Chiral spin terahertz emission device and preparation method and chiral regulation and control method thereof

Abstract

The invention discloses a chiral spin terahertz emission device and a preparation method and a chiral regulation and control method thereof, and belongs to the field of terahertz emission. The chiral spin terahertz emission device provided by the invention comprises a substrate, an antiferromagnetic layer, a chiral perovskite layer and a heavy metal layer which are stacked in sequence. The chiral regulation and control method of the terahertz emission device comprises the steps that femtosecond laser irradiates the anti-ferromagnetic layer in the chiral spin terahertz emission device, the anti-ferromagnetic layer is induced to generate spin current, meanwhile, an external magnetic field is applied, the direction of the spin current in the anti-ferromagnetic layer is changed by changing the direction of the external magnetic field, and the spin current in the terahertz emission device is regulated and controlled. A chiral structure in the chiral perovskite layer is used for inducing spin current to realize chiral transmission, finally, conversion from spin to charges is realized through the heavy metal layer, and meanwhile, electromagnetic waves with terahertz frequency are radiated, so that chiral regulation and control of terahertz wave signals are completed. The chiral spin terahertz emission device provided by the invention has the characteristics of fast response, easy preparation and capability of working at room temperature.

Description

Technical Field

[0001] This invention belongs to the field of terahertz emission, specifically relating to a chiral spin terahertz emission device and its preparation method and chiral control method. Background Technology

[0002] Terahertz waves, with their higher frequencies than microwaves, lie between the infrared and microwave bands in the electromagnetic spectrum. They possess numerous advantages, including wide bandwidth, low energy consumption, high transmittance, and fingerprint-like properties, making them promising for applications in aerospace, wireless communications, national defense, materials science, and biomedicine. In recent years, the continuous development of integrated circuits has placed higher demands on device speed and energy consumption. The combination of the high-frequency characteristics of terahertz waves and the low-energy consumption of spintronic devices offers advantages such as low power consumption, high sensitivity, and fast response speed.

[0003] Therefore, spin terahertz wave emitters have emerged, offering numerous advantages such as ease of fabrication, room-temperature operation, low cost, and miniaturization. Spin terahertz emitters like CoFeB / Pt have already entered the commercial stage. However, high-frequency, highly sensitive, tunable terahertz emitters related to antiferromagnetism are still under research. In particular, because antiferromagnets possess two sets of spin polarizations, achieving chiral spin polarization in antiferromagnetic molecules is extremely difficult, requiring a very large external magnetic field (~10 T) to overcome the degeneracy of antiferromagnetism. Consequently, related spin terahertz emitters have remained unknown. To overcome this technological bottleneck, this invention utilizes the chiral helical structure of chiral molecules to successfully achieve chiral separation of antiferromagnetic spins, thus developing a chiral spin terahertz emitter. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a chiral spin terahertz emission device and its fabrication method, as well as a chiral modulation method. This invention utilizes a linearly polarized femtosecond laser to induce the injection of magnons from an antiferromagnetic insulator into a chiral perovskite structure. Due to the chiral structure of the perovskite inducing the antiferromagnetic magnons to achieve chiral transmission, chiral-induced polarity-dependent electromagnetic wave radiation is realized.

[0005] The chiral spin terahertz emission device provided by this invention includes the following structure: Substrate; An antiferromagnetic layer is disposed on the substrate surface. The antiferromagnetic layer can generate spin flow under femtosecond laser irradiation. The chiral perovskite layer, located on the antiferromagnetic layer, can control the spin current in different directions under the action of an external magnetic field, thereby achieving the selectivity of chiral spin. A heavy metal layer is disposed on a chiral perovskite layer. Spin currents in the heavy metal layer convert spin into charge, thereby radiating terahertz wave signals.

[0006] Preferably, the antiferromagnetic layer is made of an insulating iron oxide material, specifically ferric oxide (Fe2O3). α -Fe2O3), nickel oxide (NiO) or chromium oxide (Cr2O3), etc.; Preferably, the thickness of the antiferromagnetic layer is 10 to 20 nm.

[0007] Preferably, the chiral molecular perovskite structure is left-handed or right-handed; the right-handed material is (R-NEA)2-CoCl4 or (R-NEA)2-PbSr4; the left-handed material is (S-NEA)2-CoCl4 or (S-NEA)2-PbSr4.

[0008] Preferably, the thickness of the chiral molecular perovskite is 50~200nm.

[0009] Preferably, the substrate is made of single-crystal alumina (Al2O3) or magnesium oxide (MgO).

