Tunable multilayer terahertz magnon generator

Abstract

A method for tuning the frequency of terahertz radiation is provided. The method utilizes a device comprising a spin injector, a tunneling junction coupled to the spin injector, and a ferromagnetic material coupled to the tunneling junction. The ferromagnetic material comprises a magnon gain medium (MGM). The method comprises the step of applying a bias voltage to shift the Fermi level of the spin injector relative to the Fermi level of the ferromagnetic material to initiate the generation of non-equilibrium magnons by injecting a minority of electrons into the magnon gain medium. The method also comprises tuning the frequency of the generated terahertz radiation by changing the value of the bias voltage.

Description

[0001] Citation of Related Applications

[0002] This application claims priority to U.S. non-provisional application serial number 16 / 245,224, filed on January 10, 2019, entitled “TUNABLE MULTILAYER TERAHERTZMAGNON GENERATOR,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to the field of magnon lasers for generating terahertz radiation. Background Art

[0004] Terahertz (THz) radiation is a type of electromagnetic radiation with a frequency range of 0.1THz to 30THz, which occupies the part of the electromagnetic spectrum between the microwave band and the infrared band.

[0005] The energy of terahertz photons is less than that of optical photons. This is why terahertz waves (THz-waves) can penetrate deep into materials that light waves cannot penetrate. At terahertz frequencies, molecules vibrate. This is why terahertz waves are useful in molecular research.

[0006] In fact, in the terahertz range, the unique rotational and vibrational responses of molecules provide information that is not usually present in optical, X-ray and nuclear magnetic resonance (NMR) images. Terahertz waves can easily penetrate and examine the interior of most dielectric materials, which are opaque to visible light and have low contrast to X-rays, making them a useful complementary imaging source.

[0007] For example, terahertz waves maintain reasonable penetration depth in some common materials such as clothing, plastic, wood, sand, and soil. Therefore, terahertz technology has the potential to detect explosives wrapped or buried in these materials because explosives have unique terahertz spectral characteristics compared to the surrounding materials. The spectral fingerprint of explosives can be expected to be obtained in the terahertz band, and terahertz imaging can be used for mine detection. However, there is still a lack of efficient and compact solid-state sources in the spectral range of 0.1-30 THz.

[0008] In fact, broadband pulsed THz sources are usually based on exciting different materials with ultrashort laser pulses. Several different mechanisms have been developed to generate THz radiation, including photocarrier acceleration in photoconductive antennas, second-order nonlinear effects in electro-optical crystals, etc.

[0009] For narrowband terahertz sources, solid-state lasers are usually considered. They are based on inter-band transitions or inter-sub-band transitions in narrow-gap semiconductors, i.e. transitions between restricted conductive or valence states in quantum confined structures (e.g. nanostructures). In order to obtain terahertz radiation from direct inter-band transitions, semiconductors with close to zero gap are required. For inter-sub-band transitions, conventional wide-gap materials can be used, but precise complex structures are required. It is currently feasible to construct multi-quantum well semiconductor structures for laser emission.

[0010] A quantum cascade consists of a repeating structure, in which each repeating unit consists of an injector and an active region. In the active region, there is a population inversion and electrons transition to lower energy levels, emitting photons at a specific wavelength. Kohler et al. (R. Kohler et al., Nature 417, 156 (2002)) designed a THz quantum cascade laser operating at a frequency of 4.4 THz. The laser consists of a total of more than 700 quantum wells and demonstrates pulsed operation at a temperature of 10K. For related content, see, for example, B Ferguson and X.-C. Zhang, Nat. Matter, 26 (2002).

[0011] Manijeh Razeghi et al. reported on the latest progress of QCL generators in Photonics Spectra, December, 48-51 (2016). The authors used nonlinear mixing of two QCLs. However, the use of nonlinear mixers brings inherent limitations. In fact, nonlinear QCL mixers are very complex devices (each such QCL includes multiple barrier layers and multiple well layers and should be manufactured with an accuracy of up to 0.1nm), have low output power in the continuous state (these devices can only reach a maximum power output of 0.5mW in the pulsed state); and have very limited tunability in the (2-4.45)THz region.

[0012] AdTech Optics, located in City of Industry, California, has been developing and producing innovative QC lasers since 2005. AdTech's QCLs are designed to cover most of the mid-IR spectral range, from λ = 3.8μm (78THz) to λ = 12.5μm (23.9THz). Almost all of AdTech's QCLs operate continuously at room temperature and can be designed to operate at a single frequency by using distributed feedback waveguide fabrication. However, AdTech's QCLs are only mechanically adjustable, which makes these QCLs impractical for most applications including spectroscopy, communications, to name a few. Summary of the invention

[0013] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0014] A method for tuning the frequency of terahertz radiation using a tunable multilayer terahertz magnon generator is provided.

[0015] A tunable multilayer terahertz magnon generator includes a top electrode, a pinning layer coupled to the top electrode, a spin injector coupled to the top electrode through the pinning layer, a tunnel junction coupled to the spin injector, a bottom layer including a ferromagnetic material coupled to the tunnel junction, the ferromagnetic material also including a magnon gain medium, a bottom electrode coupled to the bottom electrode, and a substrate coupled to the bottom electrode.

[0016] A method for tuning the frequency of terahertz radiation by using a tunable multilayer terahertz magnon generator, the method comprising applying a bias voltage to shift the Fermi level of a spin injector relative to the Fermi level of a ferromagnetic material to initiate the generation of unbalanced magnons by injecting minority electrons into a magnon gain medium; wherein the injected minority electrons enter a high-energy electronic state in a lower subband with spin up of the ferromagnetic material by flipping their spins in an exchange process; and wherein unbalanced magnons are generated in the process; and wherein the interaction between the unbalanced magnons causes the generation of electromagnetic radiation.

