Voltage regulation and control ferromagnetic terahertz radiation source

Abstract

The invention discloses a voltage regulation and control ferromagnetic terahertz radiation source which comprises a heavy metal layer, a ferromagnetic alloy layer, a heavy metal alloy layer, an oxide layer and a conductive layer which are sequentially deposited, the oxide layer is a gadolinium oxide layer, the ferromagnetic alloy layer is a ferro-gadolinium alloy layer, the conductive layer serves as an upper electrode to be connected with a voltage source, and the heavy metal layer serves as a lower electrode to be grounded. The purpose of ionizing water molecules into hydrogen ions is achieved through the hygroscopicity of the gadolinium oxide layer, regulation and control over the terahertz wave phase generated by the ferromagnetic terahertz source are achieved in the mode that hydrogen atom injection is regulated and controlled through voltage, the structure is simple, cost is low, and the regulation and control state is stable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz generation, and particularly relates to a voltage-regulated ferrimagnetic terahertz radiation source. BACKGROUND

[0002] Terahertz (THz) waves (0.1-10 THz) are located between microwaves and infrared in the electromagnetic spectrum. Due to its unique characteristics such as wideband, penetration and fingerprint, it can deeply perceive the microstructure of matter and provide a new detection method for scientific research and technological innovation. Manipulating the phase of terahertz waves is crucial to promoting the development and application of terahertz wave-related technologies. When terahertz waves with different phases interact with materials, different reflection, absorption and scattering characteristics are produced, such as selectively exciting specific biomolecules, thereby achieving rapid detection and analysis of biomolecules. In terahertz imaging technology, due to the specific rotational and vibrational energy level transitions of different material molecules in the terahertz frequency band, the phase and absorption spectrum have unique characteristics, thereby enhancing the contrast of the image. Combined with the terahertz phase array technology, security monitoring at a certain distance can be achieved. The directional beam formed by the phased array antenna can scan a specific area, and a three-dimensional image of the detected object can be constructed by analyzing the phase and intensity information of the echo.

[0003] Although the prior art has made many efforts around the phase control of terahertz waves, it mainly involves the modulation of the transmission process, and there are still limitations in response speed, cost, etc. The current polarization control technology is difficult to integrate with other terahertz functional devices, limiting the development of system integration and miniaturization. And because the theoretical research on the phase control of terahertz waves is not deep and perfect enough, the related technology still has great limitations:

[0004] (1) The phase control of metamaterials is achieved by designing artificial electromagnetic structures at subwavelength scales to precisely control the phase of terahertz waves. Typical structures include metal resonant rings, silicon column arrays, etc. The phase response is adjusted by changing the geometric parameters or material properties of the structure. However, the resonant characteristics of metamaterials result in a phase response that is usually only effective in a narrow band, making it difficult to meet the wideband requirements of terahertz systems. Ohmic loss of metal structures and absorption of dielectric materials will cause significant attenuation of terahertz wave energy, affecting the signal-to-noise ratio of the system, and metamaterials have very high processing precision requirements.

[0005] (2), the phase of terahertz can be realized by waveguide, the modulation signal is input through the feeding metal block of the feeding metal structure, when the anode of the internal varactor diode is added with forward voltage, it will be in the on state, and when it is added with reverse voltage, it will be in the off state, at this time, by changing the size of the reverse voltage, the capacitance value of the varactor diode can be controlled, and the purpose of dynamically controlling the phase modulation of terahertz waves is achieved. However, the loss of the metal waveguide and the inserted microstructure is large, which affects the emission efficiency of the system, and the carrier lifetime of the varactor diode limits the modulation speed, which is difficult to meet the requirement of high-speed modulation. In addition, the microstructure inserted in the waveguide has very high requirements for photolithography or electron beam etching process, and the cost is high and the yield is low.

[0006] (3), some liquid crystal materials have large birefringence effect at terahertz frequency, by applying external electric field, the orientation of liquid crystal molecules can be changed, so that the liquid crystal material can dynamically control the phase of terahertz through voltage. However, the response speed of the liquid crystal material in the terahertz frequency band is relatively slow, and the stability of the liquid crystal material is poor, which is easily affected by external environmental factors, such as temperature change, which may change the orientation of the liquid crystal molecules, making the phase control result difficult to predict. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a voltage controlled ferrimagnetic terahertz radiation source, which utilizes the hygroscopicity of the gadolinium oxide layer to realize the ionization of water molecules into hydrogen ions, and realizes the control of the phase of the terahertz wave generated by the ferrimagnetic terahertz source through the voltage control of hydrogen atom injection, which has simple structure, low cost and stable control state.

[0008] The technical scheme of the present application is:

[0009] A voltage controlled ferrimagnetic terahertz radiation source, comprising a heavy metal layer, a ferrimagnetic alloy layer, a heavy metal alloy layer, an oxide layer and a conductive layer deposited in sequence, the oxide layer is a gadolinium oxide layer, the ferrimagnetic alloy layer is an iron gadolinium alloy layer, the conductive layer is connected to a voltage source as a upper electrode, and the heavy metal layer is grounded as a lower electrode.

[0010] The conductive layer is an indium tin oxide layer.

[0011] The heavy metal layer, the ferrimagnetic alloy layer, the heavy metal alloy layer, the oxide layer and the conductive layer are deposited on a transparent substrate in sequence, the transparent substrate is selected from a transparent silicon oxide film layer, a transparent magnesium oxide film layer or a transparent aluminum oxide film layer.

[0012] The heavy metal layer is a tungsten metal layer with a thickness of 1.5-2.5nm.

[0013] The thickness of the iron gadolinium alloy layer is 1.5-2.5nm.

[0014] The thickness of the gadolinium oxide layer is 28-32 nm.

[0015] The heavy metal alloy layer is a platinum-palladium alloy layer, and the thickness is 5.5-6.5 nm.

[0016] The heavy metal layer, the ferrimagnetic alloy layer and the heavy metal alloy layer are prepared by a magnetron sputtering method, and the oxide layer and the conductive layer are prepared by an electron beam evaporation method.

[0017] When the voltage source provides a voltage, the water absorbed in the gadolinium oxide layer is electrolyzed in the vicinity of the interface between the gadolinium oxide layer and the conductive layer to form hydrogen ions; when the voltage source selects a positive voltage, under the action of the positive voltage, the hydrogen ions migrate to the iron-gadolinium alloy layer, first combine with the electrons of the heavy metal alloy layer to form neutral hydrogen atoms, and then the neutral hydrogen atoms are injected into the iron-gadolinium alloy layer to fill the gap between the transition metal iron and the rare earth element gadolinium in the iron-gadolinium alloy layer; since the rare earth element gadolinium has a strong affinity for hydrogen, the rare earth element gadolinium combines with the neutral hydrogen atoms, which causes the magnetic moment of the rare earth element gadolinium to decrease, so that the iron-gadolinium alloy layer changes from being dominated by the magnetic moment of gadolinium to being dominated by the magnetic moment of iron; under the condition of applying an external magnetic field, the total magnetic moment direction of the iron-gadolinium alloy layer does not change, but since the magnetic moment of the iron-gadolinium alloy layer has changed to be dominated by the magnetic moment of iron, the direction of the magnetic moment of iron is flipped to the same direction as the external magnetic field; when the voltage source changes from a positive voltage to a negative voltage, the neutral hydrogen atoms injected into the iron-gadolinium alloy layer are extracted back to the gadolinium oxide layer, and the magnetic moment of the iron-gadolinium alloy layer switches back to the initial state, i.e., the magnetic moment of the iron-gadolinium alloy layer switches back to being dominated by the magnetic moment of gadolinium.

[0018] Advantages of the present application:

[0019] (1) The voltage-controlled ferrimagnetic terahertz radiation source disclosed in the present application utilizes the hygroscopicity of the gadolinium oxide layer, electrolyzes the water absorbed in the gadolinium oxide layer by voltage to generate hydrogen atoms, and adjusts the injection of the hydrogen atoms into the ferrimagnetic alloy layer, i.e., the iron-gadolinium alloy layer, by voltage, so as to realize the phase control of terahertz waves, without introducing additional dielectric loss, and effectively improving the signal-to-noise ratio of the system.

