Internal Magnetic Field Distribution Research Articles

Evidence of Spin Density Waves in La_{3}Ni_{2}O_{7-δ}.

The recently discovered superconductivity with critical temperature T_{c} up to 80K in the double-layer Nickelate La_{3}Ni_{2}O_{7-δ} under pressure has drawn great attention. Here, we report the positive muon spin relaxation (μ^{+}SR) study of polycrystalline La_{3}Ni_{2}O_{6.92} under ambient pressure. Zero-field μ^{+}SR experiments reveal the existence of magnetic order in La_{3}Ni_{2}O_{6.92} with T_{N}=154 K. The weak transverse field μ^{+}SR measurements reveal the bulk nature of magnetism. In addition, a small quantity of oxygen deficiencies can greatly broaden the internal magnetic field distribution sensed by muons.

Influence of uncertainty factors on the dynamic characteristics of magnetorheological damper

The magnetorheological damper (MRD) is a kind of energy dissipation device, which converts vibration mechanical energy into self-heat energy during operation. The dynamic performance of MRD is affected by uncertain factors such as temperature and external magnetic field. In this paper, basing on the temperature rise theory and external magnetic field interference theory of MRD, it analyses the influence of temperature effect and external magnetic field on the dynamic performance of MRD. Under sinusoidal excitation, the internal temperature field and magnetic field distribution of MRD are simulated by COMSOL, and it calculates the changes of temperature and magnetic field in MRD by the conditions of input current of 0.4A, 0.8A and 1.2A. The temperature rise and external magnetic field test are carried out. Under the same input current, the temperature rise of the outer wall of the cylinder is measured. The results show that the input current increases, the temperature rise of MRD increases, and the temperature of MRD increases, the output damping force decreases obviously. When the input current is 0.4A, the temperature of MRD rises to 40℃, the maximum output damping force decreases by 11.2%, and the current is 1.2A, the maximum output damping force decreases by 18.6%. When external magnetic field is applied, the output damping force of MRD increases. The magnetic induction intensity of the external magnetic field increases from 10mT to 30mT, when the incoming current is 0.4A, the maximum output damping force increases by 5.9%, and the current is 1.2A, the maximum output damping force increases by 5.1%. Therefore, applying external magnetic field to compensate the decreasing value of output damping force caused by temperature rise effect has a certain effect. The results show that the variation trend of theoretical analysis, simulation calculation and experimental verification is consistent.

Electromagnetic transient model and field-circuit coupling numerical calculation of Sen transformer based on finite-element method

• A finite-element (FE) model of electromagnetic transient of Sen transformer (ST) with field-circuit coupling is proposed, and the proposed model can characterize the effects of core and winding topology on the internal magnetic field distribution. • The proposed FE model can characterize the electromagnetic field changes of the ST device under different conditions, such as short-circuit fault, injected harmonics, and dynamic power flow control in the external power system. • The electromagnetic transient field-circuit co-simulation of the ST device and external power system is realized. The conventional electromagnetic transient model of Sen transformer (ST) is mainly established by the magnetic equivalent circuit method, which can be used for the fast calculation of transient characteristics for ST. Unfortunately, this approach may lead to oversimplification and missing significant information in the modeling process. To accurately calculate the transient electromagnetic field and reveal the internal magnetic field distribution of the ST under different operating conditions, an electromagnetic transient model and field-circuit coupling numerical calculation of ST based on finite-element (FE) method is proposed in this paper. The proposed model can characterize the effects of core and winding topology on the internal magnetic field distribution, as well as the complex nonlinear property of core materials, such as saturation, eddy current, and hysteresis. The field-circuit coupling method enables the FE model to establish a connection with external networks and realize the electromagnetic transient field-circuit co-simulation of the ST device and external power system. The case studies are performed on a FE model of the ST and a two-machine transmission system. The corresponding winding voltage and current variations of the ST in the presence of short-circuit fault, injected harmonics, and dynamic power flow control in the external networks are analyzed. The numerical calculation and co-simulation results of the proposed FE model of the ST and the external networks are compared with the commercial FE software, which demonstrates the effectiveness of the proposed FE model of the ST. Moreover, the co-simulation results of dynamic power flow control show that the ST can adjust the power flow distribution of two transmission lines through changing compensation voltage.

