JP2546519B2 - Recording / reproducing method for magneto-optical disk - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing method for a magneto-optical disk, and more particularly, it is used for a rewritable magneto-optical disk or the like and is capable of reading a magneto-optical effect such as a magnetic Kerr effect or a magnetic Faraday effect. The present invention relates to a recording / reproducing method for a magnetic disk.

[0002]

2. Description of the Related Art Materials for magneto-optical recording media are mainly required to meet the following conditions.

(1) Perpendicular magnetization film (2) Large coercive force (3) Large Kerr rotation angle When heavy rare earths such as Tb and Gd are added to Fe, Co, etc., It is known that the magnetic anisotropy increases and the film becomes a perpendicular magnetization film. For these reasons, GdTbFe, DyFe, GdCo, TbCo, Tb are used as materials for the magneto-optical recording medium.
A heavy rare earth-3d transition metal amorphous alloy thin film such as FeCo satisfies the above conditions, is suitable for mass production, and has low read-out noise. Therefore, TbFeCo is particularly promising as a practical material.

Next, as a means for increasing the density of magneto-optical recording, there is miniaturization of the recording area by narrowing the beam diameter of laser light. In order to reduce the beam diameter without changing the NA (numerical aperture) of the objective lens of the recording / reproducing head, it is necessary to shorten the wavelength of the laser light source. For this reason, development of a short wavelength light source using a non-linear optical element and the like is in progress.
However, heavy rare earths now in practical use-3d
It is known that the transition metal amorphous alloy thin film has a smaller Kerr rotation angle as the wavelength becomes shorter. Further, the quantum conversion efficiency of the photodetector also decreases due to the decrease in wavelength.
Therefore, when reproducing with a short wavelength laser, the reproduction output is significantly reduced, and it is difficult to achieve a high recording density. Therefore, a new magneto-optical recording material having a large Kerr rotation angle in the short wavelength region is required.

The use of garnet, Pt / Co, and light rare earth-3d transition metal amorphous alloy thin films has been studied as a magneto-optical recording material for short wavelengths. However,
These materials have the following drawbacks.

Since garnet has a large Faraday rotation angle, a large reproduction output can be obtained. However, in order to grow crystals during or after film formation, heating at 600 ° C. or higher is required, which is a normal condition. It is difficult to fabricate on a glass substrate. Therefore, it is necessary to use expensive heat-resistant glass as the substrate, and there is a drawback that the recording medium becomes expensive.

Further, Pt / Co has a Kerr rotation angle larger than that of the heavy rare earth-3d transition metal amorphous alloy thin film in the short wavelength region, but it is not a large value that compensates for the decrease in the quantum conversion efficiency of the photodetector. In addition, since it is crystalline, medium noise is large and reproduction output in the short wavelength region is lowered (Japanese Patent Laid-Open No. 3-162739).

Further, the light rare earth-3d transition metal amorphous alloy thin film also has a drawback that it is not possible to obtain a sufficiently large Kerr rotation angle within a composition range where recording and reproduction are possible, as in the case of Pt / Co.

Therefore, it is necessary to use new materials in place of these recording materials. The MnBi compound becomes a C-axis-oriented MnBi compound by preserving the C-axis orientation of Bi when a Mn-Bi laminated film in which Mn and Bi are sequentially formed on a substrate is heated and reacted. This MnBi compound is
Since it has a strong magnetic anisotropy in the C-axis, it becomes a perpendicular magnetization film. Further, the MnBi compound has a wavelength of 400 nm to 9 nm.
Since the Kerr rotation angle at 00 nm is as large as 1 degree or more, it is suitable as a magneto-optical recording material for short wavelength.

Mn in which Mn and Bi are sequentially formed on a substrate
-To heat the Bi laminated film to generate a compound,
It is necessary to hold the laminated film in an atmosphere having a temperature of 300 ° C. or higher. Therefore, a glass substrate having high heat resistance is used as the substrate. When a thin film is formed on a normal tempered glass substrate, the alkali metal or the like from the glass substrate is MnBi.
In order to prevent the deterioration of the layer, a dielectric underlayer is used as a barrier layer.

From MnBi (1.p.) in the low temperature phase to Mn1.08B in the high temperature phase with disappearance of magnetization at 355.degree.
i (hp) structural transformation and decomposition of the high temperature phase into Mn and Bi at 446 ° C (1974, Journal of Applied Physics, No. 45, 2).
358). Therefore, the low temperature phase is 35
It decomposes into Mn1.08Bi and Bi in the high temperature phase at 5 ° C, and decomposes into MnBi and Mn at 340 ° C in the cooling process. Further, the original Curie temperature Tc of the low temperature phase (value obtained by extrapolating the temperature change of magnetization) is set to 480 ° C. The hot phase was quenched to room temperature q.
h. The Curie temperature of the 1-phase is 180 ° C., and q. h. The Kerr rotation angle of the l-phase is about 0.
It is known to be four times.

[0012]

MnBi compound is one of the problems in using MnBi compound as a magneto-optical recording material.
There is deterioration of a reproduction signal at the time of repeated recording / reproduction that occurs due to structural phase transition or decomposition that occurs in a temperature region where magnetization disappears. Regarding this problem, from an experiment in which a laser pulse of μs order was applied by a static read / write (R / W) device, a high temperature phase was cooled to room temperature at a recording point. Q. p. It has been reported that there is a problem with the long-term storage of data in the l-phase state (1973, AI
EE Transactions on Magnetics, No. MAG-9, p. 467). However, until now, no repeated experiment of recording and erasing of a disk medium under high-speed rotation for a high temperature holding time of the order of several hundreds ns has been conducted, and it is considered that the recording mechanism is different from that of a stationary system.

[0013]

A magneto-optical disk recording / reproducing method according to the present invention is provided with MnBi having a perpendicular magnetic easy axis.
In a magneto-optical disk having a compound thin film as an information recording layer, the maximum temperature (Tm) of the MnBi compound thin film during recording / erasing and the holding time (t) equal to or higher than the decomposition temperature (Td) (Tm-Td). It is characterized in that the recording / erasing is used so that the relationship of t ≦ 6 × 10 ⁻³ K · s (K indicates thermodynamic temperature: Kelvin, s indicates time: seconds) is satisfied.

[0014]

The authors note that the recording of the MnBi compound thin film is performed at the original Curie temperature Tc of the low temperature phase, and depending on the recording and erasing conditions, the low temperature phase has a certain rate of change α and the low temperature phase has Mn and B.
It was found to decompose into i and. Here, assuming that the number of times of recording and reproduction is n, the low temperature phase changes as shown in the following equation after n times.

L. p. → (1- (1-α) ⁿ ) ・ (Mn
+ Bi) + (1-α) ⁿ l. p. The rate of change α depends on the linear velocity during recording / erasing, the recording output, and the structure of the recording medium. The rate of change α can be reduced by increasing the linear velocity and decreasing the recording output. FIG. 2 shows a recording output of 10 mW, a linear velocity of 3.3 m / s,
It is a figure which shows the result of having calculated the time change of the temperature rise of the MnBi recording phase in 4.1 m / s and 5.1 m / s by the difference method, and used the average value of Mn and Bi as the thermal constant of MnBi. According to FIG. 2, it can be seen that the retention time above the maximum reached temperature and the phase transition temperature is significantly reduced due to the increase in the linear velocity.

FIG. 1 shows the product (Tm-T) of the temperature difference between the highest temperature (Tm) and the decomposition temperature (Td) and the holding time (t).
It is a figure which shows the relationship between d) * t and the resolution (alpha) of MnBi low temperature phase. According to FIG. 1, there is a linear relationship between the two,
The value of (Tm−Td) · t at the time of recording / reproducing is set to 6 × 10 ⁻³ K.
It can be seen that the rate of change α becomes 0 and the carrier decrease due to repetition can be prevented by setting s (K indicates thermodynamic temperature: Kelvin, s indicates time: seconds) or less.