[0020] (2) The layered deposition structure of the present application is simple and has low manufacturing cost, without the need for designing complex micro-nano structures, without the need for micro-processing technologies such as photolithography and etching, and greatly reducing the complexity and difficulty of manufacturing.

[0021] (3) The 180° phase control of terahertz waves can be accurately realized by applying positive and negative voltages to the present application, and the control state is stable, and will not cause unpredictable switching state due to external interference.

[0022] (4) The present application has a small volume and a nanometer-level thickness, is easier to integrate into a complex system, and has a radiation bandwidth of 6 THz, which exceeds that of a commercial ZnTe crystal, and has a wider application range. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Figure 2 This is a schematic diagram illustrating the principle of using positive voltage to control the terahertz phase in this invention.

[0025] Figure 3 This is a schematic diagram illustrating the principle of using negative voltage to control the terahertz phase in this invention.

[0026] Figure 4 This is a linear graph showing the effect of the proportion of rare earth element gadolinium in the iron-gadolinium alloy layer of this invention on the generated terahertz signal.

[0027] Figure 5 This is a comparison of the spectra of the voltage-controlled subferromagnetic terahertz radiation source of this invention and the terahertz generated by a commercially available ZnTe crystal.

[0028] Figure reference numerals: 1-Tungsten metal layer, 2-Gadolinium iron alloy layer, 3-Platinum palladium alloy layer, 4-Gadolinium oxide layer, 5-Indium tin oxide layer, 6-Voltage source, 7-Positive voltage, 8-Negative voltage, 9-Femtosecond laser, 10-Terahertz, 11-Water molecule, 12-Oxygen ion, 13-Hydrogen ion, 14-Ferromagnetic moment, 15-Gadolinium magnetic moment, 16-External magnetic field. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] See Figure 1 A voltage-controlled ferrimagnetic terahertz radiation source includes a heavy metal layer, a ferrimagnetic alloy layer, a heavy metal alloy layer, an oxide layer, and a conductive layer sequentially deposited on a transparent substrate. The transparent substrate is selected from transparent silicon oxide thin films, transparent magnesium oxide thin films, or transparent aluminum oxide thin films. The heavy metal layer is a tungsten (W) metal layer 1 with a thickness of 2 nm. The ferrimagnetic alloy layer is a gadolinium iron alloy layer (FeGd) 2, and the heavy metal alloy layer is a platinum palladium alloy layer (Pt). 30 Pd 70 3. The thickness is 6nm, and the oxide layer is a gadolinium oxide layer (GdO). x 4. The conductive layer is an indium tin oxide (ITO) layer 5. The indium tin oxide layer 5 serves as the upper electrode connected to the voltage source 6, and the tungsten metal layer 1 serves as the lower electrode grounded.

[0031] Among them, the tungsten metal layer 1, the iron-gadolinium alloy layer 2 and the platinum-palladium alloy layer 3 were all prepared by magnetron sputtering, while the gadolinium oxide layer 4 and the indium-tin oxide layer 5 were prepared by electron beam evaporation.

