JPH07311251A - Surface magnetism microscope - Google Patents

Abstract

PURPOSE:To provide a surface magnetism microscope which can detect the magnetic flux distribution of a sample surface with high resolution separately from the uneveness in formation of the sample, and locally measure physical characteristics such as permeability, resistivity, etc., of the sample. CONSTITUTION:A modulation magnetic field of a high frequency is applied to a sample 2 by a solenoid coil 5. An eddy current induced in the surface of the sample 2 by a magnetic flux 6 penetrating the sample 2 is detected by the probe 1 of a scanning type tunnel microscope, etc., separately from the unevenness information of the surface by a frequency, and the magnetic flux distribution of the surface of the sample 2 is measured with high resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope, and more particularly to a surface magnetic microscope for detecting magnetic characteristics of a sample surface with high resolution.

[0002]

2. Description of the Related Art Conventionally, electron microscopes such as a Lorentz microscope have been widely used as means for obtaining magnetic information on the surface of a sample. On the other hand, recently, a scanning magnetic force microscope based on an atomic force microscope having high spatial resolution has been developed. This is to obtain magnetic information on the sample surface by using a magnetic probe at the tip of the cantilever. For details, see, for example, Applied Physics Letters, Vol. 52 (1988).
Pp. 244-246 (Appl. Phys. Lett., 52 (198
8) pp.244-246). When a probe made of a magnetic material is brought close to the surface of a magnetic material as a sample, an atomic force and a magnetic force act between the probe and the surface of the sample. For example, magnetization information of the sample surface can be obtained by scanning the cantilever on the sample surface while controlling the position of the cantilever so that the displacement of the cantilever due to this force becomes constant. However, as described above, the displacement of the cantilever is caused not only by the magnetic force but also by the interatomic force, etc., so it was difficult to separate and detect only the magnetic information. Therefore, various ideas have been made so far. For example, since the magnetic force is a long-range force as compared with the atomic force, the magnetic force is efficiently detected by controlling the cantilever at a position away from the sample surface. As another method, an attempt to separate an atomic force and a magnetic force by vibrating a cantilever has been reported in Ultramicroscopy, Vol. 42-44 (1992) pp. 315-320.
Page (Ultramicroscopy, 42-44 (1992) pp.315-320).

[0003]

However, in the conventional scanning magnetic force microscope as described above, various attempts have been made to detect the magnetic force and the atomic force by separating them. Even with this method, there is no change in trying to detect the magnetic force from the displacement amount of the cantilever. Therefore, it is difficult to completely separate the atomic force and the magnetic force. When the cantilever is controlled away from the sample and only the magnetic force, which is a long-range force compared to the atomic force, is to be detected, the distance from the sample surface increases, and the surface resolution deteriorates. There was a problem of doing. Furthermore, since the magnetic force is a long-distance force as described above, the magnetic force does not act only between the closest sample surfaces at the tip of the probe, so even if the cantilever is located very close to the sample surface. Even with control, there was a limit to the improvement in resolution. Further, in the conventional means, a so-called leakage magnetic field from the sample, which is formed by the magnetization of the sample, is detected. Therefore, since it is difficult to obtain a detailed magnetization distribution on the sample surface from the leakage magnetic field and the resolution is limited, it is impossible to measure physical quantities such as local magnetic permeability and magnetic flux density of the sample. It was

The present invention has been made in order to solve the above-mentioned problems. The magnetic information on the sample surface can be detected separately from the unevenness information on the surface, and the magnetic flux distribution on the sample surface can be detected with high resolution. Therefore, it is an object of the present invention to provide a surface magnetic microscope capable of locally measuring physical properties such as magnetic permeability and resistivity of a sample surface.

[0005]

In order to achieve this object, in the present invention, a eddy current flowing around a magnetic flux induced on the surface of a sample is applied by applying a modulation magnetic field to the sample,
Detect using a scanning probe microscope. At this time, the modulation magnetic field is applied by, for example, an electromagnetic coil installed near the sample. Further, this sample and the main part of the scanning probe microscope are installed in the objective lens of the electron microscope to observe an image of the sample surface and obtain magnetic information of the sample surface. At this time, the objective lens of the electron microscope can be used as a device for applying the modulation magnetic field.

Further, as the above-mentioned means for applying the modulation magnetic field,
Separately, a magnetic probe is used, for example, the current of the coil applied to the probe is modulated, and the modulation magnetic field is concentratedly applied to a specific region of the sample. Alternatively, the modulation magnetic field is applied to a specific portion of the sample by scanning the magnetic probe near the sample.

From the distribution of the eddy current detected,
The magnetic flux distribution on the sample surface is measured, and the physical characteristics such as local permeability and resistivity of the sample surface are measured from the magnitude and distribution of the eddy current.

It is also possible to form a metal thin film on the surface of the sample and detect the eddy current flowing therein. At this time, if the metal thin film has an island structure, the magnetic flux can be efficiently detected. .

[0009]

In the process of finding the present invention, it was found that eddy currents are locally generated around each magnetic flux. Therefore, the position of each magnetic flux can be detected by measuring the eddy current, and thus, the physical quantity such as magnetic permeability can be measured in an extremely small area.

It is generally known that when a sample is in a superconducting state, the magnetic flux is quantized and discretely exists. On the other hand, it was thought that the magnetic flux was continuously distributed in the normal conduction state. However, in the process of finding the present invention, it was found that the minimum unit magnetic flux exists discretely even in the normal conduction state. The minimum unit magnetic flux in the normal conduction state is different from the magnetic flux quantum in the superconducting state. Therefore, the above-mentioned magnetic fluxes are the magnetic flux quanta in the superconducting state and the minimum unit magnetic flux found in the present invention in the normal conducting state. An eddy current flows around these magnetic fluxes.

By the way, when the eddy current flows on the surface of the sample in this way, the electron density at the location locally increases, so that, for example, when a scanning tunneling microscope is used, the tunnel current flowing through the probe increases. . As a result, the place where the eddy current is generated, that is, the presence of the magnetic flux can be detected. Since this eddy current is a function of the modulation frequency of the magnetic flux, the resistivity and the magnetic permeability of the sample, the physical properties such as the magnetic permeability and the resistivity of the sample can be determined from the magnitude and distribution of the eddy current flowing on the sample surface. It can be measured locally.

By installing and combining such a surface magnetic microscope in the objective lens of an electron microscope, it is possible to observe an image of the sample surface and confirm the probe position, and
The magnetic characteristics of the sample at that location can be detected in association with each other. At this time, the above-mentioned objective lens can also be used as a modulating magnetic field applying means.

When a magnetic probe is used as a method of applying a modulating magnetic field to a sample, a strong magnetic field can be locally and intensively applied to the sample, so that the magnetic characteristics of the sample can be efficiently detected. .

On the other hand, since the magnitude of the eddy current is inversely proportional to the resistivity of the sample, if the sample has a high insulating property, a metal thin film may be formed on the surface of the sample and the eddy current flowing therethrough may be detected. At this time, if the metal thin film has an island structure, no current flows between the separated island structures, and a closed-loop eddy current flows in each island structure. Therefore, when the magnetic flux penetrates the island structure, the eddy current flows only in the island structure, and the smaller the island structure, the more accurately the magnetic flux can be positioned.

[0015]

【Example】

(Embodiment 1) FIG. 1 shows an apparatus configuration diagram of an embodiment of a surface magnetic microscope according to the present invention.

First, when the metal probe 1 having a sharp tip is brought close to the surface of the sample 2 and a voltage is applied between them, a tunnel current flows. The probe scanner 4 is controlled by the control system 3 so that the tunnel current I becomes constant. Further, by scanning the surface of the sample 2 with the probe 1, it is possible to obtain information on the unevenness of the surface of the sample 2. The above is the same as the method of observing the sample surface with a normal scanning tunneling microscope. In the present invention, the electromagnetic coil 5 further
Apply a magnetic field to the sample. Then, the magnetic flux 6 penetrates the sample 2. When the AC signal generator 7 modulates the current flowing through the electromagnetic coil 5, the formed magnetic field is modulated. That is, since the magnetic flux 6 penetrating the sample 2 changes, an eddy current is generated on the surface of the sample 2. This eddy current is generated around the magnetic flux 6 in synchronization with the modulation of the magnetic field. Then, when the eddy current is generated, the electron density locally increases, so that, for example, if the height of the probe 1 from the surface of the sample 2 is constant, the tunnel current increases. Since the eddy current is generated in synchronization with the modulation of the magnetic field, the component of the tunnel current I synchronized with the modulation of the magnetic field is detected by the detector 8,
Of the tunnel current, only the eddy current component can be detected. If the magnetic field is modulated at a frequency higher than the response frequency of the control system 3, the probe 1 follows only the surface irregularities, and the eddy current component can be measured separately. Then, the shape of the surface of the sample 2 and the distribution of the magnetic flux due to the modulation magnetic field are simultaneously known from the surface unevenness image 9 formed by the control signal of the probe scanner 4 and the eddy current image 10 obtained by the above method. You can

FIG. 2 is a schematic diagram of magnetic fluxes 12 to 15 penetrating the sample 11 and eddy currents 16 to 19 induced on the sample surface. When the magnetic fluxes 12 to 15 penetrate the sample 11, eddy currents 16 to 19 are induced on the surface of the sample 11 in order to cancel the magnetic flux. The eddy currents 16 to 19 are generated in synchronization with the magnetic field modulation as described above. Conventionally, it was thought that the eddy current flows so as to surround the modulating magnetic flux group 20, as shown in FIG. However, in the process of finding the present invention, it was found that an eddy current is generated around each magnetic flux. In other words, there is one magnetic flux at the center of the eddy current.
Therefore, for example, the magnetic flux distribution on the sample surface can be known by detecting the eddy current by the method described in FIG.

FIG. 4 is a sectional view of an eddy current detected by this embodiment. In the figure, two eddy currents 21 and 22 are detected. From this eddy current image, it can be seen that the magnetic flux is at the position shown by the broken line in the figure. Since the eddy current is a function of the modulation frequency of the magnetic flux, the resistivity of the sample and the magnetic permeability, if the resistivity and the magnetic permeability of the sample are locally different even for one magnetic flux of the same size, The magnitude of the eddy current observed will be locally different. For example, in FIG.
Then, since the eddy current value 21 on the left side is larger, it can be seen that the value of (magnetic permeability / resistivity) is larger on the left side in the figure. Only the value of (permeability / resistivity) can be known from the magnitude of the eddy current, but since the permeability can be determined from the distribution of magnetic flux, the permeability and the resistivity can be independently obtained. Therefore, according to the present invention, the above-mentioned magnetic characteristics of the sample can be detected from the magnetic flux distribution on the surface of the sample.

(Embodiment 2) FIG. 5 is a view showing another embodiment according to the present invention. Here, a probe 26 and a scanner 27, which are movable by a sample 24 and a coarse movement mechanism 25, are inserted into the objective lens 23 of the electron microscope. By combining with the electron microscope, the position of the probe 26 can be identified and the surface image of the sample 24 at a low magnification can be easily obtained. In this embodiment, the objective lens 23 is also used as a modulating magnetic field applying device. That is, first, the surface of the sample 24 is observed and the position of the probe 26 is identified in the electron microscope mode. Then, a modulation magnetic field is applied to the sample 24 using the objective lens 23, and the eddy current accompanying the modulation magnetic field is detected. The detection is performed by the probe 26 inserted in the lens 23. With this configuration, the present invention can be easily implemented only by adding an electronic circuit system for applying the modulation magnetic field.

Of course, the present invention can be implemented by providing a modulating magnetic field applying means other than the objective lens 23. In this case, by applying a weak modulation magnetic field to the sample 24, it is possible to observe an image with an electron microscope at the same time. For example, a holographic electron microscope can be used to observe the spatial distribution of magnetic flux due to the magnetization of the sample 24. In addition to this, from the observation of the eddy current, the sample 2
Since magnetic properties such as magnetic permeability of the four surfaces can be measured at the same time, multifaceted and highly accurate magnetic measurement can be performed.

(Embodiment 3) FIG. 6 is a diagram showing another magnetic field applying method according to the present invention. A probe 30 mounted on a scanner 29 is installed close to the sample 28. A magnetic probe 31 is provided on the opposite side of the probe 30 from the sample 28. By using the magnetic probe 31 having a sharp tip, a magnetic field can be locally applied to the sample 28. Therefore, even if the total magnetic field that can be generated is small, a large magnetic field can be applied locally, so that an eddy current can be efficiently generated. The magnetic field may be modulated by modulating the current passing through the coil 32 wound around the magnetic probe 31, or by scanning the magnetic probe 31 with the scanner 33. When modulating the current flowing through the coil 32, the eddy current can be detected by the same method as in the first embodiment described above. When scanning the magnetic probe 31, a tunnel current component synchronized with the scanning speed of the magnetic probe 31 is detected. Therefore, the eddy current can be accurately detected by making the scanning speed of the magnetic probe 31 faster than the scanning speed of the tunnel current detecting probe 30 by one digit or more.

On the other hand, since the magnitude of the eddy current is inversely proportional to the resistivity of the sample, the higher the insulating property of the sample, the lower the detection sensitivity. As a countermeasure against this, if a metal thin film is coated on the sample surface, the eddy current that flows can be increased. Even if the thin metal film is coated, the position where the magnetic flux penetrates the sample does not change, so there is no problem in measurement.

However, when an island-shaped thin film (each island-shaped structure is separated) is formed on the sample surface, the eddy current can be detected with higher sensitivity. This is because no current flows between the separated island structures, so that the eddy current flowing in a closed loop around each magnetic flux flows only in the island structure through which the magnetic flux penetrates. Therefore, the smaller the island structure, the more accurately the position of the magnetic flux can be determined. At the same time, since the current path is also limited, the eddy current density is increased and the detection sensitivity is increased. In this case, since it is difficult to detect the magnetic flux that does not penetrate the island structure, it is desirable to form the island structure as densely as possible. Further, this method is effective not only for the insulating sample but also for the conductive sample. This is because the step between the island structure and the substrate sample acts as a potential barrier for the current flowing on the surface, so that the eddy current, which is the surface current, is easily closed and flows in the island structure.

Although the eddy current is detected by using the scanning tunneling microscope in the above-mentioned first, second, and third embodiments, it goes without saying that the present invention can be implemented by an atomic force microscope capable of detecting a current. Yes. Furthermore, the present invention can be implemented by using a scanning capacitance microscope or the like. In this case, the eddy current position is detected from the change in the amount of charge in synchronization with the magnetic field modulation.

[0025]

As described above, in the surface magnetic microscope according to the present invention, a modulation magnetic field is applied to a sample, and the eddy current flowing around the magnetic flux generated by this is detected by a probe to detect the magnetic flux on the sample surface. The distribution can be detected with high resolution by being separated from the unevenness information of the sample, and further, the local physical characteristics of the sample such as the magnetic permeability and the resistivity of the sample can be measured. .

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration of an embodiment of a surface magnetic microscope according to the present invention.

FIG. 2 is a schematic diagram of a magnetic flux penetrating a sample and an eddy current flowing on the surface of the sample.

FIG. 3 is a schematic diagram of an eddy current that has been conventionally considered.

FIG. 4 is a sectional view of an eddy current image detected by a probe.

FIG. 5 is a diagram showing an embodiment in which the surface magnetic microscope according to the present invention is incorporated in an objective lens of an electron microscope.

FIG. 6 is a diagram showing an embodiment in which a magnetic probe is used as a modulating magnetic field applying means.

[Explanation of symbols]

 1 probe 2 sample 3 control system 4 scanner 5 electromagnetic coil 6 magnetic flux 7 AC signal generator 8 detector 9 uneven image 10 eddy current image 11 sample 12, 13, 14, 15 magnetic flux 16, 17, 18, 19 eddy current 20 Magnetic flux group 21, 22 Eddy current 23 Objective lens 24 Sample 25 Coarse movement mechanism 26 Probe 27 Scanner 28 Sample 29 Scanner 30 Probe 31 Magnetic probe 32 Coil 33 Scanner

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Tomimatsu 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (11)

[Claims] 1. By applying a modulating magnetic field to a sample,
A surface magnetic microscope characterized by measuring the magnetic characteristics of the sample surface by detecting an eddy current flowing around a magnetic flux induced on the surface of the sample using a scanning probe microscope. 2. The surface magnetic microscope according to claim 1, wherein the modulation magnetic field is applied by an electromagnetic coil installed in the vicinity of the sample. 3. The surface magnetic microscope according to claim 1, wherein the sample and a main part of the scanning probe microscope are installed in an objective lens of an electron microscope. 4. The surface magnetic microscope according to claim 3, wherein the objective lens of the electron microscope is also used as a device for applying the modulating magnetic field. 5. The surface magnetic microscope according to claim 1, wherein the modulating magnetic field is concentratedly applied to a specific region of the sample by a magnetic probe. 6. The surface magnetic microscope according to claim 5, wherein the modulating magnetic field is generated by modulating a current passing through a coil provided on the magnetic probe. 7. The surface magnetic microscope according to claim 5, wherein a modulation magnetic field is applied to a specific portion of the sample by scanning the magnetic probe near the sample. 8. The surface magnetic microscope according to claim 1, wherein the magnetic flux distribution on the sample surface is measured from the distribution of the eddy current. 9. From the magnitude and distribution of the eddy current,
The surface magnetic microscope according to any one of claims 1 to 7, wherein the local magnetic permeability and the resistivity of the sample surface are measured. 10. The surface magnetic microscope according to claim 1, wherein a metal thin film is formed on the surface of the sample, and an eddy current flowing in the metal thin film is detected. 11. The surface magnetic microscope according to claim 10, wherein the metal thin film has an island structure.