Multiferroic Fe3O4@BiFeO3 nanoparticle film and its preparation method and application

Abstract

A multiferroic Fe3O4@BiFeO3 nanoparticle film, preparation method, and application thereof. The multiferroic Fe3O4@BiFeO3 nanoparticle film is formed on the surface of a single-crystal silicon substrate via spin coating and comprises, from bottom to top, a BiFeO3 buffer layer, a Fe3O4@BiFeO3 granular film layer, and a BiFeO3 surface layer. The present invention utilizes single-crystal silicon as a substrate and the spin coating method to improve efficiency and reduce costs. The spin coating method also allows for easy control of structural factors such as the particle size, content, and morphology of the magnetic nanoparticles, as well as the thickness of the BiFeO3 film.

Description

Technical Field

[0001] The present invention relates to the technical field of thin film preparation, and in particular to a multiferroic Fe3O4@BiFeO3 nanoparticle film and a preparation method thereof. Background Art

[0002] Multiferroicity refers to the simultaneous presence of two or more ferroic orders (such as ferromagnetism, ferroelectricity or ferroelasticity, etc.) in a material. People can use the multifunctional physical properties of multiferroic materials to design and synthesize functional materials and devices that meet specific needs, and apply such materials to fields such as magnetoelectric multistate memory, multiferroic spintronic devices, sensors and transducers, which is of great significance to the promotion of electronic information and energy industries. Among multiferroic materials, magnetoelectric multiferroic materials that have both ferromagnetism and ferroelectricity are the most widely studied. Unfortunately, there is currently no single-phase material that exhibits both ferroelectricity and ferromagnetism at room temperature. Although bismuth ferrite (BiFeO3, abbreviated as BFO) is the only room-temperature multiferroic material with strong ferroelectricity at room temperature (theoretical polarization intensity P s ≈100μC / cm 2 ), but its magnetism is very weak (antiferromagnetic), which seriously limits the application of this type of material.

[0003] Composites of BFO with strong ferromagnetic materials to create multiferroic composite materials with both strong ferroelectricity and ferromagnetism are currently a hot topic. Furthermore, the fabrication of BFO and strong ferromagnetic materials into composite thin films is more conducive to the device and product development of the material. The structural characteristic of 0-3 nanogranular films is that nanoparticles of one phase are embedded in a thin film matrix of another phase. The large interface between the two phases (ferroelectric and ferromagnetic) facilitates the generation of a significant magnetoelectric coupling effect, making the preparation of multiferroic nanogranular films crucial.

[0004] Currently, most methods for preparing BFO-based nanoparticle films or pure thin films are pulsed laser deposition (PLD), magnetron sputtering (MS), molecular beam epitaxy (MBE), or atomic layer deposition (ALD). These methods allow for precise control of sample composition, film thickness, or particle size, resulting in the production of high-quality films. For example, Tahta Amrillah et al. used the PLD method to prepare CoFe2O4@BFO nanogranular film, and the columnar array structure of nano-CoFe2O4 was vertically arranged in the BFO film (Tahta Amrillah et al, CrystEngComm. 22(3), 435-440(2020)); Chen Peng et al. used the magnetron sputtering method to prepare BaTiO3@BFO granular film, and the sputtering target used was a BFO-BaTiO3 composite target with a purity of 99.99% (Peng Chen et al, Sci Sin-Phys Mech As. 48(10), 107002(2018)). Antonio B.Me et al. used molecular beam epitaxy to prepare a high-quality BFO film about 200nm thick on a SrRuO3 substrate. The flatness of the film even reached the atomic level (Atomically smooth) (Antonio B.Mei et al, APL Mater. 7, 071101 (2019)). Pavel Kaspar et al. used atomic deposition technology to deposit a BFO film on a pyrolytic graphite substrate. The film material showed huge ferromagnetism (≈120emu / cm 3 ). (Pavel Kaspar et al, nanomaterials. 10(10), 1990(2020)).

[0005] Although PLD, MS, MBE, or ALD technologies have many advantages in preparing BFO-based nanoparticle films or pure thin film structures, such as controllable composition, adjustable particle size of magnetic particles and thickness of BFO films, and these preparation methods are also the main methods for preparing high-quality thin films in small batches in scientific research, they also have the following shortcomings:

[0006] (1) Complex operation procedures. The above preparation methods require strict control of experimental parameters, such as gas partial pressure, water content in the chamber, target material purity, substrate temperature, power level, etc. Because these devices are large, precise, and complex to operate, operators often need to undergo a long period of training and have rich operating experience to be competent.

[0007] (2) High cost. First, the equipment that costs millions to tens of millions of yuan will be prohibitive for ordinary small and medium-sized enterprises or scientific research institutions. Second, these preparation methods require expensive consumables such as targets, substrates, and high-purity gases (such as high-purity argon and high-purity nitrogen).

[0008] (3) The preparation efficiency is low, which is not conducive to mass production. Due to the limitations of the preparation method, the efficiency of preparing BFO-based thin film materials by methods such as PLD, MS, MBE, and ALD is not high. For example, Yueli Zhang et al. used magnetron sputtering to deposit a layer of BFO film with a thickness of about 400 nm on a Pt(111) / Ti / SiO2 / Si(100) substrate with a size of 10 mm × 10 mm. The deposition time for only one sample took about 2 hours (Yueli Zhang et al, J Mater Sci: Mater Electron. 26, 5877-5883 (2015)). It can be seen that when the number of samples prepared is large, the time cost is very high. Summary of the Invention

[0009] In view of the above situation, the purpose of the present invention is to propose a multiferroic Fe3O4@BiFeO3 nanoparticle film and its preparation method and application to improve efficiency and reduce cost.

[0010] In a first aspect, the present invention provides a multiferroic Fe3O4@BiFeO3 nanoparticle film, which is formed on the surface of a single crystal silicon substrate by spin coating, and includes, from bottom to top, a BiFeO3 buffer layer, a Fe3O4@BiFeO3 granular film layer and a BiFeO3 surface layer.

[0011] In a second aspect, the present invention provides a method for preparing a multiferroic Fe3O4@BiFeO3 nanoparticle film, comprising the following steps:

[0012] Step S11, dissolving bismuth salt and iron salt in an organic solvent, performing magnetic stirring and allowing to stand to obtain a BiFeO3 precursor solution;

[0013] Step S12, dropping a BiFeO3 precursor solution onto the surface of the single crystal silicon substrate, performing spin coating and baking to form a BiFeO3 buffer layer;

[0014] Step S13: adding magnetic Fe3O4 particles to a predetermined amount of BiFeO3 precursor solution, performing ultrasonic dispersion and allowing the solution to stand, then dropping the upper suspension onto the surface of the preheated BiFeO3 buffer layer, performing spin coating, baking, and natural cooling to form a Fe3O4@BiFeO3 particle film on the surface of the BiFeO3 buffer layer;

[0015] In step S14, a BiFeO3 precursor solution is dropped onto the surface of the Fe3O4@BiFeO3 particle film layer, and then spin-coated, baked, annealed, and naturally cooled to form a BiFeO3 surface layer on the surface of the Fe3O4@BiFeO3 particle film layer.

[0016] Furthermore, the step S11 specifically includes:

[0017] dissolving bismuth nitrate in ethylene glycol and glacial acetic acid, and performing magnetic stirring to obtain a first mixed solution;

[0018] dissolving ferric nitrate in glacial acetic acid and performing magnetic stirring to obtain a second mixed solution;

[0019] The first mixed solution and the second mixed solution are mixed, magnetically stirred, and allowed to stand to obtain a BiFeO3 precursor solution.

[0020] Furthermore, the molar ratio of glacial acetic acid to crystal water is 2:1.

[0021] Furthermore, in step S13, the preparation method of magnetic Fe3O4 particles includes:

[0022] Dissolve FeCl3·6H2O and FeSO4·7H2O in HCl solution, then add NaOH solution dropwise and stir to form a mixture with uniformly dispersed particles;

[0023] The filtered particles are repeatedly washed with deionized water and then kept warm in an atmosphere of a preset temperature to obtain the desired magnetic Fe3O4 particles.

