JP2004030717A - Magneto-optical recording medium - Google Patents

Abstract

[PROBLEMS] A front illumination system which does not decrease the Kerr rotation angle θk, has good mark shape stability, and has no increase in erasing noise even when a blue laser beam having a short wavelength is used for high density. Provided is a magneto-optical recording medium.
A heat conductive layer, a planarizing layer, an antiferromagnetic layer, a recording layer, and a protective layer are laminated on a substrate in this order. The composition of the RE-TM alloy constituting the recording layer 5 is TMrich, and the surface roughness due to the formation of the antiferromagnetic layer 4 is formed by forming the flattening layer 3 having good surface smoothness under the antiferromagnetic layer 4. Shall be.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium for recording and reproducing information by irradiating light from a side of a magnetic film or the like laminated on a substrate.
[0002]
[Prior art]
2. Description of the Related Art A magneto-optical recording medium (hereinafter, also referred to as a recording medium) in which a recording layer, a protective layer, and the like are stacked on a substrate and a recording layer is irradiated with laser light to record and reproduce information is realized. With an increase in the amount of information and the like, an improvement in the recording density has been demanded even in such a recording medium. Since there is a certain correlation between the recording density of the recording medium and the spot size of the laser beam, it is required to reduce the spot size of the laser beam in order to achieve a high recording density. Assuming that the spot size of the laser light (laser beam) incident on the recording medium is φ, the numerical aperture of the objective lens is NA, and the wavelength of the laser light is λ, the relational expression of φ = λ / 2NA holds. From this relational expression, it can be seen that it is necessary to reduce the wavelength λ and increase the numerical aperture NA to reduce the spot size φ.
[0003]
In order to reduce the wavelength λ, it is sufficient to change the conventionally used red laser light having a wavelength of 640 nm to a blue laser light having a wavelength of 405 nm. On the other hand, when the numerical aperture NA is increased, the focal length becomes shorter. Therefore, as the numerical aperture NA is increased, the aberration due to the thickness and tilt of the substrate increases. Therefore, it is necessary to reduce the thickness of the substrate as much as possible. In other words, compared to a so-called back-illumination type magneto-optical recording medium that performs recording and reproduction by irradiating light to a recording layer via a conventional substrate, a laser is used from the recording layer side laminated on the substrate without passing through the substrate. A so-called front illumination type magneto-optical recording medium that performs recording and reproduction upon incidence of light is more preferable for realizing higher density.
[0004]
FIG. 5 is a configuration diagram of a conventional magneto-optical recording medium.
In the conventional recording medium, reference numeral 1 denotes a substrate made of polycarbonate or the like. On the substrate 1, a heat conductive layer 2, a recording layer 5, and a protective layer 6 are formed in this order. This is a front illumination type recording medium in which laser light LB is incident on the recording layer 5 via the objective lens L from the side of the protective layer 6 laminated on the substrate 1. The heat conductive layer 2 is usually made of a metal film such as Ag, and functions as a reflective layer that reflects the laser beam LB incident on the recording layer 5 from the direction of the protective layer 6 via the objective lens L to the protective layer 6 side. Further, in order to form a well-formed recording mark (magnetic domain; hereinafter, also simply referred to as a mark) on the recording layer 5, a heat radiation function is required. The recording layer 5 is made of a rare earth transition metal alloy (hereinafter, also referred to as RE-TM alloy) film, and is made of, for example, a TbFeCo film.
[0005]
The Kerr rotation angle θk obtained from the recording layer 5 depends on the wavelength of the incident laser light, and in the case of blue laser light, the Kerr rotation angle of the RE-TM alloy film is about 1 to 2 more than the Kerr rotation angle of the red laser light. It decreases by about 30%. Since the Kerr rotation angle of the RE-TM alloy film is mainly caused by the electronic state of the RE-TM alloy, in order to obtain a large Kerr rotation angle θk, a composition containing as much transition metal as possible within the range showing perpendicular magnetization. (Hereinafter also referred to as TMrich). However, the RE-TM alloy film forming the recording layer 5 is generally an alloy film near the compensation composition from the viewpoint of the stability of the recording mark and the recording / erasing magnetic field. Since the RE-TM alloy film having the compensation composition has a very small saturation magnetization Ms at room temperature, the influence of the leakage magnetic field on the erasing magnetic field is reduced. Further, since the coercive force Hc is large, the stability of the recording mark is good.
[0006]
It is known that when the RE-TM alloy film is made to be TMrich in order to improve the Kerr rotation angle θk, it particularly affects the stability of the mark forming process and causes an increase in noise and a decrease in carriers. For example, page 47 of MAG-87-178 (1987) of the Institute of Magnetics of the Institute of Electrical Engineers states that the shape of a mark in a TMrich RE-TM alloy film having a large saturation magnetization Ms is easily deformed by a recording magnetic field. Have been.
[0007]
In other words, when the outer peripheral portion of the mark is deformed irregularly in the mark forming process, the area of the domain wall increases, and the domain wall energy Ew increases. However, since the area where the positive and negative magnetizations are close to each other increases, the magnetostatic energy increases. Em decreases. At this time,
Change in domain wall energy ΔEw> Change in magnetostatic energy | −ΔEm |
In this case, even if the magnetic domain wall is deformed and irregularities are formed on the outer peripheral portion, the entire magnetic energy is lost, and a mark without deformation is formed to return to the original state.
On the other hand, in the TMrich RE-TM alloy film having a large value of the saturation magnetization Ms, the magnetostatic energy Em increases in proportion to the square of the saturation magnetization Ms,
Change in domain wall energy ΔEw <change in magnetostatic energy | −ΔEm |
, The deformed mark is formed if the outer periphery of the mark has unevenness because the entire magnetic energy is obtained.
[0008]
Therefore, when a blue laser beam is used, it is better to use a TMrich RE-TM alloy film having a large Kerr rotation angle θk, but the TMrich RE-TM alloy film has a lower coercive force Hc and a smaller mark shape. Since the stability is lost, there is a contradictory relationship that it is better to use a composition ratio near the compensation composition and the composition ratio cannot be changed from the viewpoint of the coercive force Hc and the stability of the mark shape.
[0009]
In order to improve the stability of the mark shape and the recording magnetic field sensitivity, a configuration in which a recording layer 5 and an antiferromagnetic layer are stacked has been proposed. For example, International Publication No. WO97 / 48094 discloses a back illumination type magneto-optical recording medium, in which a first dielectric layer, a recording layer, an antiferromagnetic layer, a second dielectric layer, A first dielectric layer, an antiferromagnetic layer, a recording layer, a second dielectric layer, and a reflective layer are laminated in this order on a recording medium (first conventional example of back illumination system) in which reflective layers are laminated in this order and a transparent substrate. Recording medium (back illumination type second conventional example) is described. However, these recording media relate to a back illumination type recording medium and cannot be applied to a front illumination type recording medium as described below.
[0010]
In the front illumination type medium, since laser light is incident from the side of the laminated film, the Kerr rotation angle θk decreases when an antiferromagnetic layer is disposed on the incident side. That is, the laminated structure of the second conventional example of the back illumination system in which the antiferromagnetic layer is laminated on the transparent substrate side (incident side) and the recording layer is laminated thereon cannot be applied to the front illumination system. Further, in a medium of the front illumination type, if a thick film exists between the substrate and the recording film, the surface of the film becomes rough in proportion to the thickness of the film, so that erasing noise increases. That is, the laminated structure of the first conventional example of the back illumination system and the second conventional example of the back illumination system in which the first dielectric layer is laminated on the transparent substrate cannot be applied to the medium of the front illumination system.
[0011]
[Problems to be solved by the invention]
When blue laser light is used to increase the density of a conventional front illumination type recording medium, the Kerr rotation angle θk obtained from the recording layer is reduced. In addition, when the composition of the recording layer is set so that the Kerr rotation angle θk is improved, the stability of the mark shape deteriorates. Furthermore, when an antiferromagnetic layer is used to improve the stability of the mark shape, there is a problem that erasing noise increases.
That is, when a blue laser beam is used to increase the recording density of a conventional front illumination type recording medium, all of the characteristics of the Kerr rotation angle θk, the stability of the mark shape, and the erasing noise cannot be satisfied. Did not.
[0012]
The present invention has been made in view of such circumstances, and even when using a blue laser beam having a short wavelength for high density, there is no decrease in the Kerr rotation angle θk, and the stability of the mark shape is good, It is another object of the present invention to provide a front illumination type magneto-optical recording medium which does not increase erasing noise.
[0013]
[Means for Solving the Problems]
The magneto-optical recording medium according to the first invention is a magneto-optical recording medium in which a heat conductive layer, a recording layer, and a protective layer are laminated in this order on a substrate. A flattening layer for flattening the surface and an antiferromagnetic layer are stacked in this order.
[0014]
A magneto-optical recording medium according to a second invention is characterized in that, in the first invention, the protective layer is formed of a transparent antiferromagnetic material.
[0015]
A magneto-optical recording medium according to a third invention is characterized in that, in the first invention or the second invention, the recording layer is formed of a rare-earth transition metal alloy having transition metal dominance.
[0016]
A magneto-optical recording medium according to a fourth aspect is characterized in that, in any one of the first to third aspects, the Neel temperature of the antiferromagnetic layer is equal to or higher than the Curie temperature of the recording layer.
[0017]
A magneto-optical recording medium according to a fifth aspect of the present invention is the magneto-optical recording medium according to any of the first to fourth aspects, wherein the flattening layer is made of Pd, Cu, Si, Ti, P or Cr containing Ag, Al or Ni as a main component. And a metal material having a surface tension higher than the surface tension of the heat conductive layer.
[0018]
In the first invention, the flattening layer and the antiferromagnetic layer are provided on the light incident side of the heat conducting layer. Therefore, even when blue laser light having a short wavelength is used for high density, It is possible to provide a recording medium in which the angle θk does not decrease, the mark shape is stable, and the erasing noise does not increase.
[0019]
In the second invention, since the protective layer is made of a transparent antiferromagnetic layer, the recording layer is sandwiched between the antiferromagnetic layers, so that the apparent coercive force can be improved and the CNR characteristics can be further improved. It becomes possible.
[0020]
In the third aspect, since the recording layer is made of a rare earth transition metal alloy in which the transition metal is dominant, the Kerr rotation angle θk can be increased.
[0021]
In the fourth aspect, since the Neel temperature of the antiferromagnetic layer is equal to or higher than the Curie temperature of the recording layer, the apparent coercive force Hc of the recording layer can be increased within the temperature range during recording and reproduction.
[0022]
In the fifth invention, the flattening layer is made of a material containing Ag, Al or Ni as a main component and containing at least one of Pd, Cu, Si, Ti, P and Cr. The flattening can be performed with high accuracy. In addition, since the flattening layer is made of a metal material having a surface tension stronger than the surface tension of the heat conductive layer, it is possible to reliably and accurately flatten the surface.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.
<Embodiment 1>
FIG. 1 is a configuration diagram of the magneto-optical recording medium according to the first embodiment.
In the recording medium according to the first embodiment, reference numeral 1 denotes a substrate, for example, polycarbonate is used. On the substrate 1, a heat conductive layer 2, a planarizing layer 3, an antiferromagnetic layer 4, a recording layer 5, and a protective layer 6 are laminated in this order. The recording medium according to the first embodiment is a front illumination type recording medium that records and reproduces information by making a laser beam LB incident on the recording layer 5 via the objective lens L from the side of the protective layer 6. The recording layer 5 is made of a rare earth transition metal alloy (RE-TM alloy), and is TbFeCo here. In addition, as the RE-TM alloy, for example, DyFeCo, GdTbFeCo, or the like can be used. In such a configuration, the composition of the RE-TM alloy forming the recording layer 5 is set to a composition containing a large amount of transition metal (TMrich) so that the Kerr rotation angle θk is increased. Deterioration of the stability of the mark shape caused by changing the RE-TM alloy to TMrich is dealt with by forming the antiferromagnetic layer 4. An increase in erase noise due to surface roughness due to the formation of the antiferromagnetic layer 4 is dealt with by forming the flattening layer 3 having good surface smoothness under the antiferromagnetic layer 4.
[0024]
(Improvement of car rotation angle θk)
FIG. 2 is a graph showing the relationship between the Tb composition ratio and the Kerr rotation angle / coercive force in the TbFeCo recording layer. FIG. 6A shows the relationship between the Tb composition ratio and the Kerr rotation angle θk in the case of a TbFeCo recording layer in which the recording layer 5 is made of TbFeCo, and FIG. 6B shows the relationship between the Tb composition ratio and the coercive force Hc. Show. The horizontal axis is the Tb composition ratio (%), and the vertical axis is the Kerr rotation angle θk (degree) in (a), and the coercive force Hc (kOe) in (b). The value of the coercive force Hc of the recording layer 5 is a value at 100 ° C. Note that 1 (Oe) = 1000 / 4π (A / m). The incident laser light LB is a blue laser light. Further, since the protective layer 6 located on the incident side of the laser beam LB has the function of enhancing the Kerr rotation angle θk, the thickness of the protection layer 6 is set so that the value of “reflectance R × Kerr rotation angle θk” becomes maximum. It is.
[0025]
The smaller the Tb (rare earth) composition ratio (the smaller the Tb content), that is, the larger the FeCo (transition metal) content, the larger the Kerr rotation angle θk. Therefore, the Tb content is reduced from near the conventional compensation composition (Tb composition ratio 24%). To make the composition of the RE-TM alloy TMrich. The Kerr rotation angle θk when the Tb composition ratio is 24% is about 0.55 (degree), and the Kerr rotation angle θk when the Tb composition ratio is 13% is about 0.88 (degree). Is reduced from 24% to 13%, the Kerr rotation angle θk can be improved by about 1.6 times. The coercive force Hc at this time is 15 kOe at a Tb composition ratio of 24% and 2.2 kOe at a Tb composition ratio of 13%. Since the reflectance R does not greatly depend on the composition of the RE-TM alloy, the value of “reflectance R × Kerr rotation angle θk” that contributes to the reproduction signal by increasing the Kerr rotation angle θk even when the reflectance R is the same is calculated as follows. Can be larger. It is desirable that the Tb composition ratio be in a range (about 12 to 20) in which the Kerr rotation angle θk can be surely increased as compared with the case of the compensation composition. Further, in consideration of the balance with the coercive force Hc as described later, the Tb composition ratio is preferably about 13 to 20, more preferably about 14 to 17.
[0026]
(Improved mark stability)
As the coercive force Hc of the recording layer 5 decreases, the recording layer 5 is easily affected by an external magnetic field. As a countermeasure, an antiferromagnetic layer 4 is provided as a base layer of the recording layer 5.
Assuming that the saturation magnetization of the recording layer 5 is Ms, the film thickness is t, and the interface domain wall energy density between the recording layer 5 and the antiferromagnetic layer 4 is σw, it acts between the antiferromagnetic layer 4 and the recording layer 5. The exchange coupling force Hex is Hex = σw / (2Ms × t). By the action of the exchange coupling force, the external magnetic field required for the magnetization reversal of the recording layer 5 becomes “coercive force Hc + exchange coupling force Hex”, so that the apparent coercive force (Hc + Hex) can be increased.
[0027]
An external magnetic field Hr applied to the mark in a direction to crush the mark is
Hwb + Hr> Hstry + He + Hc
If the relationship is satisfied, the mark disappears. Hwb is a magnetic field that acts to eliminate the domain wall of the magnetic domain formed around the mark due to the presence of the mark, and has a magnitude of Hwb = σwb / (2Ms × r) where r is the radius of the mark. In the direction of crushing. Hstray is a leakage magnetic field from the recording layer 5 and has a magnitude proportional to Ms / r.
On the other hand, the leakage magnetic field Hstray is large,
| -Hstory |> He + Hc-Hwb
, The change | -ΔEm | of the magnetostatic energy becomes larger than the change ΔEw of the domain wall energy, so that the outer peripheral portion is deformed unevenly in the direction in which the mark spreads.
[0028]
That is, the conditions for forming a stable minute mark that is not deformed and does not disappear are Hr <Hstry + He + Hc−Hwb and | −Hstra | <He + Hc−Hwb. For example, the saturation magnetization Ms is 400 (emu / cc. 1 (emu / cc) = 4π / 10000 (Wb / m ³ ) = 1.257 mT) When a mark having a radius r = 0.1 μm is formed on the recording layer 5, the magnitude of the magnetic field applied in the direction in which the mark is expanded at the edge of the mark is estimated by simulation to be about 0.69 kOe. However, by designing the apparent coercive force (Hc + Hex) to be equal to or more than the estimated value (about 0.69 kOe), a stable minute mark without deformation can be formed.
It can be considered that the influence of the leakage magnetic field is conceptually smaller than when the antiferromagnetic layer 4 is not provided because the magnetic field lines penetrate into the antiferromagnetic layer 4 to form a magnetic path.
[0029]
In order to increase the apparent coercive force Hc of the recording layer 5 within the temperature range at the time of recording / reproducing, the Neel temperature of the antiferromagnetic layer 4 is the same as or higher than the Curie temperature of the recording layer 5. Further, in the recording medium of the front illumination type, since the heat radiation characteristic is important, a metal material is used for the antiferromagnetic layer 4 so that the thermal conductivity does not deteriorate. For example, PtMn, PtMnCr, or the like can be applied. Further, the antiferromagnetic layer and the recording layer may be alternately laminated to form a multilayer.
[0030]
(Reduction of erase noise)
To increase the effect on the exchange coupling force Hex acting between the antiferromagnetic layer 4 and the recording layer 5, it is conceivable to increase the thickness of the antiferromagnetic layer 4. The film surface of the layer 4 becomes rough, which increases erasing noise. For example, when the antiferromagnetic layer 4 is formed to have a thickness of 30 nm or more and the surface roughness of the film surface exceeds Ra = 0.9 nm, erasing noise in a low frequency region of 10 MHz or less increases. In order to improve the smoothness of the film surface of the antiferromagnetic layer 4, a flattening layer 3 is formed as a base layer of the antiferromagnetic layer 4.
[0031]
FIG. 3 is an explanatory view of the surface shape of the heat conductive layer and the flattening layer of the present invention. FIG. 3A shows the surface shape of the heat conduction layer, and FIG. 3B shows the surface shape of the flattening layer. The heat conductive layer 2 is formed on the side of the substrate 1 where the laser beam LB (not shown) is incident. The heat conductive layer 2 is formed by a DC sputtering method using a solid target of a metal such as Ag or Al, and has a thickness of 20 to 40 nm. Although the surface roughness Ra of the substrate 1 is as small as about 0.3 nm, the surface of the heat conductive layer 2 has irregularities in the process of forming a film by sputtering, and the surface roughness Ra increases to about 0.5 to 1.0 nm. . The surface roughness Ra is offset to form the planarized layer 3 whose surface is planarized.
[0032]
The flattening layer 3 is made of a material containing Ag, Al, or Ni as a main component and a predetermined amount (about several percent) of at least one of Pd, Cu, Si, Ti, P, and Cr by DC sputtering. It is formed. If the film is formed to a thickness of about 5 nm, the unevenness on the surface of the heat conductive layer 2 can be filled, and the surface of the heat conductive layer 2 can be sufficiently flattened.
[0033]
As a method of forming the flattening layer 3, besides this, a single metal having a surface tension larger than the surface tension of the heat conductive layer 2 can be formed at a low gas pressure. Ta, Mo, W, Fe, Co, Ni, Cr, Pt, Ti, or the like having a large surface tension can be used as a simple metal. At the time of this film formation, since the film thickness is as thin as 2 nm or less, or when the film formation gas pressure is high, concavities and convexities of a fine structure are formed on the surface. Is good. When the antiferromagnetic layer 4 is formed on the surface of the flattening layer 3 having good surface smoothness, the exchange coupling force Hex with the recording layer 5 (ferromagnetic material) is improved, and Hex larger than when the surface is roughened. As a result, the apparent coercive force is improved. When the heat conductive layer 2 is made of, for example, Ag, the surface tension of Ag is 1052 (mN / m) at 30 ° C., and therefore, Ta, Mo, W, Fe, Co, Ni, and Cr having a larger surface tension than this. , Pt, Ti and the like can be used. The surface tensions of Ta, Mo, W, Fe, Co, Ni, Cr, Pt, Ti, Au, Cu, and Al at 30 ° C. are 2887, 3023, 3471, 2610, 2590, 2319, 2290, 2096, and 2080, respectively. , 1677, 1422, 1135 (mN / m).
[0034]
(Example 1)
A detailed example of the first embodiment will be described as a first embodiment.
The configuration (material, film thickness, etc.) of each layer is shown below.
Thermal conductive layer 2: Ag, 35 nm
Flattening layer 3: AgPdCuSi, 5 nm
Antiferromagnetic layer 4: PtCrMn, 10 nm
Recording layer 5: TbFeCo (composition ratio Tb: Fe: Co = 13: 68: 19), 25 nm
Protective layer 6: SiN, 50 nm
The thickness of the protective layer 6 of 50 nm was determined so that the reflectance R × Kerr rotation angle θk at the wavelength of 405 nm of the blue laser light was maximized. At this time, the reflectance R = 0.3, the Kerr rotation angle θk = 0.88 degrees, and the reflectance R × the Kerr rotation angle θk = 0.264.
[0035]
Each layer was formed sequentially by DC magnetron sputtering. The gas pressure, target supply power, and the like during the formation of each layer are shown below.
Thermal conductive layer 2: 0.15 Pa, Ag target 0.5 kW
Flattening layer 3: 0.15 Pa, AgPdCu target 0.5 kW, Si target 0.32 kW
Antiferromagnetic layer 4: 0.5 Pa, Pt target 0.5 kW, Cr target 0.1 kW, Mn target 0.3 kW
Recording layer 5: 1.5 Pa, Tb target 0.08 kW, FeCo target 0.25 kW
Protective layer 6: 0.3 Pa, SiN target 0.5 kW
[0036]
The marks were optically modulated and recorded on the recording medium of Example 1, and the CNR (Carrier to Noise Ratio; signal-to-noise ratio) was measured. Using an optical system having a wavelength of blue laser light λ = 405 nm and a numerical aperture NA of the objective lens L = 0.85, a mark length of 0.2 μm under the conditions of a linear velocity of 7.5 m / s, a recording power of 8 mW, and a reproduction power of 3 mW. , And a CNR of 45 dB for a mark length of 0.16 μm.
[0037]
(Comparative Example 1)
For comparison with Example 1, a recording medium without the flattening layer 3 and the antiferromagnetic layer 4 was prepared under the same conditions as in Example 1, and the heat conductive layer 2 (Ag, 40 nm) and the recording layer 5 ( TbFeCo, 25 nm) and a protective layer 6 (SiN, 50 nm). Recording and reproduction were attempted under the same conditions as in Example 1, but there was no margin for the recording magnetic field, and a CNR of 40 dB was obtained with a mark length of 0.2 μm only in the range of 0 to 50 Oe. Since the antiferromagnetic layer 4 is not provided, the mark is deformed by an external magnetic field and noise is increased.
[0038]
(Comparative Example 2)
For comparison with the first embodiment, a recording medium having no flattening layer 3 and a slightly thicker antiferromagnetic layer 4 was prepared under the same conditions as the first embodiment, and a heat conductive layer 2 (Ag, 40 nm) was formed. An antiferromagnetic layer 4 (PtCrMn, 30 nm), a recording layer 5 (TbFeCo, 25 nm), and a protective layer 6 (SiN, 50 nm) were used. When recording and reproduction were performed under the same conditions as in Example 1, a CNR of 45 dB was obtained with a mark length of 0.2 μm, which was 2 dB lower than that in Example 1. This is because the surface of the recording layer 5 is roughened by reflecting the antiferromagnetic layer 4 serving as the underlayer, and the erasing is performed by laminating the thick antiferromagnetic layer 4 on the Ag heat conductive layer 2 having a surface smoothness not so high. This is because noise increased. With respect to the recording magnetic field, no deterioration of the CNR is observed up to 250 Oe, and the effect of the antiferromagnetic layer 4 is somewhat observed, but there is no recording magnetic field margin as in the first embodiment. It is considered that this is because the exchange coupling force between the recording layer 5 and the antiferromagnetic layer 4 is weakened by the roughening of the film surface of the antiferromagnetic film 4.
[0039]
(Example 2)
A second embodiment will be described in which the structure of the flattening layer 3 of the first embodiment is Ta having a thickness of 5 nm, that is, a metal having a higher surface tension than the heat conductive layer 2. The deposition conditions for the planarizing layer 3 are a gas pressure of 0.15 Pa and a target power of 0.5 kW. Other configurations and film forming conditions were the same as in Example 1. The same CNR was obtained under the same evaluation conditions as in Example 1. With respect to the recording magnetic field, no decrease in CNR was observed even at +500 Oe. This is presumably because the surface roughness Ra of the flattening layer 3 was 0.5 nm or less, and a stronger exchange coupling force than that of AgPdCuSi worked to stabilize the fine marks.
[0040]
<Embodiment 2>
FIG. 4 is a configuration diagram of the magneto-optical recording medium according to the second embodiment. The protective layer 6 in the first embodiment is replaced with a transparent antiferromagnetic layer 6a, and the recording layer 5 is sandwiched between the antiferromagnetic layer 4 and the transparent antiferromagnetic layer 6a to further reduce the apparent coercive force Hc. Can be larger. The reason why the transparent antiferromagnetic layer 6a is made transparent is that it is disposed on the laser beam incident side. Examples of materials applicable to the transparent antiferromagnetic layer 6a include NiO, Cr (2 atoms) O (3 atoms), α-Fe (2 atoms) O (3 atoms), and the like.
[0041]
(Example 3)
A detailed example of the second embodiment will be described as a third embodiment. The only difference is that the protective layer 6 in the first embodiment is replaced with a transparent antiferromagnetic layer 6a, and the protective layer 6 (SiN) in the first embodiment is a transparent antiferromagnetic layer 6a made of NiO. It is. The transparent antiferromagnetic layer 6a (NiO) was formed to a thickness of 46 nm by DC magnetron sputtering in an Ar atmosphere at a gas pressure of 0.3 Pa into which a trace amount of oxygen was introduced. Other configurations of each layer, film forming conditions, and the like are the same as those in the first embodiment. The CNR of the recording medium of Example 3 showed the same characteristics as Example 1 for both the mark lengths of 0.2 μm and 0.16 μm. However, with respect to the recording magnetic field, the CNR was reduced by about 0.5 dB when the recording magnetic field exceeded +450 Oe in Example 1, whereas the CNR was reduced even at the recording magnetic field of +500 Oe in Example 3 using NiO. Was not seen.
(Example 4)
The NiO film forming the transparent antiferromagnetic layer 6a of Example 3 was formed in an Ar atmosphere at a gas pressure of 0.3 Pa by an RF magnetron sputtering method using a NiO target. The configuration of each of the other layers, film forming conditions, and the like are the same as those in the third embodiment. The CNR of the recording medium of Example 4 was 47.3 dB at a mark length of 0.2 μm, which was slightly improved from Example 1. This is probably because the surface of NiO constituting the transparent antiferromagnetic layer 6a became smoother than when the film was formed by a DC magnetron sputtering method using Ar oxygen gas, and scattered light was reduced.
[0042]
【The invention's effect】
As described above in detail, according to the first invention, in the recording medium of the front illumination system, by providing the flattening layer and the antiferromagnetic layer on the light incident side of the heat conducting layer, it is possible to increase the density. Even when blue laser light having a short wavelength is used, it is possible to obtain a recording medium in which the Kerr rotation angle θk does not decrease, the mark shape is stable, and the erasing noise does not increase.
[0043]
According to the second aspect of the invention, by making the protective layer a transparent antiferromagnetic layer, the apparent coercive force can be improved and a recording medium with better CNR characteristics can be obtained.
[0044]
According to the third aspect of the present invention, since the transition metal is predominant in the rare earth transition metal alloy of the recording layer, the Kerr rotation angle can be increased, and a recording medium having good CNR characteristics can be obtained.
[0045]
According to the fourth aspect of the invention, it is possible to provide a recording medium having a good CNR characteristic in which the apparent coercive force Hc of the recording layer can be increased within the temperature range during recording and reproduction.
[0046]
According to the fifth aspect, the flattening layer can be surely flattened, and a recording medium having good CNR characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a magneto-optical recording medium according to a first embodiment.
FIG. 2 is a graph showing a relationship between a Tb composition ratio and a Kerr rotation angle / coercive force in a TbFeCo recording layer.
FIG. 3 is an explanatory view of a surface shape of a heat conductive layer and a planarizing layer of the present invention.
FIG. 4 is a configuration diagram of a magneto-optical recording medium according to a second embodiment.
FIG. 5 is a configuration diagram of a conventional magneto-optical recording medium.
[Explanation of symbols]
1 substrate
2 Thermal conduction layer
3 Flattening layer
4 Antiferromagnetic layer
5 Recording layer
6 Protective layer
6a Transparent antiferromagnetic layer
L Objective lens
LB laser light

Claims (5)

In a magneto-optical recording medium in which a heat conductive layer, a recording layer and a protective layer are laminated in this order on a substrate, a flattening layer for flattening the surface of the heat conductive layer is provided between the heat conductive layer and the recording layer. A magneto-optical recording medium, wherein a ferromagnetic layer is laminated in this order. 2. The magneto-optical recording medium according to claim 1, wherein said protective layer is formed of a transparent antiferromagnetic material. 3. The magneto-optical recording medium according to claim 1, wherein the recording layer is formed of a rare earth transition metal alloy having a transition metal dominance. 4. The magneto-optical recording medium according to claim 1, wherein the Neel temperature of the antiferromagnetic layer is equal to or higher than the Curie temperature of the recording layer. The flattening layer is made of a material containing Ag, Al, or Ni as a main component and containing any one or more of Pd, Cu, Si, Ti, P, and Cr, or stronger than the surface tension of the heat conductive layer. 5. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is formed of a metal material having a surface tension.

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