Preparation method of multiferroic thin film material with double perovskite structure

Abstract

The invention discloses a multiferroic thin film material with a double perovskite structure. The multiferroic thin film material is a Bi2FeCrO6 thin film material. The preparation method comprises the following steps: firstly, preparing a Bi2FeCrO6 system powder sample by adopting a sol-gel method, then drying the powder sample of the material and preparing a block target material, and finally, depositing the block target material on an FTO (Fluorine-doped Tin Oxide) substrate by adopting a pulse laser deposition method to prepare the Bi2FeCrO6 system film, and the material has ferromagnetism, ferroelectricity and photovoltaic characteristics at the same time. According to the method disclosed by the invention, good film quality, high phase purity, stable film element proportion and good adhesion between the film and the substrate can be ensured, the success rate of pure-phase film preparation is high, the repeatability is good, and obvious magnetic, ferroelectric and photovoltaic effects can be observed in a Bi2FeCrO6 system film sample.

Description

Technical Field

[0001] The invention belongs to the field of composite materials, and in particular relates to a method for preparing a double perovskite structured multiferroic thin film material. Background Art

[0002] Multiferroic materials refer to materials that can exhibit two or more intrinsic iron orders in a single phase, such as ferromagnetism, ferroelectricity, ferroelasticity, ferrovalley or ferrovorticity. This concept can also be generally extended to antiferromagnetism and complex multiferroic materials. In such materials, order parameters such as electric, magnetic and elastic coexist and form a series of interesting physical phenomena such as magnetoelectric coupling. In recent years, bismuth-based multiferroic materials have attracted much attention and research due to their unique multiferroicity, magnetoelectric coupling effect and significant bulk photovoltaic effect. Such materials have a non-centrosymmetric crystal structure, that is, there is a breaking of spatial inversion symmetry, which can generate spontaneous electric polarization. The spontaneous polarization phenomenon promotes the effective separation of carriers, so that the voltage generated by these materials under illumination far exceeds their band gap value, even up to 5 times. Theoretically, it is predicted that devices based on such materials are expected to achieve a photovoltaic efficiency of up to 70%, showing great application potential and research value in many fields such as information storage, photoelectric detection, self-powered sensing and light energy conversion. Since the discovery and successful experimental preparation of multiferroic materials, the ferroelectric photovoltaic effect has gradually become a research hotspot. Among them, thin film ferroelectric materials, such as BiMnO3 and BaTiO3, are difficult to obtain significant efficiency due to their wide band gap (more than 2.5 eV), but the research has not stopped. By using magnetic transition metals to partially replace A / B position elements, the band gap of the material can be effectively reduced. In particular, after the introduction of Cr-doped BiFeO3, the band gap value of the obtained Bi2FeCrO6 material was adjusted to the range of 1.4 to 2.4 eV. This finding has been verified by both theory and experiment. It is worth noting that Bi2FeCrO6 materials not only have complex internal microstructures, but also show unique mesostructure characteristics, such as the coexistence of g-type antiferromagnetic domains and ferroelectric domains. These structural characteristics bring it rich mutual coupling of magnetoelectric and optoelectronic properties, further broadening its application prospects. Therefore, the core of the research focuses on finding a substrate material that can be used for both magnetoelectric coupling devices and photovoltaic devices, and can withstand high temperature environments during the film preparation process. The preparation of thin films in inorganic material research is an important basic research process, so the preparation method of Bi2FeCrO6 system thin film materials is the basis for research in the field of multifunctional materials. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing Bi2FeCrO6 system thin film preparation process, such as low phase formation rate and insufficient film density, and to provide a method for preparing a double perovskite structured multiferroic thin film material, specifically a method for preparing a Bi2FeCrO6 system thin film material.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for preparing a double perovskite structure multiferroic thin film material comprises the following steps:

[0006] 1: Preparation of Bi2FeCrO6 powder by sol-gel method

[0007] 1-1: Bismuth nitrate, ferric nitrate and chromium nitrate are accurately weighed in a molar ratio of 2:1:1, and added to an appropriate amount of ethylene glycol successively to completely dissolve them to obtain solution A; wherein the amount of ethylene glycol is determined according to the dissolution conditions of bismuth nitrate, ferric nitrate and chromium nitrate;

