Patent Publication Number: US-2009237833-A1

Title: Magnetic tape apparatus using perpendicular magnetic recording

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic tape apparatus for recording data to the magnetic tape, especially to a magnetic tape apparatus for recording by perpendicular magnetic recording technology. 
     2. Description of the Related Art 
     In recent years, magnetic recording and reproducing apparatuses have been remarkably improved in capacity of storage data, corresponding to the widespread use of multimedia and the Internet. And magnetic tape apparatuses for backing up or storing data or for recording and reproducing audio video information and so on are no exception of this trend of larger capacity. They have been required to be improved in areal recording density corresponding to the larger capacity. 
     To achieve the higher recording density, perpendicular magnetic recording has been adopted instead of conventional longitudinal magnetic recording, and actually contributes to the significant improvement in areal recording density. In the perpendicular magnetic recording, demagnetization field drastically decreases in the magnetization transition region between record bits formed on a magnetic recording medium; therefore, the magnetization transition width can become much smaller than that of the longitudinal magnetic recording. Furthermore, the record bits formed by the perpendicular magnetic recording are not greatly affected by thermal fluctuation that becomes serious problem for achieving higher recording density in the longitudinal magnetic recording. As described above, the perpendicular magnetic recording has a potential to realize more stable and higher recording density. 
     Currently, in the thin-film magnetic head for the perpendicular magnetic recording, a shielded pole structure is mainly adopted, which includes a main magnetic pole, an auxiliary magnetic pole as a return yoke, and a write coil for exciting magnetic flux in these magnetic poles. Whereas, the corresponding magnetic recording medium mainly has a stacked structure of: a perpendicular magnetization layer on which record tracks are formed; and a soft-magnetic under layer (SUL) for acting as a part of magnetic circuit in which magnetic flux starts from the main magnetic pole and is lead to the auxiliary magnetic pole through the perpendicular magnetization layer. 
     Further currently, the application of the perpendicular magnetic recording to magnetic tape apparatuses proceeds to improve recording densities of the apparatuses, as described in, for example, Japanese Patent Publication No. 59-019213A. Further, Japanese Patent Publication No. 2007-220179A discloses a technique, though not for perpendicular magnetic recording, in which DC erasing is performed by applying magnetic fields perpendicularly to the record layer of a magnetic tape. And Japanese Patent Publication No. 11-149635A describes a technique, also though not for perpendicular magnetic recording, in which recording is performed by irradiating light perpendicularly to a tape on which material for optical recording medium is applied. 
     When applying the perpendicular magnetic recording to magnetic tape apparatuses, there occurs a problem of setting the SUL. In fact, because a magnetic head for magnetic tapes (tape head) is greatly larger in size than a thin-film magnetic head for hard disks, the magnetic circuit of the tape head becomes a larger loop. Therefore, the thickness of the SUL for magnetic tapes, which acts as a part of the magnetic circuit, must be set to be one or more order of magnitude larger than that of the SUL for hard disks. Actually, in the thin-film magnetic head for hard disks, the space between the main magnetic pole and the auxiliary magnetic pole is of, for example, the order of 10 nm (nanometers) or the vicinity, whereas, the space in the tape head would be of, for example, the order of 0.1 μm (micrometer) or the vicinity. Therefore, the SUL for magnetic tapes must have a significantly larger thickness according to the difference between both spaces. However, the significantly larger thickness of the SUL would be likely to cause the decrease in recording density per volume in the form of a reel of magnetic tape, the degradation in flexibility of the magnetic tape which would lead an inadequate contact with the head, or the damage such as for the constituent film being peeled from the magnetic tape. 
     As an approach for resolving the problems about the SUL, Japanese Patent Publication No. 63-122001A describes a technique for the perpendicular magnetic recording, in which an auxiliary tape with SUL is provided in addition to a main tape with perpendicular magnetization layer, and recording is performed under the condition that the auxiliary tape is contacted with the main tape at the position of tape head. Further Japanese Patent Publication No. 63-122001A discloses an embodiment of helical-scanning cylinder heads. Helical-scanning cylinder heads are also disclosed in, for example, Japanese Patent Publication No. 09-154096A. 
     However, in Japanese Patent Publication No. 63-122001A, the auxiliary tape, as well as the main tape, is wound around reels; and especially in the case using a tape cartridge, both tapes must be stored within the tape cartridge. Therefore, it is significantly difficult to provide an SUL with a thickness sufficiently large for avoiding the above-described problems about the SUL. 
     Further, a magnetic tape for the perpendicular magnetic recording is set to have a markedly smaller thickness according to higher recording density. Therefore, there is a possibility that the magnetic tape would be stretched over time; and thus the magnetic tape would have a shorter lifetime. Generally, the running of the magnetic tape is regulated with reels and a capstan. The capstan governs the running speed of the magnetic tape. Then, a tensile stress is brought about in the magnetic tape by the capstan as well as the tape head. The tensile stress would be likely to cause the stretch of the thin magnetic tape to be enhanced. However, it is difficult to resolve this problem by using the above-described prior art. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a magnetic tape apparatus using perpendicular magnetic recording, which has the function corresponding to an SUL with sufficiently large thickness and enables the magnetic tape to maintain life sufficiently. 
     Before describing the present invention, terms used herein will be defined. In a structure of element(s) formed on/above an element formation surface of the substrate in a magnetic head part, one side closer to the substrate when viewed from a standard layer or element is referred to as being “lower” than, “beneath” or “below” the standard layer or element, and the opposite side is referred to as being “upper”, “on” or “above” the standard layer or element. Further, a portion on the substrate side of a layer or element is referred to as a “lower” portion, and a portion on the opposite side is referred to as an “upper” portion. 
     Furthermore, in some figures showing embodiments of magnetic tape apparatuses according to the present invention, X-axis direction, Y-axis direction and Z-axis direction are defined, according to need. Further, a surface having a loading slot for a tape cartridge is defined as a “front” surface, and the direction of the axis of a drive motor driving a real for a magnetic tape is defined as an upper-and-lower direction (a direction along Z-axis). 
     According to the present invention, provided is a magnetic tape apparatus for recording data to a magnetic tape with a perpendicular magnetization layer, which comprises: a tape head comprising at least one write head element for perpendicular magnetic recording; and a soft-magnetic capstan belt having a surface contact with the magnetic tape and pressing the magnetic tape to the tape head at least during recording, for controlling running speed of the magnetic tape by causing the magnetic tape to run together with the soft-magnetic capstan belt. 
     The soft-magnetic capstan belt described above is not stored within, for example, a tape cartridge, and is a constituent element of the magnetic tape apparatus. This soft-magnetic capstan belt has a surface contact with the magnetic tape, and presses the tape to the tape head to stabilize the contact between the tape and the head. The soft-magnetic capstan belt further controls stably the running speed of the magnetic tape by carrying the magnetic tape along with itself, and thus prevents the stretch of the magnetic tape over time. Furthermore, the soft-magnetic capstan belt plays the same role as a soft-magnetic under layer (SUL) in hard disks for perpendicular magnetic recording, which contributes to adequately perform perpendicular magnetic recording. 
     In the magnetic tape apparatus according to the present invention, it is preferable that at least two capstan-belt axes are further provided and the soft-magnetic capstan belt is a loop running among the at least two capstan-belt axes. Further in the case, it is also preferable that the soft-magnetic capstan belt comprises a plurality of through holes and at least one of the at least two capstan-belt axes comprises at least one pin that can be fit into the through hole for preventing the soft-magnetic capstan belt from slipping. Providing the through holes (perforation) and the pins enables the soft-magnetic capstan belt to be prevented from slipping from the capstan-belt axis. As a result, the rotational motion of a driving motor is directly transmitted to the soft-magnetic capstan belt, and thus, the running speed of the magnetic tape, which runs together with the soft-magnetic capstan belt, can be more stabilized. 
     Further, in the magnetic tape apparatus according to the present invention, the tape head is preferably a rotary head that can rotate. In this case, it is further preferable that: at least during recording, two capstan-belt axes are positioned, so as to interpose the tape head between the two capstan-belt axes, and on a rear side of an end surface of the tape head, the end surface being opposed to the magnetic tape, when viewed from a side of reels for the magnetic tape; and one capstan-belt axis is positioned closer to the reels for the magnetic tape than the tape head in order to bring about tensile stress in the soft-magnetic capstan belt. 
     Further, in the magnetic tape apparatus according to the present invention, the write head element for perpendicular magnetic recording preferably comprises: a main magnetic pole layer for generating magnetic flux used during write operation; and a write shield layer for receiving the magnetic flux that is generated from the main magnetic pole layer and returns through the soft-magnetic capstan belt. And the soft-magnetic capstan belt is preferably a ribbon formed of a soft-magnetic metal. 
     According to the present invention, further provided is a tape cartridge used for the magnetic tape apparatus as described above, which comprises a magnetic tape without a soft-magnetic under layer, the magnetic tape comprising a perpendicular magnetization layer on which record tracks are formed. This tape cartridge can keep sufficiently large recording density per volume in the form of a reel of magnetic tape. 
     Further objects and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention as illustrated in the accompanying figures. In each figure, the same element as an element shown in other figure is indicated by the same reference numeral. Further, the ratio of dimensions within an element and between elements becomes arbitrary for viewability. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIGS. 1   a  to  1   d  show schematic views illustrating the configuration of an embodiment of magnetic tape apparatus according to the present invention; 
         FIGS. 1   e  and  1   f  show top views illustrating another embodiment concerning the configuration of capstan-belt axes; 
         FIG. 2  shows a perspective view schematically illustrating the configuration around the capstan-belt axis; 
         FIG. 3  shows a perspective view schematically illustrating the head part provided in the rotary head; 
         FIG. 4  shows a cross-sectional view taken along plane A in  FIG. 3 , schematically illustrating the structure of the head part; 
         FIG. 5  shows a cross-sectional view corresponding to the cross-section taken along plane A in  FIG. 3 , for explaining the principle in which perpendicular magnetic recording can be performed adequately by using the soft-magnetic capstan belt according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1   a  to  1   d  show schematic views illustrating the configuration of an embodiment of magnetic tape apparatus  10  according to the present invention. Here,  FIGS. 1   a  and  1   b  show the state just after inserting a tape cartridge  20  into the magnetic tape apparatus  10 , and are a top view and a side view, respectively. While,  FIGS. 1   c  and  1   d  show the state when just completing the loading of the tape cartridge  20  into the magnetic tape apparatus  10 , and are also a top view and a side view, respectively. Further,  FIGS. 1   e  and  1   f  show top views illustrating another embodiment concerning the configuration of capstan-belt axes. 
     As shown in  FIGS. 1   a  and  1   b , the magnetic tape apparatus  10  includes: a rotary head  11  as a tape head for perpendicular magnetic recording; three capstan-belt axes  130 ,  131  and  132 ; a soft-magnetic capstan belt  12  that is a loop running among these capstan-belt axes; and two pinch rollers  140  and  141  formed of, for example, a rubber. The tape cartridge  20 , which is inserted in the figures, includes: a magnetic tape  21  as a magnetic recording medium with a perpendicular magnetization layer; and two reels  220  and  221  for winding and unwinding (feeding) the magnetic tape  21 . The magnetic tape apparatus  10  further includes a recording/reproducing control circuit for controlling read and/or write operations of the rotary head  11 , though not shown in the figures. 
     The rotary head  11  includes one or more head part  30  (two head parts in the present embodiment), and corresponds to helical-scanning method in the present embodiment; that is, the rotary head  11  is contacted with the magnetic tape  21  and rotates obliquely to read and write data. The peripheral velocity in rotation of the rotary head  11  is set to be sufficiently larger than the running speed of the magnetic tape  21 . The head part  30  includes: an electromagnetic transducer for writing data to the magnetic tape  21  by using perpendicular magnetic recording method; and a magnetoresistive (MR) element for reading data from the magnetic tape  21 , as detailed later. In the helical-scanning method, the record tracks formed by the electromagnetic transducer extends, on the magnetization layer in the magnetic tape, obliquely to the direction in which the tape runs. Tape heads for perpendicular magnetic recording used in the magnetic tape apparatus  10  according to the present invention are not limited to the above-described rotary head  11 ; that is, a linear head can also be used, which has electromagnetic transducer(s) for perpendicular magnetic recording. 
     As detailed later, the soft-magnetic capstan belt  12  has a surface contact with the magnetic tape  21 , and presses the tape  21  to the rotary head  11  to stabilize the contact between the tape  21  and the head  11 . The soft-magnetic capstan belt  12  further controls stably the running speed of the magnetic tape  21  by carrying the magnetic tape  21  along with itself, and thus prevents the stretch of the magnetic tape  21  over time. Furthermore, the soft-magnetic capstan belt  12  plays the same role as a soft-magnetic under layer (SUL) in a hard disk for perpendicular magnetic recording. The soft-magnetic capstan belt  12  is required to have much higher tensile strength than the magnetic tape  21 , and may be a metal ribbon formed of a soft-magnetic material such as, for example, NiFe (Permalloy) or FeCoMnCrSiB in which Cr (chromium), Si (silicon) and B (boron) are added in FeCoMn. The width of the soft-magnetic capstan belt  12  is preferably the same as, or larger than the width of the magnetic tape  21  in order to provide perforation  120  ( FIG. 2 ) described later; thus the width of the soft-magnetic capstan belt  12  could be set to be, for example, approximately 22 mm (millimeters) in the case that the magnetic tape  21  has a width of 12.65 mm. 
