SPUTTERING TARGET FOR HEAT-ASSISTED MAGNETIC RECORDING MEDIUM

Abstract

Provided is a sputtering target to be used for forming a granular magnetic thin film in which FePt magnetic grains are isolated by an oxide and which constitutes a heat-assisted magnetic recording medium having enhanced uniaxial magnetic anisotropy, thermal stability, and SNR (signal-to-noise ratio).

The sputtering target for a heat-assisted magnetic recording medium contains an FePt alloy and a nonmagnetic material as main components, where the nonmagnetic material is an oxide having a melting point of 800° C. or higher and 1100° C. or lower.

Claims

1. A sputtering target for a heat-assisted magnetic recording medium, wherein the sputtering target comprises an FePt alloy, a nonmagnetic material, and incidental impurities, wherein the nonmagnetic material is an oxide having a melting point of 800° C. or higher and 1100° C. or lower.

2. The sputtering target for a heat-assisted magnetic recording

1. according to claim 1, wherein the sputtering target further comprises one or more elements selected from Ag, Au, and Cu.

3. The sputtering target for a heat-assisted magnetic recording medium according to claim 1, wherein the nonmagnetic material is one or more oxides selected from SnO, PbO, and Bi.sub.2O.sub.3.

4. The sputtering target for a heat-assisted magnetic recording medium according to claim 1, comprising, relative to the sputtering target for a heat-assisted magnetic recording medium, 25 vol % or more and 40 vol % or less of the nonmagnetic material.

5. The sputtering target for a heat-assisted magnetic recording medium according to claim 2, wherein the nonmagnetic material is one or more oxides selected from SnO, PbO, and Bi.sub.2O.sub.3.

6. The sputtering target for a heat-assisted magnetic recording medium according to claim 2, comprising, relative to the sputtering target for a heat-assisted magnetic recording medium, 25 vol % or more and 40 vol % or less of the nonmagnetic material.

7. The sputtering target for a heat-assisted magnetic recording medium according to claim 3, comprising, relative to the sputtering target for a heat-assisted magnetic recording medium, 25 vol % or more and 40 vol % or less of the nonmagnetic material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] FIG. 1 shows magnetization curves of FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0040] FIG. 2 is a graph showing the relationship between the magnetocrystalline anisotropy (K.sub.u.sup.grain) and the melting point of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0041] FIG. 3 is a graph showing the relationship between the saturation magnetization (M.sub.s.sup.grain) and the melting point of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0042] FIG. 4 is a graph showing the relationship between the coercivity (H.sub.e) and the melting point of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0043] FIG. 5 shows X-ray diffraction profiles in which the crystal orientation of perpendicular and parallel components of some heat-assisted FePt granular magnetic recording media is measured by X-ray diffraction.

[0044] FIG. 6 is a graph showing the relationship between the degree of order (S.sub.in) and the melting point of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0045] FIG. 7 is a graph showing the relationship between the grain diameter (GD) and the melting point of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0046] FIG. 8 is a graph showing the relationship between the degree of order (S.sub.in) and the grain diameter (GD) of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0047] FIG. 9 is a graph showing the relationship between the coercivity (H.sub.e) and the grain diameter (GD) of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0048] FIG. 10 is a graph showing the relationship between the coercivity (H.sub.e) and the degree of order (S.sub.in) of each nonmagnetic material for the FePt granular magnetic recording media having an FePt-30 vol % X (X is a nonmagnetic material) magnetic film.

[0049] FIG. 11 is a graph showing the relationship between the magnetocrystalline anisotropy (K.sub.u.sup.grain) and the nonmagnetic material content for FePt granular magnetic recording media having an FePt-SnO magnetic film.

[0050] FIG. 12 is a graph showing the relationship between the saturation magnetization (M.sub.s.sup.grain) and the nonmagnetic material content for the FePt granular magnetic recording media having an FePt-SnO magnetic film.

[0051] FIG. 13 is a graph showing the relationship between the coercivity (H.sub.e) and the nonmagnetic material content for the FePt granular magnetic recording media having an FePt-SnO magnetic film.

EXAMPLES

[0052] Hereinafter, the present invention will be described specifically, but the present invention is by no means limited thereto.

Example 1

[0053] Targets of FePt-30 vol % X (X is a nonmagnetic material) were produced through mixing with 30 vol % of the respective nonmagnetic materials shown in Table 1.

[0054] First, a 50Fe-50Pt alloy atomized powder was prepared. Specifically, the 50Fe-50Pt alloy atomized powder was prepared by weighing each metal to satisfy the composition of 50 at % of Fe and 50 at % of Pt and by heating both the metals to 1,500° C. or higher to form a molten alloy, followed by gas atomization.

[0055] The prepared 50Fe-50Pt alloy atomized powder was classified through a 150 mesh sieve to obtain a 50Fe-50Pt alloy atomized powder having a particle size of 106 μm or less.

[0056] To satisfy the composition of (50Fe-50Pt)-30 vol % X (X is each nonmagnetic material shown in Table 1), each nonmagnetic material powder as X shown in Table 1 was added to the classified 50Fe-50Pt alloy atomized powder and mixed/dispersed in a ball mill to yield 16 mixed powders for pressure sintering, each containing a different nonmagnetic material.

[0057] Subsequently, each prepared mixed powder for pressure sintering was hot-pressed under vacuum conditions to yield a sintered body. For example, a stepped target of (50Fe-50Pt)-30 vol % SnO having a diameter of 153.0×1.0 mm (upper level) +a diameter of 161.0×4.0 mm (lower level) was produced using SnO as a nonmagnetic material X by hot pressing under vacuum conditions of a sintering temperature of 960° C., a sintering pressure of 24.5 MPa, a sintering time of 60 minutes, and an atmosphere of 5×10′ Pa or lower. The produced target had a relative density of 96.5%. For other nonmagnetic materials, sintered bodies were prepared under the conditions shown in Table 2 to produce the respective targets.

[0058] Sputtering was performed using the produced target in a DC sputtering apparatus (from Canon Anelva Corporation) to form a magnetic thin film of (50Fe-50Pt)-30 vol % X on a glass substrate, thereby preparing a sample for magnetic characteristics measurement and a sample for structure observation. Specifically, each heat-assisted FePt granular magnetic recording medium was obtained by depositing a CoW seed layer at a thickness of 80 nm on a glass substrate by DC sputtering (1.5 kW, 0.6 Pa), depositing a MgO underlayer at a thickness of 5 nm on the CoW seed layer by RF magnetron sputtering (0.5 kW, 4.0 Pa), depositing an FePt-30 vol % X (X is each nonmagnetic material shown in Table 1) magnetic film at a thickness of 10 nm on the MgO underlayer by DC sputtering (0.1 kW, 8.0 Pa, Ar gas), and depositing a C surface protective layer at a thickness of 7 nm on the magnetic film by DC sputtering (0.3 kW, 0.6 Pa). The magnetic characteristics (magnetocrystalline anisotropy and saturation magnetization) were measured using a SQUID-VSM (max. 7 T) and a PPMS torque magnetometer (max. 9 T). The measured results are shown in Table 1, and the magnetization curve is shown in FIG. 1. Moreover, the relationships between the melting point of each nonmagnetic material and the respective magnetocrystalline anisotropy (K.sub.u.sup.grain) saturation magnetization (M.sub.s.sup.grain), .sub.and coercivity (H.sub.c) for heat-assisted FePt granular magnetic recording media are plotted and shown in FIGS. 2, 3, and 4. Further, FIG. 5 shows the crystal orientation of perpendicular and parallel components of some heat-assisted FePt granular magnetic recording media measured by X-ray diffraction.

[0059] Furthermore, the degree of order (S.sub.in) of each heat-assisted FePt granular magnetic recording medium was calculated according to formula (1) from the integral intensities of FePt(110) and FePt(220) diffraction peaks in the measured results of the crystal orientation of perpendicular components in FIG. 5. FIG. 6 is a graph on which the relationship between the degree of order (S.sub.in) and the melting point of each nonmagnetic material is plotted. The degree of order S.sub.in represents the extent of a structure in which Fe and Pt atoms are repeatedly stacked in the film thickness direction. When Fe and Pt atoms are repeatedly stacked completely without defects, S.sub.in is 1.0 (theoretical value). Meanwhile, when Fe and Pt atoms are never repeatedly stacked completely, S.sub.in is 0.

[00001]$\left[\mathrm{Formula}1\right]$$\begin{array}{cc}{S}_{in}=\sqrt{\frac{{\left(I\text{?}/I\text{?}\right)}_{\mathrm{measured}}}{{\left(I\text{?}/I\text{?}\right)}_{\mathrm{calculated}}}}& \left(1\right)\end{array}$$\text{?}\text{indicates text missing or illegible when filed}$

[0060] Further, the grain diameter (GD) of each heat-assisted FePt granular magnetic recording medium was assessed according to formula (2) by using the FePt(200) diffraction peak in the in-plane diffraction profile of FIG. 5. FIG. 7 is a graph on which the relationship between the grain diameter (GD) and the melting point of each nonmagnetic material is plotted.

[00002]$\left[\mathrm{Formula}2\right]$$\begin{array}{cc}\mathrm{GD}=\frac{0.9\lambda }{\mathrm{\beta cos}\mathrm{\theta \chi }}& \left(2\right)\end{array}$

[0061] Here, λ is the wavelength of 0.1542 nm for the radiation source of the X-ray diffractometer, β is a full width at half maximum of the FePt(200) diffraction peak, and θ.sub.χ is a diffraction angle of the FePt(200) diffraction peak.

[0062] Further, the correlation between the degree of order and the grain diameter, the correlation between the coercivity (H.sub.c) and the grain diameter, and the correlation between the coercivity (H.sub.c) and the degree of order are collectively shown in FIGS. 8, 9, and 10, respectively.

TABLE-US-00001 TABLE 1 Measured Results Non- Melting H.sub.c magnetic point M.sub.s.sup.grain K.sub.u.sup.grain (coercivity) material ° C. emu/cm.sup.3 erg/cm.sup.3 kOe B.sub.2O.sub.3 450 1079 1.28E+07 3.50 MoO.sub.3 795 1059 1.86E+07 0.26 SnO 1080 1014 3.04E+07 29.00 PbO 886 955 2.55E+07 24.00 Bi.sub.2O.sub.3 817 975 2.70E+07 26.00 GeO.sub.2 1115 914 2.54E+07 19.50 WO.sub.3 1473 944 1.26E+07 8.50 Nb.sub.2O.sub.5 1512 881 1.08E+07 15.63 SiO.sub.2 1723 836 2.27E+07 19.00 TiO.sub.2 1857 837 1.21E+07 9.50 MnO 1945 823 1.82E+07 26.68 Y.sub.2O.sub.3 2425 796 1.89E+07 6.50 Zr.sub.2O 2715 824 0.83E+07 6.50 MgO 2852 791 1.86E+07 26.08 BN 2973 764 2.94E+07 21.50 C 3500 710 2.23E+07 29.25

TABLE-US-00002 TABLE 2 Sintering Conditions for Nonmagnetic Materials and Relative Density of Targets Sintering Non- temper- Sintering Sintering Atmos- Relative magnetic ature pressure time phere density material ° C. MPa min Pa % B.sub.2O.sub.3 800 30.6 60 5 × 10.sup.−2 102.5 MoO.sub.3 980 24.5 60 5 × 10.sup.−2 101.4 SnO 960 24.5 60 5 × 10.sup.−2 96.5 PbO 960 24.5 60 5 × 10.sup.−2 96.8 Bi.sub.2O3 960 24.5 60 5 × 10.sup.−2 97.2 GeO.sub.2 770 24.5 60 5 × 10.sup.−2 102.0 WO.sub.3 1040 24.5 60 5 × 10.sup.−2 101.2 Nb.sub.2O.sub.5 1070 24.5 60 5 × 10.sup.−2 102.4 SiO.sub.2 990 30.6 60 5 × 10.sup.−2 95.7 TiO.sub.2 1020 24.5 60 5 × 10.sup.−2 96.8 MnO 950 24.5 60 5 × 10.sup.−2 98.8 Y.sub.2O.sub.3 1200 24.5 60 5 × 10.sup.−2 96.5 Zr.sub.2O 1000 24.5 60 5 × 10.sup.−2 97.1 MgO 940 24.5 60 5 × 10.sup.−2 95.7 BN 900 65.7 60 5 × 10.sup.−2 90.2 C 900 30.6 60 5 × 10.sup.−2 91.2

[0063] FIG. 1 reveals that the hysteresis of magnetic recording media is dependent on grain boundary materials (nonmagnetic materials of sputtering targets) and that satisfactory results are obtained when SnO (melting point of 1080° C.), MnO (melting point of 1945° C.), MgO (melting point of 2852° C.), or C (melting point of 3500° C.) is used as a grain boundary material. Moreover, it is found from Table 1 that the coercivity is also high when SnO (melting point of 1080° C.), MnO (melting point of 1945° C.), or C (melting point of 3500° C.) is used.

[0064] FIG. 2 reveals that the magnetocrystalline anisotropy (K.sub.u.sup.grain) of .sub.magneti.sub.c recording media is dependent on grain boundary materials (nonmagnetic materials of sputtering targets) and that a large magnetocrystalline anisotropy of 2.5×10.sup.7 erg/cm.sup.3 or more is exhibited when SnO (melting point of 1080° C.), PbO (melting point of 886° C.), Bi2O3 (melting point of 817° C.), GeO2 (melting point of 1115° C.), or BN (melting point of 2973° C.) is used as a grain boundary material.

[0065] FIG. 3 reveals that the saturation magnetization (ngra.sup.in) of .sub.magneti.sub.c recordin.sub.g media is dependent on grain boundary materials (nonmagnetic materials of sputtering targets); the high correlation particularly with the melting point of each grain boundary material is observed; the saturation magnetization is higher at a lower melting point; a saturation magnetization of 950 emu/cm.sup.3 or more is exhibited when SnO (melting point of 1080° C.), PbO (melting point of 886° C.), or Bi2O3 (melting point of 817° C.) is used as a grain boundary material; and a saturation magnetization of 1000 emu/cm.sup.3 or more is exhibited particularly when SnO (melting point of 1080° C.) is used.

[0066] In FIG. 4, no correlation is observed between the coercivity (H.sub.c) of magnetic recording media and the melting point of each grain boundary material (each nonmagnetic material of sputtering targets). However, it is found that high coercivities of 24 kOe, 26 kOe, and about 30 kOe are exhibited when PbO (melting point of 886° C.), Bi2O3 (melting point of 817° C.), and SnO (melting point of 1080° C.) are respectively used as grain boundary materials.

[0067] FIG. 5 reveals in the out-of-plane diffraction profile of some magnetic recording media that the FePt(001) diffraction peak is more intense when SnO (melting point of 1080° C.) is used as a grain boundary material than when another grain boundary material of C (melting point of 3500° C.), B2O3 (melting point of 450° C.), or TiO2 (melting point of 1857° C.) is used. Moreover, in the in-plane diffraction profile of the magnetic recording media, it is found further clearly due to the reduced overall noise that the FePt(110) diffraction peak is more intense when SnO (melting point of 1080° C.) is used as a grain boundary material than when another grain boundary material of C (melting point of 3500° C.), B2O3 (melting point of 450° C.), or TiO2 (melting point of 1857° C.) is used. Accordingly, it is confirmed that the perpendicular direction is an easy axis direction when SnO is used.

[0068] FIG. 6 reveals that the degree of order of magnetic recording media weakly correlates with the melting point of each grain boundary material (each nonmagnetic material of sputtering targets) and that a high degree of order close to 1.0 is exhibited when SnO (melting point of 1080° C.) is used as a grain boundary material.

[0069] FIG. 7 reveals that the grain diameter of magnetic recording media weakly correlates with the melting point of each grain boundary material (each nonmagnetic material of sputtering targets) and that a large grain diameter of about 8 nm is exhibited when SnO (melting point of 1080° C.) is used as a grain boundary material.

[0070] FIG. 8 reveals that the degree of order of magnetic recording media satisfactorily correlates with the grain diameter and that the degree of order is higher at a larger grain diameter.

[0071] FIG. 9 reveals that the coercivity (H.sub.e) of magnetic recording media satisfactorily correlates with the grain diameter and that the coercivity is higher at a larger grain diameter.

[0072] FIG. 10 reveals that the coercivity (H.sub.e) of magnetic recording media satisfactorily correlates with the degree of order and that the coercivity is higher at a higher degree of order.

[0073] From the foregoing results, it was found that a grain boundary material that can satisfy all of satisfactory hysteresis, high coercivity, high magnetocrystalline anisotropy (K.sub.u.sup.grain), hi.sub.gh .sub.saturation magnetization (M.sub.s.sup.grain), an easy axis direction in the perpendicular direction, high degree of order, and satisfactory columnar growth of grains is an oxide having a melting point of 800° C. or higher and 1100° C. or lower, as typified by SnO. Although only SnO, PbO, or Bi2O3, which is an oxide having a melting point of 800° C. or higher and 1100° C. or lower, was used as a grain boundary material in the present working example, it is considered that similar effects are exhibited also when another oxide having a melting point within the same range is used as a grain boundary material.

Example 2

[0074] In the same manner as Example 1 except for changing the 50Fe-50Pt alloy atomized powder into a 47.5Fe-47.5Pt-5Y alloy atomized powder (Y is Au, Ag, or Cu) containing 5 at % of Au, Ag, or Cu as shown in Table 3, each stepped target of FePtY-30 vol % SnO (Y is Au, Ag, or Cu) having a diameter of 153.0×1.0 mm (upper level) +a diameter of 161.0×4.0 mm (lower level) was prepared through hot pressing under vacuum conditions of a sintering temperature of 960° C., a sintering pressure of 24.5 MPa, a sintering time of 60 minutes, and an atmosphere of 5×10.sup.-2 Pa or lower; and each heat-assisted FePt granular magnetic recording medium was produced as well. The magnetic characteristics (magnetocrystalline anisotropy and saturation magnetization) were measured, and the measured results are shown in Table 3.

TABLE-US-00003 TABLE 3 Measured Results Melting point of nonmagnetic M.sub.s.sup.grain H.sub.c Target material emu/ K.sub.u.sup.grain (coercivity) composition ° C. cm.sup.3 erg/cm.sup.3 kOe (50Fe50Pt)-30 1080 1014 3.04E+07 29 vol % SnO (47.5Fe47.5Pt5Au)- 1080 953 3.20E+07 31 30 vol % SnO (47.5Fe47.5Pt5Ag)- 1080 955 3.50E+07 33 30 vol % SnO (47.5Fe47.5Pt5Cu)- 1080 960 3.80E+07 36 30 vol % SnO

[0075] The addition of Au, Ag, or Cu tends to reduce saturation magnetization (M.sub.s.sup.grain) and to increase magnetocrystalline anisotropy (K.sub.u.sup.grain) and coercivity (H.sub.e) although the variation ranges are small. Accordingly, it is confirmed that a heat-assisted magnetic recording medium even produced using an FePt-based alloy sputtering target containing Au, Ag, or Cu exhibits magnetic characteristics similar to those of a recording medium produced using a 50Fe-50Pt alloy sputtering target. Meanwhile, it was confirmed that an FePt-based alloy sputtering target containing Au, Ag, or Cu can increase the relative density as shown that the sputtering targets of (50Fe50Pt)-30 vol % SnO, (47.5Fe47.5Pt5Au)-30 vol % SnO, (47.5Fe47.5Pt5Ag)-30 vol % SnO, and (47.5Fe47.5Pt5Cu)-30 vol % SnO had relative densities of 96.5%, 98.2%, 97.8%, and 97.3%, respectively.

Example 3

[0076] In the same manner as Example 1 except for changing as shown in Table 4 the content of SnO nonmagnetic material, each stepped target of FePt-SnO having a diameter of 153.0×1.0 mm (upper level) +a diameter of 161.0×4.0 mm (lower level) was prepared through hot pressing under vacuum conditions of a sintering temperature of 960° C., a sintering pressure of 24.5 MPa, a sintering time of 60 minutes, and an atmosphere of 5×10.sup.-2 Pa or lower; and each heat-assisted FePt granular magnetic recording medium was produced as well. The magnetic characteristics (magnetocrystalline anisotropy and saturation magnetization) were measured, and the measured results are shown in Table 4. The relationships between the SnO content and the respective magnetocrystalline anisotropy (K.sub.u.sup.grain), saturation magnetization (M.sub.s.sup.grain), and coercivity (H.sub.c) for heat-assisted FePt granular magnetic recording media are plotted and shown in FIGS. 11, 12, and 13.

TABLE-US-00004 TABLE 4 Measured Results Melting point of nonmagnetic M.sub.s.sup.grain H.sub.c Target material emu/ K.sub.u.sup.grain (coercivity) composition ° C. cm.sup.3 erg/cm.sup.3 kOe (50Fe50Pt)-20 1080 1025 2.49E+07 21 vol % SnO (50Fe50Pt)-25 1080 1035 3.20E+07 28 vol % SnO (50Fe50Pt)-30 1080 1014 3.04E+07 29 vol % SnO (50Fe50Pt)-35 1080 1001 3.11E+07 29 vol % SnO (50Fe50Pt)-40 1080 985 3.01E+07 27 vol % SnO (50Fe50Pt)-45 1080 948 2.75E+07 22 vol % SnO

[0077] FIGS. 11 and 12 reveal that the saturation magnetization (M.sub.s.sup.grain) and magnetocrystalline anisotropy (K.sub.u.sup.grain) are maxima when the content of SnO nonmagnetic material is 25 vol % and decrease as the content increases over 25 vol %; a high saturation magnetization (M.sub.s.sup.grain) of 950 emu/cm.sup.3 or more is exhibited when the content of SnO nonmagnetic material is 20 vol % or more and 45 vol % or less and a high saturation magnetization exceeding 980 emu/cm.sup.3 is exhibited particularly when the content is 20 vol % or more and 40 vol % or less; and a high magnetocrystalline anisotropy (K.sub.u.sup.grain) of 2.5×10.sup.7 erg/cm.sup.3 or more is exhibited when the content of SnO nonmagnetic material is 20 vol % or more and 45 vol % or less and a high magnetocrystalline anisotropy exceeding 2.6×10′ erg/cm.sup.3 is exhibited particularly when the content is 25 vol % or more and 45 vol % or less.

[0078] FIG. 13 reveals that the coercivity (H.sub.c) is maximum when the content of SnO nonmagnetic material is 30 vol % and 35 vol % and that a high coercivity exceeding 25 kOe is exhibited when the content of SnO nonmagnetic material is 25 vol % or more and 40 vol % or less.

[0079] As in the foregoing, it is confirmed that all the saturation magnetization (M.sub.s.sup.grain), magnetocrystalline anisotropy (K.sub.u.sup.grain), and .sub.coerci.sub.vit.sub.y (H.sub.c) are high when the content of SnO nonmagnetic material is 25 vol % or more and 40 vol % or less.

[0080] It is considered that a heat-assisted magnetic recording medium having the above-described magnetic characteristics and structure increases the signal due to its high saturation magnetization (M.sub.s.sup.grain) and th.sub.us im.sub.proves SNR (signal-to-noise ratio). Further, the high uniaxial magnetic anisotropy is considered to increase the magnetic energy of such a heat-assisted magnetic recording medium, thereby improving the thermal stability.