[0008] 1-2: Mix citric acid according to {m 柠檬酸 =n Bi2FeCrO6 ×[3×2+3×1+3×1] / 4×M 柠檬酸} (where m is mass and n is amount of substance) is accurately weighed, and added into a proper amount of deionized water to completely dissolve to obtain solution B; wherein the amount of deionized water is determined according to the dissolution of the complexing agent citric acid;

[0009] 1-3: Slowly add solution A to solution B (the order cannot be changed so that the citric acid solution is kept in excess in the system during the entire operation), mix thoroughly to obtain solution C, place in a 75-85°C water bath and stir to make it viscous and yellow to obtain a wet gel;

[0010] 1-4: The wet gel is placed in a blast drying oven, slowly hydrolyzed and dried at 95-105°C for 4-5 days to form a dry gel, organic matter is removed at 380-420°C, and annealed at 580-620°C to obtain Bi2FeCrO6 powder A;

[0011] 2: Calcine Bi2FeCrO6 powder at high temperature to make bulk target

[0012] 2-1: Grind the Bi2FeCrO6 powder A into fine powder B, the powder B is of μm size (50±10 μm);

[0013] 2-2: Place the fine powder B in a crucible and calcine it at 580-620° C. in a muffle furnace for 2-2.2 hours to obtain a brown-black Bi2FeCrO6 powder C;

[0014] 2-3: Using a metal mold, the powder C is pressed into a cylindrical target material with a diameter of 30 mm ± 1 and a thickness of 2 to 3 mm, and the pressure used is 20 to 22 MPa;

[0015] 2-4: placing the cylindrical target in a muffle furnace at 580-620° C. and annealing for 55-65 min to obtain a Bi2FeCrO6 bulk target;

[0016] 3: Use pulsed laser deposition to deposit the bulk target on the FTO substrate to obtain Bi2FeCrO6 thin film

[0017] 3-1: The Bi2FeCrO6 bulk target and the FTO substrate are respectively placed and fixed at appropriate positions of the target position and the backing plate, the vacuum chamber is closed, and the mechanical pump and the molecular pump are turned on successively to evacuate the vacuum chamber;

[0018] 3-2: When the vacuum degree of the vacuum chamber reaches 1×10 -5 When the pressure reaches 10 Pa, turn off the molecular pump, open the oxygen valve, and adjust the oxygen pressure in the vacuum chamber to 10 Pa.

[0019] 3-3: Setting the temperature of the FTO substrate in the vacuum chamber to 500-600° C., and covering the FTO substrate with a baffle;

[0020] 3-4: Set the voltage of the pulse laser to 19kV and the frequency to 1Hz for pre-shooting. The time is determined according to the actual surface conditions of the target material.

[0021] 3-5: Set the energy of the pulse laser to 350 mJ and the frequency to 4 Hz, remove the baffle, start deposition, introduce 300 atm of oxygen after deposition, and keep it in situ for 1 to 1.2 hours before cooling to room temperature to obtain a Bi2FeCrO6 film, i.e., the double perovskite structure multiferroic film material.

[0022] The Bi2FeCrO6 thin film material has ferromagnetic, ferroelectric and photovoltaic properties at the temperature of 300K.

[0023] When the electric field of the Bi2FeCrO6 thin film material increases from 58 to 176 kV / cm at 300 K, the saturated polarization intensity, residual polarization intensity and coercive field of the Bi2FeCrO6 thin film material all increase as the applied electric field increases.

[0024] When the magnetic field increases from 0 to 5000 Oe at 300 K, the magnetization intensity of the Bi2FeCrO6 thin film material increases with the increase of the magnetic field and reaches saturation at 5000±100 Oe. The saturation magnetization intensity is 18 emu / cm 3 , and increases with decreasing temperature.

[0025] The present invention adopts the above technical scheme to prepare Bi2FeCrO6 system thin film, and uses physical property comprehensive measurement system (PPMS), ferroelectric comprehensive test system and photovoltaic measurement system to test the magnetic, ferroelectric and photovoltaic performance of Bi2FeCrO6 system thin film; because the sol-gel method is used to prepare Bi2FeCrO6 system powder, the obtained Bi2FeCrO6 system powder has small particle size and high uniformity, and the sol-gel method has the characteristics of simple principle, low preparation requirements, and easy control of element ratio; finally, the pulsed laser deposition method is used to deposit the Bi2FeCrO6 system thin film, and the thin film obtained by the method has the characteristics of good quality, high density, high uniformity, stable material components, good synchronization with target material components, etc. At the same time, the Bi2FeCrO6 system thin film structure prepared by using the temperature required for annealing and conductive FTO substrate is more stable. In addition, obvious magnetic, ferroelectric and photovoltaic effects are observed in the Bi2FeCrO6 system thin film sample. The method of the present invention can ensure that the film has excellent quality, high purity phase, stable element ratio, good film and substrate adhesion, and at the same time improves the success rate and repeatability of pure phase film preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments;

[0027] Figure 1 It is a schematic flow chart of the method for preparing the Bi2FeCrO6 system thin film material of the present invention;

[0028] Figure 2 This is the XRD pattern of the Bi2FeCrO6 thin film material prepared in Example 3 of the present invention;

[0029] Figure 3 This is the hysteresis loop of the Bi2FeCrO6 thin film material prepared in Example 3 of the present invention at room temperature;

[0030] Figure 4 The hysteresis loops of the Bi2FeCrO6 thin film material prepared in Example 3 of the present invention under different electric fields;

[0031] Figure 5 This is the IT characteristic curve of the Bi2FeCrO6 thin film material prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] Example 1

[0033] A Bi2FeCrO6 system thin film material, which has ferromagnetic, ferroelectric and photovoltaic properties. The preparation method of the Bi2FeCrO6 system thin film material (wherein the film annealing temperature is 500°C, i.e., the substrate temperature and in-situ annealing temperature in the following steps 3-3 and 3-5) comprises the following steps:

[0034] 1: Bi2FeCrO6 powder sample was prepared by sol-gel method.

[0035] 1-1: Bismuth nitrate, ferric nitrate and chromium nitrate are accurately weighed in a molar ratio of 2:1:1, and are successively added into an appropriate amount of ethylene glycol to completely dissolve to obtain solution A; wherein the amount of ethylene glycol is determined according to the dissolution conditions of bismuth nitrate, ferric nitrate and chromium nitrate.

[0036] 1-2: Add citric acid according to m 柠檬酸 =n Bi2FeCrO6 ×[3×2+3×1+3×1] / 4×M 柠檬酸 Weigh accurately, where m is the mass and n is the amount of the substance, and add an appropriate amount of deionized water to completely dissolve to obtain solution B; the amount of deionized water is determined according to the dissolution of the complexing agent citric acid;

[0037] 1-3: Slowly add solution A to solution B and mix thoroughly to obtain solution C. Place the solution in a water bath at 80°C and stir until it becomes viscous and turns yellow to obtain a wet gel.

[0038] 1-4: The wet gel was placed in a forced air drying oven, slowly hydrolyzed and dried at 100°C for 5 days to form a dry gel, and then organic matter was removed at 400°C and annealed at 600°C to obtain Bi2FeCrO6 powder A.

[0039] 2: Calcine Bi2FeCrO6 powder A at high temperature to make a bulk target.

[0040] 2-1: Grind the Bi2FeCrO6 powder A obtained in step 1 into fine powder B;

[0041] 2-2: The fine powder B is placed in a crucible and calcined at 600° C. in a muffle furnace for 2 hours to obtain a brown-black Bi2FeCrO6 powder C;

[0042] 2-3: Using a metal mold, the powder C is pressed into a cylindrical target material with a diameter of 30 mm and a thickness of 2 to 3 mm, and the pressure used is 20 MPa;

[0043] 2-4: The cylindrical target is placed in a muffle furnace at 600° C. and annealed for 60 minutes to obtain a Bi2FeCrO6 bulk target.

[0044] 3: The bulk target material is deposited on the FTO substrate by pulsed laser deposition to obtain Bi2FeCrO6 thin film.

[0045] 3-1: Place the Bi2FeCrO6 bulk target and FTO substrate on the target and backing plate at appropriate positions, close the vacuum chamber, and start the mechanical pump and molecular pump to evacuate the vacuum chamber;

[0046] 3-2: When the vacuum degree of the vacuum chamber reaches 1×10 -5 When the pressure reaches 10 Pa, turn off the molecular pump, open the oxygen valve, and adjust the oxygen pressure in the vacuum chamber to 10 Pa.

[0047] 3-3: Setting the temperature of the FTO substrate in the vacuum chamber to 500° C., and covering the FTO substrate with a baffle;

[0048] 3-4: Set the voltage of the pulse laser to 19kV and the frequency to 1Hz for pre-shooting. The time is determined according to the actual surface conditions of the target material.

