Spin-Wave Phase Inverter upon a Single Nanodefect

Investigation of Mode-Induced Spin Wave Transmission Blockage by In Situ Nanoscale Grooves

In the pursuit of advancing spin-wave optics, the propagation of magnetostatic surface spin-waves is investigated in a uniform permalloy waveguide with in-situ nanopatterned grooves created through Atomic Force Microscopy nanolithography and Focused Ion Beam etching. The study unveils that the introduction of narrow constrictions and grooves leads to a non-monotonic reduction of the transmitted spin-wave signal intensity as the spin-wave pathway is shrinked. The remarkable feature that a stronger signal extinction is obtained for a narrow groove compared to a spin-waveguide interrupted by a full gap, where only inefficient transport through dipolar coupling is allowed, is highlighted. Combining experimental and numerical analyses, the intricate interplay between spin-wave diffraction and reflection at the waveguide edges is unraveled, being at the origin of a transverse-mode variation responsible for the signal extinction when detected using coplanar antennas. The findings offer insights into the controllable manipulation of detected spin-wave intensity, thereby opening promising avenues for the improvement of spin-wave switches and interferometers, and for the nanopatterning of graded index magnonics.

Dominant higher-order vortex gyromodes in circular magnetic nanodots

The transition to the third dimension enables the creation of spintronic nanodevices with significantly enhanced functionality compared to traditional 2D magnetic applications. In this study, we extend common two-dimensional magnetic vortex configurations, which are known for their efficient dynamical response to external stimuli without a bias magnetic field, into the third dimension. This extension results in a substantial increase in vortex frequency, reaching up to 5 GHz, compared to the typical sub-GHz range observed in planar vortex oscillators. A systematic study reveals a complex pattern of vortex excitation modes, explaining the decrease in the lowest gyrotropic mode frequency, the inversion of vortex mode intensities, and the nontrivial spatial distribution of vortex dynamical magnetization noted in previous research. These phenomena enable the optimization of both oscillation frequency and frequency reproducibility, minimizing the impact of uncontrolled size variations in those magnetic nanodevices.

3D Magnonic Conduits by Direct Write Nanofabrication

Magnonics is a rapidly developing domain of nanomagnetism, with application potential in information processing systems. Realisation of this potential and miniaturisation of magnonic circuits requires their extension into the third dimension. However, so far, magnonic conduits are largely limited to thin films and 2D structures. Here, we introduce 3D magnonic nanoconduits fabricated by the direct write technique of focused-electron-beam induced deposition (FEBID). We use Brillouin light scattering (BLS) spectroscopy to demonstrate significant qualitative differences in spatially resolved spin-wave resonances of 2D and 3D nanostructures, which originates from the geometrically induced non-uniformity of the internal magnetic field. This work demonstrates the capability of FEBID as an additive manufacturing technique to produce magnetic 3D nanoarchitectures and presents the first report of BLS spectroscopy characterisation of FEBID conduits.

Additive Manufacturing of Co3Fe Nano-Probes for Magnetic Force Microscopy

Magnetic force microscopy (MFM) is a powerful extension of atomic force microscopy (AFM), which mostly uses nano-probes with functional coatings for studying magnetic surface features. Although well established, additional layers inherently increase apex radii, which reduce lateral resolution and also contain the risk of delamination, rendering such nano-probes doubtful or even useless. To overcome these limitations, we now introduce the additive direct-write fabrication of magnetic nano-cones via focused electron beam-induced deposition (FEBID) using an HCo₃Fe(CO)₁₂ precursor. The study first identifies a proper 3D design, confines the most relevant process parameters by means of primary electron energy and beam currents, and evaluates post-growth procedures as well. That way, highly crystalline nano-tips with minimal surface contamination and apex radii in the sub-15 nm regime are fabricated and benchmarked against commercial products. The results not only reveal a very high performance during MFM operation but in particular demonstrate virtually loss-free behavior after almost 8 h of continuous operation, thanks to the all-metal character. Even after more than 12 months of storage in ambient conditions, no performance loss is observed, which underlines the high overall performance of the here-introduced FEBID-based Co₃Fe MFM nano-probes.

New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures

Traditionally, the primary field, where curvature has been at the heart of research, is the theory of general relativity. In recent studies, however, the impact of curvilinear geometry enters various disciplines, ranging from solid-state physics over soft-matter physics, chemistry, and biology to mathematics, giving rise to a plethora of emerging domains such as curvilinear nematics, curvilinear studies of cell biology, curvilinear semiconductors, superfluidity, optics, 2D van der Waals materials, plasmonics, magnetism, and superconductivity. Here, the state of the art is summarized and prospects for future research in curvilinear solid-state systems exhibiting such fundamental cooperative phenomena as ferromagnetism, antiferromagnetism, and superconductivity are outlined. Highlighting the recent developments and current challenges in theory, fabrication, and characterization of curvilinear micro- and nanostructures, special attention is paid to perspective research directions entailing new physics and to their strong application potential. Overall, the perspective is aimed at crossing the boundaries between the magnetism and superconductivity communities and drawing attention to the conceptual aspects of how extension of structures into the third dimension and curvilinear geometry can modify existing and aid launching novel functionalities. In addition, the perspective should stimulate the development and dissemination of research and development oriented techniques to facilitate rapid transitions from laboratory demonstrations to industry-ready prototypes and eventual products.

Inverse-design magnonic devices

The field of magnonics offers a new type of low-power information processing, in which magnons, the quanta of spin waves, carry and process data instead of electrons. Many magnonic devices were demonstrated recently, but the development of each of them requires specialized investigations and, usually, one device design is suitable for one function only. Here, we introduce the method of inverse-design magnonics, in which any functionality can be specified first, and a feedback-based computational algorithm is used to obtain the device design. We validate this method using the means of micromagnetic simulations. Our proof-of-concept prototype is based on a rectangular ferromagnetic area that can be patterned using square-shaped voids. To demonstrate the universality of this approach, we explore linear, nonlinear and nonreciprocal magnonic functionalities and use the same algorithm to create a magnonic (de-)multiplexer, a nonlinear switch and a circulator. Thus, inverse-design magnonics can be used to develop highly efficient rf applications as well as Boolean and neuromorphic computing building blocks.

Spin-wave spectroscopy of individual ferromagnetic nanodisks

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.

Nanoimaging of Ultrashort Magnon Emission by Ferromagnetic Grating Couplers at GHz Frequencies

On-chip signal processing at microwave frequencies is key for modern mobile communication. When one aims at small footprints, low power consumption, reprogrammable filters, and delay lines, magnons in low-damping ferrimagnets offer great promise. Ferromagnetic grating couplers have been reported to be specifically useful as microwave-to-magnon transducers. However, their interconversion efficiency is unknown and real-space measurements of the emitted magnon wavelengths have not yet been accomplished. Here, we image with subwavelength spatial resolution the magnon emission process into ferrimagnetic yttrium iron garnet (YIG) at frequencies up to 8 GHz. We evidence propagating magnons of a wavelength of 98.7 nm underneath the gratings, which enter the YIG without a phase jump. Counterintuitively, the magnons exhibit an even increased amplitude in YIG, which is unexpected and due to a further wavelength conversion process. Our results are of key importance for magnonic components, which efficiently control microwave signals on the nanoscale.

Writing 3D Nanomagnets Using Focused Electron Beams

Focused electron beam induced deposition (FEBID) is a direct-write nanofabrication technique able to pattern three-dimensional magnetic nanostructures at resolutions comparable to the characteristic magnetic length scales. FEBID is thus a powerful tool for 3D nanomagnetism which enables unique fundamental studies involving complex 3D geometries, as well as nano-prototyping and specialized applications compatible with low throughputs. In this focused review, we discuss recent developments of this technique for applications in 3D nanomagnetism, namely the substantial progress on FEBID computational methods, and new routes followed to tune the magnetic properties of ferromagnetic FEBID materials. We also review a selection of recent works involving FEBID 3D nanostructures in areas such as scanning probe microscopy sensing, magnetic frustration phenomena, curvilinear magnetism, magnonics and fluxonics, offering a wide perspective of the important role FEBID is likely to have in the coming years in the study of new phenomena involving 3D magnetic nanostructures.

Ultra-fast vortex motion in a direct-write Nb-C superconductor

The ultra-fast dynamics of superconducting vortices harbors rich physics generic to nonequilibrium collective systems. The phenomenon of flux-flow instability (FFI), however, prevents its exploration and sets practical limits for the use of vortices in various applications. To suppress the FFI, a superconductor should exhibit a rarely achieved combination of properties: weak volume pinning, close-to-depairing critical current, and fast heat removal from heated electrons. Here, we demonstrate experimentally ultra-fast vortex motion at velocities of 10-15 km s-1 in a directly written Nb-C superconductor with a close-to-perfect edge barrier. The spatial evolution of the FFI is described using the edge-controlled FFI model, implying a chain of FFI nucleation points along the sample edge and their development into self-organized Josephson-like junctions (vortex rivers). In addition, our results offer insights into the applicability of widely used FFI models and suggest Nb-C to be a good candidate material for fast single-photon detectors.

Spin Wave Injection and Propagation in a Magnetic Nanochannel from a Vortex Core

Spin waves can be used as information carriers with low energy dissipation. The excitation and propagation of spin waves along reconfigurable magnonic circuits is the subject of much interest in the field of magnonic applications. Here we experimentally demonstrate an effective excitation of spin waves in reconfigurable magnetic textures at frequencies as high as 15 GHz and wavelengths as short as 80 nm from Ni₈₀Fe₂₀ (Py) nanodisk-film hybrid structures. Most importantly, we demonstrate these spin wave modes, which were previously confined within a nanodisk, can now couple to and propagate along a nanochannel formed by magnetic domain walls at zero magnetic bias field. The tunable high-frequency, short-wavelength, and propagating spin waves may play a vital role in energy efficient and programmable magnonic devices at the nanoscale.