Patent Application
20240209494
This disclosure relates to an ordered-alloy ferromagnetic nanowire structure and a method of producing the same.
In the field of ferromagnetic materials with strong perpendicular magnetic anisotropy (PMA) and large coercive force (Hc), the technology has been widely studied for application to spintronics devices such as tunnel magneto resistive (TMR) heads used in magnetoresistive random access memory (MRAM) and ultra-high density hard disk drives (HHD), and ferromagnetic single-electron transistors (FM-SET). Among them, ordered alloys of iron group elements and platinum group elements are considered to be one of the most promising next-generation ferromagnetic materials. It is known that alloys of iron group elements and platinum group elements with the A1-disordered phase undergo a phase transition to ordered alloys when subjected to heat treatment under predetermined conditions. For example, when the atomic composition ratio of CoPt is Co:Pt=1:1, an L10-ordered CoPt alloy can be obtained. When the atomic composition ratio of CoPt is Co:Pt=1:3 or 3:1, an L12-ordered CoPt alloy can be obtained. Although the “L” in L10 and L12 is formally written in italics, it is written in normal typeface herein.
The following technologies are known for ordered-alloy ferromagnetic materials. JP 2016-42399 A (PTL 1) describes “[a] magnetic recording medium comprising a substrate made of a non-magnetic material; and a magnetic material layer formed on the substrate, wherein the magnetic material layer includes ordered crystal magnetic nanoparticles having an average particle size of 3 nm to 20 nm formed directly or via a base layer on the substrate, and a protective layer made of an inorganic material for covering a surface of the ordered crystal magnetic nanoparticles to maintain a dispersion state of the ordered crystal magnetic nanoparticles” (see claim 1), and that the ordered crystalline magnetic nanoparticles are L10-ordered CoPt magnetic nanoparticles (see claim 3).
R. Toyama et al., Formation of L10-ordered CoPt during interdiffusion of electron-beam-deposited Pt/Co bilayer thin films on Si/SiO2 substrates by rapid thermal annealing, Mater. Res. Express 7 (2020) 066101 (NPL 1) and R. Toyama et al., Ti underlayer effect on the ordering of CoPt in (Cp/Pt)4 multilayer thin films on Si/SiO2 substrates, Jpn. J. Appl. Phys. 59, 075504 (2020) (NPL 2) were authored by the present inventors. NPL 1 describes experiments in which a 3.0 nm thick Ti layer was deposited on SiO2/Si substrates by electron-beam evaporation as an under layer to enhance adhesion, followed by the fabrication of equiatomic bilayer films (Co50Pt50) made of a 6.6 nm thick Pt layer and a 4.8 nm thick Co layer, followed by heat treatment by a rapid thermal annealing (RTA) apparatus with temperatures ranging from 200° C. to 900° C. in increments of 100° C. for 30 seconds at a heating rate of 30° C./s under a vacuum. It is shown that at the heat treatment temperature of 800° C., a graded thin film containing L12-ordered CoPt3, L10-ordered CoPt, and L12-ordered Co3Pt was formed during interdiffusion of Co/Pt bilayer thin films, with an in-plane coercivity of Hc=2.1 kOe and a saturation magnetization of Ms=600 emu/cm3.
NPL 2 describes experiments in which a 1.2 nm thick Co layer and a 1.6 nm thick Pt layer were repeatedly stacked four times on SiO2/Si substrates by electron-beam evaporation, followed by the fabrication of equiatomic (Co/Pt)4 eight-layer thin films, followed by heat treatment with a temperature of 900° C. under a vacuum for 1 hour+30 seconds using an RTA apparatus. It is shown that after the heat treatment, L10-ordered round CoPt was observed, with an in-plane coercivity of Hc=2.7 kOe.
Yoshiharu Hotta, et al., “Phase Transformation and Photoemission Electron Microscopy of Fe50Pd50-xNix Processed by Severe Plastic Deformation,” SPring-8/SACLA Research Report, January 2021, Vol. 8, No. 3, pp. 493-496 (NPL 3) describes a method in which a mixed powder of Fe50Pd50-x Nix (x=6, 12, 25, 38, 44) is subjected to high-pressure torsion (HPT) processing at a high pressure of 6 GPa, huge strain is introduced for solidification to create a bulk state in a solid solution, and then heat treatment is performed to obtain L10-ordered alloys.
