The present study focuses on the investigation of the magnetization reversal process in amorphous microwires of the composition Co64.82Fe3.9B10.2Si12Cr9Mo0.08, which possesses a low Curie temperature T-C of 61 degrees C. The microwire retains a nearly rectangular hysteresis loop, an axial anisotropy and a positive magnetostriction up to T-C . The coercivity decreases with temperature, following the decrease in the saturation magnetization M-S , but it has a different dependence on M-S far from and near T-C , which suggests different mechanisms of magnetostriction in these temperature intervals. Furthermore, the harmonic spectrum of the voltage induced during remagnetization is also temperature sensitive. The area under the voltage pulse is directly proportional to M-S , resulting in a comparable dependence of the harmonic amplitudes. In the context of potential applications in wireless temperature sensors, measuring the harmonic spectrum offers distinct advantages based on lock-in techniques. In addition, the temperature range over which the harmonic spectrum varies most is extended by using two (or potentially few) microwires with different T-C . The change in T-C from 61 degrees C to 57 degrees C is achieved by current annealing of the same microwire, which helps to extend the temperaturesensitive range of the two microwire harmonic response between 40 degrees C and 61 degrees C.

This study explores the influence of the molecular weight and phase composition of polyvinylidene fluoride (PVDF) precursors on the structural, mechanical, and magnetoelectric properties of PVDF/cobalt ferrite (PVDF/CFO) composites fabricated by fused deposition modeling (FDM). It was shown that the composite PVDF/CFO printed from a precursor with a lower molecular weight contains a higher content of the electroactive phase, which eventually leads to a higher magnitude of the magnetoelectric coefficient. The lower molecular weight is advantageous due to its reduced melting point which simplifies the printing process. Despite the higher magnitude of the Young’s modulus of the composite PVDF/CFO printed from low molecular weight PVDF, the filaments remain suitable for additive manufacturing. Overall, the results demonstrate that precursor selection is a key parameter for optimizing the functionality and printability of FDM-printed magnetoelectric composites.

Anisotropic ferromagnetic micro- and nanoparticles made of 3d metals demonstrate the ability to effectively influence micro- and nanoscale biological entities through hyperthermia and mechanical vibrations induced by magnetic fields. Multifunctional nanoparticles designed for combined therapies are particularly effective. This study explores the potential application of Ni@Au nanotubes to synergize magnetomechanical effects with photothermal heating. The orientation of nanotubes in a magnetic field was demonstrated by changes in the intensity of the light beam passing through a water suspension of nanotubes. The gold coating doubled the optical absorption of the solution in comparison with pure nickel nanotubes and resulted in the appearance of a resonance-enhanced peak in the range of 700–800 nm, the position of which is in accordance with theoretical calculations. The photothermal performance of nanotube solu-tions was quantitatively assessed by determining the photothermal conversion coefficient, which increased due to gold coating. However, it’s worth noting that the gold coating did not significantly reduce nanotube cytotoxicity in hepatocyte-derived cellular carcinoma cells (Huh7). The potential reasons for this outcome include the large particle size and non-uniform gold coating. Nevertheless, the combination of two anti-cancer therapies employing the same type of particles offers the opportunity to reduce particle concentration while maintaining the required therapeutic efficacy.

This study explores the influence of the molecular weight and phase composition of polyvinylidene fluoride (PVDF) precursors on the structural, mechanical, and magnetoelectric properties of PVDF/cobalt ferrite (PVDF/CFO) composites fabricated by fused deposition modeling (FDM). It was shown that the composite PVDF/CFO printed from a precursor with a lower molecular weight contains a higher content of the electroactive phase, which eventually leads to a higher magnitude of the magnetoelectric coefficient. The lower molecular weight is advantageous due to its reduced melting point which simplifies the printing process. Despite the higher magnitude of the Young's modulus of the composite PVDF/CFO printed from low molecular weight PVDF, the filaments remain suitable for additive manufacturing. Overall, the results demonstrate that precursor selection is a key parameter for optimizing the functionality and printability of FDM-printed magnetoelectric composites.

