JPH10188230A - Test method for magneto-resistive magnetic head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic head test method capable of quantitatively evaluating Barkhousen noise being the noise of a magneto-resistive magnetic head. SOLUTION: In this method, when the magneto-resistive effect type-magnetic head 2 provided with a magneto-resistive effect element changing resistivity by applying a magnetic field is tested, an AC magnetic field is generated by a magnetic field generation means 4 consisting of an oscillator 4a, a coil 4b, etc. Then, the AC magnetic field from this magnetic field generation means 4 is detected by the magneto-resistive magnetic head 2, and the Barkhousen noise is tested.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for inspecting a magneto-resistance effect type magnetic head, and more particularly to a method for inspecting Barkhausen noise of a magneto-resistance effect type magnetic head.

[0002]

2. Description of the Related Art In recent years, the recording density of a magnetic recording medium has increased,
2. Description of the Related Art Thin film magnetic heads are widely used to improve frequency characteristics when recording and reproducing signals from a magnetic recording medium.
Here, in a magnetic induction type reproducing magnetic head,
The reproduction output depends on the relative speed between the magnetic recording media. For this reason, the magnetic induction type reproducing magnetic head has a problem that the reproducing output becomes small when scanning over the magnetic recording medium at a low speed.

On the other hand, as a reproducing magnetic head, a magnetoresistive effect type magnetic head provided with a magnetoresistive effect element (hereinafter referred to as an MR element) whose resistivity changes according to an externally applied magnetic field. (Hereinafter, referred to as an MR head). This MR head has a feature that, during reproduction, the reproduction output does not depend on the speed of the magnetic recording medium, and a high reproduction output can be obtained even when scanning over the magnetic recording medium at a low speed.

The principle of operation of this MR head utilizes the fact that the resistance value of the MR element changes when an external magnetic field is applied while a constant current I is supplied to the MR element.
Therefore, the information signal recorded on the magnetic recording medium is reproduced by detecting the voltage change of the MR element. The reproduction output at this time is as follows: the rate of change of the voltage is ΔV,
Assuming that the resistance change rate of the MR element is △ R and the current supplied to the MR element is I, △ V = △ R · I.

[0005]

However, the MR head provided with the above-described MR element has the following two problems in practical use as a magnetic head for reproducing information signals recorded on a magnetic recording medium. Need to be considered.

As a first problem, it is necessary to make the output of the MR element linearly respond to an information signal recorded on a magnetic recording medium. For this problem, the MR head
This is dealt with by setting the angle between the current I supplied to the R element and the magnetization direction of the MR element to 45 °.

The second problem is that during reproduction, M
The purpose is to reduce Barkhausen noise generated in the R element. When this Barkhausen noise is generated in the MR element during reproduction, pulse-like noise is generated in the reproduction signal, and the reproducibility of the reproduction signal is reduced. The cause of the Barkhausen noise is that a domain wall in the MR element moves due to the generation of a demagnetizing field at an end portion or the like of the MR element. For this reason, as a method for preventing Barkhausen noise, a method has been proposed in which the magnetic domain wall is eliminated in the MR element by forming the MR element into a single magnetic domain.

However, it is difficult to eliminate this Barkhausen noise at the stage of designing the MR head. Therefore, in the MR head, it is necessary to inspect Barkhausen noise at the time of shipment after the MR head is completed. However, since this Barkhausen noise is usually detected as a jump in the waveform of a reproduced output, it is difficult to quantitatively evaluate the Barkhausen noise, which is a problem when inspecting the Barkhausen noise of the MR head. .

As a method of detecting the Barkhausen noise, it is possible to detect the reproduction output of the MR head by passing it through a differentiating circuit when reproducing the magnetic recording medium.

However, since the Barkhausen noise has a reproduced output waveform after passing through the differentiating circuit including the output of the MR head, even if the reproduced output passing through the differentiating circuit is detected, the Barkhausen noise can be accurately detected. The quantitative evaluation cannot be performed.

Further, Barkhausen noise is reproduced when a magnetic recording medium is reproduced even if an attempt is made to pass a filter circuit for blocking only the output signal of the MR head from the waveform after passing through the differentiating circuit. Since the output is nonlinear and the reproduced output waveform is distorted, it is not possible to prevent only the reproduced output of the MR head.

The present invention has been proposed in view of the above-mentioned problems, and it is an object of the present invention to quantitatively evaluate Barkhausen noise that causes noise when an MR head reproduces a magnetic recording medium. An object of the present invention is to provide a method of inspecting an MR head that can be performed.

[0013]

SUMMARY OF THE INVENTION A method for inspecting a magneto-resistance effect type magnetic head according to the present invention, which solves the above-mentioned problems, comprises:
When inspecting a magnetoresistive head having a magnetoresistive element whose resistivity changes when a magnetic field is applied, a step of generating a magnetic field by a magnetic field generating means, and a step of generating a magnetic field from the magnetic field generating means. And an inspection step of inspecting Barkhausen noise by detecting with a resistance effect type magnetic head.

Preferably, the magnetic field generating means generates an alternating magnetic field having a predetermined frequency.

Preferably, the magnetic field generating means generates a magnetic field by applying a voltage having a magnetic field modulation frequency to a coil by an oscillator.

The inspection step includes a signal detection step of detecting a signal based on a magnetic field detected by the magnetoresistive magnetic head, a differentiation step of differentiating the signal detected by the signal detection step, and a differentiation step of the differentiation step. Detecting a signal obtained by blocking the magnetic field modulation frequency from the output signal.

In such a method of inspecting a magneto-resistance effect type magnetic head, since the inspection is performed by detecting the magnetic field generated by the magnetic field generating means with the magneto-resistance effect type magnetic head, the information signal recorded on the magnetic recording medium can be obtained. Unlike the case where the inspection is performed by reproduction, the Barkhausen noise can be detected by supplying an input signal without noise to the magnetoresistive head having the inspection symmetry.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for inspecting a magnetoresistive head according to the present invention will be described in detail with reference to the drawings.

First, FIG. 1 shows an example of an inspection circuit of an MR head used in an inspection method of a magneto-resistance effect type magnetic head (hereinafter referred to as an MR head) to which the present invention is applied.

As shown in FIG. 1, the MR head inspection circuit 1 is a circuit for inspecting a magnetoresistive head 2 (hereinafter referred to as an MR head 2). A constant current source 3 for supplying a current to the MR head 2, a magnetic field generating means 4 for applying a magnetic field to the MR head 2,
An amplifier 5 for amplifying a signal detected by the head 2, a differentiator 6 to which a signal from the amplifier 5 is input, a notch filter 7 to which a signal passed through the differentiator 6 is input, and a notch And a detecting means 8 for detecting a signal passed through the filter 7.

The MR head 2 is a magnetic head having a magnetoresistive element whose resistivity changes when a magnetic field is applied. This MR head 2 is used during reproduction.
A signal is reproduced by applying a magnetic field while a constant DC current is supplied and detecting a voltage change due to a change in resistance value.

The constant current source 3 supplies the MR head 2 with a sense current. The constant current source 3 always supplies a predetermined value of current to the MR head 2 during the reproduction of the MR head 2 described above.

The magnetic field generating means 4 applies a magnetic field of a predetermined single frequency to the MR head 2 when inspecting the MR head 2. As shown in FIG. 1, the magnetic field generating means 4 includes, for example, an oscillator 4a for generating a voltage having a predetermined frequency.
And a coil 4b to which the voltage output from the oscillator 4a is applied. Magnetic field generating means 4 configured in this way
Generates a voltage of a single frequency of a sine wave or a cosine wave by the oscillator 4a, and applies a voltage from the oscillator 4a to the coil 4b to apply a magnetic field having a single frequency to the MR head 2.

The amplification amplifier 5 is for amplifying the signal detected by the MR head 2. The amplification amplifier 5 is configured to output the current supplied to the MR head 2 and the M
This is an amplifier that amplifies a voltage determined by a product of the resistance value of the R element.

The differentiating circuit 6 receives the signal passed through the amplifier 5 and differentiates the signal. The signal that has passed through the amplification amplifier 5 is input to the differentiating circuit 6. Then, this differentiating circuit 6, as shown in FIG.
It is composed of a resistor, a capacitor, an operational amplifier and the like, and performs differential processing on a signal input by these components.
The differentiating circuit 6 changes the reactance of the capacitor according to the frequency of the input signal and changes the amplification of the operational amplifier to differentiate the input signal.

The notch filter 7 is a circuit for blocking a signal of a predetermined frequency. This notch filter 7
Is to input a signal passed through the differentiating circuit 6 and block a signal of a predetermined frequency. In the present embodiment, as shown in FIG. 1, a filter that blocks a signal of a predetermined frequency is configured by using a resistor, a capacitor, an operational amplifier, and the like. This notch filter 7
For example, when a sine wave is input, the output is shifted in phase. The notch filter 7 blocks the head output component of the signal that has passed through the differentiating circuit 6 and outputs only the Barkhausen noise component. That is, the notch filter 7 blocks a signal component corresponding to only the head output, and leaves only a Barkhausen noise component. That is, the notch filter 7 is connected to the oscillator 4b
Block the signal component having substantially the same frequency as the frequency of the voltage output from.

The detection means 8 receives only the signal of the Barkhausen noise component which has passed through the notch filter 7, and
Quantify Barkhausen noise components. In the present embodiment, the detection means 8 is constituted by an oscilloscope, and displays a signal that has passed through the notch filter 7.

Next, a method of inspecting the MR head 2 by the MR head inspection apparatus 1 configured as described above will be described.

In the method of inspecting the MR head 2, as shown in the flowchart of FIG. 2, a magnetic field generating step S-1 for generating a magnetic field by the magnetic field generating means 4 and a magnetic field generating step S-1 are performed. A signal detecting step S-2 for detecting the applied magnetic field by the MR head 2, and an amplifying step S for amplifying the signal detected by the signal detecting step S-2.
-3, a differentiating step S-4 for differentiating the signal having passed through the amplifying step S-3 by a differentiating circuit 6, and a noise detecting step S for blocking a signal of a predetermined frequency by a notch filter 7 to detect Barkhausen noise. −5. In the inspection method of the MR head 2 according to the present embodiment, as a premise, a constant current source 3 supplies a predetermined value of sense current to the MR head 2.

The magnetic field generating step S-1 is a step of generating a magnetic field by the magnetic field generating means 4 described above. In the magnetic field generation step S-1, first, a voltage having a predetermined frequency is output by the oscillator 4b. Then, the voltage output from the oscillator 4a is input to the coil 4b, and the magnetic field generated from the coil 4b is applied to the MR head 2 to be inspected. Here, the oscillator 4a applies a voltage having a single frequency of a sine wave or a cosine wave to the coil 4b. The magnetic field applied to the MR head 2 by the magnetic field generating means 4 applies a magnetic field which is easily processed in a noise detection step S-5 described later.

The signal detecting step S-2 is a step of detecting a reproduction output from the MR head 2 to which a magnetic field has been applied by the magnetic field generating means 4 described above. Here, the MR head 2
A reproduction output corresponding to the magnetic field applied from the magnetic field generator 4 is output. At this time, the reproduction output by the MR head 2 is
If the bias point is appropriate, the resistance value operates linearly with respect to the magnetic field, so that the reproduced output substantially corresponds to the magnetic field applied by the magnetic field generating means 4. The reproduction output output from the MR head 2 includes a head output component,
The output includes a Barkhausen noise component. Here, FIGS. 3A and 4A show an example of a signal detected in the signal detection step S-2. In addition,
FIGS. 3 and 4 and FIGS. 6 and 7 to be described later are diagrams showing voltage waveforms detected by, for example, an oscilloscope.

FIG. 3A shows an example of a signal detected from the MR head 2 having Barkhausen noise. The waveform corresponding to the head output component includes a distortion 9 corresponding to the Barkhausen noise component. On the other hand, FIG. 4A is an example of a signal detected from the MR head 2 having no Barkhausen noise, and no distortion corresponding to the Barkhausen noise component is generated in the waveform corresponding to the head output component.

The amplification step S-3 includes the signal detection step S described above.
This is a step of amplifying the signal detected at -2 by the amplifier 5. The signal amplified in this amplification step S-3 is
The signal is input to the differentiating circuit 6, and the process proceeds to a differentiating step S-4.

The differentiating step S-4 is a step of differentiating the signal from the amplifier 5. Here, the waveform of the signal that has passed through the differentiating circuit 6 is output with a phase shift of about 90 degrees from the waveform input to the MR head 2. In the present embodiment, a signal obtained by differentiating the signal shown in FIG. 3A is shown in FIG. FIG.
FIG. 4B shows a signal obtained by differentiating the signal shown in FIG.

The waveform of the signal that has passed through the differentiating circuit 6 is
When the MR head 2 has Barkhausen noise, a pulse-like waveform 10 corresponding to the Barkhausen noise component is generated as shown in FIG. on the other hand,
When there is no Barkhausen noise in the MR head 2, as shown in FIG. 4B, no pulse-shaped waveform corresponding to the Barkhausen noise component is generated.

Here, as a comparative example, FIG. 5 shows a signal obtained by detecting a signal recorded on a magnetic recording medium by an MR head and passing the signal through a differentiating circuit. FIG.
FIG. 3A is a diagram illustrating a signal detected by the MR head 2. FIG. 5B is a diagram in which the signal shown in FIG. 5A is differentiated by a differentiating circuit. According to FIG. 5, since the output of the MR head itself is distorted, when the signal passes through the differentiating circuit, the distortion is further increased. Therefore, the MR from the magnetic recording medium
In the case of detection by the head, it is difficult to block only the head output component of the signal subjected to the differential processing by the notch filter. Therefore, it is difficult to quantify the Barkhausen noise of the signal detected by the MR head from the magnetic recording medium.

Next, the signal passed through the differentiating circuit 6 is input to the notch filter 7, and a signal of a predetermined frequency is blocked to detect a Barkhausen noise.
Go to -5. Here, the notch filter 7 blocks a frequency component corresponding to the head output component from the reproduction output from the MR head 2 so that only the Barkhausen noise component is left. Therefore, the signal that has passed through the notch filter 7 is as shown in FIGS. 6B and 7B.

FIG. 6A shows the reproduction output of the MR head 2 when Barkhausen noise is generated in the MR head 2, and FIG. 6A shows the reproduction output of the signal shown in FIG. FIG. 6B is a diagram showing a signal waveform when the signal has passed through the notch filter 6 and the notch filter 7. FIG.
FIG. 7A shows the reproduction output of the MR head 2 when no Barkhausen noise is generated in the MR head 2, and the signal shown in FIG. 7A passes through the differentiating circuit 6 and the notch filter 7. Fig. 7 shows the signal waveform when
It is the figure shown to (b).

According to FIG. 6B, a signal corresponding to the Barkhausen noise component is generated as a pulse-like waveform 10 in the reproduction output of the MR head 2. On the other hand, FIG.
According to (b), since there is no Barkhausen noise in the MR head 2, there is no pulse-shaped waveform corresponding to the Barkhausen noise component. FIG. 6 (b)
As the amplitude A of the pulse-like waveform shown in FIG.
The Barkhausen noise generated in the head 2 is large.

According to such an inspection method of the MR head 2, the magnetic field from the magnetic field generating means 4 constituted by the oscillator 4a and the coil 4b is applied to the MR head 2, and the amplification amplifier 5,
By passing the signal through the differentiating circuit 6 and the notch filter 7, it is possible to detect only the signal corresponding to the Barkhausen noise component from the reproduction output of the MR head 2. Therefore, according to the inspection method of the MR head 2, the Barkhausen noise of the MR head 2 can be quantified by measuring the pulse-shaped amplitude A of the output waveform after passing through the notch filter 7. is there.

The MR head inspection method according to the present embodiment is applicable as a recording / reproducing apparatus using a magnetic disk such as a flexible disk or a hard disk as a recording medium, or any MR head inspection method. Used in a recording / reproducing apparatus using a magnetic tape as a recording medium, such as a QIC (Quarter Inch Cartridge) or the like.
It is applicable as an inspection method of the R head.

[0042]

As described above in detail, the method of inspecting a magneto-resistance effect type magnetic head according to the present invention applies a magnetic field generated from a magnetic field generation means comprising, for example, an oscillator and a coil to the magneto-resistance effect type magnetic head. To apply a signal without distortion to the magnetoresistive head,
Barkhausen noise of the magnetoresistive head can be detected. Therefore, such a method for inspecting a magneto-resistance effect type magnetic head can quantitatively detect the Barkhausen noise of the magneto-resistance effect type magnetic head and easily evaluate the Barkhausen noise in the magneto-resistance effect type magnetic head. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an MR head inspection apparatus used in an MR head inspection method to which the present invention is applied.

FIG. 2 is a process chart showing a method of inspecting a magnetoresistive magnetic head according to the present invention.

FIG. 3 is a diagram showing a waveform of a reproduction output from the MR head when Barkhausen noise is present in the MR head, and a waveform after passing the reproduction output waveform through a differentiating circuit.

FIG. 4 is a diagram showing a reproduction output waveform from the MR head when there is no Barkhausen noise in the MR head and a waveform after passing the reproduction output waveform through a differentiating circuit.

FIG. 5 shows an MR when a signal from a magnetic recording medium is detected.
FIG. 4 is a diagram showing a reproduced output waveform from a head and a waveform after the reproduced output waveform has passed through a differentiating circuit.

FIG. 6 is a diagram showing a reproduced output waveform from the MR head when Barkhausen noise is present in the MR head, and a waveform after the reproduced output waveform has been passed through a differentiating circuit and a notch filter.

FIG. 7 is a diagram showing a reproduction output waveform from the MR head when there is no Barkhausen noise in the MR head, and a waveform after the reproduction output waveform has passed through a differentiating circuit and a notch filter.

[Explanation of symbols]

Reference Signs List 1 MR head inspection apparatus, 2 MR head, 3 constant current source, 4 magnetic field generating means, 5 amplifying amplifier, 6 differentiating circuit, 7 notch filter, 8 detecting means

Claims (4)

[Claims] A step of generating a magnetic field by means of a magnetic field generating means when inspecting a magnetoresistive magnetic head having a magnetoresistive element whose resistivity changes when a magnetic field is applied; An inspection step of inspecting Barkhausen noise by detecting a magnetic field from the means with a magnetoresistive magnetic head. 2. The method according to claim 1, wherein said magnetic field generating means generates an alternating magnetic field of a predetermined frequency. 3. The magnetoresistive effect type magnetic device according to claim 1, wherein said magnetic field generating means generates an AC magnetic field of a predetermined frequency by applying an AC voltage of a predetermined frequency to a coil by an oscillator. How to inspect the head. 4. The inspection step includes a signal detection step of detecting a signal based on a magnetic field detected by a magnetoresistive magnetic head, a differentiation step of differentiating a signal detected by the signal detection step, and a differentiation step of Detecting a signal obtained by blocking a predetermined frequency with respect to the signal differentiated by the following method. 2. The method according to claim 1, further comprising the steps of: