This study presents the design and simulation of a two-directional (2D) magnetic field source based on a nested and orthogonal Helmholtz coil structure. Simulations were conducted using Comsol Multiphysics software to evaluate the source's characteristics, including the uniform magnetic field region, the current-magnetic field relationship, and field stability under both DC and AC currents. Crucially, the modeling included a detailed analysis of the mutual influence (cross-talk) between the two intersecting magnetic fields within the uniform region. This validated design provides a foundation for fabricating a multi-directional magnetic field generator capable of simultaneously assessing the electromagnetic immunity of sensitive electronic components (particularly sensors and high-frequency devices) across two orthogonal axes.

This study presents a comprehensive fabrication process for dielectric ceramic capacitor derived from lead-free Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) in bulk and powder form, synthesized by sol–gel method. Both the BNKT powder and the bulk ceramic were rigorously analyzed and compared for their crystal structure, morphology, magnetic and optical properties. Through XRD and Raman results, the structure in the form of morphological phase boundary (MPB) was detected. In addition, the morphological structure, grain size evolution and purity of the samples were also confirmed by SEM and EDX. The weak ferromagnetic property of the BNKT powder sample was replaced by the diamagnetic property of the bulk ceramic sample and a decrease in the band gap (Eg) from 3.33 eV to 3.13 eV was also observed in the corresponding samples. At room temperature, the dielectric constant (εr) of the bulk ceramic reached 2193 with a dielectric loss (tanδ) of 0.332 at 1 kHz. It also exhibits typical ferroelectric behavior with slim P–E loop, a recoverable energy density (Wrec) of 12.541 mJ/cm3, and a high energy storage efficiency (η) of 46.44

This study demonstrated a synthesis of high-crystallinity Bi1/2(Na0.8K0.2)1/2TiO3 (BNKT) powders using a sol-gel method through optimizing calcination conditions. Thermogravimetric analysis was utilized to monitor the decomposition and phase evolution of BNKT powders in the calcination temperature (Tcal) range of 600–800 °C. The BNKT powder with a single perovskite crystal phase was obtained by calcining xerogel for 1 h at Tcal = 800 °C. This result was also confirmed by X-ray diffraction and Raman scattering analyses and further explained through the main chemical reaction equations given at each calcination stage of the sol-gel process. In addition, the modification of associated physical properties (microstructure, magnetic, and optical properties) in BNKT powders was also investigated following the structural phase evolution induced by the calcination condition. Furthermore, a single-phase BNKT powder at Tcal = 800 °C was optimal for fabricating bulk ceramics. By sintering the pellets of an optimized powder at 1100 °C for 2 h, the obtained BNKT bulk ceramics showed a dense microstructure with an average grain size of about 1.75 μm. Interestingly, the BNKT bulk ceramics exhibited a high dielectric constant (εr) of 2193.4 with a dielectric loss tangent (tanδ) of 0.334 at 1 kHz, room temperature (RT). These findings indicate that optimizing the calcination temperature during the sol–gel process leads to fundamental improvements in the dielectric behavior of bulk BNKT ceramics, providing a promising basis for future studies aimed at enhancing their performance in potential dielectric capacitor applications.

