JPH09231628A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording medium which can be used for magnetooptical recording by using short wavelength laser light, by forming a multilayered film comprising alternately deposited Co alloy layers and noble or noble-alloy layers as a recording layer and forming the Co alloy layers having the compsn. expressed by formula 1(at.%). SOLUTION: A Pt/CoNd film is formed on a glass substrate by using a two-dimensional magnetron sputtering device to obtain a magnetooptical recording medium. A Pt layer having 1nm thickness and a CoNd layer having 0.5nm thickness are formed under 10 mTorr Ar gas pressure and the procedure is repeated by 33 times to form 33 pairs of CoNd(0.5nm)/Pt(1nm)} layers. The compsn. of the CoNd layer obtd. by chemical analysis (1CP) is Co97.2Nd2.8(at.%). The Kerr rotation angle is measured by phase modulation method. The Kerr rotation angle for 350 nm wavelength light is 0.43 deg., which is 2.1 times as much as the Kerr rotation angle for 780 nm wavelength light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium suitable for high density recording using a short wavelength laser (which has a wavelength of 300 nm to 500 nm).

[0002]

2. Description of the Related Art A magneto-optical recording medium (hereinafter sometimes abbreviated as a recording medium or a medium) is recorded and reproduced by a laser beam and an external magnetic field. Recording is performed by heat from a laser beam and an external magnetic field. That is, the coercive force of the medium (hereinafter sometimes referred to as Hc) decreases due to the temperature rise due to the laser light, and the direction of magnetization is recorded by the external magnetic field.

The reproduction is performed by detecting the change in polarization (Kerr rotation angle) of the laser light reflected by the medium. A typical medium currently on the market is a 3.5-inch magneto-optical disk. Its typical capacity is 230 megabytes, but higher capacity is required.

As a method of increasing the capacity, studies are being made to shorten the wavelength of the laser. This is because the diameter of the laser spot focused by the lens is inversely proportional to the wavelength, and thus the recording density is increased by the laser light having a short wavelength. Currently, the wavelength is generally 780 nm, which is 400n.
If m, the recording density can be expected to be 3 to 4 times that of 780 nm.

However, a TbFeCo type thin film generally used as a medium has a small Kerr rotation angle at a wavelength of 400 nm (about half of 780 nm), which causes a problem of reduction in reproduction signal. A Pt / Co-based multilayer film or the like has a large Kerr rotation angle at a wavelength of 400 nm.

[0006]

Since the Pt / Co based multi-layered film is polycrystalline, the medium using this has a larger disturbance (noise) of the reproduced signal than the medium using the amorphous TbFeCo based thin film. Therefore, although the Pt / Co-based multilayer film has a large Kerr rotation angle and a large amplitude of the reproduction signal, the noise ratio is large, so that the CN ratio is equal to that of the TbFeCo-based thin film.

For this reason, the Pt / Co-based multilayer film is required to reduce noise by making the crystal grains finer and further improve the Kerr rotation angle. The present invention has been made in view of the above circumstances, and an object thereof is to provide a magneto-optical recording medium suitable for high density recording.

[0008]

The inventors of the present invention have made extensive studies to solve the above-mentioned problems, and as a result, have realized high-density recording with a special recording layer structure and completed the present invention. That is, the gist of the present invention is a magneto-optical recording medium in which a recording layer is provided directly on a substrate or via an underlayer,
A magneto-optical recording medium characterized in that the recording layer is a multilayer film in which a Co alloy layer and a noble metal or a noble metal alloy layer are alternately laminated, and the Co alloy has a composition (atomic%) shown in the following formula (1). .

[0009]

Embedded image CoxAyBz (1) (x + y + z = 100, 0 ≦ y ≦ 30, 0 <z ≦ 30 A is at least 1 selected from Pt, Pd, Fe, Ni, Cr, and Mn. Indicates the species, B indicates Nd or Pr.)

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as a substrate, a resin substrate such as a polycarbonate resin, an acrylic resin, a polyolefin resin or the like, which is usually provided with irregularities for tracking servo, a ceramic substrate such as glass, a metal substrate such as an aluminum alloy, Alternatively, a laminated substrate of these or the like can be used.

The thickness of the substrate is generally 0.3 mm to 2 mm. A recording layer is provided on these substrates. The recording layer is a multilayer film in which a Co alloy layer and a noble metal or a noble metal alloy layer are alternately laminated. The Co alloy forming the multilayer film is characterized by having a composition (atomic%) shown in the following formula (1).

[0012]

Embedded image CoxAyBz (1) (x + y + z = 100, 0 ≦ y ≦ 30, 0 <z ≦ 30 A is at least 1 selected from Pt, Pd, Fe, Ni, Cr, and Mn. Indicates the species, B indicates Nd or Pr.)

Although it is not clear why these multilayer films increase the Kerr rotation angle at short wavelengths, Nd and Pr of the B group are not known.
It is inferred that etc. play an important role. Nd, Pr
It is known that the Kerr rotation angle also increases with the concentration of light rare earths in alloys of light rare earths and Co (P.H.
ansen: Handbook of Magneti
c Materials, vol6, ed. by K.
H. Buschow, North-Holland, A
msterdam, 1991, p406).

Noble metals include Pt, Pd, Au, Ag, Rh and alloys thereof. When Pt is the main component, the Kerr rotation angle is large and is practically preferable. From the viewpoint of coercive force and perpendicular magnetic anisotropy, it is more practically preferable to add a small amount of Pd, Au, Ag and Rh to Pt. The elements of the group A are considered to play a role of increasing the magnetic moment, and it is preferable that Fe be the main component.

When the addition amount of the group A exceeds 30%, the perpendicular magnetic anisotropy becomes small, which is not preferable in practical use. Although the addition amount of the group B depends on the composition and the addition amount of the group A, it is preferably 30% or less, more preferably 1% to 10% from the viewpoint of perpendicular magnetic anisotropy. Usually, a multilayer film is produced by alternately stacking a noble metal layer and a Co alloy layer by binary sputtering using a noble metal or noble metal alloy target and a Co alloy target.

The alternate stacking is performed by opening and closing a shutter or rotating the substrate. The noble metal or noble metal alloy layer and the Co alloy layer may be produced by co-sputtering using a single target. There is no problem in practical use even if the layers are continuous films in which the layers are not completely separated but diffused with each other, that is, the composition is periodically modulated.

The thickness of the recording layer is preferably about 5 nm to 300 nm. If it is smaller than 5 nm, a sufficient Kerr rotation angle cannot be obtained, and if it is larger than 300 nm, the magnetic field sensitivity is deteriorated due to the leakage magnetic field due to the magnetization of the film itself, which is not preferable in practice. Usually, the film thickness of the recording layer is 10 nm to 40 nm in order to utilize the interference effect.

The lamination cycle is usually 0.2 nm for the Co alloy layer.
To 1 nm, and the noble metal or noble metal alloy layer is adjusted to 0.5 nm to 2 nm. Co alloy layer is 0.2 nm
If it is smaller, it is difficult to obtain a sufficient car rotation angle. 1
If it is larger than nm, the perpendicular magnetic anisotropy is lowered. On the contrary, when the thickness of the noble metal or the noble metal alloy layer is smaller than 0.5 nm, the perpendicular magnetic anisotropy decreases, and when it is larger than 2 nm, a sufficient Kerr rotation angle cannot be obtained.

The sputtering conditions also have a great influence on the film quality. For example, if the film forming pressure is too low, a sufficient coercive force cannot be obtained, and if it is too high, the reflectance decreases, which is not preferable. Although it is highly dependent on the device, about 10 mTorr is appropriate. An underlayer may be provided between the substrate and the recording layer. The underlying layer is usually SiO ₂ , Al ₂ O ₃ ,
Ta ₂ O _5, Si ₃ N oxide such _4, nitrides, and mixtures thereof are used.

