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We investigate the effect of focused-ion-beam (FIB) irradiation on spin waves with sub-micron wavelengths in Yttrium-Iron-Garnet (YIG) films. Time-resolved scanning transmission X-ray (TR-STXM) microscopy was used to image the spin waves in irradiated regions and deduce corresponding changes in the magnetic parameters of the film. We find that the changes of Ga$^+$ irradiation can be understood by assuming a few percent change in the effective magnetization $M_\mathrm{eff}$ of the film due to a trade-off between changes in anisotropy and effective film thickness. Our results demonstrate that FIB irradiation can be used to locally alter the dispersion relation and the effective refractive index $n_\textrm{eff}$ of the film, even for submicron wavelengths. To achieve the same change in $n_\textrm{eff}$ for shorter wavelengths, a higher dose is required, but no significant deterioration of spin wave propagation length in the irradiated regions was observed, even at the highest applied doses., Comment: 5 pages, 6 figures

This work examines the impact of electromagnetic cross-talk in magnonic devices when using inductive spin-wave (SW) transducers. We present detailed electrical SW spectroscopy measurements showing the signal contributions to be considered in magnonic device design. We further provide a rule of thumb estimation for the cross-talk that is responsible for the secondary SW excitation at the output transducer. Simulations and calibrated electrical characterizations underpin this method. Additionally, we visualize the secondary SW excitation via time-resolved MOKE imaging in the forward-volume configuration in a 100nm Yttrium-Iron-Garnet (YIG) system. Our work is a step towards fast yet robust joint electromagentic-micromagnetic magnonic device design., Comment: 5 pages, 5 figures

We present the design and experimental realization of a device that acts like a spin-wave lens i.e., it focuses spin waves to a specified location. The structure of the lens does not resemble any conventional lens design, it is a nonintuitive pattern produced by a machine learning algorithm. As a spin-wave design tool, we used our custom micromagnetic solver "SpinTorch" that has built-in automatic gradient calculation and can perform backpropagation through time for spin-wave propagation. The training itself is performed with the saturation magnetization of a YIG film as a variable parameter, with the goal to guide spin waves to a predefined location. We verified the operation of the device in the widely used mumax3 micromagnetic solver, and by experimental realization. For the experimental implementation, we developed a technique to create effective saturation-magnetization landscapes in YIG by direct focused-ion-beam irradiation. This allows us to rapidly transfer the nanoscale design patterns to the YIG medium, without patterning the material by etching. We measured the effective saturation magnetization corresponding to the FIB dose levels in advance and used this mapping to translate the designed scatterer to the required dose levels. Our demonstration serves as a proof of concept for a workflow that can be used to realize more sophisticated spin-wave devices with complex functionality, e.g., spin-wave signal processors, or neuromorphic devices., Comment: 5 pages, 4 figures

We demonstrate direct focused ion beam (FIB) writing as an enabling technology for realizing spin-wave-optics devices. It is shown that ion-beam irradiation changes the characteristics of YIG films on a submicron scale in a highly controlled way, allowing to engineer the magnonic index of refraction adapted to desired applications. This technique does not physically remove material, and allows rapid fabrication of high-quality architectures of modified magnetization in magnonic media with minimal edge damage (compared to more common techniques such as etching or milling). By experimentally showing magnonic versions of a number of optical devices (lenses, gratings, Fourier-domain processors) we envision this technology as the gateway to building magnonic computing devices that rival their optical counterparts in their complexity and computational power., Comment: 11 pages, 7 figures

We experimentally demonstrate the operation of a spin-wave Rowland spectrometer. In the proposed device geometry, spin waves are coherently excited on a diffraction grating and form an interference pattern that spatially separates spectral components of the incoming signal. The diffraction grating was created by focused-ion-beam irradiation, which was found to locally eliminate the ferrimagnetic properties of YIG, without removing the material. We found that in our experiments spin waves were created by an indirect mechanism, by exploiting nonlinear resonance between the grating and the coplanar waveguide. Our work paves the way for complex spin-wave optic devices -- chips that replicate the functionality of integrated optical devices on a chip-scale., Comment: 7 pages, 5 figures, presented at Joint European Magnetic Symposia (JEMS) 2020

Comprehensive control of the domain wall nucleation process is crucial for spin-based emerging technologies ranging from random-access and storage-class memories over domain-wall logic concepts to nanomagnetic logic. In this work, focused Ga+ ion-irradiation is investigated as an effective means to control domain-wall nucleation in Ta/CoFeB/MgO nanostructures. We show that analogously to He+ irradiation, it is not only possible to reduce the perpendicular magnetic anisotropy but also to increase it significantly, enabling new, bidirectional manipulation schemes. First, the irradiation effects are assessed on film level, sketching an overview of the dose-dependent changes in the magnetic energy landscape. Subsequent time-domain nucleation characteristics of irradiated nanostructures reveal substantial increases in the anisotropy fields but surprisingly small effects on the measured energy barriers, indicating shrinking nucleation volumes. Spatial control of the domain wall nucleation point is achieved by employing focused irradiation of pre-irradiated magnets, with the diameter of the introduced circular defect controlling the coercivity. Special attention is given to the nucleation mechanisms, changing from a Stoner-Wohlfarth particle's coherent rotation to depinning from an anisotropy gradient. Dynamic micromagnetic simulations and related measurements are used in addition to model and analyze this depinning-dominated magnetization reversal.