Optical, photocatalytic, magnetic and microwave-shielding properties correlated with electronic structures of ZnO nanoparticles (NPs) hydrogenated at the annealing temperature (Tan) ranging from 400 to 900 ?C have been investigated. All fabricated samples are hexagonally monophasic with more lattice defects generated by hydrogenation that have changed the bandgap energy, and the features of luminescence and Raman-scattering spectra. Hydrogenation-induced defects also stimulated an anomalous Raman mode (AM) peaked at similar to 477 cm(-1). Interestingly, all samples exhibit ferromagnetism. Magnetic ordering gradually increases when T-an increases from 400 to 700 degrees C, but decreases for T-an > 700 degrees C. Upon the results obtained from analyzing X-ray absorption, magnetic-resonant and luminescent spectra, we believe that hydrogenation-induced ferromagnetism and AM are mainly due to Zn-related defects. These together with other hydrogen-related defects could form clusters to cause the magnetic coercivity. For T-an > 700 degrees C, the defects migrate to grain surfaces/boundaries while unstable defects move out of the ZnO lattice that reduce magnetic ordering. We have also found ZnO NPs hydrogenated at 700 degrees C with suitable thicknesses absorbing above 99.5 % incident microwaves at frequencies 8.6 and 10.4 GHz, corresponding to reflection-loss magnitudes of 25 similar to 38 dB. Concurrently, this sample shows the best photocatalytic performance of Rhodamine-B (RhB) degradation, about 67 % RhB decomposed under visible light irradiation for 3 h. Though its photodegradation kinetics obey the pseudo-first-order model, their pseudorate constant is dependent on irradiation time, which is related to the location of accessible-active sites on both surface and internal layers of NPs.

Impacts of hydrogen annealing on crystallographic characterization, electronic structure, and optical, photocatalytic, and magnetic properties of polycrystalline Zn1−xCoxO (x = 0.01–0.06) samples have been considered. Structural analyses based on powder X-ray diffraction, Rietveld refinement, and Raman spectroscopy prove all materials having the P63mc wurtzite-type structure. The Co-doping and hydrogenation changed the concentration of Zn– and O–related defects whose energy levels occupy the band gap. This also enhanced photocatalytic performance of hydrogenated samples with x > 0.02. X-ray and UV–Vis absorption analyses indicate the substitution of Co2+ for Zn2+ in the wurtzite-type ZnO lattice, leading to irregularly changed the unit-cell parameters. While all the as-prepared samples are paramagnetic, the hydrogenated ones exhibit weak ferromagnetism. Ferromagnetic (FM) ordering increases when x increases, particularly for x ≥ 0.02. According to the results achieved from studying crystalline and electronic structures, we believe that oxygen-vacancies-mediated interactions between Co2+ ions and H–Co–H exchange dimers enhanced FM ordering in hydrogenated Zn1−xCoxO. Computational investigations have also indicated that the magnetization value of H–Zn1−xCoxO is influenced by the positioning of the H dopant, meaning that the couplings between Co and H play an essential role in establishing FM order in H–Zn1−xCoxO.

The development of flexible electronic devices, particularly flexible and bendable energy storage devices, has catalyzed significant interest in the research of flexible composite materials. In this study, conductive paper membranes were synthesized by polymerizing polypyrrole (PPy) on the surface of cellulose fibers. The cellulose material, derived from cardboard, underscores an eco-friendly approach to waste reduction and environmental protection. Characterization of the cellulose/PPy conductive membranes using Fourier-transform infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM), and differential scanning calorimetry (DSC) confirmed the formation and uniform coverage of PPy on the cellulose surface. To enhance the uniformity of PPy polymerization on cellulose relative to previous studies, this work focuses on elucidating the formation and deposition of PPy particles on cellulose fibers, leading to the development of a homogeneous membrane. The membrane exhibited a peak electrical conductivity of 18.04 mS/cm at 0.1 mA, with conductivity increasing alongside PPy concentration, albeit at the expense of mechanical properties. Additionally, the membrane demonstrated charge storage capability, with specific capacitance values ranging from 22.5 to 50 pF/cm2 at a frequency of 1 kHz. The uniformity of PPy coverage on the cellulose surface was a crucial factor influencing the electrical properties of the composite membrane. This research highlights the significant potential of conductive membranes for application in flexible and bendable energy storage devices.

In recent years, ultrasonic welding technology has developed rapidly and is applied in many fields. The research and application of piezoelectric ceramic materials in ultrasonic welding have received significant attention from researchers and commercial manufacturers. In this work, we have studied, designed and fabricated piezoelectric ceramic materials described by the general formula Pb(1_x)Srx(Zr0.53Ti0.47)O3 or (PSZT) with x = 0.6 mol%. In addition, the experimental fabrication process of PSZT piezoelectric ceramic transducer in the form of a ring by ball milling and solid-state reaction process are also presented. Adding hard dopants Sr2+ to the A (of Pb2+) position in the perovskite structure is considered to improve the dielectric and piezoelectric properties of Pb(Zr0.53Ti0.47)O3. The results show that the dielectric constant (3/4r) is 1707.4, and the dielectric loss (tan & curren;) is 0.0034 at room temperature and 1 kHz. The hysteresis loop of the non -polar PSZT piezoelectric ceramic sample shows the same behaviour as the hard PZT ceramic with a remnant polarization of 2.0 mu C/cm2 and a force field of 5.5 kV/cm. The Curie temperature (TC) is determined to be about 342 degrees C. The piezoelectric properties of the PSZT piezoelectric ceramic ring were also measured: the effective electromechanical coupling coefficient (keff) of 0.40, electromechanical coupling coefficient (kp) of 0.48, mechanical quality factor (Qm) of 270.92, piezoelectric coefficient (d33) is 314 pC/N, respectively. This result demonstrates that the fabrication process of Pb1_xSrx(Zr0.53Ti0.47)O3 or (PSZT) ceramic rings with x = 0.6 mol%, exhibiting superior characteristics, is entirely suitable for practical applications such as the production and substitution of piezoelectric sensors for high -power ultrasonic welding technology operating at a resonant frequency ranging from 30 to 40 kHz. [doi:10.2320/matertrans.MT-MG2022030]

We synthesized ZnFe2O4 and CoFe2O4 nanoparticles and investigated their magnetic and electromagnetic behaviors at room temperature. X-ray diffraction analyses indicated that these materials having average crystallite sizes of 22–31 nm, and their crystal structure belongs to the cubic-spinel class. While ZnFe2O4 exhibits soft magnetic behavior, with Ms = 88 emu/g and Hc = 130 Oe, CoFe2O4 exhibits hard magnetic behavior, with Ms = 65 emu/g and Hc = 620 Oe. Investigations into the complex permittivity and permeability dependent on the frequency (f) and thickness (t) revealed remarkable changes in their values at frequencies f = 12–16 GHz for both samples. In the range f = 13.5–13.8 GHz, reflection loss magnitudes of devices based on ZnFe2O4– and CoFe2O4– with t = 2.25–2.75 mm were about 11.3–14.2 dB, corresponding to electromagnetic wave absorption of 90–95

Polycrystalline BaFe12-xMnxO19 (x = 0.5, 1 and 2) hexaferrites have fabricated by using normal solid-state reactions. Rietveld refinement of powder X-ray diffraction patterns reveals the specimens having the single-phase hexagonal structure. The analysis of X-ray absorption spectra indicates a mixed oxidation state of Fe2+,3+ and Mn2+,3+ ions. There are chemical shifts of Fe2+ → Fe3+ and Mn2+ → Mn3+, and a decrease of Ms from ~31 to 24 emu/g when x increases from 0.5 to 2, respectively. Large M(H) hysteresis loops with Hc increasing from 3.2 kOe for x = 0.5 to ~4.1 kOe for x = 2 prove the hard-magnetic behavior of all the specimens. The ionic-radius difference between Mn and Fe, and Mn3+-related Jahn-Teller effect at the octahedral sites have enhanced the unit-cell volume when x increases. Having studied microwave absorption, we have found strong changes in values of the permittivity and permeability at frequencies f = 10~15 GHz. For a thickness t = 2.4 mm, reflection loss magnitudes are about 10~11 dB (i.e., above 90% microwave being absorbed), with an absorption bandwidth of ~3 GHz. Assessments of loss tangents and Cole-Cole curves prove electrical energy dissipation due to interfacial/dipolar polarizations and conductive loss playing a dominant role in microwave shielding of BaFe12-xMnxO19.

This paper presents the design and manufacture of ultrasonic emitters for welding machines using piezoelectric ceramic materials for welding on non-woven fabrics. The ultrasonic vibrating membrane (UVB) used for the transducer is investigated to ensure that there are no cracks in the material structure. These parameters serve as the basis for evaluating the quality of the ultrasonic vibrating membrane in the fabrication of an oscillator for ultrasonic transducer welding (USTW). The ultrasonic power generator (USPG) is made of high-frequency components and power components to supply electrical oscillations to the UVB. This vibrating source must be compatible with the USTW to operate at maximum efficiency. Due to the influence of the manufacturing process and USTW usage environment, after operating for a long time, the resonant frequency (fr) will be changed. Therefore, the USPG needs to monitor the frequency of the USTW automatically. Matching the impedance of USTW and USPG is very important to get the most out of USPG power. The fabrication results show that the use of high-resolution timer to generate the control frequency for USPG achieves high accuracy, with the largest error of 0.006% at 18401.12 Hz when surveyed in the range of 18 to 22 kHz. The parameters of control signal delay between two phases and pulse width also give very good results. Impedance-matching (IM) networks also show good exploitation of USPG when compared to USPG without IM.

Recently, two-dimensional (2D) layered organic-inorganic perovskites have been a hot topic not only in photovoltaics but also in optoelectronic applications due to their remarkable optical and electronic properties. In this study, the multiferroic property of the 2D layered (C6H5CH2CH2NH3)2NiCl4, abbreviated PEA-NiCl4, perovskite single crystals has been first reported. The crystals were synthesized by anti solvent evaporation method by a layer-by-layer mode with relative smooth surface that confirmed by SEM image. The XRD patterns reveal the high crystalline quality with (n00) dominant plane (n = 2, 4, 6, +). The 180 degrees reproducible hysteresis phase loop, butterfly-like amplitude curve, and an effective piezoelectric coefficient of 327 pm/V was evaluated using Piezoelectric Force Microscopy (PFM) measurement. The multiferroic properties has been confirmed by P-E hysteresis loops with PS = 16.3 mu C/cm2 Pr = 14.8 mu C/cm2, and EC = 6.7 kV/cm and M-H hysteresis loops with HC = 151 G. The 80-nm-width ferroelectric domains orienting along the crystal surface have been observed by the PFM images. This study offers an opportunity to develop new multiferroics material based on 2D layered hybrid perovskite single crystals.

Magnetic phase transitions are important for the application of individual materials toward modern spintronics and sensing. Using high-resolution sound velocity and pyrocurrent measurements, we have obtained a detailed magnetic phase diagram of multiferroic Ca2CoSi2O7 for magnetic fields applied along the crystallographic [100]- and [001]-directions. The magneto-acoustic measurements were conducted for both longitudinal and transverse modes in both static and pulsed magnetic fields up to 17 and 68 T, respectively. Distinct anomalies with significant changes in sound velocity and sound attenuation were observed at the onset of the structural and magnetic phase transitions. Interestingly, results obtained for fields parallel to the [100]-direction reveal a hysteresis and step-like decrements in ultrasound indicating a transition into a different metastable structural distortion below TN and at magnetic fields between 4 and 10 T that has not been previously reported. We believe that this field-induced distorted structure phase may be the cause of the subsequent phase transition at 11 T. At low temperatures, a softening of the lattice within the ordered phases is also observed, which may be due to residual spin fluctuations.

M-type hexaferrites doped with transition metals are important materials used widely in modern electronic devices. Although many research works considered their magnetic properties, the relation between their electronic structure and electromagnetic behaviors have been less taken into account, particularly Mn-doped M-type hexaferrites. This work presents a detailed study on the electronic structure, and dielectric, magnetic and reflection-loss behaviors of BaFe12-xMnxO19 (x = 0.5, 1 and 2) hexaferrite specimens prepared by conventional solid-state reactions. The analysis of X-ray absorption spectra proves a mixed oxidation state of Fe-2+,Fe-3+ and Mn-2+,Mn-3+ ions, and chemical shifts of Fe2+ -> Fe3+ and Mn2+ -> Mn3+ when x increases from 0.5 to 2. These factors change the unit-cell volume, and cause Mn3+-related Jahn-Teller distortions. Concurrently, the saturation magnetization M-s varies in the range from 24 to similar to 31 emu/g, which is associated with interaction competitions between Fe-2+,Fe-3+-Mn-2+,Mn-3+ pairs and Fe2+-related spin canting. Having studied electromagnetic behaviors, we have found strong changes in values of the permittivity and permeability at frequencies f = 10 similar to 15 GHz. For a thickness t = 2.4 mm, reflection-loss magnitudes of microwave are about 10 similar to 11 dB (corresponding to above 90% microwave being absorbed), with an absorption bandwidth of similar to 3 GHz. Assessments of the magnetic and dielectric loss tangents, and Cole-Cole curves indicate electrical energy dissipation associated with interfacial/dipolar polarizations and conductive loss playing a dominant role in microwave absorption of BaFe12-xMnxO19.

We report a detailed study on the magnetic behaviors and magnetocaloric (MC) effect of a single crystal of lithium samarium tetraphosphate, LiSm(PO3)4. The analyses of temperature-dependent magnetization data have revealed magnetic ordering established with decreasing temperature below Tp, where Tp is the minimum of a dM/dT vs. T curve and varies as a linear function of the applied field H. The Curie temperature has been extrapolated from Tp(H) data, as H → 0, to be about 0.51 K. The establishment of magnetic-ordering causes a substantial change in the heat capacity Cp. Above Tp, the crystal exhibits paramagnetic behavior. Using the Curie-Weiss (CW) law and Arrott plots, we have found the crystal to have a CW temperature θCW ≈ -36 K, and short-range magnetic order associated with a coexistence of antiferromagnetic and ferromagnetic interactions ascribed to the couplings of magnetic dipoles and octupoles at the Γ7 and Γ8 states. An assessment of the MC effect has shown increases in value of the absolute magnetic-entropy change (|ΔSm|) and adiabatic-temperature change (ΔTad) when lowering the temperature to 2 K, and increasing the magnetic-field H magnitude. Around 2 K, the maximum value of |ΔSm| is about 3.6 J kg-1 K-1 for the field H = 50 kOe, and ΔTad is about 5.8 K for H = 20 kOe, with the relative cooling power (RCP) of ∼82.5 J kg-1. In spite of a low MC effect in comparison to Li(Gd,Tb,Ho)(PO3)4, the absence of magnetic hysteresis reflects that LiSm(PO3)4 is also a candidate for low-temperature MC applications below 25 K.

In this work, we carried out survey on magnetic field strength and gradient in space around arrays of micro-sized parallelepipedic magnets by simulation and calculation. Magnetic field distributions are a function of magnet’s size and position with respect to magnet’s surface. Our purpose is to explain how magnetic interactions evolve while dimensions of magnetic sources are reduced. Firstly, the simulations and calculations were executed for a magnet with a large surface size of 1,000×1,000 µm2, a thickness of 5 µm, and a residual magnetism of 1.6T perpendicular to its surface. Then, the similar works were also performed for arrays of magnets with smaller surface sizes, e.g. 1,000×500 µm2; 1,000×200 µm2; 1,000×100 µm2; 1,000×50 µm2 and 1,000×10 µm2. Consequently, both the magnetic field strength and gradient in the space which is above and near the surface of the magnets, particularly, the space from the surface of the magnets to the height of 100 µm far from the surface of the magnets, were enhanced when the magnets’ size were appropriately reduced. This suggests that the application field of the magnets will be expanded and their integration into microsystems will be grown as the size of the magnets is reduced.

