Low Field Range Research Articles

Suppression of magnetic vortex losses in submicron NbN coplanar waveguide resonators

We present a method for improving the performance of microwave coplanar resonators in magnetic fields, by using narrow superconducting strips of width close to the London penetration depth. In a range of low fields, the narrow strips inhibit the presence of magnetic vortices, thus preventing the generation of losses caused by their motion, leading to enhanced resistance to magnetic fields. Our method provides a more straightforward solution compared to previously proposed techniques designed to restrict vortex motion, holding potential for the development of improved devices based on microwave resonators.

Domain Dynamics and Resistive Switching in Ferroelectric Al1–xScxN Thin Film Capacitors

AbstractIn this paper, using a combination of pulse testing measurements and piezoresponse force microscopy (PFM), an investigation of the polarization reversal behavior and the accompanying resistive switching in the Al0.72Sc0.28N thin film capacitors is reported. The obtained results reveal a transition from the nucleation‐limited switching (NLS) in the low field range toward the more uniform switching described by the Kolmogorov–Avrami–Ishibashi (KAI) model in the high field range. It is found that the Al0.72Sc0.28N capacitors exhibit an unusually steep change in the switching time– it decreases by five orders of magnitude with a moderate increase of the applied field. This feature is caused by a significantly higher activation field value (≈126 MV cm−1) in comparison with the conventional perovskite ferroelectrics. PFM visualization of the field‐induced domain dynamics has allowed the evaluation of the nucleation rate and domain wall velocity. Furthermore, capacitors in the polydomain state generated by partial switching of polarization exhibit a significant (up to two orders of magnitude) increase in the steady‐state conductance. This effect is likely caused by the injection of strongly inclined conducting 180° domain walls. Resistance tunability offers additional functionalities to the Al1‐xScxN devices where conductive domain walls are used as active elements.

Model-Based Theoretical Prediction of the Electric Field Dependence of the Diffusion Coefficients of Various Semiconductor Wires

This paper investigates how the diffusion coefficients of various semiconductor wires - namely Si, Ge, and 4H-SiC - are modulated by an external electric field assuming steady-state transport. This theoretical investigation consists of two steps. In the first step, we derive a model-based theoretical expression of the diffusion coefficient based on the continuity equation. Since this consideration is too simplified, in the second step, we perform Monte Carlo simulations to investigate how the electric field alters the electron occupation fraction of energy band valleys; for this, quantum mechanical scattering events during transport are calculated. Using these calculations, the electric field dependence of the diffusion coefficients of Ge and 4H-SiC wires with various cross-sectional areas is investigated because the conduction process of such materials is strongly ruled by the multi-valley transport of electrons. The obtained results reveal that the diffusion coefficient of Ge wires is constant when the electric field rises at 200 K and 400 K; but it rebounds under very high electric fields above 400 K due to the increase in the intrinsic carrier concentration. On the other hand, it is shown that the diffusion coefficient of 4H-SiC wires increases as the electric field rises in a low electric field range regardless of temperature, but it drops under high electric fields. Thus, it is considered that the theