JPH11175966A - Method for measuring medium noise of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method precisely measuring a medium noise of a magnetic recording medium and further, measuring the medium noise and evaluating the magnetic recording medium even in a high density recording area exceeding reproducing power of a recording/reproducing head. SOLUTION: This method contains a step performing DC erase for the magnetic recording medium recorded with a signal by the recording head, a step making a probe of a magnetic force microscope scan for the part with the erased signal and reproducing magnetization intensity of a signal erased part, the step reading out a magnetization intensity waveform in the track width direction related to an obtained reproduced pattern and the step measuring a width (w) of a pulse 30 incorporated in the read out magnetization intensity waveform, and sets the width (w) of the pulse 30 of the measured magnetization intensity waveform as an index of the medium noise of the magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring and evaluating medium noise of a magnetic recording medium used in a magnetic recording / reproducing apparatus such as a hard disk drive.

[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 is recorded with an electric signal converted into a magnetic signal by a recording / reproducing head and recorded on the magnetic recording medium. The magnetic signal is converted into an electric signal by the recording / reproducing head and output.

As a method for evaluating the characteristics of a magnetic recording medium, there is a method using noise (medium noise) caused by the magnetic recording medium itself as an index.

[0004]

Heretofore, a recording / reproducing head has been used for measuring the medium noise. However, when the medium noise of the magnetic recording medium is measured using the recording / reproducing head, in addition to the medium noise caused by the magnetic recording medium, noise of the head and the measurement system itself (system noise),
There is a disadvantage that external noise and the like are measured at the same time, and it is difficult to extract only the medium noise from the total measured noise, so that accurate measurement and evaluation of the medium noise cannot be performed.

In recent years, the recording density of magnetic recording media has been rapidly increased, and in the development of magnetic recording media, in order to observe and inspect the magnetic characteristics of the magnetic recording media,
A recording / reproducing head capable of recording and reproducing in a target high recording density area is required. However, the recording / reproducing capability of the signal of the recording / reproducing head is lower than the signal 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.
Thus, in a recording density region higher than the signal reproduction capability,
It is difficult to measure medium noise of a magnetic recording medium with a recording / reproducing head.

SUMMARY OF THE INVENTION It is an object of the present invention to evaluate a magnetic recording medium by accurately measuring the medium noise of a magnetic recording medium and measuring the medium noise even in a high-density recording area exceeding the reproducing capability of a recording / reproducing head. To provide a method by which

[0007]

According to the present invention, a magnetic force microscope (hereinafter referred to as "MFM") is used for measuring medium noise of a magnetic recording medium.
Performing DC erasing using a recording head on a magnetic recording medium on which a signal is recorded. A step of causing a probe of a magnetic force microscope to scan a portion from which the signal has been erased to reproduce the magnetization intensity of the signal erasure portion. Reading a magnetization intensity waveform in the track width direction from the obtained reproduction pattern. Measuring the width w of the pulse (30) included in the read magnetization intensity waveform; And the width w of the pulse (30) of the magnetization intensity waveform measured in the step is used as an index of medium noise of the magnetic recording medium.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. First, a signal is written to a magnetic recording medium for measuring medium noise using a recording head.

Next, the signal recorded on the magnetic recording medium is DC-erased by using a recording head.

[0010] The reproduction pattern of the portion where the signal is DC-erased is reproduced using a magnetic force microscope (MFM). FIG.
FIG. 4 is a diagram illustrating a method of measuring a reproduction pattern of 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). 12) and magnetic recording media
The magnetic force acting between the spring (14) is detected by the displacement of the spring (10). The MFM is a device used for observation and analysis of a minute range. For example, it takes several tens minutes to several hours to observe a range of about several μm ^2, so that the entire surface of the magnetic recording medium is observed. It is difficult.
Therefore, the measurement of the reproduction pattern is performed only on a part of the magnetic recording medium.

FIG. 2 shows a reproduction pattern of the MFM image of the magnetic recording medium measured by the MFM. Referring to FIG. 2, there is a portion (20) in which a signal remains without being completely erased in a reproduction pattern of an MFM image even though DC erasure is performed on a magnetic recording medium. You can see that. From the reproduction pattern of the obtained MFM image, the magnetization intensity in the track width direction (assuming the gap width of the recording head) is read. FIG. 3 shows the obtained magnetization intensity waveform. Referring to FIG. 3, it can be seen that in the obtained magnetization intensity waveform, a pulse (30) having a larger undulation than other portions exists at a position corresponding to the signal remaining portion in FIG. This large undulation pulse (30), as shown in the examples described below,
Since there is a correlation with the medium noise, an index of the medium noise can be obtained by measuring the width w of the pulse (30). That is, in order to select a magnetic recording medium having a small medium noise, a magnetic recording medium having a small width w of the pulse (30) may be selected. The current recording density (approximately 1
In order to achieve low noise at about 60 to 200 kfci), the width w of the pulse 30 should be smaller than 2.5 nm.

[0012]

EXAMPLE A medium noise value measured by the method of the present invention using an MFM was compared with a medium noise value measured using an actual recording / reproducing head. Five magnetic recording media having different medium noises were used for the measurement. As a magnetic force microscope (MFM), Nano Scope III (Digital Instr.
uments). Also, as a recording / reproducing head,
Maximum recording capacity: 200 kfci, maximum reproduction capacity: 160
A kfci magnetoresistive head (hereinafter referred to as "MR head") was used.

First, after a signal of 140 kfci was written to each test medium using the above-mentioned recording / reproducing head, DC erasing of the recorded signal was performed using the same recording / reproducing head. The reproduction pattern of the magnetization intensity of the signal erased portion was measured using the MFM on the test medium on which the DC erasure was performed (see FIG. 2). As shown in FIG. 3, the magnetization intensity in the width including the track width was read from the obtained MFM reproduction pattern. Next, among the pulses included in the measured magnetization intensity waveform, for a pulse (30) having large undulations, the width w of the pulse (30) was obtained and used as an index indicating medium noise. Also, for the signal erased portion of the test medium, M
The medium noise was measured using the R head. As shown in FIG. 4, the obtained measurement results are plotted on a graph in which the vertical axis represents the pulse width of the magnetization intensity waveform measured by the MFM and the horizontal axis represents the medium noise measured by the MR head.

Referring to FIG. 4, the pulse width of the magnetization intensity waveform measured by the method of the present invention and the medium noise measured using an actual MR head (however, a predetermined system noise is included). It can be seen that there is a substantially proportional relationship with the value of. In other words, instead of the measurement by the conventional recording / reproducing head, by the method of the present invention using MFM,
It can be seen that the medium noise can be measured.

When the pulse width of the magnetization intensity waveform obtained by using the MFM is evaluated in the same dimension as that of the actual recording / reproducing head, the MFM and the pulse width of the recording / reproducing head can be measured. The pulse width of the magnetization intensity waveform and the medium noise may be measured using a recording / reproducing head, and conversion may be performed based on the correlation between the two.

[0016]

According to the measuring method of the present invention, a magnetic force microscope (MFM) having an excellent ability to measure the magnetization intensity can be used even for a magnetic recording medium recorded at a density higher than the signal reproducing ability of the recording / reproducing head. ) Can be used to measure the magnetization intensity of the magnetic recording medium, and the width w of the pulse (30) having a correlation with the medium noise can be calculated from the obtained magnetization intensity waveform.
In the measurement using the recording / reproducing head, when measuring the medium noise, there was a disadvantage that the system noise and the like were mixed. However, according to the measuring method of the present invention, the medium of the magnetic recording medium was mixed without mixing other noise. Only noise can be accurately evaluated. In addition, without using a recording / reproducing head having a reproducing ability in a desired high recording density region, a pulse of a magnetization intensity waveform (30) using a magnetic force microscope (MFM) is used.
Of the magnetic recording medium can be evaluated based on the width w, which is useful for the development of a magnetic recording medium.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing the principle of MFM measurement.

FIG. 2 is a diagram showing an MFM image of a magnetic recording medium.

FIG. 3 is a graph showing a magnetization intensity waveform obtained from an MFM image.

FIG. 4 is a graph showing a relationship between a pulse width of a magnetization intensity waveform measured by the MFM measured by the MFM and a medium noise measured by the recording / reproducing head.

[Explanation of symbols]

 (10) Spring (12) Magnetic probe (14) Magnetic recording medium (30) Pulse

 ──────────────────────────────────────────────────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 (1)

[Claims] A step of performing DC erasure on a magnetic recording medium on which a signal is recorded by using a recording head; scanning a probe of a magnetic force microscope on a portion where the signal has been erased; Reproducing the magnetization intensity of the erased portion; reading the magnetization intensity waveform in the track width direction for the obtained reproduction pattern; width w of the pulse (30) included in the read magnetization intensity waveform
And measuring the width w of the pulse (30) of the measured magnetization intensity waveform as an index of the medium noise of the magnetic recording medium.