Magnetic Surface Research Articles

Structural Magnetic Resonance Imaging-Based Surface Morphometry Analysis of Pediatric Down Syndrome.

Down syndrome (DS) is a genetic disorder characterized by intellectual disability whose etiology includes an additional partial or full copy of chromosome 21. Brain surface morphometry analyses can potentially assist in providing a better understanding of structural brain differences, and may help characterize DS-specific neurodevelopment. We performed a retrospective surface morphometry study of 73 magnetic resonance imaging (MRI) examinations of DS patients (aged 1 day to 22 years) and compared them to a large cohort of 993 brain MRI examinations of neurotypical participants, aged 1 day to 32 years. Surface curvature measurements, absolute surface area measurements, and surface areas as a percentage of total brain surface area (%TBSA) were extracted from each brain region in each examination. Results demonstrate broad reductions in surface area and abnormalities of surface curvature measurements across the brain in DS. After adjusting our regional surface area measurements as %TBSA, abnormally increased presentation in DS relative to neurotypical controls was observed in the left precentral, bilateral entorhinal, left parahippocampal, and bilateral perirhinal cortices, as well as Brodmann's area 44 (left), and the right temporal pole. Findings suggest the presence of developmental abnormalities of regional %TBSA in DS that can be characterized from clinical MRI examinations.

Magnetic nanocomposite for lead (II) removal from water

A magnetic perovskite-spinel oxide nanocomposite synthesized through a sol–gel self-combustion process is used for the first time as an adsorbent to remove toxic heavy metals (i.e., Pb2+). The synthesized LaFeO3:CoFe2O4 ((LFO)1:(CFO)x) (x = 0.11–0.87) nanocomposites possess good stability, abundant oxygenated active binding sites, and unique structural features, making them suitable for removing divalent Pb2+ ions. Scanning electron microscopy, X-ray diffraction, BET surface area, magnetization measurements, zeta-potential analyses, and X-ray photoelectron spectroscopy were used to analyze the nanocomposites, and their structural changes after Pb2+ ions adsorption. Batch tests confirmed that (LFO)1:(CFO)x efficiently removes Pb2+ from water with a maximum adsorption capacity of 105.96 mg/g. The detailed quantitative study indicates that the interaction of hydroxyl groups with Pb2+ ions occurs through electrostatic interactions and complex formation. We also demonstrate a new ring-magnetic separator system that allows magnetic separation of the toxic ions at a higher speed compared to traditional block magnets. The unique structure, high porosity, large specific surface area, and oxygenated functional groups of (LFO)1:(CFO)x nanocomposites make them promising materials for removal of heavy metal ions and possibly other environmental pollutants. This study provides a new approach to preparing nanocomposites of magnetic spinel ferrites with perovskite oxides for environmental applications.

The surface defect of Fe2Ge (001) induces a synergistic spin effect and regulates the surface magnetism

The defect structure leads to the fracture and recombination of chemical bonds, lattice distortion, electron localization, etc., which has a significant improvement on the physical properties of materials, and give them new functions. The unique structure of Fe2Ge forms the surface structure of Ge end face and Fe end face in the direction of (001), but the surface is easy to form defect structure, and affecting its properties. It is found that the spin direction of Ge atom is opposite to the spin direction of Fe atom in perfect Fe2Ge (001) surface structure. When there is VGe defect, the magnetic moments of the perfect Fe2Ge (001) surface and Fe atoms are enhanced. When there are VFe, VFe-Ge and VGe-Fe defects, the magnetic moments of defects Fe2Ge (001) surface and Fe atoms are weakened. The reason is that the spin state electrons of Fe atoms induce Ge atoms to produce spin electrons, which forms a synergistic spin effect. The Hirshfeld Charge distribution and charge spin of Fe and Ge atoms are affected by the local potential field, Ge atoms are excited with spin direction of Fe atoms with VFe and VFe-Ge, and Ge atoms induce magnetic moments with spin direction of Fe atoms with VGe and VGe-Fe. The effects mechanism is that the five orbitals dzz, dxy, dzy, dzx and dxx-yy of Fe atom are greatly affected by the structure of the defect under the action of crystal field, while the s, px, py and pz orbitals are less affected. In VGe and VFe-Ge defects, the spin splitting of the d orbitals is larger to form a larger magnetic moment. In VFe and VGe-Fe defects, the d orbital spin splitting is smaller, and resulting in a smaller magnetic moment. The s, px, py and pz of Ge atoms are greatly affected, the spin splitting of pz is larger than that of px and py orbitals, and indicating that the spin of Ge atoms mainly comes from pz orbitals.

Geometry and Surface Area Optimization in Iron Oxide Nanoparticles for Enhanced Magnetic Properties.

Iron oxide nanoparticles (IONPs) are recognized for their potential in biomedical applications due to their distinctive physicochemical properties. This study investigates the synthesis of IONPs with various geometric morphologies-cubic, star-like, truncated icosahedron, and spherical-via thermal decomposition to enhance their utility in magnetic resonance imaging (MRI) and targeted drug delivery. X-ray diffraction analysis verified the Fe3O4 phase in all nanoparticles, illustrating the synthesis's efficacy. Particle morphologies were well-defined, with sizes ranging from 10 to 150 nm, as determined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Magnetic evaluations using a vibrating sample magnetometer (VSM-PPMs) demonstrated their superparamagnetic behavior, with larger particles exhibiting greater saturation magnetization. Notably, truncated icosahedron and cubic IONPs showed superior transverse relaxation rates, with r2 values of 56.77 s1 mM1 and 42.67 s1 mM1, respectively. These results highlight the potential of customizing IONP geometries to optimize their magnetic properties and increase surface area available for functionalization, thereby improving their efficacy for biomedical applications.

Air‐gap field prediction in tubular doubly sided surface magnet machine using Bessel–Fourier series

Abstract2‐D air‐gap magnetic field distribution is the essential prerequisite of electrical machine analysis. Because of the natural periodicity of rotary machines, Fourier analysis is a suitable choice for air‐gap field prediction. However, due to the end‐effect, periodicity is not present in linear machines and the Fourier series is not appropriate. In engineering mathematics, a rigorous method of solving partial differential equations is the separation of the variables method (SVM) which is based on the hypothesis that the field solution is in the form of the product of two functions of orthogonal directions; for example, in an axisymmetric structure, a longitudinal harmonic function (LHF) and a radial harmonic function (RHF). A particular case of these functions is trigonometric functions, which result in the Fourier series. SVM is imposed in a different manner, where RHF is approximated by the Bessel–Fourier series and consequently LHF has a (piecewise) exponential behaviour. This choice of basis functions not only serves the purpose of modelling the end‐effect but also removes the Gibbs phenomenon, that is, it precisely models discontinuities of flux density at the surface of PMs. A numerical case‐study of a slotless double‐sided linear tubular surface‐PM machine shows that the piecewise exponential approximation can attain 1% error while utilising only three harmonics, whereas the trigonometric approximation, due to the Gibbs phenomenon, slowly arrives at 20% error with 100 harmonics for approximating flux density. Results of both methods were validated using the finite element method (FEM). Additionally, it was discovered that the computational complexity of the model is independent of varying position; therefore, the analytical method could yield the back electromotive force and electromagnetic thrust force for a number of 320 positions at merely 0.2 s while the FEM software required 5 min.

The importance of long range Fe–Fe interactions in magnetically ordered 2D Fe0.2Ni0.8/Ni(001) and Fe0.3Ni0.7/Ni(001) alloy systems

We develop a theoretical approach to study the magnonic properties of the 2D ordered surface Fe–Ni alloys with 20% and 30% Fe on a face-centered cubic Ni(001) surface substrate. The surface alloy nanostructures in stable equilibrium are determined by computing the lowest energy configurations of constitutive supercells of the ordered alloys. The magnetic exchange constants of the ground state of the stable systems are calculated to define their Heisenberg Hamiltonians using the DFT Spin-Polarized Relativistic Korringa–Kohn–Rostoker (SPRKKR) method and considering Fe–Fe interactions up to third nearest neighbors. To determine the propagating exchange spin-wave modes, evanescent modes, and the consequent magnonic properties, the spin dynamics of the magnetic surface alloy nanostructures are solved using the phase field matching theory (PFMT). Our results indicate that the Fe–Fe exchange interactions up to third nearest neighbors are vital for accurately describing their magnonics. In particular, the exchange interactions influence the form of dispersion branches for the high-energy spin-wave modes of the Fe–Ni surface alloys considered. Appropriate Green’s functions are also derived from the PFMT method to compute the local densities of states (LDOS) for the atomic sites at the surface boundary. For the case of 20% Fe surface alloy, the Fe–Fe exchange interactions shift the Fe LDOS peaks to lower frequency intervals. We also distinguish the emergence of remarkable LDOS peaks for the he case of the 30% Fe surface alloy at specific Ni sites. These peaks change positions under second and third nearest neighbor Fe–Fe interactions, heralding new accessible spin-wave channels. Our results contribute to establishing a systematic understanding of the magnonics of the magnetic surface alloys of transition metal (TM) materials. This new knowledge will enable the study of the quantum transport of spin waves at interfacial alloy nanojunctions composed of such materials. The present DFT-PFMT theoretical approach is general and can be applied to other surface TM alloy magnetic nanostructures.

A comprehensive review on the Dynamical behavior of heat and fluid flow mechanism: Thermal performance across different geometries

The prominent novelty of current review is to exhibit the fluctuating and oscillatory convective heat transfer properties along various geometries with magnetic force, variable density, Prandtl number, buoyancy force and magnetic Prandtl number effects. The significance of present work is to illustrate a comprehensive review on transient convective heat transfer. Transient convective heat transfer plays an essential role in various technological and environmental applications, including climate control, structure safety, engines, thermal control, computer heating and cooling, and energy safety. The literature primarily focuses on steady temperature and velocity domains, with few studies exploring time-varying fluid flow in forced, natural, or mixed convective mechanisms with different methods. In current review, justification of results was performed by using oscillating stokes conditions directly in partial differential models. The similarity variables and stream functions are used in literature but in current review, the primitive variable transformation is used with implicit form of finite difference method and Gaussian elimination technique through FORTRAN and Tecplot-360 programming tools. The governing model is reduced into steady, real and imaginary form to explore steady and oscillating convective heat transmission. Transient flows have gained significance due to their ability to achieve large oscillating convective heat transfer rates. Compared with steady movement, oscillating flows exhibit higher velocity variations along the heated surface. Periodic flow produces an improved transient surface heat transmission rate than steady flow. Predicting and controlling transients in thermal exchangers requires a concept of transient forced convection heat transport. Transient convective thermal transmission solutions are important for ensuring the effectiveness and reliability of electrical components, nuclear and thermal power stations, heat-generating engines, steam turbines, condensation systems, catalytic converters, heat shielding for spacecraft, electrical devices, internal combustion engines, air conditioning and refrigerator components, cooling networks for batteries, generators, and transformers. It is found that the frequency of convective heat transport enhances through periodic and oscillating stokes variables. It was depicted that the higher amplitude in convective heat transfer was displayed for each choice of magnetic force parameter around two angles π/4 and π of circular magnetized surface. It was depicted that the maximum transient convective heat transmission was reported along vertical angle π/2 with buoyancy force, Prandtl and magnetic Prandtl values.

Surface plasma wave excitation using laser beat-wave and terahertz generation

In this paper, a study of surface plasma wave excitation from a magnetized metallic surface using two co-propagating lasers is conducted. Two lasers propagating in the same direction with frequency difference of plasmon frequency of the metal excite plasma oscillations on the metallic surface, which generate surface plasma waves. The transverse components of the field associated with these surface plasma wave lead to excite transverse current at terahertz frequency. We report a systematic theoretical model for this study and subsequent numerical results are presented for THz field estimation.

A double boronic acid affinity "sandwich" SERS biosensor based on magnetic boronic acid controllable-oriented imprinting for high-affinity biomimetic specific recognition and rapid detection of target glycoproteins.

Transferrin (TRF), recognized as a glycoprotein clinical biomarker and therapeutic target, has its concentration applicable for disease diagnosis and treatment monitoring. Consequently, this study developed boronic acid affinity magnetic surface molecularly imprinted polymers (B-MMIPs) with pH-responsitivity as the "capture probe" for TRF, which have high affinity similar to antibodies, with a dissociation constant of (3.82 ± 0.24) × 10-8M, showing 7 times of reusability. The self-copolymerized imprinted layer synthesized with dopamine (DA) and 3-Aminophenylboronic acid (APBA) as double monomers avoided nonspecific binding sites and produced excellent adsorption properties. Taking the gold nanostar (AuNS) with a branch tip "hot spot" structure as the core, the silver-coated AuNS functionalized with the biorecognition element 4-mercaptophenylboronic acid (MPBA) was employed as a surface-enhanced Raman scattering (SERS) nanotag (AuNS@Ag-MPBA) to label TRF, thereby constructing a double boronic acid affinity "sandwich" SERS biosensor (B-MMIPs-TRF-SERS nanotag) for the highly sensitive detection of TRF. The SERS biosensor exhibited a detection limit for TRF of 0.004ng/mL, and its application to spiked serum samples confirmed its reliability and feasibility, demonstrating significant potential for clinical TRF detection. Moreover, the SERS biosensor designed in this study offers advantages in stability, detection speed (40min), and cost efficiency. The portable Raman instrument for SERS detection fulfills the requirements for point-of-care testing.

Isochronous bifurcations of magnetic islands in tokamaks

On a rational magnetic surface, an isochronous bifurcation transforms one island chain into another chain with the same winding number. This transformation has been the subject of recent studies in tokamak plasmas. Namely, visco-resistive magnetohydrodynamic simulations of NSTX-U and DIII-D plasmas showed the onset of bifurcations with new magnetic isochronous islands for two competing helical perturbations on the same rational magnetic surface. To investigate these bifurcations, we use a cylindrical plasma model, with first-order correction for toroidicity, subject to externally applied magnetic perturbations, generated by a pair of resonant helical windings (RHWs) on the external wall and superposed to a helical current sheet (HCS) located on a rational plasma surface. We numerically integrate the magnetic field line equation and show that isochronous islands emerge when the perturbation created by the HCS increases. We present examples of such bifurcations on primary and secondary magnetic surfaces for different RHW configurations.

Magnetic carbon nanotube sorbents with macropores formed by salts for oily wastewater treatment

The development of carbon-based sorbents that are simple to fabricate, possess high sorption capacity and are easily collected and reusable has been of great interest for oily wastewater remediation. A magnetic carbon nanotube (CNT) oil sorbent is proposed to cleanup of oily wastewater, offering effortless and complete recovery and enabling reusability. The sorbent, characterized by easy preparation of multi-walled CNT (MWCNT) with m-cresol for macronization, is coupled with a space-holder technique that employs salts for open pore formation for oil sorption. Four sorbents were prepared with varying ratios of sodium chloride (NaCl) and monosodium L-glutamate (MSG), resulting in surface open pores corresponding to salt particle sizes. The sorbents formed an extensive macropore network of more than 200 μm while enhancing the specific surface area. Their bulk densities ranged from 126 kg/m3 to 139 kg/m3, indicating CNT powder densification and suitability for wastewater oil absorption. With its elongated rectangle shape, the MSG-prepared sorbent, exhibited the widest specific surface area and diverse macropores, including those larger than 800 μm. The sorbents exhibited sorption capacities of 2.37–13.60 g of oil/g of sorbent and volume gains of 44–123 %, depending on the oil and solvent types. These values were comparable to or exceeded those of previous carbon-based sorbents. The sorption capacities of the sorbents remained consistent over ten sorption-heat treatment cycles, highlighting recyclability. Sorbents of MWCNT grown from iron catalysts exhibited easy recovery by a magnet after oil sorption, with surface magnetism. Despite their promise for oily wastewater treatment, CNT sorbents must address challenges related to capacity improvement, scalability, economic viability, and environmental impact to be practical for widespread application.

