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.

This paper introduces a new methodology for the fabrication of strain-sensor elements for MEMS and NEMS applications based on the tunneling effect in nano-granular metals. The strain-sensor elements are prepared by the maskless lithography technique of focused electron-beam-induced deposition (FEBID) employing the precursor trimethylmethylcyclopentadienyl platinum [MeCpPt(Me)₃]. We use a cantilever-based deflection technique to determine the sensitivity (gauge factor) of the sensor element. We find that its sensitivity depends on the electrical conductivity and can be continuously tuned, either by the thickness of the deposit or by electron-beam irradiation leading to a distinct maximum in the sensitivity. This maximum finds a theoretical rationale in recent advances in the understanding of electronic charge transport in nano-granular metals.

Recently, focused electron beam-induced deposition has been employed to prepare functional magnetic nanostructures with potential in nanomagnetic logic and sensing applications by using homonuclear precursor gases like Fe(CO) ₅ or Co ₂ (CO) ₈ . Here we show that an extension towards the fabrication of bi-metallic compounds is possible by using a single-source heteronuclear precursor gas. We have grown CoFe alloy magnetic nanostructures from the HFeCo ₃ (CO) ₁₂ metal carbonyl precursor. The compositional analysis indicates that the samples contain about 80 at% of metal and 10 at% of carbon and oxygen. Four-probe magnetotransport measurements are carried out on nanowires of various sizes down to a width of 50 nm, for which a room temperature resistivity of 43 μ Ωcm is found. Micro-Hall magnetometry reveals that 50 nm × 250 nm nanobars of the material are ferromagnetic up to the highest measured temperature of 250 K. Finally, the transmission electron microscopy (TEM) microstructural investigation shows that the deposits consist of a bcc Co-Fe phase mixed with a FeCo ₂ O ₄ spinel oxide phase with nanograins of about 5 nm diameter.

Additive nanotechnology enable curvilinear and three-dimensional (3D) magnetic architectures with tunable topology and functionalities surpassing their planar counterparts. Here, we experimentally reveal that 3D soft magnetic wireframe structures resemble compact manifolds and accommodate magnetic textures of high order vorticity determined by the Euler characteristic, χ. We demonstrate that self-standing magnetic tetrapods (homeomorphic to a sphere; χ = + 2) support six surface topological solitons, namely four vortices and two antivortices, with a total vorticity of + 2 equal to its Euler characteristic. Alternatively, wireframe structures with one loop (homeomorphic to a torus; χ = 0) possess equal number of vortices and antivortices, which is relevant for spin-wave splitters and 3D magnonics. Subsequent introduction of n holes into the wireframe geometry (homeomorphic to an n-torus; χ < 0) enables the accommodation of a virtually unlimited number of antivortices, which suggests their usefulness for non-conventional (e.g., reservoir) computation. Furthermore, complex stray-field topologies around these objects are of interest for superconducting electronics, particle trapping and biomedical applications.

Ultrafast vortex motion has recently become a subject of extensive investigations, triggered by the fundamental question regarding the ultimate speed limits for magnetic flux quanta and enhancements of single-photon detectors. In this regard, the current-biased quench of a dynamic flux-flow regime—flux-flow instability (FFI)—has turned into a widely used method for the extraction of information about the relaxation of quasiparticles (unpaired electrons) in a superconductor. However, the large relaxation times ${\tau }_{ϵ}$ deduced from FFI for many superconductors are often inconsistent with the fast relaxation processes implied by their single-photon counting capability. Here, we investigate FFI in $15$-nm-thick $182$-$\mu \mathrm{m}$-wide MoSi strips with rough and smooth edges produced by laser etching and milling by a focused ion beam. For the strip with smooth edges we deduce, from current-voltage ($I$-$V$) curve measurements, a factor of 3 larger critical currents $I_c$, a factor of 20 higher maximal vortex velocities of 20 km/s, and a factor of 20 shorter ${\tau }_{ϵ}$. We argue that for the deduction of the intrinsic ${\tau }_{ϵ}$ of the material from the $I$-$V$ curves, utmost care should be taken regarding the edge and sample quality and such a deduction is justified only if the field dependence of $I_c$ points to the dominating edge pinning of vortices.