A method for generating skyrmions in a magnetic multilayer film by current induction, a magnetic storage unit, and a memory

Abstract

The present invention provides a method for generating skyrmions in a magnetic multilayer film by current induction. The method includes the following steps: S1. Provide the magnetic multilayer film, which includes a first magnetic layer, a non-magnetic metal layer, and a second magnetic layer stacked in sequence. One or more first stripes with antiferromagnetic coupling and one or more second stripes with ferromagnetic coupling are formed in the magnetic multilayer film, and the first stripes and the second stripes are alternately formed; the first stripes and the second stripes are parallel to each other in a first direction; S2. Connect the magnetic multilayer film to a circuit and pass an alternating current, and generate the skyrmions at the junction of the first stripes and the second stripes; wherein, the frequency of the alternating current is 47 kHz - 52 kHz, and the peak value is 37 mA - 39 mA. This method can be used to prepare highly integrated devices and is also compatible with existing semiconductor processes.

Description

Technical Field

[0001] The present invention relates to the field of magnetic storage technology, and particularly to a method for generating skyrmions in a magnetic multilayer film by current induction, a magnetic storage unit, and a memory. Background Art

[0002] Magnetic skyrmions are spatial spin structures with topological invariance at the micro-nano scale, and can stably exist in bulk magnets with extremely strong spin-orbit coupling or in nano-magnetic thin films adjacent to heavy metals. Due to their small size, low power consumption, and the non-volatile advantages of storage devices based on this structure, they are regarded as one of the choices for the next-generation information units. The generation of this topological magnetic structure is mainly the result of the mutual competition of three effects: magnetic exchange interaction, magnetic anisotropy, and the Dzyaloshinskii-Moriya interaction (DMI effect) provided by the interface in the material. Therefore, if skyrmions are to be stably generated in the thin film, it is necessary to manipulate the external conditions to make the competition among the three reach an ideal state.

[0003] Currently, the methods for generating skyrmions in the field mainly include applying an external magnetic field, irradiation induction, and current induction. Due to technical limitations, the first two methods are difficult to apply to actual industrial production. For example, the method of applying an external magnetic field will make the device structure too complex and is not conducive to achieving a high storage density of information, while the method of using X-ray irradiation has too high requirements for equipment and requires the use of synchrotron radiation light sources, making large-scale production impossible. Compared with these two methods, the current induction method is more conducive to combining with existing semiconductor processes. Summary of the Invention

[0004] The present invention introduces a new method for generating skyrmions by current induction. By applying a pulsed current with an appropriate magnitude and frequency at the junction of the antiferromagnetic and ferromagnetic regions of an artificially synthesized antiferromagnetic thin film, regular-shaped and relatively dispersed skyrmions can appear at the junction. Compared with existing other methods for generating skyrmions, this method can be used to prepare high-integration devices and is also compatible with existing semiconductor processes.

[0005] An embodiment of the present invention provides a method for generating skyrmions in a magnetic multilayer film by current induction, and the method includes the following steps:

[0006] S1. Provide the magnetic multilayer film, which includes a first magnetic layer, a non-magnetic metal layer, and a second magnetic layer stacked in sequence. The non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer. In the magnetic multilayer film, one or more first magnetic layers and second magnetic layers form a first strip in antiferromagnetic coupling, and one or more first magnetic layers and second magnetic layers form a second strip in ferromagnetic coupling. The first strip and the second strip are alternately formed; the first strip and the second strip are parallel to each other in a first direction, and the first strip and the second strip are alternately distributed in a second direction, where the first direction is perpendicular to the second direction, and the first direction is perpendicular to the thickness direction of the magnetic multilayer film;

[0007] S2. Connect the magnetic multilayer film to a circuit and pass an alternating current through it. The alternating current passes through the magnetic multilayer film in the first direction and generates skyrmions at the junction of the first strip and the second strip;

[0008] Among them, the frequency of the alternating current is 47 kHz - 52 kHz, and the peak value of the alternating current is 37 mA - 39 mA.

[0009] Preferably, the alternating current includes a square wave pulse current;

[0010] Preferably, the number of applied current pulses is 10000.

[0011] Preferably, both the first magnetic layer and the second magnetic layer are perpendicularly magnetized layers, that is, the direction of the net magnetic moment of the first magnetic layer and the second magnetic layer is perpendicular to the film surface.

[0012] Preferably, the non-magnetic metal layer includes Ru;

[0013] Preferably, the non-magnetic metal layer is formed as a wedge-shaped film;

[0014] Preferably, the non-magnetic metal layer has a thickness that gradually changes in the second direction;

[0015] Preferably, the maximum thickness of the non-magnetic metal layer is 3 nm.

[0016] Preferably, the first magnetic layer and the second magnetic layer include a Co / Pt multilayer film structure;

[0017] Preferably, the first magnetic layer includes a [Pt / Co]n multilayer film structure, where n is a natural number greater than 1;

[0018] Preferably, the second magnetic layer includes a [Co / Pt]m multilayer film structure, where m is a natural number greater than 1;

[0019] Preferably, m = n;

[0020] Preferably, the first magnetic layer includes a [Pt(0.5nm) / Co(0.5nm)]n multilayer film structure;

[0021] Preferably, the second magnetic layer includes a [Co(0.5nm) / Pt(0.5nm)]m multilayer film structure.

[0022] Preferably, there is one or more of the boundaries distributed in the second direction;

[0023] There are two of the boundaries distributed in the second direction;

[0024] Preferably, the external magnetic field strength is zero in steps S1 and S2.

[0025] The present invention also provides a magnetic multilayer film, which includes a first magnetic layer, a non-magnetic metal layer, and a second magnetic layer stacked in sequence. The non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer. One or more first magnetic layers and second magnetic layers in the magnetic multilayer film are in an antiferromagnetic coupling first strip, and one or more first magnetic layers and second magnetic layers are in a ferromagnetic coupling second strip. The first strip and the second strip are alternately formed; the first strip and the second strip are parallel to each other in the first direction, and the first strip and the second strip are alternately distributed in the second direction, wherein the first direction is perpendicular to the second direction, and the first direction is perpendicular to the thickness direction of the magnetic multilayer film; the non-magnetic metal layer has a thickness that gradually changes in the second direction.

[0026] Preferably, both the first magnetic layer and the second magnetic layer are perpendicular magnetization layers, that is, the net magnetic moment directions of the first magnetic layer and the second magnetic layer are perpendicular to the film surface.

[0027] Preferably, the non-magnetic metal layer includes Ru;

[0028] Preferably, the maximum thickness of the non-magnetic metal layer is 3 nm.

[0029] Preferably, the first magnetic layer and the second magnetic layer include a Co / Pt multilayer film structure;

[0030] Preferably, the first magnetic layer includes a [Pt / Co]n multilayer film structure, where n is a natural number greater than 1;

[0031] Preferably, the second magnetic layer includes a [Co / Pt]m multilayer film structure, where m is a natural number greater than 1;

[0032] Preferably, m = n;

[0033] Preferably, the first magnetic layer includes a [Pt(0.5 nm) / Co(0.5 nm)]n multi-layer film structure;

[0034] Preferably, the second magnetic layer includes a [Co(0.5 nm) / Pt(0.5 nm)]m multi-layer film structure.

[0035] Preferably, more than one of the boundaries are distributed in the second direction.

[0036] The present invention also provides a magnetic storage unit, which includes any one of the above-mentioned magnetic multi-layers.

[0037] The present invention also provides a magnetic memory, which includes the above-mentioned magnetic storage unit.

[0038] The present invention provides a brand-new method for generating current-induced, mainly by applying a pulsed current with appropriate magnitude and frequency at the junction of the antiferromagnetic and ferromagnetic regions of an artificially synthesized antiferromagnetic thin film, so that regularly shaped and relatively dispersed skyrmions can appear in the antiferromagnetic region. Compared with other existing methods for generating skyrmions, this method has no specific requirements for the shape and size of the device, can be used to prepare highly integrated devices, and is also compatible with existing semiconductor processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings. The drawings are schematic and should not be construed as any limitation to the present invention. In the drawings:

[0040] Figure 1 Shown is the thin film structure diagram (side view) (a) of the magnetic multi-layer in the present invention, the distribution diagram of the ferromagnetic and antiferromagnetic regions of the thin film (top view) (b), the shape of the strip-shaped constriction device (top view) (c), and the change of the magnetic domain with the magnetic field when the device is not energized (d).

[0041] Figure 2 Shown is the magnetic domain distribution of the device before applying the pulsed current (a) of the present invention, and the skyrmions generated respectively after applying the pulsed current twice (b) and (c), with different positions.

[0042] Figure 3 Shown is the distribution of skyrmions in the device when applying currents with different peak magnitudes of the present invention.

[0043] Figure 4 Shown is the strip-shaped domain moving along the current direction that appears in the device when passing direct current (a), and the strip-shaped domain that appears when applying a pulsed current with a peak value of 41 mA on both sides of the sample (b). Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] The present invention provides a method for generating skyrmions in a magnetic multilayer film through current induction. The invention can generate skyrmions in the antiferromagnetic region by applying a pulsed current at the ferromagnetic and antiferromagnetic junction. The specific structure of the magnetic multilayer film is Ta(5nm) / [Pt(0.5nm) / Co(0.5nm)]3 / Ru(0 - 3nm) / [Co(0.5nm) / Pt(0.5nm)]3 / Ta(5nm), where [Pt(0.5nm) / Co(0.5nm)]3 and [Co(0.5nm) / Pt(0.5nm)]3 are two perpendicularly magnetized layers, and the Ru layer is a non-magnetic metal layer. The Ru layer is a wedge-shaped film and is uniformly distributed on the thin film from thin to thick, as Figure 1 (a) shown. The upper and lower Ta are protective layers and capping layers. The first magnetic layer includes [Pt(0.5nm) / Co(0.5nm)]3, and the second magnetic layer includes [Co(0.5nm) / Pt(0.5nm)]3. By changing the thickness of the non-magnetic layer Ru between the two magnetic layers, the ferromagnetic interaction (preferably parallel arrangement) can be adjusted to an antiferromagnetic interaction (preferably antiparallel arrangement), so that the ferromagnetic and antiferromagnetic regions on the thin film are staggered, as Figure 1 (b), where regions 1 and 3 are both antiferromagnetic stripes, and regions 2 and 4 are both ferromagnetic stripes. The antiferromagnetic stripes and ferromagnetic stripes are alternately distributed on the magnetic multilayer film. Define the direction of the gradual change in the thickness of the non-magnetic layer Ru as the second direction ( Figure 1 (a) the horizontal direction), then the antiferromagnetic stripes and ferromagnetic stripes are alternately distributed along the second direction. The antiferromagnetic stripes and ferromagnetic stripes extend parallel to each other along the first direction ( Figure 1 (a) the direction perpendicular to the paper plane), then the first direction is perpendicular to the second direction. Both the first direction and the second direction are in the plane of the magnetic multilayer film, and the first direction is perpendicular to the thickness direction of the magnetic multilayer film.

[0046] When preparing the sample, make the boundary between the ferromagnetic region and the antiferromagnetic region exactly fall on the strip-shaped constriction block of the device, and then apply a pulsed current with appropriate conditions, so that magnetic skyrmions can be generated.

[0047] Preparation of the device:

[0048] The specific structure of the device including the magnetic multilayer film is Ta(5) / [Pt(0.5) / Co(0.5)]3 / Ru(0 - 3nm) / [Co(0.5) / Pt(0.5)]3 / Ta(5), with the unit of nanometer. Ta is used as the underlayer and the protective layer.

[0049] The device is grown on the device that has been lithographed. The lithographed device includes a silicon wafer (300nm thermal oxide layer) as shown in Figure 1 (c). First, a 5 - nanometer Ta is deposited as the buffer layer using an ultra - high vacuum magnetron sputtering instrument from AJA Corporation, then the magnetization layer of Pt / Co and the wedge - shaped structure of Ru, and finally 5nm of Ta is deposited as the protective layer.

[0050] After growth, the photoresist on the surface of the silicon wafer is cleaned ultrasonically with acetone, leaving only the device in the shape as shown in Figure 1 (c). It should be emphasized that when preparing the Ru layer of the sample, a uniformly - graded wedge - shaped thin film with a thickness ranging from 0 to 3nm needs to be prepared on the sample using the baffle equipped in the magnetron sputtering, so that the ferromagnetic and antiferromagnetic regions alternately appear on the sample. As shown in Figure 1 (d), the boundary between the ferromagnetic and antiferromagnetic regions just falls on the strip - shaped constriction region 30 of the device.

[0051] Characterization of device characteristics:

[0052] Magneto - optical Kerr is a technique that can be used to detect the magnetic domain imaging of magnetic thin films and also to observe the imaging of current - driven magnetic domain motion. We use a magneto - optical Kerr microscope to characterize the magnetic domain distribution of the device. Figure 1 (d) shows the change of the device magnetic domain with the external magnetic field without passing current. As shown in Figure 1 (d), above the strip - shaped constriction region 30 is the antiferromagnetic region, and below is the ferromagnetic region. Starting from the positive saturation, when changing the external magnetic field towards the negative saturation direction, the magnetic moment of the antiferromagnetic region flips first (single - domain flip). Continuing to reduce the magnetic field, the magnetic moment of the ferromagnetic region flips (labyrinth domain). It can be seen that the boundary between the ferromagnetic and antiferromagnetic regions falls on the strip - shaped constriction region 30 of the device.

[0053] As shown in Figure 1 (c), regions 10 and 20 are the positive and negative electrodes respectively. The positive and negative electrodes are connected to a current source to provide direct current and pulsed current. The device is placed on the electromagnet under the magneto - optical Kerr microscope, and the magnetic field direction is perpendicular to the film plane. Before passing current through the device, the external magnetic field in which the device or the magnetic multilayer film is located is gradually reduced from the positive saturation magnetic field of 200mT to zero. As shown in Figure 2As shown in (a), when the external magnetic field is 0 mT, the white magnetic domains representing the antiferromagnetic layer flipping just stay on both sides of the strip region (but do not touch). Keeping the magnetic field at 0 mT unchanged, a square pulse current with a frequency of 50 kHz and a peak value of 39 mA is applied to the electrodes on both sides of the sample by the current source connected to the sample. The number of current pulses applied each time is 10,000. It is observed that relatively scattered and regularly shaped skyrmions appear in the strip constriction region of the device, and they have the same color as the flipped magnetic domains of the antiferromagnetic layer. Figure 2 The skyrmions generated after applying the pulse current twice are shown in (b) and (c), and their positions are different. It is worth noting that each time the pulse current is applied, the positions of the generated skyrmions are random and have good dispersion and can exist stably for a long time.

[0054] When changing the peak value of the applied pulse current, as Figure 3 shown, gradually reducing the magnetic field from the positive saturation magnetic field of 200 mT to zero, keeping the magnetic field at 0 mT unchanged, and applying square pulse currents with different peak values and a frequency of 50 kHz to the sample on both sides of the device. There is no obvious phenomenon at 35 mA, a few clear skyrmions appear at 37 mA, more and regularly shaped skyrmions appear at 39 mA, and at 41 mA, a few skyrmions appear simultaneously with the strip domains. Therefore, only when the peak value of the pulse current is appropriate and within a certain range (37 mA - 39 mA) can independent and scattered skyrmions be generated.

[0055] Comparative example:

[0056] When a direct current flowing from bottom to top is applied to both sides of the sample, white strip domains moving along the direction of the direct current and a small number of skyrmions appear above the strip region, as Figure 4 shown in (a). From this, it can be judged that there is a strong DMI in this system, and all the generated ones should be Néel-type magnetic domains. However, when passing a direct current, due to the long action time of the current, only irregularly shaped and relatively dense small magnetic domains can appear in the strip region. Therefore, it is impossible to generate skyrmions with good dispersion using a direct current. Similarly, when the peak value of the pulse current is too large (for example, greater than 50 mA), as Figure 4 shown in (b), white Néel-type strip domains will also be generated in the strip region. Therefore, when applying a pulse current, controlling the peak value and frequency of the pulse current are the keys to generating skyrmions with good dispersion.

[0057] The present invention provides a brand-new method for generating current, mainly by applying a pulsed current with appropriate magnitude and frequency at the junction of the antiferromagnetic and ferromagnetic regions of an artificially synthesized antiferromagnetic thin film, so that regular-shaped and relatively dispersed skyrmions can appear near the junction. Compared with other existing methods for generating skyrmions, this method can be used to fabricate highly integrated devices and is also compatible with existing semiconductor processes. Logic devices based on magnetic skyrmions are smaller in volume, higher in stability, and lower in energy consumption.

[0058] The above embodiments merely illustrate the principles and effects of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for generating skyrmions in a magnetic multilayer film by current induction, characterized in that, The method includes the following steps: S1. Provide the magnetic multilayer film, which includes a first magnetic layer, a non-magnetic metal layer, and a second magnetic layer stacked in sequence. The non-magnetic metal layer is located between the first magnetic layer and the second magnetic layer. In the magnetic multilayer film, one or more first magnetic layers and second magnetic layers form a first strip in antiferromagnetic coupling, and one or more first magnetic layers and second magnetic layers form a second strip in ferromagnetic coupling. The first strip and the second strip are alternately formed; the first strip and the second strip extend parallel in a first direction, and the first strip and the second strip are alternately distributed in a second direction, where the first direction is perpendicular to the second direction, and the first direction is perpendicular to the thickness direction of the magnetic multilayer film; S2. Connect the magnetic multilayer film to a circuit and pass an alternating current through it. The alternating current passes through the magnetic multilayer film along the first direction and generates skyrmions at the junction of the first strip and the second strip; wherein, the frequency of the alternating current is 47 kHz - 52 kHz, and the peak value of the alternating current is 37 mA - 39 mA.

2. The method according to claim 1, characterized in that, The alternating current includes a square wave pulse current.

3. The method according to claim 2, wherein The number of applied current pulses is 10000.

4. The method according to claim 1, 2 or 3, characterized in that, Both the first magnetic layer and the second magnetic layer are perpendicular magnetization layers, that is, the net magnetic moment directions of the first magnetic layer and the second magnetic layer are perpendicular to the film surface.

5. The method according to claim 1, 2 or 3, characterized in that, The non-magnetic metal layer includes Ru.

6. The method according to claim 5, wherein The non-magnetic metal layer is formed as a wedge-shaped film.

7. The method according to claim 5, wherein The non-magnetic metal layer has a thickness that gradually changes in the second direction.

8. The method according to claim 1, 2 or 3, characterized in that The first magnetic layer and the second magnetic layer include a Co / Pt multilayer film structure.

9. The method according to claim 8, wherein The first magnetic layer includes a [Pt / Co]n multilayer film structure, where n is a natural number greater than 1.

10. The method according to claim 9, wherein The second magnetic layer includes a [Co / Pt]m multilayer film structure, where m is a natural number greater than 1.

11. The method according to claim 10, wherein m = n.

12. The method according to claim 9, characterized in that, In any layer of [Pt / Co] film, the thickness of the Pt layer is 0.5 nm, and the thickness of the Co layer is 0.5 nm.

13. The method according to claim 10, wherein In any layer of [Co / Pt] film, the thickness of the Co layer is 0.5 nm, and the thickness of the Pt layer is 0.5 nm.

14. The method according to claim 1, 2 or 3, characterized in that, One or more boundaries are distributed in the second direction.

15. The method according to claim 14, wherein Two boundaries are distributed in the second direction.

16. The method according to claim 14, wherein In steps S1 and S2, the external magnetic field strength is zero.

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