A heterojunction exhibiting an anomalous hall effect at low temperature and a method of manufacturing the same

Abstract

The application relates to a heterojunction showing abnormal Hall effect at low temperature and a preparation method thereof, in particular to the following steps: taking a gadolinium gallium garnet substrate as a base, after the substrate is treated through cleaning and the like, the substrate is placed in a vacuum system, and through steps of heating annealing and degassing, a Tm3Fe5O 12 thin film is grown on the substrate by using pulse laser deposition; and the grown thin film is taken as a base and is placed into a molecular beam epitaxy device, and a SnTe thin film with a certain thickness is grown on the base by using a molecular beam epitaxy technology. By using the method, a high-quality thin film material with abnormal Hall effect under specific temperature conditions can be obtained, the thin film material can show abnormal Hall effect at a temperature below 20K, and the temperature has a regulating effect on the signal size of the abnormal Hall effect.

Description

Technical Field

[0001] This invention belongs to the field of condensed matter physics and relates to a method for generating an interface effect at the interface between a ferromagnetic insulator and a topological crystal insulator by constructing a heterojunction, and a method for influencing the transport properties of the topological crystal insulator by the lattice mismatch between the topological crystal insulator and the ferromagnetic insulator, thereby generating an anomalous Hall effect at a certain temperature. Background Technology

[0002] Topological crystal insulators, as an emerging material, possess many unique properties. The most important of these is the influence of band topology on their transport characteristics, making the surface or edge states of topological crystal insulators dissipateless. This makes them an excellent source material for superconductivity research and the study of the quantum Hall effect. However, the surface or edge states of topological crystal insulators are highly susceptible to bulk state influences, often requiring high-quality growth. Complete surface or edge states of topological crystal insulators correspond to the quantum spin Hall effect, while moderately disrupted surface or edge states often correspond to the anomalous quantum Hall effect. The anomalous quantum Hall effect is an important physical phenomenon in spintronics, possessing significant theoretical and practical value. Materials exhibiting the anomalous quantum Hall effect are helpful in developing novel spintronic devices with low power consumption, high speed, small size, and no information loss. Moderate disruption of the surface or edge states of topological crystal insulators is often achieved by introducing long-range ferromagnetic order or lattice mismatch. Therefore, it is necessary to provide a magnetic thin film exhibiting the anomalous Hall effect under specific conditions and its preparation method.

[0003] Tm3Fe5O 12 It exhibits out-of-plane ferromagnetism and a Curie temperature as high as 549 K. Under a certain film thickness, a ferromagnetic insulator Tm3Fe5O can be constructed. 12 The interface effect can be induced by the SnTe heterojunction with the topological crystal insulator, thereby realizing a material with an anomalous Hall effect, namely Tm3Fe5O provided by this invention. 12 / SnTe heterojunction epitaxial film. Summary of the Invention

[0004] This invention provides a heterojunction exhibiting an anomalous Hall effect at low temperatures and its preparation method. Using this method, a high-quality thin film material exhibiting an anomalous Hall effect under specific temperature conditions can be obtained. It can exhibit an anomalous Hall effect with adjustable intensity at temperatures below 20K. The heterojunction can be used to prepare low-energy-consumption spintronic devices.

[0005] The technical solution of this invention is as follows:

[0006] A heterojunction exhibiting an anomalous Hall effect at low temperatures is characterized by: epitaxial growth of Tm3Fe5O on the surface of a gadolinium gallium garnet (111) substrate. 12 Single-crystal thin films, and using these as substrates, were developed in Tm3Fe5O4. 12 Epitaxial growth of SnTe single-crystal thin films.

[0007] As a preferred technical solution:

[0008] The Tm3Fe5O 12 The thickness of single-crystal thin films is 50-100 nm, and the thickness of SnTe single-crystal thin films is 15 nm.

[0009] The heterojunction exhibits an anomalous Hall effect at temperatures below 20K, and temperature modulates the signal magnitude of the anomalous Hall effect.

[0010] The present invention also provides a method for preparing the heterojunction exhibiting the anomalous Hall effect at low temperature, characterized by comprising the following steps:

[0011] a) Place the gadolinium gallium garnet (111) substrate in a laser pulse deposition vacuum system;

[0012] b) Using pulsed laser deposition technology, Tm3Fe5O was grown on the surface of a gadolinium gallium garnet (111) substrate. 12 Epitaxial single-crystal thin films;

[0013] c) The already grown Tm3Fe5O 12 Epitaxial single-crystal thin films are placed in an ultra-high vacuum system and grown using molecular beam epitaxy on Tm3Fe5O4. 12 SnTe single-crystal thin films are epitaxially grown on the surface of epitaxial single-crystal thin films, ultimately yielding Tm3Fe5O. 12 / SnTe epitaxial single-crystal thin-film heterojunction.

[0014] As a preferred technical solution:

[0015] In step a), before placing the gadolinium gallium garnet (111) substrate in the vacuum system, it is sonicated with acetone for 300-500s and then with ethanol for 300-500s.

[0016] In step b), during the growth of Tm3Fe5O 12 When epitaxial single crystal thin films are used, a gadolinium gallium garnet (111) substrate is used as the substrate, and its temperature is maintained at 600℃-800℃.

[0017] During the growth of Tm3Fe5O 12During the epitaxial deposition of single-crystal thin films, elemental oxygen is introduced into the pulsed laser deposition chamber and maintained at an oxygen pressure of 1 Pa. Tm3Fe5O is then bombarded with a pulsed laser at a repetition frequency of 3-5 Hz and a laser energy of 300-400 mJ. 12 Target material to achieve Tm3Fe5O 12 Epitaxial growth on a gadolinium gallium garnet (111) substrate; after laser blasting, the oxygen pressure was adjusted to 10 at a substrate temperature of 600-800℃. 4 Pa was used for annealing for 1 hour; after annealing, the substrate and film were cooled in the furnace.

[0018] In step c), before growing the SnTe epitaxial single crystal epitaxial film, Tm3Fe5O2 is used as the substrate. 12 The thin film was sonicated with isopropanol, acetone, and ethanol for 10-30 min respectively; Tm3Fe5O 12 After the thin film is placed in an ultra-high vacuum system, it is heated to 600-950℃ and annealed for 1-3 hours to further remove surface impurities.

[0019] During the growth of SnTe epitaxial single-crystal thin films, a Sn source and a Te source are provided. The evaporation temperature of the Sn source is maintained at 900℃-1000℃, and the growth temperature of the Te source is maintained at 250℃-350℃. Tm3Fe5O4 is used as the substrate during the growth of the SnTe epitaxial single-crystal thin film. 12 The film temperature is maintained at 200-500℃; after growing the SnTe single crystal film, the resulting heterojunction is annealed at 250-500℃ for 1 hour.

[0020] This invention helps accelerate the design and development of novel spintronic devices based on the anomalous Hall effect under different temperature conditions. By utilizing SnTe, a topological crystal insulator whose electrical transport is spin-dependent, as a carrier and preserving its lattice to the greatest extent possible during growth, it is hoped that by elucidating its mechanism, low-energy-consumption novel spintronic devices can be designed and invented.

[0021] Compared with the prior art, the present invention has at least the following advantages:

[0022] First, by utilizing molecular beam epitaxy, precise control over the growth process and morphology of SnTe single crystal thin films at the atomic level can be achieved, resulting in the preparation of high-quality SnTe thin films with strictly controllable chemical composition.

[0023] Second, Tm3Fe5O is used. 12 Thin film as substrate, Tm3Fe5O 12 The lattice constant of Tm3Fe5O is an integer multiple of the lattice constant of SnTe. In RIG materials, Tm3Fe5O 12The lattice mismatch with SnTe single crystal is minimal, ensuring that SnTe can be grown in Tm3Fe5O 12 Two-dimensional epitaxial growth on the surface. And Tm3Fe5O 12 It exhibits a high dielectric constant at low temperatures, effectively shielding the interactions between charge carriers and yielding a strong SnTe / Tm3Fe5O3 composite. 12 Interface effect.

[0024] Third, Tm3Fe5O 12 Exhibiting out-of-plane magnetism, SnTe can influence the surface states through interface effects, potentially leading to an anomalous Hall effect.

[0025] Fourth, the ferromagnetic insulator (Tm3Fe5O) prepared using the method of the present invention 12 An anomalous Hall effect was observed in a heterojunction thin film of a topological crystal insulator (SnTe) and a superstructured crystalline insulator (SnTe) at a certain temperature (<20K). Furthermore, the magnitude of the anomalous Hall resistance could be adjusted by changing the temperature. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the heterojunction structure of the present invention.

[0027] Figure 2 Tm3Fe5O is grown on a gadolinium gallium garnet (111) substrate provided in Embodiment 1 of the present invention. 12 X-ray diffraction (XRD) pattern of single-crystal epitaxial thin films.

[0028] Figure 3 The Tm3Fe5O substrate provided in Embodiment 1 of the present invention is based on gadolinium gallium garnet. 12 (111) X-ray diffraction (XRD) pattern of single-crystal epitaxial SnTe heterojunction grown on thin film.

[0029] Figure 4 Tm3Fe5O provided in Embodiment 1 of the present invention 12 The curve of longitudinal resistance versus temperature for / SnTe epitaxial single-crystal thin-film heterojunction.

[0030] Figure 5 Tm3Fe5O provided in Embodiment 1 of the present invention 12 The curve of the anomalous Hall resistance of the / SnTe epitaxial single crystal thin film heterojunction as a function of magnetic field.

[0031] Figure 6 This is a surface morphology image obtained by atomic force microscopy in an embodiment of the present invention.

[0032] Figure 7 Tm3Fe5O as described in Comparative Example 1 12 / SnTe single-crystal epitaxial thin film heterojunction, the relationship between lateral resistance Rxy and magnetic field. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0034] Please refer to Figure 1. An embodiment of the present invention provides a thin film with an anomalous Hall effect. The thin film includes a gadolinium gallium garnet (111) substrate and a Tm3Fe5O3 substrate. 12 / SnTe epitaxial single-crystal thin-film heterojunction. The gadolinium gallium garnet (111) substrate, Tm3Fe5O 12 / SnTe epitaxial single-crystal thin-film heterojunction, sequentially stacked. Among them, Tm3Fe5O 12 The single-crystal thin film is located on a gadolinium gallium garnet substrate and is stacked by pulsed laser deposition. The SnTe single-crystal thin film and Tm3Fe5O... 12 The thin films are stacked together by molecular beam epitaxy.

[0035] Tm3Fe5O 12 The thin film has a high dielectric constant, which is beneficial for shielding the interaction between charge carriers. To facilitate the observation of the anomalous Hall effect and Curie temperature of the thin film using electrical transport measurements, a high-resistivity insulating substrate can be selected. Preferably, the gadolinium gallium garnet substrate is a single-crystal insulating substrate.

[0036] The lattice constant of the gadolinium gallium garnet substrate is 1.238 nm. The gadolinium gallium garnet substrate and Tm3Fe5O 12 The lattice mismatch of the single-crystal thin film is about 0.4%, which is beneficial for growing high-quality Tm3Fe5O on this substrate. 12 Single-crystal thin film. SnTe has a lattice constant of 0.63 nm, similar to Tm3Fe5O. 12 The lattice mismatch is approximately 2.5%, which is beneficial for growing high-quality SnTe single-crystal thin films on this substrate. In this embodiment, the thickness of the gadolinium gallium garnet substrate used is approximately 0.5 mm.

[0037] The Tm3Fe5O 12 The anomalous Hall effect of the / SnTe heterojunction mainly comes from the interfacial interaction between the ferromagnetic insulator and the topological crystal insulator in the thin film, which makes the single crystal thin film have the anomalous Hall effect.

[0038] Example 1

[0039] The thickness of the gadolinium gallium garnet substrate used is approximately 0.5 mm, Tm3Fe5O 12The thickness of the single-crystal epitaxial film is 100 nm, and the thickness of the SnTe single-crystal epitaxial film is 15 nm.

[0040] The preparation method of this thin film is as follows:

[0041] a) Sonicate the gadolinium gallium garnet (111) substrate with acetone for 480s, then sonicate with ethanol for 300s, and then place the substrate in a vacuum system.

[0042] b) Tm3Fe5O is grown using pulsed laser deposition technology. 12 Single-crystal epitaxial thin films were grown on the surface of gadolinium gallium garnet (111) substrates; Tm3Fe5O was grown on these substrates. 12 When epitaxial single-crystal thin films, a Tm3Fe5O layer with a diameter of 10 cm is provided. 12 The target material and substrate temperature are maintained at 700-750℃. Elemental oxygen is introduced into the PLD cavity, and the oxygen pressure is maintained at 1 Pa. Tm3Fe5O is then struck with a pulsed laser at a laser repetition frequency of 3-5 Hz and a laser energy of 300-400 mJ. 12 Target material to achieve Tm3Fe5O 12 Epitaxial growth on a gadolinium gallium garnet (111) substrate; after laser blasting, the oxygen pressure was adjusted to 10 at a substrate temperature of 700-750℃. 4 The substrate and film were annealed at 1 Pa for 1 hour. After annealing, the substrate and film were cooled in the furnace.

[0043] c) The already grown Tm3Fe5O 12 Single-crystal epitaxial films were grown on Tm3Fe5O4 using molecular beam epitaxy in an ultra-high vacuum system. 12 The surface of the thin film was finally prepared with Tm3Fe5O. 12 / SnTe epitaxial single-crystal thin film heterostructure. Before growing the SnTe single-crystal thin film, Tm3Fe5O is used as the substrate. 12 The thin film was sequentially sonicated with isopropanol, acetone, and ethanol for 10 min each, then annealed at 800℃ for 1 h. During the growth of the SnTe single crystal thin film, Tm3Fe5O4 was used as the substrate. 12 The film temperature was maintained at 350°C. A Sn source and a Te source were provided, with the Sn source evaporating at 950°C and the Te source evaporating at 290°C. After growing the SnTe single-crystal film, the resulting Tm3Fe5O... 12 The / SnTe epitaxial single crystal thin film heterojunction was annealed at 350℃ for 1 hour.

[0044] The parameters used in this embodiment can ensure the growth of Tm3Fe5O 12 / SnTe epitaxial single-crystal thin-film heterojunctions have better film quality, which is beneficial for obtaining Tm3Fe5O with anomalous Hall effect. 12 / SnTe epitaxial single-crystal thin-film heterojunction.

[0045] Please see Figure 2 , Figure 2 In this embodiment, Tm3Fe5O is grown on a gadolinium gallium garnet (111) substrate. 12 XRD pattern of single-crystal epitaxial thin film. Figure 2 This indicates that the thin film Tm3Fe5O 12 On the gadolinium gallium garnet substrate, it is along <111> It grows in a directional manner, and no impurity phase was detected in the XRD pattern.

[0046] Please see Figure 3 , Figure 3 This embodiment uses Tm3Fe5O as a substrate based on gadolinium gallium garnet. 12 (111) XRD pattern of SnTe heterojunction single crystal epitaxial film grown on thin film. Figure 3 This indicates that the SnTe thin film in Tm3Fe5O 12 (111) The film is along <100> It grows in a directional manner, and no impurity phase was detected in the XRD pattern.

[0047] Please see Figure 4 , Figure 4 This embodiment uses Tm3Fe5O 12 The curve showing the longitudinal resistance R of a SnTe epitaxial single-crystal thin-film heterojunction as a function of temperature. Figure 4 It can be seen that as the temperature decreases, the longitudinal resistance of the SnTe thin film decreases, exhibiting metallic behavior.

[0048] Please see Figure 5 , Figure 5 For this embodiment, Tm3Fe5O 12 The curves showing the relationship between the anomalous Hall resistance and magnetic field of a SnTe epitaxial single-crystal thin-film heterojunction after removing the linear background at temperatures of 5-20K. Figure 5 It can be seen from the image that the thin film exhibits the characteristics of the anomalous Hall effect.

[0049] Comparative Example 1

[0050] Tm3Fe5O 12 The thickness of the single-crystal epitaxial film is 50 nm, and the thickness of the SnTe single-crystal epitaxial film is 5 nm.

[0051] The obtained Tm3Fe5O 12 The linear magnetoresistance of the / SnTe single-crystal epitaxial thin film heterojunction mainly comes from the interface interaction between the ferromagnetic insulator and the topological crystal insulator in the heterojunction.

[0052] See Figure 7 , Figure 7 Tm3Fe5O as described in Comparative Example 1 12 / SnTe single-crystal epitaxial thin film heterojunction, curves showing the relationship between lateral resistance Rxy and magnetic field at different temperatures. From Figure 7 It can be seen that the thin film does not have the dual-carrier characteristics of the Hall effect, but rather the linear characteristics of the Hall effect curve.

[0053] The vacuum system refers to a system with a pressure of less than or equal to 10. -4 A closed system. In this embodiment of the invention, the vacuum system may be a high-vacuum system equipped with a pulsed laser deposition apparatus.

[0054] The ultra-high vacuum system refers to a system with a pressure of less than or equal to 10. -8 A closed system. In this embodiment of the invention, the ultra-high vacuum system may be an ultra-high vacuum system equipped with a molecular beam epitaxy (MBE) device.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A heterojunction exhibiting an anomalous Hall effect at low temperatures, characterized in that: Tm3Fe5O was epitaxially grown on a gadolinium gallium garnet (111) substrate. 12 Single-crystal thin films, and using these as substrates, were developed in Tm3Fe5O4. 12 Epitaxial growth of SnTe single crystal thin films; Tm3Fe5O 12 The thickness of single-crystal thin films is 50-100 nm, and the thickness of SnTe single-crystal thin films is 15 nm. The heterojunction exhibits an anomalous Hall effect at temperatures below 20K, and temperature modulates the signal magnitude of the anomalous Hall effect.

2. A method for preparing a heterojunction exhibiting an anomalous Hall effect at low temperatures as described in claim 1, characterized in that, Includes the following steps: a) Place the gadolinium gallium garnet (111) substrate in a laser pulse deposition vacuum system; b) Using pulsed laser deposition technology, Tm3Fe5O was grown on the surface of a gadolinium gallium garnet (111) substrate. 12 Epitaxial single-crystal thin films; c) The already grown Tm3Fe5O 12 Epitaxial single-crystal thin films are placed in an ultra-high vacuum system and grown using molecular beam epitaxy on Tm3Fe5O4. 12 SnTe single-crystal thin films are epitaxially grown on the surface of epitaxial single-crystal thin films, ultimately yielding Tm3Fe5O. 12 / SnTe epitaxial single-crystal thin-film heterojunction.

3. The method for preparing a heterojunction exhibiting an anomalous Hall effect at low temperatures according to claim 2, characterized in that: In step a), before placing the gadolinium gallium garnet (111) substrate in the vacuum system, it is sonicated with acetone for 300-500s and then with ethanol for 300-500s.

4. The method for preparing a heterojunction exhibiting an anomalous Hall effect at low temperature according to claim 2, characterized in that: In step b), during the growth of Tm3Fe5O 12 When epitaxial single crystal thin films are used, a gadolinium gallium garnet (111) substrate is used as the substrate, and its temperature is maintained at 600℃-800℃.

5. The method for preparing a heterojunction exhibiting an anomalous Hall effect at low temperature according to claim 2, characterized in that: In step b), during the growth of Tm3Fe5O 12 During the epitaxial deposition of single-crystal thin films, elemental oxygen is introduced into the pulsed laser deposition chamber and maintained at an oxygen pressure of 1 Pa. Tm3Fe5O is then bombarded with a pulsed laser at a repetition frequency of 3-5 Hz and a laser energy of 300-400 mJ. 12 Target material to achieve Tm3Fe5O 12 Epitaxial growth on a gadolinium gallium garnet (111) substrate; after laser blasting, annealing treatment was carried out for 1 hour at a substrate temperature of 600-800℃ and an oxygen pressure of 104 Pa; after annealing, the substrate and film were cooled with the furnace.

6. The method for preparing a heterojunction exhibiting an anomalous Hall effect at low temperature according to claim 2, characterized in that: In step c), before growing the SnTe epitaxial single crystal epitaxial film, Tm3Fe5O2 is used as the substrate. 12 The thin film was ultrasonicated with isopropanol, acetone, and ethanol for 10-30 min respectively; after the Tm3Fe5O12 thin film was placed in an ultra-high vacuum system, it was heated to 600-950℃ and annealed for 1-3 h.

7. The method for preparing a heterojunction exhibiting an anomalous Hall effect at low temperature according to claim 2, characterized in that: In step c), during the growth of the SnTe epitaxial single crystal thin film, a Sn source and a Te source are provided. The evaporation temperature of the Sn source is maintained at 900℃-1000℃, and the growth temperature of the Te source is maintained at 250℃-350℃. During the growth of the SnTe epitaxial single crystal thin film, Tm3Fe5O3 serves as the substrate. 12 The film temperature is maintained at 200-500℃; after growing the SnTe single crystal film, the resulting heterojunction is annealed at 250-500℃ for 1 hour.

8. An application of the heterojunction exhibiting an anomalous Hall effect at low temperatures as described in claim 1, characterized in that: The heterojunction is used to fabricate low-energy spintronic devices.

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