Abstract:
A thermally assisted magnetic recording method includes the following steps. The recording layer of a magnetic recording medium is irradiated with a laser beam to produce a locally heated region. This heated region is moved by causing the recording layer and the laser beam to move relative to each other. To record desired information, a recording magnetic field is applied to the heated region of the recording layer. The laser beam has a cross section elongated in the direction in which the heated region is moved.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a thermally assisted magnetic recording method, for recording information on a magnetic recording medium assisted by heat.  
         [0003]     2. Description of the Related Art  
         [0004]     Existing recording mediums for constituting a storage unit such as a hard disk include a magnetic disk (magnetic recording medium). The magnetic disk has a stacked structure including a disk substrate and a recording layer provided with a predetermined magnetic structure. The increase in amount of information to be processed by a computer system is generating a demand for higher recording density from the magnetic disk.  
         [0005]     When recording information on the magnetic disk, a recording magnetic head is placed close to the recording surface (including the recording layer) of the magnetic disk, so that the magnetic head applies to the recording layer a recording magnetic field stronger than the coercivity of the recording layer. The magnetic head is relatively moved with respect to the magnetic disk to sequentially invert the direction of the recording magnetic field applied by the magnetic head, so as to form a plurality of record marks (magnetic domains) having sequentially inverted magnetizing directions on the recording layer, along a circumferential direction of the magnetic disk or along the extension of the track. At this stage, the timing for inverting the direction of the recording magnetic field is controlled so as to form the record marks in the respective predetermined lengths. That is how predetermined signals or information is recorded on the recording layer represented by the variation in magnetizing directions.  
         [0006]     In the technical field associated with the magnetic disk, it is known that the higher coercivity the recording layer has, the higher thermal stability the magnetic domain formed on the recording layer acquires, thus constituting a minute or extremely narrow and stable magnetic domain. Reducing a minimum attainable size of the magnetic domain stably formed on the recording layer leads to increasing the recording density of the magnetic disk.  
         [0007]     Thus, when recording information on the magnetic disk, it is necessary to apply a recording magnetic field stronger than the coercivity of the recording layer, for properly forming a record mark. Accordingly, increasing the intensity of the recording magnetic field to be applied by the magnetic head could be an option, based on the increase in coercivity granted to the recording layer. The intensity of the recording magnetic field that the magnetic head can apply is, however, subject to a certain limitation from the viewpoint of the structure of the magnetic head as well as the power consumption.  
         [0008]     As a solution, a thermally assisted magnetic recording method may be employed for recording information on the magnetic disk. When employing the thermally assisted magnetic recording method to record information on the magnetic disk, for example an optical head disposed close to the recording surface of the rotating magnetic disk emits a laser beam, so as to form a generally circular beam spot on the recording surface such that the beam spot moves thereon, thus locally heating the recording layer of the magnetic disk sequentially. The heated region of the recording layer where the temperature has been elevated incurs degradation in coercivity, in comparison with the surrounding regions where the temperature remains unchanged. Under such state, a magnetic head disposed close to the recording surface of the magnetic disk applies to the heated region a recording magnetic field stronger than the coercivity of the heated region of the recording layer, thus magnetizing a portion of the heated region in a predetermined direction. Such magnetization is fixed during a cooling process of the magnetized portion. By the thermally assisted magnetic recording method, a plurality of magnetic domains (record marks), each having a sequentially inverted magnetizing direction and a predetermined length according to the recorded signal, is thus formed along a track extending circumferentially of the disk. When employing the magnetic disk designed in accordance with the thermally assisted magnetic recording method, the recording magnetic field is applied to the region in the recording layer where the coercivity is degraded by heating, when recording information. Therefore, the intensity of the recording magnetic field to be applied by the magnetic head does not have to be largely increased, even when the coercivity of the recording layer under a normal temperature, i.e. for storing or reproducing the information, is set at a high level. Such thermally assisted magnetic disk is disclosed, for example in the following documents.  
         [0009]     Patent document 1: JP-A-H06-243527  
         [0010]     Patent document 2: JP-A-2003-157502  
         [0011]     In the conventional thermally assisted magnetic recording method, the laser beam is emitted to form a generally circular beam spot on the recording surface such that the beam spot moves on the recording surface, thereby locally heating the recording layer of the magnetic disk sequentially. Heating thus the portion of the recording layer where information is to be recorded leads to a significant increase in temperature of the heated portion, as well as of a peripheral portion. Whereas, with the thermally assisted magnetic disk, it is preferable to grant the recording layer with a higher coercivity for increasing the recording density, and the higher coercivity of the recording layer requires more intense heating of the recording layer. With the conventional thermally assisted magnetic recording method, however, if the heating is so intense when recording information that the temperature is increased over a too extensive region on the recording layer, a cross-write effect may be incurred, for example the record mark excessively spreads over to another track adjacent to the track where the record mark is being formed, thus to erase or degrade the record mark on the adjacent track. The cross-write effect discourages the attempt of making the track finer, and is hence obviously undesirable from the viewpoint of increasing the recording density of the magnetic disk. Consequently, the conventional thermally assisted magnetic disk (thermally assisted magnetic recording medium) has a drawback against increasing the recording density.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention has been conceived in view of the foregoing situation, with an object to provide a thermally assisted magnetic recording method that effectively prevents the heat from spreading transversely of the track in the recording layer.  
         [0013]     A first aspect of the present invention provides a thermally assisted magnetic recording method comprising the steps of: irradiating a recording layer of a magnetic recording medium with a laser beam to produce a locally heated region; moving the heated region by causing the recording layer and the laser beam to move relative to each other; and applying a recording magnetic field to the heated region to record information. In this method, the laser beam has a cross section which is elongated in the moving direction of the heated region (i.e. in the extending direction of a track).  
         [0014]     By the thermally assisted magnetic recording method thus arranged, the heated region (region enclosed in an isotherm of a significantly higher temperature predetermined from the viewpoint of the effectiveness of the thermally assisted magnetic recording method) formed on the recording layer by the laser beam irradiation is elongated in the moving direction of the heated region.  
         [0015]     By a thermally assisted magnetic recording method in general, the maximum attainable temperature of a region on the track of the recording layer, heated and subjected to application of the recording magnetic field for formation of a record mark, primarily depends on the total amount of the heating energy supplied thereto per a predetermined minute time. In light of this, the method of forming the heated region in an elongated shape in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy (originating from the laser beam in this method) to the region on the recording layer where the record mark is to be formed. It is also possible to prevent heat from spreading transversely of the track. The thermally assisted magnetic recording method according to the present invention is, therefore, advantageous in inhibiting or restraining the occurrence of the cross-write effect, so as to increase the recording density of the track.  
         [0016]     A second aspect of the present invention provides a thermally assisted magnetic recording method comprising the steps of: causing a heating element to face a recording layer of a magnetic recording medium to produce a locally heated region; moving the heated region by causing the recording layer and the heating element to move relatively to each other; and applying a recording magnetic field to the heated region to record information.  
         [0017]     By the thermally assisted magnetic recording method thus arranged, the heated region formed on the recording layer by the heating element facing the recording layer is elongated in the moving direction of the heated region, i.e. in the extending direction of the track. As stated above, the maximum attainable temperature of a region on the recording layer, where the record mark is to be formed, primarily depends on the total amount of the heating energy supplied thereto per a predetermined minute time. Thus, the method of forming the heated region in a shape elongated in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy (originating from the heating element in this method) to the region on the recording layer where the record mark is to be formed, while preventing the heat from spreading transversely of the track.  
         [0018]     A third aspect of the present invention provides a thermally assisted magnetic recording method comprises the steps of: producing a locally heated region in a recording layer of a magnetic recording medium; and applying a recording magnetic field to the heated region while moving the heated region, to record information. The heated region is produced by forming a plurality of heated spots in the recording layer, where the heated spots area aligned in the moving direction of the heated region in an overlapping manner.  
         [0019]     In the thermally assisted magnetic recording method thus arranged, the heated region is a composite heated spot including a plurality of aligned heated spots, in a shape elongated in the moving direction of the heated region.  
         [0020]     According to the third aspect of the present invention, preferably, the recording layer may be irradiated with a plurality of laser beams, thus to form a plurality of heated spots. Alternatively, a plurality of heating elements may be disposed so as to face the recording layer and to relatively move with respect thereto, to form a plurality of heated spots. Such methods facilitate properly forming the heated region including a plurality of heated spots aligned in a predetermined direction.  
         [0021]     In the third aspect of the present invention, a plurality of peak temperatures of the heated spots may be controlled, in accordance with the moving speed of the heated region on the recording layer. For example, it is preferable to reduce a ratio of peak temperatures of the subsequent heated spots with respect to the peak temperature of the first heated spot in the moving direction of the heated region, when the heated region moves slower. In the thermally assisted magnetic recording method executed with the magnetic recording medium being rotated, controlling thus a plurality of peak temperatures may be beneficial in leveling off the heating energy amount supplied per unit time to the track during the recording, irrespective of a distance between the track and the rotation center of the medium.  
         [0022]     In the third aspect of the present invention, distance between positions at which the peak temperatures of the plurality of heated spots are attained may be controlled in accordance with the moving speed of the heated region on the recording layer. For example, it is preferable to increase the distance between the positions corresponding to the peak temperature of the plurality of heated spots, when the heated region moves slower. In the thermally assisted magnetic recording method executed with the magnetic recording medium being rotated, controlling thus the distance between positions corresponding to the peak temperature may be beneficial in leveling off the heating energy amount supplied per unit time to the track during the recording, irrespective of a distance between the track and the rotation center of the medium. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a schematic diagram showing a part of a magnetic disk apparatus for executing a thermally assisted magnetic recording method according to a first embodiment of the present invention;  
         [0024]      FIG. 2  is a schematic cross-sectional view of a laser beam employed in the first embodiment;  
         [0025]      FIG. 3  is graphic diagram showing a temperature distribution created by the thermally assisted magnetic recording method according to the first embodiment;  
         [0026]      FIG. 4  includes a schematic cross-sectional view and a plan view showing a mask that may be employed for shaping the laser beam in the first embodiment;  
         [0027]      FIG. 5  is a schematic diagram showing a part of a magnetic disk apparatus for executing a thermally assisted magnetic recording method according to a second embodiment of the present invention;  
         [0028]      FIG. 6  is a plan view showing a side of a recording/reproducing head facing the magnetic disk of the magnetic disk apparatus of  FIG. 5 ;  
         [0029]      FIG. 7  is a schematic diagram showing a part of a magnetic disk apparatus for executing a thermally assisted magnetic recording method according to a third embodiment of the present invention;  
         [0030]      FIG. 8 ( a ) is a schematic plan view showing two beam spots formed on the cover layer by the thermally assisted magnetic recording method according to the third embodiment, while  FIG. 8 ( b ) is a graph showing a temperature distribution on the recording layer created by the thermally assisted magnetic recording method according to the third embodiment;  
         [0031]      FIG. 9  is a schematic diagram showing a part of a magnetic disk apparatus for executing a thermally assisted magnetic recording method according to a fourth embodiment of the present invention;  
         [0032]      FIG. 10  is a plan view showing a side of a recording/reproducing head facing the magnetic disk of the magnetic disk apparatus of  FIG. 9 ;  
         [0033]      FIG. 11  is a graph showing a temperature distribution on the recording layer created by the thermally assisted magnetic recording method according to the fourth embodiment;  
         [0034]      FIG. 12  is a schematic diagram showing a part of a magnetic disk apparatus for executing a thermally assisted magnetic recording method according to a fifth embodiment of the present invention;  
         [0035]      FIG. 13 ( a ) is a schematic plan view showing two beam spots formed on the cover layer by the thermally assisted magnetic recording method according to the fifth embodiment, while  FIG. 13 ( b ) is a graph showing a temperature distribution on the recording layer created by the thermally assisted magnetic recording method according to the fifth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]      FIG. 1  is a schematic diagram showing a part of a magnetic disk apparatus X 1  for executing a thermally assisted magnetic recording method according to a first embodiment of the present invention. The magnetic disk apparatus X 1  includes a magnetic disk  10 , a magnetic head  20 , an optical head  30 , and a composite element  40 , for recording and reproducing information on and from the magnetic disk  10 , by the thermally assisted magnetic recording method.  
         [0037]     The magnetic disk  10  has a stacked structure including a disk substrate  11 , a recording layer  12 , and a cover layer  13 , so as to serve as a magnetic recording medium under the thermally assisted magnetic recording system. The disk substrate  11  primarily serves for granting the magnetic disk  10  with sufficient rigidity, and may be constituted of an aluminum alloy, a glass, or a resin. The recording layer  12  is constituted of a vertical magnetized layer or a in-plane magnetized layer, and serves as a recording surface on which information is recorded, in the magnetic disk  10 . The recording layer  12  may be constituted of a Co alloy, a Fe alloy, or a rare earth transition metal amorphous alloy. Examples of the Co alloy include a CoCr alloy. Examples of the Fe alloy include a FePt alloy. As the rare earth transition metal amorphous alloy, a TbFeCo alloy may be employed. The cover layer  13  serves to physically and chemically protect the recording layer  12  from the external environment, and may be constituted of SiN, SiO 2 , or a diamond-like carbon. The stacked structure of the magnetic disk  10  may include an additional layer where appropriate. The magnetic disk  10  is supported by a spindle motor (not shown), to be rotationally driven by the rotation of the spindle motor.  
         [0038]     The magnetic head  20  includes a slider body  21 , a recording element  22 , and a reproducing element  23 , and is disposed so as to face the recording layer  12  of the magnetic disk  10 , when the magnetic disk apparatus X 1  records or reproduces information. The slider body  21  has a predetermined shape so as to cause gas lubrication between the magnetic disk  10  and the magnetic head  20 , when the linear speed of a point on the rotating magnetic disk  10  facing the magnetic head  20  exceeds a predetermined level. The recording element  22  serves to apply a recording magnetic field M of a predetermined intensity to the recording layer  12 , and includes a coil through which a current for generating a magnetic field is supplied, and a magnetic pole that converts the generated magnetic field into a more intense magnetic field. The intensity of the magnetic field by the recording element  22  and the timing for applying the magnetic field are controlled based on a predetermined control signal from a control unit, which is not shown. The reproducing element  23  serves to detect a magnetic signal generated according to a magnetized status of the recording layer  12  and to convert the magnetic signal into an electrical signal, and is constituted of a GMR device or a MR device. The magnetic head  20  thus constituted is connected to a magnetic head actuator (not shown) constituted of for example a voice coil motor, via a suspension arm, for example made of a leaf spring. The suspension arm serves to bias the magnetic head  20  against the magnetic disk  10 .  
         [0039]     The optical head  30  is constituted as an optical pickup device, and includes a condenser lens  31 , a lens actuator  32 , a mask  33 , and a mirror  34 . The optical head  30  encloses therein an optical waveguide that transmits a laser beam L from a light source (not shown) such as a semiconductor laser diode. For the sake of simplification of the drawing, the laser beam L employed in this embodiment is schematically indicated by a single-dot chain line representing the optical axis thereof. The condenser lens  31  serves to converge the laser beam L and emit the converged beam to the magnetic disk  10 . The lens actuator  32  adjusts the position of the condenser lens  31  in a vertical direction in  FIG. 1  for example by an electromagnetic driving force, thus to adjust the focal point of the laser beam converged by the condenser lens  31 . The movement of the lens actuator  32  is controlled based on a predetermined control signal from a control unit (not shown). The mask  33  serves to adjust a spot diameter of the beam spot formed by the laser beam on the surface of the magnetic disk  10 . The mirror  34  reflects the laser beam L emitted by the light source (not shown) and transmitted through a predetermined passage, toward the condenser lens  31  inside the optical head  30 . The optical head  30  thus constituted is installed so as to translationally move driven by an optical head actuator (not shown) along a guiderail (not shown) installed so as to extend radially of the magnetic disk  10 .  
         [0040]     The composite element  40  includes a plurality of prisms of different refractive indices, so as to incline the incident angle of the laser beam L, emitted by the light source (not shown) and transmitted through a collimator lens (not shown) on the composite element  40 , to thereby trim the cross-sectional shape of the laser beam L into a circle for example, and to serve as a polarizing beam splitter for splitting the laser beam L. A portion of the laser beam L thus split is led to the optical head  30 , and the other portion is led to a photodetecting unit (not shown) that monitors the intensity of the laser beam L to execute a feedback control.  
         [0041]     When recording information with the magnetic disk apparatus X 1  on the magnetic disk  10 , by the thermally assisted magnetic recording method according to the first embodiment of the present invention, the magnetic head actuator disposes the magnetic head  20  so as to float above the magnetic disk  10  and sets the magnetic head  20  at the recording position, with the magnetic disk  10  being rotated at a predetermined constant speed, while the optical head actuator sets the optical head at the recording position. The relative moving direction of the magnetic head  20  and the optical head  30  with respect to the rotating magnetic disk  10  is indicated by the arrow D.  
         [0042]     According to the thermally assisted magnetic recording method, the laser beam L of a predetermined power converged through the condenser lens  31  of the optical head  30  is continuously emitted onto the recording layer  12  of the magnetic disk  10 . In this embodiment, the laser beam L has an elliptical cross-sectional shape with the major axis oriented along the arrow D (substantially circumferentially of the disk or in the extending direction of the track) as shown in  FIG. 2 . Accordingly, the heated region (region enclosed in an isotherm of a significantly higher temperature predetermined from the viewpoint of the effectiveness of the thermally assisted magnetic recording method) formed on the recording layer  12  by irradiation with the laser beam has a shape elongated in the direction of the arrow D.  FIG. 3  is graphic diagram showing a temperature distribution created by the laser beam irradiation on the recording layer  12 , in this embodiment. In  FIG. 3 , the inner ellipses represent the isotherms of higher temperatures. Referring to the mask  33 , employing a mask having an elliptical opening  33   a  as shown in  FIG. 4  enables trimming the laser beam L so as to have an elliptical cross-sectional shape, elongated in the direction of the arrow D. Alternatively, the composite element  40  may be provided with an incident surface oriented at a predetermined angle so as to trim the cross-sectional shape of the laser beam into an ellipse of a predetermined aspect ratio, so that the laser beam L is emitted onto the incident surface at an angle specifically predetermined for that surface. Such arrangement can also trim the laser beam L in an elliptical cross-sectional shape elongated in the direction of the arrow D.  
         [0043]     In this thermally assisted magnetic recording method, the recording element  22  in the magnetic head  20  applies a recording magnetic field M to the heated region on the recording layer  12 , while the recording layer  12  is locally heated as described above. Also, the direction of the recording magnetic field M output by the recording element  22  is sequentially inverted, so as to form on the recording layer  12  a plurality of magnetic domains (record marks) having sequentially inverted magnetizing directions, aligned circumferentially of the magnetic disk  10  or in the extending direction of the track. At this stage, the timing for inverting the recording magnetic field M is controlled so as to form each record mark in a predetermined length.  
         [0044]     By this thermally assisted magnetic recording method, in a word, the laser beam L is emitted onto the recording layer  12  of the magnetic disk  10  such that the irradiated spot moves on the recording layer  12 , so as to form the locally heated region which moves on the recording layer  12 , and the recording magnetic field M is applied to the heated region, so that information is recorded.  
         [0045]     By the thermally assisted magnetic recording method thus arranged, the heated region formed on the recording layer  12  by the laser beam irradiation obtains a shape elongated in the direction of the arrow D (moving direction of the heated region), i.e. along the extending direction of the track. Here, by a thermally assisted magnetic recording method in general, a maximum attainable temperature of a region on the track on the recording layer, to be heated and subjected to application of the recording magnetic field for formation of a record mark, primarily depends on a total amount of the heating energy supplied thereto per a predetermined minute time. Based on this, the method of forming the heated region in a shape elongated in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy (originating from the laser beam in this method) to the region on the recording layer  12  where the record mark is to be formed, while restraining the heat from spreading transversely of the track. The thermally assisted magnetic recording method according to this embodiment is, therefore, advantageous in inhibiting or restraining emergence of the cross-write effect, so as to increase the recording density of the track.  
         [0046]      FIG. 5  is a schematic diagram showing a part of a magnetic disk apparatus X 2  for executing a thermally assisted magnetic recording method according to a second embodiment of the present invention. The magnetic disk apparatus X 2  includes a magnetic disk  10  and a recording/reproducing head  50 , for recording and reproducing information on and from the magnetic disk  10 , by the thermally assisted magnetic recording method.  
         [0047]     The magnetic disk  10  has a stacked structure including a disk substrate  11 , a recording layer  12 , and a cover layer  13 , so as to serve as a magnetic recording medium under the thermally assisted magnetic recording system. The materials constituting the magnetic disk  10  are the same as those employed in the first embodiment.  
         [0048]     The recording/reproducing head  50  includes a slider body  51 , a heating element  52 , a recording element  53 , and a reproducing element  54 , and is disposed so as to face the recording layer  12  of the magnetic disk  10 , when the magnetic disk apparatus X 2  records or reproduces information. The slider body  51  has a predetermined shape so as to cause gas lubrication between the magnetic disk  10  and the recording/reproducing head  50 , when the linear speed of a point on the rotating magnetic disk  10  facing the recording/reproducing head  50  exceeds a predetermined level. The heating element  52  is a medium heater in the thermally assisted magnetic recording system, and generates heat when a current is supplied. The temperature of the heating element  52  can be controlled by a control unit, which is not shown. The heating element  52  is installed on the side of the slider body  51  facing the medium, and has a shape elongated in a direction of an arrow D to be described later, as shown in  FIG. 6 .  FIG. 6  is a plan view showing a side of a recording/reproducing head  50  facing the magnetic disk  10 . The recording element  53  serves to apply a recording magnetic field M of a predetermined intensity to the recording layer  12 , and the reproducing element  54  serves to detect a magnetic signal generated according to a magnetized status of the recording layer  12 , and to convert the magnetic signal into an electrical signal. The materials constituting the recording element  53  and the reproducing element  54  are the same as those of the recording element  22  and the reproducing element  23  of the first embodiment. The heating element  52 , the recording element  53 , and the reproducing element  54  are aligned in a row along the rotating direction of the magnetic disk  10  or a circumferential direction thereof, for example in a manner as shown in  FIG. 6 . The recording/reproducing head  50  thus constituted is connected to a recording/reproducing head actuator (not shown) constituted of for example a voice coil motor, via a suspension arm, for example made of a leaf spring. The suspension arm serves to bias the recording/reproducing head  50  against the magnetic disk  10 .  
         [0049]     When recording information with the magnetic disk apparatus X 2  on the magnetic disk  10 , by the thermally assisted magnetic recording method according to the second embodiment of the present invention, the recording/reproducing head actuator disposes the recording/reproducing head  50  so as to float above the magnetic disk  10  and sets the recording/reproducing head  50  at the recording position, with the magnetic disk  10  being rotated at a predetermined constant speed. The relative moving direction of the recording/reproducing head  50  with respect to the rotating magnetic disk  10  is indicated by the arrow D.  
         [0050]     In this thermally assisted magnetic recording method, the heating element  52  of the recording/reproducing head  50  is disposed so as to face the recording layer  12 , and continuously generates heat at a predetermined temperature. In this embodiment, the heating element  52  has a shape elongated in the direction of the arrow D (substantially circumferentially of the disk or in the extending direction of the track) as shown in  FIG. 6 , and hence the heated region formed on the recording layer  12  by the heat ray from the heating element  52  has a shape elongated in the direction of the arrow D, as the heated region described above referring to  FIG. 3 .  
         [0051]     In this thermally assisted magnetic recording method, the recording element  53  in the recording/reproducing head  50  applies a recording magnetic field M to the heated region on the recording layer  12 , while the recording layer  12  is locally heated as described above. Also, the direction of the recording magnetic field M output by the recording element  22  is sequentially inverted, so as to form on the recording layer  12  a plurality of magnetic domains (record marks) having sequentially inverted magnetizing directions, aligned circumferentially of the magnetic disk  10  or in the extending direction of the track. At this stage, the timing for inverting the recording magnetic field M is controlled so as to form each record mark in a predetermined length.  
         [0052]     By this thermally assisted magnetic recording method, in a word, the heating element  52  is disposed so as to face the recording layer  12  of the magnetic disk  10  so as to form the locally heated higher temperature region which moves on the recording layer  12 , and the recording magnetic field M is applied to the heated region, so that information is recorded.  
         [0053]     By the thermally assisted magnetic recording method thus arranged, the heated region formed on the recording layer  12  by the heating element  52  facing the recording layer  12  obtains a shape elongated in the direction of the arrow D (moving direction of the heated region), i.e. along the extending direction of the track. Whereas, as already stated, by a thermally assisted magnetic recording method, a maximum attainable temperature of a region on the recording layer, where the record mark is to be formed, primarily depends on a total amount of the heating energy supplied thereto per a predetermined minute time. Based on this, the method of forming the heated region in a shape elongated in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy (originating from the heating element  52  in this method) to the region on the recording layer  12  where the record mark is to be formed, while restraining the heat from spreading transversely of the track. The thermally assisted magnetic recording method according to this embodiment is, therefore, advantageous in inhibiting or restraining emergence of the cross-write effect, so as to increase the recording density of the track.  
         [0054]      FIG. 7  is a schematic diagram showing a part of a magnetic disk apparatus X 3  for executing a thermally assisted magnetic recording method according to a third embodiment of the present invention. The magnetic disk apparatus X 3  includes a magnetic disk  10  and a recording/reproducing head  60 , for recording and reproducing information on and from the magnetic disk  10 , by the thermally assisted magnetic recording method.  
         [0055]     The magnetic disk  10  has a stacked structure including a disk substrate  11 , a recording layer  12 , and a cover layer  13 , so as to serve as a magnetic recording medium under the thermally assisted magnetic recording system. The materials constituting the magnetic disk  10  are the same as those employed in the first embodiment.  
         [0056]     The recording/reproducing head  60  includes a slider body  61 , laser elements  62 A,  62 B, a recording element  63 , and a reproducing element  64 , and is disposed so as to face the recording layer  12  of the magnetic disk  10 , when the magnetic disk apparatus X 3  records or reproduces information. The slider body  61  has a predetermined shape so as to cause gas lubrication between the magnetic disk  10  and the recording/reproducing head  60 , when the linear speed of a point on the rotating magnetic disk  10  facing the recording/reproducing head  60  exceeds a predetermined level. The laser elements  62 A,  62 B are medium heaters in the thermally assisted magnetic recording system, and includes a semiconductor laser module (light source) that emits the laser beam L when a voltage is applied, and so called an optical waveguide that leads the laser beam L from the laser module to the recording/reproducing head  60 . The laser elements  62 A,  62 B are disposed so as to emit the laser beam L from the side of the slider body  61  facing the medium, such that the two laser beams L overlap with each other on the surface of the magnetic disk  10 . For the sake of simplification of the drawing, the laser beam L employed in this embodiment is schematically indicated by a single-dot chain line representing the optical axis thereof. The power of the laser beam L emitted by the laser elements  62 A,  62 B can be controlled by a control unit, which is not shown. The recording element  63  serves to apply a recording magnetic field M of a predetermined intensity to the recording layer  12 , and the reproducing element  64  serves to detect a magnetic signal generated according to a magnetized status of the recording layer  12 , and to convert the magnetic signal into an electrical signal. The materials constituting the recording element  63  and the reproducing element  64  are the same as those of the recording element  22  and the reproducing element  23  of the first embodiment. The laser elements  62 A,  62 B, the recording element  63 , and the reproducing element  64  are aligned in a row along the rotating direction of the magnetic disk  10  or a circumferential direction thereof. The recording/reproducing head  60  thus constituted is connected to a recording/reproducing head actuator (not shown) constituted of for example a voice coil motor, via a suspension arm, for example made of a leaf spring. The suspension arm serves to bias the recording/reproducing head  60  against the magnetic disk  10 .  
         [0057]     When recording information with the magnetic disk apparatus X 3  on the magnetic disk  10 , by the thermally assisted magnetic recording method according to the third embodiment of the present invention, the recording/reproducing head actuator disposes the recording/reproducing head  60  so as to float above the magnetic disk  10  and sets the recording/reproducing head  60  at the recording position, with the magnetic disk  10  being rotated at a predetermined constant speed. The relative moving direction of the recording/reproducing head  60  with respect to the rotating magnetic disk  10  is indicated by the arrow D.  
         [0058]     In this thermally assisted magnetic recording method, the two laser beams L emitted by the laser elements  62 A,  62 B are continuously made incident upon the recording layer  12  of the magnetic disk  10 . In this embodiment, the two laser beams L overlap with each other on the surface of the magnetic disk  10  or the cover layer  13 , so as to form two beam spots S 1 ′, S 2 ′ aligned in the direction of the arrow D (substantially circumferentially of the disk or in the extending direction of the track) on the cover layer  13 , as shown in  FIG. 8 ( a ). On predetermined positions on the recording layer  12 , two heated spots S 1 , S 2  having a temperature distribution as shown in the graph of  FIG. 8 ( b ) are formed, so as to respectively correspond to the two beam spots S 1 ′, S 2 ′. In  FIG. 8 ( b ), the horizontal axis represents the position in the circumferential direction of the magnetic disk  10 , and the vertical axis represents the temperature. The graph of  FIG. 8 ( b ) also indicates by a single-dot chain line a temperature distribution in the heated spot S 1  formed on the recording layer  12  when the beam spot S 2 ′, hence the heated spot S 2  is not formed, and by a double-dot chain line a temperature distribution in the heated spot S 2  formed on the recording layer  12  when the beam spot S 1 ′, hence the heated spot S 1  is not formed. The solid line in  FIG. 8 ( b ) represents the temperature distribution of the heated region S 3  composed of the heated spots S 1 , S 2 .  
         [0059]     In this thermally assisted magnetic recording method, the recording element  63  in the recording/reproducing head  60  applies a recording magnetic field M to the heated region S 3  on the recording layer  12 , while the recording layer  12  is locally heated as described above. Also, the direction of the recording magnetic field M output by the recording element  63  is sequentially inverted, so as to form on the recording layer  12  a plurality of magnetic domains (record marks) having sequentially inverted magnetizing directions, aligned circumferentially of the magnetic disk  10  or in the extending direction of the track. At this stage, the timing for inverting the recording magnetic field M is controlled so as to form each record mark in a predetermined length.  
         [0060]     By this thermally assisted magnetic recording method, the locally heated higher temperature region S 3  that moves on the recording layer  12  of the magnetic disk  10  is formed as described above, and the recording magnetic field M is applied to the heated region S 3 , so that information is recorded.  
         [0061]     By the thermally assisted magnetic recording method thus arranged, the heated region S 3  composed of the two aligned heated spots S 1 , S 2  is formed in a shape elongated in the direction of the arrow D (moving direction of the heated region), i.e. along the extending direction of the track. Whereas, as already stated, by a thermally assisted magnetic recording method, a maximum attainable temperature of a region on the recording layer, where the record mark is to be formed, primarily depends on a total amount of the heating energy supplied thereto per a predetermined minute time. Based on this, the method of forming the heated region S 3  in a shape elongated in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy to the region on the recording layer  12  where the record mark is to be formed, while restraining the heat from spreading transversely of the track. The thermally assisted magnetic recording method according to this embodiment is, therefore, advantageous in inhibiting or restraining emergence of the cross-write effect, so as to increase the recording density of the track.  
         [0062]     In this thermally assisted magnetic recording method, the peak temperatures P 1 , P 2  of the heated spots S 1 , S 2  shown in  FIG. 8 ( b ) may be controlled according to the moving speed of the heated region S 3 . In this method, provided that the disk rotation speed and the irradiation power of the laser beam L are constant irrespective of a radial position of the spot on the recording layer  12  where information is to be recorded, the heated region S 3  moves slower as the track on which the information is being recorded comes to an inner position of the magnetic disk  10 . Accordingly, it is preferable to control the power of the laser beams L output by the laser elements  62 A,  62 B such that the peak temperatures P 1 , P 2  of the heated spots S 1 , S 2  both drop, and a ratio of the peak temperature P 2  of the subsequent heated spot S 2  with respect to the peak temperature P 1  of the first heated spot S 1  becomes smaller, as the track on which the information is being recorded comes to an inner position of the magnetic disk  10  (i.e. the slower the heated region S 3  moves). The downwardly oriented arrows in  FIG. 8 ( b ) indicate a variation of the peak temperatures P 1 , P 2 . Controlling thus the peak temperatures P 1 , P 2  of the heated spots S 1 , S 2  composing the heated region S 3  allows leveling off the heating energy amount supplied to the track per unit time, irrespective of the radial position of the track on the disk.  
         [0063]      FIG. 9  is a schematic diagram showing a part of a magnetic disk apparatus X 4  for executing a thermally assisted magnetic recording method according to a fourth embodiment of the present invention. The magnetic disk apparatus X 4  includes a magnetic disk  10  and a recording/reproducing head  70 , for recording and reproducing information on and from the magnetic disk  10 , by the thermally assisted magnetic recording method.  
         [0064]     The magnetic disk  10  has a stacked structure including a disk substrate  11 , a recording layer  12 , and a cover layer  13 , so as to serve as a magnetic recording medium under the thermally assisted magnetic recording system. The materials constituting the magnetic disk  10  are the same as those employed in the first embodiment.  
         [0065]     The recording/reproducing head  70  includes a slider body  71 , heating elements  72 A,  72 B, a recording element  73 , and a reproducing element  74 , and is disposed so as to face the recording layer  12  of the magnetic disk  10 , when the magnetic disk apparatus X 4  records or reproduces information. The slider body  71  has a predetermined shape so as to cause gas lubrication between the magnetic disk  10  and the recording/reproducing head  70 , when the linear speed of a point on the rotating magnetic disk  10  facing the recording/reproducing head  70  exceeds a predetermined level. The heating elements  72 A,  72 B are medium heaters in the thermally assisted magnetic recording system, and generate heat when a current is supplied. The temperature of the heating elements  72 A,  72 B can be controlled by a control unit, which is not shown. The heating elements  72 A,  72 B are installed on the side of the slider body  71  facing the medium. The recording element  73  serves to apply a recording magnetic field M of a predetermined intensity to the recording layer  12 , and the reproducing element  74  serves to detect a magnetic signal generated according to a magnetized status of the recording layer  12 , and to convert the magnetic signal into an electrical signal. The materials constituting the recording element  73  and the reproducing element  74  are the same as those of the recording element  22  and the reproducing element  23  of the first embodiment. The heating element  72 A,  72 B, the recording element  73 , and the reproducing element  74  are aligned in a row along the rotating direction of the magnetic disk  10  or a circumferential direction thereof, for example in a manner as shown in  FIG. 10 .  FIG. 10  is a plan view showing a side of a recording/reproducing head  70  facing the magnetic disk  10 . The recording/reproducing head  70  thus constituted is connected to a recording/reproducing head actuator (not shown) constituted of for example a voice coil motor, via a suspension arm, for example made of a leaf spring. The suspension arm serves to bias the recording/reproducing head  70  against the magnetic disk  10 .  
         [0066]     When recording information with the magnetic disk apparatus X 4  on the magnetic disk  10 , by the thermally assisted magnetic recording method according to the fourth embodiment of the present invention, the recording/reproducing head actuator disposes the recording/reproducing head  70  so as to float above the magnetic disk  10  and sets the recording/reproducing head  70  at the recording position, with the magnetic disk  10  being rotated at a predetermined constant speed. The relative moving direction of the recording/reproducing head  70  with respect to the rotating magnetic disk  10  is indicated by the arrow D.  
         [0067]     In this thermally assisted magnetic recording method, the heating elements  72 A,  72 B of the recording/reproducing head  70  are disposed so as to face the recording layer  12 , and continuously generate heat at a predetermined temperature. In this embodiment, the heating elements  72 A,  72 B are aligned in the direction of the arrow D (substantially circumferentially of the disk or in the extending direction of the track) as shown in  FIG. 10 , so that the heat of the heating elements  72 A,  72 B forms two heated spots S 4 , S 5  having a temperature distribution as shown in the graph of  FIG. 11 . In  FIG. 11 , the horizontal axis represents the position in the circumferential direction of the magnetic disk  10 , and the vertical axis represents the temperature. The graph of  FIG. 11  also indicates by a single-dot chain line a temperature distribution in the heated spot S 4  formed on the recording layer  12 , when the heating element  72 B does not generate heat and hence the heated spot S 5  is not formed, and by a double-dot chain line a temperature distribution in the heated spot S 5  formed on the recording layer  12 , when the heating element  72 A does not generate heat and hence the heated spot S 4  is not formed. The solid line in  FIG. 11  represents the temperature distribution of the heated region S 6  composed of the heated spots S 4 , S 5 .  
         [0068]     In this thermally assisted magnetic recording method, the recording element  73  in the recording/reproducing head  70  applies a recording magnetic field M to the heated region S 6  on the recording layer  12 , while the recording layer  12  is locally heated as described above. Also, the direction of the recording magnetic field M output by the recording element  73  is sequentially inverted, so as to form on the recording layer  12  a plurality of magnetic domains (record marks) having sequentially inverted magnetizing directions, aligned circumferentially of the magnetic disk  10  or in the extending direction of the track. At this stage, the timing for inverting the recording magnetic field M is controlled so as to form each record mark in a predetermined length.  
         [0069]     By this thermally assisted magnetic recording method, the locally heated higher temperature region S 6  that moves on the recording layer  12  of the magnetic disk  10  is formed as described above, and the recording magnetic field M is applied to the heated region S 6 , so that information is recorded.  
         [0070]     By the thermally assisted magnetic recording method thus arranged, the heated region S 6  composed of the two aligned heated spots S 4 , S 5  is formed in a shape elongated in the direction of the arrow D (moving direction of the heated region), i.e. along the extending direction of the track. Whereas, as already stated, by a thermally assisted magnetic recording method, a maximum attainable temperature of a region on the recording layer, where the record mark is to be formed, primarily depends on a total amount of the heating energy supplied thereto per a predetermined minute time. Based on this, the method of forming the heated region S 6  in a shape elongated in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy to the region on the recording layer  12  where the record mark is to be formed, while restraining the heat from spreading transversely of the track. The thermally assisted magnetic recording method according to this embodiment is, therefore, advantageous in inhibiting or restraining emergence of the cross-write effect, so as to increase the recording density of the track.  
         [0071]     In this thermally assisted magnetic recording method, the peak temperatures P 4 , P 5  of the heated spots S 4 , S 5  shown in  FIG. 11  may be controlled according to the moving speed of the heated region S 6 . In this method, provided that the disk rotation speed and the irradiation power of the laser beam L are constant irrespective of a radial position of the spot on the recording layer  12  where information is to be recorded, the heated region S 6  moves slower as the track on which the information is being recorded comes to an inner position of the magnetic disk  10 . Accordingly, it is preferable to control the power of the laser beams L output by the laser elements  72 A,  72 B such that the peak temperatures P 4 , P 5  of the heated spots S 4 , S 5  both drop, and a ratio of the peak temperature P 5  of the subsequent heated spot S 5  with respect to the peak temperature P 4  of the first heated spot S 4  becomes smaller, as the track on which the information is being recorded comes to an inner position of the magnetic disk  10  (i.e. the slower the heated region S 6  moves). The downwardly oriented arrows in  FIG. 11  indicate a variation of the peak temperatures P 4 , P 5 . Controlling thus the peak temperatures P 4 , P 5  of the heated spots S 4 , S 5  composing the heated region S 6  allows leveling off the heating energy amount supplied to the track per unit time, irrespective of the radial position of the track on the disk.  
         [0072]      FIG. 12  is a schematic diagram showing a part of a magnetic disk apparatus X 5  for executing a thermally assisted magnetic recording method according to a fifth embodiment of the present invention. The magnetic disk apparatus X 5  includes a magnetic disk  10 , a magnetic head  80 , an optical head  90 , a composite element  41 , and a diffraction grid  42 , for recording and reproducing information on and from the magnetic disk  10 , by the thermally assisted magnetic recording method.  
         [0073]     The magnetic disk  10  has a stacked structure including a disk substrate  11 , a recording layer  12 , and a cover layer  13 , so as to serve as a magnetic recording medium under the thermally assisted magnetic recording system. The materials constituting the magnetic disk  10  are the same as those employed in the first embodiment.  
         [0074]     The magnetic head  80  includes a slider body  81 , a recording element  82 , and a reproducing element  83 , and is disposed so as to face the recording layer  12  of the magnetic disk  10 , when the magnetic disk apparatus X 5  records or reproduces information. The materials constituting the slider body  81 , the recording element  82 , and the reproducing element  83  are the same as those of the slider body  21 , the recording element  22 , and the reproducing element  23  of the first embodiment. The magnetic head  80  thus constituted is connected to a magnetic head actuator (not shown) constituted of for example a voice coil motor, via a suspension arm, for example made of a leaf spring. The suspension arm serves to bias the magnetic head  80  against the magnetic disk  10 .  
         [0075]     The optical head  90  includes a condenser lens  91 , a lens actuator  92 , a mask  93 , and a mirror  94 , and is capable of emitting a plurality of laser beams L (two in this embodiment) toward the magnetic disk  10 . For the sake of simplification of the drawing, the laser beam L employed in this embodiment is schematically indicated by a single-dot chain line representing the optical axis thereof. The optical head  90  encloses therein an optical waveguide that transmits a laser beam L from a light source (not shown) such as a semiconductor laser diode. The materials of the condenser lens  91 , the lens actuator  92 , the mask  93 , and the mirror  94  are the same as those of the condenser lens  31 , the lens actuator  32 , the mask  33 , and the mirror  34  of the first embodiment. The optical head  90  thus constituted is installed so as to translationally move driven by an optical head actuator (not shown) along a guiderail (not shown) installed so as to extend radially of the magnetic disk  10 .  
         [0076]     The composite element  41  includes a plurality of prisms of different refractive indices, so as to incline the incident angle of the laser beam L, emitted by the light source (not shown) and transmitted through a collimator lens (not shown), on the composite element  41 , to thereby trim the cross-sectional shape of the laser beam L into a circle for example, and to serve as a polarizing beam splitter for splitting the laser beam L. A portion of the laser beam L thus split is led to the optical head  90 , and the other portion is led to a photodetecting unit (not shown) that monitors the intensity of the laser beam L to execute a feedback control.  
         [0077]     The diffraction grid  42  serves to split a laser beam L from a single light source into two beams, in various splitting manners through a control of a predetermined actuator that microadjusts the position and the rotation angle (posture) of the diffraction grid  42 .  
         [0078]     When recording information with the magnetic disk apparatus X 5  on the magnetic disk  10 , by the thermally assisted magnetic recording method according to the fifth embodiment of the present invention, the magnetic head actuator disposes the magnetic head  80  so as to float above the magnetic disk  10  and sets the magnetic head  80  at the recording position, with the magnetic disk  10  being rotated at a predetermined constant speed, while the optical head actuator sets the optical head  90  at the recording position. The relative moving direction of the magnetic head  80  and the optical head  90  with respect to the rotating magnetic disk  10  is indicated by the arrow D.  
         [0079]     In this thermally assisted magnetic recording method, the two laser beams L emitted by the optical head  90  and converged through the condenser lens  91  are continuously made incident upon the recording layer  12  of the magnetic disk  10 . In this embodiment, the two laser beams L overlap with each other on the surface of the magnetic disk  10  or the cover layer  13 , so as to form two beam spots S 7 ′, S 8 ′ aligned in the direction of the arrow D (substantially circumferentially of the disk or in the extending direction of the track) on the cover layer  13 , as shown in  FIG. 13 ( a ). On predetermined positions on the recording layer  12 , two heated spots S 7 , S 8  having a temperature distribution as shown in the graph of  FIG. 13 ( b ) are formed, so as to respectively correspond to the two beam spots S 7 ′, S 8 ′. In  FIG. 13 ( b ), the horizontal axis represents the position in the circumferential direction of the magnetic disk  10 , and the vertical axis represents the temperature. The graph of  FIG. 13 ( b ) also indicates by a single-dot chain line a temperature distribution in the heated spot S 7  formed on the recording layer  12  when the beam spot S 8 ′, hence the heated spot S 8  is not formed, and by a double-dot chain line a temperature distribution in the heated spot S 8  formed on the recording layer  12  when the beam spot S 7 ′, hence the heated spot S 7  is not formed. The solid line in  FIG. 13 ( b ) represents the temperature distribution of the heated region S 9  composed of the heated spots S 7 , S 8 .  
         [0080]     In this thermally assisted magnetic recording method, the recording element  82  in the magnetic head  80  applies a recording magnetic field M to the heated region S 9  on the recording layer  12 , while the recording layer  12  is locally heated as described above. Also, the direction of the recording magnetic field M output by the recording element  82  is sequentially inverted, so as to form on the recording layer  12  a plurality of magnetic domains (record marks) having sequentially inverted magnetizing directions, aligned circumferentially of the magnetic disk  10  or in the extending direction of the track. At this stage, the timing for inverting the recording magnetic field M is controlled so as to form each record mark in a predetermined length.  
         [0081]     By this thermally assisted magnetic recording method, the locally heated higher temperature region S 9  that moves on the recording layer  12  of the magnetic disk  10  is formed as described above, and the recording magnetic field M is applied to the heated region S 9 , so that information is recorded.  
         [0082]     By the thermally assisted magnetic recording method thus arranged, the heated region S 9  composed of the two aligned heated spots S 7 , S 8  is formed in a shape elongated in the direction of the arrow D (moving direction of the heated region), i.e. along the extending direction of the track. Whereas, as already stated, by a thermally assisted magnetic recording method, a maximum attainable temperature of a region on the recording layer, where the record mark is to be formed, primarily depends on a total amount of the heating energy supplied thereto per a predetermined minute time. Based on this, the method of forming the heated region S 9  in a shape elongated in the moving direction thereof is quite advantageous for supplying a sufficient amount of heating energy to the region on the recording layer  12  where the record mark is to be formed, while restraining the heat from spreading transversely of the track. The thermally assisted magnetic recording method according to this embodiment is, therefore, advantageous in inhibiting or restraining emergence of the cross-write effect, so as to increase the recording density of the track.  
         [0083]     In this thermally assisted magnetic recording method, the peak temperatures P 7 , P 8  of the heated spots S 7 , S 8  may be controlled according to the moving speed of the heated region S 9 . In this method, provided that the disk rotation speed and the irradiation power of the laser beam L are constant irrespective of a radial position of the spot on the recording layer  12  where information is to be recorded, the heated region S 9  moves slower as the track on which the information is being recorded comes to an inner position of the magnetic disk  10 . Accordingly, it is preferable to control the power of the laser beams L such that the peak temperatures P 7 , P 8  of the heated spots S 7 , S 8  both drop, as the track on which the information is being recorded comes to an inner position of the magnetic disk  10  (i.e. the slower the heated region S 9  moves). The downwardly oriented arrows in  FIG. 13 ( b ) indicate a variation of the peak temperatures P 7 , P 8 . Controlling thus the peak temperatures P 7 , P 8  of the heated spots S 7 , S 8  composing the heated region S 9  allows leveling off the heating energy amount supplied to the track per unit time, irrespective of the radial position of the track on the disk.  
         [0084]     Instead of or in addition to the foregoing control of the peak temperatures P 7 , P 8 , in this thermally assisted magnetic recording method, the positions x 7 , x 8  corresponding to the peak temperatures of the heated spots S 7 , S 8  may be controlled according to the moving speed of the heated region S 9 . In this method, provided that the disk rotation speed and the irradiation power of the laser beam L are constant irrespective of a radial position of the spot on the recording layer  12  where information is to be recorded, the heated region S 9  moves slower as the track on which the information is being recorded comes to an inner position of the magnetic disk  10 . Accordingly, it is preferable to control the position and the rotation angle of the diffraction grid  42  so as to increase the distance between the positions x 7 , x 8  corresponding to the peak temperatures of the heated spots S 7 , S 8 , as the track on which the information is being recorded comes to an inner position of the magnetic disk  10  (i.e. the slower the heated region S 9  moves). The horizontally oriented arrows in FIG.  13 ( b ) indicate a variation of the positions x 7 , x 8  corresponding to the peak temperatures. Controlling thus the positions x 7 , x 8  corresponding to the peak temperatures of the heated spots S 7 , S 8  composing the heated region S 9  is advantageous in leveling off the heating energy amount supplied to the track per unit time, irrespective of the radial position of the track on the disk.