Magnetic recording medium sputtering target

Abstract

The present invention relates to a magnetic recording medium sputtering target for forming a buffer layer between a base film and a magnetic thin film when the magnetic thin film is formed on the base film. A buffer layer-forming target according to the present invention comprises: a magnetic phase that is formed from an Fe-Pt-based alloy composed of Fe, Pt, and an element M; and a non-magnetic phase that is formed from at least one of C, a carbide, and a nitride. The element M of the Fe-Pt-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. The magnetic phase in this case is preferably formed from the Fe-Pt-based alloy composed of 20-95 mol% of the element M, with the remainder being Fe and Pt.

Description

Sputtering target for magnetic recording media 【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. 【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, temporarily reducing the coercivity of magnetic particles (magnetic clusters) and writing 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 applied to magnetic thin films of heat-assisted magnetic recording media. ｕ As for materials with high magnetic properties, L1 ０ FePt alloys and CoPt alloys with a type structure are known. These L1 ０ When a magnetic material having a specific structure is suitably applied to a recording medium, the crystal orientation of the magnetic particles and the miniaturization of the particle size are required. 【0004】 L1 ０ Regarding the orientation of magnetic particles such as FePt alloys having a type structure, it is preferable that the

[001] orientation (c axis), which is the easy magnetization axis, is grown in the direction perpendicular to the plane. Furthermore, it is known that in order to ensure the orientation of magnetic particles such as FePt alloys, it is preferable to form (100) oriented MgO as an underlayer. This is because the (100) plane of MgO is L1 ０It utilizes the fact that it has lattice matching with the (001) plane of the FePt alloy having a L1-type structure. 【0005】 On the other hand, the refinement of magnetic particles in a magnetic recording medium is a characteristic necessary for improving the S / N ratio and increasing the recording density, and is a characteristic generally required for the magnetic thin film of a magnetic recording medium not limited to the heat-assisted recording method. And as a means for refining the magnetic particles of the magnetic thin film, SiO ２ , TiO ２ , B ２ O ３ etc. The application of a granular structure having oxides etc. as non-magnetic grain boundaries is considered effective. In the granular magnetic thin film, the non-magnetic grain boundaries contribute to noise reduction by separating and refining the magnetic particles while reducing the magnetic interaction between the particles. The application of the granular structure is also effective for magnetic thin films made of FePt alloys etc. having a L1 ０ -type structure. In addition to the above oxides, there are granular magnetic thin films having C (carbon: Non-Patent Document 1), MgO (Non-Patent Document 2), ZrO ２ (Non-Patent Document 3), GeO ２ (Patent Document 1), etc. as non-magnetic grain boundaries. 【0006】 In the granular magnetic thin film made of FePt alloy, CoPt alloy, etc. having the above L1 ０ -type structure, it has been clarified that the constituent material of the non-magnetic grain boundary affects magnetic properties such as the saturation magnetization M ｓ and the magnetic anisotropy constant K ｕ of the magnetic thin film. One of the effects is the orientation of magnetic particles. As described above, in a magnetic thin film such as an FePt alloy having a L1 ０ -type structure, it is preferable that the c-axis of the magnetic particles is (001)-oriented perpendicular to the plane. However, depending on the material of the non-magnetic grain boundary, in-plane-oriented magnetic particles with the c-axis existing in the magnetic thin film plane may be generated, and the ratio of (001)-oriented magnetic particles may change (Non-Patent Document 4). The existence of such in-plane-oriented magnetic particles will deteriorate 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 the magnetic particles on the underlying film. 【0008】 Therefore, the present inventors have found L1 ０ As a method for suppressing the in-plane orientation of magnetic particles such as FePt alloys having a type structure, it has been reported that a C (carbon) buffer layer is formed on the underlying film 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. 