JP2006079661A - Magneto-optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium suited for obtaining high magnetic wall mobility regarding a reproducing layer in which magnetic wall movement occurs during information reproduction. <P>SOLUTION: The magneto-optical recording medium X is provided with a recording layer 11 as a recording function, a reproducing layer 13 as a reproducing function accompanied by magnetic wall movement, and an intermediate layer 12 disposed between the recording and reproducing layers 11 and 13 to change the exchange coupled state thereof. The reproducing layer 13 is made of a amorphous alloy containing a rare earth element and a transition metal, and the rare earth element contains Gd and Y or La. The content of Y or La in the reproducing layer 13 is 1 to 20 at %. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magneto-optical recording medium having a reproducing layer that causes domain wall movement or domain expansion during information reproduction.

  A magneto-optical disk is known as one form of optical media from which information is optically read. A magneto-optical disk is a rewritable magneto-optical recording medium that is thermomagnetically recorded and reproduced using the magneto-optical effect. Further, the magneto-optical disk has a recording layer made of a perpendicular magnetization film, and a predetermined signal is recorded in the recording layer as a change in the magnetization direction. This recording signal is read by a predetermined optical system and output as a reproduction signal.

  In the technical field of magneto-optical disks, a reproduction system with domain wall movement or domain expansion has been developed to practically reproduce signals recorded at a high density exceeding the resolution limit in a reading optical system. . For example, DWDD (domain wall displacement detection) and MAMMOS (magnetic amplifying magneto-optical system). For example, the following Patent Documents 1 to 3 describe a magnetic domain expansion type magneto-optical disk employing such a reproduction method.

Japanese Patent Application Laid-Open No. 6-290496 JP 2001-56777 A JP 2003-132599 A

  In a magnetic domain expansion system magneto-optical disk, a recording magnetic part including a laminated structure of a recording layer, a reproducing layer, and an intermediate layer therebetween is provided on a substrate to constitute a recording surface. Each of these three layers is a perpendicular magnetization film made of a rare earth-transition metal amorphous alloy, and is laminated so that exchange interaction works between two adjacent layers when not heated. The recording layer exhibits a relatively large domain wall coercivity, the reproducing layer exhibits a relatively small domain wall coercivity, and the intermediate layer has a lower Curie temperature than the other two layers. In addition, in such a recording magnetic part or recording surface, information tracks (tracks for signal recording) are provided spirally or concentrically.

  In information recording on a magnetic domain expansion system magneto-optical disk, while the disk is rotated, the recording layer is irradiated with a recording laser beam to sequentially increase the temperature of the recording layer locally. A predetermined magnetic field is applied to the temperature rising point. In this way, a predetermined signal is recorded on the recording layer in the information track. Specifically, the recording layer forms a boundary between a magnetic section and a plurality of magnetic domains each having a predetermined length corresponding to a recording signal, the magnetization of which is alternately reversed continuously along the disk circumferential direction. A domain wall is formed. Under a temperature condition lower than the Curie temperature of the intermediate layer, the recording layer and the intermediate layer are exchange-coupled and the intermediate layer and the reproduction layer are exchange-coupled, and the intermediate layer and the reproduction layer are magnetized in the same direction as the recording layer. The magnetic domain and the domain wall of the magnetic domain are formed.

  In the information reproduction from the magnetic domain expansion system magneto-optical disk, the information track is scanned by irradiating the information track with a reproduction laser beam while the disk is rotated. At this time, a temperature gradient having a temperature peak near the center of the irradiation region is generated in the scanning direction in the information track of the irradiation region. In the irradiation region, the domain wall moves to the higher temperature side in the reproducing layer at the moment when the magnetic wall of the reproducing layer passes through the isothermal line of the Curie temperature of the intermediate layer from the low temperature region to the high temperature region with the scanning. To do. As the domain wall moves in the reproducing layer, the magnetization of the domain wall moving region is reversed. The domain wall motion is detected by detecting this magnetization reversal with a predetermined optical system as a change in the polarization plane of the light reflected on the surface of the reproducing layer. By irradiating the reproducing laser beam along the information track and sequentially detecting the domain wall movement, the recording signal of the magneto-optical disk is read. According to such reading, the recording pattern of the reproducing layer or recording layer in the information track is discriminated not by the entire spot of the reproducing laser beam but by the isotherm in the beam spot (the Curie temperature isotherm of the intermediate layer). The Therefore, according to the magnetic domain expansion system magneto-optical disk, even a signal recorded at a high density on the recording layer exceeding the resolution limit in the reproducing optical system, that is, the recording mark (the length corresponding to the signal is tracked). Even a recording pattern in which the length of the signal magnetic domain) formed in the recording layer in the extending direction is smaller than the spot diameter can be reproduced practically.

  As a constituent material of the recording layer and the intermediate layer of such a magnetic domain expansion magneto-optical disk, generally an amorphous alloy of Tb, which is a rare earth element, and a 3d transition metal is employed. It is known that an amorphous alloy of Tb and a 3d transition metal has a relatively large domain wall coercive force, so that it is easy to form a perpendicular magnetization film suitable for a recording layer or an intermediate layer. On the other hand, as a constituent material of the reproducing layer, an amorphous alloy of Gd, which is a rare earth element, and a 3d transition metal is generally used. It is known that an amorphous alloy of Gd and a 3d transition metal has a relatively small domain wall coercive force, so that it is easy to form a perpendicular magnetization film suitable for the reproducing layer. The smaller the domain wall coercive force, the faster the domain wall movement in the reproducing layer.

  On the other hand, in the technical field of magnetic domain expansion type magneto-optical disks, the smaller the minimum recording mark (magnetic domain) that can be stably formed in the recording layer by information recording as described above, the more the recording layer to the intermediate layer. It is known that a higher recording density can be realized as the minimum magnetic domain that can be transferred to the reproducing layer via the recording medium and stably formed in the reproducing layer is smaller. As the amount of information processing in a computer system increases, a higher recording density is required for recording media including magneto-optical disks.

  In a conventional magneto-optical disk, information reproduction is practically performed when the minimum recording mark length in the recording layer is set to about 100 nm or more, but the minimum recording mark length in the recording layer is set to be as short as about 60 nm. When the information is reproduced, the lack of a reproduction signal becomes significant during information reproduction. The main reason why such a problem occurs is that the domain wall moving speed in the reproducing layer is insufficient. The smaller the recording mark length in the recording layer, the higher the required minimum speed required for the domain wall movement in the beam spot irradiation region reproducing layer for information reproduction. However, an amorphous alloy of Gd, which is a rare earth element, and a 3d transition metal In the conventional reproducing layer, a sufficient domain wall moving speed cannot be obtained when the minimum recording mark length of the recording layer is set to be as short as about 60 nm. According to the conventional technique, the domain wall mobility of the reproducing layer is not sufficient as described above, and it is difficult to practically increase the recording density of the magnetic domain expansion type magneto-optical disk.

  The present invention has been conceived under such circumstances, and provides a magneto-optical recording medium suitable for obtaining high domain wall mobility for a reproducing layer in which domain wall movement occurs during information reproduction. Objective.

  The magneto-optical recording medium provided by the present invention includes a recording layer responsible for a recording function, a reproducing layer responsible for a reproducing function accompanied by domain wall movement, and the recording layer and the reproducing layer interposed between the recording layer and the reproducing layer. And an intermediate layer for changing the exchange coupling state. In the present invention, the reproduction layer is made of an amorphous alloy containing a rare earth element and a transition metal. The rare earth element contains Gd and Y or La, and the transition metal preferably contains Fe and / or Co. The content of Y or La in the reproduction layer is 1 to 20 at% (atomic percent).

  According to such a configuration, it was found that the domain wall mobility of the reproducing layer can be improved while ensuring the required perpendicular magnetic anisotropy.

  A factor that affects the mobility of the domain wall in the perpendicular magnetization film is the orbital angular momentum of the elements constituting the perpendicular magnetization film. The smaller this value, the easier the domain wall moves in the perpendicular magnetization film (that is, suitable for speeding up the domain wall movement in the perpendicular magnetization film), but the rare earth element constituting the reproducing layer in the present invention. The orbital angular momentum of Gd is 0, and the orbital angular momentum of Y and La, which are the rare earth elements constituting the reproducing layer in the present invention, is also zero. Y and La are elements that exhibit non-magnetic properties by themselves. However, even if Y or La is contained as a part of the rare earth element in the reproduction layer (made of a rare earth-transition metal amorphous alloy), the reproduction is also performed. The magnetic properties of the layer do not deteriorate in proportion to the Y or La content (this is probably because the 5d electrons of Y and La contribute to the magnetism of the reproducing layer). Therefore, even if a relatively large amount of Y or La is contained in the reproducing layer as a rare earth element, the magnetic properties of the reproducing layer are not excessively deteriorated, and a predetermined perpendicular magnetic anisotropy can be secured for the reproducing layer. Is possible. The fact that high domain wall mobility can be obtained while ensuring the perpendicular magnetic anisotropy in the reproducing layer in the present invention is based on these facts.

  According to the present invention as described above, it is possible to obtain a magneto-optical recording medium suitable for achieving high domain wall mobility for a reproducing layer in which domain wall movement occurs during information reproduction. Such a magneto-optical recording medium is suitable for increasing the recording density of the medium.

Preferably, the perpendicular magnetic anisotropy constant Ku of the reproducing layer is 1 × 10 ^{4 to} 5 × 10 ⁵ erg / cm ³ . When Ku is less than 1 × 10 ⁴ erg / cm ³ , Ku tends to be an in-plane magnetization film because Ku is too small (that is, Ku−2πMs ² <0 [Ms: Saturation magnetization] is likely to occur. When Ku exceeds 5 × 10 ⁵ erg / cm ³ , the domain wall coercive force of the reproducing layer becomes too large, and domain wall movement hardly occurs in the reproducing layer.

Preferably, the Curie temperature of the reproduction layer is 180 to 350 ° C. If the Curie temperature is less than 180 ° C., the Curie temperature of the reproduction layer is too close to the Curie temperature of the intermediate layer (for example, about 130 ° C.), so that it is difficult to ensure the reproduction signal amplitude accompanying the domain wall movement. When the Curie temperature exceeds 350 ° C., the saturation magnetization Ms of the reproduction layer becomes too large, and thus the reproduction layer tends to become an in-plane magnetization film (that is, Ku−2πMs ² <0 tends to be obtained for the reproduction layer). ).

  Preferably, the thickness of the reproduction layer is 10 to 50 nm. If the thickness is less than 10 nm, the reproducing layer is too thin, and the transmittance of the reproducing layer becomes high (thus, the reflectance becomes low), and the Kerr rotation angle during information reproduction becomes small. When the thickness exceeds 50 nm, since the reproducing layer is too thick, the exchange coupling force between the reproducing layer and the recording layer becomes small, and it becomes difficult to appropriately transfer a signal from the recording layer to the reproducing layer.

  FIG. 1 is a partial sectional view of a magneto-optical disk X according to the present invention. The magneto-optical disk X includes a substrate S, a recording magnetic unit 10, a pre-groove layer 21, a heat conductive layer 22, dielectric layers 23 and 24, and a protective film 25, and includes a front illumination type magneto-optical disk. It is configured as. The magneto-optical disk X has a structure from the pre-groove layer 21 to the protective film 25 on only one side or both sides of the substrate S.

  The substrate S is a part for ensuring the rigidity of the magneto-optical disk X, and is, for example, a disk substrate made of resin, silicon, aluminum, or glass.

  The recording magnetic unit 10 has a laminated structure composed of a recording layer 11, an intermediate layer 12, and a reproducing layer 13, and a magnetic domain expansion system reproducing system (for example, DWDD, MAMMOS, etc.) accompanied by domain wall movement or magnetic domain expansion in the reproducing layer 13 is used. ) Is configured to be reproducible based on.

  The recording layer 11 is a part responsible for the recording function in the magneto-optical disk X, is made of an amorphous alloy containing a rare earth element and a transition metal, and has a perpendicular magnetic anisotropy and is perpendicularly magnetized in the perpendicular direction. It is a magnetized film. The vertical direction means a direction perpendicular to the film surface of the magnetic film constituting the layer. Such a recording layer 11 is made of, for example, TbFeCо or TbDyFeCо having a predetermined composition ratio. The recording layer 11 has a thickness of 40 to 100 nm, for example.

  The intermediate layer 12 is a part for changing the exchange coupling state of the recording layer 11 and the reproducing layer 13, and changes from the perpendicular magnetization state to the spontaneous magnetization disappearance state (state change) at the Curie temperature when the temperature rises. It consists of a rare earth-transition metal amorphous alloy that transitions from a spontaneous magnetization disappearance state to a perpendicular magnetization state at the Curie temperature due to a temperature drop. In this embodiment, the Curie temperature of the intermediate layer 12 is, for example, 100 to 150 ° C. Therefore, the intermediate layer 12 is a perpendicular magnetization film at room temperature. Such an intermediate layer 12 is made of, for example, TbFe or TbFeCо having a predetermined composition ratio. Moreover, the thickness of the intermediate layer 12 is, for example, 10 to 30 nm.

The reproducing layer 13 is a part that bears a reproducing function accompanied by domain wall movement or domain expansion, and is a perpendicular magnetization film made of a rare earth-transition metal amorphous alloy. As the rare earth element constituting the reproducing layer 13, at least Gd and Y or La are adopted, and as the transition metal, for example, Fe or Co is adopted. Specifically, the reproducing layer 13 is made of GdYFeCo, GdLaFeCo, or a rare earth-transition metal amorphous alloy having a composition in which other rare earth elements or transition metals are added thereto. The content of Y or La in the reproducing layer 13 is 1 to 20 at% (atomic percent). Preferably, the perpendicular magnetic anisotropy constant Ku of the reproducing layer 13 is 1 × 10 ^{4 to} 5 × 10 ⁵ erg / cm ³ , the Curie temperature of the reproducing layer 13 is 180 to 350 ° C., and the reproducing layer 13 The thickness is 10 to 50 nm.

  The pregroove layer 21 is made of a resin material, and a pregroove 21 a is formed on the contact surface with the heat conductive layer 22. The pregroove 21a has a spiral or concentric pattern shape, and a land groove shape in the magneto-optical disk X is realized based on the pregroove 21a. A so-called 2P resin is employed as the resin material constituting the pregroove layer 21. In the present invention, the pregroove may be formed on the substrate S itself without providing the pregroove layer 21. In that case, the substrate S with pregroove is made of polycarbonate, for example, and is manufactured by an injection molding method.

  The heat conductive layer 22 is a part for efficiently transferring heat generated in the recording magnetic unit 10 or the like to the substrate S when the magneto-optical disk X is irradiated with a recording or reproducing laser. , Ag, Ag alloy (AgPdCuSi, AgPdCu, etc.), Al alloy (AlSi, AlTi, AlCr, etc.), Au, or Pt. The thickness of the heat conductive layer 22 is, for example, 10 to 50 nm.

The dielectric layers 23 and 24 are portions for avoiding or suppressing an external magnetic influence or the like on the recording magnetic part 10 and are made of, for example, SiN, SiO ₂ , YSiO ₂ , ZnSiO ₂ , AlO, or AlN. . The thickness of the dielectric layers 23 and 24 is, for example, 30 to 100 nm.

  The protective film 25 covers the recording magnetic part 10 in order to protect the recording magnetic part 10 from dust and the like, and is made of a resin having sufficient transparency for the recording laser and the reproducing laser of the magneto-optical disk X. Examples of the resin for forming the protective film 25 include an acrylic resin and a urethane resin.

  In manufacturing the magneto-optical disk X having such a configuration, first, the pregroove layer 21 is formed on the substrate S by, for example, a so-called 2P method. Next, the heat conductive layer 22, the dielectric layer 23, the recording layer 11, the intermediate layer 12, the reproducing layer 13, and the dielectric layer 24 are sequentially formed on the pre-groove layer 21, for example, by sputtering. Thereafter, the protective film 25 is formed on the dielectric layer 24 by, eg, spin coating.

  In recording information on the magneto-optical disk X, the recording magnetic part 10 is irradiated from the protective film 25 side with a recording laser beam while the magneto-optical disk X is rotated at a predetermined rotational speed. A predetermined magnetic field is applied to the temperature rise portion while locally raising the temperature of the recording layer 11 sequentially. In this way, a predetermined signal is recorded on the recording layer 11 in the recording magnetic unit 10 along the circumferential direction of the disk. Specifically, the recording layer 11 has a predetermined length corresponding to the recording signal and the magnetization is alternately reversed continuously along the information track extending in the circumferential direction of the disk (the track for recording and reproducing the signal). Are formed, and a domain wall forming a boundary between the magnetic sections is formed. Under a temperature condition lower than the Curie temperature of the intermediate layer 12, the recording layer 11 and the intermediate layer 12 are exchange-coupled, and the intermediate layer 12 and the reproduction layer 13 are exchange-coupled. A magnetic domain magnetized in the same direction as the recording layer 11 and a domain wall of the magnetic section are formed.

  FIG. 2 shows a method for reproducing information from the magneto-optical disk X. From the viewpoint of simplifying the drawing, in FIG. 2, components other than the recording layer 11, the intermediate layer 12 and the reproducing layer 13 are omitted from the magneto-optical disk X. In reproducing information from the magneto-optical disk X, the recording magnetic unit 10 is irradiated from the reproducing layer 13 side along the information track with the reproducing laser beam L while the magneto-optical disk X is rotated. The direction of relative movement of the area irradiated by the laser beam L with respect to the magneto-optical disk X is represented by an arrow D. By irradiation with the laser beam L, the temperature in the recording magnetic unit 10 is locally increased, and a temperature gradient is generated in the recording magnetic unit 10 in the circumferential direction of the disk as shown in the graph of FIG. In the intermediate layer 12, a region R (shown with hatching) in which the spontaneous magnetization disappears due to the temperature rising above the Curie temperature Tc is generated. The isotherm of the Curie temperature Tc of the intermediate layer 12 in the irradiation region is changed from the low temperature region to the high temperature region as the domain wall W of the magnetic domain 13a of the reproducing layer 13 corresponding to the predetermined magnetic domain 11a of the recording layer 11 moves. At the moment of passing, the domain wall W moves in the reproducing layer 13 to a higher temperature side. When the domain wall W moves in the reproducing layer 13 from the front to the rear in the irradiation region movement direction D, the magnetization of the domain wall movement region is reversed. The domain wall motion is detected by detecting this magnetization reversal with a predetermined optical system as a change in the polarization plane of the light reflected on the surface of the reproducing layer 13. By irradiating the reproducing laser beam along the information track and sequentially detecting the domain wall movement, the recording signal of the magneto-optical disk X is read.

  In the magneto-optical disk X of the present invention, it is possible to obtain a high domain wall mobility during information reproduction as described above while ensuring the required perpendicular magnetic anisotropy for the reproducing layer 13. This is because the reproducing layer 13 of the magneto-optical disk X is made of a rare earth-transition metal amorphous alloy containing 1 to 20 at% Y or La in addition to Gd as a rare earth element. Such a magneto-optical disk X is suitable for increasing the recording density of the medium.

  A factor that affects the mobility of the domain wall in the perpendicular magnetization film is the orbital angular momentum of the elements constituting the perpendicular magnetization film. The smaller this value, the easier the domain wall moves in the perpendicular magnetization film (that is, suitable for speeding up the domain wall movement in the perpendicular magnetization film), but it is a rare earth element constituting the reproducing layer 13. The orbital angular momentum of Gd is 0, and the orbital angular momentums of Y and La, which are also rare earth elements constituting the reproducing layer 13, are also 0. In addition, the reproducing layer 13 contains Y or La that exhibits non-magnetic properties alone, but the magnetic characteristics of the reproducing layer 13 do not deteriorate so as to be proportional to the Y or La content. This is presumably because 5d electrons of Y and La contribute to the magnetic properties of the reproducing layer 13. Therefore, even if a relatively large amount of Y or La is contained in the reproducing layer 13 as a rare earth element, the magnetic characteristics of the reproducing layer 13 are not excessively deteriorated, and the perpendicular magnetic anisotropy required for the reproducing layer 13 is ensured. It is possible to do. Based on these facts, it is possible to obtain high domain wall mobility while ensuring perpendicular magnetic anisotropy for the reproducing layer 13 in the present invention.

  Examples of the present invention will be described below together with comparative examples.

[Example 1]
<Production of magneto-optical disk>
A magneto-optical disk of this example was manufactured as a front-illuminated magneto-optical disk having the laminated structure shown in FIG.

  In the production of the magneto-optical disk of this example, a pregroove layer having a thickness of 10 μm was first formed on a glass substrate (diameter 120 mm, thickness 1.2 mm) by the 2P method. As the pregroove layer forming material, a resin for 2P method (photopolymer) was employed. Further, the surface irregularity shape of the pregroove layer was a land groove shape with a track pitch of 300 nm and a pregroove depth of 50 nm.

  Next, a 30 nm thick thermal conductive layer was formed by depositing AlSi on the pregroove layer by sputtering. Specifically, AlSi was formed on the substrate by co-sputtering using an Al target and an Si target. In this sputtering, Ar gas is used as the sputtering gas (the same applies to the following sputtering except reactive sputtering), the sputtering gas pressure is 0.6 Pa, and the sputtering power is 300 W (Al target) and 200 W (Si target). did.

Next, a dielectric layer having a thickness of 15 nm was formed by depositing SiN on the heat conductive layer by sputtering. Specifically, SiN was formed on the substrate by reactive sputtering performed using an Si target and using Ar gas and N ₂ gas as sputtering gas. In this sputtering, the flow ratio of Ar gas and N ₂ gas was 7: 3, the sputtering gas pressure was 0.5 Pa, and the discharge power was 800 W.

Next, a recording layer having a thickness of 60 nm was formed by depositing Tb ₂₄ Fe ₅₆ Co ₂₀ on the dielectric layer by sputtering. Specifically, Tb ₂₄ Fe ₅₆ Co ₂₀ was formed on the dielectric layer by co-sputtering using a Tb target and an FeCo target. In this sputtering, the sputtering gas pressure was 1.5 Pa, and the sputtering power was 500 W (Tb target) and 1500 W (FeCo target). The Curie temperature Tc of the recording layer was 280 ° C.

Next, an intermediate layer having a thickness of 15 nm was formed by depositing Tb ₂₂ Fe ₇₈ on the recording layer by sputtering. Specifically, TbFe was formed on the recording layer by co-sputtering using a Tb target and an Fe target. In this sputtering, the sputtering gas pressure was 1.0 Pa, and the sputtering power was 300 W (Tb target) and 900 W (Fe target). The Curie temperature Tc of this intermediate layer was 130 ° C.

Next, a reproducing layer having a thickness of 25 nm was formed by depositing Gd ₂₅ Y ₁ Fe ₆₉ Co ₅ on the intermediate layer by sputtering. Specifically, Gd ₂₅ Y ₁ Fe ₆₉ Co ₅ was formed on the intermediate layer by co-sputtering performed using a Gd target, a Y target, and an FeCo target. In this sputtering, the sputtering gas pressure was 0.4 Pa, and the sputtering power was 400 W (Gd target), 50 W (Y target), and 800 W (FeCo target). The regeneration layer had a Curie temperature Tc of 248 ° C.

Next, a dielectric layer (enhancement layer) having a thickness of 60 nm was formed by depositing SiN on the reproducing layer by sputtering. Specifically, SiN was formed on the reproduction layer by reactive sputtering using an Si target and using Ar gas and N ₂ gas as sputtering gas. In this sputtering, the flow ratio of Ar gas and N ₂ gas was 7: 3, the sputtering gas pressure was 0.5 WPa, and the sputtering power was 800 W.

  Next, a protective film having a thickness of 20 μm was formed on the dielectric layer. Specifically, first, a UV curable transparent resin was applied on the dielectric layer by spin coating. Next, the resin film was cured by ultraviolet irradiation. As described above, the magneto-optical disk of this example was manufactured. The structure of the reproducing layer and the Curie temperature in this example are listed in the table of FIG.

<Waveform missing rate measurement>
For the magneto-optical disk of this example, the missing rate of the waveform of the reproduction signal was examined. Specifically, first, a recording mark having a mark length of 60 nm was repeatedly recorded on the information track of the magneto-optical disk of this example through a space having a length of 60 nm. This recording was performed by a laser pulse magnetic field modulation recording system using a predetermined apparatus. The numerical aperture NA of the laser focusing objective lens of this apparatus is 0.85, and the laser wavelength is 405 nm. The peripheral speed of laser scanning was 3.0 m / s, the recording laser power was 7.0 mW, and the recording magnetic field was 600 Oe. Next, the magneto-optical disk was reproduced, and the missing rate of the reproduced signal waveform was measured. The reproduction signal waveform missing ratio is the ratio of the number of reproduced waveform missing to the number of recorded signals. The missing or missing reproduction waveform is caused by the fact that the domain wall of a predetermined magnetic domain does not move properly during reproduction. It occurs as a result. This reproduction is performed using the same apparatus as the recording, the reproduction laser power is set to an optimum value in the range of 1.0 to 2.0 mW, the peripheral speed of the laser scanning is set to 3.0 m / s, and the reproduction magnetic field is reproduced. Was set to 0 Oe. The results of this waveform loss rate measurement are listed in the table of FIG.

[Examples 2 to 7]
Instead of Gd ₂₅ Y ₁ Fe ₆₉ Co ₅ as a reproducing layer, Gd ₂₅ Y ₅ Fe ₆₅ Co ₅ (Example 2), Gd ₂₅ Y ₅ Fe ₆₄ Co ₆ (Example 3), Gd ₂₅ Y _{5 with} a thickness of 25 nm are used. Fe ₆₂ Co ₈ (Example 4), Gd ₂₅ Y ₁₀ Fe ₆₀ Co ₅ (Example 5), Gd ₂₅ Y ₁₅ Fe ₅₅ Co ₅ (Example 6), or Gd ₂₅ Y ₂₀ Fe ₅₀ Co ₅ (Example) Magneto-optical disks of Examples 2 to 7 were produced in the same manner as Example 1 except that 7) was formed. In the production of the magneto-optical disk of each example, the composition ratio of GdYFeCo was adjusted by appropriately adjusting the sputtering conditions in the reproducing layer forming step. In addition, with respect to the magneto-optical disk of each example formed in this way, the missing rate of the waveform of the reproduction signal was measured in the same manner as in Example 1. The structure of the reproduction layer, the Curie temperature, and the measurement result of the waveform loss rate in each example are listed in the table of FIG.

Example 8
A magneto-optical disk of this example was fabricated in the same manner as in Example 1 except that Gd ₂₅ La ₁ Fe ₆₉ Co ₅ was formed instead of Gd ₂₅ Y ₁ Fe ₆₉ Co ₅ as the reproducing layer. In the reproduction layer forming step in this example, specifically, Gd ₂₅ La having a thickness of 25 nm is formed on the intermediate layer (Tb ₂₂ Fe ₇₈ ) by co-sputtering using a Gd target, an La target, and an FeCo target. ₁ Fe ₆₉ Co ₅ was deposited. In this sputtering, the sputtering gas pressure was 0.4 Pa, and the sputtering power was 400 W (Gd target), 50 W (La target), and 800 W (FeCo target). Further, with respect to the magneto-optical disk of the present example formed in this way, the rate of waveform loss of the reproduction signal was measured in the same manner as in Example 1. The configuration of the reproducing layer, the Curie temperature, and the measurement result of the waveform dropout rate in this example are listed in the table of FIG.

[Examples 9 to 14]
As a reproduction layer, Gd ₂₅ La ₅ Fe ₆₅ Co ₅ (Example 9), Gd ₂₅ La ₅ Fe ₆₃ Co ₇ (Example 10), Gd ₂₅ La ₅ having a thickness of 25 nm instead of Gd ₂₅ La ₁ Fe ₆₉ Co ₅ was used. Fe ₆₁ Co ₉ (Example 11), Gd ₂₅ La ₁₀ Fe ₆₀ Co ₅ (Example 12), Gd ₂₅ La ₁₅ Fe ₅₅ Co ₅ (Example 13), or Gd ₂₅ La ₂₀ Fe ₅₀ Co ₅ (Example) Magneto-optical disks of Examples 9 to 14 were produced in the same manner as Example 8 except that 14) was formed. In producing the magneto-optical disk of each example, the composition ratio of GdLaFeCo was adjusted by appropriately adjusting the sputtering conditions in the reproducing layer forming step. In addition, with respect to the magneto-optical disk of each example formed in this way, the missing rate of the waveform of the reproduction signal was measured in the same manner as in Example 1. The structure of the reproduction layer, the Curie temperature, and the measurement result of the waveform dropout rate in each example are listed in the table of FIG.

[Comparative Example 1]
Except for forming a Gd ₂₅ Fe ₇₀ Co ₅ instead of Gd ₂₅ Y ₁ Fe ₆₉ Co ₅ as the reproduction layer in the same manner as in Example 1 to prepare a magneto-optical disk of this comparative example. In the reproduction layer forming step in this comparative example, specifically, Gd ₂₅ Fe ₇₀ Co ₅ having a thickness of 25 nm is formed on the intermediate layer (Tb ₂₂ Fe ₇₈ ) by co-sputtering using a Gd target and an FeCo target. A film was formed. In this sputtering, the sputtering gas pressure was 0.4 Pa, and the sputtering power was 430 W (Gd target) and 800 W (FeCo target). Further, with respect to the magneto-optical disk of this comparative example formed in this way, the missing rate of the waveform of the reproduction signal was measured in the same manner as in Example 1. The configuration of the reproducing layer and the Curie temperature and the measurement result of the waveform dropout rate in this comparative example are listed in the table of FIG.

[Comparative Example 2]
A magneto-optical disk of this comparative example was manufactured in the same manner as in Example 1 except that Gd ₂₅ Y ₃₀ Fe ₄₀ Co ₅ was formed instead of Gd ₂₅ Y ₁ Fe ₆₉ Co ₅ as the reproducing layer. In producing the magneto-optical disk of this comparative example, the composition ratio of GdYFeCo was adjusted by appropriately adjusting the sputtering conditions in the reproducing layer forming step. Further, with respect to the magneto-optical disk of this comparative example formed in this way, the missing rate of the waveform of the reproduction signal was measured in the same manner as in Example 1. The configuration of the reproducing layer and the Curie temperature and the measurement result of the waveform dropout rate in this comparative example are listed in the table of FIG.

[Comparative Example 3]
Except for forming a Gd ₂₅ La ₃₀ Fe ₄₀ Co ₅ instead of Gd ₂₅ La ₁ Fe ₆₉ Co ₅ as the reproduction layer in the same manner as in Example 8, to prepare a magneto-optical disk of this comparative example. In the production of the magneto-optical disk of this comparative example, the composition ratio of GdLaFeCo was adjusted by appropriately adjusting the sputtering conditions in the reproducing layer forming step. Further, with respect to the magneto-optical disk of this comparative example formed in this way, the missing rate of the waveform of the reproduction signal was measured in the same manner as in Example 1. The configuration of the reproducing layer and the Curie temperature and the measurement result of the waveform dropout rate in this comparative example are listed in the table of FIG.

[Evaluation]
As shown in the table of FIG. 6, the magneto-optical disks of Examples 1 to 14 according to the present invention have a lower reproduction signal waveform drop rate (record mark length 60 nm) than the magneto-optical disks of Comparative Examples 1 to 3. . Specifically, the magneto-optical disk of Comparative Example 1 having a reproducing layer (made of a rare earth-transition metal amorphous alloy) containing no Y or La as a rare earth element, or a reproducing layer containing 30 at% Y or La as a rare earth element In the magneto-optical disks of Comparative Examples 2 and 3 having the above, the reproduction signal waveform missing rate (record mark length 60 nm) is 50% or more, while the rare earth element contains 1 to 20 at% Y or La In the magneto-optical disks of Examples 1 to 14 having the above, the waveform missing ratio (record mark length 60 nm) of the reproduction signal is suppressed to 35% or less. In particular, in the magneto-optical disks of Examples 3, 4 and 11, the waveform drop rate is suppressed to less than 1%. The difference between the magneto-optical disks of Examples 1 to 14 and the magneto-optical disks of Comparative Examples 1 to 3 is such that the difference in the reproduction waveform missing rate occurs compared to the magneto-optical disks of Comparative Examples 1 to 3. It is considered that the magneto-optical disks of Examples 1 to 14 are more likely to move the domain wall in the reproducing layer, and thus move the domain wall in the reproducing layer at a higher speed during reproduction.

1 is a partial cross-sectional view of a magneto-optical disk according to the present invention. 1 illustrates a magneto-optical disk reproducing method according to the present invention. A common laminated structure is shown in the magneto-optical disks of Examples 1 to 7 and Comparative Example 2. A common laminated structure is shown for the magneto-optical disks of Examples 8 to 14 and Comparative Example 3. 2 shows a stacked structure of a magneto-optical disk of Comparative Example 1. For the magneto-optical disks of Examples 1 to 14 and Comparative Examples 1 to 3, the structure of the reproducing layer, the Curie temperature Tc, and the measurement result of the waveform dropout rate are shown.

Explanation of symbols

X magneto-optical disk S substrate 10 recording magnetic part 11 recording layer 12 intermediate layer 13 reproducing layer 21 pregroove layer 22 heat conducting layer 23, 24 dielectric layer 25 protective film

Claims (5)

A recording layer responsible for the recording function;
A playback layer that plays a playback function with domain wall movement,
An intermediate layer interposed between the recording layer and the reproducing layer for changing the exchange coupling state of the recording layer and the reproducing layer,
The regeneration layer is made of an amorphous alloy containing a rare earth element and a transition metal,
The rare earth element includes Gd and Y or La,
The magneto-optical recording medium, wherein the Y or La content in the reproducing layer is 1 to 20 at%.   The magneto-optical recording medium according to claim 1, wherein the transition metal includes Fe and / or Co. The magneto-optical recording medium according to claim 1, wherein the reproducing layer has a perpendicular magnetic anisotropy constant of 1 × 10 ^{4 to} 5 × 10 ⁵ erg / cm ³ .   4. The magneto-optical recording medium according to claim 1, wherein the reproducing layer has a Curie temperature of 180 to 350 ° C. 5.   The magneto-optical recording medium according to claim 1, wherein the reproducing layer has a thickness of 10 to 50 nm.

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