JP2005044440A - Magneto-optical recording medium and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium capable of performing good domain wall motion reproduction without being affected by an MO signal from a servo area in which pits for performing sample servo control, pits indicating address information, and the like are formed. A manufacturing method thereof is provided.
An annealing region is formed between recording tracks, and the domain wall has a data region for recording data on the recording track, and a servo region in which pits for performing sample servo control and pits indicating address information are formed. In the movable magneto-optical recording medium, the servo region on the recording track is annealed. By performing this annealing process, the servo region is transformed into an in-plane magnetized film, so that no domain wall movement occurs and no DC fluctuation is induced.
[Selection] Figure 5

Description

  The present invention relates to a magneto-optical recording medium in which information is recorded as a magnetic domain pattern on a magnetic film and information is reproduced using a magneto-optical effect, and a method for manufacturing the same.

  In recent years, there has been an increasing demand for higher recording density of magneto-optical recording media, and in order to meet this demand, a technology for reproducing very fine recording marks exceeding the optical resolution has been developed. For example, a magnetic super-resolution reproduction method is known as a method for achieving this by devising a recording medium. 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 area that is effectively used, and thus there is a problem that the reproduction signal amplitude itself decreases.

  As a method for solving the above-mentioned problem, Japanese Patent Laid-Open No. 6-290496 proposes a method for enlarging and reproducing a recording mark instead of narrowing the signal detection area (see Patent Document 1). In the method of this publication, a magneto-optical medium composed of a plurality of magnetic layers is irradiated with a light spot, magnetic domains recorded as perpendicular magnetization are transferred to the reproducing layer, and the domain walls of the magnetic domains transferred to the reproducing layer are moved. Thus, reproduction is performed with a size larger than the magnetic domain of the recording layer. This domain wall motion detection method will be briefly described.

FIG. 6 is a schematic diagram for explaining the operation of the domain wall motion detection type magneto-optical recording medium and the reproducing method thereof. FIG. 6A shows the configuration of the recording medium and the magnetization state of each magnetic layer during reproduction. Here, the recording medium includes a first magnetic layer 11 having a small domain wall coercivity, a second magnetic layer 12 having a relatively low Curie temperature T _s, and a third magnetic layer 13 having a large domain wall coercivity. It has an exchange coupling three-layer film structure. An arrow 14 in each layer represents the direction of atomic spin, and a domain wall 15 is formed at the boundary between regions where the directions of spin are opposite to each other. The layer structure of the recording medium is not limited to this.

  When the reproducing laser beam 16 is scanned over the recording film surface and locally heated, a temperature distribution as shown in FIG. 6B is formed, and the domain wall energy density distribution is shown in FIG. 6C. As 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, the magnetic layers are exchange coupled. Therefore, even if the domain wall driving force F due to the temperature gradient described above acts, the third magnetic layer 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.

Each time domain walls formed in the recording film at intervals corresponding to signals pass through the position of temperature T _{s as} the medium scans, domain wall movement occurs in the moving layer. When the medium is scanned at a constant speed, this domain wall movement occurs at time intervals corresponding to the spatial intervals 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 utilizing 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 moving 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 domain wall motion detection method, in order to obtain a good reproduction signal with little 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 increases and the energy of the domain wall increases, and as a result, the domain wall movement operation becomes unstable.

  There are three methods for breaking the magnetic coupling. As a first method, a rectangular guide groove is provided between information tracks to reduce the magnetic film thickness on the side of the guide groove, and as a second method, a guide groove between the information track and the information track. This is a method of changing the magnetic properties by subjecting a part of the magnetic film to an annealing process with a high-power laser, and a third method of patterning by an etching process.

As a modification of the first method, a method (so-called land / groove recording method) in which the land portion and the rectangular groove portion are configured to have the same width and both the land and the rectangular groove are used for the information track is conceivable. In all of these methods, adjacent information tracks are divided by a method involving a change in physical shape and physical properties, and the recording mark is expanded without increasing the domain wall area.
Japanese Patent Application Laid-Open No. 6-290496

  When a magneto-optical recording medium having a servo area is annealed using the second method, the MO signal often causes DC fluctuations triggered by the servo area. For example, when a DC fluctuation occurs in each servo area, the signal quality may be deteriorated by causing a duty shift or worsening jitter. This phenomenon is considered to be caused by domain wall movement also occurring in the servo region, the reflectance changing at the pit portion, and the like.

  As a method for preventing the above-mentioned phenomenon, it has been proposed to devise a drive like masking by applying a DC magnetic field to the servo area during recording, but there is a problem that the magnetic head circuit control system becomes complicated. . Therefore, it has been desired to prevent the above-described phenomenon from occurring in the medium itself.

  The present invention has been made in view of the above-described conventional problems, and the object thereof is to make the domain wall moving and reproducing well without affecting the MO signal from the servo area by making the servo area an in-plane magnetization film. It is an object of the present invention to provide a magneto-optical recording medium that can be used and a manufacturing method thereof.

  In order to achieve the above object, according to the present invention, an annealing region is formed between recording tracks, and a data region for recording data, a pit for performing sample servo control, and a pit indicating address information are recorded on the recording track. In the domain wall motion type magneto-optical recording medium having the servo area formed with the servo area, the servo area on the recording track is an in-plane magnetization film.

  In the present invention, an annealing area is formed between recording tracks, and a data area for recording data, a pit for performing sample servo control, and a servo area having a pit indicating address information are formed on the recording track. In the method of manufacturing a domain wall motion type magneto-optical recording medium having the above-mentioned structure, the servo area of the recording track is annealed to form an in-plane magnetic film.

  According to the present invention, by making the servo area on the recording track an in-plane magnetic film, it is possible to prevent DC fluctuations in the MO signal caused by the servo area. Therefore, it is possible to obtain a good reproduction signal that is free from duty shift and jitter. Further, since a drive-like process for preventing a phenomenon that deteriorates the signal characteristics is not required, the recording control system is not complicated.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the layer structure of the magneto-optical recording medium of this embodiment. In FIG. 1, reference numeral 26 denotes a substrate, on which at least a dielectric layer 25, a first magnetic layer 21 (reproduction layer), a second magnetic layer 22 (adjustment layer), and a third magnetic layer 23 ( Recording layer) and dielectric layer 24 are sequentially laminated.

  As the substrate 26, for example, polycarbonate, acrylic, glass or the like is used. As the dielectric layer 24 and the dielectric layer 25, for example, a dielectric material such as SiN, AiN, SiO, ZiS, MgF, TaO can be used. If the movement of the domain wall is not detected optically, it does not necessarily have to be a translucent material. Note that layers other than the magnetic layer are not essential, and the stacking order of the magnetic layers may be reversed.

  A thermal property may be adjusted by adding a metal layer made of Al, AlTa, AlTi, AlCr, Cu, Pt, Au, or the like to this configuration. Moreover, you may provide the protective coat which consists of polymer resins. Each of these layers can be deposited by, for example, continuous sputtering using a magnetron sputtering apparatus or continuous vapor deposition. In particular, each magnetic layer is exchange-coupled by being continuously formed without breaking the vacuum.

In the magneto-optical recording medium, when the Curie temperature of the first magnetic layer 21 is T _c1 , the Curie temperature of the second magnetic layer 22 is T _c2 , and the Curie temperature of the third magnetic layer 23 is T _c3. The Curie temperature of the magnetic layer satisfies the following conditions: T _c1 > T _c2 , T _c3 > T _c2 .

  Various magneto-optical recording materials are conceivable. For example, one or more rare earth metal elements such as Pr, Nd, Sm, Gd, Tb, Dy, and Ho are 10 to 50 atomic%, Fe, Co, It may be composed of a rare earth-iron group amorphous alloy in which one or more of iron group elements such as Ni are composed of 90 to 50 atomic%. Further, in order to improve the corrosion resistance, a small amount of elements such as Cr, Mn, Cu, Ti, Al, Si, Pt, and In may be added thereto.

  The saturation magnetization can be controlled by the composition ratio of the rare earth element and the iron group element. The coercive force can be controlled by adjusting the saturation magnetization. Essentially, the perpendicular magnetic anisotropy is adjusted by selecting a material element. In general, materials such as Tb and Dy have a large perpendicular magnetic anisotropy and a large coercive force, whereas Gd materials have a small anisotropy and a small coercive force. In addition, the perpendicular magnetic anisotropy is reduced by the addition of a nonmagnetic element.

  The Curie temperature can also be controlled by the composition ratio. However, in order to control the Curie temperature independently of the saturation magnetization, there is a method for controlling the amount of substitution by using a material in which part of Fe is replaced with Co as an iron group element. More preferably, it can be used. That is, since the Curie temperature rise of about 6 ° C. can be expected by substituting 1 atomic% of Fe with Co, the addition amount of Co is adjusted so as to obtain a desired Curie temperature using this relationship. In addition, the Curie temperature can be lowered by adding a small amount of a nonmagnetic element such as Cr or Ti. Alternatively, the Curie temperature can be controlled by adjusting the composition ratio of two or more kinds of rare earth elements.

