Nanocrystal antiferromagnetic material, preparation method and application

Abstract

The invention discloses a nanocrystal antiferromagnetic material, a preparation method and application, the nanocrystal antiferromagnetic material is a cobalt-nickel-silicon (Co-Ni-Si) ternary polycrystalline material, the chemical components of the nanocrystal antiferromagnetic material comprise three elements of cobalt (Co), nickel (Ni) and silicon (Si), and the atomic number ratio of cobalt to nickel to silicon is (33 + / -1): (21 + / -1): (46 + / -1). The preparation method comprises the following steps: (1) burdening; (2) packaging; (3) chemical vapor transport reaction; and (4) sampling. The antiferromagnetic material is widely applied to preparation of spintronics devices, such as magnetic tunnel junctions, spin valves, magnetic random access memories and magnetic sensors; the material is used as an antiferromagnetic pinning layer, a reference layer or an antiferromagnetic-based active layer in spintronics devices.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of magnetic materials, and particularly relates to a nanocrystalline antiferromagnetic material, a preparation method and application. BACKGROUND

[0002] Antiferromagnetism is a kind of magnetism of a material. The magnetic moments are antiparallel and ordered, but do not exhibit a macroscopic net magnetic moment. This magnetic order is called antiferromagnetism. Like ferromagnetism, the small magnetic moments are aligned within magnetic domains, but unlike ferromagnetism, the antiparallel alignment is opposite. The lower the temperature, the tighter the alignment within the material. When the temperature rises above the Neel temperature, the relative magnetic permeability is slightly greater than 1 and increases with temperature, and the substance becomes paramagnetic above this temperature.

[0003] In antiferromagnetic substances, the spins of adjacent valence electrons tend to be in opposite directions. The net magnetic moment of such a substance is zero, and it does not produce a magnetic field. In the absence of an external magnetic field, the magnetic moments of adjacent atoms or ions are in a state of mutual cancellation due to interaction, resulting in a zero net magnetic moment per unit volume. Theoretically and experimentally, it has been shown that under the action of "exchange coupling", it is possible for the magnetic moments of adjacent atoms to spontaneously arrange in an antiparallel and orderly state. Although the magnetic moments are in an orderly state, the net magnetic moment per unit volume is zero in the absence of an external magnetic field, and macroscopically, no magnetism is exhibited. This phenomenon is called antiferromagnetism. Such substances are relatively rare, and most antiferromagnetic substances only exist at low temperatures. If the temperature exceeds the Neel temperature, they will generally become paramagnetic. For example, chromium, manganese, and light lanthanide elements all have antiferromagnetism.

[0004] Traditional antiferromagnetic materials have many limitations in practical applications due to low Neel temperature and weak exchange bias field. SUMMARY

[0005] The present application aims to provide a nanocrystalline antiferromagnetic material, a preparation method and application.

[0006] The technical solution of the present application is as follows: The nanocrystalline antiferromagnetic material is a cobalt-nickel-silicon (Co-Ni-Si) ternary polycrystalline material, and its chemical composition is composed of three elements of cobalt (Co), nickel (Ni) and silicon (Si), and the atomic ratio of cobalt, nickel and silicon is (33±1):(21±1):(46±1).

[0007] The preparation method of the nanocrystalline antiferromagnetic material comprises the following steps: (1) ingredient: providing pure Co, Ni, Si single element raw materials with purity greater than 99.9%, and weighing and mixing according to the atomic ratio Co:Ni:Si =(33±1):(21±1):(46±1); (2) encapsulation: vacuum encapsulating the mixed raw materials and transport agent iodine single element together in a quartz tube; using chemical vapor transport method, realizing atomic level uniform mixing and crystal growth through forming gaseous iodide intermediates; (3) chemical vapor transport reaction: placing the encapsulated quartz tube in a double-temperature-zone tube furnace for chemical vapor transport reaction, and the reaction procedure is: rising to a first temperature at a first heating rate and keeping for a first period of time, and then rising to a second temperature at a second heating rate and keeping for a second period of time; (4) sampling: after the reaction is completed, taking out the reaction product in the quartz tube, and obtaining the nanocrystalline antiferromagnetic material.

[0008] Further, in the step (2), the size of the quartz tube is 10 mm in diameter and 200 mm in length; the mass of the transport agent iodine single element is 10 mg.

[0009] Further, in the step (3), the first heating rate rising to the first temperature and keeping for the first period of time is specifically rising from room temperature to 940-960 ℃ at a heating rate of 2.5-3.5 ℃ / min, and keeping at the temperature for 22-26 hours; the second heating rate rising to the second temperature and keeping for the second period of time is specifically rising to 1040-1060 ℃ at a heating rate of 0.5-0.6 ℃ / min, and keeping at the temperature for 160-176 hours.

[0010] Further, the first heating rate is 3.0 ℃ / min, the first temperature is 950 ℃, and the first period of time is 24 hours; the second heating rate is 0.55 ℃ / min, the second temperature is 1050 ℃, and the second period of time is 168 hours.

[0011] The application of the nanocrystalline antiferromagnetic material is in the preparation of spintronic devices, including but not limited to magnetic tunnel junctions, spin valves, magnetic random access memories, and magnetic sensors; the material is used as an antiferromagnetic pinning layer, a reference layer, or an active layer based on antiferromagnetism in spintronic devices.

[0012] Further, as a pinning layer: using its high exchange bias field and good thermal stability to pin the magnetization direction of a ferromagnetic free layer, and improving the thermal stability and anti-interference ability of magnetic tunnel junction and spin valve devices; As a reference layer: In magnetic random access memory (MRAM) cells, its antiferromagnetic order provides a stable reference magnetization direction to achieve non-volatile data storage; As an active layer: directly utilize the Née vector of its antiferromagnetic order for information storage and reading and writing, constructing a fully antiferromagnetic memory. This type of device has the great advantages of fast writing speed (picosecond level), extremely high integration density, and strong resistance to magnetic interference; Application in terahertz oscillators: using ultrafast laser or current pulses to excite antiferromagnetic spin precession, generating high-frequency terahertz electromagnetic wave output for use in high-speed communications and imaging; Application in neuromorphic computing: Utilizing the multiple metastable states of its antiferromagnetic state (such as Née vectors in different directions) to simulate the plasticity of neuronal synapses and construct low-energy neuromorphic computing devices; Application in high-sensitivity sensors: Utilizing its magnetoresistance effect or sensitive response to external stimuli (such as magnetic field, current, stress), new magnetic sensors, current sensors or stress sensors can be developed.

[0013] The present invention has the following beneficial effects: The disclosed nanocrystalline antiferromagnetic material, a cobalt-nickel-silicon (Co-Ni-Si) ternary polycrystalline material, effectively improves its performance by precisely controlling the atomic ratio of cobalt, nickel, and silicon to (33±1):(21±1):(46±1). This unique chemical composition ensures that the material maintains antiferromagnetism while possessing a higher exchange bias field and excellent thermal stability, significantly expanding its application range.

[0014] The present invention utilizes chemical vapor transport (CVT), an advanced material synthesis technique. During the batching process, cobalt, nickel, and silicon are selected as raw materials with a purity exceeding 99.9% and weighed and mixed in specific proportions, laying the foundation for high-quality materials. During the packaging process, the mixed raw materials and the transport agent, iodine, are vacuum-encapsulated within a quartz tube of specific dimensions (10 mm diameter, 200 mm length). CVT is used to form a gaseous iodide intermediate, achieving uniform mixing and crystal growth at the atomic level, ensuring material uniformity and purity.

[0015] Chemical vapor transport reaction stage, accurate control of the reaction procedure is essential. With a specific heating rate (such as the first heating rate is 3.0 ℃ / min) to the first temperature (950 ℃) and keep for a certain time (24 hours), and then with another heating rate (0.55 ℃ / min) to the second temperature (1050 ℃) and keep for a longer time (168 hours), this fine temperature control enables the material to grow crystals and optimize the structure under optimal conditions, so as to obtain excellent performance of nanocrystalline antiferromagnetic material.

[0016] In the application aspect, the nanocrystalline antiferromagnetic material of the application has great potential in the field of spintronics. As an antiferromagnetic pinning layer, it can effectively pin the magnetization direction of the ferromagnetic free layer with high exchange bias field and good thermal stability, significantly improving the thermal stability and anti-interference ability of magnetic tunnel junction and spin valve devices, and providing reliable material support for high-performance magnetic storage and magnetic sensing equipment. As a reference layer, its antiferromagnetic order can provide a stable reference magnetization direction in the magnetic random access memory (MRAM) cell, realizing non-volatile storage of data, which is of great significance to improve the reliability and data retention ability of the memory.

[0017] In addition, as an active layer, it directly uses the Néel vector of its antiferromagnetic order for information storage and reading and writing, and the all-antiferromagnetic memory constructed has the great advantages of fast writing speed (picosecond level), high integration density and strong anti-magnetic interference ability, which is expected to promote the development of memory technology to higher performance and smaller size. In the terahertz oscillator field, the antiferromagnetic spin precession is excited by ultrafast laser or current pulse, which can generate high-frequency terahertz electromagnetic wave output, providing a new technical means for high-speed communication and imaging. In the neuromorphic computing field, the multiple metastable states (such as Néel vectors in different directions) of its antiferromagnetic state are used to simulate the plasticity of neuron synapses, and the low-energy neuromorphic computing device constructed brings new opportunities for the development of artificial intelligence and neural network computing. At the same time, in the field of high-sensitivity sensors, the developed new type of magnetic sensor, current sensor or stress sensor has higher sensitivity and wider application prospect by using its magnetoresistance effect or sensitive response to external stimuli (such as magnetic field, current, stress). BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description.

[0019] Figure 1 : The magnetic intensity change graph of the material with temperature change.

[0020] Figure 2 : The magnetic intensity change graph of the material with temperature change.

[0021] Figure 3 : Magnetic intensity variation graph of the material with the variation of magnetic field intensity.

[0022] Figure 4 : Magnetic intensity variation graph of the material with the variation of magnetic field intensity.

[0023] Figure 5 : Magnetic intensity variation graph of the material with the variation of magnetic field intensity.

[0024] Figure 6 : Magnetic intensity variation graph of the material with the variation of magnetic field intensity under different temperature conditions (10K, 20K, 30K, 50K, 100K respectively).

[0025] Figure 7 : High-resolution diffraction pattern.

[0026] Figure 8 : High-resolution diffraction pattern.

[0027] Figure 9 : High-resolution diffraction pattern.

[0028] Figure 10 : Selected electron diffraction pattern.

[0029] Figure 11 : Selected electron diffraction pattern.

[0030] Figure 12 : Si, Ni, Co element distribution plane scanning electron micrograph.

[0031] Figure 13 : Si element distribution plane scanning electron micrograph.

[0032] Figure 14 : Co element distribution plane scanning electron micrograph.

[0033] Figure 15 : Ni element distribution plane scanning electron micrograph.

[0034] Figure 16 : Mappinp element analysis graph. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments.

[0036] The nanocrystal antiferromagnetic material is a Co-Ni-Si ternary polycrystal material, and the chemical composition of the material is composed of three elements of cobalt (Co), nickel (Ni) and silicon (Si), and the atomic number ratio of cobalt, nickel and silicon is (33±1):(21±1):(46±1). Among them, the introduction of silicon element effectively controls the electronic structure of the material, and forms a stable intermetallic compound phase with transition metals cobalt and nickel, which lays the foundation for the crystal structure of the antiferromagnetic order.

[0037] The preparation method of the nanocrystal antiferromagnetic material comprises the following steps: (1) batching: providing cobalt, nickel and silicon elemental raw materials with a purity of greater than 99.9%, and weighing and mixing according to the atomic number ratio Co:Ni:Si =(33±1):(21±1):(46±1); the high purity of the silicon raw material is the key to ensure that there is no magnetic impurity phase in the final product and to obtain intrinsic antiferromagnetism.

[0038] (2) packaging: vacuum packaging the mixed raw materials and the transport agent iodine element in a quartz tube; the size of the quartz tube is 10 mm in diameter and 200 mm in length; the mass of the transport agent iodine element is 10 mg. The chemical vapor transport method is especially suitable for elements such as silicon with high melting point, and realizes uniform mixing and crystal growth at the atomic level by forming a gaseous iodide intermediate; this small amount of iodine element is sufficient as an effective transport medium, while avoiding excessive introduction of impurities affecting the intrinsic antiferromagnetism of the material.