[0017] A method for tuning the frequency of terahertz radiation using a tunable multilayer terahertz magnon generator also includes tuning the frequency of the generated terahertz radiation by changing the value of a bias voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present technology and, together with the description, explain the following principles:

[0019] Figure 1 A cross-sectional view of a tunable multilayer terahertz magnon laser with a pinned layer of RUDERMAN-KITTEL-KASUYA-YOSIDA (RKKY) is depicted, for purposes of the present technology, the tunable multilayer terahertz magnon laser comprising a substrate, a bottom electrode, a bottom layer, a tunneling junction, a top layer, a pinned layer, a reference layer, and a top electrode.

[0020] Figure 2 The dependence of the RUDERMAN-KITTEL-KASUYA-YOSIDA (RKKY) interaction on the thickness of the spacer layer of ruthenium (Ru) for the purposes of the present technology is described.

[0021] Figure 3 The electronic spectrum and the generation of nonequilibrium magnons in a half-metal for the purposes of this technique are shown.

[0022] Figure 4 The design of a tunable terahertz magnon laser with a tunneling junction for the purpose of the present technology is depicted.

[0023] Figure 5 For the purpose of this technology, Figure 4 Mechanism of continuous voltage-based tuning of tunneling junction tunable terahertz magnon lasers. DETAILED DESCRIPTION

[0024] Reference will now be made in detail to embodiments of the present technology, examples of which are illustrated in the accompanying drawings. Although the present technology will be described in conjunction with various embodiments, it should be understood that they are not intended to limit the present technology to these embodiments. On the contrary, the present technology is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the various embodiments defined by the appended claims.

[0025] Furthermore, in the following detailed description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. However, it is apparent to one of ordinary skill in the art that the presented embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail to avoid unnecessarily obscuring aspects of the presented embodiments.

[0026] In one embodiment of the present technology, Figure 1A cross-sectional view of a tunable multilayer terahertz magnon laser 10 with a RUDERMAN-KITTEL-KASUYA-YOSIDA (RKKY) pinned layer is depicted, which for purposes of the present technology includes a substrate 12, a bottom electrode 14, a bottom layer 16, a tunneling junction 18, a top layer 20, a pinned layer 22, a reference layer 24, and a top electrode 28. A single multilayer pillar 26 includes layers 16-28.

[0027] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes gallium arsenide (GaAs).

[0028] Gallium arsenide (GaAs) is a compound of gallium and arsenic. It is a III-V group direct bandgap semiconductor with a zincblende crystal structure. GaAs is used in the manufacture of monolithic microwave integrated circuits.

[0029] GaAs is often used as a substrate material for epitaxial growth of other III-V semiconductors, including indium gallium arsenide, aluminum gallium arsenide, etc.

[0030] GaAs can be produced using molecular beam epitaxy (MBE). MBE occurs in a high vacuum or ultra-high vacuum (10 -8 -10 -12 )Torr.

[0031] The most important aspect of MBE is the deposition rate (typically less than 3,000nm per hour) that allows epitaxial growth of thin films. These deposition rates require proportionally better vacuum to achieve the same impurity levels as other deposition techniques. The absence of carrier gases and the ultra-high vacuum environment allow for the highest purity of grown films.

[0032] In solid source MBE, ultrapure forms of elements such as gallium and arsenic are heated in separate quasi-Kundsen effusion cells or electron beam evaporators until they begin to slowly sublime. The gaseous elements then condense on a wafer where they can react with each other. In the case of gallium and arsenic, single crystal gallium arsenide is formed. When using evaporation sources such as copper or gold, gaseous elements impinging on the surface may be adsorbed (after a time window in which the impinging atoms will jump on the surface) or reflected. Atoms on the surface may also desorb.

[0033] Controlling the temperature of this source will control the rate at which material strikes the substrate surface, and the temperature of the substrate will affect the rate of hopping or desorption. The term "beam" refers to the fact that the evaporated atoms do not interact with each other or the vacuum chamber gases before reaching the wafer because the mean free path of the atoms is long.

[0034] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes aluminum oxide (Al2O3).

[0035] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes aluminum nitride (AlN).

[0036] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes indium tin oxide (InTnO).

[0037] Indium tin oxide (ITO) is a ternary composition consisting of indium, tin and oxygen in varying proportions. Depending on the oxygen content, it can be described as a ceramic or an alloy. Indium tin oxide is usually encountered as an oxygen-saturated composition, with a formula of 74% In, 18% O2 and 8% Sn by weight. The oxygen-saturated composition is so typical that the unsaturated composition is called oxygen-deficient ITO. It is transparent and colorless in thin layers, while in bulk form it is yellowish to gray. In the infrared region of the spectrum, it acts as a mirror like a metal.

[0038] Indium tin oxide is one of the most widely used transparent conductive oxides because it has two main properties: electrical conductivity and optical transparency, and it can be easily deposited as a thin film. As with all transparent conductive films, a compromise must be made between conductivity and transparency, as increasing thickness and increasing the concentration of charge carriers increases the conductivity of the material but decreases its transparency. Indium tin oxide thin films are most often deposited on a surface by physical vapor deposition. Electron beam evaporation, or a range of sputtering deposition techniques, are often used.

[0039] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes silicon (Si).

[0040] Silicon is a chemical element with the symbol Si and atomic number 14. Silicon is a hard and brittle crystalline solid with a blue-grey metallic luster. It is a tetravalent metalloid. Silicon is a member of Group 14 in the periodic table, above carbon and below germanium, tin, lead and flint. Silicon is quite inactive, although not as active as germanium, but it has a strong chemical affinity for oxygen. Therefore, it was introduced in 1823 by It was first prepared and characterized in pure form by Jakob Berzelius.