In this paper, we have investigated piezoelectric, magnetic and magnetoelectric properties of composite materials, consisting of polyvinylidene fluoride (PVDF) matrix and CoFe2O4 nanoparticles in the form of filament extrusion and 3D printed films. We used PVDF powders from different manufacturers each with different molecular weights and phase compositions. For PVDF with lower molecular weight and higher electroactive phase content of the, we observed that approximately 80 % of the electroactive phase in the starting polymer was effectively transferred to the printed films through all technological stages. The composite filaments exhibited ferromagnetic behavior with a large coercive force of 1.7±0.1 kOe consistent with a particle size of about 20 nm. The magnetoelectric coefficient was about 2 mV/(Oe∙cm) for printed composite films from both precursors, which is sufficient for a range of applications including microelectronics and tissue engineering using magnetically stimulated electric fields.

This study investigates the effect of polyvinylidene fluoride–CoFe2O4 (PVDF-CFO) composite film thickness on their supramolecular structure, phase composition, and dielectric properties. The composites were synthesized from PVDF with CFO nanoparticles using the Dr. Blade method to obtain film thicknesses ranging from 15 to 58 μm. The data obtained show that the thinner film (15 μm) has a higher β-phase content compared to the thicker films (58 μm), as confirmed by FTIR and Raman spectroscopy. Scanning electron microscopy (SEM) showed that increasing film thickness within the studied range leads to the development of larger spherulitic structures and increased porosity. Atomic force microscopy (AFM) analysis also showed that thicker films have higher tensile strength due to their larger cross-sectional area, while thinner films exhibit lower elasticity. A more uniform microstructure and an increased electroactive phase in thin films result in increased permittivity, which is critical for PVDF-based sensors and energy devices.

Low temperature magnetization measurements of citrate precursor-synthesized magnesium ferrite nanoparticles (MFNPs) of - 27 nm were conducted by progressively lowering the temperature from 300 K to 100 K. Hysteresis curves revealed unsaturated magnetization even at +/- 15 kOe, attributed to surface spins. Specific saturation magnetization (sigma s) and coercivity (Hc) experienced an increase from 26.46 emu/g (300 K) to 34.79 emu/g (100 K), and from 92 Oe (300 K) to 187 Oe (100 K), respectively. Specific remanence magnetization (sigma r) rose from 5.58 emu/g (300 K) to 10.14 emu/g (100 K), indicating a notable shift in magnetic behavior. Effective anisotropy constant (Keff) showed significant growth from 2474.14 erg/g (300 K) to 6635.04 erg/g (100 K), highlighting low magnetocrystalline anisotropy at room temperature. The rise in magnetic moment (nB) from 0.95 Am2 at 300 K to 1.25 Am2 at 100 K indicates improved magnetic alignment and stability, particularly at lower temperatures. Correlation analysis revealed strong negative curvilinear correlations between magnetic properties and temperature. Extrapolation estimated the blocking temperature (-573 K), coercivity at 0 K (-249 Oe), and Curie temperature (-660 K). These results suggest promising applications in space technology, underscoring the enhanced sensitivity of MFNPs to external magnetic fields in cold environments.

Glass-coated microwires exhibiting magnetic bistability have garnered significant attention as promising wireless sensing elements, primarily due to their rapid magnetization switching capabilities. These microwires consist of a metallic core with diameter d, encased in a glass coating, with a total diameter D. In this study, we investigated how the dimensions of both components and their ratio (d/D) influence the magnetization reversal behavior of Fe-based microwires. While previous studies have focused on either d or d/D individually, our research uniquely considered the combined effect of both parameters to provide a comprehensive understanding of their impact on magnetic properties. The metallic core diameter d varied from 10 to 19 µm and the d/D ratio was in the range of 0.48–0.68. To assess the magnetic properties of these microwires, including the shape of the hysteresis loop, coercivity, remanent magnetization, and the critical length of bistability, we employed vibrating sample magnetometry in conjunction with FORC-analysis. Additionally, to determine the critical length of bistability, magnetic measurements were conducted on microwires with various lengths, ranging from 1.5 cm down to 0.05 cm. Our findings reveal that coercivity is primarily dependent on the d/D parameter. These observations are effectively explained through an analysis that considers the competition between magnetostatic and magnetoelastic anisotropy energies. This comprehensive study paves the way for the tailored design of glass-coated microwires for diverse wireless sensing applications.

The study encompasses an investigation of optical, photothermal and biocompatibility properties of a composite consisting of golden cores surrounded by superparamagnetic CoFe2O4 nanoparticles. Accompanied with the experiment, the computational modeling reveals that each adjusted magnetic nanoparticle redshifts the plasmon resonance frequency in gold and nonlinearly increases the extinction cross-section at ~800 nm. The concentration dependent photothermal study demonstrates a temperature increase of 8.2 K and the photothermal conversion efficiency of 51% for the 100 μg/mL aqueous solution of the composite nanoparticles, when subjected to a laser power of 0.5 W at 815 nm. During an in vitro photothermal therapy, a portion of the composite nanoparticles, initially seeded at this concentration, remained associated with the cells after washing. These retained nanoparticles effectively heated the cell culture medium, resulting in a 22% reduction in cell viability after 15 min of the treatment. The composite features a potential in multimodal magneto-plasmonic therapies.

The effect of doping of Co2+ and Sn4+ in Ba0.5Sr0.5Fe12-2xO19 hexaferrite with different concentrations (x = 0.2, 0.4, 0.6, 0.8, and 1.0) was studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), complex impedance spectroscopy, and analyzed as a dielectric resonating antenna (DRA) at room temperature. The samples were produced and sintered by the solid-state reaction method. Their structure appeared from the M-phase type while their increase in grain size evidenced a dependency on Co-Sn content. The dielectric constant and loss tangent, inferred from impedance spectroscopy, also decreased with the corresponding increase in doping. The real and imaginary impedance decreased with the frequency increment. An electrical equivalent circuit using the Resistance-Constant Phase Element (R-CPE) association was thus proposed, the best-simulated components fitting with the observed structural and microstructure properties. It enabled a better understanding of the microstructure through simulated values of grain/grain boundaries and its effect on tuning the electrical properties in the low-frequency regime. The ferrite characteristics were tested for dielectric resonator antenna applications owing to their good inherent behavior than microstrip patch antenna. Measurement of the radiation efficiency, gain and bandwidth parameters of all the produced ceramics showed that the non-doped one (x = 0.0) exhibits the optimum values: 99.91

Composite nanoparticles with a gold core enveloped by cobalt ferrite nanoparticles show potential for enhanced photothermal therapy. Determining the optimal gold-to-cobalt ferrite nanoparticle ratio, dependent on size, is vital for improving treatment efficiency. We address the urgent need for advancing photothermal therapy through utilising combined plasmon-magnetic composites with potential of controlled directional delivery. Our computational modeling and experimental absorption spectra analysis reveal that adjusting the cobalt ferrite nanoparticle content redshifts the plasmon resonance frequency in gold nanoparticles, which is accompanied by increase in the extinction cross-section. As a result, cobalt ferrite nanoparticle absorption dominates. Our experiments on photothermal response in aqueous solutions of composite nanoparticles of various concentrations demonstrate that 100 μg/ml solution yields a significant temperature increase of ~8.2 K and a photothermal conversion efficiency of ~51%. At this concentration, the composite nanoparticles effectively heat the cell culture medium under photothermal conditions, leading to 22% reduction in cell viability.

The identification of high-energy compounds in trace concentrations not only in the laboratory, but also in field conditions is of particular interest. The process should be clear, easy, and well-recognizable. We formed SERS-active substrates by using elongated nickel nanotubes synthesized by electrochemical deposition in the pores of ion-track membranes and coated them with gold for further application in the detection of low concentrations of analytes. The substrates were characterized using various techniques to determine the morphology of the nanotubes and modifying gold layer. The possibility of obtaining two types of gold-layer morphology was shown: in the form of a smooth film up to 20–50 nm thick and a coating with nanoneedles up to 250 nm long. The electric fields around the nanotubes were simulated at a laser wavelength of 532 nm to demonstrate the influence of the gold-layer morphology on the field distribution. The “needle” morphology was chosen to form the most effective SERS-active substrates for detection of low concentrations of aromatic polynitro compounds. The spectral peaks were identified by comparing the model and experimental Raman spectra at concentrations down to 10−5 M. Within this limit, all peaks (“fingerprints” of the substance) were clearly distinguishable.

1D cylindrical magnetic nanostructures (FeNi, FeCo, FeCoP) of complex topology such as nanowires (NWs), nanotubes (NTs), multilayered nanowires, and core–shell structures are discussed from the perspective of engineering a wide variety of magnetic materials from hard to semihard to soft. Most of recent data are given for the materials synthesized in the pores of polymer ion‐track membranes, which makes it possible to tune systematically the geometrical parameters, morphology, and composition. The key properties including crystal and micromagnetic structure, magnetic anisotropy, and coercivity are analyzed. Co‐based NWs with uniform morphology demonstrate coercivity of more than 10 kOe due to the combination of crystalline and shape anisotropies. In the case of NTs, the demagnetizing effect is reduced owing to a helical arrangement of the magnetization, which leads to low values of coercivity and remanence magnetization. Varying the geometrical parameters of multilayered NWs, the alternating soft and semihard magnetic layers can be made within a single nanowire, which is important for spin‐valve magnetoresistance. Au‐coated ferromagnetic nanostructures are biocompatible and can be used to enhance optical absorption. Ni@Au NTs used as substrates for Raman spectroscopy demonstrate the enhancement factor of the order of 104. Some aspects related to applications of 1D magnets are briefly overviewed.

The importance of magnetic micro- and nanoparticles for applications in biomedical technology is widely recognised. Many of these applications, including tissue engineering, cell sorting, biosensors, drug delivery, and lab-on-chip devices, require remote manipulation of magnetic objects. High-gradient magnetic fields generated by micromagnets in the range of 103–105 T/m are sufficient for magnetic forces to overcome other forces caused by viscosity, gravity, and thermal fluctuations. In this paper, various magnetic systems capable of generating magnetic fields with required spatial gradients are analysed. Starting from simple systems of individual magnets and methods of field computation, more advanced magnetic microarrays obtained by lithography patterning of permanent magnets are introduced. More flexible field configurations can be formed with the use of soft magnetic materials magnetised by an external field, which allows control over both temporal and spatial field distributions. As an example, soft magnetic microwires are considered. A very attractive method of field generation is utilising tuneable domain configurations. In this review, we discuss the force requirements and constraints for different areas of application, emphasising the current challenges and how to overcome them.

This work presents the dielectric properties of YNbO4 (YNO)-TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)(2)O-6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of -8.96 ppm.degrees C-1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below 10 dB at the resonant frequency, with a realised gain of 4.94 - 5.76 dBi, a bandwidth of 665-1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO-TiO2 composites are interesting candidates for microwave operating devices.

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, a deeper understanding of the magnetization reversal process is required, because it determines the measurable response (such as induced voltage waveform and its spectrum). However, the experimental observation of micromagnetic structure of micro-scale amorphous objects has strict size limitations. In this work we proposed a novel experimental technique for evaluating the microstructural characteristics of glass-coated microwires. The cross-sectional permeability distribution in the sample was obtained from impedance measurements at different frequencies. This distribution enables estimation of the prevailing anisotropy in the local region of the wire cross-section. The results obtained were compared with the findings of magnetostatic measurements and remanent state analysis. The advantages and limitations of the methods were discussed.

Magnetoimpedance (MI) in Co-based microwires with an amorphous and partially crystalline state was investigated at elevated frequencies (up to several GHz), with particular attention paid to the influence of tensile stress on the MI behavior, which is called stress-MI. Two mechanisms of MI sensitivity related to the DC magnetization re-orientation and AC permeability dispersion were discussed. Remarkable sensitivity of impedance changes with respect to applied tensile stress at GHz frequencies was obtained in partially crystalline wires subjected to current annealing. Increasing the annealing current enhanced the axial easy anisotropy of a magnetoelastic origin, which made it possible to increase the frequency of large stress-MI: for 90mA-annealed wire, the impedance at 2 GHz increased by about 300% when a stress of 450 MPa was applied. Potential applications included sensing elements in stretchable substrates for flexible electronics, wireless sensors, and tunable smart materials. For reliable microwave measurements, an improved SOLT (short-open-load-thru) calibration technique was developed that required specially designed strip cells as wire holders. The method made it possible to precisely measure the impedance characteristics of individual wires, which can be further employed to characterize the microwave scattering at wire inclusions used as composites fillers.

Ni nanotubes (NTs) were produced by the template method in the pores of ion-track membranes and then were successfully functionalized with gold nanoparticles (Ni@Au NTs) using electroless wet-chemical deposition with the aim to demonstrate their high catalytic activity. The fabricated NTs were characterized using a variety of techniques in order to determine their morphology and dimensions, crystalline structure, and magnetic properties. The morphology of Au coating depended on the concentration of gold chloride aqueous solution used for Au deposition. The catalytic activity was evaluated by a model reaction of the reduction of 4-nitrophenol by borohydride ions in the presence of Ni and Ni@Au NTs. The reaction was monitored spectrophotometrically in real time by detecting the decrease in the absorption peaks. It was found that gold coating with needle-like structure formed at a higher Au-ions concentration had the strongest catalytic effect, while bare Ni NTs had little effect. The presence of a magnetic core allowed the extraction of the catalyst with the help of a magnetic field for reusable applications.