Nanostructure comprising an isolated skyrmion, fabrication process therefor and use thereof in microscopy and sensing

Abstract

The present description relates to a process for fabricating a nanostructure comprising an isolated skyrmion in which a focused ion thinning technique is applied to a base material, generating a thinned structure in the shape of columns (20), followed by a technique for depositing thin metallic films on the columns (20) forming a nanostructure (10) capable of generating a single isolated skyrmion on the top thereof. The fabricated nanostructures (10) and use thereof in magnetic microscopy and magnetic sensing are also described.

Description

NANOSTRUCTURE COMPRISING AN ISOLATED SKYRMION, ITS MANUFACTURING PROCESS AND ITS USE IN MICROSCOPY AND SENSING DESCRIPTION FIELD

[0001] This description concerns the fabrication or processing of nanostructures formed by the individual manipulation of atoms, molecules, or limited groups of atoms or molecules as discrete units. This description also concerns the specific uses or applications of nanostructures for sensing. STATE OF THE TECHNIQUE

[0002] The recent discovery of magnetic skyrmions has sparked intense interest in condensed matter physics and materials science. The unique spin texture of magnetic skyrmions leads to a number of unique phenomena due to their topologically protected quantum state and the emerging electromagnetic field.

[0003] The state of the art includes some technologies for manufacturing Skyrmion-generating surfaces and their intended use, mainly for applications in low-dissipation magnetic information storage devices, but also in magnetic field sensors.

[0004] Patent document WO2017024253A1 describes a method for fabricating room-temperature stable artificial Skyrmions and Skyrmion lattices. 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 single layers of FePt, FePd, CoPt, CoPd, GdFeCo, TbFeCo) on a substrate with perpendicular magnetic anisotropy by sputtering; forming asymmetric patterns in the material layer to expose portions of the substrate; irradiating the exposed substrate with ions; removing the material layer; and finally, applying a specific magnetic field sequence to prepare the state of the Skyrmions. The result of the process is a surface that generates multiple Skyrmions at room temperature, and applications of these in magnetic memory devices, logic devices, and sensors are described.

[0005] Patent document WO2018203554A1 describes a method for manufacturing a magnetic device that generates Skyrmions at room temperature. The device is capable of generating one to three Skyrmions on structures with a substantially triangular (with sides between 150 and 800 nm), circular (with a radius of approximately 120 nm), or square (dimensions unspecified) shape. The method involves producing a plurality of nanometric point-shaped defects on a flat magnetic material by exposing the material to an electron beam. The described use for the device includes application as a magnetic memory capable of storing information and application in magnetic sensors for detecting magnetism or magnetic tracks.

[0006] Based on the aforementioned literature, techniques for fabricating nanometric structures that generate skyrmions and their application as magnetic sensors are known. However, previous techniques are based on flat magnetic substrates and have not overcome the challenges of their application in situations with particular geometry, such as those related to sensing applications where a single skyrmion is isolated, for example, in a magnetic tip of an atomic force microscopy probe (herein referred to by the English acronym AFM). BRIEF DESCRIPTION

[0007] It is one of the objectives of the present description to reveal a process for manufacturing a nanostructure that generates a single stable Skyrmion, which can be grown on different materials as a substrate, including on a magnetic tip of an AFM probe, increasing the magnetic resolution of this tip and considerably increasing the lifetime. comparison with commercial tips (coated with cobalt film). Another objective of this description is to reveal the use of this nanostructure in atomic force microscopy, with an emphasis on magnetic application, and as a nanometric sensor in different types of spatial arrangements.

[0008] The objectives of this description are achieved by a process that comprises the steps of:

[0009] roughen a material that will serve as a substrate, preferably the top material of an AFM probe magnetic tip, using a focused ion roughening technique (here referred to by the English acronym FIB - Focus Ion Beam), preferably focused Ga ion FIB, generating in the roughed material at least one column in the form of a cylindrical pillar with a diameter on a manometric scale;

[0010] grow one or more thin metallic films on the column of ground material, preferably using the physical vapor deposition technique, generating a multilayer nanostructure with perpendicular magnetic anisotropy, with said nanostructure having an approximately conical shape, capable of generating a single stable Skyrmion at its top.

[0011] The objectives of the present description are also achieved by using the aforementioned nanostructure in performing microscopy, in which the thinning and growth process is performed at the tip of an AFM probe, and the microscopy performed is magnetic force microscopy (hereinafter referred to as MFM).

[0012] The objectives of the present description are also achieved by the use of said nanostructure in carrying out magnetic sensing, in which a plurality of structures are grown on a roughened substrate, preferably a silicon substrate, said structures keeping regular distances between them, forming a planar geometric arrangement appropriate for the type of sensing intended, for example, a planar geometric arrangement that forms a circle, triangle, rectangle, pentagon, hexagon or any polygon appropriate for the intended sensing application. BRIEF DESCRIPTION OF THE FIGURES

[0013] The present disclosure is illustrated in the modalities represented in figures, as briefly described below.

[0014] Figure 1 is a schematic representation of a column of FIB-thickened base material comprising a Skyrmion-generating nanostructure deposited on top thereof, in accordance with one embodiment of the present disclosure.

[0015] Figure 2A is a schematic representation of metallic layers deposited for the formation of Skyrmion-generating nanostructure, according to one embodiment of the present disclosure.

[0016] Figures 2B-2D are scanning electron microscopy images of three 9-column planar geometric arrangements of Skyrmion-generating nanostructures, according to one embodiment of the present disclosure, while Figures 2E-2G are magnetic force microscopy images of the nanostructures of Figures 2B-2D, respectively. Figure 2H is an enlargement of a single nanostructure of Figure 2G, featuring a single Skyrmion centered at its inner diameter, according to one embodiment of the present disclosure.

[0017] Figures 3A and 3B are, respectively, magnetic force microscopy of a structure of the array shown in Figure 2F and a graph of the magnetic amplitude of that single nanostructure as a function of radial position, according to an embodiment of the present disclosure.

[0018] Figures 3C and 3D are, respectively, magnetic force microscopy of a structure of the array shown in Figure 2G and a graph of the magnetic amplitude of that single nanostructure as a function of radial position, according to an embodiment of the present disclosure.

[0019] Figure 4A is a scanning electron microscopy image of an AFM tip prior to the grinding step, according to a modality of the manufacturing process of the present description.

[0020] Figures 4B to 4D are scanning electron microscopy images from various angles of an AFM tip after deposition of a 250 nm diameter cylindrical structure on its tip, according to one embodiment of the fabrication process of the present disclosure.

[0021] Figures 5A and 5B are two Magnetic Force Microscopy images of a hard drive, generated using an AFM tip modified by an embodiment of the present process and a prior art AFM tip, respectively. DETAILED DESCRIPTION OF THE MODALITIES

[0022] This description refers to a nanostructure capable of generating a single stable Skyrmion at its tip. This description also refers to the fabrication process of this nanostructure and its uses in microscopy and sensing.

[0023] Figure 1 is a schematic representation of the main elements of the single Skyrmion generating structure, in which the structure comprises: a column (20) roughed by FIB technique applied to a base material; and a nanostructure (10) comprising one or more metallic layers grown by thin film deposition techniques. In the embodiment illustrated in Figure 1, the shape of a roughed column (20) has a cross-section variation along its length, having a conical section at its base and a cylindrical section at its top. In other embodiments, the column (20) may have uniform cross-sections along its length, and also cross-sections with other geometries, such as rectangular, triangular, tubular, and any other polygonal sections, regular or not.

[0024] In one embodiment, the process of fabricating said nanostructure comprising a single isolated Skyrmion is conducted in two steps, comprising:

[0025] (i) roughing a base material using FIB technique, forming in the ground material a column with an external diameter varying between 150 and 2500 nm;

[0026] (ii) grow one or more metallic thin films on the column of ground material, generating a nanostructure with perpendicular magnetic anisotropy, said nanostructure having a diameter between 100 and 400 nm, preferably between 100 and 300 nm. The nanostructure obtained by this process is capable of generating a single stable Skyrmion at its top.

[0027] In one embodiment of the described process, the technique for roughing said base material is preferably focused ion FIB of Ga, Xe or Ar.

[0028] In one embodiment of the described process, said base material is the top of an AFM probe magnetic tip.

[0029] In one embodiment of the described process, said base material is a silicon wafer.

[0030] Figure 2A is a schematic representation of a nanostructure (10) of multiple layers of metallic thin films deposited on a base material. In this example, the metallic layers begin and end with thicker Pt films, and present in their middle alternating layers of Pt and Co (represented only once, for simplification, but, in this modality, repeated alternately 15 times), with these alternating layers having a thickness smaller than the initial and final layers.

[0031] In one embodiment of the described process, the metallic thin film layers comprise: a first Pt seed layer, with a thickness greater than 0.5 nm, at the base of the structure; followed by one or more alternating layers of Pt and Co, the first and last of the alternating layers being made of Pt; and, finally, a final Pt buffer layer, with 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 to optimize Skyrmion generation, according to the dimensions of the desired structure and applications, thus modifying the magnetic intensity and line width (focusing) of the produced nanostructure.

[0032] In one embodiment of the process described, the layers of thin metallic films are arranged in the same order described herein, in which Co is replaced by Ni or Fe, and / or, in which Pt is replaced by Pd, W, Hf or Ru.

[0033] In one embodiment of the process described, the metallic nanostructure is constituted by a single metal, selected from the group comprising: FePt, FePd, CoPt, CoPd, GdFeCo, TbFeCo, CoGd, or any other metals that present formation of Skyrmions, readily known by a person versed in this technological area.

[0034] In what follows, examples of implementation of the process and product described will be presented, in an illustrative manner, but not restrictive of the scope of protection. EXAMPLE 1 - OPTIMIZATION OF THE TOP AREA OF THE NANOSTRUCTURE

[0035] In order to exemplify the preferred dimensions for implementing the present description, cylindrical nanostructures (10) and columns (20) with different dimensions were tested.

[0036] Figures 2B to 2C show scanning electron microscopy images of the cylindrical structures, viewed from above. The structures were prepared using the focused Ga ion grinding technique. The grinding process leaves the cylindrical structure surrounded by a cylindrical hole on the substrate. Figures 2B to 2D show the outer diameter of the cylindrical hole and the inner diameter, which is the size of the structure. In Figure 2B, the inner diameters are 1000 nm and the outer diameters are 3000 nm. In Figure 2C, the inner diameters are 500 nm and the outer diameters are 2500 nm. In turn, in Figure 2D, the inner diameters are 250 nm and the outer diameters are 2250 nm. The planar spatial arrangement of the nanostructures in these figures forms a square, composed of nine nanostructures, in a 3x3 matrix.

[0037] Figures 2E–2G show the results of magnetic measurements using atomic force microscopy equipped with a magnetically sensitive tip, known as a magnetic force microscopy measurement. Figure 2H is a magnification of the region marked with the green square in Figure 2G. Typically, each isolated bright circle can be associated with the formation of a skyrmion, which is confirmed by the magnetic intensity and line width (in the graphs of Figure 3, described in the following example).

[0038] Figure 2E shows the formation of multiple skyrmions in a single cylindrical structure and in all cylindrical structures. Figure 2F shows the formation of three single skyrmions in three distinct cylindrical structures, and in the remaining cylindrical structures, two or more skyrmions are formed. Finally, Figure 2G shows the formation of seven single skyrmions in distinct structures and two empty structures. Figure 2H shows the presence of the isolated skyrmion in detail. Thus, it is demonstrated that the process described here is capable of generating a metallic nanostructure with an isolated skyrmion at its apex, with a diameter between 100 and 400 nm, preferably between 200 and 300 nm, most preferably around 250 nm. EXAMPLE 2 - MAGNETIC AMPLITUDE PROFILE

[0039] Figures 3A and 3C show an enlargement of Figures 2F and 2G, with the magnetic amplitude profiles of one of the isolated skyrmions in the graph on the right side, in Figures 3B and 3D. For the 250 nm cylindrical structures (Fig. 3C), the growth of the layer that generates the skyrmions resulted in 7 nanostructures with isolated and centered skyrmions and 2 nanostructures without skyrmions, out of the 9 nanostructures fabricated. The magnetic amplitude profile of a skyrmion from the 500 nm cylindrical nanostructure is shown in Figure 3B, in which a spatial linewidth of 250 nm is highlighted, while the profile of the skyrmion generated in the 250 nm cylindrical structure (Fig. 3D) presents a linewidth of 90 nm. Thus, it is demonstrated that it is possible to control the linewidth and magnetic amplitude of skyrmions through the process and product described above. It should be noted that the smaller the linewidth, the greater the magnetic resolution of the cylindrical structure. EXAMPLE 3 - FABRICATION ON AN AFM TIP

[0040] After demonstrating the dimensional optimization of the cylindrical nanostructure for the generation of isolated Skyrmions, 250 nm cylindrical structures were fabricated using AFM tips, as shown in Figures 4A to 4E. Figure 4A shows a scanning electron microscopy image of an AFM tip. Figure 4B shows the same AFM tip after fabrication of the 250 nm diameter cylindrical structure; again, it can be seen that the structure was fabricated using a localized ion beam (FIB). Figure 4C is a side view of the same AFM tip with the fabricated structure, and Figure 4D is a magnification of the observed tip. EXAMPLE 4 - APPLICATION IN MAGNETIC FORCE MICROSCOPY

[0041] After fabricating the cylindrical structures on AFM tips, as described above, skyrmion-generating metallic layers were deposited on the AFM tips with the cylindrical structures. The results were tested using a standard sample for testing magnetic AFM tips, on a piece of a hard drive. Figures 5A and 5B show the results of Magnetic Force Microscopy (MFM) measurements for the two AFM tips. Figure 5A shows a tip with isolated skyrmion, as described herein, and Figure 5B shows a commercial tip. It is noteworthy that the measurement using the AFM tip with skyrmion presents a more detailed image compared to the image generated with the commercial tip.Another important point to highlight is that the same measurement with the AFM tip with the skyrmion was performed months later and the image continues to be performed with the same consistency, while the commercial magnetic AFM tip becomes unusable after 1 day of use or a few scans.

[0042] Although exemplary modalities of products and processes Although the described materials have been presented in this report, it is not intended that the scope of protection be limited to their literal meaning. Therefore, the description should not be interpreted as limitative, but merely as examples of particular embodiments that maintain a unity of invention with the subject matter presented herein. A person skilled in the art may readily apply the teachings presented herein to analogous solutions arising therefrom, limited only by the scope of the claims of this application.

Claims

CLAIMS 1. Process for manufacturing a nanostructure comprising an isolated Skyrmion, characterized by comprising: (i) roughing a base material using the FIB technique, forming a column (20) with a diameter between 150 and 2500 nm in the roughed material; (ii) growing one or more thin metallic films on the column (20) of ground material, generating a nanostructure (10) with perpendicular magnetic anisotropy, said nanostructure having a diameter between 100 and 400 nm, preferably between 200 and 300 nm.

2. The nanostructure fabrication process of claim 1, wherein said base material is the top of an AFM probe magnetic tip.

3. The nanostructure manufacturing process of claim 1, wherein said base material is a silicon wafer.

4. Nanostructure manufacturing process according to any one of claims 1 to 3, characterized in that the grinding technique of said base material is preferably FIB with focused ions selected from the group comprising Ga, Xe and Ar ions.

5. Nanostructure manufacturing process according to any one of claims 1 to 4, characterized in that the growth of thin films is done by physical vapor deposition technique.

6. Nanostructure comprising an isolated Skyrmion, characterized by being produced by the process of claims 1 to 5, and by comprising a nanostructure (10) of multiple metallic layers that begin and end with thicker films of a first metallic material, and present in their middle alternating layers of a first metallic material and a second metallic material, these alternating layers having a thickness smaller than the initial and final layers, in which at least one of the first and second metallic material is a magnetic material.

7. Nanostructure, according to claim 6, characterized by the fact that the layers of metallic thin films comprise: an initial layer of the first metallic material, with a thickness greater than 0.5 nm; followed by one or more alternating layers of the first metallic material and the second metallic material; and a last layer of the first metallic material, with a thickness greater than 0.5 nm, on top of the nanostructure (10).

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

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

10. Use of the nanostructure of claims 6 to 9, characterized in that it is for performing microscopy, in which the grinding and deposition process is carried out on the tip of an AFM probe.

11. Use, according to claim 10, characterized by being for performing atomic force microscopy and magnetic force microscopy.

12. Use of the nanostructure of claims 6 to 9, characterized by being for performing magnetic sensing.

13. Use, according to claim 12, characterized by the fact that a plurality of nanostructures are provided in a plane, keeping regular distances between them, forming a flat geometric arrangement with a shape selected from the group comprising approximately circular shapes and approximately polygonal shapes.

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