Patent Publication Number: US-2016225392-A1

Title: Recording head, magnetic recording device comprising recording head and method of manufacturing recording head

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of applicatoin Ser. No. 14/800,295, filed Jul. 15, 2015 and is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-017165, filed Jan. 30, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a recording head comprising a high-frequency oscillator, a magnetic recording device using the recording head, and a method of manufacturing the recording head. 
     BACKGROUND 
     As a disk device, for example, a magnetic disk device comprises a magnetic disk provided in a case, a spindle motor which supports and rotates the magnetic disk, and a magnetic head which reads/writes data with respect to the magnetic disk. 
     A microwave-assisted recording magnetic head has recently been suggested. In this magnetic head, to improve the recording density, a spin-torque oscillator is provided as a microwave oscillator near the main magnetic pole of the magnetic head. By the spin-torque oscillator, a high-frequency magnetic field (microwave) is applied to the magnetic recording layer of the magnetic disk. The microwave-assisted recording has an advantage in its capability to record data on a recording medium having a high magnetic anisotropy compared to the conventional technique if the spin-torque oscillator radiates sufficiently strong microwaves. However, the microwave-assisted recording has an issue in which the characteristics of the spin-torque oscillator occasionally become uneven. For stable mass-production, the quality of the spin-torque oscillator needs to be improved. 
     The spin-torque oscillator is formed of a magnetic material. Therefore, when the spin-torque oscillator does not sufficiently oscillate due to oscillation trouble or characteristic reduction, this spin-torque oscillator absorbs the recording magnetic field in the recording gap. As a result, in this type of recording head, the recording magnetic field applied to the recording medium is reduced compared to a normal recording head which does not comprise a spin-torque oscillator; in a normal recording head, the recording gap is an air gap which does not include a magnetic material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically showing a magnetic disk drive (HDD) according to a first embodiment; 
         FIG. 2  is a side view showing a magnetic head, a suspension and a recording medium in the HDD; 
         FIG. 3  is a schematic cross-sectional view in which a head portion of the magnetic head and a magnetic disk are partially enlarged; 
         FIG. 4  is a cross-sectional view in which a distal end portion of a recording head and a spin-torque oscillator (STO) are enlarged; 
         FIG. 5  is a plan view when the distal end portion of the recording head is viewed from an ABS side; 
         FIG. 6  is a diagram showing comparison of recording magnetic fields of (a) a magnetic head when an STO oscillates, (b) a magnetic head which comprises an STO when the STO does not oscillate, and (c) a magnetic head which does not comprise an STO; 
         FIG. 7  a diagram showing comparison of signal-to-noise ratios of signals recorded in a magnetic recording medium by the magnetic heads (a), (b) and (c) described above; 
         FIG. 8  is a flowchart showing an operation for inspecting and destroying the STO by an inspection circuit of the HDD; 
         FIG. 9  a diagram showing the relationship between driving current applied to the STO and resistance of the STO; 
         FIG. 10  is a cross-sectional view showing the STO which is physically and magnetically destroyed and the distal end portion of the recording head; 
         FIG. 11  is a plan view when the STO which is physically and magnetically destroyed and the distal end portion of the recording head are viewed from the ABS side; 
         FIG. 12  is a plan view schematically showing a head wafer in which many magnetic heads are formed according to a second embodiment; 
         FIG. 13  is a plan view in which a bar-shaped piece cut from the head wafer is enlarged; 
         FIG. 14  a diagram showing the relationship between the resistance of a spin-torque oscillator and magnetic field characteristics; 
         FIG. 15A ,  FIG. 15B  and  FIG. 15C  are cross-sectional views schematically showing a process for forming a magnetic head and an STO, a process for disintegrating and destroying the STO and a process for forming an ABS; and 
         FIG. 16  is a perspective view showing the magnetic head manufactured by a manufacturing method according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment, a recording head comprises a recording magnetic pole which applies a recording magnetic field, a write shield which faces the recording magnetic pole across a recording gap, and a spin-torque oscillator portion provided in the recording gap between the recording magnetic pole and the write shield, wherein the spin-torque oscillator portion is physically and/or magnetically destroyed and has resistance greater than or equal to a predetermined value. 
     First Embodiment 
       FIG. 1  is a block diagram schematically showing a hard disk drive (HDD) as a disk device according to a first embodiment.  FIG. 2  is a side view showing a magnetic head in a flying state and a magnetic disk. 
     As shown in  FIG. 1 , an HDD  10  comprises a rectangular housing  11 , a magnetic disk  12  as a recording medium provided in the housing  11 , a spindle motor  14  which supports and rotates the magnetic disk  12 , and a plurality of magnetic heads  16  which write and read data with respect to the magnetic disk  12 . 
     The HDD  10  further comprises a head actuator  18  which moves the magnetic heads  16  onto an arbitrary track of the magnetic disk  12  and determines the position of the magnetic heads  16 . The head actuator  18  includes a suspension assembly  20  which movably supports the magnetic heads  16 , and a voice coil motor (VCM)  22  which rotates the suspension assembly  20 . 
     The HDD  10  comprises a head amplifier IC  30  and a main controller  40 . The head amplifier IC  30  is provided in, for example, the suspension assembly  20 , and is electrically connected to the magnetic heads  16 . The main controller  40  is constructed on, for example, a control circuit substrate (not shown) provided on the back surface of the housing  11 . The main controller  40  comprises an R/W channel  42 , a hard disk controller (HDC)  44 , a microprocessor (MPU)  46 , an inspection circuit  48  which inspects recording and reading characteristics of the magnetic heads  16 , and a driver IC  50 . The main controller  40  is electrically connected to the magnetic heads  16  via the head amplifier IC  30 . The main controller  40  is electrically connected to the VCM  22  and the spindle motor  14  via the driver IC  50 . The HDD  10  is connectable to a host computer  51 . 
     As shown in  FIG. 1  and  FIG. 2 , the magnetic disk  12  is structured as a perpendicular magnetic recording medium. For example, the magnetic disk  12  comprises a substrate  101  which is formed of a nonmagnetic material in the shape of a circular plate having a diameter of approximately 2.5 inches (6.35 cm). On each surface of the substrate  101 , a soft magnetic layer  102  is formed as an underlayer. On the soft magnetic layer  102 , a magnetic recording layer  103  and a protective film  104  are stacked in series. The magnetic disk  12  concentrically fits in the hub of the spindle motor  14 . The magnetic disk  12  is rotated in the direction of an arrow B at a predetermined speed by the spindle motor  14 . 
     The suspension assembly  20  comprises a bearing  24  which is rotatably attached to the housing  11 , and a plurality of suspensions  26  which extend from the bearing  24 . As shown in  FIG. 2 , the magnetic head  16  is supported by the extended end of each suspension  26 . The magnetic head  16  is electrically connected to the head amplifier IC  30  via an interconnection member  28  provided on the suspension  26 . 
     Now, the specification explains the structure of the magnetic head  16  in detail.  FIG. 3  is an enlarged sectional view of the head portion of the magnetic head and the magnetic disk.  FIG. 4  is an enlarged cross-sectional view showing the distal end portion of the recording head and the magnetic disk.  FIG. 5  is a plan view of the distal end portion of the recording head viewed from the air bearing surface (ABS) side. 
     As shown in  FIG. 2  and  FIG. 3 , the magnetic head  16  is structured as a flying head, and comprises a slider  15  formed in the shape of a substantially rectangular parallelepiped, and a head portion  17  formed in the end portion on the outflow end (trailing) side of the slider  15 . For example, the slider  15  is formed of a sintered alumina-titanium carbide body (AlTiC). The head portion  17  is formed by a plurality of thin films of layers. 
     The slider  15  comprises a disk-facing surface (a medium-facing surface or an air bearing surface [ABS])  13 . The disk-facing surface  13  is rectangular and faces the surface of the magnetic disk  12 . The slider  15  is maintained in a state where the slider  15  is floated with a predetermined amount from the magnetic disk surface by an aerial flow C generated between the disk surface and the ABS  13  by rotation of the magnetic disk  12 . The direction of the aerial flow C conforms to the rotation direction B of the magnetic disk  12 . The slider  15  comprises a reading end  15   a  positioned on the inflow side of the aerial flow C, and a trailing end  15   b  positioned on the outflow side of the aerial flow C. 
     As shown in  FIG. 3 , the head portion  17  comprises a reproduction head  54  formed by a thin-film process and a recording head  58  in the trailing end  15   b  of the slider  15 . The head portion  17  is formed as a separation type of magnetic head. The head portion  17  comprises a spin-torque oscillator (STO)  65  as a microwave oscillator. 
     The reproduction head  54  comprises a magnetic film  55  having a magnetoresistive effect, and shield films  56  and  57  allocated on the trailing and reading sides of the magnetic film  55  so as to sandwich the magnetic film  55 . The lower ends of the magnetic film  55  and the shield films  56  and  57  are exposed on the ABS  13  of the slider  15 . 
     The recording head  58  is provided on the trailing end  15   b  side of the slider  15  relative to the reproduction head  54 . The recording head  58  comprises a main magnetic pole (recording magnetic pole)  60 , a write shield (trailing shield)  62  provided on the trailing side of the main magnetic pole  60  across a write gap WG, a connection portion  67  is a magnetic material, a recording coil  70 , and a high-frequency oscillator such as the spin-torque oscillator  65 . The main magnetic pole  60  is formed of a soft magnetic material having a high magnetic permeability and a high saturation magnetic flux density, and generates a recording magnetic field in a direction perpendicular to the surface (recording layer) of the magnetic disk  12 . The write shield  62  is formed of a soft magnetic material, and is provided to efficiently close a flux path via the soft magnetic layer  102  positioned immediately under the main magnetic pole. An electronic insulating layer  61  is provided in the connection portion  67  connecting the main magnetic pole  60  and the write shield  62 . The main magnetic pole  60  is electrically insulated from the write shield  62 . The STO  65  is provided in a portion facing the ABS  13  between a distal end portion  60   a  of the main magnetic pole  60  and the write shield  62  and applies a high-frequency magnetic field (microwave) to the recording layer of the magnetic disk  12 . 
     The recording coil  70  is provided so as to wind around a magnetic circuit (core) including the main magnetic pole  60  and the write shield  62 . In the present embodiment, for example, the recording coil  70  winds around the connection portion  67  between the main magnetic pole  60  and the write shield  62 . The recoding coil  70  is connected to a write current terminal  64  provided in the trailing end  15   b  of the slider  15 . The write current terminals  64  are connected to the head amplifier IC  30  via interconnections. When data is written to the magnetic disk  12 , recoding current is supplied to the recording coil  70 . The recording coil  70  excites the main magnetic pole  60  and supplies a magnetic flux to the main magnetic pole  60 . The recording current supplied to the recording coil  70  is controlled by the head amplifier IC  30  and the main controller  40 . 
     As shown in  FIG. 3 ,  FIG. 4  and  FIG. 5 , the main magnetic pole  60  extends substantially perpendicularly to the surface of the magnetic disk  12 . The distal end portion  60   a  of the main magnetic pole  60  on the ABS  13  side tapers toward the disk surface. The distal end portion  60   a  of the main magnetic pole  60  has, for example, a trapezoidal cross-sectional surface. The distal end surface of the main magnetic pole  60  is exposed on the ABS  13  of the slider  15 . The width of a trailing-side end surface  60   b  of the distal end portion  60   a  substantially corresponds to the width of the track of the magnetic disk  12 . 
     The write shield  62  is formed in a substantially L-shape. Its distal end portion  62   a  is formed in the shape of a slender rectangle. The distal end surface of the write shield magnetic pole  62  is exposed on the ABS  13  of the slider  15 . The distal end portion  62   a  of the write shield  62  comprises a leading-side end surface (magnetic pole end surface)  62   b  facing the distal end portion  60   a  of the main magnetic pole  60 . The leading-side end surface  62   b  is sufficiently longer than the width of the distal end portion  60   a  of the main magnetic pole  60  and the track width of the magnetic disk  12  and extends along the track width of the magnetic disk  12 . On the ABS  13 , the leading-side end surface  62   b  faces the trailing-side end surface  60   b  of the main magnetic pole  60  in parallel across the write gap WG. 
     The spin-torque oscillator (STO)  65  is provided between the distal end portion  60   a  of the main magnetic pole  60  and the leading-side end surface  62   b  of the write shield  62  near the ABS  13 . The STO  65  is allocated in the write gap WG. In the present embodiment, the STO  65  is structured by stacking an underlayer (conductive metal layer)  66   a,  a spin injection layer (SIL) (second magnetic layer)  65   a,  an intermediate layer (conductive metal layer)  66   b,  an Field Generating layer (FGL: Oscillation layer) (first magnetic layer)  65   b  and a cap layer (conductive metal layer)  66   c  in order from the main magnetic pole  60  side to the write shield  62  side. This stacking order can be reversed. 
     The width of the STO  65  (in other words, the width in the track width direction) is substantially equal to or slightly less than that of the distal end portion  60   a  of the main magnetic pole  60 . The STO  65  aligns relative to the main magnetic pole so as to face the whole distal end portion  60   a  of the main magnetic pole. 
     The underlayer  66   a  is formed by a monolayer film or a laminated film containing a conductive material such as Ta and Cu. The spin injection layer  65   a  is formed by alloy or a laminated film containing Co, Pt and the like, or a laminated film containing Fe, Co, Ni and the like. The intermediate layer  66   b  contains a conductive material such as Cu. The oscillation layer  65   b  is formed by alloy or a laminated film containing Fe, Co, Ni and the like. The cap layer  66   c  is formed by a monolayer or a laminated film containing Ta, Ru and the like. 
     The underlayer  66   a  is joined to the trailing-side end surface  60   b  of the main magnetic pole  60  and is electrically connected to the main magnetic pole  60 . The cap layer  66   c  is joined to the reading-side end surface  62   b  of the write shield and is electrically connected to the write shield  62 . The write shield  62  and the main magnetic pole  60  also function as an electrode for perpendicular conduction to the spin-torque oscillator  65 . 
     The main magnetic pole  60  and the write shield  62  are electrically connected to the respective electrode terminals  63  provided in the trailing end  15   b  of the slider  15 . These electrode terminals  63  are connected to the head amplifier IC  30  via interconnections. In this manner, a current circuit is structured so as to distribute STO driving current from the head amplifier IC  30  to the main magnetic pole  60 , the STO  65  and the write shield  62  in series. The power distribution to the STO  65  is controlled by the head amplifier IC  30  and the main controller  40 . 
     As shown in  FIG. 3 , the reproduction head  54  and the recording head  58  are covered by an insulating material  76  except for the portion exposed on the ABS  13  of the slider  15 . The insulating material  76  forms the outer shape of the head portion  17 . 
     As shown in  FIG. 1 , the head amplifier IC  30  driving the magnetic head  16  having the above structure comprises a recording current supply circuit  32  which supplies recording current to the recording coil  70  via the interconnection member  28  and the write current terminal  64 , an STO current supply circuit  31  which supplies driving current to the STO  65  via the interconnection member  28  and the electrode terminal  63 , and a recording current waveform generator  34  which generates a recording current waveform in accordance with a recording pattern signal generated in the R/W channel  42 . 
     When the HDD  10  is operated, the main controller  40  drives the spindle motor  14  by the driver IC  50  under control of the MPU  46  and rotates the magnetic disk  12  at a predetermined speed. The main controller  40  drives the VCM  22  by the driver IC  50 , moves the magnetic head  16  onto a desired track of the magnetic disk  12  and determines the position of the magnetic head  16 . 
     At the time of recording, the recording current supply circuit  32  of the head amplifier IC  30  distributes recording current to the recording coil  70  in accordance with the recording signal and recording pattern generated by the R/W channel  42 . In this manner, the recording coil  70  excites the main magnetic pole  60  and generates a recording magnetic field from the main magnetic pole  60 . 
     The STO current supply circuit  31  distributes driving current in series through the interconnection member  28 , the electrode terminal  63 , the main magnetic pole  60 , the STO  65  and the write shield  62  by applying voltage to the main magnetic pole  60  and the write shield  62  under control of the MPU  46 . In short, the STO current supply circuit  31  distributes current in the direction of the film thickness of the STO  65 . By this distribution, the magnetization of the oscillation layer  65   b  of the STO  65  is rotated. Thus, a high-frequency magnetic field (microwave) can be generated. The STO  65  applies a high-frequency magnetic field to the magnetic recording layer  103  of the magnetic disk  12  and reduces the coercive force of the magnetic recording layer  103 . In this state, the recording magnetic field is applied to the magnetic recording layer  103  from the recording head  58 , and desired data is written to the magnetic recording layer  103 . In this manner, the recording head  58  can record data in a recording medium which has a high magnetic anisotropy. 
       FIG. 6  shows comparison of effective recording magnetic field distributions (magnetic field strengths) in positions in the direction of the track width of a magnetic disk with respect to (a) a recording head when an STO oscillates, (b) a recording head which comprises an STO when the STO does not oscillate and (c) a recording head which does not comprise an STO in a recording gap.  FIG. 7  shows comparison of signal-to-noise ratios of signals recorded in a magnetic recording medium by the recording heads (a), (b) and (c). Only spin-torque oscillators showing good oscillation are selected for experiment. 
     As shown in  FIG. 6  and  FIG. 7 , in the recording head (a) in which the STO oscillates at a high frequency, the magnetic permeability around the STO is substantially the same as the air gap (recording gap) relative to the recording magnetic field response. Thus, the recording magnetic field is not decreased in the recording medium. The recording head (a) shows the best signal-to-noise ratio. 
     In the recording heads (b) and (c) which do not have STO oscillation assist, the effective magnetic field strength is decreased more than that in the recording head (a). Between the recording heads (b) and (c), the signal-to-noise ratio of recorded signals is different. The signal-to-noise ratio of the recording head (c) is higher than that of the recording head (b). 
     The STO is formed of a magnetic material. Therefore, in the case of the recording head (b) in which the STO does not oscillate, the STO absorbs the recording magnetic field in the recording gap. In this manner, the recording magnetic field applied to the recording medium is more decreased in the recording head (b) than in the normal recording head (c) which does not include a magnetic material in the recording gap. 
     When a recording head showing a high signal-to-noise ratio is used in combination with a recording medium in a magnetic recording device, the magnetic recording device can realize a large recording capacity and have high reliability. Now, this specification assumes a case where STO oscillation characteristics are not uniform and some STOs are defective and do not oscillate in the actual product. In a recording head in which the STO does not oscillate, the magnetic recording characteristics are reduced compared to a recording head in which the STO oscillates. However, for example, if the recording capacity of the recording medium is relaxed, the recording head in which the STO does not oscillate can be used. In this case, decrease in the recording performance should be preferably minimized. 
     As shown in  FIG. 7 , the signal-to-noise ratio indicated as (b) can be obtained by a recording head in which the STO does not oscillate. The performance of a group of these recording heads is preferably increased to (c). Specifically, it is possible to obtain the characteristics of the recording head (c) which does not comprise an STO by losing the magnetic portion of the STO when the recording head is manufactured or after the recording head is mounted on the HDD. 
     In the present embodiment, the HDD  10  comprises the inspection circuit  48  which inspects the oscillation characteristics of the STO  65 . When or after the HDD is shipped, the inspection circuit  48  inspects the oscillation characteristics of the STO  65  at intervals of certain periods of use. Specifically, in the inspection, the oscillation characteristics may be determined by monitoring the resistance of the STO  65  or monitoring the resistance-change frequency (which is equivalent to the oscillation frequency). Alternatively, the oscillation characteristics may be inspected by monitoring change in the error rate when data is recorded and reproduced and determining whether or not the error rate is within a desired range of data error rate. In the former case, a circuit resistance detector or a frequency detector can be provided as the inspection circuit. In the latter case, the normal R/W channel  42  can be also used as the inspection circuit. If a defective STO  65  is detected through the inspection of oscillation characteristics, excessive current is applied to the STO  65  by using the STO current supply circuit  32 , thereby physically and/or magnetically destroying the STO  65 . 
     In the present embodiment, the oscillation characteristics of the STO  65 , here, the recording and reproduction characteristics of the magnetic head  16 , are inspected regardless of whether the STO  65  is good or defective before the HDD is shipped after the magnetic head  16  is mounted on the HDD. As shown in  FIG. 8 , the inspection circuit  48  of the HDD  10  applies a predetermined driving current (bias current) D to the STO  65  via the head amplifier IC  30  in order to oscillate the STO  65  (S 1 ). In this state, the inspection circuit  48  writes inspection data A to the magnetic disk  12  by using the recording head  58  (S 2 ). The inspection circuit  48  reads the written inspection data by using the magnetic head  16  and detects recording and reproduction characteristics A 1  (S 3 ). In this case, the R/W channel  42  is employed to detect the recording and reproduction characteristics. 
     Subsequently, the inspection circuit  48  writes inspection data A to the magnetic disk  12  by using the recording head  58  in a state where driving current is not applied to the STO  65  (S 4 ). The inspection circuit  48  reads the written inspection data by using the magnetic head  16  and detects recording and reproduction characteristics A 2  (S 5 ). The inspection circuit  48  compares the detected recording and reproduction characteristics A 1  and A 2  (S 6 ). If the recording and reproduction characteristics A 1  and A 2  differ greatly, the inspection circuit  48  determines that the STO  65  is a good product which normally oscillates at a high frequency. The inspection circuit  48  terminates the inspection. 
     If the difference between the recording and reproduction characteristics A 1  and A 2  is very little, the inspection circuit  48  determines that the STO  65  is defective (in oscillation) with respect to the magnetic head  16 . In other words, the inspection circuit  48  determines that the STO  65  does not normally oscillate at a high frequency. In this case, the inspection circuit  48  applies driving current excessively larger than the predetermined driving current D to the recording head  58  comprising the defective STO. For example, as shown in  FIG. 9 , the element resistance of the STO  65  is steadily and reversibly increased by the Joule heat generated by application of driving current. When driving current is further increased, the resistance of the STO  65  is unsteadily changed and never returns to the previous state because the STO  65  which is a microscopic element having a diameter of several tens of nanometers is disintegrated and destroyed by the Joule heat generated by driving current. For example, the resistance of the STO  65  is 25 to 65 Q before destruction. After disintegration and destruction, the resistance of the STO  65  is increased to more than the initial value; to 100 Q to infinity. 
       FIG. 10  and  FIG. 11  show the recording head  58  around the STO after disintegration and destruction. The magnetic layers and the conductive metal layers constituting the STO  65  are disintegrated and mixed. The laminated structure of the STO is destroyed and is changed to a mixed structure. In this manner, the STO  65  is physically and magnetically destroyed by disintegrating and mixing the plurality of layers of the STO  65 . By disintegrating and mixing the magnetic layers and the conductive metal layers, the STO  65  is changed to a metal mixture having a weak magnetization of 100 emu/cc or less. The resistance of the STO  65  is changed to 100 Q or greater and thus, is higher than the resistance before disintegration and destruction. 
     As shown in  FIG. 8 , the inspection circuit  48  detects resistance R 1  of the STO  65  (S 8 ) and determines whether or not resistance R 1  after application of excessive current is greater than the predetermined resistance R 2  (S 9 ). The inspection circuit  48  increases the driving current applied to the STO  65  until R 1 &gt;R 2 . When the detected resistance R 1  is greater than the predetermined resistance R 2 , the inspection circuit  48  determines that the STO  65  has been disintegrated and destroyed, stops applying driving current to the STO  65  and terminates the inspection. 
     By the disintegration with excessive driving current, the STO is physically and magnetically destroyed and lost. In this manner, the recording magnetic field strength of the recording head  58  can be recovered to a value substantially equal to that of a recording head which does not comprise an STO. When the destroying and losing process of the present embodiment was applied to a magnetic head which had been determined as having a detective STO in oscillation, the average recording capacity of the HDD was improved by approximately 10% compared to before the application of the process. 
     When the STO  65  is disintegrated and destroyed as described above, the recording capacity of the magnetic disk  12  is decreased compared to an HDD comprising a good STO. Therefore, in the present embodiment, an HDD in which the STO  65  has been disintegrated and destroyed is shipped as an HDD having a recording capacity less than an HDD comprising a good STO. The above inspection of the STO  65  may be performed at intervals of predetermined periods of use after shipment. 
     As explained above, the HDD of the present embodiment comprises a magnetic recording head comprising a spin-torque oscillator near a main magnetic pole. The HDD may use microwave-assisted recording or may not use microwave-assisted recording depending on variation or defectiveness of oscillation characteristics of the spin-torque oscillator. When microwave-assisted recording is not used; in other words, when recording is performed without distributing power to the spin-torque oscillator, the magnetization of the oscillation layer of the spin-torque oscillator is lost or removed in advance, and then, the recording head is used as a magnetic recording head. Thus, the recording head can maintain the recording performance substantially equivalent to a recording head which does not comprise an STO. 
     In the present embodiment, it is possible to provide a recording head which is allowed to selectively use a microwave-assisted recording head comprising a spin torque oscillator depending on the characteristics, and a magnetic recording device comprising the recording head. 
     Now, this specification explains a magnetic head of an HDD of another embodiment, and a method for manufacturing the magnetic head. In the embodiment explained below, the structural elements identical to those of the first embodiment are denoted by the same reference numbers or symbols. Thus, detailed explanations of such elements are omitted. In the embodiment below, structural elements different from those of the first embodiment are mainly explained in detail. 
     Second Embodiment 
       FIG. 12  is a plan view showing a head wafer in which many magnetic heads are formed by stacking thin films.  FIG. 13  is a plan view in which a bar-shaped piece cut from the head wafer is enlarged. 
     As shown in  FIG. 12 , in a magnetic head manufacturing process, many magnetic heads each comprising a slider, a reproduction head, a recording head and an STO are continuously arranged in a plurality of lines  82  on a head wafer  80  by a thin-film lamination process. Each magnetic head is structured in the same manner as the magnetic head  16  of the first embodiment. As shown in  FIG. 13 , the magnetic heads of the lines  82  are cut from the head wafer  80  and are separated into a plurality of bar-shaped pieces  84  each including continuous magnetic heads  16 . 
     Subsequently, an inspection device  86  inspects oscillation defectiveness of the spin-torque oscillator of each recording head of the bar-shaped pieces  84 . For example, the inspection device  86  monitors resistance change or resistance-change frequency by power distribution to the spin-torque oscillator. The inspection device  86  comes in contact with the STO distribution terminal of each recording head through pins and has a function for distributing power to the STO and a function for detecting the STO resistance. 
       FIG. 14  shows the magnetic resistance change when the spin-torque oscillator (STO) oscillates. A good STO oscillates when certain current is applied in a state where a magnetic field is applied from outside. At this time, the magnetized angle between magnetic films in the STO is changed by oscillation. Therefore, the magnetic resistance of the STO is changed. A magnetic field may be applied to the STO from outside of the bar-shaped piece  84  by a magnetic field generator. Alternatively, the magnetic field generated in the recording gap in which the STO is present due to application of current to the recording head may be applied to the STO. 
     The magnetization of an oscillation layer (FGL)  65   b  of the STO is rotated in accordance with the oscillation frequency. In connection with the rotation, the resistance frequency is changed by approximately 15 to 30 GHz in synchronization with the oscillation frequency. It is possible to inspect whether or not the STO generates good oscillation by monitoring the magnetic resistance change and the resistance frequency change. When the inspection device  86  detects oscillation defectiveness from the STO, the inspection device  86  applies excessive driving current (bias current) to the STO compared to a normal case in order to disintegrate and destroy the STO. 
     After all of the magnetic heads  16  have been inspected, an ABS pattern for ensuring floating characteristics is formed by lapping the surface to be an air bearing surface (ABS)  13  and etching and polishing the surface. 
     As shown in  FIG. 15A  and  FIG. 15B , when the spin-torque oscillator is disintegrated and destroyed, the disintegrated oscillator portion may project from the head surface and become a projection. As shown in  FIG. 15C , the projection can be removed by lapping and patterning the ABS after the spin-torque oscillator  65  is disintegrated and destroyed. In this manner, the head surface can be smoothed. 
     Subsequently, the bar-shaped pieces  84  in which the ABS pattern is formed are divided into the respective magnetic heads  16 . In this manner, many magnetic heads  16  each having the structure shown in  FIG. 16  can be obtained. 
     By means of the manufacturing method of the above embodiment, it is possible to manufacture a recording head and a magnetic head having good recording characteristics both when the spin-torque oscillator is used in an on-state and when it is used in an off-state. In other words, it is possible to obtain a recording head manufacturing method which allows selective use of a microwave-assisted recording head comprising a spin-torque oscillator depending on the characteristics. In addition, it is possible to remove the projection of a spin-torque oscillator due to disintegration and obtain a smooth head surface by applying an ABS process after inspection, disintegration and destruction of the oscillator. 
     The present invention is not limited to the above-described embodiments, but may be realized by modifying structural elements without departing from the scope. Various inventions can be realized by appropriately combining the structural elements disclosed in the embodiments. For instance, some of the disclosed structural elements may be deleted. Some structural elements of different embodiments may be combined appropriately. 
     For example, the spin-torque oscillator may not be provided on the trailing side of the main magnetic pole, and may be provided on the reading side of the main magnetic pole. In the above embodiments, the spin-torque oscillator is magnetically and physically destroyed by disintegrating and mixing the magnetic layers and the conductive metal layers of the spin-torque oscillator. However, the spin-torque oscillator may be magnetically destroyed by applying doping of excessive oxygen and nitrogen to the magnetic layer portion of the spin-torque oscillator and reducing the magnetization of the magnetic layer.