A EuIG / SnTe heterojunction single crystal epitaxial film and its preparation method

Abstract

The present invention relates to a EuIG / SnTe heterojunction single crystal epitaxial film and its preparation method. The preparation method comprises: providing a GGG substrate and placing the GGG substrate in a vacuum system; growing a EuIG film on the surface of the GGG substrate using pulsed laser deposition; and then growing a SnTe film on the surface of the EuIG film as the substrate using molecular beam epitaxy. The method can produce a high-quality single crystal epitaxial ferromagnetic / topological crystalline insulator heterojunction, demonstrating the linear magnetoresistance effect and the Hall effect, a dual-carrier phenomenon, at 5K.

Description

Technical Field

[0001] The present invention belongs to the field of condensed matter physics, and more particularly, relates to a method for generating an interface effect between a ferromagnetic insulator material and a topological crystalline insulator material by constructing a heterojunction, thereby observing a linear magnetoresistance effect and a double-carrier phenomenon accompanied by a Hall effect at 5K. Background Art

[0002] The magnetoresistance effect, also known as the magnetoresistance effect, refers to the phenomenon in which the resistance of a metal or semiconductor through which an electric current flows changes significantly when a magnetic field is applied to it. The magnetoresistance effect was first discovered by Thomson (Lord Kelvin) in 1857 while studying the electrical transport behavior of Fe and Ni under an applied magnetic field. An increase in resistance is usually defined as a positive magnetoresistance effect, while a decrease in resistance is defined as a negative magnetoresistance effect. Semiconductors have large magnetoresistance anisotropy, and the magnetoresistance effect can be used to make magnetoresistive elements, which can be used to construct displacement sensors, speed sensors, position sensors, and velocity sensors. When the magnetoresistance increases linearly with increasing magnetic field and does not saturate at high fields, this phenomenon is called the linear magnetoresistance effect. Research on the linear magnetoresistance phenomenon can probe the properties of electrons and the conduction mechanism in solids and has potential applications in magnetoelectric sensors and storage.

[0003] The Hall effect is a common electromagnetic effect. When a conductor is placed in an external magnetic field and the current in the conductor is perpendicular to the external magnetic field, a significant potential difference will appear between the two end faces of the conductor that are perpendicular to the magnetic field and the direction of the current. This phenomenon is the Hall effect. This is mainly because the electrons that generate the current are affected by the Lorentz force, causing them to move to both sides of the conductor, resulting in charge accumulation and the Hall effect. The Hall effect is a basic phenomenon in condensed matter physics. It is widely used in fields such as determining the carrier type and carrier density of samples and measuring magnetic field strength. Among them, the two-carrier phenomenon of the Hall effect is a relatively unique physical phenomenon that plays an important role in exploring the electron transport mechanism of materials. Summary of the Invention

[0004] In view of this, there is a real need to provide a magnetic film with linear magnetoresistance and a method for preparing the same. The present invention describes a EuIG / SnTe heterojunction single-crystal epitaxial film in which EuIG exhibits out-of-plane ferromagnetism and a Curie temperature of up to 568K. Under certain film thicknesses, the formation of a heterojunction between the ferromagnetic insulator EuIG and the topological crystalline insulator SnTe can induce an interface effect, thereby achieving a material with linear magnetoresistance, namely the EuIG / SnTe heterojunction single-crystal epitaxial film provided by the present invention. The present invention also provides a method for preparing the film, which can produce a high-quality thin film material with linear magnetoresistance that exhibits a linear magnetoresistance effect at 5K and a two-carrier phenomenon associated with the Hall effect.

[0005] The technical solutions of the present invention are as follows:

[0006] A EuIG / SnTe heterojunction single crystal epitaxial film is characterized in that a EuIG (110) single crystal epitaxial film is grown on the surface of a GGG (110) substrate, and a SnTe (100) single crystal epitaxial film is grown on the surface of the film.

[0007] As a preferred technical solution, the substrate has a thickness of 0.2-1.0 mm, the EuIG single crystal epitaxial film has a thickness of 10-100 nm, and the SnTe single crystal epitaxial film has a thickness of 5-30 nm.

[0008] A method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film, characterized by comprising the following steps:

[0009] a) placing the GGG(110) substrate in a vacuum system;

[0010] b) growing a EuIG single crystal epitaxial thin film on the surface of a GGG (110) substrate using pulsed laser deposition technology;

[0011] c) placing the grown EuIG single crystal epitaxial film in an ultra-high vacuum system, and growing a SnTe single crystal epitaxial film on the surface of the EuIG film using molecular beam epitaxial growth technology, thereby finally preparing a EuIG / SnTe heterojunction single crystal epitaxial film.

[0012] As the preferred technical solution:

[0013] In step a), before placing the substrate in a vacuum system, the substrate is ultrasonicated with acetone for 300s-500s, and then ultrasonicated with ethanol for 200s-400s.

[0014] In step b), when growing the EuIG single crystal thin film, the substrate temperature is maintained at 650° C.-800° C.

[0015] When growing EuIG single crystal thin films, a EuIG target is provided, the chamber temperature is maintained at 650°C-800°C, oxygen is introduced, and the oxygen pressure is maintained at 0.5Pa-5.0Pa; a pulsed laser is used to strike the EuIG target at a laser repetition frequency of 3Hz-5Hz and a laser energy of 350mJ-450mJ to obtain a EuIG thin film; after the laser striking is completed, an annealing treatment is performed at 650°C-750°C for 1h-3h, and the EuIG thin film sample is taken out.

[0016] In step c), before growing the SnTe single crystal thin film, the EuIG thin film serving as the substrate is ultrasonically treated for 10-30 minutes using isopropyl alcohol, acetone, and ethanol, respectively. The ultrasonic treatment removes impurities from the substrate surface to ensure a clean and flat surface. The substrate is then heated to 700-900°C and annealed for 1-1.5 hours.

[0017] When growing the SnTe single crystal thin film, the temperature of the EuIG thin film as the substrate is maintained at 300°C-400°C.

[0018] When growing the SnTe single crystal thin film, a Sn source and a Te source are provided respectively. The growth temperature of the Sn source is maintained at 970° C.-1000° C., and the growth temperature of the Te source is maintained at 270° C.-330° C.

[0019] After growing the SnTe single crystal thin film, the obtained EuIG / SnTe heterojunction single crystal epitaxial thin film is annealed at 300° C.-400° C. for 1 h-1.5 h.

[0020] Compared with the prior art, the present invention has at least the following advantages:

[0021] First, the molecular beam epitaxial growth technology can achieve precise control of the growth process and morphology of SnTe single crystal thin films at the atomic level, and produce high-quality SnTe films with strictly controllable chemical composition.

[0022] Second, using EuIG thin film as the substrate, the lattice constants of EuIG and SnTe are integer multiples, resulting in a small lattice mismatch between single crystals, which ensures the two-dimensional epitaxial growth of SnTe on the EuIG surface. Furthermore, EuIG has a high dielectric constant at low temperatures, effectively shielding the interactions between charge carriers and achieving a strong EuIG / SnTe interface effect.

[0023] Third, EuIG has out-of-plane magnetism, which can affect the surface state of SnTe through the interface effect, and is expected to produce a linear magnetoresistance effect.

[0024] Fourth, the ferromagnetic insulator and topological crystalline insulator heterojunction film prepared by the method of the present invention can exhibit a linear magnetoresistance effect and a double-carrier phenomenon accompanied by the Hall effect at 5K. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Example 1.

[0026] Figure 2 This is the X-ray diffraction pattern (XRD) of the EuIG (110) single crystal epitaxial thin film grown on the GGG (110) substrate provided in Example 1.

[0027] Figure 3 The X-ray diffraction pattern (XRD) of the SnTe(100) heterojunction single crystal epitaxial thin film grown on the EuIG(110) thin film with GGG(110) as the substrate provided in Example 1.

[0028] Figure 4 This is the atomic force topography image of the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Example 1.

[0029] Figure 5 This is a curve showing the change in longitudinal sheet resistance of the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Example 1 as a function of temperature.

[0030] Figure 6 This is a curve showing the change of magnetoresistance with magnetic field at 5K for the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Example 1.

[0031] Figure 7 This is a curve showing the change of the lateral resistance of the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Example 1 at 5K as a function of the magnetic field.

[0032] Figure 8 This is a curve showing the change of magnetoresistance with magnetic field at 5K for the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Example 2.

[0033] Figure 9 This is a curve showing the change of magnetoresistance with magnetic field at 5K for the EuIG / SnTe heterojunction single crystal epitaxial thin film provided in Comparative Example 1.

[0034] Figure 10 The lateral resistance R of the EuIG / SnTe heterojunction single crystal epitaxial film at 5K provided in Comparative Example 1 is xy The relationship curve with the change of magnetic field.

[0035] Figure 11This is a curve showing the change of magnetoresistance with magnetic field at 5K for the YIG / SnTe heterojunction single crystal epitaxial film provided in Comparative Example 2.

[0036] Figure 12 The lateral resistance R of the YIG / SnTe heterojunction single crystal epitaxial film at 5K provided in Comparative Example 2 is xy The relationship curve with the change of magnetic field. DETAILED DESCRIPTION

[0037] The EuIG / SnTe heterojunction single crystal epitaxial thin film and the preparation method thereof provided by the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] See Figure 1 The embodiment of the present invention provides a thin film with a linear magnetoresistance effect, which includes a GGG (110) substrate and a EuIG / SnTe heterojunction single crystal epitaxial film. The GGG (110) substrate and the EuIG / SnTe heterojunction single crystal film are stacked in sequence. The EuIG single crystal film is located on the GGG substrate and is stacked by pulsed laser deposition growth, and the SnTe single crystal film and the EuIG film are stacked by molecular beam epitaxial growth.

[0039] The EuIG film has a high dielectric constant, which helps shield carrier interactions. To facilitate observation of the film's magnetoresistance and Hall effects using electrical transport measurements, a high-resistance insulating substrate can be selected. Preferably, the GGG substrate is a single-crystalline insulating substrate.

[0040] The lattice constant of the GGG substrate is 1.238 nanometers. The lattice mismatch between the GGG substrate and the EuIG single crystal thin film is approximately 0.9%. This small lattice mismatch facilitates the growth of high-quality EuIG single crystal thin films on this substrate. The lattice constant of SnTe is 0.63 nanometers, and the lattice mismatch with EuIG is approximately 0.8%. This small lattice mismatch facilitates the growth of high-quality SnTe single crystal thin films on this substrate.

[0041] The vacuum system refers to a system with an air pressure less than or equal to 10 -4 In the embodiment of the present invention, the vacuum system can be a high vacuum system equipped with a pulsed laser deposition device.

[0042] The ultra-high vacuum system refers to a system with an air pressure less than or equal to 10 -8 In the embodiment of the present invention, the ultra-high vacuum system can be an ultra-high vacuum system equipped with a molecular beam epitaxial growth device.

[0043] Example 1

[0044] The thickness of the GGG substrate used is about 0.5 mm, the thickness of the EuIG single crystal epitaxial film is 25 nm, and the thickness of the SnTe single crystal epitaxial film is 15 nm.

[0045] The linear magnetoresistance of the EuIG / SnTe heterojunction single crystal epitaxial film mainly comes from the interface interaction between the ferromagnetic insulator and the topological crystalline insulator in the film. The film is prepared as follows:

[0046] a) using acetone to sonicate the GGG(110) substrate for 480 s, then sonicating it with ethanol for 280 s, and then placing the substrate in a vacuum system;

[0047] b) growing a EuIG single crystal epitaxial thin film on the surface of a GGG (110) substrate using pulsed laser deposition technology;

[0048] During the growth of EuIG single crystal thin films, the substrate temperature was maintained at approximately 700°C. A EuIG target was provided, the chamber temperature maintained at 700°C, and oxygen was introduced, maintaining the oxygen pressure at 0.5 Pa to 1.5 Pa. A pulsed laser was then applied to the EuIG target at a laser repetition rate of 5 Hz and a laser energy of 400 mJ to produce the EuIG thin film. Following the laser strike, the target was annealed at 700°C to 750°C for 1 hour to obtain a single crystal epitaxial EuIG thin film with good crystallinity. The resulting EuIG film sample was then removed.

[0049] c) placing the grown EuIG single crystal epitaxial film in an ultra-high vacuum system, and growing a SnTe single crystal epitaxial film on the surface of the EuIG film using molecular beam epitaxial growth technology, thereby finally preparing a EuIG / SnTe heterojunction single crystal epitaxial film.

[0050] Before growing the SnTe single crystal film, the EuIG film as the substrate was ultrasonically treated with isopropyl alcohol, acetone, and ethanol for 10 minutes, and then heated to 800°C and annealed for 1 hour.

[0051] When growing the SnTe single crystal thin film, the temperature of the EuIG thin film as the substrate is maintained at 350°C. A Sn source and a Te source are provided respectively. The growth temperature of the Sn source is maintained at 985°C, and the growth temperature of the Te source is maintained at 300°C.

[0052] After the growth of the SnTe single crystal thin film, the obtained EuIG / SnTe heterojunction single crystal epitaxial thin film was annealed at 350° C. for 1 hour.

[0053] The various parameters adopted in the embodiments of the present invention can ensure that the grown EuIG / SnTe heterojunction single crystal epitaxial thin film has good film quality, thereby facilitating the acquisition of a EuIG / SnTe heterojunction single crystal thin film with a linear magnetoresistance effect.

[0054] See Figure 2 , Figure 2 This is the XRD spectrum of the EuIG single crystal epitaxial thin film grown on the GGG (110) substrate in an embodiment of the present invention. Figure 2 It shows that the thin film EuIG on the GGG substrate is along <110> direction, and no impurity phase was detected in the XRD pattern.

[0055] See Figure 3 , Figure 3 This is the XRD spectrum of the SnTe heterojunction single crystal epitaxial film grown on the EuIG (110) film with GGG as the substrate in an embodiment of the present invention. Figure 3 It shows that the SnTe film is formed on the EuIG(110) film along the <100> The peak of Te in the XRD pattern comes from the Te covering layer grown to prevent the sample from oxidation.

[0056] See Figure 4 , Figure 4 This is an atomic force topography image of the EuIG / SnTe heterojunction single crystal epitaxial film according to an embodiment of the present invention. The area of the image is 3μm×3μm. Figure 4 It can be seen that the film shows cubic shaped grains.

[0057] See Figure 5 , Figure 5 : is a curve showing the change of the longitudinal sheet resistance Rs of the EuIG / SnTe heterojunction single crystal epitaxial thin film with temperature in the embodiment of the present invention. Figure 5 It can be seen that as the temperature decreases, the longitudinal resistance of the SnTe film decreases, showing metallic behavior.

[0058] See Figure 6 , Figure 6 This is a curve showing the relationship between the magnetoresistance MR and the magnetic field of the EuIG / SnTe heterojunction single crystal epitaxial film according to the embodiment of the present invention at a temperature of 5K. Figure 6 It can be seen that the film has the characteristics of linear magnetoresistance effect.

[0059] See Figure 7 , Figure 7 The lateral resistance R of the EuIG / SnTe heterojunction single crystal epitaxial thin film at a temperature of 5K is xy The relationship curve with the change of magnetic field. Figure 7It can be seen that the film has the dual-carrier characteristics of the Hall effect.

[0060] Example 2

[0061] The thickness of the GGG substrate used is about 0.5 mm, the thickness of the EuIG single crystal epitaxial film is 75 nm, and the thickness of the SnTe single crystal epitaxial film is 15 nm.

[0062] The linear magnetoresistance of the EuIG / SnTe heterojunction single crystal epitaxial film mainly comes from the interface interaction between the ferromagnetic insulator and the topological crystalline insulator in the film. The preparation method of this film is the same as that of Example 1, except that the thickness of the EuIG single crystal epitaxial film is 75 nm.

[0063] The various parameters adopted in the embodiments of the present invention can ensure that the grown EuIG / SnTe heterojunction single crystal epitaxial thin film has good film quality, thereby facilitating the acquisition of a EuIG / SnTe heterojunction single crystal thin film with a linear magnetoresistance effect.

[0064] See Figure 8 , Figure 8 This is a curve showing the relationship between the magnetoresistance MR and the magnetic field of the EuIG / SnTe heterojunction single crystal epitaxial film according to the embodiment of the present invention at a temperature of 5K. Figure 8 It can be seen that the film has the characteristics of linear magnetoresistance effect.

[0065] Comparative Example 1

[0066] The thickness of the GGG substrate used is about 0.5 mm, the thickness of the EuIG single crystal epitaxial film is 150 nm, and the thickness of the SnTe single crystal epitaxial film is 15 nm.

[0067] The linear magnetoresistance of the EuIG / SnTe heterojunction single crystal epitaxial film mainly comes from the interface interaction between the ferromagnetic insulator and the topological crystalline insulator in the film. The preparation method of this film is the same as that of Example 1, except that the thickness of the EuIG single crystal epitaxial film is 150 nm.

[0068] See Figure 9 , Figure 9 This is the curve of the magnetoresistance MR of the EuIG / SnTe heterojunction single crystal epitaxial film described in Comparative Example 1 of the present invention as a function of the magnetic field at a temperature of 5K. Figure 9 It can be seen that the film does not have the characteristics of linear magnetoresistance effect.

[0069] See Figure 10 , Figure 10 The lateral resistance R of the EuIG / SnTe heterojunction single crystal epitaxial thin film described in Comparative Example 1 of the present invention at a temperature of 5K is xy The relationship curve with the change of magnetic field. Figure 10 It can be seen that the film does not have the dual-carrier characteristics of the Hall effect, but rather a linear Hall effect curve characteristic.

[0070] Comparative Example 2

[0071] The thickness of the GGG (111) substrate used is about 0.5 mm, the thickness of the YIG (111) single crystal epitaxial film is 150 nm, and the thickness of the SnTe single crystal epitaxial film is 15 nm.

[0072] The difference from the embodiment is that YIG has in-plane ferromagnetism and the Curie temperature can reach 550 K. The linear magnetoresistance of the YIG (111) / SnTe (100) heterojunction single crystal epitaxial film is parabolic at 5 K, and the Hall effect curve is linear.

[0073] See Figure 11 , Figure 11 This is the relationship curve of the magnetoresistance MR of the YIG / SnTe heterojunction single crystal epitaxial film described in Comparative Example 2 of the present invention as a inverse of the magnetic field at a temperature of 5K. Figure 11 It can be seen that the film does not have the characteristics of linear magnetoresistance effect and exhibits a parabolic curve characteristic.

[0074] See Figure 12 , Figure 12 The lateral resistance R of the YIG / SnTe heterojunction single crystal epitaxial film described in Comparative Example 2 of the present invention at a temperature of 5K is xy The relationship curve with the change of magnetic field. Figure 12 It can be seen that the film does not have the dual-carrier characteristics of the Hall effect, but rather a linear Hall effect curve characteristic.

[0075] Matters not covered by the present invention are known technologies.

[0076] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A EuIG / SnTe heterojunction single crystal epitaxial thin film, characterized by: A EuIG (110) single crystal epitaxial film is grown on the surface of a GGG (110) substrate, and a SnTe (100) single crystal epitaxial film is grown on the surface of the film; the EuIG single crystal epitaxial film has a thickness of 10-100 nm, and the SnTe single crystal epitaxial film has a thickness of 5-30 nm.

2. A method for preparing the EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 1, characterized in that: The following steps are involved: a) placing the GGG(110) substrate in a vacuum system; b) growing a EuIG single crystal epitaxial thin film on the surface of a GGG(110) substrate using pulsed laser deposition technology; c) placing the grown EuIG single crystal epitaxial film in an ultra-high vacuum system, and growing a SnTe single crystal epitaxial film on the surface of the EuIG film using molecular beam epitaxial growth technology, thereby finally preparing a EuIG / SnTe heterojunction single crystal epitaxial film.

3. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: In step a), before placing the substrate in a vacuum system, the substrate is ultrasonicated with acetone for 300s-500s, and then ultrasonicated with ethanol for 200s-400s.

4. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: In step b), when growing the EuIG single crystal thin film, the substrate temperature is maintained at 650° C.-800° C.

5. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: In step b), when growing a EuIG single crystal thin film, a EuIG target is provided, the chamber temperature is maintained at 650°C-800°C, oxygen is introduced, and the oxygen pressure is maintained at 0.5Pa-5.0Pa; a pulsed laser is used to strike the EuIG target at a laser repetition frequency of 3Hz-5Hz and a laser energy of 350mJ-450mJ to obtain a EuIG thin film; after the laser striking is completed, annealing treatment is performed at 650°C-750°C for 1h-3h, and the EuIG thin film sample is taken out.

6. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: In step c), before growing the SnTe single crystal thin film, the EuIG thin film as the substrate is ultrasonically treated with isopropyl alcohol, acetone, and ethanol for 10-30 minutes, and then heated to 700° C.-900° C. for 1-1.5 hours for annealing.

7. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: In step c), when growing the SnTe single crystal thin film, the temperature of the EuIG thin film serving as the substrate is maintained at 300°C-400°C; when growing the SnTe single crystal thin film, a Sn source and a Te source are provided respectively, the growth temperature of the Sn source is maintained at 970°C-1000°C, and the growth temperature of the Te source is maintained at 270°C-330°C.

8. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: In step c), after growing the SnTe single crystal thin film, the obtained EuIG / SnTe heterojunction single crystal epitaxial thin film is annealed at 300° C.-400° C. for 1 h-1.5 h.

9. The method for preparing a EuIG / SnTe heterojunction single crystal epitaxial thin film according to claim 2, characterized in that: The EuIG / SnTe heterojunction single crystal epitaxial thin film exhibits a linear magnetoresistance effect and a double-carrier phenomenon accompanied by a Hall effect at 5K.

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