A method and device for generating and erasing magnetic skyrmions by photoinduced strain

Abstract

A method for generating and erasing magnetic skyrmions using photoinduced strain induction includes the following steps: S1: preparing a magnetic multi-period film with a critical anisotropy between perpendicular and horizontal anisotropy on an azobenzene liquid crystal film by magnetron sputtering; S2: fabricating a magnetic nanodot array on the magnetic multi-period film prepared in step S1 using micro-nanofabrication technology; S3: generating skyrmions using photoinduced strain by applying a 355-375 nm light pulse; S4: erasing skyrmions using photoinduced strain by applying a 510-530 nm light pulse to destabilize the skyrmion state and restore it to a ferromagnetic state. The present invention also provides a device for writing and erasing magnetic skyrmions, comprising a magnetic multi-period film, a photoinduced strain substrate, and a photoinduced unit. The method and device of the present invention consume low energy to generate and erase skyrmions, enhance device stability, and facilitate device miniaturization.

Description

Technical Field

[0001] The present invention relates to the field of magnetic storage technology, and in particular to a method and device for generating and erasing magnetic skyrmions by utilizing photoinduced strain. Background Art

[0002] With the rapid development of the information age, the explosive growth of data has placed higher demands on information storage media. As the size of traditional magnetic storage media shrinks, the size limitations caused by quantum effects and the resulting thermal effects have created a bottleneck in the development of traditional information storage materials. Spintronics technology introduces a new degree of freedom: electron spin. Spintronic devices offer advantages such as low static power consumption, unlimited high-speed read / write capabilities, and non-volatile storage. It is considered a key technology to overcome this bottleneck, promising significant reductions in device power consumption and breaking the shackles of thermal effects.

[0003] Topological magnetic structures (magnetic skyrmions, vortex domains, etc.) are particle-like spin structures with topological protection. Their related spintronics applications have broad development prospects and are expected to become the next generation of new information storage media. Topological magnetic structures have obvious advantages over traditional information storage media: (1) Compared with traditional magnetic domains, topological magnetic structures can be made very small. Currently, a single magnetic skyrmion can be as small as 5nm; (2) Topological magnetic structures have the characteristics of topological protection. Compared with traditional magnetic domains, they are more stable and less susceptible to external conditions (magnetic field, temperature, etc.), which improves the stability of the device.

[0004] Currently, the primary method for erasing and programming magnetic skyrmions is spin-polarized current, such as the method proposed in patent application CN112510146A, "A method for generating skyrmions in a magnetic multilayer film by current induction, a magnetic storage unit, and a memory device." This method relies on high current density, which consumes a lot of energy. Heat generation also affects device stability, hindering device miniaturization. Therefore, this method is not suitable for low-energy, high-density device applications. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a method for generating and erasing magnetic skyrmions by using photoinduced strain. The method is based on a photoinduced strain substrate (azobenzene liquid crystal film) and uses light to regulate the cis-trans isomerism of azo bonds to generate strain in the magnetic multi-period film, which can significantly reduce the nucleation energy threshold of magnetic skyrmions in the magnetic multi-period film.

[0006] The technical solution adopted by the present invention is: a method for generating and erasing magnetic skyrmions by photoinduced strain, comprising the following steps:

[0007] S1: preparing a magnetic multi-periodic film having a critical anisotropy between perpendicular anisotropy and horizontal anisotropy on an azobenzene liquid crystal film by magnetron sputtering, wherein the magnetic multi-periodic film comprises, from bottom to top, a buffer layer, a heavy metal layer, a magnetic layer, and a non-magnetic layer;

[0008] S2: preparing a magnetic nanodot array on the magnetic multi-periodic film prepared in step S1 by micro-nanofabrication technology;

[0009] S3: Photoinduced skyrmions: By applying a 355-375nm light pulse, the azo bonds undergo a cis-trans isomerization reaction, causing the azobenzene liquid crystal film to bend in a preset direction, generating uniaxial compressive strain on the magnetic layer, reducing the perpendicular magnetic anisotropy of the magnetic material, and thus making the ferromagnetic state unstable, thus generating skyrmions.

[0010] S4: Erasing skyrmions using light: By applying a light pulse of 510-530nm, the cis isomer in the azobenzene liquid crystal film is rendered unstable and restored to a flat state; at this time, the magnetic layer is in a strain-free state, and the perpendicular magnetic anisotropy of the magnetic material is restored, thereby making the skyrmion state unstable and restoring to a ferromagnetic state.

[0011] Compared to existing technologies, this method, based on a photoinduced strain substrate (azobenzene liquid crystal film), utilizes light to modulate the cis-trans isomerism of azo bonds to generate strain within a magnetic multiperiod film, thereby generating skyrmions. This method significantly reduces the nucleation energy threshold for magnetic skyrmions within the film. By applying light pulses of varying wavelengths, this method conveniently manipulates the magnetic anisotropy state within the film, thereby altering the magnetic domain state and enabling the generation and erasure of skyrmions. This method consumes relatively low energy to generate and erase skyrmions, enhances device stability, and facilitates device miniaturization.

[0012] Preferably, step S1 includes the following steps:

[0013] S11: depositing a buffer layer on the azobenzene liquid crystal film by magnetron sputtering;

[0014] S12: A heavy metal layer, a magnetic layer, and a non-magnetic layer are sequentially deposited on the buffer layer to produce a magnetic multi-periodic film. The thicknesses of the heavy metal layer, the magnetic layer, and the non-magnetic layer are adjusted to achieve a critical anisotropy between perpendicular anisotropy and horizontal anisotropy in the magnetic multi-periodic film. The thicknesses of the heavy metal layer, the magnetic layer, and the non-magnetic layer are related to the materials used for the heavy metal layer, the magnetic layer, and the non-magnetic layer.

[0015] Preferably, in step S1, the material of the buffer layer is any one of Ta, Pt, and Cu.

[0016] Preferably, in step S1, the material of the heavy metal layer is Pt or Ir; the material of the magnetic layer is any one of Co, Ni, and Fe; and the material of the non-magnetic layer is any one of Ta, Ir, IrMn, MgO, and TaO.

[0017] Preferably, in step S1, the parameters of magnetron sputtering are: power of 100 W, sputtering atmosphere of argon, sputtering pressure of 5 Pa, and temperature of 30°C.

[0018] Furthermore, step S2 includes the following steps:

[0019] S21: Drop a mixed solution of PS beads with a diameter of 500 nm and ethanol into a Petri dish filled with deionized water, and add a dispersant so that the PS beads are arranged in a single layer on the surface of the deionized water;

[0020] S22: treating the thin film sample obtained in step S1 with oxygen plasma for 5 minutes;

[0021] S23: Use tweezers to place the treated film sample under a single layer of PS beads, and then gently lift it out horizontally; after the water evaporates naturally, a single layer of tightly packed PS beads forms on the surface of the film sample;

[0022] S24: placing the thin film sample with the PS ball mask in an oxygen plasma etcher for etching for 25 to 35 minutes, thereby reducing the diameter of the PS balls and separating the closely packed PS balls;

[0023] S25: placing the sample obtained in step S34 in an ion beam etcher for etching;

[0024] S26: removing the remaining single-layer PS ball mask to obtain an ordered magnetic nanodot array.

[0025] Furthermore, in step S25, at a vacuum degree of 8.0×10 -4 Pa, under room temperature conditions, the cathode current of the ion beam etching system is maintained at 16.8A, the anode voltage is 50V, the screen voltage is 300V, the acceleration voltage is 250V, the neutralization current is 13A, the bias current is 1.2A, and the etching is performed for 400s.

[0026] Furthermore, in step S26, the sample obtained in step S25 is ultrasonicated for 10 min in chloroform, alcohol and deionized water respectively to remove the residual PS ball mask, and then blown dry with a nitrogen gun to obtain an ordered magnetic nanodot array.

[0027] The present invention also provides a magnetic skyrmion writing and erasing device, comprising a magnetic multi-periodic film having a multi-layer film structure, which includes a buffer layer, a heavy metal layer, a magnetic layer, and a non-magnetic layer from bottom to top; a magnetic nanodot array is formed on the upper surface of the magnetic multi-periodic film by micro-nano processing;

[0028] A photoinduced strain substrate is provided at the bottom of the magnetic multi-period film and is used to provide compressive stress or tensile stress to the magnetic multi-period film; the photoinduced strain substrate is an azobenzene liquid crystal film;

[0029] The light induction unit is used to apply light pulses of different specific wavelengths to the magnetic multi-period film so as to write or erase magnetic skyrmions.

[0030] Preferably, the light induction unit writes magnetic skyrmions by applying a 355-375 nm light pulse to the magnetic multi-period film, and erases magnetic skyrmions by applying a 510-530 nm light pulse. The light induction unit is usually an LED light source.

[0031] Compared to existing technologies, the present invention's magnetic skyrmion writing and erasing device, based on a photoinduced strain substrate (azobenzene liquid crystal film), utilizes light to modulate the cis-trans isomerism of azo bonds, generating strain within the magnetic multiperiod film and thereby generating skyrmions. This significantly reduces the skyrmion nucleation energy threshold within the film. By applying specific light pulses of varying wavelengths via a photoinduced unit, the device conveniently modulates the magnetic anisotropy state within the film, thereby altering the magnetic domain state and enabling the generation and erasure of skyrmions. This device consumes relatively low energy to generate and erase skyrmions, resulting in high device stability and favorable device miniaturization.

[0032] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the photoinduced strain experiment;

[0034] Figure 2 Schematic diagram of the structure of the magnetic multi-periodic film described in Example 1;

[0035] Figure 3 Schematic diagram of the principle of writing magnetic skyrmions into a magnetic multi-periodic film based on a photoinduced strained substrate;

[0036] Figure 4 Schematic diagram of the principle of erasing magnetic skyrmions in a magnetic multi-periodic film based on a photoinduced strained substrate;

[0037] Figure 5 Magnetic force microscopy characterization of a skyrmion-like magnetic nanodot array;

[0038] Figure 6 Magnetic force microscopy characterization of ferromagnetic magnetic nanodot array. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to specific embodiments. It should be understood that the present invention is not limited to the following embodiments, and any modifications or variations based on the present invention will fall within the scope of the present invention.

[0040] The instruments used in the following examples are shown in Table 1:

[0041] Table 1. Experimental instruments

[0042]

[0043] Example 1

[0044] This embodiment provides a method for generating and erasing magnetic skyrmions by photoinduced strain, which specifically includes the following steps:

[0045] S1: Platinum / cobalt / tantalum multi-periodic films prepared by magnetron sputtering on azobenzene liquid crystal films;

[0046] like Figure 2 As shown, a buffer layer (tantalum) is first deposited on the azobenzene liquid crystal film 10 by magnetron sputtering, and then a multilayer film structure with a magnetic skyrmion structure (i.e., a platinum / cobalt / tantalum multi-periodic film) is deposited, so that due to the broken interface symmetry, there is a large interface Dzyaloshinskii-Moriya interaction, and by regulating the thickness of the heavy metal layer, the magnetic layer, and the non-magnetic layer, the magnetic multi-periodic film has a critical anisotropy between the vertical anisotropy and the horizontal anisotropy.

[0047] The molecular formula of azobenzene liquid crystal is like Figure 1 As shown, a photoinduced strain experiment is conducted on the azobenzene liquid crystal film. By applying light pulses of different specific wavelengths, the azobenzene liquid crystal film can be switched back and forth between the bent state and the flat state. The subsequent steps S3 and S4 of the present invention use this principle to induce the generation and erasure of magnetic skyrmions.

[0048] In this embodiment, the thickness of the heavy metal layer (platinum) in the platinum / cobalt / tantalum multi-periodic film is 3 nm, the thickness of the magnetic layer (cobalt) is 2.3 nm, and the thickness of the non-magnetic layer (tantalum) is 1.9 nm. The magnetron sputtering parameters are: power of 100 W, sputtering atmosphere of argon, sputtering pressure of 5 Pa, and temperature of 30°C.

[0049] In other embodiments, other buffer layer, heavy metal layer, magnetic layer, and non-magnetic layer materials may be selected. Specifically, the buffer layer material may be any one of Ta, Pt, and Cu. The buffer layer has two functions: one is to serve as an upper electrode, and the other is to improve the growth quality of the magnetic multi-period film. The heavy metal layer material may be Pt or Ir, the magnetic layer material may be any one of Co, Ni, and Fe, and the non-magnetic layer material may be any one of Ta, Ir, IrMn, MgO, and TaO. The thickness of the heavy metal layer, magnetic layer, and non-magnetic layer varies depending on the selected material. The thickness is controlled so that the magnetic multi-period film has a critical anisotropy between perpendicular anisotropy and horizontal anisotropy.

[0050] The Dzyaloshinskii-Moriya interaction, also known as the antisymmetric exchange interaction, is the contribution of two adjacent magnetic spins, Si and Sj, to the total magnetic exchange interaction. It was first proposed by Igor Dzyaloshinskii based on Landau phenomenological theory. Toru Moriya defined spin-orbit coupling as the microscopic mechanism of the antisymmetric exchange interaction. In magnetically ordered systems, this tendency for spins to tilt, forming parallel or antiparallel aligned magnetic moments, is the cause of the spin-tilted weak ferromagnetism seen in antiferromagnetic systems.

[0051] S2: Preparation of magnetic nanodot arrays by micro-nanofabrication technology, including the following steps:

[0052] S21: Drop a mixed solution of PS beads with a diameter of 500 nm and ethanol into a Petri dish filled with deionized water, and add a dispersant so that the PS beads are arranged in a single layer on the surface of the deionized water;

[0053] S22: treating the thin film sample obtained in step S1 with oxygen plasma using a plasma etcher for 5 minutes;

[0054] S23: Use tweezers to place the treated film sample under a single layer of PS beads, and then gently lift it out horizontally; after the water evaporates naturally, a single layer of tightly packed PS beads forms on the surface of the magnetic film;

[0055] S24: placing the thin film sample with the PS ball mask in a plasma etcher for etching for 25 to 35 minutes, thereby reducing the diameter of the PS balls and separating the closely packed PS balls;

[0056] S25: The sample obtained in step S34 is placed in an ion beam etcher for etching at a vacuum degree of 8.0×10 - 4Pa, under room temperature conditions, the cathode current of the ion beam etching system is maintained at 16.8A, the anode voltage is 50V, the screen voltage is 300V, the acceleration voltage is 250V, the neutralization current is 13A, the bias current is 1.2A, and the etching is performed for 400s.

[0057] S26: The sample obtained in step S25 is ultrasonically treated with isopropyl alcohol, anhydrous ethanol and deionized water for 10 minutes respectively to remove the residual PS ball mask, and then blown dry with a nitrogen gun to obtain an ordered magnetic nanodot array.

[0058] S3: Photoinduced generation of skyrmions: Figure 3 As shown in the figure, by applying a 365nm light pulse, the azo bonds undergo a cis-trans isomerization reaction (most azo bonds are stable in the cis isomerization state), causing the azobenzene liquid crystal film to bend in a preset direction, thereby generating a uniaxial compressive strain on the magnetic layer. This compressive strain will reduce the perpendicular magnetic anisotropy of the magnetic material due to the inverse magnetostrictive effect, making the ferromagnetic state unstable and generating skyrmions. The magnetic force microscopy characterization of the magnetic nanodot array in the skyrmion state obtained using a multifunctional scanning microscope is shown in the figure below. Figure 5 As shown in the figure, the nanodots are downward-pointing magnetic domains with uniform black contrast. Within the nanodots, there are dots with white contrast, representing skyrmions. In the figure, white contrast represents spin-up, and black represents spin-down. The nanodots are surrounded by non-magnetic areas, the white contrast of which is caused by the height of the phase. In this embodiment, the wavelength of the light pulse used to write skyrmions is 365 nm. In other embodiments, this wavelength can be adjusted within ±10 nm.

[0059] S4: Erasing skyrmions using light: Figure 4 As shown in the figure, by applying a 520nm light pulse, the cis isomer in the azobenzene liquid crystal film cannot exist stably and returns to a flat state; at this time, the magnetic layer is in a strain-free state, and the perpendicular magnetic anisotropy of the magnetic material is restored, so that the skyrmion state cannot exist stably and returns to a ferromagnetic state. The magnetic force microscope characterization of the ferromagnetic magnetic nanodot array is shown in the figure. Figure 6 As shown, the nanodots are downward-pointing magnetic domains with uniform black contrast (white contrast in the figure represents spin-up, black represents spin-down, and the non-magnetic area surrounding the nanodots has a white contrast caused by the height of the surface). In this embodiment, the wavelength of the light pulse applied to erase skyrmions is 520 nm, and in other embodiments, this wavelength can be adjusted within a range of ±10 nm.

[0060] Compared to existing technologies, this method, based on a photoinduced strain substrate (azobenzene liquid crystal film), utilizes light to modulate the cis-trans isomerism of azo bonds to generate strain within a magnetic multiperiod film, thereby generating skyrmions. This method significantly reduces the nucleation energy threshold for magnetic skyrmions within the film. By applying light pulses of varying wavelengths, this method conveniently manipulates the magnetic anisotropy state within the film, thereby altering the magnetic domain state and enabling the generation and erasure of skyrmions. This method consumes relatively low energy to generate and erase skyrmions, enhances device stability, and facilitates device miniaturization.

[0061] Example 2

[0062] See also Figures 2-4 This embodiment provides a device for writing and erasing magnetic skyrmions, comprising a photo-strained substrate 10, a magnetic multi-periodic film 20, and an external light-inducing unit 50. The magnetic multi-periodic film 20 is disposed on the upper surface of the photo-strained substrate 10 and comprises a multilayer film structure, comprising, from bottom to top, a buffer layer, a heavy metal layer, a magnetic layer, and a non-magnetic layer. A magnetic nanodot array 31 is formed on the upper surface of the magnetic multi-periodic film 20 through micro-nanofabrication. The external light-inducing unit 50 is used to apply light pulses of different specific wavelengths to the magnetic multi-periodic film to write or erase magnetic skyrmions 32.

[0063] The photoinduced strained substrate 10 is an azobenzene liquid crystal film, which is used to provide compressive or tensile stress to the magnetic multi-periodic film. The magnetic multi-periodic film 20 is prepared according to step S1 of Example 1 and processed into a magnetic nanodot array according to step S2. The buffer layer material can be any of Ta, Pt, and Cu; the heavy metal layer material can be Pt or Ir; the magnetic layer material can be any of Co, Ni, and Fe; and the non-magnetic layer material can be any of Ta, Ir, IrMn, MgO, and TaO.

[0064] The light-inducing unit 50 can be an LED light source. It applies 355-375 nm light pulses to the magnetic multi-period film to write magnetic skyrmions and applies 510-530 nm light pulses to erase magnetic skyrmions 32. The detailed principle is described in Example 1 and is not further described here.

[0065] Compared to existing technologies, the present invention's magnetic skyrmion writing and erasing device, based on a photoinduced strain substrate 10 (azobenzene liquid crystal film), utilizes light to modulate the cis-trans isomerism of azo bonds to induce strain within the magnetic multi-period film, thereby generating skyrmions. This significantly reduces the nucleation energy threshold for magnetic skyrmions within the magnetic multi-period film 20. By applying specific light pulses of varying wavelengths via a photoinduced unit, the device conveniently modulates the magnetic anisotropy state within the magnetic multi-period film 20, thereby altering the magnetic domain state and enabling the generation and erasure of skyrmions. This device consumes relatively low energy to generate and erase skyrmions, resulting in high device stability and favorable device miniaturization.

[0066] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications of the present invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims of the present invention and equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A method for generating and erasing magnetic skyrmions using photoinduced strain, characterized in that: The following steps are involved: S1: preparing a magnetic multi-periodic film having a critical anisotropy between perpendicular anisotropy and horizontal anisotropy on a photo-strained substrate by magnetron sputtering, wherein the magnetic multi-periodic film comprises, from bottom to top, a buffer layer, a heavy metal layer, a magnetic layer, and a non-magnetic layer; the photo-strained substrate is an azobenzene liquid crystal film; S2: preparing a magnetic nanodot array on the magnetic multi-periodic film prepared in step S1 by micro-nanofabrication technology; S3: Photoinduced skyrmions: By applying a 355-375nm light pulse, the azo bonds undergo a cis-trans isomerization reaction, causing the azobenzene liquid crystal film to bend in a preset direction, generating uniaxial compressive strain on the magnetic layer, reducing the perpendicular magnetic anisotropy of the magnetic material, and thus making the ferromagnetic state unstable, thus generating skyrmions. S4: Erasing skyrmions using light: By applying a light pulse of 510-530nm, the cis isomer in the azobenzene liquid crystal film is rendered unstable and restored to a flat state; at this time, the magnetic layer is in a strain-free state, and the perpendicular magnetic anisotropy of the magnetic material is restored, thereby making the skyrmion state unstable and restoring to a ferromagnetic state.

2. The method for generating and erasing magnetic skyrmions by photoinduced strain according to claim 1, wherein: Step S1 includes the following steps: S11: depositing a buffer layer on the azobenzene liquid crystal film by magnetron sputtering; S12: depositing a heavy metal layer, a magnetic layer, and a non-magnetic layer in sequence on the buffer layer to obtain a magnetic multi-periodic film; and adjusting the thicknesses of the heavy metal layer, the magnetic layer, and the non-magnetic layer to make the magnetic multi-periodic film have a critical anisotropy between perpendicular anisotropy and horizontal anisotropy.

3. The method for generating and erasing magnetic skyrmions by photoinduced strain according to claim 1, wherein: In step S1 , the material of the buffer layer is any one of Ta, Pt, and Cu.

4. The preparation method according to claim 1, characterized in that In step S1 , the material of the heavy metal layer is Pt or Ir; the material of the magnetic layer is any one of Co, Ni, and Fe; and the material of the non-magnetic layer is any one of Ta, Ir, IrMn, MgO, and TaO.

5. The method for generating and erasing magnetic skyrmions by photoinduced strain according to claim 1, wherein: In step S1, the parameters of magnetron sputtering are: power of 100 W, sputtering atmosphere of argon, sputtering pressure of 5 Pa, and temperature of 30°C.

6. The method of generating and erasing magnetic skyrmions by photoinduced strain according to claim 1, wherein: Step S2 includes the following steps: S21: Drop a mixed solution of PS beads with a diameter of 500 nm and ethanol into a Petri dish filled with deionized water, and add a dispersant so that the PS beads are arranged in a single layer on the surface of the deionized water; S22: treating the thin film sample obtained in step S1 with oxygen plasma for 5 minutes; S23: Use tweezers to place the treated film sample under a single layer of PS beads, and then gently lift it out horizontally; after the water evaporates naturally, a single layer of tightly packed PS beads forms on the surface of the film sample; S24: placing the thin film sample with the PS ball mask in an oxygen plasma etcher for etching for 25 to 35 minutes, thereby reducing the diameter of the PS balls and separating the closely packed PS balls; S25: placing the sample obtained in step S34 in an ion beam etcher for etching; S26: removing the remaining single-layer PS ball mask to obtain an ordered magnetic nanodot array.

7. The method for generating and erasing magnetic skyrmions by photoinduced strain according to claim 6, wherein: In step S25, the vacuum degree is 8.0×10 -4 Pa, under room temperature conditions, the cathode current of the ion beam etching system is maintained at 16.8A, the anode voltage is 50V, the screen voltage is 300V, the acceleration voltage is 250V, the neutralization current is 13A, the bias current is 1.2A, and the etching is performed for 400s.

8. The method of generating and erasing magnetic skyrmions by photoinduced strain according to claim 6, wherein: In step S26, the sample obtained in step S25 is ultrasonically treated with isopropyl alcohol, anhydrous ethanol and deionized water for 10 minutes respectively to remove the residual PS ball mask, and then blown dry with a nitrogen gun to obtain an ordered magnetic nanodot array.

9. A magnetic skyrmion writing and erasing device, characterized in that: include A magnetic multi-periodic film having a multi-layer structure, comprising, from bottom to top, a buffer layer, a heavy metal layer, a magnetic layer, and a non-magnetic layer; a magnetic nanodot array is formed on the upper surface of the magnetic multi-periodic film by micro-nano processing; A photoinduced strain substrate is provided at the bottom of the magnetic multi-period film and is used to provide compressive stress or tensile stress to the magnetic multi-period film; the photoinduced strain substrate is an azobenzene liquid crystal film; The light induction unit is used to apply a 355-375 nm light pulse to the magnetic multi-period film to write magnetic skyrmions; and apply a 510-530 nm light pulse to erase the magnetic skyrmions.

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