JPH10320701A - Measuring method of s/n of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure an S/N in a high density recording area surpassing reproducing performance of a recording and reproducing head. SOLUTION: The measuring method is composed of a step of reproducing the signal pattern of a high recording density signal recorded on a magnetic recording medium, a step of reading out a magnetizing intensity waveform in width including all the track width from the reproducing pattern, a step of uniformizing both ends of the read-out magnetizing intensity waveform through a filter and a step of Fourier-transforming the obtained magnetizing intensity waveform at high speed, dividing a data into a signal part and a noise part and calculating a ratio of the signal part to the noise part (S/N).

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 in a magnetic recording / reproducing device such as a hard disk drive, and more particularly to a method for evaluating a magnetic recording medium in a recording density region higher than the signal reproducing capability of a recording / reproducing head. The present invention relates to a method for measuring the S / N ratio of a recording medium.

[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.

One method of evaluating magnetic recording media is S / N
Measurement of the ratio (signal / noise ratio) is known. The S / N ratio is generally represented by the ratio of the amplitude of a signal to be received at a certain point on a magnetic recording medium to the amplitude of a noise signal. S /
The measurement of the N ratio is performed by reproducing a signal recorded by a recording / reproducing head, separating the reproduced signal into a signal and a noise by using a spectrum analyzer, and obtaining a ratio of a signal amplitude to a noise amplitude.

[0004]

In recent years, the recording density of magnetic recording media has been rapidly increasing, and in the development of magnetic recording media, the magnetic characteristics of the magnetic recording media have been observed and inspected. Therefore, 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. For this reason, the recording density (approximately 1
Even if a signal is recorded at 20 kfci to about 160 kfci), the signal cannot be reproduced by the same recording / reproducing head. As described above, in the recording density region higher than the signal reproducing capability, the recording / reproducing head could not be used for measuring the S / N ratio of the magnetic recording medium.

An object of the present invention is to provide a magnetic recording medium having a high recording density in a high-density recording area exceeding the reproducing capability of a recording / reproducing head.
To provide a method for measuring the / N ratio.

[0006]

The present invention utilizes a magnetic force microscope for measuring the S / N ratio of a magnetic recording medium, and comprises the following steps. Reproducing a signal pattern of a magnetic recording medium on which a signal of a high recording density is recorded by using a magnetic force microscope; Reading a magnetization intensity waveform having a width including the entire track width from the obtained reproduction pattern. A step of passing the read magnetization intensity waveform through a filter to align both ends of the waveform. Fast Fourier transform (FFT) of the obtained magnetization intensity waveform
And dividing the data into a signal portion and a noise portion, and calculating a ratio (S / N ratio) between the signal portion and the noise portion.

In the step (1), the S / N ratio is obtained by dividing the data subjected to the fast Fourier transform into a signal portion and a noise portion, calculating the ratio of the peak height of the signal portion to the area of the noise portion, and calculating the ratio of the signal portion. It can be obtained by calculating the ratio between the area and the area of the noise part.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. First, a signal having a high recording density is recorded on a magnetic recording medium for which the S / N ratio is measured by using a recording / reproducing head. A reproduction pattern of the recorded signal is reproduced using a magnetic force microscope (hereinafter, referred to as “MFM”). FIG. 1 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-shaped spring (10).
(12) is scanned over the magnetic recording medium (14), and the magnetic probe (12) is scanned.
The magnetic force acting between the magnetic recording medium (14) and the spring (10)
Is detected by the displacement of 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 mm ^2, so that the entire surface of the magnetic recording medium is observed. It is difficult to do. Therefore, the measurement of the reproduction pattern is performed only on a part of the magnetic recording medium.

FIG. 2 shows an example of the MFM image of the magnetic recording medium measured by the MFM. In FIG. 2, the horizontal axis indicates a signal recording direction, and the horizontal axis indicates a direction perpendicular to the recording direction. From the reproduction pattern of the MFM image, the magnetization intensity in a width including the entire track width (assuming the gap width of the recording / reproduction head) is read. FIG. 3A shows a waveform of the magnetization intensity. In FIG. 3A, the horizontal axis indicates the measurement length (μm), and the vertical axis indicates the amplitude (Hz). The waveform of the magnetization intensity of MFM is
As described above, since the measurement is performed only on a part of the magnetic recording medium, the number of measured data is small. Therefore, by passing the waveform through a data window composed of a trapezoidal waveform filter as shown in FIG. 3B, both ends of the waveform are aligned to zero, so that the continuity of the waveform is not impaired.

FIG. 3 (c) shows a waveform obtained by making the signal waveform of the magnetization intensity of the magnetic recording medium by MFM continuous through a data window. Fast Fourier transform of this waveform
When (FFT) is performed, the peak of the wave number of the magnetization intensity waveform is measured.

FIG. 3D shows a waveform of a wave number obtained by performing a fast Fourier transform on the magnetization intensity waveform. Referring to the figure, it can be seen that there is a peak of the wave number of the magnetization intensity waveform at about 3 (1 / λ (1 / μm)). The height of the peak of the obtained wave number waveform is defined as the signal portion height, and the area below the height position of the waveform when the width of the peak waveform becomes a predetermined value (w).
The S / N ratio can be calculated by calculating the ratio of the height of the signal portion to the area of the noise portion by setting the (shaded portion in FIG. 3D) a noise portion. Note that the width of the peak waveform is
The area above the height position of the waveform at the time of (w) is defined as a signal part, the area below the height is defined as a noise part, and the ratio of the area of the signal part to the area of the noise part is calculated as the S / N ratio. You may.

[0012]

EXAMPLE An S / N ratio value measured by a method of the present invention using a magnetic recording medium on which a signal having a recording density of 140 kfci was recorded, and an S / N ratio measured using an actual recording / reproducing head. The ratio values were compared. Measurement conditions MFM of the present invention : Nano Scope III (manufactured by Digital Instruments) Number of measurement points: Measurement conditions with 256-point recording / reproducing head Recording / reproducing head: MR head Maximum signal recording capability: 200 kfci Maximum signal reproducing capability: 160 kfci

FIG. 4 shows the obtained results. Referring to FIG. 4, the value of the S / N ratio measured by the method of the present invention,
It can be seen that the value of the S / N ratio measured using the actual recording / reproducing head is in a proportional relationship. That is, it can be seen that the S / N ratio can be measured by the method of the present invention using MFM instead of the measurement by the conventional recording / reproducing head.

When the S / N ratio obtained by using the MFM is evaluated in the same dimension as the actual recording / reproducing head, the MF is determined in the recording density range where the recording / reproducing head can reproduce.
The S / N ratio may be measured using M and the recording / reproducing head, and conversion may be performed based on the proportional relationship between the two.

[0015]

According to the measuring method of the present invention, the signal reproducing capability of the recording / reproducing head, and even the magnetic recording medium recorded at a density higher than the signal recording capability, can be measured immediately. The magnetic intensity of the magnetic recording medium is measured using a magnetic force microscope (MFM), and S
/ N ratio can be calculated. Therefore, the S / N ratio can be measured and the magnetic recording medium can be evaluated without using a recording / reproducing head having a reproducing capability in a desired high recording density range, and thus the magnetic recording medium is used for developing a magnetic recording medium. be able to.

[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 diagram showing a flow of processing of a magnetization intensity waveform.

FIG. 4 is a graph showing a relationship between an S / N ratio measured by an MFM and an S / N ratio 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, Namiwa-ku, Osaka-shi, Osaka (72) Inventor Yoshinobu Okumura 1 Shikitsu-higashi, Naniwa-ku, Osaka-shi, Osaka No. 2-47 Kubota Corporation

Claims (1)

[Claims] A step of reproducing a signal pattern of a magnetic recording medium on which a signal of a high recording density is recorded by using a magnetic force microscope; and a magnetization intensity waveform having a width including the entire track width for the obtained reproduction pattern. Reading the data, passing the read magnetization intensity waveform through a filter, and aligning both ends of the waveform.Fast Fourier transforming the obtained magnetization intensity waveform, dividing the data into a signal part and a noise part, Noise part ratio (S
/ N ratio). A method for measuring the S / N ratio of a magnetic recording medium, comprising: