JP2006059500A - Magnetic wall movement type magneto-optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic wall movement type magneto-optical recording medium which needs annealing processing for obtaining good recording/reproducing characteristics in a simple step when reproduction is carried out by using a blue purple laser with a wavelength of about 350 nm to 450 nm. <P>SOLUTION: The magnetic wall movement type magneto-optical recording medium for performing reproduction by using a blue purple laser with a wavelength of about 350 nm to 450 nm is characterized in that when the minimum thickness of a first dielectric layer whose reflectance becomes minimum is defined as dRmin1 and the minimum thickness of the first dielectric layer whose reflectance becomes maximum is defined as dRmax1 when a laser beam used for reproduction is applied from the first dielectric layer side, dRmax1-4(dRmax1-dRmin1)/5≤d≤dRmax1+4(dRmax1-dRmin1)/5 is satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a domain wall motion type magneto-optical recording medium suitable for ultra high density recording utilizing domain wall motion during reproduction, in which reproduction is performed using a blue-violet laser having a wavelength of about 350 nm to 450 nm as laser light. is there.

  Various magnetic recording media have been put into practical use as rewritable information recording media. In particular, a magneto-optical recording medium that records information by writing magnetic domains in a magnetic thin film using the thermal energy of a semiconductor laser and reads out recorded information using a magneto-optic effect (Keer effect) has a high density. It is expected to be a large capacity interchangeable medium that can be recorded.

  In recent years, with the digitization of moving images, there is an increasing demand for recording media with higher capacity by increasing the recording density of these magnetic recording media.

  In general, the linear recording density of an optical recording medium greatly depends on the wavelength of the laser beam of the reproducing optical system and the numerical aperture NA of the objective lens. That is, since the beam waist diameter is determined by determining the wavelength λ of the laser beam of the reproducing optical system and the numerical aperture NA of the objective lens, the spatial frequency of recording pits capable of signal reproduction is limited to about 2 NA / λ. . Therefore, in order to realize high density in the conventional optical disc, it is necessary to shorten the wavelength λ of the laser beam of the reproducing optical system or increase the numerical aperture NA of the objective lens.

  On the other hand, various so-called super-resolution techniques have been proposed in which the recording density is improved by devising the configuration and reproducing method of the recording medium without changing the wavelength λ of the laser beam and the numerical aperture NA of the objective lens.

  For example, Japanese Patent Application Laid-Open No. 3-93058 discloses a multilayer film structure including a reproducing layer and a recording holding layer that are magnetically coupled. In the signal reproducing method disclosed in Japanese Patent Laid-Open No. 3-93058, a signal is recorded on the recording holding layer, the direction of magnetization of the reproducing layer is aligned, and then the reproducing layer is heated while being irradiated with laser light. The signal recorded on the recording holding layer is transferred to the temperature rising region, and the signal transferred to the reproducing layer is read.

  According to this signal reproduction method, the intersymbol interference during reproduction can be reduced, and the signal is detected when the beam spot diameter of the reproduction laser beam is heated by the laser beam to reach the transfer temperature. Therefore, it is possible to reproduce a signal having a spatial frequency of 2 NA / λ or more.

  However, in the signal reproduction method described above, since the signal detection area that is effectively used becomes smaller with respect to the beam spot diameter of the reproduction laser beam, the amplitude of the reproduction signal is reduced and sufficient reproduction output can be obtained. There may not be. In such a case, the effective signal detection area cannot be made very small with respect to the beam spot diameter, and in the end, the recording density determined by the diffraction limit of the optical system can be greatly increased. I can't.

  As one method for solving such a problem, Japanese Patent Application Laid-Open No. 6-290498 proposes a domain wall motion type magneto-optical recording medium and a reproducing method thereof. The reproducing method of the domain wall motion type magneto-optical recording medium is such that the domain wall existing at the boundary part of the recording mark is moved to the high temperature side by the temperature gradient, and the domain wall motion is detected, thereby reducing the optical signal without reducing the reproduction signal amplitude. It is possible to reproduce a signal having a recording density exceeding the resolution of the system.

  In order to smoothly move the domain wall, for example, Japanese Patent Application Laid-Open No. 2002-150631 proposes to divide the magnetic coupling between adjacent recording tracks. Japanese Patent Laid-Open No. 2002-150631 irradiates a high-power laser beam between recording tracks, and performs a laser annealing process to change the magnetic layer between the tracks into an in-plane magnetization film, so that the magnetic field between the recording tracks is changed. This cuts or reduces the effective coupling and realizes a good domain wall motion domain expansion reproduction.

  Furthermore, Japanese Patent Laid-Open No. 2002-203343 proposes that the magnetic film be annealed from the opposite side of the substrate while performing tracking control by a sample servo method. Proposals have been made to use land / groove recording in order to reduce the track pitch, and to perform an annealing process on the side wall portion between the land and the groove which are recording tracks.

  In the super-resolution technique described above, when the wavelength λ of the laser light is shortened to reduce the diffraction limit of the optical system, the track pitch can be further reduced, and the density can be increased in the track density direction.

It is known that C / N, which is a reproduction characteristic, is proportional to a figure of merit (R) ^0.5 × θk (R is a reflectance, and θk is a Kerr rotation angle). Therefore, conventionally, the dielectric layer disposed on the incident side of the laser beam has been used under such a condition that the figure of merit becomes larger with respect to the wavelength of the laser beam used during reproduction.

Japanese Patent Application Laid-Open No. 2001-126330 discloses a laser beam incident side in which (R) ^0.5 × θk becomes large in magnetic super-resolution reproduction using a blue-violet laser having a wavelength of about 350 nm to 450 nm as a laser beam. The conditions for the dielectric layer disposed on the substrate have been proposed.

However, when reproduction is performed using a blue-violet laser having a wavelength of about 350 nm to 450 nm as the laser beam, the quantum efficiency of the photodetector decreases, and the signal for converting the optical information obtained from the magneto-optical recording medium into an electrical signal The amount of the light decreases, the detector noise is large, and the Kerr rotation angle and the Faraday rotation angle detected as the reproduction signal of the rare earth-transition metal magnetic film conventionally used as the reproduction layer may decrease. Are known. For this reason, when reproduction is performed using a blue-violet laser, the signal amount (carrier level) of the reproduction signal becomes small, and it becomes easy to be affected by system noise and medium noise of the reproduction system, resulting in deterioration of reproduction characteristics. .
In a magneto-optical recording medium to be reproduced using a blue-violet laser, when a thickness that increases the figure of merit (R) ^0.5 × θk is selected as the dielectric layer provided on the substrate, Japanese Patent Application Laid-Open No. 2001-126330 As described in the publication, the reflectance R is low. Therefore, the thermal sensitivity is high, and the reproduction power required for reproduction is further reduced. As a result, the amount of signal entering the detector is reduced, and the reproduction characteristics are greatly deteriorated.

  In order to solve the above problem, increasing the laser power to increase the signal amount and increase the signal amount entering the detector leads to a temperature rise of the magneto-optical recording medium and a decrease in the stability of the recorded information. As a result, problems such as a reduction in reproduction power margin occur.

Therefore, conventionally, a method has been used in which the thermal sensitivity is lowered by providing a thermal control layer having a high thermal conductivity, and the laser power during reproduction is increased by suppressing the temperature rise.
Japanese Patent Laid-Open No. 3-93058 Japanese Patent Application Laid-Open No. 6-290496 JP 2002-150631 A JP 2002-203343 A JP 2003-317336 A JP 2001-126330 A

  In order to smoothly move the domain wall during reproduction, the magnetic layer is irradiated with a high-power laser beam between the recording tracks in order to cut or reduce the coupling due to the exchange interaction between the recording tracks in the domain wall moving layer. (Laser annealing) If a thermal control layer is provided, the thermal sensitivity will be reduced due to the influence of the thermal control layer even during the laser annealing process, so it is very high to ensure a sufficient temperature rise. It is necessary to perform annealing with laser power, which may be a problem.

  In order to solve this problem, conventionally, an annealing process is performed before the thermal control layer is deposited, or a laser annealing process is performed at a reduced linear velocity.

  For example, when annealing is performed before the thermal control layer is deposited, at least the dielectric layer, the magnetic layer, and the dielectric layer are sequentially deposited on the substrate by successive sputtering using a magnetron sputtering apparatus. Then, the vacuum of the film forming chamber is leaked to atmospheric pressure, the magneto-optical recording medium is taken out into the atmosphere, annealed, and then returned to the chamber of the film forming apparatus, evacuated, and the thermal control layer is covered. It must be formed.

  As described above, when reproduction is performed using a blue-violet laser having a wavelength of about 350 nm to 450 nm, the domain wall motion type magneto-optical recording medium requiring laser annealing has a problem that the production efficiency is remarkably poor.

  The present invention has been made in view of the above problems, and provides a domain wall motion type magneto-optical recording medium that requires an annealing process capable of obtaining good recording and reproducing characteristics by a simple process. is there.

On the transparent substrate, at least one of the first dielectric layer 4, the magnetic layer 10, and the second dielectric layer 5 are sequentially formed. Further, the magnetic layer 10 contributes at least to reproduction of information and has a domain wall. A first magnetic layer 1 (domain wall moving layer) that moves, a third magnetic layer 3 (recording layer) that retains a recording magnetic domain according to information, and the first magnetic layer 1 and the third magnetic layer 3 are disposed. The magnetic layer includes a plurality of magnetic layers including a second magnetic layer 2 (switching layer) having a Curie temperature lower than the two layers, and the first magnetic layer 1, the second magnetic layer 2, and the third magnetic layer 3 are the second magnetic layer 2 A domain wall motion magneto-optical recording medium having exchange coupling below the Curie temperature of the magnetic layer,
The domain wall motion type magneto-optical recording medium has a plurality of recording tracks, and irradiates the magnetic layer 10 from the second dielectric layer 5 side with a high-power laser beam between the recording tracks. By performing processing for cutting or reducing the magnetic coupling between recording tracks in one magnetic layer 1, the domain wall of the recording magnetic domain transferred from the third magnetic layer 3 to the first magnetic layer 1 is moved, and the recording In a domain wall motion magneto-optical recording medium that reproduces information by expanding a magnetic domain,
When the thickness d of the first dielectric layer is irradiated with laser light used for reproduction from the first dielectric layer side, the minimum thickness of the first dielectric layer at which the reflectance is minimized. Is dRmin1, and the minimum thickness of the first dielectric layer at which the reflectance is maximized is dRmax1,
dRmax1-4 (dRmax1-dRmin1) / 5≤d≤dRmax1 + 4 (dRmax1-dRmin1) / 5
By using a domain wall motion magneto-optical recording medium that performs reproduction using a blue-violet laser having a wavelength of about 350 nm to about 450 nm, it is possible to solve the above problem.

  According to the present invention, as the first dielectric layer, by selecting a specific thickness that increases the reflectance R, the thermal sensitivity can be lowered when irradiated with laser light. It is possible to increase a reproduction power level required for reproduction by suppressing an excessive temperature rise. As a result, a sufficient signal amount for reproduction can be put in the detector and the figure of merit becomes small, but good reproduction characteristics with no problem in practical use can be obtained. According to the present invention, since it is not necessary to provide a thermal control layer for lowering the thermal sensitivity, it is not necessary to reduce the linear velocity when performing the annealing process, and after the annealing process is performed, the film is evacuated again by the film forming apparatus. It is possible to provide a domain wall motion type magneto-optical recording medium subjected to laser annealing, which can obtain good recording / reproduction characteristics by a simple process, without requiring a process of forming a thermal control layer. .

