JP3866879B2 - Magnetic head evaluation method, inspection apparatus having magnetic head evaluation function, and magnetic disk apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic head evaluation method, an inspection apparatus and a magnetic disk apparatus having the magnetic head evaluation function, and more particularly to a magnetic head capable of detecting magnetic reversal of a fixed layer of a GMR head. The present invention relates to an evaluation method, an inspection device, and a magnetic disk device.
[0002]
[Prior art]
In general, as shown in FIG. 3, a magnetic disk device includes a plurality of recording media 1 stacked so as to be driven to rotate, and a plurality of magnetic heads 2 positioned on the recording medium 1 for recording and reproducing data. An actuator 3 that rotationally moves the magnetic head 2 on the recording medium 1, and the actuator 3 positions the magnetic head 2 on an arbitrary track on the recording medium 1 while the recording medium 1 is rotationally driven. And recording / reproducing data.
[0003]
As shown in FIG. 4, the magnetic head 2 includes a slider 5 on which one end of a magnetic head element 6 is mounted and a spring 4 that elastically supports the slider 5, and the slider is placed on a recording medium 1 that rotates at high speed. 5 is levitated at intervals of several tens of nanometers by aerodynamic action, and data is recorded / reproduced. In recent years, with the miniaturization and increase in capacity of magnetic disk devices, higher reproduction sensitivity is required. ing.
[0004]
Therefore, an MR head (magneto resistive head) using a magnetic resistance effect has been adopted in recent magnetic heads. As shown in FIG. 5, this MR head includes a coil 8 and a magnetic core 9, and includes an inductive recording head element 7 for recording a signal on a recording medium, an MR film 11 for reproducing data, and a reproducing electrode 12. The MR head element is provided.
[0005]
This MR head has a feature that the film thickness of the MR film 11 is as thin as 20 nm and it is very weak against ESD (electro static dischage) due to static electricity. This withstand voltage is about 40V or lower for the MR head compared to the withstand voltage of the previous inductive thin film head of about 100V or more, and the MR head has a semiconductor withstand voltage of about 100V. It can be said that the electronic device is very sensitive to ESD.
[0006]
On the other hand, MR heads are known to have two breakdown modes according to the ESD and EOS (Electro over stress: high voltage load) from the above research. One is physical destruction caused by heat generated by high voltage discharge or high current. This physical breakdown is caused by melting of the MR element itself due to rapid heat generation, and is accompanied by an abnormal increase or decrease in the resistance value, and can be detected by an abnormal appearance shape. Further, discharge breakdown due to a high electric field is accompanied by an abnormal increase or decrease in the resistance value, and can be detected by an abnormal appearance shape.
[0007]
Another breakdown mode is magnetic breakdown caused by a high current magnetic field. This is a phenomenon in which a magnetic domain is formed although the magnetic stability in the MR film is destroyed by a magnetic field due to a high current and physical destruction does not occur. This magnetic breakdown is not accompanied by a resistance change or shape abnormality but appears as an abnormality in the reproduction waveform of the MR element. For example, it appears as an unstable reproduction waveform or an abnormality in the positive and negative amplitudes.
[0008]
When such a magnetic breakdown occurs, the magnetic head cannot accurately detect data, an error occurs in data, a servo signal cannot be reproduced, and positioning cannot be performed.
[0009]
As a method for solving the magnetic breakdown according to the prior art, it has been proposed to re-magnetize the MR element of the magnetic head and initialize it to restore the original magnetic characteristics.
[0010]
[Problems to be solved by the invention]
In recent years, a GMR head (Giant MR head) using a GMR element with higher reproduction sensitivity is used instead of the MR element shown in FIG. 5 in response to a further increase in recording density. As shown in FIG. 6, the GMR element has a fixed layer 15, a free layer 14, and an antiferromagnetic layer 16, and the magnetization directions of the fixed layer 15 and the free layer 14 are opposite to each other as shown in FIG. At this time, the resistance value becomes high and positive output is obtained, and as shown in FIG. 6B, the resistance is low and negative output is obtained when the magnetization direction is the same direction.
[0011]
The fixed layer 15 is directed in the direction in which the signal magnetic flux from the recording medium is perpendicular to the track width direction by exchange coupling with the antiferromagnetic layer 16, and the free layer 14 has magnetic domains placed on both sides thereof. Since the control permanent magnet faces the direction perpendicular to the direction in which the signal magnetic flux from the recording medium comes in the same direction as the track width direction, the magnetization direction of the fixed layer 15 determines the positive / negative polarity of the output waveform. is important.
[0012]
The ESD breakdown voltage of this GMR element is 10 to 30 V lower than that of the MR head, and the magnetization direction of the fixed layer 15 is a normal direction as shown in FIG. It has the characteristic that it reverse | inverts from and turns to the opposite direction like FIG.7 (b). That is, the GMR element has the characteristic that the polarity of the reproduction waveform is normal and reversed because the relationship between the magnetization directions of the fixed layer and the free layer is reversed by ESD and the direction of the magnetic field from the recording medium is the same. .
[0013]
The relationship between the applied magnetic field and the reproduction output is shown in FIG. As described above, in the GMR element, when the magnetization direction of the fixed layer 15 is reversed by ESD, the polarity of the reproduction output is completely reversed as shown by the characteristic A to the characteristic B shown in FIG. Therefore, when ESD occurs during the process of manufacturing or assembling the magnetic head and the fixed layer is reversed, the positive and negative polarities of the output waveform are reversed, and the conventional inspection method has a large reproduction amplitude. However, there was a problem that it was impossible to detect the one with reversed polarity.
[0014]
Further, when a magnetic head having a GMR element with the polarity reversed is assembled in a magnetic disk device, the polarity of the reproduction signal is reversed in the device, causing a problem that a data signal or a servo signal is erroneous.
[0015]
An object of the present invention is to eliminate the problems caused by the above-described prior art, and includes a magnetic head evaluation method capable of detecting the magnetic pole reversal of the fixed layer of the head element, and the magnetic head evaluation process. It is an object of the present invention to provide a method for manufacturing a magnetic head, an inspection device having the magnetic head evaluation function, and a magnetic disk device.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for evaluating a magnetic head including a head element including a fixed layer, wherein a time interval from a positive pulse to a negative pulse is different from a time interval from a negative pulse to a positive pulse. A pattern is recorded on a recording medium, and the time interval from the positive pulse to the negative pulse and the time interval from the negative pulse to the positive pulse of the reproduced waveform obtained by reproducing the recording pattern from the recording medium are compared. The first characteristic is that the reversal of the magnetization direction of the fixed layer of the head element is evaluated based on the difference between the two, and in this magnetic head evaluation method, the time interval from the positive pulse to the negative pulse is T1, and the negative The time interval from the pulse to the positive pulse is a time interval T2 shorter than the time interval T1, and the head element is fixed when the value obtained by subtracting the time interval T2 from the time interval T1 is negative. The direction of magnetization is the second feature to be evaluated and inverted.
[0017]
The present invention also provides a recording medium, a spindle motor that rotationally drives the recording medium, a data recording / reproducing circuit that records and reproduces data on the recording medium using a magnetic head for evaluation, and a control circuit that controls these In the magnetic head evaluation apparatus for evaluating a magnetic head equipped with a head element including a fixed layer, the data recording / reproducing circuit includes a time interval from a positive pulse to a negative pulse and a negative pulse to a positive pulse. A recording pattern having a different time interval is recorded on a recording medium, the recording pattern is reproduced from the recording medium to obtain a reproduced waveform, and the control circuit is configured to obtain a time interval from the positive pulse to the negative pulse of the reproduced waveform. And the time interval from the negative pulse to the positive pulse, and the reversal of the magnetization direction of the fixed layer of the head element is evaluated by the difference between the time intervals. In the magnetic head evaluation apparatus having the above characteristics, the data recording / reproducing circuit has a time interval from the positive pulse to the negative pulse as T1, and a time interval from the negative pulse to the positive pulse is shorter than the time interval T1. A recording pattern having a time interval T2 is recorded on a recording medium, and the control circuit evaluates that the magnetization direction of the fixed layer of the head element is reversed when the value obtained by subtracting the time interval T2 from the time interval T1 is negative. This is the fourth feature.
[0018]
Furthermore, the present invention relates to a recording medium, a spindle motor that rotationally drives the recording medium, a magnetic head on which a head element including a fixed layer is mounted, and data recording that records and reproduces data on the recording medium by the magnetic head. In a magnetic disk device including a reproducing circuit and a control circuit for controlling these, the data recording / reproducing circuit includes a time interval T1 from a positive pulse to a negative pulse and a time from a negative pulse to a positive pulse shorter than the time interval T1. The recording pattern consisting of the interval T2 is recorded on the recording medium, and the recording pattern is reproduced from the recording medium to obtain a reproduction waveform. The control circuit subtracts the time interval T2 from the time interval T1 is negative. In this case, it is a fifth feature that it is determined that the magnetization direction of the fixed layer of the head element is reversed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a magnetic head evaluation method according to an embodiment of the present invention, a magnetic head manufacturing method including the magnetic head evaluation process, and an inspection apparatus and a magnetic disk apparatus having the magnetic head evaluation function. Will be described in detail with reference to FIG.
[0020]
FIG. 1 is a diagram for explaining the principle of a magnetic head evaluation method according to the present invention, and is a magnetic disk device / inspection apparatus having a magnetic head evaluation function (hereinafter referred to as a magnetic head evaluation method, etc.). FIG. 4 is a diagram showing a relationship between a recording current waveform applied to a recording medium and a magnetization state or a reproduction waveform of a recording medium (magnetic disk).
[0021]
In the magnetic head evaluation method according to the present embodiment, first, as shown in FIG. 1, recording is performed on a recording medium in which the time interval from the positive pulse to the negative pulse and the time interval from the negative pulse to the positive pulse are different. Data recording is performed using a current waveform. That is, the recording current waveform switching time is asymmetrical, specifically, recording with a current waveform in which the time interval T1 from the positive pulse to the negative pulse and the time interval T2 from the negative pulse to the positive pulse are shorter than the time interval T1. When the magnetization state of the medium is high level, a black line is recorded, and when the medium state is low level, a white line is recorded.
Next, in the magnetic head evaluation method, the asymmetrically recorded signal is reproduced using the GMR head. This reproduced waveform becomes a positive pulse when the free layer faces upward due to the magnetic flux from the recording medium and is antiparallel to the direction of the fixed layer. This is because the resistance of the GMR element is increased by the GMR effect described above. Further, when the free layer is directed downward by the magnetic flux from the recording medium and parallel to the direction of the fixed layer, a negative pulse is generated. This is because the resistance of the element is lowered by the GMR effect.
[0022]
Next, in this evaluation method, the time interval T1 from the positive pulse to the negative pulse and the time interval T2 from the negative pulse to the positive pulse are measured. When the GMR head is normal, the asymmetry (T1-T2) of the time interval T1-T2 is greater than zero.
[0023]
However, when ESD occurs during the process of manufacturing or assembling the magnetic head and the fixed layer is reversed, the polarity of the output waveform is reversed, the magnetization direction of the fixed layer is reversed, and the positive and negative are reversed. The polarity of is reversed. For this reason, the reproduced waveform at the time of ESD generation is an asymmetry (T1′−) of the time interval T1 ′ (= T2) from the positive pulse to the negative pulse and the time interval T2 ′ (= T1) from the negative pulse to the positive pulse. It can be seen that T2 ′) is smaller than 0.
[0024]
The magnetic head evaluation method according to the present invention measures the time interval T1 from the positive pulse to the negative pulse and the time interval T2 from the negative pulse to the positive pulse, and determines whether the asymmetry value is positive or negative. , Whether or not ESD has occurred is evaluated. The magnetic disk apparatus according to the present invention adds the above evaluation process to the control program of the actual apparatus itself, performs the above evaluation for every predetermined drive time, for example, in the idle time other than the time of data recording / reproduction, and detects the occurrence of ESD. The magnetic head inspecting apparatus according to the present invention performs processing such as error warning and recovery processing, and similarly evaluates the occurrence of ESD by adding the evaluation process to the magnetic head manufacturing process.
[0025]
Next, the algorithm of the magnetic head evaluation method according to the embodiment will be described with reference to FIG. This algorithm records on the recording medium using the recording pattern 201 of the time interval T1 from the asymmetric positive pulse to the negative pulse and the time interval T2 from the negative pulse to the positive pulse, and this recording signal is the GMR to be evaluated. A reproduction waveform 202 is obtained by reproduction by the head. Next, the time interval T1 (symbol 204) from the positive pulse to the negative pulse, the time interval T2 (symbol 205) from the negative pulse to the positive pulse, and the waveform amplitude E (symbol 206) are measured from the reproduced waveform 202. Based on the interval T1 / T2 and the waveform amplitude E, it is determined whether ESD has occurred in the GMR head using the algorithm 207 described above.
[0026]
This algorithm 207 determines that no ESD has occurred in the GMR head when interval T1−interval T2> 0, amplitude E> E0, and read (R) is successful (OK) as shown in FIG. (2) When interval T1-interval T2> 0, amplitude E <E0, and lead (R) is successful (OK), ESD is generated and the GMR element is determined to be the fixed layer inversion 211, and (3) ▼ When interval T1−interval T2> 0, amplitude E <E0, and read (R) is unsuccessful (NG), it is determined that an error (NG) has occurred due to a read error although ESD has not occurred. 4) Interval T1−Interval T2 = 0, and when Read (R) is successful (OK), ESD is generated and the GMR element is determined to be the fixed layer inversion 211. (5) Interval T1−Interval T2 = 0 And when lead (R) is unsuccessful (NG), E Although D has not occurred, it is determined that an error (NG) has occurred due to a read error. (6) When interval T1-interval T2 <0 and read (R) is successful (OK), no ESD has occurred. However, it is determined that an error (NG) occurs due to a read error. (7) If interval T1−interval T2 <0 and read (R) is unsuccessful (NG), an ESD occurs and an error due to a read error ( NG) It is determined that it has occurred. The E0 represents the standard waveform amplitude of a normal GMR head, and E represents the observed waveform amplitude of the GMR head.
[0027]
As a result, the algorithm 207 can determine normal (OK) in which ESD does not occur, read error (NG) in the absence of ESD, and an abnormal head in which the magnetization direction of the fixed layer is reversed by ESD. it can.
[0028]
For the GMR head that has determined the fixed layer reversal 211, this embodiment returns the data to the normal magnetization by performing the fixed layer magnetization reversal correction 208 to restore the normal magnetization or the reproduction waveform reversal 209 to determine the GMR element. , Or by applying the sense current direction reversal 210 to initialize the magnetization reversal of the fixed layer, it is possible to cope with the abnormality of the GMR head. In the case where the fixed layer magnetization reversal correction 208 is performed, in order to confirm the correction, the reproduced waveform 202 is obtained again and fed back to adjust the degree of magnetization reversal correction of the GMR head.
[0029]
In the case of (2) to (5), even if the interval T1 to the interval T2 are positive or equal, a low output is partially reversed, and a combination of the output and the like is a sign of abnormality of the GMR head. Can be evaluated. For example, when there is no abnormality in the resistance value and the value is close to the interval T1 to the interval T2 = 0, if the fixed layer faces the same horizontal direction (track width direction) as the free layer in the middle of inversion, the reproduction output disappears and the interval Since a value close to T1−interval T2 = 0 is indicated, a precursor of abnormality can be evaluated.
[0030]
The magnetic head evaluation method according to the present invention writes the asymmetric interval T1 and interval T2, reproduces the written interval T1 and interval T2, and uses the algorithm 207 shown in FIG. Are incorporated into a magnetic disk device, a magnetic head manufacturing apparatus, and an inspection apparatus, so that abnormalities of the GMR head can be evaluated in the actual apparatus, manufacturing process, and evaluation process.
[0031]
This magnetic disk device is composed of a normal magnetic head, a magnetic disk, a spindle motor (drive mechanism), an actuator, and a control circuit, and incorporates the algorithm 207 shown in FIG. 2 into the control program of the control circuit. The head inspection apparatus has the same configuration as the magnetic disk apparatus, and can replace the magnetic head to be evaluated or the magnetic head assembly on which the magnetic head is mounted. The algorithm shown in FIG. 207 and others are incorporated.
[0032]
Specifically, an evaluation apparatus for a magnetic head for evaluating a magnetic head on which a GMR element including a fixed layer according to the present invention is mounted includes a recording medium, a spindle motor that rotationally drives the recording medium, and an evaluation. A magnetic head comprising a data recording / reproducing circuit for recording / reproducing data on / from a recording medium using a magnetic head to be performed, and a control circuit for controlling them, and for evaluating a magnetic head equipped with a GMR element including a fixed layer In the evaluation apparatus, the data recording / reproducing circuit records on the recording medium a recording pattern in which a time interval from a positive pulse to a negative pulse and a time interval from a negative pulse to a positive pulse are different from the recording medium. To obtain a reproduced waveform, and the control circuit compares the time interval from the positive pulse to the negative pulse of the reproduced waveform with the time interval from the negative pulse to the positive pulse. Then, the reversal of the magnetization direction of the fixed layer of the GMR element is evaluated based on the difference between the two time intervals, the time interval from the positive pulse to the negative pulse is T1, and the time interval from the negative pulse to the positive pulse is the time interval. When the time interval T2 is shorter than T1, when the value obtained by subtracting the time interval T2 from the time interval T1 is negative, it is evaluated that the magnetization direction of the fixed layer of the GMR element is reversed.
[0033]
The magnetic disk apparatus according to the present invention includes a recording medium, a spindle motor that rotationally drives the recording medium, a magnetic head on which a GMR element including a fixed layer is mounted, and data recording / reproduction on the recording medium by the magnetic head. A data recording / reproducing circuit for performing the above and a control circuit for controlling these, the data recording / reproducing circuit including a time interval T1 from the positive pulse to the negative pulse and a time from the negative pulse to the positive pulse shorter than the time interval T1. The recording pattern consisting of the interval T2 is recorded on the recording medium, and the recording pattern is reproduced from the recording medium to obtain a reproduction waveform. The control circuit subtracts the time interval T2 from the time interval T1 is negative. In this case, it is determined that the magnetization direction of the fixed layer of the GMR element is reversed.
[0034]
The magnetic head evaluation apparatus and the magnetic disk apparatus are not limited to determining that the magnetization direction of the fixed layer of the GMR element is reversed when the value obtained by subtracting the time interval T2 from the time interval T1 is negative. As described in the embodiment, even if the interval T1 to the interval T2 are positive or equal, those having a low amplitude of the reproduced waveform are partially inverted, and are combined with the amplitude, output, etc., and a sign of abnormality of the GMR head. Can also be evaluated. Further, in the above description, the GMR head has been described as an example, but the same effect can be applied to GMR heads other than the spin valve type GMR head, tunnel effect type MR heads, superlattice type MR heads, and the like.
[0035]
As described above, the magnetic head evaluation method according to the present embodiment, the inspection apparatus and the magnetic disk apparatus having the magnetic head evaluation function are provided with the time interval from the positive pulse to the negative pulse and the time interval from the negative pulse to the positive pulse. And recording the recording pattern different from the recording medium, comparing the time interval from the positive pulse to the negative pulse and the time interval from the negative pulse to the positive pulse of the reproduced waveform obtained by reproducing the recording pattern from the recording medium, The reversal of the magnetization direction of the fixed layer of the GMR element can be detected and evaluated by the difference between the time intervals.
[0036]
In the embodiment, as shown in FIG. 1, data recording is performed using a recording current waveform in which the time interval T1 from the positive pulse to the negative pulse is longer than the time interval T2 from the negative pulse to the positive pulse. Although the example of performing is described above, the present invention is not limited to this, and the time interval is reversed as T2> T1, and (T1-T2) in the algorithm 207 of FIG. 2 is reversed as (T2-T1). Thus, it may be configured to detect an abnormality of the GMR head. Furthermore, in the above-described embodiment, the time interval is detected as the peak time interval, but the time interval can be obtained even at an arbitrary waveform position even if it is not a peak.
[0037]
The present invention can also be expressed as an embodiment described below.
First Embodiment At the time of signal recording, the recording medium has a recording function having different time intervals from a positive pulse to a negative pulse and a time interval from a negative pulse to a positive pulse, and a time from a positive pulse to a negative pulse during reproduction. Polarity judgment function by measuring time interval from negative pulse to positive pulse and asymmetry of the time interval.
Second Embodiment At the time of signal recording, the recording medium has a recording function having different time intervals from a positive pulse to a negative pulse and a time interval from a negative pulse to a positive pulse, and a time from a positive pulse to a negative pulse during reproduction. A magnetic head inspection apparatus having a polarity determination function by measuring an interval and a time interval from a negative pulse to a positive pulse and asymmetry of the time interval.
<Embodiment 3> At the time of signal recording, the recording medium has a recording function having a different time interval from a positive pulse to a negative pulse and a time interval from a negative pulse to a positive pulse. A magnetic recording apparatus that measures an interval and a time interval from a negative pulse to a positive pulse and has a polarity determination function by asymmetry of the time interval.
[0038]
【The invention's effect】
As described above, the magnetic head evaluation method according to the present invention, the inspection apparatus having the magnetic head evaluation function, and the magnetic disk apparatus include the time interval from the positive pulse to the negative pulse and the time interval from the negative pulse to the positive pulse. And recording the recording pattern different from the recording medium, comparing the time interval from the positive pulse to the negative pulse and the time interval from the negative pulse to the positive pulse of the reproduced waveform obtained by reproducing the recording pattern from the recording medium, The reversal of the magnetization direction of the fixed layer of the GMR element can be evaluated by the difference between the two time intervals. In particular, by using a magnetic head inspection apparatus having the function of the present invention, a highly reliable GMR head without magnetic abnormality can be provided. In addition, a magnetic recording apparatus (magnetic disk apparatus) having the function of the present invention can be mounted with a highly reliable GMR head that is not magnetically abnormal and can improve reliability.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a recording pattern and a reproduction waveform for explaining the principle of the present invention.
FIG. 2 is a diagram for explaining an algorithm of a magnetic head evaluation method according to the present invention.
FIG. 3 is a diagram for explaining a magnetic disk device;
FIG. 4 is a diagram for explaining a magnetic head.
FIG. 5 is a diagram for explaining an MR head.
FIG. 6 is a diagram for explaining the GMR effect.
FIG. 7 is a diagram for explaining reversal of the magnetization direction of the fixed layer.
FIG. 8 is a diagram for explaining inversion of output polarity due to inversion of a fixed layer;
[Explanation of symbols]
1: recording medium, 2: magnetic head, 3: actuator, 4: spring, 5: slider, 6: element, 7: inductive head for recording, 8: coil, 9: magnetic core, 10: recording magnetization on the recording medium 11: MR film, 12: reproducing electrode, 13: external magnetic field, 14: free layer, 15: fixed layer, 16: antiferromagnetic film.

Claims (3)

A recording medium, a spindle motor for rotating the recording medium, a magnetic head on which a head element including a fixed layer is mounted, a data recording / reproducing circuit for recording / reproducing data on the recording medium by the magnetic head, and In a magnetic disk device comprising a control circuit for controlling
The data recording / reproducing circuit records a recording pattern comprising a time interval T1 from a positive pulse to a negative pulse and a time interval T2 from a negative pulse to a positive pulse shorter than the time interval T1 on the recording medium. To reproduce the recorded pattern to obtain a reproduced waveform,
When the value obtained by subtracting the time interval T2 from the time interval T1 is negative, the control circuit determines that the magnetization direction of the fixed layer of the head element is reversed,
A magnetic disk drive characterized in that when it is determined that the magnetization direction of the fixed layer of the head element has been reversed, reproduction waveform inversion is performed and data is normally reproduced by waveform inversion. A recording medium, a spindle motor for rotating the recording medium, a magnetic head on which a head element including a fixed layer is mounted, a data recording / reproducing circuit for recording / reproducing data on the recording medium by the magnetic head, and In a magnetic disk device comprising a control circuit for controlling
The data recording / reproducing circuit records a recording pattern comprising a time interval T1 from a positive pulse to a negative pulse and a time interval T2 from a negative pulse to a positive pulse shorter than the time interval T1 on the recording medium. To reproduce the recorded pattern to obtain a reproduced waveform,
When the value obtained by subtracting the time interval T2 from the time interval T1 is negative, the control circuit determines that the magnetization direction of the fixed layer of the head element is reversed,
A magnetic disk device, wherein when it is determined that the magnetization direction of the fixed layer of the head element has been reversed, the sense current direction is reversed to initialize the magnetization reversal of the fixed layer. 3. The magnetic disk apparatus according to claim 1, wherein an abnormality of the head element is evaluated by combining a value obtained by subtracting the time interval T2 from the time interval T1 and a resistance value of the head element.

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