The efficient production of ordered alloys at the nanoscale would be very advantageous from the viewpoint of application to various spintronics devices. In particular, if wire-type ordered alloys can be formed during the semiconductor process, useful applications such as facilitating miniaturization of MTR devices are possible. However, in PTL 1, L10-ordered CoPt magnetic nanoparticles were fabricated, in NPLs 1 and 2, CoPt thin films containing L10 phase were fabricated, and in NPL 3, materials of FePdNi L10-ordered alloys in bulk form were fabricated, and hence none of them fabricate ordered-alloy nanowires. Until now, no suitable method has been found to efficiently fabricate ordered-alloy ferromagnetic nanowires with nanometer-order widths as narrow as 100 nm or less.
It would thus be helpful to provide an ordered-alloy ferromagnetic nanowire structure and a suitable method of producing the same.
In order to solve the above issues, the present inventors conducted a diligent study and made the following findings. By combining the deposition of an iron group element and a platinum group element with the lift-off process, a nanowire made of the iron group element and the platinum group element can be produced. The present inventors found that if the width of the nanowire is limited below a predetermined upper limit and the nanowire is subjected to heat treatment under predetermined conditions, the iron group element and the platinum group element in the nanowire become an ordered alloy, and an ordered-alloy ferromagnetic nanowire can be obtained.
In addition, if the width of the nanowire is set to a predetermined lower limit or higher and the ratio of thickness to width (hereinafter referred to as “aspect ratio”) in a cross-section perpendicular to a direction in which the nanowire extends is set to a predetermined value or higher, and if the nanowire is subjected to heat treatment under predetermined conditions, the iron group element and the platinum group element become an ordered alloy without interruption in the nanowire, and an ordered-alloy ferromagnetic nanowire with a sufficient length can be obtained. As used herein, “nanowire” means a nanowire that is made of an iron group element and a platinum group element before undergoing heat treatment, and “ordered-alloy ferromagnetic nanowire” means a ferromagnetic nanowire that is formed by the nanowire undergoing heat treatment and made of an ordered alloy of the iron group element and the platinum group element.
Based on these discoveries, we provide:
According to the production method disclosed herein, an ordered-alloy ferromagnetic nanowire structure can be suitably produced.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of necessary fee. In the accompanying drawings:
A method of producing an ordered-alloy ferromagnetic nanowire structure according to the present disclosure comprises: forming a nanowire on or above a substrate, the nanowire having a width of 100 nm or less and a length of at least twice the width, and made of an iron group element and a platinum group element; and subjecting the nanowire to heat treatment to obtain an ordered-alloy ferromagnetic nanowire structure in which an ordered-alloy ferromagnetic nanowire made of an ordered alloy of the iron group element and the platinum group element is formed on or above the substrate.
From the viewpoint of chemical stability and defect-resistant structure, it is possible to use any of Co, Fe, and Ni as the iron group element, and any of platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir) as the platinum group element. As the platinum group element, any of Pt and Pd, which have low melting points, can be suitably used. In the present disclosure, the combination of the iron group element and the platinum group element can be any combination selected from the above elements. The following is a typical example of an embodiment in which Co is used as the iron group element and Pt as the platinum group element to produce an ordered CoPt ferromagnetic nanowire structure. However, the present disclosure is not limited to this embodiment. The following description applies to any combination of iron group elements and platinum group elements.
Referring to
The step (I) of forming CoPt nanowires 16 on or above the substrate 10 will be described in detail below.
Referring to
The substrate 10 is not limited as long as it is rigid enough to support the CoPt nanowires 16 and has an insulating surface. However, the substrate 10 is preferably a magnesium oxide (MgO) substrate, an alumina (Al2O3) substrate, a strontium titanate (SrTiO3) substrate (STO substrate), or a silicon substrate with a silicon oxide film formed on a surface thereof (referred to herein as “SiO2/Si substrate”). Since these substrates are suitable as substrates for various spintronics devices, the formation of ordered CoPt ferromagnetic nanowires on or above these substrates is expected to be applicable to various spintronics devices. In particular, the substrate 10 is preferably a SiO2/Si substrate. This setup makes it possible to fabricate elements of various spintronics devices on or above the same substrate as ICs and ULSIs that integrate circuits using Si semiconductors. The shape and dimensions of the substrate 10 are not particularly limited, yet in a case where a substrate with a rectangular main surface is used as the substrate 10, the dimensions can be, for example, 4 mm to 300 mm in length×4 mm to 300 mm in width×0.3 mm to 1.2 mm in thickness.
Referring now to
Referring now to
Referring now to
By combining the above steps (I-1) through (I-4), i.e., electron beam lithography and deposition of Co and Pt by electron-beam evaporation, CoPt nanowires 16 can be fabricated on or above the substrate 10. As can be seen from
In the present disclosure, it is important that the width of the CoPt nanowires 16 be 100 nm or less. If the width exceeds 100 nm, it is difficult to cause ordering of CoPt while maintaining the shape of nanowires. Therefore, the width of the CoPt nanowires 16 is 100 nm or less, and preferably 50 nm or less. With this setup, by subjecting the CoPt nanowires 16 to heat treatment under optimized conditions, the CoPt nanowires 16 can be ordered, making is possible to obtain ordered CoPt ferromagnetic nanowires 18. From the viewpoint of making the CoPt nanowires 16 less likely to break, or less prone to interruption, the width of the CoPt nanowires 16 is 10 nm or more, and preferably 20 nm or more. This is necessary to obtain ordered CoPt ferromagnetic nanowires 18 with sufficient length.
The aspect ratio in the cross-section perpendicular to the direction in which the CoPt nanowires 16 extend is preferably 0.7 or more, and more preferably 1.5 or more. The aspect ratio is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.5 or less. With the width of the CoPt nanowires 16 set to 10 nm or more and the aspect ratio to 0.7 or more, preferably 1.5 or more, by subjecting the CoPt nanowires 16 to heat treatment under optimized conditions, the CoPt nanowires 16 can be ordered without interruption, making it possible to obtain ordered CoPt ferromagnetic nanowires 18 with sufficient length. In other words, setting of the aspect ratio is also necessary to obtain ordered CoPt ferromagnetic nanowires 18 with sufficient length. On the other hand, if the aspect ratio exceeds 3.0, it becomes difficult to form the CoPt nanowires 16 by the lift-off process. From this perspective, the aspect ratio is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.5 or less.
The length of the CoPt nanowires 16 is not limited as long as it is at least twice the width. In other words, in the present disclosure, a structure with a length that is at least twice the width is referred to as a “nanowire”. However, from the viewpoint of obtaining ordered CoPt ferromagnetic nanowires 18 with sufficient length, the length of the CoPt nanowires 16 is preferably 800 nm or more, more preferably 1 μm or more, and even more preferably 10 μm or more. On the other hand, due to process constraints, the length of the CoPt nanowires 16 is preferably 10 mm or less.
In one embodiment, the atomic composition ratio of the CoPt nanowires 16 can be Co:Pt=1:1. In this case, the CoPt nanowires 16 can be subjected to heat treatment under predetermined conditions to obtain ordered CoPt ferromagnetic nanowires 18, which are L10-ordered CoPt.
In another embodiment, the atomic composition ratio of the CoPt nanowires 16 can be Co:Pt=1:3 or 3:1. In this case, the CoPt nanowires 16 can be subjected to heat treatment under predetermined conditions to obtain ordered CoPt ferromagnetic nanowires 18, which are L12-ordered CoPt.
In one embodiment, as can be seen from
However, as can be seen from
In another embodiment, in the step (I-3), by depositing Co and Pt simultaneously by electron-beam evaporation or sputtering, CoPt nanowires formed from a CoPt composite can be obtained. The Co and Pt feed ratios may be determined as appropriate to achieve the desired atomic composition ratio.
In this embodiment, there should be no adhesive layer such as a Ti layer between the substrate 10 and the CoPt nanowires 16. In other words, the CoPt nanowires 16 are preferably formed on (i.e., in contact with) the substrate 10. This setup will promote the ordering of CoPt, since Ti does not interfere with such ordering due to its migration.
Referring now to
The heat treatment is performed preferably in an atmosphere containing hydrogen and inert gas, and more preferably in an atmosphere containing hydrogen with the balance being inert gas and gases of inevitable impurities that may optionally be contained. Performing the heat treatment in a hydrogen-containing atmosphere can promote the ordering of CoPt. The hydrogen content is preferably 1 vol % to 5 vol %, and the inert gas in the balance can be one or more selected from the group consisting of, for example, argon (Ar), helium (He), and neon (Ne).
