Magnetic domain structure

Abstract

The present invention is a magnetic domain structure (100) having, on a support substrate (10), multilayer films each comprising a plurality of dielectric layers (41) and a plurality of magnetic insulator layers (43) that are alternately stacked. Each of the support substrate (10), the dielectric layers (41), and the magnetic insulator layers (43) comprises a material having a garnet structure. The magnetic domain structure (100) has: on the support substrate (10), a first multilayer film (20) in which the plurality of dielectric layers (41) and the plurality of magnetic insulator layers (43) are alternately stacked; a defect layer (30) that is formed on the first multilayer film (20), and that comprises a magnetic insulator layer (43) that is thicker than the thickness of each of the magnetic insulator layers (43) in the first multilayer film (20); and, on the defect layer (30), a second multilayer film (40) in which the plurality of dielectric layers (41) and the plurality of magnetic insulator layers (43) are alternately stacked. The magnetic domain structure exhibits, in the absence of a magnetic field, a magnetic domain in which magnetization is directed vertically toward the surface of the support substrate and which has a width of 200 nm or more. Thus, provided is a magnetic domain structure that has a large light transmittance and large magneto-optical effect, while exhibiting a magnetic domain having a size that is about the wavelength of used light.

Description

magnetic domain structure

[0001] The present invention relates to a magnetic domain structure.

[0002] With the recent development of an advanced information society, magnetic devices are being widely used and are attracting renewed attention. Magnetic devices have long been used as recording media in hard disk drives, tape recorders, and other devices, primarily because of their non-volatility, stability, and robustness. In addition to these features, development of applied devices has recently been progressing that take advantage of the high-speed operation and freedom of shape of magnetism. These features are useful when used in optical communications and optical devices, and applications are progressing in high-speed displays, optical memory, high-speed laser switches, and more. The magnetic materials used in these magnetic devices have magnetic patterns within them called magnetic domains, and it is important to effectively control these domains.

[0003] A magnetic domain is a tiny region that exists within a magnetic material, and within this region, the magnetic moments (which can be thought of as small magnets) are aligned in a certain direction. The existence of magnetic domains is a natural phenomenon that allows a magnetic material to reach a minimum energy state. This characteristic appears only when using magnetic materials, and is highly unique and cannot be obtained with materials that use other electrical properties.

[0004] Magnetic domains can be used to modulate the direction of light and cause phase interference (holography), which can be applied to three-dimensional displays, optical holographic memory, laser switches, and more. To realize such devices, magnetic materials must have the following three properties: first, magnetic domains of a size comparable to the wavelength of light must be present within the magnetic material; second, the magneto-optical effect, which indicates the degree to which light can be modulated by magnetism, must be large; and third, optical transmittance must be high. Materials that simultaneously possess all three properties do not exist in nature, which has hindered the development of the optical devices mentioned above.

[0005] Generally, magnetic materials are produced by depositing a film on a substrate. During this film formation, stress and strain originating from the difference in atomic and molecular size between the substrate and the film enter the film, and magnetic anisotropy energy originating from this accumulates. As a result, the direction perpendicular to the film surface becomes the magnetic easy axis, and magnetic domains appear. As the film becomes thicker, stress and strain become smaller, and so does the magnetic anisotropy energy. For this reason, magnetic domains are less likely to form in magnetic materials with thick films.

[0006] A simple way to increase light transmittance is to decrease the film thickness, while a common way to increase the magneto-optical effect is to increase the film thickness of the magnetic material.

[0007] In other words, it is theoretically impossible to fabricate a device that utilizes magnetic domains and light by simply varying the thickness of the film.

[0008] Three-dimensional displays, optical holographic memories, and laser switches using magneto-optical materials are described in Non-Patent Documents 1, 2, and 3.

[0009] Non-Patent Document 1 is a paper demonstrating that a 3D image can be output by writing a hologram pattern for a 3D display into a magneto-optical material. The material described in Non-Patent Document 1 can create magnetic domains perpendicular to the film surface, and it is described that an image such as that shown in Figure 5 of Non-Patent Document 1 can be displayed. However, the brightness of the image is low, and it has not yet been commercialized. This is because a material with magnetic domains, a large magneto-optical effect, and transmittance has not yet been created.

[0010] Non-Patent Document 2 is a paper showing an example of the application of magneto-optical materials to magneto-optical holographic memory. Non-Patent Document 2 describes the formation of magnetic domains of arbitrary shapes by concentrating and irradiating a magnetic garnet film, which is a magneto-optical material, with light, and the fabrication of a magneto-optical holographic memory using these. The greater the magneto-optical effect and the higher the transmittance of the magneto-optical material used in this memory, the lower the error rate and the greater the amount of information that can be recorded.

[0011] Non-Patent Document 3 is an example of the application of magneto-optical materials to optical switches called laser Q-switches. It has been discovered that inserting a magneto-optical material with magnetic domains into an optical resonator can function as a Q-switch, leading to the development of kilowatt-class high-power pulsed lasers.

[0012] Japanese Patent Application Laid-Open No. 2001-194639

[0013] 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).Yuichi Nakamura, Zen Shirakashi, Hiroyuki Takagi, Pang Boey Lim, Taichi Goto, Hironaga Uchida and Mitsuteru Inoue, "Error-free reconstruction of magnetic hologram via improvement of recording conditions in collinear optical system", Optics Express, 25, 15349-15357 (2017 / 06 / 26).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).Hideki Kato, Takeshi Matsushita, Akio Takayama, Motoji Egawa, Kazuhiro Nishimura and Mitsuteru Inoue, "Theoretical analysis of optical and magneto-optical properties of one-dimensional magnetophotonic crystals", Journal of Applied Physics, 93, 3906-3911 (2003 / 04 / 01).

[0014] As mentioned above, to develop magneto-optical devices (such as three-dimensional displays, optical holographic memories, and laser switches) using light with wavelengths in the near-ultraviolet, visible, and near-infrared regions, it is necessary to develop magnetic domains of a size comparable to the wavelength of the light being used, while also having a large optical transmittance and a large Faraday rotation angle (i.e., the magnitude of the magneto-optical effect of light transmitted through the magnetic material). However, these conditions could not be met simply by increasing the film thickness of the magnetic material used.

[0015] The present invention has been made in consideration of the above problems, and aims to provide a magnetic domain structure that exhibits magnetic domains of a size approximately equal to the wavelength of light used for the magnetic domain structure, while having high light transmittance and a large magneto-optical effect.

[0016] In order to achieve the above object, the present invention provides a magnetic domain structure having a multilayer film composed of a plurality of dielectric layers and a plurality of magnetic insulator layers alternately stacked on a support substrate, wherein the support substrate, the dielectric layers, and the magnetic insulator layers are all made of materials having a garnet structure, a first multilayer film on the support substrate, in which a plurality of the dielectric layers, each having a constant thickness, and a plurality of the magnetic insulator layers, each having a constant thickness, are alternately stacked, and a second multilayer film formed on the first multilayer film, in which a defect layer is formed of the magnetic insulator layer, the defect layer being thicker than the thickness of one of the magnetic insulator layers in the first multilayer film, and in which a plurality of the dielectric layers and a plurality of the magnetic insulator layers, each having a thickness equivalent to that of the first multilayer film, are alternately stacked, and wherein, in a no-magnetic-field environment, magnetic domains having a width of 200 nm or more and in which magnetization is oriented perpendicular to the surface of the support substrate are generated.

[0017] Such a magnetic domain structure can exhibit magnetic domains of a size approximately equal to the wavelength of the light used, and can have a high optical transmittance and a large magneto-optical effect.

[0018] Here, it is preferable that the thickness of the defect layer is twice the thickness of one of the magnetic insulator layers in the first multilayer film.

[0019] By doubling the thickness of the defect layer in this way, it is possible to make it function more effectively as a defect layer, and it is possible to obtain a large light transmittance and a large magneto-optical effect.

[0020] It is also preferable that the support substrate is made of gadolinium gallium garnet, the dielectric layer is made of gadolinium gallium garnet, and the magnetic insulator layer is made of cerium-substituted yttrium iron garnet.

[0021] In the magnetic domain structure of the present invention, these materials can be suitably used.

[0022] In this case, the gadolinium gallium garnet may be one in which gadolinium is not substituted, or one in which a portion of gadolinium is substituted with another element.

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

[0024] Furthermore, in the magnetic domain structure of the present invention, it is preferable that 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) (where λ is a design wavelength [nm] that is a wavelength at which the magnetic domain structure is intended to be used), where n1 is a refractive index of the dielectric layer and n2 is a refractive index of the magnetic insulator layer.

[0025] By designing the thickness of each layer in this way based on the wavelength of light for which the magnetic domain structure is intended to be used, a more preferable embodiment of the magnetic domain structure can be achieved.

[0026] It is also preferable that the normals to the respective crystal planes of the support substrate, the dielectric layer, and the magnetic insulator layer are all in the <111> direction.

[0027] By forming such a crystal plane structure, it is possible to obtain a more preferable embodiment as a magnetic domain structure.

[0028] The support substrate may have a reflective film on the opposite side to the first multilayer film.

[0029] By providing a reflective film in this manner, the magnetic domain structure of the present invention can also be made to operate in response to reflected light.

[0030] The magnetic domain structure of the present invention can be a magnetic domain structure that exhibits magnetic domains of a size approximately equal to the wavelength of light used, and has high light transmittance and a large magneto-optical effect.

[0031] 1 is a schematic cross-sectional view showing an example of a magnetic domain structure of the present invention; 2 is a cross-sectional TEM image of a magnetic domain structure produced in an example; 3 is a photograph of the surface of the magnetic domain structure produced in an example (surface of the second multilayer film) observed using a polarizing microscope in a magnetic field-free environment of 0 Oe; 4 is a photograph of the surface of the magnetic domain structure produced in an example (surface of the second multilayer film) observed using a polarizing microscope in a magnetic field environment of 350 Oe; and 5 is a graph showing the results of measuring the transmittance and Faraday rotation angle when light is incident perpendicularly to the surface of the magnetic domain structure produced in an example (surface of the second multilayer film).

[0032] Hereinafter, the present invention will be described in detail with reference to the preferred embodiments, but the present invention is not limited to these.

[0033] The present invention provides a magnetic domain structure having a multilayer film on a support substrate, the multilayer film being composed of a plurality of dielectric layers and a plurality of magnetic insulator layers stacked alternately, the support substrate, the dielectric layers, and the magnetic insulator layers all being made of materials having a garnet structure, the support substrate having a first multilayer film on which a plurality of the dielectric layers, each having a constant thickness, and a plurality of the magnetic insulator layers, each having a constant thickness, are alternately stacked, the support substrate having a first multilayer film on which a defect layer is formed and which is composed of a magnetic insulator layer that is thicker than the thickness of one of the magnetic insulator layers in the first multilayer film, the second multilayer film on which a plurality of the dielectric layers and a plurality of the magnetic insulator layers, each having a thickness equivalent to that of the first multilayer film, are alternately stacked, the second multilayer film being characterized in that, in a no-magnetic-field environment, magnetic domains having a width of 200 nm or more and whose magnetization is oriented perpendicular to the surface of the support substrate are generated.

[0034] FIG. 1 shows a magnetic domain structure 100 of the present invention. The magnetic domain structure 100 includes a support substrate 10, a first multilayer film 20, a defect layer 30, and a second multilayer film 40, all of which are made of a material having a garnet structure. The first multilayer film 20 is formed by alternately stacking a plurality of dielectric layers 21 having a uniform thickness and a plurality of magnetic insulator layers 23 having a uniform thickness. The uniform thickness of the plurality of dielectric layers 21 in the first multilayer film 20 may have an error of about ±20%. The uniform thickness of the plurality of magnetic insulator layers 23 in the first multilayer film 20 may also have an error of about ±20%. Similarly, the second multilayer film 40 is formed by alternately stacking a plurality of dielectric layers 41 having a uniform thickness and a plurality of magnetic insulator layers 43 having a uniform thickness, similar to the first multilayer film 20. The plurality of dielectric layers 41 and the plurality of magnetic insulator layers 43 have thicknesses equivalent to the thicknesses of the plurality of dielectric layers 21 and the plurality of magnetic insulator layers 23 in the first multilayer film 20, respectively. In the second multilayer film 40 as well, the plurality of dielectric layers 41 and the plurality of magnetic insulator layers 43 may each 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 a magnetic insulating material and is thicker than the thickness of one layer of the magnetic insulating layer 23 in the first multilayer film 20. In particular, the thickness of the defect layer 30 is preferably twice the thickness of one layer of the magnetic insulating layer 23 in the first multilayer film 20. By making the defect layer 30 twice as thick as the magnetic insulating layer 23, it can function more effectively as a defect layer, thereby achieving high light transmittance and a large magneto-optical effect. This "double thickness" may have an error of about ±20%.

[0036] Furthermore, the structure of the magnetic domain structure 100 of the present invention provides an enhanced magneto-optical effect, i.e., the magneto-optical effect is greater when a multilayer film portion other than the defect layer is provided on the support substrate than when a single defect layer film is provided. The thickness of the defect layer 30 can 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 multilayer film. Specifically, an integral multiple of 2 is desirable, and 4, 6, etc. are also preferable. However, if the thickness is greater than 1, the rate of increase in the magneto-optical effect decreases, but both the development of the magnetic domain and the increase in the magneto-optical effect can be simultaneously achieved. Therefore, 3, 5, 1.5, 3.5, etc. are also acceptable.

[0037] The presence of the defect layer 30 (e.g., a double-thickness Ce:YIG layer) can increase the transmittance at the design wavelength (the wavelength of light for which the magnetic domain structure 100 is intended to be used) and at the same time increase the Faraday rotation angle (the magnitude of the magneto-optical effect of the transmitted light). Such a layer is generally called a defect layer in magneto-optical materials, and is also called a defect layer in the description of the present invention.

[0038] 1 illustrates a first multilayer film 20 in which ten dielectric layers 21 and nine magnetic insulator layers 23 are alternately stacked, and a second multilayer film 40 in which ten dielectric layers 41 and nine magnetic insulator layers 43 are alternately stacked. The number of alternate stacking times in the present invention must be at least two, and there is no upper limit. From the perspective of fabricating the magnetic domain structure 100, the preferred range of the number of alternate stacking times is 5 to 20.

[0039] Furthermore, in the present invention, the magnetic domain structure 100 exhibits magnetic domains having a width of 200 nm or more, in which the magnetization is oriented perpendicular to the substrate surface of the support substrate 10, under a magnetic field-free environment. Under a magnetic field-free environment, a magnetic field is not applied to the magnetic domain structure 100. In the present invention, it has been found that the structure of the magnetic domain structure 100 shown in Fig. 1 (a structure incorporating a nano-micro structure) can exhibit 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). The dielectric layers (the dielectric layer 21 in the first multilayer film 20 and the dielectric layer 41 in the second multilayer film 40) are preferably made of gadolinium gallium garnet. The magnetic insulator layers (the magnetic insulator layer 23 in the first multilayer film 20 and the magnetic insulator layer 43 in the second multilayer film 40) are preferably made of cerium-substituted yttrium iron garnet (Ce:YIG). Use of these materials makes it possible to more reliably realize the magnetic domains essential to the magnetic domain structure of the present invention (magnetic domains having a width of 200 nm or more and whose magnetization is oriented perpendicular to the substrate surface of the support substrate 10).

[0041] Furthermore, in this case, the gadolinium gallium garnet constituting the dielectric layer is preferably one in which gadolinium is not substituted, but it may be one in which part of gadolinium is substituted with another element (for example, a rare earth element), provided that epitaxial crystal growth is possible during fabrication.

[0042] In this case, the Ce:YIG constituting the magnetic insulating layer is a magnetic material and an insulator, that is, a magnetic insulator. The molecular structure of YIG is ３ Fe ５ O １２ The material can be based on the above, with the Y portion or the Fe portion substituted with other elements. Among rare earth elements, Sc, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu are used as substitution elements. It is known that, in particular, when the Y portion is substituted with a rare earth element or Bi or Gd, a large magneto-optical effect is achieved. In the present invention, Ce is particularly selected and used as the substitution element.

[0043] In the first multilayer film 20 and the second multilayer film 40 of the magnetic domain structure 100 of the present invention, the thickness t1 [nm] of the dielectric layers 21, 41 and the thickness t2 [nm] of the magnetic insulator layers 23, 43 are preferably as follows, where n1 is the refractive index of the dielectric layers 21, 41 and n2 is the refractive index of the magnetic insulator layers 23, 43: t1=λ / (4×n1), t2=λ / (4×n2) (where λ is the design wavelength [nm], which is the wavelength of light for which the magnetic domain structure 100 is intended to be used).

[0044] That is, in both cases, it is preferable that the relational expression be film thickness = design wavelength / (4 × refractive index). This is the same as the film thickness relationship of a general Bragg mirror (also called a dielectric mirror or a multilayer mirror). By designing the thickness of each layer in this way based on the wavelength of light for which the magnetic domain structure 100 is intended to be used, it is possible to make it a more preferable embodiment of the magnetic domain structure.

[0045] In the magnetic domain structure 100 of the present invention, it is preferable that the normals to the crystal planes of the support substrate 10, the dielectric layers 21 and 41, and the magnetic insulator layers 23 and 43 are all in the <111> direction. By adopting such a crystal plane structure, the magnetic domain structure 100 can be made into a more preferable embodiment.

[0046] The magnetic domain structure 100 of the present invention may have a reflective film on the side of the support substrate 10 opposite to the first multilayer film 20. Although the structure of the present invention is for transmitted light, it is not limited to transmitted light because a similar function can be achieved for reflected light by placing a reflective film (mirror) made of aluminum or the like behind the magnetic domain structure 100 (on the side of the support substrate 10 opposite to the first multilayer film 20, i.e., below the support substrate 10 as shown in FIG. 1). The reflective film may be in close contact with the support substrate 10 or may be separated from it, as long as it is located below the support substrate 10.

[0047] The magnetic domain structure of the present invention can be applied to many devices using magneto-optical materials. Magnetic domains are difficult to predict through calculations or simulations, and have only recently begun to be understood through large-scale calculations using supercomputers. However, it is difficult to estimate the specific size of the structure. With the above-mentioned configuration, the present invention can achieve high transmittance and a large magneto-optical effect while expressing magnetic domains.

[0048] As mentioned above, the magnetic domain structure of the present invention has a ripple effect on related fields, such as three-dimensional displays, optical holographic memories, and laser switches.

[0049] (1) Three-dimensional displays are expected to be used in the gaming, entertainment, medical, and other industries using next-generation displays.

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

[0051] (3) Because laser switches can increase optical power, they are being used in high-power laser applications, and are expected to be used in optical processing and the processing industry.

[0052] Multilayer film structures using magneto-optical materials in the defect layer are known as magneto-photonic crystals (see, for example, Non-Patent Document 4). Non-Patent Document 4 shows through calculations and experiments that they exhibit high magneto-optical effects and high transmittance. However, Non-Patent Document 4 does not discuss magnetic domains, and since there were no applications at the time, it does not mention what kind of magnetic domains they have or whether they even have magnetic domains.

[0053] Furthermore, Patent Document 1 describes a multilayer film structure. Patent Document 1 is characterized by the fact that a large magneto-optical effect can be obtained, but unlike the present invention, not all of the components have a garnet structure, and furthermore, there is no mention of magnetic domains.

[0054] EXAMPLES The present invention will be explained in more detail below by showing examples of the present invention, but the present invention is not limited to these examples.

[0055] [Example] A magnetic domain structure 100 according to the present invention was fabricated as shown in Fig. 1. Fig. 2 shows a transmission electron microscope image of a cross section of a sample of the magnetic domain structure 100 that was actually fabricated.

[0056] The following specific materials were used. A GGG (gadolinium gallium garnet) substrate was used as the support substrate 10. GGG was used as the material for the magnetic insulator layers (the magnetic insulator layer 23 in the first multilayer film 20 and the magnetic insulator 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 (the dielectric layer 21 in the first multilayer film 20 and the dielectric layer 41 in the second multilayer film 40) and the defect layer 30. Films of each layer were alternately stacked on the GGG substrate of the support substrate 10.

[0057] Radio frequency ion beam sputtering was used to form each layer. The sample was maintained at approximately 900°C during film formation. This allowed the lattice constants of the support substrate 10 and the materials of each layer to match, enabling epitaxial growth. The orientation of the support substrate 10 and all layers was <111> in the direction perpendicular to the surface.

[0058] GGG is not a magnetic material, but it is a type of yttrium iron garnet (YIG, Y ３ Fe ５ O １２ ) Similarly, it has a garnet structure, and the crystal structure is Gd ３ Ga ５ O １２－ｘ The lattice constant of GGG is 1.238 nm, which is close to that of cerium-substituted yttrium iron garnet (Ce:YIG). Therefore, Ce:YIG (magnetic insulator layers 23, 43, defect layer 30) could be epitaxially grown on the GGG support substrate 10 and the GGG film (dielectric layers 21, 41).

[0059] The refractive index of GGG at a wavelength of 1064 nm is 1.89. The gadolinium in GGG in the examples was unsubstituted, with no intentional substitution being performed.

[0060] Ce:YIG is a magnetic material and an insulator, that is, a magnetic insulator. The molecular structure of YIG is ３ Fe ５ O １２ It is possible to use a material based on the above, in which the Y portion or the Fe portion is substituted with other elements. In particular, it is known that when the Y portion is substituted with a rare earth element, Bi, or Gd, the magneto-optical effect is large. In this example, Ce was selected and used among the rare earth elements. The substitution amount of Ce in this example is 1, and the composition formula is written as Ce １ Y ２ Fe ５ O １２－ｘ X represents the deviation in composition. It is written this way because it is generally difficult to accurately measure the oxygen content in a molecule. 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 example, the thickness of the GGG layer was 148.7±2.5 nm, where the number after ± represents the standard deviation of the variation in thickness of all the GGG layers in the structure of the magnetic domain structure 100 actually fabricated in this example.

[0062] In this example, the thickness of the Ce:YIG layer other than the defect layer 30 was 119.5±2.6 nm. The number after ± here represents the standard deviation of the variation in thickness of all Ce:YIG layers other than the defect layer 30 in the structure of the magnetic domain structure 100 actually fabricated in this example. However, the thickness of the Ce:YIG layer that is twice as thick as the defect layer 30 was 240.0 nm.

[0063] The thickness t1 [nm] of the GGG layer (dielectric layer 21, 41) and the thickness t2 [nm] of the Ce:YIG layer (magnetic insulator layer 23, 43) in the first multilayer film 20 and the second multilayer film 40 were determined as values ​​calculated by t1 = λ / (4 × n1) and t2 = λ / (4 × n2), where n1 is the refractive index of the dielectric layer 21, 41 and n2 is the refractive index of the magnetic insulator layer 23, 43. The design wavelength λ in this case was 1064 nm.

[0064] FIG. 3 shows a top view of the sample surface of the magnetic domain structure 100 fabricated in this manner. The observation here was made using a polarizing microscope, a microscope that shows the magnitude of the magneto-optical effect as shades of light and dark. That is, the black and white parts shown in FIG. 3 represent reversals in the polarity of magnetization, which correspond to magnetic domains. FIG. 3 shows that magnetic domains with widths of about 200 to 1000 nm were expressed. When the photograph in FIG. 3 was taken, no magnetic field was applied to the sample (in a magnetic-field-free environment (or in a geomagnetic environment)). The magnitude of the magnetic field is expressed as 0 Oe (oersteds).

[0065] 4 is a diagram showing the sample surface of the magnetic domain structure 100 viewed from above when a magnetic field of 350 Oe is applied to the sample of the magnetic domain structure 100. The conditions are the same as those in FIG. 3 except that a magnetic field is applied. In FIG. 4, the size of the magnetic domains on the surface of the magnetic domain structure 100 has changed compared to FIG. 3, and it can be seen that the black and white contrast is not due to unevenness or the like on the surface of the sample.

[0066] Furthermore, light was incident perpendicularly to the film surface of a sample of the magnetic domain structure 100 fabricated in this example, and the transmittance and Faraday rotation angle (magnitude of the magneto-optical effect of transmitted light) were measured. The results are shown in FIG. 5. It can be seen that the transmittance and Faraday rotation angle are large at the wavelengths indicated by the arrows in FIG. 5. This is caused by the presence of the defect layer 30 made of double-thick Ce:YIG. As shown in FIG. 5, the transmittance was approximately 50%, and the magnitude of the Faraday rotation angle was approximately 3.5°. The wavelength indicated by the arrow is the wavelength at which an increase in the magneto-optical effect was confirmed.

[0067] It is known that if the thickness of each Ce:YIG layer exceeds 1 μm, the stress strain in the film is relaxed as the thickness increases, and magnetic domains do not occur. In contrast, in the structure shown in the example according to the configuration of the present invention, the thickness of each Ce:YIG layer is as thin as 300 nm or less, so a sufficient amount of stress strain remains. As a result, magnetic domains appear.

[0068] At the same time, in the structure shown in the examples, the total number of Ce:YIG layers can be increased, allowing for the development of magnetic domains and achieving a large magneto-optical effect. Based solely on the above considerations, Ce:YIG and GGG layers would simply be alternately stacked. This would result in an alternating stack structure acting as a Bragg mirror, reflecting light at the design wavelength and reducing transmittance to an extremely low level, approaching zero. This is known as a photonic band gap. Because of this reduced transmittance, the device applications described above in (1) to (3) are not possible. Therefore, a defect layer 30 is required.

[0069] The presence of the defect layer 30 causes an extremely narrow band, called a defect layer mode (or localized mode), to appear in the photonic band gap, through which light propagates. This allows a large magneto-optical effect to be obtained while maintaining a high transmittance. In the above example, the defect layer 30 is twice as thick as the first multilayer film 20. However, the magneto-optical effect can also be obtained when the defect layer 30 is made thicker than the first multilayer film 20 (i.e., a thickness greater than one or an integral multiple of two).

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

[0071] This specification includes the following aspects: [1]: A magnetic domain structure having a multilayer film composed of a plurality of dielectric layers and a plurality of magnetic insulator layers alternately stacked on a support substrate, wherein the support substrate, the dielectric layers, and the magnetic insulator layers are all made of materials having a garnet structure, a first multilayer film composed of a plurality of dielectric layers having a constant thickness and a plurality of magnetic insulator layers having a constant thickness alternately stacked on the support substrate, a defect layer formed on the first multilayer film and composed of a magnetic insulator layer thicker than the thickness of one of the magnetic insulator layers in the first multilayer film, and a second multilayer film composed of a plurality of dielectric layers and a plurality of magnetic insulator layers alternately stacked on the defect layer, each having a thickness equivalent to that of the first multilayer film, wherein the magnetic domain structure exhibits magnetic domains having a width of 200 nm or more and whose magnetization is oriented perpendicular to the surface of the support substrate in a non-magnetic field environment. [2]: The magnetic domain structure of [1] above, wherein the thickness of the defect layer is twice the thickness of one of the magnetic insulator layers in the first multilayer film. [3]: The magnetic domain structure of the above [1] or [2], wherein the support substrate is made of gadolinium gallium garnet, the dielectric layer is made of gadolinium gallium garnet, and the magnetic insulator layer is made of cerium-substituted yttrium iron garnet. [4]: ​​The magnetic domain structure of the above [3], wherein the gadolinium gallium garnet is not substituted for gadolinium, or a portion of the gadolinium is substituted with another element. [5]: The magnetic domain structure of any of the above [1] to [4], wherein 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 expressed as t1 = λ / (4 × n1), t2 = λ / (4 × n2), where λ is a design wavelength [nm] at which the magnetic domain structure is intended to be used, where n1 is the refractive index of the dielectric layer and n2 is the refractive index of the magnetic insulator layer.[6]: The magnetic domain structure according to any one of [1] to [5], wherein the normals of the crystal planes of the support substrate, the dielectric layer, and the magnetic insulator layer are all in the <111> direction. [7]: The magnetic domain structure according to any one of [1] to [6], wherein the support substrate has a reflective film on the opposite side of the first multilayer film.

[0072] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A magnetic domain structure having a multilayer film composed of a plurality of dielectric layers and a plurality of magnetic insulator layers alternately stacked on a support substrate, wherein the support substrate, the dielectric layers, and the magnetic insulator layers are all made of materials having a garnet structure; a first multilayer film on the support substrate, in which a plurality of the dielectric layers having a constant thickness and a plurality of the magnetic insulator layers having a constant thickness are alternately stacked; a defect layer formed on the first multilayer film and composed of the magnetic insulator layer which is thicker than the thickness of one of the magnetic insulator layers in the first multilayer film; and a second multilayer film on the defect layer, in which a plurality of the dielectric layers and a plurality of the magnetic insulator layers each having a thickness equivalent to that of the first multilayer film are alternately stacked; and the magnetic domain structure characterized in that, in a no-magnetic-field environment, magnetic domains having a width of 200 nm or more are manifested, with magnetization oriented perpendicular to the surface of the support substrate.

2. The magnetic domain structure according to claim 1, wherein the thickness of said defect layer is twice the thickness of one of said magnetic insulator layers in said 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 made of gadolinium gallium garnet, and the magnetic insulator layer is made of cerium-substituted yttrium iron garnet.

4. The magnetic domain structure according to claim 3, wherein the gadolinium gallium garnet is one in which gadolinium is not substituted, or one in which gadolinium is partially substituted with another element.

5. A magnetic domain structure according to any one of claims 1 to 4, characterized in that 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), t2 = λ / (4 × n2) (where λ is a design wavelength [nm] that is a wavelength at which the magnetic domain structure is intended to be used), where n1 is a refractive index of the dielectric layer and n2 is a refractive index of the magnetic insulator layer.

6. The magnetic domain structure according to claim 1, wherein the normals to the crystal planes of the support substrate, the dielectric layer, and the magnetic insulator layer are all in the <111> direction.

7. The magnetic domain structure according to claim 1, wherein the support substrate has a reflective film on the side opposite to the first multilayer film.

Images