[0010] The fabrication method of the chiral spin terahertz emission device described above includes the following steps: A substrate is provided, and an antiferromagnetic layer is grown on the substrate, as follows: at 10 -5Under a vacuum environment on the order of Pa, argon gas was introduced into the vacuum chamber at a flow rate of 20 SCCM. After the gas pressure stabilized, the sputtering vacuum was set to 0.4–0.8 Pa. Under a gas pressure environment of 0.4–0.8 Pa, a pulsed laser was turned on, and the antiferromagnetic target was sputtered at a laser frequency of 3 Hz. The baffle of the substrate stage was opened, and the sample stage was rotated at a constant speed. After the set growth time was reached, the sputtering power supply and the baffle were turned off, and the antiferromagnetic layer was obtained. Subsequently, a chiral perovskite layer was prepared. Right-handed (R-NEA)2-CoCl4 and left-handed (S-NEA)2-CoCl4 were selected as chiral perovskite layer materials for illustration. Using a solution method, 11 mmol of right-handed amine molecules (R-NEA) or left-handed amine molecules (S-NEA) and 0.5 mmol of CoCl2·6H2O were dissolved in 2 mL of HCl, with 0.5 mL of ethanol as a co-solvent. The solution was stirred at 80 °C to form a bright blue solution. The chiral perovskite crystals were then cooled to room temperature at a slow cooling rate (10 °C / h) to synthesize right-handed (R-NEA)₂CoCl₄ crystals or left-handed (S-NEA)₂CoCl₄ crystals (blue, plate-like). The crystals were then washed with diethyl ether and dried overnight under vacuum at 60 °C. The synthesized chiral perovskite crystals were dissolved in dimethylformamide (DMF) solvent to form a precursor solution (10 wt%). The antiferromagnetic layer film was washed with acetone, ethanol, deionized water, and acetone respectively in an ultrasonic bath for 10 min, followed by oxygen plasma cleaning for 3 min. A (R-NEA)₂CoCl₄ or (S-NEA)₂CoCl₄ film was prepared at 4000 rpm for 30 s using spin coating technology, followed by annealing at 100 °C for 10 min to obtain the chiral perovskite layer. Subsequently, a 5 nm heavy metal film (e.g., Pt, W, Ta, etc.) was deposited to form a heavy metal layer.

[0011] This invention also provides a chiral modulation method for a chiral spin terahertz emission device, comprising the following steps: Under the action of femtosecond laser, the transmission of magnons in the antiferromagnetic insulating layer is induced. The magnons are injected into the chiral molecular perovskite structure to achieve chiral polarization of the magnons. The chiral polarized magnons form a polarized spin current and realize spin-charge conversion in the heavy metal layer, thereby radiating terahertz signals. Terahertz signals are obtained using the above method; chiral control of spin magnons is achieved by detecting signals in different chiral spin current directions.

[0012] Specifically, when the external magnetic field applied to the transmitting device is a positive saturation magnetization field, when the antiferromagnetic layer combines with the left-handed perovskite structure and is covered with a heavy metal layer, the light-induced antiferromagnetic spin current is injected into the left-handed perovskite structure. Thus, the left-handed polarized spin current can be transmitted through the perovskite layer, and the chiral polarized spin current is further injected into the heavy metal layer, realizing the conversion of spin to charge, while radiating electromagnetic waves at the terahertz frequency.

[0013] Specifically, when the applied magnetic field is changed to a negative saturation magnetization field, the direction of the out-of-plane spin induced by the femtosecond laser changes, the spin current cannot pass through the left-handed perovskite structure, so the spin cannot reach the heavy metal layer to achieve the conversion of spin to charge, and at the same time, the terahertz electromagnetic wave signal cannot be detected.

[0014] Specifically, when the applied magnetic field is kept in negative saturation magnetization, the antiferromagnetic layer combines with the right-handed perovskite layer to form and cover it with a heavy metal layer. The light-induced antiferromagnetic spin current is injected into the right-handed perovskite structure, thereby the right-handed polarized spin current can be transmitted through the perovskite layer. The chiral polarized spin current is further injected into the heavy metal layer to realize the conversion of spin to charge, while radiating electromagnetic waves at the terahertz frequency.

[0015] The present invention has the following beneficial effects: This invention utilizes the chiral properties of perovskite molecules to induce the transport of chiral spins in an antiferromagnetic layer material. By applying external magnetic fields in different directions, the magnetic moment direction of the antiferromagnetic layer is altered, and the chirality of the spin is adjusted through the chiral molecular structure. The measured terahertz electromagnetic wave signal is changed due to the adjustment effect of the chiral molecules.

[0016] This invention utilizes femtosecond laser excitation to transport spins in antiferromagnetic materials, and simultaneously achieves chiral transport of antiferromagnetic spins through a chiral molecular perovskite structure, thus realizing a chiral-related spin terahertz emission device. This is a chiral spin terahertz nanoradiation source with the characteristics of fast response, easy fabrication, and room temperature operation. Attached Figure Description

[0017] Figure 1 A schematic diagram of the structure of a terahertz emitting device fabricated for comparison. Figure 2 For comparison, the terahertz wave signal was measured by changing the polarity of the magnetic field when there was no chiral perovskite layer in the terahertz emitting device.

