Small Dc Magnetic Field Research Articles

Magnetoimpedance Biosensors and Real-Time Healthcare Monitors: Progress, Opportunities, and Challenges.

A small DC magnetic field can induce an enormous response in the impedance of a soft magnetic conductor in various forms of wire, ribbon, and thin film. Also known as the giant magnetoimpedance (GMI) effect, this phenomenon forms the basis for the development of high-performance magnetic biosensors with magnetic field sensitivity down to the picoTesla regime at room temperature. Over the past decade, some state-of-the-art prototypes have become available for trial tests due to continuous efforts to improve the sensitivity of GMI biosensors for the ultrasensitive detection of biological entities and biomagnetic field detection of human activities through the use of magnetic nanoparticles as biomarkers. In this review, we highlight recent advances in the development of GMI biosensors and review medical devices for applications in biomedical diagnostics and healthcare monitoring, including real-time monitoring of respiratory motion in COVID-19 patients at various stages. We also discuss exciting research opportunities and existing challenges that will stimulate further study into ultrasensitive magnetic biosensors and healthcare monitors based on the GMI effect.

Effect of static magnetic field bias on dynamic hysteresis loops of a magnetic nanoparticle suspension

Herein, dynamic hysteresis loops of Fe3O4 suspension were investigated at different amplitudes of AC magnetic field (AMF) with simultaneously applied parallel DC magnetic fields (DC-MF). Consequently, the dynamic magnetization induced by a small AMF showed approximately the same gradient as that of thermal equilibrium magnetization at large DC-MF. However, the slope of the dynamic magnetization was smaller than that of thermal equilibrium value at small DC-MF. At large AMF, the addition of DC-MF caused simple shifts in the MH curves. The dynamic loop area, which is considered to be equal to the heating ability, decreased at small DC-MF and dampened the heat generation characteristics. At large AMF amplitudes, the reduction in the loop area due to the application of DC-MF was suppressed.

Observation of the non-linear Meissner effect

A long-standing theoretical prediction is that in clean, nodal unconventional superconductors the magnetic penetration depth λ, at zero temperature, varies linearly with magnetic field. This non-linear Meissner effect is an equally important manifestation of the nodal state as the well studied linear-in-T dependence of λ, but has never been convincingly experimentally observed. Here we present measurements of the nodal superconductors CeCoIn5 and LaFePO which clearly show this non-linear Meissner effect. We further show how the effect of a small dc magnetic field on λ(T) can be used to distinguish gap nodes from non-nodal deep gap minima. Our measurements of KFe2As2 suggest that this material has such a non-nodal state.

Suppressing DC Current Injection in Transformerless Grid-Connected Inverter Using a Customized Current Sensor

Transformerless grid-connected inverters are widely applied due to their low cost and small volume. But the dc current injection (DCI) is one of the main problems that need to be solved. It is difficult to measure milliamperes dc current mixed in large (≥10 A peak) ac current, which causes it difficult to suppress the DCI using the ordinary current sensor (CS). To solve this problem, a novel CS is proposed. It uses a current transformer (CT), a power amplifier, and an additional winding to cancel the ac magnetic field in a commercial current sensor (CCS). Under this circumstance, the CCS is used to detect the remaining small dc magnetic fields. As the range of CCS does not need to be large, the dc current measurement error is significantly reduced. Meanwhile, the CT can measure the ac current and provide feedback to control the inverter. In this way, the proposed CS can replace the original CS instead of adding a new CS to the inverter, which relatively reduces the cost. The volume of CT is relatively small; hence, the CT can be integrated with the CCS, which achieves a relatively small volume of the sensor. A dc current suppression experiment using a 1.5-kVA transformerless grid-connected inverter verified the effectiveness of the proposed technique.

Magnetic Nanoparticle Detection by Utilizing Nonlinear Magnetization for Sentinel Lymph Nodes of Breast Cancer Patients

To minimize the invasiveness and improve the patient's quality of life, sentinel lymph node (SLN) biopsy with magnetic nanoparticles (MNPs) containing superparamagnetic iron oxide is performed on breast cancer patients. Identifying the first SLN by quantification of the amount of MNPs can help to investigate the cancer metastasis. We developed the device for performing iron quantification during surgery. The compact desktop-size device can be easily introduced into operation rooms, and simple system of the device enables identification of the first SLN. We investigated the optimum nonlinear magnetic responses that are attributed to magnetic relaxations under moderate small ac and dc magnetic fields (~1 mT) and found that ac magnetic fields with <; 5 kHz are effective in the detection of MNPs. In addition, our clinical trials revealed more iron (40 μg) in the first lymph node than in the second lymph node (10 μg), clearly indicating intraoperative quantification in the first node.

Simple, Hackable, Size-Selective, Amine-Functionalized Fe-Oxide Nanoparticles for Biomedical Applications.

A facile one-pot method for synthesizing amine-functionalized nonspherical Fe3O4 nanoparticles in gram-scale quantities is presented using just a single source of iron (iron(II) chloride) and an amine (triethylamine). The amine not only transforms iron salt to Fe3O4, but also directs the morphology of the nanoparticles along with the temperature of the reaction and functionalizes them, making the synthesis very economical. By modifying the surface further, these nanoparticles promise to offer useful biomedical applications. For example, after biocide coating, the particles are found to be 100% effective in deactivating methicillin-resistant Staphylococcus aureus (MRSA) bacteria in 2 h. Cellular-uptake studies using biocompatible EDTA-Na3 (N-(trimethoxysilyl-propyl)ethylenediaminetriacetate, trisodium salt)-coated nanoparticles in human glioblastoma U-251 cells show that the majority of the particles are internalized by the cells in the presence of a small dc-magnetic field, making these particles a potential candidate as drug carriers for magnetic field-targeted delivery and hyperthermia.

Slow magnetic relaxation in a neodymium metallocene tetraphenylborate complex

Lanthanide-based single-molecule magnet research has historically focused on molecules of the highly anisotropic Dy3+ and Tb3+ ions, while studies on the lighter, more abundant lanthanides are still relatively scarce. Recent advances with Dy3+ metallocene complexes in particular have led to some truly exceptional systems and the highest relaxation barrier to date, in excess of 1200 cm−1. Even still, the design and understanding of systems incorporating the earlier lanthanides is arguably of great importance if the field is to shift in the direction of identifying systems for practical application. Herein, we present magnetic characterization of the mononuclear metallocene complex Cp*2Nd(BPh4) ([Cp*]− = pentamethylcyclopentadienyl anion), which exhibits slow magnetic relaxation with a relaxation barrier of Ueff = 29(1) cm−1 in the presence of a small dc magnetic field, illustrating that the metallocene ligand framework can also be utilized in the design of single-molecule magnets of the earlier lanthanides. We also discuss dynamic magnetic susceptibility data for the Cp*2Ho(BPh4) and Cp*2Er(BPh4) congeners, which reveal that this particular ligand field is best suited to lanthanides ions exhibiting an oblate 4f electron density.

Note: Resonance magnetoelectric interactions in laminate of FeCuNbSiB and multilayer piezoelectric stack for magnetic sensor.

This paper develops a simple miniature magnetoelectric (ME) laminate FeCuNbSiB/PZT-stack made up of magnetostrictive Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB) foils and piezoelectric Pb(Zr, Ti)O3 (PZT) multilayer stack vibrator. Resonant ME interactions of FeCuNbSiB/PZT-stack with different layers of FeCuNbSiB foil (L) are investigated in detail. The experimental results show that the ME voltage coefficient reaches maximum value of 141.5 (V/cm Oe) for FeCuNbSiB/PZT-stack with L = 6. The AC-magnetic sensitivities can reach 524.29 mV/Oe and 1.8 mV/Oe under resonance 91.6 kHz and off-resonance 1 kHz, respectively. The FeCuNbSiB/PZT-stack can distinguish small dc-magnetic field of ∼9 nT. The results indicate that the proposed ME composites are very promising for the cheap room-temperature magnetic field sensing technology.

New salen-type dysprosium(III) double-decker and triple-decker complexes

We report on the synthesis of two dysprosium(III) containing complexes with double-decker and triple-decker sandwich structures. These two complexes have formulae (NMe4)[Dy(dsp)2] (1) and [Dy2(dsp)3(EtOH)] (2), where H2dsp is a salen type ligand. Both compounds were characterized by X-ray structural analysis, UV–Vis, IR spectral and magnetic studies. Complex 1 crystallized in the space group Pna21. This X-ray structural data provides the first example of the structure of [Ln(dsp)2]−. Compound 2 crystallized in a triclinic space group P1¯. In both cases, two similar but symmetry-independent molecules are present. The UV–Vis spectra of the complexes indicate that they are ligand-based π–π∗ transitions, which was further supported by DFT calculations. Both compounds display field-induced out-of-phase signals. In particular, step-wise slow magnetization relaxation processes are observed in the case of complex 2. This indicates that compound 1 and 2 undergo slow magnetization relaxation when a small dc magnetic field is applied.

Electrically small ferrite antenna gain with dc magnetic field for mobile device application

ABSTRACTWe demonstrate that electrically small ferrite antenna gain is significantly increased with a small dc magnetic field of compact Nd‐Fe‐B permanent magnet (9.5 × 4.6 × 1.5 mm3). The experimental magnetic tangent loss of the Ni‐Mn‐Co ferrite decreased by about 62%, which was from 0.509 with 0 Gauss to 0.192 with 750 Gauss. The antenna gain increased by 54% (from −10.58 to −4.81 dBi) when the magnetic field of 1600 Gauss was applied to the antenna. The ferrite antenna has the volume of 0.346 cm3 and shows omnidirectional patterns, which are suitable for hand‐held mobile device applications. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1531–1534, 2014

Influence of Pyrazolate vs N-Heterocyclic Carbene Ligands on the Slow Magnetic Relaxation of Homoleptic Trischelate Lanthanide(III) and Uranium(III) Complexes

Two isostructural series of trigonal prismatic complexes, M(Bp(Me))3 and M(Bc(Me))3 (M = Y, Tb, Dy, Ho, Er, U; [Bp(Me)](-) = dihydrobis(methypyrazolyl)borate; [Bc(Me)](-) = dihydrobis(methylimidazolyl)borate) are synthesized and fully characterized to examine the influence of ligand donor strength on slow magnetic relaxation. Investigation of the dynamic magnetic properties reveals that the oblate electron density distributions of the Tb(3+), Dy(3+), and U(3+) metal ions within the axial ligand field lead to slow relaxation upon application of a small dc magnetic field. Significantly, the magnetization relaxation is orders of magnitude slower for the N-heterocyclic carbene complexes, M(Bc(Me))3, than for the isomeric pyrazolate complexes, M(Bp(Me))3. Further, investigation of magnetically dilute samples containing 11-14 mol % of Tb(3+), Dy(3+), or U(3+) within the corresponding Y(3+) complex matrix reveals thermally activated relaxation is favored for the M(Bc(Me))3 complexes, even when dipolar interactions are largely absent. Notably, the dilute species U(Bc(Me))3 exhibits Ueff ≈ 33 cm(-1), representing the highest barrier yet observed for a U(3+) molecule demonstrating slow relaxation. Additional analysis through lanthanide XANES, X-band EPR, and (1)H NMR spectroscopies provides evidence that the origin of the slower relaxation derives from the greater magnetic anisotropy enforced within the strongly donating N-heterocyclic carbene coordination sphere. These results show that, like molecular symmetry, ligand-donating ability is a variable that can be controlled to the advantage of the synthetic chemist in the design of single-molecule magnets with enhanced relaxation barriers.

Tb0.3Dy0.7Fe1.9/PbZr0.52Ti0.48O3 Micro-Bridge on SiNx Thin Film for Low Frequency Magnetic Sensing Applications

A micro-fabricated bridge sensor for determining minute magnetic field variation is proposed. A micro-bridge with 100×400 µm2 dimensions (width × length) comprises a multi-layered structure of Tb0.3Dy0.7Fe1.9/SiO2/Pt/PbZr0.52Ti0.48O3/Pt/Ta on a SiNx supporting layer. We observed the limit of detection under small DC magnetic field as 1×10-11 T which was converted electrically to 77 µV with a 5 µV noise floor via elastic coupling between magnetostrictive and piezoelectric thin film. The magnetoelectric (ME) voltage was linearly proportional to small magnetic field variance, and the experimental ME coefficient was measured as 9.9 V/(cm·Oe).

Heavy-Ion Patterned Micro-Channels in YBCO Microwave Resonators

Microcollimated swift heavy-ion irradiation has been employed to carve channels with micron-sized width in YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) superconducting coplanar microwave resonators. Comparative analysis of the first two resonant modes as a function of temperature, magnetic field, and input power was used to characterize the properties of the microchannels. As expected, due to the high fluence, increase of penetration depth and microwave resistivity have been found in the irradiated channels. It is shown that the microchannels can be driven into a highly dissipative and nonlinear regime while the rest of the resonator still persists in a low-dissipation and linear state. Thus, an external control signal (e.g., a small dc magnetic field) can tune the response of the resonator, in the modes coupled to the microchannel, when properly biased. This study is preliminary to the employment of such approach in the design of novel YBCO sensors operating above 77 K.

Control of magnetic loss tangent of hexaferrite for advanced radio frequency antenna applications

We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from −22.9 to −9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range.

Comment on "Al-in-Hornblende Thermobarometry and Sr-Nd-O-Pb Isotopic Compositions of the Early Miocene Alaçam Granite in NW Anatolia (Turkey)"

High harmonic response of high-Tc and Chevrel-phase polycrystalline superconductors are measured in the presence of small ac excitation field and dc magnetic field applied on it. The aim of this work is to study the Josephson weak link behavior and compare the two systems in order to understand the granular nature of polycrystalline superconductors. Critical state models are used to explain the nonlinear magnetic response in polycrystalline superconductors.

Low Field ac Susceptibility and High Harmonics Studies in PbMo6S8 Polycrystalline Superconductor

The ac susceptibility and high harmonic response of polycrystalline PbMo6S8 superconductor are measured in the presence of small ac excitation field and dc magnetic field applied on it. Our experimental results could be explained by the classical Bean critical state model, when the current does not depend on the field and even harmonics are not observed.

Modeling of Small DC Magnetic Field Response in Trilayer Magnetoelectric Laminate Composites

We consider a magnetoelectric laminate which comprises two magnetostrictive (Ni) layers and an in-between piezoelectric layer (PZT). Using the finite-element method-based software COMSOL, we numerically calculate the induced voltage between the two faces of the PZT piezoelectric layer, by an external homogeneous small-signal magnetic field threading the three-layer Ni/PZT/Ni laminate structure. A bias magnetic field is simulated as being produced by two permanent magnets, as it is done in real experimental setups. For approaching the real materials’ properties, a measured magnetization curve of the Ni plate is used in the computations. The reported results take into account the finite-size effects of the structure, such as the fringing electric field effect and the demagnetization, as well as the effect of the finite conductivity of the Ni layers on the output voltage. The results of the simulations are compared with the experimental data and with a widely known analytical result for the induced magnetoelectric voltage.

Cofired Magnetoelectric Laminate Composites

We report the structural, electrical, and magnetoelectric (ME) properties of cofired ME laminate composites synthesized using tape-casting approach. Compositions corresponding to 0.2Pb(Zn1/3Nb2/3)–0.8Pb(Zr0.5Ti0.5)O3 [PZNT] and (Ni0.6Cu0.2Zn0.2) Fe2O3 [NCZF] were used as piezoelectric and magnetostrictive phases, respectively. In order to reduce the sintering temperature of the ferrite layer, NZF was modified with Cu and thereafter the laminate composite was successfully sintered at 930°C. The interface between PZNT and NCZF was found to exhibit strong bonding with no structural defects, which was correlated with cross diffusion of ions. The laminate composite was found to exhibit the ME coefficient of 82 mV·(cm·Oe)−1 at Hdc=67 Oe and was able to detect a small DC magnetic field of 1 μT under Hac=1 Oe at 1 kHz. This sensitivity was attributed to the effectiveness of elastic coupling in the laminate structure. Fabrication of cofired laminate composites with high magnetic field sensitivity will lead to their wide-scale application.

Optimizing the retrieval efficiency of stored light pulses

We study the retrieval efficiency of stored light pulses based on electromagnetically induced transparency in multiple simultaneously driven Lambda-systems. The light pulses are stored in coherences between different Zeeman states of laser-cooled atoms. When the stray magnetic field from the environment is minimized by compensation coils we observed a smaller retrieved probe pulse amplitude than for a small externally applied magnetic field, i.e., a seemingly shorter coherence time. We identify this effect as a beating of several coherences due to a very small uncompensated dc magnetic stray field. By intentionally applying a small magnetic field larger than this stray field we were able to increase the retrieved probe pulse amplitude up to five-fold to the value determined by the true coherence time of our system.

Low Field High Harmonic Response of Tl2Ba2Ca2Cu3O10 and SnMo6S8 Polycrystalline Superconductors

High harmonic response of polycrystalline Tl2Ba2Ca2Cu3O10 and SnMo6S8 superconductors are measured in the presence of small ac excitation field and dc magnetic field applied on it. A purpose of this work is to study the Josephson weak link behavior and make comparison between two systems in order to understand a granular nature of polycrystalline superconductors. Critical state models are used to explain the nonlinear magnetic response in polycrystalline superconductors. For High-Tc superconductor the Anderson-Kim critical state model and for Chevrel-phase superconductors a field independent Bean’s model, are observed to work reasonably well.