In the step (II), the heat treatment temperature is preferably 500° C. or higher and 900° C. or lower, and the heat treatment time is preferably 30 mins or more and 360 mins or less. As used herein, “heat treatment temperature” means the ambient temperature during heat treatment. In addition, “heat treatment time” means the holding time at the heat treatment temperature. If the heat treatment temperature is lower than 500 ºC, Co and Pt do not interdiffuse, and ordering does not occur. If the heat treatment temperature exceeds 900° C., the ordered CoPt becomes disordered again due to thermal disturbance. If the heat treatment time is less than 30 mins, neither interdiffusion nor surface diffusion necessary for ordering take place sufficiently. If the heat treatment time exceeds 360 mins, the ordered CoPt becomes disordered again due to thermal disturbance.
These heat treatment temperatures and heat treatment times are in the range necessary for the ordering of CoPt. In order to obtain ordered CoPt ferromagnetic nanowires 18 with sufficient length in which the CoPt nanowires 16 are ordered without interruption, it is preferable to select an optimized range from among the aforementioned ranges as appropriate depending on the structure of the CoPt nanowires 16 (such as the width, the aspect ratio, the atomic composition ratio, the thickness of each Co layer, the thickness of each Pt layer, and the total number of layers of Co and Pt layers).
The means of heat treatment is not limited, and general heat treatment furnaces may be used, or Rapid Thermal Anneal (RTA) equipment may be used.
The ordered-alloy ferromagnetic nanowire structure according to the present disclosure comprises: a substrate; and an ordered-alloy ferromagnetic nanowire formed on or above the substrate, the ordered-alloy ferromagnetic nanowire having a width of 100 nm or less and a length of at least twice the width, and made of an ordered alloy of an iron group element and a platinum group element.
From the viewpoint of chemical stability and defect-resistant structure, it is possible to use any of Co, Fe, and Ni as the iron group element, and any of platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir) as the platinum group element. As the platinum group element, any of Pt and Pd, which have low melting points, can be suitably used. In the present disclosure, the combination of the iron group element and the platinum group element can be any combination selected from the above elements. The following is a typical example of an embodiment of an ordered CoPt ferromagnetic nanowire structure in which Co is used as the iron group element and Pt as the platinum group element. However, the present disclosure is not limited to this embodiment. The following description applies to any combination of iron group elements and platinum group elements.
Referring to
The description of the substrate 10 is covered in the previous section.
The ordered CoPt ferromagnetic nanowires 18 are either L10 ordered CoPt or L12 ordered CoPt, depending on the atomic composition ratio of the CoPt nanowires 16 before the heat treatment. As used herein, “L10-ordered CoPt” means that superlattice reflections due to L10-ordered CoPt 001, 110 are observed in the GI-XRD pattern obtained by the GI-XRD measurement as described in the EXAMPLES section below. Similarly, as used herein, “L12-ordered CoPt” means that in the case of L12-ordered Co3Pt, due to the Co-rich, cubic ordered structure with small atomic radius, superlattice reflections due to L12-ordered Co3Pt 001,110 are observed on the higher angle side compared to the peaks of L10-ordered CoPt 001,110 in the GI-XRD pattern obtained by the GI-XRD measurement as described in the EXAMPLES section below. In addition, as used herein, “L12-ordered CoPt” means that in the case of L12-ordered CoPt3, due to the Pt-rich, cubic ordered structure with large atomic radius, superlattice reflections due to L12-ordered CoPt3 100,110 are observed on the lower angle side compared to the peaks of L10-ordered CoPt 001, 110 in the GI-XRD pattern obtained by GI-XRD measurement as described in the EXAMPLES section below.
As illustrated in
The surface tension of the iron group element and the platinum group element is about 2000 mN/m, and the pressure difference ΔP at which L10 ordering occurs is about 100 MPa. In this situation of large pressure difference, Co and Pt are L10-ordered as they undergo interdiffusion and even surface diffusion under surface tension. During ordering, the cross-sectional shape is deformed and slightly collapsed so that the CoPt nanowires 16 are blunted in the direction of increasing curvature radius to reduce surface energy. Accordingly, L10 ordering occurs if the curvature radius r is within 50 nm. This is consistent with the present finding that the width of nanowires is 100 nm or less. Such a geometry has the advantage that magnetization can be formed in all directions because the c-axis of the crystal tends to orient radially in the cross-section perpendicular to the direction in which the ordered CoPt ferromagnetic nanowires 18 extend.