[0049] 3-5: Set the energy of the pulse laser to 350 mJ and the frequency to 4 Hz, remove the baffle, start deposition, and the deposition time is 0.5 h. After the deposition is completed, introduce 300 atm of oxygen, and keep it at 500° C. for 1.2 h and then cool it to room temperature to obtain a Bi2FeCrO6 thin film.

[0050] Example 2

[0051] A Bi2FeCrO6 system thin film material, which has ferromagnetic, ferroelectric and photovoltaic properties. The preparation method of the Bi2FeCrO6 thin film material (wherein the film annealing temperature is 550°C, i.e., the substrate temperature and in-situ annealing temperature in the following steps 3-3 and 3-5) comprises the following steps:

[0052] 1: Bi2FeCrO6 powder sample was prepared by sol-gel method.

[0053] 1-1: Bismuth nitrate, ferric nitrate and chromium nitrate are accurately weighed in a molar ratio of 2:1:1, and are successively added into an appropriate amount of ethylene glycol to completely dissolve to obtain solution A; wherein the amount of ethylene glycol is determined according to the dissolution conditions of bismuth nitrate, ferric nitrate and chromium nitrate.

[0054] 1-2: Add citric acid according to m 柠檬酸 =n Bi2FeCrO6 ×[3×2+3×1+3×1] / 4×M 柠檬酸 Weigh accurately, add appropriate amount of deionized water to completely dissolve to obtain solution B; the amount of deionized water is determined according to the dissolution of the complexing agent citric acid;

[0055] 1-3: Slowly add solution A to solution B and mix thoroughly to obtain solution C. Place the solution in a water bath at 80°C and stir until it becomes viscous and turns yellow to obtain a wet gel.

[0056] 1-4: The wet gel was placed in a forced air drying oven, slowly hydrolyzed and dried at 105°C for 4 days to form a dry gel, and then organic matter was removed at 420°C and annealed at 600°C to obtain Bi2FeCrO6 powder A.

[0057] 2: Calcine Bi2FeCrO6 powder A at high temperature to make a bulk target.

[0058] 2-1: Grind the Bi2FeCrO6 powder A obtained in step 1 into fine powder B;

[0059] 2-2: The fine powder B is placed in a crucible and calcined at 600° C. in a muffle furnace for 2 hours to obtain a brown-black Bi2FeCrO6 powder C;

[0060] 2-3: Using a metal mold, the powder C is pressed into a cylindrical target material with a diameter of 30 mm and a thickness of 2 to 3 mm, and the pressure used is 20 MPa;

[0061] 2-4: The cylindrical target is placed in a muffle furnace at 600° C. and annealed for 60 minutes to obtain a Bi2FeCrO6 bulk target.

[0062] 3: The bulk target material is deposited on the FTO substrate by pulsed laser deposition to obtain Bi2FeCrO6 thin film.

[0063] 3-1: Place the Bi2FeCrO6 bulk target and FTO substrate on the target and backing plate at appropriate positions, close the vacuum chamber, and start the mechanical pump and molecular pump to evacuate the vacuum chamber;

[0064] 3-2: When the vacuum degree of the vacuum chamber reaches 1×10 -5 When the pressure reaches 10 Pa, turn off the molecular pump, open the oxygen valve, and adjust the oxygen pressure in the vacuum chamber to 10 Pa.

[0065] 3-3: Setting the temperature of the FTO substrate in the vacuum chamber to 550° C., and covering the FTO substrate with a baffle;

[0066] 3-4: Set the voltage of the pulse laser to 19kV and the frequency to 1Hz for pre-shooting. The time is determined according to the actual surface conditions of the target material.

[0067] 3-5: Set the energy of the pulse laser to 350 mJ and the frequency to 4 Hz, remove the baffle, start deposition, and the deposition time is 0.5 h. After the deposition is completed, introduce 300 atm of oxygen, and keep it at 550° C. for 1 h before cooling to room temperature to obtain a Bi2FeCrO6 thin film.

[0068] Example 3

[0069] A Bi2FeCrO6 system thin film material, which has ferromagnetic, ferroelectric and photovoltaic properties. The preparation method of the Bi2FeCrO6 thin film material (wherein the film annealing temperature is 600°C, i.e., the substrate temperature and in-situ annealing temperature in the following steps 3-3 and 3-5) comprises the following steps:

[0070] 1: Bi2FeCrO6 powder sample was prepared by sol-gel method.

