A terahertz radiation source based on inverse orbital hall effect and a preparation method thereof

Abstract

This invention provides a terahertz radiation source based on the inverse orbit Hall effect and its fabrication method. A ferromagnetic / non-magnetic heterojunction is constructed by using a weak spin-orbit coupling material instead of heavy metals or topological insulators as the non-magnetic layer. Based on the inverse orbit Hall effect of this weak spin-orbit coupling material, a terahertz radiation source is built. The terahertz radiation source and its fabrication method based on the inverse orbit Hall effect of this application have numerous advantages, including low cost, high stability, simple process, and suitability for industrialization.

Description

Technical Field

[0001] This invention relates to the field of terahertz band device technology, and more specifically, to a terahertz radiation source based on the inverse orbit Hall effect and its preparation method. Background Technology

[0002] Terahertz waves, with frequencies ranging from 0.1 to 10 THz, lie between submillimeter waves and infrared waves. They possess numerous advantages, including low photon energy, high frequency, and good penetration, making them significant for fields such as food inspection, environmental monitoring, non-destructive testing, and national defense. Therefore, the search for and research of effective and reliable terahertz radiation devices has significant strategic value and importance.

[0003] The applicant found the following documents after searching:

[0004] Reference 1: CN110416862B, A terahertz radiation source based on van der Waals heterojunction.

[0005] Reference 2: CN110676673A, Terahertz radiation source device based on multi-finger grating structure and its control method.

[0006] Reference 3: CN108566164A, A terahertz oscillation circuit and oscillator based on a resonant tunneling diode.

[0007] Reference 4: CN111082287B, A MoSe2 / ferromagnetic metal terahertz radiation source, preparation and terahertz wave excitation method.

[0008] The development of terahertz radiation sources based on spintronics provides a novel approach for achieving low-cost, high-efficiency terahertz radiation sources and opens up new avenues for the development and application of terahertz technology.

[0009] Terahertz radiation sources based on spintronics typically construct ferromagnetic / nonmagnetic heterojunctions by combining ferromagnetic materials (Co, Fe, CoFeB, etc.) with nonmagnetic heavy metals (Au, Pt, Ta, W, Pd, etc.) or topological insulators (BiSe, BiTe, etc.). Driven by femtosecond lasers, these sources generate terahertz electromagnetic radiation through the inverse spin Hall effect, leveraging the strong spin-orbit coupling of the heavy metals or topological insulators. The terahertz emission efficiency of spintronics-based terahertz radiation sources can reach levels comparable to ZnTe crystals, and their low-cost manufacturing process and excellent performance make them commercially promising. However, in such ferromagnetic / nonmagnetic heterojunction terahertz radiation sources, heavy metal materials are generally expensive, while topological insulators are relatively difficult to prepare industrially.

[0010] Based on the weak spin-orbit coupling effect, the orbital Hall effect in light metals (Al, Ti, V, Cr, Mn, Cu) and their oxides and nitrides can be similar to the spin Hall effect, converting charge flow into spin flow.

[0011] Therefore, it is promising to replace heavy metals or topological insulators in ferromagnetic / nonmagnetic heterostructures with light metals and their oxides and nitrides. Terahertz radiation can be achieved based on the inverse orbital Hall effect of materials with weak spin-orbit coupling, which can significantly reduce the cost of spin terahertz radiation sources.

[0012] Meanwhile, the applicant's search for "Hall effect terahertz radiation source" in the EPO database yielded no relevant research results. Summary of the Invention

[0013] The purpose of this invention is to address the shortcomings of the prior art by providing a terahertz radiation source based on the inverse orbit Hall effect and its preparation method.

[0014] The technical solution of this invention is:

[0015] A terahertz radiation source based on the inverse orbit Hall effect is proposed. A ferromagnetic / non-magnetic heterojunction is constructed by using a material with weak spin-orbit coupling effect to replace heavy metals or topological insulators as the non-magnetic layer. The terahertz radiation source is constructed based on the inverse orbit Hall effect of the material with weak spin-orbit coupling effect.

