Device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide and preparation method thereof

Abstract

The invention discloses a device for realizing a low-field room-temperature colossal magnetoresistance effect in manganese oxide and a preparation method of the device. The preparation method comprises the following steps: preparing a colossal magnetoresistance-doped rare earth manganese oxide thin film on a substrate to realize an intrinsic phase transition temperature of more than 300K and to be in an antiferromagnetic insulation state; preparing a rare gas solid buffer layer on the surface of the manganese oxide film; depositing isolated ferromagnetic nano islands on the buffer layer so as to directly induce ferromagnetic domain nucleation in an antiferromagnetic phase; and depositing a protective layer on the surface of the iron nano island. The phase separation scale and the original ferromagnetic domain percentage are controlled through the prepared iron nano island, so that the phase separation scale and the original ferromagnetic domain percentage are slightly lower than a seepage threshold value; by applying a small magnetic field, a ferromagnetic domain is induced to grow to form seepage, and the colossal magnetoresistance effect is realized in a low field. The preparation method is simple, and the device can simultaneously realize the colossal magnetoresistance effect at low field and room temperature, is a major breakthrough in the field of spintronics, and is of great significance in application of sensing, storage, brain-like computing and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of colossal magnetoresistance devices, and in particular, relates to a device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide and a preparation method thereof. Background Art

[0002] Spin-related transport properties are the cornerstone of the development of spin electronics. Looking at the development of spin electronics, the key to each breakthrough is the discovery of materials and structures with large magnetoresistance and high spin polarization (half metallic). In the 1990s, astonishingly large magnetoresistance effects (up to 10) were measured in perovskite manganese oxide systems. 6 %), which is the colossal magnetoresistance (CMR) effect, which is several orders of magnitude larger than the GMR and TMR effects, and has attracted great attention. The CMR effect is the result of strong spin-charge correlation. A notable feature is that the metal-insulator phase transition is accompanied by a magnetic phase transition. The energies of the ferromagnetic metal phase (FMM) and the antiferromagnetic charge-ordered insulating phase (AFM-COI) in manganese oxides are very close, and the coexistence of multiple electronic states in space is their ground state. Under the action of an external magnetic field, the antiferromagnetic phase will transform into a ferromagnetic phase, and the latter will reach percolation under a critical magnetic field, resulting in a huge change in resistivity, which is also the main source of the CMR effect. In the past few decades, there have been a large number of studies on the application of the CMR effect in spin electronics such as magnetic storage and magnetic sensors. However, compared with the highly commercialized application of TMR, the CMR effect has not been able to achieve real device applications due to its need for large magnetic fields and phase transition temperatures below room temperature. Therefore, finding new methods to enable the colossal magnetoresistance material system to have a phase transition temperature above room temperature and to achieve percolation under a small field is the key to realizing the application of CMR devices. Summary of the invention

[0003] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide and a preparation method thereof. The present invention completes the ferromagnetic nucleation process in the antiferromagnetic-dominated film by depositing ferromagnetic nanodots on the film surface to create a built-in magnetic exchange field, thereby reducing the external magnetic field required for CMR. The present invention realizes the research and development and application of room-temperature low-field CMR devices through the preparation of high phase transition temperature films, the creation of interface magnetic exchange fields, and small field-induced percolation. With the corresponding control scheme, the phase transition temperature of the CMR device, the size of the required external field, and the range of magnetoresistance values ​​can be controlled.

[0004] The present invention adopts the following technical solutions.

[0005] The present invention provides a method for preparing a device that realizes low-field room-temperature colossal magnetoresistance effect in manganese oxide. The invention relates to inducing ferromagnetic nucleation in a manganese oxide film having an intrinsic phase transition temperature higher than 300K by using iron nano-islands, thereby realizing a low-field room-temperature colossal magnetoresistance effect; the invention comprises the following steps: (1) Under low oxygen pressure conditions, a rare earth-doped manganese oxide film is grown on a substrate, so that the grown manganese oxide film is in an antiferromagnetic insulating state and has an intrinsic phase transition temperature higher than 300K; (2) Under low temperature conditions, preparing a rare gas solid buffer layer on the manganese oxide film obtained in step (1) to regulate the surface energy of the film; (3) In situ deposition of isolated iron nano-islands on the surface of a rare gas solid buffer layer to induce ferromagnetic nucleation in an antiferromagnetic manganese oxide film, thereby reducing the external field for percolation. (4) Sodium chloride is deposited on the surface of the iron nano-islands as a protective layer to prevent the iron nano-islands from being oxidized.

[0006] In the present invention, in step (1), a manganese oxide film is grown by pulsed laser deposition, and the oxygen pressure condition is 5×10 -4 -2×10 -2 Torr, substrate temperature is 1053-1093K; substrate is SrTiO 3 , doped with rare earth manganese oxide as La 0.8 Ca 0.2 MnO 3 or La 0.8 Ca 0.2 MnO 3 / Pr 0.8 Ca 0.2 MnO 3 Superlattice, manganese oxide film thickness is 15-25 nm.

[0007] In the present invention, in step (2), the manganese oxide film is placed in a Xe gas atmosphere and cooled by liquid helium, so that the Xe atoms adsorbed on the surface of the manganese oxide film form a solid Xe atom buffer layer at a low temperature of 15K-30K; -6 Under Torr Xe gas pressure, it is maintained for 200-428 seconds, and the thickness of the rare gas solid buffer layer is between 20 and 40 layers.

[0008] In the present invention, in step (3), an electron beam deposition method is used to evaporate iron at a temperature of 15-30K and ultra-vacuum conditions, and an iron nano-island with a diameter of 5-10nm and a height of 2-10nm is grown at a rate of 0.02-0.06Å / min. The density and size of the obtained iron nano-islands satisfy that: when the rare gas solid buffer layer is vaporized, the iron nano-islands fall onto the surface of the manganese oxide, and the iron nano-islands induce ferromagnetic nucleation in the antiferromagnetic manganese oxide film, and the volume percentage of the ferromagnetic domain is slightly lower than the percolation threshold.

[0009] In the present invention, in step (4), an electron beam deposition method is used to grow a 5-15 nm sodium chloride film covering layer at a temperature of 15-30 K using an electron beam to heat the crucible; the sodium chloride growth rate is 0.2-0.8 Å / min.

[0010] The present invention also provides a device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide obtained by the above-mentioned preparation method, which comprises, from bottom to top, a substrate, a manganese oxide film, a rare gas solid buffer layer, an iron nano-island and a sodium chloride protective layer. Preferably, the substrate is SrTiO 3 , manganese oxide film is La 0.8 Ca 0.2 MnO 3 or La 0.8 Ca 0.2 MnO 3 / Pr 0.8 Ca 0.2 MnO 3 The thickness of the superlattice film and the manganese oxide film is 15-25 nm; the rare gas solid buffer layer is a solid Xe atomic buffer layer, the thickness of which is between 20 and 40 layers, and the thickness of the sodium chloride protective layer is 5-15 nm.

[0011] Furthermore, the present invention provides an application of the above device in realizing low-field room-temperature colossal magnetoresistance effect, and the application method is as follows: 1) The device is placed in a room temperature environment. The rare gas solid buffer layer vaporizes during the heating process, and the iron nano-islands fall onto the surface of the manganese oxide. The magnetic exchange field between the iron nano-islands and the surface of the manganese oxide is used to induce ferromagnetic nucleation in the antiferromagnetic manganese oxide film. At this time, the volume percentage of the ferromagnetic domain is lower than the percolation threshold, the ferromagnetic domain is close to the edge of the percolation, and the film is in an insulating state. 2) Apply a small external magnetic field of tens to hundreds of Gauss to the film to induce the growth of ferromagnetic domains. When the ferromagnetic volume percentage exceeds the percolation threshold, the system undergoes an insulator-metal transition, forming a low-resistance state and realizing the low-field colossal magnetoresistance effect.

[0012] Compared with the existing magnetoresistance effect device, the beneficial effects of the present invention are: (1) By regulating substrate stress (which includes in-plane stress caused by lattice mismatch between substrate and film, and out-of-plane stress caused by film thickness), rare earth doping concentration and oxygen defects, the film is in an antiferromagnetic state at room temperature but has an intrinsic phase transition temperature (when there is no oxygen deficiency) higher than room temperature. This is the key to achieving room-temperature colossal magnetoresistance.

[0013] (2) The present invention forms a buffer layer with extremely low surface energy by low-temperature adsorption of rare gases, and uses the thickness of the buffer layer to control the size and density of iron nano-islands; the interfacial magnetic exchange field between the iron nano-islands and manganese oxides is used to achieve nucleation of ferromagnetic domains in the antiferromagnetic phase, and the size and density of the iron nano-islands are used to control the size and density of nucleation, thereby greatly reducing the external field required for the percolation of ferromagnetic metal domains and achieving a low-field colossal magnetoresistance effect.

[0014] (3) The device prepared by the present invention can ensure that the percolation temperature of the system is higher than room temperature, and does not require a large external magnetic field to induce the transition from antiferromagnetism to ferromagnetism, and maintains a large magnetoresistance effect. The realization of low-field colossal magnetoresistance at room temperature in the device of the present invention will be a major breakthrough in the field of spin electronics, and is of great significance for applications such as sensing, storage, and brain-like computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the sample preparation system of the present invention.

[0016] Figure 2 It is a schematic diagram of the device preparation process of the present invention.

[0017] Figure 3 FIG. 4 is a surface morphology diagram of a manganese oxide film in one embodiment of the present invention.

[0018] Figure 4 1 is a comparison diagram of the magnetic properties of a manganese oxide film prepared under oxygen saturation and oxygen-deficient conditions in one embodiment of the present invention.

[0019] Figure 5 Schematic diagram of three different growth modes of a thin film in one embodiment of the present invention.

[0020] Figure 6 It is a schematic diagram of low temperature refrigeration in one embodiment of the present invention.

[0021] Figure 7 It is a schematic diagram of controlling the thickness, density and volume of the Xe atomic buffer layer as the iron deposition amount changes in one embodiment of the present invention, and a schematic diagram of regulating the size and density of iron nano-islands with different Xe atomic buffer layer thicknesses.

[0022] Figure 8 Schematic diagram of the change in size and density of iron nano-islands in one embodiment of the present invention.

[0023] Fig. 9FIG. 4 is a schematic diagram of the morphology of iron nano-islands in one embodiment of the present invention.

[0024] Fig.10 It is a schematic diagram of percolation formed by a low-field room-temperature colossal magnetoresistance effect device under the action of a small field in one embodiment of the present invention.

[0025] Markings in the figure: 1- sample transfer rod, 2- fast sample introduction chamber, 3- reflection high energy electron diffractometer, 4- first gate valve, 5- main cavity, 6- fluorescent screen, 7- infrared fiber alignment system, 8- ultraviolet laser lens system, 9- sample holder, 10- adapter flange, 11- second gate valve, 12- molecular beam epitaxy cavity, 13- sample holder with reduced temperature, 14- electron beam evaporator, 15- film thickness monitor, 16- sample transfer rod. DETAILED DESCRIPTION

[0026] In order to make the technical solution of the present invention clearer, the following is further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described below are only used to explain the present invention and are not used to limit the present invention.

[0027] The following describes a portion of several possible embodiments of the present invention, which is intended to provide a basic understanding of the present invention, but is not intended to identify the key or decisive elements of the present invention or to limit the scope of protection claimed.

[0028] The present invention provides a device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide, wherein a manganese oxide film is grown by pulsed laser deposition (PLD), and an iron nano-island and a sodium chloride protective layer are grown by molecular beam epitaxy.

[0029] The present invention provides a method for preparing a low-field room-temperature colossal magnetoresistance effect device in a manganese oxide film, which comprises: The manganese oxide film is grown on a tensile stress substrate. By regulating stress and doping, the manganese oxide film has an intrinsic phase transition temperature higher than 300K. By reducing the oxygen pressure, the film grown under oxygen-deficient conditions is in an antiferromagnetic insulating state, but has an intrinsic phase transition temperature higher than room temperature. T C (When there is no lack of oxygen).

[0030] Prepare rare gas solid buffer layers of different thicknesses under low temperature conditions to control the surface energy of the film; In-situ deposition of isolated iron nanoislands on the film surface under ultra-high vacuum; Sodium chloride is deposited on the top of the film as a protective layer to protect the iron nano-islands from oxidation; The huge magnetic exchange field between the Fe spin of the iron nano-island and the Mn spin of the manganese oxide below it is used to induce the Mn spin to be parallel to the Fe spin, thereby directly inducing a ferromagnetic phase in the antiferromagnetic phase (i.e., ferromagnetic domain nucleation), forming a coexistence state of the antiferromagnetic insulating phase and the ferromagnetic metal phase. This process is completely completed by the built-in magnetic exchange field, and does not require any external magnetic field. By changing the thickness of the rare gas solid buffer layer, the size and density of the iron nano-island are controlled, so that the ferromagnetic domains in the film are close to the edge of the percolation, and the system is still in a high-resistance state. However, since the ferromagnetic domains have been nucleated, the system only needs a small magnetic field (usually tens to hundreds of Gauss) to align the magnetization direction of the nucleated ferromagnetic domains along the external field direction, and under the action of the huge magnetic exchange between the ferromagnetic / antiferromagnetic domains, the adjacent antiferromagnetic phase is assisted to transform into the ferromagnetic phase to complete the growth of the ferromagnetic domain, thereby forming a conductive path between the discrete ferromagnetic domains, resulting in a sharp decrease in resistivity and reaching a low-resistance state. In this process, the huge built-in magnetic exchange field of the iron nano-island completely replaces the role of the external magnetic field to complete the nucleation of the ferromagnetic domain, which can greatly reduce the size of the external field required for CMR; at the same time, it also effectively increases the ferromagnetic ratio, allowing the system to return to a high phase transition temperature above room temperature. The role of the external field is only to align the spins of the ferromagnetic domains, and the solid external field consumption will be greatly reduced. As a result, the external field required by the system is minimized and high magnetic resistance is guaranteed, achieving room temperature low-field CMR effect.

[0031] Figure 1 The present invention is a system for preparing a device that can realize low-field room temperature colossal magnetoresistance effect in a manganese oxide thin film according to an embodiment of the present invention. The system consists of two parts, a pulsed laser deposition system (PLD) on the left and a molecular beam epitaxy system (MBE) on the right, which are connected in the middle by an adapter flange 10 and a second gate valve 11. The PLD system includes a sample transfer rod 1, a fast sample injection chamber 2 and a main chamber 5, a first gate valve 4, which is used to separate the fast sample injection chamber and the main chamber 5, and the main chamber 5 is provided with a reflection high-energy electron diffractometer 3, and works together with a fluorescent screen 6. Component 7 is an infrared fiber collimation system, and the infrared heating laser can be focused on the substrate through the infrared fiber collimation system 7 to achieve heating of the substrate. Component 8 is an ultraviolet laser lens system, and an excimer laser can generate ultraviolet laser, which can be focused on the target material through the ultraviolet laser lens system 8, thereby generating plasma. Component 9 is a sample holder. The MBE system includes a molecular beam epitaxy chamber 12 and a sample transfer rod 16, with a sample holder 13 on top that can be cooled, an electron beam evaporator 14, and a film thickness monitor 15. In addition, there are some mechanical pumps, molecular pumps, ion pumps, and vacuum gauges to maintain and monitor the vacuum degree of the system.

[0032] like Figure 2 FIG. 1 is a process for preparing a room temperature low field colossal magnetoresistance device in a manganese oxide thin film according to an embodiment of the present invention.0.8 Ca 0.2 MnO 3 The film can achieve temperatures above 300K under specific tensile stress (~2%) and specific Ca doping concentration (~0.2). T C , exceeding any doping concentration of La 1-x Ca x MnO 3 The present invention uses pulsed laser deposition to deposit SrTiO 3 Large-area La epitaxial growth on (001) substrate 0.8 Ca 0.2 MnO 3 The surface morphology of the film was obtained by atomic force microscopy ( Figure 3 ), its surface is flat at the atomic level. Under the action of substrate stress and doping, its intrinsic phase transition temperature of oxygen saturation state can reach above 300K; by controlling the growth conditions (such as low oxygen pressure), the LCMO film is in an antiferromagnetic insulating state due to lack of oxygen at room temperature ( Figure 4 ).

[0033] like Figure 5 As shown in a, the growth mode of the film on the substrate depends on the surface energy γ of the substrate. s , the surface energy of the film γ f and the interface energy γ between substrate and film sf When γ s >γ f+ γ sf When the film is in the layered growth mode ( Figure 5 b); when γ s <γ f+ γ sf When the film is in a three-dimensional island growth mode ( Figure 5 c); when γ s >γ f+ γ sf When there is a lattice mismatch between the substrate and the film, the film is a layered growth + island growth mode ( Figure 5 d). Due to La 0.8 Ca 0.2 MnO 3 The surface energy of the film is high, which cannot guarantee the three-dimensional island growth of iron atoms. In the present invention, a low surface energy buffer layer is constructed to achieve the three-dimensional growth of iron nano-islands. 0.8 Ca 0.2 MnO 3 The film is placed in a Xe gas atmosphere, and the sample holder is cooled by liquid helium. The Xe atoms adsorbed on the surface of the manganese oxide film form a solid Xe atomic buffer layer at low temperature ( Figure 2b). The thickness of the solid Xe atom buffer layer is adjusted by controlling the adsorption time to control the surface energy. Isolated iron nano-islands are deposited on the surface of the film, and a NaCl protective layer is grown on the top layer to protect the iron nano-islands from oxidation ( Figure 2 c). After the deposition is completed, the sample is transferred from the low-temperature sample holder to the room-temperature sample storage table. As the temperature rises, the Xe atoms vaporize and desorb, and the iron nano-islands fall onto the surface of the manganese oxide ( Figure 2 d). The built-in magnetic exchange field between the iron nano-islands and manganese oxides can induce ferromagnetic nucleation and ferromagnetic domain growth. The La 0.8 Ca 0.2 MnO 3 The electronic phase separation state and ferromagnetic ratio of the film put it on the edge of percolation, so it is expected that by applying a small magnetic field, the ferromagnetic domains can grow to form percolation, causing an insulator-metal phase transition and realizing the colossal magnetoresistance effect at room temperature and low field.

[0034] In a specific embodiment, a SrTiO 3 The (001) substrate is cleaned and mounted on the sample holder, and the sample holder is placed on the trolley in the sample transfer rod 1. The rapid sample chamber 2 is evacuated, and then the sample is transferred from the rapid sample chamber to the sample rack 9 in the main chamber 5 by the sample transfer rod 1. Oxygen is introduced into the main chamber 5 through the oxygen tube to a pressure of 8×10 -4 In an oxygen environment of 1000 Torr, the infrared heating laser was turned on to gradually heat the sample to 1073 K at a rate of 20 K / min. The excimer laser was turned on and the target stage self-propagation program was turned on at λ = 248 nm, 2 Hz, 1 J / cm 2 Laser strike La 0.8 Ca 0.2 MnO 3 Target material, grow 20nm La 0.8 Ca 0.2 MnO 3 During the growth process, the number of layers grown was monitored in real time using a reflection high energy electron diffractometer 3. Figure 2 As shown in a.

[0035] After the growth is completed, the temperature is lowered and the oxygen is turned off. The second gate valve 11 is opened, and the sample is transferred to the sample holder 13 in the molecular beam epitaxy chamber 12 through the sample transfer rod 16, and the second gate valve 11 is closed. Liquid helium is introduced from the liquid helium pipeline to cool the sample holder, and the film sample is cooled to 15K. Figure 6 As shown. Xe gas was introduced and the pressure was controlled at 10 -6 Torr, maintained for 200-428 seconds, that is, the exposure amount of Xe is 200-428L (1L=1*10 -6Torr*s), so that the Xe atoms adsorbed on the surface of manganese oxide form a solid buffer layer, and about 20-40 layers of Xe are grown, such as Figure 2 As shown in b.

[0036] Then, iron nanoparticles ( Figure 2 c) A 1.58A current was passed through the tungsten wire of the electron beam evaporator and a voltage of 800V was applied to the iron rod, growing at a rate of 0.055 Å per minute. Figure 7 As shown, the size and density of the iron nanoparticles can be determined by the thickness of the adsorbed Xe atomic buffer layer and the dosage of the growing iron. By controlling the Xe adsorption time and adjusting the time of iron growth, iron nanoparticles of different sizes and densities can be obtained ( Figure 8 Specifically, for example, when the Xe exposure is 200 L and the Fe dose is 1 layer, the average volume of the Fe nanoparticles obtained is 12 nm. 3 , the average density is 1.0*10 4 / μm -2 .

[0037] Electron beam evaporation is used to heat the sodium chloride in the crucible ( Figure 2 c) Growing sodium chloride as a protective layer to protect the iron nano-islands from oxidation.

[0038] Finally, the sample is transferred from the low-temperature sample rack to the room-temperature sample rack. When the sample is heated to room temperature, the Xe atoms vaporize and desorb, and the iron nano-islands fall onto the surface of the manganese oxide ( Figure 2 d). This process was used to prepare a SrTiO 3 La on (001) substrate 0.8 Ca 0.2 MnO 3 Colossal magnetoresistance device ( Fig. 9 ).

[0039] After the growth is completed, the device is taken out and placed on the trolley of the sample transfer rod 16, and the second gate valve 11 is opened to transfer the device to the sample rack 8. The second gate valve 11 is closed, the first gate valve 4 is opened, the sample is transferred to the trolley in the sample transfer rod 1, and then transferred to the fast sample injection chamber and the first gate valve 4 is closed. After the vacuum in the fast sample injection chamber is broken, the prepared device can be taken out.

[0040] The performance of the device obtained above was tested by using a multi-functional physical property measurement system (PPMS). By applying a very small field (tens to hundreds of gauss), a conductive path can be formed between discrete ferromagnetic domains, resulting in a sharp decrease in resistivity (percolation) and reaching a low resistance state, such as Fig.10As shown. The test data also show that its phase transition temperature is around 300 K. In this way, a device that realizes low-field room-temperature colossal magnetoresistance effect in manganese oxide thin film is obtained.

[0041] In summary, the present invention uses pulsed laser deposition (PLD) to prepare a colossal magnetoresistance manganese oxide film on a substrate, and realizes an intrinsic phase transition temperature of more than 300K under the action of substrate stress and doping, which is the basis for realizing the colossal magnetoresistance effect at room temperature; by changing the growth conditions (such as reducing the oxygen pressure), the manganese oxide film is in an antiferromagnetic insulating state due to lack of oxygen at room temperature; the cavity is filled with xenon (Xe) gas to adsorb xenon gas on the surface of the film; liquid helium is used for cooling, so that the xenon gas forms a solid xenon atomic buffer layer under extremely low temperature conditions, and the thickness of the buffer layer is used to control the size of the surface energy; isolated ferromagnetic nano-islands are deposited on the solid xenon atomic buffer layer by electron beam evaporation, and the built-in magnetic exchange field between the iron nano-islands and the surface of the manganese oxide film is used to directly induce the nucleation of ferromagnetic domains in the antiferromagnetic phase; finally, NaCl is deposited on the surface of the iron nano-islands by electron beam evaporation as a protective layer to prevent the iron nano-islands from being oxidized. By preparing iron nano-islands of different sizes and densities, the phase separation scale and the percentage of original ferromagnetic domains are controlled to be slightly below the percolation threshold; by applying a small magnetic field, the ferromagnetic domains are induced to grow to form percolation, completing the insulator-metal phase transition, thereby realizing the colossal magnetoresistance effect under low field. The preparation method of the present invention is simple, and the device can simultaneously meet the colossal magnetoresistance effect under low field and room temperature, which is a major breakthrough in the field of spin electronics and is of great significance for applications such as sensing, storage, and brain-like computing.

[0042] The above embodiments mainly illustrate a device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide and a method for preparing the same. Although only one embodiment of the present invention is described, the present invention can be implemented in many other ways without departing from its subject matter and scope. Therefore, it should be understood that the above embodiments are not limited to the present invention, and any modifications, substitutions, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a device that realizes low-field room-temperature colossal magnetoresistance effect in manganese oxide, characterized in that: The device uses iron nano-islands to induce ferromagnetic nucleation in a manganese oxide film with an intrinsic phase transition temperature higher than 300K, thereby realizing a low-field room-temperature colossal magnetoresistance effect; the device comprises the following steps: (1) Under low oxygen pressure conditions, a rare earth-doped manganese oxide film is grown on a substrate, so that the grown manganese oxide film is in an antiferromagnetic insulating state and has an intrinsic phase transition temperature higher than 300K; (2) Under low temperature conditions, preparing a rare gas solid buffer layer on the manganese oxide film obtained in step (1) to regulate the surface energy of the film; (3) In situ deposition of isolated iron nano-islands on the surface of a rare gas solid buffer layer to induce ferromagnetic nucleation in an antiferromagnetic manganese oxide film, thereby reducing the external field that causes percolation; (4) Sodium chloride is deposited on the surface of the iron nano-islands as a protective layer to prevent the iron nano-islands from being oxidized.

2. The preparation method according to claim 1, characterized in that In step (1), a manganese oxide film is grown by pulsed laser deposition, and the oxygen pressure condition is 5×10 -4 -2×10 -2 Torr, substrate temperature is 1053-1093K; substrate is SrTiO3, doped rare earth manganese oxide is La 0.8 Ca 0.2 MnO3 or La 0.8 Ca 0.2 MnO3 / Pr 0.8 Ca 0.2 MnO3 superlattice, manganese oxide film thickness is 15-25 nm.

3. The preparation method according to claim 1, characterized in that: In step (2), the manganese oxide film is placed in a Xe gas atmosphere and cooled by liquid helium. The Xe atoms adsorbed on the surface of the manganese oxide film form a solid Xe atom buffer layer at a low temperature of 15K-30K.

4. The preparation method according to claim 3, characterized in that In 1*10 -6 Under Torr Xe gas pressure, it is maintained for 200-428 seconds, and the thickness of the rare gas solid buffer layer is between 20 and 40 layers.

5. The preparation method according to claim 1, characterized in that: In step (3), an electron beam deposition method is used to evaporate iron at a temperature of 15-30K using an electron beam to grow iron nano-islands with a diameter of 5-10nm and a height of 2-10nm at a rate of 0.02-0.06Å / min.

6. The preparation method according to claim 1, characterized in that: In step (4), an electron beam deposition method is used to grow a 5-15 nm sodium chloride film covering layer at a temperature of 15-30 K using an electron beam heated crucible; the sodium chloride growth rate is 0.2-0.8 Å / min.

7. A device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide, prepared by the preparation method according to any one of claims 1 to 6, characterized in that: From bottom to top, it includes a substrate, a manganese oxide film, a rare gas solid buffer layer, an iron nano-island and a sodium chloride protective layer.

8. The device for realizing low-field room-temperature colossal magnetoresistance effect in manganese oxide according to claim 7, characterized in that: The substrate is SrTiO3; the manganese oxide film is La 0.8 Ca 0.2 MnO3 or La 0.8 Ca 0.2 MnO3 / Pr 0.8 Ca 0.2 The thickness of the MnO3 superlattice film and the manganese oxide film is 15-25 nm; the rare gas solid buffer layer is a solid Xe atomic buffer layer, and its thickness is between 20-40 layers; the diameter of the iron nano-island is 5-10nm and the height is 2-10nm; the thickness of the sodium chloride protective layer is 5-15nm.

9. Use of the device according to claim 7 in realizing low-field room-temperature colossal magnetoresistance effect, characterized in that: The application method is as follows: 1) The device is placed in a room temperature environment. The rare gas solid buffer layer vaporizes during the heating process, and the iron nano-islands fall onto the surface of the manganese oxide. The magnetic exchange field between the iron nano-islands and the surface of the manganese oxide is used to induce ferromagnetic nucleation in the antiferromagnetic manganese oxide film. At this time, the volume percentage of the ferromagnetic domain is lower than the percolation threshold, the ferromagnetic domain is close to the edge of the percolation, and the film is in an insulating state. 2) Apply a small external magnetic field of tens to hundreds of Gauss to the film to induce the growth of ferromagnetic domains. When the ferromagnetic volume percentage exceeds the percolation threshold, the system undergoes an insulator-metal transition, forming a low-resistance state and realizing the low-field colossal magnetoresistance effect.

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