Generation method of magnetic skyrmion chain

Abstract

The invention provides a method for generating a magnetic skyrmion chain, and relates to the field of magneto-optical devices, and the method specifically comprises the following steps: placing a sample capable of generating a skyrmion structure in a magnetic field, applying a certain magnetic field to the sample, rotating the sample to enable the magnetic field and the sample to form a certain magnetic field included angle alpha, the horizontal component of the magnetic field turns the magnetic moment direction to the horizontal direction of the sample; the magnetic field included angle alpha is kept unchanged, the magnetic field is gradually increased, the magnetic moment is turned over again, and the strip-shaped skyrmion intermediate state is formed; the sample is rotated to enable the direction of the magnetic field to be perpendicular to the plane where the sample is located, then the magnetic field is gradually increased, the strip-shaped Skyrmion is converted into a complete Skyrmion in an intermediate state, and the Skyrmion is self-assembled into a Skyrmion chain under the action of attraction force. According to the technical scheme, the problems that in the prior art, the Skyrmion chain can only be generated accidentally through a vertical magnetic field, the occurrence condition of the Skyrmion chain is unclear, the length and other characteristics are uncontrollable, and application of the Skyrmion chain is seriously hindered are solved.

Description

Technical Field

[0001] The present invention relates to the field of magneto-optical devices, and particularly to a method for generating a magnetic skyrmion chain. Background Art

[0002] A skyrmion is a particle-like magnetic structure with topological protection properties. As an information carrier, it has natural advantages and is suitable for application in magnetic track storage devices and brain-like devices. First of all, as a codable particle-like structure, a plurality of skyrmions can aggregate to form multi-valued information, and can be distinguished by differences in regional magnetoresistance and the like caused by differences in the number of skyrmions. Secondly, the movement of skyrmions driven by current, electric field, heat flow, magnetic field, etc. is controllable, making this multi-valued information closely related to the excitation field. Finally, due to the particle characteristics of skyrmions, when multiple skyrmions aggregate, the positions of each skyrmion have a certain degree of randomness. The above "multi-valued", "controllable" and certain "randomness" characteristics make skyrmions particularly...

[0003] A single, isolated skyrmion is easily affected by thermal excitation and pinning at defect sites in the material, and its movement behavior is prone to exhibit the characteristics of Brownian random motion. Therefore, it is very difficult to precisely control by external means. Secondly, an isolated skyrmion itself has high energy and poor thermal stability, and is easily annihilated under thermal perturbation, resulting in information loss and extremely difficult error correction in practical applications. In the prior art, skyrmion-based devices such as the designs of Song et al. and Yokouchi et al. rely on single skyrmion states, which is the fundamental reason for the current insufficient device performance and limited subsequent development. The new structure of the skyrmion chain provides a new choice for the information carrier of skyrmion-based devices. As the information carrier of the device, the stability and reliability of the many-body structure of the skyrmion chain will be greatly enhanced compared to the skyrmion monomer system. Secondly, the scheme of applying the skyrmion chain to a brain-like device can inherit the existing design while having structural innovation. An artificial synapse is divided into a presynaptic stage and a postsynaptic stage. The skyrmion chain is formed in the presynaptic stage and enters the reading area of the postsynaptic stage, mimicking the leak-collect-excite model in neurons. The advantage of the skyrmion chain is that there is no need to set an energy barrier between the presynaptic stage and the postsynaptic stage, and the one-dimensional property of the chain structure constitutes a natural "barrier". However, in the prior art, skyrmion chains can only be accidentally generated by a perpendicular magnetic field, the appearance conditions of skyrmion chains are unclear, and characteristics such as length are uncontrollable, seriously hindering their application.

[0004] Therefore, there is a need for a simple and controllable method for generating skyrmion chains. Summary of the Invention

[0005] The main object of the present invention is to provide a method for generating a magnetic skyrmion chain, so as to solve the problem in the prior art that skyrmion chains can only be accidentally generated by a perpendicular magnetic field, the appearance conditions of skyrmion chains are unclear, and characteristics such as length are uncontrollable, seriously hindering their application.

[0006] To achieve the above object, the present invention provides a method for generating a magnetic skyrmion chain, which specifically includes the following steps:

[0007] S1. Place a sample capable of generating a skyrmion structure in a magnetic field, apply a certain magnetic field to the sample, rotate the sample so that the magnetic field forms a certain magnetic field angle α with the sample, and the horizontal component of the magnetic field flips the magnetic moment direction to the horizontal direction of the sample.

[0008] S2. Keep the magnetic field angle α unchanged, gradually increase the magnetic field so that the magnetic moment flips again to form an intermediate state of strip-shaped skyrmions.

[0009] S3. Rotate the sample so that the magnetic field direction is perpendicular to the plane where the sample is located, and then gradually increase the magnetic field so that the intermediate state of strip-shaped skyrmions is transformed into a complete-form skyrmion, and the skyrmions self-assemble into a skyrmion chain under the action of attraction.

[0010] Further, the sample includes: FeGe.

[0011] Further, in step S1, the range of the magnitude of the magnetic field applied to the sample is between 80 mT and 100 mT, and the magnetic field angle α is between 2° and 18°.

[0012] Further, in step S1, the magnetic field where the sample is located increases to between 80 mT and 100 mT within five seconds.

[0013] Further, in step S1, when the magnetic field magnitude is 80 mT, the magnetic field angle α is 18°; when the magnetic field magnitude is 100 mT, the magnetic field angle α is 2°.

[0014] Further, in step S2, the range of the magnetic field magnitude is 260 mT to 340 mT.

[0015] Further, in step S2, the magnetic field is increased to 260 mT to 340 mT within 20 seconds.

[0016] Further, in step S3, the magnetic field range is 340 mT to 440 mT.

[0017] Further, in steps S1 to S3, the ambient temperature is between 180 K and 280 K.

[0018] Further, in steps S1 to S3, the ambient temperature is 220 K.

[0019] The present invention has the following beneficial effects:

[0020] The method for generating skyrmion chains provided by the present invention, the finally generated skyrmion chains are tested by driving under a thermal gradient field and an electric current field. The movement speed of the skyrmion chains reaches several meters per second at an order of magnitude of the current density of 10 10 A / m 2 , and the skyrmion chains do not cluster or break during the movement process, proving their good stability and movement performance, and showing advantages in the applications of magnetic storage and brain-like devices.

[0021] Moreover, the present invention realizes a new way to generate skyrmion chains, controls the length of the chains by the magnitude of the magnetic field, and changes the number distribution of monomers in the skyrmion chains through external excitation so as to simulate the plasticity function of nerve synapses in brain-like devices, with simple operation, energy conservation and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required to be used in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts. In the drawings:

[0023] Figure 1 It shows a schematic diagram of the magnetic field and the sample placement.

[0024] Figure 2 It shows a transmission electron microscope image when the magnetic field magnitude is 80 mT.

[0025] Figure 3 It shows a transmission electron microscope image when the magnetic field magnitude is 200 mT.

[0026] Figure 4 It shows a transmission electron microscope image when the magnetic field magnitude is 340 mT.

[0027] Figure 5 It shows a transmission electron microscope image when the magnetic field magnitude is 360 mT.

[0028] Figure 6 It shows a transmission electron microscope image when the magnetic field magnitude is 400 mT.

[0029] Figure 7 It shows a transmission electron microscope image when the magnetic field magnitude is 420 mT.

[0030] Figure 8 It shows a graph of the variation of the number of skyrmion chain monomers with the magnetic field.

[0031] Figure 9 It shows a graph of the influence of the magnetic field angle on the number of skyrmion chain monomers.

[0032] Figure 10 The transmission electron micrograph when the thermal gradient is 22 K / μm is shown.

[0033] Figure 11 The transmission electron micrograph when the thermal gradient is 28 K / μm is shown.

[0034] Figure 12 The transmission electron micrograph when the thermal gradient is 34 K / μm is shown.

[0035] Figure 13 The transmission electron micrograph when the thermal gradient is 49 K / μm is shown.

[0036] Figure 14 The transmission electron microscope image when the pulse number is 0 is shown.

[0037] Figure 15 The transmission electron microscope image when the pulse number is 12 is shown.

[0038] Figure 16 The transmission electron microscope image when the pulse number is 8 is shown.

[0039] Figure 17 The transmission electron microscope image when the pulse number is 6 is shown.

[0040] Figure 18 A graph showing the relationship between the movement speed of the skyrmion chain and the current density is shown. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] like Figure 1 A method for generating a magnetic skyrmion chain as shown in the figure specifically comprises the following steps:

[0043] S1, place the sample that can produce skyrmion structure in a magnetic field, apply a certain magnetic field H to the sample, rotate the sample so that the magnetic field forms a certain magnetic field angle α with the sample, and the horizontal component of the magnetic field causes the magnetic moment direction to flip to the horizontal direction of the sample. Figure 1 The horizontal component of the magnetic field is Hx, and the vertical component of the magnetic field is Hy.

[0044] S2, keeping the magnetic field angle α unchanged, gradually increase the magnetic field, so that the magnetic moment flips again, forming a strip skyrmion intermediate state.

[0045] S3, rotate the sample so that the direction of the magnetic field is perpendicular to the plane where the sample is located, and then gradually increase the magnetic field so that the intermediate state of the strip skyrmion is transformed into the complete form of skyrmion. The skyrmions self-assemble into skyrmion chains under the action of attraction.

[0046] Specifically, the sample includes: FeGe.

[0047] Specifically, in step S1, a magnetic field with a magnitude ranging from 80 mT to 100 mT is applied to the sample, and a magnetic field angle α is between 2° and 18°.

[0048] Specifically, in step S1, the magnetic field in which the sample is located increases to between 80 mT and 100 mT within five seconds.

[0049] Specifically, in step S1, when the magnetic field magnitude is 80 mT, the magnetic field angle α is 18°; when the magnetic field magnitude is 100 mT, the magnetic field angle α is 4°.

[0050] Specifically, in step S2, the magnetic field magnitude ranges from 260 mT to 340 mT.

[0051] Specifically, in step S2, the magnetic field is increased to 260 mT to 340 mT within 20 seconds.

[0052] Specifically, in step S3, the magnetic field ranges from 340 mT to 440 mT.

[0053] Specifically, in step S1 to step S3, the ambient temperature is between 180K and 280K.

[0054] Specifically, in step S1 to step S3, the ambient temperature is 220K.

[0055] The sample used in this example is FeGe.

[0056] First, if Figure 1 As shown, the sample is placed in a magnetic field, and the magnetic field is increased from 0mT to 80mT within 5 seconds. Then, the sample is tilted so that the angle between the magnetic field and the sample is 8°, and the magnetic moment flips to the horizontal direction under the action of the horizontal component of the magnetic field. Next, the magnetic field is gradually increased from 80mT to 340mT within 20 seconds, and it is allowed to stand for 2 minutes to obtain the intermediate state of skyrmions. Then, the sample is rotated to reduce the angle from 8° to 0°, and it is allowed to stand for 2 minutes. After standing, the magnetic field is increased from 340mT to 440mT, and the intermediate state of skyrmions is transformed into a complete skyrmion state, and self-assembled into a skyrmion chain.

[0057] The transmission electron microscope electron beam is irradiated on the sample, and the transmission electron microscope photos of the prepared skyrmion chain and the skyrmion chain formation process are shown in the figure. Figures 2 - 7 The number of skyrmions changes with the magnitude of the magnetic field asFigure 8 shown.

[0058] The magnetic skyrmion chain structure generated by the method of the present invention is in the shape of a micrometer-scale one-dimensional chain, and the length can be regulated by the magnetic field and the angle.

[0059] In order to explore the relationship between the magnetic field and the magnetic field angle α and the number of monomer skyrmions Ns that make up the skyrmion chain, the method of generating the skyrmion chain repeats the above process and only changes α. Figure 9 As shown in the figure, as α increases, Ns increases and reaches a maximum value when α = 10°. α continues to increase, resulting in the appearance of magnetic domain structure, which leads to a decrease in Ns. At the same time, the critical magnetic field H* corresponding to the maximum value of Ns changes with α is also shown in the figure. Figure 9 In the figure, when α is less than 6°, H* decreases with the increase of α, indicating that the appearance of the horizontal magnetic field is conducive to the nucleation of skyrmions to a certain extent. However, since the vertical component of the magnetic field plays a major role in the formation of skyrmions, the vertical component of the magnetic field decreases as θ increases, so when α is too large, H* tends to increase. Therefore, it is proved that the skyrmion chain generated by the method of this embodiment is highly controllable under an external field.

[0060] In order to study the performance of skyrmion chains driven by thermal gradient field, the skyrmion chains were first allowed to stand for 2 minutes. Then, the heat flow entered the sample from the right end, diffused in the sample and generated a thermal gradient effect. The camera was then used to capture the changes in the skyrmion chains as the thermal gradient increased from 0K / μm to 70K / μm. Figures 10 - 13 As shown, the skyrmion chain moves from the hot end to the cold end of the sample under the induction of thermal gradient. In the process, except for folding at the boundary due to the geometric confinement effect, the chain can maintain its state without aggregation and breakage. This shows that the skyrmion chain produced by the method provided by the present invention is drivable and has high stability.

[0061] The present invention uses a magnetic field to change its size to control the length of the skyrmion chain. When the magnetic field is greater than 260mT and less than 340mT, the length of the skyrmion chain gradually increases. When the magnetic field is greater than 340mT and less than 440mT, the length becomes shorter. The performance of the skyrmion chain under thermal gradient field and current field was tested. The thermal gradient field ranges from 0K / μm to 70K / μm, and the skyrmion chain can be driven when the thermal gradient is greater than 22K / μm.

[0062] In order to study the stability of the skyrmion chain and its motion performance under current drive, the skyrmion chain was left to stand for 2 minutes, and then a 2×10 10 A / m 2 , a current pulse with a width of 70ns is applied to the sample from left to right through the sample rod. Figures 14 - 17As shown in the figure, there is no breakage or folding during the movement of the skyrmion chain, indicating its good stability. The movement direction of the skyrmion chain is opposite to the direction of the current, and the driving force of the skyrmion chain comes from the spin transfer torque effect of the electron. Subsequently, the direction of the current pulse changes from right to left, and the movement direction of the skyrmion chain also reverses. The speed of the skyrmion movement during the process is calculated to be 1.1 m / s. This example tests the skyrmion chain at a current density of 1×10 10 A / m 2 Up to 4×10 10 A / m 2 The drivers between them are explored in detail, such as Figure 18 As shown, the driving speed of the skyrmion chain increases with the increase of current density, and can reach a maximum of 3.6 m / s, showing good controllability and high driveability, and has great application value.

[0063] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for generating a magnetic skyrmion chain, characterized in that: The specific steps include: S1, placing a sample capable of producing a skyrmion structure in a magnetic field, applying a certain magnetic field to the sample, rotating the sample so that the magnetic field forms a certain magnetic field angle α with the sample, and the horizontal component of the magnetic field causes the magnetic moment direction to flip to the horizontal direction of the sample; S2, keep the magnetic field angle α unchanged, and gradually increase the magnetic field, so that the magnetic moment flips again, forming a strip skyrmion intermediate state; S3, rotate the sample so that the direction of the magnetic field is perpendicular to the plane where the sample is located, and then gradually increase the magnetic field so that the intermediate state of the strip skyrmion is transformed into the complete form of skyrmion. The skyrmions self-assemble into skyrmion chains under the action of attraction.

2. The method for generating a magnetic skyrmion chain according to claim 1, characterized in that: Samples include: FeGe.

3. The method for generating a magnetic skyrmion chain according to claim 1, characterized in that: In step S1, a magnetic field with a magnitude ranging from 80 mT to 100 mT and a magnetic field angle α ranging from 2° to 18° is applied to the sample.

4. A method for generating a magnetic skyrmion chain according to claim 3, characterized in that: In step S1, the magnetic field in which the sample is located increases to between 80 mT and 100 mT within five seconds.

5. The method for generating a magnetic skyrmion chain according to claim 4, characterized in that: In step S1, when the magnetic field magnitude is 80 mT, the magnetic field angle α is 18°; when the magnetic field magnitude is 100 mT, the magnetic field angle α is 2°.

6. A method for generating a magnetic skyrmion chain according to claim 1, characterized in that: In step S2, the magnitude of the magnetic field ranges from 260 mT to 340 mT.

7. A method for generating a magnetic skyrmion chain according to claim 6, characterized in that: In step S2, the magnetic field is increased to 260 mT to 340 mT within 20 seconds.

8. The method for generating a magnetic skyrmion chain according to claim 1, characterized in that: In step S3, the magnetic field ranges from 340 mT to 440 mT.

9. The method for generating a magnetic skyrmion chain according to claim 1, characterized in that: In step S1 to step S3, the ambient temperature is between 180K and 280K.

10. A method for generating a magnetic skyrmion chain according to claim 9, characterized in that: In step S1 to step S3, the ambient temperature is 220K.

Images