JP2844604B2 - Magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording / reproducing information using a laser beam or the like by utilizing a magneto-optical effect, and in particular, to suppress corrosion and pitting corrosion. The present invention relates to a magneto-optical recording medium capable of stably maintaining magneto-optical characteristics while maintaining stability.

[Summary of the Invention]

According to the present invention, an artificial lattice film in which Co layers and Pt layers and / or Pd layers are alternately stacked is used as a recording layer, and the total thickness of the recording layer is set to 50%.
By setting the angle to 800 °, it is an object to provide a magneto-optical recording medium capable of stably maintaining magneto-optical characteristics while suppressing corrosion and pitting.

Further, the present invention provides a magneto-optical recording medium having the above-mentioned artificial lattice film as a recording layer, by forming a base film made of at least one of Cu, Rh, Pd, Ag, W, Ir, Pt and Au. It is intended to further improve the magnetic force.

[Related Art] In recent years, as a rewritable high-density recording method, a magneto-optical recording method in which recording and reproduction are performed using a semiconductor laser beam or the like has attracted attention.

As a recording material used in this magneto-optical recording method,
An amorphous alloy combining rare earth elements such as Gd, Tb, and Dy with transition elements such as Fe and Co has been a typical example in the past. However, the rare earth elements and Fe constituting these amorphous alloys are very easily oxidized, and easily bond with oxygen in the air to form oxides. If such oxidation progresses and leads to corrosion or pitting, the signal will be lost.In particular, when the rare earth metal undergoes selective oxidation, the C / N ratio decreases with the decrease in coercive force and remanent magnetic Kerr rotation angle. Is deteriorated. Such a problem cannot be avoided as long as a rare earth element is used.

On the other hand, Co-Pt-based or Co-Pd-based materials using noble metals such as Pt and Pd instead of rare earth elements have excellent corrosion resistance, and are expected to be applied as recording materials for magnetic recording media, for example. ing.

However, regarding these Co-Pt or Co-Pd materials, Journal of Magnetism and Agnetic Materials (Journal of Mag.
Netism and Magnetic Materials) No. 66, pp. 351-355 (1987), etc., only perpendicular magnetic anisotropy has been found in a relatively thick layer thickness region of about 2000 mm. Application to magneto-optical recording media has not been attempted yet.

[Problems to be solved by the invention]

Therefore, the present invention has been proposed in view of the above-described conventional circumstances, and uses a noble metal element instead of a rare earth element to stably maintain the magneto-optical characteristics while effectively suppressing corrosion and pitting. It is an object of the present invention to provide a magneto-optical recording medium capable of performing the above.

[Means for solving the problem]

The inventors of the present invention have repeatedly studied to achieve the above-described object, and as a result, an artificial lattice film in which a Co layer and a Pt layer and / or a Pt layer having a predetermined layer thickness are superlatticely stacked has an extremely large thickness. The present inventors have found that good magneto-optical properties are exhibited in a thin region, and that this artificial lattice film can be used for magneto-optical recording, and have led to the present invention.

That is, the magneto-optical recording medium according to the present invention has a Co layer
An artificial lattice film in which Pt layers and / or Pd layers are alternately laminated is used as a recording layer, and the total thickness of the recording layer is 50 to 800 °.

Further, the magneto-optical recording medium according to the present invention has a Co layer and Pt
A magneto-optical recording medium, wherein the recording layer is an artificial lattice film in which layers and / or Pd layers are alternately stacked, and the total thickness of the recording layer is 50 to 800 °, wherein Cu, Rh, Pd, Ag, W , Ir, Pt, and Au.

First, an artificial lattice film that can be used as a recording layer in the magneto-optical recording medium according to the present invention is a Co-Pt-based artificial lattice film in which a Co layer and a Pt layer are laminated, and a Co-Pd in which a Co layer and a Pd layer are laminated.
System artificial lattice film and three layers of Co layer, Pt layer and Pd layer
It is a Co-Pt-Pd-based artificial lattice film.

In any case, the total thickness of the artificial lattice film serving as the recording layer is preferably in the range of 50 to 800 °. this is,
If the ratio is out of the range, the magneto-optical characteristics such as the magnetic Kerr rotation angle and the coercive force are deteriorated.

In particular, in the case of a Co-Pt-based artificial lattice film, the Co layer is 2 to 8２〜,
More preferably, the Pt layer has a thickness of 3 to 40 ° and a total thickness of 50 to 400 °, and exhibits good magneto-optical characteristics in such a range. Of course, the magneto-optical characteristics are exhibited in a range other than this, for example, a region having a layer thickness of 800 mm or less, but the squareness ratio is slightly reduced in a region exceeding 400 mm.

Similarly, in the case of a Co—Pd-based artificial lattice film, Co layers 1 to 9
Å, Pd layer 2２〜40Å, total thickness 50〜800Å exhibit good magneto-optical properties.

The above range of the layer thickness is set from the viewpoint of optimizing the magneto-optical characteristics. In any case, outside the above-mentioned range, an in-plane magnetization component is generated and the magneto-optical characteristics deteriorate.

In the case of a Co-Pt-Pd-based artificial lattice film, the laminated structure may be a layer in which a Co layer and a Pt-Pd alloy layer are alternately laminated, or a Co layer-Pt layer-Co layer- Pd layer-or Co
The layers may be stacked in the order of layer-Pt layer-Pd layer-Co layer-.

The interface between the metal layers constituting the above-described artificial lattice films is ideally formed as a superlattice structure in which heterogeneous metal atoms are formed flat without disturbing each other, and ideally a so-called superlattice structure. May have a so-called modulation structure (composition modulation structure) in which the composition fluctuates while maintaining a fixed period as a whole while causing the above.

The above artificial lattice film can be formed by sputtering, vacuum evaporation, molecular beam epitaxy (MBE), or the like.

