Voltage regulated ferrimagnetic terahertz radiation source

Abstract

This invention discloses a voltage-controlled subferromagnetic terahertz radiation source, comprising a sequentially deposited heavy metal layer, a subferromagnetic alloy layer, a heavy metal alloy layer, an oxide layer, and a conductive layer. The oxide layer is a gadolinium oxide layer, the subferromagnetic alloy layer is an iron-gadolinium 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. This invention utilizes the hygroscopic property of the gadolinium oxide layer to achieve the ionization of water molecules into hydrogen ions, and achieves phase control of the terahertz wave generated by the subferromagnetic terahertz source by voltage-controlled hydrogen atom injection. The structure is simple, low-cost, and the controlled state is stable.

Description

Technical Field

[0001] This invention relates to the field of terahertz generation technology, specifically a voltage-controlled subferromagnetic terahertz radiation source. Background Technology

[0002] Terahertz (THz) waves (0.1–10 THz) lie between the microwave and infrared bands of the electromagnetic spectrum. Due to their unique characteristics such as broadband, penetrability, and fingerprint-like properties, they can deeply perceive the microscopic structure of matter, providing novel detection methods for scientific research and technological innovation. Manipulating the phase of terahertz waves is crucial for promoting the development and application of related technologies. When terahertz waves of different phases interact with materials, they produce different reflection, absorption, and scattering characteristics. For example, selectively exciting specific biomolecules can enable rapid detection and analysis of these molecules. In terahertz imaging technology, the specific rotational and vibrational energy level transitions of molecules in different materials within the terahertz band result in unique phase and absorption spectrum characteristics, thereby enhancing image contrast. Combining terahertz phase array technology enables secure monitoring at a certain distance. The directional beam formed by the phased array antenna can scan a specific area, and a three-dimensional image of the inspected object can be constructed by analyzing the phase and intensity information of the echo.

[0003] While existing technologies have made significant efforts in terahertz wave phase modulation, they primarily focus on modulation during transmission, and remain limited in terms of response speed and cost. Current polarization control techniques struggle to integrate with other terahertz functional devices, hindering system integration and miniaturization. Furthermore, due to the insufficient depth and refinement of theoretical research on terahertz wave phase modulation, related technologies still possess considerable limitations.

[0004] (1) Metamaterial phase modulation achieves precise control of the terahertz wave phase by designing artificial electromagnetic structures at the subwavelength scale. Typical structures include metal resonant rings and silicon pillar arrays, and the phase response is modulated by changing the geometric parameters of the structure or the material properties. However, the resonant characteristics of metamaterials mean that the phase response is usually only effective in a narrow band, which is difficult to meet the broadband requirements of terahertz systems. Ohmic losses in metal structures and absorption by dielectric materials can lead to significant attenuation of terahertz wave energy, affecting the signal-to-noise ratio of the system. Furthermore, metamaterials have extremely high requirements for processing precision.

[0005] (2) The terahertz phase can be adjusted through waveguides. The modulation signal is input through the feed metal block of the feed metal structure. When a forward voltage is applied to the anode of the varactor diode inside, it will be in the conducting state and in the off state when a reverse voltage is applied. At this time, by changing the magnitude of the reverse voltage, the capacitance value of the varactor diode can be controlled, thereby achieving the purpose of dynamic control of the terahertz wave phase modulation. However, the metal waveguide and the inserted microstructure have large losses, which affect the system's transmission efficiency. The carrier lifetime of the varactor diode limits the modulation speed, making it difficult to meet the requirements of high-speed modulation. In addition, the microstructure inserted in the waveguide has extremely high requirements for photolithography or electron beam etching processes, which are expensive and have low yield.

[0006] (3) Some liquid crystal materials exhibit significant birefringence at terahertz frequencies. By applying an external electric field, the orientation of liquid crystal molecules can be altered, allowing the liquid crystal material to dynamically control the terahertz phase through voltage. However, the response speed of liquid crystal materials in the terahertz band is relatively slow, and the stability of liquid crystal materials is poor, making them susceptible to external environmental factors. For example, temperature changes may cause changes in the orientation of liquid crystal molecules, making the phase modulation results difficult to predict. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a voltage-controlled subferromagnetic terahertz radiation source that utilizes the hygroscopicity of the gadolinium oxide layer to achieve the ionization of water molecules into hydrogen ions, and achieves the control of the phase of the terahertz wave generated by the subferromagnetic terahertz source by voltage-controlled hydrogen atom injection. The structure is simple, the cost is low, and the control state is stable.

[0008] The technical solution of this invention is as follows:

[0009] 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 deposited sequentially. The oxide layer is a gadolinium oxide layer, the ferrimagnetic alloy layer is an iron-gadolinium 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.

[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 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.

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

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

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

[0015] The heavy metal alloy layer is a platinum-palladium alloy layer with a thickness of 5.5–6.5 nm.

[0016] 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.

[0017] 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.

[0018] Advantages of this invention:

[0019] (1) The voltage-controlled subferromagnetic terahertz radiation source disclosed in this invention utilizes the hygroscopicity of the gadolinium oxide layer, generates hydrogen atoms by voltage electrolysis of the water absorbed in the gadolinium oxide layer, and injects the hydrogen atoms into the subferromagnetic alloy layer, i.e., the iron-gadolinium alloy layer, by adjusting the voltage, thereby achieving the control of the terahertz wave phase without introducing additional dielectric loss, effectively improving the system signal-to-noise ratio.

[0020] (2) The layered deposition structure of the present invention is simple and has low manufacturing cost. It does not require the design of complex micro-nano structures or micro-processing techniques such as photolithography and etching, which greatly reduces the complexity and difficulty of manufacturing.

[0021] (3) By applying positive and negative voltages to the present invention, the terahertz phase can be precisely controlled at 180°, the control state is stable, and the switching state will not be unpredictable due to external interference.

[0022] (4) The present invention is small in size and has a thickness on the nanometer scale, making it easier to integrate into complex systems. Moreover, its radiation bandwidth reaches 6THz, which exceeds that of commercial ZnTe crystals, and its application range is wider. 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. 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.

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 1.5~2.5nm.

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

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

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.

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