The base film is usually provided for the purpose of preventing the recording layer from oxidizing, improving the magnetic properties of the recording layer, and optical interference. The film thickness is preferably about 10 nm to 300 nm. Pt / Co based multilayer films are generally Pt,
It is known that the magnetic characteristics are significantly improved when Pd or the like is used for the underlayer.

Therefore, these alloy layers may be provided very thinly on the substrate or the underlayer. If the film thickness is small,
2nm because it has little effect of improving the characteristics and blocks light when it is thick.
To 10 nm is suitable. Usually, in addition to these layers, a reflective layer is used for the purpose of adjusting reflectance, recording sensitivity, signal intensity and the like.

As the reflective layer, Al, Ag, Au, Pt,
A metal film of Pd or an alloy thereof is used. These reflective layers are used for the purpose of adjusting heat conduction, which improves recording sensitivity, resistance to repeated reproduction, etc. of the magneto-optical recording medium in addition to the reflection of light. Furthermore, another layer may be provided between each layer. In particular, a heat insulating layer is usually provided between the magneto-optical recording layer and the reflective layer.

[0023]

The present invention will be described in detail below with reference to examples.
However, the present invention is not limited to the following examples unless the gist thereof is exceeded.
It is not limited. Example 1 On a glass substrate with a binary magnetron sputtering device
A Pt / CoNd film was produced to obtain a magneto-optical recording medium. A
r gas pressure was 10 mTorr and Pt layer thickness was 1 n
m and the film thickness of the CoNd layer are 0.5 nm, respectively, 3
Three layers were alternately stacked ([CoNd (0.5 nm) / Pt
(1 nm)] 33 layers). C by chemical analysis (ICP)
When the composition of oNd was analyzed, Co_97.2, Nd
_2.8(Atomic%). Kerr rotation angle uses phase modulation method
And measured. Kerr rotation angle at wavelength 350nm is 0.4
It was 3 degrees. This is the Kerr rotation angle at a wavelength of 780 nm
Was 2.1 times.

Example 2 A magneto-optical recording medium was obtained in the same manner as in Example 1 except that the Co alloy composition was Co _93.3 and Nd _6.7 (atomic%). The Kerr rotation angle at a wavelength of 350 nm was 2.4 times the Kerr rotation angle at a wavelength of 780 nm.

Example 3 A magneto-optical recording medium was obtained in the same manner as in Example 1 except that the Co alloy composition was Co _98.6 and Pr _1.4 (atomic%). The Kerr rotation angle at a wavelength of 350 nm was 2.3 times the Kerr rotation angle at a wavelength of 780 nm.

Comparative Example 1 A magneto-optical recording medium was obtained in the same manner as in Example 1 except that Nd and Pr were not included. The Kerr rotation angle at a wavelength of 350 nm was 1.9 times the Kerr rotation angle at a wavelength of 780 nm.

Comparative Example 2 A magneto-optical recording medium was obtained by forming an amorphous Tb ₂₁ Fe ₇₀ Co ₉ film on glass by binary magnetron sputtering to a film thickness of 100 nm. The Kerr rotation angle at a wavelength of 350 nm was 0.6 times the Kerr rotation angle at a wavelength of 780 nm.

[0028]

INDUSTRIAL APPLICABILITY The medium of the present invention has a remarkably large Kerr rotation angle at a short wavelength as compared with the medium currently used at a wavelength of 780 nm, and therefore can be applied to magneto-optical recording using a short wavelength laser High density recording can be realized.

Claims (1)

[Claims] 1. A magneto-optical recording medium in which a recording layer is provided on a substrate directly or via an underlayer, wherein the recording layer is a multilayer film in which a Co alloy layer and a noble metal or a noble metal alloy layer are alternately laminated, A magneto-optical recording medium characterized in that a Co alloy has a composition (atomic%) represented by the following formula (1). Embedded image CoxAyBz (1) (x + y + z = 100, 0 ≦ y ≦ 30, 0 <z ≦ 30 A is at least 1 selected from Pt, Pd, Fe, Ni, Cr, and Mn. Indicates the species, B indicates Nd or Pr.)