In this case, in the case of a two-component system such as a Co-Pt system or a Co-Pd system, the evaporation source must be prepared independently for each component metal. In the case of a three-component system such as a Co-Pt-Pd system, in addition to a method of independently preparing an evaporation source for each component metal, particularly, a method of combining Pt and Pd to form an alloy evaporation source. Alternatively, a method in which an evaporation source of a small amount of component metal is placed on an evaporation source of another metal is also possible. For example, when a three-component magneto-optical recording medium as described above is prepared by sputtering, simultaneous dual sputtering using a Pd target on which a Pt chip is mounted and a Co target, a Co target, a Pd target, and a Pt target are used. Simultaneous ternary sputtering used,
Alternatively, a method such as simultaneous quaternary sputtering in which each metal layer is stacked in the order of Co-Pd-Pt-Pd- using a Co target, a Pt target, and two Pd targets, is possible.

In addition, various elements may be appropriately added to the artificial lattice film as additional elements for the purpose of increasing thermal stability or reducing the Curie point.

In this case, the optimum added element and the added amount differ depending on the type of the artificial lattice film and the type of the metal layer to be added.

For example, in an artificial lattice film in which a Co layer and a Pt layer are stacked, when an additive element is added to the Co layer, the Co layer is made of Co.
_100-x M _x (where x represents the substitution amount in atomic% and M represents an additive element), and the additive element M is B, C, A
l, Si, P, Ti, V, Fe, Ni, Cu, Ga, Ge, Zr, Nb, Mo, In, Sn, Sb, Gd, T
It is preferably at least one of b, Dy, and Ta. The optimum substitution amount is slightly different for each element, and when M = Al, 0.1 ≦
x ≦ 7, 0.1 ≦ x ≦ 14 when M = Zr, 0.1 ≦ x ≦ 20 when M = Si, Mo, Ta, 0.1 ≦ x ≦ 25 when M = Fe, M = B, C, T
0.1 ≦ x ≦ 30 for i, V, Cu, Ga, Ge, Nb, In, Sn, 0.1 ≦ x ≦ 35 for M = P, 0.1 ≦ x ≦ 40 for M = Gd, Tb, Dy, M =
In the case of Sb, 0.1 ≦ x ≦ 45, and in the case of M = Ni, 0.1 ≦ x ≦ 70.

The lower limit of the substituent x of each of the above elements is 0.1 atomic%, but if it is lower than this, the effect of reducing the Curie point does not appear. The upper limit of the substitution amount x of each element differs from 7 to 40 at% depending on the element to be added. However, if the upper limit is higher than these values, the magneto-optical characteristics may be deteriorated instead.

Further, the third element described above is added to the Pt layer, and the composition of the Pt layer is represented by Pt _100-x M _x (where x represents the substitution amount in atomic%,
0 ≦ x ≦ 15, and M represents an additive element. However, in this case, the main purpose should be to adjust the Curie point, not to improve the magneto-optical characteristics and thermal stability. This is because when the third element is added to the Pt layer, the Curie point increases and the magnetic Kerr rotation angle decreases with some exceptions. However, since the Curie point does not have to be infinitely low from the viewpoint of protection of recorded information, the Curie point of the recording layer should be raised to a practical range by such means when the Curie point of the recording layer is extremely low. It is possible. Elements that can be added to the Pt layer include, in addition to the same elements as the Co layer, Cr, Mn, Co, Zn, Y, Rh, Ag, La, Nd, Sm, Eu, Ho, Hf,
W, Ir, Au, Pb, Bi and the like. Further, the Pt layer may be replaced with Pd at an arbitrary ratio.

On the other hand, in the artificial lattice film in which the Co layer and the Pd layer are laminated,
When an additional element is added to the Co layer, the Co layer is
_100-x M _x (where x represents the substitution amount in atomic% and M represents an additive element), and P, Ti, V, N
It is preferably at least one of i, Ga, Ge, B, C, Al, Si, Fe, Cu, Zr, Nb, Mo, In, Sn, Sb, Ta, and W. Also in this case, the optimum amount of addition depends on the type of the added element.
0.1 ≦ x ≦ 10, M = P, for Al 0.1 ≦ x ≦ 12, M = Sn, Sb,
0.1 ≦ x ≦ 20 for W, 0.1 for M = Ti, V, Ni, Ga, Ge, Nb
≦ x ≦ 25, M = B, C, Si, Fe, Cu, Mo, In 0.1 ≦ x ≦ 3
0, when M = Ta, 0.1 ≦ x ≦ 40. The reason for the limitation is
This is the same as the case of the Co-Pt-based artificial lattice film.

Further, an additional element may be added to the Pd layer. In this case, the type and amount of the additional element are the same as in the case of the Pt layer.

Further, prior to forming the above-described artificial lattice film as a recording layer, a base film may be first formed on a suitable substrate such as glass by sputtering, vacuum deposition, MBE or the like.

As an element constituting this underlayer, at least one of Cu, Rh, Pd, Ag, Ir, Pt, Au having a face-centered cubic structure (fcc structure) and W having a body-centered cubic structure (bcc structure) Is used. The types of elements exhibiting particularly remarkable effects are slightly different depending on the type of the recording layer formed on the underlayer. For example, in the case of a Co-Pt recording layer, the underlayer of Pd, Ag, W, Pt, and Au is used. In the case of a Co-Pd-based recording layer, it is effective to use a Pd, Ag, Pt, Au underlayer. These elements may be used alone or in combination of two or more.

The thickness of the underlayer is preferably 5 to 5000 °, and more preferably 5 to 500 °. If the thickness of the underlayer is too small, the coercive force is not sufficiently improved. Conversely, if the thickness is too large, the coercive force reaches saturation, so that no further effect can be expected. In particular, when reading a signal from the substrate side (that is, the base film side), the angle is preferably 10 to 200 °, and when reading a signal from the artificial lattice film side, 200 to 2 ° is preferable.
Preferably it is 000 °.

As a writing method for such a magneto-optical recording medium, in addition to a light beam, any method such as a needle-type magnetic head, a hot pen, and an electron beam can be used as long as it can supply the energy necessary to generate a reversal magnetic domain. But it goes without saying that it is good.

[Action]

A magneto-optical recording medium having a recording layer of an artificial lattice film in which at least one of Co and Pt or Pd is alternately laminated has excellent corrosion resistance because it does not contain a rare earth element. And
Particularly, when the total thickness is 50 to 800 °, extremely good magneto-optical characteristics are achieved.

In such a magneto-optical recording medium, Cu, Rh, Pd, Ag, G
When a base film made of at least one of d, W, Ir, Pt, and Au is formed, the coercive force is greatly improved.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

First Embodiment This embodiment is an example of a Co-Pt magneto-optical recording medium in which a recording layer is a metal film in which Co layers and Pt layers are alternately superlatticely stacked.

First, Co and Pt targets each having a diameter of 100 mm were set in the chamber. A glass substrate was placed at a position facing these targets, and binary simultaneous sputtering was performed while rotating the glass substrate at a predetermined speed (6 to 60 rpm) in an argon atmosphere at a predetermined gas pressure. At this time, DC sputtering (input power: 0.2 to 1A, 300
V) and Pt for DC sputtering (input power: 0.
(2 to 1 A, 300 V) or high frequency sputtering (input power: 200 to 500 W) was performed, and Co layers and Pt layers were alternately laminated on a glass substrate to form a recording layer having a predetermined total thickness.

FIG. 1 shows the actually formed Co of each recording layer having a total thickness of 100 mm.
The layer thicknesses of the layer and the Pt layer are shown. In the figure, the vertical axis represents the layer thickness of the Co layer (Å), and the horizontal axis represents the layer thickness of the Pt layer (Å). Here, 2.5 ° for Co and 2.8 ° for Pt correspond to the thickness of one atomic layer. Each point in the drawing represents the layer thickness of each atomic layer in each formed recording layer, and a thick line frame indicates a preferable range of the layer thickness of each layer. The fact that each recording layer was a superlattice metal film was confirmed by small-angle X-ray scattering.

Of these recording layers, the results of measuring the magneto-optical effect at a wavelength of 780 nm from the recording layer side using a polar car measuring device were measured for some of the recording layers existing within the thick line frame shown in FIG. 2 (A) to 2 (C). The recording layer was 100 g at 5 mTorr argon gas pressure.
Å is formed in the entire thickness, and FIG.
(Co = 3.3 °, Pt = 6.2 °), FIG. 2 (C) shows the point b (Co =
4.5Å, Pt = 6.3Å), FIG. 2 (C) shows the point c (Co = 6Å, Pt)
= 11 °) shows a magnetic Kerr curve of the recording layer corresponding to (11). The vertical axis represents the magnetic car rotation angle (°), and the horizontal axis represents the intensity of the external magnetic field (kOe). From these figures, it can be seen that the squareness ratio of each recording layer is 1, indicating that the recording layers have extremely good magneto-optical characteristics. Here, the squareness ratio is a ratio (= θ _K ^r /) of the rotation angle θ _K ^r of the residual magnetic Kerr and the rotation angle θ _K ^s of the saturated magnetic Kerr.
θ _K ^s ), and indicates that the closer this value is to 1, the better the C / N ratio during reproduction becomes.

On the other hand, for comparison, a recording layer in which the thickness of each atomic layer does not belong to the frame of the bold line was formed in the same manner, and the results of measuring the magneto-optical characteristics are shown in FIGS. 3 (A) and 3 (B). ). FIG. 3A shows a point d (Co = 3.3 °, Pt = 2.8 °),
FIG. 3B shows a magnetic Kerr curve of the recording layer corresponding to the point e (Co = 0.6 °, Pt = 1.7 °). Looking at these figures,
All of the recording layers have a coercive force close to zero, indicating that they do not serve as a magneto-optical recording medium.

The same measurement was performed for the other recording layers, and the coercive force determined from the magnetic Kerr curve is shown in FIG. 4, and the magnetic Kerr rotation angle is shown in FIG. From these figures, values of several tens to 200 Oe can be obtained as the coercive force, and the magnetic car rotation angle is the highest.
It was found that a large value of 0.5 ° was obtained.

Next, the results of measuring the Curie points of some recording layers are shown in FIG. The Curie point is first measured in a vacuum at a wavelength of 78
After measuring the magneto-optical properties of each recording layer at 0 nm, 500
The temperature was raised while applying an Oe magnetic field, and the temperature (° C.) at which the magnetic Kerr rotation angle became zero was determined.
The Curie points are distributed in a range of approximately 100 to 500 ° C., and it is understood that these recording layers can be used in a practical temperature range as a magneto-optical recording medium and can be arbitrarily set depending on the thickness of each atomic layer. It is also possible to change the Curie point by adding another element.

Next, the manner in which the magneto-optical characteristics of the recording layer depended on the argon gas pressure during sputtering was examined. As an example,
The thickness of each atomic layer is the point h (Co = 6Å, Pt = 17.2) in FIG.
A recording layer having a total thickness of 100 mm was formed by sputtering under various argon gas pressures, and the magneto-optical characteristics were measured to determine the coercive force and the squareness ratio. FIG. 7 shows these values plotted against the argon gas pressure. In the figure, the vertical axis represents coercive force (Oe) or squareness, and the horizontal axis represents argon gas pressure (mTorr).
Black circle plots indicate coercive force, and white circle plots indicate squareness ratio. FIGS. 8A to 8C show magnetic Kerr curves under typical argon gas pressures. FIG. 8 (A) shows a case where the argon gas pressure is 5 mTorr.
FIG. 8 (B) shows the case of 11 mTorr, and FIG. 8 (C) shows the case of 25 mTorr.
Respectively. FIG. 7 and FIG.
From FIGS. 8A to 8C, the coercive force sharply decreases from around 11 mTorr and the squareness ratio sharply decreases from around 16 mTorr.
5mTorr argon gas pressure for good magneto-optical properties
It turned out to be near.

