Sputtering target for magnetic recording media

Abstract

This invention provides a sputtering target for forming a buffer layer that suppresses the in-plane orientation of magnetic particles in a magnetic thin film made of FePt alloy or the like for a magnetic recording medium, while also miniaturizing the magnetic particles. [Solution] The present invention relates to a sputtering target for a magnetic recording medium for forming a buffer layer between a substrate film and a magnetic thin film when forming a magnetic thin film on a substrate film. The buffer layer forming target according to the present invention consists of a magnetic phase made of an FePt-based alloy composed of Fe and Pt and element M, and a non-magnetic phase made of at least one of C, carbide, and nitride. The element M of the FePt-based alloy constituting the magnetic phase is at least one of Cu, Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, Au, Ag, and Ge. Preferably, the magnetic phase is made of an FePt-based alloy consisting of 20 mol% to 95 mol% of element M and the remainder being Fe and Pt.

Description

[Technical Field]

[0001] The present invention relates to a sputtering target for forming a buffer layer that suppresses the in-plane orientation of magnetic particles constituting a magnetic thin film such as a heat-assisted magnetic recording medium. More specifically, the present invention relates to a sputtering target that consists of a magnetic phase and a non-magnetic phase and is useful for forming a buffer layer that can reduce the particle size while suppressing the in-plane orientation of magnetic particles when a magnetic thin film is formed. [Background technology]

[0002] Recording density in magnetic recording media such as hard disk drives (HDDs) has been increasing rapidly, and the demand and trend for higher recording density is expected to continue. Against this backdrop, thermally assisted recording media have recently attracted attention as a next-generation recording method. Thermally assisted magnetic recording media are recording media that use a recording method in which the surface of a thin magnetic film is locally heated by irradiating it with near-field light, etc., to temporarily reduce the coercivity of magnetic particles (magnetic clusters) and write data. With this thermally assisted method, even with current recording heads, writing to magnetic thin films with high coercivity becomes easier, thus improving magnetic anisotropy K u High-quality materials can be miniaturized and used.

[0003] Magnetic anisotropy K u Highly magnetic materials include FePt alloys and CoPt alloys having an L10-type structure. When these magnetic materials having an L10-type structure are suitably applied to recording media, the crystal orientation of the magnetic particles and the miniaturization of the particle size are required.

[0004] Regarding the orientation of magnetic particles such as FePt alloys having an L10 type structure, it is preferable that the

[0001] orientation (c axis), which is the easy magnetization axis, is grown in the direction perpendicular to the plane, resulting in a (001) orientation. Furthermore, it is known that it is preferable to form (100) oriented MgO as an underlayer in order to ensure the orientation of magnetic particles such as FePt alloys. This utilizes the fact that the (100) plane of MgO has lattice matching with the (001) plane of the FePt alloy having an L10 type structure.

[0005] On the other hand, miniaturization of magnetic particles in magnetic recording media is a necessary characteristic for improving the signal-to-noise ratio and recording density, and is a characteristic generally required for magnetic thin films of magnetic recording media, not limited to heat-assisted recording methods. As a means of miniaturizing magnetic particles in magnetic thin films, the application of a granular structure with non-magnetic grain boundaries such as oxides SiO2, TiO2, and B2O3 is considered effective. In granular magnetic thin films, the non-magnetic grain boundaries miniaturize the magnetic particles while separating them, and contribute to noise reduction by reducing the magnetic interaction between particles. The application of granular structures is also effective for magnetic thin films made of FePt alloys with an L10 structure, and in addition to the above oxides, there are granular magnetic thin films with non-magnetic grain boundaries such as C (carbon: Non-Patent Document 1), MgO (Non-Patent Document 2), ZrO2 (Non-Patent Document 3), and GeO2 (Patent Document 1).

[0006] In granular magnetic thin films made of FePt alloys, CoPt alloys, etc., having the L10 type structure described above, the constituent material of the non-magnetic grain boundary is the saturation magnetization M of the magnetic thin film. s or magnetic anisotropy constant K uIt has become clear that these have an effect on the magnetic properties. One of these effects is the orientation of the magnetic particles. As described above, in magnetic thin films such as FePt alloys having an L10 type structure, it is preferable that the c-axis of the magnetic particles is oriented in a direction perpendicular to the plane (001). However, depending on the material of the non-magnetic grain boundary, in-plane oriented magnetic particles may be produced in which the c-axis exists within the plane of the magnetic thin film, and the proportion of (001) oriented magnetic particles may change (Non-Patent Literature 4). The presence of such in-plane oriented magnetic particles will degrade the magnetic properties of the medium.

[0007] The reason why in-plane orientation occurs in magnetic particles depending on the material of the non-magnetic grain boundary is not entirely clear, but the inventors consider that this is due to the oxides forming the non-magnetic grain boundary acting at the interface between the underlying film, such as MgO, and the magnetic thin film, such as FePt alloy, thereby inhibiting the epitaxial growth of the (001) plane of magnetic particles on the underlying film.

[0008] Therefore, the present inventors have reported a method for suppressing the in-plane orientation of magnetic particles such as FePt alloys having an L10 type structure by forming a C (carbon) buffer layer on the underlayer using a C (carbon) sputtering target before depositing the FePt alloy granular magnetic thin film (Non-Patent Literature 5). According to this report, it has been revealed that by forming a C buffer layer with a thickness of 0.6 nm or more, the in-plane orientation of magnetic particles is suppressed, and an FePt alloy granular magnetic thin film with a large proportion of (001) oriented magnetic particles can be deposited. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 6168066 [Non-patent literature]

[0010] [Non-Patent Document 1] A. Perumal, YKTakahashi, and K. Hono, Appl. Phys. Exp. 1, 101301 (2008). [Non-Patent Document 2] T. Suzuki and K. Ouchi, IEEE Trans. Magn. 37,1283 (2001). [Non-Patent Document 3] KF Dong, HH Li, YG Peng, G. Ju, GM Chow, and JS Chen, Appl. Phys.Lett.104, 192404 (2014). [Non-Patent Document 4] Takashi Saito, Kim Kong Tham, Ryosuke Kushibiki, Tomoyuki Ogawa, and Shin Saito, Jpn. J. Appl. Phys., 60, 075505 (2021). [Non-Patent Document 5] KimKong Tham, Ryosuke Kushibiki, Shin Saito, AIPAdvances 14, 025102 (2024) [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] The carbon (C) buffer layer described above has the effect of suppressing the in-plane orientation of magnetic particles without changing the material of the non-magnetic grain boundary, such as the oxide. However, there is one challenge in applying the carbon buffer layer. That is, when a magnetic thin film is deposited after the formation of the carbon buffer layer, the particle size of the magnetic particles tends to coarseen. As mentioned above, the particle size of the magnetic particles in a magnetic thin film is an important factor that affects the magnetic properties and recording density of the magnetic thin film, as well as the control of orientation, so the coarsening of magnetic particles is an unavoidable problem.

[0012] This invention was made against the background described above, and aims to clarify a means for suppressing in-plane orientation and achieving grain refinement for magnetic particles constituting a magnetic thin film made of FePt alloy, CoPt alloy, etc., having an L10 type structure. In this study, the present invention provides a sputtering target for a magnetic recording medium for forming a buffer layer that effectively acts at the interface between the underlying layer such as MgO and the magnetic thin film. [Means for solving the problem]

[0013] In the buffer layer disclosed in Non-Patent Document 5 mentioned above, carbon (C) is an effective element in that it suppresses the in-plane orientation of magnetic particles such as FePt alloys that constitute the magnetic thin film and promotes epitaxial growth of the c-axis of the magnetic particle crystals. However, the growth of magnetic particles in this case extends not only in the perpendicular direction (longitudinal direction) but also in the planar direction (lateral direction). Therefore, the inventors decided to investigate improvements to the structure of the buffer layer. As a result, they came up with the idea of ​​combining a non-magnetic phase consisting of carbon (C) and the like with an FePt-based alloy phase as the structure of the buffer layer. The FePt-based alloy phase may form a crystal structure and crystal orientation common to the magnetic particles that constitute the magnetic thin film. Such an FePt-based alloy phase is thought to exert a pinning effect that suppresses the growth of magnetic particles in the planar direction on the buffer layer, thereby enabling the refinement of the crystal grains of the magnetic thin film.

[0014] However, since FePt alloys are magnetic materials, the buffer layer will consist of a non-magnetic phase such as C and a magnetic phase made of FePt alloy. In this case, it is necessary to avoid the buffer layer degrading the magnetic properties of the magnetic thin film formed on it. From this viewpoint, the inventors considered that it is preferable to use an FePt alloy with low saturation magnetization as the magnetic phase to be combined with the buffer layer. As an example of a low-saturation magnetization FePt alloy, they determined that an FePt alloy containing a predetermined additive element such as Cu should be used as the magnetic phase, and that this should be combined with a non-magnetic element such as C to form a buffer layer. The inventors found that with such a buffer layer, it is possible to suppress the in-plane orientation and refine the crystal grains while maintaining the magnetic properties of the magnetic thin film, and they came up with a sputtering target that enables the deposition of this buffer layer.

[0015] In other words, the present invention, which solves the above problems, is a sputtering target for a magnetic recording medium for forming a buffer layer between a base film and a magnetic thin film when forming a magnetic thin film on a base film on a substrate, comprising a magnetic phase made of an FePt-based alloy consisting of Fe and Pt and element M, and a non-magnetic phase consisting of at least one of C, carbide, and nitride, wherein element M of the FePt-based alloy constituting the magnetic phase is at least one of Cu, Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, Au, Ag, and Ge.

[0016] The following describes the configuration of a sputtering target for a magnetic recording medium according to the present invention, as well as a method for forming a buffer layer using this sputtering target and its effects.

[0017] (A) Configuration of a sputtering target for a magnetic recording medium according to the present invention As described above, the sputtering target for magnetic recording media according to the present invention is a sputtering target for forming a buffer layer between the underlying layer of the magnetic recording media and the magnetic thin film which is the recording layer. The sputtering target for magnetic recording media according to the present invention is composed of a magnetic phase made of an FePt-based alloy and a non-magnetic phase made of C, etc. The "phases" of the magnetic phase and the non-magnetic phase are regions that are separated and distinct from each other. That is, in terms of material structure, the sputtering target according to the present invention has a structure in which regions made of an FePt-based alloy and regions made of C, etc. are separated and mixed together.

[0018] (A-1) Magnetic phase (FePt alloy phase) When the sputtering target according to the present invention is sputtered, the constituent elements of its magnetic phase, Fe and Pt, and element M form an FePt-based alloy phase in the buffer layer. The FePt-based alloy phase in the buffer layer exhibits a pinning effect during the process of forming a magnetic thin film on the buffer layer, suppressing grain growth in the in-plane direction (lateral direction) of magnetic particles such as FePt alloy, and suppressing the coarsening of magnetic particles.

[0019] The magnetic phase of the sputtering target according to the present invention is made of an FePt-based alloy in which element M is added to an FePt alloy. Element M is at least one of Cu, Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, Au, Ag, or Ge. Adding these elements to the FePt alloy makes it possible to create a low-saturation magnetized FePt-based alloy. This reduces the saturation magnetization of the buffer layer and maintains the magnetic properties of the magnetic thin film. Element M may contain at least one of the aforementioned elements, but may also contain two or more. Of these added elements M, Cu is particularly preferred because it readily dissolves in FePt-based alloys. Therefore, it is preferable that the FePt-based alloy constituting the magnetic phase contains Cu as element M.

[0020] The composition of the magnetic phase is preferably an FePt alloy consisting of 20 mol% to 95 mol% of element M and the remainder being Fe and Pt. Increasing the content of element M reduces the saturation magnetization of the buffer layer. If the content of element M is less than 20 mol%, the saturation magnetization of the formed buffer layer becomes high, and its effect on the magnetic thin film becomes difficult to ignore. On the other hand, if the content of element M exceeds 95 mol%, the FePt alloy becomes almost amorphous, which is undesirable. The content of element M is more preferably 30 mol% to 85 mol%, and even more preferably 40 mol% to 85 mol%. Furthermore, the total content of Fe and Pt in the magnetic phase is preferably 5 mol% to 80 mol%, and within this range, the respective content of Fe and Pt in the magnetic phase is preferably 2.5 mol% to 45 mol% for Fe and 2.5 mol% to 45 mol% for Pt.

[0021] A-2 Non-magnetic phase When the sputtering target according to the present invention is sputtered, a non-magnetic phase is formed in the buffer layer from non-magnetic phases such as C (carbon), carbides, and nitrides. The non-magnetic phase of the buffer layer is deposited on an underlying layer such as MgO, and mitigates the effect of non-magnetic grain boundary materials such as oxides on the interface between the underlying layer and the magnetic thin film during the deposition process of the magnetic thin film. This effect suppresses the in-plane orientation of magnetic particle crystals. The non-magnetic phase of the sputtering target (buffer layer) consists of C, as well as carbides and nitrides. Specific examples of carbides include NbC, TiC, Si, ZrC, B4C, HfC, and TaC. Specific examples of nitrides that can be used include BN, Si3N4, AlN, TiN, TaN, Cr2N, NbN, HfN, VN, and GaN.

[0022] The reason why carbon (C) is effective as a constituent element of the buffer layer is mentioned in the prior art (Non-Patent Literature 5) above, as C has the property of separating magnetic particle crystals such as FePt, thereby suppressing in-plane orientation. Carbides also have a similar effect to C and can therefore suppress in-plane orientation. Regarding nitrides, the present inventors consider that nitrides mitigate the influence of oxides that may form at the interface between the underlayer and the magnetic thin film, thereby suppressing the in-plane orientation of magnetic particle crystals.

[0023] (A-3) Overall configuration of the sputtering target according to the present invention In the sputtering target of the present invention, which consists of a magnetic phase and a non-magnetic phase, the proportion of the magnetic phase is preferably 90% by volume or less. The composition of the buffer layer corresponds to the composition of the sputtering target. In the present invention, the presence of the magnetic phase is essential, but if its proportion increases, magnetic properties will be imparted to the buffer layer, which may affect the magnetic properties of the magnetic thin film formed on the buffer layer. For this reason, it is preferable that the proportion of the magnetic phase be 90% by volume or less. Furthermore, if the proportion of the magnetic phase is too low, the effect of suppressing the coarsening of magnetic particles in the magnetic thin film may be insufficient. For this reason, it is preferable that the proportion of the magnetic phase be 10% by volume or more. A more preferable proportion of the magnetic phase is 50% by volume or more and 80% by volume or less.

[0024] Furthermore, in the sputtering target according to the present invention, the magnetic phase and the non-magnetic phase are dispersed as phases that are separated from each other in the material structure. In this case, the shape and dimensions of the magnetic phase and the non-magnetic phase vary depending on the proportion of each phase in the sputtering target, the manufacturing conditions, etc., and are not particularly limited.

[0025] When the proportion of the magnetic phase is within the preferred range described above (50% by volume or more), the material structure of the sputtering target will have a magnetic phase matrix with dispersed non-magnetic phase. In this case, the particle size of the non-magnetic phase is preferably 0.1 μm to 30 μm in equivalent circle diameter. If the non-magnetic phase is too fine, aggregation of the non-magnetic phase is likely to occur in the material structure. Also, if the non-magnetic phase is too coarse, the contact cross-section with the magnetic phase becomes small, and it may fall off during sputtering, generating particles. Conversely, when the proportion of the non-magnetic phase is high (for example, 50% to 90% by volume), the material structure of the sputtering target will have a non-magnetic phase matrix with dispersed magnetic phase. In this case, the particle size of the magnetic phase is preferably 0.1 μm to 100 μm in equivalent circle diameter. To manufacture a sputtering target in which the magnetic phase is less than 0.1 μm, the particle size of the raw material powder must also be fine. In that case, excessive energy is required for mixing, and there is a risk of increased contamination from impurities from the mixing device (mixing medium, mixing container). Also, if the magnetic phase exceeds 100 μm, the contact area between the magnetic and non-magnetic phases becomes small, which can lead to detachment during sputtering and particle generation.

[0026] Regarding the composition of the sputtering target according to the present invention, it is preferable that the constituent elements consist only of the constituent elements of the magnetic phase and non-magnetic phase described above. However, the presence of unavoidable impurities is permissible. Unavoidable impurities include elements other than the metallic and non-metallic elements listed above, and specifically include oxygen (O). Unavoidable impurities are elements derived from the raw material powder and elements derived from the manufacturing equipment in the manufacturing method described later. Unavoidable impurities are contained in the magnetic phase and / or non-magnetic phase. The content of unavoidable impurities is preferably 1000 ppm and more preferably 500 ppm or less relative to the total mass of the sputtering target.

[0027] (B) Method for manufacturing a sputtering target for a magnetic recording medium according to the present invention The sputtering target according to the present invention consists of a magnetic phase made of the FePt alloy described above and a non-magnetic phase made of C, etc. As a method for manufacturing a sputtering target with such a configuration, it is preferable to apply powder metallurgy in order to uniformly disperse the magnetic phase and the non-magnetic phase. In powder metallurgy, powders containing Fe, Pt, and element M, which constitute the magnetic phase, and powders containing C, carbides, and nitrides, which constitute the non-magnetic phase, are used as raw material powders. After mixing these and forming them appropriately, the sputtering target can be manufactured by pressure sintering.

[0028] As raw material powders containing Fe, Pt, and element M, which constitute the magnetic phase, powders consisting of each element (Fe powder, Pt powder, element M powder) as well as alloy powders in which each element is alloyed (FePt alloy powder, FePtM alloy powder) can be used. Furthermore, as raw material powders containing C, carbides, and nitrides, which constitute the non-magnetic phase, C powder, carbide powders (NbC powder, TiC powder, etc.), and nitride powders (BN powder, Si3N4 powder, etc.) can be used. These raw material powders are preferably of high purity (99% or higher). These raw material powders can also be manufactured by known methods such as atomization methods such as gas atomization. In the manufacture of the sputtering target according to the present invention, the particle size of the raw material powder is preferably 20 μm or less.

[0029] It is preferable to thoroughly mix the raw material powders that will become the magnetic phase and the non-magnetic phase before sintering to form a mixed powder. Mixing can be performed using mixing and dispersion methods such as a ball mill, bead mill, or rocking mill. The mixed powder obtained by these mixing methods may be pre-molded before the next step of pressurized sintering. After appropriately molding the mixed powder, the sputtering target according to the present invention can be obtained by pressurized sintering. The sintering method at this time can be the hot press method (HP), hot isostatic sintering method (HIP), or discharge plasma sintering (SPS). The sintering temperature during pressurized sintering is preferably 600°C to 1500°C, and the applied pressure is preferably 10 MPa to 200 MPa. Furthermore, the heating atmosphere is preferably a vacuum or a non-oxidizing atmosphere.

[0030] (C) Method for manufacturing a magnetic recording medium involving the formation of a buffer layer using a sputtering target according to the present invention The present invention is useful for forming a buffer layer for forming a magnetic thin film on a magnetic recording medium, such as a heat-assisted magnetic recording medium. In a method for manufacturing a magnetic recording medium, a buffer layer can be formed on a substrate underlayer by sputtering with a sputtering target according to the present invention.

[0031] There are no particular restrictions on the material, dimensions, or shape of the substrate. Furthermore, the underlayer is not particularly limited as long as it is an underlayer applied to form a magnetic material such as an FePt alloy having an L10 type structure. As mentioned above, (100)-oriented MgO is well known as an underlayer for providing (001) orientation to a magnetic thin film such as an FePt alloy having an L10 type structure, and an MgO underlayer can also be applied in this invention. In addition, MgTiO2, MgSiO2, MgAl2O5, RuAl, etc. can be applied as underlayers.

[0032] The sputtering of the sputtering target according to the present invention can be carried out using a normal sputtering apparatus and sputtering conditions. By sputtering, atoms of Fe, Pt, and element M constituting the magnetic phase and atoms of nonmetallic elements constituting the nonmagnetic phase are sputtered onto the underlying film, forming a buffer layer. The buffer layer formed at this time may be a thin film in which the magnetic phase and nonmagnetic phase are continuous and bonded, or each phase may be formed in an island-like manner on the surface of the underlying film.

[0033] Also, when forming the buffer layer with the sputtering target according to the present invention, it is preferable that the thickness of the buffer layer in terms of film thickness is 0.1 nm or more and 1.0 nm or less. If the film thickness is too small, it becomes difficult to obtain the effect as a buffer layer, particularly the effect of suppressing the in-plane orientation of magnetic particles. In addition, a buffer layer with an excessive film thickness results in less exposure of the magnetic phase on the surface, making it difficult to exhibit the pinning effect by the magnetic phase, which can be a factor in the random growth or in-plane orientation of magnetic particles. The film thickness of the buffer layer is more preferably 0.1 nm or more and 0.8 nm or less. Note that the film thickness conversion is considered in view of the fact that the buffer layer can be formed in an island shape as described above. The film thickness conversion is the film thickness assuming that metal atoms and non-metal atoms are uniformly arranged on the underlying film.

[0034] And, the sputtering target according to the present invention having the above-described configuration preferably can form a thin film (buffer layer) with a low saturation magnetization M s because the saturation magnetization M s of the buffer layer can affect the magnetic properties of the magnetic thin film formed thereon. Specifically, the saturation magnetization M s of the buffer layer formed by the sputtering target according to the present invention is preferably 350 emu / cm 3 or less, and more preferably 300 emu / cm 3 or less.

[0035] After forming the buffer layer on the underlying film in the above steps, a magnetic recording medium can be manufactured by forming a magnetic thin film according to a conventional method. According to the gist and problems of the present invention described so far, as the magnetic thin film, a magnetic thin film composed of an FePt alloy, CoPt alloy, FePd, CoPd, etc. having an L10-type structure is preferably applied. These magnetic thin films can also be formed by sputtering. Note that after forming the magnetic thin film, an additional structure such as a protective layer of the magnetic thin film may be provided to form a magnetic recording medium.

Effects of the Invention

[0036] As described above, the present invention is a sputtering target for forming a buffer layer on an underlayer such as MgO, which acts on a magnetic thin film such as an FePt alloy having an L10 type structure. The sputtering target according to the present invention makes it possible to form a buffer layer that suppresses the in-plane orientation of magnetic particles by nonmetal atoms from a nonmagnetic phase such as C, and enables the refinement of magnetic particles by metal atoms from a magnetic phase made of an FePt-based alloy. [Brief explanation of the drawing]

[0037] [Figure 1] In-plane XRD profile of a buffer layer deposited using the Fe50-xPt50-xCu2x-30vol%C sputtering target (2x:0,30,50,70) of the first embodiment. [Figure 2] A graph showing the relationship between the Cu concentration (2x) and the saturation magnetization Ms of the buffer layer deposited using the Fe50-xPt50-xCu2x-30vol%C sputtering target (2x: 0, 30, 50, 70) of the first embodiment. [Figure 3] In-plane XRD profile of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer using the Fe50-xPt50-xCu2x-30vol%C sputtering target (2x:0,30,50,70) of the first embodiment. [Figure 4] In-plane XRD profile of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer (film thickness: 0~1.0nm) using a Fe35Pt35Cu30-30vol%C sputtering target of the first embodiment. [Figure 5] Planar TEM image of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer using the Fe50-xPt50-xCu2x-30vol%C sputtering target (2x:30,50,70) of the first embodiment. [Figure 6] Planar TEM image of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer using a 100%C sputtering target in the comparative example of the first embodiment. [Figure 7] Cross-sectional TEM image of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer using the Fe50-xPt50-xCu2x-30vol%C sputtering target (2x:30,50,70) of the first embodiment. [Figure 8] Cross-sectional TEM image of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer using a 100%C sputtering target in the comparative example of the first embodiment. [Figure 9] This graph shows the measurement results of the magnetic anisotropy constant Ku of a magnetic thin film (Fe50Pt50-30vol%B2O3) deposited on a buffer layer (film thickness: 0~1.0nm) using the Fe50-xPt50-xCu2x-30vol%C sputtering target (2x:30,50,70) of the first embodiment. [Modes for carrying out the invention]

[0038] First Embodiment The embodiments of the present invention are described below. In this embodiment, Cu is applied as the element M of the FePt-based alloy constituting the magnetic phase of the sputtering target, and a sputtering target for forming a buffer layer (FePtCuC sputtering target) is manufactured, which consists of a magnetic phase made of FePtCu alloy and a non-magnetic phase made of C. Then, a buffer layer is formed on an MgO underlayment using the manufactured FePtCuC sputtering target, and the structure and magnetic properties (saturation magnetization M) of the buffer layer are described below. s The following was investigated: Furthermore, a magnetic thin film made of FePt alloy was deposited on the buffer layer, and the orientation and particle size of the magnetic particles constituting the magnetic thin film were investigated.

[0039] [Manufacturing of sputtering targets for buffer layer formation] In this embodiment, Fe powder, Pt powder, and Cu powder, which are raw material powders for the magnetic phase, were mixed with C powder, which is a raw material powder for the non-magnetic phase, and the mixed powder was sintered to produce a sputtering target for forming a buffer layer.

[0040] The raw material powders used in this embodiment were all commercially available, and the average particle sizes of the Fe powder, Pt powder, Cu powder, and C powder were 5 μm, 2 μm, 4 μm, and 3 μm, respectively. The Fe powder, Pt powder, Cu powder, and C powder were then mixed in a ball mill (grinding medium: ceramic balls) to produce a mixed powder.

[0041] The FePtCuC sputtering target manufactured in this embodiment is an FePtCuC sputtering target with a magnetic phase (FePtCu) of 70 volume% and a non-magnetic phase (C) of 30 volume%. Multiple FePtCuC sputtering targets were manufactured with the same Fe concentration (mol%) and Pt concentration (mol%) for the magnetic phase, but with different Cu concentrations (mol%). Hereinafter, this FePtCuC sputtering target will be referred to as Fe 50-x Pt 50-x Cu 2x This is sometimes referred to as -30 vol% C. 2x is the Cu concentration (mol%), and in this embodiment, 2x = 0 mol%, 30 mol%, 50 mol%, and 70 mol%. The composition of this magnetic phase was adjusted by the mixing ratio of the Fe powder, Pt powder, and Cu powder described above. The volume percentages of the magnetic phase and the non-magnetic phase were also adjusted by the mixing ratio of the raw material powder that becomes the magnetic phase and the C powder that becomes the non-magnetic phase.

[0042] Sputtering target for buffer layer formation (Fe 50-x Pt 50-x Cu 2x -30 vol% C) was produced by pressure sintering the mixed powder prepared above. Pressure sintering was carried out by the hot press method, with a sintering temperature of 900°C, a pressure of 60 MPa, and a pressure sintering time of 60 min, in an atmosphere of 5 × 10 -2 Vacuum conditions below Pa were maintained. The manufactured Fe 50-x Pt 50-x Cu 2x - The dimensions of the C sputtering target were 161 mm in diameter and 4 mm in thickness, with a relative density of 96% to 99%.

[0043] [Formation of a buffer layer] And the Fe manufactured as described above 50-x Pt50-x Cu 2x -A buffer layer was formed on the MgO underlayment using a C sputtering target in the following steps. For the substrate preparation, underlayment deposition, buffer layer formation, and magnetic thin film deposition described below, an RF / DC magnetron sputtering system (Canon Anelva Corporation, C3010) was used as the sputtering apparatus.

[0044] An amorphous glass substrate (thickness 0.635 mm) was prepared by depositing an 80 nm amorphous Co60 at%-W40 at% layer by sputtering (Ar gas pressure: 0.6 Pa, input power: 500 W). Subsequently, a 5 nm MgO underlayer was deposited by sputtering (Ar gas pressure: 0.6 Pa, input power: 500 W) to prepare a substrate sample.

[0045] The buffer layer is formed using the Fe fabricated above. 50-x Pt 50-x Cu 2x A buffer layer was formed using four sputtering targets of -30 vol% C (2x=0, 30, 50, 70). The sputtering conditions for forming the buffer layer were Ar gas pressure: 0.6 Pa and input power: 60 W. In this embodiment, the sputtering time was adjusted to form a buffer layer with a thickness equivalent to 0.2 nm to 2.0 nm.

[0046] [Investigation of the crystal structure and saturation magnetization of the buffer layer] Fe produced in this embodiment 50-x Pt 50-x Cu 2x Analysis of the crystal structure and saturation magnetization M of buffer layers deposited using a -30 vol% C sputtering target (2x=0, 30, 50, 70). s Measurements were performed. The crystal structure was determined by XRD analysis. For the XRD analysis, a high-resolution X-ray diffraction analyzer (SmartLab, manufactured by Rigaku Corporation) was used, with the X-ray source being Cu Kα rays (wavelength: 1.5418 Å), and structural analysis was performed by in-plane diffraction at an incident angle of 0.4°. In addition, the saturation magnetization M sThe measurement was performed using a vibration sample magnetometer (MPMS3: manufactured by Quantum Design Japan Co., Ltd.) equipped with a superconducting quantum interference detector to measure the hysteresis loop. From the measured hysteresis loop, the saturation magnetization M was determined. s (memu / cm 3 ) was read.

[0047] Figure 1 shows Fe 50-x Pt 50-x Cu 2x This is the XRD diffraction pattern of buffer layers deposited using a -30 vol% C sputtering target (2x = 0, 30, 50, 70). From Figure 1, (200) diffraction lines are observed from all buffer layers, regardless of the concentration (2x) of Cu in the magnetic phase. In other words, (200) diffraction lines are observed even if the magnetic phase of the buffer layer contains Cu (element M), and this trend is maintained even as the Cu concentration increases. From this, it can be predicted that the buffer layer has the same fct structure as the magnetic thin film and does not degrade the crystal structure of the magnetic layer deposited on top of the buffer layer.

[0048] Figure 2 shows Fe 50-x Pt 50-x Cu 2x Saturation magnetization M of the buffer layer deposited using a -30 vol% C sputtering target (2x=0, 30, 50, 70) s These are the measurement results, and the Cu concentration (2x) and M s This graph shows the relationship between the two. Figure 2 shows that as the Cu concentration of the magnetic phase (FePtCu alloy phase) increases, the saturation magnetization M s It can be seen that the saturation magnetization decreases. In particular, buffer layers with a Cu concentration (2x) of 30 mol% or more have a saturation magnetization of less than half that of buffer layers without Cu addition (2x=0). From the above XRD analysis and saturation magnetization measurement results, it was confirmed that when a buffer layer consisting of a magnetic phase (FePt-based alloy) and a non-magnetic phase is applied, it does not affect the crystal structure of the magnetic layer deposited on it, and that by adding element M to the magnetic phase, the saturation magnetization of the buffer layer is reduced, thereby suppressing the effect on the magnetic properties of the magnetic layer.

[0049] [Deposition and evaluation of magnetic thin films] Next, Fe 50-x Pt 50-x Cu 2x A FePt magnetic thin film was deposited on a buffer layer formed using a -30 vol% C sputtering target, and the magnetic properties of the magnetic thin film and the change in magnetic particle size were evaluated.

[0050] FePt magnetic thin film deposition is performed using Fe as the sputtering target. 50 Pt 50 Sputtering was performed using -30 vol% B2O3, with an Ar gas pressure of 8.0 Pa, an input power of 100 W, and a substrate temperature of 550°C. The thickness of the magnetic thin film was set to 5 nm. Furthermore, a 7 nm carbon film was deposited as a surface protective film with an Ar gas pressure of 0.6 Pa and an input power of 300 W. For comparison, the case of forming a magnetic thin film on a buffer layer using a commercially available carbon (C) sputtering target was also considered as a conventional technique (Non-Patent Literature 5). In this conventional technique as well, the buffer layer was deposited in the same manner as in each example, and then the FePt magnetic thin film was deposited.

[0051] [Evaluation of magnetic particle orientation and morphological observation] Magnetic thin film (Fe 50 Pt 50 XRD analysis was performed on samples with a film of -30 vol% B2O3 to examine the presence or absence of in-plane orientation and the quality of (001) orientation for magnetic particles having an L10 type structure. Figure 3 shows buffer layers (Fe) with different Cu concentrations in the magnetic phase. 50-x Pt 50-x Cu 2x This is the XRD diffraction pattern when an FePt magnetic thin film is deposited on -30 vol% C (film thickness 0.6 nm). In this XRD diffraction profile, the diffraction peaks around 2θ = 33°, 47°, and 69° correspond to the (110), (200), and (220) planes of the L10 type FePt structure, respectively.

[0052] In in-plane XRD measurements of FePt magnetic thin films having an L10 type structure, (001) superlattice reflection is observed when crystals oriented (001) in the in-plane direction are present. This (001) superlattice reflection peak is observed near 2θ = 24°. Referring to Figure 3, the buffer layer ((Fe 50-x Pt 50-x Cu 2x In the XRD profile of a magnetic thin film on -30 vol% C: 2x = 0 mol% ~ 70 mol), the (001) superlattice reflection peak is not observed. This suggests that the presence of a buffer layer can suppress the in-plane orientation of the magnetic thin film. Furthermore, from the perspective of suppressing in-plane orientation alone, the FePt-based alloy phase of the magnetic phase is effective even without the addition of element M. This is thought to be because the suppression of in-plane orientation is mainly carried out by the non-magnetic phase (C, etc.).

[0053] Figure 4 shows a buffer layer with a Cu concentration of 30 mol% (Fe 35 Pt 35 Cu 30 -30 vol% C) and the thickness of the buffer layer (d BL This shows the XRD diffraction patterns of FePt magnetic thin films when the buffer layer thickness is 0 nm to 1.0 nm. Referring to Figure 4, the (001) superlattice reflection peak clearly appears when the buffer layer thickness is 1.0 nm. From this, it can be considered that to suppress in-plane orientation of the magnetic thin film, it is preferable to set the buffer layer thickness to 1.0 nm or less, and more preferable to 0.8 nm or less.

[0054] [Evaluation of magnetic particle size] Next, magnetic thin film (Fe 50 Pt 50 TEM observations of the (-30vol%B2O3) in both planar and cross-sectional views were performed to investigate the particle size of the magnetic particles. Figure 5 shows the buffer layer (BL:Fe) manufactured in this embodiment. 50-x Pt 50-x Cu 2x Figure 6 is a planar TEM image of a magnetic thin film to which -30 vol% C) was applied. Figure 6 is a planar TEM image of an FePt magnetic thin film when C (100% C) was used as a buffer layer (BL) in the conventional technique. Figure 7 is a buffer layer (BL: Fe) manufactured in this embodiment.50-x Pt 50-x Cu 2x Figure 8 shows a cross-sectional TEM image of an FePt magnetic thin film with a buffer layer (BL) of -30 vol% C. Figure 8 shows a cross-sectional TEM image of an FePt magnetic thin film when C (100% C) is used as a buffer layer (BL) in the conventional technique. Each figure also shows a planar TEM image and a cross-sectional TEM image of a magnetic thin film deposited without a buffer layer.

[0055] Referring to the planar TEM images of the magnetic thin films in Figures 5 and 6, both magnetic thin films show magnetic particles (Fe) separated by non-magnetic grain boundaries (B2O3). 50 Pt 50 It is observed that the structure is composed of the above. Furthermore, in the magnetic thin film to which the conventional C buffer layer (0.6 nm) shown in Figure 6 is applied, the particle size of the magnetic particles is clearly coarser than in the magnetic thin film without the buffer layer. In addition, in this conventional technique, the width of the non-magnetic grain boundaries is wider, and magnetic particles with a wide particle size distribution are observed. In contrast, referring to the planar TEM image of the magnetic thin film to which the buffer layer of this embodiment is applied shown in Figure 5, it can be seen that the coarsening of magnetic particles, as seen in the C buffer layer, is suppressed. Regarding the buffer layer of this embodiment, even if the Cu concentration of the FePt-based alloy, which is the magnetic phase, increases, there is no significant difference in the particle size of the magnetic particles in the magnetic thin film. However, when a Cu-free FePt alloy is used as the magnetic phase, the particle size of the magnetic particles is slightly coarser.

[0056] The same results can be confirmed from the cross-sectional TEM images of the magnetic thin films in Figures 7 and 8. In the magnetic thin film with the C buffer layer introduced in Figure 8, the magnetic particles grow laterally and appear to coalesce with adjacent magnetic particles having the same crystal orientation. On the other hand, the cross-sectional TEM of the magnetic thin film of this embodiment in Figure 7 shows that the lateral grain growth of the magnetic particles on the buffer layer of this embodiment is suppressed, resulting in a smaller average cluster size.

[0057] From the observation results of the planar and cross-sectional morphologies of the magnetic thin film on the buffer layer described above, it was confirmed that the introduction of the C buffer layer causes the particle size of the magnetic particles to coarseen, and that the introduction of a magnetic phase (FePt-based alloy phase) into the buffer layer suppresses the coarsening of the magnetic particles.

[0058] [Evaluation of magnetic properties of magnetic thin films] The buffer layer of this embodiment (Fe 50-x Pt 50-x Cu 2x A magnetic thin film (Fe) deposited on -30 vol% C 50 Pt 50 For -30 vol% B2O3), the magnetic anisotropy constant K is used as a magnetic property. u The magnetic anisotropy constant K was measured. u The measurements were taken using a torque magnetometer-equipped physical property measurement system (PPMS: manufactured by Quantum Design Japan Co., Ltd.). As a result, Figure 9 shows the film thickness and magnetic anisotropy constant K for each Cu concentration of the buffer layer. u This shows the relationship.

[0059] From Figure 9, the buffer layer (Fe) of this embodiment 50-x Pt 50-x Cu 2x A magnetic thin film to which -30 vol% C is applied exhibits a magnetic anisotropy constant K at all Cu concentrations, compared to a magnetic thin film without a buffer layer (thickness 0 nm). u It can be seen that it tends to increase. The buffer layer (Fe) of this embodiment 50-x Pt 50-x Cu 2x It was also confirmed that the magnetic anisotropy constant K(-30 vol%C) has the effect of improving the magnetic properties of the magnetic thin film deposited on it. u It can also be seen that the thickness of the buffer layer, which shows a maximum value, shifts towards becoming thinner as the Cu concentration increases.

[0060] The above magnetic thin films (Fe 50 Pt 50From the results of various studies on (-30vol%B2O3), it was confirmed that applying a buffer layer (sputtering target) consisting of a magnetic phase made of an FePt-based alloy with element M added and a non-magnetic phase such as C is preferable in order to achieve various requirements such as suppression of in-plane orientation of magnetic particles, suppression of coarsening of magnetic particles, and reduction of the influence of the magnetic properties of the magnetic thin film in a suitable balance. Furthermore, it was found that setting the buffer layer to an appropriate thickness also leads to an improvement in the magnetic properties of the magnetic particles.

[0061] Second Embodiment In this embodiment, four types of sputtering targets were manufactured: (1) a sputtering target using an FePtCu alloy with a Cu concentration of 0 to 90 mol% as the magnetic phase; (2) a sputtering target using an FePt-based alloy to which various elements M are applied as the magnetic phase; (3) a sputtering target using an FePt-based alloy to which a non-magnetic phase consisting of carbides and nitrides is applied as the magnetic phase; and (4) a sputtering target in which the volume ratio of the magnetic phase (FePtCu) is 10 vol% to 100 vol%. The magnetic properties of the buffer layer deposited on these sputtering targets, as well as the orientation of the magnetic thin film deposited on the buffer layer and the particle size of the magnetic particles were evaluated.

[0062] The sputtering target for buffer layer formation in this embodiment was manufactured using Fe powder, Pt powder, element M powder, and carbon powder or various carbide / nitride powders, basically the same as in the first embodiment. All raw material powders had a purity of 99% or higher and a particle size of 20 μm or less. The mixed powder, obtained by mixing each raw material powder, was then sintered to form the sputtering target for buffer layer formation. The sintering conditions were also the same as in the first embodiment.

[0063] Then, using the various sputtering targets for buffer layer formation that were manufactured, a buffer layer was formed on the same substrate as in the first embodiment (film thickness 0.6 nm). For the formed buffer layer, the saturation magnetization M s (memu / cm 3 ) was measured.

[0064] After measuring the saturation magnetization of the buffer layer, a magnetic thin film (Fe 50 Pt 50 -30 vol%B2O3) was formed under the same conditions as in the first embodiment. Also, as a reference example, a sample was prepared in which a magnetic thin film was formed on the MgO underlayer under the same conditions as in the first embodiment without forming a buffer layer.

[0065] After forming the magnetic thin film, XRD analysis was performed on it. In this embodiment, the presence or absence of the (001) superlattice reflection peak in the XRD profile of the magnetic thin film was confirmed. Also, the particle size of the magnetic particles was calculated from the half-value width of the (200) diffraction peak (2θ = 47°) and Scherrer's formula.

[0066] The configurations of the sputtering targets for forming buffer layers of various configurations examined in this embodiment, and the evaluation results for the buffer layers and magnetic thin films are shown in Tables 1 to 4. Each table shows the measurement results of the saturation magnetization M s of the buffer layer, the presence or absence of the (001) peak of the magnetic thin film (Fe 50 Pt 50 -30 vol%B2O3), and the particle size of the magnetic particles. Note that the numerical values indicating the composition of the magnetic phase (FePtM) of the buffer layer in the table are mol% of element M, and the numerical values of the non-magnetic phases (C, BN, etc.) mean volume% in the sputtering target. Also, for Table 1, the evaluation results for the buffer layer and magnetic thin film performed in the first embodiment are also described.

[0067]

Table 1

[0068]

Table 2

[0069]

Table 3

[0070]

Table 4

[0071] While referring to Tables 1 to 4, the effects and suitable configurations of the buffer layer are confirmed. First, looking at Table 1, for the magnetic thin film without the buffer layer as a reference example (in No. 11, since a (001) peak was observed in the XRD diffraction pattern, it is confirmed that in the case without the buffer layer, in-plane orientation is developed in the magnetic thin film. And for the in-plane orientation of the magnetic thin film, although it can be solved by the conventional setting of the C buffer layer, in that case, coarsening of magnetic particles occurs (No. 12).

[0072] From the results of these reference examples and the prior art, it can be seen that by adopting a buffer layer combining a FePt-based alloy phase (magnetic phase) with C (non-magnetic phase), both problems of in-plane orientation and coarsening of magnetic particles are solved (No. 1 to 10).

[0073] However, when a FePt alloy not containing element M is used as the magnetic phase, the saturation magnetization M s of the buffer layer becomes as high as 470 memu / cm 3 , and there is concern about its influence on the magnetic properties of the magnetic thin film formed thereon (No. 1). Therefore, when applying a FePt-based alloy phase with element M (Cu) added to the magnetic phase, it can be seen that the saturation magnetization M s of the buffer layer decreases (No. 2 to 10). At this time, the saturation magnetization M s of the buffer layer decreases with an increase in the Cu concentration. Regarding the Cu concentration of the FePt-based alloy as the magnetic phase, by setting it to 20 mol% or more, the saturation magnetization M s of the buffer layer can be made 350 emu / cm 3 or less (No. 3 to 10). And if the concentration of element M in the FePt-based alloy is 30 mol% or more, the saturation magnetization M s of the buffer layer is in a particularly preferable range of 300 emu / cm 3 or less.

[0074] Furthermore, referring to Table 2, elements other than Cu are also effective as element M in the FePt-based alloy, which is the magnetic phase. Numbers 13-27 in Table 2 show the results for buffer layers in which the magnetic phase is an FePt-based alloy containing 30 mol% of any of the following elements as element M: Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, Au, Ag, or Ge. In these cases as well, the effect of suppressing in-plane orientation of the magnetic thin film and coarsening of magnetic particles is demonstrated. Also, the saturation magnetization M of the buffer layer s It is 300 emu / cm 3 It is as follows:

[0075] Furthermore, referring to Table 3, it can be seen that there is a range of choices regarding the composition of the non-magnetic phase. Numbers 28 to 40 in Table 3 show the application of carbides (NbC, TiC, SiC, ZrC) and nitrides (BN, Si3N4, AlN, TiN, etc.) as non-magnetic phases other than C (carbon). Similar effects to those confirmed in Tables 1 and 2 can be observed with these as well.

[0076] Furthermore, referring to Table 4, regarding the volume ratio of magnetic phase to non-magnetic phase, as the proportion of the magnetic phase increases, the saturation magnetization M of the buffer layer... s The saturation magnetization M of the buffer layer increases. s A particularly preferred value is 300 emu / cm². 3 To achieve the following, it is preferable to have a magnetic phase ratio of 10% to 90% (No. 43-50). Furthermore, when using a sputtering target consisting only of a magnetic phase, the buffer layer without a non-magnetic phase should be saturated with magnetized M s High (385 emu / cm 3 ), the particle size of the magnetic particles in the magnetic thin film was also coarser (No. 41). In this buffer layer, the particle size becomes coarser because there is no non-magnetic material (C) acting as a grain boundary, and the magnetic particles on top of it also become coarser. It can be said that a thin film without a non-magnetic phase does not function as a buffer layer. [Industrial applicability]

[0077] As described above, the present invention is a sputtering target for forming a buffer layer between a magnetic thin film made of an FePt alloy or the like having an L10 type structure and an underlying layer. The buffer layer formed by the present invention can suppress the coarsening of magnetic particles while promoting the growth of (001) planes perpendicular to the plane by suppressing in-plane orientation of magnetic particles in the magnetic thin film. This buffer layer is composed of a magnetic phase and a non-magnetic phase, and an FePt-based alloy to which element M is added to optimize the saturation magnetization of the buffer layer is applied as the magnetic phase. The sputtering target according to the present invention is useful for magnetic thin films that become recording layers of heat-assisted recording media.

Claims

1. A sputtering target for a magnetic recording medium, for forming a buffer layer between a base film and a magnetic thin film when forming a magnetic thin film on a base film on a substrate, A magnetic phase made of an FePt alloy consisting of Fe, Pt and element M, It consists of a nonmagnetic phase made of at least one of C, carbides, or nitrides, A sputtering target for a magnetic recording medium, wherein the element M of the FePt-based alloy constituting the magnetic phase is at least one of Cu, Si, Ti, Cr, B, V, Nb, Ta, Ru, Mn, Zn, Mo, W, Au, Ag, and Ge.

2. A sputtering target for a magnetic recording medium according to claim 1, comprising 10% to 90% by volume of the magnetic phase, with the remainder being the non-magnetic phase and unavoidable impurities.

3. The sputtering target for a magnetic recording medium according to claim 1 or claim 2, wherein the magnetic phase is made of an FePt alloy consisting of 20 mol% to 95 mol% of element M and the remainder being Fe and Pt.

4. A sputtering target for a magnetic recording medium according to claim 1 or claim 2, wherein Cu is essentially included as element M of the FePt-based alloy constituting the magnetic phase.

5. Saturation magnetization is 350 emu / cm ３ A sputtering target for a magnetic recording medium according to claim 1 or claim 2, capable of forming the following thin films.

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