WO2017178704A1

WO2017178704A1 - Magnonic element and related method

Info

Publication number: WO2017178704A1
Application number: PCT/FI2017/050263
Authority: WO
Inventors: Sebastiaan VAN DIJKEN; Ben VAN DE WIELE
Original assignee: Aalto-Korkeakoulusäätiö; Universiteit Gent
Priority date: 2016-04-12
Filing date: 2017-04-11
Publication date: 2017-10-19
Also published as: FI20165312A

Abstract

The invention relates to a magnonic element and a method of redirecting spin waves (301, 302, 303). The element comprises a magnonic layer (35) capable of conveying spin waves (301, 302, 303). In addition, there is provided at least one input port (37) for coupling spin waves (301, 302, 303) to the magnonic layer (35), and at least one output port (38) for coupling spin waves (301, 302, 303) out of the magnonic layer (35). According to the invention, there is provided at least one magnetic anisotropy boundary (36AB, 36BC) in the magnonic layer for redirecting spin waves (301, 302, 303) propagating within the magnonic layer (35) between the at least one input port (37) and the at least one output port (38). The invention allows for providing new kinds of magnonic devices.

Description

Magnonic element and related method

Field of the Invention

The invention relates to magnonic elements, i.e. elements taking advantage of magnetic waves known as spin waves. The element can be used in electronic devices utilized in information and communication technology, for example.

Background of the Invention

Modern information and communication technology (ICT) has experienced vast advancements during recent decades thanks to miniaturization in semiconductor electronics and progress in optical (photonic) technologies. Severe challenges are, however, foreseen in nanoelectronics when further downscaling (following Moore's law) leads to more and more heat dissipation per unit area. Therefore, ICT demands new materials for post-silicon computing. Novel technologies and complementary logic circuits need to be developed to overtake special-task data processing that challenges

semiconductor-based processors (e.g. pattern recognition and image processing). High- speed optical data processing cannot meet this demand as it does not allow for circuits with the ultrasmall feature sizes known from semiconductor technology due to the relatively large photonic wavelengths. Moreover, although powerful schemes for computing have been discussed since decades, photonic materials and devices have not yet reached a mature state for computing purposes. One major obstacle is the lack of optical components for nanoscale interconnections in existing electronics.

To fulfill future requirements for data transmission and processing rates with low power consumption, a paradigm shift away from purely charge-based electronics is needed. Recently, post-silicon computing with spins and magnets has been identified as a promising route. Here, sequential data processing is still relevant and might limit the bandwidth. Collective spin wave excitations (magnons) in tailored magnets go beyond this approach and offer low power parallel data processing in cellular networks, thereby optimizing computationally demanding tasks like image processing and speech

recognition. Interestingly, contrary to light waves, the wavelength of spin waves matches the nano manufacturing space scales at GHz frequencies. Brandl F, et al. 2014 discusses broadband spin wave spectroscopy measurements on a system that comprises a BaTi0₃ substrate and a magnetostrictive CoFeB layer. Excitation and probing of spin waves are performed at the same location of the CoFeB layer. The document does not disclose routing of spin waves in the CoFeB layer. Propagation of spin waves in materials has been studied for several years. In currently disclosed approaches, some of which are introduced below, spin waves are mainly routed through long magnetic strip-lines with reduced cross-sectional dimensions.

CN 105070824 A describes a spin wave conductive wire network based on a magnetic domain wall between different magnetic domains. In the proposed solution, the spin waves propagate along the domain walls, which is a well-known phenomenon. A solution, where total internal reflections are utilized for confining spin waves to a single domain, is disclosed in CN 104767020 A.

Bance, S. et al. 2008 investigate spin wave propagation through a bended permalloy strip in backward- volume spin wave modes, i.e., modes in which the magnetization is aligned with the propagation direction. With a step-like excitation a broad spectrum of spin waves is excited. Also Xing, X. et al. 2013 disclose numerical simulations on a permalloy nanostrip in backward- volume spin wave modes.

Tkachenko, V. S. et al. 2012 discuss spin wave propagation in curved, cylindrical waveguides, still in backward- volume modes. In that solution, changes of spin wave properties are only negligible when R » λ, with R the radius of curvature and λ the spin wave wavelength. This limits the practical use of the solution.

Vogt, K. et al. 2012 disclose experimental spin wave propagation through an S-shaped permalloy- Au bilayer strip for Damon-Eshbach modes, i.e., magnetization being perpendicular to the propagation direction, through the application of a DC current in the Au layer. This technique allows spin waves to better propagate through bends without changing properties. A drawback of the approach is that it suffers from serious Joule heating due to the large current densities (order 10¹¹ A/m²) applied through the Au layer. Moreover, a resulting Oersted magnetic field can influence the magnetization dynamics in neighboring magnetic strips. Both these drawbacks hinder miniaturization. Vogt, K. et al. 2014 show how spin waves are routed from one input line to one of two output arms of a Y-shaped structure. Again, the Y-shaped structure is covered with Au and a DC current passes through the Au layer from the input line to an output arm of choice, saturating the magnetization underneath perpendicular to the local strip axis. In the other arm, the magnetization remains parallel to the axis. The spin waves in the permalloy follow the direction set by the DC current in the Au. Disadvantages of this approach include Joule heating, stray fields, and reduced range of opening angles.

Garcia-Sanchez, F. et al. 2014 present numerical simulations of spin wave propagation along domain walls in an out-of-plane magnetized strip with Dzyaloshinskii-Moriya interaction. The strip is bended and has over its complete length one or more parallel domain walls of the Neel type. The spin waves are confined within the domain walls where the propagation direction is perpendicular to the local magnetization. Bends with a large radius of curvature can be taken. A drawback of this approach is that it is difficult to stabilize domain walls over the complete strip length independent of its geometry. This is seen e.g. in the large radius of curvature of bends required.

In summary, in the strip-line approaches discussed above, spin waves have optimal propagation properties when the strip-line is magnetized perpendicular to its axis. This requires in general large global magnetic fields and hinders miniaturization of the technology. Moreover, in current approaches, either the properties (wavelength, propagation speed, etc.) of spin waves change when propagating through bended strip-lines and/or there are practical constraints for implementations, such as Joule heating, stray fields and/or large radius of curvature required. Spin wave property changes are unwanted as they may damage signal integrity.

Furthermore, the strip-line approach has a general disadvantage that spin wave routing through strip-lines is not flexible as it has a fixed input- and output preset by its geometry. This hinders routing and multiplexing of spin wave signals, and therefore the

implementation of practically operating magnonic components.

Thus, there are no convincing materials or nanotechnology platforms to flexibly interconnect spin wave based devices in active magnonic networks. Thus, there is a need for improved magnonic elements. Summary of the Invention

It is an aim of the invention to overcome at least some of the abovementioned

disadvantages and to provide a magnonic element with improved signal routing

capabilities as concerns e.g. the radius of turning, changing of wave properties or heating of components.

A particular aim is to provide an element capable of connecting multiple magnonic input ports with any number of magnonic output ports, or vice versa, in a controlled manner. An exemplary target application is a spin wave multiplexing and/or demultiplexing element.

One aim of the invention is to provide a novel method of routing spin waves. One particular aim of the invention is to provide spin wave routing solutions that do not require the utilization of strip lines as magnonic waveguides, therefore overcoming the problems related to strip lines.

The invention is based on utilizing anisotropic propagation properties of spin waves for controlling their routes in a material. The inventors have observed that a magnetic anisotropy boundary contained in a magnonic layer, i.e. material layer capable of conveying spin waves, is capable of redirecting spin waves propagating across the anisotropy boundary.

Thus, the invention provides a magnonic element comprising a magnonic layer capable of conveying spin waves, at least one input port for coupling spin waves to the magnonic layer, and at least one output port for coupling spin waves out of the magnonic layer. The magnonic layer comprises at least one magnetic anisotropy boundary for redirecting spin waves propagating within the magnonic layer between the at least one input port and the at least one output port.

The invention also provides a method of redirecting spin waves in a magnonic layer capable of conveying spin waves. In the method, a spin wave is coupled to the magnonic layer at a first location such that the spin wave propagates to a magnetic anisotropy boundary contained in the magnonic layer, the spin wave is redirected within the magnonic layer due to said at least one magnetic anisotropy boundary, and the redirected spin wave is coupled out of the magnonic layer at a second location. Finally, the invention provides a new use for magnetic anisotropy boundaries.

More specifically, the invention is defined by what is stated in the independent claims.

The invention provides significant advantages. In particular, redirection of a spin wave at magnetic anisotropy boundaries keeps the frequency properties of the wave intact, whereby the design of practical signal- carrying components is much easier. Thus, the propagating waves can preserve the analog or digital data encoded therein. The element is simple to operate as no external bias fields are required. Moreover, the radius of curvature of wave turns is extremely short, in particular when the magnetic anisotropy changes abruptly, i.e. the magnetic anisotropy boundary is narrow. An important practical advantage of the invention is that no strip line formations are required, whereby active control of wave routes is possible and manufacturing of the elements is relatively simple. This allows for designing of magnonic elements with new functionalities and further new magnonic data processing devices.

One additional advantage of the present invention is that it allows the spin waves to propagate in Damon-Eshbach mode, i.e., perpendicular to magnetization of the magnonic layer. This is of significance because the propagation speeds in Damon-Eshbach mode are superior to those of backward- volume spin wave modes. Also, in general, spin waves can propagate over much larger distances in Damon-Eshbach mode compared to backward- volume spin wave mode. By controlling local magnetization of the magnonic layer, the propagation direction can be controlled.

The present invention allows for the use of several magnetic anisotropy boundaries for causing the spin waves to be redirected not only once but several times on their way between the input and output ports.

Structures are also presented herein that are capable of conveying several parallel spin waves in a single uniform magnonic layer. In addition, a controlled alteration of the properties of the magnonic layer, notably the location of the at least one anisotropy boundary with respect to the input and output ports is described for providing controllable routing of the waves between the ports.

In some embodiments, the magnonic element comprises a ferroelectric layer having a ferroelectric domain structure comprising at least one domain wall and the magnonic layer is magnetoelectrically coupled to the ferroelectric layer. The domain structure of the ferroelectric layer is adapted to induce the magnetic anisotropy boundary or boundaries in the magnonic layer. This has the advantage that ferroelectric domain walls are capable of inducing very narrow magnetic anisotropy boundaries whereby spin waves crossing the anisotropy boundary will make a turn such that their properties are conserved. However, suitable magnetic anisotropy boundaries can be induced to the magnonic layer also by other means than coupling to a ferroelectric layer. Examples of such techniques include ion beam irradiation and film growth on pre-patterned substrates. Also other lithography- defined structures can be used. Magnetoelectric coupling of the layers can be ensured by a structure where the magnonic layer is a ferromagnetic layer, ferrimagnetic layer or a magnetic layer exhibiting another type of magnetic order superimposed on the ferroelectric layer such that it overlaps said at least one domain wall. Thus, in preferred embodiments, the magnonic layer, such as a ferromagnet, and a ferroelectric material are combined to form a ferroelectric- ferromagnetic bilayer. Using this kind of bilayer structure, the resulting ferromagnetic domain pattern fully correlates with the ferroelectric domain structure and magnetic domain walls are strongly pinned onto the ferroelectric domain boundaries by abrupt, typically 90° rotations of magnetic anisotropy. In such bilayer, the ferroelectric domain structure in the ferroelectric layer determines the local magnetic anisotropy direction in the magnonic layer. As magnetic anisotropy changes occur on space scales smaller than the spin wave wavelength, a variation in the spin wave propagation direction comes without changes in spin wave properties or with only minimal changes in properties.

