JP3448808B2 - Method and apparatus for improving characteristics of thin-film magnetic head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for improving noise characteristics of a composite thin film magnetic head having an inductive write head element and a magnetoresistive effect (MR) read head element.

[0002]

2. Description of the Related Art In recent years, as the areal recording density of hard disk devices has increased, there has been a demand for improved performance of thin film magnetic heads. Therefore, as a thin-film magnetic head, instead of one that performs both writing and reading by an inductive head element, writing is performed by an inductive head element, and reading is performed by an MR head element stacked on this inductive head element. Composite thin film magnetic heads are widely used.

In this type of composite thin-film magnetic head, when a read operation is performed after a write operation, the read signal has a pulse-like noise (popcorn) having a peak value significantly higher than that of normal white noise. It is known that noise) may occur. The generation of the popcorn noise causes various problems such as a reading error of read information.

In order to reduce such popcorn noise, measures have been taken in the design and manufacturing process of thin film magnetic heads such as optimization of the shape and composition of the magnetic layer of the inductive write head element.

[0005]

However, it is very difficult to surely reduce the popcorn noise by the conventional measures as described above.

Further, for example, a thin film magnetic head is mounted on a suspension, and signal lead wires and terminals are connected,
After becoming products with high added value, all the products that were detected to have popcorn noise were discarded as defective products, resulting in poor yield and large loss.

In the patent application (Japanese Patent Application No. 11-352538) prior to the present application, the applicant improves the popcorn noise characteristic of the magnetic head by causing a current larger than the normal write current to flow in the write head element. Proposing a method. However, according to this method, since the noise characteristic is improved by the heat generated by the current, the processing time becomes long, and there is a possibility that the element may be deteriorated by passing the current more than the specified value.

Therefore, an object of the present invention is to provide a novel method and apparatus for improving the characteristics of a thin film magnetic head capable of improving the characteristics so that the popcorn noise is surely eliminated or reduced.

Another object of the present invention is to provide a method and apparatus for improving the characteristics of a thin film magnetic head, which can improve the characteristics in a short time and with good reproducibility.

Still another object of the present invention is to provide a method and apparatus for improving the characteristics of a thin film magnetic head, which can easily improve the characteristics without applying a load to the head element.

[0011]

According to the present invention, a composite thin film magnetic head comprising an inductive write head element and an MR read head element is provided with a write current flowing through the inductive write head element. Provided is a method for improving characteristics of a thin film magnetic head, which suppresses or reduces noise generated in a read signal after a write operation by applying an external alternating magnetic field to the thin film magnetic head.

The inventors of the present application, when an external alternating magnetic field is applied to a composite type thin film magnetic head which generates popcorn noise while applying a write current to an inductive write head element, the popcorn is generated in many magnetic heads. It was found that noise will not occur.
Therefore, even a magnetic head having popcorn noise can be improved in characteristics and is not discarded as a defective product, and the yield is greatly improved. Moreover, since only a normal write current is applied and an external magnetic field is applied at the same time, the characteristic improvement process is simple, unnecessary load is not applied to the head element, and the characteristic is improved in a short time and with good reproducibility. It can be performed.

The external alternating magnetic field applied to the composite thin film magnetic head is preferably larger than the magnetic field normally applied to the composite thin film magnetic head from the magnetic medium.

After a write current is passed through the inductive write head element, it is determined whether popcorn noise is generated in the read signal from the MR read head element, and it is determined that popcorn noise is generated. It is more preferable to perform the above-described noise characteristic improvement processing.

A noise characteristic improving process is performed on a plurality of composite type thin film magnetic heads arranged on a head block.
For a composite thin film magnetic head separated into a single body, for a composite thin film magnetic head mounted on a suspension, or for a plurality of composite thin film magnetic heads in a plurality of head suspension assemblies mounted on a head stack assembly. It is preferable that this is performed.

According to the present invention, means for determining whether or not noise has occurred in the read signal after the write operation of the composite thin film magnetic head having the inductive write head element and the MR read head element. A means for applying a write current to the inductive write head element, a means for applying an external alternating magnetic field to the composite thin film magnetic head, and a determining means when it is determined that noise has occurred,
Improving the characteristics of a thin film magnetic head provided with a control means for suppressing or reducing the above noise by applying an external alternating magnetic field from an external alternating magnetic field applying means while applying a write current to the inductive type write head element from the energizing means A device is provided.

The external alternating magnetic field applying means is preferably a means for applying an external alternating magnetic field larger than the magnetic field normally applied to the composite type thin film magnetic head from the magnetic medium.

[0018]

1 is a block diagram schematically showing the structure of a characteristic improving apparatus for a thin film magnetic head according to an embodiment of the present invention. In this embodiment, for a plurality of thin film magnetic heads aligned on the head block (bar),
It is a device that tries to improve the popcorn noise characteristic when the electrical characteristic is inspected by the ρ-H tester. Therefore, many elements of the commonly used ρ-H tester can be used, which makes it very easy to configure the device.

In FIG. 1, reference numeral 10 is a Helmholtz coil (air core coil) for generating an external magnetic field applied to a composite type thin film magnetic head including an inductive type element as a write head element and an MR type element as a read head element. Therefore, in the present embodiment, the major axis is installed so as to be parallel to the vertical direction. A Helmholtz coil excitation power supply 11 is electrically connected to the Helmholtz coil 10, and its drive is controlled by an instruction given from the control computer 12. In the Helmholtz coil 10, a mounting table 13a for the XYZ- [theta] table 13 and a head block or bar 14 temporarily fixed on the mounting table 13a are provided.

The head block 14 is formed by forming a number of composite type thin film magnetic heads on a wafer by a thin film technique.
This wafer was cut in row units so that each wafer contained a plurality of composite thin film magnetic heads, and the air bearing surface (A
BS) 14a is polished and the gap depth processing is finished. Therefore, the head block 14 has a plurality of composite thin-film magnetic heads in a row before being separated into a single body.

The first probe pin 15a is an output terminal (61) of the MR element of each head in the head block 14.
a) (see FIG. 6), the probe pin 15 a and each output terminal are provided so as to be electrically contactable so as to be stationary, and the XYZ-θ table 13 and the drive control of the XYZ-θ table 13. It is aligned by the XYZ-θ driver 16. The position of the first probe pin 15a and each output terminal is aligned by C for imaging this portion via the optical system 17.
It can be monitored by a CD imager 18 and a TV monitor 19 displaying this image.

The second probe pin 15b is an input terminal (61b, FIG. 6) of the inductive head element of each head.
The probe pin 15b and each of the input terminals are provided so as to be able to make electrical contact with the probe pin 15b at a fixed position.
X-Y-Z-θ table 13 and X for driving and controlling the table 13
-Alignment is performed by the YZ-θ driver 16.
This position alignment part is also imaged through the optical system 17 C
It can be monitored by a CD imager 18 and a TV monitor 19 displaying this image. Actually, the first probe pin 15a and the second probe pin 15b are integrally fixed, and the XYZ-θ table 13 is aligned at one time.

A head amplifier circuit 20 used in a disk drive, for example, is connected to the second probe pin 15b. An oscillator 21 is connected to the head amplifier circuit 20, which allows the head amplifier circuit 20 to be connected.
Therefore, a high-frequency write current can be supplied to the inductive head element of the magnetic head through the second probe pin 15b. This write current is
It is a rectangular wave in the frequency band (1 MHz to 200 MHz) normally used for writing in the magnetic head.

A head amplifier circuit 20 that supplies a sense current to the MR head element and receives an output voltage from the MR head element is connected to the first probe pin 15a. The head amplifier circuit 20 has a sense circuit. A constant current source 22 for current is connected.

The head amplifier circuit 20 is connected to a noise detection circuit 23 that detects the number of times noise has been generated by repeatedly performing writing and reading operations a predetermined number of times. The noise detection circuit 23 receives its output. A control computer 12 is connected to determine whether popcorn noise has occurred and to perform characteristic improvement processing.

The head amplifier circuit 20, the Helmholtz coil power supply 11, and the XYZ-θ driver 16 are also connected to the control computer 12, and perform predetermined control operations according to instructions from this computer.

FIG. 2 is a block diagram schematically showing a configuration example of the noise detection circuit 23.

In the figure, reference numeral 231 is a high pass filter for extracting only high frequency components from the output voltage of the MR type read head element output from the head amplifier circuit 20. The output side of the high pass filter 231 is connected to one input terminal of two comparators 232 and 233. An upper threshold voltage V _TH for identifying popcorn noise is applied to the other input terminal of the comparator 232, and a lower threshold value for identifying popcorn noise is applied to the other input terminal of the comparator 233. The voltage V _TL is applied. The outputs of the comparators 232 and 233 are connected to one input terminal of an AND circuit 235 via a pulse generation circuit 234 such as a monostable multivibrator.

To the other input terminal of the AND circuit 235,
Read gate signal R from the timing signal generation circuit 237
G is applied. AND circuit 23
The output terminal of 5 is connected to the input terminal of the noise counter 236. The noise counter 236 is configured so that a timing signal is applied from the timing signal generation circuit 237. The noise counter 236 further
The count value is output to the control computer 12.

The timing signal generation circuit 237 is configured to output the read gate signal RG and the timing signal with reference to the time when the count value of the noise detection cycle counter 238 changes.

FIG. 3 is a flow chart showing a control program for the computer 12, and the method for improving the characteristics of the thin film magnetic head according to the present invention will be described below with reference to the same figure.

First, the positions of the output terminal of the MR element of the target magnetic head and the first probe pin 15a on the head block 14 fixed on the mounting table 13a of the XYZ-θ table 13. The alignment and the input terminal of the write element of the magnetic head and the second probe pin 15b are aligned (step S1). For this alignment, a well-known alignment technique for moving the XYZ-θ table 13 by instructing the XYZ-θ driver 16 is used.

Next, the occurrence frequency of popcorn noise is detected (step S2).

FIG. 4 is a flow chart for explaining in detail an example of the detection processing in step S2.

First, the noise detection cycle counter 238
Is set to the number of noise detection cycles, and the noise counter 236 is reset to the initial value (step S2).
1). The value of the number of noise detection cycles is set appropriately. For example, it may be 100, 500, 5000, or any other constant value.

Next, the write operation is performed by controlling the head amplifier circuit 20 (step S22).
This write operation is performed by applying a rectangular-wave write current having a preset frequency and amplitude to the inductive write head element of the magnetic head, for example, for several tens to several hundreds of microseconds. The frequency of the write current is the frequency band (1 MHz to 200 MH) normally used for writing.
z).

Next, a predetermined period D is delayed (step S23). This delay time is, for example, several microseconds. The delay period D is provided to perform the read operation after the transient response of the head amplifier circuit 20 at the time of shifting from the write operation to the read operation is completed.

Next, the read operation is performed by controlling the head amplifier circuit 20 (step S24).
In this read operation, a sense current is applied to the MR read head element of the magnetic head, and the read gate signal R is output from the timing signal generation circuit 237 of the noise detection circuit 23.
It is performed by applying G to the head amplifier circuit 20 and the AND circuit 235. The read operation period is, for example, several tens of microseconds.

Next, the read signal RS output from the head amplifier circuit 20 is applied to the comparators 232 and 233 via the high pass filter 231 of the noise detection circuit 23 and compared with the threshold voltage V _TH and the threshold voltage V _TL. ,
It is determined whether it is within the set range (step S25).

When the read signal RS is not within the set range,
Since the trigger signal is output from the AND circuit 235 and applied to the noise counter 236, the noise counter 2
In 36, the content advances by +1 (step S2
6). When the read signal RS is within the set range, the AND circuit 235 does not output the trigger signal and the content of the noise counter 236 does not change.

Next, the content of the noise detection cycle counter 238 is incremented by -1 according to the timing signal output from the timing signal generation circuit 237 (step S27).

After that, the noise detection cycle counter 23
It is determined whether the content of 8 has become zero (step S28). If it becomes zero, the popcorn noise occurrence frequency detection process is terminated and step S3 in FIG.
Go to. If it is not zero, the process returns to step S22, and the series of processes from the write operation is repeated.

FIG. 5 is a waveform diagram for explaining the relationship among the read signal, the threshold voltage, the trigger signal, the read gate signal RG, etc. of the composite type thin film magnetic head in one write operation and one read operation.

In the figure, W is a write operation period, D is a delay period after the write operation, R is a read operation period, RG is a read gate signal which becomes high level only during the read operation period, and RS is from the MR read head element. Read signal of
V _TH represents the upper threshold voltage, V _TL represents the lower threshold voltage, and TG represents the counting trigger signal of the noise counter.

When the read operation is performed after the write operation, there is a magnetic head that generates pulsed popcorn noise PN having a peak value considerably higher than normal white noise in the voltage waveform of the read signal RS. Such popcorn noise PN has a threshold voltage V as shown in FIG.
Since it exceeds _TH or V _TL , the output of the comparator 232 or 233 is inverted, and the trigger signal T is output from the pulse generation circuit 234.
G is output and the noise counter 236 advances.

Therefore, according to the detection processing of FIG. 4, it is possible to obtain the frequency of popcorn noise occurrence, which is the number of times popcorn noise has occurred in a predetermined number of noise detection cycles.

After the detection processing is completed, it is determined whether or not the detected popcorn noise occurrence frequency (number of occurrences / number of noise detection cycles) exceeds an allowable value (step S3).

If the frequency of occurrence does not exceed the allowable value, it is determined that the magnetic head is a good product for popcorn noise (step S4), and the characteristic improving process is not performed.

When the occurrence frequency exceeds the allowable value, the write current and the external alternating magnetic field are simultaneously applied to the magnetic head to perform the characteristic improving process (step S).
5). Specifically, by controlling the head amplifier circuit 20, a rectangular wave write current having a preset frequency and amplitude is applied to the inductive write head element of the magnetic head, and the excitation power supply 11 is further controlled. This is done by simultaneously applying an external alternating magnetic field to the head block 14.

The frequency of the write current is in a frequency band (1 MHz to 200 MHz) used for normal writing, and its strength is the current value used for normal writing.

The strength of the external alternating magnetic field is set to a value higher than the magnetic field normally applied to the magnetic head from the magnetic medium. The frequency of the external alternating magnetic field is not particularly limited, and may be a low frequency to a microwave band. Even with DC, an external alternating magnetic field can be obtained by changing the polarity and applying it a plurality of times. For example, in this embodiment, 1 kHz is used.

As is well known, the Helmholtz coil 10
Generates a magnetic field having a strength proportional to the applied current in the major axis direction, so that the magnitude and frequency of the drive current may be indicated to the excitation power supply 11.

FIG. 6 also illustrates the external alternating magnetic field applied to the head block 14. In this embodiment, the direction of the external magnetic field is the same as the magnetic field applied when the magnetic head is actually traveling on the magnetic medium, that is, the direction perpendicular to the ABS 14a of the head block 14. However, as this external alternating magnetic field, the same result can be expected in any other direction. Further, in the present embodiment, the waveform of the external magnetic field is an AC waveform that changes positively and negatively into a sine wave shape as shown by 60 in FIG.

In FIG. 6, 61a is an output terminal of the MR element, 61b is an input terminal of the write element, and the first probe pin 15a is connected to the output terminal 61a of the MR element of the magnetic head to be inspected. The second probe pins 15b are in contact with the input terminals 61b of the write element.

Then, noise detection processing similar to that in step S2 is performed (step S6).

Thereafter, similarly to step S3, it is determined whether or not the frequency of occurrence of the detected popcorn noise exceeds an allowable value (step S7).

If the frequency of occurrence does not exceed the allowable value, it is determined that the magnetic head has become good for popcorn noise as a result of the characteristic improvement (step S).
4).

If the frequency of occurrence exceeds the permissible value, it is determined that the magnetic head is defective, and all processing relating to this magnetic head is ended (step S8).

As described above, according to this embodiment,
It is determined whether popcorn noise occurs in the magnetic head at an allowable frequency, and if it occurs, a write current and an external alternating magnetic field are simultaneously applied to perform characteristic improvement processing. Hereinafter, regarding the characteristic improvement that the generation of popcorn noise is eliminated by simultaneously applying the write current and the external alternating magnetic field in this way, the experimental results using a magnetic head sample without popcorn noise and a plurality of existing magnetic head samples are shown. Will be described with reference to.

FIGS. 7A and 7B are waveform diagrams showing read signals of the magnetic head sample without popcorn noise and the magnetic head sample with popcorn noise, respectively.

In the figure, 71 and 72 are the maximum and minimum values of the read signal at each time when the cycle of the write operation and the read operation is repeated 5000 times,
Reference numeral 73 indicates the value of the read signal at each time in the last cycle, and RG indicates the read gate signal. It can be seen that the sample with popcorn noise is considerably disturbed in the maximum value and the minimum value 71 and 72 during the read period when the read gate signal RG is at the high level, as compared with the sample without the popcorn noise.

FIG. 8 shows an external alternating magnetic field of 1600 A / m (20
It is a figure which shows a part of the count value and read-out signal waveform of a noise counter at the time of performing noise detection by increasing by Oe). However, each signal waveform is the same as in the case of FIG. The number of write and read operations is 5000, and the write current is 40 mA _0-P and 50 M.
Hz, the delay period D is 3.0 μsec.

The counting operation changes while noise is being detected by applying an external alternating magnetic field of 38400 A / m shown in FIG. 8E.
As shown in (F), the generation of popcorn noise was drastically reduced.

FIG. 9 shows an external alternating magnetic field of 4000 A / m for a separate sample in the presence of popcorn noise.
It is a figure which shows the count value and read-out signal waveform of a noise counter at the time of performing noise detection by incrementing by (50 Oe) and stopping application of an external alternating magnetic field on the way. The signal waveforms are the same as those in FIG. 7, the write operation and read operation cycles are 5000 times, and the write current is 40 mA.
_0-P and 50 MHz, the delay period D is 3.0 μsec.

As shown in FIG. 9C, 20000 A / m
After the external alternating magnetic field of (250 Oe) was applied to detect noise, the external alternating magnetic field was stopped to detect noise as shown in FIG. 9D, but the generation of popcorn noise was drastically reduced. There is. This was the same even when an external alternating magnetic field of 20000 A / m (250 Oe) was applied again, as shown in FIG. 9 (E).

FIG. 10 shows the presence of popcorn noise.
Apply an external alternating magnetic field to the sample by sequentially increasing it
Instead of 40,000 A / m (500 Oe) diplomatic relations
No. when noise is detected by applying a magnetic field at once
In the figure which shows the count value and readout signal waveform of the counter
is there. However, each signal waveform is the same as in the case of FIG.
It The cycle of write operation and read operation is 5000
Time, write current is 40mA _0-PAnd 50MHz, delay
The period D is 3.0 μs.

When noise is detected by applying an external alternating magnetic field of 40000 A / m shown in FIG. 10B, the generation of popcorn noise is drastically reduced. This is shown in FIG.
As shown in, even if the application of the external alternating magnetic field was stopped, it was the same. Therefore, it has been proved that by applying an external alternating magnetic field having a certain strength or more in the state where the write current is applied, the generation of popcorn noise can be drastically reduced and the characteristics can be improved.

