide will decrease, impairing thermal stability and making it more susceptible to thermal fluctuations. Therefore, it is also important to reduce the intergranular interaction between the CoPt-based alloy crystal grains.

[0007] Strategies to increase the Ku content of CoPt-based alloy crystal grains include increasing spin-orbit interaction and reducing stacking faults by adjusting the Co and Pt content in each CoPt-based alloy crystal grain, and improving the periodicity of the stacked structure of Co and Pt atoms by depositing the film during a high-temperature substrate heating process (see, for example, Non-Patent Documents 3 and 4). However, the composition of current CoPt-based alloy-oxide magnetic thin films has already been sufficiently optimized and cannot be adjusted further. Furthermore, it is known that the Ku content of current CoPt-based alloy-oxide granular magnetic thin films deteriorates when fabricated using a high-temperature substrate heating process (see, for example, Non-Patent Document 5). In addition, it is known that interfacial magnetic anisotropy is exhibited in the direction perpendicular to the plane by multilayering Co and Pt thin films deposited at room temperature (see, for example, Non-Patent Document 6). [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] T. Oikawa et al., IEEE Trans. Magn., 38, 1976 (2002) [Non-Patent Document 2] SN Piramanayagam, J. Appl. Phys., 102, 011301 (2007). [Non-Patent Document 3] A. Ishikawa and R. Sinclair, IEEE Trans. Magn., 32, 3605 (1996). [Non-Patent Document 4] S. Saito, S. Hinata, and M. Takahashi, IEEE Trans. Magn., 50, 3201205 (2014). [Non-Patent Document 5] KK Tham, S. Hinata, S. Saito, and M. Takahashi, J. Appl. Phys., 115, 17B752 (2014). [Non-Patent Document 6] CJ Lin, GL Gorman, CH Lee, RFC Farrow, EE Marinero, HV Do, H. Notarys, and CJ Chien, J. Magn. Magn. Mat., 93, 194 (1991). [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a magnetic recording medium with high crystal magnetic anisotropy constant Ku and coercivity Hc, and to provide a sputtering target used for manufacturing the magnetic recording medium. [Means for solving the problem]

[0010] The inventors of the present invention have discovered that the crystalline magnetic anisotropy constant Ku and coercivity Hc of a magnetic recording medium can be improved not by optimizing the composition of the magnetic thin film constituting the magnetic layer, but by laminating a thin film layer (buffer layer) of a different composition above or below the magnetic layer, and have completed the present invention.

[0011] According to the present invention, a Pt-oxide sputtering target is provided, comprising a Pt-based alloy phase of 60 vol% or more and less than 100 vol%, and an oxide of more than 0 vol% and 40 vol% or less, wherein the Pt-based alloy phase contains 50 at% or more and 100 at% or less of Pt.

[0012] Preferably, the Pt-based alloy phase further contains one or more elements selected from Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, and Ge in a total amount of 0 at% to 50 at%.

[0013] The oxide is preferably one or more selected from B2O3, WO3, Nb2O5, SiO2, Ta2O5, TiO2, Al2O3, Y2O3, Cr2O3, ZrO2, and HfO2.

[0014] Also, according to the present invention, there is provided a perpendicular magnetic recording medium including a thin layer of a Pt-based alloy-oxide containing Pt-rich crystallites (Pt-rich buffer layer) laminated on or under a magnetic layer having a granular structure of a CoPt-based alloy-oxide containing Co-rich crystallites. The magnetic layer having the granular structure is composed of a CoPt-based alloy phase of 60 vol% or more and less than 100 vol% and an oxide of more than 0 vol% and 40 vol% or less. The CoPt-based alloy phase of the magnetic layer contains 60 at% or more and 85 at% or less of Co and 15 at% or more and 40 at% or less of Pt. The thin layer of the Pt-based alloy-oxide (Pt-rich buffer layer) is composed of a Pt-based alloy phase of 60 vol% or more and less than 100 vol% and an oxide of more than 0 vol% and 40 vol% or less. The Pt-based alloy phase of the thin layer of the Pt-based alloy-oxide (Pt-rich buffer layer) contains more than 50 at% and 100 at% or less of Pt.

[0015] In the first embodiment of the perpendicular magnetic recording medium of the present invention, the thin layer of the Pt-based alloy-oxide (P-rich buffer layer) is laminated under the magnetic layer having a granular structure of the CoPt-based alloy-oxide, and the thickness of the thin layer of the Pt-based alloy-oxide (P-rich buffer layer) is more than 0 nm and 2 nm or less.

[0016] In the second embodiment of the perpendicular magnetic recording medium of the present invention, the thin layer of the Pt-based alloy-oxide (Pt-rich buffer layer) is laminated on the magnetic layer having a granular structure of the CoPt-based alloy-oxide, and the thickness of the thin layer of the Pt-based alloy-oxide (Pt-rich buffer layer) is more than 0 nm and 4 nm or less.

[0017] In the third embodiment of the perpendicular magnetic recording medium of the present invention, a plurality of combinations of thin layers of the Pt-based alloy-oxide (Pt-rich buffer layer) laminated on the magnetic layer having a granular structure of the CoPt-based alloy-oxide are included, and the total thickness of the thin layers of the Pt-based alloy-oxide (Pt-rich buffer layer) included in the perpendicular magnetic recording medium is more than 0 nm and 4 nm or less.

[0018] Preferably, the Pt-based alloy phase of the thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) further contains one or more elements selected from Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, and Ge in a total amount of 0 at% to 50 at%.

[0019] The thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) preferably contains a total of 0 vol% to 40 vol% of one or more oxides selected from B2O3, WO3, Nb2O5, SiO2, Ta2O5, TiO2, Al2O3, Y2O3, Cr2O3, ZrO2, and HfO2. [Effects of the Invention]

[0020] The perpendicular magnetic recording medium of the present invention includes a thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) laminated above or below a granular magnetic layer of CoPt-based alloy-oxide. Compared to conventional perpendicular magnetic recording media, this allows for better separation of magnetic crystal grains within the granular magnetic layer, resulting in interfacial magnetic anisotropy in the direction perpendicular to the plane. This improves the overall crystalline magnetic anisotropy constant Ku of the magnetic thin film, and consequently, the coercivity Hc also improves. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic vertical cross-sectional view showing the stacking state of the Ru underlayer, Pt-rich thin layer (Pt-rich buffer layer), and Co-rich magnetic layer of the magnetic recording medium of the present invention. [Figure 2] This is a schematic vertical cross-sectional diagram showing the stacking state of the Ru underlayer and CoPt magnetic layer in a conventional magnetic recording medium. [Figure 3-A] This is a schematic diagram showing the stacked structure of magnetic recording medium sample A prepared in Examples 1 to 108. [Figure 3-B] This is a schematic diagram showing the stacked structure of magnetic recording medium sample B prepared in Examples 109-119. [Figure 3-C] This is a schematic diagram showing the stacked structure of magnetic recording medium sample C prepared in Examples 120-122 and Comparative Example 16. [Figure 4]This graph shows the relationship between the film thickness of the Pt-rich thin layer (Pt-rich buffer layer) measured in Examples 1 to 108 and the Kugrain crystal magnetic anisotropy constant of only the magnetic particles in the magnetic recording medium sample. [Figure 5] This graph shows the relationship between the film thickness of the Pt-rich thin layer (Pt-rich buffer layer) measured in Examples 1 to 108 and the coercivity Hc of the magnetic recording medium sample. [Figure 6] This graph shows the relationship between the oxide content of the Pt-rich thin layer (Pt-rich buffer layer) measured in Examples 1 to 108 and the Kugrain crystal magnetic anisotropy constant of only the magnetic particles in the magnetic recording medium sample. [Figure 7] This graph shows the relationship between the film thickness of the Co-rich magnetic layer measured in Examples 1 to 108 and the Kugrain crystal magnetic anisotropy constant of only the magnetic particles in the magnetic recording medium sample. [Figure 8] This graph shows the relationship between the film thickness of the Co-rich magnetic layer measured in Examples 1 to 108 and the coercivity Hc of the magnetic recording medium sample. [Figure 9] This graph shows the relationship between the Co content of the Co-rich magnetic layer measured in Examples 1 to 108 and the Kugrain crystal magnetic anisotropy constant of only the magnetic particles in the magnetic recording medium sample. [Figure 10] This graph shows the relationship between the Co content of the Co-rich magnetic layer measured in Examples 1 to 108 and the coercivity Hc of the magnetic recording medium sample. [Figure 11] This graph shows the relationship between the film thickness of the Pt-rich buffer layer (BL film thickness) measured in Examples 120-122 and Comparative Examples 15-16, and the Kugrain crystal magnetic anisotropy constant of only the magnetic particles in the magnetic recording medium sample. [Figure 12] This graph shows the relationship between the film thickness of the Pt-rich buffer layer (BL film thickness) measured in Examples 120-122 and Comparative Examples 15-16, and the coercivity Hc of the magnetic recording medium samples. [Figure 13]This graph shows the relationship between the total film thickness (total BL film thickness) of the Pt-rich buffer layer measured in Examples 111, 121, 123-130 and Comparative Examples 15 and 17, and the crystal magnetic anisotropy constant Kugrain of only the magnetic particles of the magnetic recording medium sample. [Figure 14] This graph shows the relationship between the total thickness of the Pt-rich buffer layer (total BL thickness) measured in Examples 111, 121, 123-130 and Comparative Examples 15 and 17, and the coercivity Hc of the magnetic recording medium samples. [Modes for carrying out the invention]

[0022] The present invention provides a Pt-oxide sputtering target comprising a Pt-based alloy phase of 60 vol% or more and an oxide of 40 vol% or less. The Pt-oxide sputtering target preferably comprises a Pt-based alloy phase of 65 vol% or more (excluding 100 vol%) and an oxide of 35 vol% or less (excluding 0 vol%), and more preferably comprises a Pt-based alloy phase of 70 vol% to 90 vol% and an oxide of 10 vol% to 30 vol%.

[0023] The Pt-oxide sputtering target of the present invention is characterized in that the Pt-based alloy phase contains 50 at% or more (including 100 at%) of Pt. Preferably, the Pt-based alloy phase contains 60 at% to 100 at% of Pt, and more preferably 70 at% to 100 at% of Pt.

[0024] The Pt-based alloy phase may further contain one or more elements selected from Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, and Ge in a total amount of 50 at% or less (including 0 at%), preferably 0 at% to 40 at% and more preferably 0 at% to 30 at%.

[0025] The following are examples of suitable compositions (at%) for the Pt-based alloy phase. (Pt) (Pt95Si5) (Pt95Ti5) (Pt95Cr5) (Pt95B5) (Pt95V5) (Pt95Nb5) (Pt95Ta5) (Pt95Ru5) (Pt95Mn5) (Pt95Zn5) (Pt95Mo5) (Pt95W5) (Pt95Ge5) (Pt95Ti5) (Pt 9 0Ti10) (Pt80Ti20) (Pt70Ti30) (Pt60Ti40) (Pt50Ti50)

[0026] The oxide used in the Pt-oxide sputtering target of the present invention can preferably be one or more selected from B2O3, WO3, Nb2O5, SiO2, Ta2O5, TiO2, Al2O3, Y2O3, Cr2O3, ZrO2, and HfO2. The oxide content can be 40 vol% or less in total (excluding 0 vol%), preferably 10 vol% to 40 vol%, more preferably 20 vol% to 40 vol%, and particularly preferably 25 vol% to 35 vol%.

[0027] The Pt-oxide sputtering target of the present invention preferably has a microstructure in which the Pt-based alloy phase and oxide are finely dispersed. By finely dispersing the oxide, the particles generated during sputtering can be reduced.

[0028] The Pt-oxide sputtering target of the present invention can be manufactured by preparing a sintering mixture powder by mixing Pt metal powder or atomized powder of a Pt-based alloy with oxide powder using a ball mill, and then performing vacuum pressure sintering at a sintering temperature of 1000°C to 1300°C.

[0029] The Pt-oxide sputtering target of the present invention can be suitably used in the manufacture of perpendicular magnetic recording media. For example, using the Pt-oxide sputtering target of the present invention, a novel perpendicular magnetic recording media can be manufactured by (1) laminating a thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) on a Ru underlayment and then laminating a granular magnetic layer thereon, or (2) laminating a thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) on a granular magnetic layer laminated on a Ru underlayment using the Pt-oxide sputtering target of the present invention, or (3) laminating a thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) on a granular magnetic layer laminated on a Ru underlayment using the Pt-oxide sputtering target of the present invention, then laminating a granular magnetic layer, and then repeatedly laminating another thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) using the Pt-oxide sputtering target of the present invention.

[0030] The perpendicular magnetic recording medium of the present invention is characterized by comprising a thin layer of Pt-based alloy oxide containing Pt-rich crystal grains, which is laminated above or below a magnetic layer having a granular structure of CoPt-based alloy oxide containing Co-rich crystal grains. That is, it is important to laminate Pt-rich crystal grains above or below the magnetic layer containing Co-rich crystal grains. For example, as shown in Figure 1, a thin layer of Pt-based alloy oxide containing Pt-rich crystal grains can be interposed between a base layer containing Ru crystal grains and a magnetic layer containing Co-rich crystal grains. Alternatively, a magnetic layer containing Co-rich crystal grains may be laminated on top of a base layer containing Ru crystal grains, and a thin layer of Pt-based alloy oxide containing Pt-rich crystal grains may be laminated on top of the magnetic layer containing Co-rich crystal grains. Alternatively, a magnetic layer containing Co-rich crystal grains may be laminated on top of a base layer containing Ru crystal grains, a thin layer of Pt-based alloy oxide containing Pt-rich crystal grains may be laminated on top of the magnetic layer containing Co-rich crystal grains, and then another magnetic layer containing Co-rich crystal grains may be laminated. By providing a thin layer of Pt-based alloy oxide containing Pt-rich crystal grains above or below a magnetic layer containing Co-rich crystal grains, as shown in Figure 1, oxides are present between the Co-rich magnetic crystal grains, Pt-rich crystal grains, and Ru crystal grains of the magnetic layer, acting as barriers. This effectively separates these crystal grains, reduces the magnetic interaction between the magnetic crystal grains, and increases the coercivity Hc of the magnetic layer.

[0031] The magnetic layer of the granular structure of the perpendicular magnetic recording medium of the present invention consists of a CoPt-based alloy phase of 60 vol% or more (excluding 100 vol%) and an oxide of 40 vol% or less (excluding 0 vol%). Preferably, the magnetic layer consists of a CoPt-based alloy phase of 60 vol% to 90 vol% and an oxide of 10 vol% to 40 vol%, and more preferably, a CoPt-based alloy phase of 70 vol% to 80 vol% and an oxide of 20 vol% to 30 vol%.

[0032] The CoPt-based alloy phase of the granular magnetic layer consists of Co-rich crystal grains containing 60 at% to 85 at% Co and 15 at% to 40 at% Pt. Co is a ferromagnetic metallic element and plays a central role in the formation of the granular magnetic crystal grains (tiny magnets). Pt has the function of reducing the magnetic moment of the alloy phase and plays a role in adjusting the magnetic strength of the magnetic crystal grains.

[0033] The CoPt-based alloy phase contains 60 at% to 85 at% of Co, preferably 65 at% to 80 at% and more preferably 70 at% to 75 at%, and 15 at% to 40 at% of Pt, preferably 20 at% to 35 at% and more preferably 25 at% to 30 at%. The CoPt-based alloy phase may contain elements other than Co and Pt, as long as they do not impair the magnetic properties. Other elements include Cr, Ru, B, Ti, Si, V, and Nb. 、 Ta 、 Mn, Zn, Mo, W, and Ge are suitable examples. The content of other elements can be 0 at% to 20 at% in total, preferably 5 at% to 15 at% and more preferably 5 at% to 10 at%.

[0034] The following compositions (at%) are examples of suitable CoPt-based alloy phases. (Co80Pt20) (Co85Pt15) (Co70Pt30) (Co60Pt40) (Co75Pt20Cr5) (Co75Pt20B5) (Co75Pt20Ru5) (Co75Pt20Ti5)

[0035] The oxide in the granular magnetic layer exists between Co-rich crystal grains, acting as a barrier separating them. Suitable oxides include at least one or any combination selected from B2O3, WO3, Nb2O5, SiO2, Ta2O5, TiO2, Cr2O3, GeO2, Al2O3, Y2O3, ZrO2, HfO2, and CoO. The total oxide content can be 40 vol% or less (excluding 0 vol%), preferably 5 vol% to 40 vol%, and more preferably 10 vol% to 35 vol%.

[0036] A thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) laminated above or below a Co-rich magnetic layer consists of a Pt-based alloy phase of 60 vol% or more and less than 100 vol%, and an oxide of more than 0 vol% and 40 vol% or less. Preferably, the thin layer of Pt-based alloy-oxide consists of a Pt-based alloy phase of 65 vol% or more (excluding 100 vol%) and an oxide of 35 vol% or less (excluding 0 vol%), and more preferably consists of a Pt-based alloy phase of 70 vol% or more and 90 vol% or less and an oxide of 10 vol% or more and 30 vol% or less.

[0037] The Pt-based alloy phase of the Pt-based alloy-oxide thin layer (Pt-rich buffer layer) is a Pt-rich crystal grain containing 50 at% to 100 at% of Pt. Including 50 at% or more of Pt can improve the crystal magnetic anisotropy constant Ku. The Pt-based alloy phase preferably contains 60 at% to 100 at% of Pt, and more preferably contains 70 at% to 100 at% of Pt. The Pt-based alloy phase may contain elements other than Pt, as long as it does not interfere with the magnetic properties of the Co-rich magnetic layer. Suitable other elements include one or more selected from Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, and Ge. The total content of other elements can be 50 at% or less (including 0 at%), preferably 0 at% to 40 at%, and more preferably 0 at% to 30 at%.

[0038] The following are examples of suitable compositions (at%) for the Pt-based alloy phase in a thin layer of Pt-based alloy-oxide (Pt-rich buffer layer). (Pt) (Pt95Si5) (Pt95Ti5) (Pt95Cr5) (Pt95B5) (Pt95V5) (Pt95Nb5) (Pt95Ta5) (Pt95Ru5) (Pt95Mn5) (Pt95Zn5) (Pt95Mo5) (Pt95W5) (Pt95Ge5) (Pt95Ti5) (Pt 9 0Ti10) (Pt80Ti20) (Pt70Ti30) (Pt60Ti40) (Pt50Ti50)

[0039] The oxide of the thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) laminated above or below the Co-rich magnetic layer can preferably be one or more selected from B2O3, WO3, Nb2O5, SiO2, Ta2O5, TiO2, Al2O3, Y2O3, Cr2O3, ZrO2, and HfO2. The oxide content can be 40 vol% or less in total (excluding 0 vol%), preferably 10 vol% to 40 vol%, more preferably 20 vol% to 40 vol%, and particularly preferably 25 vol% to 35 vol%. By setting the oxide content within the above range, the crystalline magnetic anisotropy constant Ku of the magnetic recording medium can be increased (see the examples described later).

[0040] The thickness of the thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) laminated beneath the Co-rich magnetic layer is greater than 0 nm and less than or equal to 2 nm. Our research has shown that the thickness of the thin layer of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layer) affects the crystalline magnetic anisotropy constant Ku and coercivity Hc of the magnetic recording medium, that the crystalline magnetic anisotropy constant Ku is maximized at a thickness of 0.6 nm, and that the coercivity Hc is maximized at a thickness of 1.0 nm (see the examples described later). Therefore, in order to produce a magnetic recording medium with high crystalline magnetic anisotropy constant Ku and coercivity Hc, the thickness of the thin layer of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layer) is greater than 0 nm and less than or equal to 2 nm, preferably between 0.5 nm and 1.5 nm, and more preferably between 0.8 nm and 1.2 nm.

[0041] The thickness of the thin layer of Pt-based alloy-oxide (Pt-rich buffer layer) laminated on the Co-rich magnetic layer is greater than 0 nm and less than or equal to 4 nm. Our research has shown that the thickness of the thin layer of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layer) affects the crystalline magnetic anisotropy constant Ku and coercivity Hc of the magnetic recording medium, that the crystalline magnetic anisotropy constant Ku is maximized at a thickness of 0.9 to 1.3 nm, and that the coercivity Hc is maximized at a thickness of 2.6 nm (see the examples described later). Therefore, in order to produce a magnetic recording medium with high crystalline magnetic anisotropy constant Ku and coercivity Hc, the thickness of the thin layer of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layer) is greater than 0 nm and less than or equal to 4 nm, preferably 0.4 nm to 3 nm, and more preferably 0.8 nm to 2.6 nm.

[0042] When multiple combinations of thin layers of Pt-based alloy-oxide (Pt-rich buffer layers) are laminated on a Co-rich magnetic layer, the total thickness of the thin layers of Pt-based alloy-oxide (Pt-rich buffer layers) is greater than 0 nm and less than or equal to 4 nm. Our research has shown that the total thickness of the thin layers of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layers) affects the crystalline magnetic anisotropy constant Ku and coercivity Hc of the magnetic recording medium, that the crystalline magnetic anisotropy constant Ku improves with a total film thickness of 0.4 to 4 nm, that the crystalline magnetic anisotropy constant Ku is maximized with a total film thickness of 1.6 nm (= 0.4 nm × 4 layers), and that the coercivity Hc is maximized with a total film thickness of 0.4 nm (see the examples described later). Therefore, in order to produce a magnetic recording medium with high crystal magnetic anisotropy constant Ku and coercivity Hc, the total thickness of the thin layer of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layer) is greater than 0 nm and less than or equal to 4 nm, preferably between 0.4 nm (=0.2 nm × 2 layers) and 4 nm (=0.4 nm × 10 layers), more preferably between 0.8 nm (=0.2 nm × 4 layers or 0.4 nm × 2 layers) and 3.2 nm (=0.32 nm × 10 layers or 0.4 nm × 8 layers), and particularly preferably between 1 nm and 3 nm. If the total thickness of the thin layer of Pt-rich Pt-based alloy-oxide (Pt-rich buffer layer) is greater than 0 nm and less than or equal to 4 nm, the number of layers is not limited, but the number of layers is preferably between 1 and 10, and more preferably between 1 and 8.

[0043] The underlying layer of the perpendicular magnetic recording medium of the present invention is not particularly limited, but it is preferably a Ru underlying layer made of a Ru-based alloy phase-oxide. For example, Ru-SiO2, Ru-TiO2, Ru-Ta2O5, Ru-B2O3, Ru-WO3, Ru-Nb2O5, Ru-MoO3, Ru-SnO, Ru-Cr2O3, RuCo-SiO2, RuCo-TiO2, RuCo-Ta2O5, RuCo-B2O3, RuCo-WO3, RuCo-Nb2O5, RuCo-MoO3, RuCo-SnO, RuCo-Cr2O3, RuCoCr-SiO2, RuCo Cr-TiO2, RuCoCr-Ta2O5, RuCoCr-B2O3, RuCoCr-WO3, RuCoCr-Nb2O5, RuCoCr-MoO3, RuCoCr-SnO, RuCoCr-Cr2O3, RuTi-TiO2, RuTa-Ta2O5, RuB-B2O3, RuW-WO3, RuNb-Nb2O5, RuMo-MoO3, RuSn-SnO, and RuCr-Cr2O3 are preferred examples.

