JP2822280B2 - Near-field scanning microscope for magnetic domain observation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-field scanning microscope for observing a magnetic domain, and more particularly, to the use of a polarization-dependent pickup means to change the polarization direction of light transmitted through or reflected by a magnetic material. The present invention relates to a high-resolution optical microscope for magnetic domain observation to be detected.

[0002]

2. Description of the Related Art Conventionally, a polarizing microscope has been known as an optical microscope for observing magnetic domains on a magnetic tape or a magnetic disk. The polarization microscope is a so-called Faraday effect in which the polarization direction of the illumination light rotates in proportion to the strength of the magnetic field in the sample when light passes through the sample,
This utilizes the so-called magnetic Kerr effect in which the direction of polarization of the reflected light rotates according to the magnetic field of the sample when light is reflected on the surface of the sample. Observation was possible for large magnetic domains.

[0003]

However, in such a polarizing microscope, the resolution is limited by the diffraction limit of the light used for illumination, and there is a disadvantage that a resolution of only about λ / 4 can be obtained at most. there were. This means that, for example, when illumination light of λ = 500 nm is used, the theoretical limit of resolution is only 125 nm, and
In practice, it has been difficult to achieve this theoretical limit of 125 nm. The size of the magnetic domain formed in the magnetic material actually used at present is on the order of 10 nm to 1 μm, and the resolution of the conventional polarizing microscope cannot be said to be sufficient.

An object of the present invention is to provide a magnetic field observing near-field scanning microscope capable of achieving high resolution without being limited by the wavelength of illumination light, in view of the above-mentioned problems in the conventional apparatus. .

[0005]

SUMMARY OF THE INVENTION A near-field scanning microscope for observing magnetic domains according to the present invention (ie, NFM for observing magnetic domains).
The inner transmission type is a light irradiation means for irradiating linearly polarized light from the back surface of the sample, and is capable of scanning relative to the sample and detects a change in the rotation angle of the polarization of the evanescent wave on the sample surface. A polarization-dependent pickup means.

In such a near-field scanning microscope for magnetic domain observation, second pickup means is provided which is capable of scanning relative to the sample and detects the intensity of the evanescent wave on the sample surface. Conveniently, the output of the second pickup means is used to correct the change in the output signal intensity of the polarization dependent pickup means due to the shape of the sample surface.

[0007] Further, the polarization dependent pickup means and means for relatively rotating the sample, and means for detecting the direction of magnetization from the change in the output signal intensity of the polarization dependent pickup means caused by the rotation. It can also be provided.

According to the present invention, there is further provided a reflection-type near-field scanning microscope for observing a magnetic domain, wherein the microscope is capable of scanning linearly polarized light with respect to a sample and light source means for outputting linearly polarized light. Having an opening smaller than the wavelength of the light output from the light source means, receiving light from the light source means and irradiating the sample through the opening, and reflecting the light from the sample surface due to this irradiation again. A polarization-dependent pick-up means for detecting a change in the rotation angle of the polarization of the light returning through the aperture.

In the near-field scanning microscope for observing reflection magnetic domains, the sample can be relatively scanned with respect to the sample, and has an aperture smaller than the wavelength of light output from the light source means. A second pickup unit for receiving light from the light source unit and irradiating the sample through the opening, and detecting the intensity of light returning through the opening again by reflection from the sample surface due to the irradiation; It is convenient to use the output to correct the change in the output signal intensity of the polarization dependent pickup means due to the shape of the sample surface.

Furthermore, in the near-field scanning microscope for reflecting magnetic domain observation, a means for relatively rotating the polarization dependent pickup means and the sample, and an output signal intensity of the polarization dependent pickup means caused by the rotation. And means for detecting the direction of magnetization from the change in

[0011]

In the transmission type magnetic domain observation NFM according to the above configuration, the linearly polarized light radiated from the back surface of the sample causes
An evanescent wave is emitted from the surface of the sample, and the polarization direction of the evanescent wave rotates according to the magnetization of the sample.
Therefore, the magnitude and presence / absence of the magnetization at each point on the sample are detected by taking out the output corresponding to the polarization direction by the polarization dependent pickup means. By detecting such a state of magnetization at each point on the sample by scanning the sample with the polarization-dependent pickup means, it is possible to observe the presence or absence of magnetization of each part of the sample.

In this case, the change in the output signal intensity of the polarization dependent pickup means due to the shape of the sample surface is corrected by the second pickup means for detecting the intensity of the evanescent wave on the sample surface. The magnetic domain observation can be accurately performed without being affected by the magnetic field.

Further, the polarization dependent pickup means and the sample are relatively rotated, and for example, a point at which the output of the polarization dependent pickup means is maximized is determined to determine the direction of magnetization at each point on the sample. Can be detected.

Further, in the reflection type magnetic domain observation NFM according to the above configuration, the linearly polarized light output from the light source means is transmitted to the sample as an evanescent wave from an aperture smaller than the light wavelength of the polarization dependent pickup means. Irradiated. Then, the evanescent wave reflected from the sample is taken in again through the opening of the polarization dependent pickup means and detected. Thereby, the polarization direction of the evanescent wave is rotated according to the magnetization of the sample, and an output corresponding to the magnetization of the sample is obtained as the output of the polarization dependent pickup means. By obtaining such an output at each point on the sample, it becomes possible to observe the magnetic domains of the sample.

Also, in the reflection type NFM for magnetic domain observation, the light output from the light source means is received and irradiated on the sample through an aperture smaller than the wavelength of the light, and the reflected light from the sample is again reflected. An output signal corresponding to the shape of the sample surface can be obtained using the second pickup means for detecting through the opening. Then, by using this output signal to correct the change in the output signal intensity of the polarization dependent pickup means due to the shape of the sample surface, more accurate magnetic domain observation can be performed without being affected by the shape of the sample surface. it can.

In the same manner, the polarization dependent pickup means and the sample are relatively rotated, and for example, the direction in which the output of the polarization dependent pickup means caused by the rotation is maximized is determined, thereby obtaining the magnetization of the sample. Can be detected.

[0017]

Next, a magnetic domain observation N according to an embodiment of the present invention will be described.
Before describing the FM, the principle of a general transmission type NFM will be described with reference to FIG. In the transmission type NFM shown in FIG. 3, a sample 1 is placed on an XY stage 3, and light from a laser light source 5 is applied to the sample via an acousto-optic cell 7, a lens 9, a reflecting mirror 11, and a prism 13. Irradiate 1 In this case, the light is irradiated at an angle at which the light applied to the sample 1 is totally reflected within the sample, that is, at an incident angle equal to or greater than the critical angle. As a result, an evanescent wave that attenuates rapidly according to the distance from the sample 1 is generated on the surface of the sample 1. At this time, when a pickup 17 composed of an optical fiber attached to the Z-direction driving device 15 is brought close to the surface of the sample 1, light corresponding to the intensity of the evanescent wave, that is, the distance from the sample 1 is generated in the optical fiber of the pickup 17. The light is introduced, detected by a synchronous detector 21 via an optical fiber 19, and applied to a plotter or a display device 23. A synchronous signal is supplied from the modulator 25 to the synchronous detector 21 and the acousto-optic cell 7.

Accordingly, when the XY stage 3 is caused to scan relative to the pickup 17 by the operation of the control unit 27, an output corresponding to the shape of the surface of the sample 1 is obtained from the pickup 17, and the sample is displayed on the plotter or display device 23. It becomes possible to display the shape of the surface. Instead of moving the sample 1 by the XY stage 3, the pickup 17 can be moved along the surface of the fixed sample 1.

FIG. 1 shows a schematic configuration of a transmission type magnetic domain observation NFM according to a first embodiment of the present invention. The apparatus shown in FIG. 1 includes a prism 3 for placing a sample 31 and irradiating light.
3, laser light source 35, beam expander 37, polarization dependent pickup 39, photomultiplier 41 and XYZ stage 43 provided in polarization dependent pickup 39,
Fiber pickup 45, fiber pickup 45
, A photomultiplier 47 and an XYZ stage 49, XYZ drive circuits 51 and 53, a display circuit 55, a display device 57, a microcomputer 59, and the like.

The prism 33 mounts the sample 31 and irradiates the sample with linearly polarized light at an incident angle equal to or greater than the critical angle. The polarization-dependent pickup 39 is configured by providing an opening smaller than the wavelength of light at the tip of the polarization-maintaining optical fiber, and a photomultiplier 41 is optically coupled to the other end. Are input to the display circuit 55. The fiber pickup 45 has an opening smaller than the wavelength of light at the tip of a normal optical fiber, and another photomultiplier 47 is optically coupled to the other end. The output of the photomultiplier 47 is supplied to the XYZ drive circuit 53. The XYZ drive circuit 53 includes an XYZ stage 49 for the fiber pickup 45.
Is to be driven. The other XYZ drive circuit 51 drives the XYZ stage 43 for the polarization dependent pickup 39. Each of these XYZ drive circuits 51,
53 is connected to a microcomputer 59.

In the transmission type NFM according to the configuration shown in FIG. 1, linearly polarized light is output from a laser light source 35, and this light is turned into a wide light beam by a beam expander 37, and the sample 31 is placed on the back surface through a prism 33. Irradiate from In this case, since the light applied to the sample 31 is applied at an incident angle equal to or greater than the critical angle of the sample 31, the light is totally reflected on the surface of the sample 31 and is emitted to the outside again via the prism 33. As a result, an evanescent wave that attenuates rapidly according to the distance from the sample 1 is generated on the surface of the sample 31. The evanescent wave is detected by the polarization-dependent pickup 39, and the polarization-maintaining fiber used in the polarization-dependent pickup 39 functions as a polarizing plate that transmits only light of a specific polarization plane. Further, the evanescent wave emitted from the sample 31 has its polarization plane rotated in accordance with the magnetization of the sample 31 due to the Faraday effect, so that an output corresponding to the intensity of the magnetization of the sample 31 is output from the polarization dependent pickup 39. This output is obtained from the photomultiplier 41.
Are multiplied and photoelectrically converted and supplied to the display circuit 55. Therefore, the polarization dependent pickup 39 is
By scanning along the surface of the sample 31 by the stage 43, a signal corresponding to the magnetization intensity of each part of the sample is obtained, and this is synchronously displayed on the display 57 via the display circuit 55, whereby the sample 31 is displayed. An image corresponding to the intensity or presence or absence of the surface magnetization can be displayed.

In the above operation, the fiber pickup 45 is also scanned along the surface of the sample 31 by the XYZ stage 49, and detects a signal corresponding to the intensity of the evanescent wave on each part of the sample surface. This signal is multiplied by the photomultiplier 47, photoelectrically converted, and supplied to the XYZ drive circuit 53. The XYZ drive circuit 53
Fiber pickup 45 by XYZ stage 49
The distance from the surface of the sample 31 is also adjusted, and the output of the fiber pickup 45 is controlled to be constant. Then, a signal corresponding to the control signal for controlling the XYZ stage 49, that is, a signal corresponding to the distance from the sample surface, is input from the XYZ drive circuit 53 to the microcomputer 59. Such a signal causes the fiber pickup 45 to move along the surface of the sample 31 by X
While scanning in the Y direction, all points are detected and input to the microcomputer 59.

The microcomputer 59 inputs to the XYZ drive circuit 51 a correction signal generated based on the control signals of the respective parts on the sample 31 input from the XYZ drive circuit 53, and the XYZ drive circuit 51 receives the correction signal based on the correction signal. The height of the XYZ stage 43 in the Z direction, that is, the distance from the surface of the sample 31 to the tip of the polarization dependent pickup 39 is corrected. Thereby, the polarization dependent pickup 3
The output of No. 9 is obtained by removing the change in the signal intensity due to the uneven shape of the surface of the sample 31, and it is possible to pick up only the data relating to the magnetization.

In the configuration shown in FIG. 1, it is convenient that the plane of polarization of the polarization dependent pickup 39 is perpendicular to the plane of polarization of the light emitted from the laser light source 31. That is, in this case, when the sample 31 has no magnetization, no signal is detected from the polarization dependent pickup 39, and a good signal-to-noise ratio (S / N) observation without a DC component can be performed.

Further, the intensity or presence or absence of the magnetization of the sample 31 can be measured by the above method. When the direction of the magnetization is measured, the sample 31 is rotated by the XYZ stage 43 or by means for rotating the sample 31. The polarization dependent pickup 39 is relatively rotated with respect to 31, and the direction of magnetization is detected from a change in the output of the polarization dependent pickup 39.
That is, for example, the direction of the magnetization can be detected by obtaining the angle at which the output of the polarization-dependent pickup 39 is maximized. The maximum signal intensity at this time is used to observe the surface shape of the sample, and the intensity and direction of the magnetization can be obtained from the rotation angle of the polarization-dependent fiber at which the maximum signal intensity is obtained. Therefore, in this case, there is no need to provide a fiber probe for surface shape measurement, and the apparatus can be simplified.

FIG. 2 shows a schematic configuration of a reflection type magnetic domain observation NFM as another embodiment of the present invention. In the NFM shown in the figure, a polarization dependent pickup 65 and a fiber pickup 67 are used to scan a sample 63 placed on a sample table 61. The sample-side tips of the polarization-dependent pickup 65 and the ordinary fiber pickup 67 have openings smaller than the wavelength of the illumination light. The polarization-dependent pickup 65 is constituted by a polarization-maintaining fiber as in FIG. 1 and is driven by an XYZ stage 69. The other end of the polarization dependent pickup 65 is connected via a half mirror 71 to a photomultiplier 73 and an illumination optical system from a laser light source 75. The output optical path of the laser light source 75 is provided with a half mirror 77 and a reflecting mirror 79, and the half mirror 71 of the polarization-dependent pickup 65 is linearly polarized through the optical path including the half mirror 77 and the reflecting mirror 79. Light is incident. An ordinary fiber pickup 67 is also provided with a driving XYZ stage 81, and a photomultiplier 85 is optically coupled to the other end of the fiber pickup 67 via a half mirror 83. The half mirror 83 is configured to receive illumination light from a laser light source 75 via the half mirror 77.

XYZ stages 69 and 8 for polarization dependent pickup 65 and fiber pickup 67
1 are connected to the outputs of the XYZ drive circuits 87 and 89, respectively. Also, the photomultiplier 7
The output of 3 is a display circuit 9 similar to that in the device of FIG.
1 and the output of the other photomultiplier 85 is input to the XYZ drive circuit 89. The output of the XYZ drive circuit 89 is also input to the microcomputer 93, and a control signal for driving is input to the XYZ drive circuit 87 from the microcomputer 93. The output of the display circuit 91 is connected to the display device 95.

In the apparatus shown in FIG. 2, linearly polarized light output from a laser light source 75 passes through a half mirror 77 and a reflecting mirror 79, further passes through a half mirror 71, passes through a fiber portion of a polarization dependent pickup 65, and has an opening at the tip. From the sample 63 and emitted to the sample 63. Then, the light reflected by the surface of the sample 63 and returned has its polarization plane rotated by the so-called magnetic Kerr effect according to the magnetization of the sample 63. Therefore, when this light is picked up again by the polarization dependent pickup 65, an optical output corresponding to the rotation of the polarization plane of the return light is input to the photomultiplier 73 via the half mirror 71. The photomultiplier 73 multiplies the input optical signal and converts it into an electric signal, which is input to the display circuit 91. Such a signal is obtained while scanning the surface of the sample 63 using the XYZ stage 69 driven by the XYZ drive circuit 87. Such a signal corresponds to the intensity of the magnetization at the point to be detected on the sample, and thus a signal corresponding to the magnitude and presence or absence of the magnetization of the sample 63 is obtained by such an operation.
1 and the display device 95 can display an image corresponding to the state of magnetization of the sample 63.

On the other hand, the output light of the laser light source 75 also enters one end of the ordinary fiber pickup 67 via the half mirrors 77 and 83. This light is transmitted from the opening at the tip of the fiber pickup 67 to the sample 6 as an evanescent wave.
3 is irradiated. Then, the evanescent wave reflected from the sample 63 is detected again by the fiber pickup 67.
The output of the photomultiplier 85 corresponds to the shape of the sample surface because it varies according to the distance between the tip 7 and the surface of the sample 63. Accordingly, the output of the photomultiplier 85 can be used to remove the shape dependence of the output of the polarization dependent pickup 65 in the same manner as described above, and the magnetization characteristics can be observed more accurately.

As described above, the reflection type NFM for magnetic domain observation
Is different from the above-mentioned transmission type magnetic domain observation NFM in that the sample is irradiated with an evanescent wave through an opening at the tip of the probe, and the evanescent wave reflected on the sample surface is picked up again by the same probe. In the reflection type magnetic domain observation NFM, the light returning from the fiber in the probe overlaps with the evanescent wave reflected on the sample surface and the light reflected from the laser light source 75 at the probe tip and returned. Utilizing the distance between the probe and the sample of the evanescent wave, that is, the Z-direction dependency (which is proportional to Z- ^3.8 ), the fiber of the probe is modulated in the Z-axis direction to perform synchronous detection.

Further, in order to detect the direction of magnetization on the surface of the sample 63, the polarization dependent pickup 65 is rotated relative to the sample 63 to determine the direction of the maximum output, as in the apparatus shown in FIG. , The direction of magnetization can also be determined.
The maximum signal intensity at this time is used to observe the surface shape of the sample, and the intensity and direction of magnetization can be obtained from the rotation angle of the polarization-dependent fiber at which the maximum signal intensity is obtained. There is no need to provide a fiber probe for use, and the apparatus can be simplified.

[0032]

As described above, according to the present invention, linearly polarized light is used as illumination light for a sample, an analyzer using a polarization-maintaining fiber is used as a detector, and the polarization direction of the illumination light is so-called. By utilizing the fact that the sample rotates by the Faraday effect or the magnetic Kerr effect according to the magnetization of the sample, the direction and presence or absence of the magnetization can be measured. Therefore, unlike the conventional polarization microscope, the resolution is not limited by the wavelength of the irradiation light, and a high-resolution optical microscope for observing magnetic domains, which is sufficiently compatible with the size of magnetic domains formed in a sample such as a magnetic material, is realized. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a transmission magnetic domain observation NFM as a magnetic domain observation near-field scanning microscope according to one embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a reflection type magnetic domain observation NFM as a magnetic domain observation near-field scanning microscope according to another embodiment of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of a general near-field scanning microscope.

[Explanation of symbols]

 31, 63 Sample 33 Prism 35, 75 Laser light source 37 Beam expander 39 Polarization dependent pickup 41, 47, 73, 85 Photomultiplier 43, 49, 69, 81 XYZ stage 45 Fiber pickup 51, 53, 87, 89 XYZ drive Circuit 55, 91 Display circuit 57, 95 Display device 59, 93 Microcomputer 61 Sample table 65 Polarization dependent pickup 67 Fiber pickup 71, 77, 83 Half mirror 79 Reflector

Claims (6)

(57) [Claims] 1. A light irradiation means for irradiating linearly polarized light from the back surface of a sample, and a polarization-dependent pickup which is relatively scannable with respect to the sample and detects a change in the rotation angle of the polarization of the evanescent wave on the surface of the sample. Means for observing a magnetic domain in a near-field scanning microscope. 2. The apparatus according to claim 1, further comprising: a second pickup unit which is relatively scannable with respect to the sample and detects an intensity of an evanescent wave on the surface of the sample. 2. The near-field scanning microscope for magnetic domain observation according to claim 1, wherein a change in an output signal intensity of the polarization dependent pickup means due to a surface shape is corrected. 3. A means for relatively rotating the polarization dependent pickup means and the sample, and a means for detecting the direction of magnetization from a change in the output signal intensity of the polarization dependent pickup means caused by the rotation. The near-field scanning microscope for magnetic domain observation according to claim 1, comprising: 4. A light source means for outputting linearly polarized light, and an aperture which is scannable relative to a sample and has an aperture smaller than a wavelength of the light output from the light source means. Polarization-dependent pickup means for receiving light from the sample and irradiating the sample through the opening, and detecting a change in the rotation angle of the polarization of light returning through the opening again by reflection from the sample surface due to the irradiation. Near field scanning microscope for magnetic domain observation. 5. The apparatus according to claim 1, further comprising an opening which is relatively scannable with respect to said sample, has an aperture smaller than a wavelength of light output from said light source means, receives light from said light source means, and passes said sample through said opening. And a second pickup means for detecting the intensity of light returning through the opening again by reflection from the sample surface due to the irradiation, and using the output of the second pickup means to change the shape of the sample surface. The near-field scanning microscope for magnetic domain observation according to claim 4, wherein a change in the output signal intensity of the polarization dependent pickup means is corrected. 6. A means for relatively rotating the polarization dependent pickup means and the sample, and a means for detecting a direction of magnetization from a change in output signal intensity of the polarization dependent pickup means caused by the rotation. The near-field scanning microscope for magnetic domain observation according to claim 4, wherein the microscope is provided with: