Patent Publication Number: US-2009231748-A1

Title: Magnetic recording medium, apparatus and method for recording reference signal in the same

Description:
This application is a continuation based on International Application No. PCT/JP2006/323850. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a manufacturing method of a magnetic recording medium, and more particularly to a method and apparatus configured to record a reference signal in the magnetic recording medium. The present invention is suitable, for example, for a method and apparatus configured to record a servo signal in a magnetic disc having discontinuing magnetic films in a recording layer, such as a discrete track medium (“DTM”) and a patterned medium (“PM”). 
     2. Description of the Related Art 
     Along with the recent demand for large capacity, it is proposed to use of a DTM and a PM for a magnetic disc mounted in a hard disc drive (“HDD”). The magnetic disc is partitioned into a multiplicity of concentric tracks, and each track has a multiplicity of sectors that are partitioned for every preset angle. Both the DTM and PM reduce or remove magnetic transition areas that cause noises by partitioning adjacent tracks and/or sectors with a nonmagnetic material. As a result, the recording density can be improved by improving the signal quality. 
     The magnetic disc needs to record a reference information signal of a recording position for user data (which will also be simply referred to as a “servo signal” hereinafter). The servo signal contains address information and burst information. The address information is information indicative of an address of a track and a sector. A position corresponding to the track/sector of a magnetic head can be roughly recognized based on the address information. The burst information includes a predetermined patterned row, and provides a deviation (positional shift) between the magnetic head and the corresponding track/sector. Since the servo signal is thus used for positioning of the magnetic head, it is necessary to record the servo signal precisely. 
     Prior art include Patent Reference 1 (U.S. Pat. No. 6,834,005), Patent Reference 2 (Japanese Patent Laid-Open No. 2004-134079 (see, in particular, claims 3-6, and 9, paragraphs nos. 0012 and 0013)), and Literature Reference 1 (A. Yamaguchi, et al., “Real-Space Observation of Current-Driven Domain Wall Motion in Submicron Magnetic Wires,” Physical Review Letters, Vol. 92, No. 7, 20 Feb. 2004, The American Physical Society (2004)). 
     Prior art use a clock head that is a dedicated servo-signal writing head separate from a magnetic head mounted in the HDD. However, a core width of the magnetic head has become as fine as or finer than 0.2 μm, and it becomes difficult to maintain the precision of the core width of the clock head. On the other hand, there are proposed a push-pin method that uses the magnetic head itself to write the servo signal and a magnetic transfer method that simultaneously transfers a data area and a servo area from a master medium. However, these methods have technical problems and have difficulties in stably and precisely recording a servo signal. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method for precisely recording a reference signal in a magnetic recording medium, and a magnetic recording medium in which the reference signal has been written down. 
     A magnetic recording medium according to one aspect of the present invention includes a reference signal recording area used for a magnetic recording and reproducing head to confirm a position on the magnetic recording medium, the reference signal recording area including a conductive member that enables a reference signal to be written using a domain wall movement caused by a current conduction, and a nonconductive member that encloses the reference signal recording area. This magnetic recording medium can record the reference signal in the entire reference signal recording area simultaneously. 
     The magnetic recording medium may further include a magnetic recording area that is magnetically divided for each track by a nonmagnetic member. This DTM and PM structures are suitable for the magnetic recording medium of the present invention. 
     A part of the track may serve as the reference signal recording area, and electric conductivity exists between the track and a center of the magnetic recording medium. In this case, the current conduction direction is a radial direction. A part of the track may have a circumferential shape and serves as the reference signal recording area, wherein a part of a circumference of the reference signal recording area may include a nonconductive member, and wherein the magnetic recording medium further comprises a pair of electrodes at both parts of the conductive member of the reference signal recording area which contact the nonconductive member, and a reference signal may be written using a domain wall movement caused by electrifying both the electrodes. This structure uses the electrodes to record the reference signal in the entire reference signal recording area simultaneously rather than for each track. The magnetic recording area may be magnetically divided for each sector by a nonmagnetic member. The present invention is applicable to this PM structure. The reference signal recording area may be a servo area, and wherein the magnetic recording medium may further includes a pair of electrodes provided to an outer circumference and an inner circumference of the servo area, and a reference signal may be written using a domain wall movement caused by electrifying both the electrodes. 
     A reference signal recording apparatus according to another aspect of the present invention is configured to write a reference signal in the above magnetic recording medium, and includes a reference signal generator configured to generate the reference signal, and a contact part that contacts the reference signal recording area, the reference signal using a domain wall movement being written by electrifying the contact part. This recording apparatus can write down the reference using the domain wall movement. 
     A reference signal recording method for writing a reference signal in the above magnetic recording medium according to another aspect of the present invention includes a reference signal generating step of generating the reference signal, a contact step of contacting the reference signal recording area, and a writing step of writing the reference signal using a domain wall movement caused by electrifying a contact point on the reference signal recording area. This recording method can write down the reference using the domain wall movement. 
     A method for manufacturing a magnetic recording medium that includes a conductive magnetic body as a recording layer partitioned by a nonmagnetic insulator includes the step of recording a servo signal by injecting into the magnetic body spin-polarized current having an inversion pattern corresponding to a servo signal used to position a head that is configured to record information in the magnetic recording medium and to reproduce the information from the magnetic recording medium. This method can manufacture the servo signal using the spin-polarized current. 
     The method may further include the step of rotating the magnetic recording medium, wherein the recording step injects the spin-polarized current perpendicular to a surface of the magnetic recording medium using a tunneling current probe in synchronization with a target position on the magnetic recording medium, or the recording step may inject the spin-polarized current into a current conduction path along a surface of the magnetic recording medium by using a domain wall movement. 
     The method may further include the step of forming an electrode to flow the spin-polarized current in the limited servo area. This structure can flow the spin-polarized current in the entire servo area simultaneously rather than for each track. The method may further include the step of heating the magnetic recording medium during the injecting step. This structure can reduce the current density of the spin-polarized current. 
     The method may further include the steps of forming on the magnetic body by a film formation apparatus a sacrifice layer configured to prevent an oxidization of the magnetic body, moving the magnetic recording medium from the film formation apparatus to a recording apparatus configured to record a servo signal, moving the magnetic recording medium from the recording apparatus to the film formation apparatus after the recording apparatus executes the injecting step, and removing the sacrifice layer by the film formation apparatus. The sacrifice layer can prevent an oxidation of the magnetic body. The method can further include the step of forming a protective layer and a lubrication layer on the magnetic body after the injecting step. Since the protective layer and the lubrication layer are electric insulators and therefore layered afterwards, the servo signal can be recorded on the recording layer. 
     A recording apparatus according to another aspect of the present invention is configured to record a servo signal used to position on a magnetic recording medium, a head that is configured to record information in and reproduce the information from the magnetic recording medium. The magnetic recording medium includes a conductive magnetic body as a recording layer partitioned by a nonmagnetic insulator. The recording apparatus includes an electrifier/modulator configured to generate and output spin-polarized current having an inversion pattern corresponding to the servo signal. This recording apparatus uses the electrifier/modulator to generate and output the spin-polarized current, realizing the above recording method. This recording apparatus may further include a tunneling current probe configured to inject the spin-polarized current. Thereby, the spin-polarized current can be injected perpendicular or parallel to the surface of the magnetic recording medium. 
     A magnetic recording medium according to another aspect of the present invention includes a conductive magnetic body as a recording layer partitioned by a nonmagnetic insulator. This magnetic recording medium has a nonmagnetic insulator, and can secure a channel of the spin-polarized current. 
     For example, the magnetic recording medium is a discrete track medium, and the nonmagnetic insulator is arranged between adjacent tracks. Alternatively, the magnetic recording medium may be a patterned medium, and the nonmagnetic insulator is arranged between adjacent tracks, wherein magnetic bodies may be discretely arranged on the same track and have bit shapes, and a nonmagnetic conductor may be arranged between magnetic bodies having bit shapes on the same track. Moreover, the magnetic recording medium may be a patterned medium, and magnetic bodies may be discretely arranged on the same track and have bit shapes, wherein the nonmagnetic insulator may extend in a radial direction and arranged between adjacent magnetic bodies having bit shapes on the same track, and a nonmagnetic conductor may be arranged between the adjacent magnetic bodies having the bit shape which are aligned with each other in the radial direction between adjacent tracks. 
     Preferably, the nonmagnetic insulator has an ion milling speed lower than that of the magnetic body. Thereby, the amount of the necessary nonmagnetic insulator to be removed by the ion milling can be reduced. The magnetic recording medium may be a patterned medium in which each magnetic body has preferably an aspect ratio of 1 so as to improve the recording density. 
     The magnetic body may have an insulation part adjacent to a start position from which the spin-polarized current is injected. This structure can restrict a direction in which the spin-polarized current flows. 
     A magnetic storage including the above magnetic recording medium also constitutes one aspect of the present invention. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plane view of a magnetic disc having a servo area. 
         FIG. 2  is a flowchart for explaining a servo signal recording method according to a first embodiment of the present invention. 
         FIG. 3  is a schematic block diagram of a servo signal recording apparatus according to the first embodiment. 
         FIG. 4  is a schematic view of a recording method according to the first embodiment. 
         FIG. 5  is a schematic sectional view for explaining a flow of the tunneling current in the first embodiment. 
         FIG. 6  is a flow chart for explaining a servo signal recording method according to a second embodiment of the present invention. 
         FIG. 7  is a schematic block diagram of a servo signal recording apparatus according to the second embodiment. 
         FIG. 8  is a schematic view of a recording method according to the second embodiment. 
         FIG. 9  is a schematic view for explaining a domain wall movement by current injections. 
         FIG. 10  is an enlarged plane view of three adjacent tracks in a DTM applicable to the second embodiment. 
         FIG. 11  is an enlarged plane view of three adjacent tracks in a PM applicable to the second embodiment. 
         FIG. 12  is an enlarged plane view of three adjacent tracks in another PM applicable to the second embodiment. 
         FIG. 13  is a schematic sectional view for explaining a flow of the tunneling current in the second embodiment. 
         FIG. 14  is a flowchart for explaining a manufacturing method of a DTM usable for the first and second embodiments. 
         FIG. 15A  to  FIG. 15F  are schematic sectional views of the DTM corresponding to each step of  FIG. 14 . 
         FIG. 16  is a flowchart for explaining a manufacturing method of a PM usable for the first and second embodiments. 
         FIG. 17  is a schematic plane view of a magnetic disc of a DTM applicable to a third embodiment. 
         FIG. 18  is a flowchart for explaining a servo signal recording method according to the third embodiment of the present invention. 
         FIG. 19  is a schematic block diagram of the servo signal recording apparatus according to the third embodiment. 
         FIG. 20A  and  FIG. 20B  are schematic block diagrams for explaining a layered structure of a magnetic recording medium having an insulation layer. 
         FIG. 21  is a plane view of an HDD having a magnetic disc in which the servo signal has been written down. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic plane view of a magnetic disc  50 . A recording surface (or surface)  52  of the magnetic disc  50  is divided into a plurality of servo areas  53   a  and a plurality of user data areas  53   b . The number of servo areas  52   a  and their intervals, and a central angle of each servo area  53   a  are not limited to the structure shown in  FIG. 1 , but the respective servo areas  53   a  have the same shape, and are distributed around a center O of the magnetic disc  50  at regular intervals in this embodiment. The servo area  53   a  is defined by a pair of nonmagnetic insulators  53   a   1 , each of which extends in a radial direction and, for example, is an area made by removing a fan area having a central angle θ and a radius r 2  from a fan area having the same central angle θ and a radius r 1 . 
     A recording method and apparatus of this embodiment are a recording method and apparatus for recording a servo signal in the servo area  53   a . In writing the servo signal, a phenomenon of the magnetization inversion induced by the spin-polarized current injection is used, which is a phenomenon in which a magnetization direction of a magnetic body changes due to a spin-torque interaction when the spin-polarized current is flowed in the magnetic body. By inverting the polarity of the spin-polarized current, the magnetization direction of the magnetic body can be arbitrarily determined. When an inversion pattern of the spin-polarized current is made identical to the servo signal pattern, the servo signal can be more precisely recorded than the clock head and the magnetic transfer method. 
     This embodiment is particularly suitable for the DTM and PM that are magnetic recording media using discontinuing magnetic films for a magnetic layer, because they have recording densities which the conventional clock head cannot handle. It is said that the magnetization inversion by the spin-torque requires the current density in the order of 10 6  A/cm 2 , but an application of the current with the above density is easy if the track width of about 0.1 μm in the DTM and PM. In order to reduce the current density, the disc may be heated while the spin-polarized current is injected. Heating facilitates the magnetization inversion. 
     Since the DTM or PM has no electrode through which the current is injected, a spin-polarized current flowing means is necessary. It is also necessary to define a current conduction channel through which the spin-polarized current flows. When the current conduction channel is not defined, the spin-polarized current spreads and a servo signal is recorded beyond the servo area. 
     First Embodiment 
     A first embodiment uses a conductive magnetic layer in the servo area  53   a  so as to flow the spin-polarized current in a recording layer (magnetic body) to be recorded with a servo signal. 
       FIG. 2  is a flowchart for explaining a servo signal recording method according to a first embodiment.  FIG. 3  is a schematic block diagram of a servo signal recording apparatus  10  according to a first embodiment. Referring to  FIG. 3  the recording apparatus  10  includes a controller  11 , a memory  12 , an electrifier/modulator  13 , a tunneling current probe  14 , a probe moving part  15 , a rotating part  16  for a magnetic disc  50 , and a heater  17 . 
     The controller  11  controls each part, such as the memory  12 , the electrifier/modulator  13 , and the moving part  15 , and may be a CPU or MPU irrespective of its name. Information stored in the memory  12  contains a structure of the disc  50 , a recording method shown in  FIG. 2 , and a variety of data. The structure of the magnetic disc  50  contains a type of the magnetic disc  50  (DTM or PM), a direction of an axis of easy magnetization in the magnetic disc  50  (whether it is parallel or perpendicular to a surface), an arrangement of the servo areas  53   a  and the user data areas  53   b , and information of the servo signal. A variety of data contains a scanning result and rotation information of the disc  50 . The controller  11  refers to the memory  12 , and controls the electrifier/modulator  13  so that the inversion pattern corresponds to the servo signal pattern. 
     The electrifier/modulator  13  outputs from the probe  14  the spin-polarized current having an inversion pattern corresponding to a given servo signal or a modulation pattern in the polarized direction, under the control of the controller  11 . In addition, the electrifier/modulator  13  can flow the non-spin-polarized current (which will also be referred to as “normal current” in this embodiment), or stop outputting the current. The normal current cannot provide a function of the magnetization inversion. The controller  11  controls the timing and turning on and off of an output of the electrifier/modulator  13 . 
     The electrifier/modulator  13  can modulate the current by applying an external magnetic field, by irradiating a circularly polarized light, or by using a semiconductor device. 
     In applying the external magnetic field, part of the probe  14  is made of a ferromagnetic material, and an external coil is wound so as to cross the probe current that flows in this part. When the tunneling current is flowed while an AC signal corresponding to the servo signal pattern is applied to the coil, the polarization direction of the electronic spin changes according to changes of the external magnetic field. 
     In using the circularly polarized light, the tunneling current is flowed while the polarization direction of the laser beam irradiated onto the tip of the probe  14  is changed according to the servo signal pattern. Thereby, the electronic spin-polarized direction in the tunneling current changes according to changes of the polarized light direction of the laser beam. 
     In using the semiconductor device, a CMOS device that uses a magnetic semiconductor doped with a magnetic element, such as manganese and chrome. For example, a device that uses a magnetic semiconductor for a source of the p-channel MOS and a device that uses a magnetic semiconductor for a drain of the n-channel MOS are arranged (although reverse polarities are applicable), and an AC signal is applied to both gates in accordance with the servo signal pattern. Thereby, the electronic spin-polarized direction of the drain current switches according to the AC signal. 
     The tunneling current probe  14  is widely used as a means for analyzing a fine structure of a material surface, and the probe moving part  15  can move the probe  14  with precision of ±0.1 μm. It is easy to position the probe at the track having a width of 0.1 μm in the DTM or PM. The controller  11  controls the probe moving part  15  so that the probe  14  can move to a target track in the servo area. 
     The rotating part  16  includes a spindle that rotates the disc  50 , and a motor (not shown) that rotates the spindle. In an alternate embodiment, the rotating part  16  is a spindle motor  106  mounted on the HDD  100 . The magnetic disc  50  in which the servo signal is recorded becomes a magnetic disc  104 , which will be described later. The conventional method that uses a clock head writes a servo signal in the HDD  100 , whereas the recording apparatus  10  is different from the conventional recording apparatus in having the rotating part  16 , although the other embodiment of the present invention allows the rotating part  16  to be the spindle motor mounted in the HDD  100 . 
     The heater  17  heats the disc  50 . The heater  17  may be attached to a spindle or may heat the disc  50  from the top. As described above, when the disc  50  is heated, the magnetization inversion is likely to occur even with low electric density. 
     In operation shown in  FIG. 2  of the recording apparatus  10 , the magnetic disc  50  is initially mounted on the rotating part  16  of the HDD  100  or the HDD  100  mounted with the magnetic disc  50  is prepared. Of course, the present invention allows the recording apparatus  10  to have the independent rotating part  16 . 
     Next, the controller  11  controls the moving part  15  to arrange the tunneling current probe  14  close to the disc surface  52  (step  1002 ). A distance of the close arrangement differs according to the environments of the disc  50 , but the close arrangement intends to exclude the contact. As described later, the disc  50  rotates and the probe  14  or the disc  50  may get damaged when the probe  14  contacts the disc  50 . When the servo signal is written down in vacuum, the close arrangement is within a distance of several tens of nanometers from the surface  52 . When the servo signal is written down in vacuum, the close arrangement is within a distance of several nanometers from the surface  52 . 
     Next, the controller  11  controls the electrifier/modulator  13 , the moving part  15 , and rotating part  16  to scan the disc surface  52  using the non-spin-polarized tunneling current in the radial direction (step  1004 ). The scan uses, for example, a scanning tunneling microscope “STM” system. Then, a magnetic track part and a nonmagnetic part can be recognized as contrasts of the conductive part and the nonconductive part, as shown in  FIGS. 10 to 12 , which will be described later. The scanning result is stored in the memory  12 . 
     In case of a DTM, the scan is a raster scan in which the probe  14  is moved from the center of the disc  50  to the outer circumference in the radial direction and then returned to the center. In this case, rotating of the disc  50  during scanning is unnecessary. 
     On the other hand, the scan of a PM associates with a rotation of the disc  50  in this embodiment. The disc  50  is not necessarily rotated in order to detect the tracks. Whether the rotation is necessary depends upon the bit pattern of the magnetic bodies. When the bit width is shorter on the inner circumference side and longer on the outer circumference side, the bits are aligned in the radial direction and thus the disc  50  may be maintained stationary, similar to the DTM. On the other hand, when the number of bits on the inner circumference side is smaller and the number of bits on the outer circumference side is larger, the bits shift in the radial direction and the disc  50  needs to rotate. This embodiment detects not only the tracks but also the recording start position of the servo signal through scanning. This embodiment sets a recording start position of the servo signal for the PM. In this embodiment, the recording start position is detected by deforming a bit shape of a top sector, and by detecting the deformed shape through scanning. Therefore, the disc  50  needs to be rotated. 
     Next, the controller  11  controls the moving part  15  by referring to the scanning result in the memory  12  (or by feeding back the scanning result) to move the probe  14  to a target position of a target track  54  (step  1006 ). A target position on a certain track is an arbitrary position in the DTM, but it is necessary to align the target positions with each other the radial direction between the adjacent tracks. As a result, the target positions on the respective tracks are aligned with each other in the radial direction. In the PM, the probe is moved to the preset recording start position. 
     Since the conventional recording method using the clock head has no positioning clue on the disc surface  52 , the positioning accuracy is limited to the mechanical precision. On the other hand, this embodiment can improve the positioning precision through the feedback utilizing the electric conduction difference on the disc surface  52 . 
     Next, the controller  11  controls the electrifier/modulator  13  and the rotating part  16  to inject the spin-polarized current to the target position and to rotate the disc  50  at the same time. At this time, as necessity arises, the controller  11  controls the heater  17  to heat the disc  50 . The number of rotations of the disc  50  depends upon the writing frequency into the servo area  53   a , and sets to the number of rotations or lower used for the recording and reproducing time in the HDD  100 . 