Next, the total thickness dependency of the magneto-optical characteristics of the same recording layer was examined. The argon gas pressure during sputtering was set to 5 mTorr based on the above experimental results. The results are shown in FIG. In the figure, the vertical axis indicates the magnetic Kerr rotation angle (°), the squareness ratio or coercive force (Oe), the horizontal axis indicates the total thickness (Å), the black circle plot indicates the magnetic Kerr rotation angle, the white circle plot indicates the squareness ratio, The black triangle plots represent the coercive force, respectively. In this figure, the squareness ratio sharply drops from around 400 °, and the magnetic Kerr rotation angle and the coercive force show a change with a maximum value. The total thickness at which the magnetic Kerr rotation angle is maximized is generally in the range of 80 to 150 ° depending on the layer thickness of each atomic layer, and has a substantially constant low value when the total thickness is 500 ° or more. Therefore, the value of the magnetic Kerr rotation angle shown in FIG. 5 can be said to be a substantially maximum value.

FIG. 10 (A) and FIG. 10 (A) show the results of looking at the total thickness dependence of the magneto-optical characteristics of another recording layer using a magnetic Kerr curve.
It is shown in FIG. In this recording layer, the thickness of each atomic layer is the first.
It is represented by a point g (Co = 3.5 °, Pt = 5.4 °) in the figure, and was prepared with an argon gas pressure of 4 mTorr. FIG. 10 (A) shows a total thickness of 100 °, and FIG. This corresponds to a case of a total thickness of 500 mm. This figure shows that the recording layer having a total thickness of 100 mm has better magneto-optical characteristics than the recording layer having a total thickness of 500 mm, and corresponds to the tendency shown in FIG. 9 described above.

The fact that the magnetic Kerr rotation angle increases in a region where the layer thickness is extremely small is a characteristic characteristic of the magneto-optical recording medium according to the present invention, and is extremely advantageous for improving the transfer rate and the recording density.

Next, the corrosion resistance of the Co—Pt-based recording layer was examined by an accelerated deterioration test. First, the thickness of each atomic layer is set to the point C in FIG.
(Co = 6t, Pt = 11Å) The Co-Pt-based recording layer with a total thickness of 100Å is left for a certain period of time in a high-temperature and humid environment of 80 ° C and 75% relative humidity, and the change in magneto-optical characteristics is examined. Was. The result is shown in FIG. In the figure, the vertical axis represents the coercive force reduction rate (H _{c (t)}
/ H _{c (t} = ₀ )) or reduction rate of magnetic Kerr rotation angle (θ _{K (t)}
/ Θ _{K (t} = ₀ )), the horizontal axis represents the standing time (hours), the white circle plot represents the coercive force, and the black circle plot represents the magnetic Kerr rotation angle. Here, the decrease rate of the coercive force is the coercive force after standing for a certain time with respect to the coercive force _{Hc (t} = ₀ ) before leaving.
_{Hc (t)} , and the rate of decrease in the magnetic car rotation angle is the magnetic car rotation angle θ _{K (t)} after standing for a certain time with respect to the magnetic car rotation angle θ _{K (t} = ₀ ) before standing. Is the ratio of Further, typical magnetic Kerr curves in this experiment are shown in FIGS. 12 (A) and 12 (B). FIG. 12A corresponds to the Co-Pt-based recording layer before standing, and FIG. 12B corresponds to the Co-Pt-based recording layer after standing for 300 hours. From these figures, it was found that the degradation of the magneto-optical characteristics was practically negligible even when left for 300 hours in a high-temperature and humid environment, and almost no degradation was observed particularly within 100 hours.

Further, the layer thickness of each atomic layer is set at the point a (Co = 3.3Å,
An accelerated deterioration test was also performed under another condition for a Co-Pt-based recording layer having a total thickness of 100 mm expressed by Pt = 6.2 mm). The results are shown in FIGS. 13 (A) to 13 (D). Where the thirteenth
Figure (A) is before leaving, Figure 13 (B) is one week after leaving in the air,
FIG. 13 (C) shows the magnetic card of each recording layer 5 hours after the start of the accelerated deterioration test in a high-temperature and humid environment at a temperature of 80 ° C. and a relative humidity of 90%, and FIG. Each curve is shown. From these figures, it can be seen that this recording layer maintains a sufficient coercive force and a squareness ratio close to 1, and has extremely stable magneto-optical characteristics, although the magnetic Kerr rotation angle slightly decreases after 100 hours from the start of the accelerated deterioration test. I understood.

As a comparison with this experiment, a similar test was performed on a recording layer containing rare earth element Tb instead of Pt. The recording layer used had a total thickness of 200 ° formed by alternately laminating about one atomic layer of a Tb layer and about two atomic layers of a Co layer. The results are shown in FIGS. 14 (A) to 14 (E). Where
14 (A) is before leaving, FIG. 14 (B) is one week after standing in the air, and FIG. 14 (C) is two hours after the start of the accelerated deterioration test in a high temperature and humidity environment of 80 ° C. and 90% humidity. FIG. 14 (D) shows the magnetic Kerr curve of each recording layer 5 hours after the start of the accelerated deterioration test, and FIG. 14 (E) shows the magnetic Kerr curve of each recording layer 30 hours after the start of the accelerated deterioration test. From these figures, it can be seen that the magneto-optical properties of this recording layer were significantly degraded after one week in the air, and the magneto-optical properties were no longer lost 2 hours after the start of the accelerated test.

Second Embodiment This embodiment is an example of a Co-Pd-based magneto-optical recording medium in which a recording layer is a metal film in which Co layers and Pd layers are alternately superlatticely stacked.

First, Co and Pd targets each having a diameter of 100 mm were set in the chamber. A glass substrate was placed at a position facing these targets, and binary simultaneous sputtering was performed while rotating the glass substrate at a predetermined speed (6 to 60 rpm) in an argon atmosphere at a predetermined gas pressure. At this time, DC sputtering (input power: 0.2 to 1A, 300
V), DC sputtering for Pd (input power: 0.
(2 to 1 A, 300 V) or high-frequency sputtering (input power: 200 to 500 W) was performed, and a Co layer and a Pd layer were alternately laminated on a glass substrate to form a recording layer having a predetermined total thickness.

