Nano oscillator based on magnetic skyrmion, oscillator array and oscillation method

Abstract

The invention relates to the technical field of nanometer oscillators, in particular to a nanometer oscillator based on magnetic skyrmion, an oscillator array and an oscillation method, and the nanometer oscillator comprises a first heavy metal layer, a first magnetic layer, a second heavy metal layer, an insulating layer, a third heavy metal layer, a second magnetic layer and a fourth heavy metal layer. According to the nano oscillator, the central positions of the first skyrmion in the first magnetic layer and the second skyrmion in the second magnetic layer are fixed, and the area of the skyrmion is periodically oscillated under the action of the direct current driving current, so that the magnetization intensity component in the axial direction (Z axis) in the magnetic layers is periodically oscillated, and the stability of the magnetic layer is improved. Therefore, a detection structure for detecting the microwave signal of the nano oscillator can be simplified, for example, the diameter of the detection structure is the same as that of the magnetic layer.

Description

Technical Field

[0001] The present application relates to the technical field of nano-oscillators, and in particular to nano-oscillators, oscillator arrays and oscillation methods based on magnetic skyrmions. Background Art

[0002] The original working principle of the spin nano-oscillator was to achieve consistent precession of the magnetic moment of the uniformly magnetized film in the magnetic layer of the spin valve or tunnel junction structure through the spin transfer torque, and later gradually expanded to the regulation of magnetic domain structures (including magnetic vortices, magnetic domain walls, magnetic skyrmions, etc.). Magnetic skyrmions are a nanoscale topological spin structure with topological stability and high controllability. Nano-oscillators based on magnetic skyrmions have the advantages of low driving current density, narrow frequency linewidth and wide adjustable frequency range.

[0003] The working principle of the nano-oscillator based on magnetic skyrmions in the prior art is mainly that the skyrmions can be driven by a physical field, thereby performing periodic precession along the circumferential direction in a disk or annular tunnel junction or spin valve. This precession causes the magnetic moment of a certain area in the disk or annular ring to oscillate, thereby causing the magnetic resistance of the nano-oscillator to oscillate, thereby generating a changing voltage signal.

[0004] However, the above precession only represents that the central position of the skyrmion has changed in the disk or ring. In order to detect the microwave signal of the nanooscillator, it is necessary to design a special and precise detection structure based on the position and size of the magnetic skyrmion. Summary of the invention

[0005] In order to solve the above technical problems, the embodiments of the present application provide a nano-oscillator, an oscillator array and an oscillation method based on magnetic skyrmions. In the nano-oscillator, the center position of the skyrmions no longer precesses in the circumferential direction, but the area oscillates periodically, so that the component of the magnetization intensity of the entire nano-oscillator on the Z-axis oscillates, so the detection structure for detecting the microwave signal of the nano-oscillator can be simplified.

[0006] In a first aspect, a nano-oscillator based on magnetic skyrmions provided in an embodiment of the present application comprises a first part, an insulating layer, and a second part which are stacked in sequence, wherein the first part comprises a first heavy metal layer, a first magnetic layer, and a second heavy metal layer, and the second part comprises a third heavy metal layer, a second magnetic layer, and a fourth heavy metal layer.

[0007] The first heavy metal layer, the first magnetic layer, the second heavy metal layer, the insulating layer, the third heavy metal layer, the second magnetic layer and the fourth heavy metal layer are all in the shape of a disk and are stacked in sequence along the axial direction.

[0008] The diameter of the first magnetic layer is equal to the diameter of the second magnetic layer, and the diameters of the first heavy metal layer, the second heavy metal layer, the third heavy metal layer and the fourth heavy metal layer are all greater than or equal to the diameter of the first magnetic layer.

[0009] The centers of the first heavy metal layer, the first magnetic layer, the second heavy metal layer, the insulating layer, the third heavy metal layer, the second magnetic layer and the fourth heavy metal layer are on an axis,

[0010] When a first skyrmion exists in the first magnetic layer, a second skyrmion coupled to the first skyrmion exists in the second magnetic layer, and an in-plane direct current is passed through the first part, the center position of the first skyrmion and the center position of the second skyrmion remain fixed, and the area of ​​the first skyrmion and the area of ​​the second skyrmion oscillate periodically.

