A nanoparticle composite magneto-optical film and its preparation method and application

Abstract

The present invention discloses a nanoparticle composite magneto-optical film, its preparation method, and its application, belonging to the technical field of magneto-optical film preparation and sensing applications. A CoFeB / W film is prepared on a silicon wafer using magnetron sputtering as a substrate. A gold-platinum nanoparticle layer, or a gold nanoparticle layer and a covering tungsten layer, is then spin-coated on the film. This method enhances the longitudinal magneto-optical Kerr effect of the CoFeB film by combining gold, which exhibits a surface plasmon effect, with platinum and tungsten, which exhibit a high spin-orbit coupling effect. This method utilizes the synergistic effect of these two effects to enhance the CoFeB film's longitudinal magneto-optical Kerr effect. As a sensitive element, the film has broad application potential in biomolecular sensors, as well as in the detection of viruses, bacteria, biofunctional molecules, and biological weapons.

Description

Technical Field

[0001] The present invention belongs to the technical field of magneto-optical film preparation, and in particular relates to a nano-particle composite magneto-optical film and a preparation method and application thereof. Background Art

[0002] Materials with large magneto-optical coefficients are favored for magneto-optical signal isolators, magneto-optical modulators, magneto-optical storage and recording, magneto-optical switches, bio-organic molecule concentration calibration, and weak magnetic field detection. Examples include transition metal sulfides, rare earth-transition metal alloy films, and doped rare earth garnets. However, significantly increasing the magneto-optical coefficient by simply manipulating a single material is difficult to achieve. The magneto-optical Kerr effect is essentially the spin-orbit coupling interaction between electromagnetic waves (light) and electrons within a material. Based on this, the morphology of materials can be modified by constructing micro- and nanostructures, enhancing the interaction between light and matter and thus improving magneto-optical properties. In recent years, micro- and nanofabrication technologies have made tremendous progress. The artificial construction of micro- and nanostructures in materials has led to rapid advancements in the study of magneto-optical effects.

[0003] The strong broadband optical absorption exhibited by metal nanoparticles in the visible region is due to the collective oscillation of free electrons on the metal surface, driven by electromagnetic fields, generating localized surface plasmons (also known as particle plasmons) within this wavelength range. The excitation of these localized surface plasmons can produce a significant electric field enhancement within a region tens of nanometers of the particle surface. This strong confinement can significantly improve the efficiency of many nonlinear optical processes in this region. For example, single-molecule signal detection can be achieved using surface-enhanced Raman scattering (SERS) of metal nanomaterials. Consequently, the introduction of localized surface plasmons into magneto-optical films can enhance the interaction between light and electromagnetic fields, giving new vitality to the study of magneto-optical effects. The enhancement of magneto-optical effects by localized surface plasmons has been demonstrated in numerous previous studies, such as nickel nanowires, pure ferromagnetic (Fe, Co) nanoparticles, and ferromagnetic metal-noble metal composite core-shell nanoparticles. In recent years, magnetoplasmonics, which combines the properties of surface plasmons and magneto-optical effects, has also gradually developed.

[0004] Microscopic quantum theory posits that the interaction between the electric field of light and electron spins through spin-orbit coupling is the essence of the magneto-optical effect. Spin-orbit coupling refers to the interaction between an electron's spin degree of freedom and its orbital degree of freedom. When electrons move through the electric field of an atomic nucleus, electromagnetic interactions are generated, coupling the electron's spin with this electromagnetic field, resulting in a strong spin-orbit correlation. 5d transition metal heavy elements (such as Pt, W, Ta, and Hf) exhibit strong spin-orbit coupling. Because magnetocrystalline anisotropy is intrinsically linked to spin-orbit coupling, the proximity of spin-orbit coupling comes into play when a two-dimensional magnet contacts a heavy element. For example, contact with WS2 enhances the spin-orbit coupling strength of graphene by three orders of magnitude. Furthermore, the introduction of a metal with giant spin-orbit coupling into a magneto-optical film results in strong 3d and 5d orbital hybridization at the interface between the magnetic layer and the heavy metal. This enhances the spin-orbit interaction in the magnetic layer, thereby enhancing the magneto-optical Kerr effect of the film.

[0005] However, there are few studies on combining localized surface plasmons and spin-orbit coupling to utilize dual-mode resonance to explore their effects on enhancing the magneto-optical Kerr effect. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a nanoparticle composite magneto-optical film and its preparation method and application, which utilizes the synergistic effect of surface plasmon resonance and spin-orbit coupling to enhance the longitudinal magneto-optical Kerr signal of CoFeB film.

[0007] The present invention adopts the following technical solutions:

[0008] In a first aspect, a nanoparticle composite magneto-optical film is provided. The nanoparticle composite magneto-optical film is prepared by using Si as a substrate and sequentially compounding a tungsten layer, a magnetic layer CoFeB, and a gold nanoparticle layer or a gold-platinum alloy nanoparticle layer.

[0009] Furthermore, the thickness of the CoFeB film of the magnetic layer is 50-100 nm, and the thickness of the tungsten layer is 2-5 nm.