[0044] The Pt-rich Pt-based alloy-oxide thin layer (Pt-rich buffer layer) of the perpendicular magnetic recording medium of the present invention can be formed by repeatedly performing the following actions: (1) stacking a Ru underlayer and then stacking it using a Pt-based alloy-oxide sputtering target; (2) stacking a Ru underlayer and a Co-rich magnetic layer and then stacking them using a Pt-based alloy-oxide sputtering target; or (3) stacking a Ru underlayer and a Co-rich magnetic layer and then stacking them using a Pt-based alloy-oxide sputtering target, followed by stacking a Co-rich magnetic layer on top of the Pt-rich buffer layer using a Co-rich sputtering target, and then stacking the Co-rich magnetic layer on top of the Co-rich magnetic layer using a Pt-based alloy-oxide sputtering target. [Examples]

[0045] The present invention will be described in more detail below using examples and comparative examples.

[0046] [Fabrication of sputtering targets] Pt powder or atomized powder of Pt alloy (hereinafter abbreviated as "Pt-containing powder") was classified by sieving to obtain Pt-containing powder with a particle size of 100 μm or less. The Pt-containing powder and oxide powder were mixed in a ball mill to obtain a mixed powder for pressure sintering so that the target composition shown in "Composition of Pt-rich layer" in the Examples and Comparative Examples below would be obtained.

[0047] Sintering temperature: 1000°C to 1300°C, Sintering pressure: 25 MPa, Sintering time: 60 minutes, Sintering atmosphere: 5 × 10 -2 A sintered body was obtained by hot-pressing a mixed powder for pressure sintering under vacuum conditions of Pa or less. The sintered body was then shaped using a lathe or surface grinder to produce a sputtering target with a diameter of 161.0 mm and a thickness of 4.0 mm.

[0048] The raw material powders used in preparing the Pt-containing powder are as follows: Pt metal powder: PtSi atomized powder: PtTi atomized powder: PtCr atomized powder: PtB Atomized Powder: PtV Atomized Powder: PtNb atomized powder: PtTa Atomized Powder: PtRu atomized powder: PtMn atomized powder: PtZn atomized powder: PtMo atomized powder: PtW Atomized Powder: PtGe atomized powder:

[0049] [Preparation of magnetic recording medium sample A] Using the fabricated sputtering target, sputtering was performed with a DC sputtering apparatus to deposit a thin layer of Pt-based alloy oxide (Pt-rich buffer layer) with the composition shown in the Examples and Comparative Examples below onto the Ru underlayer to the thickness shown in the Examples and Comparative Examples. Then, a Co-rich magnetic layer of CoPt-based alloy oxide with the composition shown in the Examples and Comparative Examples was deposited on top of the Pt-rich buffer layer to the thickness shown in the Examples and Comparative Examples to prepare sample A of the magnetic recording medium.

[0050] As shown in Figure 3-A, sample A of the magnetic recording medium was constructed by laminating the following layers on a glass substrate in the following order: Ta layer (5 nm, 0.6 Pa), Ni90W10 seed layer (6 nm, 0.6 Pa), Ru underlayer 1 (10 nm, 0.6 Pa), Ru underlayer 2 (10 nm, 8.0 Pa), Pt-rich layer (0-2.5 nm, 4 Pa), Co-rich magnetic layer (0.5-16 nm, 4 Pa), and C surface protection layer (7 nm, 0.6 Pa). Here, the numbers in parentheses indicate the film thickness (nm) and the Ar atmosphere pressure (Pa) during sputtering. Ru underlayer 2 is a layer that is laminated to form a surface uneven shape. The Pt-rich layer and Co-rich magnetic layer were deposited at room temperature without raising the temperature of the substrate.

[0051] [Preparation of magnetic recording medium sample B] Using the fabricated sputtering target, sputtering was performed with a DC sputtering apparatus to prepare sample B of the magnetic recording medium. A Co-rich magnetic layer of CoPt-based alloy oxide with the composition shown in the Examples and Comparative Examples below was laminated on the Ru underlayer to the thickness shown in the Examples and Comparative Examples. A thin layer of Pt-based alloy oxide (Pt-rich buffer layer) with the composition shown in the Examples and Comparative Examples was then laminated on the Co-rich magnetic layer to the thickness shown in the Examples and Comparative Examples.

[0052] As shown in Figure 3-B, sample B of the magnetic recording medium is constructed by laminating the following layers on a glass substrate in the following order: Ta layer (5 nm, 0.6 Pa), Ni90W10 seed layer (6 nm, 0.6 Pa), Ru underlayer 1 (10 nm, 0.6 Pa), Ru underlayer 2 (10 nm, 8.0 Pa), Co-rich magnetic layer (0.5-16 nm, 4 Pa), Pt-rich layer (0-2.6 nm, 4 Pa), and C surface protection layer (7 nm, 0.6 Pa). Here, the numbers in parentheses indicate the film thickness (nm) and the Ar atmosphere pressure (Pa) during sputtering. Ru underlayer 2 is a layer that is laminated to form a surface uneven shape. The Pt-rich layer and Co-rich magnetic layer were deposited at room temperature without raising the temperature of the substrate.

