JPH11144927A - Spin orbit compensating characteristic for ferromagnetic samarium material, its control method, and charged particle spin decomposition element utilizing the characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charged particle spin decomposition element which can realize and control a state such that the polarizing directions of electron spins in a material are directed in one direction extending over a macroscopic region and do not have magnetization, is made of a ferromagnetic material by applying the state and is not accompanied by such problems as the formation of magnetic domains, the occurrence of a leakage magnetic field, etc. SOLUTION: An appropriate ferromagnetic material in which samarium constituting the the material mainly bears magnetization is selected and controlled, so that the magnetization by spin magnetic moment and the magnetization by orbital magnetic moment offset each other at an arbitrary temperature (compensating temperature) by performing element replacement, addition, etc. An object state is obtained by directing the polarizing directions of the electron spins in the material in one direction by applying a magnetic field upon the material for temperature at which magnetization is exhibited and making the magnetic field zero by shifting the temperature to the compensating temperature. In addition, a spin decomposition element is constituted by using the substance as the material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new type of magnetic material, a method for controlling its properties, and a technique for spin decomposition of charged particles utilizing the properties. Applicable products include a charged particle beam spin polarization measurement target, a spin-polarized electron beam generation tip, and a probe for a spin-polarized tunnel microscope / exchange force microscope.

[0002]

2. Description of the Related Art Magnetic materials have been widely applied to industrial technology as permanent magnet materials, soft magnetic materials, and magnetic recording materials.
In these applications, the magnetization of a magnetic material (generated magnetic field) and its interaction with an external magnetic field are essentially utilized.

On the other hand, in recent years, coupled with the study of the dependence of various interactions on the particle spin in the fields of high energy physics and solid state physics, the improvement of techniques related to generation of spin-polarized particles and measurement of the degree of spin polarization of particles has been improved. Is desired.

[0004] A magnetic material is a substance in which the spin of electrons is (spatially) polarized in a temperature range lower than a certain temperature called a magnetic transition point, and therefore can be a device material suitable for such a spin utilization technique. That is easily imagined. However, in practice, semiconductors excited by a circularly polarized laser are used for many spin-polarized electron guns, and the mechanism for measuring the degree of spin polarization of an electron beam uses an electron beam and heavy atoms (such as gold and tungsten). Diffraction and scattering phenomena are used. That is, the use of ferromagnetic materials in this field is surprisingly small.

[0005] This situation mainly depends on the fact that the electron spin order in the macroscopic region of the ferromagnetic material usually involves the generation of magnetization. The fact that the ferromagnetic material has magnetization works disadvantageously in the following two points when it is used as a spin-resolving element.

One is that a ferromagnetic material normally in a no-magnetic field tends to maintain a stable energy state by being divided into a number of small regions (magnetic domains) having different electron spin polarization directions due to its own magnetization. Is a point. That is, although the ferromagnetic material is used, the electron spins are not always aligned over a macroscopic region, and it is generally difficult to quantitatively control and evaluate the magnetic domain structure.

When the polarization direction of electron spins in a ferromagnetic material is aligned in one direction by any method, a magnetic field leaks from the ferromagnetic material itself. Alternatively, if a magnetic field is externally applied as a method for aligning spins, there is a leakage magnetic field from the magnetic field generator. These influence the electric charge and spin magnetic moment of the spin-polarized charged particles to be detected or generated in the form of Lorentz force, magnetic force, Lamo application, and the like. This is the second point.

[0008]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above background, and an object of the present invention is to align the direction of polarization of electron spins in a material in one direction over a macroscopic region. And realizing and controlling a state without magnetization, and providing a spin-dissociation element for charged particles which is a ferromagnetic material and does not have the above-mentioned problems.

[0009]

One of the objects of the present invention is to realize a state in which the direction of polarization of electron spins in a substance is aligned in one direction over a macroscopic region and has no magnetization. The “control” is to appropriately select a ferromagnetic material whose magnetization is mainly carried by samarium (Sm) constituting the material (hereinafter, referred to as a ferromagnetic Sm material), and to control the composition and heat as described later. This can be achieved by performing a history process.

