JPH1137975A - Method for evaluating generation frequency of partial erasure of magnetic record medium body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for examining generation frequency of a partial erasure of a magnetic record medium body and quantitatively evaluating it. SOLUTION: This method records a signal in a magnetic record medium body using a record head, reproduces a pattern of a signal recorded using a magnetic force microscope, plots a reproduced pattern of a read signal on three-dimensional coordinates in which, by use of a plane containing a length direction of a track and a width direction of a track vertical thereto as a reference plane, a strength of a signal is an axis perpendicular to this reference plane, and prepares a three-dimensional pattern of the signal strength. Further, the three-dimensional pattern is cut in the plane parallel to the reference plane every specified strength, counts the number of areas (islands) formed by intersecting the cut plane with the three-dimensional pattern, and a relation between the signal strength and the number of islands is two-dimensionally graphed. The two-dimensional graph is analyzed to quantitatively evaluate generation frequency of a partial erasure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a magnetic recording medium used for a magnetic recording / reproducing apparatus such as a hard disk drive, and more particularly to a method for recording a signal at a high recording density on a magnetic recording medium. The present invention relates to a method for quantitatively evaluating the frequency of occurrence of partial erasure.

[0002]

2. Description of the Related Art A magnetic recording medium used in a magnetic recording / reproducing device such as a hard disk drive device converts an input electric signal into a magnetic signal by a recording / reproducing head and records the magnetic signal, and converts the magnetic signal recorded by the recording / reproducing head into an electric signal. The signal is converted and played back.

As shown in FIG. 1, it is desirable that the magnetization transition regions (30), which are regions where one signal is written, be independent without being connected to each other. Incidentally, in order to increase the recording density on the magnetic recording medium, it is necessary to increase the circumferential recording density of the magnetic recording medium by reducing the interval between the magnetization transition regions (30). However, if the interval between the magnetization transition regions is reduced, the intensity of the recorded magnetization varies, and a part of the magnetization intensity decreases, and the partial erasure (Partially connected) between adjacent magnetization transition regions (30) is connected.
al Erasure) (see FIG. 2) may occur. When a partial erasure occurs, the output when a signal is reproduced decreases, which is not desirable.

[0004]

In the development of a magnetic recording medium, the generation of a partial erasure of the magnetic recording medium in a desired recording density range is required in order to determine a configuration of the magnetic recording medium suitable for a desired recording density. You need to know the frequency. However, when an attempt is made to measure the frequency of occurrence of partial erasure by a recording / reproducing head, the recording / reproducing head reproduces a signal in the entire width direction of a track.
It is difficult to detect a decrease in output due to the appearance of a partial erasure, which is a minute magnetic defect. Further, when a signal is reproduced by the recording / reproducing head, various noises are mixed in the reproduced signal. Therefore, it is difficult to measure only the output decrease caused by the appearance of the partial erasure and to quantitatively evaluate the output. is there. Further, when comparing the signal recording capability and the reproduction capability of the recording / reproducing head, there is a problem that the signal reproduction capability is lower than the recording capability. Therefore, even if a signal is recorded at a recording density close to the upper limit of the signal recording capability of the recording / reproducing head, the signal cannot be reproduced by the same recording / reproducing head, and the occurrence frequency of the partial erasure cannot be checked.

An object of the present invention is to provide a method capable of checking the frequency of occurrence of partial erasure of a magnetic recording medium and quantitatively evaluating the frequency.

[0006]

SUMMARY OF THE INVENTION The present invention quantitatively evaluates the frequency of occurrence of partial erasure by using a magnetic force microscope and has the following steps. Recording a signal on a magnetic recording medium using a recording head. Reproducing the recorded signal pattern using a magnetic force microscope. A signal reproduction pattern is plotted on a three-dimensional coordinate system in which a plane including a track length direction and a track width direction perpendicular thereto is set as a reference plane, and signal strength is set as an axis orthogonal to the reference plane. Creating a three-dimensional pattern of signal strength. A step of cutting the obtained three-dimensional pattern by a plane parallel to the reference plane (hereinafter referred to as a “cut plane”) for each predetermined intensity. A step of counting the number of regions formed by intersecting the cutting plane and the three-dimensional pattern (hereinafter, this region is referred to as an “island”) and forming a two-dimensional graph of the relationship between signal intensity and the number of islands . Analyzing the obtained two-dimensional graph to quantitatively evaluate the occurrence frequency of the partial erasure of the magnetic recording medium.

The occurrence frequency of the partial erasure can be evaluated by observing and measuring the change in the number of islands formed by intersecting the three-dimensional pattern of the signal and the cutting plane. When the partial erasure has not occurred, the number of islands observed for one magnetization transition region is only one for any magnetization transition region. However, when a partial erasure occurs in the signal, the magnetization intensity varies in the track width direction. Therefore, the three-dimensional pattern of the signal is converted to a signal intensity plane.
(Cut plane), when one magnetization transition region is 2
It is observed as an island above. In order to increase the signal output of the magnetic recording medium, it is desirable that the signal maintain a substantially uniform intensity over the entire width direction of the track. That is, for each magnetization transition region, the smaller the number of islands observed in the region of high intensity and the smaller the variation in the magnetic recording medium, the smaller the number of occurrences of the partial erasure,
It becomes a magnetic recording medium that can support a high recording density.

If the frequency of occurrence of a partial erasure in a signal intensity region of about 50% to about 70% of the maximum intensity of a signal recorded on a magnetic recording medium is low, it is almost impossible to reproduce a signal using a recording / reproducing head. The inventors have confirmed that there is no effect. That is, in a signal intensity region of about 50% to about 70% of the maximum intensity of the signal recorded on the magnetic recording medium, if the number of islands observed by the method of the present invention is small and the variation is small, the signal recording density It can be understood that the magnetic recording medium can cope with the above.

Therefore, in the step of evaluating the frequency of occurrence of the partial erasure, for example, the intensity of the signal when the number of islands in the obtained two-dimensional graph is maximum is measured,
The intensity of the measured signal can be evaluated as an index of the frequency of occurrence of partial erasure of the magnetic recording medium
(A in FIG. 7). Further, the length of the foot of the obtained two-dimensional graph can be measured, and the measured length of the foot can be evaluated as an index of the occurrence frequency of the partial erasure of the magnetic recording medium (FIG. 7B). . Further, taking into account the above two evaluation indices, for a two-dimensional graph, the signal intensity at the midpoint between the signal intensity when the number of islands is at a maximum and the signal intensity at the rising position of the two-dimensional graph. Can be measured and used as an index of the frequency of occurrence of partial erasure of the magnetic recording medium (C in FIG. 7).

[0010]

Embodiments of the present invention will be described below with reference to the drawings. First, a magnetic recording medium that attempts to evaluate the frequency of occurrence of partial erasure,
A signal is recorded using a recording head. A reproduction pattern of the recorded signal is reproduced using a magnetic force microscope (hereinafter, referred to as “MFM”). FIG. 3 is a diagram illustrating a method of measuring a magnetic recording medium by MFM. The MFM has a magnetic probe (12) at the tip of a plate-like spring (10), and scans the magnetic probe (12) on a magnetic recording medium (14) to obtain a magnetic probe (12). 1
The magnetic force acting between the magnetic recording medium (14) and the magnetic recording medium (14) is
0) is detected by the displacement. MFM is a device used for observation and analysis in a minute range. For example, it takes tens of minutes to several hours to observe a range of about several tens of μm ^2. It is difficult to observe. Therefore, the measurement of the reproduction pattern
This is performed only for a part of the magnetic recording medium.

FIG. 4 shows a three-dimensional pattern (20) representing a three-dimensional MFM image of the magnetic recording medium measured by the MFM. In FIG. 4, the three-dimensional pattern (2
0) is plotted on three-dimensional coordinates in which the length direction of the track and the width direction of the track are used as reference planes and the axis direction orthogonal to the reference plane is the signal intensity. The three-dimensional pattern (20) is cut by a plane parallel to the reference plane (hereinafter referred to as a "cut plane (22)") for each predetermined signal strength. FIG.
FIG. 3 is a diagram showing a state in which a three-dimensional pattern (20) is cut by a cutting plane (22). In the drawing, the region formed by the intersection of the cutting plane (22) and the three-dimensional pattern (20) is blacked out, and this region is called an island (24). FIG. 6 shows islands for each cutting plane when the three-dimensional pattern is cut by the cutting plane for each predetermined signal strength, with the maximum signal strength being 100%. In FIG. 6, the vertical axis indicates the track width direction, and the horizontal axis indicates the track length direction. As shown in the figure, as the signal intensity decreases, the islands are successively increased in the track width direction, and the number of islands decreases. Next, the number of islands for each signal strength is counted. As shown in FIG. 7, the counted results are plotted on a graph in which the horizontal axis represents the signal intensity and the vertical axis represents the number of islands. The occurrence frequency of the partial erasure is evaluated based on the obtained two-dimensional graph. By measuring the frequency of occurrence of the partial erasure, it is possible to evaluate whether or not the magnetic recording medium is suitable for the recorded signal frequency.

A method for evaluating the occurrence frequency of partial erasure using the obtained two-dimensional graph will be described below. Evaluation Method 1 With respect to the two-dimensional graph of FIG. 7, the signal strength at the position where the number of islands indicated by A is the maximum is read, and the signal strength is used as an index of the occurrence frequency of the partial erasure. This is because, as can be seen from FIG. 7, as the signal strength when the number of islands is maximized is higher, the position where the variation in the number of islands starts to decrease also becomes higher. As described above, the signal recorded on the magnetic recording medium is:
Since it is desirable that the signal intensity of the partial erasure is low at a signal intensity of approximately 50% to approximately 70% of the maximum signal intensity, the signal intensity A at which the number of islands is maximum is approximately 80% It is desirable that this is the case. That is,
When the magnetic recording medium is evaluated using the above-described method 1, if the signal strength A at which the number of islands is maximum is about 80% or more, the magnetic recording medium can be adapted to the recording frequency. Recognize.

Evaluation method 2 With respect to the two-dimensional graph shown in FIG. 7, the length of the foot indicated by B is read, and the length is used as an index of the occurrence frequency of the partial erasure. This is because the longer the tail of the graph, the larger the area of the signal where the frequency of occurrence of the partial erasure is small. As described above, the signal recorded on the magnetic recording medium has a maximum signal strength of about 5%.
Since it is desirable that the signal has a small number of partial erasures from 0% to about 70%, at least a part of the tail of the two-dimensional graph overlaps with the area of the signal strength of about 50% to about 70%. It is desirable that the length B of the skirt occupies about 15% or more of the entire signal. That is, when the magnetic recording medium is evaluated using the above method 2, the length B of the tail of the graph is about 15% of the entire signal.
If the length occupies the above, it can be understood that the magnetic recording medium is adaptable to the recording frequency.

Evaluation Method 3 The signal intensity at the midpoint between the maximum value of the signal intensity at the position where the number of islands is maximum and the signal intensity at the rising point of the two-dimensional graph of the number of islands (FIG. 7) C) is used as an index to evaluate the frequency of occurrence of partial erasure. This is an evaluation method that takes into account both the evaluation methods 1 and 2. In order for the signal recorded on the magnetic recording medium to be a signal with a small partial erasure at about 50% to about 70% of the maximum signal strength, the signal strength at C is desirably about 75% or more. That is, when the magnetic recording medium is evaluated using the above method 3, if the signal intensity at C is about 75% or more, it is understood that the magnetic recording medium is adaptable to the recording frequency.

[0015]

EXAMPLES Signals were recorded on a plurality of magnetic recording media using different recording heads, and the occurrence frequency of partial erasure was evaluated using MFM. As a recording head,
Two types of thin film heads α and β were used. Using each head, 140 kfci, 120 kfc
i, signals of recording densities of 100 kfci and 80 kfci were recorded. The signal pattern of the magnetic recording medium is reproduced using the MFM, a three-dimensional pattern is created by the method described above, and the obtained three-dimensional pattern is cut at predetermined strengths.
The relationship between the signal intensity and the number of islands was converted into a two-dimensional graph. 8 (a) to 8 (d) show two-dimensional graphs showing the relationship between the signal intensity and the number of islands for each recording density. Is recorded, and the graph shown by the solid line is a graph when a signal is recorded by the head β. Table 1 shows that the obtained graphs are A and B in the above evaluation methods 1 to 3.
And C are obtained.

[0016]

[Table 1]

Referring to FIG. 8 and Table 1, regardless of which of the heads α and β is used, as the recording density increases, the signal peak (see A in Table 1) shifts to the left side, that is, the side where the signal intensity is smaller. It can be seen that it has moved to. Further, it can be seen that the tail of the two-dimensional graph becomes shorter as the recording density becomes higher (see B in Table 1). Further, as the recording density increases, the signal intensity at the midpoint between the signal intensity when the number of islands in the two-dimensional graph becomes maximum and the signal intensity at the rising point of the two-dimensional graph also moves to the left. (See C in Table 1). This is because, when the recording density increases, the interval between the magnetization transition regions decreases, and the partial erasure tends to occur.On the other hand, when the recording density decreases, the interval between the magnetization transition regions increases. This is because erasure hardly occurs. That is, it is understood that the relationship between the recording density of the magnetic recording medium and the frequency of occurrence of the partial erasure can be quantitatively evaluated by using the evaluation method of the present invention.

[0018]

According to the present invention, the occurrence frequency of the partial erasure that cannot be measured by the recording / reproducing head can be measured and quantitatively evaluated. The MFM can reproduce a signal pattern even in a recording density region higher than the reproducing capability of the recording / reproducing head.
Therefore, it is possible to develop a magnetic recording medium by utilizing the measurement and evaluation of the occurrence frequency of the partial erasure in such a high recording density region. The present invention can also be used to determine whether a magnetic recording medium is suitable for a desired recording density.

[Brief description of the drawings]

FIG. 1 is a diagram showing a signal pattern of a magnetic recording medium having no partial erasure.

FIG. 2 is a diagram showing a signal pattern of a magnetic recording medium in which a partial erasure has occurred.

FIG. 3 is an explanatory diagram showing a measurement principle of MFM.

FIG. 4 is a diagram showing a three-dimensional pattern of a magnetic recording medium measured by MFM.

FIG. 5 is a diagram showing a state in which a three-dimensional pattern is cut at a predetermined signal intensity.

FIG. 6 is a diagram showing a cutting plane obtained by cutting a three-dimensional pattern at a predetermined signal intensity.

FIG. 7 is a two-dimensional graph showing the relationship between signal intensity and the number of islands.

FIG. 8 is a two-dimensional graph showing the result of measuring the relationship between the signal intensity and the number of islands for magnetic recording media on which signals are recorded by recording heads having different recording densities.

[Explanation of symbols]

 (10) Spring (12) Magnetic probe (14) Magnetic recording medium (20) Three-dimensional pattern (22) Cutting plane (24) Island (30) Magnetization transition region

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Akita 1-2-47, Shikitsuhigashi 1-chome, Namiwa-ku, Osaka-shi, Osaka (72) Inventor Yoshinobu Okumura 1 Shikitsu-higashi, Namiwa-ku, Osaka-shi, Osaka No. 2-47 Kubota Corporation

Claims (4)

[Claims] A step of recording a signal on a magnetic recording medium using a recording head; a step of reproducing a pattern of the recorded signal using a magnetic force microscope; A three-dimensional pattern of signal strength is created by plotting the signal strength on a three-dimensional coordinate system using a plane including the vertical direction and a track width direction perpendicular to the reference direction as a reference plane and an axis perpendicular to the reference plane. A step of cutting the obtained three-dimensional pattern by a plane parallel to a reference plane for each predetermined intensity; a region formed by the intersection of the cutting plane and the three-dimensional pattern
(Hereinafter, this area is referred to as an “island”), a step of counting the number of the islands, and forming a two-dimensional graph of the relationship between the signal intensity and the number of the islands. A method for evaluating the frequency of occurrence of a partial erasure of a magnetic recording medium, comprising the step of quantitatively evaluating the frequency of occurrence of a partial erasure. 2. In the evaluation step, for a two-dimensional graph, a signal intensity when the number of islands is maximized is measured, and the obtained signal intensity is used as an index of a frequency of occurrence of a partial erasure. 2. The method for evaluating the occurrence frequency of partial erasure of a magnetic recording medium according to item 1. 3. The magnetic recording medium according to claim 1, wherein, in the evaluation step, the length of the foot of the two-dimensional graph is measured, and the measured length of the foot is used as an index of the frequency of occurrence of the partial erasure. How to evaluate the frequency of occurrence of partial erasure. 4. In the evaluation step, for a two-dimensional graph, a signal intensity when the number of islands is maximum and a signal intensity at a position where a rising point of the two-dimensional graph is obtained are measured. 2. The signal intensity at the midpoint position of is used as an index of the frequency of occurrence of partial erasure.
3. The method for evaluating the frequency of occurrence of partial erasure of a magnetic recording medium according to item 1.