Carbon-Doped Co2MnSi Heusler Alloy Microwires with Improved Thermal Characteristics of Magnetization for Multifunctional Applications

In the current work, we illustrate the effect of adding a small amount of carbon to very common Co2MnSi Heusler alloy-based glass-coated microwires. A significant change in the magnetic and structure structural properties was observed for the new alloy Co2MnSiC compared to the Co2MnSi alloy. Magneto-structural investigations were performed to clarify the main physical parameters, i.e., structural and magnetic parameters, at a wide range of measuring temperatures. The XRD analysis illustrated the well-defined crystalline structure with average grain size (Dg = 29.16 nm) and a uniform cubic structure with A2 type compared to the mixed L21 and B2 cubic structures for Co2MnSi-based glass-coated microwires. The magnetic behavior was investigated at a temperature range of 5 to 300 K and under an applied external magnetic field (50 Oe to 20 kOe). The thermomagnetic behavior of Co2MnSiC glass-coated microwires shows a perfectly stable behavior for a temperature range from 300 K to 5 K. By studying the field cooling (FC) and field heating (FH) magnetization curves at a wide range of applied external magnetic fields, we detected a critical magnetic field (H = 1 kOe) where FC and FH curves have a stable magnetic behavior for the Co2MnSiC sample; such stability was not found in the Co2MnSi sample. We proposed a phenomenal expression to estimate the magnetization thermal stability, ΔM (%), of FC and FH magnetization curves, and the maximum value was detected at the critical magnetic field where ΔM (%) ≈ 98%. The promising magnetic stability of Co2MnSiC glass-coated microwires with temperature is due to the changing of the microstructure induced by the addition of carbon, as the A2-type structure shows a unique stability in response to variation in the temperature and the external magnetic field. In addition, a unique internal mechanical stress was induced during the fabrication process and played a role in controlling magnetic behavior with the temperature and external magnetic field. The obtained results make Co2MnSiC a promising candidate for magnetic sensing devices based on Heusler glass-coated microwires.

Unbalanced Current Identification of Three-Core Power Cables Based on Phase Detection of Magnetic Fields

Identifying unbalanced phase currents is crucial for control and fault alarm rates in power grids, especially in urban distribution networks. The zero-sequence current transformer, specifically designed for measuring unbalanced phase currents, offers advantages in measurement range, identity, and size, compared to using three separate current transformers. However, it cannot provide detailed information on the unbalance status beyond the total zero-sequence current. We present a novel method for identifying unbalanced phase currents based on phase difference detection using magnetic sensors. Our approach relies on analyzing phase difference data from two orthogonal magnetic field components generated by three-phase currents, as opposed to the amplitude data used in previous methods. This enables the differentiation of unbalance types (amplitude unbalance and phase unbalance) through specific criteria and allows for the simultaneous selection of an unbalanced phase current in the three-phase currents. In this method, the amplitude measurement range of magnetic sensors is no longer a critical factor, allowing for an easily attainable wide identification range for current line loads. This approach offers a new avenue for unbalanced phase current identification in power systems.

Ring-Core Fluxgate Sensor for High Operation Temperatures up to 220 °C

Fluxgate sensors are key devices for magnetic field surveys in geophysics. In areas such as deep drilling, fluxgate sensors may have to operate steadily at high temperatures for a prolonged period of time. We present an accordant ring-core type fluxgate sensor that is stable up to 220 °C. The high temperature consistency is achieved by using an Fe-based nanocrystalline magnetic core, PEEK structural components, an epoxy resin wrapping, as well as a broadband short-circuited working mode. The sensor was characterized at various temperatures up to 220 °C by evaluating impedance, hysteresis, permeability and sensitivity. We found a sensitivity of approximately 24 kV/T at 25 °C with an acceptable temperature coefficient of 742 ppm/°C throughout the range. The variation law of magnetic characteristics and their influence mechanism on output amplitude and phase are discussed.

Experimental Determination of a Single Atom Ground State Orbital through Hyperfine Anisotropy

Historically, electron spin resonance (ESR) has provided excellent insight into the electronic, magnetic, and chemical structure of samples hosting spin centers. In particular, the hyperfine interaction between the electron and the nuclear spins yields valuable structural information about these centers. In recent years, the combination of ESR and scanning tunneling microscopy (ESR-STM) has allowed to acquire such information about individual spin centers of magnetic atoms bound atop a surface, while additionally providing spatial information about the binding site. Here, we conduct a full angle-dependent investigation of the hyperfine splitting for individual hydrogenated titanium atoms on MgO/Ag(001) by measurements in a vector magnetic field. We observe strong anisotropy in both the g factor and the hyperfine tensor. Combining the results of the hyperfine splitting with the symmetry properties of the binding site obtained from STM images and a basic point charge model allows us to predict the shape of the electronic ground state configuration of the titanium atom. Relying on experimental values only, this method paves the way for a new protocol for electronic structure analysis for spin centers on surfaces.

Contactless Electrocatheter Tracing within Human Body via Magnetic Sensing: A Feasibility Study

During surgical procedures, real-time estimation of the current position of a metal lead within the patient's body is obtained by radiographic imaging. The inherent opacity of metal objects allows their visualization using X-ray fluoroscopic devices. Although fluoroscopy uses reduced radiation intensities, the overall X-ray dose delivered during prolonged exposure times poses risks to the safety of patients and physicians. This study proposes a potential alternative to real-time visualization of a lead inside the human body. In principle, by making a weak current flow through the lead and measuring the related magnetic field generated outside the body, it is possible to trace the position of the lead. This hypothesis was verified experimentally via two tests: one carried out on a curved copper wire in air and one carried out on a real pacemaker lead in a saline solution. In the second test, a pacemaker lead and a large return electrode were placed in a tank filled with a saline solution that reproduced the mean resistivity of the human torso. In both tests, a current flowed through the lead, which consisted of square pulses with short duration, to avoid any neuro-muscular stimulation effects in a real scenario. A small coil with a ferrite core was moved along a grid of points over a plastic sheet and placed just above the lead to sample the spatial amplitude distribution of the magnetic induction field produced by the lead. For each measurement point, the main coil axis was oriented along the x and y axes of the plane to estimate the related components of the magnetic induction field. The two matrices of measurements along the x and y axes were further processed to obtain an estimate of lead positioning. The preliminary results of this study support the scientific hypothesis since the positions of the leads were accurately estimated. This encourages to deepen the investigation and overcome some limitations of this feasibility study.

Double-enzymes-mediated Fe2+/Fe3+ conversion as magnetic relaxation switch for pesticide residues sensing

It is a great challenge to develop a newly rapid and accurate detection method for pesticide residues. In this work, based on acetylcholinesterase (AChE) and choline oxidase (CHO), a double-enzymes-mediated Fe²⁺/Fe³⁺ conversion as magnetic relaxation switch was explored for the measurement of acetamiprid residue. In the double-enzymes reactions, acetylcholine chloride (ACh) can be catalyzed to produce choline by AChE, which is successively hydrolyzed to betaine and hydrogen peroxide (H₂O₂) by CHO. According to the enzyme inhibition principle, AChE activity will be inactivated in the presence of acetamiprid, thus leading to the less production of H₂O₂. Wherein, Fe²⁺, ACh, AChE and CHO were optimized as the reaction substrates. In the reaction system, acetamiprid can be reflected by the transverse relaxation time (T₂) that related with H₂O₂ mediated Fe²⁺ variations, which was further developed as an enzyme cascade amplification method. The detection linear range is 0.01∼1000 μg mL^-1 (R² = 0.99), and the limit of detection (LOD) is 2.66 ng mL^-1 (S/N = 3, n = 3), behaving a 335-fold improvement in LOD than that of traditional enzyme inhibition method (0.89 μg mL^-1). This method can realize "one-step mixing" detection of acetamiprid, which makes it a promising analytical tool for monitoring pesticide residue in complicated samples.

Tuning Single-Atom Electron Spin Resonance in a Vector Magnetic Field

Spin resonance of single spin centers bears great potential for chemical structure analysis, quantum sensing, and quantum coherent manipulation. Essential for these experiments is the presence of a two-level spin system whose energy splitting can be chosen by applying a magnetic field. In recent years, a combination of electron spin resonance (ESR) and scanning tunneling microscopy (STM) has been demonstrated as a technique to detect magnetic properties of single atoms on surfaces and to achieve sub-microelectronvolts energy resolution. Nevertheless, up to now the role of the required magnetic fields has not been elucidated. Here, we perform single-atom ESR on individual Fe atoms adsorbed on magnesium oxide (MgO) using a two-dimensional vector magnetic field as well as the local field of the magnetic STM tip in a commercially available STM. We show how the ESR amplitude can be greatly improved by optimizing the magnetic fields, revealing in particular an enhanced signal at large in-plane magnetic fields. Moreover, we demonstrate that the stray field from the magnetic STM tip is a versatile tool. We use it here to drive the electron spin more efficiently and to perform ESR measurements at constant frequency by employing tip-field sweeps. Lastly, we show that it is possible to perform ESR using only the tip field, under zero external magnetic field, which promises to make this technique available in many existing STM systems.

Magnetic Detection Structure for Lab-on-Chip Applications Based on the Frequency Mixing Technique

A magnetic frequency mixing technique with a set of miniaturized planar coils was investigated for use with a completely integrated Lab-on-Chip (LoC) pathogen sensing system. The system allows the detection and quantification of superparamagnetic beads. Additionally, in terms of magnetic nanoparticle characterization ability, the system can be used for immunoassays using the beads as markers. Analytical calculations and simulations for both excitation and pick-up coils are presented; the goal was to investigate the miniaturization of simple and cost-effective planar spiral coils. Following these calculations, a Printed Circuit Board (PCB) prototype was designed, manufactured, and tested for limit of detection, linear response, and validation of theoretical concepts. Using the magnetic frequency mixing technique, a limit of detection of 15 µg/mL of 20 nm core-sized nanoparticles was achieved without any shielding.

Subsea Cable Tracking by Autonomous Underwater Vehicle with Magnetic Sensing Guidance

The changes of the seabed environment caused by a natural disaster or human activities dramatically affect the life span of the subsea buried cable. It is essential to track the cable route in order to inspect the condition of the buried cable and protect its surviving seabed environment. The magnetic sensor is instrumental in guiding the remotely-operated vehicle (ROV) to track and inspect the buried cable underseas. In this paper, a novel framework integrating the underwater cable localization method with the magnetic guidance and control algorithm is proposed, in order to enable the automatic cable tracking by a three-degrees-of-freedom (3-DOF) under-actuated autonomous underwater vehicle (AUV) without human beings in the loop. The work relies on the passive magnetic sensing method to localize the subsea cable by using two tri-axial magnetometers, and a new analytic formulation is presented to compute the heading deviation, horizontal offset and buried depth of the cable. With the magnetic localization, the cable tracking and inspection mission is elaborately constructed as a straight-line path following control problem in the horizontal plane. A dedicated magnetic line-of-sight (LOS) guidance is built based on the relative geometric relationship between the vehicle and the cable, and the feedback linearizing technique is adopted to design a simplified cable tracking controller considering the side-slip effects, such that the under-actuated vehicle is able to move towards the subsea cable and then inspect its buried environment, which further guides the environmental protection of the cable by setting prohibited fishing/anchoring zones and increasing the buried depth. Finally, numerical simulation results show the effectiveness of the proposed magnetic guidance and control algorithm on the envisioned subsea cable tracking and the potential protection of the seabed environment along the cable route.

Photoreceptor-based magnetoreception: optimal design of receptor molecules, cells, and neuronal processing

The sensory basis of magnetoreception in animals still remains a mystery. One hypothesis of magnetoreception is that photochemical radical pair reactions can transduce magnetic information in specialized photoreceptor cells, possibly involving the photoreceptor molecule cryptochrome. This hypothesis triggered a considerable amount of research in the past decade. Here, we present an updated picture of the radical-pair photoreceptor hypothesis. In our review, we will focus on insights that can assist biologists in their search for the elusive magnetoreceptors.