Spintronics device based on staggered magnet KV2Se2O

Abstract

The invention discloses a spintronics device based on staggered magnets KV2Se2O, which comprises a left electrode, a central scattering region and a right electrode, and is characterized in that the left electrode and the right electrode are formed by staggered magnets KV2Se2O, the central scattering region is an expansion structure formed by a KV2Se2O material, and the transport direction of the device is a z direction; according to the invention, the research of the magnetic material KV2Se2O in the aspect of spin quantum transport properties is supplemented.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of spintronics, and particularly relates to a spintronics device based on staggered magnet KV2Se2O. BACKGROUND

[0002] The spintronics device refers to a left electrode-center scattering region-right electrode structure with ferromagnetic bodies on the left and right sides, but the staggered magnet is found, and the ferromagnetic body is replaced by the staggered magnet. The control means is changed from adjusting the magnetic moment of one side of the ferromagnetic body to adjusting the Néel vector of one side of the staggered magnet. When the Néel vectors on the two sides of the staggered magnetic tunnel junction are in a parallel state, due to the zero net magnetic moment and spin splitting of the staggered magnet, the spin-up state and the spin-down state are equal, but due to the different positions in the K space, the spin-up and spin-down electrons in the parallel configuration have different transport channels; and when the Néel vectors on the two sides of the staggered magnetic tunnel junction are in an antiparallel state, due to the spin flip of the free layer, the spin-down state cannot be transmitted to the spin-up state, so the channel is closed, and the antiparallel configuration will produce a very low transmission coefficient, which is much lower than the parallel configuration, thereby showing the magnetic resistance characteristics as a whole.

[0003] The existing RuO2 / TiO2 / RuO2 staggered magnetic tunnel junction uses RuO2 to achieve a magnetic resistance rate of about 500%, but since the staggered magnet is a brand-new concept proposed in recent years, the research on the spin quantum transport of the staggered magnet still needs to be enriched. Although the magnetic resistance rate of the spintronics device based on RuO2 can reach 500%, it is not excellent in terms of numerical value compared with other spintronics devices based on traditional ferromagnets. SUMMARY

[0004] The purpose of the present application is to provide a spintronics device based on staggered magnet KV2Se2O, to provide more references for the research on the spin quantum transport of the staggered magnet KV2Se2O, especially the magnetic resistance effect, to provide more material selection for the spintronics device based on the staggered magnet, and to seek a greater magnetic resistance rate.

[0005] The spintronics device based on the staggered magnet KV2Se2O comprises a left electrode, a center scattering region and a right electrode, wherein the left electrode and the right electrode are both composed of the staggered magnet KV2Se2O, the center scattering region is an extended structure composed of the KV2Se2O material, and the transport direction of the device is the z direction.

[0006] Further, the magnetic moment configuration of the left electrode and the right electrode can be adjusted to be parallel or antiparallel to realize different spin transport characteristics.

[0007] The application discloses a spintronic device design method based on an interlaced magnet KV2Se2O, which comprises the following steps: optimizing a crystal structure of the KV2Se2O; calculating a band structure of the KV2Se2O; constructing a device structure comprising a left electrode, a central scattering region and a right electrode; calculating spin transport properties of the device in parallel and anti-parallel configurations; calculating a magnetoresistance value based on the transport properties; and analyzing intrinsic states of the device to explain a high magnetoresistance mechanism.

[0008] Further, the optimization of the crystal structure is specifically as follows: performing atomic position relaxation and adjusting a cell shape and volume of the KV2Se2.

[0009] Further, the calculation of the band structure of the KV2Se2O is specifically as follows: a first principle method is adopted, and different atomic magnetic moments are set to simulate the interlaced magnetism.

[0010] Further, the construction of the device structure comprising the left electrode, the central scattering region and the right electrode is specifically as follows: a cell expansion operation is performed on the KV2Se2O, and a transport path is set along a z direction.

[0011] Further, the calculation of the spin transport properties of the device in the parallel and anti-parallel configurations is specifically as follows: a method combining a density functional theory and a non-equilibrium Green's function is adopted.

[0012] Further, the calculation of the magnetoresistance value based on the difference between the transmission coefficients in the parallel and anti-parallel configurations.

[0013] Further, the analysis of the intrinsic states of the device is specifically as follows: transport channels of spin-up and spin-down electrons and orbital contributions thereof are identified.

[0014] Advantages: Compared with the prior art, the application has the following remarkable advantages: the design of the spintronic device based on the interlaced magnet KV2Se2O of the application further supplements the research on spin quantum transport properties of the magnetic material KV2Se2O; by utilizing the characteristics of the interlaced magnet KV2Se2O, the designed spintronic device reaches a magnetoresistance of 2.83*10 8 % which is much larger than that in the previous research. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a band structure diagram of the application;

[0016] Figure 2 is a spintronic device structure based on KV2Se2O of the application;

[0017] Figure 3 is I-V characteristic curves of the application in (a) parallel and (b) anti-parallel configurations, and (c) a transmission coefficient of the application in the parallel configuration (k A ,k B) = (0, 0.25) and (k A ,k B ) = (0.25, 0) at the eigenstate;

[0018] Figure 4 is the (a) traditional ferromagnetic material-based magnetoresistance schematic (b) new type of magnetoresistance schematic based on staggered magnet material of the application. DETAILED DESCRIPTION

[0019] The technical solutions of the application will be further described below with reference to the drawings.

[0020] As Figure 1 shown, the embodiment of the application provides a spintronics device based on staggered magnet KV2Se2O and a design method thereof, comprising the following steps:

[0021] Step 1: optimizing the crystal structure of KV2Se2O by VASP. Import the structure file of CsV2Se2O primitive cell, replace the Cs element with K, and optimize the crystal structure by VASP. When optimizing, the structure is completely released, including atomic position relaxation, changing the shape of the primitive cell, and changing the volume of the primitive cell. The force on the atom is less than 0.01. After optimization, the structure is as shown in Figure 1 (a) and (b), and the lattice constant

[0022] Step 2: calculating the band structure of KV2Se2O, and the result is as shown in Figure 1 (c). In the calculation, the electron exchange correlation potential adopts PBE-GGA, the plane wave cutoff energy is set to 600eV, the Brillouin zone integration grid is 9x9x5, and the convergence standard of electron energy is set to 10 -5 eV. In order to more accurately describe the electronic properties of KV2Se2O, the magnetic moments of the two V atoms in the input file are set to 1 and-1 respectively. The U value is selected according to the reference, and is determined to be 1eV on the 3d orbital of V for fine tuning.

[0023] Step 3: building a spintronics device based on KV2Se2O. Perform 1x1x4 cell expansion operation on KV2Se2O, and convert it into a device, including left electrode-center scattering region-right electrode, the transport direction is z direction, and the device structure is as shown in Figure 2 .

[0024] Step 4: calculating the transport properties by the density functional theory and non-equilibrium Green's function method and software Quantum ATK. By changing the Néel vector (magnetic moment of V1 atom-magnetic moment of V2 atom) of the right KV2Se2O, two configurations of parallel and antiparallel are obtained. In the two configurations, the transmission spectrum is calculated and analyzed by the transmission coefficient formula , and the spin current formula The current value under zero bias is obtained, where σ represents the spin index, σ = ↑ / ↓, e represents the electron charge, h represents the Planck constant, G R (E, V) and G A (E, V) are the retarded and advanced Green's functions of the scattering region, respectively, while Γ L and Γ R are the coupling matrices of the left (right) electrode. f L / R represents the Fermi-Dirac distribution of the left and right electrodes in the non-equilibrium state. The calculation results are shown in Figure 3 (a) and (b).

[0025] Step 5: The obtained transmission spectrum curve is calculated by the formula of magnetoresistance The magnetoresistance value under equilibrium state is 2.83*10 8 %, where T P(up) represents the transmission coefficient of spin-up electrons in the parallel state, T AP(down) represents the transmission coefficient of spin-down electrons in the anti-parallel state, and other symbols are similarly defined.

[0026] Step 6: Based on the unique properties of the staggered magnet, the eigenstates of (k A , k B ) = (0, 0.25) and (k A , k B ) = (0.25, 0) are calculated as shown in Figure 3 (c), where (k A , k B ) = (0, 0.25) is spin-up and (k A , k B ) = (0.25, 0) is spin-down. Analysis shows that the system has high magnetoresistance because the spin-up electron transport in the parallel configuration is mainly contributed by the d yz orbital of V1 atom, and the spin-down electron transport is mainly contributed by the d xz orbital of V2 atom, and the spin-up and spin-down electrons are in different transport channels. When the configuration is anti-parallel, the spin electrons provided by the left KV2Se2O cannot be transmitted to the right opposite spin.

[0027] The principle of magnetoresistance effect based on staggered magnet is summarized and compared with traditional magnetoresistance effect, as shown in Figure 4As shown, in the conventional ferromagnetic-based TMR, due to the ferromagnetic non-zero net magnetic moment and spin splitting, there must be a multi-state and a few-state (spin polarization rate is not 0). In the parallel configuration, spin-up electrons occupy the main transport position; in the anti-parallel configuration, due to the spin flip of the free layer, spin-up can only receive a small amount of electrons, and spin-down is the same as the parallel configuration and can only provide a small amount of electrons. Therefore, the transmission of the anti-parallel configuration is much weaker than that of the parallel configuration, thereby showing the magnetic resistance effect. Based on the staggered magnet, due to the zero net magnetic moment and spin splitting, the spin-up state and the spin-down state are certainly equal, but due to the different positions in the K space, the spin-up and spin-down electrons have different transport channels in the parallel configuration; in the anti-parallel configuration, due to the spin flip of the free layer, the spin-down state cannot be transmitted to the spin-up state, so the channel is closed, and the anti-parallel configuration will produce a very low transmission coefficient, much lower than the parallel configuration, thereby showing the magnetic resistance effect as a whole.

[0028] In summary, the present application designs a spintronics device based on KV2Se2O, and by calculating the transmission coefficient along the electron transport direction and the eigenstate, it is proved that due to the different transmission paths of spin-up and spin-down electrons, the device produces a high magnetic resistance rate of 2.83*10 8 The spintronics device based on KV2Se2O is expected to be applied to MRAM and other spin multifunctional devices, and effectively avoid the many limitations brought by the conventional ferromagnetic material.

Claims

1. A spintronic device based on the intercalated magnet KV2Se20, characterized in that, The device comprises a left electrode, a central scattering region, and a right electrode, wherein the left electrode and the right electrode are both composed of staggered magnetic body KV2Se2O, and the central scattering region is an extended structure composed of KV2Se2O material, and the transport direction of the device is the z direction.

2. A spintronic device based on the intercalated magnet KV2Se20 of claim 1, wherein, The magnetic moment configuration of the left electrode and the right electrode can be adjusted to be parallel or antiparallel state to realize different spin transport characteristics.

3. A spintronics device design method based on staggered magnet KV2Se2O according to claim 1, characterized in that, The method comprises the following steps: optimizing the crystal structure of KV2Se2O; calculating the energy band structure of KV2Se2O; constructing a device structure comprising a left electrode, a central scattering region, and a right electrode; calculating the spin transport properties of the device under parallel and antiparallel configurations; calculating the magnetoresistance value based on the transport properties; and analyzing the eigenstate of the device to explain the high magnetoresistance mechanism.

4. The spintronics device design method based on intercalated magnet KV2Se20 of claim 3, wherein, The optimization of the crystal structure is specifically as follows: atomic position relaxation and adjustment of the cell shape and volume are performed on KV2Se2.

5. The spintronics device design method based on intercalated magnet KV2Se20 of claim 3, wherein, The calculation of the energy band structure of KV2Se2O is specifically as follows: a first-principles method is adopted, and different atomic magnetic moments are set to simulate staggered magnetism.

6. The method of designing spintronic devices based on intercalated magnet K V2Se20 according to claim 3, wherein, The construction of the device structure comprising a left electrode, a central scattering region, and a right electrode is specifically as follows: the cell expansion operation is performed on KV2Se2O, and the transport path is set along the z direction.

7. The spintronics device design method based on intercalated magnet KV2Se20 of claim 3, wherein, The calculation of the spin transport properties of the device under parallel and antiparallel configurations is specifically as follows: the method combining the density functional theory and the non-equilibrium Green's function is adopted.

8. The spintronics device design method based on intercalated magnet KV2Se20 of claim 3, wherein, The magnetoresistance value is calculated based on the difference between the transmission coefficients under parallel and antiparallel configurations.

9. The spintronics device design method based on intercalated magnet KV2Se20 of claim 3, wherein, The analysis of the eigenstate of the device is specifically as follows: the transport channels of spin-up and spin-down electrons and their orbital contributions are identified.

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