[0041] Silicon is the eighth most common element in the universe by mass, but rarely occurs as a pure element in the Earth's crust. It is most widely distributed in dust, sand, asteroids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust after oxygen (about 28% by mass). Highly purified silicon is used in integrated circuits.

[0042] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes silicon-on-sapphire (SoS).

[0043] Silicon-on-sapphire (SOS) is a heteroepitaxial process used in integrated circuit manufacturing consisting of a thin layer of silicon (typically less than 0.6 μm) grown on a sapphire (Al2O3) wafer.

[0044] SOS is part of the Silicon-On-Insulator (SOI) family of CMOS technologies. Typically, high-purity artificially grown sapphire crystals are used. Silicon is deposited on a heated sapphire substrate, usually by the decomposition of silane gas (SiH4). The advantage of sapphire is that it is an excellent electrical insulator, preventing stray currents caused by radiation from spreading to nearby circuit elements. SOS faced early challenges in commercial manufacturing due to the difficulty in making the very small transistors used in modern high-density applications. This is because the SOS process causes the formation of dislocations, twinning, and stacking faults due to the lattice differences between sapphire and silicon. In addition, there is some aluminum (a p-type dopant) contamination from the substrate in the silicon closest to the interface.

[0045] The use of epitaxially grown silicon on sapphire substrates for the manufacture of MOS devices involves a silicon purification process that mitigates crystal defects caused by the mismatch between the sapphire and silicon lattices. For example, Peregrine Semiconductor's SP4T switch is formed on an SOS substrate with a final thickness of silicon of approximately 95nm. The silicon is recessed in the area outside the polysilicon gate stack by poly oxidation and further recessed to a thickness of approximately 78nm by a sidewall spacer process.

[0046] In one embodiment of the present technology, ( Figure 1 The substrate 12 includes magnesium oxide (MgO).

[0047] Magnesium oxide (MgO) or magnesia is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium. It has the empirical formula of MgO and consists of a lattice of Mg2 (+ ions) and O2 (- ions) held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but this can be reversed by heating to separate the water.

[0048] Magnesium oxide was historically known as magnesia alba (literally, a white mineral from magnesium oxide - other sources refer to magnesium oxide as MgCO3) to distinguish it from magnesia negra, a black mineral containing what is now known as manganese. Although "magnesium oxide" usually refers to MgO, magnesium peroxide MgO2 is also referred to as this compound. According to evolutionary crystal structure prediction, MgO2 is thermodynamically stable at pressures above 116 GPa (gigaPascals), while the entirely new semiconducting suboxide Mg3O2 is thermodynamically stable above 500 GPa. Due to its stability, MgO is used as a model system for studying the vibrational properties of crystals. Magnesium oxide is produced by calcining magnesium carbonate or magnesium hydroxide.

[0049] In one embodiment of the present technology, still refer to Figure 1 The bottom electrode 14 is selected from the group consisting of the following materials: cobalt-iron alloy (Co 0.5 Fe 0.5 ); silver (Ag); gold (Au); platinum (Pt); cobalt (Co); palladium (Pd); titanium (Ti); and titanium tungsten (TiW).

[0050] Each of these materials can be deposited on a substrate by molecular beam epitaxy (MBE) (see discussion above) or by sputtering deposition.

[0051] Sputtering deposition is a physical vapor deposition (PVD) method of thin film deposition by sputtering. This involves ejecting material from a "target" as a source onto a "substrate", such as a silicon wafer. Re-sputtering is the re-emission of deposited material by ion or atomic bombardment during the deposition process. The sputtered atoms ejected from the target have a wide distribution of energies, typically up to tens of eV (100,000K). The sputtered ions (typically only a small fraction of the ejected particles are ionized - about 1%) can fly out of the target in a straight trajectory and produce an energetic impact on the substrate or vacuum chamber (causing re-sputtering).

[0052] Alternatively, at higher gas pressures, ions collide with gas atoms acting as a moderator and diffuse, contact a substrate or vacuum chamber wall, and condense after random walk. By changing the background gas pressure, the entire range from high-energy ballistic impact to low-energy thermal motion can be used.

[0053] The sputtering gas is usually an inert gas, such as argon. For efficient momentum transfer, the atomic weight of the sputtering gas should be close to that of the target, so neon is preferred for light elements, while krypton or xenon are used for heavy elements. Reactive gases can also be used to sputter the compound. Depending on the process parameters, the compound can form on the target surface, in flight or on the substrate. The availability of many parameters to control sputtering deposition makes it a complex process, but also allows experts to control the growth and microstructure of the film to a great extent.

[0054] An important advantage of sputtering deposition is that even materials with very high melting points can be easily sputtered, whereas evaporating these materials in a resistance evaporator or Knudsen cell is problematic or impossible. The composition of the sputtering deposited film is close to the composition of the source material. This difference is due to the fact that different elements diffuse differently due to their mass (light elements are more easily deflected by the gas), but this difference is constant.

[0055] Sputtered films generally have better adhesion to the substrate than evaporated films. The targets contain a large amount of material and require no maintenance, making the technique suitable for ultra-high vacuum applications.

[0056] Sputtering sources contain no hot parts (to avoid heating, they are usually water-cooled) and are compatible with reactive gases such as oxygen. Sputtering can be done from the top down, while evaporation must be done from the bottom up. Advanced processes such as epitaxial growth are possible.

[0057] Some disadvantages of the sputtering process are that the process is more difficult to combine with lift-off for structuring films. This is because diffusion transport, a characteristic of sputtering, makes complete shadowing impossible. Therefore, it is not possible to completely restrict where the atoms go, which leads to contamination problems. In addition, compared to pulsed laser deposition, active control of layer-by-layer growth is difficult, and the inert sputtering gas enters the growing film as impurities.

