JP2008152842A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high track density and a high linear recording density, by narrowing the effective recording track width of a magnetic recording medium, thinning the film thickness of a magnetic layer that contributes to playback, and suppressing an accompanying reduction in the playback signal amplitude. <P>SOLUTION: The magnetic recording medium is constructed, in such a manner that a magnetic wall moving layer 10, a switching layer 4, a memory layer 3 are stacked, in this order, the magnetic wall antimagnetic force of the magnetic wall moving layer 10 is relatively smaller than that of the memory layer 3, and a Curie temperature of the switching layer 4 is lower than that of the magnetic wall moving layer 10 and that of the memory layer 3. Only in a region limited in the width direction of a recording track center, will the magnetized state of the memory layer 3 be transferred to the magnetic wall moving layer 10 through an exchange coupling via the switching layer 4. In regions of both sides of the area, a reflecting layer 5 is inserted between the magnetic wall moving layer 10 and the switching layer 4, to increase the reflectance of light that entered from the magnetic wall moving layer 10 side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium that records information according to the state of magnetization of a magnetic material, and more particularly to a magnetic recording medium that enables reproduction of information at a high recording density by causing domain wall movement during information reproduction. It is.

  Various magnetic recording media have been put to 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 this information using the magneto-optic effect is a large-capacity replaceable medium capable of high-density recording. Expected. In recent years, coupled with the trend toward digitization of moving images, there has been an increasing demand for recording media with higher capacity by increasing the recording density of these magnetic recording media.

  The linear recording density of an optical disk such as a magneto-optical recording medium greatly depends on the laser wavelength of the reproducing optical system and the numerical aperture of the objective lens. That is, if the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the diameter of the beam waist is determined, and therefore, the spatial frequency at the time 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 laser wavelength of the reproducing optical system and increase the numerical aperture NA of the objective lens. However, there are limits to the laser wavelength and the numerical aperture of the objective lens. For this reason, a technique for improving the recording density by devising the configuration of the recording medium and the reading method has been developed.
Japanese Patent Application Laid-Open No. 6-290496 JP 2005-174518 A

  The inventor has proposed a technique for improving the recording density by devising the configuration of the recording medium and the reading method. Japanese Laid-Open Patent Publication No. 6-290496 proposes a magnetic recording medium and a reproducing method capable of reproducing a signal having a recording density exceeding the resolution of the optical system without reducing the reproduction signal amplitude.

  In JP-A-6-290496, a domain wall motion layer, a switching layer, and a memory layer are sequentially laminated. The domain wall motion layer has a relatively small domain wall coercive force as compared with the memory layer, and the switching layer is composed of the domain wall motion layer and the memory. A magneto-optical recording medium with a lower Curie temperature than the layer was proposed. The reproduction of the magneto-optical recording medium having this structure is performed by moving the domain wall of the domain wall moving layer existing at the boundary portion of the recording mark by the temperature gradient in the region where the exchange coupling with the memory layer is cut off. The magnetization reversal can be detected as a change in the deflection state of the reflected light. As a result, high-density recording / reproduction is possible.

  In this reproducing method, it is preferable that the domain wall at the front boundary part and the domain wall at the rear boundary part of the recording mark are formed substantially separately and independently from each other in order to stabilize the movement of the domain wall and improve the reproduction characteristics. This is because the front and back domain walls are not separated, and there are domain walls on the side of the recording mark and the recording mark is surrounded by a closed domain wall. It will generate new energy and increase energy. For this reason, the energy gain due to the decrease in the domain wall energy accompanying the temperature gradient is canceled.

  However, when a recording film is formed on a conventional substrate to produce this medium, a substantially uniform recording film is formed in the direction of the film surface, so that the front and rear domain walls are completely separated. It was often difficult to form marks.

For this reason,
1. After the recording film is formed, both sides of the track are annealed with a high-power laser, for example, to alter the magnetic film on the track side, and recording marks are formed so as to extend over this processing part. 1. Method for separating A method of optimizing the magnetic film on the track side by utilizing the change in the state of deposition of the magnetic film on the side wall of the groove accompanying the surface shape of the substrate such as the groove shape, or selectively using the magnetic film on the side wall of the groove Etching removal methods have been proposed.

  Such a method of changing the magnetic film between tracks can be used as a buffer region, and is effective in suppressing cross-write and crosstalk between tracks. In addition, by limiting the remaining effective track width, the shape of the domain wall at the boundary portion before and after the recording mark on the track becomes relatively straight, and the detection isotherm of the domain wall movement start temperature formed on the medium during reproduction. There is also an effect of improving the shape matching with.

  However, when the effective track width is reduced, the signal amplitude is reduced. Further, when the track width fluctuates at a high frequency in a period corresponding to the domain wall width, it acts as a force for preventing the domain wall movement. However, since this influence increases as the track width is narrowed, the domain wall may be difficult to move.

  Also, it is necessary to secure a certain width for the buffer area width in order to suppress cross light and the like. Furthermore, in the case of the laser annealing method, there is a limit to the narrowing of the annealing region due to the limitation of the laser spot size. Due to these problems, there is a limit to improving the track density.

For this reason, the inventor disclosed in Japanese Patent Application Laid-Open No. 2005-174518 narrows the effective recording track width involved in signal reproduction, and at the same time, suppresses a decrease in signal amplitude and prevents the domain wall movement due to high frequency fluctuations in the track width. To enable higher track density,
1. 1. A domain wall motion layer, a switching layer, and a memory layer are sequentially stacked, and the domain wall motion layer has a relatively small domain wall coercive force compared to the memory layer, and the switching layer has a lower Curie temperature than the domain wall motion layer and the memory layer. 2. Only in a region limited in the width direction of the central portion of the recording track, the magnetization state of the memory layer is transferred to the domain wall motion layer by exchange coupling via the switching layer. In the region outside the recording track, an in-plane magnetization film is inserted in contact with the domain wall moving layer, and the magnetization of the domain wall moving layer is magnetized in-plane at room temperature by exchange coupling with the in-plane magnetization film. Proposed magnetic recording media.

  In the above proposal, since the recorded magnetic domain recorded in the narrow area in the center of the track is read and expanded in the track width direction in the domain on both sides in the domain wall moving layer at the time of reproduction, the decrease in signal amplitude can be suppressed. . However, it is desirable to reduce the thickness of the domain wall moving layer as much as possible from the viewpoint of improving the linear recording density for the reason described later. In that case, it is difficult to obtain a sufficient amplitude even if the domain is expanded in the domain wall moving layer. There was a case.

  The present invention has been made in view of such problems. Narrowing the effective recording track width involved in information storage and reducing the thickness of the magnetic layer involved in reproduction, while suppressing the accompanying decrease in reproduction signal amplitude, increasing track density and recording high lines The object is to enable densification.

  In the present invention, the domain wall motion layer, the switching layer, and the memory layer are laminated in this order, and the domain wall motion layer has a relatively smaller domain wall coercive force than the memory layer, and the switching layer has a lower curie than the domain wall motion layer and the memory layer. In a magnetic recording medium with a low temperature, the magnetization state of the memory layer is transferred to the domain wall motion layer by exchange coupling via the switching layer only in the region limited in the width direction of the central portion of the recording track, In the region on both sides of the region, a magnetic recording medium is characterized in that a reflective layer for increasing the reflectance of light incident from the domain wall moving layer side is inserted between the domain wall moving layer and the switching layer. .

  The effects of the present invention are that, in a magnetic recording medium of a magnetic domain width expansion type in which the track density is greatly improved, the reproduction signal amplitude can be increased to improve the signal quality, and the reproducible minimum mark length can be shortened. Therefore, the bit density can be improved.

  In the magnetic recording medium of the present invention, the magnetization state of the memory layer is transferred to the domain wall motion layer only in the width limited region of the central portion of the recording track, and the domain wall motion layer is the magnetization of the memory layer in the regions on both sides thereof. Magnetization orientation can be freely performed regardless of the state. At the time of reproduction, the domain wall in the domain wall moving layer pinned to the central memory layer is moved to the high temperature side where the domain wall energy density is low at the moment when the coupling with the memory layer is broken, and the domain is expanded. Vertical magnetization regions in the same direction are formed on both sides, and magnetization reversal occurs in a wide region. For this reason, although the recording track width that contributes to the storage of information is narrow, the track width that contributes to reproduction becomes wide and a large signal amplitude is obtained.

  However, if the domain wall moving layers on both sides are completely free, the domain walls may be connected to form a closed domain wall, or inadvertent magnetization reversal may occur due to the effects of stray magnetic fields, resulting in signal noise. To do. For this reason, it is preferable to insert an in-plane magnetization film and to align the domain wall motion layers on both sides in the plane at room temperature by exchange coupling with the in-plane magnetization film.

The exchange coupling energy with the in-plane magnetized film decreases with increasing temperature. On the other hand, the effective anisotropy energy (Ku-2πMs ² ) of the domain wall motion layer can be artificially controlled to some extent by adjusting the temperature dependence of the saturation magnetization Ms. Here, Ku represents the magnetocrystalline anisotropy constant, and MS represents the saturation magnetization. Therefore, if the film is designed so that the magnitude relationship between the two is reversed as the temperature rises, the domain wall motion layer can be oriented in-plane at room temperature, and can be oriented vertically at the reproduction temperature. In addition, if a magnetic layer having a relatively low Curie temperature is inserted between the domain wall moving layer and the in-plane magnetization film, the exchange coupling with the in-plane magnetization film can be completely cut off on the high temperature side, so that the saturation magnetization described above Independent of the temperature dependence of Ms, the transition from the in-plane orientation to the vertical orientation can be performed more reliably.

  As described above, this medium is designed such that the domain wall motion layers on both sides of the track central portion are magnetically oriented in-plane at room temperature and perpendicularly magnetically oriented at a temperature equal to or higher than a predetermined temperature Tt. In this medium, in the heating region under the reproduction spot, the vertical alignment region of the domain wall motion layer can be expanded in the track width direction according to the heating region width. In this state, when the 180 ° domain wall in the domain wall moving layer pinned to the memory layer in the center of the track enters a region below the reproduction spot and above the temperature at which exchange coupling with the memory layer is broken, the domain wall energy The domain wall moves to the high temperature side where the density is low, and the recording magnetic domain expands in the track direction. Let Ts be the temperature at which exchange coupling with the memory layer is broken. As a result, the magnetic domain expands in the track width direction, and a large signal amplitude is obtained.

  Here, the 180 ° domain wall indicates a domain wall whose magnetization direction changes by 180 ° on both sides thereof, and the 90 ° domain wall indicates a domain wall whose magnetization direction changes by 90 ° on both sides thereof. .

  The transition process transitions while minimizing energy from moment to moment. That is, the sum of the energy gain by the domain wall movement to the high temperature region of the 180 ° domain wall and the gain of the perpendicular magnetic anisotropy energy by the extension of the 90 ° domain wall in the track side direction, and the 180 ° domain wall and the 90 ° domain wall The transition is made so that the difference from the energy loss due to the increase in area is maximized.

  1 and 2 schematically show the transition process. In the drawing, the magnetic domain of the downward magnetization orientation is represented by white, and the magnetic domain of the upward magnetization orientation is represented by black. The traveling direction of the medium is the direction of the arrow in FIG.

  The operation principle is the same as that of the magnetic recording medium described in JP-A-2005-174518, but will be described in detail with reference to the drawings.

  FIG. 1A is a diagram showing a state when the region under the reproduction laser spot is in the magnetized state shown in white. From the right side of the figure, when the magnetic domain with the magnetization orientation shown in black enters the coupling cut region under the reproduction laser spot, the 180 ° domain wall in front of the magnetic domain (left side) starts to move toward the center of the spot on the high temperature side ( Fig. 1-A: 2).

  1-A: As shown in FIGS. 3 to 4, the magnetic domains oriented vertically upward are expanded in the in-plane orientation regions on both sides of the track. Since the 180 ° moving domain wall stops at the highest temperature portion near the center of the spot, the left side of the spot remains white and the right side becomes black. In order not to increase the area of the 180 ° domain wall, the vertically oriented region has a saddle shape constricted at the moving domain wall.

  Thereafter, as shown in FIG. 2-B: 1, when the magnetic domain of the downward magnetization orientation shown in white enters the coupling cut region under the reproduction laser spot (in the figure, the laser spot is shifted to the right side), the magnetic domain The front 180 ° domain wall starts to move toward the center of the spot on the high temperature side. Similarly, at this time, as shown in FIG. 2B: 2-3, the magnetic domain oriented vertically downward is expanded to the in-plane orientation region on both sides of the track, and conversely the black magnetic domain sandwiched between white magnetic domains. Shrinks. Eventually, the 180 ° domain walls are coalesced and almost all of the area under the reproduction spot is in a white downward magnetization orientation state (see FIG. 2-B: 4).

