Evaluation Model and Comparative Analysis of Low Frequency Magnetic Field Exposure

Ir-driven anisotropy and low-field vertical magnetization shifts in Ni-Ir double perovskites

Abstract Antiferromagnetic Kagome semimetals have attracted tremendous attention for their potential application in antiferromagnetic topological spintronics. Effectively manipulating Kagome antiferromagnetic states can reveal abundant physical phenomena induced from quantum interactions between topology, spin, and correlation. Here, tunable spin textures of FeSn thin films are achieved via introducing interfacial Dzyaloshinskii–Moriya interaction from heavy‐metal Pt overlayer. With increasing FeSn thickness, the variable spin textures result in a gradual change in Hall resistivity and magnetoresistance. Importantly, an unconventional damped oscillatory‐like behavior of magnetoresistance at relatively low magnetic fields can be observed in thin FeSn/Pt samples. This oscillatory‐like magnetoresistance feature is confirmed to be related to the special topological spin textures revealed by magnetic force microscopy measurements. The formation of a rich variety of topological spin textures in association with exotic magneto‐transport properties in antiferromagnetic Kagome FeSn heterostructures offers new perspectives for understanding the novel emergent phenomena in Kagome antiferromagnets.

Abstract Inspired by the extraordinary functionality of biological systems that assemble anisotropic nanostructures, there is growing interest in designing multiscale ordered materials to modulate bio‐based micro‐ and nanoscale assemblies for high performance and exceptional functionality. Current strategies for magnetic field‐induced alignment of cellulose nanofibers face limitations, often relying on ultra‐high magnetic fields or yielding poor orientation with microspherical magnetic particles. This study proposes an ordered assembly of cellulose nanofibers decorated with magnetic nanorods, induced under low magnetic fields. The resulting cellulose films exhibit an orientation parameter greater than 0.8. It demonstrates that the mechanism behind the magnetic field‐induced alignment of magnetic nanorods with cellulose nanofibers results from a combination of magnetic torque‐induced alignment of the rods and shear orientation driven by radial flow. This highly aligned, magnetically flexible, multiresponsive film achieves a dielectric constant elevated from 8.67 to 15.21. Simply by regulating the cellulose structure, the TENG output performance is improved to 971%. Compared with other complex modified cellulose film methods, the output performance is only enhanced to 760%. This method provides new insights into anisotropic assembly, with potential applications in flexible electronics and self‐powered sensors.

The emergent Weyl modes with the broken time-reversal symmetry or inversion symmetry provide large Berry curvature and chirality to carriers, offering the realistic platforms to explore topology of electrons in three-dimensional systems. However, the reversal transition between different types of Weyl modes in a single material, which is of particular interest in the fundamental research in Weyl physics and potential application in spintronics, is scarcely achieved due to restriction of inborn symmetry in crystals. Here, by tuning the direction and strength of magnetic field in an ideal Dirac semimetal, Bi4(Br0.27I0.73)4, we report the realization of multiple Weyl modes, including gapped Weyl mode, Weyl nodal ring, and coupled Weyl mode by the magnetoresistivity measurements and electronic structure calculations. Specifically, under a magnetic field with broken mirror symmetry, anomalous Hall effect with step feature results from the large Berry curvature for the gapped Weyl mode. A prominent negative magnetoresistivity is observed at low magnetic field with preserved mirror symmetry and disappears at high magnetic field, which is correlated to the chiral anomaly and its annihilation of Weyl nodal ring, respectively. Our findings reveal distinct Weyl modes under the intertwined crystal symmetry and time-reversal breaking, laying the foundation of manipulating multiple Weyl modes in chiral spintronic network.

Interventional procedures are essential in vascular medicine, but precise navigation through tortuous vasculature remains difficult due to the limited steerability of guidewires in complex anatomical regions. Magnetic guidewires have been developed to address this limitation, yet they typically depend on accurate field control using robotic-arm-mounted magnets or electromagnets, which constrains their use in space-limited intervention room. Here, a magnetic guidewire with a micro-fin-integrated tip for multimodal vascular intervention is introduced. The micro-fins respond to external magnetic fields and generate additional torques through fluid drag and vessel wall contact forces, supplementing the magnetic torque and gradient forces of conventional designs. This combination enables the guidewire to pass bifurcations under lower magnetic field strength, reduced from 34 to 15mT in the trials, and to tolerate external field misalignments up to 45 degrees. The micro-fin structure also permits bidirectional crawling and self-correction from buckling. In vivo testing in rabbit vascular models shows the device reduced time by ≈50% compared to a commercial guidewire, even when the magnetic field is manually applied, and allows full access to major arteries within 1 min. These findings demonstrate that micro-fins integration provides advantages that improve the control and efficiency of magnetic guidewires in complex vascular environments.

This work aims to investigate how the ultimate intrinsic signal-to-noise ratio (uiSNR) varies with increasing static magnetic field in the torso of realistic body models. A dipole cloud was positioned around the realistic body model and randomly excited. The volume integral solver MARIE was used to calculate the corresponding electromagnetic fields. The uiSNR maps were calculated using these electromagnetic bases and were fitted with the power law for different ranges. The uiSNR could be reliably calculated in regions deeper than 3 cm, where convergence of uiSNR over the number of basis vectors was achieved. In a lower magnetic field range (from 0.55 to 3 T), the uiSNR increases roughly linearly versus with small variation throughout the torso (Ella: uiSNR ∝ B0 0.96±0.07, Duke: uiSNR ∝ B0 0.98±0.10). In an upper magnetic field range (from 5 to 14 T), the uiSNR increases superlinearly in the torso (Ella: uiSNR ∝ B0 1.86±0.25, Duke: uiSNR ∝ B0 1.99±0.28), with a larger variation correlated to the heterogeneous structure of the body model. The superlinear scaling exponent in the upper magnetic field range indicates the promise of applying UHF MRI for body imaging.

Water (H₂O) is a crucial resource for sustaining human activities in space. In addition to its indispensable role in supporting life, water can be electrolyzed to produce hydrogen (H₂) and oxygen (O₂), where hydrogen serves as a propellant and oxygen supports respiration. If the water resources believed to exist on the Moon can be extracted and electrolyzed in situ (hereafter referred to as water electrolysis), substantial reductions in transportation costs compared to Earth-based supply launches could be realized.Nevertheless, conducting water electrolysis in space poses significant technical challenges. Spacecraft in orbit are in a microgravity environment, and the Moon’s gravity is only about one-sixth that of Earth. As a result, the buoyant force acting on gas bubbles generated at the electrodes during electrolysis is greatly reduced. Consequently, bubbles tend to remain on the electrode surface, hindering the electrochemical reaction and decreasing the efficiency of electrolysis.To address this issue, the present study experimentally investigates the potential for enhancing electrolysis efficiency by facilitating bubble removal through magnetic manipulation. Specifically, a water-based magnetic nanofluid solution was employed. This fluid is an aqueous colloidal suspension in which ferromagnetic nanoparticles, approximately 10 nm in diameter, are stably dispersed. Dispersion stability is achieved through electrostatic repulsion between surfactant molecules adsorbed on the particle surfaces. When subjected to a spatial magnetic field gradient, gas bubbles in the fluid experience magnetic buoyancy, that is, a net force directing them toward regions of lower magnetic field strength. It is hypothesized that this phenomenon can promote effective bubble detachment from the electrode surfaces, thereby enhancing electrolysis performance.The study focuses on evaluating how variations in nanoparticle concentration within the solution affect bubble removal and electrolysis efficiency. A simple planar electrode cell was used. Titanium served as the substrate material, with an iridium catalyst deposited on the anode for the oxygen evolution reaction (OER) and a platinum catalyst on the cathode for the hydrogen evolution reaction (HER). The electrochemically active area was confined to 5 × 10 mm², while the remaining surfaces were coated with epoxy resin to prevent unintended chemical reactions.. The interelectrode spacing was set at 3 mm.The magnetic nanofluid solution used in this study was MSGW10, provided by Ferrotec Material Technologies. To avoid colloidal destabilization due to salting-out induced by the addition of electrolytes, the original stock fluid was diluted to 1/8, 1/16, and 1/32 concentrations. For comparison, pure water (i.e., without magnetic particles) was also used. A buffer solution comprising 0.5 mol/L potassium bicarbonate and potassium carbonate (pH ≈ 10) was employed as the supporting electrolyte. Although magnetic nanofluids are generally prone to particle aggregation under strongly alkaline conditions, the use of buffering ions enabled stable electrolysis. Moreover, the weakly alkaline pH range ensured chemical stability of the dispersed magnetite nanoparticles.Electrolysis performance was characterized via linear sweep voltammetry (LSV), beginning at 1.5 V and scanning at a rate of +5 mV/s. All tests were conducted under both magnetic and non-magnetic field conditions.The LSV results revealed that, under identical operating conditions, the use of magnetic nanofluid solutions led to superior electrolysis performance compared to pure water. Furthermore, when comparing electrolysis under magnetic and non-magnetic conditions, the application of a magnetic field resulted in further enhancement of electrolysis efficiency, indicating the effectiveness of magnetic forces in facilitating bubble detachment via magnetic buoyancy. Higher concentrations of nanoparticles were correlated with increased performance enhancement, likely due to more effective bubble removal under the influence of the magnetic field. However, paradoxically, lower nanoparticle concentrations exhibited even better performance overall. This counterintuitive result may be attributed to the influence of surfactants surrounding the nanoparticles. At higher concentrations, surfactant-induced Marangoni effects may reduce bubble detachment velocity, thereby suppressing electrochemical activity. Additionally, excessive nanoparticle loading may increase the electrical resistance of the solution, further limiting performance. Figure 1

Atomic magnetometers are magnetic field sensors that measure extremely weak magnetic field signals, and their measurement process typically requires a magnetic environment with high uniformity and low residual magnetic field. This paper proposes a dual-stage magnetic field compensation method for a lightweight magnetic shielding room (LMSR) based on a combination of external and internal coils. The first stage uses external coils to compensate for the residual magnetic distribution inside the LMSR, achieving a near-zero magnetic field level in the target area. Building on this initial compensation, the second stage employs internal coils designed with a particle swarm optimization algorithm that incorporates the distribution of the residual magnetic field to enhance the spatial magnetic field uniformity and compensate for magnetic field noise. Experimental results demonstrate that the dual-stage magnetic field compensation method designed for the LMSR effectively improves the uniformity of the target area with the central magnetic field close to 0 nT. After compensation with the external coils, the maximum values of the residual magnetic field components in three axes are decreased by factors of 2.5, 4.04, and 8.1, respectively. Following compensation by the internal coils, there is a significant improvement in the measurement performance of atomic magnetometers, with the maximum magnetic field fluctuation reduced by a factor of 12.6.

We investigate the effect of giant negative magnetoresistance in ultrahigh-mobility (μ≫107cm2V−1s−1) two-dimensional electron systems. These systems present a dramatic drop in the mangetoresistance at low magnetic fields (B∼0.1 T) and temperatures (T∼0.1 K). This effect is reversed by increasing the temperature or the presence of an in-plane magnetic field. The motivation for the present work is to develop a microscopical model to explain the experimental evidence, based on coherent states and Schródinger cat states of the quantum harmonic oscillator. Thus, we approach the giant negative magnetoresistance effect based on the description of ultrahigh-mobility two-dimensional electron systems in terms of Schrödinger cat states (superposition of coherent states of the quantum harmonic oscillator). We explain the experimental results in terms of the increasing disorder in the sample due to the rising temperature or the in-plane magnetic field, breaking up the Schrödinger cat states and giving rise to mere coherent states, which hold magnetoresistance in lower-mobility samples. The latter, jointly with the description of ultrahigh-mobility samples with Schrödinger cat states, accounts for the main contribution. The most interesting application of this novel description of such systems would be in the implementation of qubits for quantum computing based on bosonic models.

Localized 1H magnetic resonance spectroscopy (MRS) is a powerful tool in pre-clinical and clinical neurological research, offering non-invasive insight into neurochemical composition in localized brain regions. Zebrafish (Danio rerio) are increasingly being utilized as models in neurological disorder research, providing valuable insights into disease mechanisms. However, the small size of the zebrafish brain and limited MRS sensitivity at low magnetic fields hinder comprehensive neurochemical analysis of localized brain regions. Here, we investigate the potential of ultra-high-field (UHF) MR systems, particularly 28.2 T, for this purpose. This present study pioneers the application of localized 1H spectroscopy in zebrafish brain at 28.2 T. Point resolved spectroscopy (PRESS) sequence parameters were optimized to reduce the impact of chemical shift displacement error and to enable molecular level information from distinct brain regions. Optimized parameters included gradient strength, excitation frequency, echo time, and voxel volume specifically targeting the 0–4.5 ppm chemical shift regions. Exceptionally high-resolution cerebral metabolite spectra were successfully acquired from localized regions of the zebrafish brain in voxels as small as 125 nL, allowing for the identification and quantification of major brain metabolites with remarkable spectral clarity, including lactate, myo-inositol, creatine, alanine, glutamate, glutamine, choline (phosphocholine + glycerol-phospho-choline), taurine, aspartate, N-acetylaspartyl-glutamate (NAAG), N-acetylaspartate (NAA), and γ-aminobutyric acid (GABA). The unprecedented spatial resolution achieved in a small model organism enabled detailed comparisons of the neurochemical composition across distinct zebrafish brain regions, including the forebrain, midbrain, and hindbrain. This level of precision opens exciting new opportunities to investigate how specific diseases in zebrafish models influence the neurochemical composition of specific brain areas.

As the demand for advanced actuation strategies in soft robotics and intelligent material systems grows, magnetoactive soft actuators have attracted increasing attention for their ability to achieve flexible shape transformations through remote and untethered control. However, existing designs typically rely on continuous high magnetic fields to generate large deformations, limiting both efficiency and applicability, especially under constrained boundary conditions. Here we report a hemispherical bistable soft actuator embedded with magnetic microparticles, which enables substantial shape changes under low-intensity pulsed magnetic torques and remains stable in two configurations without external fields. We analyze the relationship between design parameters and actuator performance to clarify the bistable mechanism, and show that the actuator can achieve a large shape change ratio exceeding 0.8 under magnetic fields below 20 mT. We further demonstrate its versatility through three applications: a high-efficiency soft pump with closed-loop fluid control, a reprogrammable metamaterial, and a variable-stiffness soft gripper.

The combination of hyperpolarization methods with low and inhomogeneous fields promises to expand the application of nuclear magnetic resonance (NMR) to fields that nowadays are not standard. Reducing the magnetic field strengths and homogeneity requirements opens the door to a wide variety of magnet designs that can allow for monitoring chemical reactions in the benchtop or even larger reactors. In this work, we propose a method to monitor 15N chemical reactions at low and inhomogeneous fields based on parahydrogen-induced polarization. The concept was demonstrated at a magnetic field of 66 mT and 81ppm inhomogeneity. Specifically, we measured the conversion of 15N-boronobenzyl-2-styrylpyridinium (15N-BBSP) to 15N-2-styrylpyridin (15N-SP). This enables the detection of H2O2 with high sensitivity and selectivity, exhibiting a significant chemical shift difference of 88.4ppm, when 15N-SP is obtained after a base-assisted 1,6 elimination/rearrangement. The long T1 of 15N-BBSP at low magnetic fields (194 s at 100 mT) exemplifies the potential of hyperpolarized 15N for low field applications. We envision the implementation of our methods for studying chemical reactions in benchtop devices, drug screening, investigating biological systems in their native environments, preclinical research and contrast development for low-field and portable magnetic resonance imaging (MRI).

Electron hydrodynamics features a plethora of effects where electrons behave like a fluid. Its description relies on hydrodynamic models akin to the Navier-Stokes equations, which progressively lose accuracy when approaching the ballistic regime. In this paper, we derive a generalized Navier-Stokes differential equation with suitable boundary conditions for the drift velocity field in a channel. It still admits a closed-form solution in a uniform channel while spanning the range of validity of hydrodynamic models. It also includes electron tomographic dynamics, a realistic description of electron-electron collisions that affect electrical transport, and explains the occurrence of positive and negative magnetoresistance at low magnetic fields. The model describes phenomena missed by the conventional electron hydrodynamic description, and it generally improves its accuracy.

3D-1D modelling of cranial mesh heating induced by low or medium frequency magnetic fields.

Sm doping induced Type II spin switching of Sm Ho1-FeO3 single crystals under low magnetic fields

Abstract To enhance the practical utility of nonreciprocal thermal emission for energy harvesting and conversion purposes continuously, researchers have devoted themselves to this active research field. However, remaining challenges exist with respect to dual-polarization nonreciprocal thermal radiation, particularly at low magnetic fields and narrow angular ranges, where the level of nonreciprocal performance is suboptimal, which is quite different from that under TE and TM polarizations. This study presents a dual-polarized nonreciprocal thermal emitter utilizing a two-dimensional grated configuration. The proposed structure demonstrates high nonreciprocal efficiency exceeding 91% for both polarizations. Specifically, TE mode achieves 92.32% at 15.630 μm, while TM mode reaches 91.46% at 15.658 μm, with a mere 0.86% difference under 2 T magnetic field at incident angle of 7 °. By clarifying the physical properties of the structure, analyzing the influence of magnetic field strength and incident angle on the structure, and using the magnetic field distribution to analyze its coupling mode, the physical mechanism of this phenomenon is further explained. This structure achieves dual-polarized nonreciprocal thermal radiation under reduced magnetic field intensity and within a narrow angular range, offering a novel methodology for practical applications with significant reference implications.

Low Magnetic Fields Stimulate Cardiac Mitochondrial Bioenergetics with a Bell-Shaped Response: Possibly Via a Radical Pair Mechanism

Precision medicine aims to improve patient outcomes and minimize adverse effects by tailoring drug based therapies to each individual’s characteristics. Magnetically actuated drug delivery systems enable noninvasive, targeted, and on-demand therapeutic release. However, important challenges in the design considerations, including the drug dosage volumes and total dosage incorporated in the design, as well as the ability to batch manufacture such devices with high repeatability, still need to be addressed. In this paper, we explore the role of controlled drug delivery systems with a particular focus on magnetic field-responsive systems and the transformative impact of 3D printing technology. We use stereolithography 3D printing in combination with high-concentration magnetic composite UV curable resins for the fabrication of high-resolution, magnetically actuated drug delivery devices. By optimizing the 3D printing parameters, we achieve structurally consistent and reproducible scaffolds with high geometric fidelity. Our results show that the scaffolds based on 40 w/w% magnetic microparticles and photo-curable resin exhibit strong magnetic responsiveness when applying low magnetic field strengths, leading to compression ratios up to 52.94% and drug release amounts ranging from 8.6 ± 0.5 μl/mm to 135.9 ± 3.1 μl/mm. Comparative analysis of six scaffold designs reveals that the scaffold’s structural configuration can be used to tailor the drug release profile. The presented fabrication method and drug delivery devices are particularly suited for applications demanding accurate dose delivery and remote actuation. We present a proof-of-concept demonstration of our device for precise drug delivery in ophthalmic treatment.

Flexible ultrathin metasurface with open-ring spiral resonators for SNR enhancement in low-field 0.2T MRI.