Magnetic domain structure

Abstract

This invention relates to a magnetic domain structure (100), which has a multilayer film composed of alternatingly stacked dielectric layers (41) and magnetic insulator layers (43) on a supporting substrate (10). The supporting substrate (10), dielectric layers (41), and magnetic insulator layers (43) are all made of a material with a garnet structure. A first multilayer film (20) is formed on the supporting substrate (10), which is composed of alternatingly stacked dielectric layers (41) and magnetic insulator layers (43), and has a structure formed on the supporting substrate (10). A defect layer (30) is formed on a first multilayer film (20), the defect layer (30) being composed of a magnetic insulating layer (43) thicker than one layer of the magnetic insulating layer (43) in the first multilayer film (20). A second multilayer film (40) is formed on the defect layer (30), the second multilayer film (40) being composed of alternating layers of multiple dielectric layers (41) and multiple magnetic insulating layers (43). In a magnetic field-free environment, magnetic domains with a width of more than 200 nm are exhibited with magnetization oriented perpendicular to the surface of the supporting substrate. Thus, a magnetic domain structure is provided that exhibits magnetic domains of a size equivalent to the wavelength of light used, while having high transmittance and a large magneto-optical effect.

Description

Technical Field

[0001] This invention relates to magnetic domain structures. Background Technology

[0002] With the development of a highly information-driven society in recent years, magnetic devices have become widely used and are once again attracting attention. Since ancient times, magnetic devices have played a significant role as storage media in devices such as hard disk drives and magnetic tape recorders, utilizing the non-volatility, stability, and robustness of magnetism. In addition to these characteristics, recent research is focused on applications utilizing the high-speed operation and shape freedom of magnetism. These features are useful in optical communications and optical devices, and are driving applications in high-speed displays, optical storage, and high-speed laser switches. Among the magnetic materials used in these devices, there are magnetic patterns within magnetic materials known as magnetic domains; effectively controlling these magnetic domains is crucial.

[0003] Magnetic domains (magnetic regions) are tiny regions existing within a magnetic material, where the magnetic moments (which can be considered as tiny magnets) are oriented in a specific direction. The existence of magnetic domains is a natural phenomenon that allows magnetic materials to reach a minimum energy state. This characteristic appears only when using magnetic materials and is a highly unique feature that cannot be obtained using materials with other electrical properties.

[0004] Magnetic domains can be used to modulate the direction of light, causing phase interference (holography), thus enabling applications in 3D displays, optical holographic memories, laser switches, and more. To realize such a device, the magnetic material needs the following three properties: first, magnetic domains of a size equivalent to the wavelength of light must exist within the magnetic material; second, a large magneto-optical effect indicating how much light can be modulated by magnetism; and third, high light transmittance. Since materials possessing all three properties do not exist in nature, this hinders the development of such optical devices.

[0005] Generally, magnetic materials are fabricated by forming films on a substrate. During this film formation process, stress and strain originating from the difference in atomic and molecular dimensions between the substrate and the film enter the film, resulting in the accumulation of magnetic anisotropic energy. This results in the direction perpendicular to the film surface becoming an easy magnetization axis, manifesting magnetic domains. If the film is thicker, the stress and strain decrease, and the magnetic anisotropic energy also decreases. Therefore, it is difficult to form magnetic domains in magnetic materials with large film thicknesses.

[0006] Furthermore, reducing the film thickness is a simple way to increase light transmittance. On the other hand, increasing the film thickness of the magnetic material is a common method to enhance the magneto-optical effect.

[0007] In other words, it is theoretically impossible to fabricate a device that uses magnetic domains and light using only the thickness of the film.

[0008] Three-dimensional displays using magneto-optical materials, optical holographic memories, and laser switches have been described in non-patent documents 1, 2, and 3.

[0009] Non-Patent Document 1 describes a paper that demonstrates the ability to output three-dimensional images by writing holographic patterns for three-dimensional displays onto a magneto-optical material. It describes how magnetic domains can be created in the material of Non-Patent Document 1 in a direction perpendicular to the film surface, thus enabling the display of images as described in Non-Patent Document 1. Figure 5 The image shown is dim and not yet commercially available. This is because materials with magnetic domains, large magneto-optical effects, and high transmittance have not yet been produced.

