JP2010151455A - Observing method of magnetic sample, observing device, and observing tool thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an observing method of a magnetic sample for acquiring an observation image which shows magnetic domain structure and the like of a magnetized permanent magnet. <P>SOLUTION: The observing method of a magnetic sample is as follows: An observation image which shows micro structure of the magnetic sample is formed by irradiating a magnetized magnet sample with incident beam of radiating light and the like and detecting emission electrons emitted from the magnetic sample. The magnetic sample is observed in a state in which both ends of the magnetic sample in the magnetized direction are magnetically coupled with a coupling tool which has a higher magnetic permeability than that of the atmosphere where the magnetic sample is arranged. With this coupling tool, magnetic closed circuits are formed at both ends of the magnetic sample and the leaked magnetic field from the magnetic sample is suppressed. Consequently, distortion of the trace of the emission electron is reduced, so that a sharp observation image which shows the magnetic domain structure and the like of the magnetic sample is obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic sample observation method, an observation apparatus, and an observation jig for the magnetic sample that allow observation of the magnetized magnetic sample obtained by magnetization or the like through emitted electrons.

Conventionally, an observation beam of a sample is irradiated with an incident beam consisting of excitation light or an electron beam, and the properties or structures near the surface of the material are observed, analyzed, analyzed, etc. via emitted electrons emitted from the surface of the sample. Has been made more. As a typical apparatus, there is a scanning electron microscope (hereinafter referred to as “SEM”) which is a kind of electron microscope. In addition, when the sample is irradiated with light having a certain energy (E = hν ₀ /: ν ₀ : limit frequency, h: Planck constant), electrons are emitted from the sample (external) photoelectric effect is used. There is also an observation device. As this irradiated light, for example, an electromagnetic wave (radiated light) generated when the traveling direction of electrons traveling straight at an ultrahigh speed is changed by a deflecting electromagnet or the like is used. In particular, SPring-8 and the like are prominent as devices capable of obtaining radiation with high luminance (brightness).

Using SPring-8, magnetic domain observation of rare earth magnets (permanent magnets) was performed using the XMCD-PEEM method, which combines X-ray Magnetic Circular Dichroism and PhotoEmission Electron Microscope. Examples are reported in the following literature: In addition, the description relevant to XMCD-PEEM method itself exists in the following patent document 1 or patent document 2, for example.
SPring-8 User Experiment Report (Issue Number: 2005B0830, 2006A0229, 2006B0201) Japanese Patent Laid-Open No. 5-45304 JP 2008-66080 A

  If the magnetic domain structure of a permanent magnet is to be observed, it should be originally desirable to observe using a magnetized sample. However, in the above-mentioned document, the observation is merely performed using a sample in a state of being thermally demagnetized or magnetically demagnetized. In the range investigated by the present inventor, no example has been reported in which a magnetic domain structure or the like is observed with a photoelectron microscope or the like in a state in which a super strong permanent magnet such as an anisotropic rare earth magnet is magnetized.

  The present invention has been made in view of such circumstances, and provides an observation method and an observation apparatus for a magnetic sample capable of observing magnetic domains and the like of a magnetic sample magnetized by magnetization or the like. Objective. It is another object of the present invention to provide an observation jig effective for observing such a magnetic sample.

As a result of extensive research and trial and error, the present inventor has established a closed-loop magnetic circuit by connecting a soft magnetic material to a magnetized permanent magnet to be a sample, and thereby a permanent magnet (particularly, We have succeeded in observing the magnetic domain of an anisotropic rare earth magnet with a strong magnetic force in a magnetized state for the first time. And by developing this result, the present inventor has completed various inventions described below.
<Magnetic sample observation method>

(1) That is, in the method for observing a magnetic sample of the present invention, an irradiation step of irradiating an observation region of a magnetic sample made of a magnetized magnetic material with an incident beam made of excitation light or an electron beam, and the incident beam being irradiated. A detection step for detecting emitted electrons emitted from the observation region of the magnetic sample, and an observation image showing a fine state of the observation region of the magnetic sample based on information obtained from the emitted electrons detected in the detection step. An observation image forming step for forming a magnetic sample, comprising:

  The magnetic sample is observed in a state in which both ends in the magnetization direction of the magnetic sample are magnetically coupled by a coupler having a permeability higher than that of an atmosphere in which the magnetic sample is disposed. To do.

(2) According to the observation method of the present invention, even a magnetic sample magnetized by magnetization or the like and having magnetic lines of force from both poles at both ends, the magnetic domain structure and the like are appropriately observed through the emitted electrons. It becomes possible. The reason for this is not necessarily clear, but at present it can be considered as follows.

  First, the present inventor tried to observe a magnetized magnetic sample alone through emitted electrons, but could not obtain a desired observation image. The present inventor considered that the path (orbit) of the emitted electrons is distorted by the leakage magnetic field generated from the magnetic sample, and proper observation becomes difficult. Therefore, conventionally, it was considered that the magnetic domain structure of the magnetic sample was observed in a state where it was degaussed or not magnetized.

  However, according to the present invention, the magnetic field lines flowing out and flowing in from both ends (so-called N pole and S pole) in the magnetization direction of the magnetic sample mainly pass through a high-permeability coupler that connects both ends of the magnetic sample. Therefore, the magnetic path is hardly formed around the magnetic sample. That is, most of the magnetic flux emitted from the magnetized magnetic sample flows through a closed loop magnetic path formed by the magnetic sample and the coupling tool, and is less likely to leak around the magnetic sample.

  As a result, the trajectory of the emitted electrons emitted from the magnetic sample is very less affected by the leakage magnetic field and is hardly distorted. Thus, it is considered that an appropriate observation image can be formed by the emitted electrons, and the magnetic domain and the like of the magnetic sample that has been magnetized can be observed.

<Magnetic sample observation device>
The present invention can be grasped not only as an observation method described above but also as an observation apparatus.
That is, the present invention provides an irradiating means for irradiating an observation region of a magnetic sample made of magnetized magnetic material with an incident beam made of excitation light or an electron beam, and emitting from the observation region of the magnetic sample irradiated with the incident beam. Detection means for detecting the emitted electrons, observation image forming means for forming an observation image indicating the fine state of the observation area of the magnetic sample based on information obtained from the emission electrons detected in the detection step, and And an observation jig comprising a coupler having a magnetic permeability higher than that of an atmosphere in which the magnetic sample is arranged and magnetically connecting both ends of the magnetization direction of the magnetic sample. It may be a sample observation device.

<Magnetic specimen observation jig>
Furthermore, this invention can be grasped | ascertained not only as said observation method and observation apparatus but as an observation jig | tool required when using them. This observation jig is mainly composed of the above-described coupling tool, but also includes an attachment such as a fixing member for fixing the magnetic sample to the coupling tool and a base for holding or holding the coupling tool independently. May be.

The present invention will be described in more detail with reference to embodiments of the invention.
The contents described in this specification, including the following embodiments, can be appropriately applied not only to the observation method of the magnetic sample according to the present invention, but also to the observation apparatus and observation jig. Which embodiment is the best depends on the target, required performance, and the like. Furthermore, in addition to the above-described configuration, one or two or more configurations arbitrarily selected from various modes described below can be further added. At this time, the selected configuration can be added to a plurality of inventions in a superimposed manner and arbitrarily, and any configuration can be combined with each other as appropriate across categories. At first glance, even if it looks like a “method” or “thing” configuration, for example, by interpreting “step” as “means” or vice versa, both configurations are “method” or “thing”. Can be a limiting element.

(1) Irradiation step ("Means" may be used. The same applies hereinafter)
The irradiation step is a step of irradiating an observation region of a magnetic sample made of a magnetized magnetic material with an incident beam made of excitation light or an electron beam.
Examples of the excitation light include polarized radiation, polarized electron beam, and polarized laser. Soft X-rays having a wavelength of around 1 nm (10 ⁻⁸ to 10 ⁻¹⁰ m) have a large absorption difference when the excitation light polarization degree is changed with a 3d transition metal magnetic material, and is suitable for magnetic material observation. Such a generation source is a synchrotron radiation facility, and the above-mentioned SPring-8 is raised in Japan and is present all over the world.

  The electron beam is composed of electrons having a predetermined energy emitted from an electron gun or the like. Examples of electron guns that are electron sources include thermal electron guns, field emission electron guns, and Schottky electron guns. As long as the magnetic sample can be observed, the type, intensity, electron source, etc. of the electron beam are not limited. The SEM described above is one that uses an electron beam. The size of the magnetic sample, the size of the observation area, the resolution, and the like need only be suitable for the observation apparatus.

(2) Detection step The detection step is a step of detecting emitted electrons emitted from the observation region of the magnetic sample irradiated with the incident beam.
In addition to photoelectrons emitted by the photoelectric effect, the emitted electrons include reflected electrons and secondary electrons with respect to incident electrons. When observing the magnetic domain of a magnetic sample, photoelectrons and low energy secondary electrons are used.

  The detection of the emitted electrons can be performed by, for example, an emitter that multiplies emitted electrons attracted by applying a high voltage with a photomultiplier tube, collides with a fluorescent material, and extracts the electric signal. Even when soft X-rays generated from SPring-8 or the like are used, as described above, emitted electrons are doubled, converted into an electric signal, and detected.

(3) Observation image forming step The observation image forming step is a step of forming an observation image indicating the fine state of the observation region of the magnetic sample based on the information obtained from the detected emitted electrons. Specifically, an observation image is formed by performing image processing based on an electrical signal obtained by detecting emitted electrons.

(4) Connecting tool The connecting tool is made of a member having a magnetic permeability higher than that of the atmosphere in which the magnetic sample is arranged and having a magnetic flux density higher than that of the magnetic sample. Magnetically coupled. In short, in order to reduce the leakage magnetic flux from the magnetic sample, a closed loop magnetic circuit may be formed by the magnetic sample and the coupler. As long as the magnetic flux leaking to the periphery of the magnetic sample is reduced when the connection tool of the present invention is provided rather than when the connection tool is not provided, the material and form of the connection tool are not limited.

  However, whether the magnetic flux flowing in and out from both ends of the magnetic sample passes through a magnetic path formed naturally around the magnetic sample or through a path made of a coupling is essentially a problem of the magnetic resistance of both magnetic paths. . Then, the coupler of the present invention may form a magnetic path having a lower magnetic resistance than a magnetic path naturally formed around the magnetic sample. However, it is difficult to specifically specify the magnetic resistance of the magnetic path that is naturally formed around the magnetic sample to be compared. Incidentally, the magnetic resistance (R) is represented by R = 1 / μS by the magnetic permeability (μ), the magnetic path length (l), and the magnetic path section (S).

  Therefore, in the present invention, as described above, the magnetic characteristics of the coupler are limited by the magnitude relationship between the magnetic permeability around the magnetic sample and the permeability of the coupler. The coupling tool is often made of a soft magnetic material such as iron, and its magnetic permeability is much larger than the magnetic permeability around the magnetic sample (usually the magnetic permeability in a vacuum), and the magnetic sample is also small. Since the formed magnetic path length is also short, it can be said that, in the end, the fact that the magnetic resistance is small is equivalent to being indirectly expressed, but even the above expression has no substantial problem in specifying the present invention. . Further, since the saturation magnetization of the soft magnetic material is sufficiently large, the cross-sectional area of the magnetic path is not likely to be a problem as long as it has a cross-sectional area comparable to that of the magnetic sample.

  Thus, it is preferable that a connection tool consists of a soft magnetic material. The soft magnetic material is typically a ferromagnetic material such as Fe, Co, and Ni. In particular, pure Fe or an Fe alloy (for example, an Fe—Si alloy) is preferable from the viewpoint of acquisition cost, workability, and the like. .

  Moreover, in order to suppress the magnetic path shortening and leakage magnetic field by the coupler, it is preferable that the coupler is substantially annular or the cross section thereof is substantially circular. However, in order to ensure versatility and fine adjustment of the connector, the connector may be configured by combining square blocks of various sizes.

(5) Magnetic sample and observation object The material, composition, etc. of the magnetic sample itself are not a problem in the present invention as long as they are compatible with the observation apparatus. Therefore, in addition to a magnetized permanent magnet, a soft magnet magnetized by a permanent magnet or an electromagnet may be used.

  However, in the present invention, the main purpose is to avoid or suppress the observation obstacle caused by the distortion of the orbit of the emitted electrons due to the leakage magnetic field. As described above, the present invention is particularly effective when the magnetic sample itself is a strong permanent magnet and emits strong magnetic field lines. Examples of such a magnetic sample include a magnetized rare earth magnet, particularly an anisotropic rare earth magnet magnetized in the easy axis direction (c-axis). Such rare earth magnets include Nd—Fe—B, Sm—Co, and Sm—Fe—N, but any of them may be used. Moreover, the magnet manufactured by any method, such as a hydrodehydrogenation process (HDDR process) and a rapid solidification method, may be sufficient. Further, the magnetic sample may be a so-called sintered magnet.

  The object of observation of such a magnetic sample is to observe a magnetic domain consisting of a magnetically saturated magnetic material or a magnetic moment-enclosed region surrounded by a domain wall (a region where spins are directed in the same direction). It doesn't matter.

The present invention will be described more specifically with reference to examples.
<Magnetic sample>
As a magnetic sample for observing the magnetic domain structure, an anisotropic rare earth sintered magnet (commercially available material) was prepared. The following magnetic samples were observed in a remanent magnetization state of an Nd—Fe—B anisotropic sintered magnet that was all magnetized in the easy axis direction. All the magnetic samples were magnetized by applying a magnetic field of 10T.

<Observation by XMCD-PEEM method>
(1) The magnetic sample was observed by the XMCD-PEEM method described above. This observation was performed using the beam line BL25SU of the synchrotron radiation facility SPring-8. The outline (principle) of the XMCD-PEEM method is as shown in FIG.

  That is, when circularly polarized X-rays (excitation light, radiated light, incident beam) are incident on a magnetic sample (irradiation step, irradiation means), the number of photoelectrons or secondary electrons (emitted electrons) emitted is X-rays. It is proportional to the inner product of the polarization vector and the magnetic spin vector of the magnetic sample. By detecting this photoelectron (detection step, detection means) and image-processing it to form an image (observation image formation step, observation image formation means), an observation image (magnetic domain image) of the magnetic sample can be obtained. . This observation was performed using a photoelectron emission microscope manufactured by Ermitec, Germany.

(2) First, when a magnetized magnetic sample was observed alone by the XMCD-PEEM method, a normal observation image could not be obtained. As shown in FIG. 2, when X-rays are incident on a magnetized magnetic sample, the orbit of photoelectrons emitted from the magnetic sample is distorted by a strong magnetic field formed around the magnetic sample. I think that the.
Incidentally, the size of the magnetic sample used here was 5 × 5 × 5 mm, and the atmosphere around the magnetic sample at the time of observation was vacuum.

(3) Next, a yoke (connector, observation jig) made by combining a soft magnetic block made of a soft magnetic material was connected to the magnetized magnetic sample to form a closed loop magnetic path. The soft magnetic block used here consists of a pure iron melt. The following two observations were performed on the magnetic sample in such a state by the XMCD-PEEM method.

(i) Observation 1
A 5 × 5 × 5 mm Nd—Fe—B anisotropic rare earth magnet cut out so that the c-axis of the crystal was parallel to the side of the cube was used as a magnetic sample. For the soft magnetic block, one 5 × 5 × 5 mm cube and two 5 × 5 × 15 mm cuboids were prepared according to the size of the magnetic sample. These three soft magnetic blocks were arranged in a substantially U shape to form a yoke. Three soft magnetic blocks and a magnetic sample were assembled as shown in FIG. 3 so that the magnetic lines of force from the magnetic sample passed through the magnetic closed circuit.

  In the observation by the XMCD-PEEM method using the SPring-8 beam line BL25SU, X-rays were obliquely incident at 30 ° from the column surface of the magnetic sample at room temperature. In addition, when the magnetic field around this magnetic sample was measured with a Gauss meter manufactured by Toyo Technica, the leakage magnetic field was 80G. The XMCD-PEEM observation image thus obtained is shown in FIG. The magnetic domain image is obtained by magnetic circular dichroism, and the energy of the circularly polarized radiation is matched to the Fe-L3 absorption edge (708.6 eV), and the difference between the images formed by clockwise circularly polarized light and counterclockwise circularly polarized light. And then divided by the sum of the two.

(ii) Observation 2
The same observation as observation 1 was performed by changing the sizes of the magnetic sample and the soft magnetic block. The size of the prepared magnetic sample was 3 × 3 × 3 mm. Also, one 3 × 3 × 3 mm cubic soft magnetic block and two 3 × 3 × 9 mm rectangular soft magnetic blocks were prepared according to the size of the magnetic sample. The arrangement of the magnetic sample and each soft magnetic block, the observation conditions, etc. are basically the same as those in Observation 1. However, in observation 2, the observation surface of the magnetic sample was coated with Pt to prevent oxidation.
As in the case of Observation 1, the leakage magnetic field was measured and found to be 5G. The XMCD-PEEM observation image thus obtained is shown in FIG.

<Evaluation>
As shown in FIGS. 4 and 5, even a magnetic sample made of an Nd—Fe—B anisotropic rare earth magnet that is magnetized and emits a strong magnetic flux by using the observation method of the present invention, It became possible to observe the magnetic domain structure by the XMCD-PEEM method.

And the observation 2 with few leakage magnetic fields was able to obtain a clear XMCD-PEEM observation image. This seems to be because the orbit of the emitted photoelectrons was detected with almost no distortion and the magnetic domain image was correctly formed by reducing the leakage magnetic field to 5G.
In any case, the use of the present invention makes it possible to observe the magnetic domain structure of a magnetized permanent magnet (particularly a strong anisotropic rare earth magnet).

It is a schematic diagram which shows the principle of the XMCD-PEEM method used for observation of a magnetic domain structure. It is a schematic diagram which shows the magnetic force line discharge | released to the circumference | surroundings from the magnetized magnetic sample. It is a schematic diagram which shows the yoke (connector) which consists of a magnetic sample and a soft-magnetic block. It is a XMCD-PEEM observation image which shows the magnetic domain structure of the magnetic sample magnetized when the leakage magnetic field is 80G. It is a XMCD-PEEM observation image which shows the magnetic domain structure of the magnetic sample magnetized at the time of the leakage magnetic field 5G.

Claims (5)

An irradiation step of irradiating an observation region of a magnetic sample made of a magnetized magnetic material with an incident beam made of excitation light or an electron beam,
A detection step of detecting emitted electrons emitted from the observation area of the magnetic sample irradiated with the incident beam;
An observation image forming step for forming an observation image indicating a fine state of an observation area of the magnetic sample based on information obtained from the emitted electrons detected in the detection step,
The magnetic sample has magnetic permeability higher than the magnetic permeability of the atmosphere in which the magnetic sample is arranged at both ends in the magnetization direction of the magnetic sample, and the magnetic flux is magnetically coupled by a coupling tool larger than the magnetic sample. A method for observing a magnetic sample, characterized in that the magnetic sample is observed in a heated state.   The method of observing a magnetic sample according to claim 1, wherein the connector is made of a soft magnetic material.   The magnetic sample observation method according to claim 1, wherein the magnetic sample is made of an anisotropic rare earth magnet having the magnetization direction as an easy axis direction (c-axis). Irradiating means for irradiating an observation beam of a magnetic sample made of a magnetized magnetic material with an incident beam made of excitation light or an electron beam;
Detecting means for detecting emitted electrons emitted from the observation area of the magnetic sample irradiated with the incident beam;
An observation image forming means for forming an observation image indicating a fine state of an observation area of the magnetic sample based on information obtained from the emitted electrons detected in the detection step;
Furthermore, an observation jig is provided that has a magnetic permeability higher than the magnetic permeability of the atmosphere in which the magnetic sample is disposed, and includes a coupling device that magnetically connects both ends of the magnetization direction of the magnetic sample. Observation device for magnetic samples.   A jig for observing a magnetic sample, comprising the connector according to claim 1.