JP2650927B2 - Magneto-optical recording method - Google Patents

Description

The present invention relates to magneto-optical recording for recording, reproducing and erasing information using an energy beam such as a laser beam, and in particular, enables overwriting at high speed. Related to various magneto-optical recording methods.

[Conventional technology]

Overwriting techniques for magneto-optical disks include:
There are a magnetic field modulation method and a light modulation method.

In the magnetic field modulation method, a method of applying an external magnetic field to a magneto-optical recording film, simultaneously raising the temperature of the portion with irradiation energy, inverting the magnetization of the magneto-optical recording film, and performing overwriting is disclosed in, for example, No. 60-251539, JP-A-60-26105
And JP-A-61-22452.

On the other hand, as a method of performing overwriting by a light modulation method, a method of using two magnetic films includes Sato,
Saito, Matsumoto: Proceedings of the 34th Joint Lecture Meeting on Applied Physics, 1987, 28p-ZL-3, and JP-A-62-175948. EEE, Transactions on Magnetics, MEG 23, 1987, pp. 171 to 173
Page (IEEE Trans. Magnetics, MAG23, 1987, pp. 171-173)
Have been reported. In the light modulation overwrite method using a demagnetizing field, a recording magnetic domain is formed with a laser pulse having a predetermined time width without applying an external magnetic field, and a laser pulse having a time width shorter than the laser pulse is formed on the recording magnetic domain. Irradiation is performed to erase.

[Problems to be solved by the invention]

Among the above-mentioned prior arts, the magnetic field modulation overwrite method requires high-speed switching of a magnetic field, so that high-speed writing at a recording frequency exceeding 10 MHz is difficult.

On the other hand, light modulation overwriting using a two-layer magnetic film
The magnetic characteristics such as the compensation temperature and the coercive force of both magnetic films must be within a specific narrow range, and it is difficult to adjust the medium characteristics.

In the optical modulation overwriting method using a demagnetizing field, overwriting cannot be performed unless overwriting is performed exactly at the same position as the previously written magnetic domain. In the method, the clock signal at the time of recording is generated by a crystal oscillator with a fixed frequency, so if there is a disc eccentricity or a change in the number of revolutions, the writing timing may be shifted by several μs, and Sufficient precision required for light could not be obtained. In order to solve this, the previous information position has been read beforehand to determine the position. In addition, the previously written information is read in advance, and this is correlated with the new information to determine whether to record or erase or to retain the previous information. The lights were going. For read-ahead, an optical head dedicated to read-ahead was provided separately from the optical head for writing.
It is necessary to adopt a head structure or a two-circle writing method in which pre-reading is performed in the first rotation with one head and then writing is performed in the second rotation. The advantage as overwriting is hardly utilized. Further, a buffer memory for temporarily storing information recorded last time and a logic circuit for comparing the previous information and the write information to determine the condition of the write pulse have to be incorporated in the apparatus.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magneto-optical recording system which uses a single optical head in a magneto-optical film and realizes high-speed overwriting only by one rotation of a disk, excluding the above-mentioned problems of the prior art. .

[Means for solving the problem]

The object is to synchronize with the embedded clocking method, irradiate the light with precise timing on the previously recorded magnetic domain, and write the light by modulating the intensity or pulse length of the light with the recorded information. This is achieved by employing a magnetic recording method.

The feature of the present invention is that recording,
In the magneto-optical recording method for performing reproduction and erasure, write is performed by irradiating light onto the previous recording magnetic domain at the same timing, and when forming a recording magnetic domain, a long pulse light must be used. There is a magneto-optical recording method in which arbitrary new information is overwritten regardless of previously recorded information by irradiating a short pulse light.

The timing is obtained from pits arranged at equal intervals in advance on the track or guide groove of the disc, and based on this timing, pits or embedded signals of any shape to the next pit or embedded signals of any shape are finely divided. It is desirable to generate a clock signal that divides accurately, synchronize the information recording with this clock signal, and irradiate light onto the previously recorded magnetic domain at the same time to perform writing.

[Action]

In the overwrite method using a demagnetizing field, it is necessary that the write timing be accurate to within half of the previously written magnetic domain position and magnetic domain diameter. According to the embedded clocking method, the pit position on the track can be controlled more accurately than in the conventional case using self-clocking.
Overwriting is possible because the magnetic domains are written with an accuracy within 10.

Also, the overwriting of the conventional demagnetizing system is classified into 1 when there is a recording magnetic domain and 0 when there is no recording magnetic domain, and the state of the magnetic domain to be written is shown in Table 1 (a). . The writing light is not irradiated, is modulated by three values of short pulse and long pulse, and which one to select depends on the previous recording state, so the information of the previous recording must be known in advance. Must read data before one round.

