JP2006085804A - Magneto-optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium enabling to record a good reproduced signal even if taper angles of side wall parts of left and right are non-symmetry. <P>SOLUTION: The magneto-optical recording medium which has a land and a groove utilized as a recording track of information and in which taper angles of side wall parts are different for left and right, has a first magnetic layer in which a magnetic wall is movable, a third magnetic layer which has a recording magnetic sector and of which the magnetic wall coercive force is larger than the first magnetic layer, a second magnetic layer of which the Curie temperature is lower than the first magnetic layer and the third magnetic layer and which is arranged between the first magnetic layer and the third magnetic layer, and an anneal region formed at a side wall part between recording tracks, and it is characterized in that the anneal region is formed so as to coincide with a side wall region. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magneto-optical recording medium that records information as a magnetic domain pattern on a magnetic film and reproduces the information using a magneto-optical effect.

  In recent years, there has been an increasing demand for higher recording density of magneto-optical recording media, and in response to this, a technique for reproducing very fine recording marks exceeding the optical resolution has been developed. As a method for achieving this by devising a recording medium, a magnetic super-resolution reproduction method is known. In this method, in the magnetic multilayer film, the recording mark is transferred only to the detection area narrower than the spot diameter of the reproducing laser, and in other areas, the signal detection area is substantially masked. Therefore, reproduction exceeding the resolution of the optical system becomes possible. However, in order to improve the reproduction resolution in the magnetic super-resolution reproduction method, it is necessary to narrow the signal detection region that is effectively used, and thus there is a drawback that the reproduction signal amplitude itself decreases.

FIG. 1 is a schematic diagram for explaining the operation of the domain wall motion detection type magneto-optical recording medium and the reproducing method thereof. As shown in FIG. 1 (a), the recording medium and the first magnetic layer 11 having a small magnetic wall coercivity, a second magnetic layer 12 having a relatively low Curie temperature T _s, large wall coercivity It is comprised by the exchange coupling 3 layer film | membrane which consists of the 3rd magnetic layer 13 which has these. Arrows 14 in each layer indicate the direction of atomic spin. A domain wall 15 is formed at the boundary between regions where spin directions are opposite to each other. When the recording film surface is locally heated using the reproducing laser beam 16, a temperature distribution as shown in FIG. 1B is formed, and the domain wall energy density distribution is shown in FIG. ). Since the domain wall energy density generally decreases as the temperature rises, the distribution is such that the domain wall energy density is the lowest at the peak temperature position. As a result, a domain wall driving force F is generated which attempts to move the domain wall of the first magnetic layer existing at the position X to the high temperature side where the energy density is low. In the place where the medium temperature is lower than the Curie temperature T _s of the second magnetic layer, each magnetic layer is exchange-coupled. Therefore, even if the domain wall driving force due to the temperature gradient described above acts, The domain wall movement does not occur due to the large domain wall coercive force. However, since the exchange coupling between the first magnetic layer and the third magnetic layer is cut at a place higher than the medium temperature T _s , the domain wall in the moving layer having a small domain wall coercive force is a domain wall due to a temperature gradient. The domain wall can be moved by the driving force. Therefore, with the scanning of the medium, at the moment the domain wall has entered the binding cutting region beyond the position of the temperature T _s, the domain wall motion occurs to the high temperature side in the moving layer.

Domain walls are formed in corresponding to the signal during the recording film interval, each time through the position of the temperature T _s with the scanning of the medium, the magnetic domain wall displacement is generated in the moving bed. When the medium is scanned at a constant speed, this domain wall movement occurs at a time interval corresponding to the spatial interval of the recorded domain walls. Therefore, the recording signal can be reproduced by detecting the occurrence of the domain wall motion. The occurrence of the domain wall motion can be detected by using the rotation of the polarization plane (Kerr effect) corresponding to the magnetization direction of the domain wall motion region by the reproducing laser beam.

The signal amplitude is determined by the domain wall travel distance, and does not depend on the recorded distance between domain walls, that is, the domain length. Further, instead of the reproduction spot, since isotherm temperature T _s is to continue to discriminate recording pattern, it can be reproduced independently of the signal from the resolution of the optical system.

  In a magneto-optical recording medium using the above-described domain wall motion detection method, in order to obtain a good reproduction signal with less noise, it is necessary to break the magnetic coupling of the magnetic layer between adjacent information tracks. If the magnetic film between the information tracks is a uniform film that is physically and physically continuous, the recording mark exists as a magnetic domain surrounded by a closed domain wall. If it is attempted to move the domain wall in the direction, the domain wall area inevitably expands and the energy of the domain wall increases, and as a result, the operation of domain wall movement becomes unstable.

