CN110707208B - A method for adjusting magnetic anisotropy of magnetic tunnel junction and corresponding magnetic tunnel junction - Google Patents

Abstract

The invention belongs to the application field of spintronics, and discloses a method for adjusting the magnetic anisotropy of a magnetic tunnel junction and a corresponding magnetic tunnel junction. The contribution of the electron orbital coupling effect, thereby realizing the adjustment of the magnetic anisotropy of the magnetic tunnel junction; the initial film structure of the magnetic tunnel junction includes a barrier layer, a ferromagnetic layer and a non-magnetic metal cover layer in sequence. Based on the interface effect, the invention changes the distribution of the Bloch electronic state near the Fermi level by adding a metal interlayer, thereby controlling the contribution of the coupling action term between the electron orbitals, and realizing the precise adjustment of the magnetic anisotropy of the magnetic tunnel junction (such as the atomic magnetic field). moment and the magnetic anisotropy energy of the magnetic tunnel junction, magnetoelectric coefficient, etc.) to meet various needs in practical applications. In particular, a sufficiently high perpendicular magnetic anisotropy can be obtained to solve the problem of excessive write power consumption of the spin transfer torque magnetic memory.

Description

A method for adjusting magnetic anisotropy of magnetic tunnel junction and corresponding magnetic tunnel junction

technical field

The invention belongs to the application field of spintronics, and more particularly, relates to a method for adjusting the magnetic anisotropy of a magnetic tunnel junction and a corresponding magnetic tunnel junction.

Background technique

It is well known that electrons have two intrinsic properties, charge and spin. Charge determines how electrons behave in an electric field, while spin affects how electrons behave in a magnetic field. Different from the traditional semiconductor memory that relies on electric charge to realize the transmission and storage of data, the magnetic random access memory completes the inversion of the data state based on the electron spin effect. The development of magnetic random access memory has gone through two stages of magnetic field drive and current drive. In contrast, the current-driven type, that is, the spin transfer torque magnetic memory, has no additional writing information lines, the structure is simpler, and the switching current decreases with the reduction of the cell size, and the transistor size of the matching CMOS integrated circuit is reduced. Also smaller, scalability and storage density are improved.

The magnetic tunnel junction is the core storage unit of the spin transfer torque magnetic memory, which is a sandwich-like film structure including a pinned layer, a free layer and a barrier layer. In the magnetic tunnel junction, the storage of information depends on the retention of the magnetization state in the free layer, that is, the thermal stability of the magnetic electrode; the read operation requires that the tunneling magnetoresistance ratio of the magnetoresistive device is large enough, and the resistance value under steady state Differentiable; the write operation is performed by changing the magnetization direction of the free layer, which is affected by the critical write current density. Satisfying the performance requirements of both thermal stability and write current at the same time is a major challenge for spin transfer torque magnetic memories. Similar to early magnetic recording media, the thermal stability factor of a magnetic tunnel junction is determined by the ratio of the energy barrier at magnetization reversal and the operating temperature:

Among them, the anisotropic energy density _{Ku is jointly determined by the saturation magnetization MS and the anisotropic magnetic field H k of the} free layer. The write current is usually characterized by the critical switching current density J _c0 , _which refers to the current density required for the free-layer magnetic moment to continue precessing under the action of a small-amplitude pulse. The value of switching current density J _c is equivalent to:

where η, α, t, and H _⊥eff are the spin transport efficiency, damping coefficient, film thickness, and out-of-plane demagnetization field of the free layer, respectively. Obviously, using a material with strong perpendicular magnetic anisotropy as the magnetic layer of the magnetic tunnel junction can improve the thermal stability of the magnetic tunnel junction, but it will also bring about the problem of excessive switching current and high write power consumption. In addition, the new material system may have the problem of complex structure, which is not conducive to the experimental preparation of single crystal epitaxial magnetic tunnel junction devices.

In order to solve the above problems and control the magnetization state of the magnetic tunnel junction more efficiently, the researchers proposed some mechanisms for assisting information writing: electric field assistance, thermal assistance, and microwave assistance. Among them, the adjustment of the magnetization state of the ferromagnetic layer by the electric field is more flexible, and the reduction of the critical current density is also more significant. It is important to note that the effect of the electric field on the magnetic anisotropy is limited to a few atomic layers at the surface or interface. In particular, when the film thickness reaches the sub-micron scale, interfacial effects such as the asymmetric lattice structure, defects and stress of the interface will emerge, which will have a direct impact on the device performance. Since Ikeda et al. proposed that the perpendicular magnetic anisotropy is caused by the interface effect through function fitting in 2010, a lot of work has focused on the physical origin of the interface perpendicular magnetic anisotropy. The prevailing view is that the perpendicular magnetic anisotropy is caused by the hybridization of electron orbitals at the Fermi level. Hallal et al. decomposed the magnetic anisotropy energy by atomic layers and found that the magnetic atomic layers adjacent to the interface contributed to the magnetic anisotropy. There are also works devoted to obtaining stronger perpendicular magnetic anisotropy, investigating the effects of interfacial oxidation state, non-magnetic metal capping layers, and heavy metal doping on the magnetic anisotropy. Therefore, it is necessary to further explore the interface effect of the magnetic tunnel conjunctival layer structure to solve the process compatibility problem and guide the device design.

SUMMARY OF THE INVENTION

In view of the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a method for adjusting the magnetic anisotropy of a magnetic tunnel junction and a corresponding magnetic tunnel junction. The adjustment method is based on the interface effect. Further adjust the element type, action position and interlayer thickness of the metal interlayer, change the distribution of Bloch electronic states near the Fermi level, and control the contribution of the coupling interaction term between electron orbitals by adjusting the size of the effective angular momentum matrix unit. The precise adjustment of the magnetic anisotropy of the magnetic tunnel junction (such as the atomic magnetic moment, the magnetic anisotropy energy of the magnetic tunnel junction, the magnetoelectric coefficient, etc.) can be realized to meet various needs in practical applications. In particular, a sufficiently high perpendicular magnetic anisotropy can be obtained to solve the problem of excessive write power consumption of the spin transfer torque magnetic memory; in addition, this method can also reduce the lattice mismatch at the interface, which is helpful for Epitaxial fabrication and performance improvement of magnetic tunnel junctions.

In order to achieve the above object, according to one aspect of the present invention, a method for adjusting the magnetic anisotropy of a magnetic tunnel junction is provided, characterized in that, the method is to control electrons by inserting a metal interlayer in the film structure of the magnetic tunnel junction The magnetic anisotropy of the magnetic tunnel junction can be adjusted by the contribution of the orbital coupling effect; the initial film structure of the magnetic tunnel junction includes a barrier layer, a ferromagnetic layer and a non-magnetic metal cover layer in sequence.

As a further preference of the present invention, the adjustment of the magnetic anisotropy of the magnetic tunnel junction specifically includes: adjustment of atomic magnetic moment, magnetic anisotropy energy or magnetoelectric coefficient.

As a further preference of the present invention, the metal element used in the metal interlayer is selected from Group VIII transition metal elements, Ag and Au; preferably, the Group VIII transition metal element is selected from Rh, Ir, Ni and Pd.

As a further preference of the present invention, the inserted metal interlayer is located at the interface of the barrier layer/ferromagnetic layer, or located inside the ferromagnetic layer, or located at the interface of the ferromagnetic layer/non-magnetic metal capping layer.

As a further preference of the present invention, the thickness of the metal interlayer does not exceed 10 atomic layers.

As a further preference of the present invention, in this method, while inserting a metal interlayer into the film structure of the magnetic tunnel junction, an external electric field is additionally introduced as an auxiliary, and the external electric field can adjust the occupancy of the electron orbitals at the Fermi level, Thereby, the adjustment of the magnetic anisotropy of the magnetic tunnel junction is assisted.

As a further preference of the present invention, the initial film structure of the magnetic tunnel junction sequentially includes an MgO layer, an Fe atomic layer and a Pt atomic layer, wherein the thickness of the MgO layer is 4 atomic layers, and the thickness of the Fe atomic layer is 4 atomic layers. The thickness of the Pt atomic layer is 8 atomic layers, and the thickness of the Pt atomic layer is 3 atomic layers; and the metal interlayer is inserted into the magnetic tunnel conjunctival layer structure, specifically, the thickness of 1 to 3 atomic layers of Rh is inserted at the MgO/Fe interface Atomic layers act as metal interlayers.

According to another aspect of the present invention, the present invention provides the magnetic anisotropy-adjusted magnetic tunnel junction obtained by the above method.

Through the above technical solutions conceived of the present invention, compared with the prior art, by adding a metal interlayer, the distribution of the Bloch electronic state at the Fermi level can be changed, thereby changing the contribution of the electronic orbital coupling term, and realizing the magnetic tunnel junction. Regulation of Magnetic Anisotropy. In addition, the electric field-assisted mechanism can be introduced while inserting the metal interlayer to achieve more precise control of the magnetic anisotropy of the magnetic tunnel junction. The introduction of an external electric field can adjust the occupancy of the electron orbitals at the Fermi level.

Specifically, the adjustment method in the present invention is to insert a metal interlayer into the typical magnetic tunnel junction film layer structure to change the distribution of the interface electronic structure, thereby realizing the adjustment of the magnetic anisotropy of the magnetic tunnel junction. By inserting a metal interlayer, and preferably by improving the types of key metal interlayer elements, action positions, film thickness, etc., the perpendicular magnetic anisotropy of the magnetic tunnel junction can be significantly improved compared with the prior art, solving the problem of miniaturization of magnetic memory. Thermal stability issues encountered during the process.

Specifically, the present invention has the following advantages:

(1) The present invention can change the distribution of Bloch electronic states near the Fermi level by inserting a metal interlayer, and preferably by controlling the element species, action position and film thickness of the metal interlayer, and control the contribution of the coupling interaction term between electron orbitals, The magnetic anisotropy of the magnetic tunnel junction is precisely regulated to obtain a sufficiently high perpendicular magnetic anisotropy energy to solve the thermal stability problem encountered in the development of the spin transfer torque magnetic memory. The use of different metal elements, insertion positions, and film thicknesses in the metal interlayer will lead to different magnetic anisotropy behaviors, which can meet the needs of the magnetic anisotropy of the magnetic tunnel junction in different application scenarios.

(2) Selecting a suitable metal material as the interface interlayer of the magnetic tunnel junction can play the role of a buffer layer, reduce the lattice mismatch degree and interface stress between the barrier layer and the ferromagnetic layer, and help realize the device. Epitaxial fabrication and performance improvement.

(3) Introducing an electric field-assisted writing mechanism while adjusting the interface film layer structure, further reducing the critical current density required for magnetization reversal, and realizing high storage density and low power consumption magnetic storage.

Description of drawings

FIG. 1 is a schematic structural diagram of the magnetic tunnel junction according to the present invention.

FIG. 2 is a schematic flowchart of the method for adjusting the magnetic anisotropy of the magnetic tunnel junction according to the present invention.

FIG. 3 is a schematic diagram of a model for VASP calculation in Embodiment 1 of the present invention.

Figure 4 shows the electronic structure characteristics of MgO/Fe_8ML/Pt according to Example 1 of the present invention, and (a) and (b) in Figure 4 are the partial wave density of states of the d orbital of Fe atoms at the interface of MgO/Fe and a few self-propelled states, respectively. Spin energy band.

Figure 5 is the electronic structure characteristics of MgO/Rh_1ML/Fe_8ML/Pt according to Example 1 of the present invention, (a) and (b) in Figure 5 are the partial wave density of states of Fe atom d orbital at Rh/Fe interface and few spin bands.

FIG. 6 is the electronic structure characteristics of MgO/Ir_1ML/Fe_8ML/Pt according to Example 1 of the present invention, and (a) and (b) in FIG. 6 are the partial wave density of states of the d orbital of Fe atom at the Ir/Fe interface and few spin bands.

FIG. 7 is the differential charge density and its in-plane average distribution curve of adding metal interlayers at different positions of MgO/Fe/Pt according to Example 2 of the present invention, and (a), (b) and (c) in FIG. 7 correspond in turn In the case of adding metal interlayers at the MgO/Fe interface, inside the ferromagnetic layer, and at the Fe/Pt interface, the area corresponding to the positive peak of the curve represents electron accumulation, and the area corresponding to the negative peak of the curve represents electron dissipation.

8 shows the variation trend of the magnetic anisotropy energy density of the magnetic tunnel junction MgO/Fe/Pt according to Embodiment 4 of the present invention under an electric field, and the thickness of the ferromagnetic layer is set to 5, 9, and 13 Fe atomic layers in sequence.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

The method for adjusting the magnetic anisotropy of the magnetic tunnel junction in the present invention is specifically to adjust the magnetic anisotropy of the magnetic tunnel junction based on the interface effect. By adding a metal interlayer to the typical magnetic tunnel junction film layer structure, the effective angular momentum matrix unit can be changed. The size of , adjusts the electronic orbital coupling of interface atoms, thereby adjusting the atomic magnetic moment and the magnetic anisotropy of the magnetic tunnel junction. Furthermore, the introduction of electric field-assisted magnetization reversal can more precisely adjust the magnetic anisotropy of the magnetic tunnel junction, and the adjustment range is also larger.

Based on the density functional theory, the invention obtains the effect of the element type, action position and film thickness of the metal interlayer on the magnetic tunnel junction magnetic anisotropy by calculating the changes of the magnetic tunnel junction magnetic anisotropy and the interface electronic structure before and after adding the metal interlayer. influences. Specifically, the first-principles calculations are carried out based on the VASP software package developed by Hafner's research group. The pseudopotential plus projected wave is used to approximate the complex potential field generated by the nucleus and inner electrons, and the generalized gradient approximation is used as the exchange correlation between electrons. functional. The truncation kinetic energy of the plane wave is set to 500 eV, the sampling of the Brillouin zone uses the Monkhorst-Pack method with the Γ point as the center, and the grid size is set to 17 × 17 × 1. The magnetic anisotropy energy depends on the difference in the magnetization energy of the magnetic tunnel junction in different crystallites, and its general expression is:

MAE=E ₁₀₀ -E ₀₀₁

where E ₁₀₀ and E ₀₀₁ are the magnetization energy of the magnetic tunnel junction in the in-plane and out-of-plane directions, respectively; the magnetoelectric coefficient is the first derivative of the magnetic anisotropy energy to the electric field, and the electric field is applied by adding The dipole moment is realized; the analysis of the electronic structure is based on the second-order perturbation theory of spin-orbit coupling. Here is an empirical formula:

Among them, l _z and l _x represent the out-of-plane and in-plane angular momentum operators, respectively, and S _o and S _e represent the electron-occupied state and electron-empty state under a certain wave vector, respectively.

The process of calculating the magnetic tunnel junction magnetic anisotropy and electronic structure in the present invention is shown in Figure 2, which mainly includes:

(1) Modeling, cutting and splicing the selected bulk structure to obtain the initial interface structure;

(2) Structural relaxation, consider spin polarization, reduce the free energy of the system, and obtain a relatively stable structure. The criterion for structural convergence is that the residual stress on each atom is lower than

(3) The static self-consistent calculation is carried out in two steps, and the charge density is obtained by considering the spin polarization. wave function and other information, and then add the action of the electric field to correct the basic information of the electrons under the electric field, and set the energy convergence standard to 10 ^-6 eV;

(4) Non-self-consistent property calculation, turn on the spin-orbit coupling, set the initial magnetic moment, obtain the magnetization energy in different directions, and set the energy convergence standard to 10 ^-6 eV;

(5) Calculation of non-self-consistent properties, set the appropriate K-point sampling frequency to obtain the density of states of the structure, set the appropriate sampling path and frequency, and modify the K-POINT file to line-mode mode to obtain the energy band of the structure.

The substantive features and obvious improvements of the present invention will be further described below by means of specific examples, but the present invention is by no means limited to the following examples.

Example 1:

This example reveals through first-principles calculations that changing the element species of the metal interlayer can greatly adjust the magnetic anisotropy of the MgO/Fe/Pt magnetic tunnel junction.

The calculation model used in this embodiment is shown in Fig. 3. Along the (001) crystallographic direction, the order is 10nm vacuum layer, 4ML MgO, 1ML metal interlayer, 8ML Fe, 3ML Pt and 10nm vacuum layer. In order to ensure the consistency of the interface structure, bcc-Fe is selected as the interface matching standard, so that other layers are deformed accordingly and the in-plane lattice constant is fixed at

Alternative interlayer materials include group VIII transition metals, silver Ag, and gold Au, in which the unit cells of Co, Ru and Os are close-packed hexagonal structures, and it is difficult to find suitable crystal planes for splicing with bcc-Fe(001) planes (consider To the diversity of ferromagnetic layer materials, it does not rule out the possibility that Co, Ru and Os can be used as metal interlayers to adjust the magnetic anisotropy of the magnetic tunnel junction); Fe and Pt are the ferromagnetic layer and nonmagnetic layer of the magnetic tunnel junction memory unit, respectively. overlay. Therefore, this embodiment mainly discusses the case where Rh, Ir, Ni, Pd, Ag and Au single atomic layers are inserted at the MgO/Fe interface. Among the selected materials, the lattice mismatch degree between the Ni(001) plane and the Fe(001) plane is 13.06%, and the lattice mismatch degree between other materials and the Fe(001) plane is within 10%, which is reasonable range. After adding the metal interlayer, the model is slightly complicated. In order to take into account the calculation efficiency and accuracy, the relaxation of the model is divided into two steps: consider the single interface model formed by the metal interlayer and MgO and Fe, and relax it to obtain the structural parameters at the interface. ; On this basis, a model containing a metal interlayer is constructed for relaxation, and its magnetic anisotropy energy and electronic structure are calculated.

Table 1 shows the magnetic anisotropy energy density of the magnetic tunnel junction when 1ML of metal interlayer is added at the MgO/Fe interface, and compares it with the magnetic anisotropy energy density of the MgO/Fe_8ML/Pt magnetic tunnel junction, where Positive values indicate perpendicular magnetic anisotropy, and negative values indicate in-plane magnetic anisotropy. The larger the absolute value, the greater the magnetic anisotropy energy in the relevant direction. The data and symbols of the magnetic anisotropy energy in the following tables have the same meaning. It can be seen from Table 1 that the magnetic anisotropy energy obtained will vary greatly depending on the selected interlayer material: when 1ML Rh film is inserted, the induced atomic magnetic moment is the largest, and the perpendicular magnetic anisotropy of the magnetic tunnel junction The strongest; when 1ML Ir film is inserted, the easy magnetization axis of the magnetic tunnel junction changes from out-of-plane to in-plane, showing obvious in-plane magnetic anisotropy; when 1ML Ni or Pd film is inserted, the perpendicular magnetic anisotropy of the magnetic tunnel junction Compared with MgO/Fe_8ML/Pt, the anisotropy is improved; when 1ML Ag or Au is inserted, the magnetic anisotropy of the magnetic tunnel junction is greatly weakened. In this example, the Fe/Pt interface is consistent in all interface models, and the contribution to the magnetic anisotropy behavior is the same. Therefore, the above-mentioned difference in the magnetic anisotropy energy is mainly due to the different orbital coupling between atoms at the metal interlayer/Fe interface. caused.

Table 1 Magnetic anisotropy energy densities obtained by selecting different metal materials as interfacial interlayers

metallic material None Rh Ni Ag MAE(mJ/m²) 2.3225 9.2566 2.4709 0.3698 metallic material Ir Pd Au MAE(mJ/m²) -9.1312 5.2125 0.6859

Figure 4 shows the fractional density of states and energy band structures of Fe atomic 3d orbitals at the MgO/Fe interface in the calculated MgO/Fe_8ML/Pt interface model. It can be seen from (a) in Figure 4 that the dx ² -y ² electron orbital has an obvious DOS peak at 0 eV, and the dxz and dyz orbitals also have a certain distribution. It can be seen from (b) in Figure 4 that the dxz and dyz orbitals have band-like energy band overlaps near the Fermi level, while the overlapping area of the dx ² -y ² orbitals and dxz and dyz orbitals is smaller. . Therefore, the magnetic anisotropy of the MgO/Fe_8ML/Pt interface model is the angular momentum matrix elements <dxz|l _z |dyz>, <dx ² -y ² |l _x |dyz>, and <dx ² -y ² |l _y |dxz>The result of joint action. Among them, the <dxz|l _z |dyz> coupling term dominates, making the magnetic anisotropy of the whole model positive; <dx ² -y ² |l _x |dyz> and <dx ² -y ² |l _y The contribution of the |dxz> coupling term is small, which will lead to a weakening of the perpendicular magnetic anisotropy of the model.

Figure 5 shows the fractional DOS and energy band structure of the Fe atom 3d orbital at the Rh/Fe interface in the calculated MgO/Rh_1ML/Fe_8ML/Pt interface model. It can be seen from (a) in Fig. 5 that the dxz and dyz orbitals of Fe atoms at the Rh/Fe interface have a relatively obvious DOS peak at 0.35 eV, while the distribution of DOS on other orbital components is gentler, and the electron occupied states are also a lot less. Further analysis of the minority spin band diagram shown in (b) in Fig. 5 shows that the dxz and dyz orbitals have energy band overlap near the X point and the Γ point, and the <dxz|l _z |dyz> coupling term The independent action of , makes the interface model exhibit strong perpendicular magnetic anisotropy.

Figure 6 shows the fractional DOS and energy band structure of the Fe atom 3d orbital at the Ir/Fe interface in the calculated MgO/Ir_1ML/Fe_8ML/Pt interface model. At the Ir/Fe interface, the dx ² -y ² orbitals and dxz and dyz orbitals of Fe atoms have strong DOS peaks at the Fermi level, but the dx ² -y ² and dyz orbitals have strong DOS peaks in the X-Γ region. The band-like energy bands overlap, and the dxz orbitals are basically not coupled, so that the magnetic anisotropy of the MgO/Ir/Fe/Pt interface model is only affected by the <dx ² -y ² |l _x |dyz> coupling term, Appears as strong in-plane magnetization.

When a 1ML Ni(Pd) metal film is inserted at the MgO/Fe interface, the magnetic anisotropy of the interface model is <dx ² -y ² |l _z |dxy> and <d3z ² -r ² |l _x |dyz> The result of the joint action of angular momentum matrix elements; when 1ML Ag(Au) metal film is inserted at the MgO/Fe interface, the magnetic anisotropy of the interface model is greatly weakened, which is determined by the arrangement of its valence electrons.

This example shows that the element type of the metal interlayer has a great influence on the magnetic anisotropy of the MgO/Fe/Pt magnetic tunnel junction. Choosing Rh as the metal interlayer can significantly enhance the perpendicular magnetic anisotropy of the device; choosing Ir as the metal interlayer can Changing the direction of the easy magnetization axis of the device makes the device exhibit in-plane magnetic anisotropy to the outside; choosing other metal materials as the interface interlayer can also adjust the magnetic anisotropy of the device. In practical applications, the material type of the metal interlayer can be selected according to the requirements for the magnetic anisotropy of the magnetic tunnel junction.

Example 2:

In this example, first-principles calculations are used to calculate the magnetic properties and electronic structures of metal interlayers at different positions of MgO/Fe_8ML/Pt, so as to obtain the influence of the action positions of the metal interlayers on the magnetic tunnel junction magnetic anisotropy.

Select 1ML Rh film as metal interlayer and insert it into MgO/Fe_8ML/Pt, adjust the position and build the model: A.MgO/Rh_1ML/Fe_8ML/Pt, B.MgO/Fe_4ML/Rh_1ML/Fe_4ML/Pt, C.MgO/Fe_8ML/Rh_1ML /Pt, the magnetic anisotropy energy density was calculated, and the results are shown in Table 2.

Table 2 Magnetic anisotropy energy densities obtained by inserting 1ML Rh thin film interlayers at different positions

Rh membrane location MgO/Fe interface Inside the ferromagnetic layer Fe/Pt interface MAE(mJ/m²) 9.2566 5.1100 -5.6298

Figure 7 shows the calculated differential charge densities for the three interface models.

It can be seen from (a) in Figure 7 that when the 1ML Rh thin film interlayer is located at the MgO/Fe interface, electrons migrate from metal atoms to the interface at both the Rh/Fe interface and the Fe/Pt interface, and the amount of charge transfer is equivalent. , the analysis of its magnetic anisotropy needs to consider the role of both interfaces. More specifically, at the Rh/Fe interface, the dxz and dyz orbitals of Fe atoms and the dx ² -y ² orbitals of Rh atoms have orbital hybridization at 0.33 eV; at the Fe/Pt interface, the dyz orbitals of Fe atoms and Pt atoms The dx ² -y ² orbitals have orbital hybridization at 0.17 eV. The dxz and dyz orbitals of Fe atoms make the easy magnetization axis of the interface model A deviate from the plane, showing strong perpendicular magnetic anisotropy.

It can be seen from (b) in Fig. 7 that when the 1ML Rh thin film interlayer is located inside the ferromagnetic layer, the charge accumulation effect of electrons at the Fe/Rh interface is stronger than that at the Fe/Pt interface. The analysis of magnetic anisotropy mainly considers Fe. The role of the /Rh interface. More specifically, the 4d orbital of Rh atom is basically not occupied by electrons, and the dxy (dxz, dyz) orbitals of the two adjacent Fe atomic layers simultaneously appear DOS peaks at -0.12eV (0.14eV). The perpendicular magnetic anisotropy of interface model B is the result of the combined action of <dx|l _z |dyz>, <dxy|l _x |dxz> and <dxy|l _y |dyz> coupling terms.

It can be seen from (c) in Fig. 7 that when the 1ML Rh thin film interlayer is located at the Fe/Pt interface, not only the electrons at the Fe/Rh interface and the Rh/Pt interface are rearranged, but also at the MgO/Fei/Feii interface. The charge transfer occurs, and the amount of charge transfer is larger, and the analysis of its magnetic anisotropy focuses on the role of the MgO/Fei/Feii interface. More specifically, the pz orbital of the O atom, the dx ² -y ² orbital of the Fei atom, and the dxy orbital of the Feii atom have resonance DOS peaks at the energy levels of 0.47 eV and 0.59 eV. Since both the dx ² -y ² orbitals and the dxy orbitals are located in the plane, the easy magnetization axis of the interface model C is biased towards the plane, showing the in-plane magnetic anisotropy.

This example shows that the position of the Rh thin film interlayer also has a certain influence on the magnetic anisotropy of the MgO/Fe/Pt magnetic tunnel junction. At the MgO/Fe interface, the perpendicular magnetic anisotropy of the device can be enhanced; at the Fe/Pt interface, it can be The direction of the easy magnetization axis of the device is changed, so that the device exhibits in-plane magnetic anisotropy to the outside; the perpendicular magnetic anisotropy of the device can be adjusted when it is inside the ferromagnetic layer. The action position of the Rh thin film interlayer is selected according to the requirement for the magnetic anisotropy of the magnetic tunnel junction in practical applications.

The above conclusions are obtained by taking the Rh thin film interlayer as an example, but it is not limited to the Rh thin film interlayer, but can also be other materials such as Ir, Ni, Pd, Ag, and Au. Of course, the results of the magnetic anisotropy modulation of the magnetic tunnel junction at different positions of the interlayer of different materials will be different, which needs to be analyzed according to the application requirements of the device.

Example 3:

In this example, a 1-3ML Rh thin film interlayer was added at the MgO/Fe interface of the MgO/Fe_8L/Pt model, and first-principles calculations were performed on its magnetic anisotropy and electronic structure to obtain the thickness of the Rh thin film interlayer. The effect of magnetic anisotropy in the magnetic tunnel junction.

Table 3 shows the calculated magnetic anisotropy energy densities under different Rh film thicknesses. The results show that when the thickness of the Rh film is within a certain range, the magnetic anisotropy energy of the interface model is positive, and its perpendicular magnetic anisotropy is stronger than that of the MgO/Fe_8L/Pt model without Rh interlayer. Preferably, when 2ML Rh thin film interlayer is added, the magnetic anisotropy can be as high as 9.9921 mJ/m ² .

Table 3 Magnetic anisotropy energy density under different Rh film thickness

Rh interlayer thickness 1ML 2ML 3ML MAE(mJ/m²) 9.2566 9.9921 8.8300

This example confirms that the perpendicular magnetic anisotropy of the magnetic tunnel junction can be enhanced when the thickness of the Rh thin film interlayer is within a certain range.

The above conclusions are obtained by taking the MgO/Fe interface inserted into the Rh thin film interlayer as an example, but the role of the metal interlayer is not limited to the MgO/Fe interface, but also the interior of the ferromagnetic layer and the Fe/Pt interface; the material of the metal interlayer is not only limited to the MgO/Fe interface. It is limited to Rh, but can also be other materials such as Ir, Ni, Pd, Ag, and Au. Similarly, the magnetic anisotropy modulation results of the magnetic tunnel junction will be different for other material interlayers with different thicknesses, which need to be analyzed according to the application requirements of the device.

It can be seen from the above three embodiments that the material type, action position and thickness of the metal interlayer have a modulating effect on the magnetic anisotropy of the magnetic tunnel junction. These three factors can be screened and optimized according to the application requirements of the device. in order to achieve the desired device performance.

Example 4:

In order to study the effect of electric field on the magnetic anisotropy of the magnetic tunnel junction, MgO/Fe/Pt is selected as an example in this example, a gradient electric field of 0-5 V/nm is set, and the magnetic anisotropy under the action of different electric fields is simplified. calculation.

Fig. 8 is the variation trend of the calculated magnetic anisotropy energy with the electric field. The relative change in magnetic anisotropy energy is used here to characterize the electric field-induced magnetoelectric effect:

ΔMAE=MAE(E)-MAE(0)

Among them, MAE(E) is the magnetic anisotropy energy under the action of the electric field E, and MAE(0) is the magnetic anisotropy energy under the zero electric field. Obviously, the magnetic anisotropy energy increases in a quasi-linear trend with the increase of the external electric field, and this trend is independent of the thickness of the ferromagnetic layer. That is to say, under the action of the electric field, the easy magnetization axis of MgO/Fe/Pt will be deflected to the out-of-plane direction, and its perpendicular magnetic anisotropy will be enhanced.

This example confirms that the effect of the external electric field can linearly enhance the magnetic anisotropy of the magnetic tunnel junction.

The above conclusions are calculated based on the MgO/Fe/Pt interface model as an example, but it is not limited to this interface model. The MgO/Fe/Pt interface model after inserting the metal film interlayer also has similar conclusions, and the adjustment of the magnetic anisotropy It will be more precise and the adjustment range will be larger. Therefore, the external electric field and the metal interlayer can be used at the same time, so as to achieve the purpose of adjusting the magnetic anisotropy of the magnetic tunnel junction more precisely and in a wider range.

For the parts not described in detail in the present invention, reference can be made to the related prior art, such as modeling and first-principles calculation, etc., can be directly performed with reference to the prior art.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (7)

1. A method for adjusting magnetic anisotropy of a magnetic tunnel junction is characterized in that a metal interlayer is inserted into a film layer structure of the magnetic tunnel junction to control contribution of electron orbit coupling effect, so that adjustment of the magnetic anisotropy of the magnetic tunnel junction is realized; the initial film structure of the magnetic tunnel junction sequentially comprises a barrier layer, a ferromagnetic layer and a nonmagnetic metal covering layer;

the metal elements adopted by the metal interlayer are selected from VIII group transition metal elements, Ag and Au;

the interposed metal interlayer is located at the ferromagnetic layer/nonmagnetic metal overlayer interface.

2. The method of adjusting magnetic anisotropy of a magnetic tunnel junction of claim 1, where the adjusting of magnetic anisotropy of a magnetic tunnel junction specifically comprises: and adjusting the magnetic moment, the magnetic anisotropy energy or the magnetoelectric coefficient of the atom.

3. The method for adjusting magnetic anisotropy of a magnetic tunnel junction according to claim 1, where the group viii transition metal element is selected from Rh, Ir, Ni and Pd.

4. The method of adjusting magnetic anisotropy of a magnetic tunnel junction according to claim 1, wherein the thickness of the metal interlayer is no more than 10 atomic layers.

5. The method for adjusting the magnetic anisotropy of a magnetic tunnel junction according to claim 1, wherein the method additionally introduces an external electric field as an aid while inserting the metal interlayer into the film structure of the magnetic tunnel junction, and the external electric field can adjust the occupation of electron orbitals at the fermi level, thereby assisting in adjusting the magnetic anisotropy of the magnetic tunnel junction.

6. The method of adjusting magnetic anisotropy of a magnetic tunnel junction according to claim 1, wherein the initial film structure of the magnetic tunnel junction comprises a MgO layer, a Fe atomic layer and a Pt atomic layer in this order, wherein the MgO layer has a thickness of 4 atomic layers, the Fe atomic layer has a thickness of 8 atomic layers, and the Pt atomic layer has a thickness of 3 atomic layers.

7. A magnetic anisotropy adjusted magnetic tunnel junction obtained by the method according to any of claims 1-6.

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