[0024] Furthermore, the content of FeCl3·6H2O is 0.04 mol, the content of FeSO4·7H2O is 0.02 mol, the volume of the HCl solution is 50 ml, the concentration is 0.5 mol / L, the concentration of the NaOH solution is 1.5 mol / L, and the temperature is 80°C;

[0025] The holding temperature is 50°C and the holding time is 4 hours.

[0026] Furthermore, in step S13, the content of magnetic Fe3O4 particles is 0.001 g, the volume of BiFeO3 precursor solution is 40 ml, the ultrasonic dispersion time is 30 min, and the standing time is 20 min;

[0027] The spin coating speed is 500-2000 r / min, and the time is 5-25 s;

[0028] The baking method is as follows: baking at 80°C for 30 minutes, then heating to 200 to 500°C at a heating rate of 10°C / min, and baking for 5 minutes.

[0029] Furthermore, in step S12, the spin coating speed is 1000-3000 r / min, and the time is 5-30 s;

[0030] The baking method is: 200 to 500°C, baking for 5 to 10 minutes.

[0031] Furthermore, in step S14, the spin coating speed is 1000-3000 r / min, and the time is 5-30 s;

[0032] Baking method: 200 to 500℃, baking for 10 minutes;

[0033] The annealing method is: heating to 500-700° C. at a heating rate of 10° C. / min, and annealing for 5-30 minutes.

[0034] In a third aspect, the present invention provides an application of a multiferroic Fe3O4@BiFeO3 nanoparticle film, which is applied to information storage devices, spintronic devices, sensors or transducers.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) Low cost. Using a very low-cost sol-gel spin coating method, nanomagnetic particles are dispersed in a BFO film to prepare a BFO-based nanoparticle film with significant multiferroic properties. Furthermore, the substrate material we selected is single-crystal silicon, further reducing the sample preparation cost.

[0037] (2) This method can also conveniently regulate structural factors such as the particle size, content, morphology of magnetic nanoparticles and the thickness of the BFO film, making it easier to study the structural relationship of the particle film and explore the preparation of BFO-based particle film materials with excellent multiferroic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of Fe3O4@BiFeO3 nanoparticle film;

[0039] Figure 2 is the XRD pattern of FO magnetic particles;

[0040] Figure 3 (a), 3(b), 3(c), 3(d), correspond to the XRD patterns of samples a, b, c, and d;

[0041] Figure 4 (a), 4(b), 4(c), and 4(d) correspond to the SEM images of the surfaces of samples a, b, c, and d;

[0042] Figure 5 (a), 5(b), 5(c), and 5(d) correspond to the particle size statistical histograms of samples a, b, c, and d;

[0043] Figure 6 (a), 6(b), 6(c), and 6(d) correspond to the cross-sectional SEM images of samples a, b, c, and d;

[0044] Figure 7 (a), 7(b), 7(c), and 7(d) correspond to the hysteresis loop diagrams of samples a, b, c, and d;

[0045] Figure 8 (a), 8(b), 8(c), and 8(d) correspond to the hysteresis loop diagrams of samples a, b, c, and d.

[0046] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0047] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0048] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0050] This study uses the composite of magnetic Fe₃O₄ (FO) particles and BFO thin films as an example to fabricate FO@BFO nanoparticle films on single-crystal silicon substrates, demonstrating remarkable multiferroic properties. Compared to the two commonly used substrates for preparing BFO thin films using the MS method: Pt(111) / Ti / SiO₂ / Si(100) and SrTiO₃, the single-crystal silicon substrates used in this study are approximately 8.3% and 3.7% cheaper, respectively.

[0051] 1. Preparation of multiferroic Fe3O4@BiFeO3 granular films

[0052] See also Figure 1 The present invention disperses Fe3O4 (abbreviated as FO) magnetic particles in BiFeO3 (abbreviated as BFO) thin film to prepare multiferroic Fe3O4@BiFeO3 (abbreviated as FO@BFO) nanoparticle film material. Figure 1 As shown in Figure 1, the granular film consists of three layers: from the single-crystal silicon substrate upwards, a BFO buffer layer, a FO@BFO granular film layer, and a BFO surface layer. The BFO buffer layer reduces internal stress caused by the lattice mismatch between the substrate and the film. Furthermore, due to the high electrical conductivity of FO, overlaying the BFO surface layer on the FO@BFO granular film layer avoids leakage and ferroelectric degradation in the granular film system.