[0018] Figure 3 A schematic diagram of the structure of the chiral spin terahertz emission device provided by the present invention; Figure 4To implement Case 1, when the material in the chiral perovskite layer of the terahertz emitting device is left-handed, the polarity of the magnetic field is changed to measure the terahertz wave signal.

[0019] Figure 5 To implement Case 2, when the material in the chiral perovskite layer of the terahertz emitting device is right-handed, the polarity of the magnetic field is changed to measure the terahertz wave signal.

[0020] Figure reference numerals: 1-substrate, 2-antiferromagnetic layer, 3-chiral perovskite layer, 4-heavy metal layer. Detailed Implementation

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0022] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0023] Comparative Example The structural schematic diagram of the terahertz emitting device provided in this comparative example is for reference. Figure 1 The process includes sequentially stacking a substrate 1, an antiferromagnetic layer 2, and a heavy metal layer 4; the fabrication method includes the following steps: A 10 mm × 10 mm aluminum oxide substrate was selected as substrate 1. The substrate was heated to 600°C, and then an antiferromagnetic layer of iron oxide insulator material layer was prepared on the substrate surface by laser pulse deposition. The thickness of the antiferromagnetic layer was 15 nm. The process of the antiferromagnetic layer is as follows: at 10 -5 In a vacuum environment on the order of Pa, argon gas at a flow rate of 20 SCCM and oxygen at a flow rate of 2 SCCM were introduced into the vacuum chamber. After the gas pressure stabilized, the sputtering vacuum was set to 0.4 Pa. Under this 0.4 Pa pressure environment, a pulsed laser was turned on to deposit an iron oxide target at a pulse frequency of 3 Hz, sputtering an antiferromagnetic thin film. After the set growth time was reached, the sputtering power supply and baffle were turned off, and the antiferromagnetic layer was obtained. Subsequently, a 5 nm heavy metal Pt layer was deposited on top to obtain the terahertz emission device.

[0024] When a femtosecond laser irradiates an antiferromagnetic layer, changing the direction of the applied magnetic field causes a reversal of the signal polarity. The terahertz electromagnetic wave signal changes with the applied magnetic field, exhibiting no chiral selection effect. Figure 2 As shown.

[0025] Example 1 The schematic diagram of the chiral spin terahertz emission device provided in Example 1 is shown below. Figure 3The process includes sequentially stacking a substrate 1, an antiferromagnetic layer 2, a chiral perovskite layer 3, and a heavy metal layer 4; the preparation method is the same as that in the comparative example, except for the addition of a preparation method for the chiral perovskite layer 3, as follows: Substrate 1 and antiferromagnetic layer 2 were prepared using the same method as in the comparative example. Then, a chiral perovskite layer 3 was prepared on the antiferromagnetic layer 2. In this embodiment, the antiferromagnetic layer material is... α -Fe2O3, the chiral perovskite layer 3 is made of (S-NEA)2CoCl4 crystal, the heavy metal layer is made of Pt, and the preparation method is as follows: 11 mmol of chiral amine molecules (S-NEA) and 0.5 mmol of CoCl₂·6H₂O were dissolved in 2 mL of HCl using a solution method, with 0.5 mL of ethanol as a co-solvent. The solution was stirred at 80 °C to form a bright blue solution. The solution was then cooled to room temperature at a slow cooling rate (10 °C / h) to synthesize (S-NEA)₂CoCl₄ chiral perovskite crystals (blue, plate-like). The crystals were then washed with diethyl ether and dried overnight under vacuum at 60 °C. The synthesized chiral perovskite crystals were dissolved in dimethylformamide (DMF) to form a precursor solution (10 wt%). The solution was washed with acetone, ethanol, deionized water, and acetone, respectively, using an ultrasonic bath. α A -Fe2O3 thin film was prepared for 10 min, followed by oxygen plasma cleaning for 3 min. A (S-NEA)2CoCl4 thin film was then prepared using spin coating technology at 4000 rpm for 30 s, and subsequently annealed at 100℃ for 10 min to obtain a left-chirmic perovskite layer. Finally, a 5 nm heavy metal layer (Pt) was deposited to obtain the target product.

[0026] When a femtosecond laser irradiates an antiferromagnetic layer, changing the direction of the applied magnetic field reveals that only left-handed spins can pass through the chiral perovskite layer, thus radiating terahertz signals. Figure 4 As shown in Figure b. When the chirality of the spin is changed, the right-handed spin cannot pass through the chiral perovskite structure, and therefore cannot radiate terahertz signals, as shown in Figure b. Figure 4 As shown in Figure a.

[0027] Example 2 The schematic diagram of the chiral spin terahertz emission device provided in Example 2 is the same as that in Example 1, except that the material of the chiral perovskite layer 3 is different. The material of the chiral perovskite layer 3 in Example 2 is a right-handed (R-NEA)₂CoCl₄ crystal. The fabrication method of the emission device in Example 2 is the same as that in Example 1, except that S-NEA is replaced with R-NEA.

[0028] When a femtosecond laser irradiates an antiferromagnetic layer, changing the direction of the applied magnetic field reveals that only right-handed spins can pass through the chiral perovskite molecular layer, thus radiating terahertz signals. Figure 5 As shown in Figure a. When the chirality of the spin is changed, the left-chirm spin cannot pass through the perovskite layer structure of the chiral molecule, and therefore cannot radiate terahertz signals, such as... Figure 5 As shown in b.

[0029] It should be noted that in other embodiments, the objective of this invention can be achieved when the experimental process meets the following conditions: For the antiferromagnetic layer, insulating materials such as nickel oxide and chromium oxide can also be selected; For materials used in chiral perovskite layers, chiral materials such as (R-NEA)2-PbSr4 and (S-NEA)2-PbSr4 can also be selected. For the heavy metal layer, other heavy metal materials such as W and Ta can be selected.

[0030] The thickness of chiral molecular perovskite can be adjusted within the range of 50~200nm by adjusting process parameters such as the amount of raw materials used in the preparation method. The specific thickness can be designed as 50nm, 100nm, 150nm or 200nm, which is easy to achieve and can achieve the purpose of this invention.

[0031] The thickness of the antiferromagnetic layer can be selected from 10 to 20 nm, specifically 10 nm, 13 nm, 16 nm, or 20 nm.

[0032] Those skilled in the art can make appropriate selections of the above process parameters according to actual needs, and all of them can achieve the purpose of this invention.

[0033] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A chiral spin terahertz emitting device, characterized in that, include: Substrate; An antiferromagnetic layer is disposed on the surface of the substrate, and the antiferromagnetic layer can generate spin flow under femtosecond laser irradiation; A chiral perovskite layer, disposed on the antiferromagnetic layer, can control the spin current in different directions under the action of an external magnetic field, thereby achieving the selectivity of chiral spin. A heavy metal layer is disposed on the chiral perovskite layer, and the spin flow realizes the conversion of spin to charge in the heavy metal layer, thereby radiating terahertz wave signals.

2. The chiral spin terahertz emitting device according to claim 1, characterized in that, The substrate is a single-crystal aluminum oxide substrate.

3. The chiral spin terahertz emitting device according to claim 1, characterized in that, The heavy metal layer is made of Pt, W or Ta.

4. The chiral spin terahertz emitting device according to claim 1, characterized in that, The antiferromagnetic layer is made of an insulating material.

5. The chiral spin terahertz emitting device according to claim 4, characterized in that, The insulating material is ferric oxide, nickel oxide, or chromium oxide.

6. The chiral spin terahertz emitting device according to any one of claims 1 to 5, characterized in that, The thickness of the antiferromagnetic layer is 10~20nm.

7. The chiral spin terahertz emitting device according to any one of claims 1 to 5, characterized in that, The material of the chiral perovskite layer is left-handed or right-handed; the right-handed material is (R-NEA)2-CoCl4 or (R-NEA)2-PbSr4; the left-handed material is (S-NEA)2-CoCl4 or (S-NEA)2-PbSr4.

8. The chiral spin terahertz emitting device according to claim 7, characterized in that, The thickness of the chiral perovskite layer is 50~200 nm.

9. The method for fabricating a chiral spin terahertz emitting device as described in any one of claims 1 to 8, characterized in that: Includes the following steps: Provide substrate; An antiferromagnetic layer is grown on the substrate; A chiral perovskite precursor solution is prepared, and then coated onto the surface of the antiferromagnetic layer. After annealing, a chiral perovskite layer is obtained. By bonding a heavy metal layer onto the chiral perovskite layer, a chiral spin terahertz emission device is prepared.

10. A method for controlling the chirality of a chiral spin terahertz emission device, characterized in that, The chiral modulation method, applied to the chiral spin terahertz emission device as described in any one of claims 1 to 8, includes the following steps: A femtosecond laser irradiates the antiferromagnetic layer in a chiral spin terahertz emitting device, inducing a spin current in the antiferromagnetic layer. Simultaneously, an external magnetic field is applied, and by changing the direction of the external magnetic field, the direction of the spin current in the antiferromagnetic layer is changed. Chiral transmission is achieved by inducing spin current using the chiral structure in the chiral perovskite layer. Finally, the conversion of spin to charge is achieved through a heavy metal layer, while radiating electromagnetic waves at the terahertz frequency, thus completing the chiral modulation of the terahertz wave signal.

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