Abstract:
A magnetic recording and reproducing apparatus with a thin-film magnetic head having microwave magnetic exciting function, includes a metal housing, a magnetic recording medium, arranged in the metal housing, having a magnetic recording layer, and a thin-film magnetic head, arranged in the metal housing, having a write magnetic field production unit and a resonance magnetic field production unit. The write magnetic field production unit produces, in response to a write signal, a write magnetic field to be applied into the magnetic recording layer, and the resonance magnetic field production unit produces, in response to a microwave excitation signal, a resonance magnetic field with a frequency equal to or in a range near a ferromagnetic resonance frequency F R  of a the magnetic recording layer. The apparatus further includes a write signal generation unit, arranged in the metal housing, for generating the write signal, a microwave signal generation unit, arranged in the metal housing, for generating the microwave excitation signal, a transmission unit, arranged in the metal housing, for feeding the microwave excitation signal generated by the microwave signal generation unit to the resonance magnetic field production unit in the thin-film magnetic head and for feeding the write signal generated by the write signal generation unit to the write magnetic field production unit in the thin-film magnetic head, and a plurality of metal ribs, arranged in the metal housing, for forming a plurality of cavities, each of the plurality of cavities having a rectangular horizontal section shape and having dimensions to produce no resonance at a frequency of the microwave excitation signal.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority from Japanese patent application No. 2008-136607, filed on May 26, 2008, which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a magnetic recording and reproducing apparatus with a thin-film magnetic head having microwave magnetic exciting function for recording data signal onto a magnetic recording medium that has a large doercivity for thermally stabilizing the magnetization. 
         [0004]    2. Description of the Related Art 
         [0005]    With the demand for higher recording density of a magnetic recording and reproducing apparatus such as a magnetic disk drive apparatus, each bit cell in a magnetic recording medium for recording digital information has been miniaturized and, as a result, a signal detected by a read head element in the thin-film magnetic head sways due to such as thermal fluctuation. This causes deterioration in a signal-to-noise ratio (S/N), and in the worst case, the signal detected by the read head element may disappear. 
         [0006]    It is effective for a magnetic recording medium adopted for the perpendicular magnetic recording scheme that is recently put to practical use to increase perpendicular magnetic anisotropy energy Ku of a magnetic recording layer in this recording medium. On the other hand, a thermal stabilization factor S that corresponds to the thermal fluctuation is represented by the following equation (1) and is necessary to have in general 50 or more: 
         [0000]        S=Ku·V/K   B   ·T    (1) 
         [0000]    where Ku is perpendicular magnetic anisotropy energy, V is a volume of crystal grains that form the recording layer, k B  is the Boltzmann constant, and T is an absolute temperature. 
         [0007]    According to the so-called Stoner-Wohlfarth model, an anisotropy magnetic field Hk and a coercivity Hc of the recording layer is represented as the following equation (2): 
         [0000]        Hk=Hc= 2 Ku/Ms    (2) 
         [0000]    where Ms is a saturated magnetization of the recording layer. 
         [0008]    The coercivity Hc increase with the increase in the perpendicular magnetic anisotropy energy Ku. In a normal recording layer, however, Hk is higher than Hc. 
         [0009]    In order to perform desired inversion of magnetization in the magnetic recording layer in response to data sequence to be written, a write head element of the thin-film magnetic head is required to apply a recording magnetic field having a precipitous rising edge and a level up to about the anisotropy magnetic field Hk of the recording layer. In a hard disk drive (HDD) apparatus adopting the perpendicular magnetic recording scheme, a write head element with a single pole is used so that a recording magnetic field is applied perpendicular to the recording layer from an air-bearing surface (ABS) of the element. Since an intensity of this perpendicular recording magnetic field is proportional to a saturated magnetic flux density Bs of the soft magnetic material that forms the single pole, a material with a saturated magnetic flux density Bs as high as possible is developed and is put into practical use for the single pole. However, the saturated magnetic flux density Bs has the practical upper limit of Bs=2.4 T (tesla) from a so-called Slater-Pauling curve, and a recent value of the saturated magnetic flux density Bs of soft magnetic material closes to this practical upper limit. Also, in order to increase the recording density, the thickness and width of the single pole have to decrease from the present thickness and width of about 100-200 nm causing the perpendicular magnetic field produced from the single pole to more lower. 
         [0010]    As aforementioned, due to the limit of recording ability of the write head element, high-density recording becomes difficult now. To overcome such problems, suggested is so-called thermal assisted magnetic recording (TAMR) scheme for recording a magnetic signal on a recording layer of the magnetic recording medium under conditions where the recording layer is irradiated by a laser beam for example to increase the temperature and to lower the coercivity Hc of the magnetic recording layer. 
         [0011]    Japanese patent publication No. 2001-250201 discloses a TAMR technique in which electrons are radiated to a magnetic recording medium from an electron radiation source to heat a recording part in the magnetic recording medium so that the coercivity Hc is lowered and thus it is possible to record magnetic information on the medium using a magnetic write head. 
         [0012]    U.S. Pat. No. 7,133,230 B2 discloses another TAMR technique in which a laser beam from a semiconductor laser element formed in a perpendicular magnetic recording head is irradiated to a scattering member or near-field light probe formed in contact with a main pole of the head so as to produce a near-field light, and the produced near-field light is applied to the magnetic recording medium to heat it and rise the temperature. 
         [0013]    However, there are various difficulties and problems in these TAMR techniques. For example, (1) a structure of the thin-film magnetic head becomes extremely complicated and its manufacturing cost becomes expensive because the head has to have both a magnetic element and an optical element, (2) it is required to develop a magnetic recording layer with a coercivity Hc of high temperature-dependency, (3) adjacent track erase or unstable recording state may occur due to thermal demagnetization during the recording process. 
         [0014]    Recently, in order to increase sensitivity of a giant magnetoresistive effect (GMR) read head element or a tunnel magnetoresistive effect (TMR) read head element, study of spin transfer in electron conductivity is made active. 
         [0015]    US patent publication No. 2007/0253106 A1 and J. Zhu, “Recording Well Below Medium Coercivity Assisted by Localized Microwave Utilizing Spin Transfer”, Digest of MMM, 2005 disclose application of this spin transfer technique to the inversion of magnetization in a recording layer of a magnetic recording medium so as to reduce a perpendicular magnetic field necessary for the magnetization inversion. 
         [0016]    According to this scheme, an alternating magnetic field of high frequency is applied to the magnetic recording medium in a direction parallel to its surface together with the perpendicular recording magnetic field. The frequency of the alternating in-plane magnetic field applied to the magnetic recording medium is an extremely high frequency in the microwave frequency band such as several GHz to 10 GHz, which corresponds to a ferromagnetic resonance frequency of the recording layer. It is reported that, as a result of simultaneous application of the alternating in-plane magnetic field and the perpendicular recording magnetic field to the magnetic recording medium, a perpendicular magnetic field necessary for the magnetization inversion can be reduced to about 60% of the anisotropy magnetic field Hk of the recording layer. If this scheme is put in practical use, it is possible to increase the anisotropy magnetic field Hk of the recording layer and thus it is expected to greatly improve the magnetic recording density without utilizing the complicated TAMR system. 
         [0017]    However, according to this magnetically assisted magnetic recording scheme wherein the alternating in-plane magnetic field and the perpendicular recording magnetic field are simultaneously applied to the magnetic recording medium, since a microwave frequency band signal or microwave excitation signal of several GHz to 10 GHz is transmitted to a thin-film magnetic head, microwave excitation energy may be radiated in a housing of the magnetic disk drive apparatus from the thin-film magnetic head or from the transmission line of the microwave signal, and may be propagated there through. 
         [0018]    If the microwave excitation energy is radiated in the housing of the magnetic disk drive apparatus from the thin-film magnetic head or from its transmission line, a standing wave with peaks and valleys may occur in the housing. Due to the peaks and valleys of the standing wave, it is impossible to keep the electrical potential on the magnetic recording medium constant. Also, if a frequency resonance occurs at a part of the housing depending upon the dimension of space, partial absorption of energy may occur causing the microwave excitation energy to become unstable. 
       SUMMARY OF THE INVENTION 
       [0019]    It is therefore an object of the present invention to provide a magnetic recording and reproducing apparatus with a thin-film magnetic head having microwave magnetic exciting function, whereby a standing wave can be prevented from occurring in a housing of the apparatus and absorption of energy of a microwave excitation signal can be reduced. 
         [0020]    Another object of the present invention is to provide a magnetic recording and reproducing apparatus with a thin-film magnetic head having microwave magnetic exciting function, whereby a data signal can be precisely written onto a magnetic recording medium having a large coercivity without heating the medium. 
         [0021]    According to the present invention, a magnetic recording and reproducing apparatus with a thin-film magnetic head having microwave magnetic exciting function, includes a metal housing, a magnetic recording medium, arranged in the metal housing, having a magnetic recording layer, and a thin-film magnetic head, arranged in the metal housing, having a write magnetic field production unit and a resonance magnetic field production unit. The write magnetic field production unit produces, in response to a write signal, a write magnetic field to be applied into the magnetic recording layer, and the resonance magnetic field production unit produces, in response to a microwave excitation signal, a resonance magnetic field with a frequency equal to or in a range near a ferromagnetic resonance frequency F R  of a the magnetic recording layer. The apparatus further includes a write signal generation unit, arranged in the metal housing, for generating the write signal, a microwave signal generation unit, arranged in the metal housing, for generating the microwave excitation signal, a transmission unit, arranged in the metal housing, for feeding the microwave excitation signal generated by the microwave signal generation unit to the resonance magnetic field production unit in the thin-film magnetic head and for feeding the write signal generated by the write signal generation unit to the write magnetic field production unit in the thin-film magnetic head, and a plurality of metal ribs, arranged in the metal housing, for forming a plurality of cavities, each of the plurality of cavities having a rectangular horizontal section shape and having dimensions to produce no resonance at a frequency of the microwave excitation signal. 
         [0022]    Since the metal ribs are formed in the metal housing, transmission of microwave energy in the housing can be suppressed to some extent. Particularly, according to the present invention, the metal ribs form a plurality of cavities each having a rectangular horizontal section shape and having dimensions to produce no resonance at a frequency of the microwave excitation signal. Thus, it is possible to prevent absorption of energy of the microwave excitation signal due to the resonance. Of course, according to the present invention, a data signal can be precisely written onto a magnetic disk with a large coercivity without performing heating. 
         [0023]    It is preferred that a length of a longer side of each of the plurality of cavities is shorter than a length corresponding to a half wavelength of the microwave excitation signal. Because a resonance point in the cavity moves away from the resonance frequency of the microwave excitation signal, energy absorption due to the resonance can be greatly reduced. 
         [0024]    It is also preferred that a distance between a top end of each of the plurality of metal ribs and an inner wall surface of the metal housing, to which the top end faces, is shorter than a length corresponding to a half wavelength of the microwave excitation signal. Since a resonance point between the metal rib and the inner wall surface of the metal housing moves away from the resonance frequency of the microwave excitation signal, energy absorption due to the resonance can be greatly reduced. 
         [0025]    It is further preferred that the apparatus further includes a wave absorber attached on at least part of an inner wall surface of the metal housing, for absorbing the microwave excitation signal. The microwave does not always transmit at the lowest mode but may transmit at a higher mode. Thus, it is effective to attach a wave absorber onto a rear surface of the cover of the metal housing and onto inner wall surfaces or side surfaces of the metal housing. 
         [0026]    It is still further preferred that the thin-film magnetic head has a substrate having a recording medium facing surface and an element formed surface, and an inductive write head element formed on the element formed surface of the substrate. The inductive write head element includes a main pole for producing, when writing, a write magnetic field from its top end at a side of the recording medium facing surface, an auxiliary pole magnetically connected to the main pole at a portion discrete from its top end at a side of the recording medium facing surface, and a coil unit formed to pass through at least between the main pole and the auxiliary pole, the coil unit functioning as the write magnetic field production unit and the resonance magnetic field production unit. 
         [0027]    It is further preferred that the write magnetic field is applied to the magnetic recording layer of the magnetic recording medium in a direction substantially perpendicular to a layer plane of the magnetic recording layer, and that the resonance magnetic field runs through the magnetic recording layer in a direction substantially parallel to the layer plane of the magnetic recording layer. 
         [0028]    It is still further preferred that the thin-film magnetic head has a substrate having a recording medium facing surface and an element formed surface, and an MR read head element formed on the element formed surface of the substrate. The MR effect read head element includes a lower shield layer, an upper shield layer, and a GMR multilayer or a TMR multilayer formed between the lower shield layer and the upper shield layer. 
         [0029]    Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a perspective view schematically illustrating a partially omitted main part of a magnetic disk drive apparatus as an embodiment of a magnetic recording and reproducing apparatus according to the present invention; 
           [0031]      FIGS. 2   a  and  2   b  are a plane view and a side sectional view schematically illustrating a main part of the magnetic disk drive apparatus shown in  FIG. 1 ; 
           [0032]      FIG. 3  is a sectional view schematically illustrating a part of a head gimbal assembly (HGA) in the magnetic disk drive apparatus shown in  FIGS. 1 ,  2   a  and  2   b;    
           [0033]      FIG. 4  is a perspective view schematically illustrating the whole of a thin-film magnetic head in the embodiment of  FIGS. 1 ,  2   a  and  2   b;    
           [0034]      FIG. 5  is a perspective view illustrating the structure of a write coil in the thin-film magnetic head shown in  FIG. 4 ; 
           [0035]      FIG. 6  is an A-A sectional view of  FIG. 4  schematically illustrating the whole of the thin-film magnetic head in the embodiment of  FIGS. 1 ,  2   a  and  2   b;    
           [0036]      FIG. 7  is a sectional view illustrating the principle of a magnetic recording scheme according to the present invention and a head model in the embodiment of  FIGS. 1 ,  2   a  and  2   b;    
           [0037]      FIG. 8  is a block diagram schematically illustrating an electrical configuration of the magnetic disk drive apparatus in the embodiment of  FIGS. 1 ,  2   a  and  2   b;    
           [0038]      FIG. 9  is a graph illustrating a frequency versus intensity of resonance in a metal housing with no metal rib as the conventional art; and 
           [0039]      FIG. 10  is a graph illustrating a frequency versus intensity of resonance in a metal housing with metal ribs as the embodiment of  FIGS. 1 ,  2   a  and  2   b.    
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    Hereinafter, an embodiment according to the present invention will be described with reference to these appended drawings. In these drawings, the similar elements are indicated by using the same reference symbols, respectively. Also, in the drawings, dimensions in each element and between the elements are optional for easy understanding of the configuration. 
         [0041]      FIG. 1  schematically illustrates a partially omitted main part of a magnetic disk drive apparatus as an embodiment of a magnetic recording and reproducing apparatus according to the present invention,  FIGS. 2   a  and  2   b  schematically illustrate a main part of the magnetic disk drive apparatus shown in  FIG. 1 , and  FIG. 3  schematically illustrates a part of an HGA in the magnetic disk drive apparatus shown in  FIGS. 1 ,  2   a  and  2   b.    
         [0042]    In  FIGS. 1 ,  2   a  and  2   b,  which represent the magnetic disk drive apparatus as the embodiment of a magnetic recording apparatus, reference numeral  10  denotes a metal housing that accommodates the magnetic disk drive apparatus,  11  denotes a magnetic disk driven by a spindle motor  12  to rotate about a rotation shaft,  13  denotes a drive arm for supporting a thin-film magnetic head or magnetic head slider  14  to appropriately face a surface of the magnetic disk  11  so that the head  14  performs write and read operations of a data signal to and from the magnetic disk  11 , and  15  denotes a carriage device for positioning the thin-film magnetic head  14  on a track of the magnetic disk  11 , respectively. The carriage device  15  has a voice coil motor (VCM, not shown) for driving the drive arm  13  to swing about a pivot-bearing axis  16 . The drive arm  13  has the HGA  17  shown in  FIG. 3  at one end section thereof. At a top end section of the HGA  17 , the thin-film magnetic head  14  is mounted. 
         [0043]    As shown in  FIGS. 1 ,  2   a  and  2   b,  in an empty space within the metal housing  10 , a plurality of metal ribs  18  are formed. Structure of these metal ribs  18  will be described later in detail. 
         [0044]    As shown in  FIG. 3 , the HGA  17  has the thin-film magnetic head  14 , a load beam  30  and a flexure  31  both made of a metal conductive material for supporting the thin-film magnetic head  14 , and a write head element wiring member  32  that is a transmission line for feeding a write signal applied to a write head element of the thin-film magnetic head  14  and a microwave excitation signal there through. Although it is not shown, the HGA  17  also has a read head element wiring member for feeding a constant current to a read head element to pull out a read output voltage there from. 
         [0045]    The thin-film magnetic head  14 is attached to one end section of the resilient flexure  31 . The other end section of the flexure  31  is attached to the load beam  30 . The flexure  31  and the load beam  30  constitute a suspension for supporting the thin-film magnetic head  14 . 
         [0046]    The most part of the write head element-wiring member  32  is configured by a strip line with upper and lower ground planes. As shown in  FIG. 3 , the strip line is composed of the load beam  30  that constitutes the lower ground plane, the upper ground plane  32   a,  a central conductor  32   d  made of for example copper (Cu) sandwiched between the upper and lower ground planes  32   a  and  30 , and dielectric layers  32   b  and  32   c  made of a dielectric material such as for example polyimide for supporting the central conductor  32   d  between the upper and lower ground planes  32   a  and  30 . The write head element-wiring member  32  has a pair of the strip lines arranged in plane and in parallel to each other. Magnetic head side ends of the strip lines are in this embodiment connected to terminal electrodes of the write head element by wire-bonding using wires  33 . Although it is not shown, the read head element wiring member is configured by normal lead conductors and magnetic head side ends of the lead conductors are in this embodiment connected to terminal electrodes of the read head element also by wire-bonding. In modifications, these wiring members may be connected with the terminal electrodes by ball bonding not by wire bonding. 
         [0047]      FIG. 4  schematically illustrates the whole of the thin-film magnetic head in the embodiment of  FIGS. 1 ,  2   a  and  2   b,  and  FIG. 5  illustrates the structure of a write coil in this thin-film magnetic head. 
         [0048]    As shown in  FIG. 4 , the thin-film magnetic head  14  has a slider substrate  40  with an ABS  40   a  machined to obtain an appropriate flaying height, a magnetic head element  41  formed on an element formed surface  40   b  that is one side surface when the ABS  40   a  is defined as the bottom surface and perpendicular to this ABS  40   a,  a coating layer  42  formed on the element formed surface  40   b  for covering the magnetic head element  41 , and four terminal electrodes  43 ,  44 ,  45  and  46  exposed from a surface of the coating layer  42 . 
         [0049]    The magnetic head element  41  is constituted from an MR read head element  41   a  for reading a data signal from the magnetic disk, and an inductive write head element  41   b  for writing the data signal onto the magnetic disk. The terminal electrodes  43  and  44  are electrically connected to the MR read head element  41   a,  and the terminal electrodes  45  and  46  are electrically connected to the inductive write head element  41   b.  The positions of these terminal electrodes  43 ,  44 ,  45  and  46  are not limited to those shown in  FIG. 4 . Namely, these terminal electrodes  43 ,  44 ,  45  and  46  can be set at any positions on the element formed surface  40   b  and with any arrangement. Further, these terminal electrodes  43 ,  44 ,  45  and  46  may be formed on a slider-end face  40   c  facing opposite direction as the ABS  40   a.    
         [0050]    One ends of the MR read head element  41   a  and the inductive write head element  41   b  come at a slider-end face  40   d  facing the same direction as the ABS  40   a.  This slider-end face  40   d  is mainly configured by a surface of the coating layer  42  facing to the same direction as the ABS  40   a  but excluded the ABS  40   a  of the slider substrate  40  itself. Namely, the slider-end face  40   d  is a part of the medium facing surface of the thin-film magnetic head  14  other than the ABS  40   a.  By facing the one ends of the MR read head element  41   a  and the inductive write head element  41   b  to the magnetic disk, reading of data signal owing to receiving of signal magnetic field and writing of data signal owing to application of signal magnetic field are performed. The one end or near the ones end of each element come to the slider-end face  40   d  may be covered for protection by an extremely thin coating film of diamond like carbon (DLC) for example. 
         [0051]    As shown in  FIG. 5 , the inductive write head element  41   b  has a main pole layer  50  for outputting write magnetic field from its end edge at the side of the ABS  40   a  or the slider-end face  40   d  when writing the data signal, an auxiliary pole layer  51  magnetically connected to the main pole layer  50  at a position discrete from its end edge at the side of the ABS  40   a  or the slider-end face  40   d,  and a write coil  52  formed to have a scroll shape so that at least one turn thereof passes through between the main pole layer  50  and the auxiliary pole layer  51 . 
         [0052]    The whole of this write coil  52  is in this embodiment a shared coil used for producing both a write magnetic field and a resonance magnetic field. By feeding a write current from the terminal electrodes  45  and  46  to the write coil  52  through lead layers  53  and  54 , a magnetic flux of the write magnetic field is produced in a magnetic circuit formed by the main pole layer  50  and the auxiliary pole layer  51 . Also, by feeding a microwave excitation signal through the write coil  51 , a resonance magnetic field that is a high frequency magnetic field of a microwave frequency band with a frequency equal to or in a range near a ferromagnetic resonance frequency F R  of the recording layer of the magnetic disk. 
         [0053]    According to this embodiment, since the write coil  52  is the shared coil used for producing both the write magnetic field and the resonance magnetic field, the structure of the write head element can be simplified and interference of the drive currents can be extremely reduced from occurring in comparison with where a dedicated coil for producing a write magnetic field and a dedicated coil for producing a resonance magnetic field are separately formed. Furthermore, since both the coil for producing the write magnetic field and the coil for producing the resonance magnetic field themselves can be positioned close to the trailing gap, an efficiency of producing the write magnetic field and the resonance magnetic field can be improved. 
         [0054]    In modifications, only a part of the coil for producing the write magnetic field and the coil for producing the resonance magnetic field may be shared, or the coil for producing the write magnetic field and the coil for producing the resonance magnetic field may be completely separated. 
         [0055]      FIG. 6 , which is an A-A sectional view of  FIG. 4 , schematically illustrates the whole of the thin-film magnetic head  14  in this embodiment. 
         [0056]    In the figure, reference numeral  40  denotes the slider substrate made of Al—TiC (Al 2 O 3 —TiC) for example and provided with the ABS  40   a  facing to in operation the surface of the magnetic disk. On the element formed surface  40   b  of the slider substrate  40 , the MR read head element  41   a,  the inductive write head element  41   b  and the coating layer  42  for protecting these elements are mainly formed. 
         [0057]    The MR read head element  41   a  has an MR multilayer  41   a   1 , and a lower shield layer  41   a   2  and an upper shield layer  41   a   3  formed to sandwich the multilayer  41   a   1 . The MR multilayer  41   a   1  consists of a current in plane (CIP) type GMR multilayer, a current perpendicular to plane (CPP) type GMR multilayer or a TMR multilayer, to receive signal magnetic field from the magnetic disk with extremely high sensitivity. The lower shield layer  41   a   2  and the upper shield layer  41   a   3  prevent the MR multilayer  41   a   1  from being affected by external magnetic field or noise. 
         [0058]    In case that the MR multilayer  41   a   1  is a CIP-GMR multilayer, a lower shield gap layer for insulation is formed between the lower shield layer  41   a   2  and the MR multilayer  41   a   1 , and an upper shield gap layer for insulation is formed between the MR multilayer  41   a   1  and the upper shield layer  41   a   3 . Further, MR lead conductive layers for feeding a sense current to and extracting a reproduction output from the MR multilayer  41   a   1  are formed. In case that the MR multilayer  41   a   1  is a CPP-GMR multilayer or the TMR multilayer, the lower shield layer  41   a   2  and the upper shield layer  41   a   3  also operate as a lower electrode layer and an upper electrode layer, respectively. No lower shield gap layer, no upper shield gap layer and no MR lead conductive layer are necessary. Although it is not shown in the figure, insulation layers or bias insulation layers and hard bias layers for applying a longitudinal bias magnetic field to provide stability in the magnetic domain are formed on both sides in the track-width direction of the MR multilayer  41   a   1 . 
         [0059]    The MR multilayer  41   a   1 , in case of the TMR multilayer, has for example a multi-layered structure of sequentially stacking an anti-ferromagnetic layer, a pinned layer, a tunnel barrier layer and a free layer. The anti-ferromagnetic layer is made of for example iridium manganese (IrMn), platinum manganese (PtMn), nickel manganese (NiMn) or ruthenium rhodium manganese (RuRhMn) and has a thickness of about 5-15 nm. The pinned layer whose magnetization direction is fixed by the anti-ferromagnetic layer has three-layered films of two ferromagnetic films made of cobalt iron (CoFe) for example and a nonmagnetic metal film made of ruthenium (Ru) for example sandwiched by the two ferromagnetic films. The tunnel barrier layer consists of an oxidized nonmagnetic dielectric layer formed by oxidizing using oxygen introduced into a vacuum chamber or naturally oxidizing a metal film made of aluminum (Al), aluminum copper (AlCu) or magnesium (Mg) for example with a thickness of about 0.5-1 nm. The free layer has two-layered films of a ferromagnetic film made of CoFe for example with a thickness of about 1 nm and a ferromagnetic film made of nickel iron or permalloy (NiFe) for example with a thickness of about 3-4 nm and is tunneling-exchange coupled with the pinned layer through the tunnel barrier layer. 
         [0060]    Each of the lower shield layer  41   a   2  and the upper shield layer  41   a   3  is formed using a pattern-plating method such as a frame-plating method from NiFe, cobalt iron nickel (CoFeNi), CoFe, iron nitride (FeN) or iron zirconium nitride (FeZrN) for example with a thickness of about 0.3-3 μm. 
         [0061]    The inductive write head element  41   b  is a perpendicular magnetic recording type and has the main pole layer  41   b   1  ( 50 ), a trailing gap layer  41   b   2 , the write coil  41   b   3  ( 52 ), a write coil insulation layer  41   b   4 , the auxiliary pole layer  41   b   5  ( 51 ), an auxiliary shield layer  41   b   6  and a leading gap layer  41   b   7 . 
         [0062]    The main pole layer  41   b   1  consists of a main pole yoke layer  41   b   1 , and a main pole major layer  41   b   12  and constitutes a magnetic conduit for guiding a magnetic flux, which is produced by feeding a write current to the write coil  41   b   3 , while making convergence to a magnetic recording layer in the magnetic disk. A thickness of the main pole layer  41   b   1  at its end of the ABS  40   a  side or the slider-end face  40   d  side corresponds to the thickness of only the main pole major layer  41   b   12  and thus it is thin. Therefore, when writing data signal, it is possible to produce a fine write magnetic field from this end of the main pole layer  41   b   1  to satisfy a high recording density. The main pole yoke layer  41   b   11  and the main pole major layer  41   b   12  are formed using a sputtering method, or a pattern-plating method such as a frame-plating method from NiFe, CoFeNi, CoFe, FeN or FeZrN for example with a thickness of about 0.5-3.5 μm and a thickness of about 0.1-1 μm, respectively. 
         [0063]    The write insulation layer  41   b   4  envelops the write coil  41   b   3  to electrically insulate the write coil  41   b   3  from surrounding magnetic layers. The write coil  41   b   3  ( 50 ), and the lead layers  53  and  54  ( FIG. 5 ) are formed using a frame plating method or a sputtering method from Cu for example with a thickness of about 0.1-5 μm. The write insulation layer  41   b   4  is formed by using a photolithography method and by thermally curing a photoresist for example to have a thickness of about 0.5-7 μm. 
         [0064]    The auxiliary pole layer  41   b   5  and the auxiliary shield layer  41   b   6  are arranged at the trailing side and the leading side of the main pole layer  41   b   1 , respectively. The auxiliary pole layer  41   b   5  is magnetically connected to the main pole layer  41   b   1  at a portion discrete from its end edge at the side of the ABS  40   a  or the slider-end face  40   d  as aforementioned. Whereas the auxiliary shield layer  41   b   6  is not magnetically connected to the main pole layer  41   b   1  in this embodiment. 
         [0065]    An end section at the slider-end face  40   d  side of the auxiliary pole layer  41   b   5  constitutes a trailing shield section  41   b   51  with a wider or thicker sectional area than other section of the auxiliary pole layer  41   b   5 . This trailing shield section  41   b   51  faces the end section at the slider-end face  40   d  side of the main pole layer  41   b   1  through the trailing gap layer  41   b   2 . An end section at the side of the slider-end face  40   d  of the auxiliary shield layer  41   b   6  constitutes a leading shield section  41   b   61  with a wider or thicker sectional area than other section of the auxiliary shield layer  41   b   6 . This leading shield section  41   b   61  faces the end section at the slider-end face  40   d  side of the main pole layer  41   b   1  through the leading gap layer  41   b   7 . Thanks for such trailing shield section  41   b   51  and leading shield section  41   b   61 , the shunt effect occurs in the magnetic flux and thus a gradient of the write magnetic field between the trailing shield section  41   b   51  and the end section of the main pole layer  41   b   1  and between the leading shield section  41   b   61  and the end section of the main pole layer  41   b   1  becomes more steep. As a result, jitter in the signal output becomes smaller and an error rate in reading operation can be reduced. 
         [0066]    It is desired that thicknesses or lengths in the layer-thickness direction of the trailing shield section  41   b   51  and the leading shield section  41   b   61  are determined as about several tens to several hundreds times thicker than that of the main pole layer  42   b   1 . A gap length of the trailing gap layer  41   b   2  is preferably about 10-100 nm, more preferably about 20-50 nm. Also, gap length of the leading gap layer  41   b   7  is preferably about 0.1 μm or more. 
         [0067]    Each of the auxiliary pole layer  41   b   5  and the auxiliary shield layer  41   b   6  is formed using a pattern-plating method such as a frame-plating method from NiFe, CoFeNi, CoFe, FeN or FeZrN for example with a thickness of about 0.5-4 μm. Each of the trailing gap layer  41   b   2  and the leading gap layer  41   b   7  is formed using a sputtering method or a chemical vapor deposition (CVD) method from alumina (Al 2 O 3 ), silicon oxide (SiO 2 ), aluminum nitride (AlN) or DLC for example with a thickness of about 0.1-3 μm. 
         [0068]    According to this embodiment, not only a write signal but also a microwave excitation signal is applied to the write coil  41   b   3  so as to produce a resonance magnetic field along a track direction, that is a track direction in-plane or substantially in-plane of the surface of the magnetic disk, between the end section of the main pole layer  41   b   1  and the trailing shield section  41   b   51 . This resonance magnetic field is a high frequency magnetic field in a microwave frequency band with a frequency equal to or in a range near a ferromagnetic resonance frequency F R  of the magnetic recording layer of the magnetic disk. Because such resonance magnetic field along the track direction is applied to the magnetic recording layer when writing, an intensity of a write magnetic field in a perpendicular direction, that is a direction perpendicular to or substantially perpendicular to the layer surface of the magnetic recording layer), necessary for writing can be extremely reduced. 
         [0069]    The thin-film magnetic head according to the present invention is not limited to the aforementioned structure but it is apparent that various structures can optionally adopted for the thin-film magnetic head. 
         [0070]      FIG. 7  illustrates the principle of the magnetic recording scheme according to the present invention and a head model in the embodiment of  FIGS. 1 ,  2   a  and  2   b.    
         [0071]    First, with reference to this figure, the structure of the magnetic disk  11  is described. This magnetic disk  11  is a perpendicular magnetic recording type and has a multi-layered structure sequentially stacking, on a disk substrate  11   a,  a magnetization orienting layer  11   b,  a soft magnetic backing layer  11   c  that functions as a part of a magnetic flux loop path, an intermediate layer  11   d,  a magnetic recording layer  11   e  and a protection layer  11   f.  The magnetization orienting layer  11   b  provides a magnetic anisotropy in the track-width direction to the soft magnetic backing layer  11   c  so that the magnetic domain structure in the soft magnetic backing layer  11   c  is stabilized and a spiky noise on the reproduced output is suppressed. The intermediate layer  11   d  contributes as an under layer for controlling orientation of magnetization and a particle diameter in the magnetic recording layer  11   e.    
         [0072]    The disk substrate  11   a  is made of glass, Al alloy coated by nickel phosphorus (NiP) or silicon (Si) for example. The magnetization orienting layer  11   b  is made of an anti-ferromagnetic material such as PtMn for example. The soft magnetic backing layer  11   c  is formed from a single layer of a soft magnetic material such as cobalt (Co) family amorphous alloy represented by cobalt zirconium niobium (CoZrNb), iron (Fe) alloy or soft magnetic ferrite for example, or from a multilayer of soft magnetic film/nonmagnetic film. The intermediate layer  11   d  is made of a nonmagnetic material such as Ru alloy for example. However, this intermediate layer  11   d  may be made of other nonmagnetic metal material or alloy, or low permeability alloy if it is possible to control the perpendicular magnetic anisotropy in the magnetic recording layer  11   e.  The protection layer  11   f  is formed using a CVD method from carbon (C) for example. 
         [0073]    The magnetic recording layer  11   e  is made of cobalt chrome platinum (CoCrPt) family alloy, CoCrPt—SiO 2 , iron platinum (FePt) family alloy or artificial lattice multilayer of CoPt/palladium (Pd) family for example. It is desired that the perpendicular magnetic anisotropy in this magnetic recording layer  11   e  is adjusted to for example 1×10 6  erg/cc (0.1 J/m 3 ) or more to restrain thermal fluctuation in magnetization. In this case, the coercivity of the magnetic recording layer  11   e  becomes about 5 kOe (400 kA/m) or more for example. 
         [0074]    The ferromagnetic resonance frequency F R  of this magnetic recording layer  11   e  is an inherent value determined depending upon a shape and size of particles and constituent elements of this magnetic recording layer  11   e,  and is about 1-15 GHz. This ferromagnetic resonance frequency F R  may exist only one, or more than one in case of spin wave resonance. 
         [0075]    Hereinafter, the principle of the magnetic recording scheme according to the present invention will be described with reference to  FIG. 7 . 
         [0076]    Magnetic flux  70  corresponding to the resonance magnetic field produce by feeding of a microwave excitation signal to the write coil  41   b   3  ( 50 ) is a high frequency flux in the microwave frequency band. Thus, most of the magnetic flux  70  distributes, owing to skin effect, within an area from the trailing side surface of the main pole layer  41   b   1  to the leading side surface of the trailing shield section  41   b   51  through the magnetic recording layer  11   e.  For example, when the frequency is about 10 GHz, a penetrated depth of the magnetic flux  70  into the main pole layer  41   b   1  and the trailing shield section  41   b   51  from their surfaces is about 50 nm. Therefore, the resonance magnetic field does not have a large intensity in the layers deeper or nearer to the disk substrate  11   a  than the magnetic recording layer  11   e,  and in the magnetic recording layer  11   e,  a component of the resonance magnetic field, parallel to the plane of this layer mainly passes. 
         [0077]    Magnetization in the magnetic recording layer  11   e  orients to a direction perpendicular to or substantially perpendicular to its layer plane. When a resonance magnetic field in a direction parallel to the layer plane, which corresponds to the magnetic flux  70 , is applied to the magnetic recording layer  11   e,  by determining a frequency of the resonance magnetic field equal to or in a range near the ferromagnetic resonance frequency F R  of this magnetic recording layer  11   e,  the perpendicular write magnetic field corresponding to the magnetic flux  71  necessary for performing writing can be extremely reduced. The above-mentioned range within which the reduction effect of the write magnetic field can be expected is about ±0.5 GHz with respect to the ferromagnetic resonance frequency F R  of the magnetic recording layer  11   e.    
         [0078]    In fact, by applying a resonance magnetic field with the ferromagnetic resonance frequency F R  of the magnetic recording layer  11   e,  it is possible to reduce the perpendicular write magnetic field that can inverse the magnetization in the magnetic recording layer  11   e  by about 40%, that is, to about 60% of the original perpendicular write magnetic field. In other words, in case that the coercivity of the magnetic recording layer  11   e  before applying the resonance magnetic field is about 5 kOe (400 kA/m), if a resonance magnetic field in a direction of in-plane of the magnetic recording layer  11   e,  with the ferromagnetic resonance frequency F R  of this magnetic recording layer  11   e,  the effective coercivity can be reduced to about 2.4 kOe (192 kA/m). 
         [0079]    The intensity of the resonance magnetic field is preferably in a range of about 0.1-0.2 Hk, where Hk is an anisotropy magnetic field of the magnetic recording layer, and the frequency of the resonance magnetic field is preferably in a range of about 1-15 GHz. 
         [0080]    According to the aforementioned magnetic recording scheme, a data signal can be precisely written onto a magnetic disk with a large coercivity without performing so-called thermal assisting or heating. Since such magnetic recording can be realized without adding any special high burden element such as an electron emitting source or a laser light source to the thin-film magnetic head, a downsized and low-cost thin-film magnetic head can be provided. Particularly, in this embodiment, because no additional write coil for applying the microwave excitation signal is necessary, further downsizing and lowering of the manufacturing cost of the thin-film magnetic head can be expected. 
         [0081]      FIG. 8  schematically illustrates an electrical configuration of the magnetic disk drive apparatus in this embodiment. 
         [0082]    In the figure, reference numeral  12  denotes the spindle motor for driving the magnetic disk to rotate about the rotation shaft,  80  denotes a motor driver for the spindle motor  12 ,  81  denotes a VCM driver fro the VCM  82 ,  83  denotes a hard disk controller (HDC) for controlling the motor driver  80  and the VCM driver  82  in accordance with instructions from a computer  84 ,  85  denotes a read/ write circuit including a head amplifier  85   a  for the thin-film magnetic head  14  and a read/write channel  85   b,    86  denotes a microwave signal supply circuit fro providing a microwave excitation signal, and  87  denotes a coupling circuit inserted in the transmission line or the write head element wiring member  32  to the write head element of the thin-film magnetic head  14 , respectively. 
         [0083]    Hereinafter, the metal ribs  18  and wave absorbers  20  formed in the metal housing  10  will be described in detail. 
         [0084]    As shown in  FIGS. 1 ,  2   a  and  2   b,  the metal ribs  18  formed in the housing  10  run in a longitudinal or lengthwise direction and in a lateral or crosswise direction of the magnetic disk drive apparatus to form many cavities  19  each having a rectangular shape in its horizontal section in the metal housing  10 . A length b ( FIG. 2   a ) of the longer side or the longitudinal direction of each cavity  19  is determined less than a length corresponding to a half wavelength of the microwave excitation signal for ferromagnetic resonance. That is, each cavity  19  formed by the metal ribs  18  is set that both its longer side length b and its shorter side length a ( FIG. 2   a ) are shorter than a length corresponding to a half wavelength of the microwave excitation signal for ferromagnetic resonance. Thus, since no resonance occurs at the frequency of the microwave excitation signal, it is possible to prevent absorption of the microwave excitation signal. 
         [0085]    Also, according to this embodiment, as shown  FIG. 2   b,  a distance h between a top end of each metal rib  18  and an inner wall surface of a cover member  10   a  of the metal housing  10  is determined less than a length corresponding to a half wavelength of the microwave excitation signal for ferromagnetic resonance. Thus, since no resonance occurs at the frequency of the microwave excitation signal in this direction, it is also possible to prevent absorption of the microwave excitation signal. 
         [0086]    Furthermore, according to this embodiment, as also shown  FIG. 2   b,  the wave absorbers  20  are attached on the inner wall surface of the cover member  10   a  of the metal housing  10 , and on inner wall surfaces of four side walls including side walls  10  and  10   c.  The wave absorber  20  is a composite ferrite absorption member made of a synthetic rubber containing ferrite powder mixed. Such member is for example commercially available thin radio-wave absorber manufactured by TDK Corporation (IR-K series, IR-E series or IJ series). By using such wave absorber  20 , it becomes possible to prevent transmission of even a higher mode of microwave. 
         [0087]    As aforementioned, according to this embodiment, dimension of each cavity  19  formed by the metal ribs  18  is determined that a length of any side of the cavity  19  is shorter than a length corresponding to a half wavelength of the microwave excitation signal so that no resonance occurs at the frequency of the microwave excitation signal, it is possible to prevent absorption of energy of the microwave excitation signal due to the resonance. Of course, according to this embodiment, a data signal can be precisely written onto a magnetic disk with a large coercivity without performing heating. 
         [0088]    Also, according to this embodiment, since the distance h between the top end of each metal rib  18  and the inner wall surface of the cover member  10   a  of the metal housing  10  is determined shorter than a length corresponding to a half wavelength of the microwave excitation signal, a resonance point between the metal rib  18  and the inner wall surface of the metal housing  10  moves away from the resonance frequency of the microwave excitation signal. Thus, energy absorption due to the resonance can be greatly reduced. 
         [0089]      FIG. 9  illustrates a frequency versus intensity of resonance in the metal housing with no metal rib as the conventional art, and  FIG. 10  illustrates a frequency versus intensity of resonance in the metal housing with the metal ribs as this embodiment of  FIGS. 1 ,  2   a  and  2   b.    
         [0090]    As will be apparent by comparing these drawings, in case that the cavities  19  are formed by the metal ribs  18  as this embodiment, resonances are decreased over the frequency range of 1-10 GHz. Particularly, according to this embodiment, resonance is extremely suppressed in the frequency range of 1-2 GHz. Therefore, it is understood that, by adding the metal ribs  18  as this embodiment, energy absorption due to the resonance can be extremely reduced. 
         [0091]    Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.