JP2009004023A - Magnetic recording and reproducing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To normally operate a reproducing element even if the unidirectional anisotropy of a magnetization pinned layer of the reproducing element disappears due to a rise in temperature not lower than a blocking temperature. <P>SOLUTION: When a signal amount of a reproducing signal outputted from a reproducing element of a head 32 is lower than a prescribed value, a heater 10 starts to emit laser light 39. The emitted laser light 39 raises temperatures of a first ferromagnetic layer and an antiferromagnetic layer included in the reproducing element to temperatures not lower than the blocking temperature. A magnet 9 always generates a DC magnetic field. In a process of lowering the temperatures of the first ferromagnetic layer and the antiferromagnetic layer to the temperatures lower than the blocking temperature, the first ferromagnetic layer is imparted with the unidirectional anisotropy once again in a direction the same as the DC magnetic field generated by the magnet 9. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic recording / reproducing system.

  2. Description of the Related Art In recent years, an increasing capacity has been required for a magnetic recording / reproducing system using a hard disk drive (HDD) as an example.

  Here, the principle of recording and reproduction of the hard disk drive will be described. The hard disk drive handles the difference in the magnetization direction of the magnetic bits on the recording medium as information. The magnetization direction of the magnetic bit is determined by the recording element, and the magnetization direction of the magnetic bit is read by the reproducing element. In recent years, a magnetoresistive effect element capable of realizing a reduction in size and a large reproduction signal is used as a reproducing element in order to cope with a decrease in magnetic bits with an increase in recording density.

  The reproduction principle of a tunnel magnetoresistive element (TMR element) which is an example of a magnetoresistive element will be described. The TMR element has three layers: a ferromagnetic layer (magnetization pinned layer) whose magnetization direction is fixed, an insulating layer, and a ferromagnetic layer (magnetization free layer) that senses a leakage magnetic field from a magnetic bit. A current is passed through the insulating layer and the magnetization free layer. At this time, since the thickness of the insulating layer is as thin as several nm, a tunnel current flows through the insulating layer. Although the magnetization direction of the magnetization free layer changes depending on the direction of the leakage magnetic field from the magnetic bit, the magnetization direction of the magnetization fixed layer does not change. When the magnetization direction of the magnetization free layer and the magnetization direction of the magnetization fixed layer are nearly parallel to each other, the tunnel probability increases and the electrical resistance decreases. Further, when the magnetization direction of the magnetization free layer and the magnetization direction of the magnetization fixed layer are close to each other, the tunnel probability is low and the electric resistance is increased. The difference in electrical resistance makes it possible to determine the magnetization direction of the magnetic bit, that is, to reproduce the magnetic bit information.

  Here, in order to read the magnetization direction of the magnetic bit, the magnetization direction of the magnetization fixed layer needs to be fixed. When not only the magnetization direction of the magnetization free layer but also the magnetization direction of the magnetization fixed layer is changed by the leakage magnetic field from the magnetic bit, the magnetization directions of the magnetization free layer and the magnetization fixed layer are always the same, This is because the resistance value is always small, and the difference in the magnetization direction of the magnetic bit cannot be read.

  The internal temperature of the hard disk drive may rise to 100 degrees or more during operation. Further, the inside of the magnetoresistive effect element may be heated to a higher temperature due to self-heating generated when a current is passed or an instantaneous temperature rise due to generation of static electricity. The anti-ferromagnetic layer laminated on the magnetization fixed layer in order to fix the magnetization direction of the magnetization fixed layer by these temperature increases and the magnetization fixed layer by exchange coupling, There is a possibility that the temperature will rise above the blocking temperature, which is the temperature at which the unidirectional anisotropy disappears. When the temperature of the antiferromagnetic layer and the pinned magnetic layer rises above the blocking temperature, the exchange coupling becomes weak and the unidirectional anisotropy of the pinned magnetic layer disappears. Due to leakage magnetic fields in various directions from the bit, the magnetization direction of the magnetization fixed layer is different from the initial direction or the magnetization is reduced. If the magnetization direction of the magnetization pinned layer is different from the initial direction or the magnetization becomes small, even if the magnetization free layer detects the leakage magnetic field from the magnetic bit, the electric resistance value of the magnetoresistive effect element Does not change as normal, and information from the magnetic bit cannot be read accurately.

  In order to ensure the stable operation of the hard disk drive, Patent Document 1 discloses an exchange coupling element that improves the blocking temperature and a manufacturing method thereof. According to the method of Patent Document 1, since a high blocking temperature is obtained, the heat resistance of the magnetoresistive effect element is improved, and the disappearance of the unidirectional anisotropy of the magnetization fixed layer due to the temperature rise during the operation of the hard disk drive is suppressed. It becomes possible.

JP 2005-333106 A

  Although the heat resistance is improved and the operation is stabilized by the method disclosed in Patent Document 1, the magnetization fixed layer and the antiferromagnetic layer are not less than the blocking temperature due to an instantaneous temperature rise due to the generation of static electricity during the operation of the hard disk drive. In some cases, the temperature rises instantaneously, and the disappearance of the unidirectional anisotropy of the magnetization fixed layer of the reproducing element cannot be completely suppressed. If the unidirectional anisotropy of the magnetization fixed layer is lost once in operation, the reproducing element does not operate normally.

Means for Solving the Problems and Effects of the Invention

  The magnetic recording / reproducing system of the present invention is a magnetic recording / reproducing system having a magnetic head including a reproducing element in which an antiferromagnetic layer, a first ferromagnetic layer, an intermediate layer, and a second ferromagnetic layer are laminated in this order. The antiferromagnetic layer and the first ferromagnetic layer have a temperature equal to or higher than a blocking temperature, which is a temperature at which unidirectional anisotropy of the first ferromagnetic layer due to exchange coupling of these two layers disappears. And a magnetic field applying means for applying a DC magnetic field having a magnitude greater than the coercive force of the first ferromagnetic layer to the antiferromagnetic layer and the first ferromagnetic layer.

