CrSb single crystal film and preparation method for preparing staggered magnetic CrSb single crystal film through molecular beam epitaxy

Abstract

The invention belongs to the technical field of preparation means of functional materials, and particularly relates to a CrSb single crystal film and a preparation method for preparing a staggered magnetic CrSb single crystal film through molecular beam epitaxy. The CrSb single crystal thin film sequentially comprises a substrate SiC / a buffer layer CrTe2 / CrSb single crystal thin film from bottom to top, and when the crystal orientation of the CrSb single crystal thin film is (0001), the CrSb single crystal thin film has six-degree symmetry. A Cr source and an Sb source are placed in different evaporation sources respectively, and evaporated Cr and Sb atoms are deposited on the surface of the SiC (111) substrate subjected to surface treatment in an ultrahigh vacuum environment. The deposition rate of Cr atoms is # imgabs0 # / min; the deposition rate ratio of Cr to Sb atoms is 1: 12; and the surface temperature of the SiC (111) substrate is 370 DEG C to 400 DEG C. According to the method, the staggered magnetic CrSb single crystal film is controllably synthesized by controlling the deposition rate of raw materials and the surface temperature of a substrate on the basis of cooperative control among the processes; the staggered magnetic CrSb single crystal film with the hexagonal crystal structure prepared by the method has an atomic-scale flat surface and excellent crystal orderliness, can meet the performance requirements of spintronics device preparation, and is suitable for subsequent scientific research.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation means of functional materials, and particularly relates to a CrSb single crystal thin film and a preparation method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy. Background Art

[0002] As a prospective material for next-generation spintronic devices, antiferromagnets have attracted much attention due to their excellent stability, scalability, and dynamic characteristics. Their unique zero net magnetic moment compensated magnetization characteristics can effectively avoid the interference of external magnetic fields. Thanks to the strong antiferromagnetic exchange coupling, the precession frequency of antiferromagnets can reach the terahertz level, enabling picosecond-level rapid magnetic moment flipping. Although antiferromagnets show great potential in the field of spintronics, their compensated magnetic moment characteristics also pose challenges, such as difficult-to-control antiferromagnetic order and weak magnetoelectric response, which limit the further development of antiferromagnetic spintronics. Recent research has shown that the antiferromagnetic order can be effectively regulated by specific excitation means, triggering strong physical responses. However, the ideal next-generation spintronic materials need to combine the information easy-to-write / read characteristics of ferromagnets and the high stability, high-density storage, and ultrafast spin dynamics characteristics of antiferromagnets - this goal seems full of challenges.

[0003] Recently, based on the symmetry analysis of the non-relativistic spin group, a new class of magnets, alternating magnets, has been discovered, which is juxtaposed with ferromagnets, ferrimagnets, and traditional antiferromagnets. Ordinary collinear antiferromagnets remain invariant under time reversal (T) and space inversion (P) operations, showing high PT symmetry. However, if the non-magnetic atoms in the collinear antiferromagnet are in low-symmetry positions, the system will change under PT operations, that is, the PT symmetry is broken. This is exactly the case for alternating magnets, which show an alternating magnetic order of collinear antiferromagnetism in real space and connect the sublattices of opposite spins through crystal rotation symmetry. The correspondence between real space and reciprocal space leads to the breaking of time reversal symmetry in the electronic band structure, that is, momentum-dependent spin splitting is generated. Therefore, alternating magnets show alternating spin polarization in both real space and reciprocal space, forming a novel magnetic order arrangement. Although they have no macroscopic magnetism, they have spin-split energy bands and show spin transport behaviors similar to ferromagnets. It is worth mentioning that the peak value of spin splitting caused by spin-orbit coupling (SOC) in traditional antiferromagnets is about a few hundred meV, while the spin splitting in alternating magnets can reach 1 eV, exceeding that of traditional antiferromagnets by an order of magnitude. Spin splitting, as a key phenomenon in spintronics, can generate novel effects such as spin-polarized current, spin current, spin Hall effect (SHE), and anomalous Hall effect (AHE).

[0004] Antiferromagnetic CrSb of type A exhibits ferromagnetism within the (0001) plane and antiferromagnetic coupling between planes. Along the c-axis, the triangular arrangements of Sb atoms above and below each Cr sublattice are rotated relative to each other by 60°, resulting in an anisotropic crystal field for each Cr sublattice. Notably, the predicted amplitude of spin splitting in CrSb is as high as 1.2 eV, far greater than the spin splitting caused by SOC. This spin splitting mechanism does not depend on SOC but rather stems from the anisotropic crystal field caused by the low symmetry of non-magnetic atoms, which is a non-relativistic effect. In addition to the spin-split energy bands, the low-symmetry arrangement of Sb atoms also leads to local magnetic anisotropy of Cr atoms and non-zero Berry curvature. This novel symmetry-breaking mechanism provides a new perspective for studying the crystal Hall effect in staggered magnets and also highlights the importance of local magnetic anisotropy caused by non-magnetic atoms in symmetry analysis. Therefore, the novel band spin properties in CrSb are worthy of detailed investigation.

[0005] Current research on the band structure of CrSb mainly focuses on the dissociation of bulk materials, and there are often lattice mismatch problems in the preparation of single-crystal thin films. Therefore, in this invention, molecular beam epitaxy is used to grow CrSb single-crystal thin films on a CrTe2 buffer layer, which not only solves the problem of lattice mismatch but also can change the thickness of CrSb to explore the influence of thickness on its electronic structure. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the object of the present invention can be achieved through the following technical solutions:

[0007] A CrSb single-crystal thin film, the CrSb single-crystal thin film includes a substrate SiC, a buffer layer CrTe2, and a CrSb thin film arranged in sequence from bottom to top; when the crystal orientation of the CrSb thin film is (0001), the CrSb thin film has six-fold symmetry.

[0008] As a preferred embodiment of the present invention, when the crystal orientation of the staggered magnetic CrSb thin film is (0001), a CrTe2 buffer layer is provided between the substrate and the CrSb thin film, and the epitaxial relationship of the CrSb thin film is SiC(111) / / CrTe2(0001) / / CrSb(0001).

[0009] A preparation method for preparing a staggered magnetic CrSb single-crystal thin film by molecular beam epitaxy, the preparation method includes the following steps:

[0010] S1. Place the SiC single-crystal substrate on the sample holder in the growth chamber and anneal the substrate by direct current heating.

[0011] S2. By increasing the current, the annealed SiC single crystal substrate is first rapidly heated and then cooled. This process is repeated 15 times to obtain flash SiC. Subsequently, the temperature is reduced to the growth temperature. The Si in the upper layer of SiC after Flash is evaporated, leaving C atoms. The C atoms form a Graphene phase. Then, using this as a substrate, a buffer layer of CrTe2 thin film and a CrSb single crystal thin film are grown.

[0012] S3. Place Te and Cr in different evaporation sources, raise the temperature, and control the atomic beam flow rate ratio of Cr and Te. During growth, the substrate temperature is stabilized at 380 °C, and the growth method is co-evaporation of Cr and Te sources. At the same time, open the shutter of the Cr source and the shutter of the Te source to obtain a CrTe2 thin film.

[0013] S4. Place Sb and Cr in different evaporation sources, raise the temperature, and control the atomic beam flow rate ratio of Sb and Cr. During growth, the substrate temperature remains stabilized at 380 °C, and the growth method is co-evaporation of Cr and Sb sources. When the temperatures of both reach the target temperature, open the shutter of the Cr source and the shutter of the Sb source at the same time; obtain a CrSb single crystal thin film.

[0014] As a preferred embodiment of the present invention, in step S1, the vacuum degree of the vacuum chamber is 6×10 -10 mbar, the annealing temperature of the SiC single crystal substrate is 600 - 700 °C, and the annealing time is 30 - 35 minutes.

[0015] As a preferred embodiment of the present invention, the specific operations of heating and cooling in step S2 are: first rapidly heat the temperature to 1150 °C and maintain it for 15 seconds, then quickly reduce the temperature to about 750 °C and maintain it for 1 minute.

[0016] As a preferred embodiment of the present invention, in step S3, the bottom of the metal Te double-temperature evaporation source is heated to 320 °C, the source opening is heated to 350 °C, the Cr medium-temperature evaporation source is raised to 1180 °C, and the vacuum in the growth chamber is lower than 1.7×10 -10 mbar.

[0017] As a preferred embodiment of the present invention, in step S3, the atomic beam flow rate ratio of Cr and Te is 1:30. At this time, the atomic number ratio of Cr and Te is 1:10; for the CrTe 2 thin film, the average growth rate is controlled at 0.15 nm / min, and epitaxial growth is carried out for 30 minutes, with the thickness controlled at 4.5 nm.

[0018] As a preferred embodiment of the present invention, in step S4, the temperature in the metal Sb low-temperature source is raised to 410 °C, and the temperature in the Cr medium-temperature evaporation source is raised to 1180 °C.

[0019] As a preferred embodiment of the present invention, in step S4, the atomic beam flow rate ratio of Cr to Sb is 1:12, and at this time, the atomic number rate ratio of Cr to Sb is 1:5; the average growth rate of the CrSb thin film is controlled at 0.15 nm / min, epitaxially grown for 90 minutes, and the thickness is controlled at 15 nm.

[0020] Advantages of the present invention: The present invention provides a method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy, which can very precisely control the growth conditions and achieve the controllable growth of thin film materials. During the thin film growth process, in combination with in-situ monitoring by a reflection high energy electron diffraction instrument (RHEED) and a scanning tunneling microscope (STM), the epitaxial growth of an alternating magnetic CrSb single crystal thin film with atomic-level flatness and precisely controllable number of layers is realized. This method can be further popularized and applied to the preparation of other types of thin films; moreover, it well reflects the novel physical properties and topological electron transport properties in thin film materials, meets the performance requirements for the preparation of high-energy and low-power electronics devices, and lays a material foundation for subsequent device preparation and transport testing. Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is a flowchart for sample preparation

[0023] Figure 2 It is a schematic diagram of the molecular beam epitaxy equipment adopted by the present invention

[0024] Figure 3 It is a step diagram of the alternating magnetic CrSb single crystal thin film in the present invention

[0025] Figure 4 For the CrSb single crystal thin film in the present invention and Reflection high energy electron diffraction patterns in the directions;

[0026] Figure 5 It is a high-resolution transmission electron microscope image of the CrSb single crystal thin film in the present invention;

[0027] Figure 6 It is a characterization diagram of XRD of the CrSb single crystal thin film in the present invention;

[0028] Figure 7 It is the zero-field cooled-field cooled magnetization intensity curve and the variable-temperature vertical and parallel magnetic hysteresis loops of the CrSb single crystal thin film in the present invention. Detailed Embodiments

[0029] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0030] Example 1:

[0031] (1) Transfer the SiC(111) single crystal substrate to the sample holder in the growth chamber. The vacuum degree of the vacuum chamber is less than 8.5×10-10 mbar. The substrate is annealed by direct current heating to remove impurities adsorbed on the substrate surface. The substrate annealing temperature is 580 °C and the annealing time is 30 minutes.

[0032] (2) By increasing the current, the annealed SiC is quickly heated to 1170 °C and maintained for 15 seconds, then the temperature is quickly reduced to about 750 °C and maintained for 1 minute. This process is repeated 15 times, that is, flash SiC. Subsequently, the temperature is reduced to the growth temperature. After flash, Si in the upper layer of SiC is evaporated, leaving C atoms. The C atoms form a Graphene phase. Then, using this as a substrate, a buffer layer CrTe2 thin film and a CrSb single crystal thin film are grown.

[0033] (3) Growth of the buffer layer CrTe2: The bottom of the metal Te double-temperature evaporation source is heated to 320 °C, the source opening is heated to 350 °C, the Cr medium-temperature evaporation source is raised to 1180 °C, the vacuum in the growth chamber is less than 8.5×10-10 mbar, and the sample holder baffle is opened.

[0034] The growth rate is calibrated by an in-situ quartz crystal oscillator. The atomic beam flow rate ratio of Cr and Te is 1:30, and the atomic number ratio of Cr and Te is 1:10 at this time.

[0035] (4) During growth, the substrate temperature is stabilized at 380 °C, and the growth method is co-evaporation of Cr and Te sources. After the system runs stably, the Cr source baffle and the Te source baffle are opened simultaneously for epitaxial growth of the buffer layer CrTe2.

[0036] (5) The average growth rate of the thin film is controlled at about 0.15 nm / min, and epitaxial growth is carried out for 30 minutes to obtain a CrTe2 thin film with a thickness of 4.5 nm. The presence of the CrTe2 thin film buffer layer can release the stress between the substrate and the thin film. After the growth of the buffer layer is completed, the Cr source baffle, the Te source baffle, and the sample holder baffle are closed, and the temperatures of the Cr source and the Te source are reduced to 1000 °C and 0 °C respectively.

[0037] (6) Growth of CrSb single-crystal thin film: The low-temperature source of metallic Sb is heated to 410 °C, and the medium-temperature evaporation source of Cr is raised to 1180 °C. The baffle of the sample holder is opened. The atomic beam flow rate ratio of Cr to Sb is 1:12, and at this time, the atomic number ratio of Cr to Sb is 1:5.

[0038] (7) During growth, the substrate temperature remains stable at 380 °C. The growth method is co-evaporation of Cr and Sb sources. After the system is stable, the baffle of the Cr source and the baffle of the Sb source are opened simultaneously for epitaxial growth.

[0039] (8) The average growth rate of the thin film is controlled at about 0.15 nm / min. After 90 minutes of epitaxial growth, a CrSb single-crystal thin film with a thickness of 15 nm is obtained. After growth is completed, the baffle of the Cr source, the baffle of the Sb source, and the baffle of the sample holder are closed, and the temperatures of the Cr source and the Sb source are both reduced to 0 °C.

[0040] Figure 2 Schematic diagram of the molecular beam epitaxy equipment used in Example 1. The system operates in an ultra-high vacuum (UHV) environment to avoid interference from external impurities. By heating the evaporation source, the material forms an atomic / molecular beam in the UHV chamber through high-temperature sublimation / evaporation. The formed molecular beam further moves directionally to the substrate surface. At an appropriate substrate temperature, different atoms nucleate / react on the substrate and form crystals, thus realizing the epitaxial growth of the thin film. By controlling the temperature of the evaporation source and the substrate temperature, the thin film growth can be precisely controlled at the atomic scale.

[0041] The steps of the staggered magnetic CrSb single-crystal thin film in the present invention are as Figure 3 shown. First, the SiC is annealed to remove surface impurities, and then graphene is flashed on the SiC layer. Since there is a lattice mismatch between CrSb and graphene, in this invention, CrTe2 is used as a buffer layer to release the stress between the substrate and the thin film. After the growth of the buffer layer is completed, CrSb is grown continuously, and an atomically flat single-crystal thin film can be obtained.

[0042] Figure 4 is the reflection high-energy electron diffraction pattern (RHEED) of the CrSb(0001) thin film grown in Example 1. The incident directions of the electron beam are and The clear fringes in the RHEED indicate that the thin film exhibits an atomically flat layer-by-layer growth mode.

[0043] Figure 5 is the high-resolution transmission electron microscopy image of the CrSb(0001) thin film (15 nm) grown on the CrTe2 buffer layer in Example 1. It can be seen that the grown thin film has a clear interface and an ordered lattice.

[0044] The phase composition of the grown CrSb(0001) thin film (15 nm) in Example 1 was analyzed by thin film X-ray diffraction. As Figure 6 shown, it can be seen that the grown thin film has high quality and no impurity phases;

[0045] The grown CrSb single crystal thin film prepared in Example 1 was characterized by a superconducting quantum interference device (SQUID) to mainly judge the magnetic properties of the CrSb single crystal thin film. Figure 7 (a), (b), and (c) are respectively the curves of field-cooled magnetization intensity versus temperature, and the in-plane and out-of-plane magnetic hysteresis loops (the background signal of the substrate has been removed). This thin film exhibits very good soft magnetic properties, and the material as a whole has an out-of-plane easy axis.

[0046] Example 2: This comparative example is exactly the same as the preparation process of Example 1, except that in step (3), the Cr medium-temperature evaporation source is raised to 1210 °C, and the beam current of the Cr source is increased to The atomic beam flow rate ratio of Cr and Te is 1:28, and at this time, the atomic number ratio of Cr and Te is 1:9;

[0047] Example 3: This comparative example is exactly the same as the preparation process of Example 1, except that in step (4), the temperature of the substrate is set to 400 °C, the flow rate of the atoms remains unchanged, but the deposition rate of the atoms decreases, the growth rate of the thin film slows down, and the growth rate of CrTe2 changes from the original 0.15 nm / min to 0.8 nm / min;

[0048] Example 4: This comparative example is exactly the same as the preparation process of Example 1, except that in step (6), the temperature of the substrate is set to 400 °C, the flow rate of the atoms remains unchanged, but the deposition rate of the atoms decreases, the growth rate of the thin film slows down, and the growth rate of CrSb changes from the original 0.15 nm / min to 0.10 nm / min.

[0049] The above molecular beam epitaxy for preparing the staggered magnetic CrSb single crystal thin film has a simple process, the preparation process is controllable with atomic-level precision, the parameters are adjustable, the substrates used are all commercial products, easy to obtain, and have good repeatability. This method can be extended to the preparation of other thin films.

[0050] In the description of this specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0051] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A CrSb single crystal thin film, characterized in that: The CrSb single crystal film comprises a substrate SiC, a buffer layer CrTe2 and a CrSb film which are sequentially arranged from bottom to top; when the crystal orientation of the CrSb film is (0001), the CrSb film has six-degree symmetry.

2. The CrSb single crystal thin film according to claim 1, characterized in that: When the crystal orientation of the staggered magnetic CrSb film is (0001), a CrTe2 buffer layer is provided between the substrate and the CrSb film, and the epitaxial relationship of the CrSb film is SiC(111) / / CrTe2(0001) / / CrSb(0001).

3. A method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy, characterized in that: The preparation method comprises the following steps: S1, placing the SiC single crystal substrate on the sample holder of the growth chamber, and annealing the substrate by direct current heating; S2, by increasing the current, the annealed SiC single crystal substrate is first quickly heated up and then cooled down, and this process is repeated 15 times to obtain flash SiC, and then the temperature is lowered to the growth temperature, the Si in the upper layer of the SiC after flash is evaporated, leaving C atoms, and the C atoms form a graphene phase, and then the buffer layer CrTe2 film and CrSb single crystal film are grown on this substrate; S3, placing Te and Cr in different evaporation sources, raising the temperature, controlling the atomic beam flow rate ratio of Cr and Te, and stabilizing the substrate temperature at 380°C during growth, using the co-evaporation of Cr and Te sources, and opening the Cr source baffle and the Te source baffle at the same time to obtain a CrTe2 film; S4. Place Sb and Cr in different evaporation sources, increase the temperature, and control the atomic beam flow rate ratio of Sb and Cr. During growth, the substrate temperature remains stable at 380°C. The growth method is the co-evaporation of Cr and Sb sources. When the temperatures of both reach the target temperature, open the Cr source baffle and the Sb source baffle at the same time; and obtain a CrSb single crystal film.

4. The method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy according to claim 3, characterized in that: The vacuum degree of the vacuum chamber in step S1 is 6×10 -10 mbar, the annealing temperature of the SiC single crystal substrate is 600-700°C, and the annealing time is 30-35 minutes.

5. The method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy according to claim 3, characterized in that: The specific operation of heating and cooling in step S2 is: firstly, the temperature is quickly raised to 1150° C. and maintained for 15 seconds, and then the temperature is quickly reduced to about 750° C. and maintained for 1 minute.

6. The method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy according to claim 3, characterized in that: In step S3, the bottom of the metal Te dual-temperature evaporation source is heated to 320°C, the source port is heated to 350°C, the Cr medium-temperature evaporation source is heated to 1180°C, and the vacuum in the growth chamber is less than 1.7×10 -10 mbar.

7. The method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy according to claim 3, characterized in that: In step S3, the atomic beam flow rate ratio of Cr and Te is 1:30, and the atomic number ratio of Cr and Te is 1:10; the average growth rate of the CrTe2 film is controlled at 0.15 nm / min, the epitaxial growth is 30 minutes, and the thickness is controlled at 4.5 nm.

8. The method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy according to claim 3, characterized in that: In step S4, the temperature in the metal Sb low-temperature source is raised to 410°C, and the temperature in the Cr medium-temperature evaporation source is raised to 1180°C.

9. The method for preparing an alternating magnetic CrSb single crystal thin film by molecular beam epitaxy according to claim 3, characterized in that: In step S4, the atomic beam flow rate ratio of Cr and Sb is 1:12, and the atomic number rate ratio of Cr and Sb is 1:5; the average growth rate of the CrSb film is controlled at 0.15 nm / min, the epitaxial growth takes 90 minutes, and the thickness is controlled at 15 nm.

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