Patent Application
20110216432
The present invention relates to a magnetic head, and further relates to a magnetic head having at least two magnetic field sensing (detection) parts.
In association with high recording density on a hard disk drive (HDD), a magnetic head with high sensitivity and high output is in demand. One example of a magnetic head that satisfies this demand is a magnetic head using a magnetoresistive effect (MR) film whose electrical resistance changes according to an external magnetic field (see Japanese Laid-Open Publication No. H02-257412).
A magnetic head of a spin valve type has been invented as a magnetic head using such an MR film. In the spin valve head, as a reading element, a pair of ferromagnetic layers is disposed through a nonmagnetic intermediate layer. An antiferromagnetic layer is disposed in a contacting manner to one of the ferromagnetic layers. Due to an exchange-coupling between the one of the ferromagnetic layers and the antiferromagnetic layer, a magnetization direction of the one of the ferromagnetic layers is fixed in one direction. A magnetization direction of the other of the ferromagnetic layers freely rotates according to the external magnetic field. As described above, the ferromagnetic layer whose magnetization direction freely rotates according to the external magnetic field is also referred as a free layer. According to a change in a relative angle formed by the magnetization directions of the two ferromagnetic layers, an electrical resistance value of the spin valve head changes. Based on the change in the electrical resistance value, the external magnetic field, i.e. a magnetic field from a recording medium, can be detected. As a result, the magnetic head can determine magnetic information written on the recording medium.
Currently, a track pitch of the HDD has become narrower, and it is desired to further narrow a width of the reading element of the magnetic head in a track width direction. However, the reading element senses the external magnetic field of an area that is wider (broader) than an actual width of the reading element. In other words, magnetization of the free layer changes due to the external magnetic field of the area that is wider than the width of the track width direction of the free layer. Therefore, it has become difficult to provide a magnetic head that is compatible with the recording medium having a narrow track pitch only by narrowing the width of the reading element. There is also a manufacturing limitation for narrowing the width in the track width direction of the reading element.
Accordingly, instead of narrowing the width in the track width direction of the reading element, it is desired to develop a magnetic head that is compatible with the recording medium having a narrow track pitch.
An object of the present invention is to provide a magnetic head that is compatible with a recording medium having a narrow track pitch.
The magnetic head according to one embodiment of the present invention has a reading element that reads magnetic information written on the recording medium. The reading element has a first magnetoresistive effect part (first MR part) and a second magnetoresistive effect part (second MR part), an electrical resistance of the first MR part changing according to an external magnetic field applied to a first magnetic field sense area, an electrical resistance of the second MR part changing according to an external magnetic field applied to a second magnetic field sense area. A width of the second magnetic field sense area in a track width direction of the recording medium is larger than a width of the first magnetic field sense area in the track width direction. A phase of change in the electrical resistance of the second MR part with respect to the external magnetic field substantially reverses to a phase in the electrical resistance of the first MR part. The magnetic head produces an output signal that comprises a sum of a first sense signal and a second sense signal, the first sense signal being based on the change of the electrical resistance of the first MR part, the second sense signal being normalized to a predetermined amount and being based on the change of the electrical resistance of the second MR part, and determines the magnetic information written on the recording medium from the output signal.
The magnetic head according to the other embodiment of the present invention has a reading element that reads magnetic information written on the recording medium. The reading element has a first magnetoresistive effect part (first MR part) and a second magnetoresistive effect part (second MR part), an electrical resistance of the first MR part changing according to an external magnetic field applied to a first magnetic field sense area, an electrical resistance of the second MR part changing according to an external magnetic field applied to a second magnetic field sense area. A width of the second magnetic field sense area in a track width direction of the recording medium is larger than a width of the first magnetic field sense area in the track width direction. A phase of change in the electrical resistance of the second MR part with respect to the external magnetic field is substantially the same as a phase in the electrical resistance of the first MR part. The magnetic head produces an output signal that comprises a difference between a first sense signal and a second sense signal, the first sense signal being based on the change of the electrical resistance of the first MR part, the second sense signal being normalized to a predetermined amount and being based on the change of the electrical resistance of the second MR part, and determines the magnetic information written on the recording medium from the output signal.
In the magnetic head configured as described, a peak of the second sense signal obtained from the wide second MR part is broader than a peak of the first sense signal obtained from the first MR part. Accordingly, a width of the peak of the final output signal obtained from the first sense signal and the second sense signal, specifically a width of a skirt (skirt part) of the peak, becomes small. This means that an area where the magnetic head senses the magnetic field becomes small. Therefore, the magnetic head of the present invention can read the magnetic information of the recording medium having the narrow track pitch with higher accuracy.
The above-mentioned object, as well as other objects, characteristics, and advantages of the present invention will be described below with reference to attached drawings illustrating an embodiment(s) of the present invention.
Hereafter, a thin film magnetic head of one embodiment of the present invention will be explained with reference to the drawings.
The magnetic head 291 has a reading element 1 for detecting (reading) magnetic information written on a recording medium 262, and a writing element 120 for writing magnetic information on the recording medium 262. In the present embodiment, the magnetic head 291 having the reading element 1 and the writing element 120 will be explained. However, the magnetic head having only the reading element 1 also can be used as the magnetic head of the present invention.
In the present embodiment, as a preferable example, a so-called spin-valve type MR element (a spin-valve element) is used for the MR parts 2 and 3. The first MR part 2 is sandwiched between a pair of shield layers 4 and 5 in a film surface orthogonal direction P of the MR stack. Similarly, the second MR part 3 is sandwiched between a pair of shield layers 6 and 7 in the film surface orthogonal direction P of the MR stack. These shield layers 4, 5, 6 and 7 function to prevent an external magnetic field generated by an adjacent bit arranged on the same track of the recording medium 262 from being applied to a free layer, and function as electrodes that enable a sense current to flow through the MR stack.
In the present embodiment, the shield layer 5 and the shield layer 6 are insulated by an insulating layer 9. Alternatively, both shield layers 5 and 6 can be formed in an integrated manner without arranging the insulating layer 9 between the shield layer 5 and the shield layer 6.
The two MR stacks configuring the first MR part 2 and the second MR part 3 are configured in the same manner. Each of the MR stacks is formed such that antiferromagnetic layers (pinning layers) 21 and 25, first ferromagnetic layers (pinned layers) 22 and 26, nonmagnetic intermediate layers (spacer layers) 23 and 27, and second ferromagnetic layers (free layers) 24 and 28 are respectively laminated in this order. These layers may also be laminated in a reverse order.
The nonmagnetic intermediate layers 23 and 27 can be made of for example, a nonmagnetic conductor such as copper (Cu), or a nonmagnetic insulator such as, for example aluminum oxide (AlOx) or magnesium oxide (MgO). The antiferromagnetic layers 21 and 25 are preferably made of a platinum-manganese alloy (PtMn) or an iridium-manganese alloy (IrMn).
Materials and a thickness of each layer configuring the first MR part 2 may be either the same as or different from materials and a thickness of each layer configuring the second MR part 3. Moreover, a lamination configuration of the first MR part 2 may be different from a lamination configuration of the second MR part 3.
Magnetizations of the second ferromagnetic layers (free layers) 24 and 28 change according to the external field. The second ferromagnetic layers 24 and 28 are made of for example, CoFe/NiFe or the like. The first ferromagnetic layers (pinned layers) 22 and 26 are exchange-coupled with the antiferromagnetic layers 21 and 25. This causes magnetization directions PL1 and PL2 of the first ferromagnetic layers 22 and 26 to be fixed.
A relative angle between the magnetization direction of the first ferromagnetic layer 22 and a magnetization direction of the second ferromagnetic layer 24 changes according to the direction of the external magnetic field. The electrical resistance value of the first MR part 2 changes according to the change of the relative angle. Similarly, a relative angle between the magnetization direction of the first ferromagnetic layer 26 and a magnetization direction of the second ferromagnetic layer 28 changes according to the direction of the external magnetic field. The electrical resistance value of the second MR part 3 changes according to the change of this relative angle. As described above, each of the MR parts 2 and 3 essentially includes a pair of the ferromagnetic layers where the relative angle of the magnetizations changes according to the external magnetic field, and the free layers 24 and 28 whose magnetization directions change according to the external magnetic field configure magnetic field sense areas where a change in the external magnetic field is sensed.
In the present embodiment, the magnetization direction PL1 of the first ferromagnetic layer 22 of the first MR part 2 is substantially in an opposite direction to the magnetization direction PL2 of the second ferromagnetic layer 26 of the second MR part 3. Magnetizations of the pinned layers 22 and 26 can be directed in a desired direction by an annealing treatment in a predetermined magnetic field.
A width W2 of the second ferromagnetic layer 28 of the second MR part 3, i.e. the magnetic field sense area, in a track width direction T is wider than a width W1 of the ferromagnetic layer 24 of the first MR part 2, i.e. the magnetic field sense area, in the track width direction T.
A signal processing device 29 is included in the magnetic head 291 or a separate device such as, for example, a hard disk device. The signal processing device 29 produces a final output signal S by processing the first sense signal S1 from the first MR part 2 and the second sense signal S2 from the second MR part 3. The signal processing device 29 produces a sum of the first sense signal S1 and the second sense signal S2 as the output signal S. Herein, the second sense signal is normalized to a predetermined amount. Herein, the second sense signal S2 is normalized such that an absolute value of a peak value of the second sense signal S2 is smaller than an absolute value of a peak value of the first sense signal S1, and more preferably less than the half of the absolute value of the first sense signal S1.
The sense signals S1 and S2 obtained from the MR parts 2 and 3 do not have to be the electrical resistance value itself, and may be signals that are obtained by using voltage changes or current changes according to the change in the electrical resistance value. For example, under a condition where a constant voltage is applied to the MR parts 2 and 3, an amount of the sense current flowing in the MR parts 2 and 3 may be detected as the sense signal. Instead of such a method, under a condition where the constant sense current flows in the MR parts 2 and 3, a potential difference between both of sides in the lamination direction of the MR stack that configures the MR parts 2 and 3 may be detected as the sense signal.
An operating principle will be explained for detecting the external magnetic field, i.e., reading the magnetic information of the recording medium by the above-described magnetic head 291.
In the present embodiment, a magnetization direction PL1 of the first ferromagnetic layer 22 of the first MR part 2 is in a substantially opposite direction to a magnetization direction PL2 of the second ferromagnetic layer 26 of the second MR part 3. Therefore, when a relative angle between the magnetization direction of the first ferromagnetic layer 22 and the magnetization direction of the second ferromagnetic layer 24 is small in the first MR part 2, a relative angle between the magnetization direction of the first ferromagnetic layer 26 and the magnetization direction of the second ferromagnetic layer 28 becomes large in the second MR part 3. Additionally, when a relative angle between the magnetization direction of the first ferromagnetic layer 22 and the magnetization direction of the second ferromagnetic layer 24 is large in the first MR part 2, a relative angle between the magnetization direction of the first ferromagnetic layer 26 and the magnetization direction of the second ferromagnetic layer 28 becomes small in the second MR part 3. As described above, a phase of the resistance value with respect to the external magnetic field of the first MR part 2 is substantially shifted by 180° from the resistance value with respect to the external magnetic field of the second MR part 3. Therefore, when a sense signal, where the strength of the external magnetic field is zero, is set as zero, a sense signal S1 from the first MR part 2 has a value that is the inverse of a sense signal S2 from the second MR part 3.
As illustrated in
The signal processing device 29 produces a sum of the first sense signal S1 and the second sense signal S2 that is normalized in the predetermined size as the output signal S. Since the second sense signal S2 has a reverse sign against the first sense signal S1, the output signal S generally has a waveform of which the magnitude (signal intensity) is suppressed relative to that of the first sense signal S1. Herein, since the peak of the second sense signal S2 is broader than the peak of the first sense signal S1, a ratio of the value at the skirt part of the peak of the second sense signal S2 with respect to the value at the skirt part of the first sense signal S1 is larger than a ratio of the maximum value of the second sense signal S2 with respect to the maximum value of the first sense signal S1. Therefore, compared with the first sense signal S1, the waveform of the output signal S produced by the signal processing device 29 exhibits a suppressed signal intensity at the skirt part of the peak, i.e., the peak width (especially a width at the skirt part of the peak) is decreased.
Referring to
This means that the output signal S rapidly decreases as the magnetic head is shifted from the center of the track, and that the magnetic head 291 of the present embodiment can accurately read the magnetic information of the recording medium having the narrow track pitch.
The signal processing device 29 can be configured with an analog/digital (A/D) converter circuit for converting the first sense signal S1 to a first digital signal and transforming the second sense signal S2 to a second digital signal, and an operation part for conducting a calculation process of the first digital signal and the second digital signal. In this case, the signal processing device 29 is incorporated in a device that is separately arranged from the magnetic head 291, i.e., the hard disk device.
When the signal processing device 29 converts the sense signals S1 and S2 to the digital signals and proceeds, there is an advantage in which the first MR part 2 and the second MR part 3 do not have to simultaneously read the magnetic field from one bit of the recording medium. This is because, by storing the digital signal in a memory, positions of peak signals corresponding to the magnetic information from the same bit are synchronized, the calculation process of the first sense signal S1 and the second sense signal S2 is performed, and thereby the predetermined output signal S can be easily obtained. Therefore, the first MR part 2 and the second MR part 3 may be arranged at a certain interval such that they are positioned on different bits when the magnetic head 291 faces the recording medium 262.
