Spin-Wave Emission from Vortex Cores under Static Magnetic Bias Fields.

We studied the influence of a static in-plane magnetic field on the alternating-field-driven emission of nanoscale spin waves from magnetic vortex cores. Time-resolved scanning transmission X-ray microscopy was used to image spin waves in disk structures of synthetic ferrimagnets and single ferromagnetic layers. For both systems, it was found that an increasing magnetic bias field continuously displaces the wave-emitting vortex core from the center of the disk toward its edge without noticeably altering the spin-wave dispersion relation. In the case of the single-layer disk, an anisotropic lateral expansion of the core occurs at higher magnetic fields, which leads to a directional rather than radial-isotropic emission and propagation of waves. Micromagnetic simulations confirm these findings and further show that focusing effects occur in such systems, depending on the shape of the core and controlled by the static magnetic bias field.

Boosting the Photoelectrochemical Performance of Au/ZnO Nanorods by Co-Occurring Gradient Doping and Surface Plasmon Modification.

Band bending modification of metal/semiconductor hybrid nanostructures requires low-cost and effective designs in photoelectrochemical (PEC) water splitting. To this end, it is evinced that gradient doping of Au nanoparticles (NPs) inwards the ZnO nanorods (NRs) through thermal treatment facilitated faster transport of the photo-induced charge carriers. Systematic PEC measurements show that the resulting gradient Au-doped ZnO NRs yielded a photocurrent density of 0.009 mA/cm2 at 1.1 V (vs. NHE), which is 2.5-fold and 8-fold improved compared to those of Au-sensitized ZnO and the as-prepared ZnO NRs, respectively. The IPCE and ABPE efficiency tests confirmed the boosted photoresponse of gradient Au-incorporated ZnO NRs, particularly in the visible spectrum due to the synergistic surface plasmonic effect of Au NPs. A gradient Au dopant profile promoted the separation and transfer of the photo-induced charge carriers at the electrolyte interface via more upward band bending according to the elaborated electrochemical impedance spectroscopy and Kelvin probe force microscopy analyses. Therefore, this research presents an economical and facile strategy for preparing gradient plasmonic noble NP-incorporated semiconductor NRs, which have excellent potential in energy conversion and storage technologies.

Stable Magnetorheological Fluids Containing Bidisperse Fillers with Compact/Mesoporous Silica Coatings.

A drawback of magnetorheological fluids is low kinetic stability, which severely limits their practical utilization. This paper describes the suppression of sedimentation through a combination of bidispersal and coating techniques. A magnetic, sub-micro additive was fabricated and sequentially coated with organosilanes. The first layer was represented by compact silica, while the outer layer consisted of mesoporous silica, obtained with the oil-water biphase stratification method. The success of the modification technique was evidenced with transmission electron microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The coating exceptionally increased the specific surface area, from 47 m2/g (neat particles) up to 312 m2/g, which when combined with lower density, resulted in remarkable improvement in the sedimentation profile. At this expense, the compact/mesoporous silica slightly diminished the magnetization of the particles, while the magnetorheological performance remained at an acceptable level, as evaluated with a modified version of the Cross model. Sedimentation curves were, for the first time in magnetorheology, modelled via a novel five-parameter equation (S-model) that showed a robust fitting capability. The sub-micro additive prevented the primary carbonyl iron particles from aggregation, which was projected into the improved sedimentation behavior (up to a six-fold reduction in the sedimentation rate). Detailed focus was also given to analyze the implications of the sub-micro additives and their surface texture on the overall behavior of the bidisperse magnetorheological fluids.

Incorporation of the New anti-Octadecaborane Laser Dyes into Thin Polymer Films: A Temperature-Dependent Photoluminescence and Infrared Spectroscopy Study.

New anti-octadecaborane(22) laser dyes have been recently introduced. However, their application in solid thin films is limited, despite being very desirable for electronics. Spectroscopic methods, photoluminescence (PL), and infrared reflection-absorption spectroscopy (IRRAS), are here used to reveal structural responses to a temperature change in thin polymer films made of π- and σ-conjugated and non-conjugated polymers and anti-octadecaborane(22) and its tetra-alkylatedderivatives. It has been observed that borane clusters are not firmly fixed within polymer matrices and that their ability for diffusion out of the polymer film is unprecedented, especially at higher temperatures. This ability is related to thermodynamic transitions of polymer macromolecular chains. PL and IRRAS spectra have revealed a clear correlation with ß-transition and α-transition of polymers. The influence of structure and molecular weight of a polymer and the concentration and the substitution type of clusters on mobility of borane clusters within the polymer matrix is demonstrated. A solution is proposed that led to an improvement of the temperature stability of films by 45 °C. The well-known spectroscopic methods have proved to be powerful tools for a non-routine description of the temperature behavior of both borane clusters and polymer matrices.

CuxCo1-xFe2O4 (x = 0.33, 0.67, 1) Spinel Ferrite Nanoparticles Based Thermoplastic Polyurethane Nanocomposites with Reduced Graphene Oxide for Highly Efficient Electromagnetic Interference Shielding.

CuxCo1-xFe2O4 (x = 0.33, 0.67, 1)-reduced graphene oxide (rGO)-thermoplastic polyurethane (TPU) nanocomposites exhibiting highly efficient electromagnetic interference (EMI) shielding were prepared by a melt-mixing approach using a microcompounder. Spinel ferrite Cu0.33Co0.67Fe2O4 (CuCoF1), Cu0.67Co0.33Fe2O4 (CuCoF2) and CuFe2O4 (CuF3) nanoparticles were synthesized using the sonochemical method. The CuCoF1 and CuCoF2 exhibited typical ferromagnetic features, whereas CuF3 displayed superparamagnetic characteristics. The maximum value of EMI total shielding effectiveness (SET) was noticed to be 42.9 dB, 46.2 dB, and 58.8 dB for CuCoF1-rGO-TPU, CuCoF2-rGO-TPU, and CuF3-rGO-TPU nanocomposites, respectively, at a thickness of 1 mm. The highly efficient EMI shielding performance was attributed to the good impedance matching, conductive, dielectric, and magnetic loss. The demonstrated nanocomposites are promising candidates for a lightweight, flexible, and highly efficient EMI shielding material.

The presence of fine and ultrafine particulate matter in the work environment.

This study presents the results of pilot measurement, where the exposure of fine and ultrafine particulate matter was monitored. The measurement was performed in welding workplace, where these particles are produced unintentionally. The measurement consisted of collecting information and measuring the concentration of particles in the workplace, where data collection was focused only on inhalation exposure. During welding, primarily 300 nm size particles are produced, and their concentration is strongly influenced by the welding material, type of welding and suction. The particles are amorphous in terms of morphology and contain manganese, iron and silicon, which can cause neurodegenerative diseases. Furthermore, the results indicate the importance of monitoring oral exposure.

Optimization of CoFe2O4 nanoparticles and graphite fillers to endow thermoplastic polyurethane nanocomposites with superior electromagnetic interference shielding performance.

The rapid growth, integration, and miniaturization of electronics have raised significant concerns about how to handle issues with electromagnetic interference (EMI), which has increased demand for the creation of EMI shielding materials. In order to effectively shield against electromagnetic interference (EMI), this study developed a variety of thermoplastic polyurethane (TPU)-based nanocomposites in conjunction with CoFe2O4 nanoparticles and graphite. The filler percentage and nanocomposite thickness were tuned and optimized. The designed GF15-TPU nanocomposite, which has a 5 mm thickness, 15 weight percent cobalt ferrite nanoparticles, and 35 weight percent graphite, showed the highest total EMI shielding effectiveness value of 41.5 dB in the 8.2-12.4 GHz frequency range, or 99.993% shielding efficiency, out of all the prepared polymer nanocomposites. According to experimental findings, the nanocomposite's dipole polarization, interfacial polarization, conduction loss, eddy current loss, natural resonance, exchange resonance, multiple scattering, and high attenuation significantly contribute to improving its electromagnetic interference shielding properties. The created TPU-based nanocomposites containing graphite and CoFe2O4 nanoparticles have the potential to be used in communication systems, defense, spacecraft, and aircraft as EMI shielding materials.

Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures.

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 µm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

Comprehensive evaluation of photoelectrochemical performance dependence on geometric features of ZnO nanorod electrodes.

The impact of geometric features, light absorption spectra, and electrochemical active surface area on photoelectrochemical properties was investigated in this work. Nanoforests of ZnO nanorods with rationally controlled morphologies were grown on ITO substrates by the hydrothermal method and utilized as a model for this purpose. The size of the nanorods was systematically adjusted by varying the concentration of polyethyleneimine as a cation surfactant in the growth solution. It was found that the emergent geometric characteristics (i.e. the aspect ratio) increased almost at the same pace as the electrochemically active surface area, but the light scattering effect slightly increased as a result of the random spatial orientation of the nanorods. The large surface area and the void space between nanorods increased the photon-to-current conversion efficiency by promoting the hole transfer process at the electrode/electrolyte interface. A maximum photocurrent density of 0.06 mA cm-2 (0.5 V vs. NHE) for smaller diameter and length ZnO nanorods (ZnO-P1) was obtained under 365 nm UV light illumination. Additionally, we provide visual evidence that a shorter photogenerated hole diffusion distance results in improved charge separation efficiency using Mn2+ as the photogenerated hole imaging agent. Therefore, the present work demonstrates a facile strategy for nanoforest morphology improvement for generating strong contact at the ZnO NR electrode/electrolyte interface, which is favourable in energy conversion and storage technologies.

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.