[0017]

Next, the present invention will be described with reference to the drawings. FIG. 3 is a partial cross-sectional view showing the structure of the MnBi magneto-optical recording medium before heat treatment. As shown in FIG. 3, the MnBi magneto-optical recording medium of the present embodiment has an underlayer (silicon nitride film by sputtering method: SiN) on a disk-shaped glass substrate 1.
2 to a thickness of 85 nm, the Bi layer 3 to a thickness of 20 nm by the ion cluster beam method, the Mn layer 4 to a thickness of 8 nm by the ion cluster beam method, and the interference layer (silicon nitride film by sputtering method: SiN) 5 of 300 nm. After the reflective layer (Al film formed by sputtering) 6 having a thickness of 20 nm is sequentially formed, the disk is heat-treated at a temperature of 380 ° C. for 3 hours to cause Mn and Bi to react with each other to form a MnBi compound. Then, a magneto-optical recording medium was produced.

Next, the characteristics of this MnBi magneto-optical recording medium were measured by a differential detection type read / write (R / W) device having an LD wavelength of 830 nm and an objective lens NA (numerical aperture) of 0.55. At this time, the recording frequency is 500 kHz
The z and the duty were set to 50%, and the linear velocity and the recording output were changed for measurement. The recording output is 2mW
And the recording magnetic field was 4000e.

FIG. 4 is a diagram showing a change from the initial value of the carrier due to repeated recording when the recording output is set to 9 mW (constant). According to FIG. 4, a linear velocity of 5.1 m / s
Then, the carrier does not decrease due to repetition. On the other hand, at linear velocities of 4.1 m / s and 3.3 m / s, the carrier drops significantly. FIG. 5 is a diagram showing a change from the initial value of the carrier due to repetitive recording when the linear velocity is set to 5.1 m / s (constant). According to FIG. 5, when the recording output is 9 mW, the carrier does not decrease due to repetition. On the other hand, when the recording output is 9.5 mW and 10 mW, the carrier drops significantly. This gives (Tm-Td) * t
Table 1 summarizes the relationship between the recording conditions and the recording conditions.

[0020]

[Table 1]

According to Table 1, the recording conditions are selected and (Tm
-Td) · t is set to 6 × 10 −3 K · s or less,
It can be seen that the reproduction characteristics do not deteriorate due to repeated recording.

[0022]

As described above, according to the recording / reproducing method of the magneto-optical disk of the present invention, it is possible to prevent the deterioration of the reproducing characteristics of the magneto-optical disk due to the repetitive recording, and the reproducing method of the high-performance magneto-optical disk. Is effective.

[Brief description of drawings]

FIG. 1 is a product (Tm-Td) · t and Mn of a temperature difference between a maximum reaching temperature (Tm) and a decomposition temperature (Td) and a holding time (t).
It is a figure which shows the relationship with the resolution (alpha) of Bi low temperature phase.

FIG. 2 is a diagram showing a result of calculating a time change of temperature rise of a MnBi recording phase at a recording output of 10 mW, linear velocities of 3.3, 4.1 and 5.1 m / s by a difference method.

FIG. 3 is a partial cross-sectional view showing the structure before heat treatment of a MnBi magneto-optical recording medium that realizes one embodiment of the present invention.

FIG. 4 is a diagram showing a change from an initial value of a carrier due to repeated recording when the recording output is set to 9 mW (constant).

FIG. 5 is a diagram showing a change from an initial value of a carrier due to repetitive recording when the linear velocity is 5.1 m / s (constant).

[Explanation of symbols]

 1 Glass Substrate 2 Underlayer 3 Bi Layer 4 Mn Layer 5 Interference Layer 6 Reflective Layer

Claims (1)

(57) [Claims] 1. In a magneto-optical disk using an MnBi compound thin film having a perpendicular easy magnetic axis as an information recording layer, the maximum temperature (T
m) and the retention time (t) equal to or higher than the decomposition temperature (Td), (Tm-Td) · t ≦ 6 × 10 ⁻³ K · s, where K is a thermodynamic temperature: Kelvin, s is a time: A recording / reproducing method for a magneto-optical disk, characterized by using recording / erasing in which a second relation is established.