JP2006018949A - Magnetic recording medium, its manufacturing method, magnetic signal reproducing means and magnetic signal reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which secures a data signal area to a maximum extent by dividing and recording servo signals and data signals on separate layers, and does not destroy servo signals by a control mistake at the time of disturbance or read/write, its manufacturing method, a magnetic signal reproducing means and a magnetic signal reproducing method. <P>SOLUTION: The magnetic recording medium 1 has a substrate 2 of non-magnetic material and at least a first recording layer 5 for recording a servo signal and a second recording layer 7 for recording a data signal above this substrate 2. It is characterized in that the coercive force of the first recording layer 5 is larger than that of the second recording layer 7, and the residual magnetic flux density of the first recording layer 5 is smaller than that of the second recording layer 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium, a manufacturing method thereof, a magnetic signal reproducing means and a magnetic signal reproducing method, and more specifically, a first recording layer for recording a servo signal and a first recording layer for recording a data signal. The present invention relates to a magnetic recording medium in which two recording layers are laminated, a manufacturing method thereof, a reproducing means for a magnetic signal recorded on the magnetic recording medium, and a reproducing method thereof.

  In recent years, computer data or data such as moving images and images (hereinafter, these data are collectively referred to simply as “data”. In addition, data that is converted into a signal for recording on a recording medium is “ Recording apparatuses using magnetic recording media are widely used for recording data signals ”).

  A schematic diagram of a conventional magnetic recording medium is shown in FIG. This magnetic recording medium 101 includes a substrate 102 as a base material, a soft magnetic layer 103 for improving recording sensitivity, an underlayer 104 for improving adhesion between the soft magnetic layer 103 and a recording layer 107 described later, A recording layer 107 for recording a data signal composed of one layer and a protective layer 108 for protecting the recording layer 107 are sequentially laminated.

  As shown in FIG. 8B, the recording layer 107 includes a data signal area 107d for recording a data signal and a servo signal area for recording a servo signal in which a tracking position of the data signal is recorded. 107s is formed in a single recording layer 107.

The servo signal is indispensable for ensuring the accuracy of servo following and controlling the reading / writing by the head 201 shown in FIG. 9 with high accuracy. Therefore, in order to increase the in-plane recording density of the magnetic recording medium 101, it is necessary to record a large amount of this servo signal in proportion thereto and to control reading / writing with high accuracy.
However, if the recording layer 107 is formed with the data signal area 107d and the servo signal area 107s, the recording capacity of the data signal that can be recorded on the recording layer 107 is reduced by the amount of the servo signal area 107d. The area occupied by the servo signal area 107 s is said to cover 5 to 10% of the entire recording layer 107. Since the servo signal cannot be recorded by the user, the servo signal is required to be less susceptible to signal strength deterioration due to disturbance.

  The decrease in the data recording capacity due to the presence of the servo signal area 107 s is due to the demands of the industry that is required to increase the data capacity in the future and to provide a magnetic recording medium having an improved recording capacity to cope with it. In light of this, it cannot be said that it is light.

  Under such circumstances, as an effective means for increasing the recording capacity of the data signal, the data signal area 107d and the servo signal area 107s are separated in the recording layer (two layers), and one recording layer has a servo signal. It is conceivable that only the data signal is recorded on the other recording layer.

As a magnetic recording medium having such a configuration, for example, the magnetic recording medium 151 described in the “magnetic disk device” of Patent Document 1 (see FIG. 10 is described as “double-layer medium” in Patent Document 1. ). The magnetic recording medium 151 includes a substrate 152, a base layer 153, a lower recording layer (lower layer portion 154), a separation layer 155, a base layer 156, an upper recording layer (upper layer portion 157), and a carbon protective film 158. Yes.
The magnetic recording medium 151 records a servo signal on the lower coercive force lower layer 154 and records a data signal on the lower coercive force upper layer 157, so that the servo signal disappears or a different signal is overwritten. Although it was made for the purpose of preventing signal destruction, it is considered that the data recording capacity can be improved from the configuration of the magnetic recording medium 151.

  The magnetic recording medium 151 described in Patent Document 1 will be described. As a metal magnetic film used for the lower coercivity lower layer portion 154 and the lower coercivity upper layer portion 157, both are mainly composed of Co (cobalt) and Pt ( A metal magnetic film made of an alloy material (for example, CoCrPtTa or CoCrPtB) to which a metal such as platinum), Cr (chromium), Ta (tantalum), or B (boron) is added is used. In addition, it is described that the metal magnetic film of the lower layer portion 154 where the servo signal is recorded has a different composition of elements added to the metal magnetic film in order to make the coercive force higher than that of the metal magnetic film of the upper layer portion 157. ing.

Further, the coercive force is also specifically described. In such a magnetic recording medium 151, the upper layer portion 157 of the recording layer for recording the data signal is 3 kOe (kiloersted; 1 Oe = (1 / 4π) × 10 ³ A / m (ampere per meter)), whereas the coercive force of the lower layer part 154 for recording the servo signal is 6 kOe, so that the servo signal is not easily destroyed when recording the data signal. The coercive force of the lower layer portion 154 is relatively increased.

Note that, as described above, in an optical recording medium (not shown) that reads / writes data signals by an optical recording method, even if the recording layer is divided into two layers, an upper layer portion and a lower layer portion, a laser is used. Reading / writing can be performed easily and reliably by focusing each light.
JP 2003-228801 A (paragraphs 0009 to 0014, FIGS. 1 and 3)

However, in the conventional magnetic recording medium 151 that performs recording or the like by magnetism, when reading / writing data signals, only the upper layer portion 157 is affected by magnetic force, and the lower layer portion 154 is not affected by magnetic force. It is extremely difficult to control the range of influence of spatial magnetic force with an accuracy of several hundred μm.
Further, it is difficult to say that the lower layer portion 154 on which the servo signal is recorded in the magnetic recording medium 151 described in Patent Document 1 has a sufficiently large coercive force in practical use. Servo signals can be easily destroyed simply by the action of a magnetic force with a strength that is normally used when reading / writing data.

  Therefore, the magnetic recording medium 151 described in Patent Document 1 destroys not only the data recorded in the upper layer part 157 but also the servo signal recorded in the lower layer part 154 due to a control error or disturbance during reading / writing. It was highly possible that

  On the other hand, in order to increase the in-plane recording density of the magnetic recording medium, it is necessary to record a lot of servo signals and enlarge the servo signal area 107s (see FIG. 8), but the servo signal area 107s is enlarged. If the time is too long, the data signal area 107d is reduced.

  The present invention has been made in view of the above problems, and by recording the servo signal and the data signal in separate layers, the data signal area is ensured to the maximum and the disturbance or the control at the time of reading / writing is performed. It is an object of the present invention to provide a magnetic recording medium in which a servo signal is not destroyed by a mistake, a manufacturing method thereof, a magnetic signal reproducing means, and a magnetic signal reproducing method.

  As a result of diligent research, the inventor has made the properties of the magnetic material used for the first recording layer for recording servo signals different from the properties of the magnetic material used for the second recording layer for recording data, and The present inventors have found that the above-mentioned problems can be solved by configuring them as separate layers, and have completed the present invention.

  That is, a magnetic recording medium according to the present invention includes a nonmagnetic substrate, a first recording layer for recording a servo signal above the substrate, a second recording layer for recording a data signal, The coercive force of the first recording layer is larger than the coercive force of the second recording layer, and the residual magnetic flux density of the first recording layer is the second recording layer. It is smaller than the residual magnetic flux density of the layer (Claim 1).

Thus, by making the coercive force of the first recording layer larger than the coercive force of the second recording layer, even if a disturbance or a control error at the time of data reading / writing occurs, the recorded servo is recorded. Signal destruction can be prevented.
Further, by changing the recording density of the first recording layer and the second recording layer, the signal frequency read by the reproducing means can be made different. Therefore, the servo signal can be easily read by reading only the low frequency signal frequency by the reproducing means. Further, since the residual magnetic flux density of the second recording layer is increased, it is possible to read a data signal with a good S / N ratio and the like.

  The magnetic recording medium according to the present invention includes at least one layer selected from the group of a soft magnetic layer, a first underlayer, a second underlayer, and a protective layer above the substrate, and These layers have the following lamination positions (a) to (b), that is, (a) the lamination position of the soft magnetic layer and the lamination position of the first underlayer are below the first recording layer, (b) The lamination position of the second underlayer is below the second recording layer, and (c) the lamination position of the protective layer is above the second recording layer. 2).

  As described above, in the magnetic recording medium according to the present invention, the soft magnetic layer and / or the first underlayer can be formed below the first recording layer as needed, and below the second recording layer. In addition, a second underlayer can be formed, and a protective layer can be formed above the second recording layer. Then, by appropriately forming these layers, it is possible to impart a predetermined effect such as improving the magnetic reactivity of each recording layer or protecting the surface of the magnetic recording medium.

  In the magnetic recording medium according to the present invention, it is desirable that the first recording layer has a Curie temperature of 100 ° C. or more and 250 ° C. or less, and the first recording layer has a coercive force of 8 kOe or more. Item 3).

  Thus, since the Curie temperature of the first recording layer is regulated to an appropriate range that is relatively low, even when the magnetic recording medium is heated when recording a servo signal on the first recording layer, Adverse effects such as deterioration of the residual magnetic flux density of the two recording layers can be minimized. Further, since the coercive force of the first recording layer is set high, even if the first recording layer receives the magnetic force applied when reading / writing the data signal of the second recording layer, The servo signal recorded on the recording layer is not destroyed.

  In the magnetic recording medium according to the present invention, the first recording layer includes at least one selected from rare earth elements including Gd (gadolinium), Tb (terbium), and Sm (samarium), Fe (iron), and Co. It is made of a magnetic material containing an amorphous alloy in combination with at least one selected from transition metal elements made of (cobalt), and the composition ratio of the rare earth element and the transition metal element is 15:85 to 50:50. (Claim 4).

  By selecting a suitable element from such rare earth elements and transition metal elements, and further using a magnetic material including an amorphous alloy configured with an appropriate composition ratio, a high coercive force and a low residual magnetic flux density can be obtained. The provided first recording layer can be formed. In order to record a servo signal by applying a magnetic field to the first recording layer having such a composition, the first recording layer must be heated to a specific temperature (Curie temperature). Therefore, it is possible to prevent the servo signal from being rewritten by reading / rewriting normal data signals near room temperature.

