JPH09218213A - Method and apparatus for observing considerably minute magnetic domain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dynamically observe a generating state of a magnetic domain and an inverting state of magnetization by observing a considerably small magnetic domain of a sample while a magnetic field is impressed. SOLUTION: A sample stage 21 where a sample 21 is placed is fixed on a piezoelectric element 23. A required external magnetic field is impressed to the sample 12 by a magnetic field-impressing means 20. Coils C1 , C2 of the magnetic field-impressing means 20 are connected to independent power sources S. A supplied current from the power sources is controlled, so that the required magnetic field is impressed to the sample 12. X-, Y-direction scan circuits 25, 26 connected to the piezoelectric element 23 are controlled directly by a microcomputer 29, and a Z-direction driving circuit 87 is controlled by the microcomputer 29 directly and via a feedback circuit 28. A probe 70 and a cantilever 73 scan above the sample 12 while being oscillated by a piezoelectric oscillator 74. At this time, a change of resonating conditions because of the mutual action of a leaking magnetic field by the magnetization of a surface of the sample 12 is detected as an amplitude change or phase change. A magnetic domain is observed in this manner while the magnetic field is impressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing an extremely small magnetic domain and an apparatus for observing an extremely small magnetic domain.

[0002]

2. Description of the Related Art With the increase in density of magnetic recording and miniaturization of various magnetic devices, a technique for observing extremely small magnetic domains on the order of several tens nm has become essential. In particular, a magnetic force microscope, so-called MFM, has been rapidly prevailing in recent years due to its resolution of less than 50 nm and the ease of preparing an observation sample.

There is also an example in which a magnetic force microscope is used not only for observing magnetic domains but also for observing magnetization reversal of single domain fine particles (M. Lederman et al., JAP75, 6217 (1994); T. Chang.
et al., JAP 73,6716 (1993).

[0004]

However, in the magnetic domain observation using the magnetic force microscope as described above, for example, in the observation of the magnetization process, the magnetization reversal process, etc., when an external magnetic field is applied, conventionally, Generally, the observation with a magnetic force microscope and the application of an external magnetic field are performed independently.Therefore, when performing such an observation, first move the probe of the magnetic force microscope away from the sample surface and then place it on the sample. The magnetic field of each intensity and direction is applied to change the magnetization state of the sample, and then the probe is moved closer to perform MFM observation. The procedure is complicated and the target portion on the sample There are great difficulties in making decisions.

Further, two general problems in the magnetic force microscope are how to improve the sensitivity and how to remove the influence of forces other than the magnetic force interaction, that is, noise. As a matter of course, these are major problems in observing the above-mentioned magnetization process, magnetization reversal process, and the like.

The present invention eliminates such an inconvenience.
Provided are an ultrafine magnetic domain observation method and an ultrafine magnetic domain observation device based on FM observation.

[0007]

In the ultrafine magnetic domain observation method according to the present invention, the magnetic force microscope M is attached to the surface of the sample to be observed.
An external magnetic field is applied to the sample with the FM probe facing each other, and the change in the magnetization of the extremely small magnetic domains on the sample surface due to this magnetization application is observed based on the principle of the magnetic force microscope MFM.

Further, in the ultrafine magnetic domain observation apparatus according to the present invention, the arrangement portion of the sample to be observed, the probe of the magnetic force microscope arranged so as to face the surface of the sample, and the probe in the state where the probe is arranged are arranged. An external magnetic field applying means for applying an external magnetic field to the sample is provided, and the microscopic magnetic domains on the sample surface are observed based on the principle of the magnetic force microscope.

Further, in the method and apparatus of the present invention, the observation as described above is performed while the space containing the probe of the magnetic force microscope and the sample is kept at a pressure lower than atmospheric pressure, that is, under a reduced pressure atmosphere.

In the present invention, when performing ultra-fine magnetic domain observation by MFM by the above-described method and apparatus,
While applying a magnetic field to the sample to be observed, or after applying the magnetic field, the sample to be observed is left as it is, that is, the sample to be observed is moved to another place or the probe is removed without performing the above-mentioned operation. This is done by observing the magnetic force microscope tip after moving it away from the sample surface, applying a magnetic field of each strength and direction to the sample, and then changing the magnetization state of the sample. , The complicated procedure in the conventional method of bringing the probe close again to perform the MFM observation can be avoided, and in particular, the observation of a target portion on the sample can be accurately performed, and therefore, in the external magnetic field applied state or after the external magnetic field application. It is possible to accurately observe extremely small magnetic domains.

Further, as described above, the sensitivity is remarkably improved by performing the above-mentioned observation while keeping the space containing the probe of the magnetic force microscope and the sample at a pressure lower than atmospheric pressure, that is, under a reduced pressure atmosphere. You can measure. This is because the resonance peak in the forced vibration of the probe becomes steep due to the decrease in air resistance. Also, by observing in a decompressed atmosphere, it is possible to eliminate the noise called "air damping" out of the noise other than magnetic force interaction, that is, the effect of the resistance that the probe receives from the surrounding atmosphere. is there.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method and apparatus of the present invention will be described. The present invention basically adopts a method based on MFM observation, but in this observation, an external magnetic field is applied.

FIG. 1 is a block diagram showing an example of the device of the present invention. In this apparatus, a sample 12 to be observed as intended, for example, a magnetic substance for various memory elements, a sample constituting a magnetic recording medium, a magneto-optical medium, or the like is arranged on a piezoelectric element having a cylindrical shape, such as a piezo element 23. The sample stage 21 to be fixed is fixed.

In particular, in the apparatus of the present invention, the magnetic field applying means 20 for applying a required external magnetic field to the sample 12 arranged on the sample stage 21 is arranged. In this magnetic field applying means 20, for example, a pair of coils C ₁ and C ₂ for generating a magnetic field by energization, for example, each axial center of which is a cylindrical piezo element 23, is shown in FIG. It is arranged so as to be orthogonal to the axis O and to face each other with the piezo element 23 interposed therebetween. These coils C ₁ and C ₂ are connected to a common or independent power source S, and the required magnetic field is applied to the sample 1 by controlling the energizing current.

In this magnetic field applying means 20, the sample 12
To be able to change the direction of the magnetic field with respect to. As a method of changing the direction of the magnetic field in this manner, for example, the coils C ₁ and C ₂ may be configured to rotate in a state of facing each other around the axis O of the piezo element 23, or By reversing the direction of the current flowing through the coils C ₁ and C ₂ , the direction of the magnetic field can be reversed by 180 °, for example.

Further, the external magnetic field applying means 20 is, for example,
For example, as shown in the schematic diagram of FIG.₁
And C_Two However, for example, each axis is a cylindrical piezo element 2
The piezo element 23 is sandwiched so as to be parallel to the axis O of 3
Therefore, they can be arranged so as to face each other. Shown in Figure 3
In the example, one coil is attached to the outer circumference of the piezo element 23.
This is the case when it is arranged, but it is arranged outside the piezo element 23.
And these coils C ₁And C_Two , For example, piezo element
A state in which they are opposed to each other around an axis orthogonal to the axis O of the child 23.
The magnetic field applied to the sample 12 is configured so as to rotate in a stationary state.
You can also change the orientation.

The magnetic field applying means 20 described above can easily apply a magnetic field of, for example, several T (tesla) to the sample 12, for example.

On the other hand, a probe 70 is arranged facing the sample 12 in the vertical direction. The probe 70 is integrally provided at the tip of the cantilever 73, and the rear end of the cantilever 73 is fixed to the base 74 a of the piezoelectric vibrator 74.

The cantilever 73 is made of, for example, Si together with the probe 70 arranged at the tip of the cantilever 73, and its surface is coated with a sputtering film of, for example, Co--Cr having a high coercive force.

The piezo vibrator 74 vibrates the cantilever 73 in the vertical direction by a frequency synthesizer 86 driven by a microcomputer. Along with this, the probe 70 vibrates and hits the surface of the sample 12. That is, in this example, the tapping mode is set.

The amplitude of the vertical vibration of the probe 70 is measured by irradiating the upper portion of the cantilever 73 on the probe 70 with the laser beam L ₁ and the change in the reflected light L ₂ . The laser L ₁ is emitted from the laser light source 81, is focused on both surfaces of the cantilever 73 by the lens 82, and its reflected light L ₂
Enters a photodetector 83 such as a two-divided diode and is converted into an analog electric signal. Then, this analog electric signal is input to the RMS detector 85A.

The RMS detector 85A is a device for comparing the RMS (root-mean-square) of the vibration amplitude (displacement) of the probe 70 with a desired amplitude set value, and the RMS detector 85A-micro A / D converter 8 between the computers 29
5B is arranged, converted into a digital signal here, and input to the microcomputer 29.

The inner peripheral edge and the outer peripheral edge of the piezo element 23 in the X direction in one direction orthogonal to the axis O are connected to the X direction scanning circuit 25, and the inner peripheral edge in the Y direction orthogonal to the axis O and the Y direction. The outer peripheral edge is connected to the Y-direction scanning circuit 26 and is parallel to the axis 0, that is, the Z direction (vertical direction) orthogonal to the X and Y directions.
The upper and lower ends are connected to the Z-direction drive circuit 87. Two sets of connection ends of the piezo element 23 to each circuit in the X direction, the Y direction, and the Z direction are provided at symmetrical positions, but only one set is shown in the drawing.

The X-direction scanning circuit 25 and the Y-direction scanning circuit 26 are connected to the microcomputer 29, and the Z-direction driving circuit 87 is connected to the microcomputer 29 directly and via the feedback circuit 28.

The probe 70 vibrates in the Z direction at a constant frequency (near the resonance frequency of the cantilever 73 (about 70 kHz in this example)) by the piezoelectric vibrator 74. At this time, before the tip of the probe 70 reaches the lowest point of vibration, the sample 1
2 to collide with the surface. The amplitude of the vibration of the probe 70 is attenuated by this collision, and this attenuation amount can be measured by the photodetector 83.

This information is fed back to the Z-direction drive circuit 87, and the Z-direction drive circuit 87 drives the piezo element 23 so that the attenuation amount of the amplitude of the probe 70 becomes constant, and the position of the sample 12 in the Z-direction. To control. At the same time, the X-direction scanning circuit 25 and the Y-direction scanning circuit 26 are driven to scan the sample 12 in the X and Y directions. Based on these X, Y and Z axis control signals, a three-dimensional shape image of the surface of the sample 12 is displayed on the cathode ray tube CRT 30A and the printer 30.
You can draw on B.

Next, the cantilever 73 is moved away from the sample 12 by a certain distance, and then the feedback circuit 2
Cut 8 and scan the same trajectory as the image obtained by the above method. As a result, the influence of the shape of the sample 12 is M
It is possible to prevent mixing in the FM image. The probe 70 and the cantilever 73 scan the sky above the sample 12 while vibrating, and at this time, the resonance condition changes due to the interaction with the leakage magnetic field due to the magnetization of the surface of the sample 12. Magnetic domain observation is performed by detecting this change as a change in amplitude or phase.

In this way, the magnetic domains on the surface of the sample 12 are observed. In this observation, first, the magnetic field applying means 20 does not apply a magnetic field to the sample 12, that is, the coils C ₁ and C ₂ are not energized, and then the coil C of the magnetic field applying means 20 is observed. A magnetic field having a required orientation and magnitude is applied to the sample 12 by applying a required amount of electricity from the power source S to ₁ and C ₂ , or after applying a magnetic field having a required orientation and magnitude to the sample 12. This magnetic field application is stopped, and thereafter, the magnetization state of the surface of the sample 12 is observed by the same operation as described above.

According to the apparatus and method of the present invention, it is possible to observe an extremely small magnetic domain of the sample 12. Particularly, according to the present invention, the observation of the magnetic domain is performed under the application of a magnetic field. Not only the magnetic domain observation but also the so-called dynamic observation of the magnetic domain generation state and the magnetization reversal state can be performed. Further, not only the dynamic observation but also the change before and after the magnetic field is applied to the sample 12 can be statically observed.
In this observation, the magnetic field applying means 20 is arranged in the arrangement part of the piezo element 23 in the magnetic force microscope MFM configuration to apply the magnetic field to the sample 12, so that the sample 12 is moved to another part for applying the magnetic field. Since it is possible to avoid the work of removing the probe 70, that is, the cantilever 73 and applying the magnetic field, not only the work and the handling are simplified,
After applying the magnetic field to the sample 12, it is possible to perform accurate observation, that is, to observe the MFM image, by eliminating the need to set the position of the probe 70 again at the target portion on the sample 12. It is possible.

Further, in the present invention, the magnetic field applying means 20
By recording the above-mentioned change in the contrast of the MFM image while continuously changing the current passed through the coil, it is possible to have a function as a magnetometer with extremely high sensitivity. And by using this, for example, several hundred nm
It is possible to obtain a magnetization curve of an isolated magnetic fine particle such as a minute region.

When the applied magnetic field can be rotated as described above, the function as an extremely highly sensitive magnetic anisotropy evaluation apparatus can be obtained by observing the change of the MFM image in each direction. it can.

In the above-described structure, by setting the magnitude and direction of magnetization of the probe 70, that is, the cantilever 73 in advance, the magnetization state of the probe 70 is changed by the external magnetic field by the magnetic field applying means 20 or the like. To avoid.

Further, by increasing the coercive force of the probe 70, it is possible to avoid the influence of the external magnetic field by the magnetic field applying means 20 or the like, so that extremely small magnetic domain observation can be performed without causing any error or malfunction. In addition, the strength of the magnetic field applied by the magnetic field applying means 20 can be increased to a necessary and sufficient level.

Alternatively, in comparison with the coercive force of the sample 12, the probe 7
By selecting a large coercive force of 0, it is possible to observe the magnetization of the sample 12 without any inconvenience even if the applied magnetic field causes a change in the magnetization of the probe.

As described above, according to the present invention, the observation of extremely small magnetic domains based on the magnetic force microscope MFM is performed.
Because you can observe it while applying a magnetic field,
In the isolated fine particles, it is possible to determine the magnetic properties of the fine particles, that is, ferromagnetism, superparamagnetism, or paramagnetism, using the response to the magnetic field as a criterion.

FIG. 4 shows an apparatus for performing the magnetic force microscope observation in the magnetic field as described above with reference to FIGS. 1 and 2 under a reduced pressure atmosphere, including a probe and a sample. The space or the entire microscope apparatus is covered with a decompression container 90 made of, for example, stainless steel. The evacuation of the decompression container 90 is performed by the vacuum pump P, and the degree of vacuum is monitored by the vacuum gauge G. F is MFM
Is a feedthrough for connection with the controller section of.
In FIG. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals and duplicate description will be omitted.

In this way, the reduced pressure atmosphere can improve the sensitivity. Next, the principle of increasing the sensitivity of the magnetic force microscope in such a reduced pressure atmosphere will be described. As a method of observing a magnetic force microscope, it is common to use a dynamic mode, that is, a method in which the cantilever 73 is forcibly vibrated near its resonance frequency and a change in the resonance frequency due to an external force is detected.

FIG. 5 shows a typical resonance curve of this cantilever with a solid curve. At this time, the amplitude a _O of the photodetector 8 is measured while forcibly vibrating at the frequency ω.
3 to detect. When an external force such as a magnetic dipole interaction acts on the resonance frequency, the resonance frequency changes like the curve shown by the broken line in FIG.
Changes to ₁ . This can be detected by the photodetector 83 again, the change in the resonance frequency can be known from the gradient of the resonance peak, and the change in the magnetic force, that is, the derivative of the magnetic force can be known by solving the equation of motion of the cantilever.

In the dynamic mode, the one that dominates the measurement sensitivity is the gradient of the resonance peak of the cantilever. If this absolute value is large, even a slight magnetic force gradient can be detected as a large amplitude change. That is, the measurement sensitivity can be improved. By the way, this gradient has a positive correlation with the Q value (Q = resonance frequency / half-width of resonance peak). Here, the equation of motion of the cantilever can be expressed as the following (Equation 1).

[0040]

[Number 1] ^{(∂ 2 z / ∂t 2)} + κ (∂z / ∂t) + ω 0 2 z = F 0 cos (ω c t) / m (1) where, omega ₀ resonance frequency, m is the cantilever Mass of, ω
_c is the forced vibration frequency.

The expression (1) includes a term of frictional force or resistance force, and when the Q value is expressed by using the coefficient κ related to this term, Q = ω ₀ / 2κ is obtained. That is, the Q value can be increased by lowering the atmospheric pressure near the cantilever and decreasing the resistance, and therefore the measurement sensitivity, that is, the detection sensitivity is increased.

In FIG. 6, a curve 6a shows a resonance curve obtained in the atmosphere, and a curve 6b in the figure shows a resonance curve obtained by using the same cantilever under a reduced pressure atmosphere of 500 mTorr. As is clear from these curves, the Q value increases about 50 times.

In the magnetic force microscope, noise other than the magnetic force interaction has a resistance called "air damping", that is, a resistance that the probe receives from the surrounding atmosphere. In particular, in a place where the surface has large irregularities, the movement of the atmosphere becomes complicated, so that the resulting contrast is often superimposed on the magnetic force microscope image. However, this effect can also be solved by vibrating the cantilever in a reduced pressure atmosphere to reduce the resistance that is the source of air damping. For example, it is an effective method for observing magnetic fine particles (fine projections on a plane) which are considered to be greatly affected by air damping.

An example of observing the magnetic fine particles will be shown. Figure 7
Is a photograph of an image of the magnetic fine particles on a display by an atomic force microscope. In this case, the height is 60 nm and the diameter is 3
Two spots are observed in the observation photograph of two particles of 00 nm. On the other hand, in the magnetic force microscope apparatus according to the present invention, under the reduced pressure of 500 mTorr which is lower than the atmospheric pressure,
As shown in A, when a magnetic field in a fixed direction was applied to the probe 70 to observe the magnetic fine particles, the image of FIG. 8B was obtained. As shown in FIG. 9A, when a magnetic field in the opposite direction to that of FIG. 8 was applied to the probe 70 to observe the magnetic fine particles, the image of FIG. 9B was obtained. As shown in FIGS. 8B and 9B, light and dark are observed corresponding to the two spots, and as is clear by comparing FIGS. 8B and 9B, the light and dark are reversed in both images. It can be seen that the magnetization direction is reversed. By the way, in this example, when the same measurement was performed under atmospheric pressure, the results shown in FIGS. 8B and 9B were obtained.
It was not possible to obtain a clear image as seen in. In contrast to this, in FIGS. 8 and 9, the excellent magnetization reversal images could be observed because the influence of forces other than the magnetic force was removed by the reduced pressure.

Further, FIG. 10 shows the atmospheric pressure and 500 mTo.
Observation is performed under a reduced pressure of rr, and the "force derivative", that is, the force gradient with respect to the signal and noise calculated from the contrast is shown. This signal was calculated for the clear contrast near the spot of the observed image, and the noise was calculated from the background around the spot. Here, under the reduced pressure, there is a decrease in the signal level, which is due to the removal of air damping.
At the same time, since the noise is further reduced, it can be seen that the S / N and the detection sensitivity are greatly improved under the reduced pressure as compared with the case under the atmospheric pressure.

Further, as described above, when performing observation in a reduced pressure atmosphere, there is an advantage that contamination such as oxidation during observation of the observation sample can be avoided.

The observation in the dynamic mode described above can be performed by a method of detecting not only the change of the vibration amplitude due to the change of the resonance frequency but also the change of the vibration phase.

In the example shown in FIG. 4, the external magnetic field is applied.
Means, coil C in the example above₁And C_Two To
This is the case where the external magnetic field is placed outside the decompression container 90.
Applying means, namely coil C₁And C_Two A vacuum container
It can also be placed within 90. That is, the above-mentioned magnetic domains
When applying a pulsed magnetic field for a short time prior to observation
When the decompression container 90 has conductivity, it is
The magnetic field shielding effect is generated by the induced current due to the applied field.
Therefore, especially in this case, the magnetic field is effectively applied to the sample.
External magnetic field applying means in the decompression container 90 so that
For example coil C ₁And C_Two Want to place
Yes. In addition, the external magnetic field applying means generates a strong magnetic field.
A coil C for generating a magnetic field so that it can be generated₁You
And C_Two It is also possible to have a structure in which the magnetic core is arranged.
However, the present invention is not limited to the above embodiment,
Various modifications can be made.

[0049]

As described above, according to the present invention, the observation of the microscopic magnetic domain of the sample to be observed is performed under the application of a magnetic field, so that not only the magnetic domain observation but also the magnetic domain generation state and the magnetization reversal state Observations can be made. In addition to such dynamic observation, it is possible to statically observe changes before and after applying a magnetic field to the sample. In this observation, the magnetic field applying means is arranged in the arrangement part of the piezo element in the magnetic force microscope MFM configuration to apply the magnetic field to the sample, so that the sample is moved to another part for applying the magnetic field,
Since it is possible to avoid the work of removing the probe, that is, the cantilever and applying the magnetic field, not only the work is simplified and the handling is simplified, but also the magnetic field is applied to the sample and then the target is set on the sample 12. By eliminating the need to set the position of the probe again on the part, accurate observation becomes possible.

Further, in this observation, the S / N and the detection sensitivity can be improved and the contamination of the sample can be effectively avoided by conducting the observation under reduced pressure below the atmosphere.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an example of an extremely small magnetic domain observation apparatus according to the present invention.

FIG. 2 is a perspective view of an essential part showing an example of a magnetic field applying means of the device of the present invention.

FIG. 3 is a perspective view of an essential part showing another example of the magnetic field applying means of the device of the present invention.

FIG. 4 is a configuration diagram of an example of an extremely small magnetic domain observation apparatus according to the present invention.

FIG. 5 is a resonance curve diagram of a cantilever in an ultra-small magnetic domain observation apparatus.

FIG. 6 is a resonance curve diagram of a cantilever in the ultra-small magnetic domain observation apparatus according to the present invention.

FIG. 7 is a halftone image displayed on the display of an atomic force microscope of cobalt fine particles.

FIG. 8 is a halftone image displayed on the display of a magnetic force microscope of cobalt fine particles after setting the magnetization direction of the probe to one direction.

9 is a halftone image displayed on the display of a magnetic force microscope of cobalt fine particles after the direction of magnetization of the probe was set to one direction opposite to the case of FIG. 8.

FIG. 10 is a diagram showing a force gradient related to a signal and noise in the atmosphere and under reduced pressure.

[Explanation of symbols]

12 sample, 20 magnetic field applying means, 21 sample stage, C ₁ and C ₂ coils, 23 piezo element, 70 probe, 73 cantilever, 90 decompression container, P vacuum pump, G vacuum gauge

Claims (10)

[Claims] 1. An external magnetic field is applied to the sample with a probe of a magnetic force microscope facing the surface of the sample to be observed, and a change in magnetization of an extremely small magnetic domain on the sample surface due to the application of the external magnetic field is changed. A method for observing extremely small magnetic domains, characterized by observing based on the principle of a force microscope. 2. An arrangement part for a sample to be observed, a probe of a magnetic force microscope arranged so as to face the surface of the sample, and an external magnetic field applied to the sample with the probe arranged. An ultrafine magnetic domain observation apparatus comprising: a magnetic field applying means for observing the ultrafine magnetic domains on the surface of the sample based on the principle of a magnetic force microscope. 3. The strength of the external magnetic field with respect to the sample,
2. The method for observing a very small magnetic domain according to claim 1, wherein at least one of the directions is changed, and a change process of the magnitude of the magnetization accompanied with the change is observed. 4. The high-sensitivity magnetometer is characterized by changing the intensity of the external magnetic field with respect to the sample and recording the change in the magnitude of the magnetization associated with the change.
The method for observing extremely small magnetic domains according to. 5. The device according to claim 2, which functions as a high-sensitivity magnetic anisotropy evaluation apparatus that changes the direction of the external magnetic field with respect to the sample and records the change in the magnitude of the magnetization accompanying it. Ultra-small magnetic domain observation device. 6. The magnitude and direction of magnetization of the probe are set in advance, and the external magnetic field is applied so as not to change the magnetization state of the probe.
The ultra-small magnetic domain observation apparatus described in [3]. 7. The ultra-small magnetic domain observation apparatus according to claim 2, wherein the probe has a high coercive force so that the applied magnetic field can be selected largely. 8. The magnetization of the sample can be observed even when the coercive force of the probe and the sample are made different so that the magnetization of the probe changes due to the applied magnetic field. The ultra-small magnetic domain observation apparatus described in [3]. 9. The microscopic domain observation according to claim 1, wherein observation is performed while a space containing the probe and the sample is kept at a pressure lower than atmospheric pressure and a magnetic field is applied. Method. 10. The observation of an extremely small magnetic domain according to claim 2, wherein observation is performed while a space containing the probe and the sample is kept at a pressure lower than atmospheric pressure and a magnetic field is applied. apparatus.