[0032] See Figure 2 and Figure 3 When voltage source 6 provides voltage, water molecules 11 absorbed in gadolinium oxide layer 4 are electrolyzed at the interface between gadolinium oxide layer 4 and indium tin oxide layer 5, forming oxygen ions 12 and hydrogen ions 13. When voltage source 6 uses positive voltage 7, under the action of positive voltage 7, hydrogen ions 13 migrate to iron-gadolinium alloy layer 2. After passing through platinum-palladium alloy layer 3, they combine with electrons in platinum-palladium alloy layer 3 to form neutral hydrogen atoms. At the same time, platinum-palladium alloy layer 3 blocks oxygen ions 12 from migrating to iron-gadolinium alloy layer 2, preventing iron-gadolinium alloy layer 2 from being oxidized. Then, neutral hydrogen atoms are injected into iron-gadolinium alloy layer 2, filling the gaps between the transition metal iron (Fe) and the rare earth element gadolinium (Gd) in iron-gadolinium alloy layer 2. Gd has a strong affinity for hydrogen. Gd combines with neutral hydrogen atoms, causing the gadolinium magnetic moment 15 to decrease. This causes the gadolinium-iron alloy layer 2 to change from being dominated by gadolinium magnetic moment 15 to being dominated by ferromagnetic moment 14. Under the condition of applying an external magnetic field 16, the direction of the magnetic moment of the gadolinium-iron alloy layer 2 remains unchanged. However, since the magnetic moment of the gadolinium-iron alloy layer 2 has changed to be dominated by ferromagnetic moment 14, the direction of ferromagnetic moment 14 will be flipped to the same direction as the external magnetic field. When the voltage source 6 changes from a positive voltage 7 to a negative voltage 8, the neutral hydrogen atoms injected into the gadolinium-iron alloy layer 2 are extracted back to the gadolinium oxide layer 4, and the magnetic moment of the gadolinium-iron alloy layer 2 switches back to the initial state, that is, the magnetic moment of the gadolinium-iron alloy layer 2 switches back to being dominated by gadolinium magnetic moment 15.

[0033] The working principle of the voltage-controlled subferromagnetic terahertz radiation source is mainly based on the ultrafast spin dynamics process in the subferromagnetic / nonmagnetic heterojunction. When the pump pulse emitted by the femtosecond laser 9 excites the iron-gadolinium alloy layer 2, the spin polarization of Fe mainly comes from the 3d shell, and electrons are directly excited by the 1.55 eV 800 nm pump pulse. However, the spin polarization of Gd mainly comes from the half-filled 4f shell, and it cannot be directly excited by the 1.55 eV pump pulse. Therefore, the spin current is mainly generated from Fe. The polarization direction of the spin current is mainly controlled by the direction of the Fe magnetic moment 14. The reversal of the Fe magnetic moment will cause the polarization direction of the spin current to reverse. After generating a spin current in the gadolinium alloy layer 2, it rapidly injects into the adjacent non-magnetic layers—tungsten metal layer 1 and platinum-palladium alloy layer 3. Through the spin-orbit interaction of the non-magnetic layers, the spin current is efficiently converted into a transverse charge current. This process mainly relies on the inverse spin Hall effect. Since tungsten metal layer 1 and platinum-palladium alloy layer 3 have opposite spin Hall angles, when the spin current injected from the gadolinium alloy layer into the tungsten metal layer and the spin current injected from the gadolinium alloy layer into the platinum-palladium alloy layer are injected into tungsten metal layer 1 and platinum-palladium alloy layer 3 in opposite directions, charge accumulation of the same polarity is generated in tungsten metal layer 1 and platinum-palladium alloy layer 3, producing terahertz radiation of the same polarity, effectively improving the terahertz emission efficiency. Compared with traditional terahertz generation methods, this spin terahertz source has significant advantages such as phase tunability, broad spectrum (typically covering the 0.1-30 THz range), lower cost, and compatibility with semiconductor processes, providing a new integrated solution for terahertz spectroscopy and imaging applications.

[0034] See Figure 1 When no voltage is applied from the voltage source 6, the gadolinium magnetic moment 15 of the gadolinium alloy layer 2 is dominant, the ferromagnetic moment 14 of the gadolinium alloy layer 2 is in the initial state, and the terahertz 10 maintains the initial phase state.

[0035] See Figure 2 Since the polarization direction of the spin current is controlled by the ferromagnetic moment 14, when the voltage source is selected as positive voltage 7, the direction of the ferromagnetic moment 14 of the iron-gadolinium alloy layer 2 changes, and the polarization direction of the spin current will also reverse, resulting in the reversal of the polarity of the charge flow generated after being injected into the tungsten metal layer 1 and the platinum-palladium alloy layer 3, which ultimately causes the phase of the generated terahertz 10 to change by 180°.

[0036] See Figure 3 When the voltage source changes from positive voltage 7 to negative voltage 8, hydrogen atoms in the iron-gadolinium alloy layer 2 will be extracted, and the gadolinium magnetic moment 15 of the iron-gadolinium alloy layer 2 will once again dominate. This will cause the direction of the ferromagnetic moment 14 to flip back to the initial state, causing the terahertz 10 to reverse back to the initial phase state.

[0037] See Figure 4When the Gd content in the iron-gadolinium alloy layer 2 exceeds 30%, the terahertz phase will reverse by 180°, indicating that the gadolinium magnetic moment 15 has become dominant at this time.

[0038] See Figure 5 Compared with commercially available ZnTe crystals, the voltage-controlled subferromagnetic terahertz radiation source (Our) of this invention has a wider spectral range, exceeding 6 THz, indicating that the subferromagnetic terahertz radiation source of this invention has a wider range of applications.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A voltage-controlled subferromagnetic terahertz radiation source, characterized in that: It includes a heavy metal layer, a ferrimagnetic alloy layer, a heavy metal alloy layer, an oxide layer and a conductive layer deposited sequentially. The oxide layer is a gadolinium oxide layer, the ferrimagnetic alloy layer is a gadolinium iron alloy layer, the conductive layer serves as the upper electrode connected to the voltage source, and the heavy metal layer serves as the lower electrode grounded.

2. The voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The conductive layer is an indium tin oxide layer.

3. The voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The heavy metal layer, the ferrimagnetic alloy layer, the heavy metal alloy layer, the oxide layer and the conductive layer are sequentially deposited on a transparent substrate, which is selected from transparent silicon oxide thin film layer, transparent magnesium oxide thin film layer or transparent aluminum oxide thin film layer.

4. The voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The heavy metal layer is a tungsten metal layer with a thickness of 1.5–2.5 nm.

5. A voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The thickness of the iron-gadolinium alloy layer is 1.5 to 2.5 nm.

6. A voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The thickness of the gadolinium oxide layer is 28–32 nm.

7. A voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The heavy metal alloy layer is a platinum-palladium alloy layer with a thickness of 5.5–6.5 nm.

8. A voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: The heavy metal layer, the ferrimagnetic alloy layer, and the heavy metal alloy layer were all prepared by magnetron sputtering; the oxide layer and the conductive layer were all prepared by electron beam evaporation.

9. A voltage-controlled subferromagnetic terahertz radiation source according to claim 1, characterized in that: When the voltage source provides voltage, the water absorbed in the gadolinium oxide layer is electrolyzed at the interface between the adjacent gadolinium oxide layer and the conductive layer, forming hydrogen ions. When a positive voltage is selected as the voltage source, under the action of the positive voltage, the hydrogen ions migrate to the iron-gadolinium alloy layer. After passing through the heavy metal alloy layer, they combine with electrons in the heavy metal alloy layer to form neutral hydrogen atoms. Then, the neutral hydrogen atoms are injected into the iron-gadolinium alloy layer, filling the gaps between the transition metal iron and the rare earth element gadolinium in the iron-gadolinium alloy layer. Because the rare earth element gadolinium has a strong affinity for hydrogen, the rare earth element gadolinium combines with the neutral hydrogen atoms. The combination of these elements causes a decrease in the magnetic moment of the rare earth element gadolinium, resulting in a shift from gadolinium-dominated magnetic moment to ferromagnetic-dominated magnetic moment in the gadolinium alloy layer. Under the condition of an applied external magnetic field, the direction of the total magnetic moment of the gadolinium alloy layer remains unchanged, but since the magnetic moment of the gadolinium alloy layer has become ferromagnetic-dominated, the direction of the ferromagnetic moment will flip to the same direction as the external magnetic field. When the voltage source changes from a positive voltage to a negative voltage, the neutral hydrogen atoms injected into the gadolinium alloy layer are extracted back into the gadolinium oxide layer, and the magnetic moment of the gadolinium alloy layer switches back to its initial state, that is, the magnetic moment of the gadolinium alloy layer switches back to gadolinium-dominated magnetic moment.

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