Polymer dẫn điện là hợp chất có khả năng dẫn điện và đàn hồi, với nhiều ứng dụng trong nghiên cứu và chế tạo các thiết bị cảm biến mềm, rô bốt mềm. Để chế tạo polymer dẫn, cần sử dụng polymer dẫn điện kết hợp với vật liệu nền và dạng thức kết hợp vật liệu phù hợp. Trong nghiên cứu này, chúng tôi đã kết hợp polymer dẫn polypyrrole (PPy) với vật liệu nền là nanocellulose tinh thể (CNC) và chế tạo thành công vật liệu composite ở dạng hydrogel có khả năng dẫn điện, đàn hồi. Thí nghiệm kiểm tra được tiến hành để giám sát quá trình tổng hợp và xác nhận đặc tính của vật liệu. Sự tạo thành của CNC đã được kiểm chứng bằng cách sử dụng phương pháp tán xạ ánh sáng động, và kính hiển vi điện tử. Đường kính hạt CNC thu được nằm trong khoảng 50-650 nm. Tính chất dẫn điện của hydrogel được minh chứng thông qua việc chế tạo và khảo sát một cảm biến đo biến dạng. Thí nghiệm đồng thời cho thấy vật liệu có tiềm năng ứng dụng trong chế tạo cảm biến đo biến dạng, cảm biến lực và các ứng dụng điện tử đàn hồi, v.v.

Sorting and trapping cells play an important role in fundamental cellular and biology research that enables the study of single-cell behaviors, which are different in comparison with a cluster of cells. Contactless handling techniques using different optical, mechanical, or magnetic phenomena have been studied for single-cell trapping. Among them, the diamagnetic force created by magnetic structures on cells is significant and stable both in time and in space. In this work, arrays of hard magnetic clusters in the PDMS background (hereafter called magnetic structure) were successfully fabricated using the magnetic imprinting method. The magnetic structure shows a proper magnetic property and the possibility to sort and trap T47D single cells via the diamagnetic levitation phenomenon at defined positions, which are both experimentally observed and theoretically calculated. The obtained results show the promise of developing a simple way to separate directly living cells.

Colloidal quantum-dot-based green light-emitting diodes (QD-LEDs) are attractive for use in display devices because of the remarkable electrical and optical characteristics of quantum dot materials. In this study, ZnO NPs were synthesized as the carrier transporting layer using a solution-mediated process. After that, all solution- multilayer QD-LEDs with a structure of ITO-Glass/PEDOT:PSS/PVK/Green-QDs/ZnO/Al/Encap was fabricated. The effect of the solvent on the emission layer was investigated, along with the effect of the ZnO NPs concentration of the electron transfer layer. The regular green-QDLED device showed a maximum luminance of 9865 cd/m2, a luminance efficiency of 13.84 cd/A, and an EQE of 3.68%, at a turn-on voltage at 6.0 V.

The combination of two dielectric-magnetic components in the same composite has been shown to significantly improve the effectiveness of electromagnetic (EM) shielding and microwave absorption (MWA) because they have both a combination of high dielectric and magnetic losses and good impedance matching. The novel Bi-1/2(Na0.8K0.2)(1/2)TiO3/Fe3O4 (BNKT/Fe3O4) composite has been successfully synthesized by a two-step method with wide effective absorption bandwidth (EAB = 16 GHz) in the high-frequency (2-18 GHz). It was evident that the MWA efficiency of the BNKT/Fe3O4 composite has been significantly improved compared with pure Bi-1/2(Na0.8K0.2)(1/2)TiO3 or Fe3O4 materials. In addition, the BNKT/Fe3O4 composite could achieve reflection loss (RL = -39.41 dB, similar to 99.99% at 10.16 GHz) with a sample thickness optimal (d = 4.7 mm). This work shows that the novel BNKT/Fe3O4 composite has excellent MWA properties, all contributing to a potential candidate in the electromagnetic wave absorption and shielding fields.