     Here, the loading of the tape cartridge  20  will be explained. First, the tape cartridge  20  is moved in the lower (−Z) direction by a loading mechanism (not shown in the figure) from the state as shown in  FIGS. 1   a  and  1   b , in which the tape cartridge  20  has just been inserted from the front surface of the magnetic tape apparatus  10 . Thus, the capstan-belt axes  130 ,  131  and  132  and the soft-magnetic capstan belt  12  are inserted within the tape cartridge  20 . After that, as the capstan-belt axes  130  and  131  are moved in the —X direction by using an arm  134 , the magnetic tape  21  is directly pressed by the soft-magnetic capstan belt  12 , and is pulled out to the rotary head  11 . The arm  134  is moved until, as shown in  FIGS. 1   c  and  1   d , the capstan-belt axes  130  and the pinch roller  140  pinch the soft-magnetic capstan belt  12  and the magnetic tape  21 , and the capstan-belt axes  131  and the pinch roller  141  also do so. 
     In the state of completing the loading as shown in  FIGS. 1   c  and  1   d , that is, in the state of enabling the recording and reproducing, two capstan-belt axes  130  and  131  are positioned, so as to interpose the rotary head  11  between themselves, and on the rear side (in the —X direction) of the curved end surface of the rotary head  11 , the curved end surface being opposed and contacted with the magnetic tape  21 , when viewed from the reels  220  and  221  side (from the side of the front surface of magnetic tape apparatus  10 ). As a result, the soft-magnetic capstan belt  12  contacts and presses the magnetic tape  21  to a part of the curved end surface of the rotary head  11 . Further, the capstan-belt axis  132  is positioned closer to the reels  220  and  221  than the rotary head  11  in the direction along the X-axis, in order to bring about tensile stress in the soft-magnetic capstan belt  12 . The soft-magnetic capstan belt  12  receives a sufficiently large amount of tensile force from the capstan-belt axis  132  due to a spring  133  attached to the capstan-belt axis  132 . Therefore, the soft-magnetic capstan belt  12  presses the magnetic tape  21  to the rotary head  11  with a sufficiently large amount of press force. Conventionally, the well-known capstan method is used for contacting the magnetic tape with the rotary head, in which the pressing load of the magnetic tape to the rotary head depends on the tensile force that the capstan provides to the magnetic tape. On the contrary, the present invention uses the soft-magnetic capstan belt  12  as described above, which enables the magnetic tape  21  and the rotary head  11  to be contacted with each other more stably compared to the conventional method. 
     During recording and reproducing, the soft-magnetic capstan belt  12  has a surface contact with the magnetic tape  21  and runs together with the tape  21  in an integrated manner by a sufficiently large amount of static frictional force, in the range at least from the capstan-belt axis  130  (the pinch roller  140 ) to the capstan-belt axis  131  (the pinch roller  141 ) through the surface of the rotary head  11 . Here, in  FIG. 1   c , an arrow  16  indicates the running direction of the soft-magnetic capstan belt  12 , an arrow  17  indicates the running direction of the magnetic tape  21 , and an arrow  18  indicates the rotation direction of the rotary head  11 . Thus, the soft-magnetic capstan belt  12  acts as a tape feed mechanism, and the running of the magnetic tape  21  is brought about by the whole portion of the tape  21  having a surface contact with the soft-magnetic capstan belt  12  that is running. As a result, the running speed of the magnetic tape  21  coincides with that of the soft-magnetic capstan belt  12 . Conventionally, the magnetic tape runs only by the force transmitted from the rotation of the capstan at the position of the capstan. On the contrary, in the present invention, the soft-magnetic capstan belt  12  has a surface contact with the magnetic tape  21 , and they both run together at the same running speed, which enables the running speed of the magnetic tape  21  to be controlled more stably compared to the conventional. 
     Further, especially even in the position of the rotary head  11  in which large frictional force works to disturb the running of the magnetic tape  21 , the soft-magnetic capstan belt  12  and the magnetic tape  21  run together in an integrated manner. Therefore, the external force working to the magnetic tape  21  becomes mainly shear stress between the front and back surfaces; that is, the force pulling the magnetic tape  21  becomes smaller. Whereas, even in the conventional case of using the configuration with a main tape and an auxiliary tape disclosed in Japanese Patent Publication No. 63-122001A as described above, the auxiliary tape is likely to stretch over time more than the soft-magnetic capstan belt  12 ; that is, the configuration could not effect the suppression of the tape stretch over time. On the contrary, in the present invention, the stretch of the magnetic tape  21  can be suppressed more sufficiently compared to the conventional, which enables the magnetic tape  21  to maintain life sufficiently. 
     Further, in Japanese Patent Publication No. 63-122001A, the auxiliary tape, as well as the main tape, is wound around reels, and in the case using a tape cartridge, both tapes must be stored within the tape cartridge. Therefore, it is significantly difficult to provide an SUL with a sufficiently large thickness in the auxiliary tape. On the contrary, in the present invention, only the magnetic tape  21  is stored within the tape cartridge  20 , and the soft-magnetic capstan belt  12  is a constituent element of the magnetic tape apparatus  20 . Therefore, under the condition of keeping sufficiently large recording density per volume in the form of a reel of magnetic tape  21 , the soft-magnetic capstan belt  12  with a significantly large thickness can be provided in the tape cartridge  10 . 
     In the magnetic tape apparatus  10  according to the present invention, the number of capstan-belt axes and the number of pinch rollers are not limited to those described above. Especially, the number of capstan-belt axes may be, for example, two as shown in  FIG. 1   e  (reference numeral  13 ′). In  FIG. 1   e , a guide plate  19  is provided to guide the soft-magnetic capstan belt  12 . Further, as shown in  FIG. 1   f , four or more capstan-belt axes  13 ″ are provided to control the tensile stress in the soft-magnetic capstan belt  12  and the running condition of the belt  12  into desired ones. Furthermore, a design with no pinch rollers may be possible. 
       FIG. 2  shows a perspective view schematically illustrating the configuration around the capstan-belt axis  130 . 
     As shown in  FIG. 2 , the soft-magnetic capstan belt  12  and the magnetic tape  21  are pinched by the capstan-belt axis  130  and the pinch roller  140 , and run together in an integrated manner even on the rotary head  11 . Here, the soft-magnetic capstan belt  12  has a plurality of through holes (perforation)  120 , and the capstan-belt axis  130  has a plurality of pins  1301  each of which can be fit into the through hole (into the perforation  120 ). A single pin may be possible, though a plurality of pins  1301  is preferable. Providing the perforation  120  and the pins  1301  enables the soft-magnetic capstan belt  12  to be prevented from slipping from the capstan-belt axis  130 . As a result, the rotational motion of a capstan motor  15  is directly transmitted to the soft-magnetic capstan belt  12 , and thus, the running speed of the magnetic tape  21 , which runs together with the soft-magnetic capstan belt  12 , can be more stabilized. As described above, providing the perforation  120  and the pins  1301  is preferable; however, no provision of perforation and pins may be possible. That is, it is possible for the soft-magnetic capstan belt  12  to run depending on the static frictional force between the capstan-belt axis  130  and the soft-magnetic capstan belt  12 . 
       FIG. 3  shows a perspective view schematically illustrating the head part  30  provided in the rotary head  11 . 
     As shown in  FIG. 3 , the head part  30  includes: an MR element  33  for reading data from the magnetic tape  21 ; an electromagnetic transducer  34  for writing data to the magnetic tape  21  by using perpendicular magnetic recording method; and an inter-element shield layer  38  for shielding the MR element  33  magnetically from the electromagnetic transducer  34 . 
     A tape bearing surface (TBS)  110  of the rotary head  11  is a curved end surface opposed to the magnetic tape  21 . The TBS  110  includes: curved end surfaces of head substrates  31  and  31 ′; a curved end surface of an insulating member portion  111  surrounding the head part  30 ; and curved end surfaces of head frames  112 . 
     One ends of MR element  33  and electromagnetic transducer  34  reach the TBS  110  and contact with the magnetic tape  21 . That is, the TBS  110  is an opposed-to-medium surface as well as a sliding surface. In this configuration, during read and write operations, the electromagnetic transducer  34  writes data by applying signal magnetic fields to the running magnetic tape  21 , and the MR element  33  reads data by sensing signal magnetic fields from the running magnetic tape  21 . Here, the width P W  of a main magnetic pole layer  340  in the electromagnetic transducer  34  defines the width of the track formed on the perpendicular magnetization layer of the magnetic tape  21  by the write operation. 
       FIG. 4  shows a cross-sectional view taken along plane A in  FIG. 3 , schematically illustrating the structure of the head part  30 . 
     As shown in  FIG. 4 , the MR element  33  and electromagnetic transducer  34  are formed on/above an element formation surface  310 , which is almost perpendicular to the TBS  110 , of the head substrate  31  made of, for example, AlTiC (Al 2 O 3 —TiC). Further, the head substrate  31 ′ made of, for example, AlTiC (Al 2 O 3 —TiC) is adhered on the insulating layer  39  (a part of the insulating member portion  111  shown in  FIG. 3 ) over the formed MR element  33  and electromagnetic transducer  34 . 
     The MR element  33  is formed on an insulating layer  320  (a part of the insulating member portion  111  shown in  FIG. 3 ), and includes: an MR multilayer  332 ; and a lower shield layer  330  and an upper shield layer  334  which sandwich the MR multilayer  332  and an insulating layer  333  therebetween. The upper and lower shield layers  334  and  330  play a role of preventing the MR multilayer  332  from receiving external magnetic fields that cause noises. The upper and lower shield layers  334  and  330  are, for example, magnetic layers formed by using a frame plating method, a sputtering method or the like, and are made of soft-magnetic material containing, for example, FeSiAl (Sendust), NiFe (Permalloy), CoFeNi, CoFe, FeN, FeZrN or CoZrTaCr, or the multilayer of at least two of these materials, with a thickness of approximately 0.5 to 3 μm. 
     The MR multilayer  332  is a magneto-sensitive portion for sensing signal magnetic fields by using MR effect, and may be an anisotropic magnetoresistive (AMR) multilayer that utilizes AMR effect, a giant magnetoresistive (GMR) multilayer that utilizes GMR effect, or a tunnel magnetoresistive (TMR) multilayer that utilizes TMR effect. Further, in the case of GMR multilayer, it may be a current-in-plane (CIP) GMR multilayer or a current-perpendicular-to-plane (CPP) GMR multilayer. The MR multilayer  332 , which utilizes any of these MR effects, senses signal magnetic fields from the magnetic tape  21  with high sensitivity. In the case that the MR multilayer  332  is a CPP-GMR multilayer or a TMR multilayer, the upper and lower shield layers  334  and  330  also act as electrodes. Whereas, In the case of an AMR multilayer or a CIP-GMR multilayer, a shield layer is provided between the MR multilayer  332  and each of the upper and lower shield layers  334  and  330 , and further, formed are MR lead layers that are electrically connected with the MR multilayer  332 . 
     Also as shown in  FIG. 4 , the electromagnetic transducer  34  is designed for perpendicular magnetic recording in the present embodiment, and includes: a backing coil layer  347 , a main magnetic pole layer  340 ; a gap layer  341 ; a write coil layer  343 ; and a write shield layer  345 . 
     The main magnetic pole layer  340  is provided on an insulating layer  3491  formed of an insulating material such as Al 2 O 3  (alumina), and acts as a magnetic path for converging and guiding magnetic flux, which is excited by a write current flowing through the write coil layer  343 , toward the perpendicular magnetization layer to be written of the magnetic tape  21 . The main magnetic pole layer  340  has a double-layered structure in which a main magnetic pole  3400  and a main pole body  3401  are stacked sequentially and magnetically connected with each other. The main magnetic pole  3400  is isolated by being surrounded with an insulating layer  3491  formed of insulating material such as Al 2 O 3 . The main magnetic pole  3400  reaches the TBS  110 , and has: a main pole front end  3400   a  with a very small width P W  ( FIG. 3 ) in the track width direction; and a main pole rear end  3400   b  located at the rear of the main pole front end  3400   a  and having a width in the track width direction larger than that of the main pole front end  3400   a . Here, the very small width P W  of the main pole front end  3400   a  determines the width of the track formed on the perpendicular magnetization layer of the magnetic tape  21 . The width P W  is, for example, in the range of approximately 1 to 5 μm. Thus, the very small width P W  of the main pole front end  3400   a  enables a fine write field to be generated, so that the track width can be set to be a very small value adequate for higher recording density. 
     The main magnetic pole  3400  is formed of a soft-magnetic material with saturation magnetic flux density higher than that of the main pole body  3401 , which is, for example, an iron (Fe) alloy with Fe as a main component, such as FeNi, FeCo, FeCoNi, FeN or FeZrN. The thickness of the main magnetic pole  3400  is, for example, in the range of approximately 1 to 5 μm. 
     The gap layer  341  acts as a gap provided for magnetically separating the main magnetic pole layer  340  from the write shield layer  345  in the region near the head end surface. The gap layer  341  is formed, for example, of a non-magnetic insulating material such as Al 2 O 3  (alumina), SiO 2  (silicon dioxide), AlN (aluminum nitride) or DLC, or of a non-magnetic conductive material such as Ru (ruthenium). The thickness of the gap layer  341  determines the amount of gap between the main magnetic pole layer  340  and the write shield layer  345 , which is important for controlling write characteristics; and is, for example, in the range of approximately 0.1 to 0.5 μm. 
     The write coil layer  343  is formed, on a insulating layer  3421  made of an insulating material such as Al 2 O 3  (alumina), so as to pass through in one turn at least between the main magnetic pole layer  340  and the write shield layer  345 , and has a spiral structure with a back contact portion  3402  as a center. The write coil layer  343  is formed of a conductive material such as Cu (copper). The write coil layer  343  is covered with a write coil insulating layer  344  that is formed of an insulating material such as a heat-cured photoresist; that is, the write coil insulating layer  344  electrically isolates the write coil layer  343  from the main magnetic pole layer  340  and the write shield layer  345 . 
     The write coil layer  343  has a monolayer structure in the present embodiment, however, may have a two or more layered structure or a helical coil shape. Further, the number of turns of the write coil layer  343  is not limited to that shown in  FIG. 4 , and may be, for example, in the range from two to seven. 
     The write shield layer  345  includes: a first write shield portion  3450  that reaches the TBS  110  and is provided for receiving the magnetic flux spreading from the main magnetic pole layer  340 ; and a second write shield portion  3451  that also reaches the TBS  110 , and is magnetically connected with the first write shield portion  3450 , and acts as a magnetic path for the magnetic flux that returns from the soft-magnetic capstan belt  12  as detailed later, as well as for the magnetic flux that the first write shield portion  3450  receives. The write shield layer  345  is formed of a soft-magnetic material, and especially, the first write shield portion  3450  is formed of a material with high saturation magnetic flux density, such as NiFe (Permalloy) or an iron alloy as the main magnetic pole  3400  is formed of. The thickness of the first write shield portion  3450  is, for example, in the range of approximately 2 to 6 μm. The thickness of the second write shield portion  3451  is, for example, in the range of approximately 2 to 6 μm. 
     The first write shield portion  3450  according to the present invention is planarized together with an insulating layer  3420  and the main pole body  3401 , and has a width in the track width direction larger than the width of the main pole rear end  3400   b  and the main pole body  3401  as well as the main pole front end  3400   a . This write shield portion  3450  can cause the magnetic field gradient between the end portion of the write shield portion  3450  and the main pole front end  3400   a  to be steeper. As a result, jitter of signal output becomes smaller, and therefore, an error rate during read operation can be reduced. 
     The backing coil layer  347  is a coil for negating a magnetic flux loop, which is derived from write current applied to the write coil layer  343  of the electromagnetic transducer  34  and passes through the upper and lower shield layers  334  and  330  of the MR element  33 . That is, the backing coil layer  347  is provided for suppressing unwanted writing or erasing operation by generating magnetic flux to negate the above-described magnetic flux loop. The backing coil layer  347  has a spiral structure with a back contact portion  3402  as a center, and is electrically isolated by the surrounding coil insulating layer  348  and the insulating layers  322  and  3490 , and may be set so that write current flows in the direction opposite to the direction of write current flowing in the write coil layer  343 . The backing coil layer  347  has a monolayer structure in the present embodiment, however, may have a two or more layered structure or a helical coil shape. Further, the number of turns of the backing coil layer  347  is not limited to that shown in  FIG. 4 , and is preferably set, for example, in the range from two to seven in accordance with the number of turns of the write coil layer  343 . It should be noticed that write operation to the perpendicular magnetization layer of the magnetic tape  21  can be performed without the backing coil layer  347 ; that is, an embodiment without the backing coil layer  347  could be in the scope of the present invention. 
     Further, in the present embodiment, an inter-element shield layer  38  is provided between the MR element  33  and the electromagnetic transducer  34 , sandwiched by the insulating layers  321  and  322 . The inter-element shield layer  38  plays a role for shielding the MR element  33  from the magnetic field generated from the electromagnetic transducer  34 , and may be formed of the same soft-magnetic material as the upper and lower shield layers  334  and  330 . It should be noticed that read and write operations by the head part  30  can be performed without the inter-element shield layer  38 ; that is, an embodiment without the inter-element shield layer  38  could be in the scope of the present invention. 
       FIG. 5  shows a cross-sectional view corresponding to the cross-section taken along plane A in  FIG. 3 , for explaining the principle in which perpendicular magnetic recording can be performed adequately by using the soft-magnetic capstan belt  12  according to the present invention. 
       FIG. 5  indicates the state in which, during write operation by the rotary head  11 , the magnetic tape  21  is contacted with the rotary head  11  by being pressed with the soft-magnetic capstan belt  12 . An arrow  51  indicates the running direction of the magnetic tape  21  that has a surface contact with the soft-magnetic capstan belt  12  and is driven integrally with the belt  12 . And an arrow  52  indicates the rotation direction of the rotary head  11 . 
     As shown in  FIG. 5 , the magnetic tape  21  includes: a non-magnetic base film  210  formed of, for example, polyester or the like, with thickness of, for example, approximately 5 to 10 μm; a base layer  211 ; and a perpendicular magnetization layer  212  formed of, for example, CoCr or the like, with thickness of, for example, approximately 50 to 100 nm. The soft-magnetic capstan belt  12  is a metal ribbon formed of a soft-magnetic material such as, for example, NiFe (Permalloy) or FeCoMnCrSiB in which Cr, Si and B are added in FeCoMn, as described above, with thickness of, for example, approximately 10 to 200 μm. 
     During write operation, magnetic flux  50  corresponding to write field, which is generated from the end on the TBS  110  side of the main magnetic pole layer  340  of the electromagnetic transducer  34 , passes through the perpendicular magnetization layer  212  (causes a portion of magnetization of the perpendicular magnetization layer  212  to be turned upward or downward). Then, magnetic flux  50  folds back through the soft-magnetic capstan belt  12 , and reaches the write shield layer  345 . The magnetic flux, which has reached the write shield layer  345 , folds back in the back contact portion  3402 , and returns to the main magnetic pole layer  340 . In this way, the closed loop of magnetic flux corresponding to write field is completed, which enables perpendicular magnetic recording to be effectively performed. That is to say, the soft-magnetic capstan belt  12  according to the present invention plays the same role as a soft-magnetic under layer (SUL) in hard disks for perpendicular magnetic recording. 
     Here, considered will be the case in which an SUL is provided within the magnetic tape  21 , instead of using the soft-magnetic capstan belt  12 . Usually, the thickness of the SUL in the hard disk for perpendicular magnetic recording is, for example, in the range of approximately 30 to 100 nm. However, a tape head generally has a larger size than a thin-film magnetic head for perpendicular magnetic recording. For example, the amount of gap (the thickness of the gap layer) between the main magnetic pole and the auxiliary magnetic pole of the tape head may be ten times or more larger than that of the thin-film magnetic head. Therefore, a significantly large thickness of the SUL in the magnetic tape would be needed according to the difference in scale. However, the significantly large thickness of the SUL would be likely to cause the decrease in recording density per volume in the form of a reel of magnetic tape, the degradation in flexibility of the magnetic tape which would lead an inadequate contact with the head, or the damage such as for the constituent film being peeled from the magnetic tape. 
     On the contrary, in the case of using the soft-magnetic capstan belt  12  according to the present invention, there is no need to provide such a thick SUL within the magnetic tape  21 . Therefore, under the condition of keeping sufficiently large recording density per volume in the form of a reel of magnetic tape  21  in the tape cartridge  20 , the soft-magnetic capstan belt  12  with a significantly large thickness can be provided in the magnetic tape apparatus  10 , which can realize adequate perpendicular magnetic recording. 
     All the foregoing embodiments are by way of example of the present invention only and not intended to be limiting, and many widely different alternations and modifications of the present invention may be constructed without departing from the spirit and scope of the present invention. Accordingly, the present invention is limited only as defined in the following claims and equivalents thereto.