  When the temperature of the reproducing element rises for some reason during the operation of the magnetic recording / reproducing system, and the unidirectional anisotropy of the first ferromagnetic layer in the reproducing element disappears, the antiferromagnetic layer and the first ferromagnetic layer The layer is heated to a temperature equal to or higher than the blocking temperature, and cooled while applying a magnetic field, so that exchange coupling in a desired direction is again imparted to the first ferromagnetic layer, and the first ferromagnetic layer is unidirectionally different. A directionality can be imparted. For this reason, stable reproduction can be provided.

  In the present invention, the temperature raising means raises the temperature of the antiferromagnetic layer and the first ferromagnetic layer when the signal amount of the reproduction signal output from the reproduction element becomes smaller than a predetermined value. While the DC magnetic field is applied to the antiferromagnetic layer and the first ferromagnetic layer, the antiferromagnetic layer and the first ferromagnetic layer are blocked from the temperature equal to or higher than the blocking temperature. The temperature may be lowered to a temperature lower than the temperature. In the following explanation, “After raising the temperature of the antiferromagnetic layer and the first ferromagnetic layer to a temperature equal to or higher than the blocking temperature, the temperature is lowered to a temperature lower than the blocking temperature while applying a magnetic field, The step of re-applying exchange coupling force to the magnetic layer is referred to as an exchange coupling re-grant process.

  According to this, when the signal amount of the reproduction signal becomes smaller than a predetermined value, the exchange coupling reassignment process can be performed in real time. Further, when the exchange coupling is not lost, the exchange coupling re-applying process is not performed, so that it is possible to save energy for temperature increase and magnetic field application.

  At this time, the temperature raising means includes a heating member for heating the antiferromagnetic layer and the first ferromagnetic layer, a detection means for detecting a signal amount of the reproduction signal output from the reproduction element, Determining means for determining whether or not a signal amount detected by the detecting means is smaller than the predetermined value; and when the determining means determines that the signal amount is smaller than the predetermined value, the reaction by the heating member is performed. Heating starting means for starting heating of the ferromagnetic layer and the first ferromagnetic layer may be included.

  Further, the magnetic recording / reproducing system according to the present invention generates a near-field light that is irradiated to the recording medium when recording information on the recording medium based on the laser light source and the irradiation position of the laser light emitted from the laser light source. There may be further provided switching means for switching between a position and a position where the antiferromagnetic layer and the first ferromagnetic layer are heated. According to this, since the laser light source can be used for both generation of near-field light and heating of the antiferromagnetic layer and the first ferromagnetic layer, the configuration of the system can be simplified.

<First Embodiment>
A first embodiment of the present invention will be described. FIG. 1A is a schematic plan view of a hard disk drive included in the magnetic recording / reproducing system according to the present embodiment, and shows a case where recording or reproduction is not performed. FIG. 1B is a schematic plan view of the same hard disk drive as FIG. 1A, and shows a case where recording or reproduction is performed. FIG. 2A is a schematic longitudinal sectional view of a part of the hard disk drive shown in FIGS. 1A and 1B along the width direction of the suspension when recording or reproduction is not performed. . FIG. 2B is a schematic longitudinal sectional view of a part of the hard disk drive shown in FIGS. 1A and 1B along the longitudinal direction of the suspension when recording or reproduction is not performed. . FIG. 3 is a longitudinal sectional view of a part of the hard disk drive shown in FIGS. 1A and 1B along the longitudinal direction of the suspension during recording or reproduction.

  The magnetic recording / reproducing system according to the present embodiment includes the hard disk drive 101 shown in FIGS. 1 to 3 and a control device 120 (see FIG. 9) that controls the operation of the hard disk drive 101. The hard disk drive 101 includes a cover 1, a disk-shaped magnetic recording medium 2, a head gimbal assembly 51 adjacent to the medium 2, a lamp 8, a magnet 9, and a heater 10. The medium 2 rotates in a direction indicated by an arrow 4 at a constant speed with a motor (not shown) as a drive source around the medium support portion 3. The head gimbal assembly 51 includes a head 32, a suspension 7 having a horizontally extending tab 11 at the tip, a head arm 6, and a bearing unit 5. In FIG. 2A, a lamp 8 is provided in front of the page. In FIG. 2B, a heater 10 is provided in front of the paper surface.

  As shown in FIG. 3, the head 32 includes a slider 12 for floating the head 32 to a height of several nm to several tens of nm from the surface of the medium 2, and a recording element 33 for recording information on the medium 2. And a reproducing element 17 for reproducing information recorded on the medium 2. The suspension 7 holds the head 32. The head arm 6 holds the suspension 7.

  The bearing unit 5 connects a motor 53 (see FIG. 9) and the head arm 6. The rotation of the motor 53 causes the head gimbal assembly 51 to swing in the horizontal plane around the bearing unit 5. Thereby, as shown in FIG. 1B, the head 32 is positioned on the medium 2 at the time of recording or reproducing, and as shown in FIG. 1A, the head 32 is on the medium 2 when not recording or reproducing. Not. That is, the head 32 moves to a position facing the medium 2 on the medium 2 (hereinafter referred to as “opposing position”) before the start of recording or reproduction, and the head 32 moves from above the medium 2 after the recording or reproduction ends. Retreat to a position that does not face the medium 2 (hereinafter referred to as “retreat position”).

