JP2008135480A - Magnetic control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetism control method by which a device that uses ferromagnetic substance and requires changing to paramagnetism from ferromagnetism can be made compact. <P>SOLUTION: This method is used to change the ferromagnetism of a ferromagnetic semiconductor 110 to paramagnetism. Light is given or electric field is applied, so as to give an energy exceeding the band gap energy of the ferromagnetic semiconductor 110 to the ferromagnetic semiconductor 110 to generate conduction electrons therein and to change the valence of ions keeping the ferromagnetism in the ferromagnetic semiconductor 110 by the conduction electrons to change the ferromagnetism of the ferromagnetic semiconductor 110 to paramagnetism. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic control method, and more particularly to a method for transferring ferromagnetism of a ferromagnetic semiconductor to paramagnetism by a method other than a temperature raising method.

  In recent years, a field called spintronics (a coined word combining electron spin and electronics) has attracted attention. Spintronics is a research field in which materials and devices with completely new functions are developed by utilizing two properties of charge and spin, which are physical properties of electrons.

  In this spintronics, a semiconductor in which a magnetic element (transition element, rare earth element, etc.) responsible for magnetism is added to a semiconductor and a part of the constituent elements of the semiconductor is replaced with the magnetic element (hereinafter referred to as a magnetic semiconductor) is a viewpoint of electron spin control. Is an important material. Among them, “ferromagnetic semiconductors” with magnetic moments of magnetic elements are considered new materials necessary for realizing basic functions in semiconductor spintronics, such as a source of free electrons with uniform spin. .

When a practical device is realized using such a ferromagnetic semiconductor, it is essential to develop a ferromagnetic semiconductor that exhibits ferromagnetism at a temperature of room temperature or higher. As ferromagnetic semiconductors exhibiting ferromagnetism at room temperature, for example, GaN crystals containing Mn and oxygen as impurities and GaN crystals containing Mn and Si as impurities are disclosed (for example, Patent Documents). 1).
JP 2003-137698 A

  By the way, in general, the transition from ferromagnetism to paramagnetism is performed by raising the temperature of the ferromagnet above the ferromagnetic transition temperature (Curie temperature). Therefore, when realizing a device (magnetic memory, etc.) that performs energy conversion between magnetism and electricity using a ferromagnetic semiconductor, the temperature of the ferromagnetic semiconductor is set with high accuracy in order to develop and maintain a desired magnetic state. It becomes necessary to control. As a result, the structure of the device becomes complicated and the device becomes larger.

  Therefore, in view of such problems, the present invention has an object to provide a magnetic control method capable of downsizing a device using a ferromagnetic material that requires a transition from ferromagnetism to paramagnetism. And

  In order to achieve the above object, a magnetic control method of the present invention is a method for transferring ferromagnetism of a ferromagnetic material to paramagnetism, which generates conduction electrons or holes in the ferromagnetic material, and Alternatively, the transition is performed by trapping holes in an element responsible for ferromagnetism of the ferromagnetic material. Here, the ferromagnetic material is a ferromagnetic semiconductor, and the transition may be performed by changing a valence of ions responsible for ferromagnetism in the ferromagnetic semiconductor by the conduction electrons or holes. The ferromagnetic semiconductor is GaGdN, and the transition may be performed by changing the valence of Gd ions from 3 to 2. The generation of the conduction electrons or holes may be performed by giving the ferromagnetic semiconductor energy that is equal to or higher than the band gap energy of the ferromagnetic semiconductor by irradiating the ferromagnetic semiconductor with light. The generation of electrons or holes may be performed by applying energy higher than the band gap energy of the ferromagnetic semiconductor to the ferromagnetic semiconductor by applying an electric field to the ferromagnetic semiconductor.

  Thereby, the ferromagnetism of the ferromagnet can be transferred to paramagnetism by carriers (conduction electrons or holes). Therefore, even when a device (such as a magnetic memory) that converts energy between magnetism and electricity using a ferromagnetic material is realized, the temperature of the ferromagnetic material is highly accurate in order to develop and maintain a desired magnetic state. There is no need to control it. As a result, a device using a ferromagnetic material can be reduced in size. In addition, only the portion of the ferromagnetic material where carriers are generated transitions from ferromagnetism to paramagnetism. Therefore, a device capable of controlling the reciprocation between the ferromagnetic state and the paramagnetic state in a minute region can be realized.

  According to the present invention, a light emitting element that outputs circularly or linearly polarized second signal light in response to irradiation of the first signal light, and a polarization direction of the linearly polarized light are disposed on the optical path of the second signal light. The light-emitting element is sandwiched between a first conductivity type first cladding layer and a second conductivity type second cladding layer, and the first cladding layer and the second cladding layer. And an active layer that emits the first signal light and outputs the second signal light, and a GaGdN layer that is sandwiched between the active layer and the first cladding layer and is irradiated with control light. It can also be an optical switch.

