JPH0887701A - Method for evaluating magnetic recording medium - Google Patents

Abstract

PURPOSE: To easily evaluate reproducing noises of a magnetic recording medium by calculating an amplitude standard deviation, line width standard deviation and (bit length-line width average value)<-1> from magnetic force microscopic images and using any thereof in correspondence to the bit length. CONSTITUTION: The line width 8, the amplitude 7 and the bit length 5 are as shown in Fig. and the magnetic force microscopic images 4 are as shown by a drawing of Fig. (a). The change in the line width is as shown in Fig. (b). The information shown by the magnetic force microscopic images 4 is the interaction of the magnetic force between a probe 2 and a sample 3 and since the rugged images of the magnetic interaction are obtd. by attraction or repulsion, the line width to the wire-shaped magnetic ruggedness is obtd. The waving in the bit length 5 direction of the magnetic ruggedness is evaluated by observing the change in the line width 8 when the plural magnetic force microscopic images 4 are obtd. by shifting the sections perpendicular to a track direction toward the track direction and executing scanning in accordance with the scanning loci 6 of a magnetic force microscope.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium characteristic evaluation method, and more particularly to a method for quantitatively evaluating reproduction noise characteristics of a medium by using a magnetic force microscope image.

[0002]

2. Description of the Related Art A hard disk, which is a magnetic recording medium, is used as a main storage device of a computer. FIG. 8 is a sectional view showing a conventional hard disk. On the Al substrate 81, a nickel phosphorus NiP layer 82, a Cr underlayer 83, a Co-based alloy magnetic layer 84, a carbon protective layer 85, a liquid lubricating layer 86.
Are sequentially stacked. The NiP layer 82 has a thickness of about 10 μm and is plated on the Al substrate. Cr underlayer is 50n
A film having a thickness of m is formed by a sputtering method. The Co-based alloy magnetic layer has a thickness of 20 to 30 nm, and the carbon-based protective layer has a thickness of 15 nm. The liquid lubricating layer is formed by a dip method with a film thickness of 2 nm.

The Co type alloy magnetic layer 84 of such a magnetic recording medium has magnetic domains magnetized in the longitudinal direction. Recording, reproducing, and erasing of information for magnetic domains are performed by rotating the medium at high speed via a head (not shown) in contact with the liquid lubricating layer 86. The head converts the magnetic signal recorded on the medium into an electric signal to perform reading, which is reproduction of information,
Further, the input electric signal is converted into a magnetic signal to write information on the medium. Since reproduction noise occurs when reading information from this medium, it is necessary to improve the S / N ratio for the reproduction output (head signal) of the medium.

FIG. 9 shows reference data for S / N ratio measurement of reproduction output, and FIG. 9A is a diagram showing reproduction output voltage.
Figure (b) is a diagram showing the spectrum of the reproduction output, Figure (c)
Is a diagram showing a spectrum of circuit noise, and FIG. 7D is a diagram showing a reproduced noise region A _N. T in Figure (a)
AA indicates the peak-to-peak voltage V _PP of the reproduction output. In the figure (b), the peak corresponds to the bit frequency. This is measured using a spectrum analyzer. FIG. 6C shows the spectrum analysis with the head landing on the medium, which corresponds to circuit noise that does not include the reproduction output of the medium. FIG. 6D shows a reproduction noise area A _N obtained by subtracting circuit noise from the reproduction output of the medium.

The S / N ratio SNR of the medium using the above data
Is calculated by the equation (1).

[0006]

## EQU1 ## SNR = 20Log (S / N _rms ) [dB] (1) Here, the signal S and the reproduction noise N _rms are expressed by the equations (2) and (3), respectively.

[0007]

## EQU00002 ## S = TAA / 2 (2)

[0008]

(Equation 3) Here, N _W is the noise component of the reproduction output, and N _C is the circuit noise. Γ indicates the resolution of the spectrum analyzer.

[0009]

Since determining the S / N ratio of the reproduction output as described above requires a troublesome procedure, it is required to determine the S / N ratio of the reproduction output by a simple method. ing. As one of such methods, there is a qualitative discussion of noise characteristics using magnetic force microscope images. Yukio Honda, Mikio Suzuki, Nobuyuki Inaba, Daishi Toyama, Masaaki Nihon, No.4.
Proceedings of the 1st Joint Lecture on Applied Physics NO.
1, p67 (1994). According to the above-mentioned proceedings, for example, in a medium having a large reproduction noise, the boundary between recording bits has a broad leakage flux distribution, and magnetic interference is observed between adjacent recording areas.

The present invention has been made in view of the above points, and an object thereof is to provide a method for quantitatively evaluating the reproduction noise characteristic of a magnetic recording medium using a magnetic force microscope image.

[0011]

SUMMARY OF THE INVENTION According to the present invention, the above object is to provide a method for evaluating a magnetic recording medium having longitudinal magnetic domains in a magnetic layer, wherein a line width average value is m _W , an amplitude standard deviation and a line width standard deviation. each sigma _a, sigma _W, the magnetic layer of the medium using a magnetic force microscope when the bit length was L _B scans,
From the obtained magnetic force microscope image σ _A, σ _W or (L _B -
This is achieved by calculating m _W ⁻¹ and using any one of them in accordance with the bit length to evaluate the noise characteristic.

In the above invention, the bit length is 0.6 μm.
be used the standard deviation sigma _A amplitude when: m, the pit length is to use a standard deviation sigma _W line width when less than 0.6 .mu.m or bit length is 0.6 .mu.m,
Ki exceeds, it is effective to use (L _B -m _W) ^-1.

[0013]

The distortion of the magnetic force microscope image in the bit transition region shows a correlation with the reproduction noise.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a principle diagram showing a magnetic force microscope image measuring method. It has a magnetic probe 2 at the tip of a minute leaf spring 1,
The magnetic force interaction between the magnetic probe 2 and the sample 3 (attractive force or repulsive force) can be detected by the displacement of the leaf spring 1 to obtain a magnetic image. As a method of detecting the displacement of the leaf spring 1,
It is most common to vibrate the leaf spring 1 near the resonance frequency and monitor the conversion of the amplitude of the leaf spring 1 when the probe receives a force. Since the method of detecting the magnetic force may be slightly different depending on each device, all microscopes that capture the magnetic interaction acting between the sample 3 and the probe 2 as the displacement of the leaf spring 1 are in the category of the magnetic force microscope. In this embodiment, a magnetic force microscope is used with SFA300 (hardware) and SPI3 manufactured by Seiko Instruments Inc.
It measured using 700 (software). The probe 2 on the sample 3
When the magnetic recording is performed as shown in the drawing (the arrow indicates the direction of magnetization), the magnetic force microscope image 4 shown in the drawing is obtained by scanning with.

FIG. 2 is a perspective view showing a magnetic force microscope image of the magnetic recording medium. Since the recording portion has a width in the track direction (direction perpendicular to the plane including the magnetic force microscope image 4 in FIG. 1), a three-dimensional image can be obtained by scanning while slightly moving the probe 2 in the track direction. . 3A and 3B show definitions of line width, amplitude, and bit length in the present invention. FIG. 3A is a diagram of a magnetic force microscope image, and FIG. 3B is a plan view showing changes in line width. The information indicated by the magnetic force microscope image 4 is the magnetic force interaction between the probe 2 and the sample 3. However, since an uneven image of the magnetic interaction is obtained by the attractive force or the repulsive force, the line width is different from the linear magnetic unevenness. 8 can be defined. When a plurality of magnetic force microscope images are obtained by scanning a cross section perpendicular to the track direction by shifting the position in the track direction according to the scanning locus 6 of the magnetic force microscope,
By observing the change in the line width 8, the waviness of the magnetic unevenness in the pit length 5 direction can be evaluated. The change in the line width 8 was evaluated by the standard deviation σ _W of the line width 8 in each cross-section magnetic force microscope image. The bit length is defined by 5 and the amplitude is defined by 7.

FIG. 4 is a diagram showing the dependence of the reproduced noise on the line width standard deviation. The samples used for evaluation are the type of magnetic layer,
The medium has various noise characteristics depending on the film forming conditions, and is magnetically recorded with a bit length of 0.3 μm. The horizontal axis represents the standard deviation of the line width 8 defined above, and the vertical axis represents the reproduction noise of the medium. The line width was measured at a height of 5 × amplitude / 8 from the valley side with respect to the amplitude 7 of the magnetic force microscope image in FIG. It can be seen that the noise characteristic of this magnetic recording medium can be roughly described by the parameter σ _W. As described above, σ _W indicates the waviness of the recording bit in the bit length direction, and indicates that the larger the waviness, the greater the magnetic interference with the adjacent bit.

FIG. 5 is a diagram showing reproduction noise (bit length-line width average value) ^-1 dependence. The medium used for evaluation is
It is magnetically recorded on the same medium as in FIG. 4 with a bit length of 1 μm. The horizontal axis represents 1 / (bit length-line width average value), and the vertical axis represents reproduction noise of the medium. The parameter (bit length-line width average value) represents the steepness of the magnetic unevenness. In a sample having a relatively long bit length, a sample having a lower steepness may have stronger magnetic interference between adjacent recording bits. There is a nature.

FIGS. 6 and 7 are diagrams showing the dependence of the reproduced noise on the amplitude standard deviation. The horizontal axis indicates the standard deviation σ _A of the amplitude shown in FIG. 3 measured at several points in the same sample.
The vertical axis represents the reproduction noise of the medium. The bit lengths in FIGS. 6 and 7 are 0.3 μm and 0.6 μm, respectively, and the amplitude standard deviation has a good correlation with the reproduction noise at any bit length.

[0019]

According to the present invention, the amplitude standard deviation, line width standard deviation, (bit length-line width average value) from the magnetic force microscope image.
^{Since -1} is calculated, it is possible to easily evaluate the reproduction noise of the magnetic recording medium using any one of them in accordance with the bit length. When the bit length is 0.6 μm or less, the standard deviation of the amplitude, when the bit length is less than 0.6 μm, the standard deviation of the line width, and when the bit length exceeds 0.6 μm (bit length-line width average) It is effective to use the value) ^-1 to evaluate the reproduction noise.

[Brief description of drawings]

FIG. 1 is a principle diagram showing a magnetic force microscope image measuring method.

FIG. 2 is a perspective view showing a magnetic force microscope image of a magnetic recording medium.

3A and 3B show definitions of line width, amplitude, and bit length in the present invention, FIG. 3A is a diagram of a magnetic force microscope image, and FIG. 3B is a plan view showing changes in line width.

FIG. 4 is a diagram showing the dependence of reproduced noise on a line width standard deviation.

FIG. 5 is a diagram showing (bit length-line width average value) ⁻¹ dependence of reproduction noise.

FIG. 6 is a diagram showing amplitude standard deviation dependence of reproduction noise.

FIG. 7 is a diagram showing the dependence of reproduced noise on the amplitude standard deviation.

FIG. 8 is a sectional view showing a conventional hard disk.

9A and 9B show reference data for S / N ratio measurement of reproduction output, FIG. 9A is a diagram showing a reproduction output voltage, FIG. 9B is a diagram showing a spectrum of a reproduction output, and FIG. ) Is a diagram showing a spectrum of circuit noise, and FIG. 6D is a diagram showing a reproduced noise region A _N.

[Explanation of symbols]

 1 leaf spring 2 probe 3 sample 4 magnetic force microscope image 5 bit length 6 scanning locus of magnetic force microscope 7 amplitude 8 line width

Claims (4)

[Claims] 1. A method for evaluating a magnetic recording medium having longitudinal magnetic domains in a magnetic layer, wherein a line width average value is m _W , an amplitude standard deviation and a line width standard deviation are σ _A and σ _W , respectively, and a bit length is L.
Scans the magnetic layer of the medium using a magnetic force microscope is taken as _B, and the obtained magnetic force microscope image σ _A, σ _W, or calculates (L _B -m _W) ^-1, the bit length Correspondingly, one of these methods is used for evaluating a magnetic recording medium. 2. The method for evaluating a magnetic recording medium according to claim 1, wherein the standard deviation σ _{A of the} amplitude is used when the bit length is 0.6 μm or less. 3. The magnetic recording medium evaluation method according to claim 1, wherein a standard deviation σ _{W of the} line width is used when the bit length is less than 0.6 μm. 4. The method for evaluating a magnetic recording medium according to claim 1, wherein (L _B −m _W ) ⁻¹ is used when the pit length exceeds 0.6 μm.