The signal processing device 29 may be an analog circuit for producing the predetermined output signal S from the first sense signal S1 and the second sense signal S2. Such an analog circuit is configured with an amplifier circuit or a reduction circuit, and an analog adder circuit. The amplifier circuit amplifies the first sense signal S1 and/or the second sense signal S2 to a predetermined amount, and the reduction circuit reduces the first sense signal S1 and/or the second sense signal S2 to a predetermined amount. In this case, the signal processing device 29 can be incorporated in the magnetic head 291. Also in this case, the first MR part 2 and the second MR part 3 are preferably arranged close to one another so as to simultaneously sense the magnetic field from the one bit of the recording medium. This is because the calculation with respect to the first sense signal and the second sense signal can be performed by synchronizing the positions of the peak signals corresponding to the magnetic information from the same bit.
A width W1 of the second ferromagnetic layer 24 of the first MR part 2, i.e. a magnetic field sense area, in the track width direction is preferably as small as possible. This enables the MR part 2 to correspond to the recording medium having the narrower track pitch. On the other hand, the half width (full width at half maximum) of the peak of the sense signal S2 of the second MR part 3 is preferably equal to or less than the track width of the recording medium 262. This is because when the half width of the peak of the sense signal S2 is wider than the track width, the second MR part 3 is affected by the magnetic field from the adjacent track and it becomes difficult to accurately read the magnetic information. Since the half width of the peak of the sense signal S2 depends on the actual width W2 in the track width direction T of the second ferromagnetic layer 28 of the second MR part 3, i.e., the magnetic field sense area, the limitation with respect to the half width of the sense signal S2 indirectly normalizes the width W of the second ferromagnetic layer 28 of the second MR part 3.
Next, regarding the following three examples, a simulation result will be explained with respect to a relation between a size of the second sense signal S2 in relation to the first sense signal S1 and the produced output signal S when the signal processing device 29 produces the output signal S. As shown in Table 1, in the first through third examples, each half width of the peak of the second sense signal S2 from the second MR part 3 varied. This means that the width W2 of the second ferromagnetic layer 28 of the second MR part 3 varied.
Regarding each of the examples, a value of a ratio (hereafter, referred to as an output ratio of the sense signal) of an absolute value of a peak value of the sense signal S2 with respect to an absolute value of a peak value of the sense signal S1 was changed, and the final output signal S was produced.
When referring to
As described above, the antiferromagnetic layer 41 that is a single layer functions to fix a magnetization direction of the first ferromagnetic layer 42 of the first MR part 2, and also functions to fix a magnetization direction of the first ferromagnetic layer 46 of the second MR part 3. Thereby, even if there are two layers for the free layers 44 and 48 that sense an external magnetic field, a total thickness of the stack 50 can be reduced. Therefore, in order that the first MR part 2 and the second MR part 3 can simultaneously read magnetic information of a single bit, the first MR part 2 and the second MR part 3 can be arranged closely in a track direction of a recording medium (substantially the same direction as a film surface orthogonal direction P of the stack illustrated in
In the second embodiment, a magnetization direction PL1 of the pinned layer 42 of the first MR part 2 and a magnetization direction PL2 of the pinned layer 46 of the second MR part 3 are in opposite directions. Also, the stack 50 including the first MR part 2 and the second MR part 3 has a trapezoidal shape whose width tapers in a direction from the lower layer to the upper layer. Thereby, a width W2 in the track width direction T of the second ferromagnetic layer (the free layer) 48 of the second MR part 3 is wider than a width W1 in a track width direction T of the second ferromagnetic layer (the free layer) 44 of the first MR part 2.
In addition, shield layers 54 and 57 are arranged at an upper layer side and a lower layer side, respectively of the stack 50 that is formed in an integrated manner. A sense current flows from the shield layers 54 and 57 through the stack 50 entirely that includes the first MR part 2 and the second MR part 3. In this case, a resistance value of the stack 50 is a sum of resistances values of the first MR part 2 and the second MR part 3 (and the pinning layer 41). Accordingly, an output signal from the stack 50 corresponds to the sum of a sense signal from the first MR part 2 and a sense signal from the second MR part 3. In other words, the integrated stack 50 itself functions as a device for producing a final output signal based on the sense signals from the two MR parts 2 and 3. Therefore, similar to the magnetic head of the first embodiment, the magnetic head of the second embodiment also can read the magnetic information of a recording medium having a narrow track width.
As described above, in the present specification, the sense signal means not only a signal that is directly measured but also a signal that is not directly measured (resistance value, voltage value, current value or the like).
According to the configuration of the second embodiment, as in the first embodiment, an analog circuit, etc. as the signal processing device 29 is not required so that the configuration of the magnetic head can be simplified.
Materials, thicknesses or the like of each film configuring the stack 50 may be selected in view of design purposes. A size of the resistance value (corresponding to a size of the sense signal) of each of the MR parts 2 and 3 depends on the materials and thicknesses. Accordingly, by properly choosing the materials, thicknesses or the like, the size of the resistance of the second MR part 3 in relation to the size of the resistance value of the first MR part 2 can be controlled.
Similar to the first and second embodiments, a width W2 of a magnetic field sense area of the second MR part 3, i.e., of a free layer 28, is wider than a width W1 of a magnetic field sense area of the first MR part 2, i.e., of a free layer 24.
Using the magnetic head of the third embodiment, an operating principle will be explained with respect to reading magnetic information of a recording medium.
In the present embodiment, the magnetization direction PL1 of the first ferromagnetic layer 22 of the first MR part 2 is substantially in the same direction as the magnetization direction PL2 of a first ferromagnetic layer 26 of the second MR part 3. Therefore, being different from the first embodiment, a phase of the resistance with respect to the external magnetic field of the first MR part 2 is substantially the same as one of the resistance value with respect to the external magnetic field of the second MR part 3.
As illustrated in
Also, the peak of the second sense signal S2 is broader than the peak of the first sense signal S1. This is because a width W2 of the magnetic field sense area of the second MR part 3 is wide and the second MR part 3 can sense the external magnetic field in a wider area.
The signal processing device 29 produces a difference between the first sense signal S1 and the second sense signal S2 that is normalized to a predetermined amount as the output signal S. Herein, since the second sense signal S2 has a value that is inverted compared to that of the first embodiment, the output signal S produced by the signal processing device 29 has the same waveform as that of the output signal S described in the first embodiment. Therefore, the magnetic head of the third embodiment also has the same advantage of the magnetic head as the first embodiment. Additionally, in
Next, referring to
The auxiliary magnetic pole layer 122 is a magnetic layer that is magnetically coupled with the main magnetic pole layer 121. The auxiliary magnetic pole layer 122 is a magnetic pole layer formed with an alloy made of any two or three of Ni, Fe and Co or the like with approximately 0.01 μm to approximately 0.5 μm of film thickness. The auxiliary magnetic pole layer 122 is arranged in a manner of branching from the main magnetic pole layer 121, and faces the main magnetic pole layer 121 via the gap layer 124 and the coil insulating layer 125 at the ABS S. An edge part of the auxiliary magnetic pole layer 122 on the ABS side forms a trailing shield part of which the cross section is wider than any other part of the auxiliary magnetic pole layer 122. Establishment of such an auxiliary magnetic pole layer 122 causes a steeper magnetic field gradient between the auxiliary magnetic pole layer 122 and the main magnetic pole layer 121 in the vicinity of the ABS S. As a result, signal output jitter decreases and the error rate during a reading process is reduced.
Next, a wafer used for manufacturing the above mentioned thin film magnetic head will be explained. Referring to
Referring to
Referring to
The slider 210 is disposed in the hard disk device such that the slider 210 is opposite to the recording medium. The recording medium is disk shaped and rotatably driven. When the hard disk rotates in the z-direction of
A part in which the head gimbal assembly 220 is mounted on an arm 230 is referred to as a head arm assembly. The arm 230 allows the slider 210 to move in the track crossing direction x of the hard disk 262. One edge of the aim 230 is mounted on the base plate 224. On the other edge of the arm 230, a coil 231 is mounted, which forms one part of a voice coil motor. A bearing part 233 is disposed in the middle section of the arm 230. The arm 230 is rotatably supported by a shaft 234 mounted on the bearing part 233. The arm 230 and the voice coil motor for driving the arm 230 configure an actuator
Next, referring to
Referring to
As illustrated in
A description of the preferred embodiment according to the present invention was given above in detail. However, it should be appreciated that a wide variety of alterations and modifications are possible as far as they do not depart from the spirit and scope of the attached claims.
