Abstract:
The present invention provides a perpendicular magnetic recording medium that reduces medium noise and achieves thermal stability of recording magnetization. This perpendicular magnetic recording medium has a substrate and a recording layer formed by single-layered magnetic nanoparticles that are aligned at uniform intervals. An auxiliary magnetic film that is thinner than the recording layer is interposed between the substrate and the recording layer. The magnetization of the magnetic nanoparticles is secured by the exchange interaction effect of the auxiliary magnetic film.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention generally relates to perpendicular magnetic recording media, and, more particularly, to a perpendicular magnetic recording medium that can achieve a high recording density.  
           [0002]    Conventionally, in-plane magnetic recording media have reduced media noise and secured the S/N in reproduction signals, so as to achieve higher recording densities to compensate decreases in output voltage due to high-density recording. In recent years, perpendicular magnetic recording media have become popular in pursuit of even higher recording densities.  
           [0003]    [0003]FIG. 1 illustrates a conventional perpendicular magnetic recording medium  10 . As shown in FIG. 1, the perpendicular magnetic recording medium  10  has a substrate  11 . On the substrate  11 , the perpendicular magnetic recording medium  10  has a soft-magnetic backing layer  12 , a non-magnetic intermediate layer  13 , a recording layer  15 , and a protection layer  16  stacked in this order. The recording layer  15  is a magnetic film of a CoCr-based alloy formed by a sputtering method. Such a magnetic film is made up of the boundary of crystal grains of a high Cr concentration and crystal grains that are the cores of the crystal grains of a high Cr concentration, with Cr atoms segregating on the boundary surfaces of the crystal grains. Among these crystal grains, there are magnetostatic interactive effects and exchange interaction effects. The grain size of each of the crystal grains is large. If the distance between each two crystal grains is long, those interaction effects become greater, resulting in an increase of medium noise. To solve this problem, the materials and film-forming conditions for recording layers and underlayers have been optimized, so that the grain sizes can be reduced and uniformed.  
           [0004]    However, recording layers of CoCr-based alloys formed by a sputtering method cannot satisfy today&#39;s demand for recording densities higher than 775 Mbits/cm 2  (500 Gbits/inch 2 ), because the grain sizes cannot be reduced and uniformed sufficiently. As a result, a sufficient reduction of medium noise cannot be achieved.  
           [0005]    As a solution for achieving minute and uniform ferromagnetic crystal grains, a variety of chemical techniques have been suggested. These techniques are disclosed in publications such as Science (Vol. 287, No. 17 (2000), pages 1989-1992, Sun, et. al) and J. Mag. Soc. Japan (Vol. 25, No. 8 (2001), pages 1434-1440).  
           [0006]    In accordance with the inventions disclosed in those publications, the spherical magnetic nanoparticles have grain sizes of nanometers. FIG. 2 is a sectional view of a magnetic recording medium  20  having stacked spherical magnetic nanoparticles. As shown in FIG. 2, a recording layer  25  and a protection layer  26  are stacked on a substrate in this order. The recording layer  25  has a thickness of 20 nm to 100 nm, and is formed by stacking spherical magnetic nanoparticles.  
           [0007]    Although the recording layer  25  shown in FIG. 2 is formed by uniform magnetic nanoparticles  27 , the positions of the magnetic nanoparticles  27  are shifted on each layer in the film thickness direction if the magnetic nanoparticles  27  have a meticulous filling structure. As a result, the magnetic transition regions are disturbed at the time of recording. Because of this, the recording layer  25  cannot achieve a sufficient reduction of medium noise.  
           [0008]    To reduce medium noise, a perpendicular magnetic recording medium  30  having conventional spherical magnetic nanoparticles in the form of a single layer has been suggested. As shown in FIG. 3, the perpendicular magnetic recording medium  30  has a substrate  31 . On the substrate  31 , the perpendicular magnetic recording medium  30  has a soft-magnetic backing layer  32 , a non-magnetic intermediate layer  33 , a recording layer  35 , and a protection layer  36  stacked in this order. The recording layer  35  is formed by spherical magnetic nanoparticles  37  that are aligned at uniform intervals and formed into a single layer. In this structure, the unevenness of the magnetic nanoparticles in the film thickness direction is eliminated, and the exchange interaction effect can be reduced. Accordingly, this perpendicular magnetic recording medium  30  can reduce the medium noise and achieves a higher recording density.  
           [0009]    With the recoding layer  35  of the perpendicular magnetic recording medium  30 , however, there is a problem of thermal instability. More specifically, since the exchange interaction effect is restrained, the residual magnetization rapidly decreases after a recording operation. It is a known fact that, to achieve thermal stability of residual magnetization, the index expressed as KuV/kT should be great. Here, Ku represents the anisotropic energy, V represents the effective grain volume (equivalent to the total volume of the magnetic nanoparticles coupled by the exchange interaction effect), k represents the Boltzmann constant, and T represents the absolute temperature. Since the recording layer  35  of the perpendicular magnetic recording medium  30  has a small exchange interaction effect, the effective grain volume V becomes equal to the volume of each one of the magnetic nanoparticles  37 . As the volume V becomes smaller, the index KuV/kT also becomes smaller, resulting in thermal instability. Judging from these facts, the perpendicular magnetic recording medium  30  cannot achieve a sufficient reduction of medium noise and greater thermal stability at the same time.  
         SUMMARY OF THE INVENTION  
         [0010]    A general object of the present invention is to provide perpendicular magnetic recording media in which the above disadvantages are eliminated.  
           [0011]    A more specific object of the present invention is to provide a perpendicular magnetic recording medium that has smaller medium noise and greater thermal stability of recording magnetization.  
           [0012]    The above objects of the present invention are achieved by a perpendicular magnetic recording medium having a recording layer over a substrate. This perpendicular magnetic recording medium includes the recording layer that is a single layer formed by aligning magnetic nanoparticles of uniform particle sizes at uniform intervals, and an auxiliary magnetic film that is located between the recording layer and the substrate at such a position that has an exchange interaction effect on the magnetic nanoparticles.  
           [0013]    In this perpendicular magnetic recording medium, the magnetic nanoparticles of uniform particle sizes are aligned at uniform intervals and formed into a single layer. Because of this, the exchange interaction effect and the magnetostatic interaction effect among the magnetic nanoparticles in the film are restrained, and medium noise can be reduced. At the same time, the auxiliary magnetic film that is magnetized during a recording operation has an exchange interaction effect on the magnetic nanoparticles of the recording layer, and secures the magnetization of the magnetic nanoparticles. Thus, the thermal stability of the magnetization of the recording layer can be improved.  
           [0014]    The above objects of the present invention are also achieved by a magnetic recording device that employs the above perpendicular magnetic recording medium.  
           [0015]    The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a sectional view of a conventional perpendicular magnetic recording medium;  
         [0017]    [0017]FIG. 2 is a sectional view of a magnetic recording medium having a recording layer formed by conventional stacked magnetic nanoparticles;  
         [0018]    [0018]FIG. 3 is a sectional view of a perpendicular magnetic recording medium having a recording layer formed by single-layered magnetic nanoparticles;  
         [0019]    [0019]FIG. 4 is a sectional view of a perpendicular magnetic recording medium in accordance with the present invention;  
         [0020]    [0020]FIGS. 5A and 5B illustrate the residual magnetization states in the perpendicular recording medium immediately after a recording operation;  
         [0021]    [0021]FIG. 6 illustrates a change in the recording magnetization with time;  
         [0022]    [0022]FIG. 7 shows the parameters employed in Examples and Comparative Examples, and the results of a computer simulation;  
         [0023]    [0023]FIG. 8 is a sectional view of a magnetic recording device employing a perpendicular magnetic recording medium in accordance with the present invention; and  
         [0024]    [0024]FIG. 9 is a plan view of the magnetic recording device of FIG. 8. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    The following is a description of embodiments of the present invention, with reference to the accompanying drawings.  
         [0026]    [0026]FIG. 4 is a sectional view of a perpendicular magnetic recording medium in accordance with the present invention. As shown in FIG. 4, a perpendicular magnetic recording medium  40  has a substrate  41 . In this perpendicular magnetic recording medium, a soft-magnetic backing layer  42 , a non-magnetic intermediate layer  43 , an auxiliary magnetic film  44 , a recording layer  45  made of magnetic nanoparticles  47 , and a protection layer  46 , are stacked on the substrate  41  in this order.  
         [0027]    The substrate  41  is a conventional substrate for magnetic disks, such as a crystallized glass substrate, a tempered glass substrate, an aluminum-magnesium alloy substrate, or a Si wafer.  
         [0028]    The soft-magnetic backing layer  42  has a thickness of 100 nm to 2 μm, and is formed by a soft-magnetic material having a high saturation magnetic flux density Bs, such as permalloy (NiFe), NiFeNb, or CoCrNb. This soft-magnetic backing layer  42  is manufactured by a plating method, a sputtering method, a vapor deposition method, or a CVD method.  
         [0029]    The employment of the soft-magnetic backing layer  42  depends on the types of recording heads, such as single-pole magnetic heads and ringshaped heads. If recording is to be performed with a ring-shaped head, the soft-magnetic backing layer  42  is not necessary.  
         [0030]    The non-magnetic intermediate layer  43  has a thickness of 1 nm to 50 nm, and is formed by a non-magnetic material such as Ti, C, Pt, TiCr, CoCr, SiO 2 , MgO, or Al 2 O 3 . Alternatively, the non-magnetic intermediate layer  43  may be formed by a laminated layer including one or more of those alloys. The non-magnetic intermediate layer  43  is manufactured by a sputtering method, a vapor deposition method, or a CVD method. The non-magnetic intermediate layer  43  controls the crystallinity, the grain size, and the perpendicular orientation of the auxiliary magnetic film  44  placed on the non-magnetic intermediate layer  43 .  
         [0031]    The auxiliary magnetic film  44  is made of an alloy such as FePt, FePd, CoPt, or CoPd, or an artificial lattice film that is formed by repeatedly laminating Pt(0.5 nm in thickness)/Co(0.3 nm in thickness) or Pd(0.5 nm in thickness)/Co(0.3 nm in thickness).  
         [0032]    The auxiliary magnetic film  44  preferably has an exchange stiffness constant that is greater than 1×10 −12  J/M and smaller than 5×10 −12  J/m. The auxiliary magnetic film  44  that is magnetized by a magnetic field generated from a recording head has an exchange interaction. effect on the magnetization of the magnetic nanoparticles  47  of the recording layer  45 , and secures the magnetization of the magnetic nanoparticles  47 . The degree of the exchange interaction effect can be expressed by an exchange stiffness constant. The exchange stiffness constant is an essential factor in determining the exchange interaction between the auxiliary magnetic film  44  and the magnetic nanoparticles  47  of the recording layer  45 . The auxiliary magnetic film  44  and the magnetic nanoparticles  47  are magnetized by a recording magnetic field generated from a recording head. After the recording magnetic field is removed, the magnetization of the auxiliary magnetic film  44  has an exchange interactive effect on the magnetization of the magnetic nanoparticles  47 . The degree of the exchange interactive effect is determined by the respective exchange stiffness constants and the distance between the auxiliary magnetic film  44  and the recording layer  45 . Thus, the magnetization of the magnetic nanoparticles  47  is prevented from decreasing due to thermal instability.  
         [0033]    If the exchange stiffness constant of the auxiliary magnetic film  44  is 1×10 −12  J/m or smaller, the exchange interaction effect on the magnetization of the magnetic nanoparticles  47  of the recording layer  45  is not sufficient. As a result, the orientations of the magnetic nanoparticles  47  become random immediately after recording. More specifically, some of the magnetic nanoparticles  47  randomly face upward while the others face downward perpendicularly to the film surface. In this state, desired information recording cannot be performed. On the other hand, if the exchange stiffness constant of the auxiliary magnetic film  44  is 5×10 −12  J/m or greater, the auxiliary magnetic film  44  cannot be magnetized by a normal recording magnetic field.  
         [0034]    Further, the exchange stiffness constant of the auxiliary magnetic film  44  should preferably be equal to or greater than the exchange stiffness constant of the magnetic nanoparticles  47 . If this condition is satisfied, the exchange interaction among the magnetic nanoparticles  47  is restricted, the medium noise is reduced, and the exchange interaction effect of the auxiliary magnetic film  44  is sufficient for magnetizing the magnetic nanoparticles  47 . Thus, the thermal stability of the magnetization of the magnetic nanoparticles  47  can be improved. Meanwhile, the exchange stiffness constants are measured by a Brillouin scattering method.  
         [0035]    The auxiliary magnetic film  44  has a magnetic easy axis extending perpendicularly to the film surface. This perpendicular orientation is expressed by the ratio of the coercive force H c//2  of the longitudinal direction of the auxiliary magnetic film  44  to the coercive force H c⊥2  of the perpendicular direction of the auxiliary magnetic film  44 , i.e., H c//2 /H c⊥2 , If this ratio is small, the magnetic easy axis extends in the perpendicular direction. The ratio H c//2 /H c⊥2  should preferably be 25% or lower, more preferably, 10% or lower, so that the width of the magnetic transition region of the recording layer  45  can be narrowed. If the ratio H c//2 /H c⊥2  exceeds 25%, the magnetic transition region of the recording layer  45  becomes too wide to carry out high-density recording.  
         [0036]    The perpendicular orientation of the auxiliary magnetic film  44  can be controlled by conditions such as the material of the non-magnetic intermediate layer  43  located below the auxiliary magnetic film  44 , the film-forming conditions for forming the auxiliary magnetic film  44 , and the field thermal treatment conducted after the formation of the auxiliary magnetic film  44 . In the present invention, the magnetic nanoparticles  47  are subjected to a thermal treatment after the formation of the protection layer  46 , so that the perpendicular orientation is controlled.  
         [0037]    The product tBr of the thickness and the residual magnetic flux density of the auxiliary magnetic film  44  should preferably be 30% of the product tBr of the recording layer  45  or smaller. In the structure of the perpendicular magnetic recording medium  40  of the present invention, the magnetic field generated from the magnetic nanoparticles  47  of the recording layer  45  is overlapped with the magnetic field generated from the auxiliary magnetic film  44 , and the overlapped magnetic fields are converted into an output voltage by an MR head (magnetoresistive head). If the product tBr of the auxiliary magnetic film  44  is greater than 30% of the product tBr of the recording layer  45 , the auxiliary magnetic film  44  deforms the reproduced waveform and increases medium noise.  
         [0038]    The recording layer  45  is made up of the spherical magnetic nanoparticles  47  that align themselves at uniform intervals, and amorphous carbon that secures the alignment. The recording layer  45  has a thickness of 3 nm to 50 nm. The magnetic nanoparticles  47  are made of a regular alloy such as FePt, FePd, CoPt, or CoPd.  
         [0039]    This recording layer  45  can be formed by any of the methods disclosed in the publications mentioned earlier. For example, according to a polyol reducing method, an organometallic precursor solution containing Fe and Pt is reduced and decomposed, so as to produce the magnetic nanoparticles  47  covered with a stabilizer of oleic acid or oleyl amine. A refinement process for the magnetic nanoparticles  47  is then carried out a few times with a centrifugal separator, and the concentration of the magnetic nanoparticles  47  is adjusted. The resultant magnetic nanoparticles  47  are applied onto the auxiliary magnetic film  44  by a dipping method or a spin coating method. A thermal treatment is then conducted. In the present invention, a magnetic field of 2T is applied in the perpendicular direction to the film surface, and the thermal treatment is conducted in an Ar gas atmosphere of 3×10 4  Pa at 480° C. for 30 minutes. By this thermal treatment, the crystalline lattice of the magnetic nanoparticles  47  of FePt is regulated, and the anisotropic energy and the coercive force in the perpendicular direction to the film surface are increased. Thus, the magnetic easy axis of the magnetic nanoparticles  47  can extend perpendicularly to the film surface.  
         [0040]    The protection layer  46  has a thickness of 0.5 nm to 15 nm, and is made of a material such as carbon, hydrogenated carbon, or carbon nitride. The protection layer  46  is formed by a sputtering method or a CVD method. Further, a lubricant layer (not shown) having a thickness of 0.5 nm to 5 nm is formed on the protection layer  46 .  
       EXAMPLE 1  
       [0041]    In this example, the perpendicular magnetic recording medium  40  had a laminated structure. More specifically, the perpendicular magnetic recording medium  40  had the substrate  41  made of crystallized glass. On this substrate  41 , the perpendicular magnetic recording medium  40  had: the soft-magnetic backing layer  42  that was made of CoCrNb and had a thickness of 300 nm; the nonmagnetic intermediate layer  43  that was made of Al 2 O 3  and had a thickness of 10 nm; the auxiliary magnetic film  44 ; the recording layer  45 ; the protection layer  46  that was made of hydrogenated carbon and had a thickness of 5 nm; and a lubricant layer that was made of Z-DOL (TM) and had a thickness of 1.0 nm.  
         [0042]    The magnetic nanoparticles  47  of the recording layer  45  were made of FePt. The particle size (the diameter) of the magnetic nanoparticles  47  was 3.38 nm, and each gap among the magnetic nanoparticles  47  in the longitudinal direction was 1 nm. The recording layer  45  had a thickness of 4.38 nm, a product tBr of 2530 μT·μm (25.3 Gμ·m), and a magnetocrystalline anisotropy field H k1  of 1.6×10 6  A/m (20 kOe). Also, the coercive force H c//1  was 27.7 kA/m, the coercive force H 1⊥1  was 860 kA/m, and the ratio H c//1 /H c⊥1  was 3%. The exchange stiffness constant A 1  of the magnetic nanoparticles  47  was 2×10 −12  J/m.  
         [0043]    The auxiliary magnetic film  44  was made of CoPt and had a film thickness of 1 nm. The product tBr was 750 μT·μm, the exchange stiffness constant A 2  was 4×10 −12  J/m, the coercive force H c//2  was 27.7 kA/m, the coercive force H c⊥2  was 860 kA/m, the ratio H c//2 /H c⊥2  was 3%, and the magnetocrystalline anisotropy field H k2  was 1600 kA/m.  
       EXAMPLE 2  
       [0044]    This example had the same structure as Example 1, except for the auxiliary magnetic film.  
         [0045]    The auxiliary magnetic film  44  was made of CoPt and had a film thickness of 1 nm. The product tBr was 750 μT·μm, the exchange stiffness constant A 2  was 2×10 −12  J/m, the coercive force H c//2  was 126 kA/m, the coercive force H c⊥2  was 521 kA/m, the ratio H c//2 /H c⊥2  was 25%, and the magnetocrystalline anisotropy field H k2  was 1600 kA/m.  
       EXAMPLE 3  
       [0046]    This example had the same structure as Example 1, except for the auxiliary magnetic film.  
         [0047]    The auxiliary magnetic film  44  was made of CoPt and had a film thickness of  1  nm. The product tBr was 750 μT·μm, the exchange stiffness constant A 2  was 4×10 −12  J/m, the coercive force H c//2  was 126 kA/m, the coercive force H c⊥2  was 521 kA/m, the ratio H c//2 /H c⊥2  was 25%, and the magnetocrystalline anisotropy field H k2  was 1600 kA/m.  
       COMPARATIVE EXAMPLE 1  
       [0048]    As a comparative example, a perpendicular magnetic recording medium was formed. This perpendicular magnetic recording medium has the same structure as the perpendicular magnetic recording medium of Example 1, except for the auxiliary magnetic film.  
         [0049]    In this comparative example, the auxiliary magnetic film was made of CoPt and had a film thickness of 1 nm. The product tBr was 750 μT·μm, the exchange stiffness constant A 2  was 5×10 −12  J/m, the coercive force H c//2  was 126 kA/m, the coercive force H c⊥2  was 521 kA/m, the ratio H c//2 /H c⊥2  was 25%, and the magnetocrystalline anisotropy field H k2  was 1600 kA/m.  
       COMPARATIVE EXAMPLE 2  
       [0050]    As a second comparative example, a perpendicular magnetic recording medium having a laminated structure without the auxiliary magnetic film  44  of Example 1 was formed. The other layers were the same as those of Example 1.  
         [0051]    For the above Examples and Comparative Examples, a computer simulation according to the micro-magnetics model was performed. In this simulation, recording was performed on each perpendicular magnetic recording medium with a single-pole magnetic head, so as to determine the residual magnetization. Here, the saturation magnetic flux density Bs of the recording magnetic pole of the single-pole magnetic head was 1.4 T. The magnetic spacing between the single magnetic pole and each perpendicular magnetic recording medium was 8 nm. The magnetic field of the head was 1600 kA/m (20 kOe), with the recording layer being the center. The recording density was 30.4 k(magnetization inversion)/mm (773 kFCI).  
         [0052]    [0052]FIGS. 5A and 5B illustrate the residual magnetization states of the recording layer immediately after a recording operation on the perpendicular magnetic recording medium. FIG. 5A illustrates the residual magnetization states in Examples, and FIG. 5B illustrates the residual magnetization states in Comparative Examples. In FIGS. 5A and 5B, the abscissa axis indicates the location on the perpendicular magnetic recording medium in the track circumferential direction, and the ordinate axis indicates the magnetization My in the direction perpendicular to the film surface. The magnetization My is standardized by the saturation magnetization Ms. For instance, when the ratio My/Ms has a positive value, the surface of the perpendicular magnetic recording medium has positive magnetization. If the ratio My/Ms has a negative value, the surface of the perpendicular magnetic recording medium has negative magnetization.  
         [0053]    As can be seen from FIG. 5A, in Examples 1 and 2, the regions in which the ratio My/Ms changes from −1 to 1 or 1 to −1 show dramatic changes. In other words, the magnetic transition regions are narrow, and thus high-density recording can be performed in Examples 1 and 2. In Example 3, the magnetic transition regions are a little wider than those in Examples 1 and 2. In view of high-density recording, Examples 1 and 2 are more preferable than Example 3.  
         [0054]    As can be seen from FIG. 5B, Comparative Example 1 exhibits the same residual magnetization state as the magnetic state prior to the recording operation, though the recording operation has already been completed. The exchange stiffness constant A 2  of the auxiliary magnetic film is as large as 0.5, and the exchange interaction effect of the auxiliary magnetic film on the magnetic nanoparticles of the recording layer is great. Accordingly, the magnetization of the magnetic nanoparticles cannot be inverted by the recording magnetic field.  
         [0055]    Comparative Example 2 exhibits narrow magnetic transition regions and the same residual magnetization state as that of Example 1 or 2. However, the magnetization in Comparative Example 2 decreases rapidly with time, as described later, and is poor in thermal stability. Because of this, it is apparent that the perpendicular magnetic recording medium of Comparative Example 2 is not suitable as a recording medium.  
         [0056]    [0056]FIG. 6 illustrates residual magnetization changes with time obtained through a computer simulation. In FIG. 6, the abscissa axis indicates time t after a recording operation, and the ordinate axis indicates the residual magnetization M(t) at the time t. Here, the residual magnetization M(t) is standardized by the magnetization immediately after the recording operation, i.e., the saturation magnetization Ms. In Comparative Example 2, the ratio M(t)/Ms rapidly decreases 10 −5  or 10 −4  seconds after the recording. On the other hand, in Example 1, the ratio M(t)/Ms does not decrease even 10 4  seconds after the recording. This means that the thermal stability of the recording magnetization is excellent in Example 1. Although not shown in FIG. 6, Examples 2 and 3 showed the same results as Example 1.  
         [0057]    [0057]FIG. 7 collectively shows the above results, including the parameters used in Examples and Comparative Examples and the results of the computer simulations. In each perpendicular magnetic recording medium of Examples 1 through 3, the exchange stiffness constant A 2  of the auxiliary magnetic film satisfies the condition 0.1&lt;A 2 &lt;0.5, so that the residual magnetization state having narrow magnetic transition regions can be formed immediately after recording. At the same time, the auxiliary magnetic film has an exchange interaction effect on the magnetic nanoparticles of the recording layer, and thus secures the magnetization of the magnetic nanoparticles. In this manner, the thermal stability of the magnetization of the recording layer can be improved. Furthermore, the ratio of the coercive force H c//2  of the longitudinal direction of the auxiliary magnetic film  44  to the coercive force H ⊥2  of the perpendicular direction of the auxiliary magnetic film is lowered, so that the magnetic transition regions formed by the magnetic nanoparticles can be narrowed. Thus, a perpendicular magnetic recording medium that is suitable for high-density recording can be obtained.  
         [0058]    Referring now to FIGS. 8 and 9, an example of a magnetic recording device in accordance with the present invention will be described. FIG. 8 is a sectional view illustrating the components of a magnetic recording device  120 . FIG. 9 is a plan view illustrating the components of the magnetic recording device  120 .  
         [0059]    As shown in FIGS. 8 and 9, the magnetic recording device  120  is housed in a housing  123 . In the housing  123 , the magnetic recording device  120  has a motor  124 , a hub  125 , a plurality of magnetic recording media  126 , a plurality of recording and reproducing heads  127 , a plurality of suspensions  128 , a plurality of arms  129 , and an actuator unit  121 . The magnetic recording media  126  are attached to the hub  125  that is rotated by the motor  124 . The recording and reproducing heads  127  are complex heads including thin-film recording heads and reproducing heads of MR devices, GMR (Giant Magnetoresistive) devices, or TMR (Tunneling Magnetoresistive) devices. The recording and reproducing heads  127  are respectively attached to the corresponding arms  129  with the corresponding suspensions  128 . The arms  129  are driven by the actuator unit  121 . The fundamental structure of this magnetic recording device  120  is well-known, and therefore detailed explanation of it is omitted in this specification.  
         [0060]    The magnetic recording device  120  of this example is characterized by the magnetic recording media  126 . Each of the magnetic recording media  126  may be any of the perpendicular magnetic recording media of Examples 1 through 3 each including the laminated structure of FIG. 4. The number of the magnetic recording media  126  is not limited to 3, but may be 1, 2, or larger than 3.  
         [0061]    The structure of the magnetic recording device  120  is not limited to the structure shown in FIGS. 8 and 9. Also, the magnetic recording media  126  employed in the magnetic recording device  120  of the present invention are not limited to magnetic disks.  
         [0062]    It should be noted that the present invention is not limited to the embodiments specifically disclosed above, but other variations and modifications may be made without departing from the scope of the present invention.  
         [0063]    The present application is based on Japanese priority application No. 2002-165820 filed on Jun. 6, 2002, the entire contents of which are hereby incorporated by reference.