In order to break the magnetic coupling, the present invention uses a method in which the magnetic film on the side walls between the lands and grooves used as information tracks is annealed with a high-power laser to alter the magnetic properties. By using this method, the recording mark can be enlarged without increasing the domain wall area, and a good reproduction signal with less noise can be obtained.
Japanese Patent Application Laid-Open No. 6-290496

  However, when the sidewall treatment is performed on the substrate having the lands and grooves described above, there are cases where the annealing regions are different between the left and right sidewall portions. This is because the taper angles of the left and right side wall portions do not completely coincide with each other in an actual substrate, so that when the side wall portions are annealed with the same laser power, they are annealed asymmetrically on the left and right sides. It is done. For example, when the mark recorded on the magneto-optical recording medium subjected to the annealing treatment is observed with MFM, it can be confirmed that the edge portion of the recording mark adjacent to the annealing region is asymmetric on the left and right. Such a recording mark shape prevents smooth movement of the domain wall at the time of signal reproduction, and can be a major factor that causes a deterioration in jitter of the reproduction signal.

  Therefore, the present invention enables the recording of a good reproduction signal by forming the annealing region formed in the side wall portion between the recording tracks so as to coincide with the side wall region even if the taper angles of the left and right side wall portions are asymmetric. It is an object of the present invention to provide a magneto-optical recording medium.

  An object of the present invention is to provide a first magnetic layer having a land and a groove used as an information recording track and having a side wall with a taper angle different on the left and right, a magnetic wall of which can be moved, and a recording magnetic domain. A third magnetic layer having a domain wall coercive force greater than that of the first magnetic layer, and the first magnetic layer and the first magnetic layer having a Curie temperature lower than those of the first magnetic layer and the third magnetic layer. A second magnetic layer disposed between the three magnetic layers and an annealing region formed in a side wall portion between the recording tracks, and the annealing region is formed to coincide with the side wall region. This is achieved by the featured magneto-optical recording medium.

  Further, since the annealing region is formed so as to coincide with the sidewall region, the power during the annealing process for forming the annealing region is corrected by the left and right sidewall portions. The

  As described above, according to the magneto-optical recording medium of the present invention, even if the taper angles of the left and right side wall portions are asymmetric, the annealing region formed in the side wall portion between the recording tracks is formed so as to coincide with the side wall region. Thus, it is possible to provide a magneto-optical recording medium that can record a good reproduction signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Referring to FIG. 2, there is shown a schematic sectional view showing the layer structure of the magneto-optical recording medium used in the present invention. That is, at least the dielectric layer 25, the first magnetic layer 21 (reproducing layer), the second magnetic layer 22 (adjustment layer), the third magnetic layer 23 (recording layer), and the dielectric layer 24 are formed on the substrate 26. They are sequentially stacked.

  In the magneto-optical recording medium, the Curie temperature of the first magnetic layer is Tc1, the Curie temperature of the second magnetic layer is Tc2, and the Curie temperature of the third magnetic layer is Tc3. Satisfies the conditions of the following expressions Tc1> Tc2 and Tc3> Tc2.

  Next, a method for manufacturing the magneto-optical recording medium of the present invention will be described.

  After attaching the target of each material described above to the DC magnetron sputtering apparatus and fixing the polycarbonate substrate on which the guide groove (guide band) for tracking is formed to the substrate holder, until a high vacuum of 1 × 10 −5 Pa or less is achieved The chamber is evacuated with a cryopump. Ar gas is introduced into the chamber while being evacuated, and the layers are formed by sputtering the target while rotating the substrate.

  First, the dielectric layer 25 is formed as a base layer. Subsequently, a first magnetic layer, a second magnetic layer, and a third magnetic layer are sequentially formed.

  After the dielectric layer 24 is formed as the upper layer, the magneto-optical recording medium is taken out of the sputtering apparatus and annealed.

  FIG. 3 shows the configuration of the magneto-optical recording medium annealing apparatus of the present invention. As shown in FIG. 3, the annealing apparatus includes a spindle motor, a spindle servo circuit, a pickup, a servo circuit, a laser power control circuit, and a controller.

  It is assumed that the magneto-optical recording medium is rotated in a certain direction by a spindle motor controlled so as to maintain a prescribed linear velocity by a spindle servo circuit.

  The optical pickup unit is controlled by a servo circuit such as focus servo, tracking servo, or movement control in the radial direction. The laser beam emitted from the optical pickup unit is controlled by the laser power control circuit so as to have a predetermined annealing power.

  The control unit is a microcomputer including a CPU, a ROM, a RAM, and the like, and controls each unit of the annealing apparatus of this embodiment. The CPU knows the position on the magneto-optical recording medium being scanned based on the reproduction address data, and servos so that the target track on the magneto-optical recording medium can be scanned based on the reproduction address data. A control signal to be supplied to a circuit, a spindle circuit, etc. is formed and supplied to each part.

  The servo circuit is supplied with a focus error signal, a tracking error signal, and the like from the optical pickup unit, and is supplied with information indicating a position on the magneto-optical recording medium, for example, from the control unit. Also, the spindle servo circuit and the laser power control circuit are supplied with information from the optical pickup and a control signal from the control unit so that the target control can be performed.