However, if the medium characteristics are made appropriate, FIG. 1 (b)
It has been found that such writing characteristics as described above can be obtained. A mechanism for forming or erasing a recording magnetic domain in each of the four cases will be described below with reference to FIG.

(1) When short pulse light is irradiated to a place where there is no previously recorded magnetic domain (FIG. 1 (a)): Inverted magnetic domains are temporarily formed at the time of irradiation, but because the stable minimum domain diameter is not reached, It shrinks and disappears, and no recording magnetic domain is formed.

(2) When long pulse light is applied to a place where there is no recording magnetic domain (FIG. 1B): A recording magnetic domain is formed by the demagnetizing field of the medium itself.

(3) When short pulse light is applied to the location where the previously recorded magnetic domain exists (FIG. 1 (c)): a nucleus of a re-inversion domain is formed at the center of the previously recorded magnetic domain, which grows and erases the previously recorded magnetic domain. I do.

(4) When a long pulse light is applied to a place where there is a previously recorded magnetic domain (FIG. 1D): Since the pulse is a long pulse, a recorded magnetic domain is formed regardless of the previous recording state.

When a recording medium having the characteristics shown in Table 1 (b) is used, the recording magnetic domain remains after irradiation with the long pulse light and does not remain after irradiation with the short pulse light regardless of the state of the previous recording. This makes it possible to directly perform overwriting without having to perform pre-reading.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples. As the recording film, a Gd ₁₅ Tb ₇ Co ₇₈ film was used. FIG. 2 shows the temperature dependence of the coercive force and magnetization of this film. The carry temperature of this film is 400 ° C, and the fault temperature is 70 ° C. FIG. 3 shows the static recording / erasing characteristics of this film. Recording was possible in the area (a) of FIG. Further, in the area shown in FIG. 3B, the recorded magnetic domains recorded in advance under the write conditions of 15 wW and 100 nsec could be erased. The boundaries between these regions largely depend on the DC bias magnetic field, and an optimum value for recording can be selected. Therefore, the following recording test was performed by applying a magnetic field of 500 Oe in the same direction as the direction of magnetization at a temperature higher than the temperature at which the medium was compensated.

The recording conditions used were a laser output of 15 mW and a pulse width of 50 nsec as a long pulse, and a laser output of 15 mW and a pulse width of 20 nsec as a short pulse. 1800 rpm for 3.5 inch disc
, And the tracking was performed by the sample servo method, and the timing was obtained by the embedded clocking method. Recording was performed at a fundamental frequency of 11 MHz. With respect to digital information, as a result of recording the magnetic domain of (a) first and then performing the recording with the modulated light of (c) corresponding to the recording code of (b) in the procedure shown in FIG. 3 as an example. , (D) were obtained corresponding to the recording magnetic domains. In this way, it was confirmed that overwriting was basically possible.

〔The invention's effect〕

According to the present invention, overwriting can be performed at high speed with only one rotation of the disk with a single beam.

[Brief description of the drawings]

FIG. 1 is a diagram showing the distribution of magnetization of the magneto-optical recording film during laser beam irradiation, FIG. 2 is a diagram showing the temperature dependence of the coercive force and saturation magnetization of the magneto-optical recording film of the embodiment, and FIG.
The figure is a diagram showing the static recording characteristics of the magneto-optical recording film of the embodiment,
FIG. 4 is a schematic diagram of overwriting by a digital signal.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigenori Okamine 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. Hitachi Central Research Laboratory (72) Inventor Toshiaki Tsuyoshi 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Tokyo Central Research Laboratory (72) Inventor Seiji Yonezawa 1-1280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. In the laboratory

Claims (1)

(57) [Claims] 1. A method of irradiating a magnetic material of a disk-shaped recording medium with light to magnetically record information by a demagnetizing field of the magnetic material, and arbitrarily irrespective of the recorded information from the recorded information. A magneto-optical recording method for overwriting new information, wherein a timing signal is obtained from marks arranged at predetermined intervals on the recording medium, a clock signal is formed based on the timing signal, and a pulse is generated based on the clock signal. The above-described overwriting is performed by irradiating light, a wide pulse light is applied to a portion where a recording magnetic domain is formed, a narrow pulse light is applied to a portion where a recording magnetic domain is not formed, and the overwriting is performed simply. This is performed within one revolution of the disk without reproducing the recorded information by one light spot. Magneto-optical recording method either have a pulse light or narrow pulse light, characterized in that it is irradiated.