  In the present embodiment, the heater 10 includes a laser light source. As shown in FIG. 2A, the laser beam 39 emitted from the heater 10 is applied to the reproducing element 17 in the retracted position. Thus, the heater 10 functions to raise the temperature of the reproducing element 17. As shown in FIG. 2 (a), the magnet 9 is a permanent magnet and always generates a DC magnetic field. The direction 13 of the DC magnetic field is an upward direction on the page. As a result, the magnet 9 functions to apply a DC magnetic field to the reproducing element 17.

  As shown in FIG. 2B, a convex portion 8 a is provided on the side surface of the lamp 8. When the head 32 is in the retracted position, the tab 11 is hooked on the convex portion 8a. Thus, the head 32 is held in the air without contacting the cover 1 or the magnet 9.

  A detailed explanation of the movement of the head during recording or reproduction will be given. At the time of recording or reproducing, as shown in FIGS. 1B and 3, the head 32 is located at an opposing position on the rotating medium 2. At this time, information is recorded as a magnetization direction on the medium 2 by the recording element 33, and information recorded on the medium 2 is reproduced by the reproducing element 17. Since the concave-convex pattern shape is provided on the medium facing surface of the slider 12, a force to move away from the medium 2 is generated when the medium 2 rotates. The head 32 is held at a height of several nanometers to several tens of nanometers from the surface of the medium 2 due to a balance between the force to leave and the force to approach the medium 2 applied from the suspension 7 to the head 32. .

  Detailed explanation of the movement of the head when it is not recorded or reproduced. When recording or reproduction is not performed, the head 32 is retracted to the retracted position as shown in FIG. 1A in order to prevent a collision with the medium 2. At this time, the tab 11 provided on the suspension 7 is hooked on the convex portion 8 a of the ramp 8 so that the head 32 is held in the air without contacting any part other than the suspension 7.

  Next, the structure of the head 2 will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4A is a longitudinal sectional view of the head 32 along the longitudinal direction of the suspension 7. FIG. 4B is a bottom view of the head 32.

  4A and 4B, the head 32 includes an insulating layer 18, two electrode layers 16 that are in contact with the slider 12 via the insulating layer 18, and a gap between the two electrode layers 16. And a reproducing element 17 sandwiched therebetween. The electrode layer 16 functions to flow a sense current for measuring the resistance value of the reproducing element 17. Further, the head 32 has a recording element 33 that records magnetization information on the magnetic bits of the medium 2. The recording element 33 has a recording magnetic pole 20 and a return magnetic pole 19. A coil (not shown) is wound around the head 32, and depending on the direction of the current flowing in the coil, the direction of the magnetic field passing through the medium facing surface of the recording magnetic pole 20 (outward from the medium facing surface, or , Entering toward the medium facing surface) is controlled. The magnetization direction of the recording bit on the medium 2 is determined by the direction of the magnetic field passing through the medium facing surface of the recording magnetic pole 20. A magnetic field passing through the medium facing surface of the recording magnetic pole 20 passes in the opposite direction to the medium facing surface of the return magnetic pole 19.

  Next, the reproducing element 17 when no external magnetic field is applied will be described with reference to FIG. Here, the reproducing element 17 is a magnetoresistive effect element whose electric resistance value changes depending on the magnetization direction of the ferromagnetic layer of the reproducing element.

  The reproducing element 17 has an antiferromagnetic layer 24, a first ferromagnetic layer 25, an intermediate layer 26, and a second ferromagnetic layer 27. As an example of the configuration of the reproducing element 17, there are MnIr as the antiferromagnetic layer 24, CoFeB as the first ferromagnetic layer 25, MgO as the intermediate layer 26, and NiFe as the second ferromagnetic layer 27. The reproducing element 17 is formed by forming an antiferromagnetic layer 24, a first ferromagnetic layer 25, an intermediate layer 26, and a second ferromagnetic layer 27 in this order. Here, the blocking temperature of MnIr is 250 ° C. In addition, since NiFe has a small coercive force of several hundred A / m or less (several Oe or less), the magnetization direction can be easily changed by the leakage magnetic field from the magnetic bit 28 (see FIG. 7A) of the medium 2. It acts as a layer for sensing the magnetization information of the magnetic bit 28. The magnetization direction 22 of the first ferromagnetic layer 25 is fixed by magnetic coupling (exchange coupling: the direction of the arrow 21) provided from the antiferromagnetic layer 24. The magnetization direction 23 of the second ferromagnetic layer 27 is rotated by 90 degrees from the magnetization direction 22 of the first ferromagnetic layer 25 when there is no leakage magnetic field from the magnetic bit of the medium 2.

  Here, a method for providing exchange coupling from the antiferromagnetic layer 24 to the first ferromagnetic layer 25 will be described. The temperature is raised to a temperature equal to or higher than the temperature at which exchange coupling, which is magnetic coupling between the antiferromagnetic layer 24 and the first ferromagnetic layer 25, disappears (blocking temperature). While the magnetic field is applied to the antiferromagnetic layer 24 and the first ferromagnetic layer 25, the temperature is lowered to a temperature lower than the blocking temperature, whereby exchange coupling from the antiferromagnetic layer 24 to the first ferromagnetic layer 25 is achieved. Is granted. In the process of the temperature decreasing from a temperature higher than the blocking temperature to a temperature lower than the blocking temperature, exchange coupling is established between the antiferromagnetic layer 24 and the first ferromagnetic layer 25 in the direction of the magnetic field applied at this time. Occurs.

  Next, changes in the resistance value of the reproducing element 17 depending on the direction of the external magnetic field will be described with reference to FIGS. 6 (a) and 6 (b). Since the reproducing element 17 is a magnetoresistive effect element, the resistance value changes depending on the relative relationship between the magnetization direction 22 of the first ferromagnetic layer 25 and the magnetization direction 23 of the second ferromagnetic layer 27. The magnetization direction 22 of the first ferromagnetic layer 25 is given unidirectional anisotropy by exchange coupling provided from the antiferromagnetic layer 24 and is fixed in one direction. On the other hand, since the second ferromagnetic layer 27 is made of a material having a small coercive force, its magnetization direction is easily changed by an external magnetic field.

  As shown in FIG. 6A, when the magnetization direction 23 of the second ferromagnetic layer 27 is changed by an external magnetic field or the like and becomes the same direction as the magnetization direction 22 of the first ferromagnetic layer 25, the current is When flowing, the ratio of electrons moving from the first ferromagnetic layer 25 to the second ferromagnetic layer 27 through the intermediate layer 26 increases, so the first ferromagnetic layer 25, the intermediate layer 26, The resistance value of the current flowing through the ferromagnetic layer 27 becomes low.

  On the other hand, as shown in FIG. 6B, when the magnetization direction 23 of the second ferromagnetic layer 27 is changed by an external magnetic field or the like and is opposite to the magnetization direction 22 of the first ferromagnetic layer 25, Since the rate at which electrons move from the first ferromagnetic layer 25 through the intermediate layer 26 to the second ferromagnetic layer 27 becomes small, the first ferromagnetic layer 25, the intermediate layer 26, and the second ferromagnetic layer The resistance value of the current flowing through 27 increases. At this time, the magnetization direction 22 of the first ferromagnetic layer 25 does not change even when an external magnetic field is applied by exchange coupling provided from the antiferromagnetic layer 24. Further, even if the magnetization direction 22 of the first ferromagnetic layer 25 and the magnetization direction 23 of the second ferromagnetic layer 27 are not completely parallel or antiparallel, the direction 23 shown in FIG. If the direction is other than the direction rotated 90 degrees from the magnetization direction 22 of 25, the resistance value of the reproducing element 17 is changed from the case of FIG. 5 although the rate of change is smaller than in the case of completely parallel and antiparallel. Therefore, information can be reproduced.

  Next, the positional relationship between the reproducing element 17 and the medium 2 when the head 32 is at the opposing position will be described with reference to FIGS. 7 (a) and 7 (b). FIG. 7A is a longitudinal sectional view of the reproducing element 17 and the medium 2 along the circumferential direction of the medium 2. FIG. 7B is a longitudinal sectional view of the reproducing element 17 and the medium 2 along the radial direction of the medium 2 so as to include the second ferromagnetic layer 27. In these drawings, an arrow 30 indicates the rotation direction of the medium. As shown in FIG. 7A, the stacking direction of each layer of the reproducing element 17 is substantially parallel to the medium surface. In the present embodiment, since the magnetization direction of the magnetic bit 28 is perpendicular to the medium surface, the magnetization direction 22 of the first ferromagnetic layer 25 is the antiferromagnetic layer 24. Is fixed in a direction perpendicular to the medium surface by the exchange coupling applied from the above. The magnetization direction 23 of the second ferromagnetic layer 27 is changed by the bias magnetic field applied from a bias layer (not shown) provided adjacent to the second ferromagnetic layer 27. 25 is directed in a direction perpendicular to the magnetization direction 22 (direction perpendicular to the paper surface).

  Next, the principle of reproducing the magnetic information of the medium 2 will be described with reference to FIGS. 8 (a) and 8 (b). FIG. 8A is a longitudinal sectional view of the reproducing element 17 and the medium 2 along the radial direction of the medium 2 so as to include the second ferromagnetic layer 27, and the magnetization direction 29 of the magnetic bit 28 and the second direction. The case where the magnetization direction 22 of the one ferromagnetic layer 25 is substantially the same is shown. FIG. 8B shows a case where the magnetization direction 29 of the magnetic bit 28 and the magnetization direction 22 of the first ferromagnetic layer 25 are opposite to each other.

  When the magnetic bit 28 to be reproduced is not magnetized and there is no leakage magnetic field from the magnetic bit 28 as shown in FIGS. 7A and 7B, the magnetization direction 23 of the second ferromagnetic layer 27. Is rightward on the page. On the other hand, as shown in FIG. 8A, when the magnetization direction 29 of the magnetic bit 28 to be reproduced is upward, the upward leakage magnetic field indicated by the arrow 31 penetrates the second ferromagnetic layer 27. . Since the direction of the leakage magnetic field is the same as the magnetization direction 22 of the first ferromagnetic layer 25, the magnetization direction 23 of the second ferromagnetic layer 27 of the reproducing element 17 is inclined upward in the drawing by the leakage magnetic field. The magnetization direction 22 of the first ferromagnetic layer 25 is fixed upward by the exchange coupling from the antiferromagnetic layer 24. Thus, when the magnetization direction 29 of the magnetic bit 28 is the same as the magnetization direction 22 of the first ferromagnetic layer 25, the magnetization direction 22 of the first ferromagnetic layer 25 and the magnetization direction of the second ferromagnetic layer 27. Since 23 is substantially parallel, the electric resistance value of the reproducing element 17 which is a magnetoresistive effect element becomes small.

  On the other hand, as shown in FIG. 8B, when the magnetization direction 29 of the magnetic bit 28 to be reproduced is downward, a leakage magnetic field downward as indicated by an arrow 31 penetrates the second ferromagnetic layer 27. Since the direction of the leakage magnetic field is opposite to the magnetization direction 22 of the first ferromagnetic layer 25, the magnetization direction 23 of the second ferromagnetic layer 27 of the reproducing element 17 is inclined downward in the drawing due to the leakage magnetic field. Thus, when the magnetization direction 29 of the magnetic bit 28 is opposite to the magnetization direction 22 of the first ferromagnetic layer 25, the magnetization direction 22 of the first ferromagnetic layer 25 and the magnetization of the second ferromagnetic layer 27. Since the direction 23 is substantially antiparallel, the electrical resistance value of the reproducing element 17 is increased.

  Therefore, the magnetization information of the magnetic bit 28 in the medium 2 can be read by measuring the electric resistance value of the reproducing element 17. Thus, the reproducing element 17 is based on the relationship between the magnetization direction 22 of the fixed first ferromagnetic layer 25 and the magnetization direction 23 of the second ferromagnetic layer 27 whose direction is changed by the leakage magnetic field from the magnetic bit 28. Since information is reproduced, it is important that the magnetization direction 22 of the first ferromagnetic layer 25 is fixed in one direction for accurate reproduction.

  In the magnetic recording / reproducing system, the disappearance of the exchange coupling magnetic field due to a rise in temperature becomes a problem. As a countermeasure, Patent Document 1 (Japanese Patent Laid-Open No. 2005-333106) provides an exchange coupling element with an improved blocking temperature. A technique is disclosed. In the method of Patent Document 1, since a high blocking temperature is obtained, the heat resistance of the magnetoresistive element is improved, and it is possible to suppress the disappearance of the unidirectional anisotropy of the magnetization fixed layer due to the temperature rise during operation. Become.

  However, in the magnetic recording / reproducing system, it is difficult to completely prevent the temperature of the reproducing element 17 from being raised above the blocking temperature due to heat generation during operation or instantaneous heat generation due to static electricity. When the reproducing element 17 is at the opposite position on the recording medium 2, the reproducing element 17 receives an alternating magnetic field whose direction of magnetic field changes due to leakage magnetic fields of various magnetization directions from a large number of magnetic bits 28 while the temperature of the reproducing element 17 is increased. become. If the temperature of the antiferromagnetic layer 24 and the first ferromagnetic layer 25 of the reproducing element 17 has risen to the blocking temperature or more even once, even if the temperature is immediately lowered to a temperature lower than the blocking temperature, the medium 2 The direction of exchange coupling between the antiferromagnetic layer 24 and the first ferromagnetic layer 25 differs from the initial direction by the alternating magnetic field due to the leakage magnetic field from the many magnetic bits 28 above, or the magnetization becomes small, The magnetization direction 21 of the first ferromagnetic layer is also different from the initial direction, or the magnetization becomes small. In the conventional method, once the temperature rises to a temperature equal to or higher than the blocking temperature and the unidirectional anisotropy of the first ferromagnetic layer 25 disappears, the signal amount of the reproduction signal is reduced and reproduced. become unable.

  Therefore, in the present embodiment, the reproducing element 17 rises to a temperature higher than the blocking temperature for some reason during the operation of the magnetic recording / reproducing system, and the unidirectional anisotropy of the first ferromagnetic layer 25 in the reproducing element 17 is increased. In the case of disappearance, the antiferromagnetic layer 24 and the first ferromagnetic layer 25 are heated to a temperature equal to or higher than the blocking temperature, and cooled while applying a direct-current magnetic field, so that the first ferromagnetic layer 25 is desired again. The exchange coupling in the direction is given, and unidirectional anisotropy is given. Therefore, the magnetization information can be reliably reproduced. In the conventional method, when the temperature of the reproducing element 17 rises to a temperature equal to or higher than the blocking temperature during operation of the magnetic recording / reproducing system, and the unidirectional anisotropy of the first ferromagnetic layer 25 disappears, In this embodiment, even if the unidirectional anisotropy of magnetization of the first ferromagnetic layer 25 disappears, the unidirectional anisotropy is given again, and the magnetization information is changed. It can be reproducible.

  FIG. 9 is a block diagram according to the exchange coupling reassignment process of the magnetic recording / reproducing system according to the present embodiment. In FIG. 9, in the magnetic recording / reproducing system, illustration of members not related to the exchange coupling reassignment process is omitted.

  As shown in FIG. 9, the magnetic recording / reproducing system according to the present embodiment includes a hard disk drive 101 and a control device 120 that controls the operation of the hard disk drive 101. The hard disk drive 101 includes a motor 53 that serves as a drive source for swinging the head gimbal assembly 51 around the bearing unit 5, a reproducing element 17, and a heater 10 that is a heating member. The control device 120 includes a detection unit 121, a determination unit 122, a heating control unit 123, and a motor control unit 124. The detection unit 121 detects the signal amount of the reproduction signal output from the reproduction element 17. The determination unit 122 determines whether or not the signal amount detected by the detection unit 121 is smaller than a predetermined value. The heating control unit 123 controls the heating temperature of the regeneration element 17 by the heater 10 and the start and end timing of heating of the regeneration element 17 by the heater 10. The motor control unit 124 controls driving of the motor 53.

  Next, the exchange coupling reassignment process in this embodiment will be described in order with reference to the flowchart of FIG. The exchange coupling reassignment process described below may be performed, for example, every predetermined time in accordance with the control of the control unit 120 during a period in which recording or reproduction on the medium 2 is not performed.

  In step S10, the motor control unit 124 drives the motor 53 to move the head 23 from the retracted position to the facing position. In step S <b> 11, the detection unit 121 detects the signal amount of the reproduction signal output from the reproduction element 17. Subsequently, in step S12, the determination unit 122 determines whether or not the signal amount of the reproduction signal detected by the detection unit 121 in step S11 is smaller than a predetermined value. Here, the determination result that the signal amount of the reproduction signal is smaller than the predetermined value is that the temperature of the antiferromagnetic layer 24 and the first ferromagnetic layer 25 of the reproduction element 17 has risen above the blocking temperature in the past. This indicates that the magnetization direction 21 of the first ferromagnetic layer 25 is different from the initial direction, or that the magnetization is smaller than the initial state.

  Here, the predetermined value of the signal amount of the reproduction signal will be described. In the reproducing element 17 which is a magnetoresistive effect element, a change in electric resistance value accompanying a change in the magnetization state of the second ferromagnetic layer 27 is used as a reproduction signal. When the electric resistance in the absence of an external magnetic field is R0, when the direction 31 of the external magnetic field (leakage magnetic field) is the same as the magnetization direction 22 of the first ferromagnetic layer 25 as shown in FIG. The electric resistance becomes smaller than R0. Further, when the direction 31 of the leakage magnetic field is opposite to the magnetization direction 22 of the first ferromagnetic layer 25 as shown in FIG. 8B, the electric resistance becomes larger than R0. Therefore, whether the reproduction signal is “1” or “0” is determined based on whether the electric resistance is larger or smaller than R0. When the exchange coupling is weakened, the magnetization of the first ferromagnetic layer 25 is not fixed, so the rate of change in electrical resistance is reduced. Even if the exchange coupling is normal, there is variation in resistance change. Therefore, a value obtained by subtracting the maximum value of variation from the maximum value of resistance change may be used as a prescribed resistance change amount (predetermined value of signal amount).

  When it is determined that the signal amount of the reproduction signal is equal to or greater than the predetermined value (S12: NO), the process proceeds to step S13. In step S <b> 13, a test result indicating that the magnetization direction 21 of the first ferromagnetic layer 25 remains in the initial state and is normal and the reproducing element 17 has no abnormality is recorded in a storage device (not shown) in the control unit 120. . Then, the exchange coupling reassignment process ends.

  When it is determined that the signal amount of the reproduction signal is smaller than the predetermined value (S12: YES), the process proceeds to step S14. In step S14, the motor control unit 124 drives the motor 53 to move the head 23 from the facing position to the retracted position.

  Subsequently, in step S <b> 15, the heating control unit 123 controls the heater 10 to start emission of the laser light 39 from the heater 10. Further, in step S <b> 16, the heating control unit 123 determines that the temperature of the antiferromagnetic layer 24 and the first ferromagnetic layer 25 irradiated with the laser light 39 is the blocking temperature (250 of MnIr that is the material of the antiferromagnetic layer 24. At the timing when the temperature is raised to a temperature equal to or higher than [° C.], the heater 10 is controlled to terminate the emission of the laser light 39. Thereafter, the temperatures of the antiferromagnetic layer 24 and the first ferromagnetic layer 25 are gradually lowered to a temperature lower than the blocking temperature. The emission end timing of the laser beam 39 may be determined in advance from various conditions such as the intensity of the laser beam 39 and the heat capacity of the reproducing element 17, and the temperatures of the antiferromagnetic layer 24 and the first ferromagnetic layer 25 may be determined. It may be the timing after detecting that the temperature is higher than the blocking temperature by a temperature sensor (not shown).

  Since the magnet 9 is a permanent magnet, the DC magnetic field generated by the magnet 9 is always applied to the reproducing element 17 in the retracted position. Therefore, the first ferromagnetic layer 25 is exchange-coupled again by the magnetic field applied from the magnet 9 in the process in which the temperature falls from the temperature higher than the blocking temperature to a temperature lower than the blocking temperature, and FIG. ) Is magnetized in the upward direction. At that time, the direction of exchange coupling of the antiferromagnetic layer 24 is the same as the magnetization direction 22 of the first ferromagnetic layer 25, that is, the direction of the applied magnetic field from the magnet 9. Here, since the coercive force of CoFeB, which is the material of the first ferromagnetic layer 25, is about 800 A / m (10 Oe), when a ferrite having a magnetic field size of 160000 A / m (2000 Oe) is used as the magnet 9. It is possible to generate a sufficiently large magnetic field that is greater than the coercive force.

  As described above, according to this embodiment, it is assumed that the temperature of the reproducing element 17 rises for some reason during the operation of the magnetic recording / reproducing system, and the unidirectional anisotropy of the first ferromagnetic layer 25 disappears. In this case, again, the first ferromagnetic layer 25 can be given exchange coupling in the same direction as the initial state, and the first ferromagnetic layer 25 can be given unidirectional anisotropy. For this reason, stable reproduction can be provided.

  In addition, the exchange coupling reassignment process can be performed in real time when the signal amount of the reproduction signal becomes smaller than a predetermined value. Further, when the exchange coupling is not lost, the exchange coupling re-granting process is not performed, so that energy for temperature increase can be saved.

  Although this embodiment describes a perpendicular magnetic recording system, the present invention can also be used for an in-plane magnetic recording system. The in-plane magnetic recording method is a recording method in which the magnetization direction of the magnetic bit 28 of the medium 2 is parallel to the medium surface. In this case, the magnetization direction 22 of the first ferromagnetic layer 25 of the reproducing element 17 is fixed in a direction parallel to the medium surface. Further, the magnetization direction 23 of the second ferromagnetic layer 27 is directed perpendicular to the surface of the medium 2 when there is no leakage magnetic field from the magnetic bit. Therefore, in the in-plane magnetic recording method, the direction of the magnetic field applied by the magnet 9 may be a direction (lateral direction) parallel to the medium surface.

  In the present embodiment, the heater 10 includes a laser light source. However, the present invention is not limited to this, and the heater 10 can be a lamp heater or a nichrome wire as long as the temperature of the reproducing element 17 can be increased. Other heating means such as a heater may be included.

  The magnet 9 is not limited to a permanent magnet, but may be an electromagnet or the like. When an electromagnet is used, the magnitude of the magnetic field can be adjusted, and when it is not necessary, the magnetic field can be prevented from being generated. For example, a current may be supplied to the electromagnet after the temperature of the first ferromagnetic layer 25 heated by the laser light 39 becomes equal to or higher than the blocking temperature, and the current may be stopped after the exchange coupling re-application process is completed. Thereby, power consumption can be reduced.

  In the present invention, the reproducing element 17 may be a GMR (giant magnetoresistive effect) element whose intermediate layer is a metal, or a TMR (tunnel magnetoresistive effect) element whose intermediate layer is an insulating layer. .

  The present invention can also be applied to a magnetic recording / reproducing system in which a plurality of media are stacked and a plurality of head gimbal assemblies are stacked.

  In the present embodiment, the exchange coupling re-assignment process is performed when the signal amount of the reproduction signal becomes smaller than a predetermined value during the period when recording or reproduction to the medium 2 is not performed. The exchange coupling reassignment process may be performed regardless of whether the signal amount is smaller than a predetermined value. Alternatively, when the reproduction signal is monitored during the reproduction of the information recorded on the medium 2 and the reproduction signal becomes smaller than a predetermined signal amount, the antiferromagnetic layer 24 and the first ferromagnetic layer 24 It may be determined that the exchange coupling of layer 25 has weakened and an exchange coupling re-granting process may be performed.

<Second Embodiment>
A magnetic recording / reproducing system according to a second embodiment of the present invention will be described with reference to FIGS. 11 (a) and 11 (b). Hereinafter, the present embodiment will be described focusing on the differences from the first embodiment. Note that members similar to those in the first embodiment are denoted by the same reference numerals except that the hundreds are two, and detailed description thereof may be omitted.

  The magnetic recording / reproducing system according to the present embodiment includes a hard disk drive and a control unit that controls the hard disk drive. In the magnetic recording / reproducing system according to this embodiment, optically assisted magnetic recording is performed in the hard disk drive. Here, the optically assisted magnetic recording will be described. As the recording density increases, the magnetization volume of each magnetic bit decreases. If the magnetic bit becomes too small, the anisotropic magnetic energy expressed by the product of the magnetic energy Ku per unit volume and the volume V of the particle becomes smaller than the temperature energy kB · T, and the magnetism is caused by thermal fluctuation even at room temperature. The magnetization direction of the bit changes. If the magnetization direction changes at room temperature, the recorded information cannot be retained and magnetic recording cannot be performed. In order to prevent magnetization reversal due to thermal fluctuation, a material having a large Ku that is difficult to reverse the magnetization is used. However, if a material having a large Ku is used, a problem arises that a recording magnetic field (coercive force) necessary for the magnetization reversal increases. Since there is a limit to the magnitude of the recording magnetic field due to material limitations, it is necessary to devise in order to record on a medium with a large Ku material. Therefore, the optically assisted magnetic recording method was conceived. This is because the temperature of the medium is increased during recording to reduce the coercive force and facilitate magnetization reversal, and then recording is performed on the medium by applying a magnetic field by the recording element. It is a technique.

  Normally, the light can be reduced only to the wavelength, but by irradiating light to a minute aperture having a size smaller than the wavelength, it is possible to generate near-field light that is localized light having a size smaller than the wavelength. . In the optically assisted magnetic recording system, by raising the temperature of the medium with near-field light, it is possible to raise the temperature of a small region below the wavelength in the medium, and optically assisted magnetic recording of a magnetic bit of a small size becomes possible.

  In this embodiment, a laser light source used for generating near-field light in optically assisted magnetic recording is also used for raising the temperature when re-applying exchange coupling. FIG. 11A is a side view of the head gimbal assembly included in the hard disk drive included in the magnetic recording / reproducing system of this embodiment at the time of optically assisted magnetic recording. FIG. 11B is a side view of the head gimbal assembly during the exchange coupling re-assignment process.

  The head gimbal assembly 251 includes a head 232, a suspension 207, a head arm 206 that holds the suspension 207, and a bearing unit (not shown) provided at the base end of the head arm 206. The bearing unit connects a motor (not shown) and the head arm 206. The rotation of the motor causes the head gimbal assembly 512 to swing in a horizontal plane around the bearing unit.

  The head 232 has a slider 212 for raising the head 232 to a height of several nm to several tens of nm from the surface of the medium, a recording element 233 for recording information on the medium, and reproducing information recorded on the medium. And a reproducing element 217 for performing the above. The suspension 207 holds the head 232 in the slider 212 so that the upper surfaces of the recording element 233 and the reproducing element 217 are exposed. The reproducing element 217 has the same structure as the reproducing element 17 of the first embodiment. The recording element 233 is provided with a minute opening on the upper surface that generates near-field light when irradiated with laser light. The generated near-field light is emitted from the lower surface of the recording element 233.

  On the head arm 206, a laser light source 234 as a heating member is disposed. Laser light 239 is emitted from the laser source 234 along the longitudinal direction of the head arm 206. A support piece 238 is attached to the upper surface of the suspension 207 so as to be swingable in a vertical plane. A mirror 236 is fixed to the tip of the support piece 238. The support piece 238 can change the angle with respect to the horizontal plane based on the control of the control unit.

  As shown in FIG. 11A, at the time of optically assisted magnetic recording, the support piece 238 is such that the laser light 239 emitted from the laser light source 234 is reflected by the mirror 236 and is irradiated near the opening of the recording element 233. Is adjusted by the control unit. Thereby, the medium is irradiated with near-field light emitted from the lower surface of the recording element 233.

  On the other hand, as shown in FIG. 11B, when the exchange coupling re-granting process is executed, in particular, at the time of raising the temperature for imparting exchange coupling between the antiferromagnetic layer 24 and the first ferromagnetic layer 25, the laser light source The angle of the support piece 238 is adjusted by the control unit so that the laser beam 239 emitted from the laser beam 234 is reflected by the mirror 236 and irradiated to the antiferromagnetic layer 24 and the first ferromagnetic layer 25 of the reproducing element 217. Is done. As a result, the temperature of the antiferromagnetic layer 24 and the first ferromagnetic layer 25 becomes equal to or higher than the blocking temperature, and it becomes possible to execute the exchange coupling reassignment process as described in the first embodiment. .

