Fe (Se, Te) superconducting thin film and annealing method thereof

Abstract

The invention discloses a Fe (Se, Te) superconducting thin film and an annealing method thereof. The annealing method comprises the following steps that under the continuous vacuumizing condition, the Fe (Se, Te) superconducting thin film is subjected to annealing treatment, and the annealing temperature is lower than 150 DEG C. According to the method, the c-axis lattice constant of the Fe (Se, Te) superconducting thin film is reduced through low-temperature annealing treatment in vacuum, the crystallinity is improved, three elements of Fe, Se and Te are distributed more uniformly, and the proportion of a superconducting phase is increased; meanwhile, the superconducting transition temperature Tc and the critical current density Jc under the self field and the magnetic field are improved. The annealing method is simple, high in repeatability, free of pollution and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature superconducting materials, and in particular relates to a Fe(Se, Te) superconducting film and an annealing method thereof. Background Art

[0002] Since 2008, the Hosono research group discovered LaFeAsO 1-x F x is the superconducting critical transition temperature (T c ) as a superconductor at 26K, another high-temperature superconductor, iron-based superconductor, triggered a research boom besides copper oxide. Subsequently, Wu Maokun's research group reported the simplest iron-based superconductor, FeSe, with a T c is 8K.

[0003] FeSe superconductor is an inverse PbO structure, which is composed of FeSe4 tetrahedrons stacked along the c-axis. The inverse PbO structure means that Se atoms occupy the positions of Pb atoms and Fe atoms occupy the positions of O atoms in each unit layer. In the FeSe layer, the Fe atom is at the center of the Se atom tetrahedron. The Fe atoms and Se atoms are bound to each other through covalent bonds, and there is a weak van der Waals interaction between the layers. The superconducting transition temperature of FeSe is affected by the stoichiometric ratio of the elements and the applied pressure, among which the pressure has a great influence on T c The effect of is the largest among all iron-based superconductors, and increases sharply to 37K under a high pressure of 8.9GPa. Doping with chalcogen elements instead of Se can inhibit structural phase transition or magnetic phase transition, and also make T c Based on a large number of studies on FeSe bulk materials, two-dimensional superconducting FeSe thin films are expected to have better superconducting properties. After growing buffer layers such as CeO2, CaF2, and SrTiO3 on alloy substrates, pulsed laser deposition (PLD) is used to epitaxially grow Fe(Se,Te) thin films. Due to the different thermal expansion coefficients between the buffer layer and the Fe(Se,Te) layer, Fe(Se,Te) undergoes compressive strain during cooling, thus having a higher T c and critical current density (J c ).

[0004] Some superconductors change from weak superconductivity or filamentary superconductivity to bulk superconductivity after annealing in vacuum, and some physical quantities also undergo significant changes. For example, Seiki Komiya found that after annealing Fe(Se,Te) single crystals in vacuum, the flowing vacuum of 1Pa showed a larger superconducting volume fraction than before annealing and in sealed vacuum, and the normal state transmission characteristics were different from the other two semiconductor states (resistance increased with decreasing temperature) in the metallic state (resistance decreased with decreasing temperature), and strongly magnetic black Fe3O4 was formed on the surface after annealing. For example, Takashi Noji also annealed FeSe 1-xTe x After single crystals were annealed in vacuum, it was found that Fe(Se,Te) with different x contents all showed a larger superconducting volume fraction than before annealing, and the magnetic phase transition was suppressed faster after annealing, that is, the superconducting region in the phase diagram was expanded. For example, Sun et al. annealed in vacuum or oxygen atmosphere to remove excess Fe atoms in FST single crystal bulk, but the results showed that vacuum annealing had no effect on removing excess Fe, while annealing in oxygen removed excess Fe and improved the superconducting performance of the sample.

[0005] During the application of superconductors, the temperature, magnetic field, and current must be below the critical temperature, critical magnetic field, and critical current, otherwise they will quench. c2 High, small anisotropy, critical current density (J c ) has a high tolerance to the critical angle of grain boundaries and is particularly suitable for strong magnetic field applications. Fe(Se,Te) uses liquid helium to cool down to a superconducting state, which is much better than T c The improvement of J under self-field and magnetic field c The improvement has more application value. At present, the performance improvement of Fe(Se,Te) superconducting films is generally achieved by process improvement or ion irradiation. However, process improvement is limited, ion irradiation has high equipment requirements and high price, and is not suitable for long-band applications. Although there are reports of FST films being annealed in oxygen pressure or vacuum, FST films have a special two-dimensional layered structure, which makes FST films extremely susceptible to structural damage, sulfide volatilization and oxygen doping during annealing. For example, Li et al. found that low-temperature oxygen annealing can improve the J of FST films. c , but it reduces the T c ; "Buffer layer effect of Fe(Se,Te) superconducting film and its preparation by ion exchange method" discloses annealing FST film in different oxygen pressures and vacuum. The results show that no matter annealing in oxygen atmosphere or vacuum atmosphere, the surface structure of FST film will be destroyed and the superconducting performance will disappear completely. Moreover, with the increase of oxygen pressure, the room temperature resistance of FST film increases continuously. Even if the annealing time or temperature is changed, the superconducting destruction effect on FST film is still observed. CN114318242B discloses a Fe(Se,Te) superconducting thin and thick film and its preparation method and application. The Fe(Se,Te) superconducting thick film obtained by multi-channel pulsed laser deposition method has a critical current density of only 2.3MA / cm at 4.2K and self-field. 2 The critical current density at 4.2K and 10T is only 0.48MA / cm 2 .

[0006] Therefore, a method is needed that will not cause structural damage to the Fe(Se,Te) superconducting film, is easy to operate, and can increase the critical current density J. cand superconducting critical transition temperature T c The annealing method is imminent. Summary of the invention

[0007] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a Fe(Se, Te) superconducting film and an annealing method thereof, thereby solving the problems in the prior art.

[0008] To achieve the above objectives and other related objectives, the present invention is achieved through the following technical solutions.

[0009] A first aspect of the present invention provides a method for annealing a Fe(Se,Te) superconducting film, comprising the following steps:

[0010] Under continuous vacuum conditions, the Fe(Se,Te) superconducting film is annealed at a temperature lower than 150°C.

[0011] The applicant has also annealed Fe(Se,Te) superconducting film in air and found that the superconducting performance of Fe(Se,Te) superconducting film did not increase but decreased. In this application, the annealing temperature of the superconducting film should not be too high. If the annealing temperature is too high (over 150°C), J c The superconducting properties of the Fe(Se,Te) film after annealing are greatly reduced when the temperature exceeds 250°C.

[0012] In some embodiments, the annealing temperature is not less than 40°C, and may be 40-90°C, 80-130°C, or 120-149°C; preferably, it is 50-125°C, and specifically may be 50°C, 75°C, 100°C, and 125°C. The annealing temperature in this application should not be too low. The applicant used different temperatures for annealing and found that as the annealing temperature increases, the J of the superconducting film increases. c Gradually increase.

[0013] In certain embodiments, the heating rate of the annealing treatment is 2-10°C / min, 2-5°C / min, 4-8°C / min, 6-10°C / min, or 2.5°C / min.

[0014] In some embodiments, the annealing time is 0.5 to 16 hours, or 0.5 to 8 hours, or 6 to 10 hours, or 7 to 16 hours, or 0.5 hours, 4 hours, 8 hours, 2 hours, and 1 hour; preferably, 1 to 2 hours. The applicant has also tried to use annealing for more than 16 hours, and found that the c-axis lattice constant decreased, a large amount of Te element was lost, and the superconducting performance decreased.

[0015] In some embodiments, the vacuum is continuously drawn to a pressure of 10 -4 ~-1Pa. In this application, the vacuum pressure cannot be too low or too high. When it is too low, the magnetic field J c Lower than before annealing.

[0016] In some embodiments, the thickness of the Fe(Se,Te) superconducting film is 100-220 nm, or 100-160 nm, or 140-180 nm, or 190-220 nm. In one embodiment, the thickness is 133 nm, 154 nm, or 151 nm.

[0017] In certain embodiments, the c-axis lattice constant of the Fe(Se,Te) superconducting film is ≥ Preferably, the upper limit is The c-axis lattice constant of the Fe(Se,Te) superconducting film in the present application cannot be too low. If it is too low, it means that the Te content in the film is small. Annealing will cause a large amount of Te element to volatilize, and the Fe element will be enriched to become interstitial Fe, and the superconductivity of the Fe(Se,Te) superconducting film will be suppressed.

[0018] In some embodiments, the length and width of the Fe(Se,Te) superconducting film is (5-15) cm×1 cm. In an embodiment, the length and width is 10 cm×1 cm. The Fe(Se,Te) superconducting film within this length-to-width ratio can ensure the consistency of annealing.

[0019] In certain embodiments, the Fe(Se, Te) superconducting thin film further includes a metal substrate and a buffer layer.

[0020] In some specific embodiments, the thickness of the metal substrate is 30-80 μm, and in one embodiment, 50 μm.

[0021] In some specific embodiments, the material of the metal substrate is selected from Hastelloy C276.

[0022] In some specific embodiments, the thickness of the buffer layer is 150-220 nm, and in one embodiment, 200 nm.

[0023] In some specific embodiments, the material of the buffer layer is selected from one or more of CeO2, LaMnO3, SrTiO3 and MgO, preferably CeO2 and MgO.

[0024] In some specific embodiments, the thickness of the Fe(Se,Te) superconducting layer is 100-220 nm.

[0025] In some specific embodiments, an oxide barrier layer is further provided between the metal substrate and the buffer.

[0026] Preferably, the oxide barrier layer has a thickness of 100-200 nm. In one embodiment, the thickness is 150 nm.

[0027] Preferably, the material of the oxide barrier layer is selected from one or both of Al2O3 and Y2O3.

[0028] In some specific embodiments, the structure includes, from bottom to top, a metal substrate, an oxide barrier layer, a buffer layer, and a Fe(Se, Te) superconducting film.

[0029] In some specific embodiments, the method for preparing the Fe(Se, Te) superconducting film is: using a pulsed laser deposition method to deposit a Fe(Se, Te) superconducting target material on a metal substrate provided with a buffer layer to obtain the Fe(Se, Te) superconducting film.

[0030] In certain more specific embodiments, the plasma plume obtained by pulsed laser sputtering of a Fe(Se,Te) superconducting target is deposited on a heated metal substrate to form a Fe(Se,Te) superconducting thin film.

[0031] Preferably, in the pulse laser deposition method, the deposition conditions are: the temperature of the metal substrate is 300-600°C, the walking speed of the metal substrate is 6-12 m / h, the distance between the metal substrate and the Fe(Se,Te) superconducting target is 4-5 cm, and the laser energy is 150-250 mJ. Preferably, it is 4.5 cm, and the laser energy is 250 mJ. Preferably, it is 300-580°C.

[0032] Preferably, the method comprises the following steps:

[0033] 1) placing a Fe(Se,Te) superconducting target and a metal substrate with a buffer layer in a multi-channel pulsed laser deposition system, evacuating the system, and then heating the system;

[0034] 2) A Fe(Se, Te) superconducting layer, namely the Fe(Se, Te) superconducting film, is deposited on a metal substrate provided with a buffer layer by a multi-channel pulsed laser deposition method.

[0035] In step 1), the vacuum degree is drawn to 4×10 7 Torr or less, and then heated to 300-600°C.

[0036] Step 2) is specifically as follows:

[0037] 2-1) Start the target material motion system and the excimer laser, adjust the laser energy and frequency, then turn on the laser light path switch to start the target material surface pre-sputtering process. After adjustment, the laser energy is 150-250mJ and the laser frequency is 40-100Hz.

[0038] 2-2) After the pre-sputtering is completed, the stepper motor switch of the multi-channel transmission device is started, and the walking speed of the metal substrate is adjusted to plate the Fe(Se,Te) seed layer. The walking speed of the metal substrate is adjusted to 6-12 m / h.

[0039] 2-3) After the Fe(Se,Te) seed layer is plated, turn off the stepper motor switch, stop the tape, and cool down, then adjust the laser energy and frequency. The temperature is 300-600°C, the laser energy remains unchanged, and the laser frequency is increased to 50-120Hz. Preferably, it is 300-500°C.

[0040] 2-4) Start the stepper motor switch of the multi-channel transmission device, and adjust the walking speed of the metal substrate to plate the Fe(Se,Te) superconducting layer. The walking speed of the metal substrate is adjusted to 6-12m / h.

[0041] 2-5) Adjust the walking speed of the metal substrate and plate the Fe(Se,Te) superconducting layer in the reverse direction. The walking speed of the metal substrate is adjusted to 6-12 m / h.

[0042] 2-6) Repeat steps 2-4) and 2-5) to deposit multiple Fe(Se,Te) superconducting layers.

[0043] 2-7) After the coating is completed, the stepper motor, the heater and the laser optical path switch are turned off, and after cooling, the Fe(Se,Te) superconducting film is obtained. The deposition method can be specifically carried out with reference to CN114318242B, and the seed layer and the multi-layer superconducting layer form a film.

[0044] The second aspect of the present invention protects the Fe(Se,Te) superconducting thin film obtained by the annealing method as described above.

[0045] In certain embodiments, the c-axis lattice constant of the Fe(Se,Te) superconducting film after annealing is reduced by at least 0.1% compared to that before annealing.

[0046] In some embodiments, compared with that before annealing, the critical transition temperature of the annealed Fe(Se,Te) superconducting film is increased by at least 7%, preferably not more than 20%, and specifically 7% to 15%.

[0047] In some embodiments, the critical current density J of the annealed Fe(Se,Te) superconducting film under self-field at 4.2K isc The increase is at least 20%. Preferably, it is not higher than 100%, and specifically, it can be 23.8-96.5%.

[0048] In some embodiments, compared with the non-annealed state, the critical current density J of the annealed Fe(Se,Te) superconducting film at 4.2K and 9T magnetic field is c The increase is at least 20%. Preferably, it is not higher than 100%, and specifically, it can be 20.9-129.5%.

[0049] A third aspect of the present invention protects the use of the Fe(Se,Te) superconducting film as described above in cables and superconducting magnets.

[0050] Superconducting magnets are one of the most important applications of superconducting materials. First, superconducting wires are prepared using superconducting materials, and the superconducting wires are wound into coils. When the coils are excited and energized, a magnetic field will be generated in the middle of the coils. Among them, solenoid superconducting magnets are the most commonly used form of superconducting magnets that generate strong magnetic fields. The central hole of the solenoid superconducting magnet can generate an axial magnetic field and is used in situations where high magnetic fields are required, such as superconducting accelerators, maglev trains, the International Thermonuclear Experimental Reactor ITER, nuclear magnetic resonance NMR, magnetic resonance imaging MRI, superconducting energy storage SMES and other projects.

[0051] In certain embodiments, the superconducting magnet is used in a nuclear fusion experimental reactor ITER to confine particles.

[0052] The technical solution of the present invention has the following beneficial effects:

[0053] 1) The present invention performs annealing treatment on the Fe(Se, Te) superconducting film in a vacuum, wherein the c-axis lattice constant of the Fe(Se, Te) superconducting film after vacuum annealing is reduced, the crystallinity is improved, the distribution of the three elements Fe, Se and Te is more uniform, and the proportion of the superconducting phase is increased.

[0054] 2) The annealing method of the present invention improves the T of Fe(Se,Te) superconducting film. c And J under self-field and magnetic field c ; T after annealing c onset Compared with the pre-annealing, the critical current density J of Fe(Se,Te) film under self-field at 4.2K is increased by 7% to 15%; compared with the non-annealing, the critical current density J of Fe(Se,Te) film under self-field at 4.2K is increased by 7% to 15% c The critical current density J at 4.2K and 9T magnetic field was increased by 23.8-96.5%. c When the annealing temperature is 125℃, the critical current density J of Fe(Se,Te) superconducting film at 4.2K and self-field after vacuum annealing is cFrom 10.52MA / cm 2 Increased to 20.67MA / cm 2 , increased by 96.5%; the critical current density J of Fe(Se,Te) superconducting film at 4.2K and 9T magnetic field c From 2.06MA / cm 2 Increased to 5.05MA / cm 2 , an increase of 129.5%.

[0055] 3) The annealing method of the present invention is simple, highly repeatable, pollution-free and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 Shown is a schematic structural diagram of a vacuum annealing device used in the annealing method of the present invention.

[0057] Figure 2 1 is the XRD diffraction pattern of the Fe(Se,Te) superconducting film before and after annealing in Examples 1-4 of the present invention.

[0058] Figure 3 RT diagrams of the Fe(Se,Te) superconducting films before and after annealing in Examples 1-4 of the present invention.

[0059] Figure 4 is the critical current density J of the Fe(Se,Te) superconducting film before and after annealing in Examples 1-4 of the present invention c Curve diagram of the change with magnetic field.

[0060] Figure 5 RT diagram of the Fe(Se,Te) superconducting film when the external magnetic field is 0-9T before annealing in Example 4 of the present invention, wherein the direction of the magnetic field is the out-of-plane direction parallel to the c-axis and the in-plane direction parallel to the ab-axis.

[0061] Figure 6 RT diagram of the Fe(Se,Te) superconducting film after annealing in Example 4 of the present invention when the external magnetic field is 0-9T, wherein the direction of the magnetic field is the out-of-plane direction parallel to the c-axis and the in-plane direction parallel to the ab-axis.

[0062] Figure 7 is the critical magnetic field H on the Fe(Se,Te) superconducting film before and after annealing in Example 4 of the present invention c2 and irreversible magnetic field H irr The temperature variation curve, where the magnetic field direction is out-of-plane parallel to the c-axis.

[0063] Figure 8 is the critical magnetic field H on the Fe(Se,Te) superconducting film before and after annealing in Example 4 of the present invention c2 and irreversible magnetic field Hirr Curve diagram of the change with temperature, where the magnetic field direction is in the plane parallel to the ab axis.

[0064] Fig. 9 1 is the XRD diffraction pattern of the Fe(Se,Te) superconducting film before and after annealing in Example 5 of the present invention.

[0065] Fig.10 RT diagrams of the Fe(Se,Te) superconducting film before and after annealing in Example 5 of the present invention.

[0066] Fig.11 1 and 2 are XRD diffraction patterns of the Fe(Se,Te) superconducting thin films before and after annealing in Examples 6-9 of the present invention.

[0067] Fig.12 RT diagrams of the Fe(Se,Te) superconducting films before and after annealing in Examples 6-9 of the present invention.

[0068] Fig.13 1 is the XRD diffraction pattern of the Fe(Se,Te) superconducting film before and after annealing in Comparative Example 1-2 of the present invention.

[0069] Fig.14 RT diagrams of the Fe(Se,Te) superconducting film before and after annealing in Comparative Example 1-2 of the present invention.

[0070] Fig.15 is the critical current density J of the Fe(Se,Te) superconducting film before and after annealing in Comparative Example 1-2 of the present invention c Curve diagram of the change with magnetic field.

[0071] Fig.16 1 is the XRD diffraction pattern of the Fe(Se,Te) superconducting film before and after annealing in Comparative Examples 3-7 of the present invention.

[0072] Fig.17 RT diagrams of the Fe(Se,Te) superconducting films before and after annealing in Comparative Examples 3-7 of the present invention.

[0073] Fig.18 is the critical current density J of the Fe(Se,Te) superconducting film before and after annealing in Comparative Examples 3-6 of the present invention c Curve diagram of the change with magnetic field. DETAILED DESCRIPTION

[0074] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0075] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing the specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0076] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, the two endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0077] X-ray diffraction (XRD) is a conventional and easy-to-use crystal structure analysis method. It is widely used in crystal phase identification, single crystal orientation analysis, crystal parameter determination, and crystallinity determination. It has the advantages of non-destructive samples, high measurement accuracy, rapid detection, and no pollution. The XRD instrument used in this experiment is the DX-2700BH model produced by Haoyuan Company. The X-ray uses a Cu target K α1 Characteristic X-rays, whose characteristic wavelength λ is

[0078] Superconducting transition temperature (T c ): The temperature at which the resistance of a superconducting material is zero is the superconducting transition temperature, including the superconducting onset transition temperature (T c onset ) and zero resistance superconducting transition temperature (T c 0 ). Superconducting onset transition temperature (T c onset ): The temperature at which the resistance is equal to 90% of the normal resistance. Zero resistance superconducting transition temperature (T c 0): The temperature corresponding to when the resistance just equals 0. The superconducting transition temperature is an important parameter as it determines the temperature range for using superconducting materials. A higher superconducting transition temperature means superconductivity can be achieved at a higher temperature. The four-probe method is used to measure the T of the superconducting thin film c , which greatly eliminates the error caused by contact resistance. The curve of resistance (actually the measured voltage) versus temperature is obtained to get the R-T curve.

[0079] Transition width: The temperature interval through which a superconducting material goes from the start of resistance decline to entering the superconducting state is called the transition width. The size of the transition width is closely related to the type and crystallization properties of the material. A decrease in the transition width indicates an increase in the proportion of the superconducting phase.

[0080] Perfect diamagnetism: It means that once a superconductor enters the superconducting state, it expels the magnetic field outside the superconductor, making the magnetic induction intensity inside the superconductor always equal to zero.

[0081] Critical current density (J c ): When a superconducting material is in the superconducting state, it can carry a certain current without generating resistance. However, when an external magnetic field is introduced or the current density in the superconducting material exceeds the critical value, the superconducting state will be broken and the material will return to the normal metal state. The critical current density refers to the maximum current density that a superconducting material can withstand under given temperature and magnetic field conditions. A higher critical current density means the material can carry a larger current without losing its superconducting properties. In this patent, a Physical Property Measurement System (PPMS) is used to measure the hysteresis loop under a magnetic field of 0 - 9 T at a temperature of 4.2 K for the superconducting thin film, and then the Bean critical state model is used to calculate the critical current density J of the superconducting thin film c . In this application, a PPMS system (Physical Property Measurement System, comprehensive physical property measurement system) is used to detect the critical current density (J c ).

[0082]

[0083] In the formula: △M is the width of the hysteresis loop, with the unit of emu; V is the volume of the superconducting thin film, with the unit of cm 3 ; a and b are the width and length of the superconducting thin film, where a < b, with the unit of cm.

[0084] Upper critical magnetic field (H c2 ): For the relatively more numerous type-II superconductors in the superconducting family, when the temperature is less than T c , when the magnetic field is less than the lower critical magnetic field H c1 , the superconducting state has perfect diamagnetism and zero resistivity; when the magnetic field is between H c1 and Hc2 When the magnetic field exceeds H, although the diamagnetism disappears completely, the zero resistance still exists, which is called the mixed state. c2 When the superconductor undergoes a phase transition, the complete anti-magnetism and zero resistance disappear, and the material transforms into a normal state. c2 It is a key parameter for the application of superconducting materials. c2 One method is to measure the transport of superconducting materials under different magnetic fields. Generally, the temperature and magnetic field corresponding to 90% or 50% of the normal state resistance are selected to plot the H c2 The present invention selects Fe(Se,Te) superconducting film ρ 20K When is the normal resistivity, plot the relationship between the magnetic field corresponding to 90%, 50%, and 10% and the temperature. Furthermore, the Ginzburg-Laudau theory can describe the upper critical magnetic field H c2 Changes with temperature:

[0085]

[0086] t is the reduced temperature t = T / T c ; Werthamer-Helfand-Hohenberg theory can predict H c2 (0):

[0087]

[0088] Irreversible magnetic field (H irr ): When a magnetic field is applied to a superconducting material, a magnetic flux exists inside the second-type superconductor in a mixed state, penetrating the superconducting material with a quantized magnetic flux vortex. The arrangement of the magnetic flux lines changes with external conditions such as temperature or magnetic field. When a current is passed through the superconducting material or an external force is applied, the magnetic field is in H irr Below, the defects or impurities inside the material have a pinning effect on the magnetic flux vortex and will not produce dissipation; the magnetic field is at H irr The above results in the displacement of the vortex, which generates dissipation and cannot transmit current without loss. irr One method is to measure the transport of superconducting materials under different magnetic fields, and select the temperature and magnetic field corresponding to 10% or 1% of the normal state resistance to plot the H irr Curves changing with temperature.

[0089] Coherence length (ξ): The spatial scale of the coherence of superconducting electron pairs (Cooper pairs), which is related to the spatial variation of the superconducting order parameter. The size of the core at the center of the magnetic flux vortex is equivalent to ξ, so ξ is an important microscopic parameter of superconducting materials. Simply put, it can be expressed as H at absolute zero. c2 (0) Estimate ξ0:

[0090]

[0091] In the present application, the following Examples 1-4 and Comparative Examples 1-7 are, from bottom to top, the following: a metal substrate, an oxide barrier layer, a buffer layer, and a Fe(Se, Te) superconducting film.

[0092] The material of the metal substrate is Hastelloy C276, which is an alloy composed of nickel, molybdenum, chromium, iron and tungsten. It has good mechanical properties, corrosion resistance and high temperature resistance. As the support of the entire base strip, the thickness of the metal substrate is about 50μm.

[0093] The materials of the buffer layer are MgO and CeO2. The MgO buffer layer prepared by ion beam assisted deposition (IBAD) has a thickness of about 10nm; the CeO2 buffer layer grown by pulsed laser deposition (PLD) has a C-axis orientation and a thickness of about 200nm. Providing a buffer layer on a metal substrate is a conventional technical means, and those skilled in the art can prepare it according to known techniques. In addition, it can also be purchased.

[0094] Among them, the Fe(Se,Te) superconducting film is grown by pulsed laser deposition (PLD) epitaxially, with a thickness of 100 to 220 nm. If the superconducting layer is too thick, micron-scale cracks will form in the film.

[0095] The material of the oxide barrier layer is a double-layer oxide of Al2O3 and Y2O3. The double-layer oxide barrier layer of Al2O3 and Y2O3 is about 150nm thick in order to prevent the diffusion and reaction of atoms of the substrate.

[0096] The preparation method of the Fe(Se,Te) superconducting film in the present application is: growing a Fe(Se,Te) superconducting layer on a metal substrate provided with a buffer layer and an oxide barrier layer, the superconducting layer is also the Fe(Se,Te) superconducting film. Specifically, the Fe(Se,Te) superconducting layer is grown epitaxially.

[0097] The steps of epitaxially growing the Fe(Se,Te) superconducting layer are as follows:

[0098] 1) Place the Fe(Se,Te) target in the target holder of the multi-channel pulsed laser deposition chamber, wind one end of the metal substrate coated with the buffer layer and the oxide barrier layer onto the reel, then pull the metal substrate to wind it around the rollers of the multi-channel transmission device for multiple times to form a three-channel base tape between the rollers, and finally wind the other end onto another reel. The metal substrate is installed, and the movement speed of the metal substrate is adjusted by the encoder and the stepper motor. Close the chamber door and evacuate the chamber to 3.3×10 -7 Torr, turn on the argon mass flow meter connected to the chamber and set the flow rate of the gas flow to 10 sccm;

[0099] 2) starting the substrate heating system in the deposition chamber to a heating temperature of 580° C.;

[0100] 3) Start the target motion system and the excimer laser, adjust the laser energy to 250mJ and the laser repetition frequency to 40Hz;

[0101] 4) After the heating temperature, laser energy, and laser repetition frequency are stabilized at the above set values, the laser optical path switch is turned on to pre-sputter the Fe(Se,Te) superconducting target for 5 minutes;

[0102] 5) starting the baseband motion system, setting the motion speed of the metal substrate to 6 m / h, so that the seed layer grows epitaxially on the metal substrate;

[0103] 6) After the seed layer growth is completed, turn off the stepper motor, stop the movement of the metal substrate, change the heating temperature to 480°C, change the laser repetition frequency to 80Hz, and the laser energy remains at 250mJ;

[0104] 7) After the above parameters are stable, turn on the stepper motor, move the tape in the opposite direction to start growing the superconducting layer, and repeat this process three times;

[0105] 8) Turn off the stepper motor, change the movement speed of the metal substrate to 12m / h, change the heating temperature to 400℃, the laser repetition frequency remains at 80Hz, the laser energy remains at 250mJ, and after the parameters are stable, turn on the stepper motor to move the tape once;

[0106] 9) Turn off the stepper motor, change the movement speed of the metal substrate to 6m / h, change the heating temperature to 430℃, the laser repetition frequency remains at 80Hz, the laser energy remains at 250mJ, and after the parameters are stable, turn on the stepper motor to move the tape three times;

[0107] 10) After the epitaxial growth of the superconducting layer is completed, the baseband motion system, heating system, and laser optical path are turned off. When the heating system is cooled down to below 100°C, the target motion system and argon flow meter are turned off, the vacuum system is turned off, and the chamber door is opened to take out the Fe(Se,Te) superconducting film.

[0108] The preparation of the Fe(Se,Te) superconducting film before annealing in the present application can also be specifically referred to Reference 1 (Shaojing Mou et al. Performance improvement of iron chalcogenide films grown at high laser repetition rates by pulsed laser deposition. Am Ceram Soc. 2023; 1-10)

[0109] The c-axis lattice constant of the Fe(Se,Te) superconducting film prepared using the above parameters is The thickness of the Fe(Se,Te) superconducting layer is 133nm, T c onset At 15.70K, 4.2K, J from the field c 10.52MA / cm 2 ; At 4.2K, J in 9T magnetic field c 2.20MA / cm 2 .

[0110] The Fe(Se,Te) superconducting film was cut into short segments with a length and width of 10 cm×1 cm, and used for annealing treatment in Examples 1-4 and Comparative Examples 1-7.

[0111] The difference between the superconducting film of Example 5 and the above-mentioned Examples 1-4 is that: i) a two-channel base tape is formed between the rollers; ii) the stepper motor moves the tape 6 times in step 7); ii) the movement speed of the metal substrate in step 8) is 6 m / h and the heating temperature is 300°C; iii) the heating temperature in step 9) is 400°C and the stepper motor moves the tape 6 times; the remaining steps and conditions are the same, and the thickness of the obtained Fe(Se,Te) superconducting film is 154nm. Then it is cut into short pieces with a length and width of 10cm×1cm, which are used for annealing treatment in Example 5.

[0112] The superconducting film of Example 6-9 is different from that of Example 1-4 in the following aspects: i) the laser energy of the whole process is 240 mJ; ii) the heating temperature in step 8) is 300°C, the laser repetition frequency is 40 Hz, and the tape speed is 6 m / h; iii) the heating temperature in step 9) is 400°C, and the stepper motor tape is moved 4 times; the remaining steps and conditions are the same, and the thickness of the obtained Fe(Se,Te) superconducting film is 151 nm. Then it is cut into short pieces with a length and width of 10 cm×1 cm, which are used for annealing treatment in Example 6-9.

[0113] The annealing method of the Fe(Se,Te) superconducting film comprises the following steps: annealing the Fe(Se,Te) superconducting film obtained above under continuous vacuum conditions, and cooling the annealing temperature to below 150°C. Annealing can be performed in G-CVD. The specific steps are: open the injection valve, put the Fe(Se,Te) superconducting film into the annealing chamber of G-CVD, close the valve, turn on the vacuum pump to evacuate; turn on the heating system, raise the temperature to below 150°C and anneal for 0.5 to 16 hours; turn off the heating system, cool to room temperature 25°C; turn off the vacuum pump, and take out the annealed Fe(Se,Te) film.

[0114] A vacuum pump is used to make the vacuum pressure of the annealing chamber reach below 1 Pa.

[0115] The heating rate of the annealing treatment is 2 to 10°C / min.

[0116] The annealing method in the following embodiments of the present application is carried out in the chemical vapor deposition system (G-CVD) of Xiamen Xincheng Graphene Technology Co., Ltd. Figure 1 As shown, it comprises an annealing chamber, a heating system and a vacuum pump. The heating system is used to heat the annealing chamber. One end of the annealing chamber is connected to a vacuum pump through a bellows, and the other end of the annealing chamber is provided with a sealing valve. During annealing, the Fe(Se,Te) superconducting film is placed in the annealing chamber and the vacuum pump is evacuated. The annealing method of the present application can also be carried out in a muffle furnace.

[0117] Example 1

[0118] In this embodiment 1, a method for annealing a Fe(Se,Te) superconducting thin film is provided, comprising the following steps:

[0119] Open the injection valve, put the Fe(Se,Te) superconducting film with a length and width of 10cm×1cm into the annealing chamber of G-CVD, close the valve, turn on the vacuum pump to evacuate to 1Pa; turn on the heating system, set 10min to heat from room temperature 25℃ to 50℃, and then keep it in vacuum for 2h; turn off the heating system, cool naturally to room temperature 25℃ in vacuum, turn off the vacuum pump, and take out the annealed Fe(Se,Te) superconducting film. The results before and after annealing are shown in Table 1.

[0120] from Figure 2 From Table 1, we can see that the c-axis lattice constant of the Fe(Se,Te) superconducting film after annealing is reduced to Improved crystallinity.

[0121] from Figure 3 As shown in Table 1, the T c When the temperature is increased to 17.70K, the transition width decreases, indicating that the proportion of the superconducting phase increases.

[0122] from Figure 4 As shown in Table 1, the J of Fe(Se,Te) superconducting film under 4.2K self-field is c Increased to 13.02MA / cm 2 , J of Fe(Se,Te) superconducting films under 4.2K and 9T magnetic field c Increased to 2.73MA / cm 2 .

[0123] Example 2

[0124] In this embodiment 2, a method for annealing a Fe(Se,Te) superconducting thin film is provided, comprising the following steps:

[0125] Open the injection valve, put the Fe(Se,Te) superconducting film with a length and width of 10cm×1cm into the annealing chamber of G-CVD, close the valve, turn on the vacuum pump to evacuate to 1Pa; turn on the heating system, set 20min to heat from room temperature 25℃ to 75℃, and then keep it in vacuum for 2h; turn off the heating system, cool naturally to room temperature 25℃ in vacuum, turn off the vacuum pump, and take out the annealed Fe(Se,Te) superconducting film. The results before and after annealing are shown in Table 1.

[0126] from Figure 2 From Table 1, we can see that the c-axis lattice constant of the Fe(Se,Te) superconducting film after annealing is reduced to

[0127] from Figure 3 As shown in Table 1, the T c When the temperature is increased to 17.40K, the transition width decreases, indicating that the proportion of the superconducting phase increases.

[0128] from Figure 4 As shown in Table 1, the J of Fe(Se,Te) superconducting films after annealing at 4.2K and in self-field is c Increased to 15.88MA / cm 2 After annealing at 4.2K and 9T magnetic field, the Jc of Fe(Se,Te) superconducting film increased to 2.66MA / cm 2 .

[0129] Example 3

[0130] In this embodiment 3, a method for annealing a Fe(Se,Te) superconducting thin film is provided, comprising the following steps:

[0131] Open the injection valve, put the Fe(Se,Te) superconducting film with a length and width of 10cm×1cm into the annealing chamber of G-CVD, close the valve, turn on the vacuum pump to evacuate to 1Pa; turn on the heating system, set 30min to heat from room temperature 25℃ to 100℃, and then keep it in vacuum for 2h; turn off the heating system, cool naturally to room temperature 25℃ in vacuum, turn off the vacuum pump, and take out the annealed Fe(Se,Te) superconducting film. The results before and after annealing are shown in Table 1.

[0132] from Figure 2 From Table 1, we can see that the c-axis lattice constant of the Fe(Se,Te) superconducting film after annealing is reduced to Improved crystallinity.

[0133] from Figure 3As shown in Table 1, the T c When the temperature is increased to 16.80K, the transition width decreases, indicating that the proportion of the superconducting phase increases.

[0134] from Figure 4 As shown in Table 1, the J of Fe(Se,Te) superconducting films after annealing at 4.2K and in self-field is c Increased to 18.20MA / cm 2 , J of Fe(Se,Te) superconducting films after annealing at 4.2K and 9T magnetic field c Increased to 3.35MA / cm 2 .

[0135] Example 4

[0136] In this embodiment 4, a method for annealing a Fe(Se,Te) superconducting thin film is provided, comprising the following steps:

[0137] Open the injection valve, put the Fe(Se,Te) superconducting film with a length and width of 10cm×1cm into the annealing chamber of G-CVD, close the valve, turn on the vacuum pump to evacuate to 1Pa; turn on the heating system, set 40min to heat from room temperature 25℃ to 125℃, and then keep it in vacuum for 2h; turn off the heating system, cool naturally to room temperature 25℃ in vacuum, turn off the vacuum pump, and take out the annealed Fe(Se,Te) superconducting film. The results before and after annealing are shown in Table 1.

[0138] from Figure 2 From Table 1, we can see that the c-axis lattice constant of the Fe(Se,Te) superconducting film after annealing is reduced to

[0139] from Figure 3 As shown in Table 1, the T c When the temperature is increased to 17.34K, the transition width decreases, indicating that the proportion of the superconducting phase increases.

[0140] from Figure 4 As shown in Table 1, the J of Fe(Se,Te) superconducting films after annealing at 4.2K and in self-field is c Increased to 20.67MA / cm 2 , J of Fe(Se,Te) superconducting films after annealing at 4.2K and 9T magnetic field c Increased to 5.05MA / cm 2 .

[0141] from Figure 5 and Figure 6 It can be seen that the T of Fe(Se,Te) film before and after annealing cThe transition width decreases with increasing magnetic field, increases with increasing magnetic field, and the change is stronger when the magnetic field is parallel to the out-of-plane direction, which is consistent with other Fe-based superconductors.

[0142] from Figure 7 It can be seen that when the external magnetic field is parallel to the c-axis out-of-plane direction, the upper critical magnetic field H after annealing c2 and irreversible magnetic field H irr All of them are reduced to varying degrees, and GL theory is used to fit 50%ρ 20K The corresponding H c2 The H before and after annealing is obtained with the change of temperature c2 (0) are 104.76T and 99.23T respectively. The H before and after annealing are further calculated using WWH theory. c2 (0) are 55.34T and 51.64T respectively. The comparison shows that the GL theory overestimates the H at absolute zero. c2 After annealing, H c2 There has been a decrease, but it is still within a good range for practical applications, indicating that the annealing treatment has not destroyed the superconducting properties of the film.

[0143] from Figure 8 It can be seen that when the external magnetic field is parallel to the in-plane direction of the ab axis, the upper critical magnetic field H after annealing c2 and irreversible magnetic field H irr The H before and after annealing are obtained by fitting the GL theory. c2 (0) are 183.51T and 174.33T respectively. Similarly, after annealing, although H c2 It has decreased, but is still relatively high. Furthermore, the anisotropy of the Fe(Se,Te) film before and after annealing at absolute zero is 1.75 and 1.76 respectively, which remain basically unchanged.

[0144] from Figure 7 and 8 It can be seen from the figure that the coherence lengths in the c-axis out-of-plane direction before and after annealing are calculated to be 1.34nm and 1.37nm respectively, and the coherence lengths in the ab-plane direction are calculated to be 1.77nm and 1.82nm respectively. The coherence length changes slightly, and the γ values ​​of the coherence lengths before and after annealing are calculated to be 1.32 and 1.33 respectively.

[0145] Example 5

[0146] The differences between Example 5 and Example 4 are: 1) the Fe(Se,Te) superconducting film is different; 2) the annealing temperature is different. In this example, the annealing temperature is 40°C, and specifically, the temperature is raised from room temperature 25°C to 40°C for 8 minutes, and then kept warm for 2 hours; the rest is the same as Example 4.

[0147] from Fig. 9 It can be seen that the c-axis lattice constant of the Fe(Se,Te) superconducting film after annealing changes from Reduce to The rate of change is -0.2%.

[0148] from Fig.10 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset The temperature increased from 15.35K before annealing to 17.68K, with a change rate of 8.2%; △T c The temperature dropped from 3.98K before annealing to 2.51K, with a change rate of -36.9%; the transition width decreased and the proportion of the superconducting phase increased.

[0149] Example 6

[0150] The differences between Example 6 and Example 4 are: 1) the Fe(Se,Te) superconducting film is different; 2) the annealing time is different, the annealing time is 0.5h, specifically, it is set to be 40min from room temperature 25°C to 125°C, and then keep warm for 0.5h; the rest is the same as Example 4. The results before and after annealing are shown in Table 2.

[0151] from Fig.11 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0152] from Fig.12 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset Increasing to 17.59K, the transition width decreases slightly.

[0153] Example 7

[0154] The difference between Example 7 and Example 6 is that the annealing time is 1 hour, specifically, it takes 40 minutes to heat from room temperature 25°C to 125°C, and then keep warm for 1 hour; the rest is the same as Example 6. The results before and after annealing are shown in Table 2.

[0155] from Fig.11 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0156] from Fig.12 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset When it is increased to 17.59K, the transition width decreases, indicating that the proportion of the superconducting phase increases.

[0157] Example 8

[0158] The difference between Example 8 and Example 6 is that the annealing time is 4 hours, specifically, 40 minutes are set to increase the temperature from room temperature 25°C to 125°C, and then keep the temperature for 4 hours; the rest is the same as Example 6. The results before and after annealing are shown in Table 2. Fig.11 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0159] from Fig.12 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset It is increased to 17.37K and the transition width is slightly reduced.

[0160] Example 9

[0161] The difference between Example 9 and Example 6 is that the annealing time is 8 hours, specifically, it takes 40 minutes to heat from room temperature 25°C to 125°C, and then keep the temperature for 8 hours; the rest is the same as Example 6. The results before and after annealing are shown in Table 2.

[0162] from Fig.11 It can be seen that the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases after annealing.

[0163] from Fig.12 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset The improvement is 17.43K, and the transition width is slightly reduced.

[0164] Comparative Example 1

[0165] The difference between this comparative example 1 and example 4 is that the Fe(Se,Te) superconducting film is not annealed in a vacuum gas flow, and the entire annealing process does not use a vacuum pump to evacuate the air, and the G-CVD annealing chamber is filled with air for annealing. The results before and after annealing are shown in Table 3.

[0166] from Fig.13 It can be seen that after annealing, the crystallinity of the Fe(Se,Te) superconducting film increases, and the c-axis lattice constant decreases to

[0167] from Fig.14 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c When it increases to 17.56K, the transition width decreases, indicating that the proportion of the superconducting phase increases.

[0168] from Fig.15 It can be seen that the J of Fe(Se,Te) superconducting film after annealing at 4.2K is c Reduced to 6.69MA / cm 2 ; When the external magnetic field is 1T, Jc A sharp drop, when the magnetic field is 2.58T J c The decay is 0, indicating that annealing in air cannot improve the superconducting properties of Fe(Se,Te) superconducting films.

[0169] Comparative Example 2

[0170] The difference between Comparative Example 2 and Example 4 is that the vacuum degree is different. The Fe(Se,Te) superconducting film is placed in a quartz tube and evacuated to 5×10 -4 Pa or less, and then annealing treatment is performed, including the following steps:

[0171] 1) In an argon-protected glove box, the Fe(Se,Te) film was placed in a customized small quartz tube, which was then placed in a customized necked quartz tube and clamped at the neck with a cylindrical quartz plug. The tube joints were then connected in sequence, and the quartz tube was taken out of the glove box and fixed on a tube sealing machine (brand: Bailibo). The quartz tube was evacuated to 5×10 -4 Pa, stop vacuuming and use a hydrogen-oxygen torch to seal the quartz plug;

[0172] 2) Open the injection valve, place the sealed quartz tube into the annealing chamber of the G-CVD, and close the valve;

[0173] 3) Turn on the heating system, set it to heat from room temperature 25°C to 125°C in 40 minutes, and then keep it warm for 2 hours;

[0174] 4) Turn off the heating system, cool naturally to room temperature 25°C, and take out the annealed Fe(Se,Te) superconducting film.

[0175] The results before and after annealing are shown in Table 3.

[0176] from Fig.13 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0177] from Fig.14 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset Increased to 18.19K, but T c 0 It is 14.43K, and the transition width of the film is reduced compared with that before annealing, but is slightly larger than that of Example 4, indicating that its superconducting component ratio is smaller than that of Example 4.

[0178] from Fig.15 It can be seen that the J of Fe(Se,Te) superconducting film under 4.2K self-field is c 9.49MA / cm 2, J of Fe(Se,Te) superconducting films under 4.2K and 9T magnetic field c 1.81MA / cm 2 This indicates that too low vacuum pressure will lead to the J c less than before annealing.

[0179] Comparative Example 3

[0180] The difference between Comparative Example 3 and Example 4 is that the annealing temperature is different, specifically, the temperature is raised from room temperature 25°C to 150°C in 50 minutes, and then kept warm for 2 hours; the rest is the same as Example 4. The results before and after annealing are shown in Table 3.

[0181] from Fig.16 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0182] from Fig.17 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset When the temperature is increased to 16.97K, the transition width decreases and the proportion of the superconducting phase increases.

[0183] from Fig.18 It can be seen that the J of Fe(Se,Te) superconducting film after annealing at 4.2K is c Increased to 11.91MA / cm 2 However, when the external magnetic field is greater than 2T, the J of the annealed Fe(Se,Te) superconducting film in this comparative example is c The J of Fe(Se,Te) superconducting film after annealing at 4.2K and 9T magnetic field is less than that before annealing. c 0.63MA / cm 2 , compared with before annealing, it is reduced by 71.4%.

[0184] Comparative Example 4

[0185] The difference between this comparative example 4 and the example 4 is that the annealing temperature is 175°C, specifically, it takes 60 minutes to heat from room temperature 25°C to 175°C, and then keeps the temperature for 2 hours; the rest is the same as the example 4. The results before and after annealing are shown in Table 3.

[0186] from Fig.16 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0187] from Fig.17 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onsetAt 15.34K, the transition width decreases and the proportion of the superconducting phase increases.

[0188] from Fig.18 It can be seen that the J of Fe(Se,Te) superconducting film after annealing at 4.2K is c Dropped to 2.33MA / cm 2 , J of Fe(Se,Te) superconducting films after annealing at 4.2K and 9T magnetic field c Down to 0.05MA / cm 2 .

[0189] Comparative Example 5

[0190] The difference between this comparative example 5 and example 4 is that the annealing temperature is 200°C, specifically, it is set to be 70 minutes from room temperature 25°C to 200°C, and then kept warm for 2 hours; the rest is the same as example 4. The results before and after annealing are shown in Table 3.

[0191] from Fig.16 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0192] from Fig.17 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onset At 13.16K, the transition width decreases and the proportion of the superconducting phase increases.

[0193] from Fig.18 It can be seen that the J of Fe(Se,Te) superconducting film after annealing at 4.2K is c Dropped to 2.27MA / cm 2 , J of Fe(Se,Te) superconducting films after annealing at 4.2K and 9T magnetic field c Dropped to 0.13MA / cm 2 .

[0194] Comparative Example 6

[0195] The difference between this comparative example 6 and example 4 is that the annealing temperature is 225°C, specifically, it takes 80 minutes to heat from room temperature 25°C to 225°C, and then keep warm for 2 minutes; the rest is the same as example 4. The results before and after annealing are shown in Table 3.

[0196] from Fig.16 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0197] from Fig.17 It can be seen that the T of the Fe(Se,Te) superconducting film after annealing c onsetIt dropped to 9.88K, and the transition width remained unchanged.

[0198] from Fig.18 It can be seen that the J of Fe(Se,Te) superconducting film after annealing at 4.2K is c Dropped to 0.32MA / cm 2 , J of Fe(Se,Te) superconducting films after annealing at 4.2K and 9T magnetic field c Down to 0.0027MA / cm 2 .

[0199] Comparative Example 7

[0200] The difference between this comparative example 7 and example 4 is that the annealing temperature is 250°C, specifically, it takes 90 minutes to heat from room temperature 25°C to 250°C, and then keeps the temperature for 2 hours; the rest is the same as example 4. The results before and after annealing are shown in Table 3.

[0201] from Fig.16 It can be seen that after annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film decreases to

[0202] from Fig.17 It can be seen that the Fe(Se,Te) film does not exhibit superconductivity.

[0203] Table 1

[0204]

[0205] Table 2

[0206]

[0207] Table 3

[0208]

[0209] The present invention performs post-annealing treatment on the Fe(Se,Te) superconducting film in a vacuum. After annealing, the c-axis lattice constant of the Fe(Se,Te) superconducting film is reduced, the crystallinity is improved, the distribution of the three elements Fe, Se and Te is more uniform, and the proportion of the superconducting phase is increased. The annealing treatment of the present invention improves T c And J under self-field and magnetic field c Compared with the unannealed Fe(Se,Te) film, the T c onset The annealing temperature was 50℃ and the T c onset The highest value can reach 17.70K. Compared with the unannealed one, the critical current density J of Fe(Se,Te) film under self-field at 4.2K after annealing is cThe critical current density J at 4.2K and 9T magnetic field was increased by 23.8-96.5%. c The critical current density J under self-field at 4.2K was increased by 20.9-129.5%. c The critical current density J at 4.2K and 9T magnetic field was increased by 96.5%. c An increase of 129.5%.

[0210] The above examples are for the purpose of illustrating the embodiments disclosed by the present invention and are not to be construed as limitations of the present invention. In addition, the various modifications listed herein and the variations of methods and compositions in the invention are obvious to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been specifically described in conjunction with various specific preferred embodiments of the present invention, it should be understood that the present invention should not be limited to these specific embodiments. In fact, various modifications obvious to those skilled in the art as described above to obtain the invention should be included within the scope of the present invention.

Claims

1. A method for annealing a Fe(Se,Te) superconducting thin film, characterized in that: The steps include: Under continuous vacuum conditions, the Fe(Se,Te) superconducting film is annealed at a temperature lower than 150°C.

2. The annealing method according to claim 1, characterized in that Continue to evacuate until the vacuum pressure is 10 -4 ~1Pa; And / or, the annealing treatment time is 0.5 to 16 hours; And / or, the heating rate of the annealing treatment is 2 to 10°C / min; And / or, the temperature of the annealing treatment is not less than 40°C; preferably, it is 40-149°C.

3. The annealing method according to claim 1, characterized in that The c-axis lattice constant of the Fe(Se,Te) superconducting film is ≥ And / or, the thickness of the Fe(Se,Te) superconducting film is 100-220 nm; And / or, the Fe(Se, Te) superconducting film further includes: a metal substrate and a buffer layer.

4. The annealing method according to claim 3, characterized in that: The material of the metal substrate is selected from Hastelloy C276; And / or, the material of the buffer layer is selected from one or more of CeO2, LaMnO3, SrTiO3 and MgO; And / or, an oxide barrier layer is further provided between the metal base layer and the buffer layer.

5. The annealing method according to claim 4, characterized in that: The material of the oxide barrier layer is selected from one or both of Al2O3 and Y2O3.

6. The annealing method according to claim 3, characterized in that: The preparation method of the Fe(Se, Te) superconducting film is as follows: a pulsed laser deposition method is used to deposit a Fe(Se, Te) superconducting target material on a metal substrate provided with a buffer layer and form a Fe(Se, Te) superconducting layer to obtain the Fe(Se, Te) superconducting film.

7. The annealing method according to claim 6, characterized in that: In the pulsed laser deposition method, the deposition conditions are that the temperature of the metal substrate is 300-600°C, the moving speed of the metal substrate is 6-12 m / h, the distance between the metal substrate and the Fe(Se,Te) superconducting target is 4-5 cm, and the laser energy is 150-250 mJ.

8. A Fe(Se,Te) superconducting thin film obtained by the annealing method according to any one of claims 1 to 7.

9. The Fe(Se,Te) superconducting thin film according to claim 8, characterized in that: Compared with that before annealing, the c-axis lattice constant of the annealed Fe(Se,Te) superconducting film is reduced by at least 0.1%; and / or, compared with that before annealing, the critical transition temperature of the annealed Fe(Se,Te) superconducting film is increased by at least 7%; and / or, compared with that before annealing, the critical current density of the annealed Fe(Se,Te) superconducting film under self-field at 4.2K is increased by at least 20%; And / or, compared with that before annealing, the critical current density of the annealed Fe(Se,Te) superconducting film at 4.2K and 9T magnetic field is increased by at least 20%.

10. Use of the Fe(Se,Te) superconducting film according to claim 8 or 9 in cables and high-field superconducting magnets.

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