High External Magnetic Field Research Articles

Reflective, polarizing, and magnetically soft amorphous neutron optics with 11B-enriched B4C.

The utilization of polarized neutrons is of great importance in scientific disciplines spanning materials science, physics, biology, and chemistry. However, state-of-the-art multilayer polarizing neutron optics have limitations, particularly low specular reflectivity and polarization at higher scattering vectors/angles, and the requirement of high external magnetic fields to saturate the polarizer magnetization. Here, we show that, by incorporating 11B4C into Fe/Si multilayers, amorphization and smooth interfaces can be achieved, yielding higher neutron reflectivity, less diffuse scattering, and higher polarization. Magnetic coercivity is eliminated, and magnetic saturation can be reached at low external fields (>2 militesla). This approach offers prospects for substantial improvement in polarizing neutron optics with nonintrusive positioning of the polarizer, enhanced flux, increased data accuracy, and further polarizing/analyzing methods at neutron scattering facilities.

Quantum correlations and coherence in a mixed spin- (12,1) Heisenberg dimer under intrinsic decoherence

This research delves into the dynamical behavior of quantum correlations and coherence within a mixed Heisenberg dimer system under the intrinsic decoherence. Our approach involves the application of logarithmic negativity, local quantum uncertainty, and the ℓ 1 norm-based coherence as quantifiers for entanglement, skew information correlations, and quantum coherence in this qubit-qutrit model. Our primary objective is to explore the impact of various factors on the dynamics of quantum correlations and quantum coherence. These factors encompass the initial density matrix and its mixing parameter, the intrinsic decoherence rate (γ), the external magnetic field, as well as intrinsic system parameters, notably the XXZ and uniaxial single-ion anisotropies. Our results demonstrate that the introduction of intrinsic decoherence (ID) significantly erodes quantum resources. Particularly, for high values of the ID rate (γ), excessive damping occurs, leading to the absence of oscillations or a rapid decay of quantum resources, ultimately stabilizing in steady states. Furthermore, the presence of an external homogeneous magnetic field further diminishes quantum resources within the system. However, despite the degradation induced by the combined influence of intrinsic decoherence and high external magnetic field intensities, the judicious selection of the initial density matrix and precise adjustment of the uniaxial single-ion anisotropy enable the preservation of quantum resources within the mixed spin-(1/2, 1) Heisenberg dimer.

Nanostructure Effect on Magnetization Processes in FePt Polytwin Crystals.

In FePt polytwin crystals with large magnetocrystalline anisotropy, the boundaries may play a crucial role in the magnetization processes occurring under an external magnetic field. In this study, we employed phase-field modeling and computer simulations to systematically investigate the effect of three types of polytwin boundaries-namely, symmetric (Type I), asymmetric (Type II), and mixed (Type III) boundaries-on magnetization processes as well as coercive fields under an external magnetic field along various directions. Because of the large anisotropy of FePt, the domain wall motion mechanism is usually dominant in the domain switching processes, while the magnetization rotation mechanism only becomes important at the late magnetization stage under a high external magnetic field. Among these three types of polytwin boundaries, the low coercivity is mainly due to the domain wall motion process, which starts from the intersection point at the polytwin boundary. The coercive field for the mixed polytwin boundary (Type III) is always in between the values of Type I and II.

Experimental evidence of random shock-wave intermittency.

We report the experimental observation of intermittency in a regime dominated by random shock waves on the surface of a fluid. We achieved such a nondispersive surface-wave field using a magnetic fluid subjected to a high external magnetic field. We found that the small-scale intermittency of the wave-amplitude fluctuations is due to shock waves, leading to much more intense intermittency than previously reported in three-dimensional hydrodynamics turbulence or in wave turbulence. The statistical properties of intermittency are found to be in good agreement with the predictions of a Burgers-like intermittency model. Such experimental evidence of random shock-wave intermittency could lead to applications in various fields.

Magnetoresistance in Pd–Co/Cu/Pd–Co trilayer under hydrogen–nitrogen gas mixture

The magnetoresistance of three Pd–Co(1)/Cu/Pd–Co(3) trilayers with different Pd–Co(3) thicknesses were evaluated in a H2–N2 gas mixture. The resistance of Pd–Co/Cu/Pd–Co increased with increasing hydrogen concentration in the gas phase, which is similar to the behavior observed in the Pd metal. The peak structure was shown in the magnetoresistance under a nitrogen atmosphere and was associated with magnetic scattering at the interface between the Pd–Co and Cu layers. In the H2–N2 gas mixture, the peak position and width in the resistance profiles were independent of the hydrogen concentration for all the prepared trilayers, and the peak intensity decreased with increasing hydrogen concentration for the trilayer containing a 4.2 nm thick Pd–Co(3) layer. The decrease in intensity was due to the reduction in magnetization in the Pd–Co layer after hydrogen absorption. The change in the resistance ratio by hydrogen absorption in the trilayer was larger under a high external magnetic field of 170 mT than under a low magnetic field of 10 mT. These results confirmed that the multilayered structure of the Pd–Co/Cu enhances the resistance response to hydrogen under a high magnetic field.

Variable bandwidth, high efficiency microwave resonator for control of spin-qubits in nitrogen-vacancy centers.

Nitrogen-Vacancy (NV) centers in diamond are attractive tools for sensing and quantum information. Realization of this potential requires effective tools for controlling the spin degree of freedom by microwave (mw) magnetic fields. In this work, we present a planar microwave resonator optimized for microwave-optical double resonance experiments on single NV centers in diamond. It consists of a piece of wide microstrip line, which is symmetrically connected to two 50Ω microstrip feed lines. In the center of the resonator, an Ω-shaped loop focuses the current and the mw magnetic field. It generates a relatively homogeneous magnetic field over a volume of 0.07 × 0.1mm3. It can be operated at 2.9GHz in both transmission and reflection modes with bandwidths of 1000 and 400MHz, respectively. The high power-to-magnetic field conversion efficiency allows us to produce π-pulses with a duration of 50ns with only about 200 and 50 mW microwave power in transmission and reflection, respectively. The transmission mode also offers capability for efficient radio frequency excitation. The resonance frequency can be tuned between 1.3 and 6GHz by adjusting the length of the resonator. This will be useful for experiments on NV-centers at higher external magnetic fields and on different types of optically active spin centers.

Transition from wave turbulence to acousticlike shock-wave regime

An experiment is performed to examine the previously unobserved transition from a dispersive wave-turbulence regime to a nondispersive shock-wave regime on the surface of a fluid. Using a magnetic liquid subjected to a high enough external magnetic field, a set of random shock waves is indeed observed on the free surface. Their spectrum is then found to be well modeled by a spectrum of singularities (Kuznetsov-like spectrum), and their statistics are close to the predictions from the one-dimensional random-forced Burgers' equation.

Universal rotation gauge via quantum anomalous Hall effect

Integer quantum Hall effect allows to gauge the resistance standard up to more than one part in a billion. Combining it with the speed of light, one obtains the fine-structure constant α ≈ 1/137, a dimensionless reference number that can be extracted from a physical experiment. Most exact notion of this value and especially its possible variation on the cosmological time scales is of enormous relevance for fundamental science. In an optical experiment, the fine-structure constant can be directly obtained as purely geometrical angle by measuring the quantized rotation of light polarization in two-dimensional quantum wells. In realistic conditions, high external magnetic fields have to be applied, which strongly affects possible attainable accuracy. An elegant solution of this problem is provided by quantum anomalous Hall effect where a universal quantized value can be obtained in zero magnetic field. Here, we measure the fine-structure constant in a direct optical experiment that requires no material adjustments or technical calibrations. By investigating the Faraday rotation at the interference maxima of the dielectric substrate, the angle close to one α is obtained at liquid helium temperatures without using a dilution refrigerator. Such calibration and parameter-free experiment provides a system-of-unit-independent access to universal quantum of rotation.

A ferromagnetic topological half-metal candidate: Carbon-doped Bi2Se3

The high quality CxBi2Se3-x single crystals have been prepared by melt-grown reaction. The transport characteristicsmeasurement showed that the doping leads to the presence of ferromagnetism and the high external magnetic field could induce the metal-insulation transition. The metal-insulation transition temperature (Tm) is 169 K and 253 K for 6 T and 9 T, respectively. Analyze the curves of ρxy-B, we used the two-band model to fit MR and Hall coefficient of samples. The results indicated that electron-hole compensation may not be the only reason for the existence of unsaturated magnetoresistance in the material. To further, first principles are used to calculate the band structure of CxBi2Se3-x single crystals, and the feature of the topological half-metals has been suggested. According to the above results, we infer that CxBi2Se3-x single crystals may be candidate materials for topological half-metals.

Electric control of valley polarization in monolayer WSe2 using a van der Waals magnet.

Electrical manipulation of the valley degree of freedom in transition metal dichalcogenides is central to developing valleytronics. Towards this end, ferromagnetic contacts, such as Ga(Mn)As and permalloy, have been exploited to inject spin-polarized carriers into transition metal dichalcogenides to realize valley-dependent polarization. However, these materials require either a high external magnetic field or complicated epitaxial growth steps, limiting their practical applications. Here we report van der Waals heterostructures based on a monolayer WSe2 and an Fe3GeTe2/hexagonal boron nitride ferromagnetic tunnelling contact that under a bias voltage can effectively inject spin-polarized holes into WSe2, leading to a population imbalance between ±K valleys, as confirmed by density functional theory calculations and helicity-dependent electroluminescence measurements. Under an external magnetic field, we observe that the helicity of electroluminescence flips its sign and exhibits a hysteresis loop in agreement with the magnetic hysteresis loop obtained from reflective magnetic circular dichroism characterizations on Fe3GeTe2. Our results could address key challenges of valleytronics and prove promising for van der Waals magnets for magneto-optoelectronics applications.

Martensitic Transformation and Magnetic-Field-Induced Strain in High-Entropy Magnetic Memory Alloy Ni20Mn20Ga20Gd20Co20 by Hot-Magnetic Drawing.

The wires with chemical composition Ni20Mn20Ga20Gd20Co20 were prepared by hot-magnetic drawing and the microstructure evolution characteristics, martensitic transformation and MFIS process were investigated in detail, respectively. The results showed that a multiphase structure with γ phase and martensite was observed in samples when the magnetic field was 0 T to 0.2 T during the hot-magnetic drawing process. With the magnetic field increased to 0.5 T, due to the atomic diffusion by severe thermoplastic deformation and high external magnetic field, a single-phase structure with L10 type twin martensite was found in the sample. Moreover, an obvious increasing trend in martensitic transformation temperature in the sample was found by the enhancement of the magnetic field during the hot-magnetic drawing process. The highest phase transition temperature rose to about 600 °C when the magnetic field reached 0.5 T. Finally, the property of SME and MFIS in the sample can be enhanced by the magnetic field increasing during the hot-magnetic drawing process, excellent performance of SME was obtained at low total strain, and MFIS was achieved at 4.47% at a magnetic field of 8007 Oe in the sample in the 0.5 T magnetic field during the hot-magnetic drawing process.

Flexomagnetic effects on inhomogeneously strained multiferroics composites

Herein, the origin of flexomagnetic effect in Pb[(Zr0.52Ti0.48)0.60(Fe0.67W0.33)0.40]O3]0.80-[CoFe2O4]0.20 (PZTFW–CFO) multiferroic composite is demonstrated. An external inhomogeneous strain on thick composite films significantly changes the crystal lattice constants and phonon wave numbers related to single-phase PZTFW and CFO ceramics. Surface morphology indicates that inhomogeneous strain modified the magnetic dipole moments that partly regain their original position after removing external inhomogeneous strain. The magnitude of magnetic susceptibility increased under inhomogeneous strain for a small probe of the magnetic field. The magnetic anisotropic energy (MAE) supports that under-applied inhomogeneous strain reduces surface spin disorders and is responsible for the enhancement of zero field cooled (ZFC) and field cooled (FC) magnetization. Under a high external magnetic field (>100 Oe), it would be hard to detect the weak flexomagnetic effects. This work provides a framework for the effect of macroscopic inhomogeneous strain gradient on magnetic moments in multiferroics composites suggesting its suitability for the sensors and actuators applications.

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.

In vitro proton magnetic resonance spectroscopy at 14T for benign and malignant ovary: Part I, signal processing by the nonparametric fast Pad\xe9 transform

The present study deals with two different kinds of time signals, encoded by in vitro proton magnetic resonance spectroscopy (MRS) with a high external static magnetic field, 14.1T (Bruker 600 MHz spectrometer). These time signals originate from the specific biofluid samples taken from two patients, one with benign and the other with malignant ovarian cysts. The latter two diagnoses have been made by histopathologic analyses of the samples. Histopathology is the diagnostic gold standard in medicine. The obtained results from signal processing by the nonparametric derivative fast Padé transform (dFPT) show that a number of resonances assignable to known metabolites are considerably more intense in the malignant than in the benign specimens. Such conclusions from the dFPT include the recognized cancer biomarkers, lactic acid and choline-containing compounds. For example, the peak height ratio for the malignant-to-benign samples is about 18 for lactate, Lac. This applies equally to doublet Lac(d) and quartet Lac(q) resonating near 1.41 and 4.36 ppm (parts per million), respectively. For the choline-containing conglomerate (3.19-3.23 ppm), the dFPT with already low-derivative orders (2nd, 3rd) succeeds in clearly separating the three singlet component resonances, free choline Cho(s), phosphocholine PC(s) and glycerophosphocholine GPC(s). These constituents of total choline, tCho, are of critical diagnostic relevance because the increased levels, particularly of PC(s) and GPC(s), are an indicator of a malignant transformation. It is gratifying that signal processing by the dFPT, as a shape estimator, coheres with the mentioned histopathology findings of the two samples. A very large number of resonances is identifiable and quantifiable by the nonparametric dFPT, including those associated with the diagnostically most important low molecular weight metabolites. This is expediently feasible by the automated sequential visualization and quantification that separate and isolate sharp resonances first and subsequently tackle broad macromolecular lineshape profiles. Such a stepwise workflow is not based on subtracting nor annulling any part of the spectrum, in sharp contrast to controversial customary practice in the MRS literature. Rather, sequential estimation exploits the chief derivative feature, which is a faster peak height increase of the thin than of the wide resonances. This is how the dFPT simultaneously improves resolution (linewidth narrowing) and reduces noise (background flattening). Such a twofold achievement makes the dFPT-based proton MRS a high throughput strategy in tumor diagnostics as hundreds of metabolites can be visualized/quantified to offer the opportunity for a possible expansion of the existing list of a handful of cancer biomarkers.

Magnetic properties of chiral EuIr2P2

We present a minimal model that provides a description of the magnetic and thermodynamic properties of \Eu. The model contains two exchange coupling parameters, which are calculated using Density Functional Theory, and a local easy axis magnetic anisotropy term. The classical ground state of the system is a generalization of the well known 120$^\circ$ structure observed in triangular antiferromagnets. Monte Carlo simulations show two phase transitions as a function of the temperature. With increasing temperature, the system transitions from the ground state into a high-entropy collinear antiferromagnet, which in turn at higher temperatures presents a second order transition to a paramagnetic state. A high enough external magnetic field parallel to the anisotropy axis produces a spin-flop transition at low temperatures. The field also reduces the temperature range of stability of the collinear antiferromagnet phase and leads to a single phase transition as a function of the temperature. The reported behavior of the specific heat, the magnetization, and the magnetic susceptibility is in agreement with the available experimental data. Finally, we present the magnetic phase diagrams for magnetic fields parallel and perpendicular to the easy axis.

Integrating micromagnets and hybrid nanowires for topological quantum computing

Majorana zero modes are expected to arise in semiconductor-superconductor hybrid systems, with potential topological quantum computing applications. One limitation of this approach is the need for a relatively high external magnetic field that should also change direction at the nanoscale. This proposal considers devices that incorporate micromagnets to address this challenge. We perform numerical simulations of stray magnetic fields from different micromagnet configurations, which are then used to solve for Majorana wavefunctions. Several devices are proposed, starting with the basic four-magnet design to align magnetic field with the nanowire and scaling up to nanowire T-junctions. The feasibility of the approach is assessed by performing magnetic imaging of prototype patterns.

The Operation of UAV Propulsion Motors in the Presence of High External Magnetic Fields

The operation and maintenance of converter stations (also known as valve halls) in high voltage DC (HVDC) grids is a key element in long-term, reliable and stable operation, especially in inherently adverse offshore environments. However, the nature of the electromagnetic field environment inside HVDC valve halls presents a challenge for the operation of traditional off-shelf inspection robots. In this paper, the impact of the external magnetic field on the operation of an inspection UAV’s propulsion motors is assessed. An experimental method is proposed to simulate the maximum magnetic field interference to off-shelf UAV motors, which can be used to identify their suitability for use in HVDC valve halls inspection robots. The paper’s experimental results compare the performance of direct torque control and field-oriented control algorithms for propulsion motors under the influence of external magnetic flux. Under the influence of a 177 mT external magnetic field, it was found that using direct torque control, the motor rotational velocity steady-state error was up to 55%. With field-oriented control, the steady-state error was 0%, however the peak-to-peak current draw increased by up to 567%.

First-principles study of the anomalous Hall effect based on exact muffin-tin orbitals

Based on the exact muffin-tin orbitals (EMTOs), we developed a first-principles method to calculate the current operators and investigated the anomalous Hall effect in bcc Fe as an example, with which we successfully separated the skew scattering contribution from the side jump and intrinsic contributions by fitting the scaling law with the introduction of sparse impurities. By investigating the temperature dependence of the anomalous Hall effect in bulk Fe, we predicted a fluctuated anomalous Hall angle as a function of temperature when considering only phonons, which, in the future, can be measured in experiments by suppressing magnon excitation, e.g., by applying a high external magnetic field.

Особенности расчета и исследования вольт-эрстедной характеристики анизотропного магниторезистивного датчика

The results of experimental and theoretical studies of the influence of the current value on the characteristics of anisotropic magnetoresistive magnetic field sensors based on FeNiCo alloy with a "barber-polе" structure are presented. A significant difference was found between the volt-oersted characteristics of the forward and reverse strokes with an increase in the intrinsic current caused by the input supply voltage at sufficiently high external magnetic fields. A theoretical calculation of the volt-oersted characteristic was carried out within the framework of the model of one-dimensional heterogeneity of the magnetization distribution, which coincides with the experimental curves of the forward path.

Magnetic detwinning and biquadratic magnetic interaction in EuFe2As2 revealed by Eu153 NMR

In the nematic state of iron-based superconductors, twin formation often obscures the intrinsic, anisotropic, in-plane physical properties.Relatively high in-plane external magnetic fields $H_{\rm ext}$ greater than the typical lab-scale magnetic fields 10--15 T are usually required to completely detwin a sample. However, recently a very small in-plane $H_{\rm ext} \sim$ 0.1 T was found to be sufficient for detwinning the nematic domains in EuFe$_2$As$_2$. To explain this behavior, a microscopic theory based on biquadratic magnetic interactions between the Eu and Fe spins has been proposed. Here, using $^{153}$Eu nuclear magnetic resonance (NMR) measurements below the Eu$^{2+}$ ordering temperature, we show experimental evidence of the detwinning under small in-plane $H_{\rm ext}$. Our NMR study also reveals the evolution of the angles between the Eu and Fe spins during the detwinning process, which provides the first experimental evidence for the existence of biquadratic coupling in the system.