Manh-Huong Phan

The low signal-to-noise ratio (SNR) of existing magnetic sensors limits the detection of magnetic nanoparticles (MNPs) in microfluidic biosensing. We present a novel microfluidic coil-based impedance detection system for quantifying magnetic particles, including Fe filings and citrate-coated Fe₃O₄ MNPs, with potential applications in magnetically guided biosensing. Unlike conventional approaches that directly measure the magnetic properties of dispersed particles, our method employs an external collector magnet to concentrate particles within a copper coil detector. The accumulated particles alter the coil’s electromagnetic response through changes in the sample’s dielectric properties, producing an amplified impedance signal proportional to sample volume. We evaluated detection performance for 1–10 mg of ferromagnetic Fe filings and citrate-coated Fe₃O₄ MNPs across a broad frequency range. Results show a strong linear correlation between particle mass and impedance change, with SNR values from 25 dB to over 45 dB, demonstrating high sensitivity and precision. Coil sensitivity was further optimized by varying the number of turns (5, 10, and 15), enabling frequency-specific customization. This approach provides a scalable, low-cost platform adaptable to polymer-coated MNPs targeting biological analytes.

Iron oxides are one of the oldest magnetic systems in history and have been studied extensively due to their phase-tunable magnetic and electronic properties. The combination of ferrimagnetic half-metallic magnetite (Fe3O4) with antiferromagnetic insulating hematite (α-Fe2O3) forms a so-called biphase iron oxide (BPIO) system that exhibits highly tunable magnetic and spin-transport properties in terms of phase and volume fraction. In this work, we report the interfacial physics between variations of these iron oxide phases with graphene (Gr) on magnetotransport in these heterostructures. Our experiments reveal that the inclusion of graphene in these heterostructures induces an inversion in the sign of magnetoresistance at finite temperatures. We explain this observation with an effective percolative transport model. Interestingly, the switching temperature and the sharpness of the transition can be further tuned by varying the phase volume fractions of the iron oxide layer and the crystallinity. The BPIO films, which grow naturally on Si substrates, exhibit the highest switching temperature. Our observations underscore the ability to induce magnetoresistive switching in abundant iron oxide grown on cost-effective, CMOS-compatible substrates by including a single layer of Gr, which has potential applications in modern devices and neuromorphic computing.

Fe doping induces a synergistic enhancement of electronic conductivity and electrocatalytic activity in Gd ₂ O ₃ nanoparticles, enabling highly sensitive electrochemical detection of chloramphenicol in real pharmaceutical and milk samples.

A challenging task is to study and improve the electrochemical behaviors and sensing performance of Fe-BTC and Cu-BTC-based electrodes for sensitive detection toward lead( ii ) ions (Pb ²⁺ ).

Helimagnetic materials exhibit complex non-collinear spin structures, making them promising candidates for next-generation magnetoresistive devices. Their unique magnetic textures can yield enhanced magnetoresistance effects compared to conventional materials, potentially improving the performance of magnetic sensors and memory technologies. In this study, an interface engineering strategy is presented that leverages strain induced by the structural phase transition of Fe₃O₄ to enhance the magnetoresistance (MR) effect in nanostructured manganese phosphide (MnP) films near the ferromagnetic-to-helimagnetic (FM–HM) transition. MnP films (∼100 nm thick, grain size ∼86 nm) were grown on Si substrates using molecular beam epitaxy, followed by deposition of Fe₃O₄ layers of varying thicknesses (7 nm and 58 nm). The results show that a thin Fe₃O₄ layer (7 nm) enhances interfacial magnetic coupling and overall magnetization in the bilayer, while the thicker Fe₃O₄ layer (58 nm) dominates the magnetic response due to its soft magnetic nature. Remarkably, the MR near the FM–HM transition increases by 20% and 37% with the 7 nm and 58 nm Fe₃O₄ layers, respectively, attributed to strain-enhanced spin-dependent scattering at the interface. These findings provide new insights into strain-modulated magnetic coupling at iron oxide/helimagnet interfaces and underscore their potential for advanced spintronic applications.

The worldwide expedition for sustainable energy resources and clean electrical energy harvesting from renewable thermal energy has led to the dawn of spincaloritronics, a vast field that amalgamates spin transport and thermoelectricity. The anomalous Nernst effect (ANE) is one of the many branches of spincaloritronics which is usually observed in metallic and semiconducting magnetic materials. This effect makes use of the spin degree of freedom of an electron in those materials in addition to its charge to harvest electrical energy from renewable thermal energy. The ANE has recently attracted the attention of the spincaloritronics community as ANE-based thermoelectric generators have demonstrated superior performance and advantages over conventional Seebeck effect-based thermoelectric generators. Magnetic Heusler alloys with high Curie temperatures and large spin polarizations along with tunable magnetic and magnetotransport properties have shown emergent potential for room temperature ANE-based thermopile device applications. Particularly, topological Heusler alloys, such as Co ₂ MnGa, which exhibits large intrinsic Berry curvatures at the Fermi energy, have demonstrated the largest anomalous Nernst conductivities reported to date at room temperature amongst all conventional magnetic materials. Unlike prior reviews, which have focused on specific subclasses, our article offers a broader and more inclusive survey. In this article, we aim to review recent progress in the study of the ANE across a broad spectrum of magnetic Heusler alloys, including full, quaternary, and half Heusler compounds, and explore their potential for room-temperature ANE-based thermoelectric device applications as well as propose potential strategies for enhancing ANE in these magnetic Heusler alloys.

The magnetocaloric effect (MCE) provides a promising foundation for the development of solid-state refrigeration technologies that could replace conventional gas compression-based cooling systems. Current research efforts primarily focus on identifying cost-effective magnetic materials that exhibit large MCEs under low magnetic fields across broad temperature ranges, thereby enhancing cooling efficiency. However, practical implementation of magnetic refrigeration requires more than bulk materials; real-world devices demand efficient thermal management and compact, scalable architectures, often achieved through laminate designs or miniaturized geometries. Magnetocaloric materials with reduced dimensionality, such as ribbons, thin films, microwires, and nanostructures, offer distinct advantages, including improved heat exchange, mechanical flexibility, and integration potential. Despite these benefits, a comprehensive understanding of how size, geometry, interfacial effects, strain, and surface phenomena influence the MCE remains limited. This review aims to address these knowledge gaps and provide guidance for the rational design and engineering of magnetocaloric materials tailored for high-performance, energy-efficient magnetic refrigeration systems.

Magnetic high-entropy alloys (HEAs) with their unusual blend of long-range magnetic order and exceptional mechanical properties are beneficial for the development of next-generation spintronic devices that can withstand extreme conditions. Developing room-temperature magnetic HEAs and understanding the link among their magnetic, electronic, and mechanical properties are crucial. Here, we introduce nanocrystalline CoCrFeNiGa as a room-temperature bulk magnetic HEA candidate based on 3d-transition metals and elucidate its magnetic and electronic properties. Structural characterization reveals the existence of mixed BCC and FCC phases with a crystallite size of ∼51 nm. CoCrFeNiGa shows a high Curie temperature (T_C) of ∼872 K and soft magnetic behavior with minimal coercivity. We also observed spin freezing below 60 K, likely due to competing magnetic interactions among its 3d-transition metals. Electrical resistivity measurements confirm metallic behavior with magnon contributions below 50 K. Interestingly, CoCrFeNiGa exhibits a large anomalous Hall effect (AHE), with an anomalous Hall conductivity of ∼603 S·cm^-1 at 5 K and ∼144 S·cm^-1 at 300 K, persisting despite inherent disorder. This AHE is primarily attributed to an intrinsic mechanism. The combination of the above room-temperature magnetic order, soft magnetic properties, a large intrinsic AHE, and competing magnetic interactions positions CoCrFeNiGa as a prospective candidate for the development of next-generation robust spintronic devices and architectures using nanocrystalline magnetic HEAs, which are resilient under demanding conditions.

This article reports the effect of spherical particle size (4-30 nm) on magnetic properties and microwave (MW) reactivity of superparamagnetic iron oxide nanoparticles (SPIONs) toward environmental hyperthermia-based applications. For this, silica-coated, single domain iron oxide nanoparticles (IONPs@silica) were precisely synthesized via thermal decomposition and subsequently coated by a reverse microemulsion. Transmission electron microscopy and X-ray diffraction confirmed the formation of spherical, monodisperse, single continuous layer silica-coated magnetite nanoparticles. Magnetic measurements revealed size-dependent superparamagnetism with negligible coercivity for particles smaller than 30 nm at 300 and 350 K. Saturation magnetization increased with particle size, reaching its highest value at 30 nm due to reduced surface spin disorder. MW reactivity was evaluated by irradiating IONPs@silica in quartz sand beds (1 wt %) at 2.45 GHz for 120 s. Core sizes of 4, 17, and 30 nm IONPs@silica at 1 wt % produced statistically significant temperature increases in sand compared to the control where 17 nm particles showed the highest heating response For single-domain particles (4-21 nm), heat generationwas attributed toNéel relaxation induced by the alternating magnetic field component and electronic excitation driven by the electric field component of the MW. For larger, multidomain particles (30 nm), magnetic heating dominated, primarily through hysteresis, eddy currents, and residual losses. Among the materials evaluated, 17 nm IONPs@silica were optimal with regard to both superparamagnetism and superior MW reactivity, with their single-domain magnetic structure being retained, and relaxation mechanisms were not compromised by thermal exposure for up to five MW cycles.