JP7799546B2 - Magnetic nanowire medium, domain wall-driven spatial light modulator, and method of manufacturing magnetic nanowire medium - Google Patents

Description

The present invention relates to a domain wall-driven spatial light modulator, and in particular to a magnetic nanowire medium bonded with a topological insulator, a domain wall-driven spatial light modulator using the magnetic nanowire medium, and a method for manufacturing the magnetic nanowire medium.

Patent Document 1 discloses a domain wall-driven spatial light modulator. A domain wall-driven spatial light modulator is a device that uses some kind of forming method to introduce multiple domain walls (DWs) into a magnetic nanowire medium, which is made by processing a magnetic material into a thin wire shape. The device expresses binary information corresponding to the magnetization direction of the region surrounded by a pair of nearest domain walls as a light-dark image. Here, the region surrounded by a pair of nearest domain walls is called a magnetic domain. Furthermore, if the magnetic nanowire medium is made of a material that exhibits perpendicular magnetic anisotropy, the magnetization direction of the magnetic domain is either perpendicular, upward or downward, to the magnetic nanowire.

By utilizing the current-driven domain wall motion described in Non-Patent Document 1, it is possible to shift magnetic domains formed in a magnetic nanowire medium in one direction by applying a pulse current to each magnetic nanowire. To shift the numerous magnetic domains accumulated in a magnetic nanowire medium, a pulse current is applied, but it has been known that a large current density exceeding the order of ¹⁰⁷ A/ ^cm2 is required. Note that a shift of a magnetic domain refers to a transition of the location where the magnetization direction is expressed, and does not refer to physical movement.

Non-Patent Document 2 discloses that the topological insulator BiSb (bismuth-antimony alloy) applies a huge spin torque to a magnetic material through a junction interface, thereby achieving a lower current density than conventional materials. A topological insulator is a special material in which current flows on the surface of the material but not inside the material. According to Non-Patent Document 2, when no external magnetic field is applied, the current density required to shift the magnetic domain is reduced to the order of ¹⁰⁵ A/ ^cm2 .

Patent No. 4939489

A. Yamaguchi, et al., “Real-Space Observation of Current-Driven Domain Wall Motion in Submicron Magnetic Wires,” Phys. Rev. Lett. vol.92, 077205, 20 February, 2004 Nguyen Huynh Duy Khang, et al., “Ultralow power spin-orbit torque magnetization switching induced by a non-epitaxial topological insulator on Si substrates,” Scientific Reports vol. 10, Article number: 12185, 22 July, 2020

When considering power savings in domain wall-driven spatial light modulators, it is desirable to reduce the current density required for magnetic domain shift. Domain wall-driven spatial light modulators using magnetic nanowire media bonded with topological insulators can be expected to achieve current drive with a two-digit reduction in the current density required for magnetic domain shift. However, because BiSb, for example, is a material prone to grain growth, the BiSb film surface develops an uneven structure with a surface roughness of several nanometers. If the reflected light is scattered by the unevenness of the BiSb film surface during operation of the spatial light modulator, causing the polarization information to be lost, it becomes difficult to detect the magnetization direction of the magnetic domains using the magneto-optical Kerr effect, which ultimately interferes with the operation of the binary light modulation output.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic nanowire medium and a domain wall-driven spatial light modulator that can be driven with a low current and that can detect a magneto-optical image.
Another object of the present invention is to provide a method for manufacturing a magnetic fine wire medium that can be driven with a low current and that can detect a magneto-optical image.

To solve the above problem, the magnetic nanowire medium of the present invention is a magnetic nanowire medium for use in a domain wall-driven spatial light modulator, and comprises a magnetic nanowire, an insulating thin film formed on the magnetic nanowire, and a metal thin film formed on the insulating thin film, wherein the thicknesses of the insulating thin film and the metal thin film are smaller than the penetration length of incident light, the insulating thin film is made of a topological insulator, and the metal thin film is made of ruthenium.

The method for manufacturing a magnetic nanowire medium according to the present invention is for use in a domain wall-driven spatial light modulator, and includes the steps of forming an insulating thin film on a magnetic material using a topological insulator, and forming a metal thin film on the insulating thin film, wherein the thickness of the insulating thin film and the thickness of the metal thin film are smaller than the penetration length of incident light, and the material of the metal thin film is ruthenium.

The present invention provides the following excellent effects.
According to the magnetic nanowire medium of the present invention, an extremely thin insulating film made of a topological insulator is formed on the magnetic nanowire, thereby reducing the current density required for magnetic domain shift. Furthermore, the extremely thin metal film made of ruthenium in the magnetic nanowire medium reduces the surface roughness of the topological insulator, thereby suppressing scattering of reflected light at the surface. Therefore, the magnetic nanowire medium and a domain wall-driven spatial light modulator using it can be driven with a low current and detect magneto-optical images.
According to the method for manufacturing a magnetic nanowire medium of the present invention, it is possible to manufacture a magnetic nanowire medium that can be driven with a low current and that can detect a magneto-optical image.

1 is a schematic diagram of a domain wall-driven spatial light modulator using a magnetic nanowire medium according to an embodiment of the present invention. FIG. 2 is a schematic diagram of data recorded on a magnetic nanowire medium. FIG. 1 is a schematic diagram of a magnetic nanowire medium. FIG. 1 is a schematic diagram of a magnetic domain shift in a magnetic nanowire medium. 1 is a flowchart showing a manufacturing process of a magnetic fine wire medium according to an embodiment of the present invention. 10 is a magneto-optical microscope image when an external magnetic field is applied to the example. 7(a) and 7(b) are atomic force microscope images of the comparative example. 8(a) and 8(b) are atomic force microscope images of the example.

[Outline of domain wall-driven spatial light modulator]
First, an overview of a domain wall-driven spatial light modulator using a magnetic nanowire medium according to this embodiment will be described with reference to Fig. 1 (and Fig. 2 as appropriate). Note that the sizes and positional relationships of components shown in each drawing may be exaggerated for clarity.
The domain wall-driven spatial light modulator 1 includes a magnetic nanowire medium 10, a recording element 30, a magnetic domain formation control circuit 50, a pulse current source 60, a magnetic domain drive control circuit 70, and an optical output system 80. A large number of magnetic nanowire media 10 are arranged in parallel on a substrate 40. The recording element 30 forms magnetic domains with binary magnetization directions (upward or downward) in each magnetic nanowire medium 10. The recording element 30 may be a magnetic head generally used for magnetic recording, or may be a nanowire-shaped conductor formed above the magnetic nanowire medium 10 with an insulating layer 20 interposed therebetween.

The magnetic domain formation control circuit 50 is a control circuit that generates a bidirectional current magnetic field in the recording element 30 when writing data to the magnetic nanowire medium 10. The pulse current source 60 is connected to each magnetic nanowire medium 10, and supplies a pulse current in the longitudinal direction of the magnetic nanowire 10 when writing data to the magnetic nanowire medium 10. The magnetic domain drive control circuit 70 is a control circuit that controls the on/off of the pulse current from the pulse current source 60 to shift the magnetic domains in the longitudinal direction of the magnetic nanowire medium 10. As an example, the magnetic domain drive control circuit 70 also controls the magnetic domain formation control circuit 50, and divides externally input image data into one line's worth of data for each frame to generate pixel column data.

As shown in Figure 2, as an example, the magnetic domain drive control circuit 70 divides externally input image data horizontally into N pieces to generate horizontal data strings (data string 1, ..., data string N), and then divides each data string vertically into L pieces of pixel data. N corresponds to the total number of magnetic nanowire media 10. L pieces of pixel data constitute pixel string data, and a collection of N pieces of pixel string data constitutes one frame of image data. When shifting magnetic domains from one side (left) to the other side (right) in the longitudinal direction of the magnetic nanowire medium 10, the magnetic domain drive control circuit 70 controls the recording of the pixel data on the magnetic nanowire medium 10 in order from the first pixel data of the data string, with the other side (right) of the horizontal data string as the beginning and one side (left) as the end.

The optical output system 80 extracts a bright and dark image corresponding to the magnetic domains magnetized in two directions by using the magneto-optical Kerr effect when reproducing data from the magnetic nanowire medium 10. The magneto-optical Kerr effect is a phenomenon in which, when coherent light with a unidirectional polarization plane is incident on a magnetic material, the rotation direction of the polarization plane of the reflected light is opposite in regions where the magnetization direction of the magnetic domains is upward and downward. Therefore, by passing the reflected light through a polarizing filter 82 that is tuned to one (+ _θK ) of the two (+ _θK , _-θK ) values of polarization plane rotation, two types of output, bright and dark, corresponding to the magnetization direction of the magnetic domain rows in the magnetic nanowire, are obtained.