[0010] Non-Patent Document 2 is a paper illustrating an application example of a magneto-optical holographic memory using magneto-optical materials. In Non-Patent Document 2, it is described how light is focused and irradiated onto a magnetic garnet film, which is used as a magneto-optical material, to form magnetic domains of arbitrary shapes, and how these magnetic domains are used to fabricate a magneto-optical holographic memory. The greater the magneto-optical effect and the higher the transmittance of the magneto-optical material used, the lower the error rate and the greater the amount of information that can be recorded.

[0011] Non-Patent Document 3 describes an application example of a magneto-optical material as a Q-switch in an optical switch, referred to as a laser. It has been found that by inserting a magneto-optical material with magnetic domains into an optical resonator to operate as a Q-switch, kilowatt-level high-power pulsed lasers are being developed. Existing technical documents Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2001-194639 Non-patent literature

[0013] Non-patent document 1: Hiroyuki Takagi, Kazuki Nakamura, Sotaro Tsuda, Taichi Goto, Pang Boey Lim and Mitsuteru Inoue, "Magneto-optic three-dimensional holographic display with tilling optical addressing method", Sensors and Materials, 27, 1003-1008 (2015 / 11 / 11). Non-patent document 2: Yuichi Nakamura, Zen Shirakashi, Hiroyuki Takagi, Pang BoeyLim, Taichi Goto, Hironaga Uchida and Mitsuteru Inoue, "Error-freereconstruction of magnetic hologram via improvement of recording conditions in collinear optical system", Optics Express, 25, 15349-15357 (2017 / 06 / 26). Non-patent document 3: Taichi Goto, Ryohei Morimoto, John W. Pritchard, Mani Mina, Hiroyuki Takagi, Yuichi Nakamura, Pang Boey Lim, Takunori Taira and Mitsuteru Inoue, "Magneto-optical Q-switching using magnetic garnet film with micromagnetic domains", Optics Express, 24, 17635-17643 (2016 / 07 / 25). Non-patent document 4: Hideki Kato, Takeshi Matsushita, Akio Takayama, Motoji Egawa, Kazuhiro Nishimura and Mitsuteru Inoue, "Theoretical analysis of opticaland magneto-optical properties of one-dimensional magnetophotonic crystals", Journal of Applied Physics, 93, 3906-3911 (2003 / 04 / 01) Summary of the Invention The technical problem that the invention aims to solve

[0014] As mentioned above, in order to develop magneto-optical devices (3D displays, optical holographic memories, laser switches, etc.) that utilize light wavelengths in the near-ultraviolet, visible, and near-infrared regions, it is necessary to display magnetic domains of a size equivalent to the wavelength of the light used, while simultaneously possessing high transmittance and a large Faraday rotation angle (= the magnitude of the magneto-optical effect of the transmitted light from the magnetic material). However, these conditions cannot be met simply by increasing the film thickness of the magnetic material used.

[0015] The present invention was made in view of the above-mentioned problems, and its object is to provide a magnetic domain structure that exhibits magnetic domains of a size equivalent to the optical wavelength used in the magnetic domain structure, while having high light transmittance and a large magneto-optical effect. means of solving technical problems

[0016] To achieve the above objectives, this invention provides a magnetic domain structure having a multilayer film composed of alternating layers of dielectric and magnetic insulator layers on a supporting substrate. The supporting substrate, dielectric layers, and magnetic insulator layers are all made of a material with a garnet structure. A first multilayer film is formed on the supporting substrate by alternating layers of dielectric and magnetic insulator layers of specific thicknesses. A defect layer is formed on the first multilayer film, consisting of magnetic insulator layers thicker than one of the magnetic insulator layers in the first multilayer film. A second multilayer film is formed on the defect layer by alternating layers of dielectric and magnetic insulator layers of the same thickness as those in the first multilayer film. In a non-magnetic field environment, the structure exhibits magnetic domains with a width of 200 nm or more, magnetized in a direction perpendicular to the surface of the supporting substrate.

[0017] Such a magnetic domain structure can be used to display magnetic domains of a size equivalent to the wavelength of light used, while having high light transmittance and a large magneto-optical effect.

[0018] Preferably, the thickness of the defect layer is twice the thickness of one layer of the magnetic insulator layer in the first multilayer film.

[0019] By setting the thickness of the defect layer to twice its original thickness, it can function more effectively as a defect layer, and achieve greater light transmittance and a larger magneto-optical effect.

[0020] Alternatively, the supporting substrate is preferably made of gadolinium gallium garnet, the dielectric layer is made of gadolinium gallium garnet, and the magnetic insulator layer is made of cerium-doped yttrium iron garnet.

[0021] These materials may be appropriately used in the magnetic domain structure of the present invention.

[0022] In this case, the gadolinium gallium garnet can be gadolinium gallium garnet in which gadolinium is not replaced, or it can be gadolinium gallium garnet in which a portion of gadolinium is replaced by other elements.

[0023] In the magnetic domain structure of the present invention, either unsubstituted gadolinium gallium garnet or substituted gadolinium gallium garnet can be used as the gadolinium gallium garnet.

[0024] Furthermore, the magnetic domain structure of the present invention preferably has the refractive index of the dielectric layer set to n1 and the refractive index of the magnetic insulator layer set to n2. The thickness t1 [nm] of the dielectric layer and the thickness t2 [nm] of the magnetic insulator layer in the first multilayer film and the second multilayer film are t1=λ / (4×n1) and t2=λ / (4×n2) (here, λ is the design wavelength [nm] for the wavelength at which the magnetic domain structure is to be used).

[0025] By designing the thickness of each layer according to the wavelength of light to be used in the magnetic domain structure, it is possible to make it have a better morphology as a magnetic domain structure.

[0026] Furthermore, preferably, the normals of each crystal plane of the supporting substrate, the dielectric layer, and the magnetic insulator layer are all... <111> direction.

[0027] By designing the crystal structure in this way, it can have a better morphology as a magnetic domain structure.

[0028] Additionally, a reflective film may be provided on the opposite side of the supporting substrate, opposite to the first multilayer film.

[0029] By having a reflective film, the magnetic domain structure of the present invention can also serve as a magnetic domain structure that acts on reflected light. The effects of the invention

[0030] The magnetic domain structure of the present invention can be used as a magnetic domain structure that exhibits a size equivalent to the wavelength of light used, while having high light transmittance and a large magneto-optical effect. Attached Figure Description

[0031] Figure 1 This is a schematic cross-sectional view showing an example of the magnetic domain structure of the present invention. Figure 2 This is a cross-sectional TEM image of the magnetic domain structure fabricated in the embodiment. Figure 3 This is a photograph of the surface of the magnetic domain structure (the surface of the second multilayer film) fabricated in the embodiment, observed using a polarizing microscope in a 0Oe non-magnetic field environment. Figure 4The image shows the surface of the magnetic domain structure (the surface of the second multilayer film) fabricated in the embodiment, observed using a polarizing microscope in a magnetic field environment of 350 Oe. Figure 5 It is a graph showing the results of measuring transmittance and Faraday rotation angle when light is incident perpendicularly onto the surface of the magnetic domain structure (the surface of the second multilayer film) fabricated in the embodiment. Detailed Implementation

[0032] The following describes embodiments of the present invention, but the present invention is not limited thereto.

[0033] This invention relates to a magnetic domain structure comprising a multilayer film consisting of alternating layers of dielectric and magnetic insulator layers on a supporting substrate. The supporting substrate, dielectric layers, and magnetic insulator layers are all made of a material with a garnet structure. A first multilayer film is formed on the supporting substrate, consisting of alternating layers of dielectric and magnetic insulator layers of specific thicknesses. A defect layer is formed on the first multilayer film, consisting of magnetic insulator layers thicker than one of the magnetic insulator layers in the first multilayer film. A second multilayer film is formed on the defect layer, consisting of alternating layers of dielectric and magnetic insulator layers of the same thickness as those in the first multilayer film. In a non-magnetic field environment, magnetic domains with a width of 200 nm or more are exhibited, with magnetization oriented perpendicular to the surface of the supporting substrate.