Note that Sm generally has five 4f electrons in a solid, but there are cases where the number is six depending on the substance. Here, only the former electronic configuration is considered, and this is simply described as Sm.

In Sm, the spin magnetic moment caused by the spin polarization of the electron and the orbital magnetic moment caused by the orbital motion are substantially the same, and both of them have a spin magnetic moment.
The total magnetic moment is formed by coupling in the opposite direction by the effect of relativity called orbital interaction.

Accordingly, in the ferromagnetic Sm material, the magnetization originally caused by the spin magnetic moment and the magnetization caused by the orbital magnetic moment largely cancel each other, and the macroscopic magnetization is extremely small.

Further, Sm is 4f called a J multiplet.
Since the energy interval between the lowest energy base multiplet and the next lowest energy first excitation multiplet in the electron energy state is narrow (about 1500 K), the temperature dependence of the spin magnetic moment and orbital magnetic moment are slightly different. It has the characteristic of showing sex.

Due to these two features, the thermal average value of the total magnetic moment of Sm in the temperature range below the magnetic transition point greatly depends on the surrounding environment of the ion, and its temperature dependence is different from that of many other magnetic ions. Will be very different.

This unique temperature dependency can be easily understood by considering it in correspondence with the thermal magnetization curve of the ferrimagnetic material. That is, in the ferrimagnetic material, the difference in the temperature dependence of the thermal average value of the magnetic moment of the dissimilar magnetic element bonded in the opposite direction is embodied as the temperature dependence of various types of magnetization, whereas in the case of Sm, The difference in the temperature dependence of the thermal average value of the spin magnetic moment and the orbital magnetic moment of each Sm causes various temperature dependences of the thermal average value of the total magnetic moment of each Sm. FIG. 1 schematically shows several types of such temperature dependence of the total magnetic moment of Sm.

As can be inferred from the similarity with the ferrimagnetic material, the ferromagnetic Sm material exhibits a compensation phenomenon in which the magnetization caused by the spin magnetic moment and the magnetization caused by the orbital magnetic moment cancel each other at a certain temperature. It is possible to realize.

Ferromagnetic S exhibiting this type of thermomagnetic behavior
At the temperature where the material has macroscopic magnetization (or when it is cooled from the temperature region without spontaneous magnetization and passes through the magnetic transition point), a magnetic field is applied from outside to the material, and the electron spin in the material is reduced. After aligning the polarization in one direction, the temperature is shifted to a temperature (compensation temperature) at which the magnetization caused by the spin magnetic moment and the magnetization caused by the orbital magnetic moment cancel out, and the magnetic field is reduced to 0, so that the electron It is possible to realize a state in which spin polarization directions are aligned in one direction over a macroscopic region and have no magnetization. In this case, the stability of the spin polarization in this state is guaranteed by the strong anisotropy due to the orbital magnetic moment of Sm.

However, not all ferromagnetic Sm materials have the above-mentioned compensation characteristics, and the manifestation of these characteristics and the control of the compensation temperature are important issues when trying to use them as materials. It is clear that The control of the compensation characteristics can be achieved by appropriately substituting or adding an element to the ferromagnetic Sm substance.

The operation can be considered in the following two ways.

One is to replace a part of the elements constituting the ferromagnetic Sm substance with a nonmagnetic element having no magnetic moment, or to add a nonmagnetic element to the ferromagnetic Sm substance. The effect is to change the environment around each Sm, and to influence the temperature dependence of the total magnetic moment of the Sm through the change of the environment. However, this operation must be performed within a range that does not involve significant alteration of the magnetic properties of the base material, especially the transition of the spin magnetic moment from a ferromagnetic arrangement to an antiferromagnetic arrangement or a significant decrease in the magnetic transition point. must not.

The second effect is that by replacing a part of Sm with another magnetic rare earth element having a different ratio of the spin magnetic moment and the orbital magnetic moment from Sm, the spin magnetic moment in the macroscopic magnetization of the substance is obtained. And the ratio of the portion caused by the orbital magnetic moment is changed.

In general, substitution is easy because rare earth elements are close in size to each other, and when the spin magnetic moments of the base material are ferromagnetically arranged, the spin magnetic moments of the substituted elements are basically also small. It is empirically known to maintain ferromagnetic coupling with the surrounding spin magnetic moment.

Therefore, more specifically, regarding the magnetic moment of Sm in the base ferromagnetic Sm material, when the orbital component exceeds the spin component, the spin magnetic moment is positive with respect to the total magnetic moment. When a heavy rare earth element (a rare earth element having seven or more 4f electrons) contributing to the direction and the spin component exceeds the orbital component, the spin magnetic moment becomes the total magnetic moment. With light rare earth elements (rare earth elements having less than 7 4f electrons) contributing in the negative direction to Sm, the magnetization is reduced by appropriately substituting Sm, and a compensation phenomenon is developed and controlled. It becomes possible.

It is understood that the main driving force for magnetic domain formation in a normal ferromagnetic material is magnetostatic energy. However, in the above-described compensated state in a ferromagnetic Sm material, there is no magnetization, so There is no energy gain from forming. Rather, it is considered that the formation of the boundary region (domain wall) of the magnetic domain is disadvantageous in terms of energy from the viewpoint of the anisotropy of the magnetic moment and the ferromagnetic interaction (exchange interaction).

In addition, the magnetic moment of Sm in an ordered state generally has a strong anisotropy due to an orbital moment. Further, it is considered that the external magnetic field must be applied in that direction, and thus the polarization direction of the electron spin in the ferromagnetic Sm material once aligned over the macroscopic region is stably maintained at the compensation temperature.

Further, since there is no magnetization, the magnetic field leaking to the outside in the compensation state can be considered to be practically zero.

As described above, by using a ferromagnetic Sm material having a compensation characteristic as a material and using it in a non-magnetized state in which the polarization directions of electron spins are aligned in one direction over a macroscopic region, It is possible to provide an element for spin decomposition of charged particles, which does not have the problems of magnetic domain formation and magnetic field leakage.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings.

FIG. 2 shows an example of the temperature dependence of the thermal average value of the total magnetic moment per Sm obtained from the actual thermal magnetization curve of a ferromagnetic compound whose magnetization is carried by Sm. These materials are ferromagnetic materials in which the spin magnetic moments of each Sm are arranged in parallel in the temperature range below the magnetic transition point, but as shown in the figure, the change in the thermal average value of the total magnetic moment with temperature is a ferrimagnetic material. Is very similar to the temperature dependence of the magnetization of

The values (○) obtained for a real substance are well reproduced by a theoretical calculation curve (solid line), and the spin magnetic moment and the orbital magnetic moment of each Sm in which the ferrimagnetic temperature dependence is inversely coupled. It can be confirmed that this is due to the difference in the temperature dependence of the heat average value of
Also, from the comparison with such theoretical calculations, among the exemplified compounds, SmZn and SmCd show that the magnetization due to the spin magnetic moment is larger than the magnetization due to the orbital magnetic moment, and the opposite is true for SmAl _2. Each is concluded.

FIG. 3 shows an example of the result of actually controlling the compensation characteristics by using a method of replacing a part of Sm, which is one of the control guidelines for the compensation characteristics, with another magnetic rare earth element. As described above, when a compound in which the magnetization due to the orbital magnetic moment is predominant such as SmAl ₂ is selected as the parent compound, the magnetization is reduced by substituting a part of Sm with a heavy rare earth element such as Gd. , A compensation state can be created. Substitution of a light rare earth element such as Nd, on the contrary, would increase the magnetization in this case. SmZ
When a parent compound such as n or SmCd, in which the magnetization due to the spin magnetic moment is dominant, is selected, the substitution of a light rare earth element is effective for developing the compensation characteristics.

FIG. 4 is a schematic diagram showing some applications of a spin-decomposing device for charged particles using a ferromagnetic Sm material in a compensated state. Here, all charged particles are described as ordinary electrons.

(A) shows a state in which a spin-polarized electron beam 1 collides with a ferromagnetic Sm material 2 in a compensated state in which the spin polarization is aligned in one direction, and an electron beam 4 measured by a detector 3.
FIG. 3 is a schematic diagram of an apparatus for measuring the spin polarization of the electron beam 1 based on the scattering / diffraction intensity of the sample or the spin asymmetry of the current 5 absorbed by the target.

(B) shows the scanning of the surface of the magnetic sample 6 by the probe 7 made of a ferromagnetic Sm material in a compensated state in which the spin polarization is aligned in one direction. FIG. 3 is a schematic diagram of an apparatus for observing a spin structure on a sample surface by utilizing a spin current dependence of a tunnel current or an exchange force during the period.

(C) is a chip whose main body is made of an electron-emitting material 8 and whose tip is made of a ferromagnetic Sm material 9 in a compensated state in which the tip is spin-polarized in one direction. It is used to extract an electron beam whose spin is polarized.

The principle of operation of the spin dissociation device shown here or a similar one is described in reference R.S. J. Celotta
et al. , PRL 43,728 (1979),
H. C. See Siegmann et al. , PRL 4
6, 452 (1981); Wiesendage
r et al. , PRL 65,247 (199
0), E. Kisker et al. , PRL 3
6,982 (1976). And so on. In each of the application examples shown in FIG. 4, a mechanism for changing the temperature of the element and a mechanism for generating a magnetic field used for aligning the spin polarization directions of the element in advance are not shown in the figure. It is assumed that

[0037]

As described above in detail, the ferromagnetic Sm material has the same temperature dependence of magnetization as the existing ferrimagnetic material, but the manifestation of the diversity depends on the spin magnetic moment. It is a novel magnetic material because it is caused by the difference in the temperature dependence of two different physical quantities, magnetization and magnetization by orbital magnetic moment. Therefore, in a ferromagnetic Sm material, it is possible to realize a ferromagnetic spin arrangement over a macroscopic region, which is conventionally considered to necessarily involve the generation of magnetization, in a non-magnetized state. This suggests that the substance can function as an element that cannot be replaced with other materials, and is expected to contribute to technological progress and industrial development.

A spin-resolving element, which is one of such applications, does not require, for example, a device for generating a circularly polarized laser or a magnetic circuit for reducing a leakage magnetic field, as compared with the conventional one. It can be expected that the cost and the burden on the design will be reduced. Further, if the compensation temperature is controlled to be the liquid nitrogen temperature according to the method described above, the temperature control in the operating state of the spin decomposition element becomes unnecessary,
This is also effective for further simplification of the device.

Another advantage of the device is that the spin polarization direction of the device can be arbitrarily selected without disturbing the spin of the charged particle to be generated and detected. Since the 4f level of Sm, in which the vector component of spin polarization is arbitrary, has a spin polarization of 100%, it is more efficient to use this for the mechanism for generating and detecting spin-polarized charged particles. Are expected.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating several types of temperature dependence of a thermal average value of a total magnetic moment of Sm in a temperature region below a magnetic transition point.

FIG. 2 shows ferromagnetic Sm compounds SmZn, SmCd, and SmA.
It is a diagram showing a temperature dependence of the thermal average of the total magnetic moment per Sm in l _2.

FIG. 3 is a diagram showing an example of a control result of a compensation characteristic of a ferromagnetic Sm material SmAl ₂ .

FIG. 4 is a schematic diagram showing an application example of a ferromagnetic Sm material to (a) an electron beam spin polarization measurement device, (b) a surface spin structure observation device, and (c) a spin polarized electron beam generator. .

[Explanation of symbols]

 Reference Signs List 1 electron beam 2 target (ferromagnetic Sm substance) 3 detector 4 electron beam 5 absorption current 6 sample 7 probe (ferromagnetic Sm substance) 8 electron emitting material 9 tip of electron beam generating tip (ferromagnetic Sm substance)

Claims (3)

[Claims] 1. a ferromagnet whose magnetization is mainly carried by the samarium constituent of the substance;
A state in which the spin maintains a ferromagnetic arrangement over a macroscopic region and the magnetization due to the orbital magnetic moment does not generate magnetization to compensate for the magnetization due to the spin magnetic moment. 2. A method for realizing the condition of claim 1 at an arbitrary temperature by controlling a suitable composition and a heat hysteresis process. 3. A spin decomposition device for charged particles utilizing the characteristics of claim 1.