Magnetic Field Shift Research Articles

The evolution of penta-graphene thermoelectrics: External fields as a key enabler for High-Performance devices

The tight-binding model is used in this study to examine the electronic and thermal properties of penta-Graphene (PG). To analyze these properties, approaches including the Kubo formula, linear response theory, and Green's function method are applied. The obtained numerical results show that by introducing bias voltage U, external magnetic field Π, and electron doping μ, significant modifications in electrical conductivity, magnetic susceptibility, and thermoelectric properties including power factor PF(T), Seebeck coefficients S(T), and figure of merit ZT(T) are observed. The band structure and density of states (DOS) of PG structure can be significantly altered by applying a bias voltage or an external magnetic field. The wide band gap of PG exhibited a marked reduction with the application of these external fields, displaying greater sensitivity to Π compared to U. Thermal properties of PG, including electrical conductivity σ(T), exhibit a peak as a function of temperature, which its peak position depends on the external fields and μ. Below the peak, σ(T) increases significantly with increasing external fields and μ, due to the reduced band gap and increased number of excited charge carriers, respectively. σ(T) demonstrates greater sensitivity to μ compared to Π, and both parameters have a more pronounced effect than bias voltage U. The magnetic field and bias voltage shift the peak position of the power factor PF(T) in opposite directions. Through tuning of the external fields, which alters the electronic structure of PG, the ZT(T) can be enhanced and its rate of increase is more dependent on bias voltage than on magnetic field.

Microscopic derivation of Ginzburg–Landau theory and the BCS critical temperature shift in general external fields

We consider the Bardeen–Cooper–Schrieffer (BCS) free energy functional with weak and macroscopic external electric and magnetic fields and derive the Ginzburg–Landau functional. We also provide an asymptotic formula for the BCS critical temperature as a function of the external fields. This extends our previous results in Deuchert et al. (Microscopic derivation of Ginzburg-Landau theory and the BCS critical temperature shift in a weak homogeneous magnetic field, PMP 4(1), 1–89 (2023)) for the constant magnetic field to general magnetic fields with a nonzero magnetic flux through the unit cell.

Microscopic derivation of Ginzburg-Landau theory and the BCS critical temperature shift in a weak homogeneous magnetic field

Starting from the Bardeen-Cooper-Schrieffer (BCS) free energy functional, we derive the Ginzburg-Landau functional in the presence of a weak homogeneous magnetic field. We also provide an asymptotic formula for the BCS critical temperature as a function of the magnetic field. This extends the previous works arXiv:1102.4001 and arXiv:1410.2352 of Frank, Hainzl, Seiringer and Solovej to the case of external magnetic fields with non-vanishing magnetic flux through the unit cell.

Precise Measurement of Magnetic Shielding Residual Field and Light Shift Based on 87Rb Atomic Magnetometer

Precise Measurement of Magnetic Shielding Residual Field and Light Shift Based on ⁸⁷Rb Atomic Magnetometer

Magnetic correlations in the magnetic topological insulator (Cr,Sb)2Te3

Chromium-doped ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ is a magnetic topological insulator (MTI), which belongs to the $(\mathrm{Sb},{\mathrm{Bi})}_{2}(\mathrm{Se},{\mathrm{Te})}_{3}$ family. When doped with the transition metals V, Cr, and Mn this family displays long-range ferromagnetic order above liquid nitrogen temperature and is currently intensely explored for quantum device applications. Despite the large magnetic ordering temperature, the experimental observation of dissipationless electrical transport channels, i.e., the quantum anomalous Hall effect, is limited in these materials to temperatures below $\ensuremath{\approx}2$ K. Inhomogeneities in the MTI have been identified as a major concern, affecting the coupling between the Dirac states and the magnetic dopants. Nevertheless, details on the local magnetic order in these materials are not well understood. Here, we report the study of the magnetic correlations in thin films using a combination of muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$, and magnetic soft x-ray spectroscopy and imaging. $\ensuremath{\mu}\mathrm{SR}$ provides two key quantities for understanding the microscopic magnetic behavior: The magnetic volume fraction, i.e., the percentage of the material that is ferromagnetically ordered, and the relaxation rate, which is sensitive to the magnetic static $(\ensuremath{\approx}\ensuremath{\mu}\mathrm{s})$ and dynamic disorder. By choosing different implantation depths for the muons, one can further discriminate between near-surface and bulk properties. No evidence for a surface enhancement of the magnetic ordering is observed, but, instead, we find evidence of small magnetically ordered clusters in a paramagnetic background, which are coupled. The significant magnetic field shift that is present in all samples indicates a percolation transition that proceeds through the formation and growth of magnetically ordered spin clusters. We further find that fluctuations are present even at low temperatures, and that there appears to be a transition between superparamagnetism and superferromagnetism.

Slight Shifts in Magnetic Field Preceded California Earthquakes

Magnetometers detected faint signals that with further study, may improve our understanding of what happens before earthquakes and offer promise for early detection.

Magnetic and structural entropy contributions to the multicaloric effects in Ni-Mn-Ga-Cu

We have studied the multicaloric properties of a Ni-Mn-Ga-Cu alloy. In this alloy, application of magnetic field and uniaxial stress shift its martensitic transition towards higher temperatures which results in synergic magnetocaloric and elastocaloric effects. By a proper numerical treatment of the calorimetric curves obtained under applied magnetic field and uniaxial stress we have obtained the entropy $S(T,{\ensuremath{\mu}}_{0}H,\ensuremath{\sigma})$ as a function of the magnetic field, uniaxial stress, and temperature over the whole phase space under study. We have determined the different entropy contributions to the multicaloric effect in this alloy, and noticeably we have evidenced the role played by the interplay between magnetic and vibrational degrees of freedom. A comparison between single caloric and multicaloric effects shows that appropriate combinations of magnetic field and stress reduce the magnitude of the specific field required to obtain a given value of the isothermal entropy and adiabatic temperature changes. For example, at 299 K, to achieve an entropy change ($\mathrm{\ensuremath{\Delta}}S$) of $\ensuremath{-}14$ J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, a magnetic field of $\ensuremath{\sim}2.5$ T or a uniaxial stress of 19 MPa are required, while a combination of dual fields of (1 T, 12 MPa) yields to the same value of $\mathrm{\ensuremath{\Delta}}S$. Moreover, the maximum adiabatic temperature change is enlarged up to 9.4 K by the dual fields, higher than the value obtained by a single field ($\ensuremath{\sim}7$ K). The advantage of multicaloric effect is particularly relevant at low magnetic fields which are achievable by permanent magnets. Our findings open new avenues for using multicaloric materials in novel refrigeration technologies.

Super-resolved reconstruction method for spatiotemporally encoded magnetic resonance imaging based on deep neural network

Single-shot spatiotemporally-encoded magnetic resonance imaging (SPEN MRI) is a novel ultrafast MRI technology. The SPEN MRI possesses great resistance to inhomogeneous <i>B</i><sub>0</sub> magnetic field and chemical shift effect. However, it has inherently low spatial resolution, and the super-resolved reconstruction is required to improve the spatial resolution of SPEN MRI image without additional signal acquisition. Several super-resolved reconstruction methods have been proposed, but they all suffer the problems of long iterative solution time and/or aliasing artifacts residue in the reconstructed results. In this paper, a super-resolved reconstruction method is proposed for single-shot SPEN MRI based on deep neural network. In this method the simulation samples are used to train the deep neural network, and then the trained network model is adopted to reconstruct the real sampled signals. Experimental results of numerical simulation, water phantom and in vivo rat brain show that this method can quickly reconstruct a super-resolved SPEN image with no residual aliasing artifacts, and clear texture information. An appropriate number of training samples and an appropriate random noise level for training samples contribute to improving the reconstruction results.

Quantitative susceptibility mapping and R1 measurement: Determination of the myelin volume fraction in the aging ex vivo rat corpus callosum.

In studies of the white matter (WM) in aging brains, both quantitative susceptibility mapping (QSM) and direct R1 measurement offer potentially useful ex vivo MRI tools that allow volumetric characterization of myelin content changes. Despite the technical importance of such MRI methods in numerous age-related diseases, the supposed linear relationship between the estimates of either the QSM or R1 method and age-affected myelin contents has not been validated. In this study, the absolute myelin volume fraction (MVF) was determined by transmission electron microscopy (TEM) as a gold standard measure for comparison with the values obtained by the aforementioned MR methods. To theoretically evaluate and understand the MR signal characteristics, QSM simulations were performed using the finite perturber method (FPM). Specifically, the simulation geometry modeling was based on TEM-derived structures aligned orthogonally to the main magnetic field, the construct of which was used to estimate the magnetic field shift (ΔB) changes arising from the conjectured myelin structures. Experimentally, ex vivo corpus callosum (CC) samples from rat brains obtained at 6 weeks (n = 3), 4 months (n = 3), and 20 months (n = 3) after birth were used to establish the relationship between changes quantified by either QSM or R1 with the absolute MVF by TEM. From the ex vivo brain samples, the scatterplot of mean MVF versus R1 was fitted to a linear equation, where R1mean = 0.7948×MVFmean + 0.8118 (Pearson's correlation coefficient r = 0.9138; p < 0.01), while the scatterplot of mean MVF versus MRI-derived magnetic susceptibility (χ) was also fitted to a line where χmeasured,mean = -0.1218×MVFmean - 0.006345 (r = -0.8435; p < 0.01). As a result of the FPM-based QSM simulations, a linearly proportional relationship between the simulated magnetic susceptibility, χsimulated,mean , and MVF (r = -0.9648; p < 0.01) was established. Such a statistically significant linear correlation between MRI-derived values by the QSM (or R1 ) method and MVF demonstrated that variable myelin contents in the WM (i.e., CC) can be quantified across multiple stages of aging. These findings further support that both techniques based on QSM and R1 provide an efficient means of studying the brain-aging process with accurate volumetric quantification of the myelin content in WM.

Optical manifestation of magnetic polarons bound to excitons and resident holes in a (Cd,Mn)Te quantum well

Photoluminescence and multiple ${\mathrm{Mn}}^{2+}$ spin-flip Raman scattering (SFRS) are studied in the (Cd,Mn)Te/(Cd,Mg)Te quantum well with excess resident hole concentration under resonance continuous-wave photoexcitation in the localized states of excitons and trions at $T=1.5$ K. A magnetic polaron shift of both exciton and trion photoluminescence is observed to be increasing with an increase in the magnetic field up to 6 T applied perpendicularly to the sample growth axis (Voigt geometry). Exciton magnetic polaron shift in magnetic field is attributed to the adiabatic energy transfer from the exchange reservoir to the Zeeman reservoir during the precession of the ${\mathrm{Mn}}^{2+}$ ions in the summary field of external magnetic and exchange hole fields. A mechanism of the magnetic polaron shift of trion photoluminescence is suggested. It is related to direct photoexcitation of the triplet trion state, which is stable in the conditions which are provided by the resident hole magnetic polarons. In these conditions, the ${\mathrm{Mn}}^{2+}$ magnetic moment experiences additional magnetization in the double exchange field provided by two holes in the triplet trion state. It is observed that the maximum efficiency of multiple ${\mathrm{Mn}}^{2+}$ spin-flip Raman scattering falls into the energy range corresponding to the states of localized excitons where the exciton magnetic polaron shift is observed. From this we conclude that the magnetic polaron state could be an intermediate state of the multiple ${\mathrm{Mn}}^{2+}$ SFRS process.