[0034] exist Figure 1 The magnetic domain structure 100 of the present invention is shown in the figure. The magnetic domain structure 100 is stacked with a support substrate 10, a first multilayer film 20, a defect layer 30, and a second multilayer film 40, all made of a material having a garnet structure. The first multilayer film 20 is formed by alternating layers of multiple dielectric layers 21 with a specific thickness and multiple magnetic insulator layers 23 with a specific thickness. The specific thickness of the multiple dielectric layers 21 in the first multilayer film 20 may have an error of approximately ±20%. The specific thickness of the multiple magnetic insulator layers 23 in the first multilayer film 20 may also have an error of approximately ±20%. Similarly, the second multilayer film 40 is formed by alternating layers of multiple dielectric layers 41 with a specific thickness and multiple magnetic insulator layers 43 with a specific thickness, and the multiple dielectric layers 41 and multiple magnetic insulator layers 43 have the same thickness as the multiple dielectric layers 21 and multiple magnetic insulator layers 23 in the first multilayer film 20. In the second multilayer film 40, each of the multiple dielectric layers 41 and multiple magnetic insulator layers 43 may also have an error of about ±20%.

[0035] The defect layer 30 is located between the first multilayer film 20 and the second multilayer film 40. The defect layer 30 is a layer made of magnetic insulating material, and is thicker than the magnetic insulating layer 23 in the first multilayer film 20. Specifically, the thickness of the defect layer 30 is preferably twice the thickness of the magnetic insulating layer 23 in the first multilayer film 20. By setting the thickness of the defect layer 30 to twice the thickness of the magnetic insulating layer 23, it can function more effectively as a defect layer, and achieves higher light transmittance and a larger magneto-optical effect. This "twice the thickness" can have an error of approximately ±20%.

[0036] Furthermore, due to the structure of the magnetic domain structure 100 of the present invention, compared to the case where there is a defect layer on the supporting substrate, the magneto-optical effect is increased in the case where the multilayer film portion other than the defect layer is attached, thus achieving an increase in the magneto-optical effect. The thickness of the defect layer 30 is sufficient to function as a defect layer as long as it is thicker than the thickness of one layer of the magnetic insulator layer 23, and is not limited to twice the thickness of the magnetic insulator layer in the aforementioned multilayer film. Specifically, it is preferably an integer multiple of 2, and other than 2, it is preferably 4 times, 6 times, etc. However, if it is greater than 1 time, although the rate of increase in the magneto-optical effect decreases, the manifestation of magnetic domains and the increase in the magneto-optical effect can be satisfied simultaneously. Therefore, it can also be 3 times, 5 times, etc., or non-integer numbers such as 1.5 times, 3.5 times, etc.

[0037] By having a defect layer 30 (e.g., a Ce:YIG layer twice as thick), transmittance can be improved at the designed wavelength (the wavelength of light for which the magnetic domain structure 100 is to be used), while simultaneously increasing the Faraday rotation angle (the magnitude of the magneto-optical effect of the transmitted light). Such a layer is generally referred to as a defect layer in magneto-optical materials, and is also referred to as a defect layer in the description of this invention.

[0038] exist Figure 1 As illustrated in the diagram, in the first multilayer film 20, 10 layers of dielectric layer 21 and 9 layers of magnetic insulator layer 23 are alternately stacked; similarly, in the second multilayer film 40, 10 layers of dielectric layer 41 and 9 layers of magnetic insulator layer 43 are alternately stacked. The number of alternating stackings in this invention is at least two, but there is no upper limit. Considering the fabrication of the magnetic domain structure 100, the preferred range for the number of alternating stackings is 5 to 20 times.

[0039] Furthermore, in this invention, the magnetic domain structure 100, in a magnetic field-free environment, exhibits magnetic domains with a width of 200 nm or more, magnetized in a direction perpendicular to the substrate surface of the supporting substrate 10. A magnetic field-free environment refers to the state in which no magnetic field is applied to the magnetic domain structure 100. In this invention, it has been found that if such a magnetic field is applied… Figure 1 The illustrated magnetic domain structure 100 (which incorporates nano- to micro-scale structures) exhibits magnetic domains while achieving high transmittance and a large magneto-optical effect.

[0040] In the magnetic domain structure 100 of the present invention, the support substrate 10 is preferably made of gadolinium gallium garnet (GGG). Furthermore, the dielectric layers (dielectric layer 21 in the first multilayer film 20 and dielectric layer 41 in the second multilayer film 40) are preferably made of gadolinium gallium garnet. Additionally, the magnetic insulator layers (magnetic insulator layer 23 in the first multilayer film 20 and magnetic insulator layer 43 in the second multilayer film 40) are preferably made of cerium-substituted yttrium iron garnet (Ce:YIG). By using these materials, the magnetic domains (magnetized domains with a width of 200 nm or more in a direction perpendicular to the substrate surface of the support substrate 10) required in the magnetic domain structure of the present invention can be more reliably manifested.

[0041] Furthermore, in this case, the gadolinium gallium garnet constituting the dielectric layer is preferably gadolinium gallium garnet with unsubstituted gadolinium, but it can also be gadolinium gallium garnet in which part of the gadolinium is replaced by other elements (such as rare earth elements). However, epitaxial crystal growth must be possible during fabrication.

[0042] Furthermore, in this case, Ce:YIG, which constitutes the magnetic insulating layer, is a magnetic material and an insulator, i.e., it is a magnetic insulator. The molecular structure of YIG is Y3Fe5O. 12 The material can be based on materials where the Y or Fe portion is replaced by other elements. Even among rare earth elements, Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be used as substitution elements. In particular, it is known that when the Y portion is replaced by rare earth elements or Bi and Gd, the magneto-optical effect is large. In this invention, Ce is particularly suitable as a substitution element.

[0043] When the refractive indices of dielectric layers 21 and 41 are set to n1 and the refractive indices of magnetic insulator layers 23 and 43 are set to n2, the thicknesses t1 [nm] of dielectric layers 21 and 41 and the thicknesses t2 [nm] of magnetic insulator layers 23 and 43 in the first multilayer film 20 and the second multilayer film 40 of the magnetic domain structure 100 of the present invention are preferably t1=λ / (4×n1) and t2=λ / (4×n2). (Here, λ is the design wavelength [nm] for the optical wavelength of the magnetic domain structure 100 to be used).

[0044] That is, the preferred formula is film thickness = design wavelength / (4 × refractive index). This is the same as the film thickness relationship of a typical Bragg reflector (also known as a dielectric reflector or multilayer reflector). By designing the thickness of each layer according to the wavelength of light to be used in the magnetic domain structure 100, it can be made to have a better morphology as a magnetic domain structure.

[0045] Furthermore, the magnetic domain structure 100 of the present invention preferably has normals on each crystal plane of the supporting substrate 10, dielectric layers 21, 41, and magnetic insulator layers 23, 43. <111> Orientation. By setting the crystal plane structure in this way, it can have a better morphology as a magnetic domain structure 100.

[0046] In the magnetic domain structure 100 of the present invention, a reflective film may be provided on the side of the supporting substrate 10 opposite to the first multilayer film 20. The structure of the present invention is for transmitting light, by placing a reflective film on the rear side of the magnetic domain structure 100 (the side of the supporting substrate 10 opposite to the first multilayer film 20). Figure 1 A reflective film (mirror) made of aluminum or the like is disposed below the support substrate 10 shown in the diagram. It can also perform the same function for reflected light, and is therefore not limited to transmitted light. The reflective film can be located on the underside of the support substrate 10, and can be either closely attached to the support substrate 10 or separate from it.

[0047] The magnetic domain structure of this invention can be developed for many device applications using magneto-optical materials. Magnetic domains are difficult to predict through calculation and simulation; recently, however, they have begun to be understood through large-scale calculations using supercomputers, and the dimensions of specific structures are difficult to estimate. This invention, through the above-described configuration, reveals magnetic domains while achieving high transmittance and a large magneto-optical effect.

[0048] Regarding the radiation effect of the magnetic domain structure of the present invention on related fields, as described above, examples include three-dimensional displays, optical holographic memories, and laser switches.

[0049] (1) 3D displays are expected to be developed in the gaming, entertainment, and medical industries that use next-generation displays.

[0050] (2) Optical holographic memory is expected to be used as a storage device for storing massive amounts of data in data centers that support artificial intelligence, autonomous driving, etc. with low power consumption.

[0051] (3) Laser switches are developed in high-power laser applications because they can increase optical power, and are expected to be applied in optical processing and processing industries.

[0052] It should be noted that it is well known that multilayer film structures using magneto-optical materials in the defect layer portion are used as magnetic photonic crystals (e.g., Non-Patent Document 4). Non-Patent Document 4 describes high magneto-optical effect and high transmittance, expressed by calculation and experiment. However, Non-Patent Document 4 does not discuss magnetic domains, and there was no application field at the time, so it does not mention whether it has magnetic domains or what kind of magnetic domains it has.

