JPH04325947A - Magneto-optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To provide the large capacity magneto-optical recording and reproducing device having a high data transfer rate. CONSTITUTION:In the information recording and reproducing device enabling magnetic domain wall moving type overwrite, recorded data are reproduced by setting laser emitting power near a recording threshold value in the case of reproducing recorded information. Since reproduction beams have no inter-bit interference, even the data recorded with high density can be reproduced as well, and the capacity and the data transfer rate of the recording and reproducing device is improved.

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 and reproducing apparatus that performs direct overwriting of information by modulating a laser beam.

0002

2. Description of the Related Art With recent steady progress in magneto-optical recording and reproducing devices, overwriting, which remained a problem in first generation devices, is being solved by several means. One of the overwriting methods is H. P. D. Shie
h andM. H. Kryder. Appl. Phys.
．． Lett. 49 (1986) 473 and D. Rugar
, J. C. Suits and C-J. Lin. Ap
pl. Phys. Lett. 52, 1537 (1988
), the principle of which was announced in 1999, and is currently being applied to a method generally referred to as ``domain wall displacement type overwriting'' (hereinafter abbreviated as domain wall displacement type). A type of light modulation method,
By devising the method of irradiating the laser beam,
Direct overwriting of information is achieved without changing the direction and magnitude of the bias magnetic field. In normal magneto-optical recording, information is recorded by making the two stable magnetization directions of a perpendicular magnetic recording film correspond to 0 and 1, respectively (here, the state with no magnetic domain is assumed to be information 0). In this method, the gradient of the temperature distribution formed on the medium is controlled by changing the pulse width and intensity of the laser beam for recording and erasing information. By forming a steep temperature gradient, if a magnetic domain had already been formed there (information 1 was recorded), the domain would shrink and disappear, and if no magnetic domain existed until now (information 0), the magnetic domain would shrink and disappear. When the magnetic domain was recorded), the magnetic domain was not formed and remained as it was, and in either case, information 0 was recorded. Furthermore, by forming a relatively gentle temperature gradient, magnetic domains are formed and expanded, and bits, ie, information 1, are recorded, whether magnetic domains exist or not. Direct overwriting of information is performed by combining these two methods of providing temperature gradients according to the data to be recorded (data string of 1 and 0). On the other hand, information can be reproduced in the same way as a normal magneto-optical recording/reproducing device.
This was done by continuously irradiating a laser beam with an output energy considerably lower than the recording threshold power of the disk.

0003

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, in order to prevent recorded data from being erased when reproducing information, a laser beam with emission energy considerably lower than the recording threshold of the disk is used. This was done by continuous irradiation. Therefore, when recording at high density by making the interval between recording bits smaller than the beam radius of the reproduction beam, waveform interference occurs between bits during reproduction, making it impossible to reproduce information, making it impossible to substantially improve recording density. This poses a problem.

[0004]The present invention is intended to solve these problems, and its purpose is to use a continuous light beam with an output energy near the recording threshold of the disk as a laser beam for information reproduction. By temporarily erasing the bits that have just been reproduced during passing or making them so small that they cannot be detected optically, high-density recorded data can be reproduced without waveform interference, resulting in a large storage capacity that can be directly overwritten, and bit spacing. Since the data transfer rate is small, it is possible to provide a magneto-optical recording/reproducing device with an effective high data transfer rate. Note that the principle used in the present invention is based on experimental facts confirmed with a TbFeCo recording film. That's J. Appl. Phys. It applies the principles described in In overwrite media used for domain wall displacement type, during the recording process, if magnetic domains have been formed beforehand, when a recording pulse is irradiated, the magnetic domains disappear, and after some time elapses, magnetic domains are formed again and recording ends. . Furthermore, if no magnetic domains have been formed in advance, magnetic domains will be formed over time and recording will be completed. This is because when the temperature is raised by the laser, a situation where the gradient of the temperature distribution is large is formed, so the magnetic domains disappear, and when the temperature is reduced, a situation where the gradient of the temperature distribution is gentle is formed, the magnetic domains are formed and expanded, and pits are recorded. Use this for moving beams. In the spot area where the continuous light for reproduction is irradiated, the temperature at the beginning of the beam (front of the beam) due to the laser irradiation has not yet risen significantly, so the information in this area does not disappear and pit information is superimposed on the reflected light. ing. Near the center of the beam, the temperature rises considerably and the temperature gradient becomes steeper, causing the magnetic domains to shrink or disappear. Furthermore, at the rear end of the beam and where cooling is occurring, the temperature distribution becomes broad, and the magnetic domains that had contracted or disappeared are re-formed. When this process is observed using the reproducing system of an optical head, only the portion of the reflected light from the front part of the beam is reproduced, and furthermore, the bits remain recorded even after the beam has passed. By using this, it is possible to reproduce information bit sequences arranged no matter how limited the spatial resolution is due to the lens of the optical head.

[0005]

[Means for solving the problem] A magneto-optical recording and reproducing device that has a single-layer magnetic film for recording and reproducing information, and performs direct overwriting of information only by modulating a laser beam without changing the direction and magnitude of the bias magnetic field. The invention is characterized in that the output energy of the laser beam during information reproduction is continuous light near the recording threshold of the disk.

[0006]

EXAMPLES (Example 1) The present invention will be explained in detail below based on examples.

The magneto-optical disk used in this example was a 5.25-inch diameter glass disk substrate with continuous grooves, a 65 nm SiN protective film, a GdTbFeCo100
A protective film of 65 nm and 65 nm of SiN was sequentially laminated by sputtering. The disk was initialized in a DC magnetic field and used.

First, the recording power threshold of this disc was determined. Recording was performed at a recording frequency of 3.7 MHz and an applied magnetic field of 300 Oe, and the carrier-to-noise ratio (hereinafter referred to as CNR) of the reproduced signal was measured using a spectrum analyzer at a resolution bandwidth of 30 kHz. 0.8mW during playback
irradiated with continuous light. The measurement results are shown in Figure 2. CNR gradually rises from 3 mW and reaches almost saturation at 5 mW. The behavior is almost the same even if the recording frequency is changed. Therefore, it was found that the threshold value of this disk was approximately 3 mW.

Next, it was confirmed that this disk was overwritable. The linear velocity, applied magnetic field, and beam diameter were the same as in the reproduction experiment shown later. Recording frequency 2MHz,
When recording with a recording power of 6 mW and reproducing with a reproducing power of 0.8 mW, the CNR was 50 dB (resolution bandwidth 30 k).
Hz) was obtained. Furthermore, the recording signal frequency is 3 MHz, the recording power is 6 mW, and the repetition frequency is 10 as shown in Figure 3.
CNR was measured by irradiating a mixture of erase pulses of MHz, power 9 mW, pulse width 30 nsec. Result 2
The noise level of the MHz signal component peaked at 3 MHz, and a CNR of 48 dB was obtained, confirming that domain wall displacement type overwriting is possible.

Next, a playback experiment was conducted using this disc. Assuming that the applied magnetic field is constant at 300 Oe in the information recording direction,
It was always applied regardless of whether it was recording or erasing. The beam spot diameter is (1/e2 centered on beam intensity) 1.58 μm. Linear speed 5.7m/s, laser modulation frequency from 2MHz to 1M
The frequency was changed every Hz to 12 MHz while maintaining a duty of 30%, the recording laser power was changed to 6 mW, and the playback laser power was changed from 1 mW to every 0.5 mW, and the playback signal strength and carrier-to-noise ratio (CNR) depended on the playback power. I looked into gender. As a result, the reproduction power at each frequency is approximately 2.
It reaches a peak at 8 mW, and the CNR obtained is low regardless of whether it is higher or lower than that. The highest CNR at each frequency is shown in Figure 1. Furthermore, FIG. 4 shows the recording frequency dependence of CNR by the conventional reproduction method (reproducing optical power 0.7 mW). In the conventional reproduction method, the CNR becomes almost zero at a recording frequency of 7 MHz, indicating that this is the limit of recording density. On the other hand, it can be seen that according to the present invention, the reproducible frequency band is significantly expanded. In addition, no change was observed in the signal after playing back 1 million times at each frequency.

[0011] Incidentally, it is possible to read high-density recorded information not only on domain wall displacement type overwritable media but also on normal media by increasing the power of the reproduction light, but the pits immediately after reproduction are erased. Since the information remains unchanged, the information will be erased once it is read. In the present invention, it has also been confirmed that even after the information is reproduced, the information remains and can be read out multiple times.

As described above, the reproduction frequency of information is improved, data recorded at high density can be reproduced, and overwriting is also possible, so that a large-capacity magneto-optical recording/reproducing device with a high data transfer rate can be provided.

[0013]

[Effects of the Invention] As described above, according to the present invention,
In the domain wall motion overwrite method, by setting the laser irradiation energy during data reproduction near the recording threshold, it becomes possible to perform high-density recording and reproduction that exceeds the conventional optical limit and exceeds the high-density recording limit. A magneto-optical recording/reproducing device with a high data transfer rate that can be overwritten can be provided. The magneto-optical recording and reproducing device of the present invention can be applied to optical information recording and reproducing devices such as computer memories and optical disk files, and has great effects such as improving the performance of the device.

[0014]

[Brief explanation of drawings]

FIG. 1 is a diagram showing the dependence of the carrier-to-noise ratio of a reproduced signal on a recorded signal frequency by a magneto-optical recording/reproducing apparatus of the present invention.

FIG. 2 is a diagram showing the recording power dependence of carrier-to-noise ratio in a 3.7 MHz recording signal.

FIG. 3 is a diagram illustrating pulses used for overwriting.

FIG. 4 is a diagram showing the dependence of the carrier wave-to-noise ratio of a reproduced signal on a recorded signal frequency by the magneto-optical recording/reproducing apparatus of the present invention.

Claims (1)

[Claims] [Claim 1] In a magneto-optical recording and reproducing device in which the information recording and reproducing magnetic film is a single layer and direct overwriting of information is performed only by modulating a laser beam without changing the direction and magnitude of the bias magnetic field, information reproducing is possible. 1. A magneto-optical recording and reproducing device, characterized in that the output energy of the laser beam is continuous light in the vicinity of the recording threshold of the disk.