JP2005055921A - Magneto-optical element and optical apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magneto-optical element which is capable of obtaining a large magneto-optical effect and is suitable for application to a display and the like utilizing the visualization of a magnetized image. <P>SOLUTION: The magneto-optical element further has a magnetic layer 4 on periodic structures 3a-3d having a pitch and a depth of 0.2-2μm, that is, on the periodic structures 3a-3d of wavelength order of the used light on the surface of a substrate 2. Therefore, the large magneto-optical effect can be obtained by utilizing the diffraction, namely interference of incident light. As a result, since rotation angles of polarizing surface are quite different between a magnetized part and a non-magnetized part, a high contrast value can be obtained and the magneto-optical element is advantageously applied for a display and the like. Furthermore, since the magneto-optical effect is large and the rotation angle of the polarizing surface becomes large, excellent S/N can be obtained when being applied for a memory and the like. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a magneto-optical element and an optical apparatus that can generate a large magneto-optical effect, can be visualized as a magnetized image, can be read out with a laser beam, and can be applied to various fields.

  It is known as the Faraday effect that when a magnetic material is magnetized and linearly polarized light is incident parallel to the magnetization direction, the polarization plane of the light is rotated by passing through the magnetic material. A magnetic recording medium (magneto-optic element) or the like is made using a material having such a Faraday effect.

  For example, according to Patent Document 1, a magnetic recording medium using yttrium and rare earth iron garnet and its dielectric material, according to Patent Document 2, a magnetic recording medium using hexagonal ferrite, and according to Patent Document 3, yttrium iron garnet particles. Patent Document 4 discloses a coating type magnetic recording medium using rare earth iron garnet fine particles and the like. These magnetic recording media have a structure in which a magnetic material or magnetic fine particles are formed on a substrate as a thin film as a recording layer. According to such a magnetic recording medium, recording / erasing / reading can be performed satisfactorily.

JP-A-56-15125 JP 61-89605 A JP-A-62-1119758 Japanese Patent Laid-Open No. 4-132029

  However, the conventional magnetic recording media disclosed in these publications are limited to memory use such as recording, erasing, and reading, and are not suitable for application or diversion to other uses such as displays. It is. Further, regarding use as a memory, a sufficiently large magneto-optical effect is not necessarily obtained, and an S / N for reading or the like is not always good.

  Therefore, the present invention can obtain a very large magneto-optical effect and can be recorded / erased / read out by a magnetic head, as well as applied to a display by visualization of a magnetized image, read out by a laser beam, etc. An object of the present invention is to provide a magneto-optical element that can be applied to various fields. Furthermore, it is an object of the present invention to provide a magneto-optical element and an optical device that can be applied to a display or the like regardless of whether it is a transmission type or a reflection type. It is another object of the present invention to provide a magneto-optical element and an optical apparatus that can be displayed with improved contrast and multicolor display.

  The magneto-optical element according to the first aspect of the present invention has a periodic structure in the same direction in a grating shape having a pitch and a depth in the range of 0.2 to 2 μm on the substrate surface, and a layer of 20 to 200 nm on the periodic structure. The display has a magnetic layer having a thickness of 5 mm and the Faraday effect is increased by interference of light from the grooves and the grating portion of the periodic structure with respect to visible light.

  According to a second aspect of the present invention, in the magneto-optical element according to the first aspect, the periodic structure is two-dimensional.

  According to a third aspect of the present invention, in the magneto-optical element according to the first or second aspect, there are two or more pitch periods forming the periodic structure.

  According to a fourth aspect of the present invention, there is provided an optical device comprising the magneto-optical element according to the first, second, or third aspect, and one or two polarizers facing the magneto-optical element.

  According to the present invention, a single-layered magnetic layer having a thickness of 20 to 200 nm is formed on a periodic structure in the same direction with a grating shape having a pitch and depth in the range of 0.2 to 2 μm, so that white is displayed on the pixel. Sometimes the whiteness of the image displayed on the pixel is increased (becomes brighter). In addition, since the substrate surface has a grating-like periodic structure in the same direction and a magnetic layer on the periodic structure, the blackness of the image displayed on the pixel is increased when displaying black on the pixel. (Get dark). Thereby, the contrast of an image can be enlarged.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 schematically shows a basic configuration example of a magneto-optical element 1. A periodic structure 3 having a fine grating shape is formed on the surface of a substrate 2, and a thin magnetic film is formed over the entire surface of the periodic structure 3. Layer 4 is formed continuously. Here, the periodic structure 3 may be, for example, a rectangular wave-shaped periodic structure 3a with repeated unevenness as shown in FIG. 1A, but in addition, for example, a triangle as shown in FIG. The shape may be a wavy periodic structure 3b, a sinusoidal periodic structure 3c as shown in FIG. 1C, a trapezoidal periodic structure 3d as shown in FIG. 1D, or the like. . Or it is good also as a sawtooth wave-like periodic structure 3e like FIG. 2 (a) which shows only the periodic structure regarding a triangular wave-like periodic structure. In this case, as a modification thereof, as shown in FIGS. 2B to 2D, the periodic structure 3e may be further divided into periodic structures 3f, 3g, 3i, etc., which are further divided into steps (steps). The periodic structures 3e to 3i illustrated in FIG. 2 are actually manufactured and their effects are confirmed. The point is that the incident light is diffracted, and any structure may be used as long as the pitch P of the periodic structure 3 is accurately manufactured and satisfies the relationship of P≈λ with respect to the wavelength λ of the incident light. In consideration of laser light as well as visible light, the periodic structure 3 may have a periodic grating with a pitch P and a groove depth on the order of 0.2 to 2 μm.

  Next, the directionality of the periodic structure 3 will be described. The periodic structure 3 formed on the substrate 2 may be formed in only one direction in the vertical or horizontal direction, but for example, it may be formed two-dimensionally in both the vertical and horizontal directions as illustrated in FIG. FIG. 3 shows the case of the periodic structure 3a. At this time, the periodic structure 3 may have a different period in the vertical direction and the horizontal direction, or may be partially different in the vertical direction and the horizontal direction for only a certain region.

The substrate 2 will be described. The substrate 2 may be a transparent substrate, but may be an opaque substrate. In short, it is only necessary that diffraction occurs in the portion of the periodic structure 3 with respect to incident visible light, and a reflection type configuration may be used. Here, when the opaque substrate 2 is used as a reflection type, the magnetic layer 4 may be transparent, and incident light may be reflected by the surface of the periodic structure 3 (the surface of the grating). Furthermore, the magnetic layer 4 is also opaque. As shown in FIG. In any case, the magneto-optical effect can be increased by diffraction. As a material of the substrate 2, generally, a heat-resistant metal such as aluminum, quartz glass, GGG (gallium cadmium garnet), sapphire, lithium tantalate, crystallized transparent glass, Pyrex glass ("Pyrex glass" is a registered trademark) The same applies hereinafter), transparent ceramics such as single crystal silicon, Al ₂ O ₃ , Al ₂ O ₃ .MgO, MgO.LiF, Y ₂ O ₃ .LiF, BeO, ZrO ₂ , Y ₂₃ , ThO ₂ .CaO Materials, inorganic materials such as inorganic silicon can be used.

  Next, light to be used (incident light) will be described. The incident light to be used is basically visible light, but is not necessarily limited to visible light, and laser light having a single wavelength may be used. In this case, a laser beam having a wavelength that maximizes the diffraction efficiency of the periodic structure 3 is selected.

Regarding such a magneto-optical element 1, what is important is that incident light is diffracted, that is, interferes. For this purpose, the refractive index of the groove part and the grating part in the periodic structure 3 needs to be different. This point is easily achieved by setting the groove portion in the air. Whether the magnetic layer 4 is transparent or opaque is appropriately set according to the application, etc., but the thickness of the magnetic layer 4 is optimum according to the shape of the periodic structure 3, the refractive index of the material, etc. In general, a layer thickness of about 20 to 200 nm is preferable. However, depending on the wavelength, the magnetic material has different wavelength dependence of the magneto-optic effect, so that it may be difficult to combine with the shape of the periodic structure 3. In this respect, if the magnetic layer 4 includes a ferromagnetic material such as Fe, Co, or Ni having an average particle size of 200 mm or less or fine particles of these alloys, the wavelength dependency is small, so that even when laser light is used, the period is The design is easy regardless of the shape of the structure 3. FIG. 4 is a characteristic diagram showing the wavelength dependence of the magneto-optic effect of Fe ultrafine particles. In addition, according to the magnetic layer 4 containing such a ferromagnetic material such as Fe, Co, Ni or fine particles of these alloys, it is possible to take advantage of the fact that the magneto-optical effect alone is large, and If the average particle size is 200 mm or less, the increase in magneto-optical effect due to the quantum size effect can be used, and the light transmittance is large, which is further advantageous. Incidentally, even if the fine particles of a ferromagnetic material such as Fe, Co, and Ni or an alloy thereof are used, the quantum size effect does not occur when the average particle diameter is larger than 200 mm.

However, if the specific periodic structure 3 is a target, the magnetic material used for the magnetic layer 4 is not particularly limited and may be a general magnetic material. For example, ferrite such as γ-Fe ₂ O ₃ , Fe ₃ O ₄ , FeN _x , Ba ferrite and Co ferrite, garnet such as rare earth iron garnet, PtCo, FeTb and the like may be used.

  According to the magneto-optical element 1 having such a basic configuration and showing a large magneto-optical effect, when the magnetic head is magnetized, the rotation angle of the polarization plane of incident light differs between the magnetized portion and the non-magnetized portion. Therefore, a high contrast image can be obtained. For example, if there is a rotation angle of 22.5 °, the direction of magnetization is 45 ° different between + and −. Therefore, if the reflection type structure is used, since it passes twice, there is a difference of 90 ° between + and −. That is, since the polarization plane has a 90 ° rotation direction different between the + magnetized portion and the −magnetized portion, a crossed Nicol arrangement is obtained, and a high contrast can be obtained as in the case of a liquid crystal display. Further, if laser light is used, it can be used as a high-density magnetic memory. That is, since the rotation angle is larger than that of magneto-optical memories currently on the market, the memory has a good S / N. At this time, if the beam diameter of the laser beam is reduced, the S / N is improved, so that the density can be further increased.

  In order to erase magnetic recording, the entire magneto-optical element 1 is uniformly magnetized using a magnet so that the directions of spins are all the same, or the spin is randomly generated using an alternating magnetic field. An erasing method directed in the direction may be used.

  Further, in contrast to the magneto-optical element 1 having the periodic structure 3 and the magnetic layer 4 and capable of greatly amplifying the polarization plane of light, as shown in FIG. If it is set as the optical apparatus 7 which has arrange | positioned, it can be set as the transmission type display similar to the case of a transmission type liquid crystal display. If the magneto-optical element 1 has a reflective structure, only one polarizer 5 may be used.

  Furthermore, with respect to the above-described periodic structure 3, if a periodic structure having a different pitch and depth period is formed on the same substrate 2, the function of increasing the magneto-optical effect with respect to incident light of a plurality of wavelengths can be obtained. It can be demonstrated. Therefore, for example, if the periodic structure 3 having three kinds of periods is formed in accordance with the respective color wavelengths of R, G, and B, the display can be colored with a single magneto-optical element 1.

Hereinafter, specific configuration examples based on the above-described basic configuration examples will be described as Examples 1-4 together with Comparative Examples 1-3.
<Example 1>
Two layers of Cr ₂ O ₃ and Cr were formed on one surface of a 1 mm thick quartz substrate (substrate 2) so that the total layer thickness was 120 nm, and then a positive resist layer was formed on the surface layer. A photomask was placed on the resist layer, and exposure was performed using ultraviolet rays so that the pitch of the grating shape forming the periodic structure 3 was 1.9 μm. Next, the resist layer was etched using a wet etching method, and further the quartz substrate was etched using fluorine gas, so that the groove depth in grating of the periodic structure 3 was processed to be 0.5 μm. . Thereafter, the resist layer was peeled off. On the processed surface (periodic structure 3) of such a quartz substrate, an iron ultrafine particle film was formed as the magnetic layer 4 without heating the substrate by using a gas evaporation method. The Ar gas used was flowed at a flow rate of 50 CCM and the dry air was flowed at 2 CCM, and the total pressure was 1.3 Pa. The average film thickness was 100 nm. When the cross section after film formation was observed with a TEM (transmission microscope), the average particle diameter of iron was 60 mm, and each fine particle was isolated by a nonmagnetic layer. According to the composition of the film measured by photoelectron spectroscopy (XPS = X-ray Photoelectron Spectroscopy), iron was 72%, and later, O, C, and N were contained. The coercive force measured at the flat portion was 450 Oe, the squareness ratio in the in-plane direction was 0.8, and the magnetic layer 4 had a large in-plane anisotropy.

For such a magneto-optical element 1, the wavelength dependence of the magneto-optical effect was measured. The beam diameter of light was about 3 mm. Next, when the hysteresis was measured using a maximum magnetic field of 15 k gauss at the peak wavelength of the wavelength dependence data, the characteristics as shown in FIG. 6 were obtained in the case of 0th-order diffracted light. Although the hysteresis is not saturated, a rotation angle of 14.6 ° is obtained when the magnetic field is zero.
<Comparative Example 1>
An iron ultrafine particle film was formed on one side of a 1 mm thick quartz substrate (having no processed surface) in exactly the same manner as in Example 1 above. The average film thickness, the TEM observation of the film cross section, the average particle diameter, the film composition, the holding power, and the squareness ratio were the same as those in Example 1, but with the hysteresis measured in the same manner as described above, the magnetic field was In the case of 0, only a rotation angle of 0.09 ° was obtained.
<Comparative example 2>
An iron film was formed on the processed surface of the quartz substrate as in Example 1 without heating the substrate by vacuum evaporation. The substrate pressure was 8 × 10 to ⁵ Pa. The average film thickness was 100 nm. When the cross section after such film formation was observed with a TEM, a continuous film of iron was formed. According to the composition of the film measured by XPS, iron was 99%, and later, O, C, and N were slightly contained. The coercive force measured at the flat portion was 7 Oe, the squareness ratio in the in-plane direction was 0.96, and the film had a large in-plane anisotropy. With respect to such an element, the hysteresis was measured in the same manner as in Example 1. As a result, when the magnetic field was set to 0, only a rotation angle of 9 ° was obtained.
<Example 2>
Basically, it is the same as in the case of Example 1, but the periodic structure 3 is two-dimensional and processed so that the pitch is 1.9 μm and the groove depth is 0.5 μm in the vertical and horizontal directions. . Thereafter, the magneto-optical element 1 was produced in exactly the same manner as in Example 1, and the hysteresis was measured. As a result, a rotation angle of 15 ° was obtained when the magnetic field was zero.
<Example 3>
Basically, it is the same as in the case of the first embodiment, but with respect to the periodic structure 3, the pitch of the period is set to two types of 1.9 μm and 1.5 μm, and these two types are changed 25 times. Thus, the periodic structure 3 was formed by processing the groove depth to be 0.5 μm. After that, the magneto-optical element 1 was manufactured in exactly the same manner as in Example 1, and the wavelength dependence of the magneto-optical effect was measured. As a result, a peak was obtained at two frequencies of 475 nm and 630 nm. It is what was done. When hysteresis was measured at such two peak wavelengths, rotation angles of 14.5 ° and 13 ° were obtained when the magnetic field was zero.
<Example 4>
Both surfaces of the magneto-optical element 1 manufactured according to Example 1 were sandwiched with two commercially available film polarizers (polarizers 5 and 6). In this manner, characters were recorded on the magneto-optical element 1 from above the film polarizer using a cylindrical bar magnet having a diameter of 1 mm, a length of 1 mm, and a surface magnetic flux density of 3 k gauss. The polarization axes of the two film polarizers were relatively rotated and fixed so that the contrast between the most magnetized character and the non-magnetized portion was increased. The contrast in this case was 1.3, which proved suitable for image display.
<Comparative Example 3>
A magneto-optical element manufactured according to Comparative Example 1 was rubbed with two film polarizers as in Example 4, and characters recorded with a cylindrical bar magnet were observed, but the contrast could not be measured. It is.

It is typical sectional drawing which shows the basic structural example of one embodiment of this invention. It is typical sectional drawing which shows the modification of a triangular wave-like periodic structure. It is a block diagram which shows a two-dimensional periodic structure. It is a characteristic view which shows the wavelength dependence of the magneto-optical effect of Fe ultrafine particles. It is typical sectional drawing which shows the example of an optical apparatus which combined the polarizer. It is a systemic characteristic figure which shows the magneto-optical effect of the iron ultrafine particle film | membrane in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magneto-optical element 2 Board | substrate 3 Periodic structure 4 Magnetic layer 5,6 Polarizer 7 Optical apparatus

Claims (4)

Having a periodic structure in the same direction with a grating shape consisting of a pitch and a depth in the range of 0.2 to 2 μm on the substrate surface;
On this periodic structure, there is a single magnetic layer having a thickness of 20 to 200 nm,
A magneto-optical element constituting a display, wherein the Faraday effect is increased by interference of light from the groove portion and the lattice portion of the periodic structure with respect to visible light. The magneto-optical element according to claim 1, wherein the periodic structure is two-dimensional. The magneto-optical element according to claim 1, wherein the pitch of the periodic structure has two or more types. The magneto-optical element according to claim 1, 2, or 3,
One or two polarizers facing the magneto-optical element;
An optical device comprising:

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