  A basic configuration of the domain wall motion type magneto-optical recording medium of the present invention will be described with reference to FIG. In the domain wall motion type magneto-optical recording medium of the present invention shown in FIG. 1, a first dielectric layer 4, a magnetic layer 10, and a second dielectric layer 5 are sequentially laminated on a transparent substrate 6. Further, the magnetic layer 10 includes at least a first magnetic layer 1 (domain wall moving layer) that contributes to information reproduction and moves a domain wall, and a third magnetic layer 3 (recording layer) that holds a recording magnetic domain according to information, It consists of a plurality of magnetic layers including a second magnetic layer 2 (switching layer) disposed between the first magnetic layer 1 and the third magnetic layer 3 and having a Curie temperature lower than both layers. Layer 2 and third magnetic layer 3 are exchange coupled below the Curie temperature of the second magnetic layer. Further, the domain wall motion type magneto-optical recording medium has a plurality of recording tracks, and irradiates the magnetic layer 10 with high-power laser light between the recording tracks, so that at least the recording tracks in the first magnetic layer 1 are between the recording tracks. Processing for cutting or reducing the magnetic coupling is performed.

When the domain wall motion type magneto-optical recording medium of the present invention is irradiated with laser light used for reproduction from the first dielectric layer side under the conditions necessary for reproduction, the thickness d of the first dielectric layer is reflected. When the minimum thickness of the first dielectric layer at which the ratio is minimal is dRmin1, and the minimum thickness of the first dielectric layer at which the reflectance is maximum is dRmax1,
dRmax1-4 (dRmax1-dRmin1) / 5≤d≤dRmax1 + 4 (dRmax1-dRmin1) / 5
This is a domain wall motion magneto-optical recording medium that performs reproduction using a blue-violet laser having a wavelength of about 350 nm to 450 nm.

Furthermore, the thickness d of the first dielectric layer is:
dRmax1-3 (dRmax1-dRmin1) / 5≤d≤dRmax1 + 3 (dRmax1-dRmin1) / 5
It is more preferable that

  The first dielectric layer is preferably made of silicon nitride that does not absorb laser light having a wavelength of about 350 nm to 450 nm. In this case, for a laser beam having a wavelength of about 350 nm to 450 nm, the reflectance R shows a minimum value in the vicinity of 30 nm (dRmin1) and in the vicinity of 80 nm (dRmax1) in order from the thinner dielectric layer. Indicates the maximum value. Accordingly, when the first dielectric layer is made of silicon nitride, the thickness of the silicon nitride film is preferably 40 nm or more and 120 nm or less, and more preferably 50 nm or more and 110 nm or less.

  Here, the reflectance R from the magneto-optical recording medium is periodically increased and decreased according to the film thickness of the first dielectric layer. In order from the thinner, dRmin1 indicates a minimum value, and dRmax1 indicates a maximum value. It is known that even a thicker dRmin2 exhibits a minimum value, and even when the thickness is further increased, dRmax2, dRmin3, dRmax3,...

  For the measurement of the reflectance R, a photometer or a drive device can be used. The film thickness dependence of the reflectance R does not change whether measured with a photometer or a drive device, so that the film thickness at which an extreme value can be obtained can be measured with either measurement. As will be described later, in the present invention, the reflectance is measured using a photometer.

  By selecting a specific thickness that increases the reflectivity R as the first dielectric layer, the thermal sensitivity can be lowered when irradiated with laser light, so excessive temperature rise is suppressed. Thus, the reproduction power level required for reproduction can be increased. As a result, the amount of signals entering the detector increases and good reproduction characteristics can be obtained.

  Therefore, it is not necessary to provide a thermal control layer for the purpose of reducing thermal sensitivity. Also, during laser annealing, high-power laser light is irradiated from the second dielectric layer side, so the reflectivity R of the first dielectric layer has little effect on the laser power during laser annealing. Absent.

  In FIG. 1, the first dielectric layer 4 and the first magnetic layer (domain wall moving layer) 1 are formed in contact with the substrate 6, but the second dielectric layer 5 and the third dielectric layer 5 are formed on the substrate 6. The magnetic layer (recording layer) 3 may be in contact. In this case, the annealing with the high-power laser beam may be performed from the second dielectric layer side on the substrate side.

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

  First, basic domain wall motion domain expansion reproduction will be described.

  FIG. 6 is a diagram for explaining a basic domain wall motion type magneto-optical recording medium and its information reproducing principle. FIG. 6A shows a configuration of the magneto-optical recording medium and a portion irradiated with a reproducing light beam. FIG. 6B is a graph showing the temperature distribution formed on the magneto-optical recording medium when irradiated with the light beam, and FIG. 6C is the temperature distribution of FIG. 6B. 6 is a graph showing a domain wall energy density σ distribution and a driving force F due to a temperature gradient of a domain wall moving layer corresponding to.

  As shown in FIG. 6A, this magneto-optical recording medium has a first magnetic layer 41 (domain wall moving layer) having a small domain wall coercive force, a second magnetic layer 42 (switching layer) having a low Curie temperature on a substrate. The third magnetic layer 43 (recording layer) having a large domain wall coercive force is sequentially laminated. The second magnetic layer 42 has a Curie temperature lower than that of the first magnetic layer 41 and the third magnetic layer 43, and the first magnetic layer 41, the second magnetic layer 42, and the third magnetic layer 43 are equal to or lower than the Curie temperature of the second magnetic layer 42. It is exchange coupled with.

  In the third magnetic layer 43, recording magnetic domains 3a, 3b, 3c, 3d,... Are formed in order, and in the region where the medium temperature is equal to or lower than the Curie temperature Ts of the second magnetic layer 42, the first magnetic layer 41, the second magnetic layer 41, and the second magnetic layer 41 are formed. Since the magnetic layer 42 and the third magnetic layer 43 are exchange coupled, the recording magnetic domain of the third magnetic layer 43 is transferred as it is as the recording magnetic domain of the first magnetic layer 41. In FIG. 6A, the recording magnetic domain 1 a of the first magnetic layer 41 is a recording of the recording magnetic domain 3 a of the third magnetic layer 43.

  An arrow r represents the medium moving direction. When the recording layer moves in the medium moving direction r, the reproducing beam spot moves along the information track of the recording layer. In the portion irradiated with the reproducing beam spot, as shown in FIG. 6B, the temperature rises from the front of the spot with respect to the beam moving direction, and a temperature peak comes to the position Xb. Distribution occurs. Here, at the position Xa, the medium temperature reaches a temperature Ts near the Curie temperature of the second magnetic layer 42.

  As shown in FIG. 6C, the distribution of the domain wall energy density σ in the first magnetic layer 41 is minimized in the vicinity of the temperature peak behind the spot of the beam spot for reproduction, and becomes larger toward the front of the spot. As described above, when there is a gradient of the domain wall energy density σ in the position X direction, a force F represented by F = ∂σ / ∂X acts on the domain wall of each layer existing at the position X.

  This force F acts to move the domain wall toward the lower domain wall energy. Since the first magnetic layer 41 has a small domain wall coercive force and a large domain wall mobility, the domain wall 44 is easily moved by this force F in the case of a single layer. However, in the region located on the front side of the spot from the position Xa, the medium temperature is lower than Ts and exchange coupled with the third magnetic layer 43 having a large domain wall coercive force. The third magnetic layer 43 having a large magnetic force is fixed at a position corresponding to the position of the domain wall.

  In this magneto-optical recording medium, when the medium moves in the medium moving direction r and the domain wall 44 of the first magnetic layer 41 comes to the position Xa, the medium temperature at the domain wall 44 is changed to the second magnetic layer 42. To a temperature Ts near the Curie temperature, the exchange coupling between the first magnetic layer 41 and the third magnetic layer 43 is broken. As a result, the domain wall 44 of the first magnetic layer 41 instantaneously moves to a region where the temperature is higher and the domain wall energy density is smaller, as indicated by the dashed arrow s. When the domain wall 44 passes under the spot of the reproduction beam spot, the atomic spins of the first magnetic layer 41 are aligned in one direction in the range from the position Xa to the position Xb.

  Each time the domain wall reaches the position Xa as the medium moves, the domain wall instantaneously moves under the spot, the recording domain expands from the position Xa to the position Xb, and the atomic spin of the first magnetic layer 41 is Align in one direction. As a result, the amplitude of the reproduced signal is always constant and maximum regardless of the recorded domain wall interval (ie, recording mark length), and is completely eliminated from problems such as waveform interference due to the optical diffraction limit. To be released.

  Next, another embodiment of the magneto-optical recording medium according to the present invention will be described.

  FIG. 2 is a schematic sectional view showing another embodiment of the magneto-optical recording medium according to the present invention. As shown in FIG. 2, on the transparent substrate 16, the first dielectric layer 14, the domain wall motion layer 11, the domain wall motion auxiliary layer 18, the control layer 19, the switching layer 12, the recording layer 13, the magnetic field sensitivity auxiliary layer 20, A second dielectric layer 15 and a protective coat 17 are sequentially laminated. For example, polycarbonate, acrylic, glass, or the like can be used as the substrate 16. As the protective coat 17, for example, a protective coat made of a polymer resin can be used. As the first dielectric layer 14, for example, a translucent material such as SiN, AlN, SiO, AlO, ZnS, MgF, TaO, and TiO can be used. For the second dielectric layer 15, similarly to the first dielectric, for example, a translucent material such as SiN, AlN, SiO, AlO, ZnS, MgF, TaO, and TiO can be used.

In the following, the present invention will be described in detail by taking as an example a silicon nitride having a stoichiometric composition ratio of Si ₃ N ₄ having no absorption for a blue-violet laser having a wavelength of about 350 nm to 450 nm as a dielectric layer. The present invention is not limited to silicon nitride having a stoichiometric composition ratio of Si ₃ N ₄ without departing from the gist thereof.

  Each of these layers can be deposited by, for example, continuous sputtering using a magnetron sputtering apparatus or continuous vapor deposition. In particular, the respective magnetic layers are exchange-coupled to each other by being continuously formed without breaking the vacuum.

  In the above medium, each magnetic layer may be composed of various magnetic materials such as a magnetic bubble material and an antiferromagnetic material in addition to materials generally used for magnetic recording media and magneto-optical recording media. For example, one or more rare earth metal elements such as Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er are 10 atom% to 40 atom%, and iron group elements such as Fe, Co, and Ni. One kind or two or more kinds may be composed of a rare earth-iron group amorphous alloy composed of 90 to 60 atom%. In order to improve corrosion resistance, a small amount of elements such as Cr, Mn, Cu, Ti, Al, Si, Pt, and In may be added to these alloys. Also, platinum group-iron group periodic structure films such as Pt / Co, Pd / Co, platinum group-iron group alloy films, antiferromagnetic materials such as Co-Ni-O and Fe-Rh alloys, magnetic garnet, etc. These materials can also be used.

  In the case of a heavy rare earth-iron group amorphous alloy, the saturation magnetization can be controlled by the composition ratio of the rare earth element and the iron group element. If the compensation composition is used, the saturation magnetization at room temperature can be 0 emu / cc. The Curie temperature can also be controlled by the composition ratio. In order to control independently of the saturation magnetization, a method of using a material in which part of Fe is replaced with Co as an iron group element and controlling the amount of substitution can be used more preferably. That is, by replacing 1 atom% of the Fe element with Co, an increase in Curie temperature of about 5 to 6 ° C. can be expected. Therefore, the amount of Co added is adjusted to achieve a desired Curie temperature using this relationship. On the contrary, the Curie temperature can be lowered by adding a small amount of a nonmagnetic element such as Cr, Ti, or Al. The Curie temperature can also be controlled by adjusting the composition ratio of two or more rare earth elements.

