BaM seed crystal as well as preparation method and application thereof

Abstract

The invention provides a BaM seed crystal as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing and melting BaCO3, Fe2O3 and K2CO3 serving as a fluxing agent to obtain a uniform melt; the melt is subjected to heat preservation and staged cooling, seed crystals are spontaneously nucleated and grow, and initial seed crystals are obtained; the initial seed crystals are separated from the solidified melt and cleaned; and carrying out secondary growth on the cleaned initial seed crystal to obtain the BaM seed crystal. The initial seed crystal is obtained through melting and slow cooling, then the initial seed crystal is subjected to secondary growth, and finally the BaM seed crystal is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single crystal thin film seed crystal, and particularly relates to a BaM seed crystal and a preparation method and application thereof. BACKGROUND

[0002] With the rapid iteration of 5G communication, millimeter wave radar and other frontier technologies towards high frequency (1-100 GHz), electronic devices have put forward more stringent requirements on the performance of magnetic materials - not only need to withstand the rapid flipping of magnetic moment under high frequency signal, but also need to maintain extremely low magnetic loss and high cutoff frequency. However, the traditional polycrystalline magnetic core material has exposed significant shortcomings in this scenario: in a high frequency environment, the domain flipping frequency is accelerated, and the grain boundaries in the polycrystalline structure will exacerbate the magnetic moment disorder, resulting in the superposition of magnetic hysteresis loss and eddy current loss, and the magnetic loss rises sharply, which cannot meet the core needs of the device for low loss and high cutoff frequency, and new type of magnetic material is urgently needed to break through the technical bottleneck. BaM (barium ferrite) single crystal thin film, with its unique magnetic properties, has become an ideal candidate material in the field of high frequency and information. In the field of high frequency gyromagnetic devices, the low magnetic damping coefficient of BaM single crystal thin film (which can effectively reduce the magnetic moment relaxation loss under high frequency) and the high spin wave cutoff frequency (which is suitable for 1-100 GHz high frequency signal transmission) make it show irreplaceable application advantages: compared with traditional bulk ceramic devices, the two-dimensional layered structure of BaM single crystal thin film is more conducive to device integration, and the size of small-sized gyromagnetic devices such as isolators and circulators can be reduced to 1 / 10 of that of traditional products, and its low magnetic loss feature can accurately meet the energy efficiency requirements of 5G base stations for high frequency signal processing, significantly improving the signal transmission efficiency. In the field of information storage, the vertical magnetic recording technology is facing the constraint of "superparamagnetic limit" - when the magnetic recording unit size is reduced to nanoscale, thermal disturbance will cause the magnetic moment stability to decrease, and it is impossible to store data stably, and high vertical magnetic anisotropy is the key to break through this limit. The vertical magnetic anisotropy energy density of BaM single crystal thin film is much higher than that of the current mainstream CoCrPt alloy thin film (the vertical magnetic anisotropy energy density of the latter is usually one order of magnitude lower than that of BaM), which can effectively enhance the magnetic moment stability of the magnetic recording unit, and theoretically realize an ultra-high storage density of more than 10 Tb per square inch, providing core material support for the research and development of the next generation of high-density magnetic storage devices. In addition, the semi-metallic property of BaM single crystal thin film (only spin-up electrons participate in conduction, and the spin polarization rate is close to 100%) also opens up a new path for the development of spintronic devices. In spin injection, magnetic tunnel junction and other devices, high spin polarization rate is the core prerequisite for improving spin transport efficiency and reducing spin loss, and the semi-metallic property of BaM exactly meets this demand, which can effectively reduce the power consumption of the device, and provides a new material selection for the research and development of low-power spin logic devices, magnetic random access memory (MRAM) and other new electronic devices.

