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

Abstract

The application discloses a chiral spin terahertz emission device and a preparation method and a chiral control method thereof, and belongs to the field of terahertz emission. The chiral spin terahertz emission device provided by the application comprises a substrate, an anti-ferromagnetic layer, a chiral perovskite layer and a heavy metal layer which are stacked in sequence. The chiral control method of the terahertz emission device is as follows: a femtosecond laser irradiates the anti-ferromagnetic layer in the chiral spin terahertz emission device to induce spin current in the anti-ferromagnetic layer, and at the same time, 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; the chiral structure in the chiral perovskite layer is utilized to induce spin current to realize chiral transmission; finally, the spin is converted into electric charge through the heavy metal layer, and electromagnetic waves of a terahertz frequency are radiated at the same time, that is, the chiral control of the terahertz wave signal is completed. The chiral spin terahertz emission device provided by the application has the characteristics of fast response, easy preparation and room temperature operation.

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, 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:

[0006] Substrate;

[0007] An antiferromagnetic layer is disposed on the substrate surface. The antiferromagnetic layer can generate spin flow under femtosecond laser irradiation.

[0008] 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.

[0009] A heavy metal layer is arranged on the chiral perovskite layer, and spin current is converted into charge current in the heavy metal layer to radiate terahertz wave signals.

[0010] Preferably, the material of the antiferromagnetic layer is an insulator iron oxide material, which can be specifically Fe2O3, NiO or Cr2O3. α

[0011] Preferably, the thickness of the antiferromagnetic layer is 10-20 nm.

[0012] 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; and the left-handed material is (S-NEA)2-CoCl4 or (S-NEA)2-PbSr4.

[0013] Preferably, the thickness of the chiral molecular perovskite is 50-200 nm.

[0014] Preferably, the material of the substrate layer is single crystal aluminum oxide (Al2O3) or magnesium oxide (MgO).

[0015] The preparation method of the chiral spin terahertz emission device is as follows:

[0016] A substrate is provided, and an antiferromagnetic layer is grown on the substrate, which is prepared by the following process: 10 -5 ​In a vacuum environment of the order of Pa, argon gas with a flow rate of 20 SCCM is introduced into the vacuum chamber, and after the gas pressure is stabilized, the sputtering vacuum degree is 0.4-0.8 Pa; under the pressure environment of 0.4-0.8 Pa, the anti-ferromagnetic target is sputtered and deposited by opening the pulse laser at a laser frequency of 3 Hz; the shutter of the substrate base plate is opened, the sample plate is rotated at a uniform speed, and after the set growth time is reached, the sputtering power supply and the shutter are turned off, and the anti-ferromagnetic layer is prepared. Subsequently, a chiral perovskite layer is prepared, and right-handed (R-NEA)2-CoCl4 and left-handed (S-NEA)2-CoCl4 are selected as chiral perovskite layer materials for illustration, 11 mmol of right-handed amine molecules (R-NEA) or left-handed amine molecules (S-NEA) and 0.5 mmol of CoCl2·6H2O are dissolved in 2 mL of HCl, 0.5 mL of ethanol is used as a cosolvent, and a bright blue solution is formed by stirring at room temperature at 80℃. Then, the solution is cooled to room temperature at a slow cooling rate (10℃ / h), and right-handed (R-NEA)2CoCl4 crystals or left-handed (S-NEA)2-CoCl4 crystals (blue, plate-shaped) are synthesized. Then, the crystals are washed with diethyl ether and dried in a vacuum at 60℃ overnight. The synthesized chiral perovskite crystals are dissolved in dimethylformamide (DMF) solvent to form a precursor solution (10 wt%). The anti-ferromagnetic layer thin film is washed with acetone, ethanol, deionized water, and acetone in an ultrasonic cleaner for 10 min, and then washed with oxygen plasma for 3 min. The (R-NEA)2CoCl4 or (S-NEA)2CoCl4 thin film is prepared by using a spin coating technique at a rotation speed of 4000 rpm for 30 s, and then annealed at 100℃ for 10 min, to obtain the chiral perovskite layer. Subsequently, a 5nm thick heavy metal film (such as Pt, W, Ta, etc.) is coated to form a heavy metal layer.

[0017] The application further provides a chiral regulation method for a chiral spin terahertz emission device, which comprises the following steps:

[0018] Under the action of a femtosecond laser, the transmission of magnons in the anti-ferromagnetic insulating layer is induced, the magnons are injected into the chiral molecule perovskite structure, and the chiral polarization of the magnons is realized; the chiral polarized magnons form polarized spin current and realize spin-charge conversion in the heavy metal layer, thereby radiating a terahertz signal.

[0019] The terahertz signal is obtained according to the above method; by detecting the signals of spin current directions with different chirality, the chiral regulation of the spin magnons is realized.

[0020] Specifically, when the applied magnetic field of the emitter device is a positive saturation magnetization field, when the anti-ferromagnetic layer is combined with the left-handed structure perovskite layer and covered with a heavy metal layer, the light-induced anti-ferromagnetic spin current is injected into the left-handed structure perovskite structure, so that the left-handed polarized spin current can be transmitted through the perovskite layer, the chiral polarized spin current is further injected into the heavy metal layer, the spin-to-charge conversion is realized, and the terahertz frequency electromagnetic wave is radiated.

[0021] Specifically, when the applied magnetic field is changed to a negative saturation magnetization field, the direction of the femtosecond laser-induced out-of-plane spin is changed, the spin current cannot penetrate the left-handed perovskite structure, so that the spin cannot reach the heavy metal layer to realize the spin-to-charge conversion, and the terahertz electromagnetic wave signal cannot be detected.

[0022] Specifically, when the applied magnetic field is kept as a negative saturation magnetization, the anti-ferromagnetic layer is combined with the right-handed structure perovskite layer and covered with a heavy metal layer, the light-induced anti-ferromagnetic spin current is injected into the right-handed structure perovskite structure, so that 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, the spin-to-charge conversion is realized, and the terahertz frequency electromagnetic wave is radiated.

[0023] The present application has the following beneficial effects:

[0024] The present application utilizes the chiral effect of perovskite molecules to induce the transmission of chiral spin in the anti-ferromagnetic layer material. By changing the direction of the magnetic moment of the anti-ferromagnetic material through the application of magnetic field in different directions, and adjusting the chirality of the spin through the chiral structure molecules, the terahertz electromagnetic wave signal measured is changed due to the adjustment of the chiral molecules.

[0025] The present application utilizes the femtosecond laser to excite the transmission of spin in the anti-ferromagnetic material, and realizes the chiral transmission of anti-ferromagnetic spin through the chiral molecule perovskite structure, and realizes the chiral related spin terahertz emitter device. It is a kind of chiral spin terahertz nano radiation source, which has the characteristics of fast response, easy preparation and room temperature operation. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The structure schematic diagram of the terahertz emitter device prepared for the comparative example is shown in the figure.

[0027] Figure 2 When the polarity of the magnetic field is changed when there is no chiral perovskite layer in the terahertz emitter device, the terahertz wave signal is measured.

[0028] Figure 3 The structure schematic diagram of the chiral spin terahertz emitter device provided by the present application is shown in the figure.

[0029] Figure 4To implement case 1, when the material in the chiral perovskite layer in the terahertz emission device is left-handed, the polarity of the magnetic field is changed, and the measured terahertz wave signal is measured.

[0030] Figure 5 To implement case 2, when the material in the chiral perovskite layer in the terahertz emission device is right-handed, the polarity of the magnetic field is changed, and the measured terahertz wave signal is measured.

[0031] Reference signs: 1 - substrate, 2 - antiferromagnetic layer, 3 - chiral perovskite layer, 4 - heavy metal layer. DETAILED DESCRIPTION

[0032] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0033] The materials, reagents, etc. used in the following examples can be obtained commercially unless otherwise specified.

[0034] Comparative example

[0035] The structure of the terahertz emission device provided by the present comparative example is shown in reference to Figure 1 , which comprises a substrate 1, an antiferromagnetic layer 2 and a heavy metal layer 4 stacked in sequence; the preparation method comprises the following steps:

[0036] A 10 mm x 10 mm aluminum oxide substrate is selected as the substrate 1, the substrate is heated to 600°C, and then an antiferromagnetic layer of an insulating iron trioxide material layer is prepared on the surface of the substrate by laser pulse deposition method, and the thickness of the antiferromagnetic layer is 15 nm;

[0037] The process of the antiferromagnetic layer is as follows: under the vacuum environment of the order of 10 -5 Pa, 20 SCCM of argon and 2 SCCM of oxygen are introduced into the vacuum chamber, and the sputtering vacuum degree is 0.4 Pa after the gas pressure is stabilized; under the pressure environment of 0.4 Pa, the pulse laser is turned on, the iron oxide target material is deposited at a pulse frequency of 3 Hz, the antiferromagnetic film is sputtered, and after reaching the set growth time, the sputtering power supply and the baffle are turned off, and the antiferromagnetic layer is prepared. Then cover a 5 nm heavy metal Pt layer, and the terahertz emission device is obtained.

