JPH0240579A - Observing apparatus of domain - Google Patents

Abstract

PURPOSE:To solve the problem of a thermal effect on an observation sample by an external magnetic field impressing means and to make domain observation reliable and highly sensitive by providing a means to impress an external magnetic field on the sample. CONSTITUTION:In the case when a domain of a vertically magnetized film material is observed, for instance, a coil 14 of an external magnetic field impressing means 16 is electrified, a magnetic field is given vertically onto the surface of a sample 11 from the upper end of a center pole 13 so as to saturate the sample 11 once magnetically, and thereafter the impressed magnetic field is weakened slowly enough. On the occasion, a linear polarization from a light source element 1 is applied to the sample 11, which is picked up by a pickup camera 18 through an analyzer 17 based on a polarization plane modulation light subjected to a light-magnetism mutual action corresponding to the state of magnetization of the sample 11. Next, an output of said camera is inputted to an image processing device 19, amplified and subjected to a required signal processing, and thereafter a reflected optical image from the sample 11 is reproduced in an image casting device 20. By this constitution, the state of generation of the domain due to a change in the magnetic field impressed on the sample 11 can be observed in a real time in a direct view.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an observation device for observing magnetic domains of various magnetic materials including magnetic thin films such as perpendicular magnetic recording media and perpendicular magnetization films of magneto-optical recording media. Involved.

[Summary of the invention]

The present invention irradiates a magnetic domain observation sample with linearly polarized light, and uses optical-magnetic interaction and image processing in the magnetic domain observation sample to directly observe the magnetization state of the sample, that is, the magnetic domains, using a monitor image projection device. By applying an external magnetic field to the sample, the magnetic domain can be observed directly in real time, even if the sample has a small optical-magnetic interaction, by using a stationary core configuration. Provide observation equipment.

[Conventional technology]

Observation of magnetic domains is important in the development and research of magnetic materials such as various magnetic FJ legs and permanent magnets. For example, in order to analyze the recording state of a perpendicular magnetic recording medium or noise in a magneto-optical recording medium, it is easy and accurate to observe the magnetic domain state of the perpendicularly magnetized film material or the state of magnetic domain generation as recorded information bits. There is a high demand for being able to do this. In recent years, perpendicular magnetic domain observation devices using the polar Kerr effect and image processing have been developed for magnetic domain observation (e.g.
Ei l Lance Actions On Magnetics (TI+e In5titude of Ele
ctricaland Electronics En
gineers Transactions on Ma
genetics) Vol,? I^G-21, (19
85) PP1596-159B.

and the same magazine Vol. MAG-23, (1987) PP2
067 to 2069) In this way, based on the polar Kerr effect based on the magnetization state of the magnetic domain observation sample, that is, the rotation state of the polarization plane of linearly polarized light due to optical-magnetic interaction (in a magnetic domain observation apparatus that observes magnetic domains using optical images), teeth,
A method of observing magnetic domains by applying an external magnetic field to the observation sample to change the state of the sample's magnetic domains, and performing appropriate image processing on information based on this change and projecting it on an image projection device. is taken.

In this case, it is desirable that the external magnetic field applying means uses an electromagnet in order to vary the magnetic field applied to the sample. However, in this case, the effect of heat generated from the wire on the sample becomes a problem. If this external magnetic field applying means is moved away from the sample placement part in order to avoid the influence of heat generated from the coil, it becomes difficult to apply a large external magnetic field, which impedes reliable and highly sensitive magnetic domain observation.

[Problem to be solved by the invention]

The present invention, in which magnetic domains are observed by utilizing optical-magnetic interaction in a sample as described above, solves the problem of thermal effects caused by means for applying an external magnetic field to the sample, and also applies a sufficiently large external magnetic field. enable
To enable reliable and highly sensitive magnetic domain observation.

[Means to solve the problem]

As shown in FIG. 1, the present invention provides linearly polarized light source section 11).
, a magnetic domain observation sample placement section (12) in which the magnetic domain observation sample (11) is placed, and a center pole (13) whose end faces the magnetic domain observation sample placement section (12).
14), an external magnetic field applying means (16) for applying a DC +'FB magnetic field to the magnetic domain observation sample (11), and an analyzer (17). and,
It is equipped with an imaging camera (18), an image processing device (19), and a monitor image projection device (20). Then, the linearly polarized light from the light source section (1) is transferred to the magnetic domain observation sample (11).
To! (? A subsequent optical image is captured by an imaging camera (18), the captured image output is input to an image processing device (19), and a video based on the captured optical image is played back by a monitor image projection device (20). Magnetic Domain Observation Perform magnetic domain observation of the sample (11).

[Effect]

Magnetic domain observation using the above-mentioned apparatus of the present invention can be carried out, for example, on a perpendicular magnetic recording medium having information bits due to magnetic domains recorded by a magnetic head, or on samples with magneto-optical recording, such as bubble magnetic domains. It is possible to observe the magnetic domains of a sample having information bits, or to observe the magnetic domains of various magnetic samples including a perpendicularly magnetized film material before the formation of an IR information focus. For example, to explain the case where a perpendicularly magnetized film material is observed, in this case, the coil (14) of the external magnetic field application means (16) is energized, and the sample (11) is ) by applying a magnetic field perpendicular to the surface of the specimen (11) to magnetically saturate the sample (11), and from this state the applied magnetic field of the external magnetic field applying means (16) is sufficiently slowly weakened.

At this time, the linearly polarized light from the light source (11) is irradiated onto the magnetic domain observation sample (11), and the reflected light whose polarization plane has been rotated due to the Kerr effect generated according to the magnetization state of the sample (11) is transmitted to the analyzer ( The imaging camera takes an image through the camera (17), and the output from this is sent to the image processing device (19), which amplifies it and performs the necessary signal processing to output both images to the image processing device (20).
) to generate a reflected optical image from this sample (11). In this way, it is possible to directly observe, in real time, the manner in which magnetic domains are generated due to changes in the magnetic field applied to the sample (11), for example.

Alternatively, similarly, a large magnetic field is applied to the sample (11) to make it magnetically saturated, and in this state, an optical image as shown in FIG. 18) and stores it in the image processing device (19) as a reference image.

Next, the energizing power source of the magnetic field applying means (16) is controlled to observe the magnetic domains, and the applied magnetic field is reduced to the desired magnitude. In this state, the camera (18) captures an optical image, for example, shown in FIG. The memorized reference image is subtracted, and the subtracted image shown in FIG.
0) and observe the magnetic domains. In this way, for example, when there are polishing marks etc. on the sample (11), the so-called background noise caused by this can be eliminated by the subtraction operation, so that the sample (11) has a high S/N ratio and is made of a material with a low Kerr rotation ability. However, magnetic domain observation can be performed reliably and satisfactorily.

As described above, according to the apparatus of the present invention, a desired magnetic domain observation can be performed by applying a required external magnetic field to the sample (11) using the external magnetic field applying means (16). In this case, the external magnetic field applying means (16) has a stationary coil (15) having a center pole (13) around which a coil (14) is wound, so that a strong force is applied to the tip of the center pole (13). For example, a magnetic field of 1 OKOe can be generated, and the sample (]1)
It is possible to obtain the high magnetic field necessary to magnetically saturate the Regarding the strong magnetic field generated by this sensitive magnet, please refer to "Physics of Ferromagnetic Materials (Part 2)", published by Shokabo, written by Sonobu Chikazumi.
Since a strong magnetic field can be obtained as described on page 154, it is possible to apply a magnetic field sufficient to saturate the sample (11). In addition, since it is possible to apply a strong magnetic field in this way, it is possible to maintain a ζ gap between the sample placement section (12) and the external magnetic field application means (16) as necessary, thereby allowing this external It is possible to reduce the thermal influence on the sample (11) of heat generated by energizing the coil (14) of the magnetic field applying means (16).

〔Example〕

Linearly polarized light source yi++ (11 is, for example, as shown in FIG. 1, light tA (1) such as a 100 W ultra-high pressure mercury lamp, a Köhler lens (3), and a polarizer (4), for example, an extinction ratio of 10-5 or more. It consists of a calcite Grant-Thompson prism.

(5) shows the starting power source for the ultra-high pressure mercury lamp as the light source (1).

The external magnetic field applying means (16) has a pot-shaped configuration, as shown in FIG. 3 in a plan view and in FIG. 4 in a cross-sectional view taken along line A--A in FIG. 3. That is, they each have a center pole (13) with high magnetic permeability and a straight core (15).

In the figure of the center ball (13), the straight core (15) has a bottom plate part (15A) that is magnetically tightly coupled or integrated with the lower end thereof, and a bottom plate part (15A) that is concentric with the center pole (13) from its outer periphery. The peripheral wall part (15B) is arranged to extend upwardly, and the upper surface, the ti part (15C), which is magnetically closely coupled to the upper end and arranged opposite to the bottom plate part (15A).
). A through hole (15h) is bored in the center of the top plate (15C), and a circle 1 with a center hole (21a) is formed in the center of the center pole (13), which faces the upper end in the figure. A non-magnetic plate (21) made of, for example, non-magnetic metal SOS 304 is inserted.

In FIG. 1, (30) indicates an excitation power source for the external magnetic field applying means (16). Fluctuations in the magnetic field due to fluctuations in the current flowing to the wire ring (14) of the external magnetic field applying means (16), etc.
When observing submicron-order magnetic domains, it is desirable to suppress ζ to 3% or less.

This external magnetic field applying means (16) has a straight core with a radius of, for example, 731 mm. When the radius of the non-magnetic plate (21) is 25 mm and the voltage applied to the coil (14) is 0.21V, the generated magnetic field is 4 KOe, and when it is 0.43V, the generated magnetic field is 6.5K.
Oe.

You can get Oe at 9 when it is IV.

Furthermore, it is desirable that the external magnetic field applying means (16) be cooled by air cooling in order to avoid thermal effects on the sample (11) and the optical system even when used continuously for a long time.

The upper end of the center pole (13) is preferably formed into a conical shape, and the Vertier element (22) is disposed at this conical end.

As shown in FIG. 5, this Beltier element (22) has, for example, a cylindrical through-hole (22a), into which the conical upper end of the center pole (13) is inserted, in its center, and faces each other. A configuration may be adopted in which electrodes (231) and (232) are arranged on both main surfaces, one of which becomes a cold electrode and the other becomes a hot electrode, depending on the polarity of the applied voltage. And one electrode (231)
The side thereof is used as a magnetic domain observation sample placement part (12), and the magnetic domain observation sample (11) is placed on top of the center pole (13) so that it forms almost the same surface as the upper end surface of the center pole (13). .

Then, the side of the Vertier element (22) opposite to the sample placement portion (I2) is thermally connected to the center pole (13).

On the other hand, the fixing means (24) for fixing the magnetic domain observation sample (11)
) will be established. This fixing means (24) includes, for example, a pair of non-magnetic and low thermally conductive holding arms (24) made of aluminum, for example.
251) and (252). Each holding arm (25□)
and (252), for example, each outer end thereof has a sensitive core (1
5) Screw (261) and (26) on the upper surface (15C)
2), each inner end abutting on the side edge of the sample (11), directing the sample (11) towards the sample positioning part (12), i.e. in this example the Vertier element ( 22) and further toward the upper end surface of the center pole (13) and held.

In addition, as shown in FIG. 3, in the sample placement section (12), for example, a temperature detection element (27) such as a thermocouple of a digital thermometer (26) is placed as close as possible to or in contact with the magnetic domain observation sample (11). do. and digital temperature needle (26
) is input to the digital controller (28), and the Vertier element (22) electrodes (231) and (232)
The voltage applied to and the positive state are controlled, and the temperature of the sample mounting section (12) is controlled. This Bertier element (22
), the temperature of the mounting part (12) for the sample (11) can be variably controlled in the range of -15°C to +80°C.

On the other hand, as shown in Fig. 1, the magnetic domain observation sample arrangement section (12
) is provided with a polarizing microscope (29).

Is the analyzer (17) this polarized light microscope? It can be constituted by an analyzer in the intermediate tube of the ik mirror (29).

(31) is an objective lens, and this objective lens (31) is
For example, a lens with a magnification of 80x, 100x, etc. is used, but its numerical aperture N, A is relatively small, 0.8, such as the Nikon Ultra Long Working Distance Plan Acroart CFMPLa.
n ELJIυ (!i!! Akira name) can be used. In addition, the objective lens (31) has a magnification of 100 as described above.
With a lens of times N, ^, = 0.8, a glass correction ring (0
, 9 mm to 1.51 thick glass with refractive index correction) is used.

(32) indicates a reflective lighting device.

The imaging camera (18) may be, for example, a CCD solid-state imaging camera with a magnification of 17 times.

The image processing device (19) has a resolution of 640 x 480
It can be a high-speed image processing device with x60 bits, arithmetic functions, and a maximum integration of 256 frames.

The monitor image display device (20) may be configured with a cathode ray tube type television picture tube.

A video printer (33) is also provided, so that the image projected by the image projection device (20) can be printed as a so-called hard copy if necessary.

A light source section (1) of a magnetic domain observation device having the above-described configuration.

The external magnetic field applying means (16), the polarizing microscope (29) including the analyzer (17), the imaging camera (18), etc. are mounted on the vibration isolation table (
34) are placed on top of each other while maintaining a predetermined positional relationship with each other.

An example of magnetic domain observation using the above-described apparatus of the present invention will be explained.

Observation Example 1 The magnetic domain observation sample (11) in this case was a 5,000-meter thick (Coo, vv
Cro, 23) In the case of ss, vscoo, 2s IQ, this C.

The dependence of the magnetic domain structure of a Cr-based film on an external magnetic field was measured.

In this case, the sample temperature was set to room temperature. This sample (1
The vertical anisotropic magnetic field 11x obtained from the torque magnetometer in 1) is 5.51 JOe), and the vertical coercive force 11c (±) obtained from the VSM (vibrating sample type magnetization characteristic measuring device) is 430 (Oe). be. The observation procedure was as follows: First, the external magnetic field applying means (16) was excited to apply an external magnetic field of 10 KOe to the sample (11) to magnetically saturate the sample (11). In this state, it was observed using a microscope 5Ji (29), and the observed image was stored in a high-speed image processing device (19). Next, the current applied to the coil (14) of the external magnetic field applying means (16) is lowered sufficiently slowly to reduce the magnetic field applied to the sample (11), and the desired magnetic field is obtained, for example, the Kerr hysteresis loop shown in FIG. Each point A, B.

C, D, and E magnetic fields are set, and the image processing device (19) subtracts the previously stored observation image from each observation image of the sample (11) in the magnetic field, and further amplifies this to produce an image projection device. Observe this and print it on the printer (33).
Images observed under each observation magnetic field setting were printed using the following method.

In this case, as explained in FIG. 2, a clear magnetic domain observation image with bank ground noise eliminated was obtained.

1. In this observation, if the set value of the externally applied magnetic field changes, the observed magnetic domain also changes, and sometimes due to inertia, magnetization reversal may progress to an extreme degree. Therefore, in observation example ■, the external magnetic field is set to 10 Oe.
When the external magnetic field Hex is decreased from 10%
, 20%, and the results shown in Table 1 below were obtained.

Table 1 From the results of Table 1, as mentioned above, it is found that it is desirable to keep the external vL field fluctuation caused by the external magnetic field applying means (16) within 3%, which allows the straight core to have stable operation. It can be seen that a magnetic field applying means according to the above is used, and air cooling is also desired.

In addition, when an ultra-high pressure mercury lamp is used as the light source (2) of the light source section (1), its spectral characteristics have a spectral distribution not shown in FIG.
11) When Go-Cr n*, 490 nm
Koehler lenses (
By placing a filter before step 3), we were able to observe the magnetic domains more clearly.

This is thought to be due to the wavelength dependence of Co-Cr Iff on the Kerr rotation angle θ, where λ is the wavelength of the light source, and N and A are the numerical aperture of the objective lens (31).

Observation Example 2 In this case, as shown in FIG. 8, the magnetic domain observation sample (11) is a G d Tb F
A thin e-based magnetic crotch (43) is applied, and on top of this is a protective layer 11Q (44) made of silicon, which has been used for 1,500 times in history.
This is a magneto-optical disk having a structure in which information bits, ie, bubble magnetic domains, are formed, and this is what we are trying to observe. In this case, the objective lens (
31) used a magnification of 100 times and N,8,=0.8.

The observation was performed using the light source section (1) without applying an external magnetic field.
The polarized light is irradiated from the protective film (44), and the reflected light is imaged by an imaging camera (18) through an analyzer (8), and projected onto an image projection device for observation. At this time, by adjusting the optical axis setting of the analyzer (8), clear magnetic domain observation could be performed.

Observation Example 3 A glass substrate (birefringence double pass of 10 nm) was used as the substrate (41) of the magneto-optical disk, a signal was recorded, and the recorded information bits were observed using the same method as Observation Example 2. This was done from the substrate (4) side. Also, in this case, the objective lens (31) has a magnification of 40x, N, A, = 0.5,
A lens having a correction ring for correcting the refractive index of glass having a thickness of θ˜2 mm was used. In this case, we were able to clearly observe the magnetic domains.

Comparative Example 1 A polycarbonate group + Fi (double path of birefringence exceeds 20 nm) was used as the substrate (41) of a magneto-optical disk, a signal was recorded, and the recorded information bits were determined in the same manner as in Observation Example 3. . In this case, the observed image was so distorted that image processing magnetic domain observation could not be performed.

Observation Example 4 The same sample (11) as in Observation Example 2 was subjected to magnetic domain observation from the substrate (41) side using the same method, but in this observation example, the magnification was 100 as the objective lens (31).
times, N, A, = 0.8, glass correction ring (0.9 m
A lens with a diameter of 5 mm (m~1, which corrects the refractive index of 5 mm thick glass) was used. Clear observations were made in this case as well.

Comparative Example 2 As S.L. Shins (31), the magnification is 100 times, N
, 8, = 0.9 lens MP/an 100:
The same observation as in Observation Example 2 was carried out using the product name). In this case, the &11 detection of magnetic domains was unclear.

When N, A, is 0.9 as in Comparative Example 2, the observed image becomes unclear, but when N, A, = 0.8 as in Observation Examples 2 and 3, the magnification is 100. Clear magnetic domain observation is now possible with a 2x objective lens.

This is due to linearly polarized light, so lens distortion has a large effect, but with N, A, -0,8 lenses, distortion is less likely to occur. However, N,A, -0.8 is enough to hinder observation, so it is not necessary to use one with N,A, of less than 0.8.

In observation example 2 described above, the magnetic domain was observed from the side opposite to the base It (41), but in a general magneto-optical disk, the magnetic thin film (43) is observed from the side opposite to the substrate (4I). A reflective film such as A/% is provided, and recorded information bits are read from the substrate (41) side.
In magnetic domain observation, it is also desirable to observe from the group +M(41) side. In this case, the group ff1 (41) is the group [
In order to prevent observation of magnetic domains due to birefringence in 1i (41), it is made of a material with small birefringence, specifically, a double pass of 20 nm or less, such as a glass substrate.

Observation Example 5 A recording signal with a wavelength of 10 μm was used to record a trunk width of 26 μm using a fixed magnetic head on a perpendicular magnetic recording medium in which a 0.2 μm thick Co-Cr magnetic film was deposited on a molecular sieve film by DC magnetron sputtering. magnetic recording was performed. This magnetic recording medium was irradiated with polarized light from the light source (11) from the Co-Cr magnetic film side without applying an external magnetic field, and magnetic domains were observed using the procedure explained in Fig. 2m. In this case, the objective lens (31) has a magnification of 10
0, N, 8, = 0.8. In this case, we were able to clearly observe the magnetic domains.

Comparative Example 3 The analyzer (17) was fixed at the first rotational position for the sample in Observation Example 4, and no image processing was performed. In this case, no magnetic domains could be observed. This is Co-C
This is because the Kerr rotation angle of the r-magnetic) model is too small, so the contrast between brightness and darkness is small, and human vision cannot distinguish the inverted portion of the magnetic domains.

〔Effect of the invention〕

According to the apparatus of the present invention, by providing the external magnetic field applying means (16) for applying an external magnetic field to the magnetic domain observation sample (11), for example, as explained in FIG. It is possible to perform magnetic domain observation under the application of an external magnetic field, for example, magnetic domains can be observed under each desired magnetic field while background noise is eliminated by changing the magnetic field. In particular, in the present invention, since the external magnetic field applying means (16) has a magnetically closed electrotype core configuration, a large magnetic field can be efficiently generated from the center pole (13). Since it is possible to generate a large magnetic field up to ~10XOe, it is possible to reliably form a magnetic saturation state in the magnetic domain observation sample (II), and it is possible to reliably eliminate background noise. Accordingly, reliable magnetic domain observation can be performed even for the sample (11) made of a material with a small Kerr rotation angle. In addition, when the upper plate part (16) of the pot-shaped core is used as a non-magnetic plate (21) around the center pole (13),
Despite the path configuration, the magnetic field near the center pole (13) can be made into a magnetic field with a smaller horizontal component. When this was measured using a Hall element for measuring a minute area, it was confirmed that the horizontal component (in the direction perpendicular to the axis of the center pole (13)) was almost negligible compared to the vertical component.

In addition, a Vertier element (
22), it is possible to avoid increasing the size of the apparatus as would be the case if the entire apparatus is placed in a constant temperature bath, and it is also possible to keep only the target magnetic domain observation sample (11) at the required temperature. For example, it can be set at -15°C to 80°C, and for parts such as optical systems that do not like heating or cooling, magnetic domain observation can be performed at each temperature while avoiding heating or cooling. In addition, the center pole (1
3), heat is radiated through the center pole (13) or an effect of cooling the center pole (13) is obtained by thermally coupling it to the center pole (13), allowing for more thermally stable continuous magnetic domain observation. be able to.

In addition, in submicron-order magnetic domain observation, it is desirable to avoid movement of the sample (11) itself during magnetic domain observation, but as described above, when providing the fixing means (24), it is necessary to It is possible to avoid the inconvenience that the magnetism of the sample (11) moves due to the magnetic field fluctuation of the external magnetic field applying means (16), that is, the 71u magnet, and more stable magnetic domain observation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an example of the apparatus of the present invention, FIGS. 2A to C are explanatory diagrams of captured optical images in an example of magnetic domain observation, FIG. 3 is a top view of the magnetic field applying means, and FIG. Fig. 5 is a cross-sectional view of an example of the arrangement part of a Bertier element, Fig. 6 is a Kerr hysteresis loop diagram of an example of a magnetic domain observation sample, and Fig. 7 is a spectral distribution of an ultra-high pressure mercury lamp. 8 are cross-sectional views of an example of a magnetic domain observation sample. (1) is a linearly polarized light source section, (2) is a light source, (4) is a polarizer, (11) is a magnetic domain observation sample, (12) is a magnetic domain observation sample placement section, (13) is a center pole, (14) is a wire ring,
(15) is a straight core, (16) is an external magnetic field applying means, (
17) is an analyzer, (18) is an imaging camera, (19) is an image processing device, and (20) is a monitor image projection device.

Claims (1)

[Scope of Claims] A linearly polarized light source section, a magnetic domain observation sample placement section, a center pole whose end faces the magnetic domain observation sample placement section, and a pot-shaped core with a coil inside. The apparatus is equipped with means for applying a direct current external magnetic field to the magnetic domain observation sample, an analyzer, an imaging camera, an image processing device, and a monitor image projection device, and applies linearly polarized light from the light source to the magnetic domain observation sample. The imaging camera captures an optical image after passing through the analyzer based on the polarization plane modulated light that has undergone optical-magnetic interaction from the magnetic domain observation sample according to the magnetization state in the sample. A magnetic domain observation apparatus characterized in that an imaging output is input to an image processing apparatus, and a video based on the optical image is reproduced by the monitor image display apparatus to observe the magnetic domains of the magnetic domain observation sample.