Auswahl der wissenschaftlichen Literatur zum Thema „Three-magnon splitting“

We present an experimental and numerical study of three-magnon splitting in a micrometer-sized magnetic disk with a vortex state strongly deformed by static in-plane magnetic fields. Excited with large enough power at frequency [Formula: see text], the primary radial magnon modes of a cylindrical magnetic vortex can decay into secondary azimuthal modes via spontaneous three-magnon splitting. This nonlinear process exhibits selection rules leading to well-defined and distinct frequencies [Formula: see text] of the secondary modes. Here, we demonstrate that three-magnon splitting in vortices can be significantly modified by deforming the magnetic vortex with in-plane magnetic fields, leading to a much richer three-magnon response. We find that, with increasing field, an additional class of secondary modes is excited, which are localized to highly flexed regions adjacent to the displaced vortex core. While these modes satisfy the same selection rules of three-magnon splitting, they exhibit much lower three-magnon threshold power compared to regular secondary modes of a centered vortex. The applied static magnetic fields are small ([Formula: see text]), providing an effective parameter to control the nonlinear spectral response of confined vortices. Our work expands the understanding of nonlinear magnon dynamics in vortices and advertises these for potential neuromorphic applications based on magnons.

Magnonics is a rapidly growing field, attracting much attention for its potential applications in data transport and processing. Many individual magnonic devices have been proposed and realized in laboratories. However, an integrated magnonic circuit with several separate magnonic elements has yet not been reported due to the lack of a magnonic amplifier to compensate for transport and processing losses. The magnon transistor reported in Chumak et al. [Nat. Commun. 5, 4700 (2014)] could only achieve a gain of 1.8, which is insufficient in many practical cases. Here, we use the stimulated three-magnon splitting phenomenon to numerically propose a concept of magnon transistor in which the energy of the gate magnons at 14.6 GHz is directly pumped into the energy of the source magnons at 4.2 GHz, thus achieving the gain of 9. The structure is based on the 100 nm wide YIG nano-waveguides, a directional coupler is used to mix the source and gate magnons, and a dual-band magnonic crystal is used to filter out the gate and idler magnons at 10.4 GHz frequency. The magnon transistor preserves the phase of the signal, and the design allows integration into a magnon circuit.

We present a high throughput computational search for altermagnetism in two-dimensional (2D) materials based on the Computational 2D Materials Database (C2DB). We start by showing that the symmetry requirements for altermagnetism in 2D are somewhat more strict compared to bulk materials and applying these yields a total of seven altermagnets in the C2DB. The collinear ground state in these monolayers is verified by spin spiral calculations using the generalized Bloch theorem. We focus on four d-wave altermagnetic materials belonging to the P21′/c′ magnetic space group—RuF4, VF4, AgF2, and OsF4. The first three of these are known experimentally as van der Waals bonded bulk materials and are likely to be exfoliable from their bulk parent compounds. We perform a detailed analysis of the electronic structure and non-relativistic spin splitting in k-space exemplified by RuF4. The magnon spectrum of RuF4 is calculated from the magnetic force theorem, and it is shown that the symmetries that enforce degenerate magnon bands in anti-ferromagnets are absent in altermagnets and give rise to the non-degenerate magnon spectrum. We then include spin–orbit effects and show that these will dominate the splitting of magnons in RuF4. Finally, we provide an example of i-wave altermagnetism in the 2H-phase of FeBr3.

Les ondes de spin sont des excitations élémentaires de l’ordre ferromagnétique, et leurs propriétés, notamment la non-linéarité, les rendent intéressantes pour des applications comme le calcul neuromorphique et les dispositifs logiques magnoniques. Les antiferromagnétiques synthétiques (SAFs), constitués de deux couches ferromagnétiques séparées par une couche non magnétique, permettent une aimantation antiparallèle grâce à un couplage inter-couches. Ce couplage confère aux SAFs une grande flexibilité, les rendant particulièrement adaptés à l’étude de la non-linéarité des ondes de spin. L’utilisation des SAF nécessite une compréhension approfondie des propriétés magnétiques et de leur corrélation avec la structure du matériau. Nous avons établi une procédure pour quantifier le couplage d’échange inter-couches et la rigidité d’échange intra-couches, appliquée à une structure Co₄₀Fe₄₀B₂₀ (tmag)/Ru (0.7 nm)/CoFeB (tmag) ultra-lisse et amorphe. L’interaction entre ces échanges crée un gradient d’orientation d’aimantation dans l’épaisseur de l’empilement, modifiant l’hystérésis et les modes propres d’ondes de spin. Nous avons mesuré la dépendance fréquence-champ des quatre premiers modes d’ondes de spin confinées dans l’épaisseur, et modélisé ces fréquences à l’aide de simulations micromagnétiques. Les résultats ont permis de déduire les paramètres qui décrivent le mieux le comportement de l’échantillon. La rigidité d’échange est Aex = 16 ± 2 pJ/m, indépendante de l’épaisseur du film. Le couplage d’échange inter-couches commence de -1,7 mJ/m2 pour les couches les plus fines et peut se maintenir au-dessus de -1,3 mJ/m2 pour des couches de CoFeB aussi épaisses que 40 nm. La dépendance fréquence-champ a permis d’identifier des conditions favorisant les interactions non linéaires. Pour certaines configurations du champ magnétique statique appliqué HDC, la fréquence du mode acoustique (fac) devient la moitié de celle du mode optique (fop), ce qui favorise l’étude des phénomènes non linéaires dans les SAFs. Nous avons développé un dispositif expérimental basé sur la spectroscopie d’ondes de spin propagative, et étudié inductivement les processus non linéaires en variant HDC, la fréquence de pompage, ainsi que la puissance des micro-ondes. Deux phénomènes majeurs ont été observés : des doublets proches de fpump/2 indiquant un processus de division à trois magnons, où un magnon optique à fpump se divise en deux magnons acoustiques à fpump/2-δ et fpump/2+δ, ainsi qu’un halo autour de fpump, qui pourrait être un processus de diffusion à quatre magnons, dans lequel deux magnons optiques à fpump s’annihilent et créent deux nouveaux magnons optiques. Le processus de division à trois magnons a été étudié sur un dispositif fabriqué par lithographie optique, comprenant une antenne à fil unique de 1,8 μm de large. Nous avons montré que la population de magnons acoustiques créés varie de manière exponentielle avec l’amplitude des excitations RF au-delà d’un certain seuil de 1,8 mT. Afin d’étudier la dynamique de création de magnons, nous avons appliqué des impulsions rf de différentes durées, et avons développé un modèle analytique comparé aux résultats expérimentaux pour déterminer le taux de croissance de la population du mode acoustique. Pour étudier les ondes de spin dans des géométries nanométriques confinées, de nouveaux dispositifs ont été fabriqués par lithographie à faisceaux d’électron. Ces dispositifs contiennent des antennes en forme de U, de 100 nm et 150 nm de large, placées au-dessus de conduits magnétiques, permettant l’excitation sur une grande plage de vecteurs d’onde ∆k = 10 rad/μm, correspondant à un intervalle de fréquence de ∆f = 4,13 GHz. En comparaison, l’antenne de 1,8 μm de large excite une plage de vecteurs d’onde plus étroite ∆k = 2 rad/μm correspondant à ∆f = 0,64 GHz
Spin waves are the eigen-excitations of magnetic materials. They exhibit specific properties such as nonlinearity. This property makes them potentially suitable for applications in neuromorphic computing and magnonic logic devices. Synthetic antiferromagnets (SAFs), composed of two ferromagnetic layers separated by a non-magnetic layer that favors antiparallel magnetizations, are particularly effective for studying the nonlinearity of spin waves. A comprehensive understanding of the magnetic properties of SAFs is essential before exploring their nonlinear properties. The interlayer coupling is a degree of freedom that confers a large tunability to SAFs, which allows their customization in several spintronics applications. The efficient use of this magnetic configuration requires an in-depth understanding of the magnetic properties and their correlation with the material structure. We established a reliable procedure to quantify the interlayer exchange coupling and the intralayer exchange stiffness in SAF. We applied this procedure to the ultrasmooth and amorphous Co₄₀Fe₄₀B₂₀ (tmag)/Ru (0.7 nm)/CoFeB (tmag) structure. The complex interplay between the two exchange interactions results in a gradient of the magnetization orientation across the thickness of the stack, which alters the hysteresis and the spin wave eigenmodes of the stack in a nontrivial way. We measured the frequency-field dependence of the first four spin waves confined within the thickness of the stack. We modeled these frequencies and the corresponding thickness profiles of these spin waves using micromagnetic simulations. The comparison with the experimental results allows us to deduce the magnetic parameters that best account for the sample behavior. The exchange stiffness is Aex = 16 ± 2 pJ/m, independent of the film thickness. The interlayer exchange coupling starts from -1.7 mJ/m2 for the thinnest layers and it can be maintained above -1.3 mJ/m2 for CoFeB layers that are as thick as 40 nm. Frequency-field dependence allows the identification of conditions that exhibit nonlinear interactions. For specific configurations of the applied static magnetic field HDC the frequency of the acoustic magnon mode (fac) becomes half of the optical magnon mode frequency (fop), a favorable condition to investigate nonlinear phenomena in SAF. We developed an experimental setup based on propagating spin wave spectroscopy and we investigated the nonlinear processes inductively by varying the applied field HDC, the pumping frequency and the microwave power arriving at the simple. Two phenomena are observed: the doublets near fpump/2 evidence a three-magnon process where one optical magnon at fpump split into two acoustic magnons at fpump/2 - δ and fpump/2 + δ. 2). A strong halo around fpump could be a four-magnon scattering process, in which two optical magnons at fpump annihilate and create two new optical magnons. We focused on the three-magnon splitting process on a device patterned by optical lithography, featuring a 1.8 μm wide single-wire antenna. We showed that the population of the created magnons varies exponentially with the amplitude of the rf excitations above a certain threshold, which is 1.8 mT. Furthermore, to explore the dynamics of magnon creation, we apply rf pulses with various durations. We developed an analytical model that we compared to the experiment to effectively determine the growth rate of the population of the acoustic mode. To investigate spin waves in confined nanometric geometries, we fabricated new devices using electron beam lithography that feature 100 nm and 150 nm wide U-shaped antennas on top of magnetic conduits. This enables the excitation over a large range of wavevectors ∆k = 10 rad/μm corresponding to a frequency interval of ∆f = 4.13 GHz. In contrast to the 1.8 μm wide antenna, which excites a narrower range of wavevectors ∆k = 2 rad/μm corresponding to ∆f = 0.64 GHz