Magnetic material and magnetic recording medium

Abstract

To enhance at least one of magnetic anisotropy and saturation magnetization of an FePt-based magnetic material.SOLUTION: Er or Tm is added to FePt having a L10 structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic material and a magnetic recording medium. [Background technology]

[0002] With the advent of a society in which not only things (IoT: Internet of Things) but also people (IoH: Internet of Human) and data (IoD: Internet of Digital) are all connected, the amount of digital information handled in the world is increasing exponentially. Much of this digital information is stored in data centers, and the main storage in these data centers is hard disk drives (HDDs).

[0003] An HDD has a disk-shaped magnetic recording medium, which is a collection of nanomagnets, and a magnetic head that writes and reads information to the magnetic recording medium. The magnetic head has a write element and a tunneling magnetoresistive element, and when writing information, the magnetic field generated by the write element reverses the magnetization of the nanomagnets. Information is read by reading the leakage magnetic flux from the nanomagnets with the tunneling magnetoresistive element.

[0004] On the other hand, one material used for magnetic recording media is a material in which ferromagnetic particles of Co-Cr-Pt are uniformly dispersed in a non-magnetic matrix based on SiO2. To increase the recording density of HDDs, it is preferable to reduce the size of the ferromagnetic particles to around 5 nm.

[0005] However, the magnetic anisotropy of the Co-Cr-Pt alloy is 0.7 MJ / m 3Since the particle size is not so large, reducing the particle size to around 5 nm can cause the problem of thermal agitation, in which the magnetization fluctuates due to thermal energy. To solve this problem, it is preferable to use a material with high magnetic anisotropy for the magnetic recording medium. Furthermore, from the perspective of information reproduction, emitting as high a magnetic flux as possible from the nanomagnet leads to an improved signal-to-noise ratio, so it is preferable to increase the saturation magnetization of the ferromagnetic nanoparticles. Therefore, it is preferable to use a magnetic material with high magnetic anisotropy or saturation magnetization as the magnetic material used for the magnetic recording medium. One such material is FePt (iron platinum) ordered in the L10 structure (Non-Patent Document 1). FePt ordered in the L10 structure has only just begun to be used as a material for magnetic recording media, and there is still room for further improvement in magnetic anisotropy and saturation magnetization. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] P. Tozman, et al., "Dual-layer FePt-C granular media for multi-level heat-assisted magnetic recording", Acta Materialia, Vol. 271, pp. 119869, 2024 Summary of the Invention [Problem to be solved by the invention]

[0007] In one aspect, the present invention aims to increase at least one of the magnetic anisotropy and the saturation magnetization of an FePt-based magnetic material. [Means for solving the problem]

[0008] According to one aspect of the following disclosure, the magnetic material is FePt with an L10 structure to which Er or Tm is added.

[0009] In the magnetic material, a part of the Pt sites of the FePt may be substituted with the Er or the Tm.

[0010] In the magnetic material, the Er content may be greater than 0 atomic % and not more than 0.53 atomic %.

[0011] In the magnetic material, the Fe content may be 47.41 atomic % or more and 59.47 atomic % or less, and the Pt content may be 40.29 atomic % or more and 52.39 atomic % or less.

[0012] In the magnetic material, the Er content may be 0.35 atomic % or more and 1.05 atomic % or less.

[0013] In the magnetic material, the Fe content may be 49.30 atomic % or more and 55.94 atomic % or less, and the Pt content may be 43.60 atomic % or more and 50.17 atomic % or less.

[0014] In the magnetic material, the Tm content may be greater than 0 atomic % and not more than 0.71 atomic %.

[0015] According to another aspect of the following disclosure, a magnetic recording medium includes a recording layer containing a magnetic material in which Er or Tm is added to FePt having an L10 structure.

[0016] In the magnetic recording medium, the Er content in the magnetic material may be greater than 0 atomic % and equal to or less than 0.53 atomic %.

[0017] In the magnetic recording medium, the magnetic material may have an Fe content of 47.41 atomic % or more and 59.47 atomic % or less, and a Pt content of 40.29 atomic % or more and 52.39 atomic % or less.

[0018] In the magnetic recording medium, the content of Er in the magnetic material may be 0.35 atomic % or more and 1.05 atomic % or less.

[0019] In the magnetic recording medium, the magnetic material may have an Fe content of 49.30 atomic % or more and 55.94 atomic % or less, and a Pt content of 43.60 atomic % or more and 50.17 atomic % or less.

[0020] In the magnetic recording medium, the content of Tm in the magnetic material may be greater than 0 atomic % and not more than 0.71 atomic %.

[0021] In the magnetic recording medium, the recording layer may have a granular structure in which a non-magnetic material is dispersed in the magnetic material. [Effects of the Invention]

