JPH07334879A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To record with a specified mark width with by a specified correction of record without depending on the length of the record mark by forming an optical recording medium satisfying a specified relation. CONSTITUTION:This magneto-optical recording medium consists of a substrate 1, silicon nitride layer 2, read-out layer 3, memory layer 4, intermediate layer 5, recording layer 6, switching layer 7, initializing layer 8, and silicon nitride layer 9. This recording medium satisfies the relation expressed by formula I and formula II. In, the formulae, T is the temp. increase of the medium when the medium is irradiated with laser beams for recording or reproducing. t is the time for the beam to pass the longest recording mark, tau1 is the first thermal time const., tau2 is the second thermal time const. tR is the retardation time, L is the max. recording mark length, and V is the line velocity. Thereby, recording with a constant mark width with const. correction of record can be performed without depending on the length of the record mark.

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 for recording, erasing and reproducing with a laser beam.

[0002]

2. Description of the Related Art Recently, an optical recording / reproducing method satisfying various requirements including high density, large capacity, high access speed, and high recording / reproducing speed, and a recording apparatus, reproducing apparatus and recording medium used therefor. Efforts are being made to develop. Among a wide range of optical recording / reproducing methods, the magneto-optical recording / reproducing method has a unique advantage that information can be recorded and then erased, and new information can be recorded again and again. For being full of the greatest attraction.

A recording medium used in this magneto-optical recording / reproducing method has a perpendicular magnetic anisotropy composed of one layer or multiple layers as a layer for storing a recording.
r orlayers: hereinafter referred to as perpendicular magnetic anisotropic film). This perpendicular magnetic anisotropic film is, for example, amorphous GdF.
e, GdCo, GdFeCo, TbFe, TbCo, TbFeCo, etc. The perpendicular magnetic anisotropic film generally has concentric or spiral tracks, and information is recorded on the tracks. There are two types of tracks, explicit and implicit. [Explicit Track] The magneto-optical recording medium has a disk shape. In a disc having explicit tracks, tracks for recording information are formed in a spiral shape or a concentric circle shape when viewed in a direction perpendicular to the disk plane. There is a groove for tracking and separation between two adjacent tracks. The space between the grooves is called a land. In reality, the relationship between the land and the groove is reversed on the front and back of the disc. Then, looking at the disc from the same direction as the beam is incident, the front is a groove,
The back is called land. Since the perpendicular magnetic anisotropy film is formed on the entire surface of the groove and the land, the groove portion may be a track or the land portion may be a track. There is no particular relationship between the width of the groove and the width of the land.

As described above, generally, the substrate has a land formed in a spiral or concentric shape on the surface and a groove sandwiched between two adjacent lands. A thin perpendicular magnetic anisotropic film is formed on such a substrate. As a result, the perpendicular magnetic anisotropic film has lands and grooves. [Mark] In the present specification, “upward (upwar
d) "or" downward "
Orientation "and the other is defined as" reverse A orientation ".

The information to be recorded is binarized in advance, and this information has a mark (B ₁ ) having a magnetization in "A direction".
Then, two signals of the mark (B ₀ ) having the magnetization in the “reverse A direction” are recorded. These marks B ₁ and B ₀ correspond to either one or the other of the digital signals 1 and 0, respectively. However, generally, the magnetization of the track to be recorded is aligned in the "reverse A direction" by applying a strong external magnetic field before recording. Act to align the magnetization direction is referred to as the "initialization ^* (initialize ^*)" in the old sense. Then, the mark (B
₁ ) to form. Information is represented by the presence or absence of the mark (B ₁ ), the position, the front end position, the rear end position of the mark, the mark length, and the like. Particularly, a method in which the edge position of the mark represents information is called mark length recording. The mark has been called a pit or a bit in the past, but recently it is called a mark.

