Disk device

Abstract

The embodiment provides a magnetic disk device capable of improving recording density and reliability. According to the embodiment, the magnetic disk device comprises: a housing (11); a temperature sensor (TS) for detecting the temperature in the housing; a magnetic disk (12) rotatably arranged in the housing; a magnetic head having a write head for writing data to the magnetic disk, a read head for reading data from the magnetic disk, a first thermal actuator for controlling the protrusion amount of the write head, and a second thermal actuator for controlling the protrusion amount of the read head, and arranged in the housing so as to be movable in the radial direction of the magnetic disk; a power supply circuit for supplying a first power to the first thermal actuator and a second power to the second thermal actuator; and a controller (40) for adjusting the power ratio of the first power to the second power according to at least one of a change in the temperature in the housing and a change in the radial position of the magnetic head relative to the magnetic disk.

Description

[0001] Related Application

[0002] This application claims the priority of Japanese Patent Application No. 2021-5032 (filing date: January 15, 2021) as a basic application, and the present application incorporates the entire contents of the basic application by reference. Technical Field

[0003] An embodiment of the present invention relates to a magnetic disk device. Background Art

[0004] A disk device, such as a magnetic disk device, includes a rotatable disk-shaped recording medium having a magnetic recording layer and a magnetic head for reading and writing data on the magnetic recording layer of the recording medium. The magnetic head includes a slider and a read head (read element) and a write head (write element) provided on the slider. In such a magnetic disk device, in order to increase the recording density, especially the linear recording density, it is necessary to reduce the gap between the read head and the recording head and the magnetic disk.

[0005] In order to reduce the gap, a magnetic disk device is proposed that includes a thermal actuator embedded in a slider near a pickup head and a recording head. According to this magnetic disk device, the gap can be reduced by using the thermal actuator to bulge a portion of the slider, the pickup head, and the recording head toward the surface side of the recording medium.

[0006] However, in the above-mentioned magnetic disk device, the bulging shape of the head element portion changes due to the change of the ambient temperature, so the gap (floating amount) between the head element portion and the recording medium changes. Not only the influence of temperature, but also the floating pitch of the magnetic head changes due to the radial position on the storage medium, so there is a possibility that the above-mentioned gap (floating amount) changes.

[0007] If the floating amount (space amount) varies, it becomes difficult to obtain a desired recording density, and there is a possibility that the head element contacts the recording medium and is damaged by wear and the like. Summary of the invention

[0008] The embodiment of the present invention provides a magnetic disk device capable of suppressing the head interval variation and achieving an improvement in recording density and reliability.

[0009] According to an embodiment, a magnetic disk device comprises: a housing; a temperature sensor for detecting the temperature inside the housing; a magnetic disk rotatably arranged inside the housing; a magnetic head having a write head for writing data to the magnetic disk, a read head for reading data from the magnetic disk, a first thermal actuator for controlling the protrusion amount of the write head, and a second thermal actuator for controlling the protrusion amount of the read head, and being movably arranged inside the housing in a radial direction of the magnetic disk; a power supply circuit for supplying a first power to the first thermal actuator and a second power to the second thermal actuator; and a controller for adjusting a power ratio between the first power and the second power according to at least one of a change in the temperature inside the housing and a change in the radial position of the magnetic head relative to the magnetic disk. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a block diagram schematically showing a hard disk drive (HDD) according to the first embodiment.

[0011] Figure 2 It is a side view schematically showing a magnetic head, a suspension, and a magnetic disk in the HDD.

[0012] Figure 3 It is a cross-sectional view showing an enlarged portion of the magnetic head.

[0013] Figure 4 is a side view schematically showing the head.

[0014] Figure 5 is a side view schematically showing the magnetic head in a floating state.

[0015] Figure 6 is a side view schematically showing the head in a floating state.

[0016] Figure 7 It is a diagram showing the relationship between the radial position (radial position) of the magnetic head on the magnetic disk and the dynamic step (Dsd).

[0017] Figure 8 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the write head when the magnetic head is located at the inner periphery (ID) of the magnetic disk and during a write operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0018] Fig. 9 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the write head when the magnetic head is located at the middle circumference (MD) of the magnetic disk and during writing operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0019] Fig.10 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the write head when the magnetic head is located at the outer periphery (OD) of the magnetic disk during writing operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0020] Fig.11 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the read head when the magnetic head is located at the inner periphery (ID) of the magnetic disk during a reading operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0021] Fig.12 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the read head when the magnetic head is located at the middle circumference (MD) of the magnetic disk during a reading operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0022] Fig.13 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the read head when the magnetic head is located at the outer periphery (OD) of the magnetic disk during a reading operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0023] Fig.14 It is a diagram showing an example of a power ratio setting table.

[0024] Fig.15 It is a side view schematically showing an example of a touch operation (TD) and a floating amount adjustment operation (BO) of the magnetic head during a write operation.

[0025] Fig.16 It is a graph showing the relationship between the ratio of the driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the contact sensor CS when the head is located at the inner periphery (ID) of the magnetic disk and during the writing operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0026] Fig.17 It is a graph showing the relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the contact sensor CS when the head is located at the middle circumference (MD) of the magnetic disk and during a writing operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0027] Fig.18It is a graph showing the relationship between the ratio of the driving power supplied to the first heater and the second heater (power ratio) and the floating amount (space) of the contact sensor CS when the head is located at the outer periphery (OD) of the magnetic disk and during the writing operation under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C) environments.

[0028] Fig.19 It is a diagram showing the relationship between the pressure in the case and the floating amount of the magnetic head.

[0029] Fig. 20 It is a diagram showing the relationship between the pressure in the casing and the flying pitch of the magnetic head.

[0030] Fig.21 It is a graph showing the relationship between the pressure in the casing 11 and the power ratio (PR).

[0031] Fig. 22 It is a diagram showing another example of the power ratio setting table.

[0032] Fig.23 It is a side view schematically showing the head portion of the magnetic head according to the second embodiment.

[0033] Fig.24 is a side view of the write head schematically showing a state in which the write head portion is thermally expanded.

[0034] Fig.25 This is a diagram showing the relationship between the input value of the laser diode and the protrusion amount of the NFT element.

