JPH0624109B2 - Phase contrast electron microscope for magnetic domain observation - Google Patents

Description

The present invention relates to a phase-contrast electron microscope for observing magnetic domains, which enables observation of magnetic domains of a magnetic substance using a scanning transmission electron microscope.

[Conventional technology]

Conventionally, a phase contrast image observation method DP using a scanning transmission electron microscope
In magnetic domain observation of a magnetic material by C (Differential Phase Contrast), a diffraction image of a magnetic material sample placed immediately in front of the front focal point of the objective lens is magnified and projected by an intermediate lens and a projection lens and divided into four in a circular symmetry or The detection is performed by a detector composed of multi-divided detection elements, and the electron beam intensity of each detection element is processed as an image signal to obtain a magnetic domain contrast.

[Problems to be solved by the invention]

However, in the conventional magnetic domain observation, in order to observe the contrast in the specific magnetization direction, it is necessary to rotate the observation sample or select the image signal of the detection element.
Moreover, it is difficult to accurately obtain a contrast in an arbitrary magnetization direction with a finite detection element.

The present invention is to solve the above problems, and an object of the present invention is to provide a phase-contrast electron microscope for observing magnetic domains, which does not require rotation of an observation sample for magnetization intensity in an arbitrary direction and can be observed accurately. And

[Means for solving problems]

Therefore, the phase-contrast electron microscope for observing the magnetic domain of the present invention irradiates the magnetic material sample with an electron beam while scanning with an electron beam scanning means, and forms a diffraction image formed by the objective lens of the magnetic material sample with an intermediate lens and a projection lens. In a phase-contrast electron microscope for observing a magnetic domain, which is magnified and projected and detected by a detector composed of four divided detection elements, and the electron beam intensity of each detection element is processed as an image signal to obtain a magnetic domain contrast. X
A first arithmetic circuit that calculates a magnetization component in each direction based on two sets of difference signals in each of the direction and the y direction; a second arithmetic circuit that calculates an angle component of magnetization from the magnetization component in each direction; A comparator that outputs a gate signal when the arithmetic circuit output is within a predetermined angle range, a gate circuit that conducts control by the gate signal from the comparator, and extracts the first arithmetic circuit output, and a comparator A third arithmetic circuit for calculating the magnetization intensity from the magnetization component and a display unit for displaying an image representing the calculated magnetization intensity are provided.

[Action]

According to the present invention, the magnetization component in each direction is calculated from two difference signals in each of the x direction and the y direction, the angle component of the magnetization is calculated from the magnetization component in each direction, and the angle component of the magnetization is within the predetermined angle range. When it is, the magnetization components in each direction are extracted, and the magnetization intensity is calculated from the extracted magnetization components within the predetermined angle range and displayed, so that the magnetization intensity in any direction can be observed.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a diagram showing the structure of a phase-contrast electron microscope for observing magnetic domains of the present invention, in which 1 is an electron beam, 2 is a scanning coil, 3 is an optical axis, 4 is a magnetic sample, and 5a is an irradiation side objective. Lens, 5b is an image forming side objective lens, 6 is an intermediate lens, 7 is a projection lens,
8 is a detector, 9 is a scanning coil driving unit, 10 ₁ , 10 ₂ ,
10 ₃ and 10 ₄ are amplifiers, 11 to 13 are arithmetic circuits, and 14
Is a logic circuit, 15 is a comparator, 16 is a control device, 1
Reference numeral 7 is a gate circuit, 18 is an arithmetic circuit, and 19 is a display device.

In the figure, an electron beam 1 generated from an electron gun (not shown)
Depending on the scanning coil 2 (A-A ') or (B-
B ') and the sample 4 is scanned by the objective lens 5a.
Is converged to. The sample 4 is placed in the vicinity of the front focal point of the image-side objective lens 5b, and when viewed two-dimensionally, the optical axis 3 is centered and the sample 4 is directed leftward downward perpendicularly to the paper surface. , Right up It is assumed that each is magnetized.

When an electron beam is incident on this sample 4 at an incident angle 2α _i , as shown in FIG. 2, a diameter D is formed on the back focal plane of the objective lens 5b.
= F ₀ × 2α _i (f ₀ is the focal length).

Then, when the electron beam 1 passes through the sample 4, it is deflected by the Lorentz force according to the magnetization direction of the sample, and (A-A ') becomes (C-C') and (B-B ') corresponding to the sample irradiation angle. −
B ') becomes (DD-D), and (C-C') and (D-
D ′) is imaged and projected as a diffraction disk on the detector 8 by the image forming action of the intermediate lens 6 and the projection lens 7.

On the other hand, when the main deflection plane of the scanning coil 2 is regarded as the object plane, (AA ') and (BB') are similarly imaged on the detector 8 as a stationary disk pattern.

Therefore, when the surface of the sample is scanned by the scanning coil 2, a static diffraction disk (C-C ') or (DD') is obtained in a region where the magnetization direction of the sample 4 is constant irrespective of the scanning conditions of the sample. , Which are separated according to the magnetization direction. Detector 8
Is S ₁ in the x-axis and y-axis directions as shown in the figure,
Since it is divided into S ₂ , S ₃ , and S ₄ , for example, (S ₂
If the difference signal of −S ₃ ) is detected, the magnetic domain contrast can be obtained.

The detection signals of the detectors S ₁ , S ₂ , S ₃ , and S ₄ are amplified and input to the arithmetic circuits 11 and 12, and the next arithmetic operation is performed.

This denominator (S ₁ + S ₂ + S ₃ + S ₄ ) is for normalizing the signal. The outputs of the arithmetic circuits 11 and 12 are input to the arithmetic circuit 13. In the arithmetic circuit 13, when the magnetization is +, θ = tan ⁻¹ | y / x | + nπ / 2 is calculated for the angle component θ. In this case, the value of n is input from the arithmetic circuit 14. That is, the logic circuit 14 outputs the value of n which is determined by the following conditions (1) to (4) whether the output signals x and y are positive or negative.

When x ≧ 0, y ≧ 0: n = 0 x <0, y ≧ 0: n = 1 x <0, y <0: n = 2 When x ≧ 0, y <0: n = 3 The comparator 15 is controlled by the controller 16 that selects the arbitrary magnetization direction component θ and the selection width δθ, operates only when the output θ of the arithmetic circuit 13 is in the range of θ + δθ to θ, and the gate circuit 17 Close. As a result, the output signals of the arithmetic circuits 11 and 12 are input to the arithmetic circuit 18 via the gate circuit 17, and the magnetization intensity || of the sample is calculated by the following equation.

In this way, by selecting the angle θ (θ + δθ to θ) of the arbitrary magnetization direction by the control device, the magnetization intensity || of the sample with respect to the selected θ can be observed as magnetic domain contrast on the display 19.

〔The invention's effect〕

As described above, according to the present invention, the four-division type detection element is x,
y By extracting each as a difference signal of two sets divided into two, the vector of the magnetization direction of the sample can be extracted as, and the magnetization intensity in any direction can be observed.

[Brief description of drawings]

FIG. 1 is a diagram showing the structure of a phase-contrast electron microscope for magnetic domain observation of the present invention, and FIG. 2 is a diagram showing a disk pattern of a sample. 1 ... Electron beam, 2 ... Scanning coil, 3 ... Optical axis, 4 ...
Magnetic material sample, 5a ... Irradiation side objective lens, 5b ... Imaging side objective lens, 6 ... Intermediate lens, 7 ... Projection lens,
8 ...... detector, 9 ...... scanning coil _driver, 10 1, 10
₂ , 10 ₃ , 10 _4, ... Amplifier, 11-13 ... Arithmetic circuit, 14 ... Logic circuit, 15 ... Comparator, 16 ...
... control device, 17 ... gate circuit, 18 ... arithmetic circuit,
19 ... Display device.

Claims (1)

[Claims] 1. A magnetic material sample is irradiated with an electron beam while being scanned by an electron beam scanning means, and a diffraction image formed by an objective lens of the magnetic material sample is magnified and projected by an intermediate lens and a projection lens.
In a phase-contrast electron microscope for magnetic domain observation, which is detected by a detector including divided detection elements, and the electron beam intensity of each detection element is processed as an image signal to obtain a magnetic domain contrast, in the x direction and the y direction of the detection element. With two sets of difference signals,
A first arithmetic circuit for calculating a magnetization component in each direction, a second arithmetic circuit for calculating an angle component of magnetization from the magnetization component in each direction, and a gate when the output of the second arithmetic circuit is within a predetermined angle range. A comparator that outputs a signal, a gate circuit that conducts conduction control by a gate signal from the comparator, and extracts a first arithmetic circuit output, and a third operation that calculates a magnetization intensity from the extracted magnetization component within a predetermined angle range. Circuit,
A phase-contrast electron microscope for observing magnetic domains, comprising: a display unit that displays an image representing the calculated magnetization intensity.