[0010] Furthermore, the nanoparticle composite magneto-optical film is based on Si and is sequentially composited with a tungsten layer, a magnetic layer CoFeB, a gold nanoparticle layer, and a tungsten layer to obtain a nanoparticle composite magneto-optical film W / AuNPs / CoFeB / W / Si. The diameter of the gold nanoparticles is 1-200nm, and the thickness of each 1cm 2 The area magnetic layer substrate CoFeB / W / Si has 0.005-0.025 mg of gold nanoparticles, and the thickness of the outermost tungsten layer is 2-5 nm.

[0011] Furthermore, the nanoparticle composite magneto-optical film is based on Si, and is sequentially composited with a tungsten layer, a magnetic layer CoFeB, and a gold-platinum alloy nanoparticle layer to obtain a nanoparticle composite magneto-optical film Au@PtNPs / CoFeB / W / Si. The diameter of the gold-platinum alloy nanoparticles is 1-200nm, and the thickness of each 1cm 2 The area of ​​the magnetic layer substrate CoFeB / W / Si has 0.005 to 0.03 mg of gold-platinum alloy nanoparticles.

[0012] In a second aspect, the present invention provides a method for preparing a nanoparticle composite magneto-optical film, comprising the following steps:

[0013] (1) Preparation of magnetic layer substrate CoFeB / W / Si: A tungsten layer was sputtered on a silicon wafer using a DC sputtering method with a sputtering power of 10-30 W in an argon atmosphere at a pressure of 0.1-1 Pa. Then, a magnetic layer CoFeB was sputtered on the tungsten layer using a radio frequency sputtering method with a power of 80-100 W in an argon atmosphere at a pressure of 0.1-1 Pa.

[0014] (2) preparing gold nanoparticles or gold-platinum alloy nanoparticles, wherein the diameter of the nanoparticles is 3-10 nm; the gold nanoparticles are prepared by reducing chloroauric acid with sodium borohydride as a reducing agent through microfluidics; the gold-platinum alloy nanoparticles are prepared by reducing chloroauric acid and chloroplatinic acid with sodium borohydride;

[0015] (3) Weigh a certain amount of gold nanoparticles or gold-platinum alloy nanoparticles, add anhydrous ethanol to disperse them evenly to obtain a 1-8 mg / ml dispersion, and apply the dispersion on the magnetic layer substrate CoFeB / W / Si. 2 The area magnetic layer substrate CoFeB / W / Si is coated with 0.005-0.025mg of gold nanoparticles or 0.005-0.03mg of gold-platinum alloy nanoparticles. When gold nanoparticles are used, a rice-grain composite magneto-optical film AuNPs / CoFeB / W / Si is obtained, and when gold-platinum alloy nanoparticles are used, a rice-grain composite magneto-optical film Au@PtNPs / CoFeB / W / Si is obtained.

[0016] Furthermore, the method for preparing gold nanoparticles is as follows: using aqua regia to clean the required glassware in an ultrasonic cleaning machine, then rinsing it with ultrapure water, drying it after rinsing and setting it aside; dissolving chloroauric acid and polyvinyl pyrrolidone in N-methyl pyrrolidone or ethylene glycol as a metal salt solution for setting aside; the amount of the polyvinyl pyrrolidone is 0.006-0.01 g / ml based on the volume of N-methyl pyrrolidone or ethylene glycol; dissolving NaBH4 in N-methyl pyrrolidone or ethylene glycol as a reducing solution under nitrogen protection, the amount of the NaBH4 is 0.006-0.01 g / ml based on the volume of N-methyl pyrrolidone or ethylene glycol; the mass ratio of the chloroauric acid to the polyvinyl pyrrolidone and the NaBH4 is 0.006-0.01 g / ml; The ratio of the prepared metal salt solution and the reducing agent is 2:3 to 5:3 to 5; the prepared metal salt solution and the reducing agent are respectively sucked into the syringe in a volume ratio of 1:1, the syringe is fixed on the syringe pump platform, and the injection rate is set to 1-5 ml / min; under heating conditions, the metal salt solution and the reducing agent are fully mixed and reacted in a small Y-shaped reactor, and nitrogen is introduced to protect the inflowing product. After the reaction is completed, the resulting solution is collected, a certain amount of anhydrous ethanol is added, and centrifuged for 10-30 minutes using a centrifuge; the top supernatant is poured out, anhydrous ethanol is added to the precipitate after centrifugation, and the centrifugation is repeated several times, and finally the precipitate is placed in a vacuum drying oven for drying, thereby obtaining gold nanoparticles in a powder state. Preferably, the heating temperature is set to 100-200°C.

[0017] Furthermore, the method for preparing gold-platinum alloy nanoparticles is as follows: H2PtCl6.6H2O and HAuCl4 are ultrasonically dissolved in N-methylpyrrolidone in a molar ratio of 1-1.2:1 under nitrogen atmosphere protection, and a stabilizer polyvinyl pyrrolidone is added to stabilize and protect it to form a metal salt solution, and NaBH4 is ultrasonically uniformly dissolved in N-methylpyrrolidone under nitrogen atmosphere protection as a reducing agent; the prepared metal salt solution and reducing agent are respectively aspirated into a syringe in a volume ratio of 1:1, wherein (H2PtCl6.6H2O+HAuCl4): polyvinyl pyrrolidone: NaBH4 The mass ratio of 5:6 to 10:6 to 10 is 5:6 to 10; the syringe is fixed on the syringe pump platform and the injection rate is set to 1-5 ml / min. During the experiment, heating is performed, and the metal salt solution and reducing agent are thoroughly mixed and reacted in a small Y-shaped reactor. Nitrogen is introduced to protect the inflowing product. After the reaction is completed, the resulting solution is collected, a certain amount of anhydrous ethanol is added, and centrifuged for 10-30 minutes. The supernatant is poured out, and the precipitate after centrifugation is added to anhydrous ethanol and centrifuged repeatedly. Finally, the precipitate is placed in a vacuum drying oven for drying to obtain powdered gold-platinum nanoparticles. Preferably, the heating temperature is set to 100-200°C.

[0018] Furthermore, the dispersion can be coated on the magnetic layer substrate CoFeB / W / Si by the following steps: measuring the dispersion with a pipette, dropping it on the prepared magnetic layer substrate CoFeB / W / Si, and using a spin coater to set the rotation speed to 3000-5000r / min for spin coating; the thickness of the magnetic layer CoFeB film is 50-100nm, and the thickness of the tungsten layer is 2-5nm.

[0019] Furthermore, when gold nanoparticles are used in step (3), the method further includes step (4): depositing a tungsten layer as a covering layer on the top layer of the AuNPs / CoFeB / W / Si obtained in step (3) by direct current sputtering, thereby obtaining a composite magneto-optical film W / AuNPs / CoFeB / W / Si having a tungsten-covered gold nanoparticle deposited layer; the thickness of the covering tungsten layer is 2-5 nm. The composite magneto-optical film W / AuNPs / CoFeB / W / Si has a dual-mode resonance effect due to the heavy metal tungsten having a giant spin-orbit coupling effect and the noble metal gold having a surface plasmon resonance.

[0020] In a third aspect, the present invention also provides the use of the nanoparticle composite magneto-optical film as a magneto-optical material or sensor. As a sensitive element, it has a wide range of applications in biomolecule sensors, viruses, bacteria, biological functional molecules and biological weapons detection.

[0021] The beneficial effects of the present invention are as follows: (1) The longitudinal magneto-optical Kerr effect of the gold nanoparticle composite magneto-optical film was tested. The longitudinal magneto-optical Kerr effect test results of the CoFeB / W film show that its saturation magneto-optical Kerr angle is 0.0139° after theoretical calculation. After the gold nanoparticles are deposited on the CoFeB layer, the saturation magneto-optical Kerr angle of the longitudinal magneto-optical Kerr effect is 0.0211°. Compared with the CoFeB / W film, the saturation magneto-optical Kerr effect signal of the gold nanoparticle deposition layer composite film (AuNPs / CoFeB / W / Si) is increased by 1.5 times. The gold nanoparticle clusters generate collective oscillations on the surface of the CoFeB film, which significantly enhances the local electromagnetic field around the nanoparticle clusters, resulting in a polarization conversion rate r of P light to S light. ps increases, thereby increasing the saturation magneto-optical Kerr signal.

[0022] (2) The alternating growth of magnetic layers and heavy metal non-magnetic layers is the most common method for preparing and growing ferromagnetic multilayers. Usually, the lattice constants of the magnetic and non-magnetic layers are different, and a certain lattice mismatch will be generated at the interface between the two during the alternating growth process. This anisotropy at the interface will eventually form perpendicular magnetic anisotropy.

[0023] We introduced tungsten, a heavy metal with strong spin-orbit coupling, into gold nanoparticle composite magneto-optical films. We found that the addition of tungsten as a capping layer produced significant benefits: the longitudinal magneto-optical Kerr signal of the W / AuNPs / CoFeB / W film increased by 3.6 times compared to the CoFeB / W film and by 2.4 times compared to the AuNPs / CoFeB / W film. This is primarily due to orbital hybridization between the tungsten and the ferromagnetic layer at the interface, which enhances the spin-orbit interaction in the ferromagnetic layer and thus increases the magneto-optical effect.

[0024] (3) By combining platinum with a high spin-orbit coupling effect with gold nanoparticles with a surface plasmon effect, a gold-platinum alloy nanoparticle was constructed, thereby achieving the coupling of the spin-orbit coupling effect and the surface plasmon effect in a single nanoparticle. The longitudinal magneto-optical Kerr signal test results of the gold-platinum alloy nanoparticle composite magneto-optical film show that the magneto-optical enhancement effect of the gold-platinum alloy nanoparticles is stronger than that of pure gold nanoparticles. When the concentration of gold-platinum nanoparticles is 4 mg / ml, the magneto-optical enhancement effect of the gold-platinum alloy nanoparticles is the strongest, and its saturated Kerr rotation angle is about 4.4 times that of the CoFeB / W film and 1.5 times that of the film constructed when the concentration of pure gold nanoparticles is 3 mg / ml. It can be seen that the introduction of heavy metal Pt with a giant spin-orbit coupling effect causes the nanoparticles to produce dual-mode resonant coupling, thereby significantly improving the saturated deflection angle signal of the longitudinal magneto-optical Kerr effect of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagrams of the structures of the nanoparticle composite magneto-optical films of the present invention; (a) Schematic diagram of the structure of the magnetic substrate CoFeB / W / Si; (b) Schematic diagram of the structure of the composite magneto-optical film AuNPs / CoFeB / W / Si with a gold nanoparticle deposition layer; (c) Schematic diagram of the structure of the composite magneto-optical film W / AuNPs / CoFeB / W / Si with a tungsten capping layer and a gold nanoparticle deposition layer; (d) Schematic diagram of the structure of the composite magneto-optical film Au@PtNPs / CoFeB / W / Si with a gold-platinum alloy nanoparticle deposition layer;

[0026] Figure 2 is an elemental analysis chart of the gold-platinum alloy nanoparticles prepared in Example 3 of the present invention;

[0027] Figure 3 Schematic diagram of the longitudinal magneto-optical Kerr effect test system used in the present invention;

[0028] Figure 4 is the test result of the longitudinal magneto-optical Kerr effect of the gold nanoparticle composite magneto-optical film in Example 1 of the present invention;

[0029] Figure 5This is the test result of the longitudinal magneto-optical Kerr effect of the tungsten-coated gold nanoparticle composite magneto-optical film in Example 2 of the present invention;

[0030] Figure 6 This is the test result of the longitudinal magneto-optical Kerr effect of the gold-platinum alloy nanoparticle composite magneto-optical film in Example 3 of the present invention. DETAILED DESCRIPTION

[0031] In order to facilitate understanding of the technical solution of the present invention, a detailed description is given below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] (1) Preparation of magnetic layer substrate: Use magnetron sputtering technology to construct the magnetic layer CoFeB / W / Si as the substrate for adding nanoparticles. After cleaning the 1cm×1cm regular silicon wafer with deionized water, place it in an oven for drying. The vacuum degree of the chamber before sputtering is 5×10 -4 Pa, argon gas was introduced at a flow rate of 80 sccm. The W layer was sputtered using DC sputtering at a power of 10 W, an argon atmosphere at a pressure of 1 Pa, and a sputtering time of 6 minutes, resulting in a 3 nm thick W film. The magnetic CoFeB layer was sputtered using RF sputtering at a power of 100 W, an argon atmosphere at a pressure of 0.1 Pa, and a sputtering time of 12 minutes, resulting in a 70 nm thick CoFeB film.

[0034] (2) Preparation of gold nanoparticles: The method used to prepare gold nanoparticles is to reduce chloroauric acid with sodium borohydride as a reducing agent through microfluidics to obtain gold nanoparticles. The specific steps are as follows: Use aqua regia to clean the required glassware in an ultrasonic cleaner, and then rinse with ultrapure water. After rinsing, use a blower dryer to dry for use. Dissolve 0.6mmol HAuCl4 and 0.42g polyvinylpyrrolidone (PVP) in 50ml n-methyl-2-pyrrolidone (NMP) as a metal salt solution for use. Then, dissolve 0.4g NaBH4 in 50ml NMP as a reducing solution. This process should be under nitrogen protection. The prepared metal salt solution and reducing agent are respectively aspirated into the syringe, and the syringe is fixed on the syringe pump platform, and the injection rate is set to 3ml / min. During the experiment, an oil bath is used for heating, and the heating temperature is set to 150℃. The two solutions are fully mixed and reacted in a small Y-type reactor. Nitrogen is introduced into the three-necked flask to protect the inflowing product. After the reaction is complete, the resulting solution is collected, a certain amount of anhydrous ethanol is added, and the solution is centrifuged at 15,000 rpm for 30 minutes in a medical centrifuge. The supernatant is then poured off, and the resulting precipitate is washed by adding anhydrous ethanol and centrifuging repeatedly. Finally, the precipitate is dried in a vacuum drying oven to obtain powdered gold nanoparticles. The diameter of the gold nanoparticles ranges from 1 to 200 nm.

[0035] (3) Preparation of gold nanoparticle composite magneto-optical film: Weigh 1 mg, 2 mg, 3 mg, 4 mg, and 5 mg of powdered gold nanoparticles into a test tube, add 1 ml of anhydrous ethanol, and place them in an ultrasonic cleaner for 20-40 minutes. During the ultrasonic process, shake the test tube continuously to ensure that the nanoparticles are completely dispersed. Use a pipette to quantitatively take 5 microliters of the sonicated solution and drop it directly on the prepared CoFeB / W film with a 1 cm × 1 cm silicon wafer as the substrate. Then use a spin coater to set the speed to 5000 r / min for spin coating. This method can prepare a series of composite magneto-optical films (AuNPs / CoFeB / W / Si) containing a gold nanoparticle deposition layer on the CoFeB ferromagnetic layer.

[0036] The longitudinal magneto-optical Kerr effect of the prepared (AuNPs / CoFeB / W / Si) gold nanoparticle deposition composite magneto-optical film was tested using a magneto-optical Kerr test system. Figure 3 As shown, it mainly includes an optical vibration reduction platform, a laser 1, a polarizer 2, an aperture 3, an electromagnet 4, a magnetometer 5, an analyzer 6, a filter 7, a photodetector 8, a diode amplifier 9, a digital-to-analog converter 10, and a power supply 11. The laser 1 used is a helium-neon laser with a wavelength of 632.8 nm and an output power of 2 mW.