[0035] Fig.26 This is a diagram showing the relationship between the input value of the laser diode and the floating amount (space) of the NFT element.

[0036] Fig. 27 This is a diagram showing the relationship between the input value of the laser diode and the floating amount (space) of the read element.

[0037] Fig.28 This is a diagram showing the relationship between the input value of the laser diode and the power ratio (PR) of the heater driving current.

[0038] Fig.29 It is a side view schematically showing a touch operation (TD) and a floating amount adjustment operation (BO) of the magnetic head during a write operation. DETAILED DESCRIPTION

[0039] Below, while referring to the attached Figure 1 A magnetic disk device according to the embodiment will be described.

[0040] In addition, the disclosure is only an example, and the content that can be easily thought of by a person skilled in the art while maintaining the main idea of ​​the invention is of course included in the scope of the present invention. In addition, in order to make the description clearer, the width, thickness, shape, etc. of each part are schematically represented compared with the actual form, but it is only an example and does not limit the interpretation of the present invention. In addition, in this specification and each figure, the same elements as those described above with respect to the already appeared figures are marked with the same reference numerals, and the detailed description is sometimes appropriately omitted or simplified.

[0041] (First embodiment)

[0042] As an example of a magnetic disk device, a hard disk drive (HDD) according to the first embodiment will be described in detail. Figure 1 is a block diagram schematically showing an HDD according to the first embodiment. Figure 2 It is a side view showing the magnetic head and magnetic disk in a floating state.

[0043] like Figure 1 As shown, the HDD 10 includes a rectangular housing 11, a magnetic disk 12 as a recording medium disposed in the housing 11, a spindle motor 21 that supports and rotates the magnetic disk 12, and a plurality of magnetic heads 16 that record (write) and reproduce (read) data on the magnetic disk 12. The HDD 10 includes a head actuator 18 that moves and positions the magnetic head 16 to an arbitrary track on the magnetic disk 12. The head actuator 18 includes a carriage assembly 20 that supports the magnetic head 16 so that it can move and a voice coil motor (VCM) 22 that rotates the carriage assembly 20. A temperature sensor TS that detects the temperature in the housing 11 and a pressure sensor PS that detects the pressure in the housing 11 are disposed in the housing 11.

[0044] The HDD 10 includes a head amplifier IC 30 for driving the magnetic head 16, a main controller 40, and a driver IC 48. The head amplifier IC 30 is provided, for example, in the carriage assembly 20 and is electrically connected to the magnetic head 16. The head amplifier IC 30 includes a recording current supply circuit (recording current supply unit) 32 for supplying a recording current to a recording coil of the magnetic head 16, a first heater power supply circuit 34a and a second heater power supply circuit 34b for supplying driving power to a thermal actuator (heater) of the magnetic head 16 described later, and an amplifier (not shown) for amplifying a signal read by the magnetic head 16. The head amplifier IC 30 also includes a contact detection circuit 35 for detecting a detection signal of a contact sensor (CS) described later, and a laser drive current supply circuit 36 ​​for supplying a drive current to a laser oscillator for thermal assistance described later.

[0045] The main controller 40 and the driver IC 48 are configured, for example, on a control circuit substrate (not shown) provided on the back side of the housing 11. The main controller 40 includes an R / W channel 42, a hard disk controller (HDC) 44, a microprocessor (MPU) 46, a memory 47, etc. The main controller 40 is electrically connected to the magnetic head 16 via the head amplifier IC 30. The main controller 40 is electrically connected to the VCM 22 and the spindle motor 21 via the driver IC 48. The HDC 44 can be connected to a host computer 45.

[0046] Various data such as a power ratio setting table described later are stored in the memory 47 of the main controller 40. In the main controller 40, for example, the MPU 46 includes a heater power control unit 46a that adjusts the power supplied to the thermal actuator based on the power ratio setting table. The temperature sensor TS and the pressure sensor PS are electrically connected to the main controller 40, and transmit the detected temperature and the detected pressure to the heater power control unit 46a.

[0047] like Figure 1 and Figure 2 As shown, the magnetic disk 12 is configured as a perpendicular magnetic recording medium. The magnetic disk 12 has, for example, a substrate 101 formed in the shape of a disk having a diameter of 96 mm (about 3.5 inches) and made of a non-magnetic body. On each surface of the substrate 101, a soft magnetic layer 102 made of a material exhibiting soft magnetic properties as a base layer, and a perpendicular magnetic recording layer 103 and a protective film 104 having magnetic anisotropy in a direction perpendicular to the surface of the magnetic disk 12 are sequentially stacked. The magnetic disks 12 are coaxially engaged with the hub of the spindle motor 21. The magnetic disk 12 is rotated in the direction of arrow B at a predetermined speed by the spindle motor 21.

[0048] The carriage assembly 20 includes a bearing portion 24 rotatably supported by the housing 11, and a plurality of arms and a suspension 26 extending from the bearing portion 24. Figure 2 As shown, the magnetic head 16 is supported by the extended ends of the suspensions 26. The magnetic head 16 is electrically connected to the head amplifier IC 30 via a wiring member (flexure) 28 provided in the carriage assembly 20.

[0049] like Figure 2 As shown, the magnetic head 16 is configured as a floating type head, and has a slider 15 formed in a substantially rectangular parallelepiped shape and a head 17 formed at the end of the outflow end (trailing) side of the slider 15. The slider 15 is formed of a sintered body (aluminum titanium carbon) of aluminum oxide and titanium carbide, for example, and the head 17 is formed of a multilayer film. The slider 15 is attached to the universal joint portion 28a of the wiring member 28.

[0050] The slider 15 has a substantially rectangular disk-opposing surface (air bearing surface (ABS)) 13 that is opposed to the surface of the magnetic disk 12. The slider 15 is maintained in a state of floating a predetermined amount from the surface of the magnetic disk 12 by the air flow C generated between the disk surface and the ABS 13 due to the rotation of the magnetic disk 12. The direction of the air flow C coincides with the rotation direction B of the magnetic disk 12. The slider 15 has a leading end 15a located on the inflow side of the air flow C and a trailing end 15b located on the outflow side of the air flow C. As the magnetic disk 12 rotates, the magnetic head 16 moves relative to the magnetic disk 12 in the direction of arrow A (head travel direction), that is, in the direction opposite to the rotation direction B of the disk.

