Sputtering target for magnetic recording medium

Abstract

The present invention provides a sputtering target for forming a buffer layer that is formed between a base film and a magnetic thin film of a magnetic recording medium. A sputtering target according to the present invention is composed of: a metal phase which is composed of a non-magnetic metal that is at least one selected from among Pt, Ag, Au, Pd, Rh, Ir, Ru, and Cu; and a non-metal phase which is composed of at least one selected from among C, a carbide, and a nitride. A buffer layer that is formed according to the present invention can suppress the in-plane orientation of magnetic particles of a magnetic thin film formed on the buffer layer. According to the present invention, the magnetic particles can be refined by adding a metal such as Pt to the buffer layer.

Description

Sputtering targets for magnetic recording media

[0001] The present invention relates to a sputtering target for forming a buffer layer consisting of a metal phase and a non-metal phase on an undercoat film of a magnetic film of a magnetic recording medium, and more particularly to a sputtering target useful for forming a buffer layer that reduces the grain size while suppressing the in-plane orientation of magnetic grains that constitute the magnetic thin film of a thermally assisted magnetic recording medium or the like.

[0002] The recording density of magnetic recording media such as hard disk drives (HDDs) has been increasing rapidly for some time, and it is predicted that the demand and trend for higher recording densities will continue in the future. Against this background, magnetic recording media using a thermally assisted recording method have been attracting attention in recent years as a next-generation recording method. Thermally assisted magnetic recording media are media that use a recording method in which near-field light or the like is irradiated onto a magnetic thin film to locally heat the thin film surface, temporarily reducing the coercivity of magnetic particles (magnetic clusters) for writing. This thermally assisted method makes it easy to write to a magnetic thin film with high coercivity, even with current recording heads, and therefore improves the magnetic anisotropy K ｕ It is possible to use materials with high mechanical properties by micronizing them.

[0003] Magnetic anisotropy K applied to magnetic thin films of thermally assisted magnetic recording media ｕ As a magnetic material with high L1 ０ FePt alloys and CoPt alloys having the L1 structure are known. ０ When a magnetic material having a mold structure is suitably applied to a recording medium, the crystalline orientation of the magnetic particles and the reduction of 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] direction (c-axis), which is the axis of easy magnetization, is grown in the perpendicular direction to the surface, and that the orientation is (001). In order to ensure the orientation of magnetic particles such as FePt alloys, it is known that it is preferable to form a (100)-oriented MgO underlayer. This is because the (100) plane of MgO is aligned with the L1 ０ This utilizes the fact that it has lattice matching with the (001) plane of the FePt alloy having the type structure.

[0005] On the other hand, miniaturization of magnetic particles in magnetic recording media is a necessary characteristic for improving the S / N ratio and increasing the recording density, and is a characteristic generally required for the magnetic thin film of magnetic recording media, not just for the thermally assisted recording method. ２ , TiO ２ , B ２ O ３ It is said that the application of a granular structure in which oxides such as those mentioned above are used as non-magnetic grain boundaries is effective. In a granular magnetic thin film, the non-magnetic grain boundaries separate and refine the magnetic grains, and also contribute to noise reduction by reducing the magnetic interaction between the grains. The application of a granular structure is ０ It is also effective for magnetic thin films made of FePt alloys with a crystalline structure, and in addition to the above oxides, C (carbon: Non-Patent Document 1), MgO (Non-Patent Document 2), ZrO ２ (Non-patent Document 3), GeO ２ There are granular magnetic thin films with non-magnetic grain boundaries, such as those disclosed in Patent Document 1.

[0006] L1 as above ０ In granular magnetic thin films made of FePt alloys, CoPt alloys, etc. having a ferromagnetic structure, the constituent material of the non-magnetic grain boundaries affects the saturation magnetization (M ｓ ) and K ｕ It has been revealed that the magnetic properties such as L1 are affected. One of the effects is the orientation of the magnetic particles. ０ In magnetic thin films of FePt alloys with a lattice structure, it is preferable that the c-axes of the magnetic grains are (001) oriented in a single direction perpendicular to the surface. However, depending on the material of the non-magnetic grain boundaries, magnetic grains with in-plane orientation, in which the c-axes are located within the magnetic film surface, may be produced, changing the proportion of magnetic grains with (001) orientation (Non-Patent Document 4). The presence of such in-plane oriented magnetic grains can degrade the magnetic properties of the medium.

[0007] The reason why the material of the non-magnetic grain boundary causes in-plane orientation in the magnetic grains is not entirely clear, but the inventors believe that this is because the oxides that form the non-magnetic grain boundary act on the interface between the underlayer, such as MgO, and the magnetic thin film, such as an FePt alloy, thereby inhibiting the epitaxial growth of the (001) plane of the magnetic grains on the underlayer.

[0008] Therefore, the present inventors have ０ As a method for suppressing the in-plane orientation of magnetic grains such as FePt alloys having a (001) structure, it has been reported that a C (carbon) buffer layer is formed on an underlayer using a sputtering target made of C before depositing an FePt alloy granular magnetic thin film (Non-Patent Document 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 grains is suppressed, and an FePt alloy granular magnetic thin film with a large proportion of magnetic grains oriented in the (001) plane 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 buffer layer made of carbon (C) described above has the effect of suppressing the in-plane orientation of magnetic grains without changing the material of the oxides or other non-magnetic grain boundaries. However, the use of a C buffer layer presents one problem. That is, when a magnetic thin film is formed after the formation of a C buffer layer, the grain size of the magnetic grains tends to become coarse. As mentioned above, the grain size of the magnetic grains in the magnetic thin film, as well as the control of orientation, is an important factor that affects the magnetic properties and recording density of the magnetic thin film, so the coarsening of the magnetic grains is an unavoidable problem.

[0012] The present invention has been made under the above-mentioned background, and ０ The present invention clarifies a means for suppressing in-plane orientation and achieving miniaturization of magnetic grains constituting a magnetic thin film made of an FePt alloy, CoPt alloy, etc. having a morphology of 1000 to 10000. 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 magnetic thin film and the underlayer such as MgO described above.

[0013] The present inventors have studied the structure of the buffer layer and the sputtering target for forming the buffer layer, and have decided to add a metal to C (carbon) as the structure of the buffer layer. According to the studies of the present inventors disclosed in the above-mentioned Non-Patent Document 5, C is an effective element in suppressing the in-plane orientation of magnetic grains made of FePt alloys or the like and promoting epitaxial growth of the c-axis of the magnetic grain crystals. However, the growth of the magnetic grains at this time extends not only in the perpendicular direction (vertical direction) but also in the planar direction (horizontal direction). This grain growth in the planar direction is the cause of the in-plane orientation. The present inventors have decided to refine the crystal grains of the magnetic thin film by adding metal atoms to the buffer layer, which can suppress the in-plane growth of the magnetic grains through a pinning action.

[0014] When the buffer layer is composed of a metal together with C, the metal must be a non-magnetic metal. If the buffer layer becomes magnetic due to the addition of a magnetic metal, this will affect the magnetic properties of the magnetic thin film formed on the buffer layer. From this perspective, the inventors have conceived the present invention, believing that at least one of Pt, Ag, Au, Pd, Rh, Ir, Ru, and Cu is suitable as a metal for forming the buffer layer together with C.

[0015] That is, the present invention, which solves the above-mentioned problems, is a sputtering target for magnetic recording media, which is used to form a buffer layer between an underlayer film and a magnetic thin film when forming a magnetic thin film on an underlayer film on a substrate, and which comprises a metallic phase made of at least one non-magnetic metal selected from Pt, Ag, Au, Pd, Rh, Ir, Ru, and Cu, and a non-metallic phase made of at least one of C, carbide, and nitride.

[0016] The structure and manufacturing method of the sputtering target for a magnetic recording medium according to the present invention will be described below, along with a method for forming a buffer layer using the sputtering target for a magnetic recording medium according to the present invention.

[0017] (A) Structure 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 used to form a buffer layer between the underlayer of the magnetic recording medium and the magnetic thin film that is the recording layer. The sputtering target according to the present invention is composed of a metallic phase made of a predetermined metal and a non-metallic phase such as C. The metallic phase and the non-metallic phase are regions that are separated and distinct from each other. In other words, the sputtering target according to the present invention has a structure in which a region made of a metal such as Pt and a region made of a non-metallic element such as C are separated and mixed, as viewed from the viewpoint of material structure.

[0018] (A-1) Metal Phase When the sputtering target according to the present invention is sputtered, the metal atoms contained in the metal phase act as the metal component of the buffer layer. During the formation of the magnetic thin film, the metal of the buffer layer suppresses the in-plane (lateral) grain growth of magnetic particles composed of FePt alloys or the like through a pinning effect, thereby suppressing the coarsening of the magnetic particles. This metal phase is composed of at least one of Pt, Ag, Au, Pd, Rh, Ir, Ru, and Cu. These metals are paramagnetic or diamagnetic and do not impart magnetism to the buffer layer. Furthermore, these metals are difficult to wet and react with the underlayer film, such as MgO. For these reasons, at least one of the above metals is selected in the present invention. More preferred metals for the metal phase are Pt, Ag, Au, and Cu. The metal phase may be composed of at least one of the above metals, but may also be an alloy or intermetallic compound composed of two or more metals.

[0019] The metal phase may contain at least one of Pt, Ag, Au, Pd, Rh, Ir, Ru, and Cu as an essential metal element, and other elements as optional elements. Specifically, the metal phase may contain at least one of the nonmagnetic elements Si, Ti, Cr, B, V, Nb, Ta, Mn, Zn, Mo, W, and Ge. These elements may be included because they are expected to have the effect of reducing the grain size of the metal phase. When the metal phase contains these optional nonmagnetic elements, the content of the nonmagnetic elements in the metal phase is preferably 20 mol% or less. This is to reduce the size of the metal phase to a degree that does not cause the buffer layer to become amorphous. Note that since nonmagnetic elements such as Si are optional elements and not essential elements, the lower limit of their content in the metal phase is 0 mol%.

[0020] A-2 Non-metallic Phase When the sputtering target according to the present invention is sputtered, the non-metallic elements contained in the non-metallic phase are deposited on the underlayer such as MgO as a buffer layer. This reduces the effect of non-magnetic grain boundary materials such as oxides on the interface between the underlayer and the magnetic thin film during the formation of the magnetic thin film made of an FePt alloy or the like, and suppresses the in-plane orientation of the magnetic grain crystals. The non-metals that make up this non-metallic phase include C, carbides, and nitrides. Specific examples of carbides include NbC, TiC, Si, ZrC, and B. ４ 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.

[0021] The reason why C is effective as a constituent element of the buffer layer is also mentioned in the above-mentioned prior art (Non-Patent Document 5): C has the property of separating magnetic grain crystals such as FePt, thereby suppressing in-plane orientation. Furthermore, carbides have the same effect as C and can also suppress in-plane orientation. Regarding nitrides, the inventors believe that nitrides mitigate the effects of oxides that may form at the interface between the underlayer and the magnetic thin film, thereby suppressing in-plane orientation of the magnetic grain crystals.

[0022] (A-3) Overall Structure of the Sputtering Target According to the Present Invention The sputtering target according to the present invention, which is composed of a metal phase and a non-metal phase, preferably comprises 10% by volume or more and 70% by volume or less of the metal phase, with the remainder being the non-metal phase and unavoidable impurities. The structure of the buffer layer formed on the surface of the underlayer, i.e., the ratio of metal atoms to non-metal atoms on the surface of the underlayer, corresponds to the composition of the sputtering target. If the metal phase in the sputtering target is less than 10% by volume, it becomes difficult to obtain the effect of metal atoms such as Pt in suppressing the coarsening of magnetic particles. On the other hand, metal atoms such as Pt suppress the planar growth of FePt alloys, etc., but the presence of excessive metal atoms on the underlayer may cause crystal growth in crystal orientations other than the (001) direction. Specifically, the presence of excessive metal atoms promotes the growth of the (111) plane. For this reason, the proportion of the metal phase in the sputtering target is preferably 70% by volume or less. A more preferred proportion of the metal phase is 20% by volume or more and 50% by volume or less.

[0023] Furthermore, in the sputtering target according to the present invention, a metallic phase and a non-metallic phase are dispersed as separate phases in the material structure, and the shapes and dimensions of the metallic phase and the non-metallic phase are not particularly limited and vary depending on the proportion of each phase in the sputtering target, the manufacturing conditions, etc.

[0024] When the proportion of the metallic phase is high (50% by volume or more), the material structure of the sputtering target is a matrix of the metallic phase with a dispersed non-metallic phase. In this case, the particle size of the non-metallic phase is preferably 0.1 μm to 30 μm in equivalent circle diameter. If the non-metallic phase is too fine, aggregation of the non-metallic phase is likely to occur in the material structure. Furthermore, if the non-metallic phase becomes coarse, the contact cross section with the metallic phase becomes small, and the non-metallic phase may fall off during sputtering, generating particles. Conversely, when the proportion of the non-metallic phase is high (e.g., 50% by volume to 90% by volume), the material structure of the sputtering target is a matrix of the non-metallic phase with a dispersed metallic phase. In this case, the particle size of the metallic phase is preferably 0.1 μm to 100 μm in equivalent circle diameter. To manufacture a sputtering target with a metallic phase of less than 0.1 μm, the particle size of the raw material powder must also be fine. In this case, excessive mixing energy may be required, and the amount of impurities mixed in from the mixing device (mixing medium, mixing vessel) may increase. Furthermore, if the metal phase exceeds 100 μm, the contact area between the metal phase and the non-metal phase becomes small, which may cause separation during sputtering and generation of particles.

[0025] 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 metallic phase and non-metallic phase described above. However, the presence of unavoidable impurities is permitted. The unavoidable impurities are elements other than the metallic elements and non-metallic elements listed above, specifically O (oxygen). The unavoidable impurities are elements derived from the raw material powder and the manufacturing equipment in the manufacturing method described below. The unavoidable impurities are contained in the metallic phase and / or the non-metallic phase. The content of the unavoidable impurities is preferably 1000 ppm, more preferably 500 ppm or less, relative to the mass of the entire sputtering target.

[0026] (B) Manufacturing Method of a Sputtering Target for Magnetic Recording Media According to the Present Invention The sputtering target according to the present invention comprises a metallic phase made of the above-mentioned metal and a non-metallic phase made of C or the like. A preferred method for manufacturing a sputtering target of this configuration is powder metallurgy, which allows the metallic and non-metallic phases to be uniformly dispersed. In the powder metallurgy method, a metal powder that will form the metallic phase and a non-metallic powder that will form the non-metallic phase are mixed, appropriately molded, and then pressure-sintered to produce a sputtering target.

[0027] The metal powder used as the raw material is preferably a high-purity (99% or higher) metal powder such as Pt. Furthermore, if the metal phase contains an optional element (e.g., Si) other than essential metals such as Pt, a powder of the optional element may be used, but an alloy powder of the essential metal and the non-magnetic element can also be used as the raw material. These powders can be produced by an atomization method such as gas atomization. In producing the sputtering target according to the present invention, the particle size of the metal powder and non-metal powder used as raw materials is preferably 100 μm or less.

[0028] The above metal powders and nonmetal powders are thoroughly mixed before sintering to obtain a mixed powder. Mixing and dispersing means such as a ball mill, a bead mill, or a rocking mill can be used for this mixing. The mixed powder obtained by these mixing means may be preformed before the subsequent pressure sintering process. The mixed powder is then appropriately formed and pressure sintered to obtain the sputtering target of the present invention. Sintering means that can be used in this process include hot pressing (HP), hot isostatic sintering (HIP), and spark plasma sintering (SPS). The sintering temperature during pressure sintering is preferably 600°C or higher and 1500°C or lower, and the applied pressure is preferably 10 MPa or higher and 200 MPa or lower. The heating atmosphere is preferably a vacuum or a non-oxidizing atmosphere.

[0029] (C) A method for manufacturing a magnetic recording medium in which a buffer layer is formed 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 of a magnetic recording medium such as a thermally assisted magnetic recording medium. In the method for manufacturing a magnetic recording medium, a buffer layer can be formed on an underlayer on a substrate by sputtering the sputtering target according to the present invention.

[0030] There are no particular restrictions on the material, size, and shape of the substrate. ０ There are no particular limitations on the underlayer, as long as it is applicable to forming a magnetic material such as an FePt alloy having a L1 structure. ０ As an underlayer for providing a (001) orientation to a magnetic thin film such as an FePt alloy having a ferromagnetic structure, (100) oriented MgO is well known, and an MgO underlayer can also be applied to the present invention. ２ , MgSiO ２ , MgAl ２ O ５ , RuAl, etc. can be used as the underlayer.

[0031] The sputtering target according to the present invention can be sputtered using a conventional sputtering device under conventional sputtering conditions. The metal atoms constituting the metal phase and the nonmetal atoms constituting the nonmetal phase are sputtered onto the underlayer to form a buffer layer. The buffer layer formed in this case may be a film in which the metal atoms and the nonmetal atoms are continuously bonded, or may be in the form of islands on the surface of the underlayer.

[0032] Furthermore, when forming a buffer layer using the sputtering target of the present invention, it is preferable that the thickness of the buffer layer, calculated as a film thickness, be 0.1 nm or more and 2.0 nm or less. If the thickness is less than 0.1 nm, it is difficult to suppress the in-plane orientation of the magnetic grains. If the buffer layer is formed thicker than 2.0 nm in film thickness equivalent, the metal phase is less exposed on the surface, making it difficult to exert the pinning effect of the metal phase, which may cause random growth of the magnetic grains. Note that the reason for using a film thickness equivalent is that, as mentioned above, the buffer layer may be formed in an island shape. The film thickness equivalent is the film thickness assuming that metal atoms and non-metal atoms are uniformly arranged on the base film.

[0033] After the buffer layer is formed on the underlayer by the above steps, a magnetic thin film is formed in accordance with a conventional method to obtain a magnetic recording medium. ０ Suitable magnetic thin films are those made of FePt alloys, CoPt alloys, FePd, CoPd, etc., having a ZnO-type structure. These magnetic thin films can also be formed by sputtering. After the magnetic thin film is formed, additional components such as a protective layer for the magnetic thin film may be added to form a magnetic recording medium.

[0034] As described above, the present invention is ０ This sputtering target acts on a magnetic thin film such as an FePt alloy having a morphology structure, and is used to form a buffer layer on an underlayer 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 grains by non-metallic atoms from a non-metallic phase such as C, and enables the refinement of magnetic grains by metal atoms from a metallic phase such as Pt.

[0035] A magnetic thin film (Fe) having a buffer layer formed by a sputtering target of the comparative example (100% C) ５０ Pt ５０ -30vol%B ２ O ３ ) In-plane XRD profile of the magnetic thin film (Fe ５０ Pt ５０-30vol%B ２ O ３ ) In-plane XRD profile of the magnetic thin film (Fe) formed under the conditions after forming the buffer layer using the sputtering targets of the first embodiment (50 vol % Pt-50 vol % C) and the comparative example (100% C), and without the buffer layer. ５０ Pt ５０ -30vol%B ２ O ３ ) Planar TEM images of the magnetic thin film (Fe) formed under the conditions after forming the buffer layer using the sputtering targets of the first embodiment (50 vol % Pt-50 vol % C) and the comparative example (100% C), and without the buffer layer. ５０ Pt ５０ -30vol%B ２ O ３ ) cross-sectional TEM images of magnetic thin films (Fe) on which buffer layers are formed using sputtering targets with various Pt contents according to the second embodiment. ５０ Pt ５０ -30vol%B ２ O ３ ) in-plane XRD profile of the magnetic thin film (Fe) formed under the conditions after forming the buffer layer using the sputtering target of the second embodiment with various Pt contents, and without the buffer layer. ５０ Pt ５０ -30vol%B ２ O ３ ) are planar TEM images of the magnetic thin films (Fe) formed under the conditions after forming the buffer layer using the sputtering targets with various Pt contents according to the second embodiment, and without the buffer layer. ５０ Pt ５０ -30vol%B ２ O ３ ) Cross-sectional TEM image.

[0036] First embodiment: An embodiment of the present invention will be described below. In this embodiment, a sputtering target composed of a metallic phase made of Pt and a non-metallic phase made of C was manufactured. A buffer layer was then formed on the MgO underlayer, and a magnetic thin film made of an FePt alloy was then formed, and the orientation and particle size of the magnetic grains were investigated.

[0037] [Manufacturing of sputtering target for forming buffer layer] In manufacturing the sputtering target, commercially available Pt powder (purity 99%) and C powder were prepared. Regarding these raw material powders, the Pt powder had an average particle size of 10 μm, and the C powder had an average particle size of 30 μm. The Pt powder and C powder were then mixed in a ball mill (grinding medium: ceramic balls). In this embodiment, 50% by volume of Pt powder and 50% by volume of C powder were mixed.

[0038] Next, the mixed powder of Pt powder and C powder obtained above was pressure-sintered to form a Pt—C sputtering target. The pressure-sintering was carried out by a hot press method under the conditions of a sintering temperature of 1000° C., a pressure of 60 MPa, a pressure-sintering time of 60 min, and an atmosphere of 5×10 －２ The vacuum conditions were set to 100 Pa or less. The manufactured Pt—C sputtering target had a diameter of 161 mm, a thickness of 4 mm, and a relative density of 96.2%.

[0039] In this embodiment, a sputtering target made of carbon (C) according to the prior art (Non-Patent Document 5) was prepared for comparison with the Pt—C sputtering target. This C sputtering target is a commercially available product.

[0040] [Formation of Buffer Layer] Then, using the sputtering target manufactured as described above, a buffer layer was formed on the MgO underlayer, and then an FePt magnetic thin film was formed. In the following substrate preparation and underlayer formation, buffer layer formation, and magnetic thin film formation, an RF / DC magnetron sputtering device (C3010, manufactured by Canon Anelva Corporation) was used as the sputtering device.