  Although the domain wall area increases as the magnetic domain expands, energy loss can be suppressed by increasing the 90 ° domain wall area rather than increasing the 180 ° domain wall area. As in the process shown in FIG. 1, it is assumed that the process undergoes a state transition only by increasing the area of the 90 ° domain wall as much as possible without increasing the area of the 180 ° domain wall as much as possible. However, in order to describe an accurate process, it is necessary to perform a detailed simulation including the influence of magnetostatic energy.

  The magnetic recording medium of the present invention is characterized in that in the regions on both sides of the central region of the track where the domain wall motion layer and the switching layer are exchange-coupled, the reflection of light incident from the domain wall motion layer side is between the two layers. The reason is that a reflective layer is inserted to increase the rate. When there is no reflective layer, the light transmitted through the domain wall motion layer does not contribute to the Kerr effect. Therefore, if the domain wall motion layer is thin, the signal amplitude decreases. It is possible to enhance the Kerr effect by multiple reflection of light.

  If the thickness of the domain wall moving layer can be made sufficiently thick, the effect of enhancement by the reflective layer is small, but for the reasons described below, in order to reduce the fundamental reproduction limit magnetic domain length, It is preferable to make the film thickness as thin as possible.

  In order to smoothly move the domain wall, the domain wall moving layer needs to be made of a material having a small perpendicular magnetic anisotropy and a small domain wall coercive force, such as Gd-FeCo.

  On the other hand, the memory layer needs to be made of a material having a large perpendicular magnetic anisotropy such as Tb-FeCo in order to stably store the recording magnetic domain. Since the thickness of the domain wall formed in the magnetic material is proportional to the reciprocal of the square root of the perpendicular magnetic anisotropy constant, the domain wall thickness formed in the domain wall moving layer is increased, and the domain wall thickness in the memory layer is increased. Becomes thinner. When a magnetic domain is formed in a state where both layers are exchange-coupled and laminated, the thickness of the domain wall at the domain boundary is gradually increased in the film thickness direction so that it is thick on the surface of the domain wall moving layer and thin on the surface of the memory layer. As a result, the domain wall thickness changes. This is because if the domain wall thickness changes suddenly at the interface between the two layers, energy due to the exchange stiffness is accumulated, so that the state in which the domain wall thickness gradually changes is more energetically stable. However, the increase in energy due to the domain wall thickness of the domain wall moving layer being smaller than the original thickness is less than the increase in energy due to the domain wall thickness of the memory layer being greater than the original thickness. The change of the domain wall thickness in the film thickness direction mainly occurs in the domain wall moving layer. That is, the domain wall in the domain wall moving layer has a domain wall thickness as thin as the original domain wall thickness of the memory layer in the vicinity of the interface with the memory layer, and the domain wall thickness increases as the distance from the interface increases. If the thickness of the domain wall motion layer is sufficiently thick, the domain wall motion layer eventually reaches the original domain wall thickness and saturates. If the distance from the interface is more than the original domain wall thickness, the domain wall thickness is almost saturated. Conversely, when the thickness of the domain wall motion layer is made thinner than its original domain wall thickness, the domain wall thickness on the surface of the domain wall motion layer is reduced.

  Now, when the magnetic domain is miniaturized to a level corresponding to the domain wall thickness, the domain walls before and after the magnetic domain overlap, and the action acts in the direction of shrinking the magnetic domain. For this reason, when a magnetic domain in which the magnetic domain wall overlaps on the surface side of the domain wall moving layer is recorded on the magnetic recording medium of the present invention, the domain wall does not move to the high temperature side when the exchange coupling with the memory layer is cut. It merges with the domain wall on the low temperature side and disappears, and the reproducing operation is not realized.

  Therefore, if the thickness of the domain wall motion layer is made as thin as possible, the domain wall thickness on the surface side becomes thinner, and the limit domain size that can be reproduced by the domain wall motion detection method can be reduced.

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

  First, a typical configuration, materials used, manufacturing method, and recording method of the magnetic recording medium of the present invention will be outlined.

  A typical configuration of the magnetic recording medium of the present invention is a configuration in which an underlayer, various magnetic layers, and an upper layer are sequentially laminated on a substrate having predetermined irregularities. As the substrate material, for example, polycarbonate, acrylic, glass or the like can be used. Unless recording / reproduction is performed through the substrate, the light-transmitting material is not necessarily required. As the underlayer and the upper layer, for example, a dielectric material such as SiN, AiN, SiO, ZnS, MgF, TaO can be used. Layers other than the magnetic layer are not essential. The stacking order of the magnetic layers may be reversed. In addition, a metal layer made of Al, AlTa, AlTi, AlCr, AlSi, Cu, Pt, Au, Ag, AgSi, or the like may be added to this configuration to adjust the thermal characteristics. Moreover, you may provide the protective coat which consists of polymer resins. Alternatively, a substrate after film formation may be bonded.

  Each of these layers can be deposited by, for example, continuous sputtering using a magnetron sputtering apparatus or continuous vapor deposition. In particular, the magnetic layers are continuously formed without breaking the vacuum, so that they are exchange-coupled to each other except the magnetic layer that intentionally blocks the coupling.

  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 to 40 atomic%, 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 atomic%. 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 rare earth element sublattice magnetization and the iron group element sublattice magnetization are compensated, the saturation magnetization can be reduced as much as possible. The Curie temperature can also be controlled by the composition ratio. In order to control the Curie temperature independently of the saturation magnetization, a material in which part of Fe is replaced with Co is used as the iron group element, and the amount of substitution is controlled. The method can be used more preferably. That is, by replacing 1 atomic% of Fe with Co, an increase in Curie temperature of about 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 conditions of the substrate and the film formation conditions such as sputtering gas pressure. Tb and Dy-based materials have large domain wall coercivity and domain wall energy density, and Gd-based materials are small. The domain wall coercive force and the domain wall energy density can be adjusted by adding impurities.

  The film thickness can be controlled by the film formation speed and the film formation time.

Data signals are recorded on the magnetic recording medium of the present invention by making the magnetization orientation state of the memory layer correspond to the data signals by thermomagnetic recording. For thermomagnetic recording, the laser power is converted to information while applying a magnetic field in a certain direction and a method that modulates the external magnetic field corresponding to information while irradiating laser light with a power that causes the memory layer to be above the Curie temperature. There is a corresponding modulation method. In the latter case, in order to form a recording magnetic domain smaller than the diameter of the light spot and form a high-density recording pattern higher than the resolution of the optical system, for example,
1. Adjust the laser light intensity so that only a certain area in the light spot is above the Curie temperature of the memory layer, or
2. What is necessary is just to make it the recording medium structure which can carry out light modulation overwriting, and to leave a crescent-shaped magnetic domain, erasing the back at the time of recording.

<Example 1>
In this example, the sample servo system was used, and the following substrate having a thickness of 0.6 mm was prepared. The area around track 1 is divided into 1280 segments. At the head of each segment, a clock pit (Clock pit), servo first and second wobble pits (Wobble pits), and address pits (Address pits) are sequentially engraved as irregularities. The area following these pits is a data area used for recording / reproducing information by a magneto-optical signal. The track pitch is 160 nm, and a land portion having a top surface width of 30 nm, a bottom surface width of 65 nm, and a height of 30 nm is provided at the center of each track in the data area.

  The film formed on the land is selectively deleted by the etching process described later, and the convex portion disappears, and the data area becomes flat on the film surface side. At this time, since it is necessary to leave pits for servo or the like, the pit diameter is set larger than the land width.

A B-doped Si and Gd, Tb, Fe, Co, and Cr targets are attached to a DC magnetron sputtering apparatus, and the above substrate is fixed to the substrate holder, and then a high vacuum of 1 × 10 ⁻⁵ Pa or less is obtained. The chamber was evacuated with a cryopump. Ar gas was introduced into the chamber while being evacuated, and the layers were formed by sputtering the target while rotating the substrate. In forming the SiN layer, N ₂ gas was introduced in addition to Ar gas, and the film was formed by direct current reactive sputtering.

  First, an AlSi alloy layer having a thickness of 30 nm was formed as a heat dissipation layer. Subsequently, a TbFeCoCr layer having a Curie temperature of about 300 ° C. as a memory layer was formed to 50 nm, and a TbFeCr layer having a Curie temperature of about 160 ° C. was formed as a switching layer to a thickness of 15 nm. Next, an AlSi alloy film was formed to 10 nm as a reflective layer, a SiN dielectric film was formed to 10 nm as a reflection enhancement layer, and then a Co film was formed to 10 nm as an in-plane magnetization film. A SiN film having a thickness of 40 nm was formed thereon as a shape processing film.

  Next, the substrate after the film formation is transported to a sputter etching chamber having an accelerated ion irradiation source while maintaining a vacuum, and the accelerated Ar ion beam is irradiated while being neutralized from a direction perpendicular to the substrate surface. Then, the film formed on the substrate was sputter etched.

  Here, the land portion has a trapezoidal cross-sectional shape, and both side portions of the land are inclined by about 60 degrees with respect to the substrate surface. Therefore, in the inclined portion, ions are incident at an angle of about 60 degrees with respect to the normal direction of the film surface. For this reason, the film on the inclined portion is sputter-etched faster than the other flat portions due to the dependence of the sputtering rate on the ion incident angle. As a result, the film of the inclined portion is eroded from both sides of the land, and when the etching is advanced for a predetermined time or more, the convex portion disappears and is flattened.

  In this way, by etching the shape processing SiN film, the Land portion is planarized and removed to the reflective layer to expose the lower switching layer, while the flat portion is removed from the shape processing SiN film. The lower Co in-plane film was exposed. FIG. 3A shows the cross-sectional structure of the sample in this state.

  As shown in FIG. 3A, the heat sink 2, the memory layer 3, the switching layer 4, the AlSi reflection layer 5, the SiN reflection enhancement layer 6, the Co in-plane magnetization film 7, and the shape processing SiN film 8 are formed on the substrate 1. Are stacked in this order. The substrate 1 is provided with a land portion having a top surface width of 30 nm, a bottom surface width of 65 nm, and a height of 30 nm. The height of the land portion is 30 nm. When the SiN film for shape processing is etched until the Co in-plane magnetized film 7 formed in the recess is exposed, the Co in-plane magnetized film 7, the SiN reflection enhancement layer 6 and the AlSi reflective layer 5 formed in the land are removed. And flattened at the height of the wavy line in the figure. As a result, the Co in-plane magnetic film is exposed on the surface in the recess between the land portions, and the switching layer 4 is exposed in the land portion.

  After this step, the substrate was transferred again to the DC magnetron sputtering chamber, and a GdFeCoCr layer having a Curie temperature of 290 ° C. was formed as a domain wall moving layer 10 to a thickness of 10 nm. Finally, a SiN layer was formed to a thickness of 50 nm as the enhancement layer 11 (see FIG. 3B).

  The disk was taken out from the vacuum chamber, and a UV resin was coated on the film surface to a thickness of 15 μm as a cover layer.

<Comparative Example 1>
As a comparative example, a sample of Comparative Example 1 similar to that of Example 1 was prepared except that the reflective film and the reflective enhancement layer were not formed, but instead an in-plane magnetic film was formed to a thickness of 30 nm.

  The sample thus prepared was set in a drive device having a magneto-optical head in which an optical head having a laser wavelength of 405 nm and an objective lens NA of 0.85 and a magnetic head for magnetic field modulation recording were integrated. Thereafter, the recording / reproducing characteristics were measured by irradiating a light beam and applying a recording magnetic field through a 15 μm coat layer.

  While the sample laser of Example 1 and the sample of Comparative Example 1 are pulsed with a recording laser synchronized with a clock at a pulse duty of 33%, a magnetic field of a tone signal with a mark length of 80 nm at a magnetic field intensity of ± 200 Oe Modulation recording was performed.

  The recorded signal was read at each optimum reproduction power. In the sample of Example 1, a sufficiently large signal amplitude was obtained even though the thickness of the domain wall motion layer was as thin as 10 nm, and a carrier-to-noise ratio (C / N (Carrier to Noise ratio)) of 45 dB was obtained. . On the other hand, with the sample of Comparative Example 1, sufficient amplitude was not obtained, and only 30 dB C / N was obtained. Further, in the sample of Example 1, no signal was lost even when the mark length was 45 nm, and the C / N was 40 dB or more.

<Example 2>
A sample of Example 2 was produced in the same manner as in Example 1 except that a GdFeCoCr layer having a Curie temperature of 210 ° C. and a GdFeCoCr layer of 290 ° C. having a thickness of 7 nm were formed in this order as the domain wall motion layer.

<Comparative example 2>
A sample of Comparative Example 2 was prepared in the same manner as Comparative Example 1 except that 18 nm of a GdFeCoCr layer having a Curie temperature of 210 ° C. and 18 nm of a 290 ° C. GdFeCoCr layer were formed in this order as a domain wall motion layer.

  Magnetic field modulation recording of the tone signal was performed on the sample of Example 2 and the sample of Comparative Example 2 in the same manner as in Example 1 with the mark length changed from 30 nm to 100 nm.

  When the recorded signal was read out at each optimum reproduction power, a sufficient signal amplitude was obtained for both samples up to a mark length of 80 nm, and a good signal of 45 dB or more was obtained. Further, in the sample of Example 2, no signal loss was obtained up to the mark length of 40 nm, and C / N was 40 dB or more. However, in the sample of Comparative Example 2, signal loss occurred when the mark length was 75 nm or less, and good C / N could not be obtained.

<Example 3>
A sample of the example of the present invention was manufactured in the same manner as in Example 1 except that the reflection enhancement layer was formed to a thickness of 20 nm instead of forming the in-plane magnetized film.

  Even in this sample, a sufficiently large signal amplitude was obtained up to a mark length of about 80 nm even though the thickness of the domain wall motion layer was as thin as 10 nm, and C / N was 45 dB or more. However, when the magnetic domain is expanded in the width direction, the domain walls are connected to each other to form a closed domain wall, or inadvertent magnetization reversal is likely to occur. Therefore, a signal loss occurs at a mark length of 80 nm or less.

<Example 4 and Comparative Example 3>
A plurality of samples of Example 4 and Comparative Example 3 were produced in the same manner as Example 1 and Comparative Example 1, except that the thickness of the domain wall motion layer was changed in the range of 5 nm to 50 nm.

  As a result of investigating the C / N of these samples and the limit mark length that can be reproduced without signal loss, as the film thickness of the domain wall moving layer is made thinner than 35 m, there is no signal loss as the film thickness is reduced. The reproducible limit mark length has been shortened. Furthermore, when the film thickness is made thinner than 25 nm, C / N deteriorates rapidly in the sample of Comparative Example 3 in which no reflective layer is inserted, whereas Example 4 in which the reflective layer is inserted. In this sample, good C / N could be maintained.

The figure which showed typically the transition process of the magnetization state in the reproduction | regeneration operation | movement of the magnetic recording medium of this invention. The figure which showed typically the transition process of the magnetization state in the reproduction | regeneration operation | movement of the magnetic recording medium of this invention. 1 is a diagram showing a cross-sectional structure in the manufacturing process of a magnetic recording medium of Example 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Heat dissipation layer 3 Memory layer 4 Switching layer 5 AlSi reflection layer 6 SiN reflection enhancement layer 7 Co in-plane magnetized film 8 Shape processing SiN film (removed by accelerated ion irradiation)
9 Accelerated ion irradiation

Claims (4)

The domain wall motion layer, the switching layer, and the memory layer are laminated in this order. The domain wall motion layer has a magnetic domain coercive force relatively smaller than that of the memory layer, and the switching layer has a lower Curie temperature than the domain wall motion layer and the memory layer. A recording medium,
Only in the region limited in the width direction of the central portion of the recording track, the magnetization state of the memory layer is transferred to the domain wall motion layer by exchange coupling through the switching layer,
In the regions on both sides of the region, a reflection layer that increases the reflectance of light incident from the domain wall motion layer side is inserted between the domain wall motion layer and the switching layer. recoding media.   2. The magnetic recording medium according to claim 1, wherein an in-plane magnetization film is formed in contact with the domain wall motion layer in a region on both sides of a region limited in a width direction of the central portion of the recording track. .   The Curie temperature on the side in contact with the in-plane magnetization film of the domain wall motion layer is set lower than the Curie temperature on the side facing the side in contact with the in-plane magnetization film of the domain wall motion layer. 2. The magnetic recording medium according to 2.   4. The magnetic recording medium according to claim 1, wherein the thickness of the domain wall motion layer is 5 nm or more and 25 nm or less.

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