Controlling polarization of spintronic THz emitter by remanent magnetization texture

Terahertz (THz) sciences and technologies have contributed to a rapid development of a wide range of applications and expanded the frontiers in fundamental science. Spintronic terahertz emitters offer conceptual advantages since the spin orientation in the magnetic layer can be easily controlled either by the externally applied magnetic field or by the internal magnetic field distribution determined by the specific shape of the magnetic elements. Here, we report a switchable terahertz source based on micropatterned magnetic heterostructures driven by femtosecond laser pulses. We show that the precise tunability of the polarization state is facilitated by the underlying magnetization texture of the magnetic layer that is dictated by the shape of the microstructure. These results also reveal the underlying physical mechanisms of a nonuniform magnetization state on the generation of ultrafast spin currents in the magnetic heterostructures. Our findings indicate that the emission of the linearly polarized THz waves can be switched on and off by saturating the sample using a biasing magnetic field, opening fascinating perspectives for integrated on-chip THz devices with wide-ranging potential applications.

Vibration and damping study of multifunctional grille composite sandwich plates with an IMAS design approach

In the present study, an integrated material and structure (IMAS) design approach is proposed for fabrication of a multifunctional grille composite sandwich plate. It consists of two panels made of carbon fiber/resin polymer (CFRP) and one grille functional core that includes several grid frame beams (GFBs) and grille functional units (GFUs) via falcon riveting connections to achieve vibration sensing and damping control functions. In each GFU, it is composed of a rectangular grille (RG) and several embedded functional materials with 4-layer laminates, including a piezoelectric sensing layer, an upper copper wire layer, a magnetorheological elastomer (MRE) layer and a lower copper wire layer. To investigate the free vibration and damping characteristics of such a highly integrated sandwich structure, an analytical model is proposed that is based on the complex modulus method, the polynomial expansion approach, the improved Rayleigh-Ritz method, etc. After the natural frequencies, modal shapes and damping parameters are successfully solved, with results from literature being employed to roughly validate the model developed. Meanwhile, the dynamic experiments with different internal magnetic field distribution patterns and intensities of MRE are undertaken to give a further validation of the present model. Finally, the parameter analysis is carried out and some important conclusions are summarized to better exert active and passive vibration suppression performance of the CFRP-GFB-GFU plate.

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Advances in Fault Diagnostics and Post‐Fault Operation of Electrical Drives

Antiferromagnetic Correlations in Strongly Valence Fluctuating CeIrSn.

CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of T_{K}∼480 K. We report a negative in-plane thermal expansion α/T below 2K, which passes through a broad minimum near 0.75K. Volume and a-axis magnetostriction for B∥a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at T≪T_{K} result from geometrical frustration.

Long-range spin-wave propagation in transversely magnetized nano-scaled conduits

Magnonics attracts increasing attention in the view of low-energy computation technologies based on spin waves. Recently, spin-wave propagation in longitudinally magnetized nano-scaled spin-wave conduits was demonstrated, proving the fundamental feasibility of magnonics at the sub-100 nm scale. Transversely magnetized nano-conduits, which are of great interest in this regard as they offer a large group velocity and a potentially chirality-based protected transport of energy, have not yet been investigated due to their complex internal magnetic field distribution. Here, we present a study of propagating spin waves in a transversely magnetized nanoscopic yttrium iron garnet conduit of 50 nm width. Space and time-resolved microfocused Brillouin-light-scattering spectroscopy is employed to measure the spin-wave group velocity and decay length. A long-range spin-wave propagation is observed with a decay length of up to (8.0 ± 1.5) μm and a large spin-wave lifetime of up to (44.7 ± 9.1) ns. The results are supported with micromagnetic simulations, revealing a broad single-mode frequency range and the absence of a mode localized to the edges. Furthermore, a frequency nonreciprocity for counter-propagating spin waves is observed in the simulations and the experiment, caused by the trapezoidal cross section of the structure. The revealed long-distance spin-wave propagation on the nano-scale is particularly interesting for an application in spin-wave devices, allowing for long-distance transport of information in magnonic circuits and low-energy device architectures.

Comparative analysis of the operating performance, magnetic field, and temperature rise of the three‐phase permanent magnet synchronous motor with or without fault‐tolerant control under single‐phase open‐circuit fault

In the power transmission system, the semiconductor device in the inverter is one of the main fault points. When the open- or short-circuit fault occurs in the semiconductor device, the motor can be turned into the operation with open-phase fault. To take into account the non-ideal factors existing in the calculation, this study establishes a system-level calculation model including the permanent magnet synchronous motor (PMSM), inverter, and different control strategies, which is used to analyse the operating performance of the PMSM with or without fault-tolerant control under single-phase open-circuit fault. In addition, based on the finite element method, the current fault characteristic and the change of the internal magnetic field distribution before and after the fault are studied, and the temperature rise of the PMSM with and without fault-tolerant control is compared. The aim of this study is to compare the operating performance of the three-phase PMSM under two common fault conditions, and quantitatively give the variation range of magnetic flux density and temperature rise. The theoretical analysis in this study is verified by building a systematic experiment platform.

A Ferromagnetic Wear Particle Sensor Based on a Rotational Symmetry High-Gradient Magnetostatic Field

To improve the wear monitoring accuracy of steel tribo-pairs, a ferromagnetic particle sensor that consists of a magnetic loop with two cylindrical magnetic poles and one magnetic housing is proposed. The induction coil is placed inside the magnetic poles to shield against external electromagnetic interference. The air gap is designed to 1 mm between the two magnetic poles, where a rotational symmetric high-gradient static magnetic field will be generated under constant direct current (dc) drive. The sine-wave-like signal of one period will be induced when one ferromagnetic particle flows through the sensor. The working principle of the sensor and the internal magnetic field distribution is explained by establishing a mathematical model and finite element analysis (FEA). Furthermore, the results about the effects of coil length and position show that the output voltage is not sensitive to the axial mounting positions of the induction coil, and a shorter inductive coil produces a larger output voltage. By the oil dynamic monitoring experiment, the sensor can distinguish 13- $\mu \text{m}$ ferromagnetic particles in an oil tube of 10-mm inner diameter. With its high sensitivity to ferromagnetic particles, the sensor is suitable for online wear monitoring of steel tribo-pairs.

Theoretical study on self-biased magnetoelectric effect of layered magnetoelectric composites

By introducing a high permeability material into the traditional magnetoelectric (ME) composite, a non-zero ME coefficient can be obtained when the external DC magnetic field is zero. This is called the self-biased ME effect. In this system, the high permeability material can be regarded as a special ferromagnetic material. A magnetic field will be generated around it, which affects the internal magnetic field distribution of the ferromagnetic phase in the ME composite. In this paper, we consider the multi-field coupling characteristics of the ME composites, the non-linear characteristics of the individual component materials, and the mechanical and magnetic properties of the high permeability material, to develop a theoretical model for such self-biased ME effect. Then the finite element method is employed to solve the Maxwell equations for this complex problem. The developed theory is highlighted with a direct comparison with experiments that shows their close agreement. It is also demonstrated that, with the addition of the high permeability material, the self-biased ME coefficient can account for 47% of the maximum ME coefficient. This remarkable outcome, and the detailed distributions of the magnetic field, electric field, and elastic field inside ME structures are also presented in detail. Finally, the influence of temperature on the ME effect of the two structures was also studied, and the results showed that the higher the temperature, the smaller the ME coefficient of the structures.

Design of magnetic circuit and extraction system of ECR ion source for intense neutron tube

The magnetic circuit and extraction system were optimized to improve the utilization of neutral gas and neutron yield of a sealed intense neutron tube. An experimental system was established to study the relationship between microwave absorption efficiency and the magnetic field strength. The microwave absorption efficiency can reach 100% when the magnetic field intensity at the microwave window is 0.095 T. To further improve the distribution of ECR region, CST was used to simulate the internal magnetic field distribution of the ion source. The radial and axial magnetization results with the single and double magnetic rings were obtained by changing the position and spacing of the magnetic rings. There are three ECR regions and the location of ECR zones is suitable, when the distance between the center of the magnetic ring and the origin of the resonator is 12.5 mm and the distance between the centers of the two magnetic rings is 60 mm. A two-electrode slit extraction system was designed for uniform beam distribution on target. Compared with the original extraction system, the maximum current density is reduced by 82.5% and the target utilization area is increased by 38.54%, which will effectively reduce the thermal load of the target.

