Patent Publication Number: US-2009225465-A1

Title: Magnetic recording head and magnetic recording apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-235114, filed on Sep. 11, 2007; the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a magnetic recording head and a magnetic recording apparatus provided with a spin torque oscillator generating a high-frequency magnetic field. 
     2. Background Art 
     In the 1990s, the practical application of MR (magnetoresistive effect) heads and GMR (giant magnetoresistive effect) heads triggered a dramatic increase in the recording density and recording capacity of HDD (hard disk drive). However, in the early 2000s, the problem of thermal fluctuations in magnetic recording media became manifest, and hence the increase of recording density temporarily slowed down. Nevertheless, perpendicular magnetic recording, which is in principle more advantageous to high-density recording than longitudinal magnetic recording, was put into practical use in 2005. It serves as an engine for the increase of HDD recording density, which exhibits an annual growth rate of approximately 40% these days. 
     Furthermore, the latest demonstration experiments have achieved a recording density exceeding 400 Gbits/inch 2 . If the development continues steadily, the recording density is expected to achieve 1 Tbits/inch 2  around 2012. However, it is considered that such a high recording density is not easy to achieve even by using perpendicular magnetic recording because the problem of thermal fluctuations becomes manifest again. 
     As a recording scheme possibly solving the above problem, the “high-frequency magnetic field assisted recording scheme” is proposed. In the high-frequency magnetic field assisted recording scheme, a high-frequency magnetic field near the resonance frequency of the magnetic recording medium, which is sufficiently higher than the recording signal frequency, is locally applied. This produces resonance in the magnetic recording medium, which decreases the coercivity (Hc) of the magnetic recording medium subjected to the high-frequency magnetic field to less than half the original coercivity. Thus, superposition of a high-frequency magnetic field on the recording magnetic field enables magnetic recording on a magnetic recording medium having higher coercivity (Hc) and higher magnetic anisotropy energy (Ku) (e.g., U.S. Pat. No. 6,011,664, hereinafter referred to as Patent Document 1). However, the technique disclosed in Patent Document 1 uses a coil to generate a high-frequency magnetic field, and it is difficult to efficiently apply a high-frequency magnetic field during high-density recording. 
     A technique based on a spin torque oscillator is proposed as a means for generating a high-frequency magnetic field (e.g., US Patent Application Publication No. 2005/0023938, hereinafter referred to as Patent Document 2). In the technique disclosed in Patent Document 2, the spin torque oscillator comprises an oscillation layer, an intermediate layer and a spin injection layer. It is proposed that injection of a polarized spin current from the spin injection layer to the oscillation layer produces high-frequency oscillation of a few tens of GHz band in the magnetization of the oscillation layer. Furthermore, it is reported that laminating a bias layer having a large perpendicular magnetic anisotropy on the oscillation layer made of FeCo alloy with Bs=2.5 T can produce high-frequency oscillation of a feq tens of GHz and generate a strong high-frequency magnetic field of 3 kOe (e.g., J. Zhu et al., TMRC2007, B8, hereinafter referred to as Non-Patent Document 1). 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, there is provided a magnetic recording head including: a main magnetic pole; and a laminated body including: a first magnetic layer, a second magnetic layer, a first intermediate layer provided between the first magnetic layer and the second magnetic layer, and a third magnetic layer laminated with the first and second magnetic layers and the first intermediate layer, the third magnetic layer exerting a magnetic field on at least any of the first magnetic layer and the second magnetic layer, the third magnetic layer having larger saturation magnetization than at least any of the first magnetic layer and the second magnetic layer. 
     According to still another aspect of the invention, there is provided a magnetic recording head including: a main magnetic pole; and a laminated body including a first magnetic layer, a second magnetic layer, a first intermediate layer provided between the first magnetic layer and the second magnetic layer, and a third magnetic layer and a fourth magnetic layer provided to sandwich the first magnetic layer and the second magnetic layer on both sides, the third magnetic layer and the fourth magnetic layer having larger saturation magnetization than at least any of the first magnetic layer and the second magnetic layer. 
     According to another aspect of the invention, there is provided a magnetic recording apparatus including: a magnetic recording medium; a magnetic recording head including: a main magnetic pole; and a laminated body including: a first magnetic layer, a second magnetic layer, a first intermediate layer provided between the first magnetic layer and the second magnetic layer, and a third magnetic layer laminated with the first and second magnetic layers and the first intermediate layer, the third magnetic layer exerting a magnetic field on at least any of the first magnetic layer and the second magnetic layer, the third magnetic layer having larger saturation magnetization than at least any of the first magnetic layer and the second magnetic layer; a moving mechanism configured to allow relative movement between the magnetic recording medium and the magnetic recording head which are opposed to each other with a spacing therebetween or in contact with each other; a controller configured to position the magnetic recording head at a prescribed recording position of the magnetic recording medium; and a signal processing unit configured to perform writing and reading of a signal on the magnetic recording medium by using the magnetic recording head. 
     According to still another aspect of the invention, there is provided a magnetic recording apparatus including: a magnetic recording medium; a magnetic recording head including: a main magnetic pole; and a laminated body including a first magnetic layer, a second magnetic layer, a first intermediate layer provided between the first magnetic layer and the second magnetic layer, and a third magnetic layer and a fourth magnetic layer provided to sandwich the first magnetic layer and the second magnetic layer on both sides, the third magnetic layer and the fourth magnetic layer having larger saturation magnetization than at least any of the first magnetic layer and the second magnetic layer; a moving mechanism configured to allow relative movement between the magnetic recording medium and the magnetic recording head which are opposite to each other with a spacing therebetween or in contact with each other; a controller configured to position the magnetic recording head at a prescribed recording position of the magnetic recording medium; and a signal processing unit configured to perform writing and reading of a signal on the magnetic recording medium by using the magnetic recording head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the schematic configuration of a magnetic recording head according to an embodiment of the invention; 
         FIG. 2  is a perspective view showing a head slider on which the magnetic recording head is mounted; 
         FIG. 3  is a perspective view showing the schematic configuration of a spin torque oscillator  11  provided in this magnetic recording head; 
         FIG. 4  is a schematic view illustrating the structure of a laminated body laminating an auxiliary bias layer  111  on the spin torque oscillator  11  shown in  FIG. 3 ; 
         FIG. 5  is a schematic view illustrating the structure of a laminated body laminating an auxiliary bias layer  117  on the spin torque oscillator  11  shown in  FIG. 3 ; 
         FIG. 6  is a perspective view showing the schematic configuration of the spin torque oscillator  11  according to this embodiment provided with a shield  62 ; 
         FIGS. 7A and 7B  are schematic views illustrating the structure of a laminated body of a spin torque oscillator according to a comparative example; 
         FIG. 8  is a schematic view illustrating the structure of a laminated body of a spin torque oscillator  11  according to a second embodiment of the invention; 
         FIG. 9  is a schematic view illustrating the structure of a laminated body of the spin torque oscillator  11  according to the second embodiment of the invention; 
         FIG. 10  is a schematic view illustrating the structure of a laminated body of a spin torque oscillator  11  according to a third embodiment of the invention; 
         FIG. 11  is a principal perspective view illustrating the schematic configuration of a magnetic recording/reproducing apparatus; 
         FIG. 12  is an enlarged perspective view of a magnetic head assembly ahead of an actuator arm  155  as viewed from the disk side; 
         FIG. 13  is a schematic view Illustrating a magnetic recording medium that can be used in this embodiment; and 
         FIG. 14  is another schematic view Illustrating a magnetic recording medium that can be used in this embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention will now be described with reference to the drawings. 
     A first embodiment of a microwave assisted magnetic head of the invention is described in the case of recording on a multiparticle medium for perpendicular magnetic recording. 
       FIG. 1  is a perspective view showing the schematic configuration of a magnetic recording head  5  according to the embodiment of the invention. 
       FIG. 2  is a perspective view showing a head slider on which the magnetic recording head  5  is mounted. 
     The magnetic recording head  5  of this embodiment comprises a reproducing head section  70  and a writing head section  60 . The reproducing head section  70  comprises a magnetic shield layer  72   a , a magnetic shield layer  72   b , and a magnetic reproducing device  71  provided between the magnetic shield layer  72   a  and the magnetic shield layer  72   b.    