[0038] When the femtosecond laser irradiates the antiferromagnetic layer, the direction of the applied magnetic field is changed, and the signal polarity is observed to be reversed, the terahertz electromagnetic wave signal changes with the change of the applied magnetic field, and there is no chiral selection effect, as shown in Figure 2 .

[0039] Example 1

[0040] The structure of the chiral spin terahertz emission device provided by example 1 is shown in reference to Figure 3, including substrates 1, antiferromagnetic layer 2, chiral perovskite layer 3 and heavy metal layer 4 stacked in sequence; the preparation method refers to the method in the comparative example, the difference is that the preparation method of chiral perovskite layer 3 is added, and the method is as follows:

[0041] The substrates 1 and the antiferromagnetic layer 2 are prepared by the same method as in the comparative example, and then the chiral perovskite layer 3 is prepared on the antiferromagnetic layer 2. In this embodiment, the material of the antiferromagnetic layer is α -Fe2O3, the material of the chiral perovskite layer 3 is (S-NEA)2CoCl4 crystal, and the material of the heavy metal layer is Pt. The preparation method is as follows:

[0042] 11 mmol of chiral amine molecules (S-NEA) and 0.5 mmol of CoCl2·6H2O are dissolved in 2 mL of HCl with 0.5 mL of ethanol as a cosolvent by a solution method, and a bright blue solution is formed by stirring at 80°C under normal temperature. Then, it is cooled to room temperature at a slow cooling speed (10°C / h), and (S-NEA)2CoCl4 chiral perovskite crystal (blue, plate-shaped) is synthesized. Then, the crystal is washed with diethyl ether and dried in a vacuum at 60°C overnight. The synthesized chiral perovskite crystal is dissolved in a dimethylformamide (DMF) solvent to form a precursor solution (10 wt%). The precursor solution is washed with acetone, ethanol, deionized water, acetone, respectively in an ultrasonic cleaner α -Fe2O3 film for 10 min, and then cleaned with oxygen plasma for 3 min. A (S-NEA)2CoCl4 film is prepared by a spin-coating technique at a rotation speed of 4000 rpm for 30 s, and then annealed at 100°C for 10 min to obtain a left-handed chiral perovskite layer. Finally, a 5 nm thick heavy metal layer (Pt) is coated to obtain the target product.

[0043] When the femtosecond laser irradiates the antiferromagnetic layer, the direction of the applied magnetic field is changed, and it can be seen that only left-handed spins can pass through the chiral perovskite layer to radiate terahertz signals, as shown in FIG. b of Figure 4 . When the chirality of the spin is changed, right-handed spins cannot pass through the chiral perovskite structure, so terahertz signals cannot be radiated, as shown in FIG. a of Figure 4 .

[0044] Example 2

[0045] The structure of the chiral spin terahertz emission device provided in Example 2 is the same as that in Example 1, and the only difference is that the material of the chiral perovskite layer 3 therein is different. In Example 2, the material of the chiral perovskite layer 3 is right-handed (R-NEA)2CoCl4 crystal. The preparation method of the emission device in Example 2 refers to the method in Example 1, and the only difference is that S-NEA therein is replaced by R-NEA.

[0046] When the femtosecond laser irradiates the antiferromagnetic layer, the direction of the applied magnetic field is changed, only the right-handed spin can pass through the chiral molecular perovskite layer, thus radiating a terahertz signal, as shown in Fig. Figure 5 When the chirality of the spin is changed, the left-handed spin cannot pass through the chiral molecular perovskite layer structure, thus cannot radiate a terahertz signal, as shown in Fig. Figure 5

[0047] It should be noted that in other embodiments, when the experimental process meets the following conditions, the purpose of the present application can be achieved:

[0048] For the material of the antiferromagnetic layer, insulator materials such as nickel oxide and chromium oxide can also be selected;

[0049] For the material of the chiral perovskite layer, materials such as (R-NEA)2-PbSr4 and (S-NEA)2-PbSr4 with chirality can also be selected;

[0050] For the heavy metal layer, other heavy metal materials such as W and Ta can be selected.

[0051] For the thickness of the chiral molecular perovskite, the thickness can be adjusted to be in the range of 50-200 nm by adjusting the process parameters such as the amount of raw materials in the preparation method, and the specific thickness can be designed to be 50 nm, 100 nm, 150 nm or 200 nm, etc., which is easy to achieve and can achieve the purpose of the present application.

[0052] For the thickness of the antiferromagnetic layer, it can be selected to be 10-20 nm, and specifically can be 10 nm, 13 nm, 16 nm or 20 nm, etc.

[0053] For the above process parameters, those skilled in the art can appropriately select them according to actual needs, and all of them can achieve the purpose of the present application.

[0054] Obviously, the described embodiments are part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present application.​

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 regulate 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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