Impact of disorder on dynamics and ordering in the honeycomb-lattice iridate Na2IrO3

Kitaev's honeycomb spin-liquid model and its proposed realization in materials such as $\alpha$-RuCl$_3$, Li$_2$IrO$_3$ and Na$_2$IrO$_3$ continue to present open questions about how the dynamics of a spin-liquid are modified in the presence of non-Kitaev interactions as well as the presence of inhomogeneities. Here we use $^{23}$Na nuclear magnetic resonance to probe both static and dynamical magnetic properties in single crystal Na$_2$IrO$_3$. We find that the NMR shift follows the bulk susceptibility above 30 K but deviates from it below; moreover below $T_N$ the spectra show a broad distribution of internal magnetic fields. Both of these results provide evidence for inequivalent magnetic sites at low temperature, suggesting inhomogeneities are important for the magnetism. The spin-lattice relaxation rate is isotropic and diverges at $T_N$, suggesting that the Kitaev cubic axes may control the critical quantum spin fluctuations. In the ordered state, we observe gapless excitations, which may arise from site substitution, emergent defects from milder disorder, or possibly be associated with nearby quantum paramagnetic states distinct from the Kitaev spin liquid.

Development of a Multidirectional Controlled Small-Scale Spherical MR Actuator for Haptic Applications

In robotics and haptics, actuators that move at multiple degrees of freedom (DOFs) without the intermediate transmission mechanisms and have high force/torque output with compact size are widely expected to improve the stability and transparency of interactions. For this reason, utilizing the characteristics that the rheological properties of magnetorheological (MR) fluid can be continuously and reversibly changed by an external magnetic field within a few milliseconds, a multidirectional controlled three-DOF spherical MR actuator is proposed in this paper. Through the special design of the stator part, the actuator can implement force feedback control in multiple directions. Then, based on the calculated torque model and analysis of the magnetic circuit, finite-element analysis is used to optimize the geometry and internal magnetic field distribution of the actuator. In order to achieve precise control and positioning of multi-DOF motion, a small inertial measurement unit is integrated in the upper part of the joystick. We built a prototype of this actuator and tested its performance under various control conditions. The results show that the actuator can provide force feedback with reasonable magnitude and direction to users according to the change of interaction conditions, thus overcoming the disadvantage of the existing spherical MR actuators that limit the movement of the user in all directions after being activated.

Internal magnetic field distribution in plasmas

We calculate stationary probability distribution of a magnetic field, generated by moving charges of the plasma environment, and stationary probability distribution of force, acting on a charged particle in this environment, with the magnetic interaction taken into account. While the former happens to be the Holtsmark distribution, the latter is a modified Holtsmark distribution. In contrast to prior studies, we did no assumptions on the velocity distribution function and thus the obtained results should be applicable to a wider spectrum of models (with any velocity distribution—not only plasma may be considered). The presented results can be experimentally verified through studies of the Zeeman effect or movement of small charged Brownian particles in plasma.We calculate stationary probability distribution of a magnetic field, generated by moving charges of the plasma environment, and stationary probability distribution of force, acting on a charged particle in this environment, with the magnetic interaction taken into account. While the former happens to be the Holtsmark distribution, the latter is a modified Holtsmark distribution. In contrast to prior studies, we did no assumptions on the velocity distribution function and thus the obtained results should be applicable to a wider spectrum of models (with any velocity distribution—not only plasma may be considered). The presented results can be experimentally verified through studies of the Zeeman effect or movement of small charged Brownian particles in plasma.

Study on 3D Internal Magnetic Field Distribution and Dynamic Mechanics of a Giant Magnetostrictive Actuator

The three-dimensional (3D) coupled magneto-elastic dynamic model of a giant magnetostrictive actuator (GMA) was built based on Maxwell’s equations, elasticity, and vibration theories. The general analytical expressions for the 3D internal magnetic field distribution of GMA were derived, and the corresponding analytical solutions were obtained. This analytical model is able to predict the internal magnetic field distribution and the output displacement of GMA system with different physical parameters under external excitations. The dynamic behaviors, such as the amplitude vs. frequency responses and the time domain waveforms of the GMA, were also studied. Analytical solutions showed that the internal magnetic field has a prominent end effect along the axial direction of a giant magnetostrictive material (GMM) rod, whereas a minimal skin effect along its radial direction, which are matched very well with the FEM results. The amplitude-frequency relationship exhibited prominent resonance and anti-resonance characteristic, which is a typical hysteresis feature of the GMA system. In order to testify the validity of the model prediction, a GMA testing system was also established. Excellent agreement was found between the experiment measurements and model predictions in the range of our research (frequency is lower than 300 Hz). The analytical results of the present study have potential applications in the fields of active vibration control and other precision machining of the GMA system.

57Fe internal field nuclear magnetic resonance and Mössbauer spectroscopy study of Li-Zn ferrites

We report the internal field nuclear magnetic resonance (IFNMR) and Mössbauer spectroscopy study of Li-Zn ferrites at RT. The results were supported by the IFNMR data measured at 77 K. As Zn concentration increases the IFNMR echo amplitude decreases and below certain Zn concentration no signal was detected. At RT the echo amplitude vanishes at a lower Zn concentration, whereas at 77 K, the echo amplitude does not vanish completely (except for pure Zn-ferrite). However, in Mössbauer spectroscopy at RT, we have observed magnetically ordered state of all the Li-Zn ferrite samples. This discrepancy could be related to the difference between the time scale of detection of the spins by Mössbauer spectroscopy (10−7–10−10 s) and NMR spectroscopy (10−6 s). Hence, sensitivity of zero-field NMR depends on the magnetic hyperfine field, temperature and abundance of the magnetic cations at the lattice of the spinel ferrites. We have demonstrated that the ‘two-equal-pulses’ sequence leads to higher echo signal than the spin echo pulse sequence due to the presence of distribution of internal magnetic fields throughout the material. We obtained a limiting value for the fraction of spins needed to produce an echo signal at a particular temperature and at a particular site of the Li-Zn ferrite spinels that can be sensitively detected by pulsed IFNMR technique.

Current-induced modulation of backward spin-waves in metallic microstructures

We performed a propagating spin-wave spectroscopy for backward spin-waves in ferromagnetic metallic microstructures in the presence of electric-current. Even with the smaller current injection of A m−2 into ferromagnetic microwires, the backward spin-waves exhibit a gigantic 200 MHz frequency shift and a 15% amplitude change, showing 60 times larger modulation compared to previous reports. Systematic experiments by measuring dependences on a film thickness of mirowire, on the wave-vector of spin-wave, and on the magnitude of bias field, we revealed that for the backward spin-waves a distribution of internal magnetic field generated by electric-current efficiently modulates the frequency and amplitude of spin-waves. The gigantic frequency and amplitude changes were reproduced by a micromagnetics simulation, predicting that the current-injection of A m−2 allows 3 GHz frequency shift. The effective coupling between electric-current and backward spin-waves has a potential to build up a logic control method which encodes signals into the phase and amplitude of spin-waves. The metallic magnonics cooperating with electronics could suggest highly integrated magnonic circuits both in Boolean and non-Boolean principles.

Influence of the Internal Architecture of MgB2Conductors in the Load Line of Magnet Coils

MgB2 conductors have a multifilamentary superconducting structure encased in sheaths of different materials. Conductors with ferromagnetic sheaths, such as Ni or Fe, redistribute the magnetic field, which can affect the critical current of the superconducting filaments. The internal magnetic field distribution inside the conductor is not considered in general when modeling magnets, where the winding is considered as a bulk. The previous assumption can lead to discrepancies between the experimental results and numerical $I_{c}$ predictions. Hence, a correct analysis of the effects of the ferromagnetic matrix in conductors will lead to savings in cost and weight of the coil design. In this work, the magnetic field distribution inside tapes with different architectures based on existing MgB2 tapes has been obtained. The magnetic field in the filaments is modeled focusing on the influence of the ferromagnetic matrix in the field distribution. The study is extended to round pancake coils based on the prototype coils aimed for its application in wind turbines in the SUPRAPOWER project.

Motional Stark Effect measurements of the local magnetic field in high temperature fusion plasmas

The utilization of the Motional Stark Effect (MSE) experienced by the neutral hydrogen or deuterium injected into magnetically confined high temperature plasmas is a well established technique to infer the internal magnetic field distribution of fusion experiments. In their rest frame, the neutral atoms experience a Lorentz electric field, EL = v × B, which results in a characteristic line splitting and polarized line emission. The different properties of the Stark multiplet allow inferring, both the magnetic field strength and the orientation of the magnetic field vector. Besides recording the full MSE spectrum, several types of polarimeters have been developed to measure the polarization direction of the Stark line emission. To test physics models of the magnetic field distribution and dynamics, the accuracy requirements are quite demanding. In view of these requirements, the capabilities and issues of the different techniques are discussed, including the influence of the Zeeman Effect and the sensitivity to radial electric fields. A newly developed Imaging MSE system, which has been tested on the ASDEX Upgrade tokamak, is presented. The sensitivity allows to resolve sawtooth oscillations.A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics