Nanotwinned cr2o3 film with room-temperature ferrimagnetism and preparation method thereof

Abstract

The application relates to the field of spin electronic devices, in particular to a nano-twin Cr2O3 film with room-temperature ferrimagnetism and a preparation method thereof, which is suitable for non-volatile, low-power-consumption and high-sensitivity spin electronic devices. A Cr2O3 epitaxial film is grown on a SrTiO3 (111) substrate by using a pulse laser deposition technology, and a high-density nano-twin is grown in the film through regulation of a film growth process. Two kinds of twin boundaries with different atomic structures are formed in the nano-twin film, one of which is ferromagnetic coupling and has a net magnetic moment, so that the nano-twin Cr2O3 film presents room-temperature ferrimagnetism. The application opens up an effective way for regulating the magnetism of film materials by using nano-twins, thereby laying a foundation for the development of high-performance nano-twin magnetic materials.

Description

Technical fields:

[0001] This invention relates to the field of spintronic devices, specifically to a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film and its preparation method, which is suitable for non-volatile, low-power, and high-sensitivity spintronic devices. Background technology:

[0002] Twin boundaries are low-energy, high-symmetry interfaces widely found in materials. They can restrict dislocation movement and exhibit a significant strengthening effect, significantly influencing the deformation behavior and mechanical properties of materials. Therefore, nanotwinned materials with high-density twins often exhibit mechanical properties far superior to traditional coarse-grained materials. The idea that nanotwins can effectively enhance the mechanical properties of materials has been proven by numerous studies. However, little is known about how twin boundaries affect the physical properties of functional materials. Nevertheless, current limited research indicates that twin boundaries play a crucial role in the physical and chemical properties of functional materials, such as catalytic performance, electrical and magnetic properties. Therefore, in principle, it is feasible to utilize nanotwinned structures to regulate the physical properties of functional materials; however, there are currently almost no reports of functional materials exhibiting significant physical properties with nanotwinned structures.

[0003] Cr₂O₃ is a typical antiferromagnetic oxide with a Nell temperature of 307 K. It possesses a corundum structure and exhibits high hardness, high wear resistance, good corrosion resistance, and chemical stability, making it widely used in surface protective coatings and other fields. In addition, Cr₂O₃ possesses excellent insulation and a unique room-temperature linear magnetoelectric effect, making it an ideal material for spintronic devices such as non-volatile magnetoelectric random access memory and logic processors. Recent studies have shown that when antiferromagnetic materials are affected by changes in composition, dislocations, grain boundaries, and stress, the arrangement of their antiparallel magnetic moments can change, even exhibiting unexpected ferromagnetism. Therefore, the magnetic properties of nanotwinned antiferromagnetic materials are a very important issue. Especially in the study of the magnetic properties of nanotwinned materials at the thin-film scale, it can provide valuable reference for the selection of materials for small-sized, high-sensitivity spintronic devices.

[0004] We grew high-quality epitaxial Cr2O3 films on SrTiO3(111) substrates using pulsed laser deposition (PLD). By controlling the growth parameters, we obtained Cr2O3 films with a high-density nanotwinned structure. Magnetic measurements using a superconducting quantum interference device (SQU) showed that the films exhibited room-temperature ferrimagnetism. Further analysis using high-resolution X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), aberration-corrected transmission electron microscopy (TEM), atomic-resolution electron energy loss spectroscopy (EELS), and first-principles calculations characterized the microstructure, atomic and electronic structure of the twin boundaries, and magnetic properties of the nanotwinned Cr2O3 films, elucidating the origin of the room-temperature ferrimagnetism of the high-density nanotwinned Cr2O3 films. This provides an effective approach for controlling the physical properties of materials using nanotwins. Summary of the Invention:

[0005] The purpose of this invention is to provide a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film and its preparation method, thereby enabling the control of the material's physical properties by utilizing high-density twin boundaries. This allows the room-temperature ferrimagnetic antiferromagnetic Cr2O3 thin film to be used in advanced electromagnetic devices, thus promoting the innovation and development of high-performance nanotwinned functional materials.

[0006] The technical solution of this invention is:

[0007] A room-temperature ferrimagnetic nanotwinned Cr2O3 thin film is presented. Cr2O3 is an intrinsically antiferromagnetic oxide material with good insulation and unique room-temperature magnetoelectric effect, making it suitable for spintronic devices. Nanotwins significantly affect the mechanical and physicochemical properties of the material, thus Cr2O3 thin films with nanotwinned structures are selected as ideal magnetoelectric materials. Cr2O3 thin films are grown on SrTiO3(111) single-crystal substrates using pulsed laser deposition. By adjusting the growth parameters, high-density nanotwins are induced in the grown Cr2O3 thin film, and the nanotwins in the film have twin planes that are all (…). The nanotwinned Cr2O3 film exhibits cylindrical twins on the surface; two twin boundaries with different atomic structures are formed in the nanotwinned Cr2O3 film, one of which is ferromagnetically coupled and has a non-zero net magnetic moment, thus causing the nanotwinned Cr2O3 film to exhibit room temperature subferromagnetism, forming a nanotwinned Cr2O3 film with room temperature subferromagnetism.

[0008] The specific steps for preparing the room-temperature ferrimagnetic nanotwinned Cr2O3 thin film are as follows:

[0009] First, the SrTiO3(111) single crystal substrate was ultrasonically cleaned in acetone solution for 10 min to dissolve surface organic matter. Then, the cleaned SrTiO3 substrate was transferred to a growth chamber, and a Cr2O3 thin film was grown on the SrTiO3(111) single crystal substrate using a pulsed laser deposition system. The Cr2O3 thin film growth parameters were: growth temperature 650–850℃, laser energy 2.5 J / cm². 2 ~5J / cm 2 Laser frequency 5–10 Hz, oxygen partial pressure 1 × 10⁻⁶ -2 ~10 Pa, target-substrate spacing 8~10 cm; finally, the grown Cr2O3 film is slowly cooled to room temperature at a rate of 10~20 °C / min under growth oxygen pressure to obtain a high-density nanotwinned Cr2O3 film with high quality epitaxy.

[0010] The method for preparing room-temperature ferrimagnetic nanotwinned Cr2O3 thin films uses a target material prepared by vacuum hot pressing sintering of stoichiometric Cr2O3 compounds during the growth of Cr2O3 thin films in a pulsed laser deposition system.

[0011] The method for preparing the room-temperature ferrimagnetic nanotwinned Cr2O3 thin film involves a deposition time of 1 h to 5 h during pulsed laser deposition, resulting in a Cr2O3 thin film thickness of 60 nm to 500 nm.

[0012] The method for preparing room-temperature ferrimagnetic nanotwinned Cr2O3 films produces high-density twins in the nanotwinned Cr2O3 films. Through transmission electron microscopy analysis, the twin planes in the nanotwinned Cr2O3 films are all cylindrical.

[0013] The method for preparing nanotwinned Cr2O3 thin films with room temperature ferrimagnetism generates different types of twin boundaries in the nanotwinned Cr2O3 thin films. Analysis by scanning transmission electron microscopy shows that two types of twin boundaries with different atomic structures are formed in the nanotwinned Cr2O3 thin films.

[0014] The method for preparing the room-temperature ferrimagnetic nanotwinned Cr2O3 film involves measuring the magnetic properties of the nanotwinned Cr2O3 film using a superconducting quantum interference device. The nanotwinned Cr2O3 film exhibits room-temperature ferrimagnetism, which differs from that of bulk antiferromagnetic Cr2O3.

[0015] The method for preparing room-temperature ferrimagnetic nanotwinned Cr2O3 thin films involves two twin boundaries with different atomic structures, one of which is ferromagnetically coupled and has a net magnetic moment, thereby enabling the thin film to exhibit room-temperature ferrimagnetism.

[0016] The design concept of this invention is:

[0017] This invention discovers the correlation between the magnetic coupling of Cr2O3 twin boundaries and the atomic structure of the grain boundaries, elucidating the principle behind the room-temperature ferrimagnetism of high-density nanotwinned Cr2O3 films. First, a SrTiO3(111) single crystal with suitable mismatch and orientation to Cr2O3 is selected as the substrate for film growth. An epitaxial Cr2O3 film of a certain thickness is grown on the substrate using pulsed laser deposition. The structure of the film is controlled by the mismatch between the film and the substrate and by appropriate growth parameters during the deposition process, thereby forming high-density nanotwins within the film. The film contains two types of twin boundaries with different atomic structures, one of which is ferromagnetically coupled and has a net magnetic moment. Magnetic tests using a superconducting quantum interference device (SQI) show that the high-density nanotwinned Cr2O3 film exhibits room-temperature ferrimagnetism. This invention employs pulsed laser deposition to epitaxially grow high-quality room-temperature ferrimagnetic nanotwinned Cr2O3 films on SrTiO3(111) single-crystal substrates. By altering the magnetic coupling at the twin boundaries, unexpected room-temperature ferrimagnetism in antiferromagnetic materials is achieved, broadening the application potential of Cr2O3 films in advanced electromagnetic devices. This method of utilizing nanotwins to modulate the physical properties of materials opens up an effective pathway for promoting the innovation and development of high-performance nanotwinned functional materials and enriches the fabrication technology and theoretical foundation of spintronic devices.

[0018] The advantages and beneficial effects of this invention are:

[0019] 1. This invention proposes a method for preparing nanotwinned Cr2O3 thin films with room temperature ferrimagnetism. This method is simple, efficient, and produces high-quality Cr2O3 thin films with stable performance and obvious magnetic response.

[0020] 2. The growth process of the nanotwinned Cr2O3 thin film with room temperature ferrimagnetism obtained by the present invention is simple, easy to operate and artificially controlled, and the film crystallization quality is high, which can realize large-size mass production.

[0021] 3. The nanotwinned Cr2O3 thin film with room temperature ferrimagnetism obtained by the present invention has excellent chemical and thermal stability and can be applied to spintronic devices used under extreme conditions.

[0022] 4. The room-temperature ferrimagnetic nanotwinned Cr2O3 thin film obtained by this invention has a different magnetic response compared with other antiferromagnetic thin films, which broadens the application potential of antiferromagnetic materials in high-sensitivity spintronic devices such as magnetic random access memory.

[0023] 5. The nanotwinned Cr2O3 thin film with room temperature ferrimagnetism obtained by this invention opens up an effective way to control the physical properties of materials by utilizing nanotwins, and lays the foundation for the innovation and development of nanotwinned magnetoelectric devices. Attached image description:

[0024] Figure 1 The microstructure of nanotwinned Cr2O3 films grown on SrTiO3(111) substrates using a pulsed laser deposition system is shown. Figure (a) is an XRD pattern illustrating the epitaxial relationship between the Cr2O3 film and the substrate, with the x-axis representing the diffraction angle (°) and the y-axis representing the relative intensity (au). Figure (b) is the Cr 2p XPS spectrum showing the +3 valence state of Cr ions in the Cr2O3 film, with the x-axis representing the binding energy (eV) and the y-axis representing the relative intensity (au). Figure (c) is a bright-field TEM image of the grown Cr2O3 film, showing the high-density twins formed in the film. Figure (d) is the selected area electron diffraction pattern corresponding to the bright-field image in Figure (c), indicating the orientation relationship of the nanotwinned Cr2O3 film.

[0025] Figures 2-3 A comparison of the hysteresis loops of nanotwinned Cr₂O₃ thin films and bulk Cr₂O₃ single crystals at 300 K is shown. Figure 2 This is the hysteresis loop of the nanotwinned Cr2O3 thin film. The horizontal axis, MagneticField, represents the external magnetic field strength (Oe), and the vertical axis, Magnetization, represents the magnetic susceptibility (emu / cm). 3 The inset shows a magnified view of the hysteresis loop in the range of -500 Oe to +500 Oe, with a saturation magnetization of 0.003 emu / cm. 3 The coercivity is 80 Oe. The hysteresis loop of the magnetic test results indicates that the thin film exhibits ferrimagnetism at 300 K. Figure 3 The graph shows the response of the magnetic susceptibility of bulk Cr2O3 single crystal to an external magnetic field under the same conditions.

