JP2006059474A - Magnetic recording method, magnetic recording medium, and magnetic recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording method, a magnetic recording medium, and a magnetic recording device suitable for attaining sufficient high density recording. <P>SOLUTION: In the magnetic recording method of this invention, the magnetic recording medium 10 having a multi-layer recording film 12 is used, which includes two or more recording magnetic layers 12A, 12B differing in Curie temperature, and non-magnetic layer 12a prepared between the recording magnetic layers. This method comprises a process for raising once the temperature of the two or more recording magnetic layers 12A, 12B of the magnetic recording medium 10, and a process for sequentially applying a recording field to each of the two or more recording magnetic layers 12A, 12B having passed through the temperature-up process from a layer of relatively higher Curie temperature to a layer of lower Curie temperature and thereby magnetizing them in the direction of the magnetic field. To perform such a method, a magnetic disk device X1 of this invention is provided with a heating-up means 22 for raising the temperature of the multi-layer recording film 12, and two or more magnetic field applying means 23A, 23B located in the direction of medium rotary operation at the time of performing information recording. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording method for recording information on a magnetic recording medium with thermal assistance, and a magnetic recording medium and a magnetic recording apparatus of a thermal assist recording system.

  As the amount of information processing in a computer system increases, an increase in storage capacity is required for a magnetic recording medium constituting a storage device such as a hard disk. In recent years, perpendicular magnetic recording magnetic recording media have attracted attention as media capable of meeting such requirements.

  FIG. 25 is a schematic partial sectional view of a magnetic disk 70 which is an example of a conventional magnetic recording medium of a perpendicular magnetic recording system. The magnetic disk 70 has a laminated structure including a substrate 71, a recording layer 72, and a protective layer 73. The recording layer 72 is made of a perpendicular magnetization film, and is a part where a predetermined signal is recorded as a change in magnetization direction. The protective layer 73 is a part for physically and chemically protecting the recording layer 72 from the outside.

  When recording information on the magnetic disk 70, a recording magnetic head (not shown) is placed in close proximity to the recording layer 72 from the protective layer 73 side, and the coercive force is applied to the recording layer 72 by the magnetic head. Apply a stronger recording magnetic field. By changing the direction of the magnetic field from the magnetic head while moving the magnetic head relative to the magnetic disk 70, a plurality of magnetic domains 72 a that are magnetized in the perpendicular direction and are alternately reversed are recorded on the magnetic disk 70. It is formed continuously in the track direction. By such a recording process, a predetermined signal or information is recorded in the recording layer 72 as a change in the magnetization direction. On the other hand, when reproducing information from the magnetic disk 70, a change in the magnetization direction of the magnetic domain 72a formed in the recording layer 72 is a change in the direction of the magnetic field derived from the magnetic domain 72a. Abbreviation).

  In the technical field of magnetic recording media, the smaller the magnetic domain 72a ′ that can be stably formed in the recording process as described above, the narrower or narrower (that is, the length W shown in FIG. 25 for the magnetic domain 72a ′ is smaller). It is known that higher recording density can be realized. It is also known that the higher the coercivity of the recording layer 72, the higher the thermal stability of the magnetic domain 72a, and the easier it is to form a fine and stable magnetic domain 72a. Therefore, in order to increase the recording density of the magnetic disk 70, it is conceivable to set the minimum magnetic domain 72a 'that can be stably formed by setting the coercive force of the recording layer 72 higher.

  In the recording process as described above, the magnetic field applied to the recording layer 72 needs to be stronger than the coercive force of the recording layer 72. In order to increase the applied magnetic field strength, the magnetic field generated by the recording magnetic head It is conceivable to increase the strength or reduce the separation distance between the recording magnetic head and the magnetic disk 70 or the recording layer 72. However, it is known that an increase in the generated magnetic field strength of the recording magnetic head causes a reduction in recording speed and impairs the effect of increasing the recording density. Further, the separation distance has already been realized about several nanometers, and it is technically difficult to set a smaller distance.

  Therefore, in recording information on the magnetic disk 70, a so-called heat-assisted recording method may be employed. When information recording is performed on the magnetic disk 70 by the heat-assisted recording method, first, a predetermined portion of the recording layer 72 is locally heated, for example, by laser beam irradiation. The temperature rise location in the recording layer 72 has a lower coercive force than the surrounding non-temperature rise locations. Next, by applying a recording magnetic field stronger than the coercive force of the temperature rise point to the temperature rise point by the recording magnetic head, the temperature rise point is magnetized in a predetermined direction. This magnetization is fixed in the course of cooling the magnetized portion. According to the heat-assisted recording method, information recording is performed by applying a magnetic field to a portion where the coercive force has decreased due to heating. Therefore, when the coercive force of the recording layer 72 is set to be high at normal temperature during information retention or information reproduction. Even in such a case, it is not necessary to excessively increase the intensity of the magnetic field to be generated by the recording magnetic head. Further, it is not necessary to set the separation distance between the recording magnetic head and the magnetic disk too small. Such a heat-assisted recording magnetic recording technique is described in, for example, Patent Document 1 and Patent Document 2 below.

JP 2000-207723 A JP 2001-189002 A

  As can be understood from the above, when the heat-assisted recording method is employed in the perpendicular magnetic recording type magnetic disk 70, the recording magnetic head and the magnetic disk can be used without excessively increasing the intensity of the magnetic field generated by the recording magnetic head. Even if the separation distance from 70 is not set too small, the minimum magnetic domain 72a ′ that can be stably formed can be set minutely by setting the coercive force of the recording layer 72 at room temperature high. The smaller the minimum magnetic domain 72a 'that can be stably formed, the better the recording density in both the track extending direction and the track crossing direction.

  However, such a two-dimensional increase in recording density is restricted by the size of the stable minimum magnetic domain 72a that can be technically formed. For this reason, even with the magnetic disk 70 that employs both the perpendicular magnetic recording method and the heat-assisted recording method, it may not be possible to achieve a sufficiently high recording density in the magnetic recording medium.

  The present invention has been conceived under such circumstances, and provides a magnetic recording method, a magnetic recording medium, and a magnetic recording apparatus suitable for achieving a sufficiently high recording density. Objective.

  According to a first aspect of the present invention, a magnetic recording method is provided. In this method, a magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each recording magnetic layer is used. In this method, a temperature raising step for once raising the temperature of the plurality of recording magnetic layers, and each of the plurality of recording magnetic layers that have undergone the temperature raising step are changed from a recording magnetic layer having a relatively high Curie temperature to a low recording magnetic layer. And a magnetic field application step for sequentially applying a recording magnetic field and recording and magnetizing in the direction of the recording magnetic field. In the present invention, “recording magnetization” refers to magnetization in order to fix the magnetization direction after the recording magnetization so as to form a signal.

  In the magnetic recording medium used in the present method, a multilayer recording film including a plurality of recording magnetic layers laminated via a nonmagnetic layer spreads on a predetermined substrate, for example, to form a recording surface. In the temperature raising step, for example, the predetermined portion of the recording surface is locally irradiated with laser light from the substrate side or the side opposite to the substrate, thereby locally heating the predetermined portion. Then, the predetermined portion is locally heated to, for example, the maximum Curie temperature or more over the entire thickness of the multilayer recording film. The maximum Curie temperature is the highest temperature among the plurality of Curie temperatures of the plurality of recording magnetic layers. The temperature of the predetermined portion gradually decreases after the temperature raising step. In the magnetic field applying step, a predetermined external magnetic field (recording magnetic field) is recorded for each recording magnetic layer by a recording magnetic element in a state where the recording magnetic layer is below its Curie temperature. ) Is magnetized. At this time, the coercive force of one recording magnetic layer is equal to or greater than the coercive force of the recording magnetic layer and the other predetermined recording magnetic layer (all or part of the recording magnetic layer other than the one recording magnetic layer). By applying a predetermined recording magnetic field that is less than that, the magnetization direction of the one recording magnetic layer can be determined independently of the magnetization direction of the other predetermined recording magnetic layer. Thus, a signal magnetic field to be read by the read magnetic element is formed on the recording surface side of the predetermined portion where each recording magnetic layer is magnetized. The states (magnitude and direction) that the signal magnetic field can take may differ depending on the magnitude and direction of magnetization of each recording magnetic layer and the thickness of each recording magnetic layer. The magnitude of the magnetization of each recording magnetic layer can be appropriately set by adjusting the composition of each recording magnetic layer, and the direction of magnetization of each recording magnetic layer can be set in each recording magnetic layer in the magnetic field application step. It can be determined by appropriately selecting the direction of the recording magnetic field to be applied. The state in which the signal magnetic field can be taken varies depending on the number of recording magnetic layers included in the multilayer recording film. However, since the multilayer recording film in this method includes a plurality (two or more) of recording magnetic layers, the signal magnetic field can be taken. The state is 3 or more. That is, the signal magnetic field is multivalued to 3 or more. Thus, according to the present method, information can be recorded by a multi-value recording method of three or more values.

  In addition, in this method, each recording magnetic layer is magnetized by applying a magnetic field to a portion where the coercive force has decreased through the temperature raising step (that is, each recording magnetic layer is magnetized with thermal assistance). For example, the coercive force of each recording magnetic layer at room temperature can be set high while maintaining the strength of the recording magnetic field to be generated by the recording magnetic element. The higher the coercive force of each recording magnetic layer, the smaller the minimum magnetic domain that can be stably formed in each recording magnetic layer, and thus a two-dimensionally high recording density can be obtained in the recording in-plane direction. Is possible. Further, since the intensity of the recording magnetic field to be generated by the recording magnetic element can be kept small, the effect of increasing the recording density resulting from the increase in coercive force of each recording magnetic layer is ensured without reducing the recording speed. be able to. Furthermore, it is not necessary to set the separation distance between the recording magnetic head and the magnetic disk too small.

  As described above, according to the magnetic recording method of the first aspect of the present invention, it is possible to achieve a sufficiently high recording density in the multi-value recording system with thermal assistance.

  According to a second aspect of the present invention, a magnetic recording medium is provided. This magnetic recording medium has a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each recording magnetic layer. The magnetic recording medium having such a configuration can be used as a magnetic recording medium in the magnetic recording method according to the first aspect of the present invention.

  According to a third aspect of the present invention, a magnetic recording apparatus is provided. The magnetic recording apparatus includes a magnetic recording medium, a temperature raising unit, and a plurality of magnetic field applying units. The magnetic recording medium has a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each of the recording magnetic layers, and is accompanied by a rotation operation when information recording is performed. The temperature raising means is for locally raising the temperature of the multilayer recording film. The plurality of magnetic field applying means are for applying a magnetic field to the multilayer recording film that has been heated by the temperature raising means, and the number of magnetic field applying means is the same as that of the plurality of recording magnetic layers of the magnetic recording medium and is rotated when information recording is performed. Located in a row in the direction of movement. According to the magnetic recording apparatus having such a configuration, the magnetic recording method according to the first aspect of the present invention can be appropriately executed.

  In the first to third aspects of the present invention, preferably, each of the plurality of recording magnetic layers has magnetization under a predetermined reproduction environment in which information reproduction is performed on the magnetic recording medium. The product of the magnitude and thickness of the magnetization is different from each other. In this case, preferably, the sum of the products of the magnitude and thickness of the magnetization for each recording magnetic layer is different for all the combinations of the plurality of products. According to these configurations, the above-described signal magnetic field can be appropriately multi-valued.

  In the first to third aspects of the present invention, preferably, the magnetic recording medium includes a base material for supporting the multilayer recording film, and the plurality of Curie temperatures of the plurality of recording magnetic layers are closer to the base material. Or it is so high that it is far from a base material. According to such a configuration, in the magnetic field application step, each recording magnetic layer can be magnetized in order from the recording magnetic layer close to the base material or from the recording magnetic layer far from the base material. There is no need to apply a recording magnetic field to the recording magnetic layer to magnetize the recording magnetic layer located between the two fixed recording magnetic layers. Therefore, according to this configuration, the recording magnetic field can be appropriately applied to each recording magnetic layer in the magnetic field application step.

  The magnetic recording apparatus according to the third aspect of the present invention preferably further includes a flying slider that is placed on the magnetic recording medium so as to face the multilayer recording film when information recording is performed, The magnetic field applying means is provided on the flying slider. According to such a configuration, it is possible to efficiently ensure the functions of the temperature raising means and the magnetic field applying means of the magnetic recording apparatus.

  FIG. 1 shows a partial configuration of a magnetic disk device X1 for executing the magnetic recording method according to the first embodiment of the present invention. The magnetic disk device X1 includes the magnetic disk 10 and the flying slider 20, and is configured so that information recording and information reproduction by the heat-assisted recording method can be performed on the magnetic disk 10.

  As shown in FIG. 2 in addition to FIG. 1, the magnetic disk 10 has a laminated structure including a substrate 11, a multilayer recording film 12, and a protective layer 13, and uses a perpendicular magnetic recording system and a heat-assisted recording system. It is configured as a medium.

  The substrate 11 is a part for securing the rigidity of the magnetic disk 10 and has a disk shape. The substrate 11 is, for example, an aluminum alloy substrate, a glass substrate, or a resin substrate.

  The multilayer recording film 12 has a laminated structure composed of recording magnetic layers 12A and 12B and a nonmagnetic layer 12a, and constitutes a recording surface on which quaternary signals can be recorded at various places.

Each of the recording magnetic layers 12A and 12B is a perpendicular magnetization film that is magnetized with an easy axis in the direction perpendicular to the film surface of the magnetic film constituting the layer. For example, the recording magnetic layers 12A and 12B have a predetermined composition ratio of TbFe. , TbFeCo, FePt, or CoCr. In this embodiment, assuming that the Curie temperatures of the recording magnetic layers 12A and 12B are Tc ₁ and Tc ₂ , respectively, Tc ₁ > Tc ₂ and the coercive forces of the recording magnetic layers 12A and 12B are Hc ₁ and Hc ₂ , respectively. Then, Hc ₁ > Hc ₂ in the temperature range that the multilayer recording film 12 can take when recording information. FIG. 3 is a graph showing an example of the temperature dependence of the coercive force Hc for the recording magnetic layers 12A and 12B configured under these conditions. In the graph of FIG. 3, a line G1 represents a change in coercive force of the recording magnetic layer 12A, and a line G2 represents a change in coercive force of the recording magnetic layer 12B. In the present embodiment, if the magnetization and thickness of the recording magnetic layer 12A are Mr ₁ and d _1, and the magnetization and thickness of the recording magnetic layer 12B are Mr ₂ and d ₂ , the magnitude of the magnetization (absolute value). | Mr ₁ | × d ₁ and | Mr ₂ | × d ₂ are different from each other. For each recording magnetic layer, simply “magnetization” is magnetization in a reproducing environment in the present invention. Further, the Curie temperature, the coercive force, and the magnitude of magnetization can be appropriately set by selecting the constituent element types of the recording magnetic layers 12A and 12B and adjusting the composition ratio. Each of the recording magnetic layers 12A and 12B has a thickness of 5 to 50 nm, for example.

The nonmagnetic layer 12a is interposed between the recording magnetic layers 12A and 12B so that no exchange coupling action occurs between the recording magnetic layers 12A and 12B, and is made of, for example, Al, C, Si, SiO ₂ , or SiN. The thickness of such a nonmagnetic layer 12a is, for example, 1 to 10 nm.

The protective layer 13 is for physically and chemically protecting the multilayer recording film 12 from the outside, and is made of, for example, SiN, SiO ₂ or diamond-like carbon (DLC).

  In manufacturing such a magnetic disk 10, the recording magnetic layer 12A, the nonmagnetic layer 12a, the recording magnetic layer 12B, and the protective layer 13 are sequentially formed on the substrate 11 by sputtering, for example. In the present invention, an adhesive underlayer, a soft magnetic layer, or the like may be formed on the substrate 11 before forming the recording magnetic layer 12A.

  In the magnetic disk device X1, the magnetic disk 10 is supported by a spindle motor (not shown), and rotates when the spindle motor rotates. The rotational drive of the spindle motor is controlled based on a control signal from a predetermined control unit.

  The flying slider 20 has a slider body 21, a laser element 22, recording heads 23A and 23B, and a reproducing head 24, and faces the protective layer 13 of the magnetic disk 10 when information recording and information reproduction are performed by the magnetic disk device X1. Arranged.

  The laser element 22 is a medium heating means (specifically, a temperature raising means for locally raising the temperature of the multilayer recording film 12) in the heat-assisted recording system, and is a semiconductor element that can emit laser light when a voltage is applied. It is. In the present invention, instead of mounting such a laser element 22 on the flying slider 20, a fixed optical unit having a light source, a prism, a signal detector and the like is separately provided, and the laser light from the light source is transmitted to the magnetic disk. An optical waveguide for irradiating toward the beam 10 may be formed in the flying slider 20 or the like. The fact that such an alternative configuration can be adopted is the same in the other embodiments described below.

  Each of the recording heads 23A and 23B is for applying a predetermined magnetic field to the multilayer recording film 12, and a coil for flowing a current for generating a magnetic field and for converting the generated magnetic field into a strong magnetic field. It consists of magnetic poles. The recording heads 23A and 23B and the laser element 22 correspond to the rotational direction D (or circumferential direction) of the magnetic disk 10 in the order of the laser element 22, the recording head 23A, and the recording head 23B in the flying slider 20. It is arranged in a line along the direction.

  The reproducing head 24 is for detecting a signal magnetic field derived from the multilayer recording film 12 and converting it into an electric signal, and is composed of, for example, a GMR element or an MR element.

  Such a flying slider 20 is connected to an actuator (not shown) via a leaf spring-like suspension arm (not shown). The suspension arm is for applying a biasing force toward the magnetic disk 10 to the flying slider 20. The actuator is composed of, for example, a voice coil motor.

  4 to 6 show the process of thermal assist information recording executed in the magnetic disk device X1 based on the magnetic recording method according to the first embodiment of the present invention. 4 to 6, the magnetic disk 10 is simplified by omitting parts other than the base material 11 and the recording magnetic layers 12A and 12B, and represents a partial cross section along the circumferential direction (track extending direction). 4 to 6, the moving direction (rotating direction) of the magnetic disk 10 with respect to the flying slider 20 is indicated by an arrow D.

When recording information, the magnetic disk 10 is rotated at a predetermined speed. As a result, a gas lubrication film is formed between the magnetic disk 10 and the flying slider 20, and the flying slider 20 is arranged to float with respect to the magnetic disk 10. Then, the laser beam continues to be emitted from the laser element 22 of the flying slider 20 that is placed in a floating manner. At this time, the laser beam is irradiated with a light quantity and intensity sufficient to supply thermal energy for once raising the recording magnetic layers 12A and 12B to a predetermined temperature (initial temperature). The initial temperature is preferably a temperature exceeding the Curie temperature Tc ₁ (> Tc ₂ ) of the recording magnetic layer 12A. By such laser light irradiation, the multilayer recording film 12 (recording magnetic layers 12A and 12B) is locally heated, and the multilayer recording film 12 has an initial temperature as a peak in the circumferential direction (track extending direction). A temperature distribution with a temperature gradient occurs. A graph representing this temperature distribution is attached to each of FIGS.

As shown in FIG. 4, when the local region P ₁ on the recording surface (multilayer recording film 12) reaches the laser element 22 and is irradiated with laser, the recording magnetic layers 12A and 12B in the region P ₁ have an initial temperature. (Temperature raising step). In this step, the coercive forces Hc ₁ and Hc ₂ of the recording magnetic layers 12A and 12B are lowered to a predetermined value according to the set initial temperature. If the initial temperature is set to a temperature above Tc _1, the recording magnetic layer 12A in the region P _1, 12B are heated to a temperature above Tc ₁ as shown in the graph of FIG. 4, thereby, Both the recording magnetic layers 12A and 12B in the region P ₁ lose their spontaneous magnetization, and thus lose their coercive force.

Next, as shown in FIG. 5, when the area P ₁ reaches just below the recording head 23A by the medium movement in the direction of arrow D, the first recording magnetic field B ₁ is applied to the area P ₁ by the recording head 23A. by, magnetizing the magnetic recording layer 12A, and 12B in the first direction of the recording magnetic field B ₁ (first magnetization step of the magnetic field application step). In this step, the temperature of the region P ₁ is less than Tc _1, at least a recording magnetic layer 12A in the region P ₁ has a coercive force Hc _1, the first recording magnetic field B ₁ represents greater than Hc ₁ (Hc ₁ < B _1). If the initial temperature described above is set to a temperature above Tc _1, while the region P ₁ is moved to the position shown in FIG. 5 from the position shown in FIG. 4, region P ₁ is the initial temperature Tc ₁ of less than For example, the distance between the laser element 22 and the recording head 23A, the material composition of the recording magnetic layer 12A, and the like are adjusted on the premise of the rotational speed of the magnetic disk 10 so as to lower the temperature to a predetermined temperature. Thus, the recording magnetic layer 12A is recorded and magnetized in the first magnetization step of the magnetic field application step.

On the other hand, when the region P ₁ is in the first magnetization step as described above, the predetermined region P ₂ located upstream of the region P _{1 in the} medium rotation direction with respect to the flying slider 20 is the region P with reference to FIG. ₁ is subjected to the same heating step as described above. Further, the section from the region P ₁ to the region P ₂ (consisting of one or two or more local regions) is heated between the end of the temperature increasing process of the region P _{1 and} the temperature increasing process of the region P _2. It is attached to the process.

Next, as shown in FIG. 6, when the area P ₁ reaches just below the recording head 23B by the medium movement in the direction of arrow D, the recording head 23B applies the second recording magnetic field B ₂ to the area P ₁ . As a result, the recording magnetic layer 12B is magnetized in the direction of the second recording magnetic field B ₂ (second magnetization step of the magnetic field applying step). In this step, the temperature of the region P ₁ is less than Tc _2, the recording magnetic layer 12A of the regions P _1, 12B each have a coercive force Hc _1, Hc _2, the second recording magnetic field B ₂ than Hc ₂ It is large and less than Hc ₁ (Hc ₂ <Bc ₁ <Hc ₁ ). Therefore, the recording magnetic layer 12A is without being in effect the operation of the second recording magnetic field B _2, the magnetic recording layer 12B is magnetized under the influence of the second recording magnetic field B _2. The direction of the second recording magnetic field B ₂ is the same as or opposite to that of the first recording magnetic field B ₁ (the opposite case is shown in FIG. 6). If the temperature of the region P ₁ at the time of the first magnetization step is greater than Tc _2, while the region P ₁ to the position shown in FIG. 6 from the position shown in FIG. 5 moves, the area P ₁ is less than Tc ₂ For example, the distance between the recording head 23A and the recording head 23B, the material composition of the recording magnetic layer 12B, and the like are adjusted on the premise of the rotational speed of the magnetic disk 10 so as to lower the temperature to a predetermined temperature. Thus, the recording magnetic layer 12B is recorded and magnetized in the second magnetization step of the magnetic field application step.

Meanwhile, when such a region P ₁ is in the second magnetization step, the region P ₂ is subjected to the same first magnetization step as described above for area P ₁ with reference to FIG. 5, the floating slider 20 On the other hand, the predetermined region P ₃ located upstream of the region P _{2 in the} rotation direction is subjected to the same temperature raising process as described above with respect to the region P ₁ with reference to FIG. Further, the section from the region P ₁ to the area P ₂ is subjected to a first magnetization step between after completion of the first magnetization step region P ₁ to the first magnetization step region P _2, from region to region P ₂ section up to P ₃ is subjected to elevated process during later heating step is completed in the region P ₂ until the heating process region P _3.

  By executing the temperature raising step and the magnetic field applying step (first magnetization step, second magnetization step) as described above for each region sequentially reaching the position immediately below the laser element 22 and the recording heads 23A and 23B, FIG. As shown, a predetermined signal or information can be recorded as a change in magnetization direction in the multilayer recording film 12 (recording magnetic layers 12A and 12B) of the magnetic disk 10. In FIG. 7, from the viewpoint of simplifying the figure, the magnetic disk 10 other than the substrate 11 and the recording magnetic layers 12A and 12B is omitted.

The recording magnetic layers 12A and 12B in each region of the recording surface (multilayer recording film 12) of the magnetic disk 10 are magnetized in one of two directions perpendicular to the multilayer recording film 12, and the above-mentioned Thus, in the recording magnetic layers 12A and 12B, | Mr ₁ | × d ₁ and | Mr ₂ | × d ₂ are different (in FIG. 7, the case of | Mr ₁ | × d ₁ <| Mr ₂ | × d ₂ Show). Therefore, the recording magnetic layer 12A in each region, 12B of | Mr ₁ | × d ₁ and | Mr ₂ | sum of × d ₂ is the | Mr ₁ | × d ₁ and | Mr ₂ | all of × d ₂ It depends on the adjustment combination. Specifically, each area of the recording surface is represented by | Mr ₁ | × d ₁ + | Mr ₂ | × d ₂ (referred to as a magnetic state S1), | Mr ₁ | × d ₁ − | Mr ₂ | × d ₂ (this is the magnetic state S2), − | Mr ₁ | × d ₁ + | Mr ₂ | × d ₂ (this is the magnetic state S3), and − | Mr ₁ | × d ₁ − | Mr There are four states: ₂ | × d ₂ (this is referred to as a magnetic state S4).

  When information is reproduced by the magnetic disk device X1, the magnetic disk 10 is rotated at a predetermined speed. As a result, a gas lubrication film is formed between the magnetic disk 10 and the flying slider 20, and the flying slider 20 is arranged to float with respect to the magnetic disk 10. In this state, the reproducing head 24 detects a signal magnetic field (which can take four values) formed from the magnetic states S1 to S4 of the recording surface (multilayer recording film 12). FIG. 7 shows a voltage waveform of a reproduction signal when the reproducing head 24 reads the multilayer recording film 12 in the magnetic state shown in FIG. In this way, information reproduction for reading the quaternary signal recorded in the multilayer recording film 12 is executed.

  As described above, according to the method of the present embodiment, information can be recorded and reproduced by a four-value system. In addition, in this method, since the recording magnetic layers 12A and 12B are recorded and magnetized with thermal assistance, the recording magnetic field strength to be generated by the recording heads 23A and 23B is kept small, for example, recording at room temperature. The coercive force of the magnetic layers 12A and 12B can be set high. The higher the coercivity of the recording magnetic layers 12A and 12B, the smaller the minimum magnetic domain that can be stably formed in the recording magnetic layers 12A and 12B, and the higher the recording density two-dimensionally in the in-plane direction of the recording surface. It is possible to obtain. Therefore, according to the magnetic recording method of the present embodiment, it is possible to achieve a sufficiently high recording density in the quaternary recording / reproducing system with thermal assist.

  FIG. 8 shows a partial configuration of a magnetic disk device X2 for executing the magnetic recording method according to the second embodiment of the present invention. The magnetic disk device X2 includes a magnetic disk 30 and a flying slider 40, and is configured so that information recording and information reproduction by the heat-assisted recording method can be performed on the magnetic disk 30.

  As shown in FIG. 9 in addition to FIG. 8, the magnetic disk 30 has a laminated structure including a substrate 31, a multilayer recording film 32, and a protective layer 33, and uses a perpendicular magnetic recording system and a heat-assisted recording system for magnetic recording. It is configured as a medium.

  The substrate 31 is a part for securing the rigidity of the magnetic disk 30 and has a disk shape. The substrate 31 is, for example, an aluminum alloy substrate, a glass substrate, or a resin substrate.

  The multilayer recording film 32 has a laminated structure composed of recording magnetic layers 32A, 32B, 32C and a nonmagnetic layer 32a, and constitutes a recording surface on which eight-value signals can be recorded.

Each of the recording magnetic layers 32A, 32B, and 32C is a perpendicular magnetization film, and is made of, for example, TbFe, TbFeCo, FePt, or CoCr having a predetermined composition ratio. In this embodiment, assuming that the Curie temperatures of the recording magnetic layers 32A, 32B, and 32C are Tc ₁ , Tc ₂ , and Tc ₃ , respectively, Tc ₁ > Tc ₂ > Tc ₃ and the recording magnetic layers 32A, 32B, and 32C Assuming that the coercivity is Hc ₁ , Hc ₂ , and Hc ₃ , Hc ₁ > Hc ₂ > Hc ₃ in the temperature range that the multilayer recording film 32 can take during information recording. FIG. 10 is a graph showing an example of the temperature dependence of the coercive force Hc for the recording magnetic layers 32A, 32B, and 32C configured under these conditions. In the graph of FIG. 10, a line G1 represents a change in coercivity of the recording magnetic layer 32A, a line G2 represents a change in coercivity of the recording magnetic layer 32B, and a line G3 represents a change in coercivity of the recording magnetic layer 32C. In this embodiment, the magnetizations of the recording magnetic layers 32A, 32B, and 32C are Mr ₁ , Mr ₂ , and Mr ₃ , respectively, and the thicknesses of the recording magnetic layers 32A, 32B, and 32C are d ₁ , d ₂ , and d ₃ , respectively. Then, | Mr ₁ | × d ₁ , | Mr ₂ | × d ₂ , and | Mr ₃ | × d _3, which are products of the magnitude (absolute value) of magnetization and the thickness, are different from each other. The Curie temperature, the coercive force, and the magnitude of magnetization can be appropriately set by selecting the constituent element types of the recording magnetic layers 32A, 32B, and 32C and adjusting the composition ratio. Each of the recording magnetic layers 32A, 32B, and 32C has a thickness of, for example, 5 to 50 nm.

The nonmagnetic layer 32a is interposed between the two recording magnetic layers so that no exchange coupling action occurs between the recording magnetic layers, and is made of, for example, Al, C, Si, SiO ₂ , or SiN. The thickness of such a nonmagnetic layer 32a is, for example, 1 to 10 nm.

The protective layer 33 is for physically and chemically protecting the multilayer recording film 32 from the outside, and is made of, for example, SiN, SiO ₂ , or DLC.

  In manufacturing such a magnetic disk 30, the recording magnetic layer 32A, the nonmagnetic layer 32a, the recording magnetic layer 32B, the nonmagnetic layer 32a, the recording magnetic layer 32C, and the protective layer 33 are formed on the substrate 31, for example, by sputtering. Are sequentially formed. In the present invention, an adhesive underlayer, a soft magnetic layer, or the like may be formed on the substrate 31 before forming the recording magnetic layer 32A.

  In the magnetic disk device X2, the magnetic disk 30 is supported by a spindle motor (not shown) that is controlled based on a control signal from a predetermined control unit, and rotates when the spindle motor is driven to rotate.

  The flying slider 40 includes a slider body 41, a laser element 42, recording heads 43A, 43B, and 43C, and a reproducing head 44. When performing information recording and information reproduction by the magnetic disk device X2, the protection slider 33 of the magnetic disk 30 is used. It is arrange | positioned facing.

  The configuration of the laser element 42 itself, each recording head 43A, 43B, 43C itself, and the reproducing head 44 itself is the same as the configuration of the laser element 22, recording head 23A, 23B, and reproducing head 24 in the first embodiment, respectively. It is. Further, the recording heads 43A, 43B, 43C and the laser element 42 are arranged in the flying slider 40 in the order of the laser element 42, the recording head 43A, the recording head 43B, and the recording head 43C in the rotational direction D (or through). It is arranged in a line along a direction corresponding to (circumferential direction).

  Such a flying slider 40 is connected to an actuator (not shown) via a leaf spring-like suspension arm (not shown). The suspension arm is for applying a biasing force toward the magnetic disk 30 with respect to the flying slider 40, and the actuator is composed of, for example, a voice coil motor.

  FIGS. 11 to 14 show the process of thermal assist information recording executed in the magnetic disk device X2 based on the magnetic recording method according to the second embodiment of the present invention. 11 to 14, the magnetic disk 30 is simplified by omitting parts other than the base material 31 and the recording magnetic layers 32A, 32B, and 32C, and represents a partial cross section along the circumferential direction (track extending direction). Further, in each of FIGS. 11 to 14, the moving direction (rotational direction) of the magnetic disk 30 with respect to the flying slider 40 is indicated by an arrow D.

When recording information, the magnetic disk 30 is rotated at a predetermined speed. As a result, a gas lubrication film is formed between the magnetic disk 30 and the flying slider 40, and the flying slider 40 is arranged to float with respect to the magnetic disk 30. Then, the laser beam is continuously emitted from the laser element 42 of the flying slider 40 that is placed in a floating manner. At this time, the laser beam is irradiated with a light quantity and intensity sufficient to supply thermal energy for once raising the recording magnetic layers 32A and 32B to a predetermined temperature (initial temperature). The initial temperature is preferably a temperature exceeding the Curie temperature Tc ₁ (> Tc ₂ > Tc ₃ ) of the recording magnetic layer 32A. By such laser light irradiation, the multilayer recording film 32 (recording magnetic layers 32A, 32B, 32C) is locally heated, and the multilayer recording film 32 has a circumferential direction (track extending direction) with an initial temperature as a peak. ) Has a temperature distribution with a temperature gradient. A graph representing this temperature distribution is attached to each of FIGS.

As shown in FIG. 11, when the local region P ₁ on the recording surface (multilayer recording film 32) reaches the laser element 42 and is irradiated with laser, the recording magnetic layers 32A, 32B, 32C in the region P ₁ The temperature is raised to the initial temperature (temperature raising step). In this step, the coercive forces Hc ₁ , Hc ₂ , and Hc ₃ of the recording magnetic layers 32A, 32B, and 32C are lowered to a predetermined value according to the set initial temperature. If the initial temperature is set to a temperature above Tc _1, the recording magnetic layer 32A in the region P _1, 32B, 32C is heated to a temperature above Tc ₁ as shown in FIG. 11, thereby, The recording magnetic layers 32A, 32B, and 32C in the region P _{1 all} lose their spontaneous magnetization, and thus lose their coercive force.

Next, as shown in FIG. 12, when the area P ₁ reaches just below the recording head 43A by moving the medium in the direction of arrow D, the first recording magnetic field B ₁ is applied to the area P ₁ by the recording head 43A. Accordingly, the recording magnetic layer 32A, 32B, magnetizing the 32C in the first direction of the recording magnetic field B ₁ (first magnetization step of the magnetic field application step). In this step, the temperature of the region P ₁ is less than Tc _1, at least a recording magnetic layer 32A in the region P ₁ has a coercive force Hc _1, the first recording magnetic field B ₁ represents greater than Hc ₁ (Hc ₁ < B _1). If the initial temperature described above is set to a temperature above Tc _1, while the region P ₁ to the position shown in FIG. 12 from the position shown in FIG. 11 moves, the region P ₁ is the initial temperature Tc ₁ of less than For example, the distance between the laser element 42 and the recording head 43A, the material composition of the recording magnetic layer 32A, and the like are adjusted on the premise of the rotational speed of the magnetic disk 30 so as to lower the temperature to a predetermined temperature. Thus, the recording magnetic layer 32A is recorded and magnetized in the first magnetization step of the magnetic field application step.

On the other hand, when the region P ₁ is in the first magnetization step as described above, the predetermined region P ₂ located upstream of the region P _{1 with} respect to the flying slider 40 in the medium rotation direction is the region P with reference to FIG. ₁ is subjected to the same heating step as described above. Further, the section from the region P ₁ to the region P ₂ is subjected to the temperature raising step after the temperature raising step in the region P ₁ until the temperature raising step in the region P ₂ .

Next, as shown in FIG. 13, when the area P ₁ reaches just below the recording head 43B by the medium movement in the direction of the arrow D, the recording head 43B applies the second recording magnetic field B ₂ to the area P ₁ . Thus, the recording magnetic layers 32B and 32C are magnetized in the direction of the second recording magnetic field B ₂ (second magnetization step of the magnetic field applying step). In this step, the temperature of the region P ₁ is less than Tc ₂ , at least the recording magnetic layers 32A and 32B of the region P ₁ have coercive forces Hc ₁ and Hc ₂ , respectively, and the second recording magnetic field B ₂ is Hc _2. It is larger and less than Hc ₁ (Hc ₂ <B ₂ <Hc ₁ ). Therefore, the recording magnetic layer 32A is without being in effect the operation of the second recording magnetic field B _2, the magnetic recording layer 32B, 32C is magnetized under the influence of the second recording magnetic field B _2. The direction of the second recording magnetic field B ₂ is the same as or opposite to that of the first recording magnetic field B ₁ (the opposite case is shown in FIG. 13). If the temperature of the region P ₁ at the time of the first magnetization step is greater than Tc _2, while the region P ₁ to the position shown in FIG. 13 from the position shown in FIG. 12 moves, the region P ₁ is less than Tc ₂ For example, the distance between the recording head 43A and the recording head 43B, the material composition of the recording magnetic layer 32B, and the like are adjusted on the premise of the rotational speed of the magnetic disk 30 so as to lower the temperature to a predetermined temperature. Thus, the recording magnetic layer 32B is recording-magnetized in the second magnetization step of the magnetic field application step.

Meanwhile, when such a region P ₁ is in the second magnetization step, the region P ₂ is subjected to the same first magnetization step as described above for area P ₁ with reference to FIG. 12, the floating slider 40 On the other hand, the region P ₃ located upstream of the region P _{2 in the} medium rotation direction is subjected to the same temperature raising process as described above with respect to the region P ₁ with reference to FIG. Further, the section from the region P ₁ to the area P ₂ is subjected to a first magnetization step between after completion of the first magnetization step region P ₁ to the first magnetization step region P _2, from region to region P ₂ section up to P ₃ is subjected to elevated process during later heating step is completed in the region P ₂ until the heating process region P _3.

Next, as shown in FIG. 14, when the area P ₁ reaches just below the recording head 43C due to the medium movement in the direction of arrow D, the third recording magnetic field B ₃ is applied to the area P ₁ by the recording head 43C. Thus, the recording magnetic layer 32C is magnetized in the direction of the third recording magnetic field B ₃ (third magnetization step of the magnetic field applying step). In this step, the temperature of the region P ₁ is less than Tc ₂ , and the recording magnetic layers 32A, 32B, 32C of the region P ₁ have coercive forces Hc ₁ , Hc ₂ , Hc ₃ , respectively, and the third recording magnetic field B ₃ is greater than Hc ₃ and less than Hc ₂ (Hc ₃ <B ₃ <Hc ₂ <Hc ₁ ). Therefore, the recording magnetic layer 32A, 32B is without being in effect the operation of the third recording magnetic field B _3, the recording magnetic layer 32C is magnetized under the influence of the third recording magnetic field B _3. The direction of the third recording magnetic field B ₃ is the same as or opposite to that of the first and second recording magnetic fields B ₁ and B ₂ . If the temperature of the region P ₁ at the time of the second magnetization step is greater than Tc _3, while the area P ₁ to the position shown in FIG. 14 from the position shown in FIG. 13 moves, the region P ₁ is less than Tc ₃ For example, the distance between the recording head 43B and the recording head 43C, the material composition of the recording magnetic layer 32C, and the like are adjusted on the premise of the rotational speed of the magnetic disk 30 so that the temperature is lowered to a predetermined temperature. Thus, the recording magnetic layer 32C is recorded and magnetized in the third magnetization step of the magnetic field application step.

Meanwhile, when such a region P ₁ is in the third magnetization step, the region P ₂ is subjected to a similar second magnetization step as described above for area P ₁ with reference to FIG. 13, region P ₃ is The region P _{4 that} is subjected to the same first magnetization step as described above with reference to FIG. 12 with respect to the region P ₁ and is located upstream of the region P _{3 with} respect to the flying slider 40 in the medium rotation direction is shown in FIG. To the temperature raising step similar to that described above for the region P ₁ . Further, the section from the region P ₁ to the area P ₂ is subjected to a second magnetization step between after completion of the second magnetization step regions P ₁ to the second magnetization step regions P _2, from region to region P ₂ section up to P ₃ is subjected to a first magnetization step between after completion of the first magnetization step region P ₂ to the first magnetization step region P _3, a section from the region P ₃ to the area P ₄ is The temperature raising step is performed after the temperature raising step in the region P ₃ until the temperature raising step in the region P ₄ .

  By performing the temperature raising step and the magnetic field applying step (first to third magnetization steps) as described above for each region sequentially reaching the position immediately below the laser element 42 and the recording heads 43A, 43B, and 43C, FIG. As shown, a predetermined signal or information can be recorded as a change in magnetization direction in the multilayer recording film 32 (recording magnetic layers 32A, 32B, 32C) of the magnetic disk 30. In FIG. 15, from the viewpoint of simplifying the drawing, the magnetic disk 30 other than the substrate 31 and the recording magnetic layers 32A, 32B, and 32C is omitted.

The recording magnetic layers 32A, 32B, 32C in each region of the recording surface (multilayer recording film 32) of the magnetic disk 30 are magnetized in one of two directions perpendicular to the multilayer recording film 32, and As described above, in the recording magnetic layers 32A, 32B, and 32C, | Mr ₁ | × d ₁ , | Mr ₂ | × d ₂ , and | Mr ₃ | × d ₃ are different from each other. Therefore, the sum of | Mr ₁ | × d ₁ , | Mr ₂ | × d ₂ , and | Mr ₃ | × d ₃ of the recording magnetic layers 32A, 32B, and 32C in each region is the | Mr ₁ | × d _1. , | Mr ₂ | × d ₂ , and | Mr ₃ | × d ₃ . Specifically, each area of the recording surface is represented by | Mr ₁ | × d ₁ + | Mr ₂ | × d ₂ + | Mr ₃ | × d ₃ , | Mr ₁ | × d ₁ + | Mr ₂ | × d ₂ − | Mr ₃ | × d ₃ , | Mr ₁ | × d ₁ − | Mr ₂ | × d ₂ + | Mr ₃ | × d ₃ , | Mr ₁ | × d ₁ − | Mr ₂ | × d ₂ − | Mr ₃ | × d ₃ , − | Mr ₁ | × d ₁ + | Mr ₂ | × d ₂ + | Mr ₃ | × d ₃ , − | Mr ₁ | × d ₁ + | Mr ₂ | × d ₂ − | Mr ₃ | × d ₃ , − | Mr ₁ | × d ₁ − | Mr ₂ | × d ₂ + | Mr ₃ | × d ₃ , and − | Mr ₁ | × d ₁ − | Mr ₂ | × d ₂ Eight magnetic states of − | Mr ₃ | × d ₃ can be taken.

  When reproducing information by the magnetic disk device X2, the magnetic disk 30 is rotated at a predetermined speed. As a result, a gas lubrication film is formed between the magnetic disk 30 and the flying slider 40, and the flying slider 40 is arranged to float with respect to the magnetic disk 30. In this state, the reproducing head 44 detects a signal magnetic field (which can take eight values) formed from the magnetic state of the multilayer recording film 32. In this way, information reproduction for reading the 8-level signal recorded in the multilayer recording film 32 is executed.

  As described above, according to the method of the present embodiment, information can be recorded / reproduced by the 8-level method. In addition, in this method, since the recording magnetic layers 32A, 32B, and 32C are magnetized with thermal assistance, the intensity of the recording magnetic field to be generated by the recording heads 43A, 43B, and 43C is kept small, for example, at room temperature. The coercive force of the recording magnetic layers 32A, 32B, and 32C can be set high. The higher the coercive force of the recording magnetic layers 32A, 32B, and 32C, the smaller the minimum magnetic domain that can be stably formed in the recording magnetic layers 32A, 32B, and 32C, and two-dimensionally in the recording in-plane direction. A high recording density can be obtained. Therefore, according to the magnetic recording method of the present embodiment, a sufficiently high recording density can be achieved in the 8-level recording / reproducing system with thermal assist.

  FIG. 16 shows a partial configuration of a magnetic disk device X3 for executing the magnetic recording method according to the third embodiment of the present invention. The magnetic disk device X3 includes a magnetic disk 50 and a flying slider 60, and is configured so that information recording and information reproduction by the heat-assisted recording method can be performed on the magnetic disk 50.

  As shown in FIG. 17 in addition to FIG. 16, the magnetic disk 50 has a laminated structure including a substrate 51, a multilayer recording film 52, and a protective layer 53. It is configured as a medium.

  The substrate 51 is a part for ensuring the rigidity of the magnetic disk 50 and has a disk shape. The substrate 51 is, for example, an aluminum alloy substrate, a glass substrate, or a resin substrate.

The multilayer recording film 52 has a laminated structure composed of recording magnetic layers L ₁ , L ₂ ,... L _n and a nonmagnetic layer 52a, and can record a multilevel (for example, 2 ⁿ value) signal in various places. Configure the surface.

Each of the recording magnetic layers L ₁ , L ₂ ,... L _n is a perpendicular magnetization film, and is made of, for example, TbFe, TbFeCo, FePt, or CoCr having a predetermined composition ratio. In the present embodiment, the recording magnetic layer L _1, L _2, each Curie temperature _{··· L n Tc 1, Tc 2} , When _{··· Tc n, Tc 1> Tc} 2>···> Tc n , and the and the recording magnetic layer L _1, L _2, respectively the coercive force of the _{··· L n Hc 1, Hc 2} , When · · · Hc _n, the possible temperature range of multilayer recording film 52 during the recording of information in a _{Hc 1> Hc 2>···>} Hc n. Further, in this embodiment, the magnetizations of the recording magnetic layers L ₁ , L ₂ ,... L _n are Mr ₁ , Mr ₂ ,... Mr _n , _respectively , and the recording magnetic layers L ₁ , L ₂ ,. L each d ₁ the thickness of the _n, d _2, when the · · · d _n, is the product of the thickness and the size of the magnetization (absolute _{value) | Mr 1 | × d 1} ~ | Mr n | × d _n are preferably different from each other. The Curie temperature, coercive force, and magnitude of magnetization can be appropriately set by selecting the constituent element types of the recording magnetic layers L ₁ , L ₂ ,... L _n and adjusting the composition ratio. The recording magnetic layers L ₁ , L ₂ ,... L _n each have a thickness of, for example, 5 to 50 nm.

The nonmagnetic layer 52a is interposed between the two recording magnetic layers so as not to cause an exchange coupling action between the recording magnetic layers, and is made of, for example, Al, Al, C, Si, SiO ₂ , or SiN. The thickness of such a nonmagnetic layer 52a is, for example, 1 to 10 nm.

The protective layer 53 is for physically and chemically protecting the multilayer recording film 52 from the outside, and is made of, for example, SiN, SiO ₂ , or diamond-like carbon.

  Such a magnetic disk 50 can be manufactured by sequentially forming each layer on the substrate 51 by sputtering, for example.

  In the magnetic disk device X3, the magnetic disk 50 is supported by a spindle motor (not shown) controlled based on a control signal from a predetermined control unit, and rotates when the spindle motor is driven to rotate.

The flying slider 60 includes a slider body 61, a laser element 62, recording heads K ₁ , K ₂ ,... K _n , and a reproducing head 63. When performing information recording and information reproduction by the magnetic disk device X3, the flying slider 60 is magnetic. It is arranged to face the protective layer 53 of the disk 50.

The configuration of the laser element 62 itself, each recording head K ₁ , K ₂ ,... K _n itself, and the reproducing head 63 itself is the same as that of the laser element 22, recording heads 23A and 23B, and reproducing in the first embodiment. The configuration is the same as that of the head 24. The recording head K _1, K _2, is · · · K _n, and the laser element 62, the floating slider 60, the laser device 62 and the recording head K _1, K _2, in the order of · · · K _n, magnetic They are arranged in a line along a direction corresponding to the rotational direction D (or circumferential direction) of the disk 50.

  Such a flying slider 60 is connected to an actuator (not shown) via a leaf spring-like suspension arm (not shown). The suspension arm is for applying a biasing force toward the magnetic disk 50 against the flying slider 60, and the actuator is constituted by a voice coil motor, for example.

FIG. 18 shows heat assist information recording executed in the magnetic disk device X3 based on the magnetic recording method according to the third embodiment of the present invention. 18, the magnetic disk 50 is simplified by omitting parts other than the base material 51 and the recording magnetic layers L ₁ , L ₂ ,... L _n , and represents a partial cross section along the circumferential direction (track extending direction). . The moving direction (rotating direction) of the magnetic disk 50 relative to the flying slider 60 is indicated by an arrow D.

When recording information, the magnetic disk 50 is rotated at a predetermined speed. As a result, a gas lubrication film is formed between the magnetic disk 50 and the flying slider 60, and the flying slider 60 is arranged to float with respect to the magnetic disk 50. Then, the laser beam continues to be emitted from the laser element 62 of the flying slider 60 that is placed in a floating manner. At this time, the laser light is irradiated with a light quantity and intensity sufficient to supply thermal energy for once raising the recording magnetic layers L ₁ , L ₂ ,... L _n to a predetermined temperature (initial temperature). The initial temperature is preferably a temperature exceeding the Curie temperature Tc ₁ (> Tc ₂ >...> Tc _n ) of the recording magnetic layer L ₁ . By such laser light irradiation, the multilayer recording film 52 (recording magnetic layers L ₁ , L ₂ ,... L _n ) is locally heated, and the initial temperature is peaked in the multilayer recording film 52. A temperature distribution with a temperature gradient occurs in the circumferential direction (track extending direction). FIG. 18 is a graph showing this temperature distribution.

  In the heat assist information recording of the present embodiment, a temperature raising step and a magnetic field applying step are subsequently performed on each region of the recording surface (multilayer recording film 52). In the magnetic field application process, the first to nth magnetization steps are sequentially executed.

In the temperature raising step, a predetermined region in the multilayer recording film 52 reaches the laser element 62 and is irradiated with laser, and the recording magnetic layers L ₁ , L ₂ ,... L _n in this region are heated to the initial temperature. In this step, depending on the initial temperature that is set, the recording magnetic layer L _1, L _2, ··· L each of the coercive force Hc ₁ of _n, Hc _2, ··· Hc _n until a predetermined value descend. When the initial temperature is set to a temperature exceeding Tc ₁ , the recording magnetic layers L ₁ , L ₂ ,... L _n in the region are heated to a temperature exceeding Tc ₁ , thereby All of the recording magnetic layers L ₁ , L ₂ ,... L _n in FIG.

In the first magnetization step of the magnetic field application process, the recording magnetic layers L ₁ , L ₂ ,... L _n are applied to the first recording magnetic field B by applying the first recording magnetic field B ₁ to a predetermined area by the recording head K _1. Magnetized in the direction of ₁ . In the region to be subjected to this step, the temperature is less than Tc _1, at least a recording magnetic layer L ₁ has a coercive force Hc _1, the first recording magnetic field B ₁ represents greater than Hc ₁ (Hc ₁ <B ₁ ). Therefore, in this step, the recording magnetic layer L ₁ is recorded and magnetized in the direction of the first recording magnetic field B ₁ .

In the second magnetization step, by applying a second recording magnetic field B ₂ in a predetermined region by the recording head K _2, to magnetize the magnetic recording layer L _2, the · · · L _n in the second direction of the recording magnetic field B _2. In the region subjected to this step, the temperature is lower than Tc ₂ , at least the recording magnetic layers L ₁ and L ₂ have coercive forces Hc ₁ and Hc ₂ , and the second recording magnetic field B ₂ is larger than Hc _2. And it is less than Hc ₁ (Hc ₂ <B ₂ <Hc ₁ ). Therefore, the recording magnetic layer L ₁ is without being in effect the operation of the second recording magnetic field B _2, the magnetic recording layer L ₂ ~L _n is magnetized under the influence of the second recording magnetic field B _2. In this way, the recording magnetic layer L ₂ is recorded and magnetized in this step.

In this way, each magnetization step is executed by applying a recording magnetic field by each recording head, each recording magnetic layer is recorded and magnetized, and recording magnetization of the recording magnetic layer L _n is executed in the nth magnetization step. In the n-th magnetization step, specifically, by applying a first n recording magnetic field B _n in a predetermined area by the recording head K _n, magnetizing the magnetic recording layer L _n in the direction of the n recording magnetic field B _n. In the region to be subjected to this step, the temperature is less than Tc _n, the recording magnetic layer _{L 1, L 2, ··· L} n is the coercive force Hc _1, Hc _2, has a · · · Hc _n, the first n recording magnetic field B _n is larger and smaller than Hc _n-1 than _{Hc n (Hc n <B n} <Hc n-1 <··· <Hc 1). Therefore, the recording magnetic layers L _{1 to} L _n−1 are not substantially affected by the _n- th recording magnetic field B _n , and the recording magnetic layer L _n is magnetized by the action of the _n- th recording magnetic field B _n. . Thus, in this step, the recording magnetic layer L _n is recorded and magnetized.

Or laser device 62 or the recording head K _1, such heating process and a magnetic field applying step (first to n magnetization step) as, K _2, performed for each region sequentially reaches the position directly below the · · · K _n Thus, a predetermined signal or information can be recorded as a change in the magnetization direction in the multilayer recording film 52 of the magnetic disk 50. The recording magnetic layers L ₁ , L ₂ ,... L _n in each region of the recording surface (multilayer recording film 52) of the magnetic disk 50 are magnetized in one of two directions perpendicular to the multilayer recording film 52. It is, the recording magnetic layer L _1, L ₂ in each area of the recording surface, the _{··· L n | Mr 1 | ×} d 1 ~ | Mr n | sum of × d _n takes a plurality of values. Preferably, the recording magnetic layer L _1, L _2, of _{··· L n | Mr 1 | ×} d 1 ~ | Mr n | × d n are all different from one another, and, the | Mr ₁ | × d ₁ ~ | Mr _n | sum of × d _n is the _{| Mr 1 | × d 1 ~} | different in every degree combination of × d _n | Mr _n. In this case, each region of the recording surface (multilayer recording film 52) can take 2 ⁿ magnetic states.

  When information is reproduced by the magnetic disk device X3, the magnetic disk 50 is rotated at a predetermined speed. As a result, a gas lubrication film is formed between the magnetic disk 50 and the flying slider 60, and the flying slider 60 is arranged to float with respect to the magnetic disk 50. In this state, the reproducing head 63 detects a signal magnetic field formed due to the magnetic state of the multilayer recording film 52. In this way, information reproduction for reading out the multilevel signal recorded in the multilayer recording film 52 is executed.

As described above, according to the method of the present embodiment, information can be recorded and reproduced by a multi-value method. In addition, in this method, the recording magnetic layer L ₁ with a thermally assisted, L _2, since · · · L _n is magnetized, the recording head K _1, K _2, to be applied by · · · K _n For example, the coercive force of the recording magnetic layers L ₁ , L ₂ ,... L _n at room temperature can be set high while maintaining the recording magnetic field strength small. Recording magnetic layer L _1, L _2, the higher the coercivity · · · L _n, the recording magnetic layer L _1, L _2, to be more minute minimum magnetic domain which can stably form in · · · L _n It is possible to obtain a high recording density two-dimensionally in the recording surface direction. Therefore, according to the magnetic recording method of the present embodiment, it is possible to achieve a sufficiently high recording density in a multi-value recording / reproducing system with thermal assistance.

[Production of magnetic disk]
A magnetic disk corresponding to the first embodiment having the stacked configuration shown in FIG. 19 was produced as the magnetic disk of this example.

Specifically, first, a Tb ₂₀ Fe ₈₀ layer having a thickness of 25 nm is formed as a recording magnetic layer 12A by depositing Tb ₂₀ Fe ₈₀ on a disk substrate (65 mm in diameter) made of an aluminum alloy by a sputtering method. Formed. In this sputtering, Tb ₂₀ Fe ₈₀ was formed on the substrate by co-sputtering using a Tb target and an Fe target. In this sputtering, Ar gas was used as the sputtering gas, the sputtering gas pressure was 2.5 Pa, and the sputtering power was 80 W (Tb target) and 300 W (Fe target).

Next, an Al layer having a thickness of 3 nm was formed as the nonmagnetic layer 12a by depositing Al on the Tb ₂₀ Fe ₈₀ layer by sputtering. In this sputtering, an Al target was used, Ar gas was used as the sputtering gas, the sputtering gas pressure was 0.6 Pa, and the sputtering power was 500 W.

Next, a Tb ₁₆ Fe ₈₄ layer having a thickness of 25 nm was formed as the recording magnetic layer 12B by depositing Tb ₁₆ Fe ₈₄ on the Al layer by a sputtering method. In this sputtering, Tb ₁₆ Fe ₈₄ was formed on the substrate by co-sputtering using a Tb target and an Fe target. In this sputtering, Ar gas was used as the sputtering gas, the sputtering gas pressure was 2.5 Pa, and the sputtering power was 80 W (Tb target) and 300 W (Fe target).

Next, a diamond-like carbon (DLC) film was formed on the Tb ₁₆ Fe ₈₄ layer by sputtering, thereby forming a DLC layer having a thickness of 10 nm as the protective layer 13. In this step, Ar gas was used as the sputtering gas, the sputtering gas pressure was 0.25 Pa, and the sputtering power was 1500 W. As described above, the magnetic disk of this example was manufactured.

[Coercivity measurement]
The temperature dependence of the coercive force Hc was measured for each of the Tb ₂₀ Fe ₈₀ film and the Tb ₁₆ Fe ₈₄ film having the same composition as each recording magnetic layer in the magnetic disk of this example. The resulting graph is shown in FIG. In the graph of FIG. 20, the horizontal axis represents the film temperature (° C.), the vertical axis represents the coercive force Hc (Oe) of the film, the line F1 represents the measurement result of the Tb ₂₀ Fe ₈₀ film, and the line F2 represents Tb. The measurement result of ₁₆ Fe ₈₄ film is shown.

[Saturation magnetization measurement]
The temperature dependence of the saturation magnetization Ms was measured for each of the Tb ₂₀ Fe ₈₀ film and the Tb ₁₆ Fe ₈₄ film having the same composition as each recording magnetic layer in the magnetic disk of this example. The resulting graph is shown in FIG. In the graph of FIG. 21, the horizontal axis represents the film temperature (° C.), the vertical axis represents the saturation magnetization Ms (emu / cc) of the film, the line F1 ′ represents the measurement result of the Tb ₂₀ Fe ₈₀ film, and the line F2 ′ represents the measurement result of the Tb ₁₆ Fe ₈₄ film.

[Evaluation]
As shown in the graph of FIG. 20, the Curie temperature of the Tb ₂₀ Fe ₈₀ film was 130 ° C., and the Curie temperature of the Tb ₁₆ Fe ₈₄ film was 110 ° C. Further, as shown in the graph of FIG. 21, the saturation magnetization at 25 ° C. of the Tb ₂₀ Fe ₈₀ film was 80 emu / cc, and the saturation magnetization of the Tb ₁₆ Fe ₈₄ film was 180 emu / cc. Since the saturation magnetization at 25 ° C. is different to this extent, the magnetization at normal temperature in these magnetic films can be significantly different. Therefore, in the magnetic disk of this example, the Curie temperatures of the Tb ₂₀ Fe ₈₀ layer (thickness 25 nm) as the recording magnetic layer 12A and the Tb ₁₆ Fe ₈₄ layer (thickness 25 nm) as the recording magnetic layer 12B are different. And the product of the magnitude | size and thickness of the magnetization at normal temperature of each of these layers differs. According to such a magnetic disk, it is possible to appropriately perform information recording of the heat-assisted recording method and the multi-value recording method described above with reference to FIGS.

[Production of magnetic disk]
A magnetic disk corresponding to the second embodiment having the stacked configuration shown in FIG. 22 was produced as the magnetic disk of this example.

Specifically, first, a Tb ₂₃ Fe ₇₇ film is formed on a disk substrate (diameter 65 mm) made of an aluminum alloy by a sputtering method to form a Tb ₂₃ Fe ₇₇ layer having a thickness of 25 nm as the recording magnetic layer 32A. Formed. In this sputtering, Tb ₂₃ Fe ₇₇ was formed on the substrate by co-sputtering using a Tb target and an Fe target. In this sputtering, Ar gas was used as the sputtering gas, the sputtering gas pressure was 2.5 Pa, and the sputtering power was 80 W (Tb target) and 300 W (Fe target).

Next, an Al layer having a thickness of 3 nm was formed as the nonmagnetic layer 32a by depositing Al on the Tb ₂₃ Fe ₇₇ layer by sputtering. In this sputtering, an Al target was used, Ar gas was used as the sputtering gas, the sputtering gas pressure was 0.6 Pa, and the sputtering power was 500 W.

Thereafter, Tb ₂₀ Fe ₈₀ layer on a substrate in Example 1, an Al layer, in a manner similar to that order form Tb ₁₆ Fe ₈₄ layer, and a DLC layer, on the Al layer, Tb ₂₀ as a recording magnetic layer 32B An Fe ₈₀ layer (thickness 25 nm), an Al layer (thickness 3 nm) as the nonmagnetic layer 32a, a Tb ₁₆ Fe ₈₄ layer (thickness 25 nm) as the recording magnetic layer 32C, and a DLC layer as the protective layer 33 were formed in this order.

[Coercivity measurement]
The temperature dependence of the coercive force Hc of the Tb ₂₃ Fe ₇₇ film having the same composition as the recording magnetic layer 32A in the magnetic disk of this example was measured. FIG. 23 shows a graph in which the results are combined with the above-described coercive force measurement results for the Tb ₂₀ Fe ₈₀ film and the Tb ₁₆ Fe ₈₄ film. In the graph of FIG. 23, the horizontal axis represents the film temperature (° C.), the vertical axis represents the coercive force Hc (Oe) of the film, the line F3 represents the measurement result of the Tb ₂₃ Fe ₇₇ film, and the line F1 represents the Tb. The measurement result of the ₂₀ Fe ₈₀ film is represented, and the line F2 represents the measurement result of the Tb ₁₆ Fe ₈₄ film.

[Saturation magnetization measurement]
The temperature dependence of the saturation magnetization Ms was measured for the Tb ₂₃ Fe ₇₇ film having the same composition as the recording magnetic layer 32A in the magnetic disk of this example. FIG. 24 shows a graph in which the results are combined with the saturation magnetization measurement results for the Tb ₂₀ Fe ₈₀ film and the Tb ₁₆ Fe ₈₄ film. In the graph of FIG. 24, the horizontal axis represents the film temperature (° C.), the vertical axis represents the saturation magnetization Ms (emu / cc) of the film, the line F3 ′ represents the measurement result of the Tb ₂₃ Fe ₇₇ film, and the line F1 ′ represents the measurement result of the Tb ₂₀ Fe ₈₀ film, and the line F2 ′ represents the measurement result of the Tb ₁₆ Fe ₈₄ film.

[Evaluation]
As shown in the graph of FIG. 23, the Curie temperature of the Tb ₂₃ Fe ₇₇ film was 150 ° C. As described above, the Curie temperature of the Tb ₂₀ Fe ₈₀ film is 130 ° C., and the Curie temperature of the Tb ₁₆ Fe ₈₄ film is 110 ° C. Further, as shown in the graph of FIG. 24, the saturation magnetization of the Tb ₂₃ Fe ₇₇ film at 25 ° C. was 40 emu / cc. As described above, the saturation magnetization of the Tb ₂₀ Fe ₈₀ film at 25 ° C. is 80 emu / cc, and the saturation magnetization of the Tb ₁₆ Fe ₈₄ film is 180 emu / cc. Since the saturation magnetization at 25 ° C. is different to this extent, the magnetization at normal temperature in these magnetic films can be significantly different. Therefore, in the magnetic disk of this example, the Tb ₂₃ Fe ₇₇ layer (thickness 25 nm) as the recording magnetic layer 32A, the Tb ₂₀ Fe ₈₀ layer (thickness 25 nm) as the recording magnetic layer 32B, and the recording magnetic layer 32C. And the Tb ₁₆ Fe ₈₄ film (thickness 25 nm) are different from each other in Curie temperature, and the product of the magnitude and thickness of these layers at normal temperature is different. According to such a magnetic disk, it is possible to appropriately execute the information recording of the heat-assisted recording method and the multi-value recording method described above with reference to FIGS.

  As a summary of the above, the configurations of the present invention and variations thereof are listed below as supplementary notes.

(Appendix 1) A method for recording information on a magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each recording magnetic layer. ,
A temperature raising step for once raising the temperature of the plurality of recording magnetic layers;
In order to record and magnetize each of the plurality of recording magnetic layers that have undergone the temperature raising step by sequentially applying a recording magnetic field from a recording magnetic layer having a relatively high Curie temperature to a recording magnetic layer having a relatively low Curie temperature. Magnetic field application step.
(Supplementary note 2) The magnetic recording method according to supplementary note 1, wherein in the temperature raising step, the plurality of recording magnetic layers are heated to a temperature equal to or higher than a maximum Curie temperature.
(Appendix 3) A magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each recording magnetic layer.
(Supplementary note 4) The magnetic recording medium according to supplementary note 3, wherein each of the plurality of recording magnetic layers has magnetization, and in the plurality of recording magnetic layers, a product of magnitude and thickness of magnetization is different from each other.
(Supplementary note 5) The magnetic recording medium according to supplementary note 4, wherein the sum of the products for each of the recording magnetic layers is different for all the combinations of the plurality of products.
(Appendix 6) A magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each of the recording magnetic layers, and performing a rotation operation when performing information recording, ,
A temperature raising means for locally raising the temperature of the multilayer recording film;
The same number of magnetic field applying means as the plurality of recording magnetic layers, which are arranged in a line in the direction of the rotation operation when the information recording is performed, for applying a magnetic field to the multilayer recording film that has been heated by the heating means. And a magnetic recording device.
(Additional remark 7) It is further provided with the floating slider which floats and arrange | positions with respect to the said magnetic-recording medium, facing the said multilayer recording film at the time of the said information recording, The said temperature raising means and these magnetic field application means are the said floating The magnetic recording device according to appendix 6, provided on a slider.
(Supplementary note 8) The magnetic recording medium according to any one of supplementary notes 1 to 7 includes a base material for supporting the multilayer recording film, and a plurality of Curie temperatures of the plurality of recording magnetic layers are the base The closer to the material or the farther from the substrate, the higher.

1 shows a partial configuration of a magnetic disk device for executing a magnetic recording method according to a first embodiment of the present invention. 1 illustrates a stacked configuration of magnetic disks according to a first embodiment. An example of the temperature dependence of the coercive force Hc is shown for each recording magnetic layer in the first embodiment. 1 represents one step of the magnetic recording method according to the first embodiment. The other steps of the magnetic recording method according to the first embodiment are shown. The other steps of the magnetic recording method according to the first embodiment are shown. 2 shows an example of a magnetic state in a multilayer recording film and an example of a reproduction signal obtained when the information is recorded on a magnetic disk on which information recording is performed by the magnetic recording method of the first embodiment. 2 shows a partial configuration of a magnetic disk device for executing a magnetic recording method according to a second embodiment of the present invention. 2 illustrates a stacked configuration of magnetic disks according to a second embodiment. An example of the temperature dependence of the coercive force Hc is shown for each recording magnetic layer in the second embodiment. 1 represents one step of a magnetic recording method according to a second embodiment. The other steps of the magnetic recording method according to the second embodiment are shown. The other steps of the magnetic recording method according to the second embodiment are shown. The other steps of the magnetic recording method according to the second embodiment are shown. An example of a magnetic state in a multilayer recording film for a magnetic disk on which information recording has been performed by the magnetic recording method of the second embodiment is shown. 7 shows a partial configuration of a magnetic disk device for executing a magnetic recording method according to a third embodiment of the present invention. 4 illustrates a stacked configuration of magnetic disks according to a third embodiment. 4 illustrates a magnetic recording method according to a third embodiment. 1 illustrates a stacked configuration of a magnetic disk of Example 1. For each recording magnetic layer in the magnetic disk of Example 1, the temperature dependence of the coercive force Hc is shown. For each recording magnetic layer in the magnetic disk of Example 1, the temperature dependence of the saturation magnetization Ms is shown. 2 illustrates a stacked configuration of a magnetic disk of Example 2. For each recording magnetic layer in the magnetic disk of Example 2, the temperature dependence of the coercive force Hc is shown. For each recording magnetic layer in the magnetic disk of Example 2, the temperature dependence of the saturation magnetization Ms is shown. It is a partial cross-sectional schematic diagram of an example of the conventional perpendicular magnetic recording medium.

Explanation of symbols

X1, X2, X3 magnetic disk device 10,30,50,70 magnetic disk 11, 31, 51 substrate 12, 32, 52 multilayer recording film 12A, 12B, 32A, 32B, 32C, L 1 ~L n recording magnetic layer 12a , 32a, 52a nonmagnetic layer 13,33,53 protective layer 20, 40, 60 flying slider 22,42,62 laser device 23A, 23B, 43A, 43B, 43C, K 1 ~K n recording heads 24,44,63 Playhead

Claims (5)

A method for recording information on a magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each recording magnetic layer,
A temperature raising step for once raising the temperature of the plurality of recording magnetic layers;
In order to record and magnetize each of the plurality of recording magnetic layers that have undergone the temperature raising step by sequentially applying a recording magnetic field from a recording magnetic layer having a relatively high Curie temperature to a recording magnetic layer having a relatively low Curie temperature. Magnetic field application step.   The magnetic recording method according to claim 1, wherein, in the temperature raising step, the plurality of recording magnetic layers are heated to a temperature above a maximum Curie temperature.   A magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided between the recording magnetic layers.   4. The magnetic recording medium according to claim 3, wherein each of the plurality of recording magnetic layers has magnetization, and in the plurality of recording magnetic layers, a product of a magnitude and a thickness of magnetization is different from each other. A magnetic recording medium having a multilayer recording film including a plurality of recording magnetic layers having different Curie temperatures and a nonmagnetic layer provided for each recording magnetic layer, and accompanied by a rotation operation when information recording is performed;
A temperature raising means for locally raising the temperature of the multilayer recording film;
The same number of magnetic field applying means as the plurality of recording magnetic layers, which are arranged in a line in the direction of the rotation operation when the information recording is performed, for applying a magnetic field to the multilayer recording film that has been heated by the heating means. And a magnetic recording device.

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