In addition to the basic recording principle described above, efforts have been recently made to develop the technology in order to further enhance the functions. For example, in the conventional magneto-optical recording, when it is desired to re-record information that has already been recorded in another information, first erase the recorded information (align the magnetization of the recording portion in the initialization direction). Without it, new information could not be recorded. On the other hand, by adding a magnetic layer (which is referred to as a recording layer or a W layer in this specification) that plays a recording aid and an initializing magnetic field, the magnetization of this layer is changed by the action of exchange coupling force. Recording is performed by transferring to a magnetic layer that plays a role of recording / reproducing (this layer is referred to as a memory layer or an M layer in this specification), and thereafter, the recording layer returns to its original magnetization by an initializing magnetic field. By performing the operation of returning to the direction, new information can be overwritten without erasing the already recorded information. A medium having such a function is called an overwrite medium. As an additional technique for improving the perfection of this technique, a magnetic layer for adjusting the exchange coupling force between the recording layer and the memory layer (in this specification, this layer is referred to as an intermediate layer or an I layer). Was proposed.

In order to obtain a larger reproduced signal by transferring the magnetization of the memory layer,
Techniques such as adding a magnetic layer having a larger magneto-optical effect (this layer is referred to as a reading layer or an R layer in the present specification) have also been proposed. By the way, since increasing the recording density further enhances the attractiveness of the magneto-optical recording medium, recently efforts have been made especially for this purpose. In order to increase the recording density, the recording marks may be packed and formed small. However, if the marks are packed too much, the signal from the adjacent mark will enter and the reproduction quality of the mark will deteriorate. Therefore, there is a limit in reducing the distance between marks. So, within a certain limit,
A mark length recording method has been proposed for the purpose of recording information with the highest possible density. In this recording method, the length of information is represented by the distance between two marks, but the length of one mark represents the length of information. That is, it is a method that enables higher density recording by the principle that one mark shorter than the limit value between two marks can be recorded. However, in this method, the higher the density, the more the mark shape tends to depend on the mark length. Therefore, it is necessary to accurately record the mark length, and thus the recording correction is necessary.

[0008]

However, the recording correction methods proposed so far cannot suppress the dependence of the mark shape on the mark length, which is not a sufficient level for high density recording.

[0009]

As a result of earnest research for solving the above problem, the present inventor has found that the thermal characteristics of the recording medium greatly change in the region related to the formation of the mark.
It has been found that the reproducibility of the mark length can be kept good if the recording medium is manufactured so that the recording correction of only one kind of pattern is required, and the present invention has been completed.

Therefore, the present invention is, firstly, "an optical recording medium characterized by satisfying the following relational expression: T = A exp (-t / τ ₁ ) + B exp {(-t + t _R ) /
τ ₂ } t _R > L / V where T: rise temperature of the medium when a laser beam is irradiated for recording or reproduction on the magneto-optical recording medium t: longest recording mark length elapsed time τ ₁ : A first thermal time constant τ ₂ : a second thermal time constant t _R : delay time L: longest recording mark length V: linear velocity, and secondly, "having an initialization layer". 1
The magneto-optical recording medium described in 1.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0012]

[Example] First, a sputtering apparatus and a pitch of 1.4
We prepared a resin substrate with a diameter of 130 mm in which a tracking guide groove of μm and depth of 800 Å was engraved in a spiral shape. After setting the substrate and the sputtering target in the sputtering tank of the sputtering apparatus, the inside of the sputtering tank was once evacuated to a pressure of 5 × 10 ⁻⁵ Pa or less.

Next, Ar gas was introduced into the sputtering tank to bring the pressure to 0.2 Pa, and then N ₂ gas was further introduced while the first gas was introduced.
Reactive sputtering was performed at a sputtering rate of 10 nm / min by using the target Si of No. 1 as a target to form a silicon nitride film having a thickness of 70 nm as a first protective layer on the resin layer. Then, the second target GdFeCo was used to perform sputtering under the conditions of Ar pressure of 0.3 Pa and sputtering rate of 20 nm / min.
Gd _24.5 (Fe ₇₀ Co ₃₀ ) _75.5 readout layer with a thickness of 3
It was formed to 0 nm.

Next, the third target Tb, the fourth target Fe, and the fifth target Co are simultaneously sputtered under the conditions of Ar pressure of 0.2 Pa and sputtering rate of 20 nm / min to form Tb on the read layer. A memory layer of ₂₁ Fe ₇₅ Co ₄ was formed to a thickness of 25 nm. Next, sputtering was performed with a fifth target GdFeCo under the conditions of Ar pressure of 0.3 Pa and sputtering rate of 20 nm / min, and Gd ₃₃ (Fe ₈₀ C
An intermediate layer of o ₂₀ ) ₆₇ was formed to a thickness of 15 nm.

Next, with the sixth target Dy and the seventh target FeCo, Ar pressure 0.2 Pa and sputtering rate.
Co-sputtering was carried out under the condition of 20 nm / min to form a recording layer of Dy _28.5 (Fe ₅₀ Co ₅₀ ) _71.5 on the intermediate layer with a thickness of 50 nm. Next, the third target Tb, the fourth target
Simultaneous sputtering was performed using Fe and the fifth target Co under the conditions of Ar pressure of 0.2 Pa and sputtering rate of 20 nm / min to form a switching layer of Tb ₁₅ Fe ₈₂ Co ₃ with a thickness of 25 nm on the recording layer.

Next, again using the third target Tb, the fourth target Fe and the fifth target Co, Ar pressure of 0.2 P
Simultaneous sputtering was performed under the conditions of a and sputtering rate of 20 nm / min to form an initializing layer of Tb ₂₄ Fe ₁₀ Co ₆₆ on the switching layer. Finally, again the first target Si
Thus, a second protective layer of silicon nitride was formed to a thickness of 70 nm on the memory layer under the same conditions as the first protective layer.

Through the above steps, the thickness of the initialization layer is shown in Table 1.
Magneto-optical recording media having various thicknesses as shown in FIG. It was confirmed that the temperature drop during recording on these media satisfies the following equation at a linear velocity of 11.3 m / s. T = A exp (−t / τ ₁ ) + B exp {(−t + t _R ) /
τ ₂ } [Measurement 2] After the magnetization direction of this medium is directed (initialized) in one direction, it is set in a magneto-optical recording / reproducing apparatus having a recording magnetic field Hb of 300 Oe and an initializing magnetic field Hini. of 5000 Oe. , Wavelength of 8 μm with a linear velocity of 11.3 m / s and a diameter of about 1 μm
A 30 nm laser beam was applied. The laser beam was pulse-modulated and recorded according to the recording-corrected modulation pattern shown in FIG. At this time, the mark width of the 2T mark is
The recording laser beam intensity was set to 0.6 μm. Since the length of the 8T mark is 300 ns, the L / V value at this time is L / V = 11.3 × 300 × 10 ⁻⁹ /11.3=3×10 ⁻⁷ s = 300 ns.

The mark width and t _R of the recorded mark were measured. The results are shown in Table 1. From Table 1, when the thickness of the initialization layer is 300 nm or more, t _R > L / V, and in this case, the mark width is constant regardless of the mark length, and the mark shape depends on the mark length. I know there isn't.

[0019]

[Table 1]

[0020]

As described above, according to the present invention, it has been found that recording with a constant mark width can be performed with constant recording correction regardless of the length of the recording mark.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a magneto-optical recording medium according to the present invention.

FIG. 2 is a conceptual diagram showing thermal characteristics of a magneto-optical recording medium.

FIG. 3 is a schematic diagram of recording-corrected laser beam irradiation pulses.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Silicon nitride layer 3 ... Read-out layer 4 ... Memory layer 5 ... Intermediate layer 6 ... Recording layer 7 ... Switching layer 8 ... Initialization layer 9 ... Silicone nitride layer and above

Claims (2)

[Claims] 1. An optical recording medium satisfying the following relational expression. T = A exp (−t / τ ₁ ) + B exp {(−t + t _R ) /
τ ₂ } t _R > L / V where T: rise temperature of the medium when a laser beam is irradiated for recording or reproduction on the magneto-optical recording medium t: longest recording mark length elapsed time τ ₁ : First thermal time constant τ ₂ : Second thermal time constant t _R : Delay time L: Longest recording mark length V: Linear velocity 2. The magneto-optical recording medium according to claim 1, which has an initialization layer.