[0051] In addition, in a state where the magnetic head 16 is flying, the ABS 13 of the slider 15 is inclined at a flying pitch (flying pitch angle) P with respect to the surface of the magnetic disk 12 .

[0052] Figure 3 It is a cross-sectional view showing a portion of the head portion 17 of the magnetic head 16 and the magnetic disk 12 in an enlarged manner.

[0053] like Figure 3 As shown, the head 17 has a read head (read element) 54 and a write head (write element) 58 formed by a thin film process, forming a separate type magnetic head. The read head 54 and the write head 58 are covered by a non-magnetic protective insulating film 53 except for the portion exposed to the ABS 13 of the slider 15. The protective insulating film 53 constitutes the outer shape of the head 17. The head 17 has a first thermal actuator for controlling the protrusion amount of the write head 58 and a second thermal actuator for controlling the protrusion amount of the read head 54. The first thermal actuator has, for example, a heater 76a, which is buried in the protective insulating film 53 and is located near the write head 58. The second actuator has, for example, a heater 76b, which is buried in the protective insulating film 53 and is located near the read head 54.

[0054] The head 17 further includes a contact sensor CS. The contact sensor CS is embedded in the protective insulating film 53 and is disposed near the ABS 13 between the read head 54 and the write head 58. The contact sensor CS is, for example, a resistance detection type thermal contact sensor, which is energized by the main controller 40 and can send a detection signal to the main controller 40.

[0055] The length direction of the recording track of the perpendicular magnetic recording layer 103 formed on the magnetic disk 12 is defined as the along-track direction DT, and the width direction of the recording track perpendicular to the length direction is defined as the through-track direction.

[0056] The read head 54 includes a magnetoresistance effect element (sometimes referred to as a read element) 55, and a first magnetic shielding film 56 and a second magnetic shielding film 57 arranged on the leading side (inflow side) and the trailing side (outflow side) of the magnetoresistance effect element 55 in the track direction DT so as to sandwich the magnetoresistance effect element 55. The magnetoresistance effect element 55, the first and second magnetic shielding films 56, 57 extend substantially perpendicularly to the ABS 13. The lower end portions (top portions) of the magnetoresistance effect element 55, the first and second magnetic shielding films 56, 57 slightly protrude from the ABS 13, and constitute a first protrusion HP1. In the first protrusion HP1, the protrusion amount of the top portion of the magnetoresistance effect element 55 is greater than the protrusion amount of the top portions of the first and second magnetic shielding films 56, 57, and the top portion of the magnetoresistance effect element 55 protrudes beyond the first and second magnetic shielding films.

[0057] The write head 58 is disposed on the trailing end 15b side of the slider 15 relative to the read head 54. The write head 58 includes a main magnetic pole 60 that generates a recording magnetic field in a direction perpendicular to the surface of the magnetic disk 12, a trailing shield (first shield) 62 that is disposed on the trailing side of the main magnetic pole 60 and faces the main magnetic pole 60 with a write gap therebetween, a leading shield (second shield) 64 that faces the leading side of the main magnetic pole 60, and a pair of side shields (not shown) that are formed integrally with the trailing shield 62 and disposed on both sides of the main magnetic pole 60 in the through-track direction. The main magnetic pole 60 and the trailing shield 62 constitute a first magnetic core that forms a magnetic circuit, and the main magnetic pole 60 and the leading shield 64 constitute a second magnetic core that forms a magnetic circuit. The write head 58 includes a first recording coil 70 wound around the first magnetic core and a second recording coil 72 wound around the second magnetic core. In the following description, the main magnetic pole 60 may be referred to as a writing element.

[0058] The main magnetic pole 60 is formed of a soft magnetic material having high magnetic permeability and high saturation magnetic flux density, and extends substantially perpendicularly to the ABS 13. The top end 60a of the main magnetic pole 60 on the ABS 13 side tapers toward the ABS 13, forming a columnar shape having a width narrower than other parts. The top end 60a of the main magnetic pole 60 protrudes slightly from the ABS 13 of the slider 15.

[0059] The trailing shield 62 is formed of a soft magnetic material and is provided to efficiently close the magnetic path via the soft magnetic layer 102 of the magnetic disk 12 directly below the main magnetic pole 60. The trailing shield 62 is formed in a substantially L-shape, and its top end 62a is formed in an elongated rectangular shape. The top end 62a of the trailing shield 62 slightly protrudes from the ABS 13 of the slider 15.

[0060] The trailing shield 62 has a first connection portion 50 connected to the main magnetic pole 60. The first connection portion 50 is magnetically connected to the upper portion of the main magnetic pole 60, that is, the portion of the main magnetic pole 60 away from the ABS 13, via the non-conductive body 52. ​​The first recording coil 70 is wound around the first connection portion 50 in the first magnetic core, for example. When writing a signal to the magnetic disk 12, the first recording coil 70 excites the main magnetic pole 60 by flowing a recording current to the first recording coil 70, so that a magnetic flux flows to the main magnetic pole 60.

[0061] The leading shield 64 formed of a soft magnetic material is disposed opposite to the main magnetic pole 60 on the leading side of the main magnetic pole 60. The leading shield 64 is formed in a substantially L-shape, and the tip 64a on the ABS13 side is formed in an elongated rectangular shape. The tip 64a slightly protrudes from the ABS13 of the slider 15.

[0062] The leading shield 64 has a second connection portion 68 joined to the main magnetic pole 60 at a position separated from the ABS 13. The second connection portion 68 is formed of, for example, a soft magnetic body, and is magnetically connected to the upper portion of the main magnetic pole 60, that is, the portion of the main magnetic pole 60 separated from the ABS 13, via the non-conductive body 59. Thus, the second connection portion 68 forms a magnetic circuit together with the main magnetic pole 60 and the leading shield 64. The second recording coil 72 of the write head 58 is, for example, wound around the second connection portion 68, and applies a magnetic field to the magnetic circuit.

[0063] As described above, the top end 60a of the main magnetic pole 60, the top end 62a of the trailing shield 62, and the top end 64a of the leading shield 64 slightly protrude from the ABS13 to form the second protrusion HP2. The protrusion height (protrusion amount) of the top end 62a of the trailing shield 62 and the top end 64a of the leading shield from the ABS13 is about 4 nm. The top end 60a of the main magnetic pole 60 protrudes beyond the top end 62a of the trailing shield 62 and the top end 64a of the leading shield 64. The protrusion height (protrusion amount) of the main magnetic pole 60 from the top ends 63a and 64a is set to, for example, about 0.3 to 1 nm.

[0064] like Figure 3 As shown in FIG. 1 , a plurality of connection terminals 43 are provided at the trailing end 15b of the slider 15. The first recording coil 70 and the second recording coil 72 are connected to the connection terminals 43 via wiring, respectively, and are further connected to the head amplifier IC 30 via the flexible member 28. When writing a signal to the magnetic disk 12, a recording current flows from the recording current supply circuit 32 of the head amplifier IC 30 to the first recording coil 70 and the second recording coil 72, thereby exciting the main magnetic pole 60 and causing the magnetic flux to flow to the main magnetic pole 60. The recording current supplied to the first recording coil 70 and the second recording coil 72 is controlled by the main controller 40.

[0065] The magnetoresistive element 55 of the read head 54 is connected to the connection terminal 43 via a wiring (not shown), and further connected to the head amplifier IC 30 via the flexure 28. The signal read by the read head 54 is amplified by the head amplifier IC 30 and transmitted to the main controller 40.

[0066] The first heater 76a and the second heater 76b are connected to the connection terminal 43 via wiring, respectively, and are further connected to the head amplifier IC 30 via the flexible member 28. By applying driving power to the first heater 76a and the second heater 76b from the first heater power supply circuit 34a and the second heater power supply circuit 34b of the head amplifier IC 30, the heaters and the surroundings of the heaters can be heated, so that the write head 58 or the read head 54 is bulged toward the magnetic disk 12. The driving power supplied to the first heater 76a and the second heater 76b is controlled by the heater power control unit 46a of the main controller 40.

[0067] The contact sensor CS is connected to the connection terminal 43 via wiring, and is further electrically connected to the head amplifier IC 30 and the host controller 40 via the flexure 28. The contact sensor CS detects contact between the head 17 and the magnetic disk 12 based on a change in resistance, and transmits a detection signal to the host controller 40.

[0068] Figure 4 is a side view schematically showing the head portion 17 of the magnetic head, Figure 5 is a side view schematically showing the magnetic head 16 in a floating state, Figure 6 It is a side view schematically showing the head portion 17 of the magnetic head in a floating state.

[0069] like Figure 4 As shown, in the head 17 before floating, the interval between the read element 55 and the write element (main magnetic pole 60) in the direction parallel to the ABS 13 is set to D, and the difference in height between the protruding ends of the first and second magnetic shielding films 56 and 57 in the read head and the protruding ends of the shields 62a and 62b in the write head (the difference in height in the direction perpendicular to the disk surface) is called the step difference (Sd) (English: step delta).

[0070] like Figure 5 As shown in FIG. 1 , when the HDD is in operation, the magnetic head 16 and the slider 15 are maintained in a state of floating by a predetermined amount from the surface of the magnetic disk 12 by the air flow generated between the disk surface and the ABS 13 due to the rotation of the magnetic disk 12. In the state where the magnetic head 16 is floating, the ABS 13 of the slider 15 is inclined relative to the surface of the magnetic disk 12 at a floating pitch (floating pitch angle) P.

[0071] like Figure 6As shown in FIG. 1 , in the head 17 where the floating pitch P is generated, the height difference (the height difference in the direction perpendicular to the disk surface) between the protruding ends of the first and second magnetic shield films 56 and 57 in the read head and the protruding ends of the shields 62a and 62b in the write head is called a dynamic step difference (DSd). If the ambient temperature is set to T, the radial position (radial position) of the magnetic head on the disk is set to R, and the floating pitch angle is set to θ, DSd is represented by DSd=Sd(T)+D·θ(R, T). That is, DSd changes according to the ambient temperature T and the radial position R.

[0072] Figure 7 It is a diagram showing the relationship between the radial position of the magnetic head and DSd. As shown in the figure, it is known that as the magnetic head 16 moves from the inner periphery ID of the magnetic disk 12 to the outer periphery OD side, DSd increases. It is known that the closer to the outer periphery side of the magnetic disk 12, the faster the flow rate of the air flow, the greater the floating amount of the magnetic head 16, and Dsd increases gradually.

[0073] Figure 8 , Fig. 9 , Fig.10 The following diagram shows the magnetic head at different radial positions under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C). Figure 8 : Located on the inner periphery of the disk (ID), Fig. 9 : Located at the mid-circle (MD) of the disk, Fig.10 : Relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) during writing operation and the floating amount (space) of the write head located at the outer periphery (OD) of the magnetic disk.

[0074] Fig.11 , Fig.12 , Fig.13 The following diagram shows the magnetic head at different radial positions under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C). Fig.11 : Located on the inner periphery of the disk (ID), Fig.12 : Located at the mid-circle (MD) of the disk, Fig.13 : Relationship between the ratio of driving power supplied to the first heater and the second heater (power ratio) during a read operation and the floating amount (space) of the read head located at the outer periphery (OD) of the magnetic disk.

[0075] In the present embodiment, the power ratio (PR) indicates the ratio of the driving power supplied to the second heater 76b adjacent to the read head 55 to the total driving power supplied to the first heater 76a and the second heater 76b. For example, when the power ratio is 25%, 25% of the total driving power is supplied to the second heater 76b, and the remaining 75% is supplied to the first heater 76a.

[0076] like Figure 8, Fig. 9 , Fig.10 As shown in the figure, during the writing operation, regardless of the radial position, there is a tendency for the floating amount (space) of the write head to increase as the ambient temperature rises (-5°C → 25°C → 70°C). For example, when the power ratio during the writing operation is compared at 25%, the floating amount (space) of the write head is about 0.2nm at normal temperature and is appropriate. In contrast, at high temperature, the floating amount increases significantly to about 0.8nm. This is caused by the excessive bulging of the area between the write head and the read head due to the temperature rise. It can be seen that in order to set the write head to the lowest point at high temperature, the power ratio needs to be reduced.