  The domain wall coercive force and domain wall energy density are controlled mainly by the selection of material elements, but can also be adjusted by the state of the first dielectric layer to be subtracted and the film formation conditions such as sputtering gas pressure. Tb and Dy-based materials have large perpendicular magnetic anisotropy and large domain wall coercivity and domain wall energy density, while Gd-based materials are small. These physical property values can also be controlled by adding impurities or the like. The film thickness can be controlled by the film formation speed and the film formation time.

  More specifically, as the domain wall motion layer 11, for example, a rare earth-iron group amorphous alloy having a small domain wall coercive force such as GdCo, GdFeCo, GdFe, or NdGdFeCo, or a bubble memory material such as garnet is used. preferable.

  As the recording layer 13, for example, a rare-earth-iron group amorphous alloy made of a TbFeCo, DyFeCo, or TbDyFeCo-based material having a large perpendicular magnetic anisotropy, a large domain wall coercive force, and a stable magnetization state is preferable. .

  The switching layer 12 has a lower Curie temperature than the domain wall motion layer 11 and the recording layer 13, and examples of the material include a heavy rare earth-iron group amorphous alloy composed of TbFe, DyFe, TbDyFe, TbFeCo, DyFeCo, and TbDyFeCo. Those having a large perpendicular magnetic anisotropy and a large domain wall coercive force and capable of stably transferring the magnetization state are preferred. Further, exchange coupling is performed from the domain wall motion layer 11 to the recording layer 13 below the Curie temperature Ts of the switching layer 12. As described above, since the domain wall moving layer 11 to the recording layer 13 are exchange coupled below Ts, the recording magnetic domain formed in the recording layer 13 remains as it is in the temperature region of Ts. As a result, it has been transcribed.

  In the present embodiment, the structure provided with the domain wall motion auxiliary layer 18 proposed in Japanese Patent Application Laid-Open No. 2000-207791 is provided from the viewpoint of improving the reproduction characteristics, but in addition to this, the thickness direction of the domain wall motion layer 11 is shown. Alternatively, a composition gradient may be provided, or a configuration in which the domain wall motion layer 11 is multilayered may be used. The domain wall motion auxiliary layer 18 has a Curie temperature lower than that of the domain wall motion layer 11, and the material is, for example, a rare earth-iron group amorphous alloy or garnet having a small domain wall coercive force composed of GdCo, GdFeCo, GdFe, NdGdFeCo. It is preferable to use a material for bubble memory such as.

  Further, as proposed in Japanese Patent Application Laid-Open No. 2000-187898, the control layer 19 suppresses extra domain wall movement (ghost signal) at the rear end in the reproduction beam spot, and the domain wall moves. Preferably, it is disposed between the layer and the switching layer 12. That is, it is preferable to arrange between the domain wall motion auxiliary layer 18 and the switching layer 12 when the domain wall motion auxiliary layer 18 is provided, or when the domain wall motion auxiliary layer 18 is provided. The control layer 19 is preferably a magnetic layer having a Curie temperature higher than that of the switching layer 12 and made of a TbFeCo or TbDyFeCo-based material having a large magnetic anisotropy and a domain wall coercive force larger than the moving layer.

  In the present embodiment, an example in which the recording magnetic field sensitivity auxiliary layer 20 is provided on the side opposite to the substrate of the recording layer 13 from the viewpoint of recording characteristics is shown. The recording magnetic field sensitivity auxiliary layer 20 has a Curie temperature higher than the Curie temperature of the recording layer 13, which is a recording temperature, so that, for example, GdCo, GdFeCo, It is preferable to use a rare earth-iron group amorphous alloy having a small perpendicular magnetic anisotropy such as GdFe or NdGdFeCo and a small domain wall coercivity, or a bubble memory material such as garnet.

  Here, as the film thickness of each magnetic layer, a film thickness at which optimum characteristics can be obtained can be selected. As the composition of each magnetic layer, a composition that provides optimum characteristics can be selected.

  Further, if light modulation recording is performed, a substrate after film formation may be bonded. Further, in the case where reproduction is performed by entering laser light from the film surface side, the laser annealing process may be performed from the substrate surface side with the order of stacking the above layers reversed.

  The present invention will be described in detail below with specific examples, but the present invention is not limited to the following examples without departing from the gist thereof.

  Prior to recording, the domain wall motion magneto-optical recording medium manufactured as described above is subjected to laser annealing treatment with high-power laser light in order to cut the magnetic coupling between the recording tracks.

  FIG. 4 shows a schematic diagram of an example of an optical system provided in an apparatus for performing an annealing process. The magneto-optical recording medium 25 includes a substrate 24 and a recording film 23. The wavelength λ of the laser light 21 for laser annealing is 405 nm, the numerical aperture N.P. A is set to 0.85, and the laser beam 21 is condensed on the side wall between the land and the groove forming the recording track from the film 23 side while rotating the magneto-optical recording medium at a desired linear velocity, and the desired laser power is obtained. Laser irradiation is performed by continuous irradiation. By this processing, the perpendicular magnetic anisotropy energy of the magnetic film on the side wall portion, which is the magnetic dividing region, is reduced, and the magnetic coupling between the recording tracks is cut.

  In this embodiment, land / groove recording is used, and the side wall portion between the land and the groove, which is a recording track, is annealed. However, the present invention is not limited to this. Needless to say, the groove recording is effective even in the case where the groove land and the land between the grooves are annealed.

  Recording of a data signal on the magnetic recording medium of the present invention is performed by forming a recording magnetic domain corresponding to information on the recording layer by magnetic recording or thermomagnetic recording. In thermomagnetic recording, the external magnetic field is modulated while irradiating laser light with a power that causes the recording layer to reach the Curie temperature or higher while moving the medium, and the laser power is modulated while applying a magnetic field in a certain direction. There is a method to do.

  FIG. 3 is a schematic diagram showing an example of an optical system of a recording / reproducing apparatus for recording and reproducing data signals with respect to the magneto-optical recording medium of the present embodiment.

  As shown in FIG. 3, the optical system includes a laser light source 71 that emits laser light 20 in the order of the optical path, a collimator lens 72 that converts the laser light emitted from the laser light source 71 into parallel light, and a laser light source 71. A beam splitter 73 that transmits the laser beam 20 from the magneto-optical recording medium and reflects the return light from the magneto-optical recording medium, an objective lens 74 that focuses the laser light 20 that has passed through the beam splitter 73 on the magneto-optical recording medium, and a beam And a signal detection system 75 having a detector 76 that receives the return light reflected by the splitter 73.

  The laser light source 71 is a recording / reproducing light source, the wavelength of the laser light 20 is 405 nm, and the numerical aperture N.I. A is 0.65. The beam splitter 73 has a shaping unit that shapes the laser light 20.

  In the recording / reproducing apparatus including the optical system configured as described above, the recording / reproducing in which the laser beam 20 emitted from the laser light source 71 is condensed on the groove (or land) of the recording surface of the magneto-optical recording medium. A beam spot is formed. In recording data signals, a recording beam spot is formed while moving the recording magneto-optical recording medium at a desired linear velocity, and at the same time, an external magnetic field is generated using the magnetic field generating coil 80, and the data is recorded. The direction of the external magnetic field is changed at a high frequency to form a recording magnetic domain.

  The data signal is reproduced using a reproducing beam spot while moving the magneto-optical recording medium at a desired linear velocity. Thereby, at the time of reproduction, the magneto-optical recording medium can be heated with a temperature gradient as shown in FIG.

Example 1
In this example, a land / groove recording substrate having a thickness of 0.6 mm, a track pitch of 0.36 μm, and a groove depth of 30 nm prepared by Glass2P molding was used. The groove shape is not limited to the above shape, and an optimum groove shape can be selected depending on the stability of the servo, the control of leakage of the recording signal from the adjacent track, the configuration of the magnetic layer, and the like.

The B-doped Si and Gd, Tb, FeCr, and CoCr targets are attached to the DC magnetron sputtering apparatus, the substrate is fixed to the substrate holder, and the inside of the chamber is maintained until a high vacuum of 2 × 10 ⁻⁵ Pa or less is obtained. Was evacuated with a cryopump. Thereafter, Ar gas was introduced into the chamber while being evacuated, and each layer was formed by sputtering the target while rotating the substrate. At the time of forming the SiN layer, direct current reactive sputtering was performed by introducing N ₂ gas in addition to Ar gas.

First, Ar gas and N ₂ gas are flowed into the chamber to adjust the pressure to a desired value by conductance adjustment, and there is no absorption chemical for a blue-violet laser having a wavelength of about 350 nm to 450 nm used as the first dielectric layer. 80 nm of silicon nitride having a stoichiometric composition ratio of Si ₃ N ₄ was formed. As will be described later, the reflectance R shows a minimum value when the film thickness of Si ₃ N ₄ is around 30 nm, and shows a maximum value around 80 nm. When N2 gas is mixed during the formation of the magnetic film, nitriding occurs and affects the magnetic characteristics. Therefore, the dielectric layer and the other magnetic layers were formed in separate chambers.

  After film formation of the first dielectric layer, the substrate is transported to another chamber, Ar gas is introduced, and a desired pressure is obtained by conductance adjustment. The GdFeCoCr layer is 18 nm thick as the domain wall motion layer, and the GdFeCr layer is used as the domain wall motion auxiliary layer. Was deposited to a thickness of 18 nm. Next, similarly, Ar gas is used to obtain a desired pressure by conductance adjustment. The control layer is TbFeCoCr with a thickness of 18 nm, the switching layer is a TbFeCr layer with a thickness of 10 nm, the recording layer is TbFeCoCr with a thickness of 40 nm, and the recording magnetic field sensitivity auxiliary layer As a result, GdFeCoCr was formed to a thickness of 10 nm.

  Finally, a SiN layer having a thickness of 50 nm was formed as the second dielectric layer by direct-current reactive sputtering in the same manner as when the first dielectric layer was formed.

  The composition ratio of each magnetic layer was controlled by the ratio of power applied to each target of Gd, Tb, FeCr, and CoCr.

  Specifically, the composition is adjusted so that the Curie temperature is about 320 ° C. and the compensation temperature is about 290 ° C. as the domain wall motion layer, and the Curie temperature is about 225 ° C. and the compensation temperature is about 45 ° C. as the domain wall motion auxiliary layer. The composition is adjusted so that the Curie temperature is about 180 ° C. as the control layer and the composition is adjusted so that the rare earth element magnetization is dominant from room temperature to the Curie temperature, and the Curie temperature is about 155 ° C. and the compensation temperature is 90 ° C. The composition is adjusted so that the temperature is about 350.degree. C., the composition is adjusted so that the Curie temperature is about 330.degree. C. and the compensation temperature is about 40.degree. C., and the Curie temperature is 354.degree. It adjusted so that it might become 230 degreeC.

  In order to cut the magnetic coupling between the recording tracks prior to recording with respect to the domain wall motion type magneto-optical recording medium manufactured as described above, a high-power laser is used by using the optical system shown in FIG. Laser annealing treatment was performed with light.

  The wavelength of the laser beam 21 for laser annealing is 405 nm, the numerical aperture of the objective lens 22 is N.P. While rotating the magneto-optical recording medium with A being 0.85 and a linear velocity of 3.0 m / s, the laser beam 21 is condensed on the side wall between the land and the groove forming the recording track from the film 23 side, and the laser power is Laser annealing was performed by continuous irradiation at 5.6 mW. By this processing, the perpendicular magnetic anisotropy energy of the magnetic film on the side wall portion, which is the magnetic dividing region, is reduced, and the magnetic coupling between the recording tracks is cut.