The width of the ordered CoPt ferromagnetic nanowires 18 is 100 nm or less, preferably 10 nm or more, more preferably 20 nm or more, and preferably 50 nm or less. As used herein, the “width of the ordered CoPt ferromagnetic nanowires 18” means the maximum width in a cross-section perpendicular to the direction in which the ordered CoPt ferromagnetic nanowires 18 extend.
The thickness of the ordered CoPt ferromagnetic nanowires 18 depends on the aspect ratio of the CoPt nanowires 16 before the heat treatment. In this embodiment, however, the thickness is 10 nm or more and 100 nm or less. It is preferably 20 nm or more. It is preferably 50 nm or less.
The length of the ordered CoPt ferromagnetic nanowires 18 is not limited as long as it is at least twice the width. However, in order for the ordered CoPt ferromagnetic nanowires 18 to have a sufficient length, the length of the ordered CoPt ferromagnetic nanowires 18 is preferably 800 nm or more, more preferably 1 μm or more, and even more preferably 10 μm or more. On the other hand, due to process constraints, the length of the ordered CoPt ferromagnetic nanowires 18 is preferably 10 mm or less.
In this embodiment, there should be no adhesive layer such as a Ti layer between the substrate 10 and the ordered CoPt ferromagnetic nanowires 18. In other words, the ordered CoPt ferromagnetic nanowires 18 are preferably located on (i.e., in contact with) the substrate 10.
In this embodiment, the ordered CoPt ferromagnetic nanowires 18 are preferably L10-ordered or L12-ordered in their entirety. In this embodiment, the ordered CoPt ferromagnetic nanowires 18 each contain a plurality of grains connected together, as will be explained in detail in the EXAMPLES section with reference to
A Si (100) substrate (6 mm long×4 mm wide×525 μm thick) with a surface layer of approximately 50 nm made of SiO2 (hereinafter referred to as “SiO2/Si substrate”) was prepared. An electron beam resist (ZEP-520A available from ZEON Corporation) was applied to the SiO2/Si substrate by spin coating to form an electron beam resist film. The electron beam resist film was then irradiated with electron beam using an electron beam writer (ELS-7500EX available from Elionix Inc.) and subsequently developed to form a mask pattern with the SiO2/Si substrate exposed in the shape of nanowires. Then, Co and Pt were alternately deposited on the exposed portions of the SiO2/Si substrate and on the mask pattern by electron-beam evaporation. Then, CoPt nanowires were formed on the SiO2/Si substrate through a lift-off process to peel off the mask pattern.
The cross-sectional shape of each CoPt nanowire perpendicular to the direction of extension was configured as illustrated in
Then, heat treatment was carried out in an RTA apparatus (MILA-5000UHV available from Advance Science and Engineering Corporation) in an atmosphere containing 3 vol % hydrogen with the balance being argon gas, at the heat treatment temperature of 650° C. for four different heat treatment times of 120 mins, 180 mins, 300 mins, and 360 mins.
The surface of each sample was observed by SEM. The results are illustrated in
For each sample, the crystal structure of CoPt nanowires after the heat treatment was evaluated by grazing incidence X-ray diffraction (GI-XRD). X-ray synchrotron radiation with an energy of 11.7 keV was incident horizontally on each sample while the sample was oscillated 0° to 2°. Diffraction images were taken with a curved imaging plate to obtain a two-dimensional diffraction pattern. For each sample, the obtained GI-XRD pattern is illustrated in
The magnetic properties of each sample were measured using a vibrating sample magnetometer (VSM) on a magnetic properties measurement system (MPMS3 available from Quantum Design Japan) by sweeping external magnetic fields, maximum of 70 kOe under vacuum at room temperature (27° C.), in (i) in-plane direction perpendicular to the wire axis, (ii) in-plane direction parallel to the wire axis, and (iii) perpendicular direction. The coercive force Hc was defined as the absolute value of the magnetic field required to reduce the magnetization M to zero. The saturation magnetization Ms was defined as the value of magnetization at an applied magnetic field of +70 kOe. As representatives of the samples, the magnetic hysteresis loops (M-H curves) for the instances with the heat treatment times of 180 mins and 300 mins are illustrated in
Referring to the GI-XRD pattern in
It can be seen from
Referring to the SEM image in
CoPt nanowires were formed on a SiO2/Si substrate under the same conditions as in Experimental Example 1, except that the cross-sectional shape perpendicular to the direction in which the CoPt nanowires extended was configured as illustrated in
Then, heat treatment was carried out in an RTA apparatus (MILA-5000UHV available from Advance Science and Engineering Corporation) in an atmosphere containing 3 vol % hydrogen with the balance being argon gas, at the heat treatment temperature of 650° C. for three different heat treatment times of 30 mins, 60 mins, and 90 mins.