[0039] (3) chemical vapor transport reaction: placing the packaged quartz tube in a double-temperature zone tube furnace for chemical vapor transport reaction, and the reaction program is as follows: heating to a first temperature of 950 DEG C at a first heating rate of 3.0 DEG C / min, and the first holding time is 24 hours; then heating to a second temperature of 1050 DEG C at a second heating rate of 0.55 DEG C / min, and the second holding time is 168 hours. This precise multi-stage heating program aims to first make silicon and other metals fully react, and then anneal at a higher temperature for a long time to promote the formation of large-size, high-quality nanocrystals and the structural ordering of the antiferromagnetic phase.

[0040] (4) sampling: after the reaction is completed, the reaction product in the quartz tube is taken out, and the nanocrystal antiferromagnetic material is obtained.

[0041] The application of nanocrystalline antiferromagnetic materials, the application in the preparation of spintronic devices, the spintronic devices include but are not limited to magnetic tunnel junctions, spin valves, magnetic random access memories and magnetic sensors; the materials are used as antiferromagnetic pinning layers, reference layers or active layers based on antiferromagnetism in spintronic devices. The Co-Ni-Si material is particularly suitable for the next generation of high-density, high-stability and low-power spintronic devices due to its antiferromagnetic characteristics such as no net magnetic moment, resistance to external magnetic field interference, fast response speed, and good interface compatibility and potential electrical transport characteristic regulation ability brought by the silicon element.

[0042] As a pinning layer: it is used to pin the magnetization direction of the ferromagnetic free layer due to its high exchange bias field and good thermal stability, which improves the thermal stability and anti-interference ability of magnetic tunnel junction and spin valve devices; As a reference layer: in a magnetic random access memory (MRAM) cell, it provides a stable reference magnetization direction using its antiferromagnetic order to realize non-volatile storage of data; As an active layer: directly using the Néel vector of its antiferromagnetic order for information storage and read-write, constructing a full antiferromagnetic memory, such devices have the great advantages of fast writing speed (picosecond level), extremely high integration density and strong anti-magnetic interference ability; Applied to terahertz oscillators: using ultrafast laser or current pulse to excite its antiferromagnetic spin precession to generate high-frequency terahertz electromagnetic wave output, which is used in high-speed communication and imaging fields; Applied to neuromorphic computing: using the multiple metastable states (such as Néel vectors in different directions) of its antiferromagnetic state to simulate the plasticity of neuron synapses, constructing low-energy neuromorphic computing devices; Applied to high-sensitivity sensors: using its magnetoresistance effect or sensitive response to external stimuli (such as magnetic field, current, stress) to develop new types of magnetic sensors, current sensors or stress sensors.

[0043] Table 1: EDS / WDS quantitative analysis results data table of Si-Co-Ni antiferromagnetic materials (theoretical k factor correction)

[0044] The relevant information of different elements (Si, Co, Ni) in the nanocrystalline antiferromagnetic material is presented in detail according to Table 1. The line type determines the X-ray line system used, the k factor and its type embody certain parameter setting (here, the theoretical value) related to the material properties, the absorption correction reflects the consideration of absorption effect in the analysis process, Wt% represents the mass percentage of each element, Wt% Sigma is the corresponding standard deviation, and At% represents the atomic percentage of each element. Through these data, the key information such as the element composition and the proportion of each element of the nanocrystalline antiferromagnetic material can be clearly understood, which has important reference value for in-depth study of the properties, preparation and application of the material.

[0045] Figure 1 The magnetic intensity of the material changes with temperature. Among them, OP ZFC 300 Oe is the magnetic intensity of the material changing with temperature under the condition of no magnetic field cooling and a 300 Oe out-of-plane magnetic field.

[0046] OP FC 300 Oe is the magnetic intensity of the material changing with temperature under the condition of field cooling and a 300 Oe out-of-plane magnetic field.

[0047] OP ZFC 3000 Oe is the magnetic intensity of the material changing with temperature under the condition of no magnetic field cooling and a 3000 Oe out-of-plane magnetic field.

[0048] OP FC 3000 Oe is the magnetic intensity of the material changing with temperature under the condition of field cooling and a 3000 Oe out-of-plane magnetic field.

[0049] Figure 2 The magnetic intensity of the material changes with temperature. Among them, IP ZFC 300 Oe is the magnetic intensity of the material changing with temperature under the condition of no magnetic field cooling and a 300 Oe in-plane magnetic field.

[0050] IP FC 300 Oe is the magnetic intensity of the material changing with temperature under the condition of field cooling and a 300 Oe in-plane magnetic field.

[0051] IP ZFC 3000 Oe is the magnetic intensity of the material changing with temperature under the condition of no magnetic field cooling and a 3000 Oe in-plane magnetic field.

[0052] IP FC 3000 Oe is the magnetic intensity of the material changing with temperature under the condition of field cooling and a 3000 Oe in-plane magnetic field.

[0053] Figures 3-5Both are the magnetic intensity variation diagram of the material with the magnetic field intensity. Among them, IP 10K represents: the curve of the magnetic intensity of the material with the in-plane magnetic field intensity under the condition of 10K temperature.

[0054] OP 10K represents: the curve of the magnetic intensity of the material with the out-of-plane magnetic field intensity under the condition of 10K temperature.

[0055] According to Figures 1-5 The figure data curve shows that the material has the following magnetization-temperature (M-T) characteristics: a) under the condition of 3000 Oe high magnetic field, the zero-field cooling and field cooling measurement curves are basically coincident in the whole measurement temperature range, indicating that the magnetic domain is fully polarized under strong field, and the thermal fluctuation effect is suppressed; b) under the condition of 300 Oe low magnetic field, the zero-field cooling and field cooling measurement curves diverge in the temperature range of 0 K to 60 K, revealing that there is a significant magnetic anisotropy or spin blocking effect at low temperature; in the temperature range of 60 K to 300 K, they are coincident, indicating that the thermal activation energy overcomes the energy barrier above this characteristic temperature. This unique field-dependent and temperature-dependent behavior is determined by the intrinsic antiferromagnetic exchange interaction of the Co-Ni-Si ternary system.

[0056] Figure 6 are the curves of the magnetic intensity of the material with the in-plane magnetic field intensity under different temperature conditions (10K, 20K, 30K, 50K, 100K respectively). According to Figure 6 , it is shown that the material exhibits antiferromagnetic properties in magnetism, and there is at least one obvious magnetization step in the magnetization-magnetic field (M-H) hysteresis loop at low temperature; this step feature is due to the interaction between the specific crystal field environment and the antiferromagnetic spin configuration caused by the addition of silicon element, which may mark the occurrence of spin flip or magnetic phase transition.

[0057] Figures 10-11 Both are selected area electron diffraction patterns, and the electron diffraction patterns show continuous or intermittent polycrystalline diffraction rings, proving that the material is composed of nanoscale grains, showing a polycrystalline morphology, and the high-resolution transmission electron microscopy image shows that the grain interior has long-range ordered atomic arrangement, confirming its good crystallinity and the successful incorporation of silicon atoms into the lattice and the formation of ordered structure.

[0058] Figures 12-15 are element distribution plane scanning electron images, showing that the three elements of cobalt, nickel and silicon are uniformly distributed in space without obvious element segregation, indicating that the silicon element and cobalt, nickel element form a single phase compound with uniform composition and stable structure, rather than a simple mechanical mixture.

[0059] Figure 16: Mappinp element analysis chart, SEM electron microscope chart M-H picture intuitively shows the magnetic performance characteristics of the material. From the chart, it can be clearly observed that the magnetization intensity change of the nanocrystalline antiferromagnetic material under a specific magnetic field intensity, and the magnetization curve presents a typical antiferromagnetic characteristic, that is, with the increase of the magnetic field intensity, the magnetization intensity gradually increases, reaches a maximum value, and then begins to decrease, and finally tends to saturation, which further confirms that the material has antiferromagnetic property. At the same time, in combination with the high resolution of the electron microscope chart, the correlation between the surface morphology of the material and the magnetic performance can also be seen, which provides a strong basis for in-depth understanding of the magnetic mechanism of the material.

[0060] The embodiments are selected and specifically described in the specification in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application.

Claims

1. Nanocrystalline antiferromagnetic material, characterized in that: The material is cobalt-nickel-silicon (Co-Ni-Si) ternary polycrystalline material, whose chemical composition is composed of three elements: cobalt (Co), nickel (Ni) and silicon (Si), and the ratio of the number of atoms of cobalt, nickel and silicon is (33±1): (21±1): (46±1).

2. A method of preparing a nanocrystalline antiferromagnetic material, characterized in that: It includes the following steps; (1) Ingredients: Provide cobalt, nickel, and silicon raw materials with a purity greater than 99.9%, and weigh and mix them according to the atomic ratio of Co:Ni:Si = (33±1):(21±1):(46±1); (2) Encapsulation: The mixed raw materials and the transport agent iodine are vacuum encapsulated in a quartz tube; chemical vapor transport is used to form a gaseous iodide intermediate to achieve uniform mixing and crystal growth at the atomic level; (3) Chemical vapor transport reaction: The packaged quartz tube is placed in a dual-temperature zone tube furnace to carry out a chemical vapor transport reaction. The reaction procedure is: heating to a first temperature at a first heating rate and keeping it at that temperature for a first period of time, then heating to a second temperature at a second heating rate and keeping it at that temperature for a second period of time; (4) Sampling: After the reaction is completed, the reaction product in the quartz tube is taken out to obtain the nanocrystalline antiferromagnetic material.

3. The method of claim 2, wherein the nanocrystalline antiferromagnetic material is prepared by: In the step (2), the size of the quartz tube is 10 mm in diameter and 200 mm in length; the mass of the transport agent iodine is 10 mg.

4. The method of claim 2, wherein the nanocrystalline antiferromagnetic material is prepared by: In step (3), the first heating rate is to increase the temperature to the first temperature and keep it for the first period of time, specifically, the heating rate is 2.5-3.5 ° C / min from room temperature to 940-960 ° C, and the temperature is kept at this temperature for 22-26 hours; the second heating rate is to increase the temperature to the second temperature and keep it for the second period of time, specifically, the heating rate is 0.5-0.6 ° C / min to 1040-1060 ° C, and the temperature is kept at this temperature for 160-176 hours.

5. The method of claim 4, wherein the nanocrystalline antiferromagnetic material is prepared by: The first heating rate is 3.0°C / min, the first temperature is 950°C, and the first period of time is 24 hours; the second heating rate is 0.55°C / min, the second temperature is 1050°C, and the second period of time is 168 hours.

6. Use of a nanocrystalline antiferromagnetic material, characterized in that: Application in the preparation of spintronic devices, including but not limited to magnetic tunnel junctions, spin valves, magnetic random access memories and magnetic sensors; the material is used as an antiferromagnetic pinning layer, reference layer or antiferromagnetic-based active layer in spintronic devices.

7. The use of the nanocrystalline antiferromagnetic material according to claim 6, characterized in that: As a pinning layer: using its high exchange bias field and good thermal stability to pin the magnetization direction of the ferromagnetic free layer, improving the thermal stability and anti-interference ability of magnetic tunnel junction and spin valve devices; As a reference layer: In magnetic random access memory (MRAM) cells, its antiferromagnetic order provides a stable reference magnetization direction to achieve non-volatile data storage; As an active layer: directly utilize the Née vector of its antiferromagnetic order for information storage and reading and writing, constructing a fully antiferromagnetic memory. This type of device has the great advantages of fast writing speed (picosecond level), extremely high integration density, and strong resistance to magnetic interference; Applied to terahertz oscillators: use ultrafast laser or current pulse to excite its antiferromagnetic spin precession, produce high-frequency terahertz electromagnetic wave output, used in high-speed communication and imaging field; Applied to neuromorphic computing: use its multiple metastable states of antiferromagnetic state (such as different directions of nèel vector) to simulate the plasticity of neuron synapse, build low-energy neuromorphic computing devices; Applied to high-sensitivity sensors: use its magnetoresistance effect or sensitive response to external stimuli (such as magnetic field, current, stress) to develop new types of magnetic sensors, current sensors or stress sensors.

Images