Magnetic thin film and its manufacturing method

Abstract

To provide a magnetic thin film with excellent conduction properties due to electron spin.SOLUTION: The present invention is a magnetic thin film made of a Co-based alloy containing Al and / or Ga. The Co-based alloy contains 58 to 78 at% Co relative to its total. The Co-based alloys should have a β phase. The thickness of the magnetic thin film is, for example, 1 to 200 nm. Such magnetic thin films are obtained, for example, through a stratification process in which raw materials are deposited on a substrate or a base layer to obtain an alloy layer. In this case, a heat treatment process to heat the deposited alloy layer to 475 to 700°C should be provided. The magnetic thin film is substantially free of Mn and does not cause degradation of microstructure and properties of spintronics devices due to thermal diffusion of Mn.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic thin film and the like. [Background technology]

[0002] In the field of spintronics, which utilizes both the charge and spin properties of electrons, research and development of magnetic materials that exhibit magnetoresistance effects, such as anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunneling magnetoresistance (TMR), in which electrical resistance changes with a magnetic field, is central. Examples of such magnetic materials include half-metals with large spin polarization and Weyl semimetals, which have a unique electronic state where the conduction band and valence band meet at a single point (Weyl point / singularity). Specific examples include half-metals such as Co2MnSi and Co2MnGe, and Weyl semimetals such as Co2MnGa and Co2MnAl. All of these are types of CoMn-based (full) Heusler alloys, which are ordered X2YZ-type alloys, and exhibit excellent conductivity at room temperature. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] E. Wachtel et al., J. Phys. Chem. Solids. 34, 1461 (1973). [Non-patent document 2] A Parthasarathi et al., Solod state Comm. 18, 211 (1976). [Non-patent document 3] JY Rhee et al., J. Appl. Phys. 87, 5887(2000). [Non-patent document 4] MW Meisei et al., J. Phys. F: Met. Phys. 12, 317 (1982). [Non-Patent Document 5] AM Zeltser et al., IEEE Trans. Magn. MAG-22, 588 (1986). [Non-patent document 6] YV Kudryavtsev rt al., J. Appl. Phys. 83, 1575 (1998). [Non-Patent Document 7] T. Omori et al., Mater. Sci. Engineering A, 438-440, 1045 (2006). [Non-patent document 8] K. Bruggemann et al., Phys. Rev. Lett. 98, 037202 (2007). [Non-Patent Document 9] P. Weinberger, J. Phys. C: Solid State Phys. 10, L347 (1977). [Non-Patent Document 10] M. Okochi et al., J. Phys. Soc. Jpn. 51, 1166 (1982). [Non-Patent Document 11] M. Lahdeniemi et al., J. Phys. F: Met. Phys. 13, 513 (1983). [Non-Patent Document 12] N. Stefanou et al., Phys. Rev. B 35, 2705 (1986). Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned documents contain descriptions of CoAl and CoGa, which are different from CoMn-based Heusler alloys. All of these documents merely examine the magnetic properties and electronic states of alloy phases with a Co:Al or Co:Ga atomic ratio of approximately 1:1. In other words, there are no reports that specifically study the magnetoresistance effect or electron spin transport properties of CoAl or CoGa.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a new magnetic thin film or the like that is expected to be used in spintronics devices or the like. [Means for solving the problem]

[0006] As a result of intensive research by the inventors to solve this problem, they discovered that a magnetic thin film made of a Co-based alloy with a specific composition stably exhibits excellent conduction characteristics (magnetoresistance effect).By expanding on this finding, they have completed the present invention, as described below.

[0007] 《Magnetic thin film》 (1) The present invention is a magnetic thin film made of a Co-based alloy containing Al and / or Ga, in which Co is contained in an amount of 58 to 78 at % relative to the entire Co-based alloy.

[0008] (2) The magnetic thin film of the present invention can exhibit excellent conductivity, etc. Furthermore, unlike CoMn-based (full) Heusler alloys and the like, the Co-based alloy of the present invention does not substantially contain Mn. Therefore, even if the magnetic thin film of the present invention is subjected to heat treatment after being formed into a multilayer film with other materials, it does not suffer from deterioration of the microstructure or degradation of device characteristics due to thermal diffusion of Mn.

[0009] <Method for manufacturing magnetic thin film> The present invention can also be understood as a method for manufacturing a magnetic thin film. For example, the present invention may be a manufacturing method that includes a layering step of depositing a raw material on a substrate or an underlayer to obtain an alloy layer, and then obtaining a magnetic thin film from the alloy layer.

[0010] "others" (1) In this specification, unless otherwise specified, the alloy composition is expressed in atomic percentage (at%) of the constituent elements. The alloy may contain impurity elements or elements that improve properties (modifying elements). Examples of such elements include N, Ni, and Fe. The range is, for example, 2 at% or less, 1 at% or less, or even 0.5 at% or less. The impurity elements and modifier elements are understood to be, for example, substitutions for the main element (Co) that is contained in the largest amount in the alloy.

[0011] (2) Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b." Also, "x to ynm" in this specification means xnm to ynm. The same applies to other unit systems. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the relationship between the AMR ratio and the Co amount of a magnetic thin film (Example). [Figure 2] The graph shows XRD profiles when the amount of Co was changed. [Figure 3] The graph shows XRD profiles obtained when the heat treatment temperature of the magnetic thin film is changed. [Figure 4] The graph shows XRD profiles when the thickness of the magnetic thin film is changed. DETAILED DESCRIPTION OF THE INVENTION

[0013] The contents described in this specification may apply not only to the magnetic thin film but also to the manufacturing method thereof. One or more components arbitrarily selected from this specification may be added as components of the present invention. Components related to the manufacturing method may also be components related to the product. Which embodiment is best depends on the target, required performance, etc.

[0014] 《Co-based alloy》 (1) Composition The Co-based alloy constituting the magnetic thin film is, for example, a Co-Al alloy or a Co-Ga alloy. When the entire alloy accounts for 100 at%, Co is contained in an amount of, for example, 58 to 78 at%, 59 to 76 at%, 59 to 74 at%, 59 to 72 at%, 59 to 71 at%, or 59 to 68 at%.

[0015] The Co-based alloy may be any of the above-mentioned binary alloys, excluding impurities. However, Al and Ga, both Group 13 elements, may be partially substituted for each other. That is, a Co-Al alloy may contain Ga, and a Co-Ga alloy may contain Al. The substitution amount is, for example, 2 at% or less, or 1 at% or less, of the entire alloy.

[0016] (2) Structure Co-based alloys preferably have a β-phase crystal structure with a body-centered cubic (BCC) structure. Magnetic thin films made of this β-phase can exhibit high conductivity. Incidentally, the crystal structure of Co is face-centered cubic (FCC) or hexagonal close-packed (HCP). The crystal structure of Al is face-centered cubic (FCC). Ga has a low melting point (approximately 30°C), and the stable crystal structure varies depending on the pressure and temperature.

[0017] 《Magnetic thin film》 (1) The magnetic thin film made of a Co-based alloy has a film thickness of, for example, 1 to 200 nm, 2 to 150 nm, 3 to 125 nm, 7 to 100 nm, or 25 to 60 nm.

[0018] (2) The magnetic thin film is used, for example, in various spintronic devices (for example, next-generation sensors, memories, etc.) The magnetic thin film of the present invention can improve the performance and reduce noise (stabilize) of spintronic devices.

[0019] 《Manufacturing method》 (1) A magnetic thin film is obtained, for example, through a layering process in which raw materials are deposited on a substrate or an underlayer to obtain an alloy layer. The layering process is performed by a known thin film method such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). PVD, such as vacuum deposition (sputtering, vacuum thermal deposition, pulsed laser deposition, etc.), can obtain an alloy layer of a desired composition using various targets (raw materials). Vacuum deposition is performed, for example, in a 10 -6 ~10 -10 Pa and 10 -7 ~10 -9The deposition is preferably performed under (ultra) high vacuum of about Pa. The temperature during deposition (substrate temperature, base temperature) is, for example, from about room temperature (60°C or less, or even 40°C or less) to 600°C.

[0020] The substrate or underlayer on which the magnetic thin film is formed preferably has at least the outermost surface (the surface to be laminated) in contact with the magnetic thin film as a single crystal surface of, for example, MgO, Si, sapphire, SiC, etc. The underlayer may be a buffer layer that promotes crystal alignment and growth, or a functional layer (electrode layer, insulating layer, non-magnetic layer, etc.) laminated with the magnetic thin film. The underlayer may be, for example, a Cr layer, MgO layer, Ta layer, Mo layer, W layer, etc.

[0021] (2) The alloy layer may be heated to 475 to 700°C, 500 to 675°C, or 525 to 650°C (heat treatment step). This heat treatment ensures the formation of an alloy layer made of the β phase. The heating time is, for example, 0.1 to 3 hours, 0.5 to 2 hours, or 0.7 to 1.5 hours. The heat treatment may be performed after lamination with other layers.

[0022] The heating source may be any of electric heat, radiant heat, laser, etc. The heating atmosphere may be, for example, the high vacuum described above.

[0023] 《Application》 Magnetic thin films are used in, for example, various spintronic devices (including elements), such as magnetic sensors, magnetic random access memories (MRAMs), and magnetic logic circuits. [Example]

[0024] Various samples (magnetic thin films) were fabricated and their properties were evaluated. The present invention will be explained more specifically based on these samples.

[0025] <<Sample Preparation>> As shown in Table 1, various thin films (samples) made of Co-based alloys containing Al or Ga were formed on the single crystal surface of an MgO substrate by sputtering. Specifically, the MgO single crystal surface was the (100) surface of the substrate, which had been polished.

[0026] The film was formed using an ultra-high vacuum multi-target sputtering system (MPS-2000-C8, manufactured by ULVAC, Inc.) on a single crystal surface that had been heated and cleaned (600°C) under vacuum and then cooled to near room temperature. The ultimate vacuum before film formation was 5 × 10 -8 The film thickness was calculated from the product of the film formation rate (0.1 nm / sec or less) and the film formation time.

[0027] The targets (raw materials) used were pure Al metal or CoGa alloy and pure Co metal. Except for sample 1 (Co: 100 at%), each sample was fabricated by dual-target simultaneous sputtering using both Co and Al or CoGa as targets.

[0028] In this way, a metal layer (alloy layer) was obtained by depositing (evaporating) it onto the single crystal surface (layering process). The metal layer was then heated at 650°C for 1 hour in the ultra-vacuum described above (heat treatment process). After that, it was cooled to room temperature, and the film-formed sample was taken out into the atmosphere.

[0029] In this way, the thin films (samples 1 to 10 and samples 21 and 22) shown in Table 1 were obtained. The component compositions (Co atomic ratios) of the Co-based alloys shown in Table 1 are the results of analysis using an inductively coupled plasma (ICP) emission spectrometer.

[0030] "measurement" (1) Saturation magnetization The saturation magnetization (Ms) of the thin film (sample) was measured using a VSM (Vibrating Sample Magnetometer, manufactured by Tamagawa Seisakusho Co., Ltd.). The results are also shown in Table 1.

[0031] (2) Anisotropic magnetoresistance (AMR) The magnetoresistance of the thin film was measured in two orthogonal directions (ρ∥, ρ⊥) and the anisotropic magnetoresistance ratio (AMR ratio) was calculated. The details are as follows.

[0032] A thin film was microfabricated into a Hall bar shape to prepare a test specimen. A rotating magnetic field was applied in the in-plane direction of the film, and the resistance change as a function of the relative angle q between the current direction and the magnetic field direction was measured using the four-probe method. The applied current was 0.5 mA, and the film temperature was 5 or 300 K. The AMR ratio = 100 × (ρ∥ - ρ⊥) / ρ⊥ (%) was calculated from the resistivity ρ∥ when the applied current and magnetic field directions were parallel (q = 0° or 180°) and the resistivity ρ⊥ when they were perpendicular (q = 90° or 270°).

[0033] Giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) reflect the transport properties of multilayer thin films. In this example, the anisotropic magnetoresistance (AMR) ratio was used to properly evaluate the transport properties of a single magnetic thin film.

[0034] Magnetoresistance measurements were generally carried out at room temperature (300 K), but for representative samples, they were also carried out at cryogenic temperatures (5 K). The results are shown in Table 1. Figure 1 also shows the relationship between the AMR ratio (%) at 300 K and the amount of Co (at%) contained in the thin film.

[0035] Crystal structure The crystal structure of the thin film was analyzed from the top side using an X-ray diffractometer (Rigaku Corporation RINT-TTR II / X-ray used: Cu-Kα ray, 2θ: 20 to 90 °C). X-ray diffraction (XRD) was measured at room temperature.

[0036] The results (XRD profiles) obtained for the CoAl-based thin films (film thickness: 40 nm / heat treatment temperature: 650° C.) shown in Table 1 are summarized in FIG.

[0037] We also prepared CoAl-based thin films (film thickness: 40 nm / Co: 61 at%) with different heat treatment temperatures. The XRD profiles of these films are shown in Figure 3.

[0038] Furthermore, we also prepared CoAl-based thin films with different thicknesses (heat treatment temperature: 650°C / Co: 61 at%). The XRD profiles of these films are summarized in Figure 4.

[0039] "evaluation" (1) As is clear from Table 1 and Figure 1, the thin films (samples 4 to 6) with alloy compositions (Co content) within the specified range exhibited excellent conductivity (AMR). This tendency was observed not only in the room temperature range but also in the cryogenic temperature range.

[0040] Conversely, thin films with an excess of Co (samples 1-3) had a mixed phase structure of CoAl and Co, and had a large Ms but a small ρ⊥. Furthermore, thin films with an insufficient amount of Co (samples 7-10) had a large ρ⊥ but a small Ms. It was confirmed that none of these thin films were suitable for controlling electron spin conduction.

[0041] As is clear from FIG. 2, it was confirmed that all of the CoAl-based thin films heat-treated at 650° C. had a β-CoAl phase (002) with a BCC structure.

[0042] (2) As is clear from Figure 3, it was also found that such c-plane oriented β phase is stably generated (precipitated) by heating (heat treatment) above 450°C (e.g., 475°C or higher).

[0043] (3) As is clear from Figure 4, it was also found that such a β phase is generated stably even if the film thickness changes.

[0044] From the above, it was confirmed that the present invention provides a magnetic thin film with excellent controllability of the transport properties by electron spin.

[0045] [Table 1]

Claims

1. A Co-based alloy containing Al and the remainder being Co, The Co-based alloy contains 58 to 78 at% Co based on the entire Co-based alloy, A magnetic thin film that exhibits a magnetoresistive effect and is used in spintronics devices.

2. A Co-based alloy containing Ga and the remainder being Co, The Co-based alloy contains 58 to 78 at% Co based on the entire Co-based alloy, A magnetic thin film that exhibits a magnetoresistive effect and is used in spintronics devices.

3. 3. The magnetic thin film according to claim 1, wherein the Co-based alloy has a β phase.

4. 3. The magnetic thin film according to claim 1, wherein the film thickness is 1 to 200 nm.

5. a layering step of depositing a raw material on a substrate or an underlayer to obtain an alloy layer; A method for producing the magnetic thin film according to claim 1 or 2 from the alloy layer.

6. 6. The method for manufacturing a magnetic thin film according to claim 5, further comprising a heat treatment step of heating the alloy layer to 475 to 700.degree.

7. 6. The method for manufacturing a magnetic thin film according to claim 5, wherein at least the surface of the substrate to be deposited is made of MgO single crystal.

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