  As a result, when the GaGdN layer is supplied with energy equal to or higher than the band gap energy of GaGdN by the irradiation of the control light and the linearly polarized second signal light is output, no light is output from the polarizer. Therefore, it is possible to realize an optical switch that switches the signal light under the control of the control light. As a result, by changing the structure of the polarizer and the light emitting element, the signal light output from the optical switch can be changed, and an optical switch with a high degree of design freedom can be realized.

  Furthermore, the present invention is a memory using the above magnetic control method, comprising a recording layer composed of the GaGdN, wherein information is written by irradiating the recording layer with light. You can also

  As a result, when the recording layer is irradiated with light having an energy equal to or higher than the band gap energy of the ferromagnetic semiconductor, the magnetism of the ferromagnetic semiconductor changes to paramagnetism, and information is written to the recording layer. Therefore, since the recording layer is formed only by the ferromagnetic semiconductor, the structure of the nonvolatile random access memory (RAM) can be simplified, and a small RAM can be realized.

  According to the present invention, a device using a ferromagnetic material can be reduced in size. In addition, a device capable of controlling the reciprocation between the ferromagnetic state and the paramagnetic state in a minute region can be realized. It is possible to realize an optical switch having a high degree of design freedom for switching signal light under the control of control light. A small RAM in which information is written to the recording layer when irradiated with light can be realized.

  Hereinafter, a magnetic control method, an optical switch, and a RAM according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a cross-sectional view of a ferromagnetic semiconductor according to the present embodiment.

  The ferromagnetic semiconductor 110 exhibits ferromagnetism at room temperature and is formed on the substrate 100 using a crystal growth technique such as an RF-MBE (Radio-Frequency Molecular Beam Epitaxy) method.

As the ferromagnetic semiconductor 110, a semiconductor to which a transition metal or a rare earth element is added, for example, GaGdN in which Gd is added to GaN or the like is used. At this time, a 6H—SiC substrate or the like having a small lattice mismatch with GaN is used as the substrate 100. In the ferromagnetic semiconductor 110, for example, a molecular beam obtained by evaporating Ga and Gd and a nitrogen radical obtained by decomposing N ₂ gas using RF plasma were heated to about 400 to 800 ° C. It is formed by supplying to the substrate 100.

  Here, the term “room temperature” is used to mean a temperature existing in the range of 0 ° C. or more and 40 ° C. or less.

  In the ferromagnetic semiconductor 110 having the above structure, its magnetism is controlled as follows.

  That is, when the ferromagnetic semiconductor 110 is changed from ferromagnetic to paramagnetic, energy higher than the band gap energy of the ferromagnetic semiconductor 110 is given to the ferromagnetic semiconductor 110 by light irradiation or electric field application, and the carrier is transferred to the ferromagnetic semiconductor 110. (Conductive electrons or holes) are generated. As a result, the generated carriers are trapped by the transition metal or rare earth element ion responsible for ferromagnetism in the ferromagnetic semiconductor 110, and as a result, the valence of the transition metal or rare earth element ion is changed. Transition from ferromagnetism to paramagnetism.

  Specifically, when the ferromagnetic semiconductor 110 is GaGdN, for example, energy of 3.5 eV or more, which is the band gap energy of GaGdN, is applied to GaGdN by light irradiation, and conduction electrons are generated in GaGdN. As a result, the conduction electrons are trapped by the ferromagnetic element Gd responsible for ferromagnetism in GaGdN, and the trivalent Gd ions are changed to paramagnetic divalent Gd ions, that is, the valence of the Gd ions is changed from trivalent to 2 In order to decrease the valence, GaGdN transitions from ferromagnetism to paramagnetism.

  On the other hand, when the ferromagnetic semiconductor 110 is changed from paramagnetic to ferromagnetic, a magnetic field is applied to the ferromagnetic semiconductor 110. As a result, the direction of the magnetic moment in the ferromagnetic semiconductor 110 is aligned, so that the ferromagnetic semiconductor 110 transitions from paramagnetism to ferromagnetism.

2A and 2B are diagrams showing emission spectra of the ferromagnetic semiconductor 110. FIG. This emission spectrum is obtained when Ga _0.96 Gd _0.06 N is used as the ferromagnetic semiconductor 110 and a He—Cd laser (325 nm = 3.814 eV) is used as the excitation light source. 2A shows the case where the temperature of the ferromagnetic semiconductor 110 is changed to 20K, 50K, 100K, 150K, 200K and 300K, and FIG. 2B shows the case where the temperature of the ferromagnetic semiconductor 110 is 10K. is there.

2A and 2B, it can be seen that emission peaks appear at positions of 652 nm (1.9 eV), 755 nm (1.6 eV), and 810 nm (1.5 eV). Since these emission peaks correspond to the emission peaks of trivalent Tb ions in GaN, they are considered to be emission peaks of divalent Gd ions having the same electron arrangement as the trivalent Tb ions. Therefore, the ferromagnetic semiconductor 110, and the carrier by light irradiation is generated valence of Gd ions Ga _0.96 Gd _0.06 N layer is seen to decrease from three to two. That is, it is understood that divalent Gd ions that are partially in the same electron configuration as the trivalent Tb ions are generated by light irradiation, and the Ga _0.96 Gd _0.06 N layer is transferred from the ferromagnetic material to the paramagnetic material.

  As described above, according to the ferromagnetic semiconductor 110 of the present embodiment, the magnetism changes from ferromagnetic to paramagnetic by light irradiation or electric field application. Therefore, even when a device (magnetic memory or the like) that performs energy conversion between magnetism and electricity using the ferromagnetic semiconductor 110 is realized, the temperature of the ferromagnetic semiconductor 110 is set in order to develop and maintain a desired magnetic state. It is not necessary to control locally (submicron order) with high accuracy. As a result, a device using a ferromagnetic semiconductor can be reduced in size.

  Further, according to the ferromagnetic semiconductor 110 of the present embodiment, only the local part of the ferromagnetic semiconductor 110 that has been irradiated with light or applied with an electric field is transferred from ferromagnetic to paramagnetic. Therefore, a device capable of controlling the reciprocation between the ferromagnetic state and the paramagnetic state in a minute region can be realized.

(Second Embodiment)
FIG. 3 is a diagram showing the structure of the optical switch according to the present embodiment.

  This optical switch is an optical switch that performs switching of signal light under the control of the pulsed control light 500. The optical switch receives pulsed first signal light 510 from the outside and is circularly polarized or A light-emitting element 200 that outputs linearly polarized second signal light 520, and a polarizer 300 that is arranged on the optical path of the second signal light 520 output from the light-emitting element 200 and outputs pulsed third signal light 530; And a magnetic field applying means 400 such as a solenoid coil for applying a magnetic field to the light emitting element 200.

  The light emitting device 200 includes a GaN substrate 210 that is a conductive transparent substrate, a p-type AlGaN cladding layer 220, a ferromagnetic semiconductor layer 230, an InGaN active layer 240, and an n-type AlGaN cladding layer 250 sequentially stacked on the GaN substrate 210. A direct current that applies a voltage between the n-type electrode 260 formed on the n-type AlGaN cladding layer 250, the p-type electrode 270 formed on the GaN substrate 210, and the n-type electrode 260 and the p-type electrode 270. And a power source 280.

  The InGaN active layer 240 is applied with a voltage just before causing light emission by the DC power supply 280. Therefore, when the InGaN active layer 240 is irradiated with the Hi-level first signal light 510, light emission occurs and light is output from the InGaN active layer 240. On the other hand, when the Lo-level first signal light 510 is irradiated onto the InGaN active layer 240, no light emission occurs and no light is output from the InGaN active layer 240. As a result, the second signal light 520 having the pulse waveform corresponding to the pulse waveform of the first signal light 510 is output from the InGaN active layer 240 at the Hi level and the Lo level at the same timing as the first signal light 510. .

  As the ferromagnetic semiconductor layer 230, the ferromagnetic semiconductor 110 of the first embodiment is used. The ferromagnetic semiconductor layer 230 is irradiated with control light 500. When the ferromagnetic semiconductor layer 230 is irradiated with high-level control light 500, that is, light having energy higher than the band gap energy of the ferromagnetic semiconductor layer 230, the magnetic property of the ferromagnetic semiconductor layer 230 changes from ferromagnetic to paramagnetic. Metastasize. On the other hand, when the ferromagnetic semiconductor layer 230 is irradiated with the control light 500 at the Lo level, that is, light having energy smaller than the band gap energy of the ferromagnetic semiconductor layer 230, the magnetism of the ferromagnetic semiconductor layer 230 does not change. At this time, a constant magnetic field is always applied to the ferromagnetic semiconductor layer 230 by the magnetic field applying means 400. Accordingly, the ferromagnetic semiconductor layer 230 exhibits paramagnetism when irradiated with the control light 500 at the Hi level, and exhibits ferromagnetism when irradiated with the control light 500 at the Lo level.

  The polarization main axis of the polarizer 300 is different from, or orthogonal to, the polarization direction when the second signal light 520 is linearly polarized light. Therefore, when the second signal light 520 is linearly polarized light, the light is blocked and no light is output from the polarizer 300. On the other hand, when the second signal light 520 is circularly polarized light, part of the light passes and light is output from the polarizer 300. As a result, as shown in FIG. 4, the first signal light 510 is at the Hi level only when the control light 500 is at the Lo level, and the first signal light 510 has a pulse waveform that is at the Lo level. Three-signal light 530 is output from the polarizer 300.

  As described above, according to the optical switch of the present embodiment, the signal light output from the optical switch can be changed by changing the structures of the polarizer 300 and the light emitting element 200. Therefore, an optical switch with a high degree of design freedom can be realized.

(Third embodiment)
FIG. 5 is a diagram showing the structure of the RAM 600 according to the present embodiment.

  The RAM 600 includes a plurality of memory cells 610 formed of the ferromagnetic semiconductor 110 according to the first embodiment arranged in a matrix (for example, M columns N rows array: M × N array). In the RAM 600, each of the memory cells 610 is irradiated with light having energy equal to or higher than the band gap energy of the ferromagnetic semiconductor 110, so that the ferromagnetic semiconductor 110 changes to paramagnetism, and recorded information is written into the memory cell 610.

  As described above, according to the RAM 600 of the present embodiment, the memory cell 610 is formed only by the ferromagnetic semiconductor 110. Therefore, for example, the RAM 600 can be formed simply by forming a ferromagnetic semiconductor layer and dividing the ferromagnetic semiconductor layer into a plurality of cells. As a result, the structure of the RAM can be simplified and a small RAM can be realized.

  The magnetic control method, the optical switch, and the RAM according to the present invention have been described based on the embodiment, but the present invention is not limited to this embodiment. The present invention includes various modifications made by those skilled in the art without departing from the scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be applied to the field using ferromagnets, and particularly applicable to the field of elements using spin of electrons called spintronics.

1 is a cross-sectional view of a ferromagnetic semiconductor according to a first embodiment of the present invention. It is a figure which shows the emission spectrum of the ferromagnetic semiconductor which concerns on the same embodiment. It is a figure which shows the emission spectrum of the ferromagnetic semiconductor which concerns on the same embodiment. It is a figure which shows the structure of the optical switch which concerns on 2nd Embodiment. It is a figure which shows 1st signal light, 3rd signal light, and control light. It is a figure which shows the structure of RAM which concerns on 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Substrate 110 Ferromagnetic semiconductor 200 Light emitting element 210 GaN substrate 220 p-type AlGaN cladding layer 230 Ferromagnetic semiconductor layer 240 InGaN active layer 250 n-type AlGaN cladding layer 260 n-type electrode 270 p-type electrode 280 DC power supply 300 Polarizer 400 Magnetic field application Means 500 Control light 510 First signal light 520 Second signal light 530 Third signal light 600 RAM
610 memory cell

Claims (7)

A method for transferring the ferromagnetism of a ferromagnet to paramagnetism,
A magnetic control method characterized by generating conduction electrons or holes in the ferromagnetic body and trapping the conduction electrons or holes in an element responsible for ferromagnetism of the ferromagnetic body. The ferromagnetic material is a ferromagnetic semiconductor;
The magnetic control method according to claim 1, wherein the transition is performed by changing a valence of an ion responsible for ferromagnetism in the ferromagnetic semiconductor by the conduction electrons or holes. The ferromagnetic semiconductor is GaGdN,
The magnetic control method according to claim 2, wherein the transfer is performed by changing a valence of Gd ions from 3 to 2. 4. The generation of the conduction electrons or holes is performed by giving the ferromagnetic semiconductor energy that is equal to or higher than the band gap energy of the ferromagnetic semiconductor by irradiating the ferromagnetic semiconductor with light. The magnetic control method as described. The generation of the conduction electrons or holes is performed by applying energy higher than the band gap energy of the ferromagnetic semiconductor to the ferromagnetic semiconductor by applying an electric field to the ferromagnetic semiconductor. The magnetic control method as described. A light emitting element that outputs circularly or linearly polarized second signal light in response to irradiation of the first signal light;
A polarizer disposed on the optical path of the second signal light and having a polarization main axis different from the polarization direction of the linearly polarized light,
The light emitting device is sandwiched between a first conductivity type first cladding layer and a second conductivity type second cladding layer, the first cladding layer and the second cladding layer, and is irradiated with the first signal light, An optical switch comprising: an active layer that outputs second signal light; and a GaGdN layer that is sandwiched between the active layer and the first cladding layer and is irradiated with control light. A memory using the magnetic control method according to claim 3,
Comprising a recording layer composed of GaGdN,
Information is written by light irradiation to the recording layer.

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