Range Of Magnetic Fields Research Articles

Broadband composite pulse for quantum sensing with a solid-state spin in diamond

High fidelity quantum operation of qubits plays an important role in realistic quantum sensing. It becomes more challenging when there are inevitable interactions between qubits in the solid system. We employ a composite pulse sequence to deal with the problems. The electron spin state of the nitrogen-vacancy center in diamond is flipped with high fidelity by the composite pulse at room temperature. In contrast with traditional rectangular pulses, the composite pulse has a wider excitation profile at the same Rabi frequency. Hence, the three sublevels of host nitrogen nuclear spin can be flipped efficiently and simultaneously, which enhances the signal contrast and detection sensitivity of quantum sensing universally. The enhancement effect works over a wide range of bias magnetic fields. Our scheme can be used for sensing temperature, strain, and electric field and can be applied to other spin–spin coupling systems.

Ensemble spin relaxation of shallow donor qubits in ZnO

We present an experimental and theoretical study of the longitudinal electron spin relaxation (${T}_{1}$) of shallow donors in the direct band-gap semiconductor ZnO. ${T}_{1}$ is measured via resonant excitation of the Ga donor-bound exciton. ${T}_{1}$ exhibits an inverse-power dependence on magnetic field ${T}_{1}\ensuremath{\propto}{B}^{\ensuremath{-}n}$, with $4\ensuremath{\le}n\ensuremath{\le}5$, over a field range of 1.75 T to 7 T. We derive an analytic expression for the donor spin-relaxation rate due to spin-orbit (admixture mechanism) and electron-phonon (piezoelectric) coupling for the wurtzite crystal symmetry. Excellent quantitative agreement is found between experiment and theory suggesting the admixture spin-orbit mechanism is the dominant contribution to ${T}_{1}$ in the measured magnetic field range. Temperature and excitation-energy dependent measurements indicate a donor density dependent interaction may contribute to small deviations between experiment and theory. The longest ${T}_{1}$ measured is 480 ms at 1.75 T with increasing ${T}_{1}$ at smaller fields theoretically expected. This work highlights the extremely long longitudinal spin-relaxation time for ZnO donors due to their small spin-orbit coupling.

Lignin-containing cellulose nanofibers made with microwave-aid green solvent treatment for magnetic fluid stabilization

Lignin-containing cellulose nanofibers (LCNFs), prepared from energy cane bagasse (ECB) using microwave-assisted natural deep eutectic solvent (MW-NADES) pretreatment combined with microfluidization, are utilized as stabilizing agents for magnetic particles (MNPs) in magnetorheological fluids (MRFs). The as-prepared LCNFs helped suspend negatively charged MNPs in MRFs effectively due to the presence of physically entangled network of LCNFs and the electrostatic repulsion between LCNFs and MNPs. Consequently, the presence of LCNFs increased the viscosity, yield stress and dynamic moduli of MRFs within the entire magnetic field range (0–1 T). Moreover, the as-developed LCNF-MRFs exhibited superior magnetorheological properties, i.e., widely controllable viscosity, yield stress and dynamic moduli, rapid magnetic response, good reversibility and outstanding cycling stability. This work demonstrates the sustainable, ultrafast production of LCNFs from cellulosic biomass using MW-NADES for MRF stabilization, paving the way for the development of high-performance, and eco-friendly MRFs.

The competition between the hydrodynamic instability from noise and magnetorotational instability in the Keplerian disks

We venture for the comparison between growth rates for magnetorotational instability (MRI) and hydrodynamics instability in the presence of an extra force in the local Keplerian accretion flow. The underlying model is described by the Orr–Sommerfeld and Squire equations in the presence of rotation, magnetic field, and an extra force, plausibly noise with a nonzero mean. We obtain MRI using the Wentzel–Kramers–Brillouin approximation without extra force for a purely vertical magnetic field and vertical wavevector of the perturbations. Expectedly, MRI is active within a range of magnetic field, which changes depending on the perturbation wavevector magnitude. Next, to check the effect of noise on the growth rates, a quartic dispersion relation has been obtained. Among those four solutions for the growth rate, the one that reduces to the MRI growth rate at the limit of vanishing mean of noise in the MRI active region of the magnetic field is mostly dominated by MRI. However, in the MRI inactive region, in the presence of noise, the solution turns out to be unstable, which is almost independent of the magnetic field. Another growth rate, which is almost complementary to the previous one, leads to stability at the limit of vanishing noise. The remaining two growth rates, which correspond to the hydrodynamical growth rates at the limit of the vanishing magnetic field, are completely different from the MRI growth rate. More interestingly, the latter growth rates are larger than that of the MRI. If we consider viscosity, the growth rates decrease depending on the Reynolds number.