The surface of each sample was observed by SEM. The results are illustrated in
For each sample, the crystal structure of CoPt nanowires after heat treatment was evaluated by GI-XRD. The specific measurement method was the same as in Experimental Example 1. For each sample, the obtained GI-XRD pattern is illustrated in
Referring to the GI-XRD pattern in
As illustrated in
CoPt nanowires were formed on a SiO2/Si substrate under the same conditions as in Experimental Example 1, except that the cross-sectional shape perpendicular to the direction in which the CoPt nanowires extended was configured as illustrated in
Then, heat treatment was carried out in an RTA apparatus (MILA-5000UHV available from Advance Science and Engineering Corporation) in an atmosphere containing 3 vol % hydrogen with the balance being argon gas, at the heat treatment temperature of 650° C. for three different heat treatment times of 30 mins, 60 mins, and 90 mins.
The surface of each sample was observed by SEM. The results are illustrated in
For each sample, the crystal structure of CoPt nanowires after heat treatment was evaluated by GI-XRD. The specific measurement method was the same as in Experimental Example 1. As a representative of the samples, the GI-XRD pattern obtained for the sample with the heat treatment time of 90 mins is illustrated in
The magnetic properties of each sample were measured using a vibrating sample magnetometer (VSM) on a magnetic properties measurement system (MPMS3 available from Quantum Design Japan) by sweeping external magnetic fields, maximum of 70 kOe under vacuum at room temperature (27° C.), in (i) in-plane direction perpendicular to the wire axis, (ii) in-plane direction parallel to the wire axis, and (iii) perpendicular direction. The definitions of coercive force Hc and saturation magnetization Ms are as described in Experimental Example 1. As a representative of the samples, the magnetic hysteresis loops (M-H curves) are illustrated in
Each sample was subjected to TEM and STEM observation. As a representative of the samples, the cross-sectional TEM image perpendicular to the direction in which the ordered CoPt ferromagnetic nanowires extended is illustrated in
Referring to the GI-XRD pattern in
It can be seen from
Referring to the SEM image in
As illustrated in
The thickness of each of the Co and Pt layers is twice as thick as in Experimental Example 2, while the thickness of the CoPt nanowires is the same. In the case of each layer being thick, interlayer interdiffusion is more difficult to occur than in the thin case, and it takes a longer time for the interlayer interdiffusion to be completed.
CoPt is L10-ordered under conditions of stress at elevated temperatures. The nanowire structure in this experimental example has an extremely small curvature radius of 15 nm or less, and L10 ordering proceeds as described in paragraph 0066.
Co and Pt atoms diffuse across the nanowire surface as the nanowire structure with a rectangular cross-sectional shape is transformed into a rounded cross-sectional shape. This extremely high tensile stress situation will promote L10 ordering during surface diffusion. If the thickness of Co and Pt is thin, interlayer interdiffusion occurs in a short time and A1-disordered phases are formed and mixed. As the thickness of each layer increases, since Pt is harder than Co and has a lower surface self-diffusion coefficient than that of Co, the presence of Pt layers makes it difficult to enter the interruption mode due to Rayleigh instability when the interlayer interdiffusion has not finished. Furthermore, in this state, Co and Pt atoms are easily L10-ordered through surface self-diffusion. This is the nanostructure-induced L10 ordering process. Therefore, in order to promote L10 ordering, thicker Co and Pt layers as in this experimental example are more preferable than in the thinner case of Experimental Example 2.
The ordered-alloy ferromagnetic nanowire structure according to the present disclosure has high industrial applicability with potential applications in spintronics devices (magnetic devices) such as MRAMs, TMR heads in HHDs, and FM-SETs.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-148986 | Sep 2021 | JP | national |
| 2022-043216 | Mar 2022 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/034863 | Sep 2022 | WO |
| Child | 18597912 | US |
