JPH11110703A - Measurement of medium noise of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable measurement and evaluation of medium noise even in high density recording area exceeding reproducing capability of a magnetic reproducing head by reproducing magnetization intensity of the DC-erased area with a magnetic microscope and then defining an average frequency Mra of the obtained magnetization intensity waveform f(x) as an index of medium noise of a magnetic recording medium. SOLUTION: First, a signal is written, using a magnetic head, to a magnetic recording medium for measuring medium noise. Next, DC-erasing is conducted using the magnetic head to reproduce a reproducing pattern of the part where a signal is DC-erased using a magnetic microscope. Magnetization intensity in the width (assuming a gap width of recording head) including all track widths is read from the obtained reproducing pattern. When the obtained magnetization intensity waveform is defined as f(x), the average frequency Mra in the part having the length is calculated by the formula Mra=(1/l)∫<l> 0 |f(x)|dx.

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 accurately measure the medium noise of a magnetic recording medium, and to evaluate the magnetic recording medium by measuring the medium noise even in a high-density recording area exceeding the reproducing capability of a recording / reproducing head. Is to provide a way to

[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.
) And consists of the following steps. Performing a DC erasure on a magnetic recording medium on which a signal is recorded using a recording head. Reproducing the magnetization intensity of the DC-erased portion by MFM. Reading a magnetization intensity waveform in a width or a part including the whole of the obtained reproduction pattern of the MFM. Assuming that the read magnetization intensity waveform is f (x), an average frequency Mra of the magnetization intensity waveform f (x) is calculated by applying the following Expression 1 to the measurement length l of the waveform. Step.

(Equation 2)

The magnetization intensity waveform f calculated in the step
The average frequency Mra of (x) is an index indicating the medium noise of the magnetic recording medium.

[0009]

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 subjected to DC erasure using a recording head.

The reproduction pattern of the portion where the signal has been 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 mm ^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 a width including the entire track width (assuming the gap width of the recording head) is read. FIG. 3 shows the obtained magnetization intensity waveform. Assuming that the obtained magnetization intensity waveform is f (x), the average frequency Mr in the length l portion of the magnetization intensity waveform f (x)
a is calculated by substituting a into the following Equation 1.

[0013]

(Equation 3)

[0014]

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. For the measurement, six types of magnetic recording media (test media A to F) having different media noises were used. As a magnetic force microscope (MFM), Nano Scope
III (Digital Instruments) was used. As a recording / reproducing head, a magnetoresistive head (hereinafter, referred to as “MR head”) having a maximum recording capacity of 200 kfci and a maximum reproducing capacity of 160 kfci was used.

First, after a signal of 140 kfci was written to the test media A to F using the recording / reproducing head, DC erasing of the recorded signal was performed using the same recording / reproducing head. For the test medium on which DC erasure was performed, MF
Using M, the reproduction pattern of the magnetization intensity of the signal erased portion was measured (see FIG. 2). For the obtained MFM reproduction pattern, the magnetization intensity at a width including the track width is read,
As shown in FIG. 3, the magnetization intensity waveform f (x) of the reproduction signal was measured. Next, the length l = of the obtained magnetization intensity waveform f (x)
For the portion of 5 μm, the average frequency Mra of the magnetization intensity waveform f (x) was calculated by applying Equation 1 above, and the average frequency Mra was used as an index indicating medium noise. The medium noise was measured for the signal erased portions of the test media A to F using an MR head. Each measurement result obtained,
As shown in FIG. 4, the average frequency Mra of the magnetization intensity waveform measured by MFM is plotted on a vertical axis, and the medium noise measured by the MR head is plotted on a horizontal axis.

Referring to FIG. 4, the value of the average frequency Mra of the magnetization intensity waveform f (x) measured by the method of the present invention and the medium noise measured using an actual MR head (however, a predetermined amount of system (Including noise). That is, the medium noise can be measured by the method of the present invention using MFM instead of the measurement by the conventional recording / reproducing head.

When the average frequency Mra 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 MFM can be measured in the recording density range where the recording / reproducing head can reproduce. The average frequency Mra of the magnetization intensity waveform and the medium noise may be measured using a recording / reproducing head, and the conversion may be performed based on the proportional relationship between the two.

[0018]

According to the measuring method of the present invention, a magnetic force microscope (MFM) having an excellent ability to measure magnetization intensity can be used for a magnetic recording medium recorded at a density higher than the signal reproducing ability of a recording / reproducing head. Is used to measure the magnetization intensity of the magnetic recording medium, and apply the above equation 1 to the obtained magnetization intensity waveform f (x) to calculate the average frequency Mra having a proportional relationship with the medium noise. Can be. 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, even if there is no recording / reproducing head having a reproducing capability in a desired high recording density range, the average frequency Mra of the magnetization intensity waveform is obtained using a magnetic force microscope (MFM), and based on this, the magnetic recording medium is reproduced. The medium noise can be evaluated and used 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 f (x) obtained from an MFM image.

FIG. 4 is a graph showing a relationship between an average frequency Mra of a magnetization intensity waveform measured by an MFM measured by an MFM and a medium noise measured by a recording / reproducing head.

[Explanation of symbols]

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

 ──────────────────────────────────────────────────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] 1. A magnetic recording medium on which a signal is recorded,
DC erasing using a recording head, reproducing the magnetization intensity of a portion where a signal has been erased using a magnetic force microscope, and a magnetization intensity waveform in a width or a part including all of the obtained reproduction pattern. Readout step, where f (x) is the read magnetization intensity waveform, the following formula 1 is used for the portion of the measurement length 1 in the waveform f (x).
And calculating the average frequency Mra of the magnetization intensity waveform f (x) by applying A method for measuring medium noise of a magnetic recording medium, comprising: evaluating a calculated average frequency Mra of the magnetization intensity waveform f (x) as an index of medium noise.