Fale spinowe w magnetycznych kryształach skyrmionowych


Founded from NCN SHENG call [https://www.ncn.gov.pl/ogloszenia/konkursy/sheng1]
Contract No. UMO-2018/30/Q/ST3/00416.

Starting date: 24.07.2019
Ending day: 23.07.2023

Budged: 999 520PLN

Project realized in collaboration between

Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
Polish PI: prof. Maciej Krawczyk (krawczyk@amu.edu.pl )


The Chinese University of Hong Kong, Shenzhen, China
Chinese PI: prof. Yan Zhou (zhouyan@cuhk.edu.cn )

Research Team (Polish part):

Project description

1. Scientific goal of the project

In magnetic systems, skyrmions are solitonic metastable states, while spin waves are bosonic elementary excitations. In our joint project, we will investigate the topological properties of spin waves in magnetic skyrmions which are arranged periodically, and the interaction between spin waves and the underlying skyrmions. Utilizing the interaction between spin waves and skyrmions we aim to make valuable contribution to the two important application-related topics of modern magnetism: a) efficient generation of propagating short wavelength spin waves (SWs), and b) synchronization of the magnetization oscillations in nano-dots. Both objectives are critical for further development of the magnonics, spintronics fields of research, and SW-based devices. To reach those ambitious goals, we propose to test new approach, it is to employ non-collinear topologically protected stable magnetic states coupled to the ferromagnetic film with the imprinted magnetization texture, i.e., a heterostructure composed of the array of magnetic skyrmions and thin magnetic film. Based on the skyrmion–SW interaction we will investigate artificial skyrmionic crystals to control SW dynamic and their static properties, and to construct prototypes of magnonic logic devices. Also to explore potential of artificial skyrmionic crystals for outstanding in magnetic community problem of the spin torque oscillators (STO) synchronization. We assume, that the topological properties of SWs in skyrmionic crystal will support synchronization, as well as generation of short wavelength SWs. This hypothesis will be tested through intensive numerical simulations and developed theoretical models.

2. Concept and work plan

In order to realize the objectives, we organized the research in four main tasks: A) Study conditions for stabilization of the skyrmion state in nano-dots in contact with ferromagnetic films with imprinted magnetization structure; B) Optimization of the dynamical coupling between excitations in nano-dots and SW dynamics in ferromagnetic film; C) Study the static, SW dynamics and their topological properties in an interacting array of nano-dots deposited on ferromagnetic films; D) Evaluation of coupled skyrmion dynamics and topological properties in magnetic heterostructure for applications: synchronization and SW excitations. The above mentioned tasks will be realized by employing and developing several numerical or analytical methods. The static and dynamic properties of magnetic states in nanodot-thin film heterostructure will be investigated with the open-source numerical micromagnetic software Mumax, discrete/atomistic models (developed by the partners and opensource Fidimag and Spirit), then validated and supplemented with FEM computation with Comsol and FEMME. The analytical models, like a developed in the Project coupled mode theory, will serve to explain numerical results and estimate the coupling between skyrmion oscillations in nanodot and SWs in the film.

3. Expected impact of the research project on the development of science

The biggest advantage of the SW technology is low energy consumption at nanoscale operation length and at microwave frequencies. This Project advances the fields of magnonics and spintronics to pave the way for application of STOs and magnonic logic elements. Moreover, the Project will give deep insight into topological properties of waves in periodic structures, and evaluate the possibility of utilizing those properties. Most of the results of the Project will be published in research articles in internationally renowned journals and presented on international conferences. The IP rights, and patent protection will be considered whenever the results will facilitate the commercial utilization.

