AC Magnetic Field Research Articles

Enhancing heat generation ability and magnetic properties of MgFe2O4 with Ni substitutes for biomedical applications

Herein, using the systematic experimental characterization and density functional theory calculations, the effects of Ni elemental substitution on the crystal structure, cation distribution, magnetic properties, and heat generation ability of Mg1–xNixFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) have been reported. We demonstrate that the presence of Ni can lead the lattice shrinkage, phase transition from partially to fully inverse spinel structure, and multi-domain structures in the samples. Moreover, Ni substitutional atoms make magnetically harder ferrite, associated with increasing magnetic inhomogeneity. Remarkably, anomalous enhancements of magnetic anisotropic and coercivity have been observed in Mg0.4Ni0.6Fe2O4. Heat generation ability (SAR) increases from 242 W g−1 for x = 0–391 W g−1 for x = 0.6 at an AC magnetic field of 370 kHz frequency. Thus, the magnetic hyperthermia of Mg0.4Ni0.6Fe2O4 sample on HeLa shows promising results that the viability of cells decreases to 25 % after 5 sessions. The present experimental and theoretical systematic studies provide novel avenue and paradigm for the development of ferrite nanoparticles with high heat generation ability and magnetic properties for biomedical applications.

Improvement of magnetic field detectivity in electrical 1/f noise-dominated tunnel magnetoresistive sensors by AC magnetic field modulation technique

Suppression of 1/f noise in tunnel magnetoresistance (TMR) sensors is a central issue in the realization of magnetic field sensors with ultrafine magnetic field detectivity. Although AC modulation with an external magnetic field has been proposed as a method to shift the operating frequency of a sensor to a high frequency and substantially suppress 1/f noise, its effects on the two types of 1/f noise, that is, magnetic and electrical 1/f noise, are not well understood. In this study, we investigated the noise characteristics and signal detection performance of TMR sensors with an even-function resistance-magnetic field curve operated by the AC modulation method. For one TMR device in which the magnetic 1/f noise was dominant, AC modulation degraded the magnetic field detectivity owing to the additional noise induced by the AC modulation field. However, in another TMR device, in which the electrical 1/f noise was artificially enhanced by introducing lattice defects in the MgO tunnel barrier, AC modulation effectively suppressed the 1/f noise and improved the magnetic field detectivity by one order. This demonstrates that the AC modulation method using an external magnetic field is effective for magnetic field sensors in which electrical 1/f noise is dominant.

Process advantages of laser hybrid welding compared to conventional arc-based welding processes for joining thick steel structures of wind tower

The most common welding processes when joining thick-walled steels in the industry are arc-based welding processes such as GMAW or SAW. For this purpose, the sheets are joined in multi-layer technique, which can lead to productivity losses due to high welding times. The process-specific challenges in welding thick steels using multi-layer technique relate to the high heat input from the process. Therefore, alternative welding processes are being actively sought. A suitable alternative is provided by beam-based welding processes such as the laser hybrid welding processes, which are characterized by deep penetration welds and lower heat input. With implementation of the laser hybrid welding process in the heavy industry, such as the wind tower industry, economic benefits can be reached such as the increase in productivity by reducing the layer number, and the lower consumption of filler material and energy. When comparing SAW welded 25 mm thick steels in five to six layers and single-pass laser hybrid welding, the welding time can be reduced more than 80 % and the costs of filler material, flux and energy can be saved up to 90 %. However, the industrial use of the laser hybrid welding process is still limited to applications, where the material thickness does not exceed 15 mm due to some process-specific challenges such as the sagging, sensitivity to manufacturing tolerances such as gaps and misalignment, limited filler wire mixing, and deteriorated mechanical properties resulting from high cooling rates. To overcome these challenges, a contactless electromagnetic backing based on an externally applied AC magnetic field was used. Eddy currents are induced due to the oscillating magnetic field, and an upward-oriented Lorentz force is generated to counteract the droplets formed due to gravitational forces. It allows to weld up to 30 mm thick structural steels in a single-pass with a 20-kW fiber laser system. Additionally, the gap bridgeability and the misalignment of edges were increased to 2 mm when welding 20 mm thick steels. With the aid of the AC magnetic field, a vortex was formed in the weld root, which had a positive effect on the filler wire mixing. A further significant advantage of the EM backing was the possibility to expand the process parameter window to maintain desired cooling times and mechanical properties, without suffering adverse effects concerning the root quality of the weld.

Tin Oxide Nanoparticles: A Review

Abstract: The aim of this review article is an overview of the tin oxide (SnO2) nanoparticles, and the literature addresses the existing research related to the various modifications and characterization of SnO2 nanoparticles with their physicochemical investigations. Among various metal-oxide nanoparticles, SnO2 nanoparticles are considered one of the potential candidates for electronic and electrical device fabrication, sensors, display devices, gas sensing, photovoltaic devices, LIBs (Lithium-ion batteries), photocatalysis and optoelectronic devices, supercapacitors, SnO2 nanowires would provide electrolyte channels for effective transport, catalyst, and anode materials. Apart from their technological supremacy, SnO2 nanoparticles have demonstrated their compatibility with human cervical cancer cells and have successfully achieved hyperthermia temperature when subjected to an alternating current magnetic field. Doping with some of the potential rare-earth dopants via various synthesis methods such as Chemical co-precipitation, sol-gel, polymeric precursor method, and nebulizer spray pyrolysis method is the major highlight of this review article. As per the requirement of the system, SnO2 nanoparticles can be tuned by size, shape, and functionality.

Magnetic particle spectroscopy and magnetic particle imaging of zinc and cobalt ferrite nanoparticles: Distinct relaxation mechanisms

Magnetic particle imaging (MPI) is an emerging imaging method based on the nonlinear response of superparamagnetic tracers to a sinusoidal AC magnetic field. Higher harmonics obtained by the Fourier transform of acquired signals form a so-called magnetic particle spectrum, whereby straightforward evaluation of different nanoparticles as potential MPI tracers can be carried out. The shape of the spectra is largely dictated by the combined Néel and Brownian relaxation of superspins, whose relative contributions vary significantly depending on the tracer properties. The present study is focused on the comparison of several Zn ferrite and Co ferrite samples, selected for their different magnetic behaviors, together with the commercial tracer Resovist® (SH U 555 A). A new custom-made magnetic particle spectrometer and a commercial MPI system (Bruker) with comparable AC field amplitudes (∼14 mT) and frequencies (∼25 kHz) are used. Magnetic nanoparticles of Zn and Co ferrites have been synthesized by the thermal decomposition method and by the solvothermal/hydrothermal route, achieving four different samples of magnetic cores with the mean crystallite size in the range of 8–16 nm. From all of them, well-comparable silica-coated particles with a shell thickness of 5–6 nm have been prepared. To analyse the effect of the coating layer and hydrodynamic size, three additional samples have been supplemented: solvothermal Zn ferrite nanoparticles stabilized with a citrate monolayer, the same particles coated with 17 nm thick silica shell, and silica-coated Zn ferrite particles from the thermal decomposition with a higher degree of agglomeration. Fundamental characterizations of the nanomaterials by XRD, XRF, TEM, and DLS are followed by detailed investigations of their magnetic properties and structural peculiarities by SQUID magnetometry and 57Fe Mössbauer spectroscopy. Magnetic particle spectroscopy and subsequent MPI study demonstrate: (i) superior properties of Zn ferrite nanoparticles compared to their Co ferrite counterparts, (ii) only negligible to weak effect of the type/thickness of the coating on signal of Zn ferrite nanoparticles, (iii) comparable performance of the solvothermal Zn ferrite particles with a thin silica shell and of the Resovist® tracer, and importantly, (iv) that suitable choice of the magnetic phase enables to separate the contributions of the Néel and Brownian relaxation on the timescale of MPI.

Improvement of the Self-Controlled Hyperthermia Applications by Varying Gadolinium Doping in Lanthanum Strontium Manganite Nanoparticles

In this study, silica-encapsulated gadolinium was doped in lanthanum strontium manganite nanoparticles (NPs) with different concentrations using the citrate–gel auto-combustion method. We focused on tuning the Curie temperature and enhancing the specific absorption rate (SAR) of silica-coated gadolinium-doped lanthanum strontium manganite NPs to make them suitable for self-controlled magnetic hyperthermia. The samples were characterized by using transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and magnetic measurements to examine the structural, optical, and magnetic properties of the manganite NPs. While our results exhibit a successful doping of gadolinium in lanthanum strontium manganite NPs, we further prepared magnetic core NPs with sizes between 20 and 50 nm. The Curie temperature of the NPs declined with increasing gadolinium doping, making them promising materials for hyperthermia applications. The Curie temperature was measured using the magnetization (M-T) curve. Magnetic heating was carried out in an external applied AC magnetic field. Our present work proved the availability of regulating the Curie temperature of gadolinium-doped lanthanum strontium manganite NPs, which makes them promising candidates for self-controlled magnetic hyperthermia applications.

Surface corrosion evaluation of steel cable for suspension bridge using electromagnetic method

The cables of suspension bridges are normally made of galvanized steel wires. Corrosion may happen with the galvanized steel wires from the surface after serving for a long time. We developed a compact, low-cost electromagnetic system to evaluate the corrosion of steel cables. AC magnetic field was produced by an excitation coil and eddy current was induced in the steel wires. A detection coil was used to measure the magnetic field produced by the eddy current. In our experiments, the excitation coil was 100 turns with a diameter of 3 cm, the detection coil was 60 turns with a diameter of 1 cm and the excitation frequency was about 80 kHz. A lock-in amplifier was used to get the X signal (same phase signal with the excitation field) and Y signal (90-degree phase different signal with excitation field). From the slope of the X–Y graph, the degree of corrosion can be judged. To make the system portable, the excitation coil, detection coil, amplifier, lock-in amplifier, and AD converter were put in a small box with the size of 85 mm × 170 mm × 60 mm; only a USB cable was used for the power and data transferring. The electric power required for the system was less than 1 W. We prepared some galvanized steel wires with and without corrosion and did some experiments in the laboratory. The degree of corrosion of galvanized steel wires was successfully evaluated using the system.

A Flexible Magnetic Field Sensor Based on PZT/CFO Bilayer via van der Waals Oxide Heteroepitaxy.

Magnetoelectric (ME) magnetic field sensors utilize ME effects in ferroelectric ferromagnetic layered heterostructures to convert magnetic signals into electrical signals. However, the substrate clamping effect greatly limits the design and fabrication of ME composites with high ME coefficients. To reduce the clamping effect and improve the ME response, a flexible ME sensor based on PbZr0.2Ti0.8O3 (PZT)/CoFe2O4 (CFO) ME bilayered heterostructure was deposited on mica substrates via van der Waals oxide heteroepitaxy. A saturated magnetization of 114.5 emu/cm3 was observed in the bilayers. The flexible sensor exhibited a strong ME coefficient of 6.12 V/cm·Oe. The local ME coupling has been confirmed by the evolution of the ferroelectric domain under applied magnetic fields. The flexible ME sensor possessed a stable response with high sensitivity to both AC and DC weak magnetic fields. A high linearity of 0.9988 and sensitivity of 72.65 mV/Oe of the ME sensor were obtained under flat states. The ME output and limit-of-detection under different bending states showed an inferior trend as the bending radius increased. A flexible proximity sensor has been demonstrated, indicating a promising avenue for wearable device applications and significantly broadening the potential application of the flexible ME magnetic field sensors.

Magnetic, optical and photothermal properties of Fe3O4 and CoFe2O4 nanoparticles coated with organic materials

Nanoparticles represent a class of highly adaptable nanostructures with a remarkable surface-to-volume ratio, allowing for the precise tuning of their shape to influence their properties. Moreover, their surfaces can be functionalized with organic or inorganic materials, thereby tailoring their performance and introducing specific functionalities. Iron oxide nanoparticles including Fe3O4 and spinel Co ferrites emerge as promising candidates for medical applications due to their notable biocompatibility and appropriate magnetic properties. Their potential in cancer therapy primarily hinges on localized cancer cell heating, which can be remotely triggered by an external AC magnetic field (magnetic hyperthermia). Additional heating induced by light excitation can reduce the required particle dosages during such treatments. The optical characteristics of iron oxide nanoparticles within the wavelength range of biological transparency open up exciting prospects for utilizing these structures in adjuvant thermal therapies. In this study, we demonstrate the results of synthesis and study of magnetic and optical properties of iron oxide nanoparticles coated with organic materials. Notably, CoFe2O4 nanoparticles coated with dihydrocaffeic acid demonstrated the coefficient of heat efficiency conversion close to 100 % under 810 nm laser excitation. They also demonstrated the magnetization curves characterized by minimal hysteresis and remanent magnetization typical of superparamagnetic behavior of iron oxide nanoparticles. This suggests their potential for combined magnetic and optical hyperthermia.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Magnetically Modulated Differential Quartz Crystal Microbalances for Rapid, Ultrasensitive, and Direct Probing of Prostate-Specific Antigens Conjugated with Magnetic Beads.

The occurrence and development of diseases are closely related to overexpression of specific biomarkers in the serum of patients. Rapid and sensitive biomarker detection is beneficial for early diagnosis and treatment. However, the current laboratory processes and assays for biomarker detection are expensive and time-consuming, and their operation also requires a large number of professionals. We developed a magnetically modulated differential quartz crystal microbalance (MMD-QCM) method combined with magnetic bead (MB) labels for rapid and highly sensitive quantitative detection of prostate-specific antigen (PSA). Because MBs exhibit magnetized rotation motion under an applied AC magnetic field, a pair of QCMs are utilized to measure the difference between the magnetic motion intensities of the MBs and the MB-PSA immune complex to determine the PSA concentration. Experimental results demonstrate that the proposed method can be adopted to determine the PSA concentration in a wide range of 0.01-1000 ng/mL as well as exhibit a low detection limit of 0.065 ng/mL. In addition, the proposed scheme enables fast detection and low sample consumption. The single detection process takes less than 4 h and requires only 113 μL of sample solution. The proposed detection strategy is superior to the existing detection method and can be effectively used in early screening and prognostic diagnosis of cancer and other related diseases owing to its simplicity, low cost, and high speed.

Unconventional Nonreciprocal Voltage Transition in Ag2Te Nanobelts

Nonreciprocal effects are consistently observed in noncentrosymmetric materials due to the intrinsic symmetry breaking and in high-conductivity systems due to the extrinsic thermoelectric effect. Meanwhile, nonreciprocal charge transport is widely utilized as an effective experimental technique for detecting intrinsic unidirectional electrical contributions. Here, we show an unconventional nonreciprocal voltage transition in topological insulator Ag2Te nanobelts. The nonreciprocal voltage develops from nearly zero to giant values under the applied current I ac and external magnetic fields, while remaining unchanged under various current I dc. This unidirectional electrical contribution is further evidenced by the differential resistance (dV/dI) measurements. Furthermore, the transition possesses two-dimensional properties under a tilted magnetic field and occurs when the voltage between two electrodes exceeds a certain value. We propose a possible mechanism based on the development of edge channels in Ag2Te nanobelts to interpret the phenomenon. Our results not only introduce a peculiar nonreciprocal voltage transition in topological materials but also enrich the understanding of the intrinsic mechanism that strongly affects nonreciprocal charge transport.

Extremely low-frequency magnetic spectrum measurement method based on the NV center in diamond

Abstract In this paper, we establish a set of schemes to generate, detect, and identify the multi-frequency magnetic field in the extremely low-frequency range. Based on the magnetic sensitivity of nitrogen-vacancy centers in diamond, the schemes adopt frequency closed-loop proportion-integration-differentiation locking and microwave modulation and demodulation to obtain magnetic field information. A set of multi-coil mutual inductance devices is used to generate a multi-frequency AC magnetic field. In the schemes, the DenseNet network structure is used to train and identify the magnetic field information, with a recognition rate of 99.16%. When the Net is used to identify noisy signals, it still maintains an average recognition rate of 95.18% for random frequency noisy signals. This generating, detecting, and identifying schemes of the multi-frequency magnetic field in the extremely low-frequency range based on quantum sensors in this paper provides a novel idea for the future application of quantum sensors in biomedicine.

Magnetoelectric coupling optimization in lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 and Ni0.5Zn0.5Fe2O4 nanocomposites for magneto-mechano-electric generator

Magneto-mechano-electric (MME) generators efficiently harness ubiquitous stray magnetic fields and convert them into electricity, capturing significant attention for powering innumerable wireless sensors. In this study, lead-free 0-3 particulate magnetoelectric (ME) nano-composite ceramics, specifically x(Ba0.85Ca0.15Zr0.1Ti0.9O3)-(1-x)Ni0.5Zn0.5Fe2O4 [x(BCT-BZT)–(1-x)NZFO], were synthesized using the sol-gel method. Subsequently, a flexible MME generator was designed, incorporating the optimized ME composite. Structural parameter calculations indicated higher tetragonal distortion of 0.4% in 0.4(BCT-BZT)-0.6NZFO, possibly due to uniform particulate distribution. The ME composites displayed uniform dual-phase microstructures, with 0.4(BCT-BZT)-0.6NZFO showing a higher NZFO concentration. The maximum values of the magnetodielectric (MD) and ME coupling coefficients have been determined to be -3.6% and 2.55 mV cm -1 Oe-1, respectively, for an x = 0.4 composite. The MME generator is designed using an optimized 0.4(BCT-BZT)-0.6NZFO ME composite with film thickness of 34 μm. This MME generator harvests a sinusoidal wave with a maximum output peak-to-peak voltage of 4.1 V when exposed to a weak AC magnetic field of 10 Oe at a frequency of 50 Hz. Additionally, the device demonstrates an exceptional optimal DC power density of 3.89 μW cm-3. The lead-free 0-3 particulate ME composite enables effective magnetic energy harnessing. As a result, it holds great promise as an efficient autonomous power supply for various Internet of Things based applications.

High Isolation, Double-Clamped, Magnetoelectric Microelectromechanical Resonator Magnetometer.

Magnetoelectric (ME)-based magnetometers have garnered much attention as they boast ultra-low-power systems with a small form factor and limit of detection in the tens of picotesla. The highly sensitive and low-power electric readout from the ME sensor makes them attractive for near DC and low-frequency AC magnetic fields as platforms for continuous magnetic signature monitoring. Among multiple configurations of the current ME magnetic sensors, most rely on exploiting the mechanically resonant characteristics of a released ME microelectromechanical system (MEMS) in a heterostructure device. Through optimizing the resonant device configuration, we design and fabricate a fixed-fixed resonant beam structure with high isolation compared to previous designs operating at ~800 nW of power comprised of piezoelectric aluminum nitride (AlN) and magnetostrictive (Co1-xFex)-based thin films that are less susceptible to vibration while providing similar characteristics to ME-MEMS cantilever devices. In this new design of double-clamped magnetoelectric MEMS resonators, we have also utilized thin films of a new iron-cobalt-hafnium alloy (Fe0.5Co0.5)0.92Hf0.08 that provides a low-stress, high magnetostrictive material with an amorphous crystalline structure and ultra-low magnetocrystalline anisotropy. Together, the improvements of this sensor design yield a magnetic field sensitivity of 125 Hz/mT when released in a compressive state. The overall detection limit of these sensors using an electric field drive and readout are presented, and noise sources are discussed. Based on these results, design parameters for future ME MEMS field sensors are discussed.

Low-frequency magnetic fields potentiate plasma-modified magneto-electric nanoparticle drug loading for anticancer activity in vitro and in vivo

A multiferroic nanostructure of manganese ferrite barium-titanate called magneto-electric nanoparticles (MENs) was synthesized by a co-precipitation method. FTIR, Raman spectroscopy, TEM, and X-ray diffraction confirmed the presence of spinel core and perovskite shell phases with average crystallite sizes of 70–90 nm. Magnetic, optical, and magnetoelectrical properties of MENs were investigated using VSM, UV-Vis spectrophotometry, DLS, and EIS spectroscopy techniques. After pre-activation by low-pressure argon (Ar) plasma, the MENs were functionalized by a highly hydrophilic acrylic acid and Oxygen (AAc+O2) mixture to produce COOH and C=O-rich surfaces. The loading and release of doxorubicin hydrochloride (DOX) on MENs were investigated using UV-vis and fluorescence spectrophotometry under alternating low-frequency magnetic fields. Plasma treatment enabled drug-loading control by changing the particles’ roughness as physical adsorption and creating functional groups for chemical absorption. This led to reduced metabolic activity and cell adherences associated with elevated expression of pro-apoptotic genes (BCL-2, caspase 3) in 4T1 breast cancer cells in vitro exposed to alternating current magnetic field (ACMF) compared to MENs-DOX without field exposure. ACMF-potentiated anticancer effects of MENs were validated in vivo in tumor-bearing Balb/C mice. Altogether, our results suggest potentiated drug loading of MENs showing superior anticancer activity in vitro and in vivo when combined with ACMF.

An efficient method to create high-density nitrogen-vacancy centers in CVD diamond for sensing applications

The negatively charged Nitrogen-Vacancy (NV−) center in diamond is one of the most versatile and robust quantum sensors suitable for quantum technologies, including magnetic field and temperature sensors. For precision sensing applications, densely packed NV− centers within a small volume are preferable due to benefiting from 1/√N sensitivity enhancement (N is the number of sensing NV centers) and efficient excitation of NV centers. However, methods for quickly and efficiently forming high concentrations of NV− centers are in the development stage. We report an efficient method for creating high-density NV− centers production from a relatively low nitrogen concentration based on high-energy photons generated from Ar+ plasma source. This study was done on type-IIa, single crystal, chemical vapor deposition (CVD)-grown diamond substrates with an as-grown nitrogen concentration of 1 × 1017 cm−3. We created high NV− density (∼20,000 NVs over the diffraction limited sample volume) distributed homogeneously over 150–200 μm deep from the diamond surface. The plasma-created NV−s in CVD diamond have a spin-lattice relaxation time (T1) of 5 ms and a spin-spin coherence time (T2) of 4 μs. We measure a DC magnetic field sensitivity of ∼104 nT Hz-1/2, an AC magnetic field sensitivity of ∼0.12 pT Hz-1/2 and demonstrate real-time magnetic field sensing at a rate over 10 mT s−1 using the diffraction limited sample volume.

Quantum Logic Enhanced Sensing in Solid-State Spin Ensembles.

We demonstrate quantum logic enhanced sensitivity for a macroscopic ensemble of solid-state, hybrid two-qubit sensors. We achieve over a factor of 30 improvement in the single-shot signal-to-noise ratio, translating to an ac magnetic field sensitivity enhancement exceeding an order of magnitude for time-averaged measurements. Using the electronic spins of nitrogen vacancy (NV) centers in diamond as sensors, we leverage the on-site nitrogen nuclear spins of the NV centers as memory qubits, in combination with homogeneous and stable bias and control fields, ensuring that all of the ∼10^{9} two-qubit sensors are sufficiently identical to permit global control of the NV ensemble spin states. We find quantum logic sensitivity enhancement for multiple measurement protocols with varying optimal sensing intervals, including XY8 and DROID-60 dynamical decoupling, as well as correlation spectroscopy, using an applied ac magnetic field signal. The results are independent of the nature of the target signal and broadly applicable to measurements using NV centers and other solid-state spin ensembles. This work provides a benchmark for macroscopic ensembles of quantum sensors that employ quantum logic or quantum error correction algorithms for enhanced sensitivity.

Permeameter and solenoid measurements of Epstein strips of electrical steels.

The dc and ac flux density vs magnetic field B(H) loops of Epstein electrical strips are measured in an IEC type-A permeameter with a high-quality electrical strip wound double yokes of inside length l0 = 0.2 m and inside height h0 = 0.1 m and in a long solenoid. The relevant demagnetizing and eddy-current effects are analyzed, modeled, and discussed. It is concluded that demagnetizing corrected solenoid measurement developed for determining dc B(H) loops of the material cannot be used for the ac case, owing to complicated eddy-current demagnetizing effects. Permeameter-measured ac B(H) loops with H detected by a flat H-coil of length less than l0/2 touching the strip's middle surface may be considered representative of the actual material because H is very uniform along the strip within 3l0/4. Strips with ac B(H) loops thus determined should be used to calibrate the effective magnetic path length lm of Epstein measurements, where a very nonuniform field is applied to the strips.

Numerical Analysis of Dynamic Resistance and Total Loss in REBCO-Coated Conductors at Low Temperature Under High Perpendicular AC Magnetic Fields

In several applications of high-temperature superconductors (HTS), a REBCO-coated conductor (CC) carries a DC current under varying magnetic fields. This generates AC loss which can be an important factor to consider in the thermal design of the application. In this work, the dynamic resistance (Rdyn), and total loss in a 4 mm wide Superpower REBCO CC are numerically investigated for AC perpendicular magnetic fields ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> m) up to 1 T and temperatures ranging from 30 K to 50 K. For <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c0</sub> > 0.1 (where Idc is the DC current level and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c0</sub> is the self-field critical current of the conductor), either of the previously developed equations, the non-linear or the simple linear expression for determining B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> (threshold magnetic field), can be used to predict R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dyn</sub> . Finite dynamic loss is observed even below the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> points due to the emergence of resistance. The resistance arises from the superposition of subcritical shielding and transport currents which introduces a finite electric field in the CC. The total loss at higher fields decreases as the temperature increases from 30 K to 50 K for all current values, except for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c0</sub> = 0.9. A lift-off in the total loss is evident for fields around 1 T for all temperatures investigated.