  Thereafter, a protective coat made of a polymer resin was formed.

  With respect to the magneto-optical recording medium manufactured in this way, the optical wavelength shown in FIG. Recording / reproduction characteristics were evaluated using a signal of (1-7) modulation with A of 0.65, linear velocity of 2.4 m / s, clock of 32 MHz, and linear recording density of 0.1125 μm / bit.

  Recording was performed by continuously irradiating a laser and modulating the magnetic field in accordance with the signal in the cooling process after heating the magneto-optical recording medium to a temperature equal to or higher than the Curie temperature of the recording layer. At this time, the recording power was 3.6 mW and the modulation magnetic field strength was 200 (Oe) in the land portion, and the recording power was 3.6 mW and the modulation magnetic field strength was 250 (Oe) in the groove portion.

  When the signal is recorded under the above recording conditions and the reproduction power is changed, the dependency of the jitter on the reproduction power is measured, and the reproduction power margin at which the jitter value is 14.5% (bER is equivalent to 5E-4) or less. Compared. As a result, the jitter value of the land was 9.3%, the reproduction power margin was 1.84 mW ± 19.3%, the groove value was 9.2%, and the reproduction power margin was 1.73 mW ± 22.5%.

  Here, the thickness dependence of the first dielectric layer of the reflectance R was measured. The reflectance measurement was performed on another sample using a glass substrate.

The film formation conditions were the same as those for the recording / reproduction characteristic evaluation sample, and the thickness of the first dielectric layer was 20 nm to 100 nm.
The reflectance was measured using a spectrophotometer, and the reflectance from Glass was subtracted.
As a result, when the film thickness of the first dielectric layer was around 30 nm, the reflectance R showed a minimum value of 14%, and at around 80 nm, the reflectance R showed a maximum value of 41%.
(Example 2)
For the magneto-optical recording medium of Example 2, a magneto-optical recording medium having the same configuration as that of Example 1 except that the thickness of the first dielectric layer was 100 nm was produced. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, the laser power during annealing was increased by increasing the thickness of the first dielectric layer, and laser annealing was performed at 5.7 mW. In the land portion, the recording power was 3.6 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 3.6 mW and the modulation magnetic field strength was 250 (Oe).

As a result, in the land, the jitter value was 9.5%, the reproduction power margin was 1.98 mW ± 18.8%, in the groove, the jitter value was 9.4%, and the reproduction power margin was 1.88 mW ± 21.3%. .
(Example 3)
For the magneto-optical recording medium of Example 3, a magneto-optical recording medium having the same configuration as that of Example 1 was prepared except that the thickness of the first dielectric layer was 110 nm. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 5.8 mW during annealing. In the land portion, the recording power was 3.5 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 3.3 mW and the modulation magnetic field strength was 250 (Oe).

As a result, the jitter value of the reproduction land is 9.7% and the reproduction power margin is 1.85 mW ± 16.2%, and the groove value is 9.6% and the reproduction power margin is 1.75 mW ± 18.3%. It was.
Example 4
For the magneto-optical recording medium of Example 4, a magneto-optical recording medium having the same configuration as that of Example 1 was prepared except that the thickness of the first dielectric layer was 120 nm. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 5.9 mW during annealing. In the land portion, the recording power was 3.4 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 3.0 mW and the modulation magnetic field strength was 250 (Oe).

As a result, in the land, the jitter value was 10.3%, the reproduction power margin was 1.7 mW ± 10.5%, and in the groove, the jitter value was 10.0%, and the reproduction power margin was 1.54 mW ± 11.3%.
(Comparative Example 1)
For the magneto-optical recording medium of Comparative Example 1, a magneto-optical recording medium having the same configuration as that of Example 1 was prepared except that the thickness of the first dielectric layer was 130 nm. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 6.0 mW during annealing. In the land portion, the recording power was 2.8 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 2.5 mW and the modulation magnetic field strength was 250 (Oe).

As a result, in the land, the jitter value was 14.5% and the reproduction power margin was 1.3 mW ± 4.0%, and in the groove, the jitter value was 10.9% and the reproduction power margin was 1.25 mW ± 5%.
(Example 5)
For the magneto-optical recording medium of Example 5, a magneto-optical recording medium having the same configuration as that of Example 1 except that the thickness of the first dielectric layer was set to 60 nm was produced. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 5.6 mW during annealing. In the land portion, the recording power was 3.2 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 3.2 mW and the modulation magnetic field strength was 250 (Oe).

As a result, in the land, the jitter value was 10.0% and the reproduction power margin was 1.74 mW ± 18.5%. In the groove, the jitter value was 9.4%, and the reproduction power margin was 1.63 mW ± 19.0%.
(Example 6)
For the magneto-optical recording medium of Example 6, a magneto-optical recording medium having the same configuration as that of Example 1 except that the thickness of the first dielectric layer was 50 nm was produced. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 5.6 mW during annealing. In the land portion, the recording power was 2.9 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 2.7 mW and the modulation magnetic field strength was 250 (Oe).

As a result, in the land, the jitter value was 10.6%, the reproduction power margin was 1.55 mW ± 15.4%, in the groove, the jitter value was 9.7%, and the reproduction power margin was 1.52 mW ± 16.5%.
(Example 7)
For the magneto-optical recording medium of Example 7, a magneto-optical recording medium having the same configuration as that of Example 1 was prepared except that the thickness of the first dielectric layer was 40 nm. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 5.6 mW during annealing. In the land portion, the recording power was 2.4 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 2.2 mW and the modulation magnetic field strength was 250 (Oe).

As a result, in the land, the jitter value was 12.2% and the reproduction power margin was 1.29 mW ± 10.5%, and in the groove, the jitter value was 10.3% and the reproduction power margin was 1.3 mW ± 13.8%.
(Comparative Example 2)
For the magneto-optical recording medium of Comparative Example 2, a magneto-optical recording medium having the same configuration as that of Example 1 was prepared except that the thickness of the first dielectric layer was 30 nm. Next, in the same manner as in Example 1, laser annealing treatment and evaluation of recording / reproducing characteristics were performed. At this time, laser annealing was performed at a laser power of 5.5 mW during annealing. In the land portion, the recording power was 1.6 mW and the modulation magnetic field strength was 200 (Oe). In the groove portion, the recording power was 1.5 mW and the modulation magnetic field strength was 250 (Oe).

  As a result, in the land, the jitter value was 14.0% and the reproduction power margin was 0.9 mW ± 5.0%. In the groove, the jitter value was 10.9%, and the reproduction power margin was 0.85 mW ± 8.0%.

FIG. 5 shows the results of the above examples and comparative examples as graphs.
From FIG. 5, when the film thickness of silicon nitride having a stoichiometric composition ratio of Si ₃ N ₄ as the first dielectric layer is 40 nm to 120 nm, the reproduction power margin is as good as 10% or more. It was found that when the thickness of the dielectric layer was 50 nm to 110 nm, the reproduction power margin was 15% or more, and further excellent characteristics were obtained.

  Here, the film thickness of 40 nm is dRmax1-4 (dRmax1-dRmin1) / 5, and the film thickness of 120 nm is dRmax1 + 4 (dRmax1-dRmin1) / 5. The film thickness of 50 nm corresponds to dRmax1-3 (dRmax1-dRmin1) / 5, and the film thickness of 110 nm corresponds to dRmax1 + 3 (dRmax1-dRmin1) / 5.

  Further, from the above examples, even when the thickness of the first dielectric layer is changed from 40 nm to 120 nm, since the laser annealing treatment is performed from the second dielectric layer side, the laser annealing power has almost no influence. I understood that I was not affected.

1 is a schematic cross-sectional view of a basic domain wall motion type magneto-optical recording medium. 1 is a schematic cross-sectional view showing an embodiment of a magneto-optical recording medium according to the present invention. 1 is a schematic diagram of an example of an optical system provided in a recording / reproducing apparatus that records and reproduces a data signal with respect to a magneto-optical recording medium. The schematic diagram of an example of the optical system with which the apparatus which performs an annealing process is provided. The result of each Example and a comparative example. The figure for demonstrating a basic domain wall motion type magneto-optical recording medium and its information reproduction principle.

Explanation of symbols

41 First magnetic layer (domain wall moving layer)
42 Second magnetic layer (switching layer)
43 Third magnetic layer (recording layer)
44 Domain walls 3 a, 3 b, 3 c, 3 d... Recording domain r Direction of medium movement 11 Domain wall migration layer 12 Switching layer 13 Recording layer 14 First dielectric layer 15 Second dielectric layer 16 On transparent substrate 17 Protective coating 18 Domain wall motion auxiliary layer 19 Control layer 20 Magnetic field sensitivity auxiliary layer 21 Laser light 22 Objective lens 23 Recording film 24 Substrate 25 Magneto-optical recording medium 71 Laser light source 72 Collimator lens 73 Beam splitter 74 Objective lens 75 Signal detection system 76 Detector 80 Magnetic field generating coil

Claims (4)

On the transparent substrate, at least one of the first dielectric layer 4, the magnetic layer 10, and the second dielectric layer 5 are sequentially formed. Further, the magnetic layer 10 contributes at least to reproduction of information and has a domain wall. A first magnetic layer 1 (domain wall moving layer) that moves, a third magnetic layer 3 (recording layer) that retains a recording magnetic domain according to information, and the first magnetic layer 1 and the third magnetic layer 3 are disposed. The magnetic layer includes a plurality of magnetic layers including a second magnetic layer 2 (switching layer) having a Curie temperature lower than the two layers, and the first magnetic layer 1, the second magnetic layer 2, and the third magnetic layer 3 are the second magnetic layer 2 A domain wall motion magneto-optical recording medium having exchange coupling below the Curie temperature of the magnetic layer,
The domain wall motion type magneto-optical recording medium has a plurality of recording tracks, and irradiates the magnetic layer 10 from the second dielectric layer 5 side with a high-power laser beam between the recording tracks. By performing processing for cutting or reducing the magnetic coupling between recording tracks in one magnetic layer 1, the domain wall of the recording magnetic domain transferred from the third magnetic layer 3 to the first magnetic layer 1 is moved, and the recording In a domain wall motion magneto-optical recording medium that reproduces information by expanding a magnetic domain,
When the thickness d of the first dielectric layer is irradiated with laser light used for reproduction from the first dielectric layer side, the minimum thickness of the first dielectric layer at which the reflectance is minimized. Is dRmin1, and the minimum thickness of the first dielectric layer at which the reflectance is maximized is dRmax1,
dRmax1-4 (dRmax1-dRmin1) / 5≤d≤dRmax1 + 4 (dRmax1-dRmin1) / 5
A domain wall motion magneto-optical recording medium which performs reproduction using a blue-violet laser having a wavelength of about 350 nm to about 450 nm. The thickness d of the first dielectric layer is
dRmax1-3 (dRmax1-dRmin1) / 5≤d≤dRmax1 + 3 (dRmax1-dRmin1) / 5
2. The domain wall motion type magneto-optical recording medium according to claim 1, wherein:   2. The domain wall motion magneto-optical recording medium according to claim 1, wherein the first dielectric layer is silicon nitride having a thickness of 40 nm to 120 nm.   2. The domain wall motion magneto-optical recording medium according to claim 1, wherein the first dielectric layer is silicon nitride having a thickness of 50 nm to 110 nm.

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