4. Added value of international cooperation

Both groups have vast experience in the complementary areas of research directly related to above mentioned fields of magnetism. The group of Prof. Zhou in China is recognized expert in numerical simulations of skyrmion nucleation, transport and logic devices based on magnetic skyrmions. The group of Prof. Krawczyk in Poland has rich publication track record in magnonic band structure theory, particularly SW dynamics in magnonic crystals and spin excitations in nanopatterned elements. Our joint Project utilizes the expertise of both groups to tackle the main problems blocking further development of magnonics, it is synchronization of STOs and excitation of short wavelength SWs. The generated knowledge utilizing topological properties of waves will exceed the area of magnonics, as its influence on other modern areas of physics, like photonics, plasmonics and phononics is expected. In the course of this collaborative Project early stage researchers and students, from both China and Poland, will have opportunity to learn, practice and develop modern physics in the synergic work of the international team.

Research Tasks:

  1. Study conditions for stabilization of the skyrmion state in nano-dots in contact with ferromagnetic films (direct or dipolar): stabilization of the skyrmion texture in nano-dots & imprinting magnetization texture into the films.
  2. Optimization of the dynamical coupling between SW excitation in nano-dots and SW dynamics in ferromagnetic films: effect of the magnetization orientation and imprinting magnetization structure; sensitivity of the mode excitation on the direction of the external microwave field.
  3. Study of the static and SW dynamics in an array of nano-dots deposited on ferromagnetic films: collective and coherent dynamics in the array and coupling between skyrmions.D. Evaluation of using coupled skyrmion dynamics in magnetic heterostructures and the SW excitations for logic applications: exploitation of topological properties in the artificial skyrmionic crystals.



X. Li, L. Shen, Y. Bai, J. Wang, X. Zhang, J. Xia, M. Ezawa, O. A. Tretiakov, X. Xu, M. Mruczkiewicz, M. Krawczyk, Y. Xu, R. F. L. Evans, R. W. Chantrell, and Y. Zhou,
Bimeron clusters in chiral antiferromagnets,
npj Computational Materials 6, 169 (2020), DOI: 10.1038/s41524-020-00435-y


A magnetic bimeron is an in-plane topological counterpart of a magnetic skyrmion. Despite the topological equivalence, their statics and dynamics could be distinct, making them attractive from the perspectives of both physics and spintronic applications. In this work, we demonstrate the stabilization of bimeron solitons and clusters in the antiferromagnetic (AFM) thin film with interfacial Dzyaloshinskii–Moriya interaction (DMI). Bimerons demonstrate high current-driven mobility as generic AFM solitons, while featuring anisotropic and relativistic dynamics excited by currents with in-plane and out-of-plane polarizations, respectively. Moreover, these spin textures can absorb other bimeron solitons or clusters along the translational direction to acquire a wide range of Néel topological numbers. The clustering involves the rearrangement of topological structures, and gives rise to remarkable changes in static and dynamical properties. The merits of AFM bimeron clusters reveal a potential path to unify multibit data creation, transmission, storage, and even topology-based computation within the same material system, and may stimulate spintronic devices enabling innovative paradigms of data manipulations.

F. Groß, M. Zelent, N. Träger, J. Förster, U. T. Sanli, R. Sauter, M. Decker, C. H. Back, M. Weigand, K. Keskinbora, G. Schütz, M. Krawczyk, and J. Gräfe,
Building blocks for magnon optics: emission and conversion of short spin waves,
ACS Nano 14, 17184 (2020), DOI: 10.1021/acsnano.0c07076


Magnons have proven to be a promising candidate for low-power wave-based computing. The ability to encode information not only in amplitude but also in phase allows for increased data transmission rates. However, efficiently exciting nanoscale spin waves for a functional device requires sophisticated lithography techniques and therefore, remains a challenge. Here, we report on a method to measure the full spin wave isofrequency contour for a given frequency and field. A single antidot within a continuous thin film excites wave vectors along all directions within a single excitation geometry. Varying structural parameters or introducing Dzyaloshinskii–Moriya interaction allows the manipulation and control of the isofrequency contour, which is desirable for the fabrication of future magnonic devices. Additionally, the same antidot structure is utilized as a multipurpose spin wave device. Depending on its position with respect to the microstrip antenna, it can either be an emitter for short spin waves or a directional converter for incoming plane waves. Using simulations we show that such a converter structure is capable of generating a coherent spin wave beam. By introducing a short wavelength spin wave beam into existing magnonic gate logic, it is conceivable to reduce the size of devices to the micrometer scale. This method gives access to short wavelength spin waves to a broad range of magnonic devices without the need for refined sample preparation techniques. The presented toolbox for spin wave manipulation, emission, and conversion is a crucial step for spin wave optics and gate logic.

K. Szulc, P. Graczyk, M. Mruczkiewicz, G. Gubbiotti, and M. Krawczyk
Spin-wave diode and circulator based on unidirectional coupling
Phys. Rev. Applied 14, 34063 (2020); DOI: 10.1103/PhysRevApplied.14.034063



In magnonics, a fast-growing branch of wave physics characterized by low energy consumption, it is highly desirable to create circuit elements useful for wave computing. However, it is crucial to reach the nanoscale so as to be competitive with the electronics, which vastly dominates in computing devices. Here, based on numerical simulations, we demonstrate the functionality of the spin-wave diode and the circulator to steer and manipulate spin waves over a wide range of frequency in the GHz regime. They take advantage of the unidirectional magnetostatic coupling induced by the interfacial Dzyaloshinskii-Moriya interaction, allowing the transfer of the spin wave between thin ferromagnetic layers in only one direction of propagation. Using the multilayered structure consisting of Py and Co in direct contact with heavy metal, we obtain submicrometer-size nonreciprocal devices of high efficiency. Thus, our work contributes to the emerging branch of energy-efficient magnonic logic devices, giving rise to the possibility of application as a signal-processing unit in the digital and analog nanoscaled spin-wave circuits.

J. Feilhauer, S. Saha, J. Tobik, M. Zelent, L. J. Heyderman and M. Mruczkiewicz
Controlled motion of skyrmions in a magnetic antidot lattice
Phys. Rev. B 102, 184425 (2020); DOI: 10.1103/PhysRevB.102.184425



Future spintronic devices based on skyrmions will require precise control of the skyrmion motion. We show that this goal can be achieved through the use of magnetic antidot arrays. We perform micromagnetic simulations and semianalytical calculations based on the Thiele equation, where the skyrmion motion is driven by applied electric current via spin transfer torque (STT) or spin orbit torque (SOT) mechanism. For both torque mechanisms we demonstrate that an antidot array can guide the skyrmions in different directions depending on the parameters of the applied current pulse. Despite the fixed direction of the net driving current, due to the nontrivial interplay between the repulsive potential introduced by the antidots, the skyrmion Hall effect, and the nonuniform current distribution, full control of skyrmion motion in a 2D lattice can be achieved. Moreover, we demonstrate that the direction of skyrmion motion can be controlled by tuning only a single parameter of the current pulse, i.e., current magnitude.

S. Pan, S. Mondal, M. Zelent, R. Szwierz, S. Pal, O. Hellwig, M. Krawczyk, and A. Barman
Edge localization of spin waves in antidot multilayers with perpendicular magnetic anisotropy
Phys. Rev. B 101, 014403 (2020); DOI: 10.1103/PhysRevB.101.014403



We study the spin-wave dynamics in nanoscale antidot lattices based on Co/Pd multilayers with perpendicular magnetic anisotropy. Using time-resolved magneto-optical Kerr effect measurements we demonstrate that the variation of the antidot shape introduces significant change in the spin-wave spectra, especially in the lower frequency range. By employing micromagnetic simulations we show that additional peaks observed in the measured spectra are related to narrow shell regions around the antidots, where in-plane domain structures are formed. This is because the magnetic anisotropy in these regions is reduced due to the Ga+ ion irradiation during the focused ion beam milling process of the antidot fabrication. The results point at possibilities for exploitation of localized spin waves in out-of-plane magnetized thin films, which are easily tunable and suitable for magnonic applications.