As shown in Figure 1, the optical output system 80 includes, for example, polarizing filters 81 and 82. When light from a light source (not shown) enters the polarizing filter 81, it converts the incident light into coherent light by aligning the polarization plane of the incident light in one direction. The polarizing filter 82 transmits or blocks the light reflected from the magnetic nanowire medium 10. A detector (not shown) behind the polarizing filter 82 detects the reflected light (pixel data) that passes through the polarizing filter 82 as a bright image (white) and detects the reflected light (pixel data) that does not pass through the polarizing filter 82 as a dark image (black), making it possible to detect local changes in magnetization direction as a black and white shading image.

The domain wall-driven spatial light modulator 1 configured as described above alternately forms and shifts upward and downward magnetic domains, accumulating binary information arrays (equivalent to pixels) of magnetic domains along the length of each of the multiple parallel-arranged magnetic nanowire media 10, thereby completing the data transfer of one frame of spatial light modulation output.

[Magnetic thin wire medium]
Next, the structure of the magnetic nanowire medium 10 used in the domain wall-driven spatial light modulator 1 will be described with reference to FIG.
Each magnetic nanowire medium 10 includes a magnetic nanowire 11, an insulating thin film 13 formed on the magnetic nanowire 11, and a metal thin film 15 formed on the insulating thin film 13. The magnetic nanowire medium 10 is supported on a substrate 40. The thicknesses of the insulating thin film 13 and the metal thin film 15 are smaller than the penetration depth of the incident light. The insulating thin film 13 is made of a topological insulator. The metal thin film 15 is made of ruthenium, a metal material that reduces the surface roughness of the insulating thin film 13. The thickness of the metal thin film 15 is preferably several atoms thick. A sputtering apparatus may be used to deposit a ruthenium thin film on the topological insulator by specifying a film thickness within a range of, for example, 0.2 nm to 3 nm. An insulating layer 20 is formed on the metal thin film 15. The insulating layer 20 is made of a transparent insulating material such as SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , or AlN.
The substrate 40 is made of, for example, a surface-thermally oxidized silicon substrate, but can also be made of various other materials, such as silicon, soda glass, _SiO2 , quartz, methyl acrylate, _{LiNbO3, LiTaO3 ,} alumina, GaAlAs, and InP.
In this specification, a thin film is a solid film that is sufficiently thinner than 1 μm, is artificially produced, and cannot stand on its own.

In the following description, the topological insulator is assumed to be BiSb.
Ruthenium, the material of metal thin film 15, is a metal material that has the property of being deposited so as to penetrate into gaps between unevenness, so even with an extremely thin film thickness, it can improve the unevenness of the film surface of BiSb insulating thin film 13. Ruthenium can improve the surface flatness of BiSb even with an extremely thin film thickness, so even when ruthenium is stacked on BiSb, the distance from recording element 30 or the air layer to magnetic nanowire medium 10 remains almost unchanged, making it possible to form magnetic domains at current densities comparable to those of conventional methods and to verify operation with a magneto-optical microscope.

Next, magnetic domain shift in the magnetic nanowire medium 10 will be described with reference to FIG.
In the initial state, for example, when an external magnetic field is applied perpendicularly to the film surface of the magnetic nanowire medium 10, the magnetic nanowire 11 is magnetized upward as shown in Figure 4(a). The open upward arrow 101 indicates that the magnetization direction is upward. After that, when an external magnetic field in the opposite direction is applied near the center of the magnetic nanowire medium 10, a magnetic domain 102 with reversed magnetization is formed as shown in Figure 4(b).

Subsequently, when a pulse current is applied to the magnetic nanowire 11, the magnetic domain 102 can be shifted to the right in Figure 4(c). When the magnetic domain is shifted, a spin torque (spin-orbit torque) 103 is generated at the interface between the magnetic nanowire 11 and the insulating thin film 13 made of BiSb. At this time, the metal thin film 15 made of ruthenium does not affect the spin torque conduction generated at the interface between the BiSb and the magnetic material. Therefore, just as when ruthenium is not stacked, a huge torque is applied from the insulating thin film 13 made of BiSb to the magnetic nanowire 11, and this torque assists in shifting the magnetic domain 102. This significantly reduces the current density required to shift the magnetic domain. Therefore, the metal thin film 15 made of ruthenium can both improve the surface flatness of the BiSb and reduce the current density required to drive the magnetic domain.

The domain wall-driven spatial light modulator 1 according to this embodiment has a magnetic nanowire medium 10 bonded with an insulating thin film 13 made of a topological insulator, thereby achieving significant power reductions. Furthermore, the magnetic nanowire medium 10 has a metal thin film 15 made of ruthenium, a metal material that reduces the surface roughness of the insulating thin film 13 made of BiSb, thereby flattening the surface of the BiSb. Furthermore, the metal thin film 15 made of ruthenium can improve the surface roughness of BiSb by depositing a few atomic layers. Furthermore, the magnetic nanowire medium 10 can utilize the magneto-optical effect to reproduce the local magnetization direction.

Typically, when forming a recording element 30 for recording information on a magnetic nanowire medium 10, an insulating layer 20 is inserted to electrically isolate the magnetic nanowire medium 10 and the recording element 30. If the surface flatness of the BiSb is poor, the insulating layer 20 layered on top of it will also suffer from poor flatness. In this case, localized insulation may be insufficient, causing the current flowing through the recording element 30 to leak into the magnetic nanowire 11 and impede recording. Furthermore, the recording element 30 formed on the insulating layer 20 is also affected by the deterioration of surface flatness, which may prevent magnetic domains from being properly recorded at the specified position on the magnetic nanowire medium 10. In contrast, the magnetic nanowire medium 10 of this embodiment includes a metal thin film 15 made of ruthenium, which flattens the BiSb surface, eliminating factors that impede recording and enabling proper recording of magnetic domains. Furthermore, the magnetic nanowire medium 10 can improve undulations in the insulating layer 20 and recording element 30 caused by unevenness on the BiSb surface.

As an alternative to this embodiment, when the surface flatness of BiSb is poor, it is possible to reduce the unevenness by layering a material that is resistant to grain growth at a thickness several times greater than the BiSb unevenness. However, this approach does not allow for the reduction of the power required for the current applied to the recording element to form magnetic domains. In other words, when using a material that is resistant to grain growth with this alternative approach, the thicker the film, the greater the distance between the recording element and the magnetic material, resulting in a higher current density required for magnetic domain formation. Furthermore, if the thickness of the film used for flattening exceeds the penetration length of the incident light, light with a uniform polarization plane will not reach the magnetic material, making it impossible to detect a magneto-optical image. In contrast, the magnetic nanowire medium 10 and domain wall-driven spatial light modulator 1 according to this embodiment flatten the surface of the BiSb by including an ultrathin metal film 15 made of ruthenium, allowing for low current operation and magneto-optical image detection.

[Method of manufacturing magnetic nanowire media]
Next, a method for manufacturing the magnetic fine wire medium according to this embodiment will be described with reference to FIG. 5 (and also with reference to FIGS. 1 and 3 as appropriate).
As an example, first, a magnetic material that will become the magnetic nanowire medium 10 is formed on a substrate 40 (step S1). Next, an insulating thin film 13 is formed on the magnetic material using a topological insulator, BiSb (step S2). The BiSb film can be formed by, for example, molecular beam epitaxy or sputtering. Molecular beam epitaxy allows for the growth of single crystals of BiSb, while sputtering is suitable for mass production.

Next, a thin metal film 15 is formed on the thin insulating film 13 (step S3). The material of the thin metal film 15 is ruthenium, a metal material that reduces the surface roughness of the thin insulating film 13. Ruthenium can be deposited using common thin film techniques such as sputtering or vapor deposition. In this step (step S3), the metal film 15 is formed by depositing a metal material to a thickness of several atoms. The step of forming the thin insulating film 13 (step S2) and the step of forming the thin metal film 15 (step S3) are carried out consecutively in the same vacuum. The thicknesses of the thin insulating film 13 and the thin metal film 15 are smaller than the penetration length of the incident light.

Next, the laminate consisting of the magnetic material, insulating thin film 13, and metal thin film 15 is processed into multiple parallel thin wires in a planar view (step S4). This allows for the formation of multiple magnetic thin wire media 10 with metal thin film 15 on their upper surfaces.

Next, to form the recording element 30, an insulating layer 20 is formed on the metal thin film 15 in advance (Step S5). Next, a recording element 30 that records information on the magnetic nanowire 11 is formed on the insulating layer 20 using, for example, a conductive material (Step S6). Examples of conductive materials that can be used include common metal materials such as Cu, Al, Ta, Cr, W, Ag, Au, Pt, and other metals and alloys thereof, as well as transparent electrode materials. Examples of transparent electrode materials include IZO (Indium Zinc Oxide) and ITO (Indium Tin Oxide).

When writing data to a plurality of magnetic nanowire media 10, the magnetic domain formation control circuit 50, the pulse current source 60, and the magnetic domain drive control circuit 70 are appropriately connected to form the domain wall drive type spatial light modulator 1. When performing the light modulation operation of the domain wall drive type spatial light modulator 1, the optical output system 80 is placed at a predetermined location.
According to the method for manufacturing a magnetic nanowire medium according to this embodiment, it is possible to manufacture a magnetic nanowire medium that can be driven with a low current and that can detect a magneto-optical image.

The magnetic nanowire medium, the domain wall-driven spatial light modulator, and the method for manufacturing the magnetic nanowire medium according to the embodiments of the present invention have been described above, but the scope of the present invention is not limited to these descriptions and should be broadly interpreted based on the claims. Furthermore, it goes without saying that various changes and modifications based on these descriptions are also included in the scope of the present invention.
For example, although the material of the metal thin film 15 is ruthenium, it is not limited to ruthenium as long as it is a metal material that can reduce the surface roughness of the insulating thin film 13 and detect a magneto-optical image. Also, although the topological insulator is BiSb, it may be BiSbTe.

The films (magnetic materials) stacked to confirm the effects of the magnetic fine wire medium 10 will be specifically described below.
<Configuration of laminated films>
Cobalt (0.3 nm) and terbium (0.6 nm) were deposited four times on a thermally oxidized silicon substrate by sputtering, followed by platinum (1 nm), BiSb (10 nm), and ruthenium (0.4 nm) deposited in that order. This film (magnetic material) is used as an example.

<Observation results using a magneto-optical microscope>
Magneto-optical microscope images were examined when an external magnetic field was applied to the example. Specifically, an external magnetic field (magnetic field strength 80 kA/m) was applied to the magnetic material (example) in a downward direction perpendicular to the film surface to align the magnetization of the magnetic material in a downward direction. Then, an external magnetic field (magnetic field strength 40 kA/m) was applied in the opposite direction (upward direction perpendicular to the film surface of the magnetic material). The magnetic field strength of 40 kA/m is close to the coercive force of this magnetic material. The magnetic material was then observed using a magneto-optical microscope.
A magneto-optical microscope is a microscope that utilizes the polarization of light reflected by a magnetic material, i.e., a microscope that applies the magneto-optical Kerr effect. This magneto-optical microscope is used, for example, to detect the magnetization direction of magnetic domain rows inside a magnetic nanowire.

Figure 6 is a magneto-optical microscope image obtained at this time. The applied external magnetic field has reversed the magnetization of part of the magnetic material to an upward direction. Figure 6 shows that the grayscale image of the magnetization-reversed region is clearly different from the grayscale image of the region where the initial downward magnetization direction remains, indicating that distinguishable grayscale images were obtained. In other words, it was found that even when ruthenium is deposited on BiSb, there is no problem in extracting a binary light/dark output. Note that Figure 6(a) and Figure 6(b) are the same image; Figure 6(b) adds a boundary line along the boundary between the upward magnetic domain (light) region and the downward magnetic domain (dark) region to make it easier to understand.

<Observation results using an atomic force microscope>
Next, the surface state of the film of the example was observed using an atomic force microscope (AFM). Furthermore, as a comparative example, the surface state of BiSb without ruthenium was also observed using an atomic force microscope. FIG. 7( a) is a 2D image (top view) of the atomic force microscope image of the comparative example, and FIG. 7( b) is a 3D image of the atomic force microscope image of the comparative example. Note that FIG. 7( b) shows a scale in the film thickness direction from 0 to 65 nm. As shown in FIG. 7( a), it can be seen that the surface of BiSb has a protrusion group structure in which many protrusions deposited in a granular shape are densely packed. Because BiSb is a material that easily undergoes grain growth, the BiSb film surface has an uneven structure with a surface roughness of about several nm, as described below.

