Patent Publication Number: US-2005117242-A1

Title: Perpendicular magnetic head and perpendicular magnetic disk apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-400792, filed Nov. 28, 2003, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a perpendicular magnetic head and a perpendicular magnetic disk apparatus.  
      2. Description of the Related Art  
      A perpendicular recording magnetic disk apparatus comprises a magnetic disk (a so-called perpendicular two-layered film medium), and a perpendicular magnetic head. The magnetic disk includes a soft underlayer made of a high-permeability material, and a perpendicular recording layer having perpendicular magnetic anisotropy. The perpendicular magnetic head has a main pole made of a high-permeability material, a return yoke, and an exciting coil, which produces a perpendicular magnetic field.  
      In a conventional perpendicular magnetic head, however, a perpendicular field component larger than the anisotropy field of the medium easily remains at the distal end portion of the main pole after a write operation, and degrades information already recorded on the medium. This perpendicular field component remaining in the main pole is irregular in both magnitude and frequency of occurrence. Therefore, it is difficult to suppress the residual perpendicular magnetic field in the main pole only by controlling the material or shape of the main pole.  
      It should be noted that a technique is known which heats a magnetic pole in order to prevent the phenomenon in which stress acts on the magnetic pole due to a temperature change of the magnetic pole before and after writing data, a magnetic domain formed during the writing remains, and the movement of this magnetic domain is detected as noise (Jpn. Pat. Appln. KOKAI Publication No. 4-305809). In this technique, however, the entire surface of the return yoke is heated, so the pole may extend toward the disk because of thermal expansion if excessively heated.  
     BRIEF SUMMARY OF THE INVENTION  
      A perpendicular magnetic head according to an aspect of the present invention comprises: a write head comprising a main pole, a return yoke and an exciting coil, which produces a perpendicular magnetic field; and a heater located near the main pole.  
      A perpendicular magnetic disk apparatus according to another aspect of the present invention comprises: a perpendicular two-layered film medium comprising a soft underlayer and a perpendicular magnetic recording layer; a write head comprising a main pole, a return yoke and an exciting coil, which produces a perpendicular magnetic field; and a heater located near the main pole. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       FIG. 1  is a perspective view showing a magnetic head according to a first embodiment;  
       FIG. 2  is a sectional view showing a magnetic head and a magnetic disk of a perpendicular magnetic disk apparatus according to the first embodiment;  
       FIG. 3  is a plan view showing an example of a heater used in the magnetic head according to the first embodiment;  
       FIG. 4  is a block diagram showing an example of a control circuit for the heater used in the magnetic head according to the first embodiment;  
       FIGS. 5A and 5B  are schematic views each showing energy states of magnetic domains in a main pole;  
       FIG. 6A  is a graph showing the read output waveform of a signal already recorded on the medium;  
       FIG. 6B  is a graph showing the change in write current during overwriting;  
       FIG. 6C  is a graph showing the read output waveform of a signal already recorded on the medium and detected after overwriting is performed using a conventional magnetic head;  
       FIG. 7A  is a graph showing the read output waveform of a signal already recorded on the medium;  
       FIG. 7B  is a graph showing the change in write current during overwriting;  
       FIG. 7C  is a graph showing the read output waveform of a signal already recorded on the medium and detected after overwriting is performed by using the magnetic head according to the first embodiment;  
       FIG. 8  is a block diagram showing another example of a control circuit for the heater used in the magnetic head according to the first embodiment;  
       FIG. 9  is a sectional view showing a magnetic head and a magnetic disk of a perpendicular magnetic disk apparatus according to a second embodiment;  
       FIG. 10  is a sectional view showing a magnetic head and a magnetic disk of a perpendicular magnetic disk apparatus according to a third embodiment;  
       FIG. 11  is a perspective view showing a magnetic head according to a fourth embodiment;  
       FIG. 12  is a plan view showing an example of a heater used in the magnetic head according to the fourth embodiment; and  
       FIG. 13  is a plan view showing another example of a heater used in the magnetic head according to the fourth embodiment.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Embodiments of the present invention will be described below with reference to the accompanying drawings.  
     First Embodiment  
       FIG. 1  is perspective view showing a magnetic head according to a first embodiment of the present invention.  FIG. 2  is a sectional view showing a magnetic head and a magnetic disk used in a perpendicular magnetic disk apparatus according to the first embodiment.  FIG. 3  is a plan view showing an example of a heater used in the magnetic head according to the first embodiment.  FIG. 4  is a block diagram showing an example of a control circuit for the heater used in the magnetic head according to the first embodiment.  
      As shown in  FIG. 2 , the magnetic disk is a so-called perpendicular two-layered film medium having a soft underlayer  23  and a perpendicular recording layer  22  formed on a substrate  25 . The perpendicular recording layer  22  has anisotropy perpendicular to the disk surface.  
      The magnetic head shown in  FIGS. 1 and 2  is a separated magnetic head in which a write head and a read head are separated.  
      The write head comprises a main pole  1 , a return yoke  2  located on the leading side of the main pole  1 , and an exciting coil  6 . A heater  13  is located, in contact with or not in contact with the main pole  1 , on the trailing side of the main pole  1 . The heater  13  opposes that a narrowed neck portion (or a tapered portion) of the main pole  1  that changes from a wide portion far from the air-bearing surface (ABS) to a narrow portion close to the air-bearing surface (ABS). The main pole  1  is made of a high-permeability material, and produces a magnetic field perpendicular to the magnetic disk surface. The return yoke  2  forms a magnetic path between the main pole  1  and the soft underlayer  23  of the magnetic disk. The exciting coil  6  is wound around a connecting portion between the main pole  1  and the return yoke  2 , and excites the main pole  1  to produce magnetic flux. As shown in  FIG. 3 , for example, the heater  13  is made of a conductor which is a zigzagged wire. The heater  13  is connected to current electrodes  7   a  and  7   b.    
      The read head comprises a magnetoresistive film  5 , and shield films  3  and  4  arranged on the trailing side and the leading side, respectively, so as to sandwich the magnetoresistive film  5 .  
      As shown in  FIG. 4 , a control circuit for the heater is constituted by a current controller  51  controlling a current to the heater  13 , a decision circuit  52  deciding the operation of the current controller  51 , a write gate  57  which supplies a current to the exciting coil  6 , and a write amplifier  58 . The write amplifier  58  is connected to the decision circuit  52 . The decision circuit  52  controls the current to the heater  13  by interlocking it with the current supplied to the exciting coil  6 . The operation decision by the decision circuit  52  is so controlled that a current is supplied to the heater  13  during a write operation and for a predetermined time after the write operation. In this control, if I is the current supplied to the heater  13  during the write operation, and R is the resistance of the heater  13 , the current is preferably controlled by the current controller  51  so that R×I 2  is constant. The time at which the supply of a current to the heater  13  is terminated is preferably less than one second after the completion of the write operation. It is also possible to record a control pattern in the end portion of a data sector of the disk at a frequency which is half or more the highest frequency, and supply a current to the heater  13  until this control pattern is completed.  
       FIG. 5A  is a graph showing energy states of magnetic domains in the main pole. The lowest energy level is in a state that all magnetization in the entire magnetic domain is parallel to the easy axis, i.e., parallel to the medium surface. In the main pole  1 , however, a plurality of local minimum energy levels exist in addition to the lowest energy level. In a magnetic domain in the state of this local minimum energy level other than the lowest energy level, magnetization is not completely parallel to the medium surface, i.e., magnetization having a perpendicular component remains. If, for example, a write operation is abruptly terminated, the energy state of a magnetic domain in the main pole does not fall to the lowest energy level in some cases, and remains at the local minimum energy level. Referring to  FIG. 5A , for example, the energy state of a magnetic domain in the main pole is at the local minimum energy level indicated by a solid circle. In this case, a perpendicular field component remains at the distal end portion of the main pole, and degrades or erases information already recorded on the medium.  
      The energy state of the magnetic domain in the main pole shown in  FIG. 5A  can be changed by exposing the main pole to a high temperature. When the main pole is exposed to a high temperature, a state having no local minimum levels can be obtained, as shown in, e.g.,  FIG. 5B .  
      In the present invention, the heater  13  is located near the main pole  1  in order to obtain a state having no or few local minimum levels when a write operation is terminated. After the write operation is terminated, a current is supplied to the heater  13  for only a certain time to heat the main pole  1 , so that the energy state of a magnetic domain in the main pole falls to the lowest energy level. Consequently, all magnetization in the main pole becomes parallel to the medium surface as the direction of easy axis, so that a perpendicular field component is no longer applied from the main pole to the medium. Accordingly, information already recorded on the medium is not degraded or erased after a write operation is terminated.  
       FIGS. 6A  to  6 C are graphs showing the results when read outputs are checked before and after overwriting using the conventional magnetic head.  FIGS. 7A  to  7 C are graphs showing the results when read outputs are checked before and after overwriting using the magnetic head of this embodiment.  
       FIGS. 6A and 7A  illustrate the read output waveforms of signals already recorded on the medium.  FIGS. 6B and 7B  are graphs each showing the change in write current during overwriting.  FIGS. 6C and 7C  illustrate the read output waveforms of signals after overwriting.  
      When the conventional magnetic head was used, as shown in  FIG. 6C , the output of the already recorded signal fell after the write current was terminated. In contrast, when the magnetic head of this embodiment was used, as shown in  FIG. 7C , no degradation of the output of the already recorded signal was found after the write current was terminated.  
      It should noted that the control circuit for the heater is not limited to that shown in  FIG. 4 , and a control circuit as shown in  FIG. 8  may also be used. The control circuit for the heater shown in  FIG. 8  comprises a current controller  51  for controlling the current to the heater  13 , a decision circuit  52  for deciding the operation of the current controller  51 , and a temperature sensor  53  connected to the decision circuit  52  and installed in a hard disk drive (HDD). This control circuit decides the operation in accordance with the internal temperature of the HDD. For example, the current controller  51  controls the current supplied to the heater  13  so that the resistance of the heater  13  is larger than that at room temperature. This is so because magnetic domains in the main pole  1  readily become unstable at low temperatures, and this increases the probability that a perpendicular magnetization component will remain at the distal end portion of the main pole immediately after a write operation, making it necessary to avoid a low-temperature operation of the main pole during HDD operation.  
     Second Embodiment  
       FIG. 9  is a sectional view showing a magnetic head and a magnetic disk of a perpendicular magnetic disk apparatus according to a second embodiment.  
      The magnetic head shown in  FIG. 9  is a separated magnetic head in which a write head and a read head are separated. Referring to  FIG. 9 , the write head comprises a main pole  1 , a return yoke  15  located on the trailing side of the main pole  1 , and an exciting coil  6 . Also, a heater  13  is located, in contact with or not in contact with the main pole  1 , on the leading side of the main pole  1 .  
      The arrangement of the read head and the arrangement of the magnetic disk are the same as in the first embodiment. The shape and position of the heater  13  are also the same as in the first embodiment. As a control circuit for the heater, the circuit shown in  FIG. 4  or  8  explained in the first embodiment is used.  
      Even when the write head shown in  FIG. 9  is used, information already recorded on the medium is not degraded or erased after a write operation is terminated.  
     Third Embodiment  
       FIG. 10  is a sectional view showing a magnetic head and a magnetic disk of a perpendicular magnetic disk apparatus according to a third embodiment.  
      The magnetic head shown in  FIG. 10  is a separated magnetic head in which a write head and a read head are separated. The write head comprises a main pole  1 , a return yoke  2  located on the leading side of the main pole  1 , and an exciting coil  6 . The distal end portion of the main pole  1  is recessed relative to the air-bearing surface (ABS) of the magnetic head. The recess amount is desirably 0.1 μm or less. Also, a heater  13  is located, in contact with or not in contact with the main pole  1 , on the trailing side of the main pole  1 .  
      The arrangement of the read head and the arrangement of the magnetic disk are the same as in the first embodiment. The shape and position of the heater  13  are also the same as in the first embodiment. As a control circuit for the heater, the circuit shown in  FIG. 4  or  8  explained in the first embodiment is used.  
      In the magnetic head shown in  FIG. 10 , the main pole  1  expands as a result of thermal conduction from the heater  13  and comes close to the ABS, thereby performing a write operation.  
      Even when the write head shown in  FIG. 10  is used, information already recorded on the medium is not degraded or erased after a write operation is terminated.  
     Fourth Embodiment  
       FIG. 11  is a perspective view showing a magnetic head according to a fourth embodiment.  FIG. 12  is a plan view showing an example of a heater used in the magnetic head according to the fourth embodiment.  FIG. 13  is a plan view showing another example of a heater used in the magnetic head according to the fourth embodiment.  
      The magnetic head shown in  FIG. 11  is a separated magnetic head in which a write head and a read head are separated. The write head comprised a main pole  1 , a return yoke  2  located on the leading side of the main pole  1 , and an exciting coil  6 . As shown in  FIG. 12 , a heater  19  made of a plurality of wires branched from the exciting coil  6  is located on the leading side of a tapered portion of the main pole  1 .  
      As shown in  FIG. 13 , a heater  19  made of a zigzagged wire branched from the exciting coil  6  may also be located on the leading side of the tapered portion of the main pole  1 .  
      The arrangement of the read head and the arrangement of the magnetic disk are the same as in the first embodiment. As a control circuit for the heater, the circuit shown in  FIG. 4  or  8  explained in the first embodiment is used.  
      In the fourth embodiment, a current is also supplied to the heater  19  branched from the exciting coil  6  during a write operation, so the main pole  1  is constantly heated during the write operation and is not abruptly cooled even immediately after the write operation. Therefore, no local minimum levels exist in the main pole, the states of magnetic domains fall to the lowest energy level, and all magnetization is parallel to the easy-axis and so is stable. This prevents a perpendicular field component from remaining at the distal end portion of the main pole after a write operation is terminated, and prevents degradation or erasure of information already recorded on the medium.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.