[0053] It should be noted that, in the present invention, the preparation process of FO@BFO particle film is divided into three steps: (1) preparing BFO precursor solution; (2) preparing magnetic FO particles; and (3) preparing FO@BFO particle film by spin coating.

[0054] (1) BFO precursor solution preparation

[0055] Bismuth salt and iron salt are dissolved in an organic solvent to form a stable sol. In the present invention, bismuth nitrate and iron nitrate are dissolved in a mixed solution of ethylene glycol and glacial acetic acid, and the molar ratio of glacial acetic acid to crystal water is 2:1. The specific process is as follows: First, weigh 0.008 mol Bi (NO3) 3 · 5H2O and put it into the first beaker, add 10 ml of ethylene glycol and 4.6 ml of glacial acetic acid to the beaker, and stir magnetically for 1.5 hours; then, weigh 0.008 mol Fe (NO3) 3 · 9H2O and put it into another beaker, add 8.28 ml of glacial acetic acid, and stir magnetically for 1.5 hours. Finally, mix the solutions in the two beakers, stir magnetically for 3 hours, and let it stand for 48 hours to obtain a BFO precursor solution.

[0056] (2) Preparation of magnetic FO particles

[0057] Weigh 0.04 mol of FeCl₃·6H₂O and 0.02 mol of FeSO₄·7H₂O and dissolve them in 50 ml of 0.5 mol / L HCl. Then, add 1.5 mol / L NaOH solution at 80°C dropwise to this solution and stir vigorously to evenly disperse the resulting FO magnetic particles. Finally, filter out the prepared FO magnetic particles, wash them repeatedly with deionized water, and incubate them at 50°C for 4 hours to obtain the desired FO magnetic particles.

[0058] See also Figure 2 , Figure 2 FIG1 is the XRD pattern of the prepared FO magnetic particles. It can be seen from the figure that the FO magnetic particles prepared by this method have a pure phase structure without any impurities.

[0059] (3) Preparation of multiferroic FO@BFO nanoparticle film by spin coating

[0060] The process mainly includes the following four steps:

[0061] (I) Spin-coating a BFO precursor onto a silicon substrate to construct a BFO buffer layer. The specific steps are as follows: drop the BFO precursor onto a P-type single-crystalline Si(100) substrate at a rotation speed of 1000 to 3000 rpm (r / min), spin-coat for 5-30 seconds, and then bake at 200 to 500°C for 5 to 10 minutes. Repeat this process five times to obtain sample P1.

[0062] (II) 0.001 g of FO powder was added to 40 ml of BFO precursor solution and ultrasonically dispersed for 30 minutes. The mixture was allowed to stand for 20 minutes. The supernatant was then dropwise applied to the preheated surface of P1 at a speed of 500 to 2000 rpm for 5 to 25 seconds. The sample was then baked at 80°C for 30 minutes, then heated at a rate of 10°C / min to 200 to 500°C, baked for 5 minutes, and cooled naturally to obtain sample P2.

[0063] (III) One P1 and three P2 samples were subjected to the following treatment process, repeated 10 times, 5 times, 10 times, and 15 times, respectively, to obtain samples A, B, C, and D. The process consisted of adding a drop of BFO precursor solution to the surface of P1 or P2, spin coating at a speed of 1000 to 3000 rpm for 5-30 seconds, and then baking at 200 to 500°C for 10 minutes.

[0064] (IV) Samples A, B, C, and D were heated to 500 to 700°C at room temperature at a heating rate of 10°C / min, annealed for 5 to 30 minutes, and naturally cooled to obtain the final four samples a, b, c, and d, where sample a is a pure BFO film and samples b, c, and d are FO@BFO particle films.

[0065] It should be noted that the number of repeated spin coatings in steps (I) and (III) determines the thickness of the BFO buffer layer and the BFO surface layer, respectively. The FO concentration or the number of spin coatings used in step (II) determines the content of magnetic particles in the granular film. In addition, the experimental conditions can be controlled to prepare FO magnetic particles of different particle sizes. In short, the present invention can regulate the thickness of the granular film, the content and morphology of the magnetic particles by adjusting the experimental parameters, providing a large space for the preparation of magnetoelectric multiferroic granular films with excellent performance.

[0066] 2. XRD test of FO@BFO particle film

[0067] See also Figure 3 (a), (b), (c), and (d) are the XRD patterns of samples a, b, c, and d. Comparison of the diffraction peaks of each sample with those of standard card PDF#86-1518 shows that each sample prepared by this method has a pure phase structure and is free of impurities.

[0068] 3. Morphological Characterization of FO@BFO Particle Film

[0069] See also Figure 4 (a), 4(b), 4(c), and 4(d) are SEM images of the surfaces of samples a, b, c, and d. It can be seen from the images that the surfaces of the samples are smooth and flat, the spacing between the grains is small (about 10-20 nanometers), and there are no cracks or damage on the surface.

[0070] See also Figure 5 Figures (a), (b), (c), and (d) are statistical plots of grain size on the surface of the granular film for samples a, b, c, and d. Each sample was measured using 100 grains. The statistical results show that, with the exception of sample a, which has a larger average grain size (approximately 110 nm), the average grain sizes of samples b, c, and d are relatively close, at 66.9, 75.3, and 75.6 nm, respectively.

[0071] See also Figure 6 (a), (b), (c), and (d) are cross-sectional SEM images of samples a, b, c, and d. By measuring the thickness at 10 different locations on each sample's cross section and averaging the values, the average particle film thicknesses for the four samples were 341.6, 369.2, 449.6, and 474.9 nm, respectively. This indicates that the particle film thickness increases with the number of spin-coating cycles of the BFO surface layer.

[0072] See also Figure 7 (a), (b), (c), and (d) are the hysteresis loops of samples a, b, c, and d. Samples a, b, c, and d reach their maximum polarization values ​​at applied electric fields of approximately 250, 50, 120, and 100 kV / cm, respectively. The maximum polarization values ​​are 21.3, 8.7, 11.9, and 7.6 μC / cm, respectively. 2 After the polarization values ​​of the three particle film samples b, c, and d reach their maximum, they gradually decrease with the further increase of the applied electric field. This may be because the embedding of FO particles increases the internal stress of the film, resulting in an increase in BFO crystal defects and an increase in leakage current.

[0073] See also Figure 8 (a), 8(b), 8(c), 8(d) are the hysteresis loops of samples a, b, c, and d. As can be seen from the figure, the pure phase structure of BFO (sample a) has very weak magnetism, and its hysteresis loop shows typical linear antiferromagnetic characteristics. Due to the introduction of FO magnetic particles, the magnetism of the three granular film samples b, c, and d is greatly improved, and their saturation magnetization intensities are 28.5, 49.2, and 69.0 emu / cm, respectively. 3 .

[0074] This demonstrates that the FO@BFO granular film material prepared by the sol-gel spin-coating method not only exhibits strong ferroelectricity but also exhibits strong ferromagnetic properties. The disclosed method of combining ferromagnetic particles with a ferroelectric film using the sol-gel spin-coating method yields a nanogranular film with strong multiferroic properties at room temperature, providing a novel research approach for the development of low-cost multiferroic thin-film materials and devices.

[0075] In summary, the present invention has the following advantages:

[0076] 1. A low-cost and easy-to-control sol-gel spin coating method is used.

[0077] Expensive techniques such as PLD, MS, MBE or ALD are usually used to prepare particle films or high-quality thin film materials. However, the present invention adopts a low-cost sol-gel spin coating method that is easy to mass-produce.

[0078] 2. Growing granular films on the surface of low-cost single-crystal silicon further reduces costs.

[0079] 3. The three-layer structure design (BFO / granular film / BFO) not only avoids the problems of increased leakage current and deterioration of ferroelectric performance due to the presence of magnetic particles, but also achieves the goal of enhancing the magnetic properties of the granular film system with magnetic particles.

[0080] 4. Accurate control of the process. Control of the spin coating speed, baking temperature, and annealing temperature is very critical. Only by accurately controlling the process parameters can granular film materials with excellent multiferroic properties be prepared.

