Vu Hong Ky

Independent control of coercivity (H_C) and exchange bias (H_EB) in ferromagnetic/antiferromagnetic (FM/AFM) heterostructures is essential for optimizing perpendicular spintronic devices, including magnetic random-access memory (MRAM) and nanoscale magnetic sensors, yet remains challenging due to their shared interfacial origin. In this work, we demonstrate a systematic approach to decouple these properties in [Co/Pd] multilayers (MLs) exchange-coupled to FeMn by engineering the stacking sequence and antiferromagnetic layer thickness (t_FeMn). Two configurations—top-pinned [Co/Pd]/FeMn and bottom-pinned FeMn/[Co/Pd]—were fabricated using magnetron sputtering. Despite exhibiting similar fcc(111) texture, the two structures display markedly different magnetic responses. The bottom-pinned configuration promotes rotatable uncompensated spins, resulting in a significant enhancement of HC (up to 1440 Oe) with negligible HEB. In contrast, the top-pinned configuration stabilizes pinned uncompensated spins, leading to a pronounced perpendicular exchange bias (up to 188 Oe) with minimal impact on H_C. By varying t_FeMn, H_C and H_EB can be tuned independently over wide ranges. These results demonstrate that stacking-sequence-dependent interfacial spin configurations govern magnetic behavior rather than bulk structural differences, providing a practical and scalable strategy for designing high-stability reference layers and low-switching-energy free layers in advanced spintronic devices.

We have designed an excellent visible-light-driven and high-performance photocatalyst with a Ag-Cu₂O-ZnO nanowire heterostructure in our work by combining the hydrothermal approach with plasma–liquid technology. The structural and morphological characteristics and optical properties of the samples were evaluated using X-ray diffraction, field-emission scanning electron microscopy, and spectrophotometry, respectively. The results show that the Ag nanoparticles are mainly positioned on the Cu₂O nanoclusters compared with the ZnO nanowire surface, forming broccoli-like Ag-Cu₂O nanoclusters during the Ar gas plasma treatment process in an aqueous solution. The diameter of the Ag/Cu₂O nanoclusters ranges from 150 to 180 nm. The Ag-Cu₂O-ZnO nanowires exhibited improved photocatalytic performance, decomposing approximately 98% methyl orange dye in 30 min. This is a consequence of the synergistic interactions between the p-n heterojunction formed at the Cu₂O-ZnO interfaces and the localized surface plasmon resonance (LSPR) effect of the Ag nanoparticles, which broaden the visible light absorption range and effectively separate the photogenerated charge carriers.

In this work, nano-selenium (NSe) with different shapes (wires, rods, and spherical particles) was synthesized by a wet chemical method. These synthesized products were characterized by x-ray powder diffraction (XRD) analysis, a field emission scanning electron microscope (FE-SEM) with an energy dispersive x-ray analyzer, and Raman spectroscopy. FE-SEM images revealed that nanowires with an average diameter of 30–50 nm and length of 3–5 µm, nanorods with lengths of 400–800 nm and diameters of about 20–50 nm, and spherical-shaped nanoparticles (NPs) with diameters ranging from 40 to 60 nm were successfully synthesized. The XRD and Raman analysis confirmed that all the produced NSe samples exhibited hexagonal single-phase crystalline structure with no impurity phase. All three NSe products (SeNWs, SeNRs, and SeNPs) with a concentration range of 25–150 mg/l were used to investigate the impact of shape and concentration on seed germination and seedling vigor of four different crop species, namely, green bean, okra, wheat, and radish. The results revealed that NSe at low concentrations (≤50 mg/l for SeNWs and ≤100 mg/l for SeNRs and SeNPs) can promote seed germination, plant growth, and development of all the studied crop species. However, NSe can adversely affect the growth of plants at higher concentrations (≥75 mg/l for SeNWs).

In this study, we developed a pioneering non-enzymatic electrochemical sensor utilizing a flexible porous graphene electrode modified with ZnO nanoparticles (ZnO/fPGE sensor) to assess hypoxanthine (HXA) content in pork at post-mortem time. The ZnO/fPGE sensor was synthesized via hydrothermal method and direct laser writing with a CO2 laser on a polyimide film at ambient conditions. Its characterization was analyzed by Raman, Fourier-transform infrared spectroscopy, field-emission scanning microscopy, energy-dispersive x-ray spectroscopy, and cyclic voltammetric techniques. Linear response, the limit of detection, and sensitivity to the HXA were enhanced with the values of the range from 1.5 to 150, 0.14 µM, and 6.6 µA μM−1 cm−2, respectively. Effective resistance to common physiological interferences (such as uric acid, ascorbic acid, dopamine, glucose, and xanthine) was indicated, and additionally, the determination of HXA concentration in real samples with good selectivity is attributed to the synergistic effects between ZnO nanoparticles and fPGE. Therefore, the ZnO/fPGE has provided a favorable electrical environment for developing high-performance electrochemical biosensors to determine hypoxanthine in pork meat.

Currently, MnBi magnetic material is promising to be very potential for low-cost high-temperature permanent magnetic applications. The most attractive parameters are the high magnetocrystalline anisotropy energy and its positive thermal coefficient which allow a high coercivity of MnBi magnets working even at 150 – 200 ^oC. This advantage is paid by the moderate value of magnetization, so the high energy product of MnBi magnets depends on how one can keep a good balance between the remanent magnetization M_r and the coercivity _bH_c. The paper considers this problem and discusses how to regulate the processing route to keep this balance to enhance the performance of MnBi green powders and MnBi bulk magnets prepared thereof