JP2007004857A - Magnetic disk apparatus having tunnel magneto-resistive head element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic disk apparatus having a TMR head element capable of easily and surely monitoring the TMR head element even during actual operation, and to provide a head amplifier for a magnetic disk apparatus having the TMR head element. <P>SOLUTION: The apparatus is provided with: an applying means capable of applying a plurality of voltages or currents different in value are to the TMR head element; a measuring means for measuring a resistance value of the TMR head element while the plurality of voltages or currents are applied respectively; a resistance change rate calculating means for calculating a resistance change rate from the plurality of resistance values obtained by measurement; and a self monitor system including an identifying means for identifying a state of the TMR head element by comparing the calculated resistance change rate with at least one threshold value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic disk device having a head element utilizing a tunnel magnetoresistive effect (TMR) and a head amplifier for a magnetic disk device having a TMR head element.

  In recent years, in a magnetic disk device (hard disk drive (HDD)), the recording density has been greatly improved, and an HDD using a TMR read head element has been proposed accordingly.

  When this type of HDD is actually operated, it is predicted that the characteristics will deteriorate due to the occurrence of pinholes in the built-in TMR read head element or the increase in the number thereof.

  Conventionally, a TMR read head element has been evaluated whether it is a good product or a defective product immediately after it is manufactured or during its manufacturing. In Patent Document 1, as an inspection method for confirming reliability without damaging or destroying the TMR head element, a resistance value is measured by passing a set initial current value through the TMR head element and measuring the resistance value. The test current value is obtained using the value, or the correction current value is obtained several times based on the resistance value and the voltage value which is a measurement standard of the element, and the final corrected current value is supplied to the TMR head element. A method is disclosed in which a resistance value is measured, an inspection current value is obtained using the final resistance value, and a characteristic inspection such as an electromagnetic conversion characteristic of the TMR head element is conducted using the inspection current value thus obtained. ing.

  However, the method described in Patent Document 1 is an inspection method performed during manufacturing or during manufacturing, and does not self-monitor the TMR read head element incorporated in the HDD during its actual operation.

  As an HDD self-monitoring method or program, a SMART (Self-Monitoring, Analysis and Reporting Technology) function is known. This SMART function is intended to predict the deterioration of HDD reliability by monitoring attribute values such as the head flying height, the number of remapped sectors, the number of errors, the temperature, and the data output rate.

JP 2001-23131 A

  However, monitoring of the TMR read head element during HDD operation has not been performed at all and has not been proposed.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic disk device having a TMR head element and a head amplifier for a magnetic disk device having a TMR head element that can easily and reliably monitor a TMR head element even during actual operation. Is to provide.

  According to the present invention, an applying means capable of applying a plurality of voltages or currents having different values to the TMR head element, and a measuring means for measuring the resistance value of the TMR head element in a state where a plurality of voltages or currents are respectively applied. A resistance change rate calculating means for calculating a resistance change rate from a plurality of resistance values obtained by measurement, and an identifying means for comparing the calculated resistance change rate with at least one threshold to identify the state of the TMR head element. A magnetic disk drive having a self-monitoring system is provided.

  It is preferable that the self-monitoring system further includes notification means for notifying the identified state.

  It is also preferable that the applying means is means for applying different voltages or currents to each other discontinuously or continuously. Here, applying a voltage or current discontinuously means that after applying one voltage or current, the voltage or current application is temporarily stopped, and then the next voltage or current is applied.

  According to the present invention, there is further provided an application means capable of applying a voltage or current having a first value and a voltage or current having a second value larger in absolute value than the first value to the TMR head element, and the TMR head element. A first measuring means for measuring a resistance value in a state where a voltage or current having a first value is applied to the first resistance value and a state in which a voltage or current having a second value is applied to the TMR head element A second measuring means for measuring the resistance value to obtain a first resistance value, a resistance change rate calculating means for calculating a resistance change rate from the first resistance value and the second resistance value, and the calculated resistance There is provided a magnetic disk drive comprising a self-monitoring system including an identification means for comparing the rate of change with at least one threshold to identify the state of the TMR head element.

  The resistance value when different voltages or currents are applied to the TMR head element is obtained, and the resistance change rate is obtained. In a TMR head element having a low resistance change rate% VbdMRR (when voltage is applied) or% dMRR (when current is applied), the degree of metal conduction in the barrier layer is low and the number of pinholes is small, so that the element breakdown voltage is high. Conversely, in a TMR head element with a high rate of change in resistance, the degree of metal conduction in the barrier layer is high, and since there are many pinholes, the element breakdown voltage is low. Accordingly, the resistance change rate% VbdMRR or% dMRR is obtained from the resistance values measured at different voltages or current values, and the comparison is made with the threshold value, so that the reliability and deterioration degree of the TMR head element can be extremely easily and quickly. Can be identified and the result is notified to the user. As a result, the user can know information such as characteristic deterioration of the TMR read head element in the magnetic disk device, and can perform replacement of the magnetic disk device, backup of information, etc. before this magnetic disk device fails. It becomes possible.

  In particular, when the resistance change rate% VbdMRR is obtained from the resistance values measured with different voltage values, the load applied to this layer, that is, the voltage is equal even when the size of the TMR layer is different, so the load factor is kept constant. Measurement and identification. Moreover, the measurement can be performed under voltage conditions in a state close to a form in which the TMR head element is actually used. That is, in this case, the resistance change rate does not have a strong correlation with the resistance value of the TMR head element, and by approaching a certain value, the area effect due to the size of the TMR layer is eliminated, and the TMR layer functions sufficiently. Can be easily distinguished from those having defects. In other words, in one continuous correlation line representing the relationship between the resistance value and the resistance change rate, the slope is large and the resistance change rate decreases in a region where the resistance value is small, and the change occurs when the resistance value exceeds a certain value. As a result, the slope changes, and asymptotically approaches a certain rate of change in resistance. The region where the resistance value is small and the correlation line has a large negative slope and the region where the correlation line is transformed and the slope gradually changes to a certain resistance change rate show different film qualities. As a result, the reliability of the TMR head element can be confirmed clearly and reliably.

  It is preferable that the self-monitoring system further includes notification means for notifying the identified state.

  It is also preferable that the applying means is means for applying the first value voltage or current and the second value voltage or current discontinuously or continuously. Here, applying a voltage or current discontinuously means that after applying one voltage or current, the voltage or current application is temporarily stopped, and then the next voltage or current is applied.

The resistance change rate calculating means, the first resistance value and _{R 1,} is calculated when the second resistance value and _{R 2,} the resistance change ratio from the _{(R 2 -R 1) / R} 1 × 100 (%) Preferably it is a means.

The identification means is preferably means for identifying that the TMR head element cannot be used when the resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeds the first threshold value. .

When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is equal to or lower than the first threshold value and exceeds a second threshold value that is lower than the first threshold value, the TMR head element is It is also preferable to be a means for discriminating that it is unstable but ready for use.

When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is equal to or lower than the second threshold and exceeds a third threshold that is lower than the second threshold, the TMR head element is It is also preferable to be a means for identifying that the state is stable.

When the resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeds the third threshold, the identification means is a means for identifying that the TMR head element is in a very stable state. Is also preferable.

The tunnel barrier layer of the TMR head element is made of aluminum (Al) oxide, for example, aluminum oxide (alumina, Al ₂ O ₃ ), and the first voltage value is 25 mV, and the second voltage value is In the case of 150 mV, the first threshold value is preferably −0.8 (%). Further, in this case, the second threshold value is preferably −1.2 (%). Furthermore, it is preferable that the third threshold value is −1.8 (%).

The tunnel barrier layer of the TMR head element is made of an oxide of aluminum (Al), for example, aluminum oxide (alumina, Al ₂ O ₃ ), and the first current value is 0.1 mA, the second current When the value is 0.4 mA, the first threshold value is preferably −0.6 (%). Furthermore, in this case, it is preferable that the second threshold value is −0.8 (%). Furthermore, it is preferable that the third threshold value is −1.0 (%).

  When the tunnel barrier layer is made of a material other than the oxide of Al, the first voltage or current value, the second voltage or current value, and the first to third threshold values of the resistance change rate are set accordingly. If set, the same evaluation is possible.

  It is preferable that the self-monitoring system is operated at a set time and / or whenever instructed to identify the state of the TMR head element when starting the magnetic disk device.

  The self-monitoring system preferably operates in a state where the TMR head element is retracted from the recording area of the magnetic disk or in a state where the TMR head element is positioned on the area where specific information is recorded on the magnetic disk.

  According to the present invention, furthermore, an application means capable of applying a first value voltage or current and a second value voltage or current having an absolute value larger than the first value to the TMR head element; A first measuring means for measuring a resistance value in a state in which a voltage or current having a first value is applied to the element to obtain a first resistance value, and a voltage or current having a second value applied to the TMR head element A second measuring means for measuring a resistance value in a state to obtain a first resistance value, a resistance change rate calculating means for calculating a resistance change rate from the first resistance value and the second resistance value, and calculating There is provided a head amplifier for a magnetic disk drive having a self-monitoring system including an identification means for identifying a state of a TMR head element by comparing a resistance change rate with at least one threshold value.

  Such a head amplifier is used in a normal magnetic disk device. Thus, the resistance value when different voltages or currents are applied to the TMR head element is obtained, and the resistance change rate is obtained. In a TMR head element having a low resistance change rate% VbdMRR (when voltage is applied) or% dMRR (when current is applied), the degree of metal conduction in the barrier layer is low and the number of pinholes is small, so that the element breakdown voltage is high. Conversely, in a TMR head element with a high rate of change in resistance, the degree of metal conduction in the barrier layer is high, and since there are many pinholes, the element breakdown voltage is low. Accordingly, the resistance change rate% VbdMRR or% dMRR is obtained from the resistance values measured at different voltages or current values, and the comparison is made with the threshold value, so that the reliability and deterioration degree of the TMR head element can be extremely easily and quickly. Can be identified and the result is notified to the user. As a result, the user can know information such as characteristic deterioration of the TMR read head element in the magnetic disk device, and can perform replacement of the magnetic disk device, backup of information, etc. before this magnetic disk device fails. It becomes possible.

  In particular, when the resistance change rate% VbdMRR is obtained from the resistance values measured with different voltage values, the load applied to this layer, that is, the voltage is equal even when the size of the TMR layer is different, so the load factor is kept constant. Measurement and identification. Moreover, the measurement can be performed under voltage conditions in a state close to a form in which the TMR head element is actually used. That is, in this case, the resistance change rate does not have a strong correlation with the resistance value of the TMR head element, and by approaching a certain value, the area effect due to the size of the TMR layer is eliminated, and the TMR layer functions sufficiently. Can be easily distinguished from those having defects. In other words, in one continuous correlation line representing the relationship between the resistance value and the resistance change rate, the slope is large and the resistance change rate decreases in a region where the resistance value is small, and the change occurs when the resistance value exceeds a certain value. As a result, the slope changes, and asymptotically approaches a certain rate of change in resistance. The region where the resistance value is small and the correlation line has a large negative slope and the region where the correlation line is transformed and the slope gradually changes to a certain resistance change rate show different film qualities. As a result, the reliability of the TMR head element can be confirmed clearly and reliably.

  The applying means is preferably means for applying the first value voltage or current and the second value voltage or current discontinuously or continuously. Here, applying a voltage or current discontinuously means that after applying one voltage or current, the voltage or current application is temporarily stopped, and then the next voltage or current is applied.

The resistance change rate calculating means, the first resistance value and _{R 1,} is calculated when the second resistance value and _{R 2,} the resistance change ratio from the _{(R 2 -R 1) / R} 1 × 100 (%) Preferably it is a means.

The identification means is preferably means for identifying that the TMR head element cannot be used when the resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeds the first threshold value. .

When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is equal to or lower than the first threshold value and exceeds a second threshold value that is lower than the first threshold value, the TMR head element is It is also preferable to be a means for discriminating that it is unstable but ready for use.

When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is equal to or lower than the second threshold and exceeds a third threshold that is lower than the second threshold, the TMR head element is It is also preferable to be a means for identifying that the state is stable.

When the resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeds the third threshold, the identification means is a means for identifying that the TMR head element is in a very stable state. Is also preferable.

  According to the present invention, the resistance change rate% VbdMRR or% dMRR is obtained from the resistance values measured with different voltage or current values, and compared with the threshold value, the reliability and the degree of deterioration of the TMR head element can be extremely easily obtained. And it can identify in a short time and the result is notified to a user. As a result, the user can know information such as characteristic deterioration of the TMR read head element in the magnetic disk device, and can perform replacement of the magnetic disk device, backup of information, etc. before this magnetic disk device fails. It becomes possible.

  FIG. 1 is a block diagram schematically showing an electrical configuration of an HDD having a TMR thin film magnetic head as one embodiment of the present invention.

  In the figure, 10 is a magnetic disk as a magnetic recording medium, 11 is a spindle motor (SPM) for rotating the magnetic disk 10, 12 is a TMR thin film magnetic head provided with a TMR read head element and an inductive write head element, and 13 is A support mechanism of the TMR thin film magnetic head 12, 14 is a voice coil motor (VCM) that rotates the support mechanism 13 to position the magnetic head, 15 is a head amplifier for the TMR read head element and inductive write head element, 16 Represents a motor driver for driving the SPM 11 and the VCM 14, 17 a read / write channel, 18 a hard disk controller (HDC), 19 a microcomputer, and 20 a memory used as a data buffer.

  The head amplifier 15 includes a write driver circuit that generates a write current applied to the inductive write head element, a read amplifier circuit that supplies a predetermined sense current from the constant current circuit to the TMR read head element and amplifies its output voltage. It has. In particular, in this embodiment, the read amplifier circuit needs to apply different voltages to the TMR read head element during the self-monitoring operation, so that the sense current flowing through the TMR read head element can be gradually changed. It is configured. It is obvious that a voltage bias method of applying a constant voltage may be used instead of the current bias method of supplying a constant current as in the present embodiment.

  The read / write channel 17 mainly performs code modulation of write data and outputs the code to the head amplifier 15, and also performs processing of detecting data from the read signal waveform from the head amplifier 15 and demodulating the code.

  The HDC 18 performs error correction, buffer control, cache control, interface control, servo control, and the like, and exchanges write data and read data with a host computer connected to the HDD.

  The microcomputer 19 controls the entire HDD. The microcomputer 19 performs position control of the thin film magnetic head, interface control, initialization and setting of each circuit of the HDD by the VCM 14, and executes self-monitoring processing. In FIG. 1, the part that executes this self-monitoring process is represented as a self-monitoring system 19a.

  FIG. 2 is a flowchart for explaining the processing operation of the HDD self-monitoring system 19a.

  The microcomputer 19 executes this self-monitoring process when a predetermined time elapses and / or according to an arbitrary instruction when the HDD is activated. When the HDD is started, the self-monitoring process is executed in a state where the TMR read head element is retracted outside the recording area before moving to the recording area of the magnetic disk 10, and the TMR read head element is used every time and every instruction. The self-monitoring process is executed in a state where the disk is retracted outside the recording area of the magnetic disk 10. The state in which the TMR read head element is retracted outside the recording area of the magnetic disk 10 means that in a load / unload type HDD, a thin film magnetic head including the TMR read head element is placed on a ramp positioned outside the magnetic disk. In a contact start / stop (CSS) type HDD, the thin film magnetic head including the TMR read head element is present in the CSS area on the magnetic disk. This is because the magnetic influence applied from the magnetic disk to the TMR read head element is made as small as possible by performing the self-monitoring process in such a retracted state. Although it is desirable to perform the self-monitoring process in a state where the TMR read head element is retracted outside the recording area of the magnetic disk 10, for example, 1-1 on the area where the TMR read head element records specific information on the magnetic disk 10. The self-monitoring process may be performed in a state where it is positioned on the track where 1-1 is recorded. That is, it is also within the scope of the present invention to perform the self-monitoring process in a state where it has not been saved.

  First, a voltage having a first voltage value, for example, 25 mV, is applied to the TMR read head element provided in the HDD (step S1). In this case, a constant current circuit in the head amplifier 15 causes a current of a known current value to flow through the TMR read head element, and its output voltage is monitored by the microcomputer 19 via the head amplifier 15 and the read / write channel 17. A constant current value whose value is a first voltage value, for example, 25 mV, is known. At this time, the current from the constant current circuit may be changed stepwise to reach the first voltage value, or may be changed continuously to reach the first voltage value.

Next, the resistance value of the TMR read head element is calculated from Ohm's law from the first voltage value and the current value from the constant current circuit when this value is reached (step S2). Calculated resistance value, as the first resistance value R _1, is stored in the microcomputer 19.

  Next, a voltage having a second voltage value higher than the first voltage value, for example, 150 mV, is applied to the TMR read head element (step S3). In this case, a current having a known current value is supplied from the constant current circuit to the TMR read head element, and the output voltage is monitored by the microcomputer 19 via the head amplifier 15 and the read / write channel 17, and the value is the second value. Know the constant current value at which the voltage value is, for example, 150 mV. At this time, the current from the constant current circuit may be changed stepwise to reach the second voltage value, or may be changed continuously to reach the second voltage value.

Next, the resistance value of the TMR read head element is calculated according to Ohm's law from the second voltage value and the current value from the constant current circuit when this value is reached (step S4). Calculated resistance value, as the second resistance value R _2, is stored in the microcomputer 19.

Then, the first resistance value _{R 1} and the second resistance value _{R 2} from the resistance change ratio% VbdMRR, _{wherein% VbdMRR (%) = (R} 2 -R 1) / R 1 × 100 calculated using, It is determined whether or not the calculation result is larger than the first threshold value of −0.8%, that is, larger than −0.8% on the positive side (step S5).

  If it is large, a large number of pinholes are generated in the barrier layer of the TMR read head element, and the characteristics are deteriorated, and it is identified that the TMR read head element cannot be used (rank D) (step S6).

  In the case of −0.8% or less, it is determined whether or not this% VbdMRR is larger than the second threshold value −1.2%, that is, larger than −1.2% on the positive side ( Step S7).

  If it is larger, some pinholes are generated in the barrier layer of the TMR read head element, and the TMR read head element is identified as being in an unstable but usable state (rank C) (step S8).

  In the case of −1.2% or less, it is determined whether or not this% VbdMRR is larger than the third threshold value −1.8%, that is, whether it is larger than −1.8% on the positive side ( Step S9).

  If it is larger, almost no pinholes are generated in the barrier layer of the TMR read head element, and it is identified as being in a stable state (rank B) (step S10).

  If it is −1.8% or less, no pinhole is generated in the barrier layer of this TMR read head element, and it is identified as being in a very stable state (rank A) (step S11).

  Thereafter, the host computer is notified of the state identified in step S6, S8, S10 or S11 (step S12).

  When a plurality of TMR read head elements are provided, the same self-monitoring process is performed for all of them.

  As a result, the user can know information such as characteristic deterioration of the TMR read head element in the HDD, and can perform HDD replacement, information backup, etc. before the HDD fails.

  FIG. 3 is a diagram for explaining a voltage application sequence in the self-monitoring process of FIG.

As shown in FIG. 4A, in the case of a method in which the current from the constant current circuit is changed stepwise, first, the current from the constant current circuit is increased stepwise to output the output voltage of the TMR read head element. There obtaining the resistance value R ₁ of current supplied upon reaching the first voltage value, for example lower as 25 mV. Next, similarly, the current from the constant current circuit is increased stepwise so that the current flowed when the output voltage of the TMR read head element reaches a second voltage value higher than the first voltage value, for example, 150 mV. From this, the resistance value R ₂ is obtained. Thereafter, the resistance change rate% VbdMRR is calculated from% VbdMRR (%) = (R ₂ −R ₁ ) / R ₁ × 100, and the result is compared with the first, second, and third threshold values, and the TMR is calculated. The state of the read head element is identified. The duration at each voltage value is arbitrary, and the interval is also arbitrary.

As shown in FIG. 5B, in the case of the method of continuously changing the current from the constant current circuit, first, the current from the constant current circuit is continuously increased to output the output voltage of the TMR read head element. There obtaining the resistance value R ₁ of current supplied upon reaching the first voltage value, for example lower as 25 mV. Subsequently, similarly, the current from the constant current circuit is continuously increased, and the current flowed when the output voltage of the TMR read head element reaches a second voltage value higher than the first voltage value of, for example, 150 mV. From this, the resistance value R ₂ is obtained. Thereafter, the resistance change rate% VbdMRR is calculated from% VbdMRR (%) = (R ₂ −R ₁ ) / R ₁ × 100, and the result is compared with the first, second, and third threshold values, and the TMR is calculated. The state of the read head element is identified. The slope of the current increase is arbitrary, and the interval between the first and second voltage values is also arbitrary.

  The above voltage application sequence is a discontinuous voltage application method in which a voltage having a first voltage value is applied, the voltage application is temporarily stopped, and then a voltage having a second voltage value is applied. You may use the continuous voltage application method which raises the voltage to the 2nd voltage value from the state which applied the voltage of 1 voltage value.

Further, as shown in FIG. 2C, a method of applying a constant voltage from a constant voltage circuit and measuring current with an ammeter may be used, which is different from the processing sequence of FIG. In this case, first, for example by applying a rectangular waveform voltage of the lower first voltage value of 25 mV, determine the resistance R ₁ by measuring a current value flowing in the TMR read head element at that time. Then, for example, a rectangular waveform voltage of the first voltage a second voltage value higher than the value applied as 150 mV, obtains the resistance value R ₂ by measuring the current flowing in the TMR read head element at that time. Thereafter, the resistance change rate% VbdMRR is calculated from% VbdMRR (%) = (R ₂ −R ₁ ) / R ₁ × 100, and the result is compared with the first, second, and third threshold values, and the TMR is calculated. The state of the read head element is identified. The duration at each voltage value is arbitrary, and the interval is also arbitrary.

Furthermore, when using a method in which a constant voltage is applied from a constant voltage circuit and current measurement is performed with an ammeter, the voltage may be applied continuously. As shown in Graph 1 (D), first, for example by applying a lower voltage of the first voltage value of 25 mV, determine the resistance R ₁ by measuring a current value flowing in the TMR read head element at that time. Next, without stopping the voltage application, the voltage value is increased to a second voltage value higher than the first voltage value of, for example, 150 mV, and the current value flowing through the TMR read head element at that time is measured to measure the resistance value R _2. Ask for. Thereafter, the resistance change rate% VbdMRR is calculated from% VbdMRR (%) = (R ₂ −R ₁ ) / R ₁ × 100, and the result is compared with the first, second, and third threshold values, and the TMR is calculated. The state of the read head element is identified. The duration of each voltage value is arbitrary.

4, the number of TMR read head element, by the processing operations described above, and measuring a second resistance value _{R 2} at the time of the first resistance value _{R 1} and 150mV applied at 25mV applied, the resistance change rate% VbdMRR It is a graph showing the result of having calculated | required. However, the horizontal axis of the figure represents the TMR element resistance value (in this case, equal to the _first resistance value R1), and the vertical axis represents the resistance change rate% VbdMRR. 5 to 8 show a state in which a voltage of 150 mV is applied for a long time (12 hours) for each rank of the TMR read head element determined by the resistance change rate% VbdMRR and the resistance change rate% dMRR described later. It is a graph showing the result of having calculated | required the TMR element resistance value and the output voltage. In these figures, the horizontal axis represents time, and the vertical axis represents TMR element resistance value and output voltage.

  As shown in FIG. 4, for the resistance change rate% VbdMRR, a first threshold value of -0.8%, a second threshold value of -1.2%, and a third threshold value of -1.8% are set. For a number of TMR read head elements, Rank A (below the third threshold), Rank B (below the second threshold and greater than the third threshold), Rank C (below the first threshold and greater than the second threshold) ) And rank D (greater than the first threshold). In that case, the TMR read head element classified as rank A is also applied when 150 mV is applied for a long time, as shown in FIG. 5 as an example (TMV read head element of% VbdMRR = −2.09%). The element resistance value and the output voltage did not change at all, and a very stable state was maintained. For the TMR read head element classified as rank B, as shown in FIG. 6 as an example (% VbdMRR = −1.58% TMR read head element), even when 150 mV is applied for a long time, the element resistance The value and the output voltage hardly changed, and the stable state was maintained. On the other hand, with respect to the TMR read head elements classified as rank C, when 150 mV is applied for a long time as shown in FIG. 7 as an example (% VbdMRR = −0.89% TMR read head element), the element resistance Although the value and the output voltage were unstable, it was in a state where it could be used somehow. On the other hand, the TMR read head element classified as rank D has a very high voltage of 150 mV as shown in FIG. 8 (% VbdMRR = −0.60% TMR read head element). The device was destroyed in a short time (about 30 seconds), and was unusable.

In the embodiment described above, the first to third threshold values relating to the resistance change rate% VbdMRR are set to −0.8 (%), −1.2 (%), and −1.8 (%). The threshold value when the tunnel barrier layer of the TMR element is made of an Al oxide, for example, Al ₂ O ₃ , the first voltage value is 25 mV, and the second voltage value is 150 mV. When the tunnel barrier layer is made of a material other than the oxide of Al, the first voltage value, the second voltage value, and the first to third threshold values of the resistance change rate are set accordingly. It becomes possible to identify. Further, the number of thresholds is not limited to three, but may be one or two, or may be four or more. That is, the threshold value and number are not limited to the values and figures of the above-described embodiments, but are arbitrarily set according to the specifications of the TMR read head element and the HDD.

Further, as the voltage to be applied, and the second voltage value to be applied in measuring the first voltage value and the second resistance value R ₂ to be applied in measuring a first resistance value R _1, above The absolute value is smaller than the voltage value at which the TMR read head element is destroyed and the second voltage value is larger than the first voltage value. For example, when the first voltage value is 25 mV, the second voltage value may be higher than this and lower than the voltage value at which the TMR head element is destroyed. Of course, the first voltage value may be a value other than 25 mV. Alternatively, the voltage of the second voltage value may be applied first, and then the voltage of the first voltage value lower than this may be applied.

  In addition, the direction in which the voltage is applied may be the direction in which the direction of the flowing current is from the substrate side (lower side in the stacking direction) to the non-substrate side (upper side in the stacking direction) or vice versa. good. This is not related to the stacking order of the TMR layers.

As described above, according to the present embodiment, the first resistance value R ₁ of the TMR read head element is calculated from the current value that flows when the voltage of the first voltage value is applied to the TMR read head element. The first voltage value of the TMR read head element is determined based on the current value that flows when a voltage having a second voltage value that is discontinuous with the first voltage value and higher than the first voltage value is applied to the TMR read head element. calculating a second resistance value _{R 2,} the first resistance value _{R 1} and the second resistance value _{R 2,} the resistance change _rate% VbdMRR _(%) = determine the _{(R 2 -R 1) / R} 1 × 100 This is compared with the first to third threshold values. Therefore, the reliability and the degree of deterioration related to the TMR read head element can be identified very easily and in a short time. Since the identification result is notified, the user can know information such as characteristic deterioration of the TMR read head element in the HDD, and can perform HDD replacement, information backup, etc. before the HDD fails. It becomes.

  In particular, since the resistance change rate% VbdMRR is obtained from the resistance values measured with different voltage values, the load applied to this layer, that is, the voltage is equal even when the size of the TMR layer is different. Measurement and identification can be performed. Moreover, the measurement can be performed under voltage conditions in a state close to a form in which the TMR head element is actually used. That is, in this case, the resistance change rate does not have a strong correlation with the resistance value of the TMR read head element, and by approaching a certain value, the area effect due to the size of the TMR layer is eliminated, and the TMR layer functions sufficiently. It is easy to distinguish between those having defects and those having defects. In other words, in one continuous correlation line representing the relationship between the resistance value and the resistance change rate, the slope is large and the resistance change rate decreases in a region where the resistance value is small, and the change occurs when the resistance value exceeds a certain value. As a result, the slope changes, and asymptotically approaches a certain rate of change in resistance. The region where the resistance value is small and the correlation line has a large negative slope and the region where the correlation line is transformed and the slope gradually changes to a certain resistance change rate show different film qualities. As a result, the reliability of the TMR read head element can be clearly and reliably confirmed.

  FIG. 9 is a block diagram schematically showing an electrical configuration of an HDD provided with a TMR thin film magnetic head as another embodiment of the present invention. In the embodiment of FIG. 1, the microcomputer 19 has a self-monitoring system 19a. In the present embodiment, a self-monitoring system 15a 'using a microcomputer is provided in the head amplifier 15'. Here, the self-monitoring process is performed. Replacing such a head amplifier 15 'with a head amplifier of an HDD having a normal configuration makes it possible to perform self-monitoring processing very easily. Other configurations in the present embodiment are substantially the same as those in the embodiment of FIG. Accordingly, in FIG. 9, the same reference numerals are used for the same components as in FIG.

  In FIG. 9, 10 is a magnetic disk as a magnetic recording medium, 11 is a spindle motor (SPM) for rotating the magnetic disk 10, 12 is a TMR thin film magnetic head provided with a TMR read head element and an inductive write head element, and 13 is A support mechanism for the TMR thin film magnetic head 12, a voice coil motor (VCM) 14 for rotating the support mechanism 13 to position the magnetic head, 15 'a head amplifier for a TMR read head element and an inductive write head element, Reference numeral 16 denotes a motor driver for driving the SPM 11 and VCM 14, 17 a read / write channel, 18 a hard disk controller (HDC), 19 'a microcomputer, and 20 a memory used as a data buffer.

  The head amplifier 15 'includes a write driver circuit that generates a write current applied to the inductive write head element, and a read amplifier circuit that supplies a predetermined sense current from the constant current circuit to the TMR read head element and amplifies its output voltage. The part that executes the self-monitoring process includes a self-monitoring system 15a '. In particular, in this embodiment, the read amplifier circuit needs to apply different voltages to the TMR read head element during the self-monitoring operation, so that the sense current flowing through the TMR read head element can be gradually changed. It is configured. It is obvious that a voltage bias method of applying a constant voltage may be used instead of the current bias method of supplying a constant current as in the present embodiment. Further, the self-monitoring system 15a 'is configured so that the self-monitoring process performed by the microcomputer 19 in the embodiment of FIG. 1 is performed by the microcomputer constituting the self-monitoring system 15a' itself.

  The read / write channel 17 mainly performs code modulation of write data and outputs the code to the head amplifier 15 ′, and also performs processing of detecting data from the read signal waveform from the head amplifier 15 ′ and demodulating the code.

  The HDC 18 performs error correction, buffer control, cache control, interface control, servo control, and the like, and exchanges write data and read data with a host computer connected to the HDD.

  The microcomputer 19 'controls the entire HDD, and performs position control of the thin film magnetic head by the VCM 14, interface control, initialization and setting of each circuit of the HDD, and the like.

  The contents of the self-monitoring process in this embodiment, its operation effect, and the like are almost the same as those in the embodiment of FIG.

  FIG. 10 is a flowchart for explaining the processing operation of the HDD self-monitoring system according to still another embodiment of the present invention. The electrical configuration of the HDD in this embodiment is exactly the same as that shown in FIG. In this embodiment, the same reference numerals are used for the same components as those in the embodiment of FIG.

  The microcomputer 19 executes this self-monitoring process when a predetermined time elapses and / or according to an arbitrary instruction when the HDD is activated. When the HDD is started, the self-monitoring process is executed in a state where the TMR read head element is retracted outside the recording area before moving to the recording area of the magnetic disk 10, and the TMR read head element is used every time and every instruction. The self-monitoring process is executed in a state where the disk is retracted outside the recording area of the magnetic disk 10. The state in which the TMR read head element is retracted outside the recording area of the magnetic disk 10 means that in a load / unload type HDD, a thin film magnetic head including the TMR read head element is placed on a ramp positioned outside the magnetic disk. In a CSS type HDD, this means that a thin film magnetic head including a TMR read head element exists in the CSS area on the magnetic disk. This is because the magnetic influence applied from the magnetic disk to the TMR read head element is made as small as possible by performing the self-monitoring process in such a retracted state. Although it is desirable to perform the self-monitoring process with the TMR read head element retracted outside the recording area of the magnetic disk 10, it is also within the scope of the present invention to perform the self-monitoring process without retracting.

  First, a current having a first current value, for example, 0.1 mA is passed through the TMR read head element provided in the HDD (step S1 ′). In this case, a sense current of this current value is applied to the TMR read head element from the constant current circuit in the head amplifier 15.

Next, the resistance value of the TMR read head element is calculated according to Ohm's law from the first current value and the voltage value input to the microcomputer 19 via the head amplifier 15 and the read / write channel 17 from the output voltage of the TMR read head element. Is calculated (step S2 '). Calculated resistance value, as the first resistance value R _1, is stored in the microcomputer 19.

  Next, a current having a second current value larger than the first current value, for example, 0.4 mA, is applied to the TMR read head element (step S3 ′). In this case, a sense current having this current value is applied to the TMR read head element from the constant current circuit.

Next, the resistance value of the TMR read head element is determined by Ohm's law from the second current value and the voltage value input to the microcomputer 19 via the head amplifier 15 and the read / write channel 17 from the output voltage of the TMR read head element. Is calculated (step S4 '). Calculated resistance value, as the second resistance value R _2, is stored in the microcomputer 19.

Then, the first resistance value _{R 1} and the second resistance value _{R 2} from the resistance change ratio% DMRR, _{wherein% dMRR (%) = (R} 2 -R 1) / R 1 × 100 calculated using, It is determined whether or not the calculation result is larger than the first threshold value of −0.6%, that is, larger than −0.6% on the positive side (step S5 ′).

  If it is larger, a large number of pinholes are generated in the barrier layer of the TMR read head element, and it is identified that the characteristics are deteriorated and cannot be used (rank D) (step S6 ').

  If it is −0.6% or less, it is determined whether or not this% dMRR is larger than the second threshold value −0.8%, that is, whether it is larger than −0.8% on the positive side ( Step S7 ').

  If it is larger, some pinholes are generated in the barrier layer of the TMR read head element, and the TMR read head element is identified as being in an unstable but usable state (rank C) (step S8 ').

  In the case of −0.8% or less, it is determined whether or not this% dMRR is larger than the third threshold value −1.0%, that is, larger than −1.0% on the positive side ( Step S9 ').

  If it is large, almost no pinholes are generated in the barrier layer of the TMR read head element, and it is identified as being in a stable state (rank B) (step S10 ').

  If it is −1.0% or less, no pinhole is generated in the barrier layer of this TMR read head element, and it is identified as being in a very stable state (rank A) (step S11 ′).

  Thereafter, the host computer is notified of the state identified in the above steps S6 ', S8', S10 'or S11' (step S12 ').

  When a plurality of TMR read head elements are provided, the same self-monitoring process is performed for all of them.

  As a result, the user can know information such as characteristic deterioration of the TMR read head element in the HDD, and can perform HDD replacement, information backup, etc. before the HDD fails.

  FIG. 11 is a diagram for explaining a current application sequence in the self-monitoring process of FIG.

As shown in FIG. 6A, a rectangular current having a lower first current value of, for example, 0.1 mA is first applied from a constant current circuit, and then output from the TMR read head element. by measuring the voltage value obtaining the resistance value R _1. Next, for example, a rectangular wave current having a second current value higher than the first current value of 0.4 mA is applied, and a voltage value output from the TMR read head element at that time is measured to obtain a resistance value R ₂ . Ask. Thereafter, the resistance change rate% dMRR is calculated from% dMRR (%) = (R ₂ −R ₁ ) / R ₁ × 100, and the result is compared with the first, second, and third threshold values, and TMR is calculated. The state of the read head element is identified. The duration in each current value is arbitrary, and the interval is also arbitrary.

As described above, the current application may be performed discontinuously or continuously. As shown in FIG. 5B, first, a current having a lower first current value of, for example, 0.1 mA is applied from the constant current circuit, and the voltage value output from the TMR read head element at that time is measurements to determine the resistance R _1. Subsequently, the voltage value output from the TMR read head element is continuously increased, that is, without stopping application of the current, to a second current value higher than the first current value of, for example, 0.4 mA. the measured obtaining the resistance value R _2. Thereafter, the resistance change rate% dMRR is calculated from% dMRR (%) = (R ₂ −R ₁ ) / R ₁ × 100, and the result is compared with the first, second, and third threshold values, and TMR is calculated. The state of the read head element is identified. The duration at each current value is arbitrary.

12, for a number of TMR read head element, by the processing operations described above, and measuring a second resistance value _{R 2} at the time of the first resistance value _{R 1} and 0.4mA applied at 0.1mA is applied, the resistance It is a graph showing the result of having obtained change rate% dMRR. However, the horizontal axis of the figure represents the TMR element resistance value (in this case, equal to the _first resistance value R1), and the vertical axis represents the resistance change rate% dMRR.

  As shown in FIG. 12, for the resistance change rate% dMRR, a first threshold value of -0.6%, a second threshold value of -0.8%, and a third threshold value of -1.0% are set. For a number of TMR read head elements, Rank A (below the third threshold), Rank B (below the second threshold and greater than the third threshold), Rank C (below the first threshold and greater than the second threshold) ) And rank D (greater than the first threshold). In that case, the TMR read head element classified as rank A is also applied when 150 mV is applied for a long time as shown in FIG. 5 as an example (TMR read head element of% dMRR = −1.73%). The element resistance value and the output voltage did not change at all, and a very stable state was maintained. For the TMR read head elements classified as rank B, as shown in FIG. 6 as an example (% dMRR = −1.02% TMR read head element), even when 150 mV is applied for a long time, the element resistance The value and the output voltage hardly changed, and the stable state was maintained. On the other hand, with respect to TMR read head elements classified as rank C, when 150 mV is applied for a long time, as shown in FIG. 7 as an example (% dMRR = −0.66% TMR read head element), the element resistance Although the value and the output voltage were unstable, it was in a state where it could be used somehow. On the other hand, for the TMR read head element classified as rank D, as shown in FIG. 8 as an example (% dMRR = −0.50% TMR read head element), a very high voltage of 150 mV is applied. The device was destroyed in a short time (about 30 seconds), and was unusable.

In the embodiment described above, the first to third threshold values relating to the resistance change rate% dMRR are set to −0.6 (%), −0.8 (%), and −1.0 (%). The threshold value when the tunnel barrier layer of the TMR element is made of an Al oxide, for example, Al ₂ O ₃ , and the first current value is 0.1 mA and the second current value is 0.4 mA. It is. When the tunnel barrier layer is made of a material other than an oxide of Al, if the first current value, the second current value, and the first to third threshold values of the resistance change rate are set accordingly, similarly, It becomes possible to identify. Further, the number of thresholds is not limited to three, but may be one or two, or may be four or more. That is, the threshold value and number are not limited to the values and figures of the above-described embodiments, but are arbitrarily set according to the specifications of the TMR read head element and the HDD.

Further, as the current to be applied, and the second current value to be applied in measuring the first current value and the second resistance value R ₂ to be applied in measuring a first resistance value R _1, above The absolute value is smaller than the current value at which the TMR read head element is destroyed, and the second current value is larger than the first current value. For example, when the first current value is 0.1 mA, the second current value may be larger than this and smaller than the current value at which the TMR head element is destroyed. Of course, the first current value may be a value other than 0.1 mA. Alternatively, the current having the second current value may be applied first, and then the current having the first current value smaller than this may be applied.

  The direction of current application may be from the substrate side (lower side in the stacking direction) to the non-substrate side (upper side in the stacking direction) of the TMR read head element or vice versa. This is not related to the stacking order of the TMR layers.

As described above, according to the present embodiment, the first resistance value R ₁ of the TMR read head element is calculated from the voltage value output when the current of the first current value is applied to the TMR read head element. TMR reading is calculated from the voltage value output when a current having a second current value that is discontinuous with the current having the first current value and larger than the first current value is applied to the TMR read head element. The second resistance value R ₂ of the head element is calculated, and the resistance change rate% dMRR (%) = (R ₂ −R ₁ ) / R ₁ from the first resistance value R ₁ and the second resistance value R _2. X100 is obtained and compared with the first to third threshold values. Therefore, the reliability and the degree of deterioration related to the TMR read head element can be identified very easily and in a short time. Since the identification result is notified, the user can know information such as characteristic deterioration of the TMR read head element in the HDD, and can perform HDD replacement, information backup, etc. before the HDD fails. It becomes.

  It is of course possible to provide the self-monitoring system in the embodiment of FIG. 10 in the head amplifier as in the embodiment of FIG.

  All the embodiments described above are illustrative of the present invention and are not intended to be limiting, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

1 is a block diagram schematically showing an electrical configuration of an HDD including a TMR thin film magnetic head as one embodiment of the present invention. FIG. 2 is a flowchart for explaining a processing operation of the HDD self-monitoring system in the embodiment of FIG. 1. It is a figure explaining the voltage application sequence in the self-monitoring process of FIG. For a number of TMR read head element is a graph showing the results of measuring a second resistance value _{R 2} at the time of the first resistance value _{R 1} and 150mV applied at 25mV is applied to determine the resistance change ratio% VbdMRR. 5 is a graph showing the results of obtaining the TMR element resistance value and the output voltage by continuously applying a voltage of 150 mV for a rank A TMR read head element for a long time. 5 is a graph showing the results of obtaining the TMR element resistance value and the output voltage by continuously applying a voltage of 150 mV for a rank B TMR read head element for a long time. 5 is a graph showing the result of obtaining the TMR element resistance value and the output voltage for a rank C TMR read head element by continuously applying a voltage of 150 mV for a long time. 5 is a graph showing the results of applying a voltage of 150 mV and obtaining the resistance value and output voltage of a rank D TMR read head element. FIG. 5 is a block diagram schematically showing an electrical configuration of an HDD including a TMR thin film magnetic head as another embodiment of the present invention. It is a flowchart explaining the self-monitoring process operation | movement of HDD in other embodiment of this invention. It is a figure explaining the electric current application sequence in the process of the self-monitoring system of FIG. For a number of TMR read head element, representing the results of measuring a second resistance value _{R 2} at the time of the first resistance value _{R 1} and 0.4mA applied at 0.1mA is applied to determine the resistance change ratio% DMRR It is a graph.

Explanation of symbols

10 Magnetic disk 11 SPM
12 TMR thin film magnetic head 13 Support mechanism 14 VCM
15, 15 'Head amplifier 15a', 19a Self-monitoring system 16 Motor driver 17 Read / write channel 18 HDC
19, 19 'Microcomputer 20 Memory

Claims (29)

  Application means capable of applying a plurality of voltages or currents having different values to the tunnel magnetoresistive head element, and measurement for measuring the resistance value of the tunnel magnetoresistive head element in a state where the plurality of voltages or currents are applied respectively. Means, a resistance change rate calculating means for calculating a resistance change rate from a plurality of resistance values obtained by the measurement, and comparing the calculated resistance change rate with at least one threshold value. A magnetic disk device having a tunnel magnetoresistive head element, comprising a self-monitoring system including an identification means for identifying a state.   The magnetic disk apparatus according to claim 1, wherein the self-monitoring system further includes notification means for notifying the identified state.   3. The magnetic disk apparatus according to claim 1, wherein the applying means is means for applying different voltages or currents to each other discontinuously or continuously.   An application means capable of applying a voltage or current having a first value and a voltage or current having a second value larger in absolute value than the first value to the tunnel magnetoresistive head element; A first measuring means for measuring a resistance value in a state in which the voltage or current of the first value is applied to obtain a first resistance value; and the voltage or the second value of the tunnel magnetoresistive head element. A resistance change rate for calculating a resistance change rate from the second measuring means for measuring the resistance value in a state in which a current is applied to obtain a first resistance value, and the first resistance value and the second resistance value. A tunnel magnetoresistor comprising: a self-monitoring system comprising: calculating means; and identifying means for comparing the calculated rate of change of resistance with at least one threshold to identify the state of the tunnel magnetoresistive head element Has an effective head element The gas disk device.   5. The magnetic disk apparatus according to claim 4, wherein the self-monitoring system further includes notifying means for notifying the identified state.   The said application means is a means to apply the voltage or electric current of the said 1st value, and the voltage or electric current of the said 2nd value discontinuously or continuously to each other, The Claim 4 or 5 characterized by the above-mentioned. Magnetic disk unit. When the resistance change rate calculation means sets the first resistance value to R ₁ and the second resistance value to R ₂ , the resistance change rate from (R ₂ −R ₁ ) / R ₁ × 100 (%). The magnetic disk device according to claim 4, wherein the magnetic disk device is a means for calculating a magnetic field. The means for identifying that the tunnel magnetoresistive head element is in an unusable state when the resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeds the first threshold. The magnetic disk device according to claim 7, wherein the magnetic disk device is a magnetic disk device. When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is less than or equal to the first threshold and exceeds a second threshold that is lower than the first threshold, 9. The magnetic disk apparatus according to claim 8, wherein the tunnel magnetoresistive head element is means for identifying that the head element is unstable but is usable. When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is less than or equal to the second threshold and exceeds a third threshold that is lower than the second threshold, 10. The magnetic disk apparatus according to claim 9, wherein said magnetic disk device is means for identifying that the tunnel magnetoresistive head element is in a stable state. When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeding the third threshold, the tunnel magnetoresistive head element is in a very stable state. 11. The magnetic disk apparatus according to claim 10, wherein the magnetic disk apparatus is a means for identifying.   When the tunnel barrier layer of the tunnel magnetoresistive head element is made of an oxide of aluminum, the first voltage value is 25 mV, and the second voltage value is 150 mV, the first threshold value is 12. The magnetic disk device according to claim 8, wherein the magnetic disk device is −0.8 (%).   When the tunnel barrier layer of the tunnel magnetoresistive head element is made of an oxide of aluminum and the first voltage value is 25 mV and the second voltage value is 150 mV, the second threshold value is The magnetic disk device according to claim 9, wherein the magnetic disk device is −1.2 (%).   When the tunnel barrier layer of the tunnel magnetoresistive head element is made of an oxide of aluminum, and the first voltage value is 25 mV and the second voltage value is 150 mV, the third threshold value is 13. The magnetic disk device according to claim 10, wherein the magnetic disk device is −1.8 (%).   When the tunnel barrier layer of the tunnel magnetoresistive head element is made of an oxide of aluminum, the first current value is 0.1 mA, and the second current value is 0.4 mA, the first 12. The magnetic disk device according to claim 8, wherein a threshold value of 1 is −0.6 (%).   When the tunnel barrier layer of the tunnel magnetoresistive head element is made of an oxide of aluminum, the first current value is 0.1 mA, and the second current value is 0.4 mA, the first The magnetic disk device according to claim 9, wherein a threshold value of 2 is −0.8 (%).   When the tunnel barrier layer of the tunnel magnetoresistive head element is made of an oxide of aluminum, the first current value is 0.1 mA, and the second current value is 0.4 mA, the first 13. The magnetic disk device according to claim 10, wherein a threshold value of 3 is −1.0 (%).   18. The magnetic disk device according to claim 1, wherein the self-monitoring system is activated when the magnetic disk device is started to identify a state of the tunnel magnetoresistive head element.   The magnetic disk device according to claim 1, wherein the self-monitoring system operates every set time to identify the state of the tunnel magnetoresistive head element.   20. The magnetic disk apparatus according to claim 1, wherein the self-monitoring system is activated each time it is instructed to identify the state of the tunnel magnetoresistive head element.   21. The magnetic disk device according to claim 1, wherein the self-monitoring system operates in a state where the tunnel magnetoresistive head element is retracted from a recording area of the magnetic disk.   21. The self-monitoring system according to any one of claims 1 to 20, wherein the self-monitoring system operates in a state where the tunnel magnetoresistive head element is positioned on an area where specific information is recorded on a magnetic disk. Magnetic disk unit.   An application means capable of applying a voltage or current having a first value and a voltage or current having a second value larger in absolute value than the first value to the tunnel magnetoresistive head element; A first measuring means for measuring a resistance value in a state in which the voltage or current of the first value is applied to obtain a first resistance value; and the voltage or the second value of the tunnel magnetoresistive head element. A resistance change rate for calculating a resistance change rate from the second measuring means for measuring the resistance value in a state in which a current is applied to obtain a first resistance value, and the first resistance value and the second resistance value. A tunnel magnetoresistive effect comprising: a calculating system; and an identification unit for comparing the calculated rate of change of resistance with at least one threshold to identify the state of the tunnel magnetoresistive head element Magnetic with head element Head amplifier for disk devices.   24. The head amplifier according to claim 23, wherein the applying means is means for applying the first value voltage or current and the second value voltage or current discontinuously or continuously to each other. . When the resistance change rate calculation means sets the first resistance value to R ₁ and the second resistance value to R ₂ , the resistance change rate from (R ₂ −R ₁ ) / R ₁ × 100 (%). 25. The head amplifier according to claim 23, wherein the head amplifier is a means for calculating. The means for identifying that the tunnel magnetoresistive head element is in an unusable state when the resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeds the first threshold. 26. The head amplifier according to claim 25, wherein: When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is less than or equal to the first threshold and exceeds a second threshold that is lower than the first threshold, 27. The head amplifier according to claim 26, wherein the tunnel magnetoresistive head element is a means for identifying that the head element is unstable but is usable. When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) that is less than or equal to the second threshold and exceeds a third threshold that is lower than the second threshold, 28. The head amplifier according to claim 27, wherein the head magnetoresistive head element is means for identifying that the head element is in a stable state. When the identification means has a resistance change rate of (R ₂ −R ₁ ) / R ₁ × 100 (%) exceeding the third threshold, the tunnel magnetoresistive head element is in a very stable state. 29. The head amplifier according to claim 28, wherein the head amplifier is a means for identifying.

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