[0041] A substrate sample was prepared by depositing an 80 nm amorphous Co 60 at %-W 40 at % layer on an amorphous glass substrate (thickness: 0.635 mm) by sputtering (Ar gas pressure: 0.6 Pa, input power: 500 W), and then depositing a 5 nm MgO underlayer by sputtering (Ar gas pressure: 0.6 Pa, input power: 500 W).

[0042] The buffer layer was formed using the two types of sputtering targets manufactured above: Pt-50 vol % C and 100% C. 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 1.0 nm.

[0043] The FePt magnetic thin film was formed using Fe as a sputtering target. ５０ Pt ５０ -30vol%B ２ O ３ The magnetic thin film was sputtered at an Ar gas pressure of 8.0 Pa, an input power of 100 W, and a substrate temperature of 550° C. The film thickness was 5 nm. Furthermore, a C film was deposited as a surface protection film to a thickness of 7 nm at an Ar gas pressure of 0.6 Pa and an input power of 300 W.

[0044] [Evaluation of magnetic particle orientation and morphology observation] ５０ Pt ５０ -30vol%B ２ O ３ ) was analyzed by XRD, and L1 ０ The presence or absence of in-plane orientation and the quality of the (001) orientation of magnetic particles having a morphology were examined. XRD analysis was performed using a high-resolution X-ray diffraction analyzer (SmartLab manufactured by Rigaku Corporation), with Cu Kα radiation (wavelength: 1.5418 Å) as the X-ray source, and structural analysis was performed using in-plane diffraction at an incident angle of 0.4°. In addition, the appearance of the formed magnetic film was observed using a transmission electron microscope (TEM), and planar and cross-sectional TEM images were taken.

[0045] The results of the study in this embodiment will be described. First, the effect of a buffer layer made of only C, which is a comparative example, will be described. FIG. 1 shows a magnetic thin film (Fe) formed on a buffer layer formed in the comparative example (100% C). ５０ Pt ５０ -30vol%B ２ O ３) is an XRD profile of the buffer layer. FIG. 1 shows profiles when the thickness of the buffer layer is changed and a profile when there is no buffer layer. For convenience, the XRD profile of the comparative example in FIG. 1 shows an expanded (×5) integrated intensity in the region of 2θ = 30° or less. In FIG. 1, the buffer layer is denoted as "BL" (the same applies to FIGS. 2 to 7).

[0046] In the XRD profile of the comparative example in FIG. 1, the diffraction peaks around 2θ=33°, 47°, and 69° are L1 ０ These peaks correspond to the (110), (200), and (220) planes of FePt with a type structure, and it is confirmed that magnetic grain crystals with a (001) orientation have grown in the magnetic thin film of the comparative example.

[0047] L1 ０ In in-plane XRD measurements of FePt alloys having a ZnO-type structure, when crystals with a (001) orientation in the in-plane direction are present, a (001) superlattice reflection is observed. This (001) superlattice reflection peak is observed near 2θ = 24°. Referring to Figure 1, when looking at the XRD profile of a magnetic thin film without a buffer layer (0 nm), a weak (001) superlattice reflection peak is observed. Furthermore, this peak is weakened by increasing the film thickness of the C buffer layer to 0.6 nm or more. In other words, it can be seen that a C buffer layer of 0.6 nm or more suppresses the in-plane orientation of the FePt alloy magnetic grains, reducing the proportion of in-plane oriented crystals.

[0048] FIG. 2 shows a magnetic thin film (Fe) formed on a buffer layer formed according to this embodiment (50 vol % Pt-50 vol % C). ５０ Pt ５０ -30vol%B ２ O ３ 2 shows the XRD profile of the magnetic thin film of this embodiment, which shows the same tendency as that of the comparative example. That is, it is confirmed that the in-plane orientation of the FePt alloy magnetic grains is suppressed by the Pt-added C buffer layer of this embodiment. Furthermore, even with the Pt-added C buffer layer, the L1 ０The intensity of the (001) superlattice reflection peak of the type crystal is weakened, and the proportion of crystal grains oriented in-plane is reduced.

[0049] Next, a magnetic thin film (Fe ５０ Pt ５０ -30vol%B ２ O ３ 3 shows the magnetic thin film (Fe) formed on the Pt-added C buffer layer (50 vol % Pt-50 vol % C) of this embodiment and the C buffer layer of the comparative example. ５０ Pt ５０ -30vol%B ２ O ３ 4 is a planar TEM image of the Pt-added C buffer layer (50 vol % Pt-50 vol % C) of the embodiment and a magnetic thin film (Fe ５０ Pt ５０ -30vol%B ２ O ３ 3 and 4 also show planar and cross-sectional TEM images of a magnetic thin film formed without a buffer layer.

[0050] Referring to the planar TEM image of FIG. 3, the magnetic thin film without the buffer layer has non-magnetic grain boundaries (B ２ O ３ ) separated by magnetic particles (Fe ５０ Pt ５０ ) is observed. In the magnetic thin film of the comparative example, which incorporates a C buffer layer (0.6 nm), the grain size of the magnetic grains is clearly larger. Furthermore, in the magnetic thin film of the comparative example, the width of the nonmagnetic grain boundary is wider, and magnetic grains with a wide grain size distribution are observed.

[0051] Furthermore, the cross-sectional TEM image in Figure 4 shows that in the magnetic thin film with the C buffer layer, the magnetic grains grow laterally and appear to merge with adjacent magnetic grains with the same crystal orientation. The morphological observation of these magnetic thin films reveals that the introduction of the C buffer layer causes the grain size to increase.

[0052] In contrast, the magnetic thin film of this embodiment has magnetic grains of the same size as those formed in a magnetic thin film without a buffer layer. This means that the Pt-added C buffer layer of this embodiment can suppress the coarsening of magnetic grains. Therefore, it was confirmed that adding Pt to the buffer layer made of C suppresses the lateral growth of magnetic grains while forming magnetic grains isolated by non-magnetic grain boundaries.

[0053] Second Embodiment: The effect of adding Pt to the C buffer layer was confirmed in the first embodiment described above. Therefore, in this embodiment, the morphology of the magnetic thin film when the amount of Pt added was changed was examined.

[0054] As in the first embodiment, Pt powder and C powder were mixed and sintered to produce sputtering targets. The mixing ratio (volume ratio) of C powder was 0 vol%, 30 vol%, 40 vol%, 50 vol%, and 60 vol%. The sintering process was the same as in the first embodiment.

[0055] Then, a buffer layer was formed using various sputtering targets under the same substrate and film formation conditions as in the first embodiment, and a magnetic thin film (Fe ５０ Pt ５０ -30vol%B ２ O ３ The buffer layer was prepared in two thicknesses, 0.6 nm and 0.2 nm. XRD analysis and TEM observation were then performed.

[0056] FIG. 5 shows the magnetic thin films (Fe) formed by introducing a buffer layer (0.6 nm) using various sputtering targets (C content: 0 vol%, 30 vol%, 40 vol%, 50 vol%, 60 vol%). ５０ Pt ５０ -30vol%B ２ O ３ 5 also shows the XRD profile of Pt-50 vol % C studied in the first embodiment.

[0057] Referring to FIG. 5, the magnetic thin films incorporating the Pt—C buffer layer using various sputtering targets manufactured in this embodiment have L1 ０It can be confirmed that the (001) superlattice reflection peak of the type crystal is not observed, and the suppression of in-plane orientation is achieved. However, in the case of a magnetic thin film incorporating a buffer layer of only Pt (100% by volume Pt), the L1 ０ Since a diffraction peak of the (111) plane of the SiO2-type crystal is observed, it is believed that the (001) plane orientation is hindered. This diffraction peak of the (111) plane becomes weaker when the Pt content is 70 vol% or less (C content 30 vol% or more), and disappears when the Pt content is 60 vol% or less (C content 40 vol% or more). Therefore, it is clear that the sputtering target for forming the buffer layer must contain at least both Pt and C, and preferably the Pt content should be 70 vol% or less. A similar trend was observed when the buffer layer thickness was 0.2 nm.

[0058] FIG. 6 shows the magnetic thin films (Fe) formed by introducing a buffer layer (0.2 nm) using various sputtering targets (C content: 0 vol%, 30 vol%, 40 vol%, 50 vol%). ５０ Pt ５０ -30vol%B ２ O ３ 6 and 7 also show planar and cross-sectional TEM images of a magnetic thin film formed without a buffer layer.

[0059] The planar TEM image in Figure 6 shows that even when the Pt-C buffer layer is thinned by 0.2 nm, the lateral growth of the magnetic grains is suppressed, resulting in fine grains without coarsening. The cross-sectional TEM image in Figure 7 also shows the suppression of lateral growth of the magnetic grains by the Pt-C buffer layer, and the formation of fine magnetic grains. The same tendency as above was observed when the buffer layer thickness was set to 0.6 nm.

[0060] Third embodiment: In this embodiment, sputtering targets were manufactured that employ a metallic phase consisting of an essential metal other than Pt, a non-metallic phase consisting of carbides and nitrides, and a metallic phase consisting of an essential metal such as Pt and an optional element such as Si. The orientation and particle size of the magnetic grains in the magnetic thin films incorporating buffer layers formed using the various sputtering targets were then evaluated.

[0061] The sputtering target of this embodiment was basically manufactured in the same manner as in the first embodiment by mixing and sintering powders of various metals and powders of carbides and nitrides. Furthermore, for the metal phase consisting of essential metals and optional elements, powders obtained by melting and atomizing raw material powders of the respective metals, or a mixed powder of raw material powders of the respective metals, was used. The raw material powders used had a purity of 99% or more and a particle size of 100 μm or less. Furthermore, the sintering conditions were the same as in the first embodiment.

[0062] After manufacturing various sputtering targets, a magnetic thin film (Fe ５０ Pt ５０ -30vol%B ２ O ３ ) was deposited. XRD analysis was performed on the deposited magnetic thin film. In this embodiment, the XRD profile obtained by XRD analysis was checked for the presence or absence of a (001) superlattice reflection peak and a (111) plane diffraction peak. In addition, the particle size of the magnetic particles was calculated from the half width of the (200) peak (2θ=47°) and Scherrer's formula. Sputtering targets (buffer layers) of various configurations manufactured in this embodiment and magnetic thin films (Fe ５０ Pt ５０ -30vol%B ２ O ３ The results of XRD analysis of the buffer layer of the first embodiment and the buffer layer of the second embodiment are shown in Tables 1 to 5. Table 1 also shows the results of XRD analysis of the buffer layer of the first embodiment and the buffer layer of the second embodiment. The numerical values ​​in the table indicating the buffer layer configuration mean atomic percent.

[0063]

[0064]

[0065]

[0066]

[0067]

[0068] Tables 1 to 5 show that by adding Pt, Ag, Au, Pd, Rh, Ir, Ru, or Cu to the C buffer layer, the magnetic thin film does not exhibit a (001) superlattice reflection peak and in-plane orientation is suppressed. Furthermore, these metal-added C buffer layers can suppress the coarsening of magnetic grains and achieve fine grain sizes of 9.0 nm or less. The magnetic grains in the recording layer of thermally assisted magnetic recording media are required to be 9.0 nm or less. Therefore, the application of the metal-added C buffer layer investigated in this embodiment can be said to be useful for the recording layer of thermally assisted magnetic recording media.

[0069] In addition, the non-metallic components forming the buffer layer include nitrides (BN, Si) in addition to C. ３ N ４ , AlN, TiN, TaN, Cr ２ It was also confirmed that materials such as silicon dioxide (N, NbN, HfN, VN) and carbides (NbC, TiC, Si, ZrC) could be used.

[0070] Furthermore, it was confirmed that the metal phase may contain Si, Ti, Cr, B, V, Nb, Ta, Mn, Zn, Mo, W, and Ge in addition to essential metals such as Pt.

[0071] As described above, the present invention is ０ This sputtering target forms a buffer layer between a magnetic thin film made of an FePt alloy or the like having a .Pt structure and an underlayer. The buffer layer formed by this invention can suppress the in-plane orientation of the magnetic grains in the magnetic thin film, promoting the growth of the (001) plane in the perpendicular direction, while suppressing the coarsening of the magnetic grains. The sputtering target according to the present invention is useful for a magnetic thin film that will serve as the recording layer of a thermally assisted recording medium.

Claims

1. A sputtering target for magnetic recording media, for forming a buffer layer between an underlayer and a magnetic thin film when forming a magnetic thin film on an underlayer on a substrate, the sputtering target for magnetic recording media comprising a metallic phase made of at least one non-magnetic metal selected from Pt, Ag, Au, Pd, Rh, Ir, Ru, and Cu, and a non-metallic phase made of at least one of C, carbide, and nitride.

2. A sputtering target for magnetic recording media according to claim 1, which contains 10% by volume or more and 70% by volume or less of said metallic phase, the remainder being said non-metallic phase and unavoidable impurities.

3. A sputtering target for magnetic recording media according to claim 1 or 2, wherein the metal phase further contains at least one non-magnetic element selected from the group consisting of Si, Ti, Cr, B, V, Nb, Ta, Mn, Zn, Mo, W, and Ge, and the content of the non-magnetic element in the metal phase is 20 mol % or less.

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