[0081] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. The above-mentioned embodiments only express several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several variations and improvements can be made, which all fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of the present invention shall be based on the attached claims.

Claims

1. A multiferroic Fe3O4@BiFeO3 nanoparticle film, characterized in that: The multiferroic Fe3O4@BiFeO3 nanoparticle film is formed on the surface of a single crystal silicon substrate by spin coating, and includes, from bottom to top, a BiFeO3 buffer layer, a Fe3O4@BiFeO3 granular film layer, and a BiFeO3 surface layer. The preparation method of the multiferroic Fe3O4@BiFeO3 nanoparticle film includes the following steps: Step S11, dissolving bismuth salt and iron salt in an organic solvent, performing magnetic stirring and allowing to stand to obtain a BiFeO3 precursor solution; Step S12, dropping a BiFeO3 precursor solution onto the surface of the single crystal silicon substrate, performing spin coating and baking to form a BiFeO3 buffer layer; Step S13: adding magnetic Fe3O4 particles to a predetermined amount of BiFeO3 precursor solution, performing ultrasonic dispersion and allowing the solution to stand, then dropping the upper suspension onto the surface of the preheated BiFeO3 buffer layer, performing spin coating, baking, and natural cooling to form a Fe3O4@BiFeO3 particle film on the surface of the BiFeO3 buffer layer; In step S14, a BiFeO3 precursor solution is dropped onto the surface of the Fe3O4@BiFeO3 particle film layer, and then spin-coated, baked, annealed, and naturally cooled to form a BiFeO3 surface layer on the surface of the Fe3O4@BiFeO3 particle film layer.

2. The multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 1, characterized in that The step S11 specifically includes: dissolving bismuth nitrate in ethylene glycol and glacial acetic acid, and performing magnetic stirring to obtain a first mixed solution; dissolving ferric nitrate in glacial acetic acid and performing magnetic stirring to obtain a second mixed solution; The first mixed solution and the second mixed solution are mixed, magnetically stirred, and allowed to stand to obtain a BiFeO3 precursor solution.

3. The multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 2, characterized in that The molar ratio of glacial acetic acid to crystal water is 2:

1.

4. The multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 1, characterized in that In step S13, the method for preparing magnetic Fe3O4 particles includes: Dissolve FeCl3·6H2O and FeSO4·7H2O in HCl solution, then add NaOH solution dropwise and stir to form a mixture with uniformly dispersed particles; The filtered particles are repeatedly washed with deionized water and then kept warm in an atmosphere of a preset temperature to obtain the desired magnetic Fe3O4 particles.

5. The method for preparing the multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 4, characterized in that: The content of FeCl3·6H2O is 0.04 mol, the content of FeSO4·7H2O is 0.02 mol, the volume of HCl solution is 50 ml, the concentration is 0.5 mol / L, the concentration of NaOH solution is 1.5 mol / L, and the temperature is 80°C; The holding temperature is 50°C and the holding time is 4 hours.

6. The method for preparing a multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 5, characterized in that: In step S13, the content of magnetic Fe3O4 particles is 0.001 g, the volume of BiFeO3 precursor solution is 40 ml, the ultrasonic dispersion time is 30 min, and the standing time is 20 min; The spin coating speed is 500~2000r / min, and the time is 5~25s; The baking method is as follows: baking at 80°C for 30 min, then heating to 200 to 500°C at a heating rate of 10°C / min, and baking for 5 min.

7. The method for preparing a multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 1, characterized in that: In step S12, the spin coating speed is 1000-3000 r / min, and the time is 5-30 s; The baking method is: 200 to 500℃, baking for 5 to 10 minutes.

8. The method for preparing a multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 1, characterized in that: In step S14, the spin coating speed is 1000-3000 r / min, and the time is 5-30 s; Baking method: 200 to 500℃, baking for 10 minutes; The annealing method is: heating to 500~700℃ at a heating rate of 10℃ / min, and annealing for 5~30min.

9. A use of the multiferroic Fe3O4@BiFeO3 nanoparticle film according to claim 1, characterized in that: The multiferroic Fe3O4@BiFeO3 nanoparticle film is applied in information storage devices, spintronic devices, sensors or transducers.

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