Nanostuctures comprising isolated skyrmions, their manufacturing process and their use in microscopy and sensing

Abstract

The present disclosure relates to a process for manufacturing a nanostructure comprising isolated skyrmions, wherein a substrate is treated with a focused ion beam thinning technique, generating a column (20) shaped thinning structure, followed by deposition of a metal thin film on the column (20), thereby forming a nanostructure (10) capable of generating a single isolated skyrmion on top thereof. Furthermore, the manufactured nanostructure (10) and its use in magnetic microscopy and magnetic sensing are described.

Description

Technical Field

[0001] This disclosure relates to the field of fabricating or processing nanostructures by individually manipulating atoms, molecules, or finite groups of atoms or molecules as discrete units. This disclosure also relates to specific uses or application areas of nanostructures for sensing purposes. Background Technology

[0002] The recently discovered magnetic skyrmions have sparked intense interest in condensed matter physics and materials science. The specific spin texture of magnetic skyrmions produces a series of unique phenomena due to their topologically protected quantum states and emergent electromagnetic fields.

[0003] Existing technologies include certain manufacturing techniques for producing skyrmion surfaces and their designated uses, primarily for low-dissipation magnetic information storage devices, but also for magnetic field sensors.

[0004] Patent document WO2017024253A1 describes a method for fabricating artificial skyrmions and skyrmion lattices stable at room temperature. The method involves depositing one or more layers of material (e.g., alternating layers of Co / Pd, Co / Pt, Co / Ni, or CoFeB / MgO, or a single layer of FePt, FePd, CoPt, CoPd, GdFeCo, or TbFeCo) on a substrate having perpendicular magnetic anisotropy via physical vapor deposition (sputtering); forming an asymmetric pattern in the material layer to expose a portion of the substrate; irradiating the exposed substrate with ions; removing the material layer; and finally applying a specific magnetic field sequence to prepare the skyrmion state. The result of this process is a surface capable of generating multiple skyrmions at room temperature, which can be used in magnetic memory devices, logic devices, and sensors.

[0005] Patent document WO2018203554A1 describes a method for manufacturing a magnetic device that generates skyrmions at room temperature, wherein the resulting device is capable of generating one to three skyrmions on a structure having a basic triangular shape (side length between 150 nm and 800 nm), a circular shape (radius approximately 120 nm), or a square shape (size unspecified). The method involves generating multiple nanodot-like defects on a flat magnetic material by exposing the material to an electron beam. Uses of the described resulting device include its application as a magnetic memory capable of storing information, and its application in magnetic sensors for detecting magnetism or magnetic tracks.

[0006] Based on the aforementioned literature, techniques for fabricating skyrmion nanostructures and their applications as magnetic sensors are known. However, previous techniques are based on flat magnetic substrates and therefore have not yet overcome the difficulties associated with applications requiring specific geometries, such as the challenges related to the sensing configuration that requires isolated individual skyrmions (e.g., in the magnetic probe tip of an atomic force microscope (AFM) sensor). Summary of the Invention

[0007] One objective of this disclosure is to provide a process for fabricating nanostructures that generate single, stable skyrmions, which can be grown on various materials used as substrates, including on magnetic AFM probe tips, thereby improving the magnetic resolution and significantly extending the lifetime of such tips compared to commercially available tips (cobalt-coated). Another objective of this disclosure is to provide the use of these nanostructures in atomic force microscopy, with a focus on magnetic applications and their use as nanosensors in different types of spatial arrangements.

[0008] The objective of this disclosure is achieved through a process including the following steps: Using focused ion beam thinning technology (referred to herein as FIB), preferably focused gallium ion FIB, the material to be used as a substrate (preferably the vertex material of the magnetic AFM probe tip) is thinned to produce at least one cylindrical strut with a nanometer-scale diameter in the thinned material. Preferably, one or more metal films are grown on the thinned material column by physical vapor deposition to form a multilayer nanostructure with perpendicular magnetic anisotropy. The nanostructure has an approximately conical shape and is capable of generating a single stable skyrmion at its top.

[0009] The purpose of this disclosure is also achieved by the use of the nanostructure in microscopy, wherein the thinning and growth processes are performed on the tip of an AFM probe, and the resulting microscopy is magnetic force microscopy (hereinafter referred to as MFM).

[0010] The purpose of this disclosure is also achieved by the use of the nanostructures in magnetic sensing, wherein a plurality of structures are grown on a thinned substrate (preferably a silicon substrate) and arranged at regular intervals to form a planar geometric array suitable for the intended sensing application, for example, forming a planar geometric arrangement of circles, triangles, rectangles, pentagons, hexagons or any polygon suitable for the desired sensing application. Attached Figure Description

[0011] This disclosure is illustrated by means of embodiments shown in the accompanying drawings, which are briefly described below: According to one embodiment of this disclosure, Figure 1This is a schematic diagram of a substrate pillar thinned by FIB, the substrate pillar including a skyrmion-generating nanostructure deposited on its top.

[0012] According to one embodiment of this disclosure, Figure 2A This is a schematic diagram of a metal layer that is deposited to form a nanostructure that generates skyrmions.

[0013] According to one embodiment of this disclosure, Figures 2B to 2D It is a scanning electron microscopy image of three planar geometric arrangements of a column with a nanostructure containing nine skyrmions. Figures 2E to 2G They are Figures 2B to 2D The image shown is a magnetic force microscopy image of a nanostructure. According to one embodiment of this disclosure... Figure 2H yes Figure 2G An enlarged view of a single nanostructure in the image shows a single skyrmion at the center of its inner diameter.

[0014] According to one embodiment of this disclosure, Figure 3A and Figure 3B They are Figure 2F The image shows a magnetic microscopy image of one structure in the array and a graph of the magnetic amplitude of the single nanostructure as a function of radial position.

[0015] According to one embodiment of this disclosure, Figure 3C and Figure 3D They are Figure 2G The image shows a magnetic microscopy image of one structure in the array and a graph of the magnetic amplitude of the single nanostructure as a function of radial position.

[0016] According to one embodiment of the manufacturing method described in this disclosure, FIG4A is a scanning electron microscope image of the AFM tip before the thinning step.

[0017] According to one embodiment of the manufacturing method described in this disclosure, Figures 4B to 4D are scanning electron microscope images of the AFM probe tip from different angles after a cylindrical structure with a diameter of 250 nm has been deposited at its apex.

[0018] Figure 5A and 5B These are two magnetic force microscopy images of a hard disk obtained using an improved AFM probe tip according to an embodiment of the manufacturing method described in this disclosure and an AFM probe in the prior art. Detailed Implementation

[0019] This disclosure relates to a nanostructure capable of generating a single stable skyrmion on its top. This disclosure also relates to a process for fabricating said nanostructure and its use in microscopy and sensing.

[0020] Figure 1 This is a schematic diagram of the main components of a structure for generating a single skyrmion, wherein the structure includes: a pillar (20) thinned by FIB technology applied to a substrate; and a nanostructure (10) comprising one or more metal layers grown by thin film deposition technology. Figure 1 In the illustrated embodiment, the thinned column (20) has a cross-sectional shape that varies along its length, with a conical section at its base and a cylindrical section at its top. In other embodiments, the column (20) may have a uniform cross-section along its length, as well as cross-sections of other geometries, such as rectangular, triangular, tubular, and any other regular or irregular polygonal shapes.

[0021] In one implementation, the fabrication process of the nanostructure containing a single isolated skyrmion is carried out in two steps, including: (i) Using FIB technology to thin the substrate, thereby forming pillars with an outer diameter between 150 nm and 2500 nm in the thinned material; (ii) One or more metal films are grown on the pillar of the thinned material to form a nanostructure with perpendicular magnetic anisotropy, the nanostructure having a diameter suitable for generating a single stable skyrmion on its top, for example, between 100 nm and 400 nm, preferably between 100 nm and 300 nm.

[0022] In one embodiment of the process, the thinning technique applied to the substrate is preferably a focused ion beam technique using Ga, Xe, or Ar ions.

[0023] In one embodiment of the process, the substrate is the apex of the tip of a magnetic AFM probe.

[0024] In one embodiment of the process, the substrate is a silicon wafer.

[0025] Figure 2A This is a schematic diagram of a nanostructure (10) consisting of multiple thin metal layers deposited on a substrate. In this example, the metal layers begin and end with a thicker Pt layer and include alternating layers of Pt and Co in between (shown only once for simplicity, but in this embodiment, the alternation is repeated 15 times), the thickness of which is less than that of the initial and final layers.

[0026] In one embodiment of the method, the metal thin film layer comprises: first, a Pt seed layer having a thickness greater than 0.5 nm at the bottom of the structure; followed by one or more alternating layers of Pt and Co, wherein the alternating first and last layers are Pt; and finally, a Pt capping layer having a thickness greater than 0.5 nm at the top of the nanostructure. The thickness of the remaining layers and the number of layer repetitions can be adjusted according to the size of the structure and the intended application to optimize skyrmion generation, thereby modifying the magnetic strength and linewidth (focus) of the resulting nanostructure.

[0027] In one embodiment of the process, the metal films are arranged in the same order as described above, wherein Co is replaced by Ni or Fe, and / or wherein Pt is replaced by Pd, W, Hf, or Ru.

[0028] In one embodiment of the process, the metal nanostructure is made of a single metal selected from FePt, FePd, CoPt, CoPd, GdFeCo, TbFeCo, CoGd, or any other metal known to those skilled in the art that supports skyrmion formation.

[0029] The following are illustrative, non-limiting examples of implementation schemes for the processes and products described herein.

[0030] Example 1 - Optimization of the top region of the nanostructure To illustrate preferred dimensions for implementing this disclosure, nanostructures (10) and cylindrical pillars (20) of various sizes were tested.

[0031] Figures 2B to 2C A scanning electron microscope image of the cylindrical structure as viewed from above is shown. The structure was fabricated using a focused gallium ion beam thinning technique. The thinning process resulted in the cylindrical structure being surrounded by cylindrical trenches on the substrate, and... Figures 2B to 2D The outer diameter of the cylindrical groove and the corresponding inner diameter of the structure itself are shown. Figure 2B In the middle, the inner diameter is 1000 nm, and the outer diameter is 3000 nm. Figure 2C In the middle, the inner diameter is 500 nm, and the outer diameter is 2500 nm. Figure 2D In the figure, the inner diameter is 250 nm and the outer diameter is 2250 nm. The planar spatial arrangement of these nanostructures forms a square composed of 9 nanostructures arranged in a 3×3 matrix.

[0032] Figures 2E to 2G The results of magnetic measurements obtained by atomic force microscopy with a magnetically sensitive probe are shown, known as magnetic force microscopy (MFM) measurements. Figure 2H It is by Figure 2GAn enlarged view of the area marked with a green square in Figure 3. Typically, each isolated bright circle can be associated with the formation of skyrmions, which is confirmed by magnetic amplitude and linewidth analysis (shown in the graph in Figure 3, described in the next embodiment).

[0033] Figure 2E The image shows the formation of several skyrmions within a single cylindrical structure and across all cylindrical structures. Figure 2F The image shows three isolated skyrmions forming in three different cylindrical structures, while two or more skyrmions form in the remaining cylindrical structures. Finally, Figure 2G The diagram shows the formation of seven isolated skyrmions in different structures, with two additional empty structures. Figure 2H The presence of isolated skyrmions is shown in detail. Therefore, it is demonstrated that the process described herein can generate metallic nanostructures with a single isolated skyrmion on top, the nanostructure having a diameter of 100 nm to 400 nm, preferably 200 nm to 300 nm, and more preferably about 250 nm.

[0034] Example 2 - Magnetic Amplitude Spectrum Figure 3A and Figure 3C It shows Figure 2F and Figure 2G Enlarged image, in which Figure 3B and Figure 3D The curve on the right shows the magnetic amplitude spectrum of one isolated skyrmion. For a cylindrical structure at 250 nm ( Figure 3C Of the nine nanostructures fabricated, the growth of the layer that generates skyrmions produces seven nanostructures with isolated, centrally located skyrmions and two nanostructures without skyrmions. Figure 3B The image shows the magnetic amplitude spectrum of skyrmions in a 500 nm cylindrical nanostructure, highlighting a spatial linewidth of 250 nm, while the spectrum of skyrmions generated in a 250 nm cylindrical structure is shown in the image. Figure 3D The figure shows a linewidth of 90 nm. Therefore, it is demonstrated that the linewidth and magnetic amplitude of skyrmions can be controlled using the processes and products described herein. It should be noted that the smaller the linewidth, the greater the magnetic resolution of the cylindrical structure.

