A method for epitaxial growth of chromium telluride thin films with giant topological Hall effect

Abstract

The present invention discloses a method for epitaxially growing chromium telluride thin films exhibiting a significant topological Hall effect. This method, which belongs to the field of electronic materials technology, first prepares a substrate and a chromium-telluride compound target. After the chamber pressure is evacuated to a vacuum using a pump assembly, the substrate is heated to a constant temperature. An excimer laser is focused onto the target. The entire deposition process is monitored in real time using a RHEED high-energy electron diffractometer. After observing that the RHEED diffraction spots of the deposited film form a clear three-dimensional lattice pattern, the chamber temperature is lowered to room temperature, the substrate is removed, and the resulting chromium telluride single crystal thin film is characterized and tested. Measurement results demonstrate that this method is the first in this field to produce a chromium telluride ferromagnetic film with a Curie temperature above room temperature. The maximum amplitude of its topological Hall resistivity is the highest among all chromium telluride material systems in which the topological Hall effect has been observed. The method exhibits high production efficiency and can be expanded to produce other high-quality telluride thin films.

Description

Technical Field

[0001] The present invention discloses a method for epitaxially growing a chromium telluride thin film with a giant topological Hall effect, belonging to the field of electronic materials technology. In particular, it relates to a chromium telluride single crystal thin film material, a thin film growth method using laser molecular beam epitaxy (L-MBE), and the application of its properties in chiral spin electronics. Background Art

[0002] Chiral spin textures generated by real-space Berry curvature have attracted significant interest from researchers due to their potential applications in high-density data storage and low-power spintronic devices. Chiral spin textures typically exist in the form of skyrmions, noncollinear magnetic structures, magnetic bubbles, and merons. The exotic physical phenomena they induce have become a hot topic in the cutting-edge research of spintronic materials. Among them, the topological Hall effect is considered an effective means of detecting chiral spin textures using purely electrical methods. Typically, when carriers pass through a chiral spin texture, they acquire an additional Berry phase in the Hall test, thereby introducing an additional Hall voltage. This is the topological Hall effect. This exotic effect typically manifests as paired humps in the Hall resistance curve near the positive and negative coercive fields, which is significantly different from the anomalous Hall effect induced by Berry curvature in momentum space.

[0003] Since 2011, the topological Hall effect induced by chiral spin textures has been confirmed in multiple magnetic systems, including B20 alloys, oxide films, magnetic heterostructures, and frustrated magnet materials. In recent years, the discovery of low-dimensional ferromagnetic materials has provided more material options for exploring and understanding the topological Hall effect. People have also observed the exotic topological Hall effect in a variety of low-dimensional ferromagnetic material systems, including low-dimensional ferromagnetic heterostructures (such as: CrTe / SrTiO3, Cr2Te3 / Bi2Te3, Fe3GeTe2 / WTe2, CrTe2 / Bi2Te3, Cr2Te3 / Cr2Se3, etc.), magnetic bulks (such as: Cr5Te8, Cr 0.9 B 0.1 Te, Cr 0.8 7Te、Cr 1.53 Te2, etc.) and magnetic nanosheets (such as Cr5Si3, Cr 1.2Te2, etc.). However, to realize the practical application of its spin electronic devices, the thin film preparation of materials compatible with microelectronics technology is a prerequisite. Currently, the main preparation technologies for large-area low-dimensional magnetic thin films, such as molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), cannot be applied in actual industry due to their slow growth rate and poor film continuity. Thin film preparation methods such as laser molecular beam epitaxy and magnetron sputtering technology are currently unable to obtain large-area, thickness-controllable, high Curie temperature, and large and high-temperature topological Hall effect low-dimensional ferromagnetic single crystal films. This seriously hinders the practical application of chiral spin textures in next-generation spin electronics logic and memory devices. Summary of the Invention

[0004] Technical problem to be solved by the invention

[0005] In view of the problem that the existing technology cannot prepare low-dimensional room-temperature ferromagnetic single crystal films with a high topological Hall effect, the present invention proposes an epitaxial growth method for chromium telluride films with a huge topological Hall effect.

[0006] Technical Solution

[0007] In order to achieve the above object, the technical solution provided by the present invention is:

[0008] A method for epitaxial growth of a chromium telluride thin film having a giant topological Hall effect comprises the following steps:

[0009] Step 1: Place the pre-treated sapphire substrate (001 orientation) on the sample holder of the deposition device, place the chromium-tellurium compound target with a Cr to Te ratio of 1 to 3 on the target stage of the deposition device, close the deposition device chamber, and use the pump group to pump the chamber pressure to (7±1)×10 -6 After Pa, the substrate is heated to a constant temperature of 550±5℃, and a high vacuum degree is maintained in the chamber during the heating process;

[0010] Step 2: Turn on the RHEED high-energy electron diffractometer to generate an electron beam that irradiates the substrate and forms diffraction fringes on the fluorescent screen and camera;

[0011] Step 3: Maintaining the chamber environment unchanged, a 248nm wavelength KrF excimer laser is used. The laser is focused by a lens onto a chromium-telluride compound target through a laser incident device. The entire deposition process is monitored in real time using a RHEED high-energy electron diffractometer. The target stage rotates at a constant speed throughout the deposition process to ensure that the laser is evenly applied to the target.

[0012] Step 4: After observing the RHEED diffraction spots of the deposited film as a clear three-dimensional dot pattern through the deposition device screen and camera, the temperature in the chamber is lowered to room temperature, and the cooling rate is lower than the heating rate in step 1;

[0013] Step 5: Take out the substrate from the chamber and perform characterization tests on the obtained chromium telluride single crystal thin film.

[0014] Furthermore, the method for pre-treating the sapphire substrate in step 1 is: ultrasonically cleaning the substrate in acetone, alcohol, and deionized water for 5 minutes each.

[0015] Furthermore, the substrate is heated at a rate of 20° C. / min in step 1.

[0016] Furthermore, the process of decreasing the pressure in the chamber in step 1 is as follows: first, the pressure is pumped down to 9 Pa, and then to 7×10 - 6 Pa.

[0017] Furthermore, in step 3, the angle between the target and the laser beam is 45°, and the average energy density of the laser beam is 1.0±0.2 J / cm 2 , the laser repetition frequency is 2 Hz, and the deposition rate is 1 nm / min.

[0018] Furthermore, in step 4, the cooling rate is 15°C / min.

[0019] Furthermore, the characterization test in step 5 includes measuring the Raman scattering spectrum of the film using a Raman scatterer, scanning the film using an atomic force microscope, measuring the in-plane magnetization intensity-temperature dependence curve of the film using a superconducting quantum interference magnetic measurement system, measuring the topological Hall effect component of the film, and measuring the temperature dependence curve of the topological Hall effect amplitude value of the film.

[0020] Beneficial effects

[0021] The present invention is the first in the field of this technology to obtain a chromium telluride ferromagnetic film with a Curie temperature above room temperature through an application-oriented vacuum thin film preparation method. The maximum amplitude of its topological Hall resistivity is the highest among all chromium telluride material systems in which the topological Hall effect has been observed.

[0022] The chromium telluride film prepared by the method of the present invention has a precisely controllable thickness, good room-temperature ferromagnetism, metallic properties and air stability, and a huge topological Hall effect can be observed under an external magnetic field;

[0023] The material preparation parameters of the method of the present invention are easy to adjust, the growth process is controllable, the process repeatability is good, and the preparation efficiency is high. It can be expanded to prepare other high-quality telluride films. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a deposition device for implementing the epitaxial growth method of a chromium telluride thin film according to the present invention;

[0025] Figure 2 1. A diagram showing the steps of the epitaxial growth method of a chromium telluride thin film according to the present invention;

[0026] Figure 3 The RHEED spot of the chromium telluride single crystal thin film prepared by the method of the present invention;

[0027] Figure 4 The Raman scattering spectrum of the chromium telluride single crystal thin film prepared by the method of the present invention;

[0028] Figure 5 The atomic force microscope scanning results of the chromium telluride single crystal film prepared by the method of the present invention;

[0029] Figure 6 The temperature dependence curve of the in-plane magnetization intensity of the chromium telluride single crystal film prepared by the method of the present invention;

[0030] Figure 7 This is the topological Hall effect component (shaded part) in the chromium telluride single crystal thin film prepared by the method of the present invention;

[0031] Figure 8 The temperature dependence curve of the amplitude of the topological Hall effect in the chromium telluride single crystal thin film prepared by the method of the present invention;

[0032] Explanation of the reference numerals: 1-target stage, 2-sample holder, 3-heating wire, 4-observation window, 5-laser incident device, 6-exhaust port, 7-RHEED high energy electron diffractometer, 8-fluorescent screen and camera. DETAILED DESCRIPTION

[0033] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 As shown, when the system is working, the deposition target is placed on the target stage 1 of the deposition device, the substrate is fixed on the sample holder 2 and heated by the heating wire 3, the RHEED high-energy electron diffractometer 7 is used to generate an electron beam irradiated on the substrate, and form diffraction stripes on the fluorescent screen and the camera 8 to realize in-situ monitoring of the deposition process, the laser incident device 5 generates laser and irradiates the target located on the target stage 1, the exhaust port 6 realizes the air pressure control in the vacuum chamber, and the observation window 4 is used to observe the deposition process.

[0035] like Figure 2 As shown, the epitaxial growth method of chromium telluride thin film of the present invention mainly comprises the following steps:

[0036] Step 1: Place a sapphire Al2O3 (001 orientation) substrate that has been ultrasonically cleaned with acetone, alcohol, and deionized water for 5 minutes each on the sample holder 2, place a chromium-tellurium compound target (Cr to Te ratio of 1:3) on the target stage 1, close the deposition chamber, and use a pump group to pump the vacuum chamber to (7±1)×10 -6 Pa, the substrate is heated to a constant temperature of 550±5°C by the heating wire 3. The high vacuum degree in the chamber is maintained during the heating process, and the heating rate is about 20°C / min. In this embodiment, the air pressure is first pumped to 9Pa through the air pump 6 using a mechanical pump, and then the molecular pump is turned on to continue pumping to 7×10 -6 Pa

[0037] Step 2: After the substrate is heated to 550±5° C., the RHEED high-energy electron diffractometer 7 is turned on to generate an electron beam to irradiate the substrate, and diffraction fringes are formed on the fluorescent screen and the camera 8 to realize in-situ monitoring of the deposition process.

[0038] Step 3: Keeping the environment in the chamber unchanged, a KrF excimer laser with a wavelength of 248 nm is used. The laser is focused by the laser incident device 5 onto a target material of a chromium-tellurium compound (the ratio of Cr to Te is 1:3) through a lens. The angle between the target and the laser beam is about 45°, and the average energy density of the laser beam is 1.0±0.2 J / cm 2 The laser repetition frequency is 2 Hz, and the deposition time is determined by the selected thickness. In this embodiment, the growth rate is approximately 1 nm / min. The entire growth process is monitored in real time and in situ by a RHEED high-energy electron diffractometer 7. During the deposition process, the target stage 1 rotates at a constant speed to ensure that the laser strikes the target evenly. This is to increase the stability of the thin film growth and extend the target's service life.

[0039] Step 4: After the film growth is completed, the RHEED diffraction spots of the film are observed through the fluorescent screen and camera 8 (such as Figure 3 The spots are clear three-dimensional dot patterns, which ensure the single crystal nature of the film. The temperature in the cavity is then cooled to room temperature at a rate of 15°C / min. The cooling rate is slightly lower than the heating rate to avoid cracking of the film due to excessive temperature changes during the cooling process.

[0040] Step 5: Take out the substrate from the chamber and 1+δ Te2) single crystal thin films were characterized and tested.

[0041] Figure 4 The Raman scattering spectrum of the thin film was measured by Raman scattering instrument, in which the two Raman scattering characteristic peaks P1 and P2 belong to Cr x Te y Typical characteristic peaks of the system.

[0042] Figure 5 The scanning results of the thin film were measured using an atomic force microscope. The scanning results show that the surface of the sample is flat and the average roughness is less than 0.55nm.

[0043] Figure 6 The in-plane magnetization intensity-temperature dependence curves of the thin films (20nm, 50nm, and 80nm thickness, respectively) measured using a superconducting quantum interference magnetic measurement system indicate that the Curie temperature of the sample exceeds room temperature (about 320K). This is the first time in the prior art that a chromium telluride (CrT) with a Curie temperature above room temperature has been obtained through an application-oriented preparation method (i.e., laser molecular beam epitaxy). 1+δ Te2) ferromagnetic thin film.

[0044] Figure 7 The topological Hall effect component in the film is shown in the magnetic field-dependent Hall resistivity curve, where a clear hump can be observed near the coercive field, indicated by the shaded area. This is the chromium telluride (Cr 1+δ Giant topological Hall effect in Te2 thin films.

[0045] Figure 8 The temperature dependence curve of the amplitude of the topological Hall effect in the film shows that the topological Hall effect is maintained from 5K to 300K and reaches a maximum value of 1.6μΩ·cm at 90K. The maximum amplitude of the topological Hall magnetoresistivity is the highest among all Cr films in which the topological Hall effect can be observed with existing technology. x Te y The highest among the material systems (as shown in Table 1).

[0046] Table 1 Existing Cr x Te y Statistics of the maximum amplitude of topological Hall resistivity in material systems

[0047] <![CDATA[Cr x Te y Material System]]> Maximum topological Hall resistivity value (μΩ·cm) <![CDATA[Cr 1+δ Te2 thin film 1.6 <![CDATA[CrTe2 / Bi2Te3]]> 1.39 <![CDATA[CrTe / SrTiO3]]> 1.2 <![CDATA[Cr2Te3 / Bi2Te3]]> 0.5 <![CDATA[Cr2Te3 / Cr2Se3]]> 0.23 <![CDATA[(Cr 0.9 B 0.1 )The]]> 0.215 <![CDATA[Cr 0.87 The]]> 0.2 <![CDATA[Cr 1.53 Te2]]> 0.106 <![CDATA[Cr 1.2 Te2]]> 0.05 <![CDATA[Cr5Te8]]> 0.016

[0048] The molecular formula of the chromium telluride film material prepared by the method of the present invention is Cr 1+δTe2, where 0 < δ < 1, is a high-quality thin film grown using laser molecular beam epitaxy. The target material is a chromium telluride compound (Cr:Te ratio of 1:3). The measurement results show that the resulting film is a high-quality single crystal with a metallic luster. Magnetic characterization reveals that the magnetic easy axis (easy magnetization direction) of the film is in-plane, and the Curie temperature of films of various thicknesses (20 to 80 nm) is as high as 320 K (taken as the first differential of the temperature-dependent magnetization curve). The saturation magnetization is approximately 0.45 μB / Cr at 300 K. The resulting chromium telluride film has an average roughness of less than 0.55 nm and a precisely controllable thickness. It exhibits excellent room-temperature ferromagnetism, metallic properties, and air stability. A large topological Hall effect is observed in the presence of an applied magnetic field. This topological Hall effect persists from 5 K to room temperature at 300 K, reaching a maximum of 1.6 μΩ·cm at 90 K.

[0049] The method of the present invention is the first in the field of this technology to obtain chromium telluride (Cr telluride) with a Curie temperature higher than room temperature (about 320K) through an application-oriented vacuum thin film preparation method. 1+δ Te2) ferromagnetic film, and its maximum amplitude of topological Hall resistivity is among all Cr x Te y The highest in the material system. 1+δ Te2 thin film has uniform composition and controllable thickness; the material preparation parameters are easy to adjust, the growth process is controllable, the process repeatability is good, and the preparation efficiency is high. The "robust" chiral spin texture brought by the huge topological Hall effect has important application value in the fields of magnetic storage and magnetic information transmission, and also provides a reference for Cr 1+δ Te2 thin films and their heterostructures have laid the material foundation for the application of new chiral spintronic devices.

[0050] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A method for epitaxial growth of chromium telluride thin films with giant topological Hall effect, characterized in that: The following steps are involved: Step S1: Place the pre-treated sapphire substrate on the sample holder of the deposition device, place the chromium-tellurium compound target with a Cr to Te ratio of 1 to 3 on the target stage of the deposition device, close the deposition device chamber, and use a pump group to pump the chamber pressure to (7±1)×10 -6 After Pa, the substrate is heated to a constant temperature of 550±5℃, and a high vacuum degree is maintained in the chamber during the heating process; Step S2, turning on the deposition device RHEED high energy electron diffractometer to generate an electron beam that irradiates the substrate and forms diffraction fringes on the fluorescent screen and the camera; Step S3, keeping the environment in the chamber unchanged, using a KrF excimer laser with a wavelength of 248 nm to focus the laser through a lens by the laser incident device (5) onto the chromium telluride compound target material, and the entire deposition process is monitored in real time by a RHEED high-energy electron diffractometer. The target stage rotates at a constant speed throughout the deposition process so that the laser is evenly projected onto the target material; Step S4: After observing that the RHEED diffraction spots of the deposited film are clear three-dimensional dot patterns through the deposition device screen and camera, the temperature in the chamber is lowered to room temperature, and the cooling rate is lower than the heating rate in step S1; Step S5: taking out the substrate from the chamber and performing characterization tests on the obtained chromium telluride single crystal thin film.

2. The epitaxial growth method of a chromium telluride thin film with a giant topological Hall effect according to claim 1, wherein: The method for pre-treating the sapphire substrate in step S1 is: ultrasonically cleaning the substrate in acetone, alcohol, and deionized water for 5 minutes each.

3. The epitaxial growth method of a chromium telluride thin film with a giant topological Hall effect according to claim 1, wherein: The substrate is heated at a rate of 20° C. / min in step S1.

4. The epitaxial growth method of a chromium telluride thin film with a giant topological Hall effect according to claim 1, wherein: The process of decreasing the pressure in the chamber in step S1 is as follows: first, the pressure is pumped down to 9 Pa, and then to 7×10 -6 Pa.

5. The epitaxial growth method of a chromium telluride thin film with a giant topological Hall effect according to claim 1, wherein: In step S3, the angle between the target and the laser beam is 45°, and the average energy density of the laser beam is 1.0±0.2 J / cm 2 , the laser repetition frequency is 2 Hz, and the deposition rate is 1 nm / min.

6. The epitaxial growth method of a chromium telluride thin film with giant topological Hall effect according to claim 1, wherein: The cooling rate in step S4 is 15°C / min.

7. The epitaxial growth method of a chromium telluride thin film with giant topological Hall effect according to claim 1, characterized in that: The characterization test in step S5 includes measuring the Raman scattering spectrum of the film using a Raman scatterer, scanning the film using an atomic force microscope, measuring the in-plane magnetization intensity-temperature dependence curve of the film using a superconducting quantum interference magnetic measurement system, measuring the topological Hall effect component of the film, and measuring the temperature dependence curve of the topological Hall effect amplitude value of the film.

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