JPH05333128A - Magnetic domain structure analyzing device - Google Patents

Abstract

PURPOSE:To clear up a magnetic domain structure of a medium by changing freely the sample observing (light incident on the medium) direction in the medium in-plane direction, and measuring the magnetic domain magnetizing direction in the medium in-plane direction. CONSTITUTION:Light of a mercury lamp 1 is deflected (2), and passes through a prism 3, and is condensed, and is made incident, and is reflected on a measurement sample 5 by an objective lens 4. The reflected light is reflected in the horizontal direction by the prism 3, and an analyzer 6 generates a dark and bright magnetic domain image according to a magnetic domain structure of the sample 5, and a CCD camera 7 observes it. Image processing (8) is carried out on it, and a computer 9 to control a sample driving system 11 inputs it. The driving system 11 rotates with an observation point as its center, and changes the observing direction. The sample 5 is observed, and the range of a brightness change caused by a difference of the magnetization direction is determined, and angle dependency of the magnetic domain image is measured, and the computer 9 takes in the magnetic domain image. Next, the distribution of illumination and an angle of rotation of the sample 5 are corrected, and an average brightness value is calculated on respective microscopic parts whose images are divided, and the magnetization direction of the respective microscopic parts is determined. Thereby, the magnetic domain structure in the medium in-plane direction can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for analyzing a magnetic domain structure and a magnetization process in a film in-plane direction of a thin film magnetic tape, a thin film head, a sputtered magnetic disk, etc., particularly a metal magnetic thin film.

[0002]

2. Description of the Related Art As the magnetic recording technology has advanced, the recording density has increased, and the minimum dimension of a magnetically recorded pattern has become finer at 1 μm or less. As the recording pattern becomes smaller, the characteristics of the magnetic medium itself, such as the size, particle size, and particle-particle interaction of the single magnetic domain of the magnetic medium, have a greater influence on the recording characteristics through the behavior of the magnetic domain. In addition, the magnetic head that reads the recording pattern also needs to be reduced in size according to the recorded pattern.
As a result, it has been clarified that the magnetic domain structure of the head during reading affects the output. Conventionally, the analysis of the recording characteristics has focused on the electric characteristics such as reading and writing, and the magnetic characteristics are measured as a factor that brings about the electric characteristics.
The physical properties of the film have been analyzed as a cause of giving the magnetic properties, and the progress has been made by considering these electrical properties, magnetic properties, and physical properties of the film. In addition to these indirect methods, there are a Bitter method and a Lorentz electron microscope as a method for directly observing the magnetization state. The magnetic recording phenomenon can be intuitively grasped by directly looking at the magnetization state. In recent years, with the development of a microscope using a spin SEM and a magneto-optical effect, research on the relationship between the recording state and the behavior of magnetic domains has been further advanced.

The Pitter method, Lorentz electron microscope, and spin SEM cannot observe the dynamic magnetization phenomenon except for special cases. For this reason, research by directly looking at magnetic domains only initially observed them statically. On the other hand, the method using the magneto-optical effect is suitable for experimentally observing the behavior of the dynamic magnetic domain, as is clear from the study of magnetic bubbles.

In the Bitter method, in a strict sense, the magnetization itself is not seen, but the magnetic poles created by the magnetization are seen.
Therefore, the Bitter method is a simple and effective method for observing the recording state experimentally, but is not suitable for analyzing the magnetic domain structure.

A method using an electron microscope such as Lorentz electron microscope and spin SEM is characterized by high resolution. However, observation by Lorenz electron microscopy requires that a special sample be prepared. Lorenz electron microscope, Spin S
EM requires the sample to be placed in a vacuum sample chamber, and applying a magnetic field to the sample to observe the magnetization process of the sample is almost impossible except in special cases.

On the other hand, the method using the magneto-optical effect is inferior in resolution to an electron microscope, but it can be measured in the atmosphere, can be observed by applying an external magnetic field, and is nondestructive. There is a feature called. In particular, in the observation of the magnetic domain structure in the in-plane direction, a magnetic domain image can be obtained by using the vertical Kerr effect with a micro Kerr optical system, as described in JP-A-63-104015. In this device, an electromagnet is provided in the vicinity of the magnetic sample to actively induce a magnetic phenomenon such as magnetization reversal, and the process can be observed.

[0007]

However, JP-A-63-
The device described in Japanese Patent No. 104015 is limited to observing the magnetic domain structure from one direction and does not specify the magnetization direction of the magnetic domain. As a result, with this device, it is possible to observe the magnetic domain structure of a magnetic film that has a clear magnetic domain wall like the soft magnetic material used for magnetic heads and has a simple magnetic domain structure. There is a problem that a complicated magnetic domain structure of a magnetic film that does not have a clear domain wall structure, such as a hard magnetic material having a large coercive force, cannot be analyzed.

An object of the present invention is to clarify the magnetic domain structure of the medium by measuring the magnetization direction of the magnetic domain in the in-plane direction of the medium.

[0009]

In order to achieve this object, in an optical system similar to that of Japanese Patent Laid-Open No. 63-104015, the observation direction of the sample (direction of incidence of light on the medium) is the in-plane direction of the medium. The magnetic domain structure in the in-plane direction of the medium can be determined by combining freely variable means and analyzing a plurality of images taken while continuously changing the observation direction using a computer.

[0010]

Next, the cause will be described.

When a magnetic film having a magnetization component in the in-plane direction is observed by the Kerr effect using a deflector and an analyzer,
As shown in FIG. 1, the optical system can be adjusted so as to have light and shade depending on the magnetization direction. In this figure, the optical system is adjusted so that it becomes brightest when the magnetization direction and the observation direction match and darkest when the magnetization direction is opposite.
When the magnetic film is viewed from above, when the observation direction is continuously changed by 360 °, the brightness of the magnetic domain changes as shown in FIG. 1B according to the angle θ formed by the observation direction and the magnetization. ..
Therefore, in actuality, the magnetization direction of each point can be specified by changing the observation direction and recording in the direction that becomes the brightest or the darkest at each point within the observation range.

As a concrete example, consider a case where a magnetization reversal region as shown in FIG. 2A is written in the in-plane magnetic recording medium by the ring head. This image is divided into minute parts by a computer as shown in FIG. 2 (b). Next, observation is performed while changing the observation direction by 45 °, and each image is captured in the computer. The magnetic domain images expected in each direction are shown in FIGS. The computer checks the brightness of the pixel within the divided minute portion. For each minute portion, the brightest direction is adjusted as the magnetization direction of the minute portion, or the darkest direction is adjusted as the opposite direction of the magnetization. As a result, FIG.
The magnetization direction can be measured as shown in (a). Considering the formation process of the magnetization region, the magnetic domain structure of FIG. 4B is estimated. A finer magnetic domain structure can be obtained by changing the roughness of division for forming a minute portion and the observation direction more finely.

[0013]

Embodiments of the present invention will now be described with reference to the drawings.

A block diagram of the magnetic domain structure analysis apparatus is shown in FIG. The light from the mercury lamp 1 is linearly deflected by the deflector 2 or becomes an elliptic polarization close to the linear deflection, and the prism 3
Is projected vertically downward by the objective lens 4, and is collected by the objective lens 4 from an oblique direction onto the measuring object 5, is incident, and is reflected. When the deflected light is reflected by the measuring object, the deflecting surface of the reflected light rotates according to the in-plane magnetization component of the measuring object. The reflected light passes vertically through the objective lens 4,
It is reflected in the horizontal direction by the prism 3 and passes through the analyzer 6. Since the analyzer 6 is displaced from the crossed Nicols position by the Kerr rotation angle with respect to the deflector, it produces a grayscale image according to the magnetic domain structure of the measurement target. This magnetic domain image is observed by the CCD camera 7.

An image processing device 8 is connected to the CCD camera 7. The image processing device 8 can have a very high sensitivity and can distinguish light and shade in an extremely narrow range. Further, it is also possible to eliminate unrelated background images by performing image enhancement by adding images and subtracting between images. A computer is connected to the image processing device 8 through the GP-IB, and the computer 9 can control the image processing device 8 or transfer images between them. The computer 9 also controls the drive system of the sample through the GP-IB.
In addition, 9 is an electromagnet, 10 is an electromagnet power source, 11 is a sample drive system, and 12 is a surface plate.

FIG. 6 is a perspective view of the drive system of the sample. The driving system of this sample can change the observation direction (the incident direction of light to the sample) by rotating around the observation point. In the present embodiment, it is possible to rotate from -90 to 540 ° in 0.1 ° steps. The rotation stage is the X stage, so that the center of rotation can be selected as the observation point.
It's on the Y stage. Further, there is an XY stage on the rotary stage so that an arbitrary point of the sample can be observed. The Z stage is for focusing the microscope, and its position may be above or below the rotary stage.

An example of observation of the soft magnetic thin film by this apparatus has a triangular circulating magnetic domain structure. However, the shading changes regardless of the uniform magnetic domain structure. This is because the illumination by the light source has a brightness distribution. The distribution of brightness by this light source is larger than the difference in light and shade due to the change in the magnetization direction. In order to obtain the magnetic domain structure from the light and shade of the magnetic domain image using a computer, it is necessary to correct the brightness distribution due to the light source. In this example, first, the brightness distribution was measured for a non-magnetic sample having a mirror surface, the brightness gradient was obtained from the average value in the X and Y directions, and the maximum value was used for normalization and correction.

Next, FIG. 7 shows a flow chart of the measurement procedure. First, a specular substrate (aluminum plate that has been subjected to NiP plating and specular polishing) is measured (1-1-2).
This is because a computer creates a table for correcting the brightness of the light source. Next, the measurement target is observed, and if there is a magnetic domain, the brightness of the brightest magnetic domain and the darkest magnetic domain is measured, and the change range of the brightness due to the difference in the magnetization direction is determined (1-1-3). When no magnetic domain is found, the brightness when the magnetic body is saturated in both directions with an electromagnet is measured, and the brightness change range is set. The reason for defining the range of change in brightness depending on the difference in the magnetization direction is that the brightness may change locally depending on the surface condition of the observation target such as a scratch, in addition to the change in brightness depending on the magnetization direction. This is because the points are excluded from the evaluation. Next, the angle dependence of the magnetic domain image of the recording medium is measured, and the magnetic domain image is taken into the computer (1-2). When measuring the angle dependency, when the sample is rotated, the observation point swings from the center of rotation, so the correction is performed using the X stage and the Y stage.

Next, data processing is performed. First, the brightness of each image is corrected using the measured brightness correction table (2-1-1). Next, rotate the image on the software, and rotate the sample by the rotation stage to restore the original state (2
-1-2). Next, the image is divided into small parts (2
-2). The average value of brightness is calculated in each minute portion (2-2-1). When calculating the average brightness,
Pixels outside the brightness range defined in (1-1-3) are not included in the calculation of the average value.

From this result, the magnetic domain structure of FIG. 8 is obtained.

In this embodiment, the states of the deflector and the analyzer were kept constant during the measurement in order to influence the density of the magnetic domain image. However, if a digital encoder is attached to the analyzer and the reproducibility of the angle setting is obtained, the analyzer is moved to both sides of the crossed Nicols position during measurement to take a difference image, and the background image not related to the magnetic domain is erased, and the magnetic domain image is removed. Can be emphasized.

Further, in this embodiment, a mercury lamp is used as a white light source in order to expand the range of application. However, when the surface flatness is good and the Kerr rotation angle is large, it is possible to more clearly observe the magnetic domain image by using the laser light source.

[0023]

【The invention's effect】 [Brief description of drawings]

FIG. 1 is an explanatory diagram of a principle of a vertical Kerr effect.

FIG. 2 is an explanatory diagram showing a magnetization reversal region.

FIG. 3 is an explanatory diagram in which a magnetic domain image observed by changing a direction is divided into minute regions and an average value of brightness is taken.

FIG. 4 is an explanatory diagram of a magnetic domain structure that can be determined from the brightness distribution shown in FIG.

FIG. 5 is a block diagram of a magnetic domain structure analysis apparatus.

FIG. 6 is a perspective view of a sample drive system.

FIG. 7 is a flowchart from measurement to determination of magnetic domain structure.

8 is an explanatory diagram of an example in which the angle dependence of a magnetic domain image is imaged by the soft magnetic film shown in FIG. 7, the brightness is analyzed by a computer, and the magnetic domain structure is determined.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuo Abe 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock Engineering Institute, Hitachi, Ltd.

Claims (5)

[Claims] 1. φ0.5 to 100 μm using the vertical Kerr effect
In the device for analyzing the magnetic domain structure of the region, the light deflected from the light source, passing through the deflector, the prism, and the objective lens is obliquely incident on the measurement target, which is a magnetic thin film, and is condensed. Then, the reflected light is guided to the image pickup device by the objective lens, the prism, and the analyzer, and the incident direction of the deflected light is freely set in the in-plane direction of the measurement target in the device for obtaining the magnetic domain image by image processing. A magnetic domain structure analyzing apparatus characterized by combining means capable of changing to. 2. The objective lens according to claim 1, wherein
The magnetic domain structure analysis apparatus has a magnification of 100 times and the imaging apparatus has a magnification of 1 to 15 times. 3. The image processing according to claim 1, wherein the image processing is capable of emphasizing the image by integrating the images, deleting the background image by subtracting the images, and storing the image captured by the image capturing apparatus. A calculator having a storage device is provided, and the calculator is used to divide the magnetic domain image into fine minute regions.
A magnetic domain structure analyzing apparatus for obtaining an average brightness of the micro area and comparing the brightness of the micro area with another magnetic domain image. 4. The magnetic domain structure analysis apparatus according to claim 1, wherein the computer can control means for freely changing the incident direction of the deflected light in the in-plane direction of the measurement target. 5. The magnetic domain structure analyzing apparatus according to claim 1, further comprising an electromagnet near the measurement target, the electromagnet magnetically saturating the measurement target.