[0011] Compared with the prior art, the nano oscillator according to the embodiment of the present application has the following advantages:

[0012] The center positions of the first skyrmion in the first magnetic layer and the second skyrmion in the second magnetic layer are fixed. Under the driving action of the direct current, the area (or diameter) of the skyrmion oscillates periodically, so that the component of the magnetization intensity on the Z axis in the magnetic layer oscillates periodically. Therefore, in order to detect the microwave signal of the nano oscillator of the embodiment of the present application, such as the change of magnetoresistance, the diameter of the detection structure can be designed to be equal to the diameter of the magnetic layer. It can be seen that compared with the nano oscillator in the prior art whose area (or diameter) of the skyrmion remains unchanged and whose center position changes periodically, the nano oscillator of the embodiment of the present application can simplify the detection structure for detecting the microwave signal of the nano oscillator.

[0013] In a second aspect, an oscillator array provided in an embodiment of the present application comprises a plurality of nano-oscillators according to the first aspect, wherein the plurality of nano-oscillators are arranged in an array, and the second magnetic layers of two adjacent nano-oscillators are connected by a rectangular magnetic region, and the material of the rectangular magnetic region is the same as the material of the second magnetic layer.

[0014] Compared with the prior art, the beneficial effects of the oscillator array according to the embodiments of the present application can refer to the beneficial effects of the nano oscillator of the first aspect.

[0015] In a third aspect, an oscillation method for a nano-oscillator according to the first aspect or an oscillator array according to the second direction provided in an embodiment of the present application includes, when there is a first skyrmion in the first magnetic layer and there is a second skyrmion in the second magnetic layer that is mutually coupled with the first skyrmion, passing an in-plane direct current through the first part so that the center position of the first skyrmion and the center position of the second skyrmion are both fixed, and the area of ​​the first skyrmion and the area of ​​the second skyrmion oscillate periodically.

[0016] Compared with the prior art, the beneficial effects of the oscillation method according to the embodiment of the present application can refer to the beneficial effects of the nano oscillator of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a nano-oscillator based on magnetic skyrmions according to an embodiment of the present application is shown.

[0018] Figure 2-4 A schematic diagram showing a first skyrmion in a first magnetic layer and a second skyrmion in a second magnetic layer according to an embodiment of the present application is shown.

[0019] Figure 5 A curve diagram between current density and oscillation frequency of a nano oscillator according to an embodiment of the present application is shown.

[0020] Figure 6 Shows Figure 1 The component m of the magnetization intensity in the Z direction of the nano-oscillator at a certain current density is z Time domain oscillation diagram.

[0021] Figure 7 Shows Figure 6 Medium z Frequency domain oscillation diagram.

[0022] Figure 8 A schematic diagram showing the effect of the interaction strength between the first magnetic layer and the second magnetic layer DM on the oscillation frequency according to an embodiment of the present application is shown.

[0023] Fig. 9 A curve diagram showing the interlayer coupling strength and oscillation frequency of a nano oscillator according to an embodiment of the present application is shown.

[0024] Fig.10 A curve diagram between Gilbert damping and oscillation frequency of a nano-oscillator according to an embodiment of the present application is shown.

[0025] Fig.11 A curve diagram between the magnetocrystalline anisotropy constant and the oscillation frequency of the nano oscillator according to an embodiment of the present application is shown.

[0026] Fig.12 A top view of a first magnetic layer treated with local perpendicular magnetic anisotropy (PMA) according to an embodiment of the present application is shown.

[0027] Fig.13 A graph between anisotropy constant and oscillation frequency of a nano oscillator having a first magnetic layer treated with PMA according to an embodiment of the present application and a nano oscillator having a common first magnetic layer is shown.

[0028] Fig.14 A graph showing the relationship between current density and oscillation frequency of a nano-oscillator having a first magnetic layer treated with PMA according to an embodiment of the present application at different anisotropy constants is shown.

[0029] Fig.15 A schematic diagram showing the oscillation frequency of a nano-oscillator having a first magnetic layer with different thicknesses according to an embodiment of the present application is shown.

[0030] Fig.16 A schematic diagram showing a plurality of nano-oscillators according to an embodiment of the present application forming an oscillator array.

[0031] Fig.17 Shows Fig.16 The m of the oscillator array z Time domain oscillation diagram.

[0032] Fig.18 shows an oscillator array m z Frequency domain oscillation diagram of a single nano-oscillator m z Frequency domain oscillation diagram.

[0033] Reference numerals:

[0034] 1. The first heavy metal layer;

[0035] 2. The first magnetic layer; 21. The first skyrmion;

[0036] 3. The second heavy metal layer;

[0037] 4. Insulation layer;

[0038] 5. The third metal layer;

[0039] 6. Second magnetic layer; 61. Second skyrmion;

[0040] 7. The fourth metal layer;

[0041] 8. Rectangular magnetic area. DETAILED DESCRIPTION

[0042] The technical solution of the embodiment of the present application is further described below in conjunction with the accompanying drawings and through specific implementation methods. It is understood that the specific embodiments described herein are only used to explain the embodiment of the present application, rather than to limit the embodiment of the present application. It should also be noted that, for ease of description, only the parts related to the embodiment of the present application are shown in the accompanying drawings, rather than all.

[0043] Some directional words are defined in the embodiments of the present application. Unless otherwise specified, the directional words used, such as "up", "down", "left", "right", "inside" and "outside", are used for ease of understanding and therefore do not constitute a limitation on the scope of protection of the embodiments of the present application.

[0044] In the embodiments of the present application, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through another feature between them. Moreover, the first feature being "above", "above" and "above" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature includes the first feature being directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0045] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0046] Nano Oscillator:

[0047] like Figure 1 As shown, the magnetic skyrmion-based nano-oscillator according to the embodiment of the present application is roughly cylindrical, and the diameter may be 50nm to 200nm, for example, the diameter is 100nm.

[0048] like Figure 1 As shown, in the embodiment of the present application, the axial direction of the nano-oscillator is defined as the Z-axis direction.

[0049] like Figure 1As shown, the nano oscillator includes a first part, an insulating layer 4 and a second part which are stacked in sequence along the axial direction. The first part includes a first heavy metal layer 1, a first magnetic layer 2 and a second heavy metal layer 3, and the second part includes a third heavy metal layer 5, a second magnetic layer 6 and a fourth heavy metal layer 7.

[0050] like Figure 1 As shown, the first heavy metal layer 1, the first magnetic layer 2, the second heavy metal layer 3, the insulating layer 4, the third heavy metal layer 5, the second magnetic layer 6 and the fourth heavy metal layer 7 are all in the shape of a disc. In addition, the first heavy metal layer 1, the first magnetic layer 2, the second heavy metal layer 3, the insulating layer 4, the third heavy metal layer 5, the second magnetic layer 6 and the fourth heavy metal layer 7 are stacked in sequence along the axial direction.

[0051] In the embodiments of the present application, the term "stacked" refers to a physical combination between two adjacent layers. For example, the first part and the insulating layer 4, and the second part and the insulating layer 4 are physically combined. For another example, the first heavy metal layer 1 and the first magnetic layer 2, the first magnetic layer 2 and the second heavy metal layer 3, the second heavy metal layer 3 and the insulating layer 4, the insulating layer 4 and the third heavy metal layer 5, the third heavy metal layer 5 and the second magnetic layer 6, and the second magnetic layer 6 and the fourth heavy metal layer 7 are physically combined.

[0052] Physical bonding can be achieved by vacuum sputtering or vacuum evaporation. Further, each layer can be formed layer by layer along a certain direction, for example, along Figure 1 The layers are formed layer by layer from bottom to top or from top to bottom.

[0053] The first magnetic layer 2 and the second magnetic layer 6 have the same diameter. The diameter of the first heavy metal layer 1, the diameter of the second heavy metal layer 3, the diameter of the third heavy metal layer 5 and the diameter of the fourth heavy metal layer 7 are all greater than or equal to the first magnetic layer 2. The diameter of the first heavy metal layer 1, the diameter of the second heavy metal layer 3, the diameter of the third heavy metal layer 5 and the diameter of the fourth heavy metal layer 7 can be the same or different. The diameter of the insulating layer 4 can be greater than, equal to or less than the diameter of the first magnetic layer 2.

[0054] As an example, Figure 1 As shown, in the embodiment of the present application, the first heavy metal layer 1, the first magnetic layer 2, the second heavy metal layer 3, the insulating layer 4, the third heavy metal layer 5, the second magnetic layer 6, and the fourth heavy metal layer 7 have the same diameter.

[0055] like Figure 1As shown, the first heavy metal layer 1, the first magnetic layer 2, the second heavy metal layer 3, the insulating layer 4, the third heavy metal layer 5, the second magnetic layer 6, and the fourth heavy metal layer 7 are aligned with each other, that is, the center of the first heavy metal layer 1, the center of the first magnetic layer 2, the center of the second heavy metal layer 3, the center of the insulating layer 4, the center of the third heavy metal layer 5, the center of the second magnetic layer 6, and the center of the fourth heavy metal layer 7 are located on an axis, wherein the axis refers to a straight line parallel to the axial direction.

[0056] The thickness of the first heavy metal layer 1 is 1 to 5 nm, the thickness of the first magnetic layer 2 is 1 to 3 nm, the thickness of the second heavy metal layer 3 is 0.5 to 2 nm, the thickness of the insulating layer 4 is 0.5 to 3 nm, the thickness of the third heavy metal layer 5 is 0.5 to 2 nm, the thickness of the second magnetic layer 6 is 1 to 3 nm, and the thickness of the fourth heavy metal layer 7 is 1 to 5 nm.

[0057] As an example, the insulating layer 4 is used as a symmetry plane, and the nano-oscillator is a symmetrical structure. Specifically, the thickness of the first heavy metal layer 1 is equal to the thickness of the fourth heavy metal layer 7, the thickness of the first magnetic layer 2 is equal to the thickness of the second magnetic layer 6, and the thickness of the second heavy metal layer 3 is equal to the thickness of the third heavy metal layer 5.

[0058] The material of the first magnetic layer 2 can be selected from one of Co and CoFeB. The material of the second magnetic layer 6 can be selected from one of Co and CoFeB. The material of the first magnetic layer 2 can be the same as or different from the material of the second magnetic layer 6. Both the first magnetic layer 2 and the second magnetic layer 6 satisfy perpendicular magnetization.

[0059] The material of the first heavy metal layer 1 can be selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os. The material of the second heavy metal layer 3 can be selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os. The material of the first heavy metal layer 1 is different from the material of the second heavy metal layer 3.

[0060] The first heavy metal layer 1 and the second heavy metal layer 3 are used to provide DM interaction (Dzyaloshinsky-Moriya interaction, DMI) so that stable skyrmions can exist in the first magnetic layer 2. In addition, the first heavy metal layer 1 and the second heavy metal layer 3 are also used to provide polarization current to drive the skyrmions in the first magnetic layer 2.

[0061] The material of the third heavy metal layer 5 can be selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os. The material of the fourth heavy metal layer 7 can be selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os. The material of the third heavy metal layer 5 is different from the material of the fourth heavy metal layer 7.

[0062] The third heavy metal layer 5 and the fourth heavy metal layer 7 are used to provide DM interaction so that stable skyrmions can exist in the second magnetic layer 6. In addition, the third heavy metal layer 5 and the fourth heavy metal layer 7 are also used to provide polarization current to drive skyrmions in the second magnetic layer 6.

[0063] The material of the first heavy metal layer 1 , the material of the second heavy metal layer 3 , the material of the third heavy metal layer 5 and the material of the fourth heavy metal layer 7 can be selected according to the DM interaction strength.

[0064] The material of the insulating layer 4 can be selected from MgO, Al2O3, and oxidized Ta.

[0065] The insulating layer 4 separates the nano-oscillator into a first part and a second part. When a direct current is passed through one of the first part and the second part, the insulating layer 4 prevents the direct current from flowing into the other of the first part and the second part. Therefore, a first skyrmion 21 and a second skyrmion 61 can exist in the first magnetic layer 2 and the second magnetic layer 6, respectively, and the first skyrmion 21 and the second skyrmion 61 are coupled together in a specific manner and have different spin structures.

[0066] As an example, when an in-plane direct current flows into the first portion, due to the presence of the insulating layer 4, the second skyrmions 61 in the second magnetic layer 6 will not be destroyed by the direct current, so as to ensure that the nano-oscillator can continue to oscillate.

[0067] Similarly, when an in-plane direct current is passed through the second portion, due to the presence of the insulating layer 4, the first skyrmions 21 in the first magnetic layer 2 will not be destroyed by the direct current, thereby ensuring that the nano-oscillator can continue to oscillate.

[0068] It should be noted that in order to drive the skyrmions, it is only necessary to pass an in-plane direct current through one of the first part and the second part.

[0069] The working principle of the nano oscillator in the embodiment of the present application is as follows:

[0070] like Figure 2As shown, due to the existence of DM interaction, a stable first skyrmion 21 may exist in the first magnetic layer 2, and a stable second skyrmion 61 may exist in the second magnetic layer 6. It should be noted that the method of forming skyrmions in the magnetic layer is known and will not be described in detail herein.

[0071] It should be noted that Figure 2 The black area represents the magnetic moment direction perpendicular to the plane downward, the white area represents the magnetic moment direction perpendicular to the plane upward, and the gray area represents the area in between. In addition, it can be found that the first skyrmion 21 and the second skyrmion 61 have different spin structures.

[0072] like Figure 1 As shown, when an in-plane direct current is passed through the first part, such as the first heavy metal layer 1, the insulating effect of the insulating layer 4 ensures that the direct current only exists in the first part and does not enter the second part, thereby preventing the second skyrmion 61 from being destroyed.

[0073] like Figure 3 As shown, the direct current in the first heavy metal layer 1 injects polarization current into the first magnetic layer 2 under the action of the spin Hall effect. Under the action of the polarization current, the area (or diameter) of the first skyrmion 21 will shrink or even annihilate.

[0074] like Figure 4 As shown, since the magnetic moments between the first magnetic layer 2 and the second magnetic layer 6 are coupled by RKKY interaction and dipole interaction, the magnetic moments at the center of the second skyrmion 61 and the first magnetic layer 2 tend to be aligned, so the magnetic moment at the center of the first magnetic layer 2 is relatively easier to flip. Under the continuous action of the polarization current, the flipping area of ​​the magnetic moment of the first magnetic layer 2 gradually expands from the center, and the area of ​​the second skyrmion 61 also expands synchronously under the dipole interaction.

[0075] Due to the topological protection effect of skyrmions, as the area of ​​the second skyrmion 61 expands, the repulsive effect between the domain wall of the second skyrmion 61 and the edge of the second magnetic layer 6 also increases. After reaching a certain level, the area of ​​the second skyrmion 61 begins to shrink, and at the same time, the flipping area of ​​the magnetic moment in the first magnetic layer 2 is synchronously reduced back to the initial state, that is, back to Figure 2 Status shown.

[0076] The first skyrmion 21 and the second skyrmion 61 are Figures 2 to 4 By continuously cycling between the two, the component of the magnetization intensity of the nano-oscillator on the Z-axis oscillates with a variation amplitude of more than 50%, and the oscillation frequency is in the GHz range.

[0077] It can be seen that according to the nano oscillator of the embodiment of the present application, the center positions of the first skyrmion 21 and the second skyrmion 61 are fixed, and under the drive of the direct current, the area (or diameter) of the first skyrmion 21 and the area (or diameter) of the second skyrmion 61 oscillate periodically, so that the component of the magnetization intensity on the Z axis in the magnetic layer oscillates periodically. Therefore, in order to detect the microwave signal of the nano oscillator of the embodiment of the present application, such as the change of magnetoresistance, the diameter of the detection structure can be designed to be equal to the diameter of the magnetic layer. It can be seen that compared with the nano oscillator in the prior art, in which the area (or diameter) of the skyrmion remains unchanged and the center position changes periodically, the nano oscillator of the embodiment of the present application can simplify the detection structure for detecting the microwave signal of the nano oscillator.

[0078] In addition, since the direction of the direct current passed into the first heavy metal layer 1 is along the plane of the first heavy metal layer 1, compared with the prior art in which the polarization current is passed along a plane perpendicular to the plane where the first heavy metal layer 1 is located, it is possible to avoid processing nano-sized contacts on the first heavy metal layer 1, thereby simplifying the processing technology.

[0079] The current density of the direct current flowing into the first heavy metal layer 1 will affect the oscillation frequency of the nano-oscillator. Figure 5 As shown, as the current density (J) increases, the oscillation frequency of the nano-oscillator increases.

[0080] In a possible embodiment, the current density of the direct current flowing into the first heavy metal layer 1 is 7.5×10 11 A / m 2 , at this time, the component m of the magnetization intensity of the nano-oscillator in the Z direction z The time domain and frequency domain images are as follows: Figure 6 and Figure 7 shown.

[0081] It can be seen that according to the nano-oscillator of the embodiment of the present application, the current density only needs to be within 10 11 A / m 2 The magnitude of the current density is within the reasonable range of practical operation and will not cause damage to the device. 12 A / m 2 The skyrmions are driven by current densities of the order of magnitude.

[0082] The parameters of the first magnetic layer 2 and the second magnetic layer 6, such as DM interaction strength, interlayer coupling strength, Gilbert damping, magnetocrystalline anisotropy constant, etc., will affect the operating frequency of the nano-oscillator. Figures 8 to 11 , when the current density is fixed at 7.5×10 11 A / m 2The effects of DM interaction strength, interlayer coupling strength, Gilbert damping, and magnetocrystalline anisotropy constant on the oscillation frequency are shown respectively.

[0083] See also Figure 8 , wherein the horizontal axis is the DM interaction strength of the second magnetic layer 6, and the vertical axis is the DM interaction strength of the first magnetic layer 2. Figure 8 As shown, the DM interaction strength between the first magnetic layer 2 and the second magnetic layer 6 will affect the oscillation frequency of the nano-oscillator. Generally speaking, within the oscillation range, the greater the DM interaction, the higher the oscillation frequency.

[0084] It should be noted that Figure 8 The blank part at the edge of the graph indicates that the nano-oscillator cannot oscillate under the DM interaction condition. For example, when the DM interaction strength of the first magnetic layer 2 is 0.2 mJ / m 2 The DM interaction strength of the second magnetic layer 6 is 1.2 mJ / m 2 For example, when the DM interaction strength of the first magnetic layer 2 is 1.2 mJ / m 2 The DM interaction strength of the second magnetic layer 6 is 2.0 mJ / m 2 When the nano-oscillator cannot oscillate.

[0085] Specifically, the DM interaction strength of the first magnetic layer 2 may be 0.2 to 1.4 mJ / m 2 The DM interaction strength of the second magnetic layer 6 can be 1.2 to 2.0 mJ / m 2 .

[0086] In addition, if Figure 8 As shown, in order to start the nano-oscillator of the embodiment of the present application, the DM interaction strength of the first magnetic layer 2 and the second magnetic layer 6 is 2mJ / m 2 It is within the range of DM interaction strength that meets the requirements of existing material systems and is easy to achieve.

[0087] like Fig. 9 As shown, with the interlayer coupling strength (A RKKY ) increases, the oscillation frequency of the nano-oscillator decreases.

[0088] like Fig.10 As shown, as the Gilbert damping (α) increases, the oscillation frequency of the nano-oscillator decreases.

[0089] like Fig.11As shown, as the magnetocrystalline anisotropy constant (Ku) increases, the oscillation frequency of the nano-oscillator first decreases, then increases, and then decreases. Based on the magnetization snapshot of the nano-oscillator, the applicant infers that this is the result of the combined effect of the spin-orbit torque (SOT) and the boundary potential barrier: the effect of SOT on the frequency is inversely proportional to the size of the magnetocrystalline anisotropy constant (Ku), that is, the smaller the magnetocrystalline anisotropy constant (Ku), the more susceptible the magnetization at the center of the disk is to the torque, resulting in a higher oscillation frequency. But at the same time, the magnetization at the boundary of the disk is also affected by the SOT, causing it to tilt within the plane of the disk. This reduces the angle between the boundary magnetization and the wall of the magnetic bubble domain, thereby strengthening the exchange interaction between the boundary and the domain wall, which is generally manifested as the attraction of the boundary to the magnetic bubble, thereby slowing down the breathing rate of the magnetic bubble. The relative degree of these two opposing effects changes with the increase of the magnetocrystalline anisotropy constant (Ku).

[0090] Combination Figures 5 to 11 It can be seen that excessive current density and inappropriate parameters will cause the first skyrmions 21 in the first magnetic layer 2 and the second skyrmions 61 in the second magnetic layer 6 to annihilate together, which limits the operating frequency range of the nano-oscillator.

[0091] To solve this problem, on the one hand, the perpendicular anisotropic strength of the first magnetic layer 2 and / or the second magnetic layer 6 can be adjusted; on the other hand, the thickness of the first magnetic layer 2 and / or the second magnetic layer 6 can be reduced to increase the operating frequency of the nano oscillator.

[0092] Specifically, with respect to the first aspect, ion irradiation and other technologies can be used to enhance the perpendicular anisotropy strength of the first edge portion of the first magnetic layer 2 and the second edge portion of the second magnetic layer 6, so that the perpendicular anisotropy strength of the first edge portion of the first magnetic layer 2 is greater than the perpendicular anisotropy strength of the first middle portion of the first magnetic layer 2, and the perpendicular anisotropy strength of the second edge portion of the second magnetic layer 6 is greater than the perpendicular anisotropy strength of the second middle portion of the second magnetic layer 6, thereby enhancing the repulsive force of the edge on the magnetic bubbles and protecting the skyrmions from being destroyed, thereby expanding the adjustment range of the magnetic parameters.

[0093] As an example, Fig.12 As shown, the first edge portion of the first magnetic layer 2 may be subjected to a local perpendicular magnetic anisotropy (PMA) treatment. Fig.12 The anisotropy constant Ku of the middle shaded area (i.e. the first edge portion) is 10 6 J / m 3 Under this condition, the applicant re-studied the relationship between the anisotropy constant Ku and the oscillation frequency (F req ) and compared it with the case where there is no perpendicular magnetic anisotropy at the boundary. Fig.13As shown in the figure, the results show that at the same current density, the Ku operating range of the boundary PMA oscillator is significantly wider than that of the previous oscillator. In addition, when Ku is the same, the oscillation frequency of the boundary PMA oscillator exceeds that of the ordinary oscillator.

[0094] from Fig.13 Four data points were selected, namely Ku = 5.6 × 10 5 J / m 3 , Ku=6.0×10 5 J / m 3 , Ku=6.5×10 5 J / m 3 , and Ku=6.8×10 5 J / m 3 , respectively study the relationship between current density (J) and oscillation frequency under these four conditions. Fig.14 As shown, the results show that in these four cases, Ku = 6.5 × 10 5 J / m 3 The current operating range is the largest when Ku>6.5×10 5 J / m 3 and Ku<6.5×10 5 J / m 3 The results are the same, but the root cause is different: Ku>6.5×10 5 J / m 3 When Ku<6.5×10 5 J / m 3 When the current density is low, a stable magnetic bubble will be generated in the center of the first magnetic layer 2, causing the entire system to reach a new stable state and stop oscillating.

[0095] Regarding the second aspect, Fig.15 As shown in the figure, the thickness of the first magnetic layer 2 is changed according to the perpendicular magnetic anisotropy (PMA) boundary, in order to study the effect of the thickness of the first magnetic layer 2 on the oscillation frequency. The results show that at 5×10 11 A / m 2 Under the condition of constant current density, as the thickness of the first magnetic layer 2 decreases, the oscillation frequency increases.

[0096] Oscillator Array:

[0097] like Figures 16 to 18 As shown, in order to increase the output power of the nano-oscillator, multiple nano-oscillators can be formed into an oscillator array in an xy plane perpendicular to the axial direction, so that the multiple oscillators can oscillate in unison, thereby greatly improving the output signal strength.

[0098] Specifically, a plurality of oscillators may be arranged in a square matrix in the xy plane to form an oscillator array.

[0099] More specifically, between two adjacent oscillators in the x-direction, the corresponding two second magnetic layers 6 are connected by a rectangular magnetic region 8, and the material of the rectangular magnetic region 8 is the same as that of the second magnetic layer 6, so that the two oscillators can oscillate in unison; between two adjacent oscillators in the y-direction, the corresponding two second magnetic layers 6 are connected by a rectangular magnetic region 8, so that the two oscillators can oscillate in unison.

[0100] It is worth noting that the magnetization direction of this rectangular magnetic region 8 is opposite to that of the adjacent magnetic disk, thus forming domain walls (DMs) at the boundary. Due to the influence of the interface DM interaction, these DWs exhibit chirality, that is, their magnetization direction is opposite to that of the corresponding second skyrmion 61. This configuration alleviates the repulsive exchange interaction between the second skyrmion 61 and the rectangular magnetic region 8, preventing the rectangular magnetic region 8 from destroying the second skyrmion 61. In addition, it also enhances the coupling between the two second skyrmions 61: when a second skyrmion 61 expands, it drives the DW in the rectangular magnetic region 8, generating a spin wave that propagates to the adjacent oscillator. At the same time, the adjacent oscillator also emits a spin wave in the same direction. The superposition of these signals leads to mutual influence and eventual resonance between the two oscillators.

[0101] It should be noted that not only nano-oscillators with the same polarity can be coupled, but nano-oscillators with opposite polarity can also be effectively coupled.

[0102] Oscillation method:

[0103] Based on the aforementioned nano-oscillator or oscillator array, the oscillation method includes, when there is a first skyrmion in the first magnetic layer and there is a second skyrmion in the second magnetic layer that is mutually coupled with the first skyrmion, passing an in-plane direct current in the first part so that the center position of the first skyrmion and the center position of the second skyrmion are both fixed, and the area of ​​the first skyrmion and the area of ​​the second skyrmion oscillate periodically.

[0104] Although the embodiments of the present application have been described in detail above by means of general description, specific implementation methods and tests, it is obvious to those skilled in the art that some modifications or improvements may be made to the embodiments of the present application. Therefore, these modifications or improvements made without departing from the spirit of the embodiments of the present application all fall within the scope of protection claimed by the embodiments of the present application.

Claims

1. A nano-oscillator based on magnetic skyrmions, wherein: The invention comprises a first part, an insulating layer and a second part which are stacked in sequence, wherein the first part comprises a first heavy metal layer, a first magnetic layer and a second heavy metal layer, and the second part comprises a third heavy metal layer, a second magnetic layer and a fourth heavy metal layer, The first heavy metal layer, the first magnetic layer, the second heavy metal layer, the insulating layer, the third heavy metal layer, the second magnetic layer and the fourth heavy metal layer are all in the shape of a disk and are stacked in sequence along the axial direction. The diameter of the first magnetic layer is equal to the diameter of the second magnetic layer, and the diameters of the first heavy metal layer, the second heavy metal layer, the third heavy metal layer and the fourth heavy metal layer are all greater than or equal to the diameter of the first magnetic layer. The centers of the first heavy metal layer, the first magnetic layer, the second heavy metal layer, the insulating layer, the third heavy metal layer, the second magnetic layer and the fourth heavy metal layer are on an axis, When a first skyrmion exists in the first magnetic layer, a second skyrmion coupled to the first skyrmion exists in the second magnetic layer, and an in-plane direct current is passed through the first part, the center position of the first skyrmion and the center position of the second skyrmion remain fixed, and the area of ​​the first skyrmion and the area of ​​the second skyrmion oscillate periodically.

2. The nano-oscillator according to claim 1, wherein: The material of the first heavy metal layer is selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os; The material of the second heavy metal layer is selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os; The material of the first heavy metal layer is different from the material of the second heavy metal layer.

3. The nano-oscillator according to claim 1, wherein: The material of the third heavy metal layer is selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os; The material of the fourth heavy metal layer is selected from one of Pt, Ta, Pd, Ir, Au, Gd, Hf, W, Re, and Os; The material of the third heavy metal layer is different from the material of the fourth heavy metal layer.

4. The nano-oscillator according to claim 1, wherein: The material of the first magnetic layer is selected from one of Co and CoFeB; The material of the second magnetic layer is selected from Co and CoFeB.

5. The nano-oscillator according to claim 1, wherein: The material of the insulating layer may be selected from MgO, Al2O3, and oxidized Ta.

6. The nano-oscillator according to claim 1, wherein: The thickness of the first heavy metal layer is 1 to 5 nm; The thickness of the first magnetic layer is 1 to 3 nm; The thickness of the second heavy metal layer is 0.5 to 2 nm; The thickness of the insulating layer is 0.5 to 3 nm; The thickness of the third heavy metal layer is 0.5 to 2 nm; The thickness of the second magnetic layer is 1 to 3 nm; The thickness of the fourth heavy metal layer is 1 to 5 nm.

7. The nano-oscillator according to claim 1, wherein: The DM interaction strength of the first magnetic layer and the DM interaction strength of the second magnetic layer are both less than or equal to 2.0 mJ / m 2 .

8. The nano-oscillator according to claim 7, wherein: The DM interaction strength of the first magnetic layer is 0.2 to 1.4 mJ / m 2 ; The DM interaction strength of the second magnetic layer is 1.2 to 2.0 mJ / m 2 .

9. An oscillator array, wherein: The method comprises a plurality of nano-oscillators according to any one of claims 1 to 8, wherein the plurality of nano-oscillators are arranged in an array, and the second magnetic layers of two adjacent nano-oscillators are connected via a rectangular magnetic region, and the material of the rectangular magnetic region is the same as that of the second magnetic layer.

10. The oscillation method of the nano-oscillator according to any one of claims 1 to 8 or the oscillator array according to claim 9, wherein: include: When a first skyrmion exists in the first magnetic layer and a second skyrmion coupled to the first skyrmion exists in the second magnetic layer, an in-plane direct current is passed through the first part so that the center positions of the first skyrmion and the second skyrmion are fixed and the areas of the first skyrmion and the second skyrmion oscillate periodically.

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