O. V. Dobrovolskiy, S. A. Bunyaev, N. R. Vovk, D. Navas, P. Gruszecki, M. Krawczyk, R. Sachser, M. Huth, A. V. Chumak, K. Y. Guslienko, and G. N. Kakazei
Spin-wave spectroscopy of individual ferromagnetic nanodisks
Nanoscale 12, 21207 (2020); DOI: 10.1039/d0nr07015g


The increasing demand for nanoscale magnetic devices requires development of 3D magnetic nanostructures. In this regard, focused electron beam induced deposition (FEBID) is a technique of choice for direct-writing of complex nano-architectures with applications in nanomagnetism, magnon spintronics, and superconducting electronics. However, intrinsic properties of nanomagnets are often poorly known and can hardly be assessed by local optical probe techniques. Here, an original spatially resolved approach is demonstrated for spin-wave spectroscopy of individual circular magnetic elements with sample volumes down to about 10−3 μm3. The key component of the setup is a coplanar waveguide whose microsized central part is placed over a movable substrate with well-separated CoFe-FEBID nanodisks which exhibit standing spin-wave resonances. The circular symmetry of the disks allows for the deduction of the saturation magnetization and the exchange stiffness of the material using an analytical theory. A good correspondence between the results of analytical calculations and micromagnetic simulations is revealed, indicating a validity of the used analytical model going beyond the initial thin-disk approximation used in the theoretical derivation. The presented approach is especially valuable for the characterization of direct-write magnetic elements opening new horizons for 3D nanomagnetism and magnonics.


N. Träger, F. Lisiecki, R. Lawitzki, M. Weigand, H. Głowinski, G. Schütz, G. Schmitz, P. Kuswik, M. Krawczyk, J. Gräfe, and P. Gruszecki
Competing spin wave emission mechanisms revealed by time-resolved x-ray microscopy
Phys. Rev. B 103, 014430 (2021); DOI: 10.1103/PhysRevB.103.014430


Spin wave emission and propagation in magnonic waveguides represent a highly promising alternative for beyond-CMOS computing. It is therefore all the more important to fully understand the underlying physics of the emission process. Here, we use time-resolved scanning transmission x-ray microscopy to directly image the formation process of the globally excited local emission of spin waves in a permalloy waveguide at the nanoscale. Thereby, we observe spin wave emission from the corner of the waveguide as well as from a local oscillation of a domain-wall-like structure within the waveguide. Additionally, an isofrequency contour analysis is used to fully explain the origin of quasicylindrical spin wave excitation from the corner and its concurrent nonreflection and nonrefraction at the domain interface. This study is complemented by micromagnetic simulations which perfectly fit the experimental findings. Thus, we clarify the fundamental question of the emission mechanisms in magnonic waveguides which lay the basis for future magnonic operations.

N. Träger, P. Gruszecki, F. Lisiecki, F. Groß, J. Förster, M. Weigand, H. Głowiński, P. Kuświk, J. Dubowik, G. Schütz, M. Krawczyk, and J. Gräfe
Real-space observation of magnon interaction with driven space-time crystals
Phys. Rev. Lett. 126, 057201 (2021); DOI: 10.1103/PhysRevLett.126.057201


The concept of space-time crystals (STC), i.e., translational symmetry breaking in time and space, was recently proposed and experimentally demonstrated for quantum systems. Here, we transfer this concept to magnons and experimentally demonstrate a driven STC at room temperature. The STC is realized by strong homogeneous microwave pumping of a micron-sized permalloy (Py) stripe and is directly imaged by scanning transmission x-ray microscopy (STXM). For a fundamental understanding of the formation of the STC, micromagnetic simulations are carefully adapted to model the experimental findings. Beyond the mere generation of a STC, we observe the formation of a magnonic band structure due to back folding of modes at the STC’s Brillouin zone boundaries. We show interactions of magnons with the STC that appear as lattice scattering, which results in the generation of ultrashort spin waves (SW) down to 100-nm wavelengths that cannot be described by classical dispersion relations for linear SW excitation. We expect that room-temperature STCs will be useful to investigate nonlinear wave physics, as they can be easily generated and manipulated to control their spatial and temporal band structures.

F. Groß, M. Zelent, A. Gangwar, S. Mamica, P. Gruszecki, M. Werner, G. Schutz, M. Weigand, E. J. Goering, C. H. Back, M. Krawczyk, and J. Grafe
Phase resolved observation of spin wave modes in antidot lattices
Appl. Phys. Lett. 118, 232403 (2021); DOI: 10.1063/5.0045142


Antidot lattices have proven to be a powerful tool for spin wave band structure manipulation. Utilizing time-resolved scanning transmission x-ray microscopy, we are able to experimentally image edge-localized spin wave modes in an antidot lattice with a lateral confinement down to <80 nm×130 nm. At higher frequencies, spin wave dragonfly patterns formed by the demagnetizing structures of the antidot lattice are excited. Evaluating their relative phase with respect to the propagating mode within the antidot channel reveals that the dragonfly modes are not directly excited by the antenna but need the propagating mode as an energy mediator. Furthermore, micromagnetic simulations reveal that additional dispersion branches exist for a tilted external field geometry. These branches correspond to asymmetric spin wave modes that cannot be excited in a non-tilted field geometry due to the symmetry restriction. In addition to the band having a negative slope, these asymmetric modes also cause an unexpected transformation of the band structure, slightly reaching into the otherwise empty bandgap between the low frequency edge modes and the fundamental mode. The presented phase resolved investigation of spin waves is a crucial step for spin wave manipulation in magnonic crystals.

Iu. V. Vetrova, M. Zelent, J. Šoltýs, V. A. Gubanov, A. V. Sadovnikov, T. Šcepka, J. Dérer, R. Stoklas, V. Cambel, and M. Mruczkiewicz
Investigation of self-nucleated skyrmion states in the ferromagnetic/nonmagnetic multilayer dot
Appl. Phys. Lett. 118, 212409 (2021); DOI: 10.1063/5.0045835


Understanding the stability of magnetic textures in multilayer patterned dots would constitute a significant step toward skyrmion-based applications. Here, we report the observation of skyrmions in patterned nanodots composed of multilayers. We examine the stabilization of various magnetic states such as single-domain states, skyrmion states, horseshoe-like domain structures, and worm-like domain structures in submicrometer dots (diameters 150–525 nm). Dots are fabricated from Pt/Co/Au multilayer structures that exhibit the interfacial Dzyaloshinskii–Moriya interaction and perpendicular magnetic anisotropy. In particular, we show that a stack of six repetitions of Pt/Co/Au layers suffices to stabilize the skyrmion state inside a dot at room temperature. A micromagnetic simulation determines the regime of skyrmion stability. The results reveal a correlation between the magnetic-force microscopy measurements and the micromagnetic simulation. Furthermore, we explain the development of the magnetic state with increasing dot diameter. We envision that nanopatterning of multilayer magnetic films could serve as a versatile way of creating magnetic skyrmion states.

P. Roberjot, K. Szulc, J. W. Kłos, and M. Krawczyk,
Multifunctional operation of the double-layer ferromagnetic structure coupled by a rectangular nanoresonator
Appl. Phys. Lett. 118, 182406 (2021); DOI: 10.1063/5.0046001



The use of spin waves as a signal carrier requires developing the functional elements allowing for multiplexing and demultiplexing information coded at different wavelengths. For this purpose, we propose a system of thin ferromagnetic layers dynamically coupled by a rectangular ferromagnetic resonator. We show that single and double, clockwise and counterclockwise, circulating modes of the resonator offer a wide possibility of control of propagating waves. Particularly, at frequency related to the double-clockwise circulating spin-wave mode of the resonator, the spin wave excited in one layer is transferred to the second one where it propagates in the backward direction. Interestingly, the wave excited in the second layer propagates in the forward direction only in that layer. This demonstrates add-drop filtering and circulator functionality. Thus, the proposed system can become an important part of future magnonic technology for signal routing.

Krzysztof Szulc, Simon Mendisch, Michał Mruczkiewicz, Francesca Casoli, Markus Becherer, and Gianluca Gubbiotti
Nonreciprocal spin-wave dynamics in Pt/Co/W/Co/Pt multilayers
Phys. Rev. B 103, 134404 (2021); DOI: 10.1103/PhysRevB.103.134404



We present a detailed study of the spin-wave dynamics in single Pt/Co/W and double Pt/Co/W/Co/Pt ferromagnetic layer systems. The dispersion of spin waves was measured by wave-vector-resolved Brillouin light scattering spectroscopy while the in-plane and out-of-plane magnetization curves were measured by alternating gradient field magnetometry. The interfacial Dzyaloshinskii-Moriya interaction induced nonreciprocal dispersion relation was demonstrated for both single and double ferromagnetic layers and explicated by numerical simulations and theoretical formulas. The results indicate the crucial role of the order of layers deposition on the magnetic parameters. A significant difference between the perpendicular magnetic anisotropy constant in double ferromagnetic layer systems conduces to the decline of the interlayer interactions and different dispersion relations for the spin-wave modes. Our study provides a significant contribution to the realization of the multifunctional nonreciprocal magnonic devices based on ultrathin ferromagnetic/heavy-metal layer systems.

Mateusz Zelent, Iuliia V. Vetrova , Jan Šoltýs, Xiaoguang Li, Yan Zhou, Vladislav A. Gubanov, Alexandr V. Sadovnikov, Tomas Šcepka, Jan Dérer, Roman Stoklas, Vladimír Cambel and Michal Mruczkiewicz
Skyrmion Formation in Nanodisks Using Magnetic Force Microscopy Tip
Nanomaterials 11, 2627 (2021); DOI: 10.3390/nano11102627


We demonstrated numerically the skyrmion formation in ultrathin nanodisks using a magnetic force microscopy tip. We found that the local magnetic field generated by the magnetic tip significantly affects the magnetization state of the nanodisks and leads to the formation of skyrmions. Experimentally, we confirmed the influence of the local field on the magnetization states of the disks. Micromagnetic simulations explain the evolution of the magnetic state during magnetic force microscopy scanning and confirm the possibility of skyrmion formation. The formation of the horseshoe magnetic domain is a key transition from random labyrinth domain states into the skyrmion state. We showed that the formation of skyrmions by the magnetic probe is a reliable and repetitive procedure. Our findings provide a simple solution for skyrmion formation in nanodisks.

M. Mruczkiewicz, P. Gruszecki
The 2021 roadmap for noncollinear magnonics
Solid State Physics 72, 1 (2021); DOI: 10.1016/bs.ssp.2021.09.001


Noncollinear magnonics is a rapidly developing topic of modern magnetism focusing on spin wave (magnon) dynamics in noncollinear spin textures. One of the driving forces of this research field is to employ nanosize dynamical noncollinear spin textures for the control and guiding of magnons. An unquestionable advantage of this approach is the potential to design programmable nanochannels with sizes below patterning limits. Furthermore, the noncollinear magnetic states induce nontrivial dynamical effects suitable for tailoring of SW propagation properties and emission of SWs. In the following, we will summarize the recent achievements of the field and discuss of current and future challenges.