[0026] Figure 4 The microstructure of nanotwinned Cr2O3 films grown on SrTiO3(111) substrates using a pulsed laser deposition system is shown. In Figure (a), the TEM bright-field image of the grown Cr2O3 film shows the high-density twins formed in the film; and Figure (b) is the selected area electron diffraction pattern corresponding to the bright-field image in Figure a, showing the orientation relationship of the nanotwinned Cr2O3 film.

[0027] Figure 5 The microstructure of nanotwinned Cr2O3 films grown on SrTiO3(111) substrates using a pulsed laser deposition system after annealing is shown. Figure (a) is a bright-field TEM image of the annealed Cr2O3 film, showing the presence of high-density twins. Figure (b) is a selected area electron diffraction pattern corresponding to the bright-field image in figure (a), indicating the orientation relationship of the nanotwinned Cr2O3 film. Detailed implementation method:

[0028] In its specific implementation, this invention proposes a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film and its preparation method. A Cr2O3 thin film was grown on a SrTiO3(111) single-crystal substrate using a pulsed laser deposition system. The film forms a high-density nanotwin structure with twin boundaries of two different atomic structures. Ferromagnetic coupling of one of these twin boundaries causes the film to exhibit room-temperature ferrimagnetism. The specific steps are as follows:

[0029] (1) Preparation of Cr2O3 thin film: Cr2O3 thin film was grown on SrTiO3 substrate by pulsed laser deposition system. The specific growth parameters are as follows:

[0030] SrTiO3 single crystals were prepared using the mature flame method. After determining the crystal orientation

[111] , a 10×10×0.5mm single crystal wafer was obtained through mechanical cutting, shaping, and polishing processes to serve as the substrate for thin film growth. The surface roughness of the SrTiO3 single crystal wafer was measured. The target material used was a stoichiometric Cr2O3 compound prepared by vacuum hot pressing sintering. Before film growth, the SrTiO3(111) single crystal substrate was ultrasonically cleaned in acetone solution for 10 min to dissolve surface organic matter. The cleaned SrTiO3 substrate was then rapidly transferred to the deposition chamber to prepare for the next step of film growth. The Cr2O3 film was grown using a pulsed laser deposition system, with a COMPex-201 laser, a wavelength of 248 nm, a pulse width of 25 ns, and a growth frequency that could be continuously adjusted within the range of 1 Hz to 10 Hz. During the growth process, the O2 partial pressure was maintained at 1 × 10⁻⁶. -2 The Pa level was ~10, the growth temperature was 650~850℃, and the laser energy was 2.5J / cm². 2 ~5J / cm 2 The laser bombardment frequency of the Cr2O3 target was 5-10 Hz (the target material used was a stoichiometric Cr2O3 compound prepared by vacuum hot pressing sintering process), the distance between the substrate and the target was 8-10 cm, the growth time was 1-5 h, and the thickness of the grown Cr2O3 film was 60 nm-500 nm. The growth of high-quality nanotwin epitaxial Cr2O3 film was completed.

[0031] (2) After the growth is completed, the Cr2O3 film is slowly cooled to room temperature under the O2 partial pressure during film growth. The cooling rate is 10℃ / min. At this time, a stable room temperature ferrimagnetic nanotwin Cr2O3 film can be obtained.

[0032] (3) The room temperature ferrimagnetic nanotwin Cr2O3 film grown can be annealed to verify the stability of the nanotwin structure. The annealing temperature is 700℃ and the annealing time is 4h.

[0033] Thus, a room-temperature ferrimagnetic nanotwinned Cr2O3 film was obtained, exhibiting extremely high crystallinity and satisfying a favorable stoichiometry. High-density twinning of the film could be observed using transmission electron microscopy, confirming the twinning relationship. The twinning density was expressed as the number of twin boundaries per unit length along the statistical cross-section, ranging from 60 to 150 twins / μm. Due to the high quality, good epitaxiality, uniform composition, and stable performance of the Cr2O3 film grown on the SrTiO3 substrate, it holds promise for large-size and mass production.

[0034] The present invention will now be described in further detail with reference to embodiments and accompanying drawings.

[0035] Example 1

[0036] like Figures 1-3 As shown in this embodiment, a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film and its preparation method are as follows:

[0037] First, in this embodiment, a high-quality epitaxial nanotwinned Cr2O3 thin film was prepared using a pulsed laser deposition system. Before growing the Cr2O3 film, the SrTiO3(111) single-crystal substrate was ultrasonically cleaned in acetone solution for 10 min to dissolve and remove surface organic matter. The Cr2O3 film growth parameters were: growth temperature 750℃, pulsed laser energy 2.5 J / cm². 2 The pulse frequency was 5 Hz. A focused high-energy laser bombarded a Cr₂O₃ target, causing the atomic layer on the target surface to be stripped, forming a plasma plume. The plasma plume diffused into the substrate, with the distance between the substrate and the target maintained at 8 cm. The plasma plume combined with the atoms on the substrate surface to ultimately form a high-quality Cr₂O₃ thin film. Growth was carried out for 1 hour in an O₂ atmosphere with a partial pressure of 1 Pa, resulting in a film thickness of 60 nm. After the Cr₂O₃ film growth was complete, it was slowly cooled to room temperature at a growth oxygen pressure of 1 Pa at a cooling rate of 10 °C / min. The crystallinity, phase structure, chemical valence state, microstructure, and atomic and electronic structure of the film were characterized using high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. High-density nanotwins were found to form in the high-quality epitaxial Cr₂O₃ film. These nanotwin films contained two twin boundaries with different atomic structures, and the twin boundaries maintained the same chemical valence state as the bulk region. In this embodiment, the nanotwin density in the Cr2O3 thin film is 60–150 nanotwins / μm.

[0038] Subsequently, the magnetism of the thin film was tested using a superconducting quantum interference device (SQU), and compared with that of bulk Cr₂O₃ single crystals. It was found that the Cr₂O₃ thin film exhibited room-temperature ferrimagnetism different from that of the bulk Cr₂O₃ single crystal. This is related to the atomic structure of the twin boundaries. Analysis revealed that among the two twin boundaries with different atomic structures, one type of twin boundary is ferromagnetically coupled and possesses a net magnetic moment, which is the reason for the room-temperature ferrimagnetism of the high-density nanotwinned Cr₂O₃ thin film. This provides an effective way to control the physical properties of materials using nanotwins, laying the foundation for the innovation and development of nanotwinned magnetoelectric devices.

[0039] Example 2

[0040] like Figure 4 As shown in this embodiment, a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film and its preparation method are as follows:

[0041] First, in this embodiment, a high-quality epitaxial nanotwinned Cr2O3 thin film was prepared using a pulsed laser deposition system. Before growing the Cr2O3 film, the SrTiO3(111) single-crystal substrate was ultrasonically cleaned in acetone solution for 10 min to dissolve and remove surface organic matter. The Cr2O3 film growth parameters were: growth temperature 850℃, pulsed laser energy 5 J / cm². 2 The pulse frequency was 10 Hz. A focused high-energy laser bombarded a Cr₂O₃ target, causing the atomic layer on the target surface to be stripped, forming a plasma plume. The plasma plume diffused into the substrate, with a 10 cm distance between the substrate and the target. The plasma plume bonded with the atoms on the substrate surface, ultimately forming a high-quality Cr₂O₃ thin film. Growth was carried out for 4.5 h at an O₂ partial pressure of 1 Pa, achieving a film thickness of 500 nm. After the Cr₂O₃ film growth was complete, it was slowly cooled to room temperature at a growth oxygen pressure of 1 Pa at a cooling rate of 20 °C / min. The crystallinity, phase structure, chemical valence state, microstructure, and atomic and electronic structure of the film were characterized using high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. High-density nanotwins were found to form in the high-quality epitaxial Cr₂O₃ film. These nanotwin films contained two twin boundaries with different atomic structures, and the twin boundaries maintained the same chemical valence state as the bulk region. In this embodiment, the nanotwin density in the Cr2O3 thin film is 80–150 nanotwins / μm.

[0042] Subsequently, the magnetism of the thin film was tested using a superconducting quantum interference device (SQU), and compared with that of a bulk Cr₂O₃ single crystal and a thinner Cr₂O₃ thin film from Example 1. It was found that the nanotwinned Cr₂O₃ thin film grown in this example still exhibited room-temperature ferrimagnetism different from that of the bulk Cr₂O₃ single crystal, and its magnetization was higher than that of the thinner Cr₂O₃ thin film in Example 1. This is related to the atomic structure of the twin boundaries. Analysis revealed that among the two twin boundaries with different atomic structures, one type of twin boundary is ferromagnetically coupled and has a net magnetic moment, which is the reason for the room-temperature ferrimagnetism of the high-density nanotwinned Cr₂O₃ thin film. This provides an effective way to control the physical properties of materials using nanotwins, laying the foundation for the innovation and development of nanotwinned magnetoelectric devices.

[0043] Example 3

[0044] like Figure 5 As shown in this embodiment, a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film and its preparation method are as follows:

[0045] First, in this embodiment, a high-quality epitaxial nanotwinned Cr2O3 thin film was prepared using a pulsed laser deposition system. Before growing the Cr2O3 film, the SrTiO3(111) single-crystal substrate was ultrasonically cleaned in acetone solution for 10 min to dissolve and remove surface organic matter. The Cr2O3 film growth parameters were: growth temperature 650℃, pulsed laser energy 3 J / cm². 2 The pulse frequency was 7 Hz. A focused high-energy laser bombarded a Cr2O3 target, causing the atomic layer on the target surface to be stripped away, forming a plasma plume. This plasma plume diffused into the substrate, with the distance between the substrate and the target maintained at 10 cm. The plasma plume bonded with the atoms on the substrate surface, ultimately forming a high-quality Cr2O3 thin film. This process was carried out at an O2 partial pressure of 1 × 10⁻⁶. -2 The film was grown at an oxygen pressure of 1 × 10⁻⁶ Pa for 2 hours, achieving a thickness of 130 nm. After the Cr₂O₃ film growth was complete, the growth oxygen pressure was increased to 1 × 10⁻⁶ Pa. -2 The film was slowly cooled to room temperature at a rate of 20 °C / min under a Pa atmosphere. The crystallinity, phase structure, chemical valence state, microstructure, and atomic and electronic structure of the film were characterized using high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. High-density nanotwins were found to form in the high-quality epitaxial Cr₂O₃ film. Two types of twin boundaries with different atomic structures were formed within this nanotwin film, and the twin boundaries maintained the same chemical valence state as the bulk region. In this embodiment, the nanotwin density in the Cr₂O₃ film was 60–100 nanotwins / μm.

[0046] Subsequently, the magnetism of the thin film was tested using a superconducting quantum interference device (SQI), and compared with that of bulk Cr₂O₃ single crystals. It was found that the Cr₂O₃ thin film exhibited room-temperature ferrimagnetism different from that of the bulk Cr₂O₃ single crystals. This is related to the structure of the twin boundaries. Analysis revealed that among the two twin boundaries with different atomic structures, one type of twin boundary is ferromagnetically coupled and possesses a net magnetic moment, which is the reason for the room-temperature ferrimagnetism of the high-density nanotwinned Cr₂O₃ thin film.

[0047] Next, the Cr2O3 thin film with room-temperature ferrimagnetism was annealed in air at 700℃ for 4 hours using a muffle furnace to assess the stability of the nanotwin structure. After annealing, the film was cooled to room temperature in the furnace. Transmission electron microscopy was used to characterize the film's mass, phase structure, microstructure, and atomic and electronic structure. It was found that even with reduced thickness, the annealed Cr2O3 film maintained a high-density twin structure and exhibited twin boundaries with two different atomic structures. This broadens the application potential of Cr2O3 thin films in high-sensitivity spintronic devices such as magnetic random access memory, provides an effective way to control the physical properties of materials using nanotwins, and lays the foundation for the innovation and development of nanotwin magnetoelectric devices.

[0048] like Figure 1 The image shows the microstructure of a high-density nanotwinned Cr2O3 film grown on a SrTiO3(111) substrate using a pulsed laser deposition system. Figure (a) shows the X-ray diffraction (XRD) spectrum of the Cr2O3 film and the substrate. The diffraction peaks in the figure indicate that the Cr2O3 film is epitaxially grown, without diffraction peaks from other crystal planes or impurities. Figure (b) shows the X-ray photoelectron spectroscopy (XPS) spectrum of Cr2p in the Cr2O3 film. The standard +3 valence Cr2p peak in the figure proves the single valence state and high-quality growth of the film. Figure (c) shows the bright-field TEM image of the grown Cr2O3 film. The high density of light and dark contrast in the image indicates the formation of high-density twins in the film. Figure (d) shows the selected area electron diffraction (SED) spectrum corresponding to the bright-field image in Figure (c). The calibration of the diffraction spectrum can prove the nanotwin structure in the Cr2O3 film, obtain the orientation relationship of the twins, and determine whether all twin planes in the film are (…). The high-density nanotwin structure is the result of the combined effects of lattice mismatch and orientation relationship between the SrTiO3 substrate and the Cr2O3 film, as well as appropriate growth parameter control during pulsed laser deposition.

[0049] like Figures 2-3 The image shows a comparison of the hysteresis loops of nanotwinned Cr2O3 films and bulk Cr2O3 single crystals at 300K. Figure 2This is the hysteresis loop of a high-density nanotwinned Cr2O3 thin film. The horizontal axis, MagneticField, represents the external magnetic field strength (Oe), and the vertical axis, Magnetization, represents the magnetic susceptibility (emu / cm). 3 The illustration shows a magnified view of the hysteresis loop in the range of -500 Oe to +500 Oe. Figure 3 The graph shows the response of the magnetic susceptibility of bulk Cr2O3 single crystals to an external magnetic field under the same conditions. A comparison clearly shows that the bulk Cr2O3 single crystals exhibit intrinsic antiferromagnetism, displaying a linear magnetization curve with paramagnetic characteristics at 300K. However, the high-density nanotwinned Cr2O3 thin film exhibits a significant hysteresis loop and a magnetic susceptibility of 0.003 emu / cm². 3 The saturation magnetization and coercivity of 80 Oe are related to the high-density twins in the film. Among the two twin boundaries with different atomic structures, one twin boundary is ferromagnetically coupled and has a net magnetic moment, which is the reason for the room-temperature subferromagnetism of the high-density nanotwinned Cr2O3 film.

[0050] like Figure 4 The image shows the microstructure of a high-density nanotwinned Cr2O3 film grown on a SrTiO3(111) substrate using a pulsed laser deposition system. Figure (a) shows a bright-field TEM image of the 500 nm thick Cr2O3 film, where the contrast indicates the formation of high-density twins. Figure (b) shows the selected area electron diffraction (SED) spectrum corresponding to the bright-field image in Figure (a), confirming the nanotwinned structure in the 500 nm thick Cr2O3 film, obtaining the orientation relationship of the twins, and determining that all twin planes in the film are (…). The high-density nanotwin structure is the result of the combined effects of lattice mismatch and orientation relationship between the SrTiO3 substrate and the Cr2O3 film, as well as appropriate growth parameter control during pulsed laser deposition.

[0051] like Figure 5 As shown, the microstructure of a high-density nanotwinned Cr2O3 film grown on a SrTiO3(111) substrate using a pulsed laser deposition system after annealing is illustrated. Figure (a) shows a bright-field TEM image of the Cr2O3 film after annealing at 700℃ for 4 hours, where the contrast indicates the formation of high-density twins. Figure (b) shows the selected area electron diffraction pattern corresponding to the bright-field image in figure (a), indicating that the film retains its twinned structure after annealing, demonstrating the structural stability of this room-temperature ferrimagnetic high-density nanotwinned Cr2O3 film.

[0052] The above results demonstrate that this invention achieves the growth of room-temperature ferrimagnetic high-density nanotwinned Cr2O3 films on SrTiO3(111) substrates using a pulsed laser deposition system. Under the combined effects of lattice mismatch and orientation relationship between the substrate and the film, as well as the control of growth parameters during pulsed laser deposition, high-density nanotwins are generated in the Cr2O3 film, forming two types of twin boundaries with different atomic structures. One type of twin boundary is ferromagnetically coupled and possesses a net magnetic moment, resulting in room-temperature ferrimagnetism in the nanotwinned Cr2O3 film. The fabrication process of this room-temperature ferrimagnetic high-density nanotwinned Cr2O3 film is simple, its performance is stable, and it is easy to control. This opens up an effective way to utilize nanotwins to control the physical properties of materials and lays the foundation for the innovation and development of nanotwinned magnetoelectric devices.

Claims

1. A nanotwinned Cr2O3 thin film exhibiting room-temperature ferrimagnetism, characterized in that, Cr2O3 is an intrinsically antiferromagnetic oxide material with excellent insulation and a unique room-temperature magnetoelectric effect, making it suitable for spintronic devices. Nanotwins significantly affect the mechanical and physicochemical properties of materials, thus Cr2O3 films with nanotwin structures are chosen as ideal magnetoelectric materials. Cr2O3 films were grown on SrTiO3(111) single-crystal substrates using pulsed laser deposition. By adjusting the growth parameters, high-density nanotwins were induced in the grown Cr2O3 films, and the twin planes of the nanotwins in the films were all... The nanotwinned Cr2O3 film exhibits cylindrical twins; two twin boundaries with different atomic structures are formed in the nanotwinned Cr2O3 film, one of which is ferromagnetically coupled and has a non-zero net magnetic moment, thus causing the nanotwinned Cr2O3 film to exhibit room temperature subferrimagnetism, forming a nanotwinned Cr2O3 film with room temperature subferrimagnetism.

2. A method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film as described in claim 1, characterized in that, The specific steps are as follows: First, the SrTiO3(111) single crystal substrate was ultrasonically cleaned in acetone solution for 10 min to dissolve surface organic matter. Then, the cleaned SrTiO3 substrate was transferred to a growth chamber, and a Cr2O3 thin film was grown on the SrTiO3(111) single crystal substrate using a pulsed laser deposition system. The Cr2O3 thin film growth parameters were: growth temperature 650–850℃, laser energy 2.5 J / cm². 2 ~5J / cm 2 Laser frequency 5–10 Hz, oxygen partial pressure 1 × 10⁻⁶ -2 ~10 Pa, target-substrate spacing 8~10 cm; finally, the grown Cr2O3 film is slowly cooled to room temperature at a rate of 10~20 °C / min under growth oxygen pressure to obtain a high-density nanotwinned Cr2O3 film with high quality epitaxy.

3. The method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film according to claim 2, characterized in that, In the process of growing Cr2O3 thin films using a pulsed laser deposition system, the target material used is a stoichiometric Cr2O3 compound prepared by a vacuum hot pressing sintering process.

4. The method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film according to claim 2, characterized in that, During pulsed laser deposition, the deposition time is 1h to 5h, and the thickness of the grown Cr2O3 film is 60nm to 500nm.

5. The method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film according to claim 2, characterized in that, High-density twins are generated in nanotwinned Cr2O3 films. Through transmission electron microscopy analysis, the twin planes in the nanotwinned Cr2O3 films are all cylindrical.

6. The method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film according to claim 2, characterized in that, Different types of twin boundaries are generated in nanotwinned Cr2O3 films. Scanning transmission electron microscopy analysis revealed that two types of twin boundaries with different atomic structures are formed in the nanotwinned Cr2O3 films.

7. The method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film according to claim 2, characterized in that, The magnetic properties of nanotwinned Cr2O3 films were measured using a superconducting quantum interference device. The nanotwinned Cr2O3 films exhibited room-temperature ferrimagnetism, which is different from that of bulk antiferromagnetic Cr2O3.

8. The method for preparing a room-temperature ferrimagnetic nanotwinned Cr2O3 thin film according to claim 2, characterized in that, In two twin boundaries with different atomic structures, one twin boundary is ferromagnetically coupled and has a net magnetic moment, thus making the thin film exhibit room-temperature subferromagnetism.

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