  Furthermore, the method of manufacturing a magnetic recording medium according to the present invention includes a first step of laminating a first recording layer above a non-magnetic substrate, and laminating a second recording layer above the first recording layer. A second step of manufacturing a recording layer laminated substrate, a transfer surface of a master disk in which irregularities corresponding to servo signals to be recorded are previously formed on the transfer surface, and a second recording layer of the recording layer laminated substrate To the recording layer laminated substrate heated through the third step of heating from the substrate side of the recording layer laminated substrate to the Curie temperature of the first recording layer, and the unevenness of the transfer surface. A fourth step of cooling the recording layer laminated substrate while applying a magnetic field, and a fifth step of demagnetizing the servo signal recorded on the second recording layer are included (claims). Item 5).

  In the method for manufacturing a magnetic recording medium according to the present invention, the first recording layer is laminated on one surface of the non-magnetic substrate in the first step, and the second recording is performed above the first recording layer in the second step. The recording layer laminated substrate is manufactured by laminating the layers. Then, in the third step, the transfer surface of the master disk on which the irregularities corresponding to the servo signals are formed is attached to the second recording layer side of the recording layer laminated substrate. Then, the magnetism of the first recording layer is once demagnetized by heating from the substrate side of the recording layer laminated substrate until the Curie temperature of the first recording layer is reached. Next, the recording layer laminated substrate in contact with the master disk in the fourth step is cooled while applying a magnetic field, so that the servo signal corresponding to the unevenness of the transfer surface is transferred to the first recording layer of the recording layer laminated substrate. Recorded on the first recording layer and the second recording layer. Next, the servo signal recorded on the second recording layer in the fifth step is demagnetized, so-called initialization is performed, and a magnetic recording medium is manufactured.

  A magnetic signal reproducing means of the present invention is a means for reproducing a magnetic signal recorded on a magnetic recording medium according to any one of claims 1 to 4, comprising at least a first recording layer and a second recording layer. Magnetic signal reading means for reading a magnetic signal recorded on the recording layer as a reproduction signal in a superimposed state of a low signal frequency and a high signal frequency, and the reproduction signal in a superimposed state read by the magnetic signal reading means is low Reproduction signal separation means for separating the signal frequency into a high signal frequency is provided (claim 6).

  Thus, in the magnetic signal reproducing means of the present invention, the magnetic signal recorded on the magnetic recording medium can be read as a reproduced signal by the magnetic signal reading means. However, since the reproduction signal read by the magnetic signal reading means is in a state where a low signal frequency and a high signal frequency are superimposed, it is reproduced as an accurate servo signal and data signal recorded on the magnetic recording medium. I can't. Therefore, the reproduced signal can be reproduced as an accurate servo signal and data signal recorded on the magnetic recording medium by separating the reproduced signal into a low signal frequency and a high signal frequency by the reproduction signal separation means.

  A magnetic signal reproduction method according to the present invention is a method for reproducing a magnetic signal recorded on a magnetic recording medium according to any one of claims 1 to 4, comprising at least a first recording layer and A magnetic signal reading step for reading a magnetic signal recorded in the second recording layer as a reproduction signal in a superimposed state of a low signal frequency and a high signal frequency, and the reproduction signal in a superimposed state read by the magnetic signal reading step And a reproduction signal separating step for separating the signal into a low signal frequency and a high signal frequency (claim 7).

  As described above, in the magnetic signal reproduction method of the present invention, the reproduction signal in a state where the low signal frequency and the high signal frequency are superimposed is read by the magnetic signal reading step, and then the low signal frequency and the high signal frequency are obtained by the reproduction signal separation step. Therefore, even when a reproduction signal in which a servo signal and a data signal are superimposed is obtained, it can be reproduced as an accurate servo signal and data signal.

  According to the magnetic recording medium of the present invention, since the first recording layer for recording servo signals and the second recording layer for recording data are separated, the capacity for recording data can be improved. Also, the servo signal recorded on the first recording layer with high coercive force cannot change its magnetism unless it is heated to the Curie temperature. Therefore, the servo signal is caused by improper control when reading or writing data signals. Destruction (for example, rewriting or disappearance) can be prevented. Furthermore, since the residual magnetic flux density of the first recording layer and the residual magnetic flux density of the second recording layer are different, the signal frequency obtained based on this can be made different, so that the servo signal and the data signal can be obtained accurately. it can.

  According to the method for manufacturing a magnetic recording medium of the present invention, it is possible to manufacture a magnetic recording medium in which a first recording layer for recording a servo signal and a second recording layer for recording data are separated.

  According to the magnetic signal reproducing means and the magnetic signal reproducing method of the present invention, an accurate servo signal and data can be obtained by separating the reproduction signal obtained from the magnetic recording medium in a state in which the servo signal and the data signal are superimposed on each other. It can be reproduced as a signal.

  Next, the magnetic recording medium and the manufacturing method thereof according to the present invention will be described in detail with reference to the drawings as appropriate. In the drawings to be referred to, FIG. 1 is a cross-sectional explanatory view showing a configuration example of the best embodiment of the magnetic recording medium of the present invention. FIG. 2 is a diagram showing a hysteresis curve of the first recording layer and a hysteresis curve of the second recording layer.

[Configuration of Magnetic Recording Medium 1]
(Magnetic recording medium 1)
As shown in the cross-sectional explanatory diagram of FIG. 1, a magnetic recording medium 1 according to the best embodiment of the present invention includes a soft magnetic layer 3, a first underlayer 4, a first recording layer 5, and a second lower layer on a substrate 2. The base layer 6, the second recording layer 7, and the protective layer 8 are stacked in this order. Among these, the substrate 2, the first recording layer 5, and the second recording layer 7 are essential components, and the soft magnetic layer 3, the first underlayer 4, the second underlayer 6, and the protective layer 8 are added. It is also possible to manufacture the magnetic recording medium 1 by omitting one or more of these components as appropriate.

  Of the components of the magnetic recording medium 1 according to the best embodiment of the present invention, the substrate 2, the first recording layer 5, and the second recording layer 7 which are essential components will be described first.

(Substrate 2)
The substrate 2 serves as a base material of the magnetic recording medium 1 and is made of a nonmagnetic material such as aluminum, an aluminum alloy, or glass.

(First recording layer 5)
The first recording layer 5 is a recording layer for recording a servo signal, and is laminated as a layer above the substrate 2 as shown in FIG. More preferably, the first recording layer 5 is laminated between the substrate 2 and the second recording layer 7.
The first recording layer 5 is composed of at least one selected from rare earth elements consisting of gadolinium (Gd), terbium (Tb), and samarium (Sm), and a transition metal element consisting of iron (Fe) and cobalt (Co). It is good to comprise with the magnetic body containing the amorphous alloy which combined at least 1 type selected, and to make the composition ratio of this rare earth element and a transition metal element into 15: 85-50: 50. Specifically, magnetic materials such as Gd ₂₃ Fe ₇₂ Co ₅ , Tb ₂₄ Fe ₅₉ Co ₁₇ , Tb ₂₀ Co ₈₀ , and Sm ₅₀ Co ₅₀ can be preferably used. When a plurality of transition metal elements are used, the ratio of these transition metal elements can be arbitrarily set.

  When the first recording layer 5 is configured using such a magnetic material, it has a higher coercive force (Oe: Oersted) and a lower residual magnetic flux density (Oersted) compared to a second recording layer 7 (see FIG. 1) described later. G: Gauss) can be obtained, and the Curie temperature can be set to a relatively low temperature of 100 to 250 ° C. Therefore, the first recording layer 5 made of such a magnetic material has a high coercive force Hc1 and, due to the nature of the magnetic material, once heated to the Curie temperature and magnetized, it is heated again to the Curie temperature and no magnetic field is applied. As long as there is no loss of magnetism. Therefore, when the servo signal is recorded on the first recording layer 5, the servo signal is not destroyed by the magnetic force applied in the reading / writing of the data signal performed near room temperature (approximately 30 ° C.).

FIG. 2 shows a hysteresis curve obtained from the relationship between the magnetic field strength and the magnetic flux density in the first recording layer 5 and the second recording layer 7 used in the magnetic recording medium 1 of the present invention.
Since the first recording layer 5 needs to have a low residual magnetic flux density Br1, -Br1 and a high coercive force Hc1, -Hc1, it has a horizontally long hysteresis curve.
On the other hand, since the second recording layer 7 needs to have a high residual magnetic flux density Br2, -Br2 and a low coercive force Hc2, -Hc2, it has a long vertical hysteresis curve.
In the residual magnetic flux densities Br1, -Br1 and the coercive forces Hc1, -Hc1, the minus sign indicates the magnetization in the opposite direction, and the absolute values thereof are the same value. The same applies to the residual magnetic flux densities Br2, -Br2 and the coercive forces Hc2, -Hc2. Hereinafter, in the present specification, in order to simply show the residual magnetic flux density and the coercive force, the residual magnetic flux density Br1, the residual magnetic flux density Br2, the coercive force Hc1, and the coercive force Hc2 are simply shown.

  Here, when the magnetic field strength [Oe] when the magnetic flux density of the second recording layer 7 is saturated is Hs, −Hs, the magnetic field range indicated between the magnetic field strengths Hs and −Hs is as follows. The magnetic field range can be used for writing data signals. That is, within this magnetic field range, only the magnetization of the second recording layer 7 can be changed without changing the magnetization of the first recording layer 5.

  As described above, since the low-density servo signals are recorded on the first recording layer 5 and the high-density data signals are recorded on the second recording layer 7 described later, the head 21 (see FIG. 6). The frequency of the servo signal read in is reduced. Therefore, the data signal reproduced at a high signal frequency and the servo signal can be easily separated by using the reproduction signal separation means described later.

In order to record a servo signal on the first recording layer 5 made of the magnetic material having the above composition, it is necessary to heat to the Curie temperature, but this Curie temperature is in a relatively low temperature range, that is, 100 ° C. to Since the temperature is 250 ° C., adverse effects such as a decrease in magnetism of the second recording layer 7 and warping of the substrate 2 can be minimized even when heated to the temperature. If the Curie temperature is less than 100 ° C., the magnetic recording medium is close to the temperature at which the magnetic recording medium is commonly used. In addition, the servo signal may be rewritten. On the other hand, if the Curie temperature exceeds 250 ° C., the heating temperature is too high, which may cause a decrease in magnetism of the second recording layer 7. Therefore, the Curie temperature of the first recording layer 5 in the present invention is preferably in the temperature range of 100 ° C. to 250 ° C. In addition, the Curie temperature of the second recording layer 7 is preferably sufficiently higher than the Curie temperature of the first recording layer 5. This is to suppress adverse effects such as a decrease in magnetism of the second recording layer 7 when the first recording layer 5 is heated to the Curie temperature.
The Curie temperature means that the magnetism disappears when the magnetic material is heated and reaches a specific temperature. If a magnetic field is applied from the outside at this time, the magnetic field is reduced when the temperature decreases. Magnetize again in the direction. In the present invention, the servo signal is recorded using such a phenomenon.

  Further, if the coercive force Hc1 of the first recording layer 5 is less than 8 kOe, it cannot be said that the coercive force is sufficiently high, and there is a possibility that the servo signal may be destroyed by application during reading / writing of the data signal. Therefore, the coercive force Hc1 of the first recording layer 5 in the present invention is set to 8 kOe or more, which is larger than the application (magnetic field strength) at the time of reading / writing the data signal.

(Second recording layer 7)
The second recording layer 7 is a recording layer for recording data signals, and is laminated as a layer above the first recording layer 5 as shown in FIG. The second recording layer 7 can be laminated by appropriately selecting a magnetic material conventionally used in a magnetic recording medium. Specific examples include a recording layer made of CoCrPt and a recording layer made of CoCrPtX (X = B, Nb, Ta, O, C). More specifically, Co ₇₀ Cr ₂₀ Pt ₁₀ , Co ₆₆ Cr ₂₀ Pt ₁₀ B ₄ , Co ₆₈ Cr ₂₀ Pt ₁₀ Ta _{2 and the} like can be exemplified, and Co ₇₆ Pt ₁₉ Cr ₅ and SiO ₂ can be used. A magnetic body having a ratio of 70:30 can also be used.

The second recording layer 7 needs to have a coercive force Hc2 smaller than the first recording layer 5, less than 8 kOe, and a higher residual magnetic flux density than the first recording layer 5.
If the coercive force Hc2 of the second recording layer 7 is 8 kOe or more, the coercive force Hc2 is too high, and the data signal cannot be rewritten without heating the second recording layer 7. Therefore, in the present invention, the coercive force Hc2 of the second recording layer 7 is set to less than 8 kOe.

  If the residual magnetic flux density of the second recording layer 7 is lower than that of the first recording layer 5, it is recorded on the first recording layer 5 when reproducing a magnetic signal recorded on the magnetic recording medium 1. It becomes difficult to recognize the servo signal and the data signal recorded on the second recording layer 7 separately, which is inappropriate. Therefore, in the present invention, the residual magnetic flux density Br2 of the second recording layer 7 needs to be higher than the residual magnetic flux density Br1 of the first recording layer 5.

  Since the second recording layer 7 is a layer for recording a data signal as described above, it is preferable to make it as thick as possible from the viewpoint of thermal relaxation. However, if the thickness is excessively large, the distance between the head 21 and the soft magnetic layer 3 is increased, and a sufficient magnetic force and a large magnetic field gradient cannot be obtained. For this reason, it is preferable to form the second recording layer 7 in a range of 5 nm to 20 nm as a thickness with which thermal relaxation is small and a good magnetic field gradient can be obtained.

  Thus, since the magnetic recording medium 1 of the present invention includes the first recording layer 5 and the second recording layer 7, a servo signal area can be provided in the first recording layer 5, and the second recording layer 7. A data signal area can be provided. As a result, the data recording capacity can be increased as compared with the conventional magnetic recording medium in which the servo signal area and the data signal area are formed on the same surface.

There are a perpendicular magnetic recording method and a horizontal magnetic recording method as a method for recording data and the like on the magnetic recording medium 1 of the present invention. As the recording method of the magnetic recording medium 1 of the present invention, it is preferable to adopt the perpendicular magnetic recording method from the viewpoint of increasing the recording density, but it is also possible to adopt the horizontal magnetic recording method.
The perpendicular magnetic recording system is a magnetic recording medium in which the easy axis of magnetization of the magnetic material constituting the recording layer of the magnetic recording medium is perpendicular to the recording surface, and the magnetic material is perpendicular to the recording surface. A magnetic recording method that records data signals by performing magnetization. Adjacent magnetizations in the magnetization transition region do not face each other and the magnetization is stable. Is possible. In contrast, the horizontal magnetic recording method uses a magnetic recording medium in which the easy axis of magnetization of the magnetic material constituting the recording layer of the magnetic recording medium is parallel to the recording surface, and the circumferential direction of the recording surface. In addition, it refers to a magnetic recording system in which data signals are recorded by magnetizing a magnetic material.

  Next, the soft magnetic layer 3, the first underlayer 4, the second underlayer 6, and the protective layer 8, which are additional components, will be described.

(Soft magnetic layer 3)
The soft magnetic layer 3 functions as a part of a magnetic circuit for effectively returning a recording magnetic field (magnetic force) generated from the recording magnetic pole 21b of the head 21 (see FIG. 6) to a return magnetic pole (not shown) of the head 21. In order to generate a large magnetic field in the recording magnetic pole 21b, it is preferable to use a magnetic material having a large magnetic force (saturation magnetic flux density) and a relatively small coercive force. For example, Ni ₉₀ Fe ₁₀ or Fe ₉₀ C ₁₀ can be used as such a magnetic material.

(First underlayer 4 and second underlayer 6)
The first underlayer 4 and the second underlayer 6 are layers added so that the first recording layer 5 and the second recording layer 7 show good magnetic characteristics, respectively. Specifically, silicon nitride (Si ₃ N ₄ ) or the like can be used as the first underlayer 4 having such an action. Further, specifically, Cr, Ti, Ti ₉₀ Cr ₁₀ , Ru, or the like can be used as the second underlayer 6. When the first underlayer 4 and the second underlayer 6 are used, the first underlayer 4 and the second underlayer 6 are easy to epitaxially grow the first recording layer 5 and the second recording layer 7, so that the required magnetic properties are obtained. It becomes easy to obtain characteristics.

(Protective layer 8)
The protective layer 8 is a layer for protecting the recording surface (the upper surface is shown in FIG. 1) constituted by the second recording layer 7 and the first recording layer 5 of the magnetic recording medium 1. In addition to protecting against adverse effects due to the contact of foreign matter to the second recording layer 7 and the first recording layer 5, it also prevents the oxidation of metal elements and the like of magnetic substances contained in these recording layers. Therefore, it is preferable to use a substance having a high hardness and hardly affected by oxidation. Specifically, diamond like carbon (DLC), a polymer resin that is hardened by ultraviolet rays, or the like can be suitably used as the protective layer 8.

[Method of manufacturing magnetic recording medium]
Next, the manufacturing method of the magnetic recording medium of the present invention will be described in detail with reference to FIG. FIG. 3 is a flowchart for explaining the manufacturing method of the magnetic recording medium 1 described above.

The method for manufacturing the magnetic recording medium 1 includes the steps described below.
First, the first recording layer 5 is laminated on one surface of the nonmagnetic substrate 2 (first step). Next, the second recording layer 7 is laminated (second step) to produce a recording layer laminated substrate 9 (FIG. 4A).

  A transfer surface 10t of a master disk 10 prepared in advance is brought into contact with the second recording layer 7 side of the recording layer laminated substrate 9 produced as described above, and the substrate 2 side of the recording layer laminated substrate 9 is attached. To the Curie temperature of the first recording layer 5 (third step). As described above, the magnetic material constituting the recording layer becomes weaker as it is heated, and disappears when it reaches a specific temperature (Curie temperature). In the present invention, it is not necessary to strictly heat to the Curie temperature, and the heating temperature is appropriately changed and set near the Curie temperature in consideration of other components such as the second recording layer 4 and the substrate 2. You can also

  Next, the recording layer laminated substrate 9 is cooled while applying a magnetic field in a certain direction to the heated recording layer laminated substrate 9 through the unevenness of the transfer surface 10t of the master disk 10 (fourth step; (See FIG. 4 (a)). Thus, when the temperature is lowered from the Curie temperature, by applying a magnetic field from the outside, the magnetic material is provided with magnetism in accordance with the magnetic field, and this can be maintained. The magnetic field in a certain direction at this time is preferably a magnetic field having a magnetic flux density lower than the magnetic flux density used for the data signal recorded on the second recording layer 7. By this step, the second recording layer 7 and the first recording layer 5 in a portion where the recording layer laminated substrate 9 and the unevenness of the transfer surface 10t of the master disk 10 are in contact can be magnetized in a certain direction. That is, a servo signal can be recorded.

Then, of the first recording layer 5 and the second recording layer 7 of the recording layer laminated substrate 9 on which the servo signal is recorded, only the servo signal recorded on the second recording layer 7 is demagnetized, so-called magnetic The recording medium 1 is initialized (fifth step; see FIG. 4B). As a method of degaussing only the servo signal recorded on the second recording layer 7, for example, a method of applying a magnetic field opposite to the direction of the magnetic field used when recording the servo signal can be mentioned.
Thus, the magnetic recording medium 1 as defined in the present invention can be realized by performing the first to fifth steps.

Here, in FIG. 4, the configuration of the recording layer laminated substrate 9 is simply shown by the substrate 2, the first recording layer 5, and the second recording layer 7, but as shown in FIG. In order to produce a recording layer laminated substrate 9 in which the soft magnetic layer 3, the first underlayer 4, the first recording layer 5, the second underlayer 6, the second recording layer 7 and the protective layer 8 are laminated. The following steps (a) to (d) may be performed in the first step and the second step of the manufacturing method.

  That is, (a) in the first step, the step of laminating the soft magnetic layer 3 before laminating the first recording layer 5, and (b) the base of the first recording layer 5 before laminating the first recording layer 5 By performing the step of laminating the first underlayer 4, the soft magnetic layer 3 and the first underlayer 4 can be laminated as lower layers of the first recording layer 5, respectively. Further, (c) a step of laminating a second underlayer serving as a base of the second recording layer before laminating the second recording layer in the second step, and (d) laminating the second recording layer in the second step. By performing the step of laminating a protective layer later, it is possible to laminate the second underlayer 6 as the lower layer of the second recording layer 7 and the protective layer 8 as the upper layer of the second recording layer 7, respectively.

  Thus, by adding the above-described steps in the first step and the second step, the soft magnetic layer 3, the first underlayer 4, the first recording layer 5, the second underlayer 6, and the second recording are formed on the substrate 2. The magnetic recording medium 1 in which the layer 7 and the protective layer 8 are laminated can be manufactured. In addition, conventionally known means can be used for laminating these layers, and the soft magnetic layer 3, the first underlayer 4, the first recording layer 5, the second underlayer 6, the second recording layer 7, etc. It is preferable that these can be laminated as a thin layer having a uniform thickness by performing sputtering.

  When any one of the soft magnetic layer 3, the first underlayer 4, the second underlayer 6, and the protective layer 8, which are additional components, is not required to be laminated, the above (a) to (d) The magnetic recording medium 1 having a desired configuration can be realized by omitting an appropriate step among the steps).

[Master disk 10]
Next, the master disk 10 (see FIG. 4A) for recording servo signals will be described.
The master disk 10 that can be used in the present invention can form irregularities corresponding to servo signals on the transfer surface 10t by the following method. For example, while rotating a circular metal disk coated with a positive photosensitive anticorrosive film material (photoresist), the exposed portion of the resist is irradiated with a laser beam or electron beam modulated according to the servo signal. Is dissolved / removed with a developer, and the dissolved / removed portion is plated, and then the remaining photoresist is peeled off to obtain the master disk 10 with the irregularities corresponding to the servo signal. .

[Magnetic signal reproducing means and magnetic signal reproducing method]
Before explaining the magnetic signal reproducing means 20 for reproducing the magnetic signal recorded on the magnetic recording medium 1 of the present invention with reference to FIG. 5B, referring to FIG. The magnetic signal reproducing means 200 recorded on the medium 101 will be briefly described.
A means for reproducing a magnetic signal recorded on the conventional magnetic recording medium 101 includes a magnetic recording medium 101, a head 201, an amplifier 202, a signal processing device 203, a voice coil motor 204a and its control unit 204b, a spindle. The motor 205a and its control unit 205b are included. The head 201 (see FIG. 9) is a device for reading and reproducing a magnetic signal recorded on the recording layer 107, and has a reproducing element 201a and a recording magnetic pole 201b. The reproducing element 201a reproduces the data signal recorded in the data signal area of the recording layer and the servo signal recorded in the servo signal area of the recording layer. The recording magnetic pole 201b applies a recording magnetic field from the tip of the recording magnetic pole 201b to write or demagnetize a data signal recorded in the data signal area of the recording layer of the magnetic recording medium 101.

  Returning to FIG. 5A, the description will be continued. In this conventional magnetic signal reproducing means 200, first, the reproducing element 201a of the head 201 reads a magnetic signal (data signal and servo signal) recorded on the magnetic recording medium 101 as a reproduced signal. The read reproduction signal is input to the amplifier 202, and the signal intensity is amplified by the amplifier 202. The reproduction signal amplified in this way is input to the signal processing device 203. The signal processing device 203 performs an appropriate operation based on the data signal and the servo signal. Therefore, the data signal is output to a CPU (Central Processing Unit) (not shown), and the servo signal is output to the control unit 204b of the voice coil motor 204a and the control unit 205b of the spindle motor 205a. The control unit 204b to which the servo signal is input controls the voice coil motor 204a appropriately based on the input servo signal to adjust the reading position, and the control unit 205b to which the servo signal is input converts the servo signal to the input servo signal. Based on this, the spindle motor 205a is appropriately controlled to adjust the rotation speed of the magnetic recording medium 101.

Here, in the conventional magnetic recording medium 101, a servo signal area and a data signal area are arranged on the same surface (see FIG. 9). Therefore, the reproduction signal read by the head 201 at a time is only one of the servo signal and the data signal.
However, in the magnetic recording medium 1 of the present invention, as shown in FIG. 6, the servo signal is recorded on the first recording layer 5 and the data signal is recorded on the second recording layer 7. The reproduction signal read by the head 21 having the same configuration is obtained by superimposing the servo signal and the data signal. Even if the conventional magnetic signal reproducing means 200 shown in FIG. The signal cannot be reproduced accurately.
Therefore, in the present invention, the magnetic signal of the magnetic recording medium 1 is reproduced by the following reproducing means.

  As shown in FIG. 5B, the magnetic signal reproducing means 20 recorded on the magnetic recording medium 1 according to the present invention includes a magnetic recording medium 1, a reproducing element 21a, and a recording magnetic pole 21b. And an amplifier 22, a signal processing device 23, a voice coil motor 24 a and its control unit 24 b, a spindle motor 25 a and its control unit 25 b, and a filter 26. Since the configuration other than the filter 26 is the same as that of the magnetic signal reproducing means 200, the description thereof is omitted.

(Filter 26)
As shown in FIG. 5B, the filter 26 is disposed between the amplifier 22 and the signal processing device 23. The filter 26 includes a low-pass filter (LPF) 26a for passing a low signal frequency (blocking a high frequency) and a high-pass filter (HPF) 26b for passing a high signal frequency (cutting a low signal frequency). It consists of As described above, the reproduction signal reproduced from the magnetic recording medium 1 of the present invention can be obtained as a waveform in which a low signal frequency servo signal and a high signal frequency data signal are superimposed.

  Then, as shown in FIGS. 5B and 7, the reproduction signal is read by the head 21 which is a magnetic signal reading means and output to the amplifier 22 (magnetic signal reading step). The amplifier 22 amplifies the input reproduction signal and outputs it to the signal processing device 23 which is reproduction signal separation means. The reproduction signal at this time has a waveform in which the servo signal and the data signal are superimposed as shown in FIG.

The signal processing device 23 can separate only the servo signal having a low signal frequency by passing the amplified reproduced signal through the LPF 26a of the filter 26 (FIG. 7B); However, “reproduced signal separation step”). Similarly, only the data signal having a high signal frequency can be separated by passing the superimposed reproduction signal input from the amplifier 22 through the HPF 26b of the filter 26 (FIG. 7C). "Reproduction signal separation step"). As described above, the servo signal and the data signal which are separated and reproduced by the LPF 26 a and the HPF 26 b of the filter 26 are output to the signal processing device 23. The signal processing device 23 to which the servo signal and the data signal are input outputs the data signal to a CPU (not shown) as in the conventional magnetic reproducing means 200, and the servo signal is transmitted to the voice coil motor 24a and its control unit 24b. Output to the spindle motor 25a and its controller 25b.
Thus, the superimposed magnetic signal recorded on the magnetic recording medium 1 of the present invention can be suitably separated and reproduced by the reproducing means 20.

FIG. 2 is a cross-sectional explanatory view showing a configuration example of the best embodiment of the magnetic recording medium of the present invention. FIG. 4 is a diagram illustrating a hysteresis curve of a first recording layer and a hysteresis curve of a second recording layer. It is a flowchart for demonstrating the manufacturing method of a magnetic recording medium. It is a figure explaining a part of manufacturing method of the magnetic recording medium of this invention, Comprising: (a) is explanatory drawing for demonstrating a 3rd process and a 4th process, (b) is a 5th process. It is explanatory drawing for demonstrating. It is a block diagram for demonstrating a magnetic signal reproduction | regeneration means, (a) is a block diagram of the conventional magnetic signal reproduction | regeneration means, (b) is a block diagram of the magnetic signal reproduction | regeneration means used by this invention. . It is the figure which showed a mode that the magnetic signal recorded on the magnetic recording medium of this invention was read. (A) is a reproduction signal having a waveform obtained by superimposing a servo signal and a data signal reproduced from the magnetic recording medium of the present invention, and (b) is a reproduction obtained by separating and reproducing only a low signal frequency by LPF. (C) is a reproduced signal obtained by separating and reproducing only a high signal frequency by HPF. It is a figure explaining the conventional magnetic recording medium, Comprising: (a) is a structure sectional drawing of the conventional magnetic recording medium, (b) is a servo signal area | region and a data signal area | region in a recording layer typically. It is the shown schematic diagram. It is the figure which showed a mode that the magnetic signal recorded on the conventional magnetic recording medium was read. It is sectional drawing which shows the structure of the conventional magnetic recording medium which has an upper layer part and a lower layer recording layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Substrate 3 Soft magnetic layer 4 First underlayer 5 First recording layer 6 Second underlayer 7 Second recording layer 8 Protective layer 9 Recording layer laminated substrate

Claims (7)

A magnetic recording medium comprising at least a non-magnetic substrate, a first recording layer for recording a servo signal, and a second recording layer for recording a data signal above the substrate. And
The coercivity of the first recording layer is greater than the coercivity of the second recording layer, and
A magnetic recording medium, wherein the residual magnetic flux density of the first recording layer is smaller than the residual magnetic flux density of the second recording layer. Above the substrate, at least one layer selected from the group of a soft magnetic layer, a first underlayer, a second underlayer, and a protective layer is included, and these layers include the following (a) to (b ) Stacking position, that is,
(A) The lamination position of the soft magnetic layer and the lamination position of the first underlayer are below the first recording layer,
(B) The stack position of the second underlayer is below the second recording layer,
(C) The laminated position of the protective layer is above the second recording layer.
The magnetic recording medium according to claim 1.   3. The magnetism according to claim 1, wherein the first recording layer has a Curie temperature of 100 ° C. or more and 250 ° C. or less, and the first recording layer has a coercive force of 8 kOe or more. recoding media.   The first recording layer is selected from at least one selected from rare earth elements consisting of Gd (gadolinium), Tb (terbium) and Sm (samarium), and a transition metal element consisting of Fe (iron) and Co (cobalt). The composition ratio of the rare earth element and the transition metal element is 15:85 to 50:50. Item 4. The magnetic recording medium according to any one of Items 3 to 3. A first step of laminating a first recording layer on one surface of a non-magnetic substrate;
A second step of producing a recording layer laminated substrate by laminating a second recording layer above the first recording layer;
Concavities and convexities corresponding to servo signals to be recorded are brought into contact with the transfer surface of the master disk, which is formed in advance on the transfer surface, and the second recording layer side of the recording layer stacked substrate, and the recording layer stacked substrate A third step of heating from the substrate side to the Curie temperature of the first recording layer;
A fourth step of cooling the recording layer laminated substrate while applying a magnetic field to the heated recording layer laminated substrate through the unevenness of the transfer surface;
A fifth step of degaussing the servo signal recorded in the second recording layer;
A method of manufacturing a magnetic recording medium, comprising: A means for reproducing a magnetic signal recorded on the magnetic recording medium according to any one of claims 1 to 4,
A magnetic signal reading means for reading a magnetic signal recorded at least in the first recording layer and the second recording layer as a reproduction signal in a superimposed state of a low signal frequency and a high signal frequency;
Reproduction signal separation means for separating the reproduction signal in a superimposed state read by the magnetic signal reading means into a low signal frequency and a high signal frequency;
Magnetic signal reproducing means characterized by comprising: A method for reproducing a magnetic signal recorded on a magnetic recording medium according to any one of claims 1 to 4,
A magnetic signal reading step for reading a magnetic signal recorded in at least the first recording layer and the second recording layer as a reproduction signal in a superimposed state of a low signal frequency and a high signal frequency;
A reproduction signal separation step of separating the reproduction signal in the superimposed state read by the magnetic signal reading step into a low signal frequency and a high signal frequency;
A magnetic signal reproducing method comprising:

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