[0058] Pulsed laser deposition is a variation of the sputtering deposition technique, where a laser beam is used for sputtering. The role of sputtered and re-sputtered ions as well as the ambient gas is well studied in the pulsed laser deposition process.

[0059] Sputtering sources typically use magnetrons, which use strong electric and magnetic fields to confine charged plasma particles close to the surface of the sputtering target. In the magnetic field, the electrons follow a spiral path around the magnetic field lines, and more ionizing collisions occur with gaseous neutral particles near the target surface than would otherwise occur. (As the target material is consumed, a "racetrack" erosion profile may appear on the target surface.)

[0060] The sputtering gas is usually an inert gas such as argon. The additional argon ions produced due to these collisions lead to a higher deposition rate. The plasma can also be maintained at a lower pressure in this way. The sputtered atoms have a neutral charge and are therefore not affected by magnetic traps.

[0061] Charge accumulation on insulating targets can be avoided by using RF sputtering, where the sign of the anode-cathode bias changes at a high rate (typically 13.56 MHz). RF sputtering produces highly insulating oxide films well, but adds expense to the RF power supply and impedance matching network. Stray magnetic fields leaking from ferromagnetic targets can also interfere with the sputtering process. This usually must be compensated for by using specially designed sputtering guns with unusually strong permanent magnets.

[0062] In one embodiment of the present technology, still refer to Figure 1 The bottom layer 16 is selected from the group consisting of the following materials: chromium dioxide (CrO2); semi-metallic ferromagnetic oxide Sr2FeMoO6; Heusler alloy Co2MnGe; Heusler alloy Co2MnSi (CMS); Heusler alloy Co2FeSi (CFS); Heusler alloy Co2MnSn (CMS); and Heusler alloy Co2FeAl 0.5 Si 0.5 (CFAS).

[0063] Example 1

[0064] For example, in the paper “Direct observation of half-metallicity in the Heusler compound Co2MnSi” recently published by M. Jourdan et al. in Nat Commun., 2014 May 30;5:3974., Co2MnSi samples were grown in a sputtering chamber, a molecular beam epitaxy (MBE) chamber, and a synchrotron radiation ultraviolet photoemission spectroscopy (SRUPS) chamber equipped with a He gas discharge lamp (hν = 21.2 eV) and a hemispherical energy analyzer ( The films were prepared and studied entirely in an ultrahigh vacuum cluster consisting of a MgO(100) substrate with a Sherman function S = 0.42 ± 0.05. First, an epitaxial buffer layer of the Heusler compound Co2MnGa (30 nm) was grown on a MgO(100) substrate by radio frequency (RF) sputtering at room temperature. By an optimized additional annealing process, the L21 order was obtained at 550°C, as shown by high energy electron diffraction (RHEED) and X-ray diffraction (XRD). Co2MnSi (70 nm) was RF sputtered on top at room temperature. Induced by the buffer layer, the Co2MnSi film already exhibits a certain degree of L21 surface order as deposited. By additional annealing, the order is improved, as shown by RHEED on the film surface.

[0065] In one embodiment of the present technology, still refer to Figure 1 The tunnel junction 18 is selected from the group consisting of the following materials: magnesium oxide (MgO); aluminum oxide (Al2O3); and spinel MgAl2O4.

[0066] Example 2

[0067] In the paper "Low-temperature atomic layer deposition of MgO thin films on Si" published by S Vangelista et al. in Journal of Physics D: Applied Physics, Vol. 46, No. 48, magnesium oxide (MgO) thin films were grown by atomic layer deposition in a wide deposition temperature window of 80-350°C using bis(cyclopentadienyl)magnesium and H2O precursors. The MgO thin films were grown at a cycle temperature of ~0.12 nm. -1 The MgO films were deposited at a constant growth rate on HF-last Si (1 0 0) and SiO2 / Si substrates. The structure, morphology and chemical properties of the synthesized MgO films were investigated by X-ray reflectivity, grazing incidence X-ray diffraction, time-of-flight secondary ion mass spectrometry and atomic force microscopy measurements. Besides good chemical homogeneity and a polycrystalline structure with a thickness of more than 7 nm, the MgO layer is characterized by a sharp interface with the substrate and limited surface roughness. CV measurements were performed on Al / MgO / Si MOS capacitors with MgO thickness in the range of (4.6-11) nm, which allowed the determination of a dielectric constant (κ) of ~11. The Co layer was deposited by chemical vapor deposition in direct contact with the MgO without vacuum-break (base pressure 10 -5 -10 -6 The grown Co / MgO stacks show sharp interfaces with no interdiffusion of elements between the layers. CV and IV measurements have been performed on Co / MgO / Si MOS capacitors. The dielectric properties of MgO are not affected by the further process of Co deposition.

[0068] In one embodiment of the present technology, still refer to Figure 1 The spin injector is selected from the group consisting of the following materials: chromium dioxide (CrO2); semi-metallic ferromagnetic oxide Sr2FeMoO6; Hessler alloy Co2MnGe; Hessler alloy Co2MnSi (CMS); Hessler alloy Co2FeSi (CFS); Hessler alloy Co2MnSn; and Hessler alloy Co2FeAl 0.5 Si 0.5 (CFAS).

[0069] Example 3

[0070] In the paper “Structural and magnetic properties and tunnel magnetoresistance for Co2(Cr,Fe)Al and Co2FeSi full-Heusler alloys” published by K Inomata et al. in Journal of Physics D: Applied Physics, Vol. 39, No. 5, the structure and magnetization of Co2(Cr1-xFex)Al(0≤x≤1) and Co2FeSi full-Heusler alloys were studied. The films were deposited by ultrahigh vacuum sputtering at various temperatures on thermally oxidized Si(SiO2) and MgO(001) single crystal substrates. After deposition at room temperature (RT), the films were also post-annealed. Co2YZ(20nm) / Al(1.2nm)-oxide / Co 75 Fe 25 The stacked structure of (3nm) / IrMn(15nm) / Ta(60nm) was used to fabricate a magnetic tunneling junction with full Heusler alloy electrodes and was microfabricated using electron beam lithography and Ar ion etching. The junction area was 10 2 μm 2 , where Co2YZ represents Co2(Cr1-xFex)Al or Co2FeSi. The tunnel barrier is formed by depositing 1.2nm of aluminum followed by plasma oxidation in the chamber. X-ray diffraction reveals an A2 or B2 structure depending on the heat treatment conditions and the substrate, rather than the Co2(Cr 1-x Fe x )Al(0≤x≤1) films. However, when Co2FeSi thin films were deposited on MgO(001) substrates at high temperatures above 473K, the L21 structure was obtained. 0.4 Fe 0.6 )Al electrode, the maximum tunneling magnetoresistance (TMR) is 52% at RT and 83% at 5 K. Although the junction using Co2FeSi electrode with L21 structure exhibits 41% TMR at RT and 60% at 5 K, this can be improved by using a buffer layer to reduce the lattice misfit between Co2FeSi and MgO (001) substrate.

[0071] In one embodiment of the present technology, still refer to Figure 1The pinning layer 22 is selected from the group consisting of the following materials: iridium manganese chromium (IrMnCr); iridium manganese (IrMn); nickel manganese (NiMn); nickel manganese chromium (NiMnCr); nickel manganese iron (NiMnFe); nickel manganese iridium (NiMnIr); nickel manganese palladium (NiMnPd); nickel manganese platinum (NiMnPt); nickel manganese rhodium (NiMnRh); platinum manganese (PtMn) and nickel manganese ruthenium (NiMnRu).

[0072] Example 4

[0073] In the paper "Magnetic Tunnel Junction Materials for Electronic Applications" published by JM Slaughter et al. in JOM-e, 52(6) (2000),

[0074] http: / / www.tms.org / pubs / journals / JOM / 0006 / Slaughter / Slaughter-0006.html, Ferromagnetic films are pinned when in contact with antiferromagnetic (AF) films due to exchange coupling. For an uncoupled, free ferromagnetic film, the magnetic orientation of the film shows a hysteresis behavior pointing in the direction of the last applied saturation field. If a saturation field is applied and then removed, the magnetic orientation of the free film will be in the direction of the field. If the direction of the applied saturation field is reversed and removed again, the magnetic orientation of the film will be reversed. Thus, in zero applied field, either orientation is possible. Ferromagnetic films pinned by an AF layer show similar behavior, but with an offset. In zero field, the ferromagnetic film will align in one direction. The exchange coupling between the ferromagnetic and AF layers causes the ferromagnetic layers to align preferentially in one direction at their mutual interface. For the memory device in question, this preferential alignment or pinning serves to lock one layer in a fixed direction. Most of the work on AF pinning materials and other aspects of this field has been centered around manganese-based antiferromagnetic materials such as Pt-Mn, Ir-Mn, Rh-Mn, and Fe-Mn. Pt-Mn is a particularly interesting pinning material because it remains antiferromagnetic at relatively high temperatures. Unlike many commonly used AF alloys, as-deposited Pt-Mn is not AF. Instead, the material must be post-annealed, which causes a phase transition from a face-centered cubic (fcc) to a face-centered tetragonal (fct) crystal structure. The fct phase of Pt-Mn is AF and will pin adjacent ferromagnetic films. The pinning strength increases with annealing time. The shift and widening of the Ni-Fe hysteresis loop in the annealed material is characteristic of a pinned ferromagnetic film. Once pinned, an exchange bias causes the film to magnetically orient in one direction at zero applied field.

[0075] In one embodiment of the present technology, still refer to Figure 1 The pinned layer 22 further includes a Ruderman–Kittel–Kasuya–Yosida (RUDERMAN-KITTEL-KASUYA-YOSIDA (RKKY)) nonmagnetic pinned layer.

[0076] like Figure 2 As shown, the RKKY interaction 100 for a layer thickness of about The ruthenium spacer of (102) exhibits antiferromagnetic polarity. For reference, see SSP Parkin, "Spin Engineering: Direct determination of the Ruderman-Kittel-Kasuya-Yosida far-field function in ruthenium", Phys. Rev. B 44(13), 1991.

[0077] In one embodiment of the present technology, a Ru spacer is used as a spacer with a thickness of about The pinning layer ( Figure 1 22), we can make the direction of the magnetization of the spin injector 20 antiparallel to the direction of the magnetization of the bottom layer 16, which will allow the injection of the maximum minority current into the bottom layer 16 including the magnon gain medium. The injection of the maximum minority current will substantially simplify the access to the magnon laser point. See the following discussion.

[0078] In one embodiment of the present technology, still refer to Figure 1 , reference layer 24 includes a ferromagnetic material for selecting the orientation of bottom layer 16 in a particular direction.

[0079] In one embodiment of the present technology, the reference (or free) layer can be implemented by using CFA (B2-ordered Co2FeAl). References: Hiroaki Sukegawa, Zhenchao Wen, Kouta Kondou, Shinya Kasai, Seiji Mitani, and Koichiro Inomata; Applied Physics Letters 100, 182403 (2012); "Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions".

[0080] In one embodiment of the present technology, still refer to Figure 1 The top electrode 28 is selected from the group consisting of the following materials: cobalt-iron alloy (Co 0.5 Fe 0.5 ); silver (Ag); gold (Au); platinum (Pt); cobalt (Co); palladium (Pd); titanium (Ti); and titanium tungsten (TiW). Each of these materials can be deposited by MBE or sputtering.