FIG. 15 shows the actually formed Co of each recording layer having a total thickness of 150 mm.
The layer thicknesses of the layer and the Pt layer are shown. In the figure, the vertical axis represents the layer thickness (Co) of the Co layer, and the horizontal axis represents the layer thickness (Å) of the Pd layer. Here, 2.5 ° for Co and 2.8 ° for Pd correspond to the thickness of one atomic layer. Each point in the drawing represents the layer thickness of each atomic layer in each formed recording layer, and a thick line frame indicates a preferable range of the layer thickness of each atomic layer. The fact that each recording layer was a superlattice metal film was confirmed by small-angle X-ray scattering.

Of these recording layers, the results of measuring the magneto-optical effect at a wavelength of 780 nm from the recording layer side using a polar car measuring device for a representative example of the recording layer present in the thick line frame shown in FIG. These are shown in FIGS. 16 (A) and 16 (B). The recording layer was 150 g at an argon gas pressure of 11 mTorr.
Å is formed in the entire thickness, and FIG.
(Co = 3.8 °, Pd = 7.8 °), and FIG. 16 (B) shows the point j (Co =
3 °, Pd = 6.6 °) showing the magnetic Kerr curve of the recording layer. From these figures, it can be seen that the squareness ratio of each recording layer is 1, indicating that the recording layers have extremely good magneto-optical characteristics.

The same measurement was performed on the other recording layers, and the coercive force obtained from the magnetic Kerr curve is shown in FIG. 17, and the magnetic Kerr rotation angle is shown in FIG. From these figures, a coercive force of several hundred to 2,000 Oe was obtained, and the magnetic car rotation angle was the highest.
It was found that a large value of 0.2 ° was obtained.

Next, the results of measuring the Curie points of several Co—Pd-based recording layers are shown in FIG. Curie point is about 100-5
It can be seen that these recording layers can be used in a practical temperature range as a magneto-optical recording medium, and can be arbitrarily set depending on the thickness of each atomic layer. It is also possible to change the Curie point by adding another element.

Next, the manner in which the magneto-optical characteristics of the recording layer depended on the argon gas pressure during sputtering was examined. As an example,
The layer thickness of each atomic layer is the point i (Co = 3.8 °, Pd = 7.8 in FIG. 15).
The recording layer having a total thickness of 150 mm represented by で) was formed by sputtering under various argon gas pressures, and the magneto-optical characteristics were measured to determine the coercive force and the squareness ratio. These values are plotted against the argon gas pressure.
See Figure 20. In the figure, the black circle plot indicates the coercive force, and the white circle plot indicates the squareness ratio. 21 (A) to 21 (C) show magnetic Kerr curves under typical argon gas pressures. FIG. 21 (A) shows the case where the argon gas pressure is 5 mTorr, and FIG. 21 (B) shows the case where the argon gas pressure is 11 mTorr.
FIG. 1 (C) corresponds to the case of 25 mTorr. From the above FIG. 20 and FIGS. 21 (A) to 21 (C),
As the argon gas pressure increases, the coercive force increases while the squareness ratio is kept at 1. From the viewpoint of magneto-optical characteristics, it is particularly preferable that the argon gas pressure be as high as 11 mTorr or more.

Next, the total thickness dependency of the magneto-optical characteristics of the same recording layer was examined. The argon gas pressure during sputtering was set to 11 mTorr based on the above experimental results. The results are shown in FIG. In the figure, the vertical axis indicates the magnetic Kerr rotation angle (°), the squareness ratio or coercive force (Oe), the horizontal axis indicates the total thickness (Å), the black circle plot indicates the magnetic Kerr rotation angle, the white circle plot indicates the squareness ratio, The black triangle plots represent the coercive force, respectively. According to this figure, the squareness ratio is good up to around 800 °, and gradually decreases when it exceeds 800 °. Since the coercive force and the rotation angle of the magnetic car show a maximum value, the optimum total thickness considering various characteristics is 150 mm.
It can be said that it is near. It is for this reason that various experimental data in the present embodiment are described for a case where the total thickness is 150 mm.

Therefore, the results of looking at the total thickness dependence of the magneto-optical characteristics of another recording layer using a magnetic Kerr curve are shown in FIG. 23 (A) and FIG.
It is shown in FIG. In this recording layer, the thickness of each atomic layer is 15th.
It is represented by a point k (Co = 2.5 °, Pd = 8.4 °) in the figure, and was prepared with an argon gas pressure of 11 mTorr. FIG. 23 (A) shows a total thickness of 200 °, and FIG. This corresponds to a case of a total thickness of 500 mm. From this figure, it can be seen that the recording layer having a total thickness of 200 mm is superior to the recording layer having a total thickness of 500 mm.

Third Embodiment This embodiment is an example of a Co-Pt-Pd-based magneto-optical recording medium using a ternary metal film composed of Co, Pt, and Pd as a recording layer.

In the case of a three-component system, several systems can be considered for lamination, unlike the two-component system as in the above-described first or second embodiment. One of them is a method of laminating a Pt-Pd alloy layer and a Co layer by utilizing the fact that Pt and Pt form a complete solid solution system as shown in FIG. For example, when this is formed by sputtering, simultaneous binary sputtering using a Pt-Pd alloy target and a Co target is conceivable. More simply, instead of using a Pt-Pd alloy target, a Pd chip may be placed on the Pt target (or vice versa).

Alternatively, each metal layer can be laminated by simultaneous ternary sputtering using independent targets for each of the three components.

Further, the number of layers of the Pt layer and the Pd layer does not necessarily have to be the same. For example, a multilayer structure such as Co-Pd-Pt-Pd-... Can be formed by simultaneous quaternary sputtering.

When performing sputtering, direct current sputtering (input power: 0.2 to 1 A, 300 V) for Co, Pt, Pd,
For the Pt-Pd alloy, DC sputtering (input power: 0.1 to 1 A, 300 V) or high-frequency sputtering (input power: 200 to 500 W) is performed.

FIG. 25 (A) to FIG. 25 (C) show magnetic Kerr curves of the respective recording layers prepared as described above.
FIG. 25 (A) shows a recording layer having a total thickness of 100 ° by alternately laminating a 2.5 ° thick Co layer and a 7 ° thick Pt—Pd alloy layer by simultaneous binary sputtering. ) Is 2.5mm thick
A Co layer, a Pt layer having a thickness of 2.8 mm, and a Pd layer having a thickness of 2.8 mm were laminated by simultaneous ternary sputtering to make a total thickness of 100 mm. FIG. 25 (C) shows a 2.5 mm thick Co layer. Layer, 2.8mm thick
A Pd layer, a Pt layer having a thickness of 2.8 mm, and a Pd layer having a thickness of 2.8 mm are laminated in this order by simultaneous quaternary sputtering to correspond to a recording layer having a total thickness of 100 mm.

By the way, the Co-Pt-based recording layer described in the first embodiment was characterized in that the coercive force was slightly low (about 200 Oe), but the magnetic Kerr rotation angle was relatively large (about 0.5 °). on the other hand,
The Co-Pd-based recording layer described in the second embodiment was characterized in that a relatively high coercive force (about 500 Oe or more) was obtained, but the magnetic Kerr rotation angle was slightly small (about 0.25 minutes). But,
25 (A) to 25 (C), the recording layer is 3
It can be seen that the magneto-optical characteristics can be adjusted considerably largely by using a component system and changing the lamination method of each metal layer.

Fourth Embodiment In this embodiment, a Co layer and a Pt layer are formed by a dual simultaneous magnetron.
This is an example in which various elements serving as a material of a base film of a magneto-optical recording medium in which a recording layer is a metal thin film alternately stacked by sputtering are examined.

First, a 100 mm diameter target of the element to be the base film material and each of Co and Pt targets are set in the chamber of the magnetron sputtering apparatus, and a water-cooled glass substrate is placed on a rotating base opposed to these targets. Placed.

Next, in order to form a base film, the water-cooled glass substrate is opposed to a target of an element to be a material of the base film,
The thickness of the underlayer was formed. The elements used here are Cu, R
h, Pd, Ag, W, Ir, Pt, Au, but in addition to these elements limited in the present invention, Ti, Al, Si, V, Cr, Mn, Ge, Y, Zr, Nb, Mn, G
e, Y, Zr, Nb, Mo, Sb, Gd and Ta were studied.

Next, binary simultaneous magnetron sputtering was performed in an argon gas atmosphere at a gas pressure of 5 mTorr to form a recording layer on the underlayer. According to this apparatus, the period of the artificial lattice can be arbitrarily determined by changing the input power to each target or the rotation speed of the rotating base on which the water-cooled glass substrate is placed. In this embodiment, Co
DC sputtering (input power: 0.40Å, 30
0V) and Pt were subjected to high frequency sputtering (input power: 400 W), the rotation speed of the rotating base was set to 16 rpm, and the layer thickness of each atomic layer was the point h (Co = 4.3Å, Pt = 5.6Å) in FIG. ), A Co-Pt-based recording layer having a total thickness of 100 ° was prepared, and each sample of the magneto-optical recording medium was prepared. Here, the period of the formed metal thin film was determined from the peak angle in small-angle X-ray scattering.

For comparison, a sample in which a recording layer was formed directly on a glass substrate without providing a base film was also prepared.

Table 1 shows the coercive force of the samples having various underlayers prepared as described above. A horizontal line in the column of coercive force in the table indicates that it did not show perpendicular magnetic characteristics.

Referring to Table 1, the coercive force of the sample without the base film is 125 (Oe). Elements that have an effect of improving the coercive force when used as a base film are Pd, Ag,
W, Pt, Ti, and Gd, but Ti and Gd have small effects. Furthermore, in addition to the elements shown in the same table, Cu, Rh, Ir, and Au improve the coercive force, and those that show a particularly remarkable effect among all the above elements are Pd, Ag, W, Pt, and Au. Met.

Here, FIG. 26 shows the result of examining the relationship between the layer thickness of the base film and the coercive force for Pt, which has the largest coercive force among the above-mentioned elements, and has the largest coercive force. In the figure, the vertical axis represents the coercive force (Oe),
The horizontal axis represents the layer thickness (Å) of the Pt underlayer. According to this figure, the coercive force is about twice as early as the thin layer thickness of 10 mm (21
0 Oe), and it can be seen that it reaches about 7 times (725 Oe) at 100 °.

FIGS. 27A to 27C show magnetic Kerr curves of typical samples having the underlayer films having various thicknesses. FIG. 27 (A) shows the characteristics of a sample without an underlayer, FIG. 27 (B) shows the characteristics of a sample with a 50 ° Pt underlayer, and FIG. 27 (C) shows the characteristics of a sample with a 200 ° Pt underlayer. Things. The vertical axis in the figure is the magnetic car rotation angle θ on a relative scale.
_K (°), and the horizontal axis represents the external magnetic field strength (kOe). From these figures, it can be seen that the provision of the base film not only improves the coercive force but also improves the squareness.

Fifth Embodiment In this embodiment, a Co layer and a Pd layer are formed by a dual simultaneous magnetron.
This is an example in which various elements serving as a material of a base film of a magneto-optical recording medium in which a recording layer is a metal thin film alternately stacked by sputtering are examined.

First, a target with a diameter of 100 mm and a target of Co and Pd of an element to be a base film material are set in a chamber of a magnetron sputtering apparatus, and a water-cooled glass substrate is placed on a rotating base opposed to these targets. Placed.

Next, an underlayer having a thickness of 400 mm was formed on the water-cooled glass substrate according to the method described in the fourth embodiment. The elements used here are the same as in the fourth embodiment.

Next, binary simultaneous magnetron sputtering was performed in an argon atmosphere at a gas pressure of 11 mTorr to form a recording layer on the underlayer. In this embodiment, DC sputtering (input power: 0.35Å, 300 V) is performed for Co and high-frequency sputtering (input power: 350 W) is performed for Pd. Total thickness expressed by point l (Co = 3.5Å, Pd = 5Å) in Fig. 15
A Co-Pd-based recording layer of 100 ° was formed, and each sample of the magneto-optical recording medium was prepared.

For comparison, a sample in which a recording layer was formed directly on a glass substrate without providing a base film was also prepared.

Table 2 shows the coercive force of the samples having various underlayers prepared as described above.

Referring to Table 2, the coercive force of the sample without the base film is 825 (Oe). Elements that have an effect of improving the coercive force when used as a base film are Pd, Ag,
Pt. Further, in addition to the elements shown in the table, Cu, Rh, I
r, Au improved the coercive force, and Pd, Ag, Pt, and Au exhibited the most remarkable effects among all the above elements.

Here, FIG. 28 shows the result of examining the relationship between the layer thickness of the base film and the coercive force of Pd, which has the largest coercive force among the above-described elements, having the greatest improvement. In the figure, the vertical axis represents the coercive force (Oe),
The horizontal axis represents the thickness (層) of the Pd underlayer. From this figure, it can be seen that the effect of improving the coercive force starts to be exhibited even with a thin layer thickness of 10 mm, and reaches about 4 times (3750 Oe) at 400 mm.

29A to 29C show magnetic Kerr curves of representative samples among the samples having the base films having various thicknesses. FIG. 29 (A) shows the characteristics of a sample having no underlying film, FIG. 29 (B) shows the characteristics of a sample having a 50 ° Pd underlying film, and FIG. 29 (C) shows the characteristics of a sample having a 200 ° Pd underlying film. Things. The vertical axis in the figure is the magnetic car rotation angle θ on a relative scale.
_K (°), and the horizontal axis represents the strength (kOe) of the external magnetic field. From these figures, it is clear that the coercive force is improved by providing the base film.

〔The invention's effect〕

As is clear from the above description, the present invention has been considered for use as a recording material for a magnetic recording medium.
Utilizing the fact that a superlattice metal thin film or a modulation structure metal thin film of -Pt or Co-Pd system shows good perpendicular magnetic anisotropy and magneto-optical properties in a thin region with a total thickness of 800 mm or less, This paved the way for application to magnetic recording media.

Further, the present invention relates to a magneto-optical recording medium having such a superlattice metal thin film or a modulation structure metal thin film as a recording layer, wherein a base film comprising at least one of Cu, Rh, Pd, Ag, W, Ir, Pt and Au is provided. Is provided to further improve the coercive force.

The magneto-optical recording medium according to the present invention does not use a rare earth element which is expected to be tightly supplied in the world in the future. Therefore, stable and economical supply of the magneto-optical recording medium can be expected.

If such a magneto-optical recording medium is used as a storage medium for a magneto-optical memory such as a so-called beam-addressable file memory for performing writing using a light beam and performing reading using the magnetic Kerr effect, it is extremely high. A memory device having a high density and a high C / N ratio and maintaining high reliability for a long time can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the thicknesses of a Co layer and a Pt layer in a Co—Pt-based recording layer. 2 (A) to 2 (C) are characteristic diagrams showing magnetic Kerr curves of typical Co-Pt-based recording layers, and FIG. 2 (A) shows a 3.3% Co layer and a 6.2% FIG. 2 (B) is a recording layer in which a 4.5 ° Co layer and a 6.3 ° Pt layer are stacked, and FIG. 2 (C) is a recording layer in which a 6 ° Co layer and 11 ° Pt are stacked.
This corresponds to a recording layer in which layers are stacked. FIGS. 3 (A) and 3 (B) show, as a comparison with FIGS. 2 (A) to 2 (C) described above, the thickness of each atomic layer is not within the range limited by the present invention. FIG. 3A is a characteristic diagram showing a magnetic Kerr curve of a Pt-based recording layer, and FIG.
A recording layer in which a Pt layer and a 2.8 mm Pt layer are laminated, FIG.
This corresponds to a recording layer obtained by laminating a Co layer of Å and a Pt layer of 1.7 そ れ ぞ れ, respectively. FIG. 4 shows the coercive force of a typical Co-Pt based recording layer, FIG. 5 shows the magnetic Kerr rotation angle of a typical Co-Pt based recording layer, and FIG. 6 shows the typical Co-Pt based recording layer. FIG. 4 is a characteristic diagram showing Curie points. Figure 7 shows a 6% Co layer and 17.2
FIG. 4 is a characteristic diagram showing the dependence of the coercive force and the squareness ratio on the argon gas pressure of the recording layer in which the Pt layer is stacked. 8 (A) to 8 (C) are characteristic diagrams showing a magnetic Kerr curve of the same recording layer under a typical argon gas pressure. FIG. 8 (A) shows a case where the argon gas pressure is 5 mTorr. Fig. 8 (B)
8 corresponds to the case where the argon gas pressure is 11 mTorr, and FIG. 8 (C) corresponds to the case where the argon gas pressure is 25 mTorr. FIG. 9 is a characteristic diagram showing the total thickness dependence of the magnetic Kerr rotation angle, squareness ratio and coercive force of the same recording layer. FIGS. 10 (A) and 10 (B) are magnetic Kerr curves showing the total thickness dependence of the magneto-optical properties of a recording layer having a 3.5Å Co layer and a 5.4Å Pt layer laminated. (A) corresponds to the case of a total thickness of 100 mm, and FIG. 10 (B) corresponds to the case of a total thickness of 500 mm. Figure 11 shows 6% of Co
FIG. 9 is a characteristic diagram showing the result of performing an accelerated deterioration test by leaving a recording layer in which a Pt layer and an 11 ° Pt layer are laminated in a high-temperature and humid environment.
12 (A) and 12 (B) are characteristic diagrams showing typical magnetic Kerr curves in the same accelerated deterioration test.
Fig. (A) shows the state before standing, and Fig. 12 (B) shows the start of the accelerated deterioration test.
Each corresponds after 0 hours. Fig. 13 (A)
FIG. 13 (D) is a characteristic diagram showing a magnetic Kerr curve when left in the air or subjected to an accelerated deterioration test under another condition, and FIG. 13 (A) is a diagram before the standing and FIG. 13 (B) Is one week after standing in the air, and FIG. 13 (C) is five hours after the start of the accelerated deterioration test.
FIG. 13 (D) shows the characteristics of each recording layer 100 hours after the start of the accelerated test. FIGS. 14 (A) to 14 (E) show comparative examples of rare earth elements instead of Pt.
FIG. 14A is a characteristic diagram showing a magnetic Kerr curve when a representative recording layer containing Tb is left in the air or subjected to an accelerated deterioration test. FIG.
One week later, FIG. 14 (C) shows two hours after the start of the accelerated deterioration test.
FIG. 14 (D) shows the results 5 hours after the start of the accelerated deterioration test.
Shows the magnetic Kerr curve of each recording layer 30 hours after the start of the accelerated deterioration test. FIG. 15 is an explanatory diagram showing the thicknesses of the Co layer and the Pd layer in the Co—Pd-based recording layer. FIGS. 16 (A) and 16 (B) are characteristic diagrams showing magnetic Kerr curves of typical Co—Pd-based recording layers, and FIG. 16 (A) shows a 3.8 ° Co layer and 7.8
FIG. 16 (B) corresponds to a recording layer in which a 3Å Co layer and a 6.6d Pd layer are laminated, respectively. FIG. 17 shows the coercive force of a typical Co-Pt-based recording layer,
FIG. 18 shows the magnetic Kerr rotation angle of a typical Co-Pt-based recording layer, and FIG.
FIG. 19 is a characteristic diagram showing Curie points of typical Co—Pt-based recording layers. FIG. 20 is a characteristic diagram showing the dependence of the coercive force and the squareness ratio on the argon gas pressure of a recording layer in which a 3.8 ° Co layer and a 7.8 ° Pd layer are stacked. FIG. 21 (A) to FIG. 21
FIG. 21 (C) is a characteristic diagram showing a magnetic Kerr curve of the same recording layer under a typical argon gas pressure. FIG. 21 (A) shows a case where the argon gas pressure is 5 mTorr, and FIG. 21 (B) shows an argon gas pressure. FIG. 21 (C) corresponds to the case where the pressure is 11 mTorr, and FIG. 21 (C) corresponds to the case where the argon gas pressure is 25 mTorr. FIG. 22 is a characteristic diagram showing the total thickness dependence of the magnetic Kerr rotation angle, squareness ratio and coercive force of the same recording layer. FIGS. 23 (A) and 23 (B) are magnetic Kerr curves showing the total thickness dependence of the magneto-optical properties of a recording layer in which a 2.5 ° Co layer and a 8.4 ° Pd layer are stacked,
FIG. 23 (A) corresponds to the case of a total thickness of 200 mm, and FIG. 23 (B) corresponds to the case of a total thickness of 500 mm. FIG. 24 is a binary phase diagram of Pt and Pd. FIGS. 25 (A) to 25 (C) show typical Co.
FIG. 4 is a characteristic diagram showing a magnetic Kerr curve of a -Pt-Pd-based recording layer,
FIG. 25 (A) shows a recording layer in which a Co layer and a Pt—Pd alloy layer are stacked,
FIG. 25 (B) corresponds to a recording layer in which a Co layer, a Pt layer and a Pd layer are stacked, and FIG. 25 (C) corresponds to a recording layer in which a Co layer, a Pd layer, a Pt layer and a Pd layer are stacked in this order. Is what you do. No.
FIG. 26 is a characteristic diagram showing the relationship between the layer thickness of the Pt underlayer and the coercive force in a magneto-optical recording medium having a Co-Pt-based metal thin film as a recording layer. FIGS. 27 (A) to 27 (C) are magnetic Kerr curves showing the relationship between the layer thickness of the Pt underlayer and magneto-optical characteristics in a magneto-optical recording medium having a Co-Pt-based metal thin film as a recording layer. 27 (A) shows the case where no Pt underlayer is provided, FIG. 27 (B) shows the case where a 50 ° Pt underlayer is provided, and FIG. 27 (C)
This corresponds to the case where a 200 ° Pt underlayer is provided. FIG. 28 is a characteristic diagram showing a relationship between a layer thickness of a Pd underlayer and a coercive force in a magneto-optical recording medium having a Co-Pd-based metal thin film as a recording layer. FIG. 29 (A) to FIG. 29 (C)
FIG. 29 (A) is a magnetic Kerr curve showing the relationship between the thickness of the Pd underlayer and the magneto-optical characteristics in a magneto-optical recording medium having a Co-Pd-based metal thin film as the recording layer. FIG. 29 (B) shows a case where a 50 ° Pd underlayer is provided.
FIG. 9C corresponds to the case where a 200 ° Pd underlayer is provided.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-1699757 (JP, A) JP-A-62-289948 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 11/10 506 G11B 11/10 521

Claims (3)

(57) [Claims] An artificial lattice film in which a Co layer and a Pt layer and / or a Pd layer are alternately laminated is used as a recording layer.
A magneto-optical recording medium characterized by being 50 to 500 mm. 2. A recording layer comprising an artificial lattice film in which Co layers and Pt layers and / or Pd layers are alternately laminated, wherein the total thickness of the recording layers is
A magneto-optical recording medium characterized by being 500 to 800 mm (excluding 500 mm). 3. A recording layer comprising an artificial lattice film in which Co layers and Pt layers and / or Pd layers are alternately laminated, wherein the total thickness of the recording layer is
1. A magneto-optical recording medium having a thickness of 50 to 800 [deg.], Wherein a base film made of at least one of Cu, Rh, Pd, Ag, W, Ir, Pt, and Au is formed.