Dynamical dephasing of bipartite and tripartite quantum coherence of spin-1/2 XXZ Heisenberg model in a renormalization group approach

The dynamical dephasing of a bipartite and tripartite quantum coherence in spin-1/2 Heisenberg model, driven by an applied magnetic field, in the presence of Dzyaloshinskii-Moriya interaction is investigated. The system is renormalized through the Kadanoof’s blocks approach. It is observed for both bipartite and tripartite schemes that by increasing the size of the system, the quantum coherence measure show an abrupt change at a quantum critical point (QCP). A further increase of the Dzyaloshinskii-Moriya coupling parameter affect the QCP, causing the dynamical dephasing which is the signature of second order quantum phase transition. The displacement of the QCP reduces the Quantum coherence of the system and can be controlled by the external magnetic field strength. Moreover, in a given range of Dzyaloshinskii-Moriya interaction strength and magnetic field, the monogamous and polygamous nature of quantum coherence is related to the size of the system.

Observation of fractional spin textures in a Heusler material

Recently a zoology of non-collinear chiral spin textures has been discovered, most of which, such as skyrmions and antiskyrmions, have integer topological charges. Here we report the experimental real-space observation of the formation and stability of fractional antiskyrmions and fractional elliptical skyrmions in a Heusler material. These fractional objects appear, over a wide range of temperature and magnetic field, at the edges of a sample, whose interior is occupied by an array of nano-objects with integer topological charges, in agreement with our simulations. We explore the evolution of these objects in the presence of magnetic fields and show their interconversion to objects with integer topological charges. This means the topological charge can be varied continuously. These fractional spin textures are not just another type of skyrmion, but are essentially a new state of matter that emerges and lives only at the boundary of a magnetic system. The coexistence of both integer and fractionally charged spin textures in the same material makes the Heusler family of compounds unique for the manipulation of the real-space topology of spin textures and thus an exciting platform for spintronic and magnonic applications.

Research on optimization of magnetic field sensing characteristics of PCF sensor based on SPR.

A photonic crystal fiber utilizing surface plasmon resonance (PCF-SPR) sensor based on refractive index (RI) control of magnetic fluid (MF) is designed. The air holes of the sensor are arranged in a hexagonal shape, and the optical field transmission channels on both sides of the central air hole can effectively confine the energy of the optical field. We use MF as the sensing medium, and coat the inner wall of the central air hole with gold. It can effectively stimulate the SPR effect to achieve the purpose of magneto-refractive modulation. We study the sensing characteristics of the proposed sensor by finite element analysis. The results show that the highest refractive index sensitivity reaches 19520 nm/RIU in the RI range of 1.42-1.435 and the maximum figure of merit (FOM) is 374.3 RIU-1. In addition, the magnetic field and the temperature response characteristics of the designed sensor are also investigated. In the magnetic field range of 50-130 Oe, the magnetic field sensitivity is 590 pm/Oe. In the temperature range of 24.3-144.3 °C, the temperature sensitivity is only -29.7 pm/℃. The proposed sensor has significant advantages such as stable structure, high sensitivity, easy integration, resistance to electromagnetic interference and can be used for weak magnetic magnitude detection. It has wide application prospects in industrial production, military, and medical equipment.

Transport-magnetism correlation in layered perovskite manganite LaCaBiMn2O7

An investigation was conducted to understand the electrical behavior of the double-layered perovskite LaCaBiMn2O7 at temperatures varying from 2 to 400 K under a magnetic field range 0–5 T. At metal-insulator peak temperature (TMI), the data reveal a metal-insulator transition. The compound exhibits a strong magnetoresistance (MR) effect (∼55%) around TMI at a field of 5 T, while the highest value of temperature coefficient of resistance (TCR) is 0.89% K−1 was found at zero-field. In order to analyze the electrical behavior as well as the magnetic properties, a simulation was established with the resistivity (ρ) data using a mathematical model based on the percolation theory. The mutual relationship between transport properties and magnetic behavior has been exploited to predict the magnetic entropy change by analysis of ρ(H, T), It is demonstrated that the magnetic entropy change acquired from ρ(H, T) data is in accordance with those determined by magnetization measurements.

All-optical spin locking in alkali-metal-vapor magnetometers

The nonlinear Zeeman effect can induce splittings and asymmetries of magnetic-resonance lines in the geophysical magnetic-field range. We demonstrate an all-optical scheme, based on spin locking, to suppress the nonlinear Zeeman effect. This scheme achieves spin locking via an effective oscillating magnetic field in the form of AC Stark shifts induced by an intensity- and polarization-modulated laser beam. This results in the collapse of the multicomponent asymmetric magnetic-resonance line with $\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}$ width in the Earth-field range into a peak with a central component width of 25 Hz. The technique is expected to be broadly applicable in practical magnetometry, potentially boosting the sensitivity and accuracy of Earth-surveying magnetometers by increasing the magnetic-resonance amplitude and decreasing its width. An advantage of the all-optical approach is the absence of crosstalk between nearby sensors when they are used in a gradiometric or array arrangement.

Ultracold neutral plasma expansion in a strong uniform magnetic field.

In strongly magnetized neutral plasmas, electron motion is reduced perpendicular to the magnetic field direction. This changes dynamical plasma properties such as temperature equilibration, spatial density evolution, electron pressure, and thermal and electrical conductivity. In this paper we report measurements of free plasma expansion in the presence of a strong magnetic field. We image laser-induced fluorescence from an ultracold neutral Ca^{+} plasma to map the plasma size as a function of time for a range of magnetic field strengths. The asymptotic expansion velocity perpendicular to the magnetic field direction falls rapidly with increasing magnetic field strength. We observe that the initially Gaussian spatial distribution remains Gaussian throughout the expansion in both the parallel and perpendicular directions. We compare these observations with a diffusion model and with a self-similar expansion model and show that neither of these models reproduces the observed behavior over the entire range of magnetic fields used in this study. Modeling the expansion of a magnetized ultracold plasma poses a nontrivial theoretical challenge.

Design and research of electromagnetic generator based on Helmholtz coil

According to the technical requirements of electromagnetic-eddy current spin-off test for space targets, an electromagnetic generator is designed based on the working principle of the Helmholtz coil, the utility model is composed of a pair of square coils of the same structural size and turns of the coils. The magnetic field generated by the electromagnetic generator is simulated and analyzed by using the Maxwell electromagnetic simulation software, and the distribution of the magnetic field on the X axis, Z axis and the surface of the square coil is observed, the Tesla Meter was used to measure the magnetic field at 27 locations in the central region of the electromagnetic generator. The results show that the uniform magnetic field range, the magnetic induction and the uniformity of the magnetic field produced by the electromagnetic generator can meet the requirements of the electromagnetic eddy current damping test.

Influence of low-energy magnons on magnon Hanle experiments in easy-plane antiferromagnets

Antiferromagnetic materials host pairs of spin-up and spin-down magnons which can be described in terms of a magnonic pseudospin. The close analogy between this magnonic pseudospin systems and that of electronic charge carriers led to the prediction of fascinating phenomena in antiferromagnets. Recently, the associated dynamics of antiferromagnetic pseudospin has been experimentally demonstrated and, in particular, the first observation of the magnon Hanle effect has been reported. We here expand the magnonic spin transport description by explicitly taking into account contributions of finite-spin low-energy magnons. In our experiments we realize the spin injection and detection process by two Platinum strips and investigate the influence of the Pt-strips on the generation and diffusive transport of magnons in films of the antiferromagnetic insulator hematite. For both a 15 nm and a 100 nm thick film, we find a distinct signal caused by the magnon Hanle effect. However, the magnonic spin signal exhibits clear differences in both films. In contrast to the thin film, for the thicker one, we observe an oscillating behavior in the high magnetic field range as well as an additional offset signal in the low magnetic field regime. We attribute this offset signal to the presence of finite-spin low-energy magnons.

Influence of Ga+ milling on the spin waves modes in a Co2MnSi Heusler magnonic crystal

Ferromagnetic resonance experiment was performed to study the magnonic modes of an antidot lattice nanopatterned in a sputtered Co2MnSi Heusler alloy thin film. The magnonic crystal was prepared with a Ga+ focused ion beam, and micromagnetic simulations were used to explain qualitatively and quantitatively the complex experimental spin waves spectrum. We demonstrate the necessity to consider the geometrical imperfections and the modification of the Co2MnSi magnetic parameters induced by the nanofabrication process to describe the evolution of the frequencies and spatial profiles of the principal experimental spin waves modes in the 0–300 mT magnetic field range. In particular, our model suggests that Ga+ milling induces a drastic decrease (between 80% and 90%) in the bulk Co2MnSi magnetic parameters. In addition, simulations reveal the presence of a diversity of localized and extended spin waves modes whose spatial profiles are closely related to the evolution of the magnetic state at equilibrium from a very non-collinear configuration up to a quasi-saturated state.

Magnetic fields generated by the DC cables of offshore wind farms have no effect on spatial distribution or swimming behavior of lesser sandeel larvae (Ammodytes marinus)

In the North Sea, the number and size of offshore wind (OW) turbines, together with the associated network of High Voltage Direct Current (HVDC) subsea cables, will increase rapidly over the coming years. HVDC cables produce magnetic fields (MFs) that might have an impact on marine animals that encounter them. One of the fish species that is at risk of exposure to MF associated with OW is the lesser sandeel (Ammodytes marinus), a keystone species of the North Sea basin. Lesser sandeel could be exposed to MF as larvae, when they drift in proximity of OW turbines. Whether MFs impact the behavior of lesser sandeel larvae, with possible downstream effects on their dispersal and survival, is unknown. We tested the behavior of 56 lesser sandeel larvae, using a setup designed to simulate the scenario of larvae drifting past a DC cable. We exposed the larvae to a MF intensity gradient (150-50 μT) that is within the range of MFs produced by HVDC subsea cables. Exposure to the MF gradient did not affect the spatial distribution of lesser sandeel larvae in a raceway tank 50 cm long, 7 cm wide and 3.5 cm deep. Nor did the MF alter their swimming speed, acceleration or distance moved. These results show that static MF from DC cables would not impact behavior of lesser sandeel larvae during the larval period of their life although it does not exclude the possibility that later life stages could be affected.

Portable Diamond NV Magnetometer Head Integrated With 520 nm Diode Laser

The integrated diamond nitrogen vacancy (NV) magnetometer has attracted considerable attention in recent years and presents high potential for its use in magnetic field detection in fields such as aerospace, medical, and agriculture. A laser with a large volume seriously hampers the integration and performance of magnetometers. To solve this problem, we proposed a 520-nm laser diode with an integrated NV magnetometer. The 520-nm laser diode has a high excitation efficiency and good performance with a small size. We introduced the key steps of designing an integrated magnetometer head and tested the performance, a magnetic field sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20.77\,\,{n}T\,\,\cdot \,\,Hz^{-1/2}$ </tex-math></inline-formula> , and a shot noise sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.43\,\,{n}T\,\,\cdot \,\,Hz^{-1/2}$ </tex-math></inline-formula> . The measurable magnetic field range is from −107 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$107 ~\mu \text{T}$ </tex-math></inline-formula> , the system bandwidth is 15 Hz at the laser power of 10 mW, and the magnetic field conversion coefficient is 16.88 V/T. Thus, this paper provides a new method to minimise the light source volume and integrate it with a NV magnetometer.

High Temperature Degradation Modes Observed in Gallium Nitride-Based Hall-Effect Sensors

Abstract Magnetic field sensors based on the Hall-effect have a variety of applications such as current sensing in power electronics and position and velocity sensing in vehicles. Additionally, they have benefits such as easy integration into circuits, low manufacturing cost, and linearity over a wide range of magnetic fields. However, in order to use these devices in an industrial or automotive setting, the effect of high temperatures on the reliability of the Hall-effect sensors needs to be evaluated. This study focuses on the effect of high temperature on the electrical and material properties of novel gallium nitride (GaN)-based Hall-effect sensors and the impacts on the reliability of these devices. Changes in device properties such as resistance and electrical response, as well as on the metallic contacts, are examined, using two sets of devices made with different substrates and contact metals. A probe station is used to characterize electrical responses, while an X-ray photo-electron spectrometer (XPS) and energy-dispersive X-ray (EDX) are used to characterize material interactions. The findings include saturation curves, the presence of gallium on the contacts of the octagonal device, and the activation energy of reaction responsible for resistance increase for the octagonal AlGaN/GaN devices. Additionally, the Greek cross AlGaN/GaN Hall sensors showed excellent thermal stability.

An integrated front-end vertical hall magnetic sensor fabricated in 0.18 μm low-voltage CMOS technology

An integrated front-end vertical CMOS Hall magnetic sensor is proposed for the in-plane magnetic field measurement. To improve the magnetic sensitivity and to obtain low offset, a fully symmetric vertical Hall device (FSVHD) has been optimized with a minimum size design. A new four-phase spinning current modulation associated with a correlated double sampling (CDS) demodulation technique has been further applied to compensate for the offset and also to provide a linear Hall output voltage. The vertical Hall sensor chip has been manufactured in a 0.18 μm low-voltage CMOS technology and it occupies an area of 1.54 mm2. The experimental results show in the magnetic field range from –200 to 200 mT, the entire vertical Hall sensor performs with the linearity of 99.9% and the system magnetic sensitivity of 1.22 V/T and the residual offset of 60 μT. Meanwhile, it consumes 4.5 mW at a 3.3 V supply voltage. The proposed vertical Hall sensor is very suitable for the low-cost system-on-chip (SOC) implementation of 2D or 3D magnetic microsystems.

Non-contact torque sensor based on magnetostrictive Fe30Co70 alloy

A non-contact torque sensor based on a magnetostrictive Fe30Co70 rod wound with an excitation coil and a pickup coil is proposed in this paper. In the magnetic field range 0–30 kA/m, the changing rate and linearity of magnetostriction with a loading magnetic field of Fe30Co70 samples are significantly improved after heat treatment. Maximum magnetostriction is 103 ppm in the annealed sample in the parallel direction, while its tensile strength and allowable shear stress are 608 and 194.56 MPa, respectively. According to the mathematical model presented in this work, there is a linear relationship between the output voltage and torque. An apparent increase in the induced voltage signal (peak voltage) of 48.23 mV is observed as the torque increases to 20 Nm in the case of applying sinusoidal excitation signals. In addition, the experimental results are consistent with the calculated values within the torque range 0–16 Nm, and a good sensitivity of 2.87 mV/Nm is obtained. This work shows the prospect of Fe30Co70 alloy for non-contact torque sensing for the appropriate magnetostrictive property with no orientation requirement.

Assessing the relaxation mechanisms contributions on magnetoimpedance effect in YIG/W bilayers

Damping parameter plays a key role in the magnetization dynamics of ferri/ferromagnetic materials with potential technological applications. Experimentally the damping parameter can be estimated from the linewidth of the ferromagnetic resonance experiment, which is altered by distinct mechanisms associated with extrinsic contributions, such as spin pumping and two-magnon scattering mechanisms. Here we perform a systematic investigation of the magnetization dynamics through magnetoimpedance effect in Y5Fe3O12(t)/W(100 nm) bilayers having t YIG between 25 and 125 nm. By modifying the YIG thickness, we explore the contributions of such extrinsic mechanisms to α eff . From the structural features, quasi-static magnetic properties, and ferromagnetic resonance results, we interpret our findings for the magnetization dynamics. Our results disclose that the bilayer structure allows us to explore the magnetoimpedance effect in a wide range of frequency and magnetic fields, providing insights on the effective damping parameter.

Particle-in-cell model of a relativistic magnetron system driven by a pulse forming network Marx generator

A three dimensional particle-in-cell (PIC) model of a relativistic magnetron (RM) is established using CST Studio Suite. As we adopted a novel technique to imitate pulse forming action of pulser, simulation domain is now fully extended to include a pulser, a transmission line, and a magnetron tube. This feature enables the model to describe a dynamic power coupling process between the pulser and RM in a self-consistent manner. It is demonstrated that model accuracy is strongly dependent on user-defined parameters for an explosive electron emission model. Particularly, emission rise time for space charge formation influences significantly on an initial mode competition phase. Compared to a previous excitation method using a step voltage pulse, the new model gives more reliable results as the intrinsic impedance of the pulser is now considered. Our model is able to estimate the major RM characteristics over a wide range of an external magnetic field. As a result of dynamic power coupling, the RM impedance, the gap voltage, the excitation frequency, and the output power tend to increase at a higher external magnetic field condition. It is suitable to adopt a proposed modeling technique for the virtual assemble and simulation of the system. Hence, it will suggest a practical way to implement and verify complicated structures or innovative designs that could not be solved by existing PIC codes.