Here, the domain wall coercivity of the first magnetic layer 21 of the magneto-optical recording medium according to the present embodiment is greater than the domain wall coercivity of the third magnetic layer 23 at a temperature _{equal to} or higher than the Curie temperature T _{c2 of} the second magnetic layer 12. It is a small one. The first magnetic layer 21, that is, the reproducing layer, reproduces the magnetic domain recorded on the recording layer by using the function of the adjusting layer and the temperature gradient caused by the laser spot.

Further, in the multilayer magnetic film such as the magneto-optical recording medium of the present embodiment, an exchange force is exerted to align the same type of sub-lattice magnetization directions between adjacent magnetic layers in the same direction. This magnetic coupling between adjacent layers is called exchange coupling, but in the magneto-optical recording medium according to the present embodiment, the first magnetic layer passes from the third magnetic layer 23 through the second magnetic layer 22. A temperature at which the exchange coupling force exerted on 21 exceeds the coercive energy of the first magnetic layer 21 exists in a temperature range between ambient temperature and T _c2 . Therefore, by passing through this temperature during the temperature rising / falling operation, the magnetization directions of the first magnetic layer 21 and the second magnetic layer 22 are changed to the third temperature at the ambient temperature or a temperature between ambient temperature and T _c2 . The magnetization direction of the magnetic layer 23 can be aligned.

The third magnetic layer 23 is preferably a perpendicular magnetization film having a large perpendicular magnetic anisotropy in order to stably hold recorded information recorded as magnetic domains. The Curie temperature T _c3 of the third magnetic layer 23 needs to be higher than the Curie temperature T _c2 of the second magnetic layer 22, has practical recording sensitivity, and performs a stable reproducing operation. Is preferably 120 ° C. or higher and 360 ° C. or lower.

  Next, the manufacturing method of the magneto-optical recording medium of this embodiment will be described with reference to FIG. First, the polycarbonate substrate 26 is molded (step 101). Next, the target of each material described above is attached to the DC magnetron sputtering apparatus, and the polycarbonate substrate 26 on which the guide groove (guide band) for tracking is formed is fixed to the substrate holder, and then a high vacuum of 1 × 10 −5 Pa or less is obtained. The chamber is evacuated with a cryopump until it becomes. Ar gas is introduced into the chamber while being evacuated, and each layer is formed by sputtering the target while rotating the substrate 26.

  First, the dielectric layer 25 is formed as a base layer (step 102). Subsequently, the first magnetic layer 21, the second magnetic layer 22, and the third magnetic layer 23 are sequentially formed (step 103). Next, the dielectric layer 24 is formed as an upper layer (step 104). After the formation of the dielectric layer 24, the magneto-optical recording medium is taken out of the sputtering apparatus and annealed (step 105). When the annealing process is completed, a protective coat is formed on the substrate surface (step 106), and the magneto-optical recording medium is completed.

  FIG. 3 is a block diagram showing an example of an annealing apparatus for a magneto-optical recording medium. As shown in FIG. 3, the annealing apparatus includes a spindle motor 102 that rotationally drives the magneto-optical recording medium 101, a spindle servo circuit 103 that controls the spindle motor 102, and a pickup 104 that irradiates a laser beam for annealing the magneto-optical recording medium 101. A servo circuit 105 that performs servo control of the laser beam of the pickup 104, a laser power control circuit 106 that controls the laser power of the laser beam of the pickup 104, and a controller 107 that controls each part in the apparatus.

  The magneto-optical recording medium 101 is controlled so as to maintain a prescribed linear velocity by driving the spindle motor 102 based on the control of the spindle servo circuit 103, and rotates in the arrow direction 56 in FIG. The pickup 104 is controlled by a servo circuit 105 for focus servo, tracking servo, radial movement control, and the like. The laser beam emitted from the pickup 104 is controlled to a predetermined annealing power by the laser power control circuit 106.

  The controller 107 is a microcomputer including a CPU, a ROM, a RAM, and the like, and controls each part of the annealing processing apparatus of the present embodiment. The CPU recognizes the position on the magneto-optical recording medium 101 being scanned based on the reproduction address data, and scans the target track on the magneto-optical recording medium 101 based on the reproduction address data. Then, a control signal to be supplied to the spindle servo circuit 103 or the like is created and supplied to each unit.

  The servo circuit 105 is supplied with a focus error signal, a tracking error signal, and the like from the pickup 104, and the controller 107 is supplied with, for example, information indicating a position on the magneto-optical recording medium 101. Further, information from the pickup 104 and a control signal from the controller 107 are also supplied to the spindle servo circuit 103 and the laser power control circuit 106 to perform target control.

  The pickup 104 also includes a photodetector that receives the reflected light of the laser beam applied to the magneto-optical recording medium 101, and generates a tracking error signal and a focus error signal based on the received light signal of each detector divided by the photodetector. To do. These signals are supplied to the servo circuit 105, and the laser beam from the pickup 104 is subjected to tracking control and focus control by the control of the servo circuit 105, and the target track is scanned based on the control signal from the controller 107. can do.

  Here, when performing the annealing process, the magneto-optical recording medium 101 is controlled by the controller 107 so that the laser spot is irradiated on the innermost circumference or the outermost circumference. The magneto-optical recording medium 101 is controlled by the spindle servo circuit 103 so as to maintain the linear velocity for annealing, and the laser beam emitted from the pickup 104 is controlled by the laser power control circuit 106 so as to have a predetermined annealing power. The Further, a focus error signal and a tracking error signal are detected by a mechanism (not shown), and the laser beam is controlled so as to scan the center of the track to be annealed.

  FIG. 4 is an enlarged view showing a part of the magneto-optical recording medium during the annealing process. In FIG. 4, the magneto-optical recording medium 101 will be described for use in groove recording in which main data is recorded in a groove portion, that is, a groove track. First, the laser spot 53 is focused on the magnetic layer of the magneto-optical recording medium 101 by the objective lens 52. The magneto-optical recording medium 101 of this embodiment uses a spiral substrate. In this example, a groove portion 54 and a land portion 55 are formed in the magneto-optical recording medium 101 by forming grooves (grooves) in a spiral shape. The land portion 55 is a convex portion formed so as to be sandwiched between the grooves.

  As shown in FIG. 4, the annealing process scans the land portions 55a, 55b, 55c,... Of the magneto-optical recording medium 101 in this order, and continuously performs the annealing process from the innermost circumference to the outermost circumference.

  FIG. 5 shows the magneto-optical recording medium after the annealing treatment. FIG. 5A shows a conventional medium, and FIG. 5B shows a medium according to the present embodiment. The magneto-optical recording medium 101 is composed of a recording area and a servo area in which pits are formed in the mirror portion. In this embodiment, the recording track is annealed as shown in FIG. The servo area on the track is annealed. On the other hand, conventionally, as shown in FIG. 5A, only the recording tracks are annealed, and the servo areas on the recording tracks are not annealed.

  As a method for annealing the servo region, for example, there is a method in which after a series of land portions are annealed, the groove portion is scanned while annealing with high output power while only the servo region is gated. As described above, in the present embodiment, the annealed servo region is transformed into an in-plane magnetization film, so that the domain wall does not move at all and does not induce DC fluctuation.

  In the above embodiment, the example in which the servo region of the magneto-optical recording medium for groove recording is annealed has been described. However, the present invention is not limited to this, and all light having a servo region is provided. Needless to say, the magnetic recording medium can be used.

1 is a cross-sectional view showing a configuration of an embodiment of a magneto-optical recording medium of the present invention. 3 is a flowchart showing manufacturing steps of the magneto-optical recording medium of the present invention. It is a figure which shows an example of the annealing treatment apparatus used for manufacture of the magneto-optical recording medium of this invention. It is a figure which expands and shows a part of magneto-optical recording medium at the time of an annealing process. It is a figure which shows the medium surface after the annealing process of this invention and a prior art example. It is a figure for demonstrating a domain wall movement reproduction | regeneration system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 1st magnetic layer 22 2nd magnetic layer 23 3rd magnetic layer 24, 25 Dielectric layer 26 Substrate 52 Objective lens 53 Laser spot 54 Groove part 55a, 55b, 55c Land part 101 Magneto-optical recording medium 102 Spindle motor 103 Spindle Servo Circuit 104 Pickup 105 Servo Circuit 106 Laser Power Control Circuit 107 Controller

Claims (4)

Annealing regions are formed between the recording tracks, and the domain wall motion includes a data region for recording data on the recording tracks, and a servo region in which pits for performing sample servo control and pits indicating address information are formed. Type magneto-optical recording medium, wherein the servo area on the recording track is an in-plane magnetized film. The recording track includes a first magnetic layer in which a domain wall is movable, 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, the first magnetic layer, and a third magnetic layer 2. The magneto-optical recording medium according to claim 1, further comprising: a second magnetic layer disposed between the first magnetic layer and the second magnetic layer having a Curie temperature lower than that of the first magnetic layer and the third magnetic layer. 2. The magneto-optical recording medium according to claim 1, wherein the servo area is annealed to form an in-plane magnetization film. A domain wall motion type in which an annealing region is formed between recording tracks, and the recording track has a data region for recording data, and a servo region in which pits for performing sample servo control and pits indicating address information are formed. In the method for manufacturing a magneto-optical recording medium, a method for manufacturing a magneto-optical recording medium, wherein annealing of the servo area of the recording track is performed to make the servo area an in-plane magnetization film.

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