[0071] 1-1: Bismuth nitrate, ferric nitrate and chromium nitrate are accurately weighed in a molar ratio of 2:1:1, and are successively added into an appropriate amount of ethylene glycol to completely dissolve to obtain solution A; wherein the amount of ethylene glycol is determined according to the dissolution conditions of bismuth nitrate, ferric nitrate and chromium nitrate.

[0072] 1-2: Add citric acid according to m 柠檬酸 =n Bi2FeCrO6 ×[3×2+3×1+3×1] / 4×M 柠檬酸 Weigh accurately, where m is the mass and n is the amount of the substance, and add an appropriate amount of deionized water to completely dissolve to obtain solution B; the amount of deionized water is determined according to the dissolution of the complexing agent citric acid;

[0073] 1-3: Slowly add solution A to solution B and mix thoroughly to obtain solution C. Place the solution in a 75°C water bath and stir until it becomes viscous and turns yellow to obtain a wet gel.

[0074] 1-4: The wet gel was placed in a forced air drying oven, slowly hydrolyzed and dried at 100°C for 5 days to form a dry gel, and then organic matter was removed at 380-420°C and annealed at 600°C to obtain Bi2FeCrO6 powder A.

[0075] 2: Calcine Bi2FeCrO6 powder A at high temperature to make a bulk target.

[0076] 2-1: Grind the Bi2FeCrO6 powder A obtained in step 1 into fine powder B;

[0077] 2-2: The fine powder B is placed in a crucible and calcined at 600° C. in a muffle furnace for 2 hours to obtain a brown-black Bi2FeCrO6 powder C;

[0078] 2-3: Using a metal mold, the powder C is pressed into a cylindrical target material with a diameter of 30 mm and a thickness of 2 to 3 mm, and the pressure used is 20 MPa;

[0079] 2-4: The cylindrical target is placed in a muffle furnace at 600° C. and annealed for 60 minutes to obtain a Bi2FeCrO6 bulk target.

[0080] 3: The bulk target material is deposited on the FTO substrate by pulsed laser deposition to obtain Bi2FeCrO6 thin film.

[0081] 3-1: Place the Bi2FeCrO6 bulk target and FTO substrate on the target and backing plate at appropriate positions, close the vacuum chamber, and start the mechanical pump and molecular pump to evacuate the vacuum chamber;

[0082] 3-2: When the vacuum degree of the vacuum chamber reaches 1×10 -5 When the pressure reaches 10 Pa, turn off the molecular pump, open the oxygen valve, and adjust the oxygen pressure in the vacuum chamber to 10 Pa.

[0083] 3-3: Setting the temperature of the FTO substrate in the vacuum chamber to 600° C., and covering the FTO substrate with a baffle;

[0084] 3-4: Set the voltage of the pulse laser to 19kV and the frequency to 1Hz for pre-shooting. The time is determined according to the actual surface conditions of the target material.

[0085] 3-5: The energy of the pulsed laser was set to 350 mJ and the frequency was 4 Hz. The baffle was removed and deposition was started for 0.5 h. After the deposition was completed, 300 atm of oxygen was introduced and the film was kept at 600° C. for 1 h and then cooled to room temperature to obtain a Bi2FeCrO6 film.

[0086] In the above steps, the deposition time is adjusted according to the thickness of the film to be prepared, and the film growth rate is 95-105nm / h; the FTO substrate is a conductive glass with a softening temperature of not less than 700°C, and the conductivity of the conductive layer decreases by no more than 50% at around 650°C compared with that at room temperature.

[0087] The Bi2FeCrO6 thin film material has ferromagnetic, ferroelectric and photovoltaic properties at 300K. Figure 4 The hysteresis loop of Bi2FeCrO6 material shows that when the electric field increases from 58 to 176 kV / cm, its saturated polarization intensity, residual polarization intensity and coercive field increase with the increase of the applied electric field; at 300K, the Bi2FeCrO6 thin film material Figure 4 The hysteresis loop of Bi2FeCrO6 material shows that its magnetization increases with the increase of magnetic field from 0 to 5000Oe and reaches saturation near 5000Oe. The saturation magnetization is 18emu / cm 3 The Bi2FeCrO6 thin film material is at 300K. Figure 5The graph of the photocurrent variation over time of Bi2FeCrO6 material (IT characteristic curve) shows that Bi2FeCrO6 thin film material has good response characteristics to the standard solar field.

Claims

1. A method for preparing a double perovskite structure multiferroic thin film material, characterized in that: The following steps are involved: 1: Preparation of Bi2FeCrO6 powder by sol-gel method 1-1: bismuth nitrate, iron nitrate and chromium nitrate are added to ethylene glycol in a molar ratio of 2:1:1, and completely dissolved to obtain solution A; 1-2: Add citric acid into water and completely dissolve to obtain solution B; 1-3: Slowly add solution A into solution B, mix thoroughly to obtain solution C, and place in a water bath at 75-85°C and stir to obtain a wet gel; 1-4: The wet gel is placed in a blast drying oven, slowly hydrolyzed and dried at 95-105°C for 4-5 days to form a dry gel, organic matter is removed at 380-420°C, and annealed at 580-620°C to obtain Bi2FeCrO6 powder A; 2: Calcine Bi2FeCrO6 powder at high temperature to make bulk target 2-1: Grind the Bi2FeCrO6 powder A into fine powder B of μm size; 2-2: Place the fine powder B in a crucible and calcine it at 580-620°C in a muffle furnace for 2-2.2 hours to obtain Bi2FeCrO6 powder C; 2-3: Using a metal mold to press the powder C into a cylindrical target; 2-4: placing the cylindrical target in a muffle furnace at 580-620° C. and annealing for 55-65 min to obtain a Bi2FeCrO6 bulk target; 3: The bulk target material is deposited on the FTO substrate by pulsed laser deposition to obtain a Bi2FeCrO6 thin film, which has ferromagnetic, ferroelectric and photovoltaic properties at a temperature of 300K.

2. The method for preparing a double perovskite structure multiferroic thin film material according to claim 1, characterized in that: In step 1-1, the amount of ethylene glycol is determined according to the dissolution conditions of bismuth nitrate, ferric nitrate and chromium nitrate.

3. The method for preparing a double perovskite structure multiferroic thin film material according to claim 1, characterized in that: In step 1-2, the mass of the citric acid meets the following conditions: m 柠檬酸 =n Bi2FeCrO6 ×(3×2+3×1+3×1) / 4×M 柠檬酸 The amount of water used is determined according to the dissolution of citric acid.

4. The method for preparing a double perovskite structure multiferroic thin film material according to claim 1, characterized in that: In step 2-3, the pressure used is 20-22 MPa, the diameter of the cylindrical target is 30 mm ± 1, and the thickness is 2-3 mm.

5. The method for preparing a double perovskite structure multiferroic thin film material according to claim 1, characterized in that: Step 3 is as follows: 3-1: The Bi2FeCrO6 bulk target and the FTO substrate are respectively placed on the target position and the backing plate and fixed, the vacuum chamber is closed, and the mechanical pump and the molecular pump are turned on successively to evacuate the vacuum chamber; 3-2: When the vacuum degree of the vacuum chamber reaches 1×10 -5 Pa, turn off the molecular pump, open the oxygen valve, and adjust the vacuum chamber oxygen pressure to 10Pa; 3-3: Setting the temperature of the FTO substrate in the vacuum chamber to 500-600° C., and covering the FTO substrate with a baffle; 3-4: Set the voltage of the pulse laser to 19kV and the frequency to 1Hz for pre-shooting. The time is determined according to the actual surface conditions of the target material. 3-5: The energy of the pulsed laser was set to 350 mJ and the frequency to 4 Hz, the baffle was removed, and deposition was started. After the deposition was completed, 300 atm of oxygen was introduced, and the film was kept in situ for 1 to 1.2 hours and then cooled to room temperature to obtain a Bi2FeCrO6 film.

6. The method for preparing a double perovskite structure multiferroic thin film material according to claim 1, characterized in that: When the electric field of the Bi2FeCrO6 film increases from 58 to 176 kV / cm at 300 K, the saturated polarization intensity, residual polarization intensity and coercive field of the Bi2FeCrO6 film all increase as the applied electric field increases.

7. The method for preparing a double perovskite structure multiferroic thin film material according to claim 1, characterized in that: When the magnetic field increases from 0 to 5000 Oe at 300 K, the magnetization intensity of the Bi2FeCrO6 film increases with the increase of the magnetic field and reaches saturation at 5000±100 Oe. The saturation magnetization intensity is 18 emu / cm 3 , and increases with decreasing temperature.

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