[0016] A terahertz radiation source based on the inverse orbit Hall effect includes: a single crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer stacked sequentially.

[0017] The ferromagnetic material layer is any one or more of Co, Fe, Ni, NiFe, and CoFeB;

[0018] The light metal layer is any one or more of Al, Ti, V, Cr, Mn, Cu and their oxides and nitrides;

[0019] The light metal layer is 4-100nm in size.

[0020] Furthermore, the single-crystal substrate is made of MgO or Al2O3.

[0021] Furthermore, the protective layer target material is made of MgO or Al2O3.

[0022] A terahertz radiation source based on the inverse orbit Hall effect, which distinguishes between the inverse spin Hall effect and the inverse orbit Hall effect by the polarity of the terahertz signal;

[0023] The polarity of terahertz signals generated based on the inverse spin Hall effect depends on the spin Hall angle.

[0024] The polarity of the terahertz signal generated based on the inverse orbit Hall effect depends on the product of the orbit Hall angle of the material with weak spin-orbit coupling effect and the spin-orbit conversion efficiency of the ferromagnetic layer.

[0025] A method for preparing a terahertz radiation source based on the inverse orbit Hall effect is proposed, which involves preparing a composite heterojunction of a material with weak spin-orbit coupling effect and a ferromagnetic material to generate terahertz radiation.

[0026] Includes the following steps:

[0027] S1, Preparation of raw materials:

[0028] Choose a single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer;

[0029] S2, a terahertz radiation source is prepared by magnetron sputtering;

[0030] A ferromagnetic material layer, a light metal layer, and a protective layer are sequentially deposited on a single-crystal substrate by magnetron sputtering.

[0031] Among them, the single crystal substrate is Al2O3, the ferromagnetic material layer is a 2nm Co thin film, the light metal layer is a 4-100nm Ti thin film, and the protective layer is a 5nm MgO thin film.

[0032] The reaction parameters include: substrate temperature, sputtering atmosphere, and sputtering power;

[0033] The substrate temperature was room temperature; the argon flow rate was 20 sccm; the sputtering pressure was 2.5 mTorr; and the sputtering powers of Co, Ti, and MgO were 30, 30, and 100 W, respectively.

[0034] Controlling the growth sequence of each layer: First, grow the ferromagnetic Co film, then the non-magnetic Ti film, and finally the MgO protective layer.

[0035] Al2O3 / Co / Ti / MgO heterojunctions were prepared by controlling the thicknesses of Co, Ti, and MgO films to be 2, 4-100, and 5 nm, respectively.

[0036] A method for preparing a terahertz radiation source based on the inverse orbit Hall effect is proposed, which involves preparing a composite heterojunction of a material with weak spin-orbit coupling effect and a ferromagnetic material to generate terahertz radiation.

[0037] Includes the following steps:

[0038] S1, Preparation of raw materials:

[0039] Choose a single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer;

[0040] S2, a terahertz radiation source is prepared by magnetron sputtering;

[0041] A ferromagnetic material layer, a light metal layer, and a protective layer are sequentially deposited on a single-crystal substrate by magnetron sputtering.

[0042] Among them, the single crystal substrate is Al2O3, the ferromagnetic material layer is a 2nm Co thin film, the light metal layer is a 4-100nm Mn thin film, and the protective layer is a 5nm MgO thin film.

[0043] The reaction parameters include: substrate temperature, sputtering atmosphere, and sputtering power;

[0044] The substrate temperature was room temperature; the argon flow rate was 20 sccm; the sputtering pressure was 2.5 mTorr; and the sputtering powers of Co, Mn, and MgO were 30, 30, and 100 W, respectively.

[0045] The growth sequence of each layer is controlled: first, a ferromagnetic Co film is grown, then a non-magnetic Mn film is grown, and finally a MgO protective layer is grown.

[0046] Al2O3 / Co / Mn / MgO heterojunctions were prepared by controlling the thicknesses of Co, Mn, and MgO films to be 2, 4-100, and 5 nm, respectively.