[0081] In one embodiment of the present technology, still referring to Figure 1, the spin injector 20 and the pinning layer 22 are replaced by a single layer electron injector. In this embodiment, the electron injector is selected from the group consisting of: metal; metal alloy; ferromagnetic metal; and ferromagnetic alloy

[0082] In one embodiment of the present technology, the terahertz magnon laser 10 ( Figure 1 The invention relates to the generation of terahertz radiation based on the magnon laser effect. For reference, please refer to US patents: 7,430,074; 7,508,578; 9,136,665.

[0083] The essence of terahertz radiation based on the magnon laser effect is as follows: The magnon gain medium (MGM) includes a conduction band, which is divided into two sub-bands by an exchange energy gap, the first sub-band being spin-up and the second sub-band being spin-down (not shown).

[0084] In the case of conventional lasing, if an atom is already in an excited state (i.e. there is a population inversion), it may be disturbed by the passage of a photon with a frequency of ν21, which corresponds to the energy gap ΔE of the transition from the excited state L2 to the ground state L1 (Level 1). In this case, the excited atom relaxes to the ground state and is induced to produce a second photon with a frequency of ν21. The original photon is not absorbed by the atom, so the result is two photons of the same frequency. This process is called stimulated emission. The key detail of stimulated emission is that the induced photon has the same frequency and phase as the incident photon. In other words, the two photons are coherent. It is this property that allows optical amplification and the production of laser systems.

[0085] The magnon lasing process (I.Ya.Korenblit and BGTankhilevich, High frequency magnon generation by nonequilibrium electrons and stability of the magnonstate, Phys.Lett.A, 64, 307 (1977)) can be realized in ferromagnets with an exchange gap Δ in the electronic spectrum, that is, in ferromagnetic semiconductors and semimetals.

[0086] Figure 3 Magnon lasing in a half-metal (110) is shown. By emitting magnons 114 (at about 10 -12 seconds), and then through the Fermi level 118 (about 10 -13sec) by relaxing rapidly and then reabsorbing the same magnon, injecting a minority electron 112 into the subband 113 with spin down into a high energy state 116 in the subband 120 with spin up. As a result, the electron has strongly reduced its energy by the amount ǒE 120 and cannot therefore return to the subband with spin down by reabsorbing the magnon.

[0087] The number of nonequilibrium magnons depends on the magnon-electron damping rate Γe and the magnon-magnon damping rate Γ m ratio, and at the maximum birth rate Γ e and the minimum mortality rate Γ m This corresponds to the maximum number of non-equilibrium magnons. e Proportional to q -1 , so the lasing frequency corresponds to the minimum magnon wave vector And the magnon-magnon damping Γ m is proportional to q4, so Γ e / Γ m With q -5 The nonequilibrium magnons at the sample boundaries relax several times before they are scattered onto the equilibrium magnons. But these boundary processes are insignificant because they are elastic and do not change the energy of the magnons, and the change in momentum in an isotropic system is unimportant. Therefore, for magnon lasing, the minimum magnon wave vector Determines the lasing frequency:

[0088]

[0089] where D is the magnon stiffness.

[0090] The merging of two magnons of frequency f and almost equal antiparallel wave vectors (q / |q| and (-)q / |q|) generates a photon of frequency 2f. This process is the opposite of the well-known process of generating parametric magnons by electromagnetic radiation. It is easy to see that the required pair of magnons is always generated by an electron current with their momentum vectors oriented in the directions of (q / |q| and (-)q / |q|). In fact, the Fermi velocity of the electrons in the current is randomly oriented in all directions, since the drift velocity is very small compared to the Fermi velocity. Therefore, among the injected electrons there are always two electrons with equal but antiparallel momentum. According to the laws of conservation of energy and momentum, such electrons will generate two magnons with equal and antiparallel wave vectors, with the angle between the vector (+)p / |p| and the vector q / |q| being: From this relationship, it can be concluded that for a magnon with |q|, the lasing momentum q1 is almost antiparallel to the vector p. At the critical pumping current density j = 10 4 -10 6 A / cm 2 When the critical pump required is of the same order of magnitude as in the case of conventional semiconductor lasers, the magnon lasing process begins and the device should generate high-power narrowband terahertz radiation.

[0091] Example 5

[0092] Evaluation of lasing frequency of terahertz radiation in Co2MnSi(001) / MgO heterostructure

[0093] Stiffness (According to Ritchie L. et al., Phys. Rev. B 68, 104430) or (Based on Jan Thoene, Stanislav Chadov, Gerhard Fecher, Claudia Felser, Jurgen Kubler) J. Phys. D: Appl. Phys. 42 (2009) 084013)).

[0094] Energy gap Δ=0.6 eV (Bjorn Hulsen and Matthias Scheffler; Phys. Rev Let. 103, 046802 (2009)).

[0095] Effective electron mass m eff = (1.15–1.67)m0 (Steffen Kaltenborn and Hans Christian Schneider, Phys. Rev B 88, 045124 (23013).

[0096] The energy of terahertz is twice the minimum frequency of the non-equilibrium magnon (at the magnon laser spot)

[0097] for

[0098] for

[0099] In order for a magnon laser to work efficiently at room temperature, it is of utmost importance to have the largest possible polarization so that the majority of electrons in the spin-up subband are the only electrons present in the half-metal in equilibrium. Researchers at Johannes Gutenberg University of Mainz have directly observed 100% spin polarization in the Heusler compound Co2MnSi (CMS) up to the Curie temperature of 985 K at room temperature.

[0100] To develop a practical THz magnon laser operating at room temperature, we need to accomplish at least two things: (a) inject spin-down minority electrons into the upper subband of the half-metal, and (b) inject a threshold critical minority electron current density into the upper subband to achieve the onset of the magnon lasing process.