[0022] According to the present invention, at least one of the magnetic anisotropy and saturation magnetization of the FePt-based magnetic material can be increased. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1(a) shows the calculation results of the magnetic moment and magnetic anisotropy energy when the Fe site of FePt with an L10 structure is substituted with an additive element X, and FIG. 1(b) shows the calculation results when the Pt site of FePt with an L10 structure is substituted with an additive element X and calculations similar to those in FIG. 1(a) are performed. [Figure 2] FIG. 2(a) is a side view of the sputtering device used to deposit the magnetic film, and FIG. 2(b) is a top view thereof. [Figure 3] FIG. 3 is a schematic diagram showing the film formation process using a sputtering device. [Figure 4] FIG. 4(a) is a bottom view of the holder, and FIG. 4(b) is a cross-sectional view of each of Samples No. 2, No. 5, No. 8, and No. 11. [Figure 5] FIG. 5 is a schematic diagram of a high-throughput measurement system according to the first embodiment. [Figure 6] FIGS. 6(a) and 6(b) are graphs (part 1) obtained by investigating the relationship between the DC power applied to each target and the Er content in the magnetic film for each sample. [Figure 7]7(a) and (b) are graphs (part 2) obtained by investigating the relationship between the DC power applied to each target and the Er content in the magnetic film for each sample. [Figure 8] FIG. 8 is a diagram (part 1) summarizing the film formation conditions and characteristics of the samples used in the characteristic investigation. [Figure 9] FIG. 9 is a diagram (part 2) summarizing the film formation conditions and characteristics of the samples used in the characteristic investigation. [Figure 10] FIG. 10 is a diagram showing the X-ray diffraction intensity of the sample measured by an X-ray diffractometer. [Figure 11] FIG. 11(a) is an enlarged view of the diffraction peak at a scattering angle of about 23° in FIG. 10, and FIG. 11(b) is an enlarged view of the diffraction peak at a scattering angle of about 48° in FIG. [Figure 12] FIG. 12(a) is a cross-sectional TEM (Transmission Electron Microscope) image of the sample, and FIG. 12(b) is a cross-sectional TEM image at a higher magnification than FIG. 12(a). [Figure 13] FIG. 10 is a diagram showing the results of plotting the saturation magnetization of each sample. [Figure 14] FIG. 14 is a diagram showing the results of plotting the Curie temperatures of the samples. [Figure 15] FIG. 15 is a diagram showing the results of plotting the anisotropy magnetic field of each sample. [Figure 16] 16(a) and (b) show the magnetization curves of the magnetic film provided in the sample. [Figure 17] FIG. 17 shows the TRMOKE spectrum of the magnetic film included in the sample. [Figure 18] FIG. 18 is a diagram showing the result of Fourier transform of the Kerr signal in FIG. [Figure 19] FIG. 19 is a diagram in which the peak frequencies of the frequency components of the Kerr signal in FIG. 17 are plotted for each angle and fitted using the Kittel equation. [Figure 20] FIG. 20 is a diagram showing the effective damping constant of the magnetic film of the sample calculated for each angle. [Figure 21] FIG. 21 is a cross-sectional view of the magnetic recording medium according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are given like reference numerals and their description will be omitted.

[0025] (First embodiment) As mentioned above, FePt with an L10 structure has high saturation magnetization and magnetic anisotropy, making it a promising material for magnetic recording media. In this embodiment, we will describe a magnetic material that has at least one of higher saturation magnetization and magnetic anisotropy than FePt with an L10 structure.

[0026] The inventors of this application suspected that adding other elements to FePt with an L10 structure would further enhance the saturation magnetization and magnetic anisotropy, and performed first-principles calculations to calculate the saturation magnetization and magnetic anisotropy for various added elements. The results are shown in Figures 1(a) and 1(b).

[0027] Figure 1(a) shows the calculation results of the magnetic moment and magnetic anisotropy energy when the Fe site of FePt in the L10 structure is substituted with an additional element X. Here, the atomic ratio of each element is set to Fe:X:Pt=0.99:0.01:1. The additional elements are as follows:

[0028] Light rare earths: La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium)

[0029] Heavy rare earth elements: Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium)

[0030] 3d transition elements: Sc (Scandium), Ti (Titanium), V (Vanadium), Cr (Chromium), Mn (Manganese), Fe (Iron), Co (Cobalt), Ni (Nickel), Cu (Copper), Zn (Zinc)

[0031] 4d transition elements: Y (yttrium), Zr (zirconium), Nb (niobium), Mo (molybdenum), Tc (technetium), Ru (ruthenium), Rh (rhodium), Pd (palladium), Ag (silver), Cd (cadmium)

[0032] Others: W (tungsten), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Au (gold), Hg (mercury), Bi (bismuth), Sb (antimony)

[0033] The first-principles calculations were performed using the density functional theory, with AkaiKKR used as the calculation code for the density functional theory.

[0034] On the other hand, Figure 1(b) shows the calculation results when the Pt site of FePt with the L10 structure is substituted with an additional element X, and calculations similar to those in Figure 1(a) are performed. The atomic ratio of each element is set to Fe:Pt:X = 1:0.99:0.01. In each of Figures 1(a) and 1(b), the intersections of the dotted lines indicate the magnetic moment and magnetic anisotropy energy of FePt with the L10 structure.

[0035] As shown in Figure 1(b), it was found that among multiple additive elements X, Tm and Er are elements that have the function of clearly increasing both the magnetic anisotropy energy and the magnetic moment more than FePt with the L10 structure. Therefore, the inventors of the present application focused on Tm and Er as additive elements that increase at least either the magnetic anisotropy or the saturation magnetization.

[0036] Furthermore, comparing Figure 1(a) and Figure 1(b), the magnetic anisotropy energy is higher when Er is in the Pt site (Figure 1(b)) than when Er is in the Fe site (Figure 1(a)). The same is true for Tm. This indicates that Er and Tm are preferentially introduced into the Pt site rather than the Fe site.

[0037] Based on this result, the inventors of the present invention formed a magnetic film made of a magnetic material in which Tm or Er was added to FePt, and investigated the various physical properties of the magnetic film as follows.

[0038] FIG. 2(a) is a side view of the sputtering device used to deposit the magnetic film, and FIG. 2(b) is a top view thereof.

[0039] As shown in FIG. 2(a), the sputtering apparatus 1 is a combinatorial sputtering apparatus capable of depositing multi-component thin films, and includes a cylindrical chamber 2. First to fifth cathodes 3a to 3e for combinatorial film deposition are provided in the lower part of the chamber 2. Furthermore, a holder 4 for holding a sample with its surface facing vertically downward is provided in the upper part of the chamber 2. Examples of such a sputtering apparatus 1 include a co-sputtering apparatus manufactured by Eiko Engineering Co., Ltd. and a helicon sputtering apparatus manufactured by ULVAC, Inc.

[0040] FIG. 2(b) is a top view of the sputtering apparatus 1. As shown in FIG. 2(b), in this example, first to fifth cathodes 3a to 3e are arranged in this order counterclockwise at equal intervals around the circumference of the chamber 2. The first cathode 3a is used for sputtering Fe, the third cathode 3c is used for sputtering Er, and the fourth cathode 3d is used for sputtering Pt. Note that in this example, the second cathode 3b and the fifth cathode 3e are not used for sputtering.

[0041] Moreover, both the chamber 2 and the holder 4 are circular in top view, and are provided so that their centers coincide with each other.

[0042] 3 is a schematic diagram illustrating film formation using the sputtering apparatus 1. Each of the cathodes 3a to 3e serves as a container for accommodating a target, and also serves as an electrode for applying to the target a negative potential of a DC voltage applied between the cathode 3a and the holder 4. In this example, as shown in FIG. 3, the first cathode 3a, the third cathode 3c, and the fifth cathode 3e accommodate an Fe target 5a, an Er target 5c, and a Pt target 5d, respectively. Note that the second cathode 3b and the fifth cathode 3e do not accommodate any targets.

[0043] During film formation, DC power is applied between each of the targets 5a, 5c, and 5d and the holder 4. This causes atoms of Fe, Er, and Pt to be scattered from the surfaces of the targets 5a, 5c, and 5d, respectively, and magnetic films containing Fe, Er, and Pt are formed on the surface of the sample held by the holder 4.

[0044] The distance between each of the targets 5a, 5c, and 5d and the holder 4 is, for example, 150 mm. Each of the targets 5a, 5c, and 5d is circular and has a diameter of, for example, 76.2 mm (3 inches) when viewed from above.

[0045] Fig. 4(a) is a bottom view of the holder 4. As shown in Fig. 4(a), the holder 4 holds a plurality of samples S. The holder 4 has a built-in heater (not shown), which heats each sample S during sputtering to control the substrate temperature.

[0046] Although there is no particular limitation on the material of the holder 4, in this example, an Inconel (registered trademark) holder 4 is used. The diameter of the holder 4 is, for example, 61.5 mm.

[0047] In this example, each sample S is square in plan view, and the samples S are arranged in a matrix with intervals between them. The length of one side of each sample S is, for example, 10 mm. The distance between the centers of adjacent samples S is, for example, 13.3 mm.

[0048] In this embodiment, an imaginary line L connecting the centers of the first cathode 3a and the fourth cathode 3d is parallel to the column direction, and is perpendicular to the row direction. Samples S No. 1 and No. 2 are arranged in the first row, and samples S No. 3 to No. 6 are arranged in the second row. Samples S No. 7 to No. 10 are arranged in the third row, and samples S No. 11 and No. 12 are arranged in the fourth row. Note that the natural number "*" in "No. *" increases along the column direction in each row.

[0049] According to this, of the 12 samples S, sample No. 2 S is closest to the third cathode 3c made of Er, sample No. 7 S is closest to the cathode 3a made of Fe, and sample No. 10 S is closest to the fourth cathode 3d made of Pt.

[0050] Although the holder 4 is rotatable around its own center, in this embodiment the holder 4 is stopped and not rotated during film formation, so that the positional relationship between each sample S and each cathode 3a to 3e is fixed.

[0051] In this embodiment, the distance between each cathode 3a, 3c, 3d and the sample S is different for each sample, so the Er content can be changed for each sample S in one film formation, allowing material search to be carried out in a short time.

[0052] FIG. 4(b) is a cross-sectional view of each of Samples S No. 2, No. 5, No. 8, and No. 11.

[0053] 4(b), each of the samples S has a substrate 10, and a magnetic film 11 made of a magnetic material containing Fe, Pt, and Er is formed on the substrate 10 by deposition in a sputtering apparatus 1. In this embodiment, the substrate temperature during deposition of the magnetic film 11 is set to 400° C. or higher and 800° C. or lower, thereby depositing the magnetic film 11 ordered in an L10 structure.

[0054] There are no particular limitations on the material of the substrate 10. In this embodiment, a 0.5 mm thick single-crystal MgO (magnesium oxide) substrate is used as the substrate 10, and the magnetic film 11 is formed on the (001) plane of the magnesium oxide substrate. After the magnetic film 11 is formed, a C (carbon) film may be formed on it to a thickness of about 5 nm, so that the C film prevents the surface of the magnetic film 11 from oxidizing.

[0055] It should be noted that the samples S other than No. 2, No. 5, No. 8, and No. 11 were dummy samples using a silicon substrate as the substrate 10. This is because no significant difference was observed in the Er content of the magnetic film 11 in the samples S other than No. 2, No. 5, No. 8, and No. 11.

[0056] After simultaneously depositing the magnetic film 11 on each sample S, an operator measures the physical properties such as saturation magnetization and magnetic anisotropy of the magnetic film 11. To conduct material search in a short time, it is preferable to use a high-throughput measurement system that can efficiently measure physical properties.

[0057] 5 is a schematic diagram of a high-throughput measurement system according to this embodiment. This high-throughput measurement system 20 includes an X-ray fluorescence (XRF) analyzer 21, an X-ray diffraction (XRD) analyzer 22, a vibrating sample magnetometer (VSM) 23, a superconducting quantum interference device (SQUID)-vibrating sample magnetometer 24, and a physical property measurement system (PPMS) 25.

[0058] Of these, the X-ray fluorescence analyzer 21 is an apparatus for measuring the content of additive elements such as Er in the magnetic film 11. In this embodiment, an end-window type ZSX Primus II manufactured by Rigaku Corporation is used as the X-ray fluorescence analyzer 21. The target material of the X-ray fluorescence analyzer 21 is Rh, and the analyzing crystal is LiF(200). The voltage applied to the target during measurement is 4 kW.

[0059] The X-ray diffractometer 22 is an apparatus that measures the X-ray diffraction intensity for calculating the L10 order parameter S in the magnetic film 11. The L10 order parameter S is defined by the following formula (1).

[0060] S=r Pt +r Fe -1 (1)

[0061] In formula (1), r Pt is the occupancy rate of Pt atoms occupying the Pt sites in the L10 structure. Fe is the occupancy rate of Fe atoms occupying the Fe sites in the L10 structure. In this embodiment, a Smartlab manufactured by Rigaku Corporation is used as the X-ray diffractometer 22. The X-ray diffractometer 22 uses Cu-Kα rays as X-rays. The acceleration voltage of electrons incident on the Cu target is 40 kV, and the current due to the electrons is 45 mA.

[0062] The vibrating sample magnetometer 23 is a device used to create the magnetization curve of the magnetic film 11. In this embodiment, a TM-VSM211483ASE manufactured by Tamagawa Seisakusho Co., Ltd. is used as the vibrating sample magnetometer 23. The maximum external magnetic field generated by the vibrating sample magnetometer 23 is 2.1 T. The magnetization resolution of the vibrating sample magnetometer 23 is 1×10 -7 It's emu.

[0063] The SQUID-vibrating sample magnetometer 24 is a device used to measure the Curie temperature of the magnetic film 11. In this embodiment, an MPMS3 manufactured by Japan Quantum Design Co., Ltd. is used as the SQUID-vibrating sample magnetometer 24. The conditions for measuring the Curie temperature using the SQUID-vibrating sample magnetometer 24 are that the strength of the external magnetic field applied to the sample is 0.1 T and the sample temperature during measurement is 300 K or higher and 700 K or lower.

[0064] The physical property measuring device 25 is a device used to measure the anisotropic magnetic field of the magnetic film 11. In this embodiment, a DynaCool manufactured by Japan Quantum Design Co., Ltd. is used as the physical property measuring device 25. The conditions for measuring the anisotropic magnetic field using the physical property measuring device 25 are an external magnetic field strength of ±14 T applied to the sample and a sample temperature of 300 K during measurement.

[0065] Next, various physical property values ​​of the magnetic film 11 measured by this high-throughput measurement system 20 will be described.

[0066] First, the inventors of the present application investigated how the Er content in the magnetic films 11 of Nos. 2, 5, 8, and 11 in Fig. 4(a) changes depending on the DC power applied to each of the targets 5a, 5c, and 5d (see Fig. 3). The results are shown in Figs. 6 and 7.

[0067] 6 and 7 are graphs obtained by investigating the relationship between the DC power applied to each of the targets 5a, 5c, and 5d and the Er content in the magnetic film 11 for each sample S. The horizontal axis of the graph represents the ratio of the DC power applied to the Er target 5c to the sum of the DC power applied to the Fe target 5a and the DC power applied to the Pt target 5d.

[0068] The vertical axis of the graph represents the content (atomic %) of Er in the magnetic film 11. If the number of atoms of Fe contained in a unit volume of the magnetic film 11 is A, the number of atoms of Pt contained in a unit volume of the magnetic film 11 is B, and the number of atoms of the additional element X contained in a unit volume of the magnetic film 11 is C, the content (atomic %) of the additional element X such as Er is defined as 100×C / (A+B+C). The content was measured using an X-ray fluorescence analyzer 21 (see FIG. 5).

[0069] Furthermore, in this investigation, the DC power applied to the Fe target 5a was fixed at 40 W, and the DC power applied to the Pt target 5d was fixed at 15 W. Two DC powers, 30 W and 50 W, were applied to the Er target 5c.

[0070] Additionally, Ar gas was supplied to chamber 2 (Fig. 2(a)) as the sputtering gas at a flow rate of 30 sccm. The pressure inside chamber 2 was set to 2 Pa, and the substrate temperature was set to 500°C. Nitrogen gas or oxygen gas may be added to the Ar gas, but these gases were not added in this investigation.

[0071] As shown in Figures 6 and 7, the slope b of the graph is greatest for sample No. 2 (Figure 6(a)), and decreases in the order of No. 5 (Figure 6(b)), No. 8 (Figure 7(a)), and No. 11 (Figure 7(b)). The reason why the slope b in Figure 6(a) is greatest is thought to be that, as shown in Figure 4(a), of the multiple samples S, sample No. 2 is closest to the cathode 3c of Er, making it easier for Er to be incorporated into the magnetic film 11. In addition, the distance from the cathode 3c increases in the order of No. 5, No. 8, and No. 11, making it more difficult for Er to be incorporated into the magnetic film 11 in this order, and therefore the slope b decreases in the order of Figures 6(b), 7(a), and 7(b).

[0072] Furthermore, this result also shows that the Er content in the magnetic film 11 can be adjusted by adjusting the power ratio, regardless of the position of the sample S on the holder 4.

[0073] Next, the results of investigation into various characteristics of the magnetic film 11 will be described.

[0074] 8 and 9 are diagrams summarizing the film formation conditions and characteristics of the samples used in the characteristic investigation. In this example, a "sample number" is used as an identifier to uniquely identify each sample. Also, "added element X" indicates the element added to the magnetic film 11.

[0075] According to the results of the first-principles calculations shown in Figures 1(a) and 1(b), it is predicted that the use of Er or Tm as an additive element is preferable for increasing the saturation magnetization and anisotropy field, but the inventors of this application also used Nd (neodymium) as an additive element for reference. Note that for the FePt sample with the L10 structure to which no additive element X is added, X = None.

[0076] The deposition conditions for the samples include "power," "deposition time," and "position." Of these, "power" refers to the value of DC power applied between each of the targets 5a, 5c, and 5d and the holder 4. "Fe," "Pt," and "X" in "power" correspond to the target 5a, the target 5d, and the target 5c, respectively. Note that "X" represents any of the elements Er, Nd, and Tm. When Nd or Tm was used as the additive element X, a Tm or Nd target was used instead of the Er target 5c (see FIG. 3). Furthermore, "position" refers to each of the positions No. 1 to No. 12 in FIG. 4. When the additive element was any of Er, Nd, and Tm, the power was adjusted within a range of 5 W to 150 W.

[0077] The sputtering gas was adjusted to a flow rate of Ar gas of 50 sccm to 240 sccm, a flow rate of oxygen gas of 0 sccm to 10 sccm, and a flow rate of nitrogen gas of 0 sccm to 10 sccm. The substrate temperature was controlled to a range of 400°C to 800°C, and the pressure in chamber 2 was adjusted to a range of 0.1 Pa to 4 Pa.

[0078] On the other hand, the sample characteristics include "content," "film thickness," "S," "Ms," "Tc," and "Hk."

[0079] Among these, "content" refers to the content of each of the elements "Fe," "Pt," and "X" in the magnetic film 11, expressed in atomic percent. The content of each element was measured using an X-ray fluorescence analyzer 21 (see FIG. 5). The content can be adjusted in various ways by changing the "power" and "position."

[0080] "Film thickness" indicates the film thickness of each sample, and "Ms" indicates the saturation magnetization. An external magnetic field was applied to each sample, and a magnetization curve was created for each sample. The saturation magnetization was determined as the magnetization when the magnetic field curve reached saturation. A vibrating sample magnetometer 23 (see Figure 5) was used to create the magnetization curves.

[0081] "Tc" indicates the Curie temperature. The Curie temperature was measured using a SQUID vibrating sample magnetometer 24 (see FIG. 5). "Hk" indicates the anisotropy magnetic field. The anisotropy magnetic field was measured using a physical property measurement device 25 (see FIG. 5).

[0082] On the other hand, "S" represents the L10 order parameter. The L10 order parameter S was calculated as follows using the X-ray diffraction intensity obtained by the X-ray diffractometer 22 (see FIG. 5).

[0083] Fig. 10 is a diagram showing the X-ray diffraction intensity of sample No. 1 measured by the X-ray diffractometer 22. The horizontal axis of Fig. 10 represents the scattering angle 2θ (°) of the X-ray, and the vertical axis represents the intensity of the X-ray (cps: counts per second).

[0084] As shown in Figure 10, diffraction peaks appear when 2θ is near 23°, 42°, and 48°. Of these, the diffraction peak near 23° corresponds to the (001) plane of FePt. The diffraction peak near 42° corresponds to the (002) plane of the MgO substrate. Finally, the diffraction peak near 48° corresponds to the (002) plane of FePt.

[0085] Fig. 11(a) is an enlarged view of the diffraction peak (FePt(001)) at a scattering angle of approximately 23° in Fig. 10. Fig. 11(b) is an enlarged view of the diffraction peak (FePt(002)) at a scattering angle of approximately 48° in Fig. 10.

[0086] The L10 order parameter S is calculated using these diffraction peaks according to the following formula (2) (Papers 1-3).

[0087] S = α × (I 001 / I 002 ) 1 / 2 ···(2)

[0088] (Paper 1) C. Rong and 7 others, “Structural phase transition and ferromagnetism in monodisperse 3 nm FePt particles”, Journal of Applied Physics, Vol. 102, No. 4, No. 043913, 2007

[0089] (Paper 2) S. Granz, and 1 other, “Granular L 10 FePt (001) thin films for heat assisted magnetic recording,” Journal of Magnetism and Magnetic Materials, Vol. 324, No. 3, pp. 287-294, 2012

[0090] (Paper 3) E. Yang and two others, "Correction of Order Parameter Calculations for FePt Perpendicular Thin Films," IEEE Transactions on Magnetics, Vol. 48, No. 1, pp. 7-12, 2012

[0091] However, in equation (2), I 001 is the integrated intensity of the diffraction peak of the (001) plane of FePt. 002 is the integrated intensity of the diffraction peak of the (002) plane of FePt. In this embodiment, based on Papers 4 to 6, the value of the coefficient α in formula (2) was adopted as 0.85.

[0092] (Paper 4) A. Perumal, and 2 others, “L10FePt-C nanogranular perpendicular anisotropy films with narrow size distribution”, Applied Physics Express, Vol. 1, No. 10, No. 101301, 2008

[0093] (Paper 5) E. Yang and two others, "Buffer Layers for Highly Ordered L10FePt-Oxide Thin Film Granular Media at Reduced Processing Temperature," IEEE Transactions on Magnetics, Vol. 46, No. 6, pp. 2446-2449, 2010.

[0094] (Paper 6) J. Christodoulides, et.

[0095] When the integrated intensities of each diffraction peak in Figures 11(a) and (b) were applied to equation (2) to calculate the L10 order parameter S, the L10 order parameter S of sample number 1 in Figure 8 was found to be 0.456. If the value of the L10 order parameter S of a sample is greater than zero, the sample can be considered to be ordered in the L10 structure.

[0096] Similarly, the L10 order parameter S was calculated for each of the samples Nos. 2 to 48 in Figures 8 and 9, and it was confirmed that the L10 order parameter S was greater than zero for all samples. This indicates that all samples Nos. 1 to 48 are ordered in the L10 structure.

[0097] Fig. 12(a) is a cross-sectional TEM (Transmission Electron Microscope) image of sample No. 3. Fig. 12(b) is a cross-sectional TEM image at a higher magnification than Fig. 12(a).

[0098] As shown in Figures 12(a) and 12(b), the magnetic film 11 was grown epitaxially on the (001) plane of the single-crystal MgO substrate 10, and the grain boundaries of the fine single-crystal grains were visible. Adjacent single-crystal grains were connected in a continuous manner, making the magnetic film 11 a seamless, continuous film. Analysis of the XRD results also revealed that the c-axis direction of the magnetic film 11 was normal to the substrate 10, and the a-axis direction of the magnetic film was the MgO

[0110] direction.

[0099] Next, based on the tables of FIGS. 8 and 9, the results of plotting the relationship between the content of the additive element X and the physical property values ​​of the saturation magnetization, Curie temperature, and anisotropic magnetic field of each sample will be described.

[0100] Fig. 13 is a diagram showing the results of plotting the saturation magnetization of each sample, in which the horizontal axis represents the content of the additional element X and the vertical axis represents the saturation magnetization.

[0101] As shown in FIG. 13, for Tm and Nd, the saturation magnetization tends to decrease as the content increases.

[0102] On the other hand, for Er, the saturation magnetization was higher in the range of 0.53 atomic % or less than when X = None. Samples with Er contents of 0.53 atomic % or less are samples numbered 9 to 12, 14, and 15 in Figure 8. This result revealed that in order to increase the saturation magnetization more than that of FePt ordered in the L10 structure, it is sufficient to add Er at a content of 0.53 atomic % or less to FePt ordered in the L10 structure.

[0103] 8, in particular, in samples numbered 9 to 12, 14, and 15, the Fe content is 47.41 atomic % or more and 59.47 atomic % or less, and the Pt content is 40.29 atomic % or more and 52.39 atomic % or less. Therefore, it is particularly preferable to set the Fe and Pt contents within these ranges and to set the Er content to 0.53 atomic % or less as described above, in order to increase the saturation magnetization more than that of FePt ordered in the L10 structure.

[0104] 14 is a diagram showing the plot of the Curie temperature of each sample, in which the horizontal axis represents the content of the additional element X and the vertical axis represents the Curie temperature.

[0105] As shown in Figure 14, the Curie temperature of Er was higher at 0.35 atomic % and 0.53 atomic % than when X = None. Also, the Curie temperatures of Tm and Nd were higher at 0.71 atomic % and 0.69 atomic %, respectively, than when X = None.

[0106] 15 is a diagram showing the plotted anisotropy magnetic field of each sample, in which the horizontal axis represents the content of the additional element X and the vertical axis represents the anisotropy magnetic field.

[0107] 15, for Er, the magnetic anisotropy was higher in the range of 0.35 atomic % to 1.05 atomic % than when X=None, and the anisotropy field was lower when the Er content was outside this range than when X=None. Samples with Er contents in the range of 0.35 atomic % to 1.05 atomic % are samples numbered 3, 9 to 11, and 47 in FIGS. 8 and 9. In particular, the anisotropy field was greatest in sample number 11, which had an Er content of 0.35 atomic %.

[0108] These results reveal that in order to increase the anisotropy field compared to FePt ordered in the L10 structure, it is sufficient to add Er to FePt ordered in the L10 structure at a content of 0.35 atomic % to 1.05 atomic %.

[0109] 8 and 9, in particular, in samples 3, 9 to 11, and 47, the Fe content is 49.30 atomic % or more and 55.94 atomic % or less, and the Pt content is 43.60 atomic % or more and 50.17 atomic % or less. Therefore, it is particularly preferable to set the Fe and Pt contents within these ranges and, as described above, to set the Er content to 0.35 atomic % or more and 1.05 atomic % or less in order to increase the anisotropy field more than that of FePt ordered in the L10 structure.

[0110] Furthermore, for Tm, the anisotropy field tended to increase in the order of 2.28 atomic %, 1.74 atomic %, and 0.71 atomic %, with the anisotropy field being higher at 0.71 atomic % than when X=None. Based on this trend, it is estimated that even at a content lower than 0.71 atomic %, the anisotropy field can be increased compared to when X=None. From these results, it was found that by setting the Tm content greater than 0 atomic % and equal to or less than 0.71 atomic %, the anisotropy field is higher than when X=None.

[0111] According to the first-principles calculations shown in Figures 1(a) and 1(b), Nd is not predicted as an additive element capable of increasing saturation magnetization or anisotropy field. However, according to the results shown in Figure 15, the anisotropy field tends to increase with the Nd content in the order 2.87 atomic %, 1.47 atomic %, and 0.69 atomic %, and the anisotropy field is higher at 0.69 atomic % and 1.47 atomic % than when X = None. Based on this trend, it is estimated that the anisotropy field can be increased even at Nd contents lower than 0.69 atomic % compared to when X = None. From these results, it was found that the anisotropy field can be increased compared to when X = None by setting the Nd content to greater than 0 atomic % and less than or equal to 1.47 atomic %, more preferably between 0.69 atomic % and 1.47 atomic %.

[0112] Next, the inventors of the present invention investigated the magnetization curve of the magnetic film 11. The results of the investigation are shown in FIG.

[0113] Figure 16(a) shows the magnetization curve of the magnetic film 11 included in sample number 13, and Figure 16(b) shows the magnetization curve of the magnetic film 11 included in sample number 11. The magnetization curves were created using a vibrating sample magnetometer 23 (see Figure 5).

[0114] 8, sample number 13 has a magnetic film 11 made of FePt with an L10 structure to which no additional element X is added. On the other hand, sample number 11 has a magnetic film 11 in which 0.35 atomic % of Er is added to FePt with an L10 structure.

[0115] 16(a) and 16(b), the dotted lines represent the magnetization curves when an external magnetic field is applied in the direction of the easy axis of magnetization, and the solid lines represent the magnetization curves when an external magnetic field is applied in the direction of the hard axis of magnetization.

[0116] As shown in FIG. 16(a), in the sample to which no additional element X is added, the saturation magnetization at which the magnetization curve is saturated is 1.39 T.

[0117] On the other hand, as shown in FIG. 16(b), in the sample to which only 0.35 atomic % of Er was added, the saturation magnetization at which the magnetization curve was saturated was 1.54 T, which was higher than the saturation magnetization of the sample to which no additional element X was added (FIG. 16(a)).

[0118] The physical properties of samples 11 and 13 are summarized in Table 1.

[0119] [Table 1]

[0120] As shown in Table 1, sample No. 11, to which 0.35 atomic % of Er was added, had higher saturation magnetization, anisotropy field, and Curie temperature than sample No. 13. It is known that in FePt-based magnetic materials, the anisotropy field and Curie temperature vary depending on the L10 order parameter. However, as shown in Table 1, the L10 order parameter was approximately the same for samples No. 11 and 13.

[0121] Next, the time-resolved magneto-optical Kerr effect (TRMOKE) of the magnetic film 11 will be described.

[0122] Fig. 17 shows the TRMOKE spectrum of the magnetic film 11 included in the sample of sample number 11 in Fig. 8. Here, while applying an external magnetic field of 2.0 T strength to the magnetic film 11, the magnetic film 11 is irradiated with pump light to excite the magnetization of the magnetic film 11, and then the magnetic film 11 is irradiated with probe light to generate a Kerr signal Δφ k The horizontal axis of Fig. 17 represents the time difference Δt between the time when the pump light reaches the magnetic film 11 and the time when the probe light reaches the magnetic film 11. The vertical axis of Fig. 17 represents the Kerr signal Δφ k θ H is the angle between the external magnetic field and the magnetization, and θ H Measurements were carried out for angles of 70°, 80°, and 85°. H Measurements were also taken when the angle was 60° and 65°, but the measurement results are omitted in Figure 17.

[0123] As shown in FIG. 17, each angle θ H In the region where 0<Δt, the oscillation due to the precession of the magnetization is k It appears in.

[0124] FIG. 18 shows the Kerr signal Δφ k 18, the horizontal axis represents frequency, and the vertical axis represents the Kerr signal Δφ k Frequency components of I FFTShows.

[0125] As shown in FIG. 18, any angle θ H Even in this case, the frequency component I FFT A peak appears.

[0126] FIG. 19 shows the Kerr signal Δφ k Frequency components of I FFT The peak frequency of angle θ H The graph shows the results of fitting the data with the Kittel equation. This fitting revealed that the g-value was 2.02 and the anisotropy field was 7.1T.

[0127] FIG. 20 shows the effective damping constant α of the magnetic film 11 included in the sample of sample number 11 in FIG. eff angle θ H The effective damping constant α eff is defined by the following equation (3).

[0128] α eff =1 / (2πfτ) (3)

[0129] In equation (3), f is the frequency of the magnetization precession, which corresponds to the peak frequency in FIG. 18. τ is the lifetime of the magnetization precession, which corresponds to the Kerr signal Δφ in FIG. 17. k is the time required for the vibration to decay.

[0130] As shown in Figure 20, the effective damping constant α eff is the angle θ H The average value was 0.073.

[0131] As described above, according to this embodiment, by adding Er to FePt with an L10 structure, both the saturation magnetization and the anisotropy field can be increased (FIGS. 13 and 15). Furthermore, by adding Tm to FePt with an L10 structure, the anisotropy field can be increased (FIG. 15).

[0132] In particular, when Er is added, the saturation magnetization can be reliably increased by setting the content to 0.53 atomic % or less (FIG. 13).

[0133] 1(a) and 1(b), first-principles calculations suggest that Er and Tm are preferentially introduced into the Pt site rather than the Fe site. Therefore, in the magnetic film 11 in which Er and Tm are added to the L10 FePt, some of the Pt sites are substituted with these elements, which is presumably why the saturation magnetization and anisotropy field are increased as mentioned above.

[0134] (Second embodiment) In this embodiment, a magnetic recording medium to which the magnetic material described in the first embodiment is applied will be described.

[0135] 21 is a cross-sectional view of a magnetic recording medium 40 according to this embodiment. The magnetic recording medium 40 is a perpendicular magnetic recording medium used in HDDs, and is formed by forming a heat sink layer 31, an orientation control layer 32, and a recording layer 33 in this order on a substrate 30.

[0136] The substrate 30 is a non-magnetic substrate such as an MgO substrate or a glass substrate. The heat sink layer 31 is a layer that promotes heat dissipation when writing to the magnetic recording medium 40. As an example, in this embodiment, a metal layer with excellent thermal conductivity such as a NiTa layer or a Cr layer is formed as the heat sink layer 31 by sputtering to a thickness of 50 nm to 100 nm.

[0137] The orientation control layer 32 is a layer that controls the orientation of the magnetic material 33b of the recording layer 33. In this example, the orientation control layer 32 functions to orient the magnetic material 33b having the L10 structure in the normal direction of the substrate 30. As an example, in this embodiment, an MgO layer or an MgTiO layer is formed as the orientation control layer 32 by sputtering to a thickness of 5 nm to 10 nm.

[0138] The recording layer 33 is a layer in which information is written, and has a granular structure in which particulate magnetic material 33b with a particle size of several nanometers is uniformly dispersed in a matrix of non-magnetic material 33a. While the non-magnetic material 33a is not particularly limited, in this embodiment, any of C (carbon), BN (boron nitride), and SiO2 (silicon dioxide) is used as the non-magnetic material 33a. As described in the first embodiment, the magnetic material 33a is a material in which Er or Tm is added to FePt ordered in the L10 structure.