[0047] A method for preparing a terahertz radiation source based on the inverse orbit Hall effect includes the following steps:

[0048] S1, Preparation of raw materials:

[0049] Choose a single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer;

[0050] S2, a terahertz radiation source is prepared by magnetron sputtering;

[0051] A ferromagnetic material layer, a light metal layer, and a protective layer are sequentially deposited on a single-crystal substrate by magnetron sputtering.

[0052] The reaction parameters include: substrate temperature, sputtering atmosphere, and sputtering power;

[0053] The substrate temperature was room temperature; the argon flow rate was 20 sccm; and the sputtering pressure was 2.5 mTorr.

[0054] The ferromagnetic material layer is made of any one of Co, Fe, Ni, NiFe, or CoFeB, and the sputtering power is 30W to 50W.

[0055] The light metal layer can be any one of Al, Ti, V, Cr, Mn, and Cu, and the sputtering power is 30W to 50W;

[0056] The protective layer is made of MgO or Al2O3, and the sputtering power is 100W;

[0057] By controlling the growth sequence of each layer, a ferromagnetic material layer film is grown first, followed by a light metal layer film, and finally a protective layer is grown to obtain a heterojunction of single crystal substrate / ferromagnetic material layer / light metal layer / protective layer.

[0058] The room temperature described in this application is 15℃~25℃.

[0059] The beneficial effects of this application are as follows:

[0060] First, the basic concept of this application is to prepare a composite heterojunction of a weak spin-orbit coupling effect material and a ferromagnetic material by magnetron sputtering, use the weak spin-orbit coupling effect material to replace heavy metals or topological insulators, and construct a terahertz radiation source based on the inverse orbit Hall effect of the weak spin-orbit coupling effect material.

[0061] Second, based on the above-mentioned basic concept, the structural design proposed in this application includes: a single crystal substrate, a ferromagnetic material target, a light metal, and a protective layer target stacked sequentially; the single crystal substrate is made of MgO or Al2O3; the ferromagnetic material target is made of any one or more of Co, Fe, Ni, NiFe, and CoFeB; the light metal is made of any one or more of Al, Ti, V, Cr, Mn, Cu and their oxides and nitrides; and the protective layer target is made of MgO or Al2O3.

[0062] Third, this application investigated the preparation method. The core parameters of the preparation method are: substrate temperature, sputtering atmosphere, and sputtering power.

[0063] Fourth, compared with the prior art literature, the advantages of this application are:

[0064] 1) This application is based on the inverse orbit Hall effect, which is a novel effect because it is a novel terahertz source.

[0065] 2) The reverse orbit Hall effect can be achieved in inexpensive, light metals, enabling low-cost terahertz radiation.

[0066] 3) Terahertz sources based on the inverse orbit Hall effect have a simple preparation process and can achieve high-efficiency radiation. Attached Figure Description

[0067] The present invention will be further described in detail below with reference to the embodiments shown in the accompanying drawings, but this does not constitute any limitation on the present invention.

[0068] Figure 1 Design diagram and measurement schematic diagram of Al2O3 / Co / Ti / MgO heterojunction structure.

[0069] Figure 2This is a schematic diagram illustrating the identification of the orbital Hall effect in a composite heterostructure of ferromagnetic material Co and weak spin-orbit coupling material Ti.

[0070] Figure 3 The image shows the terahertz emission spectrum of the Al2O3 / Co / Ti / MgO heterojunction.

[0071] Figure 4 Design diagram and measurement schematic diagram of Al2O3 / Co / Mn / MgO heterojunction structure. Detailed Implementation

[0072] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the materials used in the following embodiments are conventional materials; and the experimental methods described are conventional methods.

[0073] The present invention will now be described in detail with reference to the accompanying drawings, providing a complete description of the technical solution of the present invention.

[0074] Example 1: Preparation of Al2O3 / Co / Ti / MgO heterojunction and detection of terahertz radiation signal.

[0075] (1) Sample preparation .