As described above, according to the present embodiment, by applying a strong external alternating magnetic field to the inductive write head element while flowing a write current, the characteristics can be improved so that popcorn noise does not occur. it can. In this way, even a magnetic head having popcorn noise can be improved in characteristics, so that it is not discarded as a defective product and the yield is greatly improved. Moreover, since only a normal write current is applied and an external magnetic field is applied at the same time, the characteristic improvement process is simple, unnecessary load is not applied to the head element, and the characteristic is improved in a short time and with good reproducibility. It can be performed.

In general, in order to manufacture a composite type thin film magnetic head and incorporate it into a magnetic disk device, steps as schematically shown in FIG. 11 are taken. That is, first, a large number of thin film magnetic heads are formed in a matrix on the wafer (step S111). Next, this wafer is cut to form a head block or bar in which a plurality of thin film magnetic heads are arranged in rows (step S112). Next, the head block is cut to obtain a thin film magnetic head separated into individual pieces (step S113). Then, the thin film magnetic head is mounted on a suspension to obtain a head suspension assembly (step S114). Then
A plurality of head suspension assemblies are mounted on the carriage to obtain a head stack assembly (step S
115). Then, the head stack assembly is mounted on the magnetic disk device (step S116).

In the above embodiment, step S112.
After that, that is, at the time shown in the same figure, the characteristic improving process of the thin film magnetic head is performed. However, the characteristic improving process of the present invention is performed after the wafer process is completed (shown in the same figure), after the magnetic head is separated into single bodies (shown in the same figure), after being mounted on the suspension (shown in the same figure), and after the head stack assembly is formed. Obviously, it may be performed (in the same figure) or after being mounted in the magnetic disk device (in the same figure).

The embodiments described above are merely illustrative and not limitative of the present invention, and the present invention can be implemented in various other modified modes and modified modes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

[0072]

As described in detail above, according to the present invention,
The characteristics are improved by applying an external alternating magnetic field to the composite thin film magnetic head that generates popcorn noise while applying a write current to the inductive write head element. Therefore, even a magnetic head having popcorn noise can be improved in characteristics and is not discarded as a defective product, and the yield is greatly improved. Moreover, since only a normal write current is applied and an external magnetic field is applied at the same time, the characteristic improvement process is simple, unnecessary load is not applied to the head element, and the characteristic is improved in a short time and with good reproducibility. It can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a circuit configuration of a characteristic improving apparatus for a composite type magnetic head according to an embodiment of the present invention.

FIG. 2 is a block diagram schematically showing a configuration example of a noise detection circuit in the embodiment of FIG.

FIG. 3 is a flowchart showing a computer control program in the embodiment of FIG.

FIG. 4 is a flowchart showing in detail the content of popcorn noise occurrence frequency detection processing in FIG.

5 is a waveform diagram for explaining a relationship among a read signal, a threshold voltage, a trigger signal, a read gate signal RG, etc. of the composite thin film magnetic head in one write operation and one read operation in the embodiment of FIG. .

FIG. 6 is a diagram showing the relationship between the probe pins and the electrodes of the magnetic head in the embodiment of FIG. 1 and explaining the external alternating magnetic field applied to the head block.

FIG. 7 is a waveform diagram showing read signals of a magnetic head sample without popcorn noise and a magnetic head sample with popcorn noise.

FIG. 8 is a diagram showing a part of a count value and a read signal waveform of a noise counter when noise is detected by increasing an external alternating magnetic field for a sample in which popcorn noise exists.

FIG. 9 is a diagram showing a count value of a noise counter and a read signal waveform when noise is detected by changing an external alternating magnetic field for a sample having popcorn noise.

FIG. 10 is a diagram showing a count value of a noise counter and a read signal waveform when noise is detected by changing an external alternating magnetic field for a sample having popcorn noise.

FIG. 11 is a process diagram schematically showing a process of manufacturing a composite thin-film magnetic head and incorporating it into a magnetic disk device.

[Explanation of symbols]

10 Helmholtz coil 11 Helmholtz coil excitation power supply 12 Control computer 13 XYZ-θ table 13a mounting table 14 Head block or bar 14a Air bearing surface (ABS) 15a First probe pin 15b Second probe pin 16 XYZ-θ driver 17 Optical system 18 CCD imager 19 TV monitor 20 head amplifier circuit 21 oscillator 22 constant current source 23 Noise detection circuit 60 external alternating magnetic field 61a output terminal 61b input terminal 231 High Pass Filter 232, 233 comparator 234 pulse generator 235 AND Circuit 236 Noise Counter 237 Timing signal generation circuit 238 noise detection cycle counter

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-81604 (JP, A) JP-A-6-76202 (JP, A) JP-A-2000-36101 (JP, A) JP-A-5-135315 (JP, A) JP-A-7-272230 (JP, A) JP-A-60-69810 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/02 G11B 5 / 09 311 G11B 5/465

Claims (9)

(57) [Claims] 1. A composite thin film magnetic head comprising an inductive write head element and a magnetoresistive effect read head element, wherein an external alternating magnetic field is applied to the composite thin film magnetic head while applying a write current to the inductive write head element. A method for improving the characteristics of a thin film magnetic head, characterized in that noise generated in a read signal after a write operation is suppressed or reduced by applying a voltage. 2. The method according to claim 1, wherein an external alternating magnetic field applied to the composite thin film magnetic head is larger than a magnetic field normally applied to the composite thin film magnetic head from a magnetic medium. . 3. After applying a write current to the inductive write head element, it is determined whether or not the noise occurs in a read signal from the magnetoresistive effect read head element, and the noise is generated. If it is determined that the write signal is present, an external alternating magnetic field is applied to the composite thin film magnetic head while applying a write current to the inductive write head element to suppress or reduce noise generated in the read signal after the write operation. The method according to claim 1, wherein a noise characteristic improving process is performed. 4. A noise characteristic for suppressing or reducing noise generated in a read signal after a write operation by applying an external alternating magnetic field to the composite thin film magnetic head while applying a write current to the inductive write head element. 4. The method according to claim 1, wherein the improvement process is performed on a plurality of composite thin film magnetic heads arranged on the head block. 5. A noise characteristic for suppressing or reducing noise generated in a read signal after a write operation by applying an external alternating magnetic field to the composite type thin film magnetic head while applying a write current to the inductive write head element. 4. The method according to claim 1, wherein the improvement process is performed on the composite type thin film magnetic head separated into a single body. 6. A noise characteristic for suppressing or reducing noise generated in a read signal after a write operation by applying an external alternating magnetic field to the composite thin film magnetic head while applying a write current to the inductive write head element. 4. The method according to claim 1, wherein the improvement process is performed on a composite type thin film magnetic head mounted on a suspension. 7. A noise characteristic of suppressing or reducing noise generated in a read signal after a write operation by applying an external alternating magnetic field to the composite thin film magnetic head while applying a write current to the inductive write head element. 4. The method according to claim 1, wherein the improvement processing is performed on a plurality of composite thin film magnetic heads in a plurality of head suspension assemblies mounted on the head stack assembly. 8. Means for determining whether or not noise has occurred in a read signal after a write operation of a composite type thin film magnetic head having an inductive write head element and a magnetoresistive effect read head element, and the inductive means. Type write head element, a means for supplying a write current, a means for applying an external alternating magnetic field to the composite type thin film magnetic head, and the determining means determines that the noise has occurred. Characteristics of a thin film magnetic head, characterized in that it comprises: a control means for suppressing or reducing the noise by applying an external alternating magnetic field from the external alternating magnetic field applying means in a state where a write current is applied to the type write head element. Improvement device. 9. The means for applying an external alternating magnetic field is a means for applying an external alternating magnetic field larger than a magnetic field normally applied to the composite thin film magnetic head from a magnetic medium. The described device.