[0053] Furthermore, a multilayer film structure has been described in Patent Document 1. Patent Document 1 is characterized by its ability to achieve a large magneto-optical effect, but unlike this invention, all its constituent elements have a garnet structure, and magnetic domains are not mentioned. Example

[0054] The following examples illustrate the present invention in more detail, but the present invention is not limited to these examples.

[0055] [Example] The structure of the present invention was fabricated. Figure 1 Magnetic domain structure 100. In Figure 2 The image shows a transmission electron microscope image of a cross-section of the actual fabricated magnetic domain structure 100 sample.

[0056] The following materials were used as specific materials. A GGG (Gadolinium Gallium Garnet) substrate was used as the support substrate 10. Additionally, GGG was used as the material for the magnetic insulating layers (magnetic insulating layer 23 in the first multilayer film 20 and magnetic insulating layer 43 in the second multilayer film 40), and Ce:YIG (cerium-substituted yttrium iron garnet) was used as the material for the dielectric layers (dielectric layer 21 in the first multilayer film 20 and dielectric layer 41 in the second multilayer film 40) and the defect layer 30. These layers were alternately stacked on the GGG substrate of the support substrate 10.

[0057] The film deposition method for each layer employed high-frequency ion beam sputtering. During deposition, the sample was held at approximately 900 degrees Celsius while deposition was being carried out. This ensured that the lattice constants of the supporting substrate 10 and the materials of each layer were matched, enabling epitaxial growth. The orientation of the supporting substrate 10 and all layers was perpendicular to the plane. <111> .

[0058] Although GGG is not a magnetic material, it is similar to yttrium iron garnet (YIG, Y3Fe5O). 12 Both are garnet structures, and their crystal structure can be written as Gd3Ga5O. 12-xThe lattice constant of GGG is 1.238 nm, which is similar to that of cerium-doped yttrium iron garnet (Ce:YIG). Therefore, Ce:YIG (magnetic insulator layers 23 and 43, defect layer 30) can be epitaxially grown on the GGG support substrate 10 and the GGG film (dielectric layers 21 and 41).

[0059] The refractive index of GGG at a wavelength of 1064 nm is 1.89. In the GGG of the embodiment, the gadolinium is set to be unsubstituted without deliberate substitution.

[0060] Furthermore, Ce:YIG refers to a magnetic material but is an insulator; that is, it is a magnetic insulator. The molecular structure of YIG is based on Y3Fe5O3. 12 Based on this, the material can be a material in which the Y and Fe portions are replaced by other elements. In particular, it is known that when the Y portion is replaced by rare earth elements or Bi or Gd, the magneto-optical effect is large. In this embodiment, even among rare earth elements, Ce is selected. The substitution amount of Ce in this embodiment is 1, and the composition is written as Ce1Y2Fe5O. 12-x X represents the compositional deviation. It is generally difficult to accurately determine the oxygen content in a molecule, hence this notation. The lattice constant of this Ce:YIG is 1.243 nm. The refractive index of this Ce:YIG at a wavelength of 1064 nm is 2.20.

[0061] In this embodiment, the thickness of the GGG layer is 148.7 ± 2.5 nm. The numbers following ± represent the standard deviation of the total thickness of the GGG layers in the structure of the magnetic domain structure 100 actually fabricated in this embodiment.

[0062] In this embodiment, the thickness of the Ce:YIG layer excluding the defect layer 30 is 119.5 ± 2.6 nm. The numbers following ± represent the standard deviation of the thickness of all Ce:YIG layers excluding the defect layer 30 in the structure of the magnetic domain structure 100 actually fabricated in this embodiment. However, only the Ce:YIG layer, which is twice the thickness of the defect layer 30, has a thickness of 240.0 nm.

[0063] It should be noted that the refractive indices of dielectric layers 21 and 41 are set as n1, and the refractive indices of magnetic insulator layers 23 and 43 are set as n2. The thicknesses t1 [nm] of the GGG layer (dielectric layers 21 and 41) and the Ce:YIG layer (magnetic insulator layers 23 and 43) in the first multilayer film 20 and the second multilayer film 40 are determined by values ​​calculated as t1 = λ / (4 × n1) and t2 = λ / (4 × n2). The design wavelength λ is set to 1064 nm.

[0064] An illustration of a sample surface of the magnetic domain structure 100 thus fabricated, as seen from the above, is shown in the figure. Figure 3 The observations here are made using a microscope called a polarizing microscope, where the magnitude of the magneto-optical effect is expressed in shades. That is, in Figure 3 The black and white areas shown represent the reversal of magnetization polarity, which corresponds to magnetic domains. From Figure 3 It can be seen that magnetic domains with a width of approximately 200 to 1000 nm are present. In obtaining... Figure 3 When taking the photograph, no magnetic field was applied to the sample (in a magnetic field-free environment (or a geomagnetic environment)). The magnitude of the magnetic field is recorded as 0 Oe (Oersted).

[0065] In addition, a magnetic field of magnitude 350 Oe was applied to the sample of the magnetic domain structure 100, and the sample surface of the magnetic domain structure 100 was observed from above. Figure 4 Applying a magnetic field other than Figure 3 Under the same conditions. Figure 3 In comparison, Figure 4 It can be seen that the size of the magnetic domains on the surface of the magnetic domain structure 100 changes, and the contrast between black and white is not due to the unevenness of the sample surface.

[0066] Furthermore, light was incident on the film surface of a sample perpendicular to the magnetic domain structure 100 fabricated in this embodiment, and the results of transmitting power and Faraday rotation angle (the magnitude of the magneto-optical effect of transmitted light) were measured and are shown below. Figure 5 .exist Figure 5 At the wavelength indicated by the arrow, it can be seen that the transmittance and Faraday rotation angle increase. This is due to the presence of a defect layer 30 composed of twice the thickness of Ce:YIG. Figure 5 As shown, the transmittance is approximately 50%, and the Faraday rotation angle is approximately 3.5°. The wavelengths indicated by the arrows are the wavelengths at which the magneto-optical effect has been confirmed to increase.

[0067] It is known that if the thickness of each Ce:YIG layer exceeds 1 μm, the stress in the film decreases with increasing thickness, thus preventing the formation of magnetic domains. In contrast, in the structure shown in the embodiment according to the present invention, the thickness of each Ce:YIG layer is as thin as 300 nm or less, thus still exhibiting sufficiently large stress and strain. Therefore, magnetic domains are manifested.

[0068] Meanwhile, in the structure shown in the embodiment, the total number of Ce:YIG can be increased, thus exhibiting magnetic domains while obtaining a large magneto-optical effect. If only the above idea is followed, it becomes simply alternating layers of Ce:YIG and GGG. Thus, the alternating layer structure becomes a Bragg reflector, reflecting light of the designed wavelength with extremely low transmittance, close to 0. This is called the photonic bandgap. With such low transmittance, the device applications described in (1) to (3) above are impossible. Therefore, a defect layer 30 is required.

[0069] If a defect layer 30 is present, an extremely narrow band of propagating light, known as a defect layer mode (or localized mode), appears in the photonic bandgap. Thus, a large magneto-optical effect can be obtained while maintaining high transmittance. In the above embodiment, the defect layer 30 is represented as twice the thickness of the first multilayer film 20, but a magneto-optical effect can also be obtained even when the defect layer 30 is configured to be thicker than the first multilayer film 20 (i.e., a thickness greater than an integer multiple of 1 or 2 times).

[0070] As described above, in the magnetic domain structure 100 of the present invention, a structure that exhibits magnetic domains while having high transmittance and a large magneto-optical effect can be fabricated.

[0071] This instruction manual includes the following methods. [1]: A magnetic domain structure having a multilayer film consisting of alternating layers of dielectric layers and magnetic insulator layers on a supporting substrate. The supporting substrate, the dielectric layer, and the magnetic insulator layer are all made of a material with a garnet structure. The supporting substrate has a first multilayer film, which is formed by alternating layers of a plurality of dielectric layers of a specific thickness and a plurality of magnetic insulator layers of a specific thickness. The first multilayer film has a defect layer formed thereon, the defect layer being composed of a magnetic insulating layer that is thicker than one of the magnetic insulating layers in the first multilayer film. A second multilayer film is provided on the defect layer. The second multilayer film is formed by alternating layers of a plurality of dielectric layers and a plurality of magnetic insulating layers having the same thickness as the respective layers in the first multilayer film. In a magnetic field-free environment, magnetic domains with a width of more than 200 nm are exhibited, with the magnetization orientation perpendicular to the surface of the supporting substrate. [2]: According to the magnetic domain structure of [1] above, the thickness of the defect layer is twice the thickness of one layer of the magnetic insulator layer in the first multilayer film. [3]: According to the magnetic domain structure described in [1] or [2] above, wherein, The support substrate is made of gadolinium gallium garnet. The dielectric layer is composed of gadolinium gallium garnet. The magnetic insulating layer is composed of cerium-doped yttrium iron garnet. [4]: According to the magnetic domain structure of [3] above, the gadolinium gallium garnet is gadolinium gallium garnet in which gadolinium is not replaced, or gadolinium gallium garnet in which a portion of gadolinium is replaced by other elements. [5]: According to any one of [1] to [4] above, when the refractive index of the dielectric layer is set to n1 and the refractive index of the magnetic insulator layer is set to n2, the thickness t1 [nm] of the dielectric layer and the thickness t2 [nm] of the magnetic insulator layer in the first multilayer film and the second multilayer film are t1=λ / (4×n1) and t2=λ / (4×n2); (Here, λ is the design wavelength [nm] for the wavelength at which the magnetic domain structure is to be used). [6]: According to any one of [1] to [5] above, the normal of each crystal plane of the supporting substrate, the dielectric layer, and the magnetic insulator layer is <111> direction. [7]: A magnetic domain structure according to any one of [1] to [6] above, wherein a reflective film is provided on the opposite side of the supporting substrate opposite to the first multilayer film.

[0072] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any content having a substantially similar structure to the technical concept described in the patent application of the present invention, and producing the same effect, is included within the scope of the technology of the present invention.

Claims

1. A magnetic domain structure comprising a multilayer film consisting of alternating layers of dielectric layers and magnetic insulator layers on a supporting substrate, characterized in that, The supporting substrate, the dielectric layer, and the magnetic insulator layer are all made of a material with a garnet structure. The supporting substrate has a first multilayer film, which is formed by alternating layers of a plurality of dielectric layers of a specific thickness and a plurality of magnetic insulator layers of a specific thickness. The first multilayer film has a defect layer formed thereon, the defect layer being composed of a magnetic insulating layer that is thicker than one of the magnetic insulating layers in the first multilayer film. A second multilayer film is provided on the defect layer. The second multilayer film is formed by alternating layers of a plurality of dielectric layers and a plurality of magnetic insulating layers having the same thickness as the dielectric layer and the magnetic insulating layer in the first multilayer film. In a magnetic field-free environment, magnetic domains with a width of more than 200 nm are exhibited, with the magnetization orientation perpendicular to the surface of the supporting substrate.

2. The magnetic domain structure according to claim 1, characterized in that, The thickness of the defect layer is twice the thickness of one layer of the magnetic insulator layer in the first multilayer film.

3. The magnetic domain structure according to claim 1, characterized in that, The support substrate is made of gadolinium gallium garnet. The dielectric layer is composed of gadolinium gallium garnet. The magnetic insulating layer is composed of cerium-doped yttrium iron garnet.

4. The magnetic domain structure according to claim 3, characterized in that, The gadolinium gallium garnet is gadolinium gallium garnet in which gadolinium is not replaced, or gadolinium gallium garnet in which a portion of gadolinium is replaced by other elements.

5. The magnetic domain structure according to any one of claims 1 to 4, characterized in that, When the refractive index of the dielectric layer is set to n1 and the refractive index of the magnetic insulator layer is set to n2, the thicknesses t1 and t2 of the dielectric layer and the magnetic insulator layer in the first and second multilayer films are: t1=λ / (4×n1), t2=λ / (4×n2); Here, λ is the design wavelength for using the magnetic domain structure. The units for t1, t2, and the design wavelength are nm.

6. The magnetic domain structure according to claim 1, characterized in that, The normals of each crystal plane of the supporting substrate, the dielectric layer, and the magnetic insulator layer are all in the (111) direction.

7. The magnetic domain structure according to claim 1, characterized in that, A reflective film is provided on the opposite side of the supporting substrate, opposite to the first multilayer film.

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