[0076] A magnetron sputtering device was used to install Co, Ti, and MgO targets on the sputtering head; the Al2O3 substrate was placed in the sample holder position, and the necessary process parameters were adjusted to achieve film formation.

[0077] The reaction parameters include substrate temperature, sputtering atmosphere, and sputtering power. The final optimized conditions are: substrate temperature at room temperature; argon flow rate of 20 sccm; sputtering pressure of 2.5 mTorr; sputtering powers of Co, Ti, and MgO of 30, 30, and 100 W, respectively; controlling the growth sequence of each layer, first growing the ferromagnetic Co film, then the non-magnetic Ti film, and finally the MgO protective layer; controlling the thicknesses of the Co, Ti, and MgO films to be 2, 4-100, and 5 nm, respectively, to prepare an Al2O3 / Co (2 nm) / Ti (4-100 nm) / MgO (5 nm) heterojunction (the applicant's current experiments show that the light metal layer can exhibit the orbital Hall effect at 4-100 nm).

[0078] (2) Detection of terahertz radiation signals.

[0079] Terahertz emission measurements were performed using a domestically produced terahertz emission spectrum with a center wavelength of 800 nm, a pulse duration of 100 fs, an average power of 2 W, and a repetition frequency of 80 MHz.

[0080] The femtosecond laser beam is divided into a pump beam and a probe beam. The pump beam excites the sample under normal incident conditions, while the probe beam detects the generated terahertz waves using electro-optic sampling technology.

[0081] A 2 mm thick ZnTe(110) electro-optic crystal was used for detection. An in-plane magnetic field was applied to the sample for detection. All measurements were performed in a dry, room-temperature environment. Terahertz radiation signals were detected from the ferromagnetic / nonmagnetic heterojunction prepared in this invention using femtosecond laser driving.

[0082] (3) Results comparison.

[0083] Figure 1 The diagram shows the Al2O3 / Co / Ti / MgO heterojunction structure design and measurement schematic in Example 1. Terahertz emission signals were detected by excitation from the Co side of the ferromagnetic layer using a femtosecond laser.

[0084] Figure 2 This is a schematic diagram illustrating the identification of the orbital Hall effect in the composite heterojunction of ferromagnetic material Co and weakly spin-orbit coupling material Ti in Example 1. By characterizing whether the polarity of the terahertz signal matches the sign of the spin Hall angle of the inverse spin Hall effect or the sign of the product of the orbital Hall angle and the spin-orbit conversion efficiency of the ferromagnetic layer, it is proven and identified whether the terahertz emission signal in the Co / Ti heterojunction originates from the inverse orbital Hall effect. Figure 3 The terahertz emission spectrum of the Al2O3 / Co / Ti / MgO heterojunction shows that its polarity is consistent with the sign of the product of the orbital Hall angle and the spin-orbit conversion efficiency of the ferromagnetic layer, indicating that the terahertz emission signal in the Co / Ti heterojunction originates from the inverse orbital Hall effect.

[0085] Example 2: Preparation of Al2O3 / Co / Mn / MgO heterojunction and detection of terahertz radiation signal

[0086] (1) Sample preparation.

[0087] A magnetron sputtering apparatus was used, with Co, Mn, and MgO targets mounted on the sputtering head. An Al₂O₃ substrate was placed in the sample holder, and necessary process parameters were adjusted to achieve film formation. Reaction parameters included substrate temperature, sputtering atmosphere, and sputtering power. The final optimized conditions were: substrate temperature at room temperature; argon flow rate of 20 sccm; sputtering pressure of 2.5 mTorr; and sputtering powers of 30, 30, and 100 W for Co, Mn, and MgO, respectively. The growth sequence of each layer was controlled: first, a ferromagnetic Co film was grown, followed by a non-magnetic Mn film, and finally a MgO protective layer. The thicknesses of the Co, Mn, and MgO films were controlled to be 2, 4-100, and 5 nm, respectively, to prepare an Al₂O₃ / Co (2 nm) / Mn (4-100 nm) / MgO (5 nm) heterojunction.

[0088] (2) Detection of terahertz radiation signals.

[0089] Terahertz emission measurements were performed using a domestically produced terahertz emission spectrometer with a center wavelength of 800 nm, a pulse duration of 100 fs, an average power of 2 W, and a repetition frequency of 80 MHz. The femtosecond laser beam was split into a pump beam and a probe beam. The pump beam excited the sample under normal incident conditions, while the probe beam detected the generated terahertz wave using electro-optic sampling technology. A 2 mm thick ZnTe(110) electro-optic crystal was used for detection, and an in-plane magnetic field was applied to the sample for detection. All measurements were performed in a dry, room-temperature environment. Terahertz radiation signals were detected from the ferromagnetic / non-magnetic heterojunction prepared in this invention using femtosecond laser driving.

[0090] (3) Results test.

[0091] Figure 4 The diagram shows the Al2O3 / Co / Mn / MgO heterojunction structure design and measurement schematic in Example 2. Terahertz emission signals were detected by excitation from the Co side of the ferromagnetic layer using a femtosecond laser. Similarly, the origin of the terahertz emission signal in the Co / Mn heterojunction can be determined by characterizing whether the polarity of the terahertz signal matches the sign of the spin Hall angle of the inverse spin Hall effect, or the sign of the product of the orbital Hall angle and the spin-orbit conversion efficiency of the ferromagnetic layer.

[0092] The above-described embodiments are preferred embodiments of the present invention and are only used to facilitate the illustration of the present invention. They are not intended to limit the present invention in any way. Any person skilled in the art who makes local modifications or alterations to the technical content disclosed in the present invention without departing from the scope of the technical features of the present invention shall still fall within the scope of the technical features of the present invention.

Claims

1. A terahertz radiation source based on inverse orbital Hall effect, characterized in that, include: A single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer are stacked in sequence. The terahertz radiation originates from the orbital Hall effect, and the inverse spin Hall effect and the inverse orbital Hall effect are distinguished by the polarity of the terahertz signal. The polarity of terahertz signals generated based on the inverse spin Hall effect depends on the spin Hall angle; the polarity of terahertz signals generated based on the inverse orbital Hall effect depends on the product of the orbital Hall angle of the material with weak spin-orbit coupling effect and the spin-orbit conversion efficiency of the ferromagnetic layer. The ferromagnetic material layer is any one or more of Co, Fe, Ni, NiFe, and CoFeB; The light metal layer is any one or more of Al, Ti, V, Cr, Mn, Cu and their oxides and nitrides; The light metal layer is 4-100 nm in size.

2. A terahertz radiation source based on inverse orbital-Hall effect according to claim 1, characterized in that, The single-crystal substrate is made of MgO or Al2O3.

3. A terahertz radiation source based on inverse orbital-Hall effect according to claim 1, characterized in that, The protective layer is made of MgO or Al2O3.

4. A method for preparing a terahertz radiation source based on the inverse orbit Hall effect, characterized in that, The terahertz radiation originates from the orbital Hall effect, and the inverse spin Hall effect and the inverse orbital Hall effect are distinguished by the polarity of the terahertz signal; the polarity of the terahertz signal generated based on the inverse spin Hall effect depends on the spin Hall angle; the polarity of the terahertz signal generated based on the inverse orbital Hall effect depends on the product of the orbital Hall angle of the material with weak spin-orbit coupling effect and the spin-orbit conversion efficiency of the ferromagnetic layer. Includes the following steps: S1, Preparation of raw materials: Choose a single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer; S2, a terahertz radiation source is prepared by magnetron sputtering; A ferromagnetic material layer, a light metal layer, and a protective layer are sequentially deposited on a single-crystal substrate by magnetron sputtering. Among them, the single crystal substrate is Al2O3, the ferromagnetic material layer is a 2 nm Co thin film, the light metal layer is a 4-100 nm Ti thin film, and the protective layer is a 5 nm MgO thin film. The reaction parameters include: substrate temperature, sputtering atmosphere, and sputtering power; The substrate temperature was room temperature; the argon flow rate was 20 sccm; the sputtering pressure was 2.5 mTorr; and the sputtering powers of Co, Ti, and MgO were 30, 30, and 100 W, respectively. Controlling the growth sequence of each layer: First, grow the ferromagnetic Co film, then the non-magnetic Ti film, and finally the MgO protective layer. Al2O3 / Co / Ti / MgO heterojunctions were prepared by controlling the thicknesses of Co, Ti, and MgO films to be 2, 4-100, and 5 nm, respectively.

5. A method for preparing a terahertz radiation source based on the inverse orbit Hall effect, characterized in that, The terahertz radiation originates from the orbital Hall effect, and the inverse spin Hall effect and the inverse orbital Hall effect are distinguished by the polarity of the terahertz signal; the polarity of the terahertz signal generated based on the inverse spin Hall effect depends on the spin Hall angle; the polarity of the terahertz signal generated based on the inverse orbital Hall effect depends on the product of the orbital Hall angle of the material with weak spin-orbit coupling effect and the spin-orbit conversion efficiency of the ferromagnetic layer. Includes the following steps: S1, Preparation of raw materials: Choose a single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer; S2, a terahertz radiation source is prepared by magnetron sputtering; A ferromagnetic material layer, a light metal layer, and a protective layer are sequentially deposited on a single-crystal substrate by magnetron sputtering. Among them, the single crystal substrate is Al2O3, the ferromagnetic material layer is a 2 nm Co thin film, the light metal layer is a 4-100 nm Mn thin film, and the protective layer is a 5 nm MgO thin film. The reaction parameters include: substrate temperature, sputtering atmosphere, and sputtering power; The substrate temperature was room temperature; the argon flow rate was 20 sccm; the sputtering pressure was 2.5 mTorr; and the sputtering powers of Co, Mn, and MgO were 30, 30, and 100 W, respectively. The growth sequence of each layer is controlled: first, a ferromagnetic Co film is grown, then a non-magnetic Mn film is grown, and finally a MgO protective layer is grown. Al2O3 / Co / Mn / MgO heterojunctions were prepared by controlling the thicknesses of Co, Mn, and MgO films to be 2, 4-100, and 5 nm, respectively.

6. A method for preparing a terahertz radiation source based on the inverse orbit Hall effect, characterized in that, The terahertz radiation originates from the orbital Hall effect, and the inverse spin Hall effect and the inverse orbital Hall effect are distinguished by the polarity of the terahertz signal. The polarity of the terahertz signal generated based on the inverse spin Hall effect depends on the spin Hall angle; the polarity of the terahertz signal generated based on the inverse orbital Hall effect depends on the product of the orbital Hall angle of the material with weak spin-orbit coupling effect and the spin-orbit conversion efficiency of the ferromagnetic layer; including the following steps: S1, Preparation of raw materials: Choose a single-crystal substrate, a ferromagnetic material layer, a light metal layer, and a protective layer; S2, a terahertz radiation source is prepared by magnetron sputtering; A ferromagnetic material layer, a light metal layer, and a protective layer are sequentially deposited on a single-crystal substrate by magnetron sputtering. The reaction parameters include: substrate temperature, sputtering atmosphere, and sputtering power; The substrate temperature was room temperature; the argon flow rate was 20 sccm; and the sputtering pressure was 2.5 mTorr. The ferromagnetic material layer is made of any one of Co, Fe, Ni, NiFe, or CoFeB, and the sputtering power is 30 W to 50 W. The light metal layer can be any one of Al, Ti, V, Cr, Mn, and Cu, and the sputtering power is 30 W to 50 W. The protective layer is made of MgO or Al2O3, and the sputtering power is 100 W; By controlling the growth sequence of each layer, a ferromagnetic material layer film is grown first, followed by a light metal layer film, and finally a protective layer is grown to obtain a heterojunction of single crystal substrate / ferromagnetic material layer / light metal layer / protective layer.

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