       FIG. 4  shows a schematic view of the step  1008 . As shown in  FIG. 4 , the spin-polarized current is applied to the probe  14  and injected into the track  54  on the disc  50  after the probe  14  is positioned to the same sector as the adjacent track, and the disc  50  is simultaneously rotated. Thereby, a magnetization pattern corresponding to the servo signal can be recorded on the target track  54 . 
       FIG. 5  is a schematic sectional view showing the flow of the tunneling current in the steps  1004  and  1008 . The tunneling current passes the disc  50  from the probe  14  to the spindle (the rotating part  16 ). Therefore, in the first embodiment, the tunneling current flows perpendicular to the disc surface  52 . Since the spin-polarized current flows perpendicular to the recording layer (magnetic body)  55 , the domain wall movement in the surface is negligible. Even when the tunneling current flows on the disc surface  52 , the direction of the axis of easy magnetization is not necessarily perpendicular to the surface  52  and it may be parallel to the surface. Whether it is parallel or perpendicular to the surface depends upon the anisotropy of the orientation control layer. In  FIG. 5 , reference numeral  51  denotes a substrate or a conductive layer on the substrate. TC denotes the tunneling current. 
     In the step  1008 , the controller  11  provides on/off control so that the electrifier/modulator  13  flows the current in the servo area  53   a  shown in  FIG. 1  and does not flow the current (or flows the normal current) in the user data area  53   b.    
     Next, the controller  11  determines whether writing of servo signals into a plurality of servo areas  53   a  on the track  54  for one round is completed (step  1010 ). The controller  11  continues the step  1008  until recording of the servo signals for one round is completed. Of course, in the step  1010 , the controller  11  may rotate the disc  50  for 360° or terminate the rotation when the last servo area  53   a  in the rotating direction is completed. The latter case, for example, is a case where recording starts with the right servo area  53   a  and ends with the upper-left servo area  53   a  in  FIG. 1 . 
     Next, the controller  11  refers to the memory  12 , and determines whether the servo signals have been recorded in all the tracks in the servo areas (step  1012 ). The scanning result performed in the step  1004  is stored in the memory  12 . Determining that all the servo signals are recorded (step  1012 ), the controller  11  terminates the recording action. When the controller  11  determines that all the servo signals have not yet been recorded (step  1012 ), the flow returns to the step  1006 . 
     Second Embodiment 
     Since it is necessary to flow the spin-polarized current in the recording layer (magnetic body) to be recorded with the servo signal in the servo area  53   a , the second embodiment uses a conductive magnetic layer in principle but also provides an insulator  56 . 
     The second embodiment is common to the first embodiment in injecting the spin-polarized current and in writing the servo signal, but different from the first embodiment in using the recording method shown in  FIG. 6 , the recording apparatus  10 A shown in  FIG. 7 , and the magnetic disc  50 A. The recording apparatus  10 A shown in  FIG. 7A  is different in further including a timer  18  connected to the controller  11  and configured to measure a time period. Here,  FIG. 6  is a flowchart for explaining a servo signal recording method according to a second embodiment.  FIG. 7  is a schematic block diagram of the recording apparatus  10 A according to the second embodiment. 
     The magnetic disc  50 A is different from the magnetic disc  50  in having an insulator  56  in a specific sector. In  FIG. 8 , the domain wall moving direction is clockwise, and the insulator  56  prevents the domain wall moving direction from changing to the counterclockwise direction. Therefore, the insulator  56  is arranged adjacent to the starting point of the spin-polarized current injection. The second embodiment forms the insulator  56  by embedding an insulation material into the specific sector on the track of the disc  50 A. 
     Referring now to  FIG. 6 , an operation of the recording apparatus  10 A will be described. Those elements in  FIG. 6 , which are the same as corresponding steps as those in  FIG. 2 , will be designated by the same reference numerals, and a description thereof will be omitted. Similar to  FIG. 2 , the magnetic disc  50 A is initially mounted on the rotating part  16 . Next, the controller  11  controls the moving part  15  to arrange the tunneling current probe  14  close to or bring it into contact with the disc surface  52  (step  1102 ). The step  1102  is different from the step  1002  in that the probe  14  can be brought into contact with the disc surface  52 . The close arrangement in the step  1102  is the same concept as that in the step  1002 . The contact is allowed because the disc  50  is not rotated, but the close arrangement is more preferable than the contact so as not to damage the probe  14  and the disc  50 . 
     After the steps  1004  and  1006 , the controller  11  controls the electrifier/modulator  13  and the timer  18  to inject the spin-polarized current into the target position for a predetermined time period.  FIG. 8  shows a schematic view of the step  1102 . The second embodiment sequentially supplies the magnetic pattern through the domain wall movement by applying the spin-polarized current. The insulator  56  prevents a reverse flow of the spin-polarized current in  FIG. 8 . The controller  11  controls the electrification by the electrifier/modulator  13  by measuring a necessary time period using the timer  18  for the domain wall movement. It is known that when an inversion pattern of the spin-polarized current is continuously injected as shown in  FIG. 9 , domain walls of the magnetic bodies sequentially move, and a magnetization pattern having an arbitrary bit length can be formed according to injected pulse lengths. See, for example, Literature Reference 1. 
     In the DTM, each magnetic body  55  has an annular pattern along each track  54  and is generally electrically conductive, as shown in  FIG. 10 . The tunneling current flows in the track direction or disc circumferential direction, and the domain wall can move. Here,  FIG. 10  is an enlarged plane view of adjacent three tracks  54 A 1  to  54 A 3  on the DTM. Each track has a track width TW, which is about 0.1 μm. Since a nonmagnetic insulator  57  is arranged between the two adjacent tracks and eliminates a magnetic transition area, the DTM can improve the signal quality. The insulator  56  is omitted in  FIG. 10 . 
     On the other hand, the PM has a dot pattern of electrically conductive magnetic bodies  55 . At this state, no domain wall movement can be achieved because the tunneling current flows only in the dot and does not flow in the track direction. 
     Accordingly, as shown in  FIG. 11 , a nonmagnetic insulator  57  is arranged between the two adjacent tracks, and a nonmagnetic conductor  58  is arranged between two consecutive dots in each track. Thereby, the tunneling current can flow in the circumferential or track direction, realizing the domain wall movement. 
     Alternatively, as shown in  FIG. 12 , the nonmagnetic conductor  58  may be arranged between the magnetic bodies in the radial direction rather than the circumferential direction, and the nonmagnetic insulator  57  may be arranged between the two adjacent magnetic bodies  55  in the track direction. Thereby, the dots in the adjacent tracks are connected to each other via the conductive material, and the tunneling current flows in a radial direction or a direction perpendicular to the track direction, realizing the domain wall movement. 
     Here,  FIG. 11  or  12  is an enlarged plane view of three adjacent tracks  54 B 1  to  54 B 3  or  54 C 1  to  54 C 3  in the PM. Each track has a track width TW, which is about 0.1 μm. Since the nonmagnetic body  57  or  58  between two adjacent tracks eliminates a magnetic transition area, the PM can improve the signal quality. While  FIGS. 11 and 12  makes a bit length corresponding to a lateral width of each bit smaller than the track width TW corresponding to a longitudinal width of each bit, the recording density can be preferably increased by setting an aspect ratio to 1. 
       FIG. 13  is a schematic sectional view showing the flow of the tunneling current in the step  1104 . The tunneling current passes through the disc  50 A from the probe  14  to the rotating part  16 . It is understood that the tunneling current flows along the surface of the disc surface  52  in the second embodiment. Although the tunneling current flows over approximately one round in  FIG. 13  for illustration convenience, the tunneling current actually flows only in the preset servo area  53   a  as shown in  FIG. 1 . 
     Turning back to  FIG. 6 , the steps  1010  and  1012  are executed. 
     Referring now to  FIGS. 14 and 15A  to  15 F, a description will be given of a manufacturing method of a DTM usable for the first and second embodiments. Here,  FIG. 14  is a flowchart for explaining a manufacturing method of a DTM usable for the first and second embodiment.  FIGS. 15A to 15F  are schematic sectional views of each manufacturing step of the DTM. This manufacturing method utilizes a film formation apparatus (not shown). 
     Initially, as shown in  FIG. 15A , an undercoat layer  60  made of Ni alloy, etc., and configured to maintain the strength of the film is formed on a substrate  51  made of a material, such as glass or aluminum (step  1202 ). The undercoat layer  60  may use a different material according to the anisotropy of an orientation control layer  61 . In  FIG. 5 , the undercoat layer, etc. are omitted. 
     Next, as shown in  FIG. 15B , the orientation control layer  61  configured to control the anisotropy is coated on the undercoat layer  60  (step  1204 ). For example, the orientation control layer  61  uses Cr alloy in order to orient the direction of the axis of easy magnetization along the disc surface  52  (or for the in-plane or parallel magnetization), and Ru or its alloy in order to direct the axis of easy magnetization perpendicular to the disc surface  52  (or for the perpendicular magnetization). 
     Next, as shown in  FIG. 15C , a thin conductive magnetic body (recording layer)  55  is coated on the orientation control layer  61 . The magnetic body  55  is made, for example, of CoCr (step  1206 ). 
     Next, as shown in  FIG. 15D , in order to prevent oxidization of the magnetic body  55 , an electrically conductive sacrifice layer  62  is coated (step  1208 ). The sacrifice layer  62  is made by coating, for example, Ru or Au on the magnetic body  55  by several nanometers. Coating of the sacrifice layer  62  does not conventionally exist. However, an application of the sacrifice layer  62  becomes optional if the recording apparatus  10  or  10 A is maintained in vacuum and connected to the film formation apparatus via a load lock mechanism and the magnetic body  55  is unlikely to oxidize. 
     Next, a resist pattern for the tracks is concentrically formed on the magnetic body  55  through the lithography (step  1210 ). This photography step has not yet been conventionally provided and can precisely form a track pattern, removing the unevenness on the disc surface  52 . When grooves among tracks are formed by mechanical processing, such as cutting, rather than photolithography, the disc surface  52  becomes uneven and is likely to collide with the probe  14  during scanning. In addition, it is substantially difficult to form the insulator  56  without the photolithography. When a specific sector position on each track is covered with a resist pattern through the photolithography, the magnetic disc  50 A having the insulator  56  can be formed. 
     Next, a pattern having no resist pattern is removed through ion milling (step  1212 ). Next, a nonmagnetic insulator is formed through sputtering (step  1214 ), and the resist pattern is lifted off (step  1216 ). Thereby, a model of the DTM is completed. 
     Next, the laminated member is moved from the film formation apparatus to the recording apparatus  10  or  10 A (step  1218 ). In this case, the sacrifice layer  62  prevents the oxidation of the magnetic body  55 . Next follows the servo signal recording process shown in  FIG. 2  or  6  (step  1220 ). 
     Next, the laminated member in which the servo signal has been recorded is moved from the recording apparatus  10  or  10 A to the film formation apparatus (step  1222 ). Next, as shown in  FIG. 15E , the sacrifice layer  62  is removed through sputtering etc. (step  1224 ). The step  1224  has not yet been conventionally provided. Next, as shown in  FIG. 15F , a protective layer  63  and a lubrication layer  64  are formed on the magnetic body  55  (step  1226 ). The protective layer  63  is made, for example, of a diamond like carbon, and the lubrication layer  64  is made of an organic solvent, such as Tetraol. 
     Thus, in this embodiment, before the protective layer  63  and the lubrication layer  64  are layered, the servo signal can be written in the state of the magnetic body  55  or in the state of the magnetic body  55  coated with the sacrifice layer  62 . This is because the protective layer  63  and the lubrication layer  64  are made of insulation materials and do not flow the spin-polarized current. On the other hand, since the conventional clock head writing is performed after the protective layer  63  and the lubrication layer  64  are layered, the steps  1220  and  1226  are different from the conventional steps. 
     Referring now to  FIG. 16 , a description will be given of a manufacturing method of a PM usable for the first and second embodiments. Here,  FIG. 16  is a flowchart for explaining a manufacturing method of a PM usable for the first and second embodiments. Those steps in  FIG. 16 , which are the same as corresponding steps in  FIG. 14 , will be designated by the same reference numerals, and a duplicate description thereof will be omitted. 
     In  FIG. 16 , after the step  1212 , a radial resist pattern is again formed through the photolithography (step  1302 ). Next, a pattern having no resist pattern is removed through ion milling (step  1304 ). The magnetic body  55  having a bit shape is formed by the steps  1210 ,  1212 ,  1302 , and  1304 . 
     At this time, part of the nonmagnetic insulator  57  that is not covered with the resist pattern is removed through ion milling, and thus the nonmagnetic insulator  57  is preferably made of alumina or tantalum pentoxide, etc. having an ion milling rate lower than that of the magnetic body  55 . 
     After the ion milling, the nonmagnetic conductor  58  is formed through electrolysis plating (step  1306 ), and the resist pattern is lifted off (step  1308 ). The electrolysis plating does not form a layer of the nonmagnetic conductor  58  on the nonmagnetic insulator  57 , and the nonmagnetic conductor  58  is embedded only at part from which the magnetic body  55  is removed by the ion milling. Thereby, the model of the PM shown in  FIG. 11  is completed. The subsequent steps are similar to those for the DTM. 
     The PM shown in  FIG. 12  forms a radial resist pattern through a first lithography, and an annular resist pattern through a second lithography. In other words, the steps  1210  and  1302  in  FIG. 16  will be replaced. 
     Third Embodiment 
     The third embodiment forms a pair of electrodes  59  on the magnetic disc  50 B through fine processing, as shown in  FIG. 17 , which is a plane view of the magnetic disc  50 B as the DTM.  FIG. 17  sets the servo area  53   a  to a constant angle range and the user data area  53   b  to the remaining part for convenience. 
     As shown in  FIG. 17 , the third embodiment adds a conductive wiring pattern to the laminated member of the disc  50 B, and connects the magnetic bodies (tracks or dots)  57  to each other. Thereby, the recording apparatus used for the third embodiment uses a pair of plus and minus terminals  19  instead of the tunneling current probe  14  as shown in  FIG. 19 . The pin-polarized current is injected via the terminals. The recording method is as shown in  FIG. 18 . Here,  FIG. 18  is a flowchart for explaining a servo signal recording method of the third embodiment.  FIG. 19  is a schematic block diagram of a recording apparatus  10 B of the third embodiment. 
     Referring to  FIG. 18 , the controller  11  controls the moving part  15  to move the terminals  19  to the terminals  59  (step  1402 ), and controls the electrifier/modulator and the timer to inject the spin polarized current into the electrodes  59  for a predetermined time period (step  1404 ). The third embodiment does not need the scanning step  1004  to flow the spin-polarized current to the whole servo area simultaneously, and allows the protective layer  63  and the lubrication layer  64  to be layered on the magnetic body  55  as long as the electrodes  59  exposes. 
     A description will be given of a manufacturing method of a DTM and a PM used for the third embodiment. Basic steps are similar to those of the first and second embodiments. However, in case of the DTM, the insulator  56  or the nonmagnetic insulator  53   a   1  is initially embedded into a specific sector position on each track. Next, a resist pattern is formed through the photolithography so as to expose part that serially connects the tracks and parts of the prospective electrodes  59 . After ion milling, the nonmagnetic conductor  58  is formed through the electrolysis plating, the resist pattern is lifted off, and the protective layer  63  and the lubrication layer  64  are layered. The spin-polarized current is flowed from the completed electrodes  59 . Since the electrodes  59  become unnecessary after the servo signal is written, they may be removed through etching but may be left. In removing through the etching, the sacrifice layer  62  is formed after the electrodes  59  are formed on the magnetic body  55 , and then the servo signal is written down. Thereafter, similar to the steps  1222  and  1224 , the sacrifice layer  62  is removed, and the protective layer  63  and the lubrication layer  64  are layered similar to the step  1226 . 
     In the step  1404 , the spin-polarized current may not flow parallel to the surface  52  and may flow perpendicular to the surface  52  towards the rotating part  16 . Therefore, it is preferable to arrange the insulation layer. The insulation layer  65  may be arranged on the undercoat layer  60  as shown in  FIG. 20A  or just under the magnetic body  55  as shown in  FIG. 20B . Of course, the protective layer  63  and the lubrication layer  64  may be layered on the magnetic body  55 . 
     Fourth Embodiment 
     Referring now to  FIG. 21 , a description will be given of the HDD  100  having a magnetic disc in which a servo signal has been written down. The HDD  100  includes, as shown in  FIG. 21 , one or more magnetic discs  104  as recording media, a spindle motor  106 , a head stack assembly (“HSA”)  110  in a housing  102 . Here,  FIG. 21  is a schematic plane view of an internal structure of the HDD  100 . 
     The housing  21  is made, for example, of aluminum die casting or stainless steel, and has a rectangular parallelepiped shape, and is coupled with a cover (not shown) to shield the internal space. The magnetic disc  104  can be any one of the above magnetic discs  50  to  50 B in which the servo signal is recorded, and has a high surface recording density. The magnetic disc  104  is mounted on a spindle (hub) of the spindle motor  106  via holes that are provided at the center. 
     The spindle motor  106  has, for example, a brushless DC motor (not shown) and a spindle as a rotor part. In using two discs  104 , for example, the disc, a spacer, the disc, a clamp ring are mounted in this order around the spindle, and these discs are fixed by bolts fastened with the spindle. 
     The HSA  110  includes a magnetic head part  120 , a carriage  170 , a base plate  178 , and a suspension  179 . 
     The magnetic head part  120  includes a slider and a read/write head joined with an air outflow end of the slider. 
     The slider supports the head, and floats over the surface of the rotating disc  104 . The head records information in and reproduces information from the disc  104 . A surface of the slider that opposes to the magnetic disc  104  serves as a floating surface. The airflow that is generated based on the rotations of the magnetic disc  104  is received by the floating surface. 
     The head is a magnetoresistive (“MR”) inductive composite head that includes an inductive head device that writes binary information in the magnetic disc  104  utilizing the magnetic field generated by a conductive coil pattern (not shown), and a MR head that reads the binary information based on the resistance that varies in accordance with the magnetic field applied by the magnetic disc  104 . 
     The carriage  170  serves to rotate or swing the magnetic head part  120  in arrow directions shown in  FIG. 21 , and includes a voice coil motor (not shown), a support shaft  174 , a flexible printed circuit board (“FPC”)  175 , and an arm  176 . 
     The voice coil motor has a flat coil between a pair of yokes. The flat coil opposes to a magnetic circuit (not shown) provided to the housing  102 , and the carriage  170  swings around the support shaft  174  in accordance with values of the current that flows through the flat coil. The magnetic circuit includes, for example, a permanent magnet fixed onto an iron plate fixed in the housing  102 , and a movable magnet fixed onto the carriage  170 . 
     The support shaft  174  is inserted into a hollow cylinder in the carriage  170 , and extends perpendicular to the paper surface of  FIG. 21  in the housing  102 . The FPC  175  provides a wiring part with a control signal, a signal to be recorded in the disc  104 , and the power, and receives a signal reproduced from the disc  104 . 
     The arm  176  has a perforation hole at its top. The suspension  179  is attached to the arm  176  via the perforation hole and the base plate  178 . The base plate  178  serves to attach the suspension  179  to the arm  176 . A welded portion is laser-welded with the suspension  179 , and a dent is swaged with the arm  176 . 
     The suspension  179  serves to support the magnetic head part  120  and to apply an elastic force to the magnetic head part  120  against the disc  104 . The suspension  179  has a flexure (also referred to as a gimbal spring or another name) which cantilevers the magnetic head part  120 , and a load beam (also referred to as a load arm or another name) which is connected to the base plate  178 . The load beam has a spring part at its center so as to apply a sufficient compression force in a Z direction. 
     In operation of the HDD  100 , the spindle motor  106  rotates the disc  104 . The airflow associated with the rotation of the disc  104  is introduced between the disc  104  and slider, forming a fine air film. This air film generates the floating force that enables the slider to float over the disc surface. The suspension  179  applies an elastic compression force to the slider in a direction opposing to the floating force of the slider. As a result, the balance is formed between the floating force and the elastic force. 
     The above balance spaces the magnetic head part  120  from the disc  104  by a constant distance. Next, the carriage  170  is rotated around the support shaft  174  for head&#39;s seek for a target track on the disc  104 . Since the servo signal is precisely written, the seek precision improves. In writing, data from a host (not shown) such as a PC is received through the interface and modulated, and written down in the target track via the inductive head. In reading, the MR head device is supplied with predetermined sense current, and reads desired information from the desired track on the disc  104 . 
     The present invention enables the servo signal precisely to be written down even in a DTM, a PM, or a magnetic disc  104  having a recording density of 2-3 Tbits/in2 or higher whereas the conventional method has a difficulty in so doing. 
     Further, the invention is not limited to the disclosed exemplary embodiments, and various modifications and variations may be made.