[0037] First, adjust the polarization directions of the polarizer 2 and the analyzer 6 so that they reach the extinction position. Then rotate the analyzer 6 so that it deviates from the extinction position by a very small angle δ. The reason why it is not set to the complete extinction position but to the approximate extinction position is to distinguish between positive and negative Kerr rotation angles. At the approximate extinction position, the light passing through the analyzer 6 has a background light intensity I0. When the rotation direction of the polarization plane of the reflected light is in the same direction as δ, the light intensity increases, and when it is in the opposite direction, the light intensity decreases. In this way, the magnetization direction of the sample can be distinguished by the change in light intensity. In this paper, the deflection angle δ is uniformly set to 20′ (0.333°).

[0038] After setting the small angle δ, the light passing through the analyzer 6 has a background light intensity I0, so that positive and negative Kerr rotation angles can be distinguished. When the polarization plane of the reflected light rotates in the same direction as δ, the light intensity increases, and when it rotates in the opposite direction, the light intensity decreases.

[0039] Assuming that the incident light is P-polarized, due to the Kerr effect, the reflected light contains a very small electric field component Es perpendicular to Ep, usually Es<<Ep. In the first-order approximation, we have: At this time, the light intensity passing through the analyzer prism is:

[0040] I=|Ep sinδ+Es cosδ| 2 =|Ep| 2 |sinδ+(θ k +iε k )cosδ| 2

[0041] ⑴

[0042] Usually δ is small, so we can take sinδ≈δ, cosδ≈1 to get:

[0043] I≈|Ep| 2 |δ+(θ k +iε k )| 2

[0044] ⑵

[0045] In general, θ k <<δ, and θ k and ε k At one order of magnitude, after eliminating the second-order term, equation (2) becomes:

[0046]

[0047] ⑶

[0048] where I0≈|Ep| 2 δ 2 is the light intensity when there is no external magnetic field.

[0049] The Kerr rotation angle θ is obtained by shifting the terms in formula (3) when the sample reaches magnetic saturation state: k for:

[0050]

[0051] ⑷

[0052] In actual measurement, it is best to measure the Kerr rotation angle θ at the positive saturation in the hysteresis loop. k + and the Kerr rotation angle θ at reverse saturation k -,So

[0053]

[0054] ⑸

[0055] In formula (5), I(+M Z ) and I(-M Z ) are the light intensities in the positive and negative magnetic saturation states, respectively. Equation (5) shows that the change in light intensity is determined only by the Kerr rotation angle θ k Decide.

[0056] The longitudinal magneto-optical Kerr effect test results of the (AuNPs / CoFeB / W / Si) gold nanoparticle deposition layer composite magneto-optical film are shown in Figure 2. Figure 4 As shown in Table 1. It can be concluded that at 3 mg / ml (3 mg powdered gold nanoparticles dispersed in 1 ml of anhydrous ethanol), its saturation magneto-optical Kerr rotation angle is about 0.0401°, which is 2.9 times that of CoFeB / W film.

[0057] Table 1 Calculation results of the longitudinal magneto-optical Kerr deflection angle of the gold nanoparticle composite magneto-optical film of Example 1

[0058]

[0059]

[0060] Gold nanoparticle solutions of varying concentrations can be prepared by dispersing gold nanoparticles of varying masses in anhydrous ethanol. Solutions of varying concentrations are coated on a CoFeB film, effectively resulting in different spacing between the gold nanoparticles on the film. As the concentration of gold nanoparticles increases, the spacing between the gold nanoparticles gradually decreases, and the particles aggregate more tightly. The decreasing spacing between nanoparticles leads to a gradual strengthening of the coupling between nanoparticles, and the intensity of the magneto-optical Kerr signal is continuously enhanced. At 3 mg / ml (3 mg of powdered gold nanoparticles dispersed in 1 ml of anhydrous ethanol), the saturated magneto-optical Kerr angle is approximately 0.0401°, 2.9 times that of the CoFeB / W film.

[0061] However, the enhancement effect of gold nanoparticles on the magneto-optical Kerr effect does not increase continuously with increasing concentration. When the concentration of gold nanoparticles is greater than 3 mg / ml, the enhancement of the magneto-optical Kerr signal by gold nanoparticles gradually decreases. The above phenomenon can be explained by the following three explanations. First, when the concentration of the added nanoparticles is too high, the nanoparticles on the surface of the film come into contact with each other, and charge exchange occurs, resulting in a weakening of the electric field and magnetic enhancement. Second, if the distance between the nanoparticles is less than 1 nm, a quantum tunneling effect will occur, which will also greatly weaken the ability of the nanoparticles to locally enhance the electromagnetic field. Finally, if the nanoparticles on the surface of the film directly form solid contact, the entire aggregate will become an equipotential body, resulting in electrostatic shielding, which will lead to a weakening of the nanoparticles' ability to enhance the electromagnetic field.

[0062] Example 2

[0063] (1) Preparation of magnetic layer substrate: Use magnetron sputtering technology to construct the magnetic layer CoFeB / W / Si as the substrate for adding nanoparticles. After cleaning the 1cm×1cm regular silicon wafer with deionized water, place it in an oven for drying. The vacuum degree of the chamber before sputtering is 5×10 -4 Pa, argon gas was introduced at a flow rate of 80 sccm. The W layer was sputtered using DC sputtering at a power of 10 W, an argon atmosphere at a pressure of 1 Pa, and a sputtering time of 6 minutes, resulting in a 3 nm thick W film. The magnetic CoFeB layer was sputtered using RF sputtering at a power of 100 W, an argon atmosphere at a pressure of 0.1 Pa, and a sputtering time of 12 minutes, resulting in a 70 nm thick CoFeB film.

[0064] (2) Preparation of gold nanoparticles: The method used to prepare gold nanoparticles is to reduce chloroauric acid with sodium borohydride as a reducing agent through microfluidics to obtain gold nanoparticles. The specific steps are as follows: Use aqua regia to clean the required glassware in an ultrasonic cleaner, and then rinse with ultrapure water. After rinsing, use a blower dryer to dry for use. Dissolve 0.6mmol HAuCl4 and 0.42g PVP in 50ml n-methyl-2-pyrrolidone (NMP) as a metal salt solution for use. Then, dissolve 0.4g NaBH4 in 50ml NMP as a reducing solution. This process should be under nitrogen protection. The prepared metal salt solution and reducing agent are respectively aspirated into the syringe, and the syringe is fixed on the syringe pump platform, and the injection rate is set to 3ml / min. During the experiment, the two solutions are heated in an oil bath, and the heating temperature is set to 150℃. The two solutions are fully mixed and reacted in a small Y-type reactor. Nitrogen is introduced into the three-necked flask to protect the inflowing product. After the reaction is complete, the resulting solution is collected, a certain amount of anhydrous ethanol is added, and the mixture is centrifuged at 15,000 rpm for 30 minutes in a medical centrifuge. The supernatant is then poured off, and the precipitate is washed by adding anhydrous ethanol and centrifuging repeatedly. Finally, the precipitate is dried in a vacuum drying oven to obtain powdered gold nanoparticles.

[0065] (3) Preparation of tungsten-coated gold nanoparticle composite magneto-optical film: Weigh 1 mg of powdered gold nanoparticles into a test tube, add 1 ml of anhydrous ethanol, and place it in an ultrasonic cleaner for 20-40 minutes. During the ultrasonication process, shake the test tube continuously to ensure that the nanoparticles are completely dispersed. Use a pipette to quantitatively take 5 microliters of the sonicated solution and drop it directly on the prepared CoFeB / W film with a 1 cm × 1 cm silicon wafer as the substrate. Then use a spin coater to set the speed to 5000 r / min for spin coating. This method can prepare a composite magneto-optical film (AuNPs / CoFeB / W / Si) containing a gold nanoparticle deposition layer on the CoFeB ferromagnetic layer. In order to explore the influence of heavy metal tungsten with giant spin-orbit coupling effect and precious metal gold with surface plasmon resonance on the dual-mode resonance of the magneto-optical film, a tungsten layer is deposited as a covering layer on the top layer of the composite film (AuNPs / CoFeB / W / Si) containing a gold nanoparticle deposition layer to obtain a (W / AuNPs / CoFeB / W / Si) composite magneto-optical film.

[0066] (4) The longitudinal magneto-optical Kerr effect test results of the composite magneto-optical film (W / AuNPs / CoFeB / W / Si) with tungsten coating and gold nanoparticle deposition layer are shown in Figure 4. Figure 5As shown in Table 2, the test method and system are the same as those in Example 1. It can be concluded that the use of W as the spin-orbit coupling layer and the capping layer produces a significant effect. Compared with the CoFeB / W film, the magneto-optical Kerr signal of the W / AuNPs / CoFeB / W film increases by 3.6 times, and compared with the AuNPs / CoFeB / W film, it increases by 2.4 times.

[0067] Table 2 Calculation results of the longitudinal magneto-optical Kerr deflection angle of the tungsten-coated gold nanoparticle composite magneto-optical film in Example 2

[0068]

[0069] Example 3

[0070] (1) Preparation of magnetic layer substrate: Use magnetron sputtering technology to construct the magnetic layer CoFeB / W / Si as the substrate for adding nanoparticles. After cleaning the 1cm×1cm regular silicon wafer with deionized water, place it in an oven for drying. The vacuum degree of the chamber before sputtering is 5×10 -4 Pa, argon gas was introduced at a flow rate of 80 sccm. The W layer was sputtered using DC sputtering at a power of 10 W, an argon atmosphere at a pressure of 1 Pa, and a sputtering time of 6 minutes, resulting in a 3 nm thick W film. The magnetic CoFeB layer was sputtered using RF sputtering at a power of 100 W, an argon atmosphere at a pressure of 0.1 Pa, and a sputtering time of 12 minutes, resulting in a 70 nm thick CoFeB film.

[0071] (2) Preparation of gold-platinum alloy nanoparticles: In order to further explore the magneto-optical Kerr effect of nanoparticle composite films, gold-platinum alloy nanoparticles were constructed by combining Pt with giant spin-orbit coupling effect and Au with surface plasmon resonance effect. The same microfluidic method was used to prepare Au@Pt alloy nanoparticles. Chloroauric acid, chloroplatinic acid, and sodium borohydride were prepared in proportion and ready for use. Chloroauric acid and chloroplatinic acid were reduced with sodium borohydride to prepare gold-platinum alloy nanoparticles. The specific experimental steps are as follows. First, a metal salt solution was prepared. 0.3 mmol of H2PtCl6.6H2O and 0.3 mmol of HAuCl4 were ultrasonically dissolved in N-methylpyrrolidone (NMP) under nitrogen atmosphere, and stabilized with PVP. 0.4 g of NaBH4 was ultrasonically dissolved in NMP under nitrogen atmosphere as a reducing agent. The prepared metal salt solution and reducing agent were respectively aspirated into syringes, the syringes were fixed on the syringe pump platform, and the injection rate was set to 3 ml / min. During the experiment, an oil bath was used for heating, and the temperature was set to 150°C. The two solutions were fully mixed and reacted in a small Y-type reactor. Nitrogen was introduced into the three-necked flask to protect the inflowing product. After the reaction was completed, the resulting solution was collected, a certain amount of anhydrous ethanol was added, and the solution was centrifuged at a speed of 15,000 r / min for 30 minutes using a medical centrifuge. The supernatant on the top layer was poured out, and the precipitate after centrifugation was added with anhydrous ethanol and centrifuged repeatedly to achieve the purpose of cleaning. Finally, the precipitate was placed in a vacuum drying oven for drying to obtain gold-platinum alloy nanoparticles in powder form. The diameter of the gold-platinum alloy nanoparticles is 1-200nm. The elemental analysis chart of gold-platinum alloy nanoparticles is as follows: Figure 2 shown.

[0072] (3) Preparation of gold-platinum alloy nanoparticle composite magneto-optical film: Weigh 1 mg, 2 mg, 3 mg, 4 mg, 5 mg, 6 mg, and 8 mg of powdered gold-plated nanoparticles into a test tube, add 1 ml of anhydrous ethanol, and place them in an ultrasonic cleaner for 20-40 minutes. During the ultrasonic process, shake the test tube continuously to ensure that the nanoparticles are completely dispersed. Use a pipette to quantitatively take 5 microliters of the ultrasonicated solution and drop it directly on the prepared CoFeB / W film with a 1 cm × 1 cm silicon wafer as the substrate. Then use a spin coater to set the speed to 5000 r / min for spin coating. This method can prepare a series of composite magneto-optical films (Au@PtNPs / CoFeB / W / Si) containing a gold-platinum alloy nanoparticle deposition layer on the CoFeB ferromagnetic layer.

[0073] The longitudinal magneto-optical Kerr effect test results of the composite magneto-optical film of gold-platinum alloy nanoparticle deposition layer are as follows: Figure 6and as shown in Table 3. It can be concluded that when the concentration of gold-platinum alloy nanoparticles is 4 mg / ml, the magneto-optical enhancement effect of gold-platinum alloy nanoparticles is the strongest, and its saturated Kerr rotation angle is about 4.4 times that of the CoFeB / W film and 1.5 times that of the film constructed when the concentration of pure gold nanoparticles is 3 mg / ml.

[0074] Table 3 Calculation results of the longitudinal magneto-optical Kerr deflection angle of the gold-platinum alloy nanoparticle composite magneto-optical film in this embodiment

[0075]

[0076] The present invention provides a nanoparticle composite magneto-optical film, its preparation method, and magneto-optical properties. There are many methods and approaches to implement this technical solution. The above is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A nanoparticle composite magneto-optical film, characterized in that: The nanoparticle composite magneto-optical film is prepared by sequentially composite tungsten layer, magnetic layer CoFeB, gold nanoparticle layer or gold-platinum alloy nanoparticle layer with Si as substrate; the thickness of the magnetic layer CoFeB is 50-100nm, and the thickness of the tungsten layer is 2-5nm; The diameter of the gold nanoparticles is 1-200 nm, and the diameter of each 1 cm 2 The area magnetic layer substrate CoFeB / W / Si has 0.005~0.025mg of gold nanoparticles; The diameter of the gold-platinum alloy nanoparticles is 1-200 nm, and the diameter of each 1 cm 2 The area of ​​the magnetic layer substrate CoFeB / W / Si has 0.005~0.03mg of gold-platinum alloy nanoparticles.

2. The nanoparticle composite magneto-optical film according to claim 1, wherein: The nanoparticle composite magneto-optical film is based on Si and is sequentially composited with a tungsten layer, a magnetic layer CoFeB, a gold nanoparticle layer, and a tungsten layer to obtain a nanoparticle composite magneto-optical film W / AuNPs / CoFeB / W / Si. The thickness of the outermost tungsten layer is 2-5nm.

3. The nanoparticle composite magneto-optical film according to claim 1, wherein: The nanoparticle composite magneto-optical film is based on Si and is sequentially composited with a tungsten layer, a magnetic layer CoFeB, and a gold-platinum alloy nanoparticle layer to obtain the nanoparticle composite magneto-optical film Au@PtNPs / CoFeB / W / Si.

4. The method for preparing the nanoparticle composite magneto-optical film according to any one of claims 1 to 3, wherein The following steps are involved: (1) Preparation of magnetic layer substrate CoFeB / W / Si: A tungsten layer is sputtered on a silicon wafer by DC sputtering with a sputtering power of 10-30 W in an argon atmosphere at a pressure of 0.1-1 Pa. Then, a magnetic layer CoFeB is sputtered on the tungsten layer by RF sputtering with a power of 80-100 W in an argon atmosphere at a pressure of 0.1-1 Pa. (2) preparing gold nanoparticles or gold-platinum alloy nanoparticles, wherein the diameter of the nanoparticles is 3-10 nm; (3) Weigh a certain amount of gold nanoparticles or gold-platinum alloy nanoparticles, add anhydrous ethanol to disperse them evenly to obtain a 1-8 mg / mL dispersion, and apply the dispersion on the magnetic layer substrate CoFeB / W / Si. 2 The area of ​​the magnetic layer substrate CoFeB / W / Si is coated with 0.005~0.025mg of gold nanoparticles or 0.005~0.03mg of gold-platinum alloy nanoparticles.

5. The method for preparing the nanoparticle composite magneto-optical film according to claim 4, characterized in that The method for preparing gold nanoparticles comprises: using aqua regia to clean required glassware in an ultrasonic cleaning machine, then rinsing with ultrapure water, drying after rinsing and setting aside; dissolving chloroauric acid and polyvinyl pyrrolidone in N-methyl pyrrolidone or ethylene glycol as a metal salt solution for setting aside; the amount of the polyvinyl pyrrolidone is 0.006-0.01 g / mL based on the volume of N-methyl pyrrolidone or ethylene glycol; dissolving NaBH4 in N-methyl pyrrolidone or ethylene glycol under nitrogen protection as a reducing solution, the amount of the NaBH4 is 0.006-0.01 g / mL based on the volume of N-methyl pyrrolidone or ethylene glycol; the chloroauric acid, the polyvinyl pyrrolidone and the The mass ratio of NaBH4 is 2:3~5:3~5; the prepared metal salt solution and reducing agent are respectively sucked into the syringe in a volume ratio of 1:1, the syringe is fixed on the syringe pump platform, and the injection rate is set to 1-5mL / min; under heating conditions, the metal salt solution and the reducing agent are fully mixed and reacted in a small Y-shaped reactor, and nitrogen is introduced to protect the inflowing product. After the reaction is completed, the resulting solution is collected, anhydrous ethanol is added, and centrifuged for 10-30 minutes; the top supernatant is poured out, and the precipitate after centrifugation is added with anhydrous ethanol and centrifuged repeatedly. Finally, the precipitate is placed in a vacuum drying oven for drying, thereby obtaining powdered gold nanoparticles.

6. The method for preparing the nanoparticle composite magneto-optical film according to claim 4, wherein The method for preparing gold-platinum alloy nanoparticles is as follows: H2PtCl6.6H2O and HAuCl4 in a molar ratio of 1-1.2:1 are ultrasonically dissolved in N-methylpyrrolidone under nitrogen atmosphere, and a stabilizer polyvinylpyrrolidone is added to stabilize and protect the solution to form a metal salt solution; NaBH4 is ultrasonically uniformly dissolved in N-methylpyrrolidone under nitrogen atmosphere as a reducing agent; the prepared metal salt solution and reducing agent are respectively aspirated into a syringe in a volume ratio of 1:1, wherein the mass ratio of (H2PtCl6.6H2O+HAuCl4):polyvinylpyrrolidone:NaBH4 is 5:6-10:6-10; the syringe is fixed on the syringe pump platform and the injection rate is set to 1-5mL / min; heating is carried out during the experiment. The metal salt solution and the reducing agent are fully mixed and reacted in a small Y-shaped reactor, and nitrogen is introduced to protect the inflowing product. After the reaction is completed, the resulting solution is collected, anhydrous ethanol is added, and centrifuged for 10-30 minutes. The top supernatant is poured out, and the precipitate after centrifugation is added with anhydrous ethanol and centrifuged repeatedly. Finally, the precipitate is placed in a vacuum drying oven for drying to obtain powdered gold-platinum nanoparticles.

7. The method for preparing the nanoparticle composite magneto-optical film according to claim 4, characterized in that The dispersion can be coated on the magnetic layer substrate CoFeB / W / Si by the following steps: measuring the dispersion with a pipette, dropping it on the prepared magnetic layer substrate CoFeB / W / Si, and using a spin coater to set the speed to 3000-5000r / min for spin coating; the thickness of the magnetic layer CoFeB film is 50-100nm, and the thickness of the tungsten layer is 2-5nm.

8. The method for preparing the nanoparticle composite magneto-optical film according to claim 4, wherein: When gold nanoparticles are used in step (3), the method further comprises the step (4): depositing a tungsten layer as a covering layer on the uppermost layer of the AuNPs / CoFeB / W / Si obtained in step (3) by a DC sputtering method, thereby obtaining a composite magneto-optical film W / AuNPs / CoFeB / W / Si having a tungsten-covered gold nanoparticle deposited layer; the thickness of the covering tungsten layer is 2-5 nm.

9. Use of the nanoparticle composite magneto-optical film according to any one of claims 1 to 3 as a magneto-optical material or sensor.

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