[0035] Example 3 - Fabrication on the tip of an AFM probe Following an example illustrating the size optimization for generating isolated skyrmions in cylindrical nanostructures, cylindrical structures of 250 nm were fabricated on an AFM tip, as shown in Figures 4A through 4E. Figure 4A shows a scanning electron micrograph of the AFM tip. Figure 4B shows the same AFM tip after fabricating a cylindrical structure with a diameter of 250 nm; again, the structure was observed to have been fabricated using a focused ion beam (FIB). Figure 4C is a side view of the same AFM tip with the fabricated structure, and Figure 4D is a magnified view of the observed tip.

[0036] Example 4 - Application in Magnetic Microscopy After fabricating the cylindrical structure on the AFM tip, as in the previous example, a metal layer that generates skyrmions is deposited onto the AFM tip containing the cylindrical structure. A standard sample taken from a hard drive is used for magnetic AFM probe testing to verify the results. Figure 5A and Figure 5B The results of magnetic force microscopy (MFM) measurements obtained using two AFM tips are shown: Figure 5A Corresponding to the tip containing the isolated skyrmion according to this disclosure, Figure 5B This corresponds to commercially available tips. It should be noted that test results obtained with an AFM tip containing skyrmions present images with significantly more detail compared to images generated using commercially available tips. Another important point is that when the same test was performed again several months later with an AFM tip containing skyrmions, the images remained consistent. In contrast, commercially available magnetic AFM tips become unusable after a day or a few scans.

[0037] Although exemplary embodiments of the processes and products described herein have been presented in this specification, the scope of protection is not intended to be limited to the literal representation of these embodiments. Therefore, this description should not be construed as restrictive, but merely as examples of specific embodiments that keep the invention consistent with the subject matter presented herein. Those skilled in the art can readily apply the teachings presented herein to similar solutions derived solely from the scope of the claims of this application.

Claims

1. A process for fabricating nanostructures containing isolated skyrmions, characterized in that... include: (i) Using FIB to thin the substrate, thereby forming pillars with diameters between 150 nm and 2500 nm in the thinned material (20). (ii) One or more metal films are grown on the pillar (20) of the thinned material to form a nanostructure (10) with perpendicular magnetic anisotropy, the diameter of the nanostructure being between 100 nm and 400 nm, preferably between 200 nm and 300 nm.

2. The process for manufacturing nanostructures according to claim 1, characterized in that, The substrate is a magnetic AFM probe tip.

3. The process for manufacturing nanostructures according to claim 1, characterized in that, The substrate is a silicon wafer.

4. The process for manufacturing nanostructures according to any one of claims 1 to 3, characterized in that, The thinning technique applied to the substrate is preferably a FIB technique using focused ions selected from the group consisting of gallium ions, xenon ions and argon ions.

5. The process for manufacturing nanostructures according to any one of claims 1 to 4, characterized in that, Thin films are grown using physical vapor deposition (PVD) technology.

6. A nanostructure containing isolated skyrmions, characterized in that, It is produced by the process described in claims 1 to 5 and comprises a nanostructure (10) formed of multiple metal layers, the metal layers beginning and ending with a thicker first metal material layer and including alternating layers of first and second metal materials in between, the thickness of the alternating layers being less than that of the initial and final layers, wherein at least one of the first and second metal materials is a magnetic material.

7. The nanostructure according to claim 6, characterized in that, The metal thin film layer includes: a first metal material initial layer with a thickness greater than 0.5 nm; followed by one or more alternating layers of the first metal material and the second metal material; and a first metal material final layer on top of the nanostructure (10), the first metal material final layer having a thickness greater than 0.5 nm.

8. The nanostructure according to any one of claims 6 or 7, characterized in that, The first metallic material is Pt, and the second metallic material is Co.

9. The nanostructure according to any one of claims 6 or 7, characterized in that, The first metallic material is selected from the group consisting of Pt, Pd, W, Hf and Ru, and the second metallic material is selected from the group consisting of Co, Fe and Ni.

10. The use of the nanostructure according to claims 6 to 9, characterized in that, For microscopic purposes, both the thinning process and the deposition process are performed at the tip of the AFM probe.

11. The use according to claim 10, characterized in that, Used to perform atomic force microscopy and magnetic force microscopy.

12. The use of the nanostructure according to claims 6 to 9, characterized in that, Used for magnetic sensing.

13. The use according to claim 12, characterized in that, Multiple nanostructures are arranged in a plane and maintained at regular intervals to form a planar geometric arrangement, the shape of which is selected from a group consisting of approximately circles and approximately polygons.

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