【0009】 Patent No. 6168066 【0010】 A. Perumal, YKTakahashi, and K. Hono, Appl. Phys. Exp. 1, 101301 (2008).T.Suzuki and K. Ouchi, IEEE Trans. Magn. 37,1283 (2001).KF Dong, HH Li, YG Peng, G. Ju, GM Chow, and JS Chen, Appl. Phys.Lett.104, 192404 (2014).Takashi Saito, Kim Kong Tham, Ryosuke Kushibiki,Tomoyuki Ogawa, and Shin Saito, Jpn. J. Appl. Phys.,60, 075505 (2021).KimKong Tham, Ryosuke Kushibiki,Shin Saito,AIPAdvances 14,025102(2024) 【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 oxide or other nonmagnetic grain boundary. 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】 The present invention was made against the background described above, L1 ０ This invention 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 a mold 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 aforementioned underlayer, such as MgO, and the magnetic thin film. 【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 the 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 (vertical direction) but also in the planar direction (horizontal 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 made of carbon (C) or 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 FePt alloy with low saturation magnetization, 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, a carbide, and a nitride, 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. 【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 the sputtering target for magnetic recording media 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 underlayer 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 distinguished 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-based alloy phase) When the sputtering target according to the present invention is sputtered, Fe and Pt, which are constituent elements of the magnetic phase, and element M form the FePt-based alloy phase of the buffer layer. The FePt-based alloy phase in the buffer layer exhibits a pinning effect during the process in which a magnetic thin film is formed 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 the FePt-based alloy. 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-based 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-based 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% or more and 80 mol% or less. Within this range, the respective content of Fe and Pt in the magnetic phase is preferably 2.5 mol% or more and 45 mol% or less for Fe, and 2.5 mol% or more and 45 mol% or less 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, carbides, and nitrides. Specific examples of carbides include NbC, TiC, Si, ZrC, and B ４ Examples include C, HfC, and TaC. Specific examples of nitrides include BN and Si ３ N ４ , AlN, TiN, TaN, Cr ２ N, NbN, HfN, VN, and GaN are applicable. 【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 volume% or less by volume ratio. 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 volume% or less. Furthermore, if the proportion of the magnetic phase is too small, 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 volume% or more. A more preferable proportion of the magnetic phase is 50 volume% to 80 volume%. 【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 in 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 are elements that constitute the magnetic phase, and powders containing C, carbides, and nitrides that constitute the non-magnetic phase are used as raw material powders, and after mixing these and forming them appropriately, a sputtering target can be manufactured by pressurizing and sintering. 【0028】 As powders containing Fe, Pt, and element M, which constitute the magnetic phase of the raw material powder, 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 powders containing C, carbides, and nitrides, which constitute the non-magnetic phase of the raw material powder, C powder, carbide powders (NbC powder, TiC powder, etc.), and nitride powders (BN powder, Si ３ N ４ Powders (and the like) 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 a 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 by a sputtering target according to the present invention. The present invention is useful for forming a buffer layer for forming a magnetic thin film of a magnetic recording medium such as a heat-assisted magnetic recording medium. In the method for manufacturing a magnetic recording medium, a buffer layer can be formed on a substrate underlayer by sputtering the sputtering target according to the present invention. 【0031】 There are no particular restrictions on the material, dimensions, or shape of the base material. Also, the underlayer is L1 ０ The underlying layer is not particularly limited as long as it is applied to form a magnetic material such as an FePt alloy having a mold structure. As described above, L1 ０ As a base layer for providing (001) orientation to magnetic thin films such as FePt alloys having a type structure, (100)-oriented MgO is well known, and an MgO base layer can also be applied in the present invention. In addition, MgTiO ２ MgSiO ２ MgAl ２ O ５ RuAl and the like can be used as the base layer. 【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】 Furthermore, when forming a buffer layer using the sputtering target according to the present invention, it is preferable that the thickness of the buffer layer, calculated in terms of film thickness, be 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 of the buffer layer, in particular the effect of suppressing the in-plane orientation of magnetic particles. On the other hand, if the buffer layer has an excessively large film thickness, the exposure of the magnetic phase on the surface will be reduced, making it difficult to exert the pinning effect by the magnetic phase, which can become a factor in the random growth and in-plane orientation of magnetic particles. It is more preferable that the film thickness of the buffer layer be 0.1 nm or more and 0.8 nm or less. The reason for using film thickness calculation is to take into consideration that the buffer layer may be formed in an island-like shape, as described above. Film thickness calculation refers to the film thickness assuming that metal atoms and non-metal atoms are uniformly arranged on the underlying film. 【0034】 Furthermore, the sputtering target according to the present invention having the above-described configuration has a saturation magnetization M ｓ A material capable of forming a thin film (buffer layer) with low saturation magnetization M of the buffer layer is preferred. ｓ This is because it can affect the magnetic properties of the magnetic thin film deposited thereon. Specifically, the saturation magnetization M of the buffer layer formed by the sputtering target according to the present invention ｓ It is 350 emu / cm ３ The following is preferable: 300 emu / cm ３ The following are preferable. 【0035】 After forming a buffer layer on the underlayer using the above steps, a magnetic recording medium can be manufactured by depositing a magnetic thin film according to a conventional method. Based on the main points and problems of the present invention described above, the magnetic thin film is L1０ Magnetic thin films made of FePt alloy, CoPt alloy, FePd, CoPd, etc., having a mold structure are preferably applied. These magnetic thin films can also be deposited by sputtering. Furthermore, after the formation of the magnetic thin film, additional components such as a protective layer for the magnetic thin film may be added to form a magnetic recording medium. 【0036】 As explained above, the present invention is L1 ０ This sputtering target acts on magnetic thin films such as FePt alloys having a specific structure, and is used to form a buffer layer on an underlying layer such as MgO. 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 nonmetallic atoms from a nonmagnetic phase such as C, and enables the refinement of magnetic particles by metal atoms from a magnetic phase made of FePt alloys. 【0037】 Fe of the first embodiment ５０－ｘ Pt ５０－ｘ Cu ２ｘ In-plane XRD profile of a buffer layer deposited using a -30 vol% C sputtering target (2x: 0, 30, 50, 70). First embodiment Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ Cu concentration (2x) and saturation magnetization M of buffer layers deposited using a -30 vol% C sputtering target (2x: 0, 30, 50, 70) ｓ A graph showing the relationship with the first embodiment of Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ Magnetic thin film (Fe) deposited on a buffer layer using a -30 vol% C sputtering target (2x: 0, 30, 50, 70) ５０ Pt ５０ -30 vol% B ２ O ３ In-plane XRD profile of ) Fe of the first embodiment. 35 Pt ３５ Cu ３０ A magnetic thin film (Fe) deposited on a buffer layer (film thickness: 0-1.0 nm) using a -30 vol% C sputtering target. ５０ Pt ５０ -30 vol% B ２ O ３In-plane XRD profile of ) Fe of the first embodiment. ５０－ｘ Pt ５０－ｘ Cu ２ｘ A magnetic thin film (Fe) deposited on a buffer layer using a -30 vol% C sputtering target (2x: 30, 50, 70) ５０ Pt ５０ -30 vol% B ２ O ３ Planar TEM image of ). Magnetic thin film (Fe) deposited on a buffer layer using a 100% C sputtering target in the comparative example of the first embodiment. ５０ Pt ５０ -30 vol% B ２ O ３ Planar TEM image of ) Fe of the first embodiment. ５０－ｘ Pt ５０－ｘ Cu ２ｘ A magnetic thin film (Fe) deposited on a buffer layer using a -30 vol% C sputtering target (2x: 30, 50, 70) ５０ Pt ５０ -30 vol% B ２ O ３ Cross-sectional TEM image of ). Magnetic thin film (Fe) deposited on a buffer layer using a 100% C sputtering target in the comparative example of the first embodiment. ５０ Pt ５０ -30 vol% B ２ O ３ Cross-sectional TEM image of the first embodiment of Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ A magnetic thin film (Fe) deposited on a buffer layer (film thickness: 0-1.0 nm) using a -30 vol% C sputtering target (2x: 30, 50, 70) ５０ Pt ５０ -30 vol% B ２ O ３ ) Magnetic anisotropy constant K ｕ A graph showing the measurement results. 【0038】First Embodiment: The embodiments of the present invention will be described below. In this embodiment, Cu is applied as the element M of the FePt-based alloy that constitutes the magnetic phase of the sputtering target, and a sputtering target for forming a buffer layer (FePtCuC sputtering target) composed of a magnetic phase made of FePtCu alloy and a non-magnetic phase made of C is manufactured. Then, a buffer layer is formed on the MgO base film using the manufactured FePtCuC sputtering target, and the structure and magnetic properties (saturation magnetization M ｓ ) of the buffer layer are examined. Further, a magnetic thin film made of FePt alloy is formed on the buffer layer, and the orientation and particle size of the magnetic particles that constitute the magnetic thin film are examined. 【0039】 [Manufacture of Sputtering Target for Forming Buffer Layer] In this embodiment, Fe powder, Pt powder, Cu powder, which are raw material powders of the magnetic phase, and C powder, which is the raw material powder of the non-magnetic phase, are mixed, and the mixed powder is sintered to manufacture a sputtering target for forming a buffer layer. 【0040】 All the raw material powders used in this embodiment are commercially available, and the average particle sizes of the Fe powder, Pt powder, Cu powder, and C powder are 5 μm, 2 μm, 4 μm, and 3 μm, respectively. Then, the Fe powder, Pt powder, Cu powder, and C powder are mixed in a ball mill (grinding medium: ceramic balls) to manufacture a mixed powder. 【0041】 The FePtCuC sputtering target manufactured in this embodiment is an FePtCuC sputtering target in which the magnetic phase (FePtCu) is 70% by volume and the non-magnetic phase (C) is 30% by volume. Then, for the magnetic phase, a plurality of FePtCuC sputtering targets with the same Fe concentration (mol%) and Pt concentration (mol%) but different Cu concentrations (mol%) are manufactured. Hereinafter, this FePtCuC sputtering target is referred to as Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ-30 vol% C may be referred to as such. 2x is the Cu concentration (mol%), and in this embodiment, 2x = 0 mol%, 30 mol%, 50 mol%, 70 mol% were used. The composition of this magnetic phase was adjusted by the mixing ratio of the above-described Fe powder, Pt powder, and Cu powder. Also, the volume% of the magnetic phase and the non-magnetic phase was adjusted by the mixing ratio of the raw material powder that becomes the magnetic phase and the C powder that becomes non-magnetic. 【0042】 The sputtering target for forming the buffer layer (Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ -30 vol% C) was manufactured by pressure-sintering the mixed powder manufactured above. The pressure-sintering was performed by the hot press method at a sintering temperature of 900 °C, a pressure of 60 MPa, and a pressure-sintering time of 60 min, and the atmosphere was a vacuum condition of 5×10 －２ Pa or less. The manufactured Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ -C sputtering target had a diameter of 161 mm and a thickness of 4 mm, and a relative density of 96% to 99%. 【0043】 [Formation of buffer layer] Then, using the Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘ -C sputtering target manufactured above, a buffer layer was formed on the MgO underlayer film in the following steps. In the substrate preparation, deposition of the underlayer film, formation of the buffer layer, and deposition of the magnetic thin film described below, an RF / DC magnetron sputtering apparatus (manufactured by Canon Anelva Corporation, C3010) was used as the sputtering apparatus in all cases. 【0044】 An amorphous glass substrate (thickness 0.635 mm) was prepared by depositing an amorphous Co60 at%-W40 at% layer by sputtering (Ar gas pressure: 0.6 Pa, input power: 500 W) to a thickness of 80 nm. Then, a MgO underlayer film was deposited by sputtering (Ar gas pressure: 0.6 Pa, input power: 500 W) to a thickness of 5 nm to prepare a substrate sample. 【0045】 The formation of the buffer layer was carried out using the Fe ５０－ｘ Pt ５０－ｘ Cu ２ｘA 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 manufactured 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 ｓ The measurement was performed using a vibrating 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 Cu concentration (2x) of 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 ２ｘSaturation 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, showing 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 the particle size of the magnetic particles were evaluated. 