  As described above, according to the present embodiment, the irradiation position of the laser light 239 emitted from the laser light source 234 is changed by using the support piece 238 and the mirror 236 and changing the angle of the support piece 238 by the control unit. It is possible to switch between a position for generating near-field light irradiated on the medium during recording of information and a position for heating the antiferromagnetic layer 24 and the first ferromagnetic layer 25. Therefore, since the laser light source 234 can be used for both the generation of near-field light and the heating of the antiferromagnetic layer 24 and the first ferromagnetic layer 25, the configuration of the system can be simplified.

  In this embodiment, the support piece 238 is swingable. However, the support piece 238 may be fixed and the mirror 236 may be swingable with respect to the support piece 238.

  As another variation, a laser light source used to heat the medium in an optically assisted reproduction scheme may be used for heating the antiferromagnetic layer 24 and the first ferromagnetic layer 25 in the exchange coupling re-assignment process. Optically assisted reproduction uses a ferrimagnetic material whose magnetization increases as the temperature rises as the material of the medium, and raises the magnetic bit to be reproduced on the medium with laser light during reproduction, thereby generating a signal from the magnetic bit. It is an increasing method. Since the ferrimagnetic material has a compensation temperature at which the amount of magnetization becomes zero, setting the compensation temperature to room temperature eliminates signal noise from other magnetic bits during reproduction. In the case of the optically assisted reproduction method, when the temperature of the medium is increased during reproduction, the temperature of the reproducing element in the vicinity of the medium is also increased, and the temperature of the reproducing element becomes closer to the blocking temperature than in the case of not using the optically assisted reproduction method. For this reason, the temperature of the reproducing element becomes higher than the blocking temperature, and there is a high possibility that reproduction is not normally performed. According to this modification, stable reproduction can be realized even in the optically assisted reproduction method in which there is a high possibility that reproduction is not normally performed.

1 is a schematic plan view of a hard disk drive included in a magnetic recording / reproducing system according to a first embodiment of the present invention. It is a typical longitudinal cross-sectional view of a part of hard disk drive shown in FIG. It is a typical longitudinal cross-sectional view of a part of hard disk drive shown in FIG. . It is the longitudinal cross-sectional view and bottom view of the head contained in a hard-disk drive. It is a cross-sectional schematic diagram of the head of the present invention and a schematic diagram of the medium facing surface of the head of the present invention. FIG. 3 is a schematic perspective view of a reproducing element included in a head. FIG. 3 is a schematic perspective view of a reproducing element included in a head. It is a longitudinal cross-sectional view of a reproducing element and a medium. It is a longitudinal cross-sectional view of a reproducing element and a medium. 1 is a block diagram of a magnetic recording / reproducing system according to a first embodiment of the present invention. It is a flowchart for demonstrating the exchange coupling re-assignment process in the magnetic recording / reproducing system by the 1st Embodiment of this invention. It is a side view of the head gimbal assembly included in the hard disk drive of the magnetic recording / reproducing system according to the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cover 2 Medium 8 Lamp 9 Magnet 10 Heater 12 Slider 17 Reproducing element 20 Recording magnetic pole 24 Antiferromagnetic layer 25 First ferromagnetic layer 26 Intermediate layer 27 Second ferromagnetic layer 28 Magnetic bit 32 Head 33 Recording element 39 Laser Optical 100 Magnetic recording / reproducing system 101 Hard disk drive 102 Control unit

Claims (4)

A magnetic recording / reproducing system having a magnetic head including a reproducing element in which an antiferromagnetic layer, a first ferromagnetic layer, an intermediate layer, and a second ferromagnetic layer are laminated in this order,
The antiferromagnetic layer and the first ferromagnetic layer are heated to a temperature equal to or higher than the blocking temperature, which is a temperature at which the unidirectional anisotropy of the first ferromagnetic layer disappears due to exchange coupling between these two layers. Temperature raising means for causing,
A magnetic recording / reproducing system comprising: a magnetic field applying means for applying a direct current magnetic field having a magnitude greater than the coercive force of the first ferromagnetic layer to the antiferromagnetic layer and the first ferromagnetic layer. The temperature raising means is
When the signal amount of the reproduction signal output from the reproduction element becomes smaller than a predetermined value, the antiferromagnetic layer and the first ferromagnetic layer are heated,
While the DC magnetic field is applied to the antiferromagnetic layer and the first ferromagnetic layer, the antiferromagnetic layer and the first ferromagnetic layer are moved from a temperature equal to or higher than the blocking temperature to the blocking temperature. The magnetic recording / reproducing system according to claim 1, wherein the temperature is lowered to a lower temperature. The temperature raising means is
A heating member for heating the antiferromagnetic layer and the first ferromagnetic layer;
Detecting means for detecting a signal amount of the reproduction signal output from the reproduction element;
Determination means for determining whether or not the signal amount detected by the detection means is smaller than the predetermined value;
Heating start means for starting heating of the antiferromagnetic layer and the first ferromagnetic layer by the heating member when the determination means determines that the signal amount is smaller than the predetermined value. The magnetic recording / reproducing system according to claim 2. A laser light source;
The irradiation position of the laser light emitted from the laser light source, the position for generating the near-field light irradiated to the recording medium when recording information on the recording medium, the antiferromagnetic layer and the first ferromagnetic The magnetic recording / reproducing system according to claim 1, further comprising switching means for switching between a position for heating the layer.

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