[0053] [Preparation of magnetic recording medium sample C] Using the fabricated sputtering target, sputtering was performed with a DC sputtering apparatus to deposit a Co-rich magnetic layer of CoPt-based alloy oxide with the composition shown in the Examples and Comparative Examples below onto a Ru underlayer to the thickness shown in the Examples and Comparative Examples. Then, a thin layer of Pt-based alloy oxide (Pt-rich buffer layer) with the composition shown in the Examples and Comparative Examples was deposited on top of the Co-rich magnetic layer to the thickness shown in the Examples and Comparative Examples. Subsequently, the depositing of the Co-rich magnetic layer and the Pt-rich buffer layer was repeated three times in the above order to prepare sample C of the magnetic recording medium.

[0054] As shown in Figure 3-C, sample C of the magnetic recording medium is constructed by laminating the following layers on a glass substrate in the following order: Ta layer (5nm, 0.6Pa), Ni90W10 seed layer (6nm, 0.6Pa), Ru underlayer 1 (10nm, 0.6Pa), Ru underlayer 2 (10nm, 8.0Pa), Co-rich magnetic layer 1 (4nm, 4Pa), Pt-rich layer 1 (0-0.8nm, 4Pa), Co-rich magnetic layer 2 (4nm, 4Pa), Pt-rich layer 2 (0-0.8nm, 4Pa), Co-rich magnetic layer 3 (4nm, 4Pa), Pt-rich layer 3 (0-0.8nm, 4Pa), Co-rich magnetic layer 4 (4nm, 4Pa), Pt-rich layer 4 (0-0.8nm, 4Pa), and C surface protective layer (7nm, 0.6Pa). Here, the numbers in parentheses indicate the film thickness (nm) and the Ar atmosphere pressure (Pa) during sputtering. Ru underlayer 2 is a layer that is laminated to form a surface uneven shape. The Pt-rich layer and Co-rich magnetic layer were deposited at room temperature without raising the temperature of the substrate.

[0055] Of the magnetic properties of the magnetic recording medium samples, the coercivity Hc was measured using a vibrating sample magnetometer (VSM: Tamagawa Seisakusho Co., Ltd., model TM-VSM211483-HGC), and the crystalline magnetic anisotropy constant Ku was measured using a torque magnetometer (Tamagawa Seisakusho Co., Ltd., model TM-TR2050-HGC).

[0056] [Film thickness and magnetic properties of Pt-rich buffer layer (1)] In Comparative Examples 1-2 and Examples 1-9, the magnetic properties were investigated by varying the film thickness of the Pt-rich buffer layer from 0 nm to 2.5 nm.

[0057] The Pt-rich buffer layer was made of Pt-30vol%TiO2, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 1 and Figures 4-5. In the table and figures, Ku grain indicates the crystal magnetic anisotropy constant (Ku) of each magnetic crystal grain.

[0058] [Table 1]

[0059] Based on Comparative Example 1 without a Pt-rich buffer layer, it was confirmed that when the film thickness of the Pt-rich buffer layer was 0.1 nm or more and 2.0 nm or less, both the crystalline magnetic anisotropy constant Kugrain and the coercive force Hc increased, and when it reached 2.5 nm, it returned to the same level as Comparative Example 1. For the crystalline magnetic anisotropy constant Kugrain, it was the highest at 1.38×10 7 erg / cm 3 when the film thickness was 0.6 nm, and it was 1.30×10 7 erg / cm 3 or higher in the range of 0.1 nm to 1.5 nm in film thickness. For the coercive force Hc, it was the highest at 9.94 kOe when the film thickness was 1.0 nm, and it was 9.39 kOe or higher in the range of 0.4 nm to 1.5 nm in film thickness.

[0060] [Film Thickness of Pt-rich Buffer Layer and Magnetic Properties (2)] In Comparative Examples 1, 3 and Examples 10 to 18, the magnetic properties were examined by changing the film thickness of the Pt-rich buffer layer from 0 nm to 2.5 nm.

[0061] The Pt-rich buffer layer was Pt-30vol%SiO2, and the Co-rich magnetic layer was Co80Pt20-30vol%B2O3 with a film thickness of 16 nm. The results are shown in Table 2 and Figures 4 to 5.

[0062]

Table 2

[0063] Based on Comparative Example 1 without a Pt-rich buffer layer, it was confirmed that when the film thickness of the Pt-rich buffer layer was 0.1 nm or more and 2.0 nm or less, both the crystalline magnetic anisotropy constant Kugrain and the coercive force Hc increased, and when it reached 2.5 nm, it returned to the same level as Comparative Example 1. For the crystalline magnetic anisotropy constant Kugrain, it was the highest at 1.38×10 7 erg / cm 3 when the film thickness was 1.0 nm, and it was 1.30×10 7 erg / cm 3As you can see, the values ​​are high. Regarding coercivity (Hc), it is highest at 9.35 kOe when the film thickness is 1.0 nm, and remains high at 8.90 kOe or higher in the range of film thicknesses between 0.4 nm and 1.5 nm.

[0064] Furthermore, as shown in Figures 4-5, regardless of the type of oxide, both the crystal magnetic anisotropy constant Kugrain and the coercivity Hc increase compared to Comparative Example 1 in the range where the film thickness of the Pt-rich buffer layer is greater than 0 nm and less than or equal to 2 nm.

[0065] [Oxide (TiO2) content and magnetic properties of Pt-rich buffer layer] In Comparative Examples 4-6 and Examples 19-25, the magnetic properties were investigated by varying the oxide (TiO2) content of the Pt-rich layer from 0 vol% to 45 vol%.

[0066] The Pt-rich buffer layer was made of Pt-TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 3 and Figure 6.

[0067] [Table 3]

[0068] Using Comparative Example 4, in which the Pt-rich buffer layer does not contain oxides, as a reference, when the oxide content of the Pt-rich buffer layer is between 10 vol% and 40 vol%, both the crystal magnetic anisotropy constant Kugrain and the coercivity Hc increase, and when it reaches 45 vol%, the comparative example... 4 It was confirmed that it returned to a similar level. For the crystal magnetic anisotropy constant Kugrain, it was 1.35 × 10 in the range of oxide content between 15 vol% and 40 vol%. 7 erg / cm 3 The above is 1.38 × 10 7 erg / cm 3 The following results show that the coercivity (Hc) is very high. The highest coercivity (Hc) is 10.1 kOe when the oxide content is 35 vol%, and it remains high at 8.95 kOe or higher in the oxide content range of 15 vol% to 40 vol%.

[0069] Furthermore, as shown in Figure 6, it can be seen that, regardless of the type of oxide, both the crystal magnetic anisotropy constant Kugrain and the coercivity Hc increase when the oxide content is between 10 vol% and 40 vol%.

[0070] [Oxide (SiO2) content and magnetic properties of Pt-rich buffer layer] In Comparative Examples 4, 7-8, and Examples 26-32, the magnetic properties were investigated by varying the oxide (SiO2) content of the Pt-rich buffer layer from 0 vol% to 45 vol%.

[0071] The Pt-rich buffer layer was made of Pt-SiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 4 and Figure 6.

[0072] [Table 4]

[0073] Compared to Comparative Example 4, in which the Pt-rich buffer layer does not contain oxides, it was confirmed that both the crystal magnetic anisotropy constant Kurain and the coercivity Hc increase when the oxide content of the Pt-rich buffer layer is between 10 vol% and 40 vol%, and return to the same level as Comparative Example 1 when it reaches 45 vol%. For the crystal magnetic anisotropy constant Kurain, it was 1.34 × 10⁻¹⁴ in the range of oxide content between 15 vol% and 40 vol%. 7 erg / cm 3 The above is 1.38 × 10 7 erg / cm 3 The following results show that the coercivity (Hc) is very high. The highest coercivity (Hc) is 9.55 kOe when the oxide content is 35 vol%, and it remains high at 8.95 kOe or higher in the oxide content range of 15 vol% to 40 vol%.

[0074] [Oxide types and magnetic properties of Pt-rich buffer layers] Comparative Example 1 and Example 33~ 5In experiment 3, the magnetic properties were investigated by changing the oxide of the Pt-rich buffer layer.

[0075] The Pt-rich buffer layer was made with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 5.

[0076] [Table 5]

[0077] Compared to Comparative Example 1, which does not have a Pt-rich buffer layer, it was confirmed that Examples 33 to 53, which have a Pt-rich buffer layer, all exhibited high crystal magnetic anisotropy constants (Kugrain) and coercivity (Hc), regardless of the type of oxide or whether they contained multiple oxides.

[0078] [Types of additional elements and magnetic properties of the Pt-rich buffer layer] Comparative Example 1 and Examples 54-66 investigated the magnetic properties by changing the additional elements in the Pt-based alloy of the Pt-rich buffer layer.

[0079] The Pt-rich buffer layer was made of Pt95M5-30vol%TiO2 (where M indicates an additional element) with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 6.

[0080] [Table 6]

[0081] Compared to Comparative Example 1, which does not have a Pt-rich buffer layer, it was confirmed that Examples 54 to 66, which have a Pt-rich buffer layer, all have high crystal magnetic anisotropy constants (Kugrain) and coercivity (Hc), regardless of the type of additional element.

[0082] [Pt content and magnetic properties of Pt-rich buffer layers] Comparative Examples 1 and 9 and Examples 67 to 73 investigated the magnetic properties by varying the Pt content of the Pt-rich buffer layer.

[0083] The Pt-rich buffer layer was made of PtTi-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 7.

[0084] [Table 7]

[0085] Compared to Comparative Example 1, which did not have a Pt-rich buffer layer, it was confirmed that the higher the Pt content of the Pt-rich buffer layer, the higher the crystal magnetic anisotropy constant Kugrain and coercivity Hc. Comparative Example 9, with a Pt content of 45 at%, showed values ​​similar to those of Comparative Example 1.

[0086] [Co-rich magnetic layer thickness and magnetic properties] Examples 74-78 investigated the film thickness and magnetic properties of the Co-rich magnetic layer.

[0087] The Pt-rich buffer layer was made of Pt-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3. The results are shown in Table 8, Figure 7, and Figure 8.

[0088] [Table 8]

[0089] It was confirmed that as the thickness of the Co-rich magnetic layer increases, the crystal magnetic anisotropy constant Kugrain decreases slightly, but the coercivity Hc increases.

[0090] [Oxide content and magnetic properties of Co-rich magnetic layers] Comparative Examples 10-11 and Examples 79-82 investigated the oxide content and magnetic properties of the Co-rich magnetic layer.

[0091] The Pt-rich buffer layer was made of Pt-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-B2O3 with a thickness of 16 nm. The results are shown in Table 9.

[0092] [Table 9]

[0093] It was confirmed that in the Co-rich magnetic layer, within the range of 10 vol% to 40 vol%, the crystal magnetic anisotropy constant Kugrain decreased as the oxide content increased, but the coercivity Hc increased. At an oxide content of 45 vol%, the coercivity Hc was high, but the crystal magnetic anisotropy constant Kugrain was about the same as in Comparative Example 10, which did not contain oxides.

[0094] [Types of oxides and magnetic properties of Co-rich magnetic layers] Examples 83 to 99 investigated the type of oxide and magnetic properties of the Co-rich magnetic layer.

[0095] The Pt-rich buffer layer was made of Pt-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of Co80Pt20-30vol%XO (where XO indicates an oxide) with a thickness of 16 nm. The results are shown in Table 10.

[0096] [Table 10]

[0097] It was confirmed that the crystal magnetic anisotropy constant Kugrain and coercivity Hc were high in all cases, regardless of the type of oxide in the Co-rich magnetic layer, and even when multiple oxides were present.

[0098] [Co content and magnetic properties of Co-rich magnetic layers] Comparative Examples 12-14 and Examples 100-103 investigated the Co content and magnetic properties of the Co-rich magnetic layer.