【0050】 FePt magnetic thin films are deposited using Fe as a sputtering target. ５０ Pt ５０ -30 vol% B ２ O ３ Using the above method, sputtering was performed 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 thick 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 prior art technique (Non-Patent Literature 5). In this prior art 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 -30 vol% B２ O ３ The sample on which the film was deposited was subjected to XRD analysis, and L1 ０ The presence or absence of in-plane orientation and the quality of (001) orientation for magnetic particles having a type structure were investigated. 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 a -30 vol% C film (film thickness 0.6 nm). In this XRD diffraction profile, the diffraction peaks around 2θ = 33°, 47°, and 69° are L1, respectively. ０ These are peaks corresponding to the (110), (200), and (220) planes of the FePt type structure. 【0052】 L1 ０ In in-plane XRD measurements of FePt magnetic thin films having a 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) of this embodiment ５０－ｘ Pt ５０－ｘ Cu ２ｘ In the XRD profile of a magnetic thin film on -30 vol% C (2x = 0 mol% to 70 mol%), it can be seen that the (001) superlattice reflection peak is not observed. From this, it can be said that the presence of a buffer layer can suppress the in-plane orientation of the magnetic thin film. Furthermore, from the viewpoint of suppressing in-plane orientation, 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 (Fe) with a Cu concentration of 30 mol%. ３５ Pt ３５ Cu ３０ -30 vol% C), and the thickness of the buffer layer (d ＢＬThis is the XRD diffraction pattern of the FePt magnetic thin film 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 the 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 -30 vol% B ２ O ３ TEM observations were performed on the planar and cross-sectional aspects of the material 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) is applied. Figure 6 is a planar TEM image of an FePt magnetic thin film when C (100% C) is used as a buffer layer (BL) in the conventional technology. 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 -30 vol% C applied. Figure 8 shows a cross-sectional TEM image of an FePt magnetic thin film using conventional technology with C (100% C) as a buffer layer (BL). Each figure also shows planar TEM and cross-sectional TEM images of magnetic thin films deposited without applying a buffer layer. 【0055】 Referring to the planar TEM images of the magnetic thin films in Figures 5 and 6, both magnetic thin films have nonmagnetic grain boundaries (B ２ O ３ Magnetic particles (Fe) separated by ) ５０ Pt ５０It 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 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, looking at the cross-sectional TEM of the magnetic thin film of this embodiment in Figure 7, it can be seen that the lateral grain growth of the magnetic particles on the buffer layer of this embodiment is suppressed, and the average cluster size is reduced. 【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 film] Buffer layer (Fe) of this embodiment ５０－ｘ Pt ５０－ｘ Cu ２ｘ A magnetic thin film (Fe) deposited on -30 vol% C ５０ Pt ５０ -30 vol% B ２ O ３ ) For this, the magnetic anisotropy constant K is a magnetic property. ｕ The magnetic anisotropy constant K was measured. ｕThe 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 (film thickness 0 nm). ｕ It can be seen that there is a tendency for it to increase. The buffer layer (Fe) of this embodiment ５０－ｘ Pt ５０－ｘ Cu ２ｘ It was also confirmed that the -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 film (Fe ５０ Pt ５０ -30 vol% B ２ O ３ From the results of various studies on this matter, it can be 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, the magnetic thin film (Fe) was processed under the same conditions as in the first embodiment. ５０ Pt ５０ -30 vol% B ２ O ３ A thin film was deposited. As a reference example, a sample was also prepared in which a magnetic thin film was deposited on an MgO underlayment under the same conditions as in the first embodiment, without forming a buffer layer. 【0065】After deposition of the magnetic thin film, XRD analysis was performed. In this embodiment, the presence or absence of the (001) superlattice reflection peak in the XRD profile of the magnetic thin film was confirmed. In addition, the particle size of the magnetic particles was calculated from the full width at half maximum of the (200) diffraction peak (2θ = 47°) and Scherrer's equation. 【0066】 Tables 1 to 4 show the configurations of the various buffer layer formation sputtering targets investigated in this embodiment, as well as the evaluation results for the buffer layer and magnetic thin film. Each table shows the saturation magnetization M of the buffer layer. ｓ Measurement results, magnetic thin film (Fe ５０ Pt ５０ -30 vol% B ２ O ３ This shows the presence or absence of the (001) peak and the particle size of the magnetic particles. In the table, the numerical values ​​indicating the composition of the magnetic phase (FePtM) of the buffer layer represent the mol% of element M, and the numerical values ​​for the non-magnetic phase (C, BN, etc.) represent the volume % in the sputtering target. Table 1 also includes the evaluation results for the buffer layer and magnetic thin film performed in the first embodiment. 【0067】 【0068】 【0069】 【0070】 【0071】 Referring to Tables 1 to 4, we will confirm the effect of the buffer layer and the preferred configuration. First, looking at Table 1, in the magnetic thin film without a buffer layer (No. 11), which was used as a reference example, a (001) peak was observed in the XRD diffraction pattern, confirming that in-plane orientation occurs in the magnetic thin film when there is no buffer layer. Although the in-plane orientation of the magnetic thin film can be resolved by setting the conventional C buffer layer, in that case, coarsening of the magnetic particles occurs (No. 12). 【0072】Compared to these reference examples and the results of the conventional technology, it can be seen that by employing a buffer layer combining a C (non-magnetic phase) with an FePt-based alloy phase (magnetic phase), both the problems of in-plane orientation and magnetic particle coarsening are resolved (Nos. 1-10). 【0073】 However, when using an FePt alloy that does not contain element M as the magnetic phase, the saturation magnetization M of the buffer layer ｓ It is 470 memu / cm ３ This increases the saturation magnetization M of the buffer layer, raising concerns about its impact on the magnetic properties of the magnetic thin film formed on top of it (No. 1). Therefore, when an FePt-based alloy phase with element M (Cu) added to the magnetic phase is applied, the saturation magnetization M of the buffer layer ｓ It can be seen that the saturation magnetization M of the buffer layer decreases (Nos. 2-10). ｓ This decreases with increasing Cu concentration. For the Cu concentration of the FePt alloy, which is the magnetic phase, setting it to 20 mol% or more allows the saturation magnetization M of the buffer layer to be achieved. ｓ It is 350 emu / cm ３ The following can be achieved (Nos. 3-10). Furthermore, if the concentration of element M in the FePt alloy is 30 mol% or more, the saturation magnetization M of the buffer layer ｓ It is 300 emu / cm ３ The following are particularly preferable ranges. 【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 to 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 are non-magnetic phases other than carbon (C), such as carbides (NbC, TiC, SiC, ZrC) and nitrides (BN, Si ３ N４ These materials (such as AlN and TiN) were applied. Similar effects to those confirmed in Tables 1 and 2 were observed with these materials as well. 【0076】 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 increases. 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% (Nos. 43-50). Furthermore, when using a sputtering target consisting only of a magnetic phase, the buffer layer without a non-magnetic phase is subject to saturation magnetization 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. 【0077】 As explained above, the present invention is L1 ０ This sputtering target is for forming a buffer layer between a magnetic thin film made of an FePt alloy or the like having a molded structure and an underlying layer. The buffer layer formed by this 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 used 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 substrate and a magnetic thin film when forming a magnetic thin film on a substrate substrate, comprising: a magnetic phase made of an FePt alloy consisting of Fe and Pt and element M; and a non-magnetic phase consisting of at least one of C, a carbide, and a nitride, wherein the element M of the FePt 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. The sputtering target for a magnetic recording medium according to claim 1 or claim 2, wherein the FePt-based alloy constituting the magnetic phase is essentially composed of Cu as element M.

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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