Fig. 8(a) is a 2D image (top view) of an atomic force microscope image of the example, and Fig. 8(b) is a 3D image of an atomic force microscope image of the example, where the scale in the film thickness direction is 0 to 65 nm.
In the example, a thin film of ruthenium was deposited on BiSb in a sputtering apparatus with a specified film thickness of 0.4 nm. The ruthenium was deposited so as to fill the gaps between the protrusions of the BiSb protrusion group structure. Therefore, the ruthenium film had thin and thick locations depending on the location. For example, the ruthenium film was deposited relatively thinly on the BiSb protrusions and relatively thickly in the gaps between the BiSb protrusions.

Using the results of the atomic force microscope images of the examples, the arithmetic mean roughness (Ra) of the ruthenium surface was calculated. Note that Ra is a value obtained by taking the average distance from the reference, with the average value of the surface irregularities as a reference. Furthermore, using the results of the atomic force microscope images of the comparative examples, the arithmetic mean roughness (Ra) of the BiSb surface was calculated.
The arithmetic mean roughness of the surface calculated from the observation results of the example was Ra=0.4 nm.
The arithmetic mean roughness of the surface calculated from the observation results of the comparative example was Ra=8.2 nm.
This shows that the surface roughness was significantly improved to less than one-twentieth by laminating ruthenium.

Furthermore, for the plain magnetic structure before the BiSb film was formed, the arithmetic mean roughness of the surface, calculated from the surface condition of the film observed with an atomic force microscope, was Ra = 0.3 nm. The difference between the Ra (0.4 nm) of the ruthenium surface obtained for the example and the Ra (0.3 nm) obtained for the surface of the plain magnetic structure without the BiSb film formed was kept to around 0.1 nm, demonstrating that the example achieved sufficient flatness.

REFERENCE SIGNS LIST 1 domain wall-driven spatial light modulator 10 magnetic nanowire medium 11 magnetic nanowire 13 insulating thin film 15 metal thin film 20 insulating layer 30 recording element 40 substrate 50 magnetic domain formation control circuit 60 pulse current source 70 magnetic domain drive control circuit 80 optical output system 81, 82 polarizing filter

Claims (9)

A magnetic nanowire medium for use in a domain wall-driven spatial light modulator, comprising:
a magnetic nanowire;
an insulating thin film formed on the magnetic nanowire;
a metal thin film formed on the insulating thin film,
the thickness of the insulating thin film and the thickness of the metal thin film are smaller than the penetration depth of incident light;
the material of the insulating thin film is a topological insulator,
The magnetic nanowire medium is characterized in that the material of the metal thin film is ruthenium. The magnetic nanowire medium described in claim 1, characterized in that the thickness of the metal thin film is several atoms thick of the material of the metal thin film. A magnetic nanowire medium according to claim 1 or claim 2, characterized in that the topological insulator is BiSb or BiSbTe. 3. A domain wall-driven spatial light modulator using the magnetic nanowire medium according to claim 1,
a plurality of the magnetic nanowire media;
an insulating layer formed on a plurality of the magnetic nanowire media;
a recording element formed on the insulating layer for recording information in each magnetic nanowire;
a magnetic domain formation control circuit that generates a current magnetic field in two directions in the recording element;
a pulse current source for supplying a pulse current in the longitudinal direction of each magnetic thin wire medium;
a magnetic domain drive control circuit that controls the on/off of the pulse current to shift the magnetic domains in the longitudinal direction of each magnetic nanowire medium. A method for manufacturing a magnetic nanowire medium used in a domain wall-driven spatial light modulator, comprising:
forming an insulating thin film using a topological insulator on a magnetic material;
forming a metal thin film on the insulating thin film;
the thickness of the insulating thin film and the thickness of the metal thin film are smaller than the penetration depth of incident light;
The method for manufacturing a magnetic nanowire medium is characterized in that the material of the metal thin film is ruthenium. The method for manufacturing a magnetic nanowire medium described in claim 5, characterized in that the process of forming the metal thin film comprises stacking the material of the metal thin film to a thickness of several atoms to form the metal thin film. The method for manufacturing a magnetic nanowire medium described in claim 5 or 6, characterized in that the process of forming the insulating thin film and the process of forming the metal thin film are carried out consecutively in the same vacuum. A method for manufacturing a magnetic nanowire medium according to claim 5 or claim 6, characterized in that the topological insulator is BiSb or BiSbTe. The method for manufacturing a magnetic fine wire medium described in claim 5 or 6, further comprising a step of processing a laminate consisting of the magnetic material, the insulating thin film, and the metal thin film into a plurality of parallel fine wires in a planar view.