JPS6257063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a so-called Lorentz electron microscope for observing the magnetic domain structure of a sample while applying a magnetic field perpendicular to the sample surface and keeping an objective lens in defocus.

In the so-called Lorentz electron microscope, which applies a magnetic field perpendicular to the surface of a magnetic thin film sample to observe the magnetic domain structure of the sample, the magnetic field of the objective lens is used to magnetize the sample. uses the objective lens as an imaging lens,
Because the strength of the magnetic field applied to the sample was determined by moving the sample along the optical axis, it was not possible to change the strength of the applied magnetic field rapidly. In addition, in such conventional equipment, the number of samples is
In order to apply a magnetic field of 100 Gauss or less, the sample must be moved outside the objective lens, and the strength of the magnetic field applied to the sample cannot be continuously increased from zero. Furthermore, in order to change the strength of the magnetic field applied to the sample, the sample must be moved along the optical axis by more than a few centimeters, which necessitates the use of a top-entry type sample holder. It is not possible to easily tilt or heat the sample.

The present invention solves the drawbacks of such conventional devices,
We have developed a Lorentz electron microscope that can continuously increase the strength of the magnetic field applied to the sample from zero, can quickly change the strength of the applied magnetic field, and can observe magnetic domains while tilting and heating the sample. is intended to provide.

Therefore, the present invention provides an upper magnetic pole piece 5a and a lower magnetic pole piece 5a.
b, and an excitation power source 7 for changing the excitation current of the objective lens. The hole 9 is the lower magnetic pole piece 5.
a sample holder 1 for placing a magnetic sample 11 on the optical axis through the through hole 9;
Of the portion of the lower magnetic pole piece 5b left by drilling the through hole 9, the portion M facing the upper magnetic pole piece 5a is protected from the magnetic field formed in the magnetic pole gap of the objective lens. The thickness is selected so that the sample is shielded and when the excitation current supplied from the excitation power source to the objective lens increases, magnetic saturation occurs and leaked lens magnetic field is applied to the sample. A lens 1 for forming an image on the fluorescent screen 14 based on the electron beam transmitted through the sample
It is characterized by being equipped with 2 and 13.

An embodiment of the present invention will be described in detail below based on the drawings.

FIG. 1 is for showing the outline of one embodiment of the present invention. In the figure, 1 is an electron gun, 2 and 3 are a first,
This is the second converging lens. 4 is an objective lens, 5a is an upper magnetic pole of the objective lens, 5b is a lower magnetic pole of the objective lens, 6 is an excitation coil of the objective lens, and an excitation current is supplied to the excitation coil 6 from a power source 7. . The lower magnetic pole piece 5b has a through hole 9 located near its top surface and perpendicular to the optical axis.
is formed between the upper magnetic pole 5a and the lower magnetic pole 5b due to magnetic saturation when the excitation current of the objective lens exceeds a certain value. The magnetic field is selected so that the main magnetic field applied to the sample 11 leaks and a magnetic field perpendicular to the sample surface is applied to the sample 11. A side entry type sample holder 10 made of a non-magnetic material can be freely inserted into the through hole 9, and a thin film magnetic sample 11 is mounted on the sample holder 10. 12 is an intermediate lens, 13 is a projection lens, 14
is a fluorescent plate.

