Design method of magnetic tunnel junction based on two-dimensional MnBi2Te4
By using the MoSi2N4 barrier layer in the MnBi2Te4 magnetic tunnel junction, the spin polymorphism and minor state filtration are used to improve the magnetoresistivity and the effective distinction between read and write paths, and the problems of low magnetoresistivity and read and write path interference in the prior art are solved.
Patent Information
- Application Number
- CN202510028333.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-08
- Publication Date
- 2025-05-02
AI Technical Summary
The magnetoresistivity of the existing MnBi2Te4 magnetic tunnel junction is small, and the read and write paths in STT-MRAM are prone to interference, making it difficult to effectively distinguish.
A magnetic tunnel junction based on two-dimensional MnBi2Te4 is designed, and MoSi2N4 is used as the barrier layer. Through its filtering effect on spin polymorphism and minority state, the magnetoresistive symbols at low bias voltage and high bias voltage are achieved, and the read and write paths are distinguished.
The magnetoresistiveness is improved, with an absolute value of up to 264%. Through the conversion of magnetoresistive symbols, the read and write paths in STT-MRAM are effectively distinguished, solving the problem of interference between read and write paths.
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Figure CN119918279A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of spin electronics, and in particular to a design method for a two-dimensional MnBi2Te4-based magnetic tunnel junction. Background Art
[0002] A two-dimensional magnetic tunnel junction usually refers to a sandwich structure of ferromagnet-insulator-ferromagnet, which mainly adjusts the magnetic moment of the ferromagnet on one side so that when the magnetic tunnel junction is in a parallel state, the majority sub-bands of the ferromagnets on both sides are bands of the same spin (for example, all are spin-up bands), and most electrons can pass through the potential barrier layer from the left to the right, thereby obtaining a lower resistance. When the magnetic tunnel junction is in an anti-parallel state, the spin directions of the majority band and minority band of the ferromagnets on both sides are just opposite. At this time, since the spin-up electrons cannot jump to the spin-down sub-band, a higher resistance value is resulted. That is, when the magnetic moments on both sides are in parallel and anti-parallel situations, there is a difference in resistance value, resulting in a magnetoresistance effect.
[0003] In recent years, research on MnBi2Te4 has generally focused on its topological state and the stacking of layers to achieve the quantum anomalous Hall effect, while research on spin quantum transport is still very scarce; the magnetoresistance that can be achieved by the MnBi2Te4 magnetic tunnel junction with Cu as the electrode is still very small, and the magnetoresistance with a single layer of h-BN as the barrier layer is only 76%. Although the magnetoresistance can be achieved by adding a double-layer MnBi2Te4 antiferromagnetic layer of 162.6%, it is obvious that such a structure is more complicated and not conducive to implementation; in the traditional STT-MRAM used in magnetic tunnel junctions, that is, a new type of non-volatile magnetic random access memory that uses spin current to write information, reading and writing share a path, and there is a high possibility of interference between the two. Summary of the invention
[0004] Purpose of the invention: The purpose of the present invention is to provide a design method for a two-dimensional MnBi2Te4-based magnetic tunnel junction, using MoSi2N4 as a barrier layer, and utilizing its filtering effect on spin polystates and minority states to provide more barrier layer options for MnBi2Te4-based magnetic tunnel junctions; by using the difference in the signs of magnetic resistance generated at low bias and high bias, the read and write paths in traditional STT-MRAM are distinguished to solve the problem of interference between the read and write paths.
[0005] Technical solution: The design method of a two-dimensional MnBi2Te4 magnetic tunnel junction according to the present invention is characterized by comprising the following steps: (1) Calculate the structure and electronic structure of MnBi2Te4 and MoSi2N4, and determine the electronic properties of MnBi2Te4 and MoSi2N4; (2) Expand MnBi2Te4 and MoSi2N4 cells and build device models; (3) Optimize the device model; (4) Change the magnetic moment of MnBi2Te4 to obtain parallel and antiparallel configurations, and calculate the IV curves under the two configurations; (5) Calculate the magnetoresistance based on the obtained IV curve; calculate the spin-resolved projected density of states along the electron transport direction and analyze the source of magnetoresistance; (6) Based on the unique characteristic of magnetoresistance changing from positive to negative, a theoretical model for resolving the conflict between reading and writing is obtained.
[0006] Furthermore, step (1) is as follows: the band structures of MnBi2Te4 and MoSi2N4 are analyzed by VASP, the structure files of MnBi2Te4 and MoSi2N4 unit cells are imported, and the band structures of the unit cells of the two are calculated by VASP; the electron exchange correlation potential adopts PBE-GGA, the plane wave cutoff energy is set to 500eV, the Brillouin zone integral grid is 9×9×1, and the force convergence criterion is 10-5eV; wherein, MnBi2Te4 is a ferromagnetic semiconductor, and the magnetic moment and U value are added to the input file, and the selection of U value is determined according to references and comparison with the HSE06 method.
[0007] Furthermore, step (2) is as follows: determine the lattice parameters of MnBi2Te4 and MoSi2N4 to be 4.33 Å and 2.89 Å, perform 2×2×1 and 3×3×1 cell expansion operations on them respectively, so that the lattice mismatch rate of the two is only 0.12% to ensure that the heterojunction will not be deformed; build a Cu / MnBi2Te4 / MoSi2N4 / MnBi2Te4 / Cu magnetic tunnel junction.
[0008] Furthermore, step (3) is as follows: the heterojunction structure is optimized by density functional theory and non-equilibrium Green's function method and calculation software Quantum ATK. During the optimization, the lattice constant is fixed and all atomic positions are released so that the forces between atoms are less than 0.05, and the interlayer van der Waals forces are designed and set to DFT-D3.
[0009] Furthermore, step (4) is as follows: using the optimized structure to build a spintronic device comprising a left electrode-central scattering region-right electrode, the transport direction is the z direction; by changing the magnetic moment of the right MnBi2Te4 to obtain parallel and antiparallel configurations; in the two configurations, the transmission coefficient formula is Calculate and analyze its transmission spectrum; through the spin current formula Get the current value at each voltage point; in, represents the spin index, , represents the electron charge, represents Planck's constant, and are the delayed and advanced Green's functions in the scattering region, respectively, and and are the coupling matrices of the left / right electrodes respectively. Represents the Fermi-Dirac distribution of the left and right electrodes in the nonequilibrium state.
[0010] Furthermore, in step (5), the IV curve obtained is calculated by the magnetic resistance formula The magnetoresistance curve is obtained, where represents the current in the parallel state, represents the current in the antiparallel state; Furthermore, in step (5), the values in the TMR curve are used to obtain the extreme values of positive and negative magnetoresistance at 0.1 V and 1 V, respectively, and the spin-resolved projected state density along the electron transport direction is calculated. The source of magnetoresistance is obtained by analyzing the high and low state density.
[0011] The present invention discloses a two-dimensional MnBi2Te4-based magnetic tunnel junction, with Cu as an electrode, MoSi2N4 as a barrier layer, and MnBi2Te4 as a ferromagnetic layer.
[0012] Further, the method includes in sequence: Cu / MnBi2Te4 / MoSi2N4 / MnBi2Te4 / Cu step (2) is as follows: determine the lattice parameters of MnBi2Te4 and MoSi2N4 to be 4.33 Å and 2.89 Å, perform 2×2×1 and 3×3×1 cell expansion operations on them respectively, so that the lattice mismatch rate of the two is only 0.12% to ensure that the heterojunction will not be deformed; build a Cu / MnBi2Te4 / MoSi2N4 / MnBi2Te4 / Cu magnetic tunnel junction.
[0013] The application method of the magnetic tunnel junction based on two-dimensional MnBi2Te4 described in the present invention is applied to STT-MRAM. When the two-dimensional MnBi2Te4 magnetic tunnel junction is at 0.1V, it is in the "read" state. When the two-dimensional MnBi2Te4 magnetic tunnel junction is at 1V, the device is switched to the "write" state.
[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the design of the magnetic tunnel junction device based on the two-dimensional MnBi2Te4 further supplements the research on the spin quantum transport properties of the magnetic material MnBi2Te4; by increasing the bias voltage and using the MoSi2N4 potential barrier, the phenomenon of positive and negative magnetoresistance conversion and the absolute value of the magnetoresistance ratio as high as 264% are obtained. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 is a flow chart of the present invention; Figure 2 MoSi2N4 of the present invention, wherein (a) top view (b) side view and (c) band structure, MnBi2Te4 (d) top view (e) side view and (f) band structure Figure 3 A magnetic tunnel junction device structure according to the present invention; Figure 4 The IV curve of the present invention; wherein, (a) IV characteristic curves of parallel (PC) and antiparallel (APC) and (b) TMR under different bias voltages; Figure 5 The parallel configuration in the equilibrium state of the present invention; wherein, the density of states of the spin-resolved projected density of states of (a) spin-up and (b) spin-down and (c) spin-up and (d) spin-down electrons along the transmission direction in the antiparallel configuration; the horizontal axis represents the different positions of the device z-axis, and the vertical axis represents the electron energy. The green dotted line represents the Fermi level. The yellow arrows represent possible propagation; Figure 6 The horizontal axis of the state density of the spin-resolved projected state density of the electrons along the transmission direction in (a) spin-up and (b) spin-down and (c) spin-up and (d) spin-down in the antiparallel configuration represents the different positions of the device z-axis, and the vertical axis represents the electron energy. The green dotted line represents the left electrode and right electrode The Fermi level.
[0016] Figure 7 It is a schematic diagram of the reading and writing process of the magnetic tunnel junction of the present invention. DETAILED DESCRIPTION
[0017] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.
[0018] like Figure 1 As shown, the embodiment of the present invention provides a two-dimensional MnBi2Te4-based magnetic tunnel junction device and a design method thereof, comprising the following steps: S1: Analyze the band structures of MnBi2Te4 and MoSi2N4 by VASP, and import the structure files of MnBi2Te4 and MoSi2N4 primitive cells, such as Figure 2 (a)(b)(d)(e) shows that the band structures of the two primitive cells are calculated by VASP. The results are as follows Figure 1As shown in (c)(f), MnBi2Te4 is a magnetic semiconductor and MoSi2N4 is a semiconductor. The electron exchange correlation potential uses PBE-GGA, the plane wave cutoff energy is set to 500eV, the Brillouin zone integration grid is 9×9×1, and the force convergence criterion is 10-5eV. Among them, MnBi2Te4 is a ferromagnetic semiconductor, and the magnetic moment and U value need to be added to the input file. The selection of U value is based on references and comparison with the HSE06 method, and it is determined to add 3eV to the 3d orbit of Mn.
[0019] S2: The lattice parameters of MnBi2Te4 and MoSi2N4 were determined to be 4.33 Å and 2.89 Å, and 2×2×1 and 3×3×1 cell expansion operations were performed on them, respectively, so that the lattice mismatch rate of the two was only 0.12% to ensure that the heterojunction would not be deformed.
[0020] Build a Cu / MnBi2Te4 / MoSi2N4 / MnBi2Te4 / Cu magnetic tunnel junction, such as Figure 3 As shown in the figure, in this model, the MnBi2Te4 / MoSi2N4 / MnBi2Te4 sandwich structure is sandwiched by a semi-infinite length Cu electrode. The characteristics of this magnetic tunnel junction are explored by setting the magnetic moment of the single-layer MnBi2Te4 to be parallel or anti-parallel.
[0021] S3: The heterojunction structure is optimized by density functional theory, non-equilibrium Green's function method and calculation software Quantum ATK. During the optimization, the lattice constant is fixed and all atomic positions are released so that the forces between atoms are less than 0.05, and the inter-layer van der Waals forces are considered, which is set as DFT-D3.
[0022] S4: Use the optimized structure to build a spintronic device consisting of a left electrode-central scattering region-right electrode, with the transport direction in the z direction. By changing the magnetic moment of the right MnBi2Te4, two configurations, parallel and antiparallel, are obtained. In the two configurations, the transmission coefficient formula is used respectively. The transmission spectrum is calculated and analyzed, and the spin current formula is used Get the current value at each voltage point, the result is as follows Figure 4 (a). Among them, represents the spin index, , represents the electron charge, represents Planck's constant, and are the delayed and advanced Green's functions in the scattering region, respectively, and and are the coupling matrices of the left (right) electrodes, respectively. Represents the Fermi-Dirac distribution of the left and right electrodes in the nonequilibrium state.
[0023] S5: The obtained IV curve is calculated by the magnetic resistance formula The magnetic resistivity curve is obtained, and the result is as follows Figure 4 As shown in (b), a unique phenomenon occurs in which the magnetoresistance sign changes from positive to negative as the bias voltage changes, and the positive magnetoresistance peak is 43.3% at 0.1V and the negative magnetoresistance peak is -264% at 1V. represents the current in the parallel state, represents the current in the antiparallel state.
[0024] S6: Observe the values in the TMR curve in step S5 and find that the device obtains positive and negative magnetoresistance under low bias and high bias, respectively. To understand the source of its positive and negative conversion, the equilibrium state is calculated. Figure 5 As shown and 1V bias voltage Figure 6 The spin-resolved projected state density along the electron transfer direction is shown in Figure 2. At the Fermi level in the equilibrium state, based on the parallel configuration, it can be seen that the spin-up state is the majority state and the spin-down state is the minority state. Figure 5 In (a), both the left and right ferromagnetic layers contribute polymorphisms, and spin-up electrons can tunnel through; in the antiparallel configuration, the spin-up and spin-down states of the left and right ferromagnets are exactly opposite, so Figure 5 Although the ferromagnetic layer on the left in (c) has a higher density of states, the ferromagnetic layer on the right contributes very few states, so the number of electrons passing through the barrier layer is quite small. Figure 5 (b)(d)Similarly.
[0025] After applying a 1V bias, the Fermi level of the left electrode decreases, while the Fermi level of the right electrode increases, thus forming a [-0.5, 0.5] window. In this region, we observe that near 0.5eV, the ferromagnet on the left is mostly in the spin-down state, and the minority state is in the spin-up state, while the ferromagnet on the right is mostly in the spin-up state, and the spin-down state is the minority state. Therefore, the spin-down state in the antiparallel configuration will provide excellent electron transmission, such as Figure 6 As shown in (d), this also causes the magnetic resistivity to turn from positive to negative. Figure 5 The state of MoSi2N4 near 0.5eV in the magnetoresistance is the source of the high magnetoresistance, that is, when the ferromagnetism on both sides is in the polymorphic state, MoSi2N4 will produce an extremely high state density to facilitate the transport of this state, and when the ferromagnetic states on both sides are in the minority state, MoSi2N4 will show a lower state density to block the transport of this state. This unique property is not found in potential barriers such as h-BN, reflecting the unique filtering effect of MoSi2N4 on polymorphic and minority states. With the help of this property, we obtained a magnetoresistance of up to 264% in absolute value, which is higher than 162.6% in previous studies.
[0026] The embodiment of the present invention also provides an application method of the magnetic tunnel junction, such as Figure 7 As shown, at 0.1V, the device exhibits a positive magnetoresistance effect, which is called the "read" state, and it is assumed that the data "1101" is read; when the bias voltage is increased to 1V, the device changes to the "write" state. Since the device exhibits a negative magnetoresistance effect, the writing of the "1101" data is achieved through the NOT gate.
[0027] like Figure 3 As shown, the embodiment of the present invention also provides a magnetic tunnel junction device with Cu as electrode, MoSi2N4 as barrier layer, and MnBi2Te4 as ferromagnetic layer, and proves by calculating the spin-resolved projected state density along the electron transmission direction that the device produces a unique phenomenon of positive and negative magnetoresistance conversion with the increase of bias voltage, and obtains a magnetoresistance rate of up to -264% at 1V bias voltage. Therefore, this magnetic tunnel junction device based on MnBi2Te4 is expected to be applied to spin multifunctional devices such as STT-MRAM, and enrich its application in the field of spin electronic devices.
Claims
1. A design method for a two-dimensional MnBi2Te4 magnetic tunnel junction, characterized in that: The following steps are included: (1) Calculate the structure and electronic structure of MnBi2Te4 and MoSi2N4, and determine the electronic properties of MnBi2Te4 and MoSi2N4; (2) Expand MnBi2Te4 and MoSi2N4 cells and build device models; (3) Optimize the device model; (4) Change the magnetic moment of MnBi2Te4 to obtain parallel and antiparallel configurations, and calculate the IV curves under the two configurations; (5) Calculate the magnetic reluctance based on the obtained IV curve; Calculate the spin-resolved projected density of states along the electron transport direction and analyze the source of magnetoresistance; (6) Based on the unique characteristic of magnetoresistance changing from positive to negative, a theoretical model for resolving the conflict between reading and writing is obtained.
2. The design method of a two-dimensional MnBi2Te4 magnetic tunnel junction according to claim 1, characterized in that: Step (1) is as follows: analyze the band structures of MnBi2Te4 and MoSi2N4 by VASP, import the structure files of MnBi2Te4 and MoSi2N4 unit cells, and calculate the band structures of the two unit cells by VASP; use PBE-GGA for the electron exchange correlation potential, set the plane wave cutoff energy to 500eV, the Brillouin zone integral grid to 9×9×1, and the force convergence criterion to 10-5eV; where MnBi2Te4 is a ferromagnetic semiconductor, add the magnetic moment and U value to the input file, and the selection of U value is determined based on references and comparison with the HSE06 method.
3. A design method for a two-dimensional MnBi2Te4 magnetic tunnel junction according to claim 1, characterized in that: Step (2) is as follows: Determine the lattice parameters of MnBi2Te4 and MoSi2N4 as 4.33 Å and 2.89 Å, perform 2×2×1 and 3×3×1 cell expansion operations on them respectively, so that the lattice mismatch rate of the two is only 0.12% to ensure that the heterojunction will not be deformed; build a Cu / MnBi2Te4 / MoSi2N4 / MnBi2Te4 / Cu magnetic tunnel junction.
4. The design method of a two-dimensional MnBi2Te4 magnetic tunnel junction according to claim 1, characterized in that: Step (3) is as follows: The heterojunction structure is optimized by density functional theory, non-equilibrium Green's function method and calculation software QuantumATK. During the optimization, the lattice constant is fixed and all atomic positions are released so that the forces between atoms are less than 0.05, and the interlayer van der Waals forces are designed and set to DFT-D3.
5. The design method of a two-dimensional MnBi2Te4 magnetic tunnel junction according to claim 1, characterized in that: Step (4) is as follows: Use the optimized structure to build a spintronic device consisting of a left electrode-central scattering region-right electrode, with the transport direction being the z direction; change the magnetic moment of the right MnBi2Te4 to obtain parallel and antiparallel configurations; in both configurations, use the transmission coefficient formula Calculate and analyze its transmission spectrum; Through the spin current formula Get the current value at each voltage point; in, represents the spin index, , represents the electron charge, represents Planck's constant, and are the delayed and advanced Green's functions in the scattering region, respectively, and and are the coupling matrices of the left / right electrodes respectively. Represents the Fermi-Dirac distribution of the left and right electrodes in the nonequilibrium state.
6. The design method of a two-dimensional MnBi2Te4 magnetic tunnel junction according to claim 1, characterized in that: In step (5), the IV curve is calculated by the magnetic resistance formula The magnetoresistance curve is obtained, where represents the current in the parallel state, represents the current in the antiparallel state.
7. The design method of a two-dimensional MnBi2Te4 magnetic tunnel junction according to claim 1, characterized in that: In step (5), the values in the TMR curve are used to obtain the extreme values of positive and negative magnetoresistance at 0.1 V and 1 V, respectively, and the spin-resolved projected state density along the electron transport direction is calculated. The source of magnetoresistance is obtained by analyzing the high and low state density.
8. A two-dimensional MnBi2Te4 magnetic tunnel junction, characterized in that: Cu is used as the electrode, MoSi2N4 is used as the barrier layer, and MnBi2Te4 is used as the ferromagnetic layer.
9. A two-dimensional MnBi2Te4-based magnetic tunnel junction according to claim 8, characterized in that: They include: Cu / MnBi2Te4 / MoSi2N4 / MnBi2Te4 / Cu in sequence.
10. An application method based on a two-dimensional MnBi2Te4 magnetic tunnel junction, characterized in that: Applied to STT-MRAM, the two-dimensional MnBi2Te4 magnetic tunnel junction is in the "read" state at 0.1V, and the two-dimensional MnBi2Te4 magnetic tunnel junction is in the "write" state at 1V.