     The writing head section  60  comprises a main magnetic pole  61 , a return path (shield)  62 , an excitation coil  63 , and a spin torque oscillator  11 . The components of the reproducing head section  70  and the components of the writing head section  60  are separated from each other by alumina or other insulators, not shown. The magnetic reproducing device  71  can be a GMR device or a TMR (tunnel magnetoresistive effect) device. In order to enhance reproducing resolution, the magnetic reproducing device  71  is placed between the two magnetic shield layers  72   a  and  72   b.    
     The magnetic recording head  5  is mounted on a head slider  3  as shown in  FIG. 2 . The head slider  3 , illustratively made of Al 2 O 3 /TiC, is designed and worked so that it can move relative to a magnetic recording medium  80  such as a magnetic disk while floating thereabove or being in contact therewith. The head slider  3  has an air inflow side  3 A and an air outflow side  3 B, and the magnetic recording head  5  is disposed illustratively on the side surface of the air outflow side  3 B. 
     The magnetic recording medium  80  has a medium substrate  82  and a magnetic recording layer  81  provided thereon. The magnetization of the magnetic recording layer  81  is controlled to a prescribed direction by the magnetic field applied by the writing head section  60 , and thereby writing is performed. The reproducing head section  70  reads the direction of magnetization of the magnetic recording layer  81 . 
       FIG. 3  is a perspective view showing the schematic configuration of the spin torque oscillator  11  provided in this magnetic recording head. 
     The main magnetic pole  61  and a recording track  83  in the magnetic recording medium  80  are illustratively shown. 
     The spin torque oscillator  11  has a structure in which a bias layer  112   a  (third magnetic layer), an intermediate layer  113   b  (second intermediate layer), an oscillation layer  114  (first magnetic layer), an intermediate layer  113   a  (first intermediate layer), an spin injection layer (second magnetic layer), an intermediate layer  113   c  and a bias layer  112   b  (fourth magnetic layer) are laminated in this order. The bias layers  112   a  and  112   b  can serve as electrodes. By passing a driving electron current through the spin torque oscillator  11  via the electrodes, a high-frequency magnetic field can be generated from the oscillation layer  114 . The driving current density is preferably from 5×10 7  A/cm 2  to 1×10 9  A/cm 2 , and suitably adjusted so as to achieve a desired oscillation. 
     While a case of providing both bias layers  112   a  and  112   b  is described, any one of them may be provided. When the bias layer  112   b  on the spin injection layer  116  side is only provided, the intermediate layer  113   c  between the spin injection layer  116  and the bias layer  112   b  can be omitted. 
     The oscillation layer  114  is made of material having weak magnetic anisotropy and the magnetic anisotropy energy is preferably Ku&lt;1×10 6  erg/cm 3 . A saturation magnetic flux density is preferably Bs&lt;2.0 T. Materials can be based on a CoFe alloy (Fe: 0˜30 at %), a CoFe (Fe: 0˜30 at %)/NiFe alloy laminated body or a NiFeCo alloy. Compared with a FeCo alloy having a high Fe concentration and high Bs, Bs is reduced and a high-frequency magnetic field strength per unit film thickness decreases, however, increasing a film thickness allows the whole high-frequency magnetic field strength to be set comparative to the case where a FeCo alloy is used, and the enough high-frequency magnetic field strength to be obtained. The film thickness of the oscillation layer  114  is preferably thick in terms of ensuring the high-frequency magnetic field strength, however, since a driving current necessary for the oscillation increases, there exist an optimum value. The product of Bs of the oscillation layer and the film thickness is preferably in the range of 10 nm·T to 40 nm·T. The thickness is preferably from 5 nm to 20 nm. 
     The spin injection layer  116  is made of material having strong perpendicular magnetic anisotropy and the magnetic anisotropy energy is preferably Ku&gt;1×10 6  erg/cm 3 . Materials can be based on laminated structure materials such as [Co(0.2˜2 nm)/Pd(0.2˜2 nm)]n/Co(0.2˜2 nm) or [Co(0.2˜2 nm)/Pd(0.2˜2 nm)]n/CoPt. A laminated number n is preferably from 1 to 9. The total film thickness is the order of 1˜40 nm. Furthermore, a CoFe alloy with a high Co concentration and a CoFe alloy containing Al, Si, Cr, Ge and Mn as additive elements are available. The saturation magnetization is reduced lower than that of the CoFe alloy and the spin polarizability increases. They are suitable for generating spin polarized electrons. 
     The intermediate layer  113   a  can be based on non-magnetic material having high spin permeability such as Cu. This enables spin torque oscillation characterstics to be maintained and exchange coupling between the oscillation layer  116  and the spin injection layer  114  to reduce. The thickness is preferably 0.2˜5 nm. 
     The saturation magnetic flux density Bs of the bias layers  112   a  and  112   b  is characteristically higher than the saturation magnetic flux density of the oscillation layer  114  and the spin injection layer  116 . Bs&gt;2.0 T is preferable. Materials can be based on a FeCo alloy (Fe: 30˜100 at %) with a bcc structure, Co/Pd artificial lattice with a hcp structure where a Co layer exists at the interface with the intermediate layer  113   b  or  113   c , a CoPt alloy with a hcp structure and Co with a hcp structure. The film thickness is preferably 115 nm. 
     The intermediate layer  113   b  is a layer for adjusting an exchange coupling magnetic field between the oscillation layer  114  and the bias layer  112   a , and the intermediate layer  113   c  is a layer for adjusting an exchange coupling magnetic field between the spin injection layer  116  and the bias layer  112   b . Both are preferably materials such as Ta which disturb spin polarized information and break spin torque transfer. Additionally, Nb, Ti, Cr, Zr, Hf, Ru, Rh, Pd can be used. When the magnetization in the oscillation layer oscillates in high-frequency in response to the spin torque transfer by electrons from the spin injection layer, placing the intermediate layer  113   b  is greatly effective for suppression of variation of the magnetization in the bias layer  112   a  due to the exchange coupling between the oscillation layer  114  and the bias layer  112   a . The intermediate layer  113   c  can be omitted, because the magnetization in the spin injection layer  116  is hard to move compared with the oscillation layer  114 . When the bias layer  112   a  of high Bs has enough magnetic stability, that is, magnetic anisotropy, the intermediate layer  113   b  can be also omitted. The exchange coupling magnetic field can be adjusted by the film thicknesses of the intermediate layers  113   b  and  113   c . The thickness is preferably 0.2˜2 nm. 
       FIGS. 4 and 5  are schematic views illustrating the structure of a laminated body of the spin torque oscillator  11  laminating an auxiliary bias layer  111  or  117  (fifth magnetic layer) on the spin torque oscillator  11  shown in  FIG. 3 . 
     The auxiliary bias layer  111  is further laminated on the bias layer  112   a  and the auxiliary bias layer  117  is further laminated on the bias layer  112   b.    
     The bias layers  111  and  117  characteristically have a higher magnetic anisotropy than the bias layers  112   a  and  112   b . Ku&gt;1×10 6  erg/cm 3  is preferable. 
     Materials can be based on a FePt alloy, a CoSm alloy and a CoPt alloy and the like. Moreover, a laminated film of [Co/Pd]n can be used. In this case, the film thickness of Co allows the magnetic anisotropy control. Furthermore, CoCrPtO oxide shaped like a fine particle can be used and allows high magnetic anisotropy to be obtained. The thickness is preferably 5˜40 nm. 
     A combination of the auxiliary bias layer  117  and the bias layer  112   a  or a combination of the auxiliary bias layer  111  and the bias layer  112   b  allows a bias layer having high saturation magnetization generating a high saturation magnetic flux density and having high magnetic anisotropic energy generating high coercivity to be obtained. This can add a high strength bias magnetic field which has not been realized by a conventional bias layer having small Bs to the oscillation layer  114  and suppress disturbance of the magnetization direction of the bias layer due to effects of the magnetic field from the main magnetic pole  61 . As a result, it becomes possible to achieve stable oscillation characteristics while holding the effective magnetic field applied to the oscillation layer  114  high. 
     Therefore, according to the embodiment of the invention, a high strength bias magnetic field applied to the oscillation layer  114  from the bias layer  112   a  with a high saturation magnetic flux density enables to generate a high-frequency magnetic field, allowing the magnetization of the bias layer to be stabilized by the auxiliary bias layer  111  having high magnetic anisotropy. As a result, it is possible to supply a magnetic recording head enabling stable high-frequency assisted magnetic recording. 
     In this embodiment, while description is made about the case where the auxiliary bias layer  111  is laminated to the bias layer  112   a  on the oscillation layer  114  side and the case where the auxiliary bias layer  117  is laminated to the bias layer  112   b  on the spin injection layer  116  side, respectively, both the auxiliary bias layers  111  and  117  may be laminated. 
     In the configuration described in  FIG. 3  to  FIG. 5 , the shield  62  shown in  FIG. 1  is not used. When the shield is not used, there is an advantage in reducing disturbance of an oscillation frequency by suppressing a magnetic field applied to the spin torque oscillator  11  from the main magnetic pole  61  to stabilize the magnetization of the bias layer. 
     On the other hand, providing the shield  62  taking in the magnetic field from the main magnetic pole  61  has an advantage in generating an oblique magnetic field to realize magnetization reversal more easily. 
       FIG. 6  is a perspective view showing the schematic configuration of the spin torque oscillator  11  according to this embodiment provided with the shield  62 . 
     It is possible to optimize the magnetic field applied to the spin torque oscillator  11  by adjusting a distance between the main magnetic pole  61  and the shield  62  and the shape of the main magnetic pole  61 . When the main magnetic pole  61  is far from the shield  62 , the magnetic field from the main magnetic pole is perpendicular in the medium, however, shortening the distance generates the oblique magnetic field to the perpendicular direction in the medium, allowing the magnetization reversal of the medium under a lower magnetic field to be realized more easily. 
     The spin torque oscillator  11  can be provided on either the trailing side or the leading side of the main magnetic pole  61 . This is because the medium magnetization is not reversed by the recording magnetic field of the main magnetic pole  61  alone, but is reversed only in the region where the high-frequency magnetic field of the spin torque oscillator  11  is superposed on the recording magnetic field of the main magnetic pole  61 . 
     In this embodiment, the shield  62  is placed on the leading side of the main magnetic pole  61 , and the spin torque oscillator  11  is placed between the main magnetic pole  61  and the shield  62 . The side surface of the main magnetic pole  61  and the shield  62  is perpendicular to the lamination direction of the spin torque oscillator  11 , and the spin injection layer  116  and the oscillation layer  114  are magnetized parallel to the lamination direction, i.e., in the direction from the main magnetic pole  61  to the shield  62  or in the opposite direction. 
     The laminated body of the spin torque oscillator  11  is illustratively laminated in the order of the auxiliary bias layer  111 , the bias layer  112   a , the intermediate layer  113   b , the oscillation layer  114 , the intermediate layer  113 , spin injection layer  116 , the bias layer  112   b  and the auxiliary layer  117  from the shield  62  side. 
     Providing the shield  62  on the opposite side of the main magnetic pole  61  to dispose the spin torque oscillator  11  between the main magnetic pole  61  and the shield  62  enables the magnetic field oblique from the perpendicular direction to the medium facing surface to superpose on the high-frequency magnetic field, allowing recording on the medium with high coercivity. 
       FIG. 7  are schematic views illustrating the structure of a laminated body of a spin torque oscillator  11  according to a comparative example. 
       FIG. 7A  shows lamination of the bias layer  112   a  and the oscillation layer  114 . The exchange coupling magnetic field with the bias layer  112   a  is added to the oscillation layer  114  to increase the effective magnetic field of the oscillation layer  114 , however, variation of the magnetization of the oscillation layer  114  by the spin torque from the spin injection layer  116  results in variation of the magnetization of the bias layer  112   a.    
     Furthermore, as shown in  FIG. 7B , if the intermediate layer  113   b  is inserted to weaken the coupling magnetic field so as not to vary the magnetization of the bias layer, the effective magnetic field applied to the oscillation layer  114  is reduced and the oscillation frequency is decreased, because conventionally a bias layer with preference to high Ku and sacrifice of Bs is used. 
     Next, a second embodiment of the invention will be described. 
       FIG. 8  and  FIG. 9  are schematic views illustrating the structure of a laminated body of a spin torque oscillator  11  according to the second embodiment of the invention. 
     In  FIG. 8 , film areas of the bias layers  112   a  and  112   b  are larger than that of the oscillation layer  114  or the spin injection layer  116 . 
     In  FIG. 9 , film areas of the auxiliary bias layers  111  and  117  are larger than that of the oscillation layer  114  or the spin injection layer  116 . 
     Only magnetic field generating part is made of high Bs material and the area of remaining part is broadened, thus it is possible to achieve a more stable oscillation characteristic. 
     As for the bias layer and the auxiliary bias layer, the case where a pair of them has a large film area is described, however, only one of them may have a large film area. 
     Next, a third embodiment of the invention will be described. 
       FIG. 10  is a schematic view illustrating the structure of a laminated body of a spin torque oscillator  11  according to the third embodiment of the invention. 
     The bias layers  112   a  and  112   b  characteristically serve as electrodes, and particularly have a shape being long in a direction with the distance from the medium facing surface. This realize the bias layers  112   a  and  112   b  serving as the electrodes more easily. Here, the auxiliary bias layers  111  and  117  may serve as the electrodes. Flowing a driving current with a prescribed value through the spin torque oscillator  11  via the bias layers  112   a  and  112   b  or the auxiliary bias layers  111  and  117  serving as the electrodes makes it possible to apply a high-frequency magnetic field with an enough strength to the recording medium  80  from the spin torque oscillator  11 , and it becomes possible to record onto the medium having high coercivity which is difficult to record without the high-frequency magnetic field by applying a recording magnetic field with the high-frequency magnetic field from the main magnetic pole  61  adjacent to the spin torque oscillator  11 . 
     Here, while description is made about the case where a pair of the bias layer and the auxiliary bias layer is provided, it does not always need to provide a pair of the bias layer and the auxiliary bias layer, for example, the bias layer  112   a  and the auxiliary bias layer  117  or the auxiliary bias layer  111  and the bias layer  112   b  may be provided and serve as a pair of electrodes. 
     Next, a magnetic recording apparatus according to an embodiment of the invention is described. More specifically, the magnetic recording head  5  of the invention described with reference to  FIGS. 1-6  and  8 - 10  is illustratively incorporated in an integrated recording-reproducing magnetic head assembly, which can be installed on a magnetic recording/reproducing apparatus. 
       FIG. 11  is a principal perspective view illustrating the schematic configuration of such a magnetic recording/reproducing apparatus. 
     More specifically, the magnetic recording/reproducing apparatus  150  of the invention is an apparatus based on a rotary actuator. In this figure, a recording medium disk  180  is mounted on a spindle  152  and rotated in the direction of arrow A by a motor, not shown, in response to a control signal from a drive controller, not shown. The magnetic recording/reproducing apparatus  150  of the invention may include a plurality of medium disks  180 . 
     A head slider  3  for recording/reproducing information stored on the medium disk  180  has a configuration as described above with reference to  FIG. 2  and is attached to the tip of a thin-film suspension  154 . Here, a magnetic recording head according to any one of the above embodiments is illustratively installed near the tip of the head slider  3 . 
     When the medium disk  180  is rotated, the air bearing surface (ABS)  100  of the head slider  3  is held at a prescribed floating amount from the surface of the medium disk  180 . Alternatively, it is also possible to use a slider of the so-called “contact-traveling type”, where the slider is in contact with the medium disk  180 . 
     The suspension  154  is connected to one end of an actuator arm  155  including a bobbin for holding a driving coil, not shown. A voice coil motor  156 , which is a kind of linear motor, is provided on the other end of the actuator arm  155 . The voice coil motor  156  is composed of the driving coil, not shown, wound up around the bobbin of the actuator arm  155  and a magnetic circuit including a permanent magnet and an opposed yoke disposed so as to sandwich the coil therebetween. 
     The actuator arm  155  is held by ball bearings, not shown, provided at two positions above and below the spindle  157 , and can be slidably rotated by the voice coil motor  156 . 
       FIG. 12  is an enlarged perspective view of the magnetic head assembly  160  ahead of the actuator arm  155  as viewed from the disk side. More specifically, the magnetic head assembly  160  has an actuator arm  155  illustratively including a bobbin for holding a driving coil, and a suspension  154  is connected to one end of the actuator arm  155 . 
     To the tip of the suspension  154  is attached a head slider  3  including any one of the magnetic recording heads  5  described above with reference to  FIGS. 1-6 ,  8 - 10 . The suspension  154  has a lead  164  for writing and reading signals. The lead  164  is electrically connected to each electrode of the magnetic head incorporated in the head slider  3 . In the figure, the reference numeral  165  denotes an electrode pad of the magnetic head assembly  160 . 
     According to the invention, by using the magnetic recording head as described above with reference to  FIGS. 1-6 ,  8 - 10 , it is possible to reliably record information on the perpendicular magnetic recording medium disk  180  with higher recording density than conventional. Here, for effective microwave assisted magnetic recording, preferably, the resonance frequency of the medium disk  180  to be used is nearly equal to the oscillation frequency of the spin torque oscillator  11 . 
       FIG. 13  is a schematic view illustrating a magnetic recording medium that can be used in this embodiment. 
     More specifically, the magnetic recording medium  1  of this embodiment includes perpendicularly oriented, multiparticle magnetic discrete tracks  86  separated from each other by a nonmagnetic material (or air)  87 . When this medium  1  is rotated by a spindle motor  4  and moved toward the medium moving direction  85 , a recording magnetization  84  can be produced by the magnetic recording head  5  described above with reference to  FIGS. 1-6 ,  8 - 10 . 
     By setting the width (TS) of the spin torque oscillator  11  in the width direction of the recording track to not less than the width (TW) of the recording track  86  and not more than the recording track pitch (TP), it is possible to significantly prevent the decrease of coercivity in adjacent recording tracks due to leaked high-frequency magnetic field from the spin torque oscillator  11 . Hence, in the magnetic recording medium  1  of this example, only the recording track  86  to be recorded can be effectively subjected to microwave assisted magnetic recording. 
     According to this embodiment, a microwave assisted magnetic recording apparatus with narrow tracks, i.e. high track density, is realized more easily than in the case of using a multiparticle perpendicular medium made of the so-called “blanket film”. Furthermore, by using the microwave assisted magnetic recording scheme and using a magnetic medium material with high magnetic anisotropy energy (Ku) such as FePt or SmCo, which cannot be written by conventional magnetic recording heads, magnetic medium particles can be further downscaled to the size of nanometers. Thus it is possible to realize a magnetic recording apparatus having far higher linear recording density than conventional also in the recording track direction (bit direction). 
       FIG. 14  is a schematic view illustrating another magnetic recording medium that can be used in this embodiment. 
     More specifically, the magnetic recording medium  1  of this example includes magnetic discrete bits  88  separated from each other by a nonmagnetic material  87 . When this medium  1  is rotated by a spindle motor  4  and moved toward the medium moving direction  85 , a recording magnetization  84  can be produced by the magnetic recording head  5  described above with reference to  FIGS. 1-6 ,  8 - 10 . 
     According to the invention, as shown in  FIGS. 13 and 14 , recording can be reliably performed also on the recording layer having high coercivity in a discrete-type magnetic recording medium  1 , allowing magnetic recording with high density and high speed. 
     Also in this example, by setting the width (TS) of the spin torque oscillator  11  in the width direction of the recording track to not less than the width (TW) of the recording track  86  and not more than the recording track pitch (TP), it is possible to significantly prevent the decrease of coercivity in adjacent recording tracks due to leaked high-frequency magnetic field from the spin torque oscillator  11 . Hence only the recording track  86  to be recorded can be effectively subjected to microwave assisted magnetic recording. According to this example, by downscaling the magnetic discrete bit  88  and increasing its magnetic anisotropy energy (Ku), there is a possibility of realizing a microwave assisted magnetic recording apparatus having a recording density of 10 Tbits/inch 2  or more as long as thermal fluctuation resistance under the operating environment can be maintained. 
     The embodiments of the invention have been described with reference to the examples. However, the invention is not limited to the above examples. For instance, two or more of the examples described above with reference to  FIGS. 1-6  and  8 - 14  can be combined as long as technically feasible, and such combinations are also encompassed within the scope of the invention. 
     That is, the invention is not limited to the examples, but can be practiced in various modifications without departing from the spirit of the invention, and such modifications are all encompassed within the scope of the invention.