Spintronic device for 180-degree nonvolatile flipping of magnetic moment by electric field and application

Abstract

The application relates to the technical field of information storage, in particular to a spin electronic device capable of realizing 180-degree nonvolatile flip of a magnetic moment through an electric field and an application method. The spin electronic device comprises two magnetic layers and an insulating layer or a semiconductor material arranged between the two magnetic layers, the insulating layer or the semiconductor material arranged between the two magnetic layers can isolate the direct interaction of the two magnetic layers; one of the two magnetic layers is a semi-semiconductor or a magnetic metal material, and the other is a bipolar magnetic semiconductor. The device can realize the magnetic coupling state control of the two magnetic layers through an electric field, and realize the 180-degree flip of the magnetic moment. After the electric field is removed, there is almost no coupling between the two magnetic layers, thereby realizing the nonvolatility of the magnetic moment flip.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of information storage technology, in particular to a spintronic device capable of realizing 180-degree non-volatile flipping of magnetic moment by electric field and application method. BACKGROUND

[0002] With the development of information technology, the size of devices is getting smaller and smaller, the speed is getting faster and faster, and the energy consumption is getting lower and lower. The traditional electronics utilizes the charge property of electrons to generate Joule heat, while the spintronics utilizes the spin property of electrons, and the spintronic device increases the dimension of electron spin. The spintronic device is controlled by the spin of electrons, and has lower energy consumption and running speed. This involves the control of magnetic moment, and the traditional method controls the magnetic moment of magnetic material by generating magnetic field through coil, which has high energy consumption and is not conducive to the miniaturization of devices. If the magnetic moment can be directly controlled by electric field, it is of great significance to realize the low-energy spintronic device. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application selects a suitable energy band and magnetic material to form a spintronic device structure. The device can realize the control of the magnetic coupling state of two magnetic layers by electric field, and realize the 180-degree flipping of magnetic moment. After the electric field is removed, there is almost no coupling between the two magnetic layers, thereby realizing the non-volatility of magnetic moment flipping.

[0004] The specific scheme of the present application is as follows:

[0005] A spintronic device capable of realizing 180-degree non-volatile flipping of magnetic moment by electric field, comprising two magnetic layers and an insulating layer or semiconductor material arranged between the two magnetic layers; one of the two magnetic layers is a half-semiconductor (HSC) material or a magnetic metal material, for example, the half-semiconductor material can be CrBr3, CrI3, CrCl3, etc., the magnetic metal material can be Co2FeSi, Co2MnSi, 1T-MnSe2, LSMO, Fe3O4, etc. half-metal material, or Fe, Co, Ni, 1T-VSe2, etc. common magnetic metal material; the other layer is a bipolar magnetic semiconductor (BMS) material, for example, 2H-VSe2, Cr2TiC2FCl, Cr2CFCl, etc. two-dimensional magnetic material, FeVTiSi, etc. hasel alloy, double perovskite material with general formula A2CrMO6 (A = Ca, Sr, Ba, M = Ru, Os).

[0006] If one magnetic layer is a half-semiconductor material, the valence band of the half-semiconductor material cannot be higher than the conduction band of the bipolar magnetic semiconductor material used, and the valence band of the bipolar magnetic semiconductor material cannot be higher than the conduction band of the half-semiconductor material, and if the magnetic layer is a magnetic metal material, the Fermi level of the magnetic metal material needs to fall between the valence band and the conduction band of the bipolar magnetic semiconductor material.

[0007] The application of an electric field can adjust the size of the virtual transition between the two magnetic layers, thereby controlling the magnetic coupling state between the two magnetic layers and realizing the 180-degree flip of the magnetic moment.

[0008] Specifically, assuming that the direction of the bipolar magnetic semiconductor layer pointing to the other magnetic layer (HSC or magnetic metal material layer) is the positive direction, when a positive electric field is applied, the device is in an anti-ferromagnetic coupling state, and when a reverse electric field is applied, the device is in a ferromagnetic coupling state.

[0009] Those skilled in the art know that the Fermi level and the values of the valence band and the conduction band of the material can be obtained by first principle calculation and the like. The magnetic layer-insulating layer-magnetic layer structure can be prepared by molecular beam epitaxy, magnetron sputtering, mechanical peeling and stacking, chemical vapor deposition and the like.

[0010] By inserting an insulating layer or a semiconductor material, such as hexagonal boron nitride (h-BN), between the two magnetic layers, the direct interaction between the two magnetic layers can be isolated, thereby realizing the original state of the magnetic moment without an electric field and realizing the non-volatility of the magnetic moment flip. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 Fig. 1 is a schematic diagram of the principle of the method for realizing the 180-degree non-volatile flip of the magnetic moment of the device by interlayer coupling and electric field in the embodiments of the present application: Figure 1 (a) is a magnetic moment (M)-electric field (E) diagram; Figure 1 (b) is a schematic diagram of the density of states of a half-semiconductor (HSC) and a bipolar magnetic semiconductor (BMS), Figure 1 In (b), E is energy, the arrow direction represents the upward or downward spin direction, Δ1', Δ2', and Δ3' are the semiconductor band gap, the spin flip band gap in the conduction band, and the spin flip band gap in the valence band of the HSC, respectively, and Δ1, Δ2, and Δ3 are the semiconductor band gap, the spin flip band gap in the conduction band, and the spin flip band gap in the valence band of the BMS, respectively.

[0012] Figure 2Schematic diagram of interlayer exchange coupling for two magnetic layers in the device of the present application. insulator is the insulating layer. Fig. (a) represents the ferromagnetic state, and Fig. (b) represents the antiferromagnetic state. H represents HSC, B represents BMS, o and u represent the occupied state (valence band for semiconductor) and unoccupied state (conduction band for semiconductor) respectively, and ↑ and ↓ represent spin up and spin down respectively. As φ Ho↑ i.e. represents the occupied state with spin up in HSC. The dotted line with arrow represents the virtual transition of spin electron between the two magnetic layers, and the thickness of the line represents the strength of the transition.

[0013] Figure 3 Magnetic coupling energy of the device under the bias (electric field) calculated by the tight-binding method. AFM is the antiferromagnetic coupling, FM is the ferromagnetic coupling, and NC represents the state with almost no coupling between the two magnetic layers. Fig. (a): magnetic coupling energy under different voltages when the transition integral t = 0.06 eV; Fig. (b): phase diagram of the magnetic coupling energy for different transition integrals t and different voltages.

[0014] Figure 4 Phase diagram of the magnetic coupling energy of the device for different voltages (electric fields) and spin flip band gaps Δ2', Δ3' under the voltages calculated by the tight-binding method. (a) Phase diagram of the magnetic coupling energy for Δ2' and the voltage. (b) Phase diagram of the magnetic coupling energy for Δ3' and the voltage.

[0015] Figure 5 Energy band diagram and state density diagram of CrBr3 (Fig. (a)) and 2H-VSe2 (Fig. (b)). The vertical axis is energy (Energy), and VBM and CBM distribution represent the valence band top and the conduction band bottom, E F Fermi level, spin up and spin down represent spin up and spin down respectively.

[0016] Figure 6 Model of the spintronic device of the CrBr3 / h-BN / 2H-VSe2 structure in the embodiment.

[0017] Figure 7 Magnetic coupling state / magnetic coupling energy of the CrBr3 / h-BN / 2H-VSe2 device in the embodiment under different electric fields. DETAILED DESCRIPTION

[0018] The principles and device structure, application method of the present application will be described below in combination with the drawings and embodiments, which are not limiting to the present application.

[0019] Figure 1 The principle of the method for realizing 180-degree non-volatile flip of the magnetic moment of the device by interlayer coupling and electric field in the present application is shown. As φ Figure 1The magnetic moment (M) - electric field (E) diagram in a shows that, in order to realize the 180-degree flip of the magnetic moment, the two magnetic layers should be in the ferromagnetic coupling and anti-ferromagnetic coupling states under the action of the negative and positive electric field in the i region and the ii region respectively, and vice versa, depending on the definition of the positive electric field (the i region and the ii region are in the anti-ferromagnetic coupling and ferromagnetic coupling states respectively). In the iii region, that is, the region where the electric field strength is close to 0, the coupling of the two magnetic layers needs to be weak enough to flip the magnetic moment. Therefore, the half semiconductor (which can also be a magnetic metal material) and the bipolar magnetic semiconductor are selected as the two magnetic layers, the valence band of the selected half semiconductor cannot be higher than the conduction band of the bipolar magnetic semiconductor, and the valence band of the bipolar magnetic semiconductor cannot be higher than the conduction band of the half semiconductor. If a magnetic metal material is selected, the Fermi level of the selected magnetic metal material should fall between the valence band and the conduction band of the bipolar magnetic semiconductor.

[0020] The density of states diagram of the half semiconductor (HSC) and the bipolar magnetic semiconductor (BMS) is shown in Figure 1 b, the arrow direction represents the electron spin direction. The valence band maximum (VBM) and the conduction band minimum (CBM) of the half semiconductor have the same spin state, and the valence band maximum and the conduction band minimum of the bipolar magnetic semiconductor material have opposite spin states. When Δ1' of the half semiconductor tends to 0, it is a magnetic metal material.

[0021] Similar to the superexchange effect, the coupling between the magnetic layers can be understood as the virtual transition of spin electrons between the magnetic layers, and different magnetic states correspond to different transition modes, as shown in Figure 2 For the ferromagnetic state, the interlayer transition is dominated by the transition from the valence band maximum of the bipolar magnetic semiconductor to the conduction band minimum of the half semiconductor, and for the anti-ferromagnetic state, the interlayer transition is dominated by the transition from the valence band maximum of the half semiconductor to the conduction band minimum of the bipolar magnetic semiconductor. Different transition modes of ferromagnetic and anti-ferromagnetic result in energy difference between different magnetic states, that is, magnetic coupling. By applying an electric field, the relative energy level of the two magnetic layers can be adjusted, thereby adjusting the size of the virtual transition between the two magnetic layers, and further controlling the magnetic coupling state between the two magnetic layers, realizing the 180-degree flip of the magnetic moment.

[0022] By inserting an insulating layer or a semiconductor material to isolate the direct interaction between the two magnetic layers, the magnetic moment can be kept in the original state without the electric field, realizing the non-volatility of the magnetic moment flip.

[0023] The tight-binding method can be used to calculate the magnetic coupling between the two magnetic layers, thereby verifying that the electric field can realize the 180-degree non-volatile flip of the magnetic moment of the device composed of HSC / BMS. The corresponding Hamiltonian under different magnetic coupling states is:

[0024]

[0025] where t is the hopping integral, c † and c are creation and annihilation operators, μ and v are band indices (μ, v = o, u; here o and u represent occupied and unoccupied states, respectively), σ represents the spin state of the electron, ε is the self-energy of each band, e represents the charge of the electron, V is the magnitude of the applied voltage. h.c. represents complex conjugate, δ is the Kronecker function. In the calculation process, unless specifically mentioned to change the value, Δ2', Δ3', Δ2 and Δ3 are set to 0.5 eV, Δ1' and Δ1 are set to 1 eV, t is set to 0.06 eV.

[0026] Figure 3 b is the magnetic coupling energy of the device under different hopping integrals t (reflecting the size of the interaction between the magnetic layers) under the condition of different voltages (the voltage direction is positive in the direction from the bipolar magnetic semiconductor to the half semiconductor) determined by the tight-binding method and the HSC and BMS band gap (i.e. △E = E AFM -E FM , reflecting the magnetic coupling state, △E is positive, the device is in ferromagnetic coupling (FM), △E is negative, the device is in antiferromagnetic coupling (AFM)), it is found that for each different hopping integral value, i.e. the magnetic layers with different sizes of interaction, the magnetic coupling state of the device can be controlled by applying a bias. And in the absence of bias, the two magnetic layers have no magnetic coupling, which shows that the 180-degree non-volatile flip of the magnetic moment can be realized in principle. Figure 3 a is the magnetic coupling energy under different voltages when the hopping integral t = 0.06 eV, it can be seen that when a positive bias is applied, the device is in antiferromagnetic coupling (AFM), and when the bias is greater than a certain value (such as 0.5V), the magnetic coupling energy is negative, and the antiferromagnetic coupling is obvious; otherwise, it is ferromagnetic coupling.

[0027] Figure 4 b is the magnetic coupling energy of the device with different energy gaps Δ2' (such as Figure 1 the spin flip gap in the valence band shown in b) and Δ3' (such as Figure 1 the spin flip gap in the conduction band shown in b) under the condition that the hopping integral is unchanged (t = 0.06 eV) under the action of different voltages, it can be seen that for the case where Δ2' and Δ3' are greater than 0 eV, the coupling between the magnetic layers can be changed between ferromagnetic, antiferromagnetic and no coupling by voltage control, further proving that the 180-degree non-volatile flip of the magnetic moment can be realized by voltage.

[0028] Example 1

[0029] With a CrBr3 / h-BN / 2H-VSe2 structural device as an example, modeling and calculation of magnetic coupling states under different electric fields are performed by first principles. The band structure and density of states of CrBr3 and 2H-VSe2 calculated by the first principles method are as shown in Figure 5 It can be seen that CrBr3 is a half semiconductor, 2H-VSe2 is a bipolar magnetic semiconductor, the valence band of CrBr3 is not higher than the conduction band of 2H-VSe2, and the valence band of 2H-VSe2 is not higher than the conduction band of CrBr3.

[0030] The model of the built CrBr3 / h-BN / 2H-VSe2 structural spintronic device is as shown in Figure 6 It is composed of three materials. Density functional theory is used, GGA+PBE is used to describe the exchange correlation functional, a selected cutoff energy of 500 eV is used, high precision is set, for example, energy convergence is 10 -8 eV, the Cr and V elements are corrected by DFT+U, and the van der Waals correction is used to include the long-range interaction between materials, the energy of the magnetic layer in the ferromagnetic and antiferromagnetic coupling states under different electric fields is calculated, the interaction between the magnetic layers under different electric fields is determined, and the electric field direction from 2H-VSe2 (BMS) to CrBr3 (HSC) is defined as the positive direction. As shown in Figure 7 When a positive electric field is applied, the magnetic coupling energy is negative, the device is in an antiferromagnetic coupling state, when a reverse electric field is applied, the magnetic coupling energy is positive, the device is in a ferromagnetic coupling state, and it is proved that the 180-degree non-volatile flip of the magnetic moment of the device can be realized by the electric field.

Claims

1. A spintronic device capable of achieving a 180-degree non-volatile reversal of magnetic moment through an electric field, characterized in that: The invention comprises two magnetic layers and an insulating layer disposed between the two magnetic layers, wherein the insulating layer disposed between the two magnetic layers can isolate the two magnetic layers from direct interaction; one of the two magnetic layers is a semi-semiconductor or a magnetic metal material, and the other is a bipolar magnetic semiconductor; if a semi-semiconductor is used, the valence band of the semi-semiconductor is not higher than the conduction band of the bipolar magnetic semiconductor, and the valence band of the bipolar magnetic semiconductor is not higher than the conduction band of the semi-semiconductor; if a magnetic metal material is used, the Fermi level of the magnetic metal material falls between the valence band and the conduction band of the bipolar magnetic semiconductor; The semiconductor is one of CrI3 and CrCl3.

2. The spintronic device capable of achieving a 180-degree non-volatile reversal of magnetic moment by an electric field according to claim 1, characterized in that: The magnetic metal material is one of Co2FeSi, Co2MnSi, 1T-MnSe2, LSMO, Fe3O4, Fe, Co, Ni, and 1T-VSe2, and the bipolar magnetic semiconductor is one of 2H-VSe2, Cr2TiC2FCl, Cr2CFCl, Heusler alloy, and double perovskite material.

3. The application method of the spintronic device capable of achieving 180-degree non-volatile reversal of magnetic moment by electric field according to claim 1, characterized in that: The magnetic coupling state of the spintronic device is controlled by applying an electric field.

4. The application method according to claim 3, characterized in that: Taking the direction in which the bipolar magnetic semiconductor magnetic layer points to the semi-semiconductor or magnetic metal material magnetic layer as the positive direction, a positive electric field is applied, and the spin electronic device is in an antiferromagnetic coupling state; and a negative electric field is applied, and the spin electronic device is in a ferromagnetic coupling state.

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