  Further, the optical pickup in the present invention performs tracking by the three-spot method. In the three-spot method, the outgoing beam is divided into a main beam and two sub-beams by a diffraction grating and irradiated onto the magneto-optical recording medium. FIG. 4 shows the relationship between the main spot and sub-beam spot irradiated on the magneto-optical recording medium during the annealing process. The main spot is used for annealing the side wall, and the sub beam is used for tracking the side wall. First, the two sub-beam spots are irradiated on the land and the groove, respectively, and the reflected light from these two sub-beam spots is received by a photodetector to obtain a differential push-pull signal by obtaining a difference. The differential push-pull signal is supplied to the servo circuit, and the main beam can stably scan the side wall of the target track based on the control signal from the control unit. The main beam spot is irradiated on the side wall portion at the boundary between the land and the groove, so that the side wall portion is annealed as the magneto-optical recording medium is scanned. Further, the reflected light from the main beam spot is received by a photodetector to obtain a sum signal. When the taper angle of the side wall portion is different between right and left, the change is reflected in the sum signal level, so that the asymmetry of the side wall portion can be detected by detecting the sum signal.

  In the above configuration, the magneto-optical recording medium is annealed. The magneto-optical recording medium is controlled by the control unit so that the laser spot is irradiated on the innermost circumference or the outermost circumference. The magneto-optical recording medium is controlled to maintain the linear velocity for annealing by the spindle servo circuit, and the laser beam emitted from the optical pickup unit is controlled to have a predetermined annealing power by the laser power control circuit. The

  FIG. 5 shows a sectional view of a conventional magneto-optical recording medium during annealing. It is assumed that the side wall 1 and the side wall 2 are asymmetric, and the side wall 2 has a smaller taper angle. When the same laser power is irradiated to each side wall from the main spot, it is considered that an annealing region as shown in the figure is formed as a result from the relationship between the temperature distribution during annealing and the annealing temperature serving as a threshold value. Although the side wall width in the side wall portion 1 and the annealing region width are the same, the annealing region width in the side wall portion 2 is narrower than the side wall width. Therefore, when marks are recorded on the land portion and the groove portion, the edge portion of the recording mark adjacent to the side wall portion 2 is curved and formed so as to protrude into the region of the side wall portion 2 as shown in the figure.

  FIG. 6 shows a cross-sectional view of the magneto-optical recording medium during the annealing process of the present invention. As in FIG. 5, the side wall 1 and the side wall 2 are asymmetric, and it is assumed that the side wall 2 has a smaller taper angle. In the present invention, the difference in taper angle of the side wall is detected by detecting the sum signal from the main beam spot, and the annealing power is corrected based on the detected difference. How to determine the annealing power correction amount for the actual change of the sum signal level depends on the substrate and the magnetic film to be used, so the change of the sum signal level and the optimal annealing power correction amount are determined in advance. Is obtained using a table experimentally obtained from the reproduction signal characteristics. By irradiating with the corrected annealing power, annealing is performed so that the side wall width and the annealing region width coincide with each other as shown in the drawing. Therefore, when marks are recorded in the land portion and the groove portion, the magnetic domain shape is close to a rectangle, and the domain wall movement during reproduction can be performed smoothly.

  Finally, a protective coat is formed on the magneto-optical recording medium that has been annealed.

  The magneto-optical recording medium of the present invention can be manufactured through the above steps.

FIG. 3 is a diagram schematically showing the concept of the domain wall motion reproduction method of the present invention when a magneto-optical recording medium having first to third magnetic layers is used. (A) shows a cross section of the medium in a reproduction state. (B) shows the temperature distribution on the medium at the position shown in (a), and (c) shows the domain wall at the same position. The distribution of energy density and accompanying force distribution acting on the domain wall are shown schematically. 1 is a schematic cross-sectional view showing a layer configuration of a magneto-optical recording medium of the present invention in an embodiment. 1 shows a configuration of a magneto-optical recording medium annealing apparatus of the present invention in an embodiment. The relationship between the main spot and the sub beam spot irradiated to the magneto-optical recording medium during the annealing process in the embodiment is shown. 1 shows a cross-sectional view of a magneto-optical recording medium during a conventional annealing process. 1 is a cross-sectional view of a magneto-optical recording medium during an annealing process of the present invention in an embodiment.

Explanation of symbols

11,31 1st magnetic layer
12,32 Second magnetic layer
13,33 Third magnetic layer
14 Direction of electron spin
15 Domain wall
15 Beam spot for playback
16 Domain wall travel direction
18,46 Medium moving direction
24 Dielectric layer
25 Dielectric layer
26 Board

Claims (3)

In a magneto-optical recording medium having lands and grooves that are used as information recording tracks, and the taper angles of the side walls are different on the left and right,
A first magnetic layer having a movable domain wall; a third magnetic layer that holds a recording magnetic domain and has a domain wall coercive force larger than that of the first magnetic layer; and the first magnetic layer and the third magnetic layer. The second magnetic layer having a low Curie temperature and disposed between the first magnetic layer and the third magnetic layer, and an annealing region formed in a side wall portion between the recording tracks, the annealing region Is formed so as to coincide with the side wall region.   2. The magneto-optical recording medium according to claim 1, wherein power during annealing for forming the annealing region is corrected by left and right side walls.   The means for correcting the power during annealing according to claim 2 at the left and right side walls detects a difference in taper angle between the left and right side walls at the sum signal level from the main beam irradiated to the side walls during annealing. And determining the amount of correction, and a method for annealing the magneto-optical recording medium.

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