[0003] Despite the promising applications of BaM single-crystal thin films, their fabrication technology still faces multiple challenges. Currently, the mainstream fabrication methods focus on radio frequency magnetron sputtering and pulsed laser deposition, but these two methods share common defects: the lattice constant of BaM differs significantly from that of commonly used substrates (such as sapphire and silicon substrates), with lattice mismatch generally exceeding 5%. This forces the atomic arrangement to adapt to the substrate lattice during film growth, generating significant internal stress. This internal stress further induces film defects (such as dislocations and microcracks), which not only reduce the crystallinity of the film but also result in extremely strong dispersion of magnetic properties (such as perpendicular magnetic anisotropy and magnetic loss), making it only suitable for basic magnetic property testing and unable to meet the application requirements of practical devices. To address the lattice mismatch problem, researchers proposed an improved approach by introducing a buffer layer between the substrate and the thin film. The buffer layer's lattice constant lies between that of the substrate and BaM, significantly reducing interfacial mismatch through a "lattice transition" effect. This provides an ordered growth template for BaM atoms, leading to the fabrication of highly crystalline BaM single-crystal thin films with uniform magnetic properties. However, this method also has significant limitations: the preparation of the buffer layer requires additional processing steps (such as precise control of sputtering power, growth temperature, and atmosphere), and demands extremely high purity and lattice uniformity from the buffer layer material, resulting in a significant increase in overall fabrication costs and hindering large-scale mass production. From a technical feasibility perspective, liquid-phase epitaxy is a better choice for achieving high-quality epitaxial growth of BaM single-crystal thin films—this method has a relatively low growth temperature and stronger interfacial bonding between the film and the substrate, effectively reducing film defects. However, the core bottleneck of liquid-phase epitaxy lies in "substrate matching": if the lattice mismatch of the BaM substrate is high, even in a liquid environment, film growth will still suffer from problems such as cracking and magnetic property attenuation due to interfacial stress. Currently, ideal substrates suitable for BaM are still in the exploratory stage. If seed crystals or substrates with the same hexagonal crystal structure and close lattice constant as BaM (such as high-quality BaM seed crystals or hexagonal MgO single-crystal substrates) can be used, the lattice mismatch problem can be fundamentally solved, achieving high-quality, low-cost growth of BaM single-crystal thin films. However, the preparation technology for such substrates is not yet mature and remains a key obstacle restricting the industrialization of BaM. Summary of the Invention

[0004] This invention addresses the challenge of substrate matching in BaM single-crystal thin films by proposing a method for preparing BaM thin films using BaM seed crystals.

[0005] The technical solution adopted in this invention is as follows: A method for preparing homoepitaxial BaM seed crystals, comprising: Step 1, preparing the melt: BaCO3, Fe2O3 and K2CO3 as flux are mixed and melted to obtain a homogeneous melt; Step 2, Initial growth of seed crystal: The melt is kept at a constant temperature and cooled in stages to allow the seed crystal to nucleate and grow spontaneously, thus obtaining the initial seed crystal; Step 3: Separate and clean the seed crystal: Separate and clean the initial seed crystal from the solidified melt; Step 4, Secondary growth of seed crystal: The cleaned initial seed crystal is subjected to secondary growth to obtain BaM seed crystal.

[0006] In step 1, the raw material molar ratio used in the melt is: BaCO3 4%~6%, Fe2O3 6%~24%, and K2CO3 70%~90%. The mixing step includes: placing BaCO3, Fe2O3, and K2CO3 as a flux in a tumbling barrel for mixing; wherein the mixing time is 10~14 hours; the melting step includes: heating to 1150℃ for melting and stirring; wherein the melting time is 10~14 hours.

[0007] In step 2, the staged cooling step includes cooling at a rate of 0.005~5℃ / min within a temperature range of 1150~25℃. Specifically, the cooling at a rate of 0.005~5℃ / min within the 1150~25℃ temperature range includes: a cooling rate of 2~5℃ / min within the 1150~1125℃ temperature range; a cooling rate of 0.005~0.02℃ / min within the 1125~1020℃ temperature range; a cooling rate of 0.05~1℃ / min within the 1020~920℃ temperature range; and a cooling rate of 1~5℃ / min within the 920~25℃ temperature range. The heat preservation step includes maintaining the temperature at 1150℃ for 10~14 hours.

[0008] In step 3, the cleaning step includes: using dilute nitric acid with a volume ratio of 1:1 to clean the solidified melt containing the initial seed crystal at a temperature of 60~90°C until the initial seed crystal is completely separated from the melt.

[0009] In step 4, the temperature for the secondary growth is 1080~1020℃, and the rotation speed is 50~70 rpm / min. After the secondary growth step, the process further includes cleaning, grinding, and polishing the seed crystal obtained after the secondary growth; the cleaning is performed using dilute nitric acid and deionized water, respectively, and the grinding and polishing rotation speeds are 30~50 rpm / min.

[0010] The present invention also provides a BaM seed crystal, which is prepared by the above-described method for preparing homoepitaxial BaM seed crystal.

[0011] The present invention also provides an application of BaM seed crystals in the preparation of thin film products, which are used in high-frequency rotating devices.

[0012] The beneficial effects of this invention are as follows: 1. This invention provides a method for preparing homoepitaxial BaM seed crystals, wherein an initial seed crystal is obtained by melting and slowly cooling, and then the initial seed crystal is subjected to secondary growth to finally obtain BaM seed crystals.

[0013] 2. Compared with the complex process of existing technologies that require multiple adjustments to equipment and changes to the reaction environment, the melting and secondary growth of this invention can be completed in the same furnace, resulting in high equipment utilization. At the same time, the parameters of each step can be precisely controlled by an automated control system (such as the heating rate), reducing human error and significantly reducing the cost and risk of industrial production.

[0014] 3. The raw materials used in this invention are conventional high-purity BaCO3 and Fe2O3 (purity ≥99.9%), without the need for special rare raw materials; and the core equipment are all industry-standard equipment, without the need for customized modifications. The equipment investment cost is significantly reduced compared to dedicated equipment solutions, and the overall preparation cost is significantly reduced compared to existing technologies. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the method for preparing homoepitaxial BaM seed crystals according to the present invention; Figure 2 This is a photograph of the BaM seed crystal prepared in Example 1 of the present invention. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0017] This invention provides a method for preparing homoepitaxial BaM seed crystals, such as... Figure 1 As shown, it includes: Step 1: Prepare the melt: Mix and melt BaCO3, Fe2O3 and K2CO3 as a flux to obtain a homogeneous melt.

[0018] In this embodiment, the molar ratio of the raw materials used in the melt is as follows: BaCO3 4%~6%, Fe2O3 6%~24%, and K2CO3 70%~90%. For example, BaCO3 is 5%, 5.5%, and 5.8%; Fe2O3 is 12%, 13%, 14%, 15%, and 16%; and K2CO3 is 75%, 80%, and 85%.

[0019] In this embodiment, the mixing step includes: accurately weighing BaCO3, Fe2O3, and K2CO3 as a flux are placed in a tumbler for mixing for 10-14 hours. For example, mixing for 11 hours, 12 hours, or 13 hours.

[0020] In this embodiment, the melting step includes: after mixing, placing the mixture in a crucible, heating it to 1150°C to melt, and stirring. Melting for 10-14 hours, for example, 11, 12, or 13 hours. Stirring for 10-14 hours, for example, holding at the temperature for 11, 12, or 13 hours.

[0021] Step 2, Initial growth of seed crystals: The melt is kept at a constant temperature and cooled in stages to allow the seed crystals to nucleate and grow spontaneously, thus obtaining the initial seed crystals.

[0022] In step 2, the seed crystal is first grown initially, and then a staged cooling method is used to promote spontaneous nucleation and gradual growth of the crystal to form the initial seed crystal.

[0023] In this embodiment, the heat preservation step includes: maintaining the temperature at 1150°C for 10 to 14 hours. For example, maintaining the temperature for 11 hours, 12 hours, or 13 hours.

[0024] In this embodiment, the staged cooling step includes cooling at a rate of 0.005 to 5 °C / min within a temperature range of 1150 to 25 °C. Specifically, the cooling step within the 1150 to 25 °C temperature range at a rate of 0.005 to 5 °C / min includes: using a cooling rate of 2 to 5 °C / min within a temperature range of 1150 to 1125 °C, which is above the phase transition temperature and will not result in a phase transition. For example, the cooling rate could be 3 °C / min or 4 °C / min. In the 1125 to 1020 °C temperature range, a cooling rate of 0.005 to 0.02 °C / min is used. This temperature range is within the critical range for phase transition crystallization, therefore an extremely low cooling rate is used to ensure spontaneous nucleation and gradual growth of the crystal. For example, the cooling rate could be 0.008 °C / min or 0.01 °C / min. Within the temperature range of 1020–920℃, a cooling rate of 0.05–1℃ / min is used. Within this range, the melt gradually solidifies; excessively rapid cooling will cause the already crystallized crystals to break and splatter. For example, cooling rates of 0.06℃ / min or 0.08℃ / min are suitable. Within the temperature range of 920–25℃, a cooling rate of 1–5℃ / min is used. Within this range, the melt has already solidified, and a faster cooling rate can be used. For example, cooling rates of 3℃ / min or 4℃ / min are suitable.

[0025] Step 3: Separate and clean the seed crystal: Separate and clean the initial seed crystal from the solidified melt.

[0026] In this embodiment, the cleaning steps include: using dilute nitric acid at a volume ratio of 1:1 to clean the solidified melt containing the initial seed crystal at a temperature of 60~90°C until the initial seed crystal is completely separated from the melt. The seed crystal is then cleaned with dilute nitric acid, and finally cleaned with deionized water.

[0027] Step 4, Secondary growth of seed crystal: The cleaned initial seed crystal is subjected to secondary growth to obtain BaM seed crystal.

[0028] In this embodiment, the same melt is prepared according to step (1), and the secondary growth temperature is 1080~1020℃, and the rotation speed is 50~70 rpm / min. Specifically, the cleaned seed crystal is fixed on the fixture and slowly placed into the crucible. Growth begins when the surface of the seed crystal comes into contact with the melt. The growth temperature is 1080~1020℃, and the rotation speed is 50~70 rpm / min. After the growth is completed, the seed crystal is removed at a rate of 5~20 mm / min and cleaned with dilute nitric acid and deionized water respectively.

[0029] In this embodiment, after the secondary growth step, the process further includes cleaning, grinding, and polishing the seed crystal obtained after the secondary growth; the cleaning is performed using dilute nitric acid and deionized water, respectively. The grinding and polishing speeds are 30-50 rpm / min. For example, the speeds can be 35 rpm / min, 40 rpm / min, or 45 rpm / min. Specifically, the cleaned seed crystal is first subjected to double-sided grinding to flatten its surface, using diamond grinding fluid, with the grinding disc rotating at 30-50 rpm / min; then, the seed crystal is polished, with the surface smoothed by the corrosive effect of the chemical polishing fluid and the friction of the polishing cloth, with the polishing disc rotating at 30-50 rpm / min; finally, the seed crystal is cleaned with deionized water.

[0030] The present invention also provides a BaM seed crystal, which is prepared by the above-described method for preparing homoepitaxial BaM seed crystal.

[0031] The present invention also provides an application of BaM seed crystals in the preparation of thin film products, which are used in high-frequency rotating devices.

[0032] The present invention will be described in detail below through embodiments and experimental examples. However, these are merely examples and do not limit the present invention in any way.

[0033] Example 1 This invention provides a method for preparing homoepitaxial BaM seed crystals, comprising the following steps: (1) Preparation of melt: Using BaCO3 and Fe2O3 as raw materials and K2CO3 as flux, prepare a total mass of 2kg of raw materials, in which the molar amount of BaCO3 is 5%, the molar amount of Fe2O3 is 12%, and the molar amount of K2CO3 is 83%. Calculate the mass of BaCO3, Fe2O3, and K2CO3 respectively, weigh them accurately, and place them in a rolling barrel for mixing for 12h. After mixing, put them in a crucible, heat to 1150℃ to melt and stir for 12h to obtain a uniform melt.

[0034] (2) Initial growth of seed crystals: The seed crystals were kept at 1150℃ for 12 hours, and then a segmented, slow cooling method was adopted to allow the seed crystals to spontaneously nucleate and gradually grow. The specific process was as follows: a staged cooling method was adopted to allow the seed crystals to spontaneously nucleate and gradually grow: a cooling rate of 3℃ / min was adopted in the temperature range of 1150~1125℃. This temperature range is higher than the phase transition temperature and no phase transition will occur; a cooling rate of 0.008℃ / min was adopted in the temperature range of 1125~1020℃. The cooling rate is crucial in this temperature range, which is a critical zone for phase transformation crystallization. Therefore, an extremely low cooling rate is used to ensure spontaneous nucleation and gradual growth of the crystals. Within the temperature range of 1020~920℃, a cooling rate of 0.5℃ / min is used. In this range, the melt gradually solidifies, and an excessively fast cooling rate will cause the already crystallized crystals to break and splatter. Within the temperature range of 920~25℃, a cooling rate of 3℃ / min is used. In this range, the melt has already solidified, and a faster cooling rate can be used.

[0035] (3) Separation and cleaning of seed crystals: The melt containing seed crystals is repeatedly cleaned with dilute nitric acid at a volume ratio of 1:1 at 80°C until the seed crystals are completely separated from the melt. Then, the seed crystals are cleaned with dilute nitric acid and finally cleaned with deionized water.

[0036] (4) Secondary growth of seed crystal: Prepare the same melt in the same way as in step (1), fix the cleaned seed crystal on the platinum fixture, slowly put it into the crucible, and start growth when the surface of the seed crystal comes into contact with the melt. The growth temperature is 1045℃ and the rotation speed is 55rpm / min. After the growth is completed, take out the seed crystal at a speed of 5mm / min and clean it with dilute nitric acid and deionized water respectively.

[0037] (5) Processing of seed crystals: First, the cleaned seed crystals are ground on both sides to flatten their surface. Diamond polishing fluid is used and the speed of the polishing disc is 40 rpm / min. Then, the seed crystals are polished. The surface of the seed crystals is made smooth by the corrosive effect of the chemical polishing fluid and the friction of the polishing cloth. The speed of the polishing disc is 40 rpm / min. Finally, the seed crystals are cleaned with deionized water.

[0038] like Figure 2The image shown is a physical picture of the BaM seed crystal prepared in Example 1.

[0039] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing homoepitaxial BaM seed crystals, characterized in that, include: Step 1, preparing the melt: BaCO3, Fe2O3 and K2CO3 as flux are mixed and melted to obtain a homogeneous melt; Step 2, Initial growth of seed crystal: The melt is kept at a constant temperature and cooled in stages to allow the seed crystal to nucleate and grow spontaneously, thus obtaining the initial seed crystal; Step 3: Separate and clean the seed crystal: Separate and clean the initial seed crystal from the solidified melt; Step 4, Secondary growth of seed crystal: The cleaned initial seed crystal is subjected to secondary growth to obtain BaM seed crystal.

2. The preparation method according to claim 1, characterized in that, The staged cooling process includes cooling at a rate of 0.005 to 5°C / min within a temperature range of 1150 to 25°C.

3. The preparation method according to claim 2, characterized in that, The cooling process within the temperature range of 1150~25℃ at a cooling rate of 0.005~5℃ / min includes: A cooling rate of 2 to 5 °C / min is used within the temperature range of 1150 to 1125 °C. A cooling rate of 0.005~0.02℃ / min was used in the temperature range of 1125~1020℃; A cooling rate of 0.05 to 1℃ / min is used within the temperature range of 1020 to 920℃; Within a temperature range of 920~25℃, a cooling rate of 1~5℃ / min is adopted.

4. The preparation method according to claim 1, characterized in that, The raw material molar ratio used in the melt is: BaCO3 4%~6%, Fe2O3 6%~24%, and K2CO3 70%~90%.

5. The preparation method according to claim 1, characterized in that, The mixing step includes: placing BaCO3, Fe2O3 and K2CO3 as a flux in a rolling mill for mixing; wherein the mixing time is 10-14 hours; The melting step includes: heating to 1150°C for melting and stirring; wherein the melting time is 10-14 hours. The heat preservation step includes: maintaining the temperature at 1150℃ for 10 to 14 hours.

6. The preparation method according to claim 1, characterized in that, The cleaning steps include: using dilute nitric acid with a volume ratio of 1:1 to clean the solidified melt containing the initial seed crystal at a temperature of 60~90℃ until the initial seed crystal is completely separated from the melt.

7. The preparation method according to claim 1, characterized in that, The secondary growth temperature is 1080~1020℃, and the rotation speed is 50~70rpm / min.

8. The preparation method according to claim 1, characterized in that, Following the secondary growth step, the method further includes: The seed crystals obtained after secondary growth are cleaned, ground, and polished; the cleaning is performed using dilute nitric acid and deionized water, respectively, and the grinding and polishing are performed at a speed of 30~50 rpm / min.

9. A BaM seed crystal, characterized in that, The BaM seed crystal is prepared by the method for preparing homoepitaxial BaM seed crystal according to any one of claims 1 to 8.

10. The application of BaM seed crystals according to claim 9 in the preparation of thin film products, characterized in that, The thin film product is used in high-frequency rotating devices.

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