[0139] Although the deposition apparatus and deposition method for the recording layer 33 are not particularly limited, here the recording layer 33 is combinatorially deposited using a sputtering apparatus 1 (FIG. 2(a)). In this case, for example, as shown in FIG. 3, an Fe target 5a, an Er target 5c, and a Pt target 5d are set on cathodes 3a, 3c, and 3d, respectively. When Tm is added to FePt, a Tm target can be used instead of the Er target 5c.

[0140] A target made of a non-magnetic material 33a is set on either the second cathode 3b or the fifth cathode 3e. The substrate 30 may be set at any one of positions No. 1 to No. 12 on the holder 4 (see FIG. 4).

[0141] The sputtering gas can be selected depending on the type of non-magnetic material 33a. For example, the sputtering gas may be Ar gas, or a mixed gas of Ar gas and at least one of oxygen gas and nitrogen gas. The flow rates of each gas are not particularly limited. For example, the flow rate of Ar gas is 50 sccm or more and 240 sccm or less. The flow rate of oxygen gas is 0 sccm or more and 10 sccm or less, and the flow rate of nitrogen gas is 0 sccm or more and 10 sccm or less.

[0142] In this state, the substrate temperature is maintained at 400° C. or higher and 800° C. or lower, and the pressure inside the chamber 2 is maintained at 0.1 Pa or higher and 4 Pa ​​or lower. Furthermore, the DC power applied to each target is maintained at 10 W or higher and 150 W or lower.

[0143] 6 and 7, the Er content in the magnetic material can be adjusted by the power ratio of the DC power applied to each target. Therefore, by adjusting the power ratio, the Er content in the magnetic material 33b may be set to 0.53 atomic % or less, thereby achieving a saturation magnetization higher than that of FePt with an L10 structure, as shown in FIG. 13.

[0144] By adopting such film formation conditions, the recording layer 33 is formed to a thickness of 3 nm or more and 10 nm or less.

[0145] The method for forming the recording layer 33 is not limited to the above. For example, instead of the Fe target 5a and Pt target 5d provided separately as shown in FIG. 3, a FePt composite target made of an FePt alloy may be used. Furthermore, by adding Er to the FePt composite target, the Er target 5c may be omitted. Similarly, when Tm is added to FePt, Tm may be added to the FePt composite target, and the Tm target may be omitted. Furthermore, film formation may be performed using a composite target in which a nonmagnetic material 33a is added to an FePt composite target.

[0146] According to the present embodiment described above, a magnetic material in which Er or Tm is added to FePt with an L10 structure is used as the magnetic material 33b of the recording layer 33. As described in the first embodiment, this magnetic material has at least one of a higher saturation magnetization and anisotropy field compared to FePt with an L10 structure that does not contain any additional elements. By increasing the saturation magnetization in this way, the signal-to-noise ratio when reproducing information from the recording layer 33 is improved. Furthermore, by increasing the anisotropy field, thermal disturbance of magnetization caused by thermal energy is suppressed, allowing the magnetic material 33b to have a smaller particle size, thereby achieving higher density HDDs. [Explanation of symbols]

[0147] 1...sputtering apparatus, 2...chamber, 3a to 3e...first to fifth cathodes, 4...holder, 5a...Fe target, 5c...Er target, 5d...Pt target, 10...substrate, 11...magnetic film, 20...high-throughput measurement system, 21...X-ray fluorescence analyzer, 22...X-ray diffractometer, 23...vibrating sample magnetometer, 24...SQUID-vibrating sample magnetometer, 25...physical property measurement device, 30...substrate, 31...heat sink layer, 32...orientation control layer, 33...recording layer, 33a...non-magnetic material, 33b...magnetic material, 40...magnetic recording medium.

Claims

1. L1 ０ A magnetic material in which Er or Tm is added to FePt.

2. The content of Er is greater than 0 atomic % and not more than 0.53 atomic %. The magnetic material according to claim 1 .

3. The Fe content is 47.41 atomic % or more and 59.47 atomic % or less, and the Pt content is 40.29 atomic % or more and 52.39 atomic % or less. The magnetic material according to claim 2 .

4. The Er content is 0.35 atomic % or more and 1.05 atomic % or less. The magnetic material according to claim 1 .

5. The Fe content is 49.30 atomic % or more and 55.94 atomic % or less, and the Pt content is 43.60 atomic % or more and 50.17 atomic % or less. The magnetic material according to claim 4.

6. the content of Tm is greater than 0 atomic % and not more than 0.71 atomic %; The magnetic material according to claim 1 .

7. L1 ０ A magnetic recording medium having a recording layer containing a magnetic material in which Er or Tm is added to FePt having a structure.

8. the content of Er in the magnetic material is greater than 0 atomic % and not more than 0.53 atomic %; 8. The magnetic recording medium according to claim 7.

9. The content of Fe in the magnetic material is 47.41 atomic % or more and 59.47 atomic % or less, and the content of Pt is 40.29 atomic % or more and 52.39 atomic % or less.

9. The magnetic recording medium according to claim 8.

10. the content of Er in the magnetic material is 0.35 atomic % or more and 1.05 atomic % or less; 8. The magnetic recording medium according to claim 7.

11. The magnetic material has an Fe content of 49.30 atomic % or more and 55.94 atomic % or less, and a Pt content of 43.60 atomic % or more and 50.17 atomic % or less. The magnetic recording medium according to claim 10.

12. the content of Tm in the magnetic material is greater than 0 atomic % and not more than 0.71 atomic %; 8. The magnetic recording medium according to claim 7.

13. the recording layer has a granular structure in which a non-magnetic material is dispersed in the magnetic material; 13. The magnetic recording medium according to claim 7.

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