Experimental and statistical physics illumination of Pb(II) adsorption on magnetic chitosan-graphene oxide surface

Adsorption stands for a promising technique for heavy metal remediation. Herein, a high efficiency adsorbent based on magnetic chitosan-graphene oxide (MCGO) was prepared via a simple co-precipitation procedure. Afterwards, adsorption behaviour of Pb(Ⅱ) on MCGO surface was illuminated via batch adsorption experiment and statistical physics calculation. Result presents, MCGO reaches adsorption percent and adsorption quantity 93.06 % and 372.24 mg·g−1 for Pb(Ⅱ) in 44 min, showcasing favorable remediation efficiency. Statistical physics calculation proposes multi-ionic adsorption mechanism. With the increase of temperature, adsorption site density is increased to yield ameliorated adsorption capacity. Moreover, calculation result of the thermodynamic functions designates exothermic, randomness increasing, spontaneous and energy releasing feature. Kinetic fitting based on various models assigns chemical interaction as the rate controlling step. Finally, adsorption mechanism was clarified in atomic level via spectroscopic inspection. Specifically, C=O, C–O, O–H, N+ and –C(=O)NH– contribute to Pb(Ⅱ) adsorption via donating lone pair electrons. This work provides both experimental and statistical physics insights for understanding the adsorption behaviour of typical heavy metal pollutants onto the surface of bio adsorbent like magnetic chitosan-graphene oxide.

Roles of non-axisymmetric perturbations in free drift vertical displacement events on EAST

The safe operation of most tokamaks, especially the large ones, relies on the feedback control of vertical displacement events (VDEs). However, most of these feedback control systems are based on axisymmetric VDE models. In this study, we use NIMROD simulations to study the role of non-axisymmetric perturbations in free drift vertical displacement events on EAST. The high-n modes in the non-axisymmetric VDE grow first, which drives the formation of high-n magnetic island chains. Subsequently, the magnetic island chains grow and overlap with each other, leading to the destruction of the magnetic flux surface, which induces a minor disruption and accelerates the start of the following major disruption. The magnetic island and the stochastic magnetic field allow the toroidally non-axisymmetric poloidal plasma current to jet towards the hoop force direction, forming finger-like and filamentary structures. Such a plasma current non-axisymmetry strongly depends on the anisotropy in the thermal transport coefficients.

Spontaneous Inversion Symmetry Breaking and Emergence of Berry Curvature and Orbital Magnetization in Topological ZrTe_{5} Films.

ZrTe_{5} has recently attracted much attention due to the observation of intriguing nonreciprocal transport responses which necessitate the lack of inversion symmetry (I). However, there has been debate on the exact I-asymmetric structure and the underlying I-breaking mechanism. Here, we report a spontaneous I breaking in ZrTe_{5} films, which initiates from interlayer sliding and is stabilized by subtle intralayer distortion. Moreover, we predict significant nonlinear anomalous Hall effect (NAHE) and kinetic magnetoelectric effect (KME), which are attributed to the emergence of Berry curvature and orbital magnetization in the absence of I symmetry. We also explicitly manifest the direct coupling between sliding ferroelectricity, NAHE, and KME based on a sliding-dependent k·p model. By studying the subsurface sliding in ZrTe_{5} multilayers, we speculate that surface nonlinear Hall current and magnetization would emerge on the natural cleavage surface. Our findings elucidate the sliding-induced I-broken mechanism in ZrTe_{5} films and open new avenues for tuning nonreciprocal transport properties in Van der Waals layered materials.

Confined growth with particle attachment driven self-sieving for enhanced cascade reaction via versatile core-shell-shell nanocomposites

Controlling formation of metal organic frameworks (MOFs) with embedded enzymes on magnetic surface has been achieved by a confined growth with particle attachment driven self-sieving approach for the first time. Specifically, a versatile route of silica encapsulation guided enzyme assembly for formation of ZIF-8 shell has been successfully demonstrated by shaped-controllable Fe3O4 nanoparticles, e.g., nanorod and nanocube. Interestingly, silica encapsulation can lead to structural diversity of ZIF-8 shell on the shaped-controllable Fe3O4 nanoparticles for affecting properties of the nanocomposites. Furthermore, embedded enzymes confined between silica endoskeleton and ZIF-8 exoskeleton can participate in cascade reaction with different activities and stabilities in the terms of plasmonic assemblies fabrication and cancer cell catalytic therapy. As a result, a circulation plasmonic fabrication and cancer therapy can be achieved via the magnetic nanocomposites. It can be expected that the confined growth with particle attachment driven self-sieving method can be versatile to generate diverse MOFs shell encapsulated shaped-controllable nanoparticles for efficiently embedding enzyme in the nanocomposites.

Convenient and highly efficient adsorption of diosmetin from lemon peel by magnetic surface molecularly imprinted polymers

As a typical bioflavonoid, diosmetin is desirable in the field of natural medicine, healthy food, and cosmetics by anti-cancer, antibacterial, antioxidant, estrogen-like and anti-inflammatory activities, and it comes from a wide range of sources in traditional Chinese medicine like spider fragrance, spearmint and chrysanthemum, as well as in Citrus fruit. However, traditional analytical methods such as silica gel column chromatography face multiple challenges in the selective extraction of diosmetin from biological materials and traditional Chinese medicinal materials. Therefore, it is urgent to develop a new type of absorbent with high efficiency, recyclability and good specificity to diosmetin. In this investigation, a magnetic surface molecularly imprinted polymer (labeled as Diosmetin/SMIPs) was synthesized employing magnetic nanoparticles as the carrier and 4-vinylpyridinyl (4-VP) as the functional monomer by surface imprinting technology. The functional monomer was screened by the binding energy (ΔE) between functional monomers and template molecules via computational simulation. The Diosmetin/SMIPs had a high level of specific recognition and adsorption capability towards diosmetin with a 20.25 mg g-1 adsorption capacity and an imprinting factor (IF) of 2.28. Additionally, it demonstrated excellent regeneration performance with 8 adsorption/desorption cycles. In addition, 91.20 %–94.16 % of spiked diosmetin was recovered from the lemon peel samples. The strategy of constructing Diosmetin/SMIPs based on computational simulation can effectively enhance the specific adsorption performance of diosmetin. Meanwhile, Diosmetin/SMIPs synthesized by imprinting polymerization showed excellent anti-interference and reusability, and realized efficient targeted extraction of diosmetin from lemon peel samples. The results of this investigation provide a promising adsorbent for selective enrichment of diosmetin from Citrus fruit and complicated materials.

An innovative process for recovery of ilmenite using mineral phase transformation followed by magnetic separation

Recovery of fine ilmenite is challenging, resulting in significant waste of titanium resources. In this paper, the mineral phase transformation technology was proposed to strengthen the surface magnetism of fine ilmenite. The results demonstrated that in the oxidation stage, the suitable oxidation temperature was 700 °C and the oxidation time was 30 min. In the reduction stage, the ideal reduction temperature was 575 °C, the CO concentration was 20 %, and the reduction time was 3 min. Under the optimized roasting conditions, the roasted sample was separated by staged low-intensity magnetic separation, and titanium concentrate with a TiO2 grade of 46.24 % and recovery of 67.62 % was obtained. The XRD, SEM and VSM analysis implied that the oxidation products of ilmenite were hematite and rutile, where hematite was enriched on the surface of the particles and formed a layer of 2–5 μm. After reduction roasting, the hematite layer was directionally transformed into magnetite, which significantly enhanced the magnetism of the particles and created conditions for the recovery of titanium by low-intensity magnetic separation.

A fungal hyphae-derived biomass carbon for magnetic solid-phase extraction of the organochlorine pesticides in water samples, tea beverages, and Chinese traditional medicines before gas chromatography-tandem mass spectrometry determination

A magnetic biochar nanomaterial derived from fungal hyphae was introduced into the sample preparation field. The magnetic fungal hyphae-derived biomass carbon (MFHBC) could be produced by a controllable hydrothermal method. In order to obtain the best sorbent for magnetic solid-phase extraction (MSPE), the reaction conditions containing temperature, time and the consumption of fungal hyphae were investigated. A series of MFHBC materials were characterized by vibrating sample magnetometers, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. A material with a satisfactory saturation magnetization (21.58 emu g-1) and largest surface area (88.06 m2 g-1) was selected as the sorbent to extract ten typical organochlorine pesticides (OCPs). The extraction conditions were optimized as 20 mL of sample solution with 70 mg of sorbent and 2.0 g of NaCl oscillated at 50 °C for 5.0 min. And the optimum desorption was performed by oscillating sorbent in 1.0 mL acetonitrile for 5.0 min. Then, the MFHBC-based MSPE-GC–MS/MS methods were established for different samples including water samples, tea beverages, and Chinese traditional medicines. The linearities were 10–2500 ng L−1 or 100–25,000 ng kg−1, and the limits of detection were 0.3–13.9 ng L−1 for water sample, 0.1–9.7 ng L−1 for tea beverage samples, 0.1–21.4 ng L−1 for Shenqi Fuzheng injection samples, and 7.2–278.3 ng kg−1 for Astragali Radix decoction pieces. Except for satisfactory repeatability (RSDs ≤13.8%) in intra-day and inter-day tests (n = 3), the reproducibility (RSDs ≤13.5%, n = 3) of MFHBC was acceptable. The methods were applied in the determination of OCPs from above real samples, with the recoveries of 80.5–117.2% and the RSDs (n = 3) <8.9%. The methods were suitable in the sensitive determination of OCPs from simple to complex matrix samples.

Anticorrosion behavior and enhanced wear resistance of Ni–P–GO–Y composite coating on the surface of NdFeB permanent magnet

Anticorrosion behavior and enhanced wear resistance of Ni–P–GO–Y composite coating on the surface of NdFeB permanent magnet

Symmetry, topology, and geometry: The many faces of the topological magnetoelectric effect

A delicate tension complicates the relationship between the topological magnetoelectric effect (TME) in three-dimensional (3D) Z2 topological insulators (TIs) and time-reversal symmetry (TRS). TRS underlies a particular Z2 topological classification of the electronic ground state of crystalline band insulators and the associated quantization of the magnetoelectric response coefficient calculated using bulk linear-response theory but, according to standard symmetry arguments, simultaneously forbids a nonzero magnetoelectric coefficient in any physical finite-size system. This contrast between theories of magnetoelectric response in formal bulk models and in real finite-sized materials originates from the distinct approaches required to introduce notions of (electronic) polarization and orbital magnetization in these fundamentally different environments. In this work we argue for a modified interpretation of the bulk linear-response calculations in nonmagnetic Z2 TIs that is more plainly consistent with TRS and use this interpretation to discuss the effect's observation—still absent over a decade after its prediction. Our analysis is reinforced by microscopic bulk and thin-film calculations carried out using a simplified but still realistic effective model for the well established V2VI3 [V=(Sb,Bi) and VI=(Se,Te)] family of nonmagnetic Z2 TIs. When a uniform dc magnetic field is included in this model, the anomalous n=0 Landau levels (LLs) play the central role, both in thin films and in bulk. In the former case, only the n=0 LL eigenfunctions can support a dipole moment, which vanishes if there are no magnetic surface dopants and is quantized in the thick-film limit if magnetic dopants at the top and bottom surfaces have opposite orientation. In the latter case, the Hamiltonian projected into the n=0 LL subspace is a one-dimensional Su-Schrieffer-Heeger model with ground-state polarization that is quantized in accordance with the bulk linear-response coefficient calculated for (a lattice regularization of) the starting 3D model. Motivated by analytical results, we conjecture a type of microscopic bulk-boundary correspondence: a bulk insulator with (generalized) TRS supports a magnetoelectric coefficient that is purely itinerant (which is generically related to the geometry of the ground state) if and only if magnetic surface dopants are required for the TME to manifest in finite samples thereof. We conclude that in nonmagnetic Z2 TIs the TME is activated by magnetic surface dopants, that the charge-density response to a uniform dc magnetic field is localized at the surface and specified by the configuration of those dopants, and that the TME is qualitatively less robust against disorder than the integer quantum Hall effect. Published by the American Physical Society 2024