[0101] In one embodiment of the present technology, Figure 4 Depicted is the overall design of a voltage-based tunable terahertz magnon laser 140, which includes a spin injector 144, a tunneling junction 146, a ferromagnetic material 148 containing a magnon gain medium, and a terahertz waveguide 150. The terahertz waveguide can be realized by using 3D printing technology.

[0102] In one embodiment of the present technology, Figure 5 Shows Figure 4 A mechanism 200 for continuous voltage-based tuning of the magnon laser 140 .

[0103] Generally speaking, the increase of voltage bias 210 increases the spin-down subband 202 (with Fermi level E f1 In fact, the minority electron 220 with the maximum energy has the ability to propagate to the sub-band 204 with spin up (with Fermi level E 216) by flipping its spin through the tunneling junction 214. f2 208) and produces the magnon lasing wave vector with the smallest possible This corresponds to the maximum energy ε max The momentum of the tunneling electron.

[0104] After reaching the lasing point, a further increase in the bias causes the maximum energy and momentum of the electron with the highest tunneling probability to increase further, thereby causing the magnon lasing wave vector to decrease further and the terahertz frequency to decrease accordingly.

[0105] More specifically, the tuning in this system can be achieved by changing the bias voltage eV bias 210=(D+ε p) is achieved by changing dV. This will cause df to change the lasing frequency (tuning):

[0106] (df / f) = -(dV / V)(Δ / ε p ) 1 / 2 (Equation 2)

[0107] Therefore, the tuning of the lasing frequency is parametrically larger than the shift in bias voltage, since a small change in bias leads to a large change in the electron energy and thus to a large change in the lasing frequency. Thus, we can cover the entire THz band in the (1-30) THz range by using voltage-based tuning.

[0108] Example 6

[0109] For Δ / ε p ≈10 2 ; If dV / V≈1%=>df / f≈10%, then we only need to change the tuning voltage by 1% to cover f max and 0.9f max THz frequency region between .

[0110] So, in effect we have a micro-synchrotron on a chip. In fact, the parameter (Δ / εp) is large. 1 / 2 The frequency range (from THz maximum down to THz minimum) and the high output power make the THz magnon laser device effectively a micro-synchrotron on a chip, since we can consistently cover a large lasing frequency range by using only one chip-sized device.

[0111] In one embodiment of the present technology, a method for tuning the frequency of terahertz radiation is provided. The method utilizes Figure 4 The device includes a spin injector 144, a tunneling junction 146 coupled to the spin injector, and a ferromagnetic material 148 coupled to the tunneling junction 146. The ferromagnetic material includes a magnon gain medium (MGM).

[0112] A method of tuning the frequency of terahertz radiation includes the step of applying a bias voltage 142 to shift the Fermi level of a spin injector 144 relative to the Fermi level of a ferromagnetic material 148 to initiate generation of non-equilibrium magnons by injecting minority electrons into the magnon gain medium.

[0113] By flipping its spin in the exchange process, the injected minority electron moves into a high-energy electronic state in a lower subband with the spin of the ferromagnetic material up. In this process, an unbalanced magnon is generated. The interaction between the generated unbalanced magnons results in the generation of terahertz electromagnetic radiation.

[0114] The method further comprises the step of tuning the frequency of the generated terahertz radiation by varying the value of the bias voltage 142 .

[0115] The above discussion has described the operation of various exemplary systems and devices, as well as various embodiments related to exemplary methods of operating these systems and devices. In various embodiments, one or more steps of an implementation method (e.g., calculating an optimal voltage bias) are performed by a processor under the control of computer-readable and computer-executable instructions. Therefore, in some embodiments, these methods are implemented by a computer.

[0116] In one embodiment, computer readable and computer executable instructions may reside on a computer usable / readable medium.

[0117] Therefore, one or more operations of various embodiments can be controlled or implemented using computer-executable instructions such as program modules executed by a computer. Typically, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. In addition, the present technology can also be practiced in a distributed computing environment, where tasks are performed by remote processing devices linked through a communication network. In a distributed computing environment, program modules may be located in local and remote computer storage media, including memory storage devices.

[0118] Although specific steps of an exemplary implementation method are disclosed herein, these steps are examples of steps that may be performed according to various exemplary embodiments. That is, the embodiments disclosed herein are well suited for performing various other steps or variations of the steps. Furthermore, the steps disclosed herein may be performed in an order different from that presented, and not all steps must be performed in a particular embodiment.

[0119] Although various electronic and software-based systems are discussed herein, these systems are merely examples of environments that may be utilized and are not intended to imply any limitation on the scope of use or functionality of the present technology. Such systems should also not be interpreted as having any dependency or correlation with any one or combination of components or functions illustrated in the disclosed examples.

[0120] Although the subject matter has been described in language specific to structural features and / or methodological acts, the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A device for generating tunable terahertz radiation, comprising: Spin injector; The spin injector includes a source of minority electrons having spin down; a tunneling junction coupled to the spin injector; as well as The bottom layer also includes a ferromagnetic material coupled to the tunneling junction; The ferromagnetic material comprises a magnon gain medium; the ferromagnetic material further comprises: a conduction band divided into two sub-bands by an exchange energy gap, a first sub-band having spin-up oriented along the magnetization of the ferromagnetic material; and a second sub-band having spin-down oriented opposite to the magnetization of the ferromagnetic material; wherein a majority of electrons having spin-up are located in the first sub-band having spin-up; Top electrode; Reference layers; and Pinning layer, including Ruderman–Kittel–Kasuya–Yosida a nonmagnetic pinned layer and coupled to the reference layer, wherein the spin injector is coupled to the top electrode through the pinned layer; wherein, after a bias voltage is applied to the spin injector, the minority electrons with spin down are injected from the spin injector into the magnon gain medium through tunneling of the tunneling junction; and The applied bias voltage is configured to shift the Fermi level of the spin injector relative to the Fermi level of the ferromagnetic material.

2. The device according to claim 1, wherein: The ferromagnetic material comprises the magnon gain medium, and the magnon gain medium is selected from the group consisting of: Ferromagnetic semiconductor; diluted magnetic semiconductor; half-metallic ferromagnetism; and ferromagnetic conductor, wherein there is a gap in the state density of the minority electrons around the Fermi level of the ferromagnetic material.

3. The device of claim 2, wherein: The semi-metallic ferromagnetic material is selected from the group consisting of: Spin-polarized Heusler alloys; spin-polarized giant magnetoresistance materials; and chromium dioxide.

4. The device of claim 3, wherein: The spin-polarized Hessler alloy is selected from the group consisting of: Semi-metallic ferromagnetic oxide Sr2FeMoO6; Hessler alloy Co2MnGe; Hessler alloy Co2MnSi; Hessler alloy Co2FeSi; Hessler alloy Co2MnSn; and Hessler alloy Co2FeAl 0.5 Si 0.5 .

5. The device of claim 1, wherein: The tunneling junction is selected from the group consisting of: Magnesium oxide; aluminum oxide; and spinel MgAl2O4.

6. The device of claim 1, wherein: The spin injector is selected from the group consisting of: Semimetals; and ferromagnetic alloys.

7. The device of claim 1, wherein: A minority of electrons are injected into the upper sub-band with spin down through the tunneling junction, and non-equilibrium magnons are generated by transitioning to high-energy electronic states in the lower sub-band with spin up; and wherein the interaction between the non-equilibrium magnons causes the generation of electromagnetic radiation; the device further comprises: An electromagnetic waveguide is coupled to the ferromagnetic material and configured to output the electromagnetic radiation.

8. The device of claim 1, wherein: A minority of electrons are injected into the upper sub-band with spin down through the tunneling junction, and non-equilibrium magnons are generated by transitioning to high-energy electronic states in the lower sub-band with spin up; and wherein the interaction between the non-equilibrium magnons causes the generation of terahertz electromagnetic radiation; the device further comprises: A terahertz electromagnetic waveguide is coupled to the ferromagnetic material and configured to output the terahertz electromagnetic radiation.

9. The device of claim 1, wherein: The pinning layer further comprises: The antiferromagnetic pinning layer is selected from the group consisting of the following materials: iridium manganese chromium; iridium manganese; nickel manganese; nickel manganese chromium; nickel manganese iron; nickel manganese iridium; nickel manganese palladium; nickel manganese platinum; nickel manganese rhodium; platinum manganese and nickel manganese ruthenium.

10. The apparatus of claim 1, further comprising: Bottom electrode; The bottom layer is coupled to the bottom electrode; as well as a substrate coupled to the bottom electrode; wherein the voltage applied to the device between the top electrode and the bottom electrode is configured to inject a minority current from the spin injector into the magnon gain medium through the tunneling junction; and wherein the minority current propagating through the magnon gain medium causes the generation of unbalanced magnons in the magnon gain medium; and wherein merging of the unbalanced magnons causes the generation of terahertz radiation emitted from the device to a surrounding area.

11. The device of claim 10, wherein: The substrate is selected from the group consisting of: Gallium arsenide; aluminum oxide; aluminum nitride; indium tin oxide; silicon; silicon-on-sapphire; and magnesium oxide.

12. The device of claim 10, wherein: The bottom electrode is selected from the group consisting of: Cobalt-iron alloys; silver; gold; platinum; cobalt; palladium; titanium; and titanium-tungsten.

13. The apparatus of claim 1, wherein: The spacing of the RKKY nonmagnetic pinned layer is selected so that the magnetization of the top layer is antiparallel to the magnetization of the reference layer.

14. A method of tuning the frequency of radiation using a device, the device comprising a top electrode, a reference layer, and a pinned layer coupled to the reference layer, the pinned layer comprising Ruderman–Kittel–Kasuya–Yosida A nonmagnetic pinned layer, a spin injector coupled to the top electrode via the pinned layer, a tunneling junction coupled to the spin injector, a bottom layer including a ferromagnetic material coupled to the tunneling junction, the ferromagnetic material also including a magnon gain medium, a bottom electrode coupled to the bottom layer, and a substrate coupled to the bottom electrode; the method comprising: (A) applying a bias voltage to shift the Fermi level of the spin injector relative to the Fermi level of the ferromagnetic material to initiate generation of unbalanced magnons by injecting minority electrons into the magnon gain medium; wherein the injected minority electrons enter a high energy electronic state in a lower subband having spin up of the ferromagnetic material by flipping their spins in an exchange process; and wherein unbalanced magnons are generated in the process; and wherein interactions between the unbalanced magnons result in generation of electromagnetic radiation; and (B) The frequency of the radiation generated is tuned by varying the value of the bias voltage.

15. The method of claim 14, further comprising: (C) outputting the electromagnetic radiation by using an electromagnetic waveguide coupled to the ferromagnetic material.

16. The method of claim 15, wherein: The step (C) further comprises: (C1) outputting the generated terahertz electromagnetic radiation by using a terahertz electromagnetic waveguide coupled to the ferromagnetic material.

17. The method of claim 14, wherein: The step (B) further comprises: (B1) Increasing the value of the bias voltage; wherein the injected minority electrons have increased energy due to the increased value of the bias voltage and therefore have a higher probability of transitioning to a high-energy electronic state in the lower subband having the spin-up of the ferromagnetic material by flipping their spins during an exchange process; and wherein a decrease in the energy of the unbalanced magnon caused by the increase in the energy of the injected minority electrons results in a corresponding decrease in the frequency of the generated radiation.

18. The method of claim 14, wherein: The step (B) further comprises: (B2) Tuning the applied bias voltage by using a predetermined function, wherein the frequency of the generated radiation is modulated by the predetermined function.

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