Additionally, control of the location of the magnetic anisotropy boundary is possible by using an electric field coupled to the ferroelectric layer. Thus, signals can propagate along parallel channels through the device and input-output selection can be flexibly controlled by electric fields. Spin wave properties are not affected due to electric field control. By tuning the ferroelectric domain pattern with voltages, the spin wave propagation is controlled. This unique feature cannot be attained by magnetic-field controlled magnonics because local manipulation of the magnetization state (i.e. spin wave propagation direction) is hindered by the uniform and long-range nature of applied magnetic fields.

In some embodiments, the magnonic layer comprises, or may even consist of, at least two neighboring magnetic domains with uniaxial magnetic anisotropy in each of the domains. The anisotropies are arranged at different angles, preferably perpendicular to each other, whereby the anisotropy boundary allowing the spin wave redirection is located between them. The input and output ports are coupled to different magnetic domains, where the spin waves propagate perpendicular to the corresponding magnetization and a rapid 90° turn occurs at the magnetic anisotropy boundary or boundaries. In particular, the anisotropy boundary is arranged at a 45° angle with respect to the Damon-Eshbach propagation direction of the spin waves. This kind of symmetric structure is optimal for redirecting the spin waves.

In some embodiments the magnonic layer is divided into domains where the spin waves can propagate essentially the whole path between an input and an output port in Damon- Eshbach mode.

The magnonic layer preferably comprises a magnonic crystal capable of laterally confining the propagation of spin waves. In particular, the magnonic crystal may comprise an antidot structure, magnetic dot structure or bicomponent structure capable of laterally confining spin wave propagation. In particular, the crystal may comprise a square lattice, such as an antidot lattice one having similar antidot structure in both lateral dimensions of the magnonic layer. In a still further embodiment, the magnetization of the magnonic layer in the magnetic domains are aligned along the orthogonal main axes of the square lattice. The anisotropy boundary or boundaries are preferably aligned diagonally with respect to the magnonic crystal, facilitating the laterally confined propagation of the spin waves before and after a 90° turn.

In some embodiments, there are provided two or more magnetic anisotropy boundaries for redirecting the spin waves at least twice between the input and output ports. The domain walls can be arranged parallel to each other such that a magnetic anisotropy boundary redirects the spin wave by 90° and a second domain anisotropy boundary redirects it again by 90° to its original propagation direction. Practical uses taking advantage of this setup are described later. This setup is particularly useful in combination with embodiments where the location of the anisotropy boundaries can be changed laterally such as in a bilayer structure as herein described.

In some embodiments the number of input ports, output ports or both, i.e. the number of locations where the spin waves are coupled to or from the magnonic layer, is two or more. This, together with anisotropy boundary location control, allows for designing new kinds of spin wave routing elements, such as multiple parallel magnonic signal routers and magnonic signal (de)multiplexers.

Such designs are also possible where the signal is routed along different paths between a single input and output port pair. For example, spin waves can be routed along one shorter path and a second longer path in order to provide a delay to the signal carried by the spin wave.

Next, selected embodiments of the invention and advantages thereof are discussed in more detail with reference to the attached drawings.

Brief Description of the Drawings

Figs. 1 A and IB illustrate in a cross-sectional view and perspective view a bi-layer structure that can be used in embodiments of the invention.

Fig. 1C illustrates the abrupt change of magnetic anisotropy in a magnonic layer induced by magnetoelectric coupling to a ferroelectric layer. The magnetic anisotropy boundary in the magnonic layer pins a magnetic domain wall.

Fig. 2A illustrates an element according to one embodiment of the invention with a continuous magnonic layer.

Fig. 2B illustrates an element according to one embodiment of the invention with an antidot magnonic layer.

Figs. 3A and 3B illustrate an electric-field-controlled spin wave signal routing element according to one embodiment of the invention in two different routing states.

Figs. 4A and 4B illustrate an electric-field-controlled spin wave signal multiplexing element according to one embodiment of the invention in two different multiplexing states.

Figs. 5A-F show simulated spin wave propagation through an antidot magnonic layer with diagonal magnetic stripe domains at frequencies of 8.9, 10.4, 11.3, 12.0, 12.6 and 13.7 GHz, respectively. Detailed Description of Embodiments

Definitions

The term "magnonic layer" refers to a material layer which is capable of conveying spin waves, i.e. a material layer in which spin waves can propagate. Ferromagnetic and ferrimagnetic layers are examples of magnonic layers, but there are also other magnetic materials with a different type of magnetic order that are suitable for the present use, either in combination with a ferroelectric underlayer (in a bi-layer structure) or as such. The layer can have any shape. Typically it is provided as a film on a substrate, for example. "Lateral" refers to the plane of propagation of the magnetic waves in the magnonic layer.

The term "domain" (like in "(ferro)magnetic domain" or "ferroelectric domain") refers to a region of material in which a particular property of interest (magnetization or electric polarization, respectively) is spatially uniform (aligned in a uniform direction). A "domain wall" (like in "(ferro)magnetic domain wall" or "ferroelectric domain wall") is an interface between two different domains, where the property of interest (magnetization or electric polarization, respectively) makes a transition (change of orientation) from one state to another. The width of a domain wall is defined as the distance over which the transition essentially takes place.

"(Magnetic) anisotropy boundary" refers to a region, where the direction of magnetic anisotropy of the material changes locally. In the geometries herein presented, magnetic domain walls and anisotropy boundaries are overlapping.

"Magnonic crystal" refers to a structure capable of laterally confining the propagation of spin waves, typically by a periodic array of material discontinuities provided therein, typically in two dimensions. The magnonic crystal may comprise an antidot array (also "antidot lattice") comprising a periodic array of perforations (holes), fabricated by lithography, for example. The perforations may comprise e.g. circular or square holes in a two-dimensional regular array shape. Alternatively, the magnonic crystal can comprise an ordered arrangement of nanostructures made out of two or more different materials (bicomponent array) or (nano)magnets (magnetic dot array). As an alternative to two- dimensional periodic structures of discontinuities, the magnonic crystal can comprise a one-dimensional lattice of wires or trenches.

"Plane (spin) wave" refers to a spin wave, which is not localized in the direction perpendicular to its propagation direction, as opposed to a confined spin wave propagating in an antidot lattice, for example.

"Redirecting" of spin waves refers to a process where the propagation direction of spin waves changes. In particular, the term covers 90° changes of propagation direction, but the change can be also smaller, for example 5° or more. In layer geometries where the magnonic layer is magnetized in the lateral plane, the redirection takes place also in the lateral plane.

"Input port" is understood in a broad sense covering both pathways of externally produced spin waves to the magnonic crystal and internal sources of spin waves coupled to the magnonic crystal. Likewise, an "output port" covers pathways of spin waves out of the magnonic crystal and internal terminals or drains of spin waves. Exemplary bi-layer structure

Figs. 1A and IB show schematic representations of a ferroelectric-magnonic bilayer structure 11, 15 that can be used as a basic structure of the present element. The bilayer comprises a ferroelectric layer 11, comprising two domains 11 A, 1 IB and a magnonic layer 15 superimposed on the ferroelectric layer 11. A ferroelectric domain wall 12 is located between the domains 11A, 1 IB. Magnetoelectric coupling of the two layers 11, 15, such as via strain transfer at the interface between them, induces a magnetic anisotropy in the magnonic layer 15, which changes abruptly in direction, strength and/or symmetry at the ferroelectric domain wall 12, creating a magnetic anisotropy boundary 16 in the magnonic layer 15 on top of the ferroelectric domain wall 12. The anisotropy affects the propagation properties of spin waves 10A, 10B within the magnonic layer 15.

Fig. IB shows an exemplary bilayer structure in perspective view. The ferroelectric layer 11 comprises several domains with orthogonal polarization direction (arrows and dots) between neighboring domains. Due to the magnetoelectric interaction between the layers 11, 15, the same domain pattern (arrows) is "imprinted" into the magnonic layer 15. Thus, an anisotropic magnetization pattern with neighboring zones of perpendicular magnetization and anisotropy boundaries between them, is produced. In this example, the polarization of the ferroelectric domains is aligned along the elongated in-plane axis of the ferroelectric crystal lattice, such as the tetragonal BaTi0₃ lattice, and it rotates by 90° at the domain boundaries. Via strain transfer and inverse magnetostriction, uniaxial anisotropy is induced in the magnonic layer 15.

One of the advantages of this concept is the ability to imprint ferroelectric stripe domains into a magnonic layer, providing elongated magnetic domains that are separated by perfectly straight magnetic domain walls. For systems with 90° in-plane rotations of ferroelectric polarization, the induced magnetic anisotropy is uniaxial and rotates by 90° at ferroelectric domain walls. Since the width of ferroelectric domain walls is restricted to only a few nanometers, the induced magnetic anisotropy boundaries in the magnonic layer can be considered as abrupt compared to the width of the magnetic domain walls. Fig. 1C illustrates this abrupt change in magnetic anisotropy. The width of the pinned magnetic domain wall may range from a few nanometers to more than 1000 nm, such as 5 - 500 nm, and depends on the strength of the induced magnetic anisotropy.

In a bi-layer structure of the above kind, for example, an electric field can be used to change the domain structure of the ferroelectric layer and therefore the location of the magnetic anisotropy boundary or boundaries of the magnonic layer. Thus, in some embodiments, there are provided means for applying an electric field over the ferroelectric layer so as to allow for a controlled redirection of the spin waves between the input and output ports. In particular, the electric field can be applied by providing a voltage over the ferroelectric layer.

Next, several embodiments that can take advantage of the bi-layer structure and their magnetoelectric coupling explained above are described. Redirection of plane spin waves

Fig. 2A shows a magnonic layer 25 placed on top of a ferroelectric sublayer 21 with one ferroelectric domain wall 26FE located diagonally in the sublayer 21 and defining two ferroelectric domains, i.e., a first ferroelectric domain 21A and a second ferroelectric domain 2 IB. The domain wall 26FE induces a magnetic anisotropy boundary 26FM and two magnetic domains 25A, 25B in the magnonic layer at a corresponding location.

Direction of magnetization niA in the first magnetic domain 25 A is perpendicular to the direction of magnetization !¾ in the second magnetic domain 25B. In this kind of extended thin film geometry no lateral confinement of the spin waves exist, i.e., the spin waves are plane waves. Spin waves are most dispersive when propagating perpendicular to the local magnetization (Damon-Eshbach direction). Further, the anisotropy boundary 26FM is located at a 45° angle with respect to that direction and the magnetic anisotropy rotates abruptly by 90°. Therefore, a plane wave 20A propagating in the first domain 25 A to the anisotropy boundary 26FM takes an abrupt 90 degree turn, continuing as a redirected plane wave 20B in the second domain 25B.

The embodiment illustrated in Fig. 2A makes it possible to redirect plane spin waves by 90° without changing their properties. To be noted is that the redirection takes place in absence of large magnetic fields conventionally used to control spin wave propagation direction.

According to a further embodiment, an electric field (voltage) is coupled over the ferroelectric layer 21 for shifting the ferroelectric domain wall 26FE and magnetic anisotropy boundary 26FM location, i.e. to change the location at which 90° turns of spin waves take place.

Redirection of laterally confined spin waves

Fig. 2B shows another embodiment with a magnonic layer comprising an antidot lattice placed on top of a ferroelectric sublayer again with a ferroelectric domain wall 260FE separating two ferroelectric domains 210, 210B, and therefore defining a magnetic anisotropy boundary 260FM and two magnetic domains 25 OA, 250B in the magnonic layer. Again at the magnetic anisotropy boundaries, spin waves take a 90° turn. Due to the antidot geometry, propagating spin waves 23 OA, 240 A are confined perpendicular to their propagation direction, both in the first domain 25 OA before redirection at the magnetic anisotropy boundary 260FM and in the second domain 250B. Thus, parallel signal lines through the magnonic crystal are defined. The shape of the signal lines is determined by the rows and columns of the antidot lattice and the location of the magnetic anisotropy boundary, because at the anisotropy boundary spin waves propagating along rows

[columns] of the antidot lattice take a rapid 90° turn and continue propagating along the columns [rows] of the magnonic crystal 250. The embodiment of Fig. 2B has the same benefits as that of Fig. 2A, i.e., keeping the properties of redirected spin waves unchanged and not needing external magnetic fields, and additionally allows for two or more parallel spin wave signals in a single material layer to take 90° turns. Crosstalk between parallel signal lines can be minimized by tailoring the parameters of the magnonic crystal and/or working frequency, aiming at minimizing propagation in the direction parallel to the magnetization. Throughput can be maximized by tailoring the parameters of the magnonic crystal and/or working frequency aiming at a maximal propagation speed in the direction perpendicular to the magnetization. According to a preferred embodiment, the magnonic antidot lattice 250 has a square periodicity for holes therein. Further, according to a preferred embodiment, the orientation of the antidot lattice is such that the lattice axes correspond with the magnetic anisotropy directions in the magnonic crystal 210. The holes introduce an additional shape anisotropy in the magnonic layer. In such magnonic crystals spin wave propagation properties are dictated by geometrical and material parameters, typically giving rise to dispersion diagrams containing band gaps, i.e. frequencies at which spin wave propagation is prohibited. In one embodiment, there is a band gap in the direction parallel to

magnetization at the frequency used, whereby crosstalk between parallel signals propagating perpendicular to the magnetization is minimized. Again, an electric field can be coupled over the ferroelectric layer 210 for shifting the ferroelectric domain wall 260FE and magnetic anisotropy boundary 260FM location, i.e. to change the locations at which 90° turns of the parallel spin waves take place.

Parallel spin wave router

In some embodiments, the element is a magnonic routing element provided with at least two input ports and at least two output ports, and wherein the ferroelectric domain structure is adjustable to guide spin waves along different paths between different pairs of input and output ports.

Figs. 3A and 3B illustrate an element capable of routing parallel spin wave signals using electric field control. The ferroelectric layer 31 has two ferroelectric domain walls 36AB, 36BC, dividing the ferroelectric layer 31 and the antidot lattice 35 on top of it into three domains 31 A, 3 IB, 31C and 35A, 35B, 35C, respectively. At each magnetic anisotropy boundary, parallel spin wave signals 301, 302, 303 take 90° turns, and at each domain 35 A, 35B, 35C, the antidot array facilitates the propagation of the spin waves perpendicular to the magnetization of the crystal along the dashed paths shown. The element has N input ports 37 (herein 3 pes) and M > N output ports 38 (herein 7 pes). The ports 37, 38 are arranged on outer boundaries of a magnonic crystal 35 which is superimposed on a ferroelectric sublayer 31 (for clarity reasons, the antidot lattice 35 is marked with dots only partly). The element allows to route N input signals from input ports i (i = 1...N) to M output ports A + j (j = 1 . . . M). The offset A is electrically controlled by the width of the central ferroelectric domain

31B/31B', by changing the DC voltage V, V (electric field) applied over the ferroelectric layer 31/31 ' (voltage V or V can also equal to zero in some state). The width of the central magnetic domain 35B/35B' is changed correspondingly. This width determines which set of output lines the spin waves are routed to. Thus, the signals 301, 302, 303 are routed to new paths, appearing as signals 301 ', 302' and 303', and directed to different output ports 38. In the example of Figs. 3A and 3B, there is a two port shift because of the voltage change from V to V, i.e., A = 1 in Fig. 3A and A = 3 in Fig. 3B.

Opposite working direction is equally possible, i.e. signals can be routed from a larger number of ports to a smaller number of ports using the same principle. The embodiment of Figs. 3 A and 3B allows for routing parallel spin wave signals in a flexible and controllable way. The parallel spin wave router has applications in highly parallel computing devices similar to conventional Graphics Processing Units (GPUs).

Spin wave (demultiplexer

In some embodiments, the element is a magnonic multiplexing or demultiplexing element comprising a plurality of input ports or a plurality of output ports, respectively, and wherein the ferroelectric domain structure is adjustable to guide spin waves from a selected input port to a single output port or from a single input port to a selected output port.

Figs. 4A and 4B illustrate an electric-field-controlled spin wave (de)multiplexer. The device has N input ports 47 (herein 6 pes) and one output port 48. Otherwise the layer and domain structures are similar to those of Fig. 3A and 3B. Again, electric fields, applied by voltage V, V over the ferroelectric layer 31, control the width of the central ferroelectric domain 3 IB and the central magnetic domain 35B. This width determines which input port 47 is connected to the output port 48, i.e., the pathway of the signal 40, 40'.

The embodiment of Fig 4A and 4B can be used as a multiplexer able to implement sequential multiplexing approaches. If the functions of the ports 47, 48 are interchanged, the propagation direction of the signal is the opposite and an electric-field-controlled spin wave demultiplexer is achieved. Switching frequency is determined by the speed at which the width of the ferroelectric domain 3 IB can be controlled. The properties and advantages of the previous embodiments with antidot magnonic crystals apply here. Common considerations

Next, some features applicable to all embodiments are discussed. The features can be freely combined also with each other.

The magnonic layer may comprise a ferromagnetic material, e.g. Co, Fe, Ni or an alloy containing one or more of these materials and others. One specific example of suitable materials is CoFeB. There are also many other ferromagnetic materials that suit for the present use. The magnonic layer may also comprise a ferrimagnetic material or a material with another-type of magnetic order. The ferroelectric material may comprise e.g. BaTi0₃, PbTi0₃, LiTa0₃, lead zirconium titanate (PZT), triglycerine sulfate (TGS), or

polyvinylidene fluoride (PVDF). As shown above, the ferroelectric and magnonic materials can be arranged in a layer structure where it is not the lateral shape of the layers and/or external magnetic fields, but their internal domain structure, and optionally the magnonic crystal, that determine the paths of the spin waves. This approach significantly differs from previous strip-line approaches, for example. Either single-frequency or multi-frequency spin wave signals are possible. The

frequency/frequencies may be selected e.g. from the range of 1 - 100 GHz, in particular 5 - 20 GHz, such as 8 - 15 GHz. The signals can represent analog or digital data.

The magnonic crystal is for example an antidot lattice with a square lattice with a hole periodicity of 100 - 800 nm, in particular 200 - 500 nm, and hole size of 20 - 300 nm, in particular 50 - 200 nm. The lengths of the signal paths between the input and output ports can be for example 1 - 100 μιη, in particular 1 - 20 μιη. The number of turns in each signal path can be one, two or more, such as 3 - 10. Typically, the turns are 90 degrees turns, but other, in particular lower angles are possible too. The input and output ports can comprise specific zones on the lateral boundary or surface of the magnonic layer where other magnonic elements are connected or can be connected in order to in-couple or out-couple the waves to the magnonic layer, respectively. The locations of the ports are designed together with the location(s) of the anisotropy boundary or boundaries in order to provide the intended operational function for the element. In preferred embodiments, each turn of spin waves within the magnonic layer is based on crossing a magnetic anisotropy boundary, i.e. the whole propagation path of waves between the input and output ports is defined by the magnetic properties of the element. However, it is not excluded that some other mechanism is used to cause some of the turns.

The domain structures introduced above are only examples of possible structures. By changing the geometry of the domains, signal paths can be changed and also new kinds of functional elements designed. Parallel domain walls provide for a simple and easily voltage-controllable solution. However non-parallel domain walls are possible too. For example, with two or more non-parallel domain walls, such as perpendicular domain walls, one can implement a routing or (de)multiplexing design where the input and output ports are located on the same side of the element.

The coupling mechanism between the ferroelectric layer and the magnonic layer can be strain transfer, potentially using inverse magnetostriction, but the concept can be extended to other magnetoelastic coupling mechanisms. It should be noted that no external bias magnetic fields are neither needed nor preferably used. However, it is generally not excluded that a magnetic bias field is used as an additional means for changing the propagation direction of the spin waves and/or the angle of turns of the spin waves.

Further, in all embodiments, there may be provided a controller (not shown) functionally connected to the element for adjusting the ferroelectric domain structure in order to change the signal paths in the element. In particular, the controller can be a voltage controller capable of changing the voltage (electric field) applied over the ferroelectric layer. The voltage can be applied for example as a DC voltage or a voltage pulse, depending on the application. This way, a dynamic spin wave routing, multiplexing or demultiplexing action between the at least one input port and said at least one output port can be achieved. For coupling the voltage, separate electrodes can be used on different sides of the ferroelectric layer. However, it is also possible to use at least the magnonic layer as one of the electrodes. Also configurations, where the electrodes are placed on the same side of the ferroelectric layer, i.e. lateral electrode configurations, are possible.

Simulations

Micromagnetic simulations were carried out to demonstrate the propagation of the spin waves in the bi-layer structure used in the exemplary embodiments above and therefore the feasibility of the invention in practice.

The simulated system comprised a magnonic layer on top of a ferroelectric layer with in- plane polarized domains. The magnonic layer consisted of a square antidot lattice with 400 nm x 400 nm periodicity and square holes with sizes 75 nm x 75 nm. The magnonic layer was 22 nm thick. Material parameters for the magnonic layer were: saturation

magnetization M_sat = 1.7 x 10⁶A/m, exchange stiffness k_ex = 2.1 x 10^~nJ/m, induced anisotropy strength Ku = 5 ^x 10⁴ J/m, and damping constant a = 0.005. The lattice had 32x32 periods, i.e. total size of computational domain is 12.8 μιη^χ 12.8 μιη. The ferroelectric sublayer induced a uniaxial magnetic anisotropy with 90° axis rotation between adjacent domains. The ferroelectric stripe domains were oriented with a 45° angle with respect to the antidot lattice principle axes (see. Fig. 2B). This way, the induced uniaxial magnetic anisotropy aligned with one of the principle axis of the antidot lattice. No external bias field was applied. Under this condition, the magnetization aligns along the uniaxial magnetic anisotropy axis. To exclude finite size effects, periodic boundary conditions were used in both in-plane directions. The sample was discretized with 6.25 nm x 6.25 nm x 22 nm cells.

To excite spin waves, a sinusoidal, spatially uniform, out-of-plane external magnetic field was continuously applied to one periodic cell of the array at six different frequencies and the amplitude of the out-of-plane magnetization component was computed over the whole lattice. The results are shown in Figs. 5A-F, where the logarithm of the out-of-plane magnetization component is plotted (scale indicated with Fig. 5B). The geometrical and material parameters of the magnonic crystal determine the spin wave modes able to propagate through the lattice. These dispersive modes, supported by the crystal, take 90° turns without changing properties or with only minimal change of properties. These plots proof that it is indeed possible to force spin waves to make multiple 90° turns and that it is possible to have propagation over very large distances. For example, at 11.3 GHz the signal drops only about two decades in amplitude over ±12 μιη, with a = 0.005.

Thus, the embodiments described above, as well as embodiments with considerably more than one or two turns between the input ports and output ports can be implemented in practice.

It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but can be extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In this description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

The following clauses represent embodiments: 1. A magnonic element comprising,

- a magnonic layer capable of conveying spin waves,

- at least one input port for coupling spin waves to the magnonic layer,

- at least one output port for coupling spin waves out of the magnonic layer, wherein the magnonic layer comprises at least one magnetic anisotropy boundary for redirecting spin waves propagating within the magnonic layer between said at least one input port and said at least one output port.

2. The magnonic element according to clause 1, wherein the magnonic layer comprises at least two neighboring magnetic domains with uniaxial magnetic anisotropies that are oriented at different angles, in particular perpendicularly with respect to each other, and wherein said input and output ports are coupled to different magnetic domains.

3. The magnonic element according to clause 1 or 2, wherein the at least one magnetic anisotropy boundary is arranged at an inclined angle, such as a 45° angle, with respect to the Damon-Eshbach propagation direction of the spin waves coupled to the magnonic layer through the input port for redirecting the spin waves.

4. The magnonic element according to any of the preceding clauses, wherein the at least one magnetic anisotropy boundary and magnetization directions on each side of the at least one magnetic anisotropy boundary are arranged such that the spin waves can propagate essentially the whole path between said at least one input and said at least one output port in Damon-Eshbach mode.

5. The magnonic element according to any of the preceding clauses, wherein the magnonic layer comprises a magnonic crystal, such as an antidot lattice, bicomponent array or dot array, capable of laterally confining the propagation of spin waves. 6. The magnonic element according to clause 5, wherein the magnonic crystal comprises a square lattice, and wherein the magnetization of the magnonic layer outside said at least one anisotropy boundary is aligned with orthogonal main axes of the square lattice.

7. The magnonic element according to any of the preceding clauses, wherein the magnonic layer comprises at least two magnetic anisotropy boundaries in order to redirect the spin waves at least twice between said at least one input port and said at least one output port.

8. The magnonic element according to any of the preceding clauses, comprising means for altering the location of the at least one magnetic anisotropy boundary for changing the location or locations where the redirection of the spin waves between said at least one input and said at least one output port takes place. 9. The magnonic element according to any of the preceding clauses, further comprising a ferroelectric layer having a ferroelectric domain structure comprising at least one ferroelectric domain wall, and wherein said magnonic layer is coupled to the ferroelectric layer such that the at least one ferroelectric domain wall induces the at least one magnetic anisotropy boundary. 10. The magnonic element according to clauses 8 and 9, wherein said means for altering the location of the at least one magnetic anisotropy boundary comprise means for applying an electric field over the ferroelectric layer for adjusting the location of said at least one ferroelectric domain wall. 11. The magnonic element according to any of the preceding clauses, wherein there are at least two of said input ports and/or at least two of said output ports.

12. The magnonic element according to clause 11, wherein the location of the at least one magnetic anisotropy boundary is adjustable to guide spin waves along different paths between the input port(s) and output port(s). 13. The magnonic element according to any of the preceding clauses, wherein the element is a magnonic routing element comprising at least two input ports and at least two output ports, and wherein the location or locations of the at least one magnetic anisotropy boundary is adjustable to guide spin waves, optionally simultaneously, along different paths between different pairs of input and output ports. 14. The magnonic element according to any of the preceding clauses, wherein the element is a magnonic multiplexing or demultiplexing element comprising a plurality of input ports or a plurality of output ports, respectively, and wherein the location or locations of the at least one magnetic anisotropy boundary is adjustable to guide spin waves from a selected input port to a single output port or from a single input port to a selected output port, respectively.

15. The magnonic element according to any of the preceding clauses, wherein the magnonic layer comprises a ferromagnetic layer, a ferrimagnetic layer or a layer of magnetic material with another type of magnetic order.

16. A method of redirecting spin waves in a magnonic layer capable of conveying spin waves, the method comprising

- coupling a spin wave to the magnonic layer,

- redirecting the spin wave within the magnonic layer due to at least one magnetic anisotropy boundary contained in the magnonic layer. 17. The method according to clause 16, wherein the redirecting of spin waves takes place in a magnonic layer of a magnonic element according to any of claims 1 - 15.

18. The method according to clause 15 or 16, wherein the spin wave is coupled to the magnonic layer at a first location and the method further comprising coupling the redirected spin wave out of the magnonic layer at a second location.

19. The method according to clause 18, wherein the method further comprises adjusting location or locations of the at least one anisotropy boundary in order to change said first and/or second location.

20. The method according to any of clauses 16 - 19, comprising - using a magnonic layer comprising a magnonic crystal capable of laterally confining the propagation of spin waves,

- coupling, optionally simultaneously, a plurality of spin waves to the magnonic layer, and

- redirecting the plurality of spin waves due to said at least one magnetic

anisotropy boundary such that they propagate along different paths, wherein the plurality of spin waves are coupled to the magnonic layer at different first locations and/or coupled out of the magnonic layer at different second locations.

21. Use of a magnetic anisotropy boundary for redirecting spin waves.

22. The use according to clause 20, wherein the anisotropy boundary is located in a layer of magnetic material and oriented at an inclined angle with respect to the direction of the spin waves before and after said redirecting.

Industrial Applicability

At least some embodiments of the present invention can find industrial application in various electronic devices utilized in information and communication technology. In particular, the invention allows for providing new kinds of magnonic devices. Citation List

Patent Literature CN 105070824 A CN 104767020 A

Non Patent Literature

Bance, S. et al, "Micromagnetic calculation of spin wave propagation for magneto logic devices", Journal of Applied Physics, 103 (2008) 07E735.

Xing, X. et al, "How do spin waves pass through a bend?", Sci. Rep., Macmillan

Publishers Limited, 2013, 3.

Tkachenko, V. S. et al, "Propagation and scattering of spin waves in curved magnonic waveguides", Applied Physics Letters, 101 (2012) 152402.

Vogt, K. et al, "Spin waves turning a corner", Applied Physics Letters, 101 (2012) 042410. Vogt, K. et al, "Realization of a spin- wave multiplexer" Nature Communications, 5 (2014) 3727.

Garcia-Sanchez, F. et al, "Curved magnonic waveguides based on domain walls", ArXiv e- prints, 2014, 1411.4525vl .

Brandl F, et al., 'Spin waves in CoFeB on ferroelectric domains combining spin mechanics and magnonics', Solid State Communications, vol. 198, Nov. 2014, pp. 13-17.

Claims

1. A magnonic element comprising,

- a magnonic layer (15, 25, 250, 35) capable of conveying spin waves (10A, 10B, 20A, 20B, 230A, 240A, 230B, 240B, 301, 302, 303, 301 ', 302', 303', 40, 40'), - at least one input port (37, 47) for coupling spin waves to the magnonic layer (15,

25, 250, 35), and

- at least one output port (38, 48) for coupling spin waves out of the magnonic layer (15, 25, 250, 35), wherein the magnonic layer (15, 25, 250, 35) comprises at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC), characterized in that the magnetic anisotropy boundary is adapted to redirect_spin waves propagating across the anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) within the magnonic layer (15, 25, 250, 35) between said at least one input port (37, 47) and said at least one output port (38, 48).

2. The magnonic element according to claim 1, wherein the magnonic layer (15, 25, 250, 35) comprises at least two neighboring magnetic domains (15A, 15B, 25A, 25B, 250A, 250B, 35A-C, 35A'-C) with uniaxial magnetic anisotropies that are oriented at different angles, in particular perpendicularly with respect to each other, and wherein said input and output ports (37, 38; 47, 48) are coupled to different magnetic domains (15A, 15B, 25A, 25B, 250A, 250B, 35A-C, 35A'-C).

3. The magnonic element according to any of the preceding claims, wherein the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) is arranged at an inclined angle, such as a 45° angle, with respect to the Damon-Eshbach propagation direction of the spin waves coupled to the magnonic layer (15, 25, 250, 35) through the input port for redirecting the spin waves.

4. The magnonic element according to any of the preceding claims, wherein the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) and magnetization directions on each side of the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) are arranged such that the spin waves can propagate essentially the whole path between said at least one input and said at least one output port (37, 38; 47, 48) in Damon-Eshbach mode.

5. The magnonic element according to any of the preceding claims, wherein the magnonic layer (15, 25, 250, 35) comprises a magnonic crystal, such as an antidot lattice, bicomponent array or dot array, capable of laterally confining the propagation of spin waves.

6. The magnonic element according to claim 5, wherein the magnonic crystal comprises a square lattice, and wherein the magnetization of the magnonic layer (15, 25, 250, 35) outside said at least one anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) is aligned with orthogonal main axes of the square lattice.

7. The magnonic element according to any of the preceding claims, wherein the magnonic layer (35) comprises at least two magnetic anisotropy boundaries (36AB, 36BC; 36AB', 36BC) in order to redirect the spin waves at least twice between said at least one input port (37, 47) and said at least one output port (38, 48).

8. The magnonic element according to any of the preceding claims, comprising means for altering the location of the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) for changing the location or locations where the redirection of the spin waves between said at least one input and said at least one output port (37, 38; 47, 48) takes place.

9. The magnonic element according to any of the preceding claims, further comprising a ferroelectric layer (11, 21, 210, 31) having a ferroelectric domain structure comprising at least one ferroelectric domain wall (12, 26FE, 260FE), and wherein said magnonic layer (15, 25, 250, 35) is coupled to the ferroelectric layer (11, 21, 210, 31) such that the at least one ferroelectric domain wall (12, 26FE, 260FE) induces the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC).

10. The magnonic element according to claims 8 and 9, wherein said means for altering the location of the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) comprise means for applying an electric field over the ferroelectric layer (11, 21, 210, 31) for adjusting the location of said at least one ferroelectric domain wall (12, 26FE, 260FE).

11. The magnonic element according to any of the preceding claims, wherein there are at least two of said input ports (37, 47) and/or at least two of said output ports (38, 48).

12. The magnonic element according to claim 11, wherein the location of the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) is adjustable to guide spin waves along different paths between the input port(s) (37, 47) and output port(s) (38, 48).

13. The magnonic element according to any of the preceding claims, wherein the element is a magnonic routing element comprising at least two input ports (37) and at least two output ports (38) , and wherein the location or locations of the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) is adjustable to guide spin waves, optionally simultaneously, along different paths between different pairs of input and output ports (37, 38).

14. The magnonic element according to any of the preceding claims, wherein the element is a magnonic multiplexing or demultiplexing element comprising a plurality of input ports (47) or a plurality of output ports, respectively, and wherein the location or locations of the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) is adjustable to guide spin waves from a selected input port (47) to a single output port (48) or from a single input port to a selected output port, respectively.

15. The magnonic element according to any of the preceding claims, wherein the magnonic layer (15, 25, 250, 35) comprises a ferromagnetic layer, a ferrimagnetic layer or a layer of magnetic material with another type of magnetic order.

- coupling a spin wave to the magnonic layer (15, 25, 250, 35), - redirecting the spin wave within the magnonic layer (15, 25, 250, 35), characterized in that said redirecting occurs due to propagation of the spin wave across the at least one magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) contained in the magnonic layer (15, 25, 250, 35).

17. The method according to claim 16, wherein the redirecting of spin waves takes place in a magnonic layer (15, 25, 250, 35) of a magnonic element according to any of claims

1 - 15.

18. The method according to claim 16 or 17, wherein the spin wave is coupled to the magnonic layer (15, 25, 250, 35) at a first location and the method further comprising coupling the redirected spin wave out of the magnonic layer (15, 25, 250, 35) at a second location.

19. The method according to claim 18, wherein the method further comprises adjusting location or locations of the at least one anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) in order to change said first and/or second location.

20. The method according to any of claims 16 - 19, comprising

- using a magnonic layer (15, 25, 250, 35) comprising a magnonic crystal capable of laterally confining the propagation of spin waves,

- coupling, optionally simultaneously, a plurality of spin waves to the magnonic layer (15, 25, 250, 35), and

- redirecting the plurality of spin waves due to said at least one magnetic

anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) such that they propagate along different paths, wherein the plurality of spin waves are coupled to the magnonic layer (15, 25, 250, 35) at different first locations and/or coupled out of the magnonic layer (15, 25, 250, 35) at different second locations.

21. Use of a magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) for redirecting spin waves propagating across the magnetic anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC).

22. The use according to claim 21, wherein the anisotropy boundary (16, 26FM, 260FM, 36AB, 36BC, 36AB', 36BC) is located in a layer of magnetic material and oriented at an inclined angle with respect to the direction of the spin waves before and after said redirecting.