[0099] The Pt-rich buffer layer was made of Pt-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of CoPt-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 11, Figure 9, and Figure 10.

[0100] [Table 11]

[0101] In the Co-rich magnetic layer, the crystal magnetic anisotropy constant Kugrain is 1.25 × 10⁻¹⁰ in the range of Co content between 60 at% and 85 at%. 7 erg / cm 3 The coercivity was confirmed to be high, exceeding Hc8.72kOe.

[0102] [Types of additional elements and magnetic properties of the Co-rich magnetic layer] Examples 104-107 investigated the types of additional elements and their magnetic properties in the Co-rich magnetic layer.

[0103] The Pt-rich layer was made of Pt-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of CoPtM-30vol%B2O3 (where M represents an additional element) with a thickness of 16 nm. The results are shown in Table 12.

[0104] [Table 12]

[0105] Regardless of the type of additional element in the Co-rich magnetic layer, it was confirmed that both the crystal magnetic anisotropy constant (Kugrain) and coercivity (Hc) were high in all cases.

[0106] [Stacking position and magnetic properties of Pt-rich buffer layers] Comparative Example 1 and Examples 108-109 investigated the stacking position and magnetic properties of the Pt-rich buffer layer.

[0107] The Pt-rich buffer layer was made of Pt-30vol%TiO2 with a thickness of 1.0 nm, and the Co-rich magnetic layer was made of CoPt-30vol%B2O3 with a thickness of 16 nm. The results are shown in Table 13.

[0108] [Table 13]

[0109] Compared to Comparative Example 1, which did not have a Pt-rich buffer layer, it was confirmed that both the crystal magnetic anisotropy constant Kugrain and coercivity Hc were high whether the Pt-rich buffer layer was stacked below or above the Co-rich magnetic layer, the crystal magnetic anisotropy constant Kugrain was the same value in both cases, and the coercivity Hc was higher when the layer was stacked below the Co-rich magnetic layer.

[0110] [Stacking position, film thickness, and magnetic properties of Pt-rich buffer layers] Comparative Examples 15 and 16, and Examples 110 to 122, investigated the stacking position, film thickness, and magnetic properties of the Pt-rich buffer layer.

[0111] The Pt-rich buffer layer was made of Pt-30vol%SiO2, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3. The thickness of the Co-rich magnetic layer in Examples 110-119 was 16 nm, and the thickness of the Co-rich magnetic layer in Examples 120-122 and Comparative Examples 15-16 was 4 nm for each layer, totaling 16 nm. The results are shown in Table 14. Furthermore, the relationship between the thickness of the Pt-rich buffer layer and Kugrain and Hc in Examples 120-122 and Comparative Example 16, in which the Pt-rich buffer layer was laminated between the Co-rich magnetic layers, is shown in Figures 11 and 12, respectively.

[0112] [Table 14]

[0113] Compared to Comparative Example 15, which does not have a Pt-rich buffer layer, both the crystal magnetic anisotropy constant Kugrain and the coercivity Hc are high whether the Pt-rich buffer layer is stacked on top of or between the Co-rich magnetic layers. This was confirmed. Also, when a Pt-rich buffer layer is stacked on top of a Co-rich magnetic layer... It was confirmed that the crystal magnetic anisotropy constant Kugrain was almost the same in all cases. The coercivity Hc increased as the thickness of the Pt-rich buffer layer increased, and it was confirmed that for the same thickness, stacking the Pt-rich buffer layer on top of the Co-rich magnetic layer resulted in a higher coercivity than stacking it between the Co-rich magnetic layers.

[0114] [Film thickness and magnetic properties of Co-rich magnetic layers] Comparative Examples 15 and 17, and Examples 111, 121, 123-130, were conducted by repeatedly stacking Pt-rich buffer layers on top of Co-rich magnetic layers, with each Pt-rich buffer layer having a thickness of 0.4 nm. The magnetic properties were investigated by varying the thickness of each of the multiple Co-rich magnetic layers and the number of stacking cycles between the Co-rich magnetic layer and the Pt-rich buffer layer.

[0115] The Pt-rich buffer layer was made of Pt-30vol%SiO2, and the Co-rich magnetic layer was made of Co80Pt20-30vol%B2O3. The results are shown in Table 15. buffer The relationship between the total thickness of the layer and Kugrin, and the relationship with Hc, are shown in Figures 13 and 14, respectively.

[0116] [Table 15]

[0117] Compared to Comparative Example 15, which does not have a Pt-rich buffer layer, the crystal magnetic anisotropy constant Kugrain and coercivity Hc both increase with repeated stacking of the Co-rich magnetic layer and the Pt-rich buffer layer. However, it was confirmed that when the stacking of the Co-rich magnetic layer and the Pt-rich buffer layer is repeated 11 times, and the total thickness of the Co-rich magnetic layer and the Pt-rich buffer layer exceeds 20 nm, and the total thickness of the Pt-rich buffer layer exceeds 4 nm, both the crystal magnetic anisotropy constant Kugrain and coercivity Hc decrease.

Claims

1. A Pt-oxide sputtering target comprising a Pt-based alloy phase of 60 vol% or more and less than 100 vol%, and an oxide of more than 0 vol% and 40 vol% or less, A Pt-oxide sputtering target characterized in that the Pt-based alloy phase contains Pt in an amount of 50 at% or more and less than 100 at%, and one or more elements selected from Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, and Ge in a total amount exceeding 0 at% but not exceeding 50 at%, and the total amount with Pt is 100 at%.

2. The oxide is B ２ O ３ 、WO ３ 、Nb ２ O ５ 、SiO ２ 、Ta ２ O ５ 、TiO ２ 、Al ２ O ３ 、Y ２ O ３ 、Cr ２ O ３ 、ZrO ２ 、HfO ２ The Pt-oxide-based sputtering target according to claim 1, which is one or more selected from the above.

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