[0077] In any temperature environment, the floating amount of the write head tends to decrease as the radial position of the magnetic head 16 moves from the inner periphery ID to the outer periphery OD. Therefore, it is known that in order to set the write head to the lowest point during the write operation, the power ratio needs to be increased as the magnetic head moves toward the outer periphery OD.

[0078] like Fig.11 , Fig.12 , Fig.13 As shown in the figure, during the reading operation, regardless of the radial position, there is a tendency for the floating amount (space) of the read head to decrease as the ambient temperature rises (-5°C → 25°C → 70°C). For example, when the power ratio during the reading operation is compared at 30%, the floating amount (space) of the read head is about 0.2nm at normal temperature and is appropriate. In contrast, at high temperature, the floating amount is reduced to about 0.1nm. It can be seen that in order to appropriately maintain the floating amount of the read head, the power ratio needs to be reduced as the ambient temperature rises.

[0079] In addition, no matter in which temperature environment, there is a tendency that the floating amount of the head increases as the radial position of the head moves from the inner periphery ID to the outer periphery OD. Therefore, it is known that in order to set the head to the lowest point during the read operation, the power ratio needs to be increased as the head moves toward the outer periphery OD.

[0080] In this embodiment, in order to achieve a high recording density, the main controller 40 adjusts the power ratio of the heater driving power supplied to the first heater 76a and the second heater 76b, thereby controlling the floating amount (magnetic interval) of the magnetic head in a manner that the write element (main magnetic pole) 60 becomes the lowest point during the write action and the read element 55 becomes the lowest point during the read action. At this time, as mentioned above, if the ambient temperature rises, the head element part (especially the read element part) expands due to heat, so that the step difference Sd changes compared with the normal temperature. In addition, the floating pitch changes due to the radial position of the magnetic head action, and the larger the floating pitch, the larger the dynamic step difference DSd. Therefore, according to this embodiment, the main controller 40 controls the writing element part by changing the power ratio (PR) according to the change of the ambient temperature, thereby maintaining the DSd at normal temperature, so as to make the writing element part the lowest point. In addition, the main controller 40 maintains the power ratio (PR) according to the radial position of the magnetic head, thereby properly maintaining the floating amount of the writing element part and the reading element part regardless of the radial position.

[0081] Fig.14 According to the present embodiment, the memory 47 of the main controller 40 stores a table for setting the power ratio. Fig.14 The relationship between the ambient temperature and the optimal power ratio and the relationship between the radial position of the magnetic head and the optimal power ratio are tabulated in the power ratio setting table 1. The power ratio setting table 1 is as described above. Figure 8 to Figure 13 As shown in the figure, the floating amount (space) of the write head and the read head relative to the power ratio is measured offline by temperature or radius position, and the measured data is tabulated and saved. In the power ratio setting table 1, PR represents the power ratio, and Zn represents the radius position (track of the disk). Zn: 31 corresponds to the innermost circumference position of the disk, and Zn: 0 corresponds to the outermost circumference position of the disk.

[0082] The heater power control unit 46a of the main controller 40 selects the optimal power ratio corresponding to the temperature detected by the temperature sensor TS based on the power ratio setting table 1, and sets the first power supplied to the first heater 76a and the second power supplied to the second heater 76b according to the selected power ratio. Similarly, the heater power control unit 46a selects the optimal power ratio corresponding to the radial position of the magnetic head detected by the head amplifier IC based on the power ratio setting table 1, and sets the first power supplied to the first heater 76a and the second power supplied to the second heater 76b according to the selected power ratio.

[0083] An example of the floating amount control according to the ambient temperature performed by the main controller 40 will be described.

[0084] Fig.15 It is a side view schematically showing a touch operation (TD) and a floating amount adjustment operation (BO) of the magnetic head during a write operation.

[0085] like Fig.15 As shown in (a), at room temperature (e.g., 25°C), when the magnetic head 16 is located at the radial position ID (Zn: 31), the heater power control unit 46a selects a power ratio of 25% corresponding to room temperature from the power ratio setting table 1, and sets the first power supplied to the first heater 76a and the second power supplied to the second heater 76b according to the selected power ratio. The set first power and second power are supplied to the first heater 76a and the second heater 76b from the first heater power supply circuit 34a and the second heater power supply circuit 34b. As a result, the read head, the write head and their peripheral parts are heated and expanded. The write element 60 bulges toward the lowest point on the side of the magnetic disk 12, and the read element 55 bulges toward a position away from Dsd from the write element 60.

[0086] In the touch action, the heater power control unit 46a increases the first power and the second power while maintaining the power ratio of 25% to increase the bulging amount of the write head and the read head, so that the write head contacts (touches) the magnetic disk 12. During this period, if the main controller 40 supplies power to the thermal contact sensor CS to heat the thermal contact sensor CS, the temperature of the thermal contact sensor CS decreases as it approaches the magnetic disk 12, and at the time when the write shield 62a contacts the magnetic disk 12, the AC component of the power supply contacts and vibrates. That is, if the write shield 62a contacts the magnetic disk 12, the thermal contact sensor CS outputs the contact vibration as a detection signal to the main controller 40. Thus, the main controller 40 can detect that the write element 60 contacts the magnetic disk 12 and accurately detect the first power value and the second power value at the time of contact.

[0087] like Fig.15 As shown in (a), after the touch action is completed, the main controller 40 adjusts the floating amount of the magnetic head based on the first power value and the second power value at the time of contact (BO). The main controller 40 reduces the first power and the second power by a predetermined amount based on the power value at the time of contact, thereby setting the write element 60 to a desired floating amount.

[0088] like Fig.15 As shown in (b), when the ambient temperature rises to a high temperature (e.g., 70°C), if the power ratio is set to 25% as at normal temperature, the read element 55 part expands due to heat, Dsd becomes smaller, and the middle part between the write element 60 and the read element 55 becomes the lowest point. Therefore, the floating amount (space) of the write element 60 becomes larger than that at normal temperature, and there is a concern about ADC (Areal Density Capability) loss. In addition, the floating amount of the read element 55 part becomes smaller than that at normal temperature, and there is a concern about reliability such as wear and head degradation.

[0089] In contrast, in this embodiment, if Fig.15 As shown in (c), the heater power control unit 46a of the main controller 40 changes the power ratio according to the temperature rise and sets it to a power ratio suitable for high temperature. That is, when the temperature detected by the temperature sensor TS in the state where the magnetic head 16 is located at the radial position ID (Zn: 31) becomes 70°C, the heater power control unit 46a selects a power ratio of 5% corresponding to the high temperature (70°C) from the power ratio setting table 1, and sets the first power supplied to the first heater 76a and the second power supplied to the second heater 76b according to the selected power ratio. The set first power and second power are supplied to the first heater 76a and the second heater 76b from the first heater power supply circuit 34a and the second heater power supply circuit 34b.

[0090] As described above, by reducing the power ratio PR from 25% to 5% in a high temperature environment, the dynamic step difference Dsd at room temperature can be maintained, and the floating amount can be adjusted so that the write element 60 is the lowest point. By changing the power ratio, the floating amount (space) of both the write element 60 and the read element 55 can be maintained unchanged relative to the room temperature.

[0091] In the reading operation, the heater power control unit 46a of the main controller 40 selects a corresponding power ratio from the power ratio setting table 1 according to the temperature detected by the temperature sensor TS, and sets the first power supplied to the first heater 76a and the second power supplied to the second heater 76b according to the selected power ratio. For example, when the ambient temperature changes from a normal temperature of 25°C to a high temperature of 70°C, the heater power control unit 46a selects a power ratio of 5% corresponding to the high temperature of 70°C from the power ratio setting table 1, and changes the power ratio from 25% to 5%.

[0092] By changing the power ratio, the floating amount (space) of both the read element 55 and the write element 60 can be maintained unchanged from that at room temperature.

[0093] The heater power control unit 46a can also change the power ratio according to the radial position of the magnetic head during the writing operation and the reading operation. In this embodiment, the power ratio (PR) is changed according to the temperature change and the change of the radial position to control the floating amount of the writing element and the reading element appropriately.

[0094] The heater power control unit 46a selects a corresponding power ratio from the power ratio setting table 1 according to the radial position of the magnetic head detected by the head amplifier IC, and sets the first power supplied to the first heater 76a and the second power supplied to the second heater 76b based on the selected power ratio. For example, when the radial position of the magnetic head moves from the innermost circumference (ID) to the outermost circumference (OD) at normal temperature, the heater power control unit 46a selects a power ratio of 45% corresponding to the outermost circumference (Zn:0) from the power ratio setting table 1, and changes the power ratio from 25% to 45%.

[0095] By the above control, regardless of whether the magnetic head is located on the inner circumference side ID or the outer circumference side OD, the floating amount (space) of the write element and the read element can be maintained at a predetermined appropriate value, thereby maintaining the dynamic step Dsd.

[0096] Next, a configuration example for controlling the floating amount (space) of the contact sensor CS according to the ambient temperature and / or the radial position of the magnetic head will be described.

[0097] Fig.16 , Fig.17 , Fig.18 The following diagrams show the magnetic head at different radial positions under low temperature (-5°C), normal temperature (25°C), and high temperature (70°C). Fig.16 : Located on the inner periphery of the disk (ID), Fig.17 : Located at the mid-circle (MD) of the disk, Fig.18 : The relationship between the power ratio of the driving power supplied to the first heater and the second heater and the floating amount (space) of the contact sensor CS during a write operation at the outer periphery (OD) of the magnetic disk is measured offline.

[0098] As shown in the figure, no matter at which radius position, there is a tendency that the power ratio when the floating amount (space) of the contact sensor CS becomes the lowest point decreases according to the increase of the ambient temperature (-5°C → 25°C → 70°C). Therefore, it can be seen that in a high temperature environment, in order to control the floating amount of the contact sensor CS to the minimum, it is necessary to make the power ratio smaller than the power ratio in a normal temperature environment. In addition, no matter in which temperature environment, there is a tendency that the power ratio when the floating amount of the contact sensor CS becomes the lowest point increases as the radius position of the magnetic head moves from the inner periphery ID to the outer periphery OD. Therefore, it is known that the power ratio needs to be increased as the magnetic head moves toward the outer periphery OD.

[0099] According to the present embodiment, the heater power control unit 46a changes the power ratio to an appropriate value according to the change of the ambient temperature and the radial position, and supplies driving power to the first heater 76a and the second heater 76b based on the changed power ratio. For example, when the touch detection based on the contact sensor CS is performed at the inner peripheral position (ID) under the condition of a temperature of 25°C, the heater power control unit 46a controls the power ratio to 25% at normal temperature. When the touch detection based on the contact sensor CS is performed at the outer peripheral position (OD) under the condition of a temperature of 70°C, the heater power control unit 46a changes the power ratio to 35% to control the driving power.

[0100] As described above, by changing and controlling the power ratio (PR) according to changes in the ambient temperature and radial position, the contact detection sensitivity of the contact sensor CS can be maintained by controlling the floating amount (space) of the contact sensor CS to be minimized under different temperature and radial position conditions.

[0101] Next, a configuration example for controlling the power ratio (PR) of the heater driving power according to the pressure in the housing 11 of the HDD will be described.

[0102] Fig.19 is a diagram showing the relationship between the pressure in the housing 11 and the floating amount of the magnetic head. Fig. 20 1 is a diagram showing the relationship between the pressure in the housing 11 and the floating pitch of the magnetic head. Fig.21 It is a graph showing the relationship between the pressure in the casing 11 and the power ratio (PR).

[0103] like Fig.19 As shown in FIG. 1 , in an environment with high external pressure, the internal pressure of the housing 11 also increases, and the floating amount of the magnetic head increases with the increase in pressure. Fig. 20 As shown in FIG. 1 , as the pressure increases, the floating pitch of the magnetic head also increases, and the dynamic step difference Dsd increases. Therefore, it can be seen that in order to maintain Dsd constant, the power ratio needs to be changed according to the change in pressure.

[0104] Therefore, according to the present embodiment, the heater power control unit 46a of the main controller 40 changes and adjusts the power ratio (PR) of the driving power supplied to the first heater and the second heater according to the pressure detected by the pressure sensor PS. Fig.21 As shown, the heater power control unit 46a increases the power ratio (PR) when the pressure increases, and adjusts (that is, reduces) the increase in Dsd. In addition, the main controller 40 reduces the increase in the floating amount of the entire magnetic head by changing and adjusting the heater power as a whole. Thus, even if the pressure in the housing 11 changes, the floating amount (space) of the write element 60 and the read element 55 can be properly maintained.

[0105] In addition, in an HDD sealed with a low-density gas such as helium, when a gas leak occurs, the internal pressure of the housing 11 becomes lower, so the floating amount of the magnetic head decreases and the floating pitch also becomes smaller. In such a case, the heater power control unit 46a of the main controller 40 adjusts the floating pitch of the magnetic head, that is, the reduction amount of Dsd, by reducing the power ratio (PR) according to the pressure drop. Moreover, the heater power control unit 46a reduces the overall floating amount of the magnetic head by changing and adjusting the overall heater power, that is, by increasing the overall heater power. Thus, even when the pressure in the housing 11 decreases, the floating amount (space) of the write element 60 and the read element 55 can be properly maintained.

[0106] In addition, the control of the power ratio according to the pressure change can also be carried out in the same manner as in the above-mentioned embodiment. A power ratio setting table that tabulates the relationship between pressure and optimal power ratio is stored in the memory 47, and the power ratio is changed and set based on the power ratio setting table.

[0107] Next, a configuration example for independently controlling the power ratio (PR) of heater drive power in accordance with temperature and / or radial position variation of the magnetic heads in an HDD having a plurality of magnetic heads will be described.

[0108] In an HDD having multiple heads, the step difference Sd of each head varies due to the manufacturing process. In this embodiment, in order to suppress the uneven floating amount (space) of the write element 60 and the read element 55 caused by the uneven step difference Sd, the main controller 40 is configured to control the power ratio for each head independently.

[0109] Fig. 22 The power ratio setting table 2 is shown, which tabulates the relationship between the ambient temperature and the optimal power ratio and the relationship between the radial position of the magnetic head and the optimal power ratio for each magnetic head. The power ratio setting table 2 is obtained by measuring the turning point (the power ratio PR at which the height of the write element / read element becomes the same) of each magnetic head during the adjustment process before delivery of the HDD, tabulating the measured data and storing them in the memory 47. In the power ratio setting table 2, PR represents the power ratio, Zn represents the radial position, and Hd:n (0 to n) represents the number of the magnetic head.

[0110] The heater power control unit 46 a of the main controller 40 selects a corresponding power ratio from the power ratio setting table 2 for each magnetic head 16 based on the detected temperature and radial position, and sets the heater driving power for each magnetic head to the selected power ratio.

[0111] According to such a power ratio control example, even when there is a variation in the step difference Sd among the plurality of magnetic heads 16 , the flying amount (space) of each magnetic head can be appropriately maintained.

[0112] Furthermore, in this configuration example, in addition to the power ratio control corresponding to the temperature and radial position changes, the aforementioned power ratio (RP) control corresponding to the pressure change and the floating amount control of the contact sensor CS may be implemented for each magnetic head.

[0113] According to the magnetic head and HDD of the first embodiment constructed as above, by changing the power ratio of the driving power of the control amount of the thermal actuator according to the change of the ambient temperature, the change of the radial position of the magnetic head or the change of the pressure in the housing, the optimal power ratio is set, and even under different temperature environments, radial positions, and different pressures, the floating amount of the write element and the read element can be maintained to be the lowest point, and the writing action and the reading action can be performed without damaging the recording density. Therefore, no matter in which environment, the recording density can be improved, and the wear and damage of the magnetic head can be prevented, and the reliability can be improved.

[0114] In addition, in the first embodiment, the power ratio is changed according to the change of the ambient temperature, the change of the radial position of the magnetic head or the change of the pressure in the housing, but it is not limited to this, and the power ratio can also be controlled according to at least one of the above changes. In the above structure, compared with the case where the power ratio is not changed at all, the floating amount of the write element and the read element can be properly controlled, and the improvement of the recording density and the improvement of the reliability can be sought.

[0115] (Second embodiment)

[0116] Next, the configuration of the head of the HDD according to the second embodiment will be described. In the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed descriptions thereof are omitted or simplified.

[0117] Fig.23 It is a side view schematically showing the head portion 17 of the magnetic head according to the second embodiment.

[0118] According to the second embodiment, a magnetic head with a thermal assist function is used. As shown in the figure, the head 17 also includes a laser oscillator (laser diode) 82 embedded in the head, a near-field light generating element (NFT element) 84 embedded in the head 17 and exposed to the ABS 13, for example, exposed to the top surface of the write shield 62a, 64a, and a waveguide LG embedded in the head 17 and guiding the laser light emitted from the laser diode 82 to the NFT element 84. The laser diode 82 is connected to the laser drive current supply circuit 36 ​​(refer to FIG. 1 ) of the head amplifier IC 30 via wiring and flexible parts not shown in the figure. Figure 1 )Electrical connection.

[0119] When a driving current is supplied from the laser driving current supply circuit 36 ​​to the laser diode 82, the laser diode 82 oscillates laser light, supplies laser light to the NFT element 84 via the waveguide LG, and generates near-field light from the NFT element 84. The recording layer 103 of the magnetic disk 12 is locally heated by the near-field light generated from the top of the NFT element 84, so that the coercive force of the recording layer portion is reduced. A recording magnetic field from the main magnetic pole 60 is applied to the region where the coercive force is reduced, and a signal is written. By locally heating the recording layer 103 portion and writing a signal to the region where the coercive force is sufficiently reduced, high-density recording can be achieved.

[0120] The other structures of the magnetic head 16 are the same as those of the magnetic head 16 in the above-mentioned first embodiment.

[0121] Fig.24 is a side view of the head schematically showing a state in which the write head portion is thermally expanded.

[0122] As shown in the figure, under the condition that the input of the laser diode 82, that is, the thermal assist, is large, the temperature of the NFT element 84 rises, causing the write head portion near the NFT element to thermally expand, and the step Sd increases.

[0123] Fig.25 is a diagram showing the relationship between the input value of the laser diode 82 and the protrusion amount of the NFT element 84, Fig.26 is a diagram showing the relationship between the input value of the laser diode 82 and the floating amount (space) of the NFT element 84. Fig. 27 8 is a diagram showing the relationship between the input value of the laser diode 82 and the floating amount (space) of the read element 55. Fig.28 2 is a diagram showing the relationship between the input value of the laser diode 82 and the power ratio (PR) of the heater driving current.

[0124] like Fig.25 , Fig.26 As shown in FIG. 8 , it can be seen that, as the input value of the laser diode 82 increases, the protrusion amount of the NFT element 84 increases, and the floating amount (space) of the NFT element 84 gradually decreases. Fig. 27 As shown in FIG. 1 , it can be seen that the floating amount (space) of the read element 55 increases with the increase in the input value of the laser diode 82. Therefore, in order to properly maintain the floating amounts of the NFT element 84, the write element 60, and the read element 55 during the writing operation using the thermal assist function, it is preferable to Fig.28 As shown, control is performed so that the power ratio PR increases in accordance with an increase in the input value of the laser diode 82 .

[0125] An example of the floating amount control according to the ambient temperature performed by the main controller 40 will be described.

[0126] Fig.29It is a side view schematically showing a touch operation (TD) and a floating amount adjustment operation (BO) of the magnetic head during a write operation.

[0127] like Fig.29 As shown in (a), according to the present embodiment, normally (when the thermal assist function is not used), the main controller 40 performs a touch action and a floating amount adjustment action with the power ratio (PR) set to 35% in order to suppress the wear of the NFT element 84 and avoid the write head becoming the lowest point.

[0128] like Fig.29 As shown in (b), during thermal assistance, that is, when the driving power is input to the laser diode 82, if the power ratio is set to 35% as in normal times, the dynamic step difference Dsd increases due to the thermal expansion of the NFT element 84 and the write element, and the shielding part of the write head becomes the lowest point. When the touch action and the floating amount adjustment action are performed based on the shielding part, the floating amount (space) of the write element 60 and the NFT element 84 becomes smaller than that in normal times, causing concerns about reliability. On the contrary, the floating amount of the read element 55 becomes larger than that in normal times due to the increase in the dynamic step difference Dsd, and there is a concern about the quality degradation when reading data.

[0129] Therefore, according to this embodiment, if Fig.29 As shown in (c), during thermal assistance, the main controller 40 performs touch action and floating amount adjustment action while changing the power ratio (PR) from 35% to 45% according to the input value to the laser diode 82. By increasing the power ratio to 45%, the bulge of the read head part increases, and the same dynamic step difference Dsd as in normal times can be maintained, and the floating amounts of the write element, NFT element, and read element can be maintained at appropriate values.

[0130] In addition, the control of the power ratio corresponding to the input value of the laser diode 82 can also be the same as the above-mentioned embodiment. A power ratio setting table that tabulates the relationship between the input value and the optimal power ratio is stored in the memory 47, and the power ratio is changed and set based on the power ratio setting table.

[0131] According to the magnetic head and HDD of the second embodiment constructed as above, the space (floating amount) between the magnetic head 16 and the magnetic disk 12 can be properly maintained during thermal assistance, and the recording density can be improved. At the same time, the wear and damage of the head can be prevented, and the life and reliability of the magnetic head can be improved.

[0132] In addition, the second embodiment can also be applied in combination with the aforementioned first embodiment. That is, it can also be configured to change and adjust the power ratio of the driving power supplied to the first heater and the second heater according to the change of at least one of the ambient temperature, the radial position of the magnetic head, the pressure in the housing, and the input value to the laser diode.

[0133] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the invention. These embodiments and their variations are included in the scope and purpose of the invention, and are included in the invention and its equivalent scope recorded in the claims.

[0134] For example, the write head of the magnetic head of the embodiment can also be applied to a write head without a leading shield and / or a side shield. In addition, the write head can also be configured to have a high-frequency oscillation element arranged in the write gap. In addition, the material, shape, size, etc. of the elements constituting the head of the magnetic head can be changed as needed. In the magnetic disk device, the number of magnetic disks and magnetic heads can be increased or decreased as needed, and the size of the magnetic disk can also be selected in various ways. In the magnetic head, the number of thermal actuators is not limited to 2, and it can also be configured to be provided with 3 or more thermal actuators.

Claims

1. A magnetic disk device comprising: case; A temperature sensor, for detecting the temperature inside the housing; A magnetic disk is rotatably disposed in the housing; A magnetic head having a write head for writing data to the magnetic disk, a read head for reading data from the magnetic disk, a first thermal actuator for controlling the protrusion amount of the write head, and a second thermal actuator for controlling the protrusion amount of the read head, and is arranged in the housing so as to be movable in the radial direction of the magnetic disk; a power supply circuit for supplying a first power to the first thermal actuator and a second power to the second thermal actuator; and a controller that adjusts the power ratio of the first power to the second power according to at least one of a change in temperature within the housing and a change in a radial position of the magnetic head relative to the magnetic disk, The magnetic head includes a laser oscillator and a near-field light generating element for receiving laser light oscillated from the laser oscillator and irradiating near-field light toward the magnetic disk. The magnetic disk device further includes a drive current supply circuit for supplying a drive current to the laser oscillator. The controller adjusts the power ratio according to a change in an input value of a drive current input to the laser oscillator.

2. The magnetic disk device according to claim 1, A pressure sensor is also provided to detect the pressure in the housing. The controller adjusts the power ratio based on at least one of a change in temperature within the housing, a change in a radial position of the magnetic head relative to the magnetic disk, and a change in the pressure.

3. The magnetic disk device according to claim 2, The magnetic head includes a contact sensor for detecting contact between the magnetic disk and the magnetic head. The controller adjusts the power ratio so that the contact sensor is located at the lowest point according to at least one of a change in temperature within the housing, a change in a radial position of the magnetic head relative to the magnetic disk, and a change in the pressure.

4. The magnetic disk device according to claim 1, The controller includes a memory storing a power ratio setting table that tabulates the relationship between the temperature in the shell and the appropriate power ratio and the relationship between the radial position of the head and the appropriate power ratio. The controller selects the appropriate power ratio corresponding to the temperature detected by the temperature sensor and the radial position of the head from the power ratio setting table to set the power ratio.

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