A. Barman, et al.,
The 2021 Magnonics Roadmap; Sec. 2. Magnonic crystals and quasicrystals
J. Phys.: Condens. Mater. 33, 413001 (2021); DOI: 10.1088/1361-648X/abec1a


Magnonics is a budding research field in nanomagnetism and nanoscience that addresses the use of spin last one decade in terms of upsurge in research papers, review articles, citations, proposals of devices as well as introduction of new sub-topics prompted us to present the first roadmap on magnonics. This is a collection of 22 sections written by leading experts in this field who review and discuss the current status besides presenting their vision of future perspectives. Today, the principal challenges in applied magnonics are the excitation of sub-100 nm wavelength magnons, their manipulation on the nanoscale and the creation of sub-micrometre devices using low-Gilbert damping magnetic materials and its interconnections to standard electronics. To this end, magnonics offers lower energy consumption, easier integrability and compatibility with CMOS structure, reprogrammability, shorter wavelength, smaller device features, anisotropic properties, negative group velocity, non-reciprocity and efficient tunability by various external stimuli to name a few. Hence, despite being a young research field, magnonics has come a long way since its early inception. This roadmap asserts a milestone for future emerging research directions in magnonics, and hopefully, it will inspire a series of exciting new articles on the same topic in the coming years.


Mateusz Gołębiewski  Paweł Gruszecki, and Maciej Krawczyk
Self-Imaging of Spin Waves in Thin, Multimode Ferromagnetic Waveguides
IEEE Trans. Magn. 58, 1300905 (2022); DOI: 10.1109/TMAG.2022.3140280



Self-imaging of waves is an intriguing and spectacular effect. The phenomenon was first observed for light in 1836 by Henry Fox Talbot and to this day is the subject of research in many areas of physics, for various types of waves and in terms of different applications. This article is a Talbot-effect study for spin waves (SWs) in systems composed of a thin, ferromagnetic waveguide with a series of single-mode sources of SWs flowing into it. The proposed systems are studied with the use of micromagnetic simulations, and the SW self-imaging dependencies on many parameters are examined. We formulated conditions required for the formation of self-images and suitable for experimental realization. The results of the research form the basis for the further development of self-imaging-based magnonic devices.

Krzysztof Szulc, Silvia Tacchi, Aurelio Hierro-Rodríguez, Javier Díaz, Paweł Gruszecki, Piotr Graczyk, Carlos Quirós, Daniel Markó, José Ignacio Martín, María Vélez, David S. Schmool, Giovanni Carlotti, Maciej Krawczyk, and Luis Manuel Álvarez-Prado
Reconfigurable Magnonic Crystals Based on Imprinted Magnetization Textures in Hard and Soft Dipolar-Coupled Bilayers
ACS NANO 16, 14168 (2022); DOI: 10.1021/acsnano.2c04256


Reconfigurable magnetization textures offer control of spin waves with promising properties for future lowpower beyond-CMOS systems. However, materials with perpendicular magnetic anisotropy (PMA) suitable for stable magnetization-texture formation are characterized by high damping, which limits their applicability in magnonic devices. Here, we propose to overcome this limitation by using hybrid structures, i.e., a PMA layer magnetostatically coupled to a lowdamping soft ferromagnetic film. We experimentally show that a periodic stripe-domain texture from a PMA layer is imprinted upon the soft layer and induces a no nreciprocal dispersion relation of the spin waves confined to the low-damping film. Moreover, an asymmetric bandgap features the spin-wave band diagram, which is a clear demonstration of collective spin-wave dynamics, a property characteristic for magnonic crystals with broken time-reversal symmetry. The composite character of the hybrid structure allows for stabilization of two magnetic states at remanence, with parallel and antiparallel orientation of net magnetization in hard and soft layers. The states can be switched using a low external magnetic field; therefore, the proposed system obtains an additional functionality of state reconfigurability. This study offers a link between reconfigurable magnetization textures and low-damping spin-wave dynamics, providing an opportunity to create miniaturized, programmable, and energy-efficient signal processing devices operating at high frequencies.

Mateusz Gołębiewski, Paweł Gruszecki, and Maciej Krawczyk
Self-Imaging Based Programmable Spin-Wave Lookup Tables
Advanced Electronic Materials 8, 2200373 (2022); DOI: 10.1002/aelm.202200373


Inclusion of spin waves into the computing paradigm, where complementary metal-oxide-semiconductor devices are still at the fore, is now a challenge for scientists around the world. In this work, a wave phenomenon that has not yet been used in magnonics-self-imaging, also known as the Talbot effect, to design and simulate the operation of interference systems that perform logic functions on spin waves in thin ferromagnetic multimode waveguides is utilized. Lookup tables operating in this way are characterized by high programmability and scalability; thanks to which they are promising for their implementation in field-programmable gate arrays circuits, where multiple logic realizations can be obtained.

Mateusz Zelent, Pawel Gruszecki, Mathieu Moalic, Olav Hellwig, Anjan Barman, and Maciej Krawczyk
Spin dynamics in patterned magnetic multilayers with perpendicular magnetic anisotropy
Solid State Physics 73, 1 (2022); DOI: 10.1016/bs.ssp.2022.08.002



The magnetization dynamics in nanostructures has been extensively studied in the last decades, and nanomagnetism has evolved significantly over that time, discovering new effects, developing numerous applications, and identifying promising new directions. This includes magnonics, an emerging research field oriented on the study of spin-wave dynamics and their applications. In this context, thin ferromagnetic films with perpendicular magnetic anisotropy (PMA) offer interesting opportunities to study spin waves, in particular, due to out-of-plane magnetization in remanence or at relatively weak external magnetic fields. This is the only magnetization configuration offering isotropic in-plane spin-wave propagation within the sample plane, the forward volume magnetostatic spin-wave geometry. The isotropic dispersion relation is highly important in designing signal-processing devices, offering superior prospects for direct replicating various concepts from photonics into magnonics. Analogous to photonic or phononic crystals, which are the building blocks of optoelectronics and phononics, magnonic crystals are considered as key components in magnonics applications. Arrays of nanodots and structured ferromagnetic thin films with a periodic array of holes, popularly known as antidot lattices based on PMA multilayers, have been recently studied. Novel magnonic properties related to propagating spin-wave modes, exploitation of the band gaps, and confined modes were demonstrated. Also, the existence of nontrivial magnonic band topologies has been shown. Moreover, the combination of PMA and Dzyaloshinskii–Moriya interaction leads to the formation of chiral magnetization states, including Néel domain walls, skyrmions, and skyrmionium states. This promotes the multilayers with PMA as an interesting topic for magnonics and this chapter reviews the background and attempts to provide future perspectives in this research field.

Katarzyna A. Kotus, Mathieu Moalic, Matusz Zelent, Maciej Krawczyk, and Pawel Gruszeckic
Scattering of spin waves in a multimode waveguide under the influence of confined magnetic skyrmion
APL Mater. 10, 091101 (2022); DOI: 10.1063/5.0100594


Nontrivial magnetization textures, such as skyrmions, have become a driving force in the physics of magnetism. Furthermore, the utilization of magnetization textures is fueling the development of magnon-based technologies that could provide beyond-CMOS solutions. Here, using a self-developed spin wave (SW) excitation scheme, we selectively excite specific modes and investigate the scattering of SWs on nanodot hosting a Néel-type skyrmion and placed above a multimode waveguide. In particular, at low frequencies, we observe significant reflections from the imprint induced by the skyrmion upon the waveguide. As the frequency increases, the transmission increases as well; however, it is accompanied by scattering to other types of modes. Here, we observe a direct contribution of the skyrmion to the scattering process and various types of conversions of the incident SW modes into other modes quantized by width for both reflected and transmitted SWs. The utilization of imprinted magnetization textures in nonplanar systems to control SW flow can open new possibilities for developing SW-based circuits for ultralow-power signal processing.