JPH08250331A - Magnetizing direction control method of magnetic body and magnetic device equipped therewith - Google Patents

Abstract

PURPOSE: To provide a magnetic body magnetization control method and a magnetic device obtained taking advantage of the above control method, wherein a magnetic body is capable of being controlled in magnetization without using an external magnetic field. CONSTITUTION: A magnetic device is composed of a magnetic thin film 1, a direct transition-type semiconductor 2 which comes into direct contact with the thin film 1 or contact with the film 1 through the intermediary of an intermediate layer 4, and a circular polarized light generating source 3 which irradiates the semiconductor 2 direct with polarized light rays. The direct transition-type semiconductor 2 is irradiated with a circularly polarized light from a circularly polarized light generating source 3, whereby spin polarized electrons with polarity determined based on the direction of polarization of the circularly polarized light are excited in the direct transition-type semiconductor 2, and the magnetic thin film 1 is controlled in the direction of magnetization by the polarity of the spin polarized electrons.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new method for controlling the magnetization direction of a magnetic material and a magnetic device using the same.
More specifically, the present invention relates to a method for controlling the magnetization direction of a magnetic thin film in a magnetic memory, a magnetic field generator, an actuator, a magnetic semiconductor device, etc., in which a magnetic thin film is used, and its application to the magnetic device.

[0002]

2. Description of the Related Art Conventional magnetization direction control of a magnetic thin film has been performed by externally applying a magnetic field to the magnetic thin film. Therefore, an electromagnet or a permanent magnet composed of a coil is essential as an external magnetic field generation source.

However, the presence of the coil inevitably increases the size of the device, and when using these electromagnets and permanent magnets, there is a drawback that it is difficult to narrow the spatial region to which the magnetic field is applied, and the device is light and thin. It is difficult to meet the demand for shortening. Moreover, the problem of the leakage magnetic field is unavoidable.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a method for controlling the magnetization of a magnetic body that can control the magnetization of the magnetic body without using a magnetic field generated from the outside, and An object is to provide a magnetic device using such a magnetization control method.

[0005]

In order to solve the above problems, the present invention firstly irradiates circularly polarized light on a direct transition type semiconductor which is in direct contact with a magnetic material or through an intermediate layer, A spin-polarized electron having a polarity based on the polarization direction of circularly polarized light is excited in a direct transition type semiconductor, and the direction of magnetization of the magnetic thin film is controlled by the polarity of the spin-polarized electron. A method for controlling a magnetization direction is provided.

Secondly, it has a magnetic substance, a direct transition type semiconductor in contact with the magnetic substance directly or via an intermediate layer, and a circularly polarized light generation source for irradiating the direct transition type semiconductor with circularly polarized light. A characteristic magnetic device is provided.

Thirdly, there is provided a magnetic device according to the above magnetic device, further comprising bias voltage applying means for applying a bias voltage between the magnetic body and the direct transition semiconductor.

The basic principle of the present invention is to excite spin-polarized electrons from the valence band in the semiconductor to the conduction band by irradiation with circularly polarized light, and contact the spin-polarized electrons with the semiconductor directly or via an intermediate layer. By acting on a magnetic substance such as the magnetic thin film or magnetic particles, the spin direction of the magnetic substance, that is, the magnetization direction is controlled.

As shown in FIG. 1, the basic magnetic device for carrying out this magnetization direction control method is a magnetic thin film 1, a direct transition semiconductor 2 in contact with the magnetic thin film 1, and this direct transition semiconductor. Circularly polarized light generation source 3 for irradiating circularly polarized light to 2
have. In addition, the magnetic thin film 1 and the direct transition semiconductor 2
May be in contact with each other via the intermediate layer 4, as shown in FIG.

The magnetic thin film has only to exhibit ferromagnetism, and examples thereof include 3d transition metals such as Fe, Co and Ni, rare earths such as Gd, and alloys or compounds containing these. The magnetic thin film may be any of single crystal, polycrystal, and amorphous as long as it exhibits ferromagnetism. The magnetic thin film referred to here is not limited to the literal thin film as shown in FIG. 3A, but may be linear as shown in FIG. 3B or dot-like as shown in FIG.

When magnetic particles are used as the magnetic substance, as shown in FIG. 4, a granular film in which magnetic particles 11 are dispersed in a direct transition type semiconductor matrix 12 is used, and this granular film is irradiated with circularly polarized light. You can do it.

The basic principle of the present invention will be described in more detail below. In general, in a semiconductor, electrons are excited from the valence band of the semiconductor to the conduction band by irradiation with light. At this time, if a direct transition semiconductor is used as the semiconductor and light that is circularly polarized to the right or left is used as the light, the excitation probability of the electron with the upward spin and the excitation probability of the electron with the downward spin in the semiconductor are It is known that they can be different, resulting in spin-polarized electrons with different numbers of upward and downward spins (T. Nakanishi).
i et al, Japan Jounal of Applied Physics vol.25, p.766,
(1986)). Here, the spin polarization of an electron is given by I ↑ representing the intensity of the upward spin and I ↓ representing the intensity of the downward spin.
It can be represented by (I ↑ −I ↓) / (I ↑ + I ↓).

This spin polarization depends on the type and state of the semiconductor used and the energy of the circularly polarized light that is the excitation source, but in the case of GaAs, which is a typical direct transition semiconductor, theoretically, the spin polarization is 50%. It is possible to generate conduction electrons with extreme intensity. This spin polarization is GaA
It is further improved by applying strain to s or using an artificial lattice film. Higher spin polarization is preferable for controlling the magnetization direction of the magnetic material.

Typical examples of such a direct transition type semiconductor are the above-mentioned GaAs, GaAlAs, CdSe and Cd.
Examples thereof include compound semiconductors such as Te and chalcopyrite type semiconductors such as CdSiAs ₂ . Further, the polarity of spin polarization is determined by the direction of circularly polarized light, and the polarity changes by changing the direction from rightward polarized light to leftward polarized light.

Circularly polarized light is obtained by shifting the clockwise component and the counterclockwise component of the electric field vector of linearly polarized light by a quarter wavelength. For example, as shown in FIG. 5A, linearly polarized laser light from the laser light source 5 is passed through the quarter-wave plate 6, or as shown in FIG. 5B, an electric field such as a Pockels cell is used. It can be easily obtained by a conventional technique such as passing through the optical crystal 7 to which is added. It is desirable that the degree of circular polarization is as high as possible, but it may be slightly elliptically polarized. Further, the energy of the circularly polarized light used depends on the electronic structure of the irradiated semiconductor.

The magnetic substance and the semiconductor must be in contact with each other directly or through an intermediate layer so that spin-polarized electrons excited in the semiconductor can act on the magnetic substance. The intermediate layer used here may have conductivity or insulation. When the intermediate layer has conductivity, it is preferably a material that does not hinder the movement of electrons, and a noble metal such as Au, Ag or Cu is ideal. When the intermediate layer has an insulating property, it is necessary that electrons can tunnel between the semiconductor and the magnetic substance. In practice, such an intermediate layer may be an alloy layer formed at the interface between the magnetic substance and the semiconductor. In any case, the thickness of the intermediate layer is preferably 100 nm or less, more preferably 10 nm or less so as not to hinder the above-mentioned electron transfer and tunneling.

Depending on the junction interface between the magnetic substance and the semiconductor or the state of the intermediate layer, the spin-polarized electrons in the semiconductor may not act on the magnetic substance as it is, and the magnetization of the magnetic substance may not be controlled. In this case, as shown in FIG. 6, electrodes 8 and 9 are provided on the magnetic thin film 1 as a magnetic material and the semiconductor 2, and an electric field is applied between the electrodes 8 and 9 by the potential difference generation source 10 to increase the potential of the semiconductor 2. It is necessary to cause the spin-polarized electrons generated in 2 to act on the magnetic body 1.

The direction of magnetization of the magnetic material is determined by the direction of electron spin excited in the semiconductor, and the quantization axis is determined by the direction of incident circularly polarized light. That is, in the present invention, it is determined whether the magnetization is vertical magnetization or in-plane magnetization depending on the direction of the quantization axis based on the incident direction of circularly polarized light to the magnetic substance, and which direction the spin is oriented with the quantization axis as the axis. Depends on whether the circularly polarized light is to the right or to the left. An example thereof is shown in (a) to (d) of FIG.

The circularly polarized light may be emitted not only from the magnetic body side, but also from the semiconductor side as shown in FIG. 8 if the semiconductor has a thickness of 1 μm or less. In the present invention, in order to make the magnetic substance and the semiconductor contact with each other directly or via the intermediate layer, when the magnetic substance is a magnetic thin film, the semiconductor is used as a substrate to form the magnetic thin film on the substrate, or vice versa. Further, a semiconductor may be formed on the magnetic thin film. It is also possible to form a semiconductor film and a magnetic thin film on another substrate. Furthermore, a semiconductor whose surface is clean and flat may be bonded to a magnetic material whose surface is also clean in an ultrahigh vacuum,
These can be easily formed by a conventionally used thin film forming method.

Various combinations of semiconductors and magnetic materials are possible, and one example is a combination of GaAs and Fe. It is known that the GaAs crystal and the Fe crystal have a crystal lattice constant of 1: 2 and that they can be epitaxially grown well (GAPrinz et al., Applied Physic).
s Letters, vol.39, p.397 (1981)). Therefore, GaAs
When the (001) plane is used as a substrate and Fe is vapor-deposited thereon, a single crystal of the (001) plane of Fe is obtained. The interface structure in this case is controlled by the substrate temperature during the growth of the Fe film.

[0021]

【Example】

Example 1 An Fe film was grown as a magnetic thin film on a GaAs semiconductor substrate by using a molecular beam epitaxy (MBE) device. First, GaAs was heated to 600 ° C. to obtain a clean surface, the temperature was lowered to room temperature, and Fe was evaporated by electron beam evaporation to a thickness of 3 nm. Further, a transparent protective film was formed on the surface.

With respect to the sample formed as described above, circularly polarized light was irradiated on the entire Fe film in the incident direction as shown in FIGS. 7A and 7B, and circularly polarized light at that time was irradiated. The in-plane magnetization of the Fe film with respect to the degree was determined. As a result, as shown in FIG. 9, it was confirmed that there is a strong correlation between the degree of circular polarization and the magnetization of the Fe film.

Example 2 The following experiment was conducted to confirm the generation of spin-polarized electrons due to circularly polarized light.

As shown in FIG. 10, an Fe film 21 as a magnetic thin film is formed on the GaAs semiconductor substrate 22 by the same method as in Example 1, and the surface of the Fe film 21 and the GaAs semiconductor substrate 2 are formed.
Electrodes 23 and 24 are formed on the back surface side of 2 respectively, and F by a power source 25 as bias voltage applying means.
A voltage was applied between the e film 21 and the GaAs semiconductor substrate 22. Further, an ammeter 26 was connected so that the current during this period could be monitored. On the other hand, the GaAs semiconductor substrate 22 is
Etching was performed from the surface opposite to the surface on which the Fe film 21 was formed to a thickness of about 600 nm. Next, magnets 27 are arranged on both sides of the sample consisting of the Fe film 21 and the GaAs semiconductor substrate 22, and the magnet 27 forcibly aligns the magnetization of the Fe film 21. Excited by G
The electrons excited in the aAs semiconductor substrate 12 are the Fe film 11
The current when flowing to was examined.

Here, as shown in FIG. 11B, the current flowing when the circular polarization degree of circularly polarized light is changed with time so as to draw a sin curve, as shown in FIG. 11B, It became a reflection of the degree of circular polarization.

This depends on the degree of circular polarization of circularly polarized light.
It is presumed that the conductance of the system is different between the case where many spins in the same direction as the spin of the film 11 are excited in the GaAs semiconductor substrate and the case where many spins in the opposite direction are excited. This shows that the spin polarity of excited electrons is controlled by the polarization direction of circularly polarized light.

Example 3 In the same manner as in Example 1, as shown in FIG. 12, a Pt buffer layer 23 having a thickness of 2 nm was formed as an intermediate layer on a GaAs semiconductor substrate 32, and then a magnetic thin film was formed. A Co film 31 having a thickness of 1 nm was vapor-deposited, and a Pt cap layer 34 was further formed thereon.
On the other hand, a semiconductor laser 35 having a wavelength of 830 nm is used as a light source.
By using the collimator lens 3
After converging at 6, the light was passed through the Pockels cell 37 to switch between linearly polarized light, right circularly polarized light, and left circularly polarized light. As a result, writing could be performed with a power of 10 mW while controlling the direction of magnetization of the magnetic thin film by controlling the polarization direction of circularly polarized light as shown in FIG. In addition, the written information is
It was possible to read by the polar Kerr effect using linearly polarized light with a power of 3 mW.

[0028]

According to the present invention, since the magnetization direction of the magnetic material can be controlled only by light without using an external magnetic field generated by an external magnetic field generator such as a coil, it is possible to avoid an increase in size of the device. In addition, the large current that was conventionally supplied to the coil becomes unnecessary. Further, the problem of magnetic field leakage is solved, and further local magnetization direction control and remote control become possible. Therefore, the present invention brings about great effects in a wide range of applications of magnetic materials.

[Brief description of drawings]

FIG. 1 is a schematic view showing one embodiment of a magnetic device for carrying out a magnetization direction control method of the present invention.

FIG. 2 is a schematic view showing another embodiment of a magnetic device for carrying out the magnetization direction control method of the present invention.

FIG. 3 is a diagram for explaining a state of a magnetic thin film according to the present invention.

FIG. 4 is a schematic diagram showing a granular film to which the magnetization direction control method of the present invention can be applied.

FIG. 5 is a diagram showing a configuration of a circularly polarized light generation source.

FIG. 6 is a schematic diagram showing still another embodiment of a magnetic device for carrying out the magnetization control method of the present invention.

FIG. 7 is a schematic diagram for explaining the relationship between the method of irradiating circularly polarized light from a circularly polarized light generation source and the direction of magnetization of the magnetic thin film.

FIG. 8 is a diagram showing a state where circularly polarized light is irradiated from the semiconductor side.

9 is a diagram showing the relationship between the degree of circular polarization and the magnetization of the Fe film in Example 1. FIG.

FIG. 10 is a diagram showing a configuration of a device used in Example 2.

FIG. 11 is a diagram showing a change in circular polarization degree and a corresponding change in current in Example 2.

FIG. 12 is a diagram showing a configuration of a device used in Example 3.

[Explanation of symbols]

 1 ... Magnetic thin film 2 ... Direct transition semiconductor 3 ... Circularly polarized light source 4 ... Intermediate layer 8, 9 ... Electrode 10 ... Potential difference source

[Procedure amendment]

[Submission date] May 27, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

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[Document name to be amended] Statement

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[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new method for controlling the magnetization direction of a magnetic material and a magnetic device using the same.
More specifically, a magnetic thin film is used, for example, a magnetic memory, a magnetic field generator, an actuator, a magnetization direction control method for the magnetic thin film in a magnetic semiconductor device, etc.,
The application to the magnetic device.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

[0005]

In order to solve the above problems, the present invention firstly irradiates circularly polarized light on a direct transition type semiconductor which is in direct contact with a magnetic material or through an intermediate layer, direct transition allowed excited spin-polarized electrons having a polarity based on the polarization direction of the circularly polarized light in the semiconductor, the magnetic body and controlling the magnetization direction of the magnetic member by the polarity of the spin-polarized electrons A method for controlling a magnetization direction is provided.

Claims (3)

[Claims] 1. A spin-polarized electron having a polarity based on the polarization direction of circularly polarized light in the direct transitional semiconductor by irradiating the direct transitional semiconductor in contact with a magnetic material directly or via an intermediate layer with circularly polarized light. And controlling the direction of magnetization of the magnetic thin film according to the polarity of the spin-polarized electrons. 2. A magnetic substance, a direct transition type semiconductor in contact with the magnetic substance directly or via an intermediate layer, and a circularly polarized light source for irradiating the direct transition type semiconductor with circularly polarized light. Magnetic device. 3. The magnetic device according to claim 2, further comprising bias voltage applying means for applying a bias voltage between the magnetic body and the direct transition semiconductor.