In such a configuration, if the excitation current for the excitation coil 6 of the objective lens 4 is supplied from the lens power supply 7, the magnetic field strength along the optical axis 8 of the objective lens 4 will be equal to the magnitude of the current supplied from the power supply 7 to the excitation coil 6. Depending on the situation, the result will be as shown in FIG. In Figure 2, the horizontal axis represents the position taken along the optical axis; in the figure, the position indicated by thin line O is the sample position, and the position indicated by broken line A is the gap between the upper and lower magnetic poles. The position indicated by B represents the center position of the upper magnetic pole 5 that remains after the lower magnetic pole 5b has been hollowed out.
This corresponds to the position of portion M facing a. Second
The vertical axis of the figure represents the magnetic field strength. As is clear from Fig. 2, when the current supplied to the excitation coil 6 changes by a certain amount, the magnetic field along the optical axis 8 changes as shown by A, B, C, D, and E in Fig. 2 in descending order of current value. Become. As is clear from FIG. 2, the portion M of the lower magnetic pole 5b in FIG.
The portion M shields the magnetic field from the magnetic field formed in the gap between the lower magnetic pole a and the lower magnetic pole 5b. However, if the current supplied from the power source 7 to the excitation coil 6 increases and the strength of the magnetic field exceeds a certain level, the portion M
is applied to the sample 11, causing magnetic saturation and leaking a magnetic field in the optical axis direction. Therefore, since the main magnetic field formed in the gap between the upper magnetic pole 5a and the lower magnetic pole 5b is formed above the sample 11, the objective lens does not function as an imaging lens for the sample 11, but only as an irradiation lens. Therefore, the excitation current of the objective lens does not need to be fixed to a constant value defined by the imaging conditions, but can be changed. Therefore, when considering the objective lens as an irradiation lens,
The relationship between the excitation current of the objective lens and the beam spot diameter of the electron beam irradiated onto the sample 11 is as shown in FIG. This figure shows that in the excitation current region shaded in Figure 3, the beam spot diameter is small and the parallelism of the electron beam is poor, resulting in a blurred image and is not suitable for observing transmission images. It is clear that the excitation current intensity other than that can be set arbitrarily.

Figure 4 shows the measurement of the leakage magnetic field strength at the sample surface position when the excitation current strength of the objective lens was gradually increased.As is clear from this figure, the excitation strength of the objective lens was continuously increased from 2000AT. The leakage magnetic field strength can be gradually increased from 0 as the magnetic field is increased.

Therefore, in the apparatus according to the present invention, the electron beam EB generated from the electron gun 1 is converged by the first and second converging lenses 2 and 3, and then converted into an electron beam having a certain divergence angle by the objective lens 4. After that, the sample 11 is irradiated. The electron beam transmitted through the sample 11 is guided by an intermediate lens 12 serving as an objective lens and a projection lens 13, and is projected onto a fluorescent plate 14, and an image representing the magnetic domain structure of the sample is displayed on the fluorescent plate 14. However, the strength of the magnetic field perpendicular to the sample surface applied to the sample can be quickly and easily changed by changing the excitation current of the objective lens without any mechanical movement of the sample. Furthermore, since a side entry type sample holder can be used in the apparatus of the present invention, it is possible to easily tilt the sample or observe the sample in a heated state.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic diagram of an embodiment of the present invention, FIG. 2 is a diagram showing the magnetic field strength along the optical axis 8 when the excitation current of the objective lens takes various values, Figure 3 is a diagram showing the relationship between the probe diameter of the electron beam irradiated onto the sample and the excitation intensity (AT) of the objective lens, and Figure 4 is a diagram showing the relationship between the vertical magnetic field strength applied to the sample and the excitation intensity of the objective lens. FIG. 1: Electron gun, 2: First converging lens, 3: Second
converging lens, 4: objective lens, 5a: upper magnetic pole,
5b: Lower magnetic pole, 6: Excitation coil, 7: Power supply, 8:
Optical axis, 9: Through hole, 10: Sample holder, 11:
Sample, 12: Intermediate lens, 13: Projection lens, 1
4: Fluorescent plate.

Claims (1)

[Claims] 1 An objective lens 4 consisting of an upper magnetic pole piece 5a and a lower magnetic pole piece 5b, and an excitation power source 7 for changing the excitation current of the objective lens are provided, and the lower magnetic pole piece 5
A through hole 9 is bored in the lower magnetic pole piece 5b near the top surface of the magnetic pole piece 5b and is perpendicular to the optical axis. A sample holder 10 is provided, and of the portion of the lower magnetic pole piece 5b left by drilling the through hole 9, the portion M facing the upper magnetic pole piece 5a is formed in the magnetic pole gap of the objective lens. The thickness of the lens is selected so that when the excitation current supplied from the excitation power source to the objective lens increases, magnetic saturation occurs and leaked lens magnetic field is applied to the sample. An electron microscope characterized in that it is equipped with lenses 12 and 13 for forming an image on a fluorescent screen 14 based on the electron beam transmitted through the sample.