Magnetic recording medium

A magnetic recording medium has a transparent substrate with a plurality of grooves which extend parallel with each other at regular intervals, each of the grooves having inner side walls perpendicular to the transparent substrate and a space between adjacent side walls being constant, a magnetic material layer extending in the form of a stripe, provided on the surface of the inner side walls of each of the grooves, and a pair of dielectric multi-layers which are disposed so as to sandwich the transparent substrate therebetween.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a magnetic recording medium, and in
 particular to a magnetic recording medium which is capable of repeatedly
 carrying out recording, reading and erasing operations through magnetic
 heads, and suitable for a display device for displaying recorded images by
 applying light and a magnetic field to the magnetic recording medium.
 2. Discussion of Background
 A magnetic material which can exhibit the magneto-optical effects, such as
 Faraday effect and magnetic Kerr effect is conventionally used for the
 magneto-optical disk memory capable of recording, reading and erasing
 information.
 A magnetic recording medium which employs the above-mentioned magnetic
 material with the magneto-optical effects can record an image therein, for
 example, through a magnetic head. Further, by utilizing the Faraday effect
 and Kerr effect of the above-mentioned magnetic material obtained by the
 application of light thereto, the application of the above-mentioned
 magnetic recording medium to a display device for displaying the recorded
 image has been studied.
 However, there is not obtained any magnetic recording medium that can
 repeatedly carry out the recording, reading and erasing operations through
 the magnetic heads, and in addition to the above, that can display the
 recorded image with high contrast.
 SUMMARY OF THE INVENTION
 Accordingly, an object of the present invention is to provide a magnetic
 recording medium which is capable of repeatedly carrying out the
 recording, reading and erasing operations through the magnetic heads, and
 further, is applicable to a display device that can display the recorded
 image with high contrast.
 The above-mentioned object of the present invention can be achieved by a
 magnetic recording medium comprising a transparent substrate with a
 plurality of grooves which extend parallel with each other at regular
 intervals, each of the grooves having inner side walls perpendicular to
 the transparent substrate and a space between adjacent side walls being
 constant, a magnetic material layer extending in the form of a stripe,
 provided on the surface of the inner side walls of each of the grooves,
 and a pair of dielectric multi-layers which are disposed so as to sandwich
 the transparent substrate therebetween.
 The aforementioned magnetic recording medium may further comprise a pair of
 polarizing layers, each disposed on an external side of each of the
 dielectric multi-layers.
 The above-mentioned object of the present invention can also be achieved by
 a magnetic recording medium comprising a substrate with a plurality of
 grooves which extend parallel with each other at regular intervals, each
 of the grooves having inner side walls perpendicular to the substrate and
 a space between adjacent side walls being constant, a magnetic material
 layer extending in the form of a stripe, provided on the surface of the
 inner side walls of each of the grooves, a dielectric multi-layer which is
 provided on one surface of the substrate, a polarizing layer which is
 provided on the dielectric multi-layer, and a light reflection layer which
 is provided on the other surface of the substrate, opposite to the
 dielectric multi-layer with respect to the substrate.
 It is preferable that each of the grooves have a depth of 0.1 to 5 .mu.m,
 the space between adjacent side walls be in a range of 0.2 to 2.0 .mu.m,
 and the magnetic material layer have a thickness of 5 to 100 nm.
 It is preferable that the dielectric multi-layer comprise a plurality of
 laminated dielectric material layers.
 Furthermore, an organic material is preferably used for the preparation of
 the dielectric material layers.
 In addition, it is preferable that the magnetic material layer comprise a
 magnetic material selected from the group consisting of Fe, Co, Ni and an
 alloy thereof. Such magnetic materials may be used in the form of
 ultrafine particles with an average particle diameter of 20 to 200 .ANG..

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 is a schematic cross-sectional view of a magnetic recording medium
 in accordance with one embodiment of the present invention. In the
 magnetic recording medium shown in FIG. 1, a transparent substrate 1 bears
 thereon a plurality of grooves 2, preferably having a depth (d) of 0.1 to
 5 .mu.m, the grooves 2 extending parallel with each other at regular
 intervals. Each of the grooves 2 has inner side walls 3 perpendicular to
 the transparent substrate 1, and a space (L.sub.1) or (L.sub.2) between
 adjacent side walls 3 is constant, preferably within the range of 0.2 to
 2.0 .mu.m. Further, a magnetic material layer 4 extending in the form of a
 stripe is disposed on the surface of the above-mentioned inner side walls
 3 of each groove 2. The thickness (T) of the magnetic material layer is
 preferably in the range of 5 to 100 nm.
 In addition, a pair of dielectric multi-layers 5 and 6 are disposed so as
 to sandwich the transparent. substrate 1 therebetween. In FIG. 1, the
 dielectric multi-layer 6, which is supported by another transparent
 substrate 7, is attached to the transparent substrate 1.
 The transparent substrate 1 or 7 may be a molded substrate of an organic
 material or an inorganic material.
 Specific examples of such organic and inorganic materials for use in the
 substrate include acrylic resin such as polyacrylate, polymethacrylate,
 polyacrylic acid and polyacrylamide, polycarbonate resin, styrene resin
 such as polystyrene and ABS (acrylonitrile butadiene styrene) resin,
 polysulfone, polyether sulfone, polypropylene resin, polyallylate, epoxy
 resin, poly-4-methylpentene-1, fluorinated polyimide, fluorine-containing
 resin, phenoxy resin, polyolefin resin, diethylene glycol bisallyl
 carbonate, nylon resin, fluorene polymer, cellulose acetate, glass,
 quartz, and alumina.
 It is proper that the thickness of the transparent substrate 1 be 1 mm or
 less, and more preferably in the range of 50 to 500 .mu.m. As the
 thickness of the substrate 1 decreases, the obtained recording medium is
 preferred because the magnetic material layer becomes closer to the
 magnetic head.
 For the magnetic material layer 4, magnetic materials which can exhibit
 large magneto-optical effects such as Faraday effect and Kerr effect, and
 have magnetic anisotropy in the plane of the magnetic material layer 4,
 and a coercive force of 300 to 2000 Oe are preferably employed.
 As the above-mentioned magnetic materials, there can be employed
 terromagnetic materials such as iron (Fe), cobalt (Co), nickel (Ni) and
 alloys thereof. Those metals and alloys thereof have large magneto-optical
 effects. When those metals and alloys thereof are used in the form of
 ultrafine particles, the obtained magnetic material layer 4 can be
 provided with the magnetic anisotropy in the plane thereof, and sufficient
 coercive force. In this case, it is desirable that the average particle
 size of the ultrafine particles of the metals of alloys thereof be in the
 range of 20 to 200 .ANG.. In other words, the coercive force of the
 magnetic material layer 4 can be freely changed by controlling the
 partitle size of the ultrafine particles of Fe, Co, Ni or alloys thereof
 for use in the magnetic material layer 4.
 When the magnetic material layer 4 comprises the ultrafine particles of the
 ferromagnetic materials such as Fe, Co, Ni and alloys thereof, recording
 and erasing of information can be easily carried out, and further, the
 recorded information can be clearly displayed with high contrast when the
 recording medium is used as the display device.
 Using the ultrafine particles of Fe, Co, Ni or an alloy thereof, the
 magnetic material layer 4 can be formed by evaporation under gaseous
 atmosphere mixed with a small amount of air (e.g., several 100 m-Torr) in
 the evaporation chamber.
 Each of the dielectric multi-layer 5 or 6 comprises a plurality of
 laminated dielectric material layers. For instance, to prepare the
 dielectric multi-layer, a large refractive index dielectric material layer
 and a small refractive index dielectric material layer are alternately
 laminated, with the optical thickness of each dielectric material layer
 being the same (.lambda./4).
 A material that is transparent in the visible spectral region is preferably
 used for preparation of the dielectric multi-layers 5 and 6. Specific
 examples of the inorganic material for use in the dielectric multi-layer
 are Na.sub.3 AlF.sub.6, MgF.sub.2, SiO.sub.2, SiO, Al.sub.2 O.sub.3,
 CeF.sub.3, PdF.sub.2, Nd.sub.2 O.sub.3, ZrO.sub.2, TiO.sub.2, CeO.sub.2
 and ZnS.
 When the organic material is employed for preparation of the dielectric
 multi-layers 5 and 6, any organic materials can be employed as long as
 they do not exhibit absorption with respect to the visible light range.
 Specific examples of the organic material for the preparation of the
 dielectric multi-layers 5 and 6 include acrylic resin such as
 polyacrylate, polymethacrylate, polyacrylic acid and polyacrylamide,
 polycarbonate resin, styrene resin such as polystyrene and ABS resin,
 polysulfone, polyether sulfone, polypropylene resin, polyallylate, epoxy
 resin, poly-4-methylpentene-1, fluorinated polyimide, fluorine-containing
 resin, phenoxy resin, polyolefin resin, diethylene glycol bisallyl
 carbonate, nylon resin, fluorene polymer, and cellulose acetate.
 By employing the above-mentioned organic materials for preparation of the
 dielectric multi-layers 5 and 6, the dielectric multi-layers 5 and 6 can
 be provided by, for example, coating method, without using a large-sized
 vacuum apparatus. Further, if the vacuum deposition is not carried out, it
 is not necessary to heat the substrate in the course of the formation of
 the dielectric multi-layer. Therefore, the substrates 1 and 7 made of
 plastic materials can be used, with the result that the magnetic recording
 medium can be made flexible.
 The number of laminated dielectric material layers for use in the
 dielectric multi-layer is preferably in the range of 2 to 50 layers. To
 obtain high contrast of the recorded image and to reduce the manufacturing
 cost, it is more preferable that the number of laminated dielectric
 material layers be in the range of 6 to 10 layers. The thinner the
 dielectric multi-layer 5 or 6, the more easily the magnetic field can
 reach the magnetic material layer 4 in the course of recording.
 Furthermore, it is preferable that the transparency of the dielectric
 multi-layers 5 and 6 be 50% or more, that is, the reflectance thereof be
 less than 50%.
 FIG. 2 is a schematic cross-sectional view of a magnetic recording medium
 in accordance with another embodiment of the present invention. In FIG. 2,
 polarizing layers 8 and 9 are respectively disposed on the external side
 of the dielectric multi-layers 5 and 6 shown in FIG. 1. As the polarizing
 layers 8 and 9, commercially available film-shaped iodine-containing
 polarizers are usable.
 FIG. 3 is a schematic cross-sectional view of a magnetic recording medium
 in accordance with a further embodiment of the present invention. The
 magnetic recording medium of FIG. 3 comprises a substrate 1 which bears
 thereon a plurality of grooves 2, each groove preferably having a depth of
 0.1 to 5 .mu.m. The grooves 2 extend parallel with each other at regular
 intervals, and each of the grooves 2 has inner side walls 3 perpendicular
 to the substrate 1. The space between the adjacent side walls is constant,
 preferably within a range of 0.2 to 2.0 .mu.m. A magnetic material layer 4
 extending in the form of a stripe is disposed on the side walls 3 of each
 groove 2. The thickness of each magnetic material layer 4 is preferably in
 the range of 5 to 100 nm. Further, a dielectric multi-layer 6 which is
 provided on a substrate 7 is attached to one surface of the substrate 1, a
 polarizing layer 9 is overlaid on the substrate 7, and a light reflection
 layer 10 is provided on the other surface of the substrate 1, opposite to
 the dielectric multi-layer 6 with respect to the substrate 1.
 The material for use in the light reflection layer 10 may exhibit a high
 reflectance in the particular visible spectral region. Specific examples
 of the material for use in the light reflection layer 10 include Cu, Al,
 Ag, Au, Pt, Rh, TeO.sub.x, TeC, SeAs, TeAs, TiN, TaN and CrN.
 The light reflection layer 10 may be formed by the conventional film
 formation method such as vacuum deposition, sputtering or ion-plating
 method. It is preferable that the light reflection layer 10 have a
 thickness in the range of 500 to 1000 .ANG..
 In addition, there can be used as the light reflection layer 10 an
 alternating multi-layer prepared by laminating a plurality of metal thin
 films and dielectric material thin films, and a hologram reflecting plate,
 for instance, a commercially available product "HoloBright" (Trademark),
 made by Nippon Polaroid Kabushikikaisha.
 Since the magnetic recording medium shown in FIG. 3 comprises the light
 reflection layer 10, the quality of the recorded image has no connection
 with the transmission of the substrate 1. Therefore, a transparent
 substrate is not always necessary in the magnetic recording medium as
 shown in FIG. 3. To be more specific, a substrate 1 which exhibits a
 visible light transmission of about 70% or less is usable in this
 embodiment.
 The image recorded in the magnetic recording medium as shown in FIG. 3 is
 visible as a reflected image, so that this type of magnetic recording
 medium can be used as the image display device without illuminating the
 recording medium with a backlight. As a result, there can be obtained a
 compact and portable magnetic recording medium which can serve as the
 image display device.
 When the magnetic recording medium of the present invention is used as the
 display device, it is particularly desirable that a light reflection
 preventing layer be provided on the outermost layer of the recording
 medium on the side of incidence of light, opposite to the side of the
 light reflection layer. Namely, as shown in FIG. 3, the light reflection
 preventing layer (not shown) may be provided on the polarizing layer 9. By
 the provision of the light reflection preventing layer, not only the light
 transmittance can be increased, but also the surface of the recording
 medium can be protected from chemical corrosion and chemical change which
 may take place by the application of light to the recording medium.
 The method of fabricating the magnetic recording medium according to the
 present invention as illustrated in FIG. 1, 2 or 3 comprises the steps of:
 (1) forming a plurality of grooves 2 which extend parallel with each other
 on a substrate 1 by photolithography;
 (2) providing a thin layer comprising the ferromagnetic substance
 (hereinafter referred to as a magnetic thin layer) on the whole grooved
 surface of the substrate 1;
 (3) removing some portions of the magnetic thin layer provided by the step
 (2) from the grooved surface of the substrate 1 by etching so that the
 magnetic thin layer may be retained only on the surface of the two facing
 inner side walls of each groove, thereby forming a magnetic layer 4 which
 is disposed on each side wall;
 (4) providing a dielectric multi-layer 5 (as shown in FIGS. 1 and 2) or a
 light reflection layer 10 (as shown in FIG. 3) on the back side of the
 substrate 1;
 (5) attaching a dielectric multi-layer 6 which is provided on a substrate 7
 to the grooved surface of the substrate 1, opposite to the side of the
 dielectric multi-layer 5 or the light reflection layer 10 with respect to
 the substrate 1; and
 (6) disposing polarizing layers 8 and 9' respectively on the external side
 of the dielectric multi-layers 5 and 6 so as to sandwich the dielectric
 multi-layers 5 and 6 therebetween, as illustrated in FIG. 2, or providing
 a polarizing layer 9 on the external side of the dielectric multi-layer 6,
 as illustrated in FIG. 3.
 FIG. 4 shows one embodiment of the process for forming the grooves 2 on the
 substrate 1 and providing the magnetic material layer 4 on the surface of
 the two facing inner side walls 3 of each groove 2.
 As shown in FIG. 4(a), a layer of a photoresist material, which is
 hereinafter referred to as a resist layer 11, is formed on a substrate 1
 which is, for example, made of quartz.
 A photomask which has a striped pattern, with the stripes being arranged in
 parallel with each other at regular intervals is placed on the thus formed
 resist layer 11, and exposed to ultraviolet light. The UV-exposed surface
 is then subjected to wet etching, so that a grooved pattern is formed in
 the surface of the resist layer 11 corresponding to the striped patter of
 the photomask, as shown in FIG. 4(b).
 Thereafter, grooves 2 each having a predetermined depth extending from the
 grooved pattern formed in the resist layer 11 are formed on the surface of
 the substrate 1 by etching the substrate 1, as shown in FIG. 4(c).
 Then, the resist layer 11 is peeled away from the substrate 1, thereby
 obtaining the substrate with grooves 2, as shown in FIG. 4(d). Through the
 above-mentioned steps, a plurality of grooves 2 can be relatively easily
 formed so as to have a depth (up to about 10 microns) vertically to the
 surface of the substrate 1. In addition, fine grooves with excellent
 straightness and smooth edges can be formed by lithography.
 When a transparent plastic plate is used as the substrate 1, a transparent
 thin layer of SiO.sub.2 may be overlaid on the plastic substrate 1 by
 physical vapor deposition (PVD) in advance. Thereafter, the groove 2 may
 be formed on the surface of the SiO.sub.2 thin layer. Alternatively, a
 resin substrate with grooves can be molded as a replica using an original
 quartz substrate provided with grooves.
 A magnetic material layer 4 is throughout coated on the grooved surface of
 the substrate 1, as shown in FIG. 4(e). The method of forming the magnetic
 material layer 4 is not particularly limited, and physical vapor
 deposition (PVD), chemical vapor deposition (CVD) or plating is usable.
 The thus formed thin film of the magnetic material layer 4 is subjected to
 a sputtering process using Ar ions 12 to remove the portions of the
 magnetic material layer 4 on horizontal faces of the grooved substrate 1
 so that the magnetic material layer 4 remains only on the surface of two
 facing inner side walls 3 of each groove 2 as shown in FIG. 4(f). Although
 the method of removing a part of the magnetic material layer 4 includes
 dry and wet methods, the above-mentioned Ar ion sputtering is preferably
 used over other methods, wherein the sputtering is preferably carried out
 under the reverse biased condition with a negative voltage applied to a
 substrate electrode. Thus, a magnetic material layer 4 can be provided on
 the surface of the two facing inner side walls 3 of each groove 2
 perpendicularly to the substrate 1 as shown in FIG. 4(g).
 To record image information in the magnetic recording medium of the present
 invention, a magnetic field may be applied to the magnetic material layer
 4 in the vertical direction to the substrate 1 corresponding to the image
 information, for example, using a bar magnet or a magnetic head such as a
 vertical magnetic head employing an inductance coil.
 To erase the recorded information, a magnetic field may be uniformly
 applied to the magnetic material layer 4 so as to magnetize the whole
 magnetic material layer 4 in the same direction, for instance, in the
 upward, downward or horizontal direction when viewed in the direction
 perpendicular to the surface of the substrate 1. Alternatively, with the
 application of an AC magnetic field, the bar magnet or the magnetic head
 may be withdrawn from the surface of the magnetic recording medium until
 the magnetic field applied to the recording medium is extinguished.
 Alternatively, a laser beam is imagewise applied to heat the recording
 medium with the application of a bias field thereto so as to record
 information in the magnetic recording medium of the present invention.
 When the recorded information is erased from the recording medium, the
 laser beam may be also applied to the recording medium, with the bias
 field being applied to the recording medium in the direction opposite to
 that for the above-mentioned recording operation.
 When the magnetic recording medium of the present invention is used as the
 image display device, the recorded image can be displayed in the recording
 medium of the present invention by the following principle.
 FIG. 5 is a schematic diagram which explains the manifestation of the image
 contrast of an image recorded in the magnetic recording medium of
 reflection type as shown in FIG. 3.
 In a magnetic material layer 4 shown in FIG. 5, an image area 4a is
 magnetized in a direction of arrow 13 perpendicular to the surface of the
 magnetic material layer 4 using a bar magnet or a magnetic head. On the
 other hand, a non-image area 4b is not magnetized.
 When a light beam 15 strikes the surface of a polarizing layer 9 as shown
 in FIG. 5(a), the light having a plane of polarization 14 which can pass
 through the polarizing layer 9 enters the magnetic material layer 4 via a
 dielectric multi-layer (not shown). A light beam 15' shown in FIG. 5 is
 incident on the image area 4a; while a light beam 15' is incident on the
 non-image area 4b.
 The plane of polarization 14 of the light 15' which has struck the
 magnetized image area 4a is rotated at a Faraday rotational angle
 (.theta.), as shown in FIG. 5(b). Thus, the light with the plane of
 polarization 14a is reflected by the light reflection layer 10. In
 contrast to this, the plane of polarization 14 of the incident light 15"
 which has struck the non-image area 4b is not rotated, and the light with
 the plane of polarization 14 is reflected by the light reflection layer 10
 as it is.
 The plane of polarization 14b of the light 15' is not changed when the
 light strikes the light reflection layer 10 and is reflected thereby, as
 shown in FIG. 5(c). After reflected by the light reflection layer 10, the
 light 15' is again incident on the magnetic material layer 4, as a shown
 in FIG. 5(d). While passing through the magnetized image area 4a, the
 plane of polarization 14b is again rotated at a Faraday rotational angle
 (.theta.). Thereafter, as shown in FIG. 5(e), the light with the plane of
 polarization 14c is directed toward the polarizing layer 9 via the
 dielectric multi-layer 6 (not shown). The rotational angle from the plane
 of polarization 14 to the plane of polarization 14c is 2.theta. in total.
 In this case, the plane of polarization 14c of the light 15' in FIG. 4(e)
 is in such a direction that cannot pass through the polarizing layer 9, so
 that the magnetized image area 4a appears dark and can be displayed as a
 dark portion.
 The incident light 15" which has entered the non-magnetized non-image area
 4b is directed toward the polarizing layer 9 via the dielectric
 multi-layer 6 (not shown), with the plane of polarization 14 being not
 rotated. Since the plane of polarization 14 is not changed, the light 15"
 can pass through the polarizing layer 9. As a result, the non-image area
 4b appears light. As mentioned above, the magnetized image area 4a appears
 dark while the non-magnetized non-image area 4b becomes light, with the
 result that the image contrast can be manifested.
 In the magnetic recording medium of the present invention, the magnetic
 material layer is disposed on the side wall of each groove in parallel
 with the direction of light. When the light passes through the air space
 between the two facing inner side walls on which the magnetic material
 layer 4 is disposed, or passes through the substrate portion between the
 adjacent grooves, it is considered that the light is reflected by the
 magnetized magnetic material layer 4. Consequently, the magneto-optical
 effect is remarkably enhanced and the rotational angle of the plane of
 polarization becomes large. Therefore, it is possible to display an image
 with high image contrast.
 In the magnetic recording medium with such a structure as shown in FIG. 1
 or 2, the substrate 1 with a plurality of grooves 2 is sandwiched between
 a pair of dielectric multi-layers 5 and 6. When the light passes through
 the air space between the two facing inner side walls on which the
 magnetic material layers 4 is disposed or the substrate portion between
 the adjacent grooves 2, the light trapped between the dielectric
 multi-layers 5 and 6 is considered to be reflected by the dielectric
 multi-layers 5 and 6. Therefore, the rotation of the plane of polarization
 is further amplified, thereby increasing the contrast of the image
 recorded in the recording medium.
 Other features of this invention will become apparent in the course of the
 following description of exemplary embodiments, which are given for
 illustration of the invention and are not intended to be limiting thereof.
 EXAMPLE 1
 On the surface of a substrate with a thickness of 0.5 mm made of quartz, a
 thin layer of Cr.sub.2 O.sub.3 and a thin layer of Cr were successively
 provided to have a total thickness of 120 nm, and a positive resist layer
 was further provided on the above two laminated thinlayers.
 There was placed on the positive resist layer a photomask carrying many
 straight lines which extended parallel with each other with a space
 between adjacent lines being 1.0 .mu.m and a width of each line being 1.0
 .mu.m. The photomask was exposed to UV light, and the resist layer was
 subjected to wet etching.
 Further, using the thus formed pattern, the quartz substrate 1 was etched
 under a fluorine gas ambient, thereby forming in the surface of the quartz
 substrate 1 a plurality of grooves 2 with a width of 1.0 .mu.m and a depth
 of 0.4 .mu.m extending parallel with each other, with a space between the
 adjacent grooves being 1.0 .mu.m. After the completion of the etching, the
 resist layer and the At two thin layers of Cr.sub.2 O.sub.3 and Cr were
 removed from the quartz substrate 1.
 Subsequently, a thin film of iron was deposited on the grooved surface of
 the quartz substrate 1 throughout by an evaporation method under gaseous
 atmosphere without heating the substrate 1. A mixture of argon (Ar) and
 the air was caused to flow into the evaporation chamber at the respective
 rates of 50 ccm and 5 ccm, and the total pressure was 1.3 Pa. Thus, a
 magnetic thin layer was coated on the entire grooved surface of the quartz
 substrate 1.
 It was observed that the magnetic thin layer thus formed on the entire
 grooved surface of the substrate 1 was made of finely-divided particles of
 iron with an average particle diameter of 7 nm. The average thickness of
 the magnetic thin layer was 76 nm.
 When a magnetic thin layer was independently formed on a glass plate in the
 same manner as mentioned above, the coercive force of the thus formed
 magnetic thin layer was 450 Oe, and a magnetic anisotropy was present in
 the plane direction.
 The grooved quartz substrate 1 with the magnetic thin layer was then
 subjected to a sputtering process.
 Using an ion etching apparatus, parts of the magnetic thin layer were
 removed from the grooved-surface of the substrate 1 so that only the
 magnetic thin layer attached to the side walls might remain with argon gas
 being introduced into the sputtering chamber, under the application of a
 voltage of -350 V to the substrate electrode (i,e., under the reverse
 biased condition). Thus, a magnetic material layer 4 was disposed on the
 two facing inner side walls of each groove, extending in the form of
 stripes.
 The magneto-optical effect of the magnetic material layer 4 was measured
 using a magneto-optical effect measuring apparatus. As a result, the
 rotational angle of the plane of polarization was 16.degree. when the
 light with a wavelength of 630 nm was employed, with the magnetic material
 layer 4 being magnetized by the application of a magnetic field of 15
 kilogauss, followed by no application of magnetic field thereto.
 Thereafter, a dielectric material layer of SiO.sub.2 with a low refractive
 index of 1.46 and a dielectric material layer of TiO.sub.2 with a high
 refractive index of 2.45 were alternately laminated by ion-plating method
 on the non-grooved surface of the quartz substrate 1, with the substrate 1
 being heated at 400.degree. C. Thus, a dielectric multi-layer 5 with a
 total thickness of 90 nm was provided. In this case, the number of the
 above-mentioned laminated dielectric material layers was 10.
 A dielectric multi-layer 6 was provided on a quartz substrate 7 with a
 thickness of 0.5 mm in the same manner as mentioned above, and the
 dielectric multi-layer 6 was closely attached to the grooved surface of
 the substrate 1. The transmittance of the dielectric multi-layers 6 and 7
 was about 90%.
 Commercially available iodine-containing polarizing films 8 and 9 were
 respectively disposed on the external side of the dielectric multi-layer 5
 and the quartz substrate 7 so as to interpose the dielectrie multi-layers
 5 and 6 between the polarizing films 8 and 9.
 Thus, a magnetic recording medium No. 1 according to the present invention
 with such a structure as illustrated in FIG. 2 was fabricated.
 The magneto-optical effect of the magnetic material layer 4 was measured
 using the magneto-optical effect measuring apparatus. As a result, the
 rotational angle of the plane of polarization was 24.degree. when the
 light with a wavelength of 630 nm was employed, with the magnetic material
 layer 4 being magnetized by the application of a magnetic field of 15
 kilogauss, followed by no application of magnetic field.
 Since the magnetic material layer 4 was sandwiched between the dielectric
 multi-layers 5 and 6 in the above prepared magnetic recording medium No.
 1, the energy of light incident on the magnetic recording medium No. 1 is
 localized on the magnetic material layer 4. As a result, the
 magneto-optical effect of the magnetic material layer 4 was enhanced and
 the rotational angle of the plane of polarization was increased.
 An image was recorded in the recording medium No. 1 by applying a magnetic
 field to the magnetic recording medium No. 1 from the outside of the
 polarizing film 8 or 9 using a magnetic pen equipped with a permanent
 magnet having a diameter of 2 mm and a surface magnetic flux density of 3
 kilogauss. An area of the magnetic material layer 4 corresponding to the
 image portion was thus magnetized. The magnetized image area appeared
 dark, thereby obtaining an image contrast of 1.8.
 Alternatively, to record an image in the magnetic recording medium No. 1,
 the magnetic material layer 4 was entirely magnetized in a vertical
 direction, that is, in a downward direction. Thereafter, an area of the
 magnetic material layer corresponding to the image portion was magnetized
 in the opposite direction, that is, in the upward direction, using a
 magnetic pen equipped with a permanent magnet having a diameter of 2 mm
 and a surface magnetic flux density of 3 kilogauss. The image contrast
 obtained by this method was two times that obtained by the previously
 mentioned image recording method.
 The polarizing films 8 and 9 were disposed with turning the direction of
 each polarizing film so as to obtain the maximum image contrast.
 COMATIVE EXAMPLE 1
 The procedure for fabrication of the magnetic recording medium No. 1 in
 Example 1 was repeated except that the dielectric multi-layers 5 and 6
 employed in Example 1 were not provided on both surfaces of the quartz
 substrate 1.
 Thus, a comparative magnetic recording medium No. 1 was fabricated.
 An image was recorded in the comparative magnetic recording medium No. 1 by
 applying a magnetic field to the comparative magnetic recording medium No.
 1 from the outside of the polarizing film 8 or 9 using the same magnetic
 pen as employed in Example 1. Thus, an area of the magnetic material layer
 4 corresponding to the image portion was magnetized, and appeared dark,
 thereby obtaining an image contrast of 0.9.
 EXAMPLE 2
 The procedure for fabrication of the magnetic recording medium No. 1 in
 Example 1 was repeated except that the dielectric multi-layers 5 and 6,
 each prepared by alternately laminating the SiO.sub.2 dielectric material
 layers and the TiO.sub.2 dielectric material layers by ion-plating method
 in Example 1 were replaced by dielectric multi-layers 5 and 6, each
 prepared by alternately laminating a low-refractive index resin layer and
 a high-refractive index resin layer by a coating method,
 To be more specific, a commercially available one-pack type
 ultraviolet-curing epoxy resin (Trademark "Adeka Optomer KR567", made by
 Asahi Denka Kogyo K.K.) for the formation of the low-refractive index
 resin layer with a refractive index of 1.35, and a commercially available
 one-pack type ultraviolet-curing polyene polythiol resin (Trademark
 "BY-305", made by Asahi Denka Kogyo K.K.) for the formation of a
 high-refractive index layer with a refractive index of 1.57 were
 alternately coated by spin coating and cured by the application of a
 mercury lamp of 80 W/cm. In this case, the number of the above-mentioned
 laminated dielectric material layers was 20, and the total thickness of
 the dielectric multi-layer was 200 nm. The transmittance of the thus
 obtained dielectric multi-layer was 85%.
 Thus, a magnetic recording medium No. 2 according to the present invention
 was fabricated.
 An image was recorded in the magnetic recording medium No. 2 by applying a
 magnetic field to the magnetic recording medium No. 2 from the outside of
 the polarizing film 8 or 9 using the same magnetic pen as employed in
 Example 1. Thus, an area of the magnetic material layer 4 corresponding to
 the image portion was magnetized, and appeared dark, thereby obtaining an
 image contrast of 1.6.
 EXAMPLE 3
 The procedure for fabrication of the magnetic recording medium No. 1 in
 Example 1 was repeated except that the dielectric multi-layer 5 provided
 on the non-grooved surface of the substrate 1 in Example 1 was replaced by
 a light reflection layer with a thickness of about 200 nm made by
 aluminum, and that the polarizing film 8 employed in Example 1 was not
 provided.
 Thus, a magnetic recording medium No. 3 according to the present invention
 with such a structure as shown in FIG. 3 was fabricated.
 When the light entered the magnetic recording medium No. 3 from the side of
 the polarizing film 9, The light was trapped in a space between the
 dielectric multi-layer 6 and the light reflection layer 10, where multiple
 reflection took place. The incident light was turned into a linearly
 polarized light through the polarizing film 9. After the linearly
 polarized light thus obtained passed through the magnetized image area of
 the magnetic material layer, the plane of polarization was rotated.
 Thereafter the light was reflected by the light reflection layer 10, and
 the reflected light passed through the magnetized image area of the
 magnetic material layer 4 again. At that time, the plane of polarization
 was again rotated, so that the rotation angle was doubled. Due to the
 rotation of the plane of polarization, it became impossible for the light
 to pass through the polarizing film 9, whereby the magnetized image area
 appeared dark.
 An image was recorded in the magnetic recording medium No. 3 by applying a
 magnetic field to-the magnetic recording medium No. 3 from the outside of
 the polarizing film 9 using the same magnetic pen as employed in Example
 1. Thus, an area of the magnetic material layer 4 corresponding to the
 image portion was magnetized, and appeared dark, thereby obtaining an
 image contrast of 1.6.
 As previously explained, image can be recorded in the magnetic recording
 medium, and in addition, the recorded image can be reproduced or erased
 from the recording medium using a magnetic head. Further, the magnetic
 recording medium of the present invention is applicable to the image
 display device capable of displaying the recorded image with a high image
 contrast.