Battery Characterization via Eddy-Current Imaging with Nitrogen-Vacancy Centers in Diamond

Sensitive and accurate diagnostic technologies with magnetic sensors are of great importance for identifying and localizing defects of rechargeable solid batteries using noninvasive detection. We demonstrate a microwave-free alternating current (AC) magnetometry method with negatively charged NV centers in diamond based on a cross-relaxation feature between nitrogen-vacancy (NV) centers and individual substitutional nitrogen (P1) centers occurring at 51.2 mT. We apply the technique to non-destructively image solid-state batteries. By detecting the eddy-current-induced magnetic field of the battery, we distinguish a defect on the external electrode and identify structural anomalies within the battery body. The achieved spatial resolution is μμμ360μm. The maximum magnetic field and phase shift generated by the battery at the modulation frequency of 5 kHz are estimated as 0.04 mT and 0.03 rad respectively.

Controllable gap in microsphere resonator integrated with a deformable ferrofluid droplet for magnetic field sensing

Abstract A magnetic field sensor based on silica microsphere resonator and ferrofluid is proposed and experimentally demonstrated in this paper. A silica fiber taper with a waist diameter of 2 μm is employed to couple the evanescent light into the microsphere with a diameter of 31.21 μm. Whispering gallery modes (WGMs) are excited inside the microsphere resonator and circulate inside the equatorial plane. The essence of the sensing concept is to control the coupling gap between fiber taper and microsphere using the magnetically induced deformation of ferrofluid droplet. The shape-varying ferrofluid droplet is operated under different magnetic fields to observe the resonance shift and Q-factors of WGMs. As the magnetic field rises gradually, a longer resonant wavelength shifts with a decreasing Q-factor and a high maximum sensitivity of 120.9 pm/mT in the vertical magnetic field. On the contrary, resonance under the parallel magnetic field shifts to shorter wavelength with an increasing Q-factor and a low maximum sensitivity of 16.4 pm/mT. All experimental results are in good agreement with the theoretical model, which provides a disparate approach to integrate photonics with ferrofluid for signal processing and sensing applications.

The role of the sonic scale in the growth of magnetic field in compressible turbulence

ABSTRACT We study the growth of small fluctuations of magnetic field in supersonic turbulence, the small-scale dynamo. The growth is due to the smallest and fastest turbulent eddies above the resistive scale. We observe that for supersonic turbulence these eddies are localized below the sonic scale ls, defined as the scale where the typical velocity of the turbulent eddies equals the speed of sound, and are therefore effectively incompressible. All previous studies have ignored the existence of the sonic scale and consequently treated the entire inertial range as made up of compressible eddies. However, at large Mach numbers ls is much smaller than the integral scale of the turbulence so the fastest growing mode of the magnetic field belongs to small-scale incompressible turbulence. We determine this mode and the associated growth rate numerically with the aid of a white noise in time model of turbulence whose approximate validity for the description of the Navier–Stokes turbulence is explained. For that purpose, we introduce a new non-dimensional number Rsm that we name the magnetosonic Reynolds number that describes the division of the magnetic field amplification range between small-scale incompressible eddies and large-scale supersonic ones. We show that indeed, as Rsm grows (which means that the incompressible eddies occupy a larger portion of the magnetic field amplification range) the growth rate of the fastest growing mode increases, while the spatial distribution of the growing magnetic field shifts to smaller scales. Our result implies the existence of small-scale dynamo for compressible homogeneous turbulence.

Study on Dynamic Hysteretic and Loss Properties of Silicon Steel Sheet Under Hybrid Harmonic and DC Bias Excitation

The dynamic and static hysteresis properties as well as loss properties of grain oriented (GO) silicon steel sheet are measured under the AC-DC hybrid excitation containing both DC bias and harmonic components. The influence of the DC-biasing magnetic field, harmonic orders and phase shift angles on the iron loss is analyzed in depth based on the experimental data under different excitations. A dynamic hysteresis model and the parameter identification method is presented to simulate the asymmetrical hysteresis curve with minor loops. According to the equivalence between loss separation and field separation, the static part of magnetic field intensity are calculated by an improved Preisach model, while the dynamic parts are obtained by fitting the classical loss as well as excess loss. The consistency between simulation and measurement verifies the effectiveness and accuracy of the proposed method.

Robust optical clock transitions in trapped ions using dynamical decoupling

We present a novel method for engineering an optical clock transition that is robust against external field fluctuations and is able to overcome limits resulting from field inhomogeneities. The technique is based on the application of continuous driving fields to form a pair of dressed states essentially free of all relevant shifts. Specifically, the clock transition is robust to magnetic field shifts, quadrupole and other tensor shifts, and amplitude fluctuations of the driving fields. The scheme is applicable to either a single ion or an ensemble of ions, and is relevant for several types of ions, such as , , and . Taking a spherically symmetric Coulomb crystal formed by 400 ions as an example, we show through numerical simulations that the inhomogeneous linewidth of tens of Hertz in such a crystal together with linear Zeeman shifts of order 10 MHz are reduced to form a linewidth of around 1 Hz. We estimate a two-order-of-magnitude reduction in averaging time compared to state-of-the art single ion frequency references, assuming a probe laser fractional instability of . Furthermore, a statistical uncertainty reaching 2.9 × 10−16 in 1 s is estimated for a cascaded clock scheme in which the dynamically decoupled Coulomb crystal clock stabilizes the interrogation laser for an clock.

Entanglement and physical attributes of the interaction between two SC-qubits and thermal field in the presence of a magnetic field

The interaction between two superconducting (SC) qubits and thermal field in the presence of a magnetic field, the qubit–qubit interaction and the Stark interaction are investigated. The wave function, and hence density matrix, that describe this system is obtained and the behavior of physical quantities that characterize it are evaluated. In particular, the von Neumann entropy and quantum concurrence as a measure of entanglement between parts of the system are discussed in detail. The effects of thermal and low temperature on the dynamical properties of the von Neumann entropy and nonclassical correlation are discussed. Also, the influences of the atomic coherence and magnetic field on the statistical properties of the physical quantities are examined. Moreover, some important physical phenomena during the time evolution of the interaction between the two SC-qubits, thermal field, and magnetic field are explored. The nonclassical correlation between the thermal field and the two SC-qubits is enhanced by increasing temperature whereas the SC qubit–qubit entanglement decreases. The magnetic field and Stark shifts play a central role in the dynamical and physical attributes of the two types of entanglement.

Study of phase transformations, structural, corrosion properties and cytotoxicity of magnetite-based nanoparticles

This paper presents the results of the structural, corrosion, magnetic properties and cytotoxicity of magnetite nanoparticles, phase transformations was studied by thermal annealing. It was established that thermal annealing of Fe3O4 nanoparticles led to three stages of phase transformations from magnetite to maghemite, with the subsequent formation of the hematite structure. Increasing annealing temperature lead to a change in the magnitudes of the hyperfine magnetic field, quadrupole displacement and isomeric shift that indicates a change in the crystal structure and annealing of defects, which eventually leads to the ordering of magnetic nanoparticles. Studying the degradation of nanoparticles in PBS solution shows us that a change in the crystal structure as a result of a decrease in the degree of perfection and the formation of amorphous inclusions leads to magnetic disordering and a subsequent change in the magnitude of the hyperfine magnetic field. Cytotoxicity results indicate that nanoparticles do not show cytotoxic activity against tested L929, PC-3 and HeLa cell lines, because in all experimental series metabolic activity of studies cells was not below 70% of control.

Influence of metal magnetic state and metal-insulator-semiconductor structure composition on magnetoimpedance effect caused by interface states

This article presents the results of a study of the transport properties of metal/insulator/semiconductor (MIS) hybrid structures in alternating current (ac) mode. We prepared a series of samples with different layers of metal, insulator, and semiconductor. We prepared a series of samples with different layers of metal, insulator and semiconductor. Ferromagnetic Fe and non-magnetic Cu and Mn were chosen as metals, the insulators were SiO2 and Al2O3, and n- and p-type Si substrates were used as semiconductors. Temperature dependence of the real part of the impedance showed peculiar peaks below 40К for different combinations of metals, insulators and semiconductors. For all samples the effect of the magnetic field on the transport properties was studied. At low temperatures, the magnetic field shifts peaks toward higher temperatures. Metal magnetic state does not significantly affect this phenomenon. Changing the type of the insulator and its thickness also did not cause any significant effect. However, the effect was observed for samples with different composition. Moreover, the type of conductivity of the substrate, as well as the type of metal, determines the value of magnetoimpedance. The main role in the magnetoimpedance effect is played by recharge of the energy states localized at the insulator/semiconductor interface. This mechanism allows obtaining a MI effect even in “nonmagnetic” MIS structures; magnetoimpedance can be either positive or negative, depending on temperature and frequency. We suggest that the observed ac magnetotransport phenomena could be used for creating magnetic field sensors, working on new principles.

Measurement and correction of the bulk magnetic susceptibility effects of fat: application in venous oxygen saturation imaging.

To develop a correction method for the effects of the magnetic susceptibility of fat (χFat ) on the calculation of venous oxygen saturation (SvO2 ). The magnetic field shifts associated with the magnetic susceptibility of deoxyhemoglobin can be used to estimate SvO2 , a measure of oxygen extraction and metabolism. However, the distinct magnetic susceptibility of fat surrounding targeted veins will give rise to magnetic field perturbations that will extend into the vein and surrounding tissues, potentially confounding the calculation of SvO2 . Multi-echo modified Dixon fat-water separated imaging was used to quantify fat-water distributions around the superficial femoral vein (venous return from the lower leg). Fat fraction images were used to generate χFat images, to calculate and remove the associated fat-susceptibility-induced magnetic field shifts before the estimation of SvO2 . This approach was evaluated at rest and with plantar flexion exercise to evaluate calf muscle oxygen extraction in 10 healthy subjects. The presence of fat around the vein resulted in complex magnetic field shifts and errors in estimated SvO2 . Corrected resting SvO2 values were significantly larger than those measured with conventional methods, at rest (72.6 ± 11.0% vs. 65.2 ± 12.2%, P < 0.05) and post-exercise (37.4 ± 12.3% vs. 31.7 ± 12.7%, P < 0.05), with larger errors in individuals and/or regions with increased fat volumes. Estimation and removal of the field-effects from χFat enabled the use of fat tissues for the measurement and removal of the background magnetic field. The magnetic susceptibility effects of fat can confound SvO2 estimation, but the susceptibility field effects can estimated and removed with the use of modified Dixon fat-water separated imaging.

Heat capacity and magnetocaloric effect in CoS1.84Se0.16

Abstract The first order paramagnetic (PM)-ferromagnetic (FM) transition in CoS 1.84 Se 0.16 is studied using in-field heat capacity measurement. From the low temperature C P data at zero field, the coefficient of electronic contribution to heat capacity ( γ ) and Debye temperature ( θ D ) are found to be 25 mJ/mol-K2 and 490 K, respectively. Heat capacity shows a sharp, symmetric peak at the magnetic transition ≈ 67 K in the absence of applied magnetic field and peak position shifts towards high temperature with magnetic field. The entropy of the transition is found to be ≈ 0.68 J/mol-K which is dominated by electronic contribution. In-field heat capacity measurement allowed us to estimate all the magnetocaloric (MCE) parameters relevant for magnetic refrigeration i.e. isothermal change in entropy ( - Δ S th ), adiabatic change in temperature ( Δ T ad ), relative cooling power (RCP), cooling capacity (q) etc. Temperature dependence of both - Δ S th and Δ T ad show a table-top like behaviour with almost field independent maxima above 4 Tesla.