JPH0454336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the measurement of the spin polarization of an electron beam in a two-dimensional plane, and particularly to an apparatus suitable for detecting the direction of spin polarization.

[Background of the invention]

Spin polarization detectors utilize the fact that when an object consisting of a magnetized ferromagnetic material or heavy atoms is irradiated with an electron beam, the amount of electron beam absorbed by the object depends on the spin. Pierce et al., Review of Science Instruments, 52.
(10) 1981, 1437 D. T. Pierce et al., Rev. Sci.
Disclosed in Instrum.52(10) 1981, 1437.

First, the outline of this method will be explained with reference to FIG. As shown in FIG.
If the spin polarization of the incident electron beam e is zero, the energy E _i of the incident electron beam e is
The relationship between the current I _AB absorbed by the polycrystalline gold 10 and the value Is = I _AB /I _IN normalized by the incident current I _IN is the second
This will be the straight line shown by Iso in the figure. However, in Figure 2, α
= 25° is shown. Moreover, the incident electron beam e is
When the polarization is +100% or -100% in the direction of the paper normal n, these relationships are expressed as Is in Figure 2, respectively.
It becomes a straight line shown by ↑ and Is↓. Let E _ip be the incident energy E _i at which Iso becomes zero, and at this E _ip
If the values of Is↑ and Is↓ are +Io and −Io, respectively,
By measuring Is=Is _x for an incident electron beam of unknown polarization with energy _Eip , it is possible to know the polarization P=Is _x /Io in the direction of the normal n to the paper surface.

However, this method can only measure spin polarization in one dimension, changes in the surface state of polycrystalline gold 10 greatly change _Eip , making stable measurements impossible, and However, there were drawbacks such as the need to measure with high precision.

[Purpose of the invention]

Therefore, an object of the present invention is to provide an electron beam that can measure the direction and magnitude of a two-dimensional in-plane component of spin polarization with high precision, almost independently of changes in the surface state of an object irradiated with an electron beam. An object of the present invention is to provide a spin polarization detector.

[Summary of the invention]

Even with conventional detectors, for electron beams where only the polarization direction can be reversed without changing the absolute value of the polarization rate, it is almost unaffected by changes in the surface state of the object irradiated with the electron beam. Polarization rate measurement is possible.
Instead of reversing the polarization direction, the present invention changes the direction of irradiation onto the object while keeping the polarization direction constant, and obtains the same result as equivalently reversing the polarization direction. By adopting this method, it has become possible to measure the direction and size of two-dimensional in-plane components, which was not possible with conventional methods.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. A spin polarization measurement electron beam 1 incident along the central axis 9 of the detector is collimated by a collimator 2. An arrow S in the figure indicates the spin polarization direction of the incident electron beam 1. This electron beam 1 is transferred to the generator 7
Two pairs of deflection electrodes 3 arranged perpendicularly to each other to which sinusoidal voltages v _r and v _r ' with a phase shift of 90° from
3', and the angle α between the central axis 9 and the electron beam 1 is
The electron beam 1 is rotated around the central axis 9 as shown by an arrow R while keeping it constant. Furthermore, this electron beam 1 is passed through the inside of an axially symmetric DC electric field E _r created by a ring-shaped deflection electrode system 4, 4', and the central axis 9
The beam is made incident on the upper surface of a gold polycrystalline target 6 having a surface perpendicular to , while only the direction of incidence is rotated while keeping the angle α formed with the central axis 9 constant.

Here, since the spin direction S is constant regardless of the direction of electron movement, when viewed from a coordinate system that is stationary with respect to the rotating electron orbit 1 (that is, assuming that the direction of incidence of the electron is fixed) , central axis 9
The electron spin direction S rotates in a plane parallel to the target surface (that is, around the central axis 9). Therefore, the absorbed current is to the target 6 becomes an alternating current signal that changes sinusoidally between + _in and _-in as shown in FIG. The signal processor 8 synchronously detects the absorbed current is with the signal v _r from the generator, and measures the phase shift difference Δ between is and v _r and the magnitude in of _is . The polarization direction is calculated from this Δ, and the ratio of this i _n to the sum of the secondary electron current i ₂ from the target collected by the collector 5 and the absorption current is (=incident current) [i _n /(i ₂ + is)] to calculate the spin polarization rate.

That is, in the signal processor 8, the polarization direction and spin polarization rate P are determined according to the following equations.

=Δ P=i _n /I ₀ (i ₂ +is) Here, it is the angle measured from the normal to the surface of the deflection electrode 3 in the rotation direction of the beam. I _p is given in FIG. 2 and is a constant that depends only on the surface condition of the target 6. Here, I _p is affected by E ₀ mentioned above, but I _p is not affected as much as E _p is affected by the surface condition of the target.

〔Effect of the invention〕

As detailed above, according to the present invention, the direction and magnitude of the two-dimensional in-plane component of spin polarization can be detected almost independently of the surface state of the object irradiated with an electron beam. In particular, the polarization direction can be easily detected simply by measuring the phase without being affected by the surface condition. Furthermore, since the object to be measured is an alternating current signal, by adopting the lock-in method, stable measurement is possible without being affected by noise.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams and curve diagrams for explaining the principle of spin polarization measurement using the conventional method, and FIGS. 3 and 4 are diagrams of the electron spin polarization detector according to the present invention. FIG. 2 is a basic configuration diagram and an explanatory curve diagram thereof. 1...Electron beam to be measured, 2...Collimator, 3,
3'... Deflection electrode, 4,4'... Ring-shaped deflection electrode, 5... Secondary electron collector, 6... Polycrystalline gold target, 7... Generator, 8... Signal processor.

Claims (1)

[Claims] 1 means for supplying a collimated electron beam, means for tilting the electron beam at a predetermined angle with respect to its central axis and rotating it around the central axis while holding the angle; means for changing the direction so as to irradiate a target placed on the central axis; means for detecting current absorbed by the target due to the electron beam irradiated to the target; and secondary electrons from the target due to the electron beam irradiated to the target. a means for detecting a current, a signal from the means for detecting the secondary electron current by calculating the polarization direction of the electron beam from a signal given to the means for rotating the electron beam and a signal from the means for detecting the absorbed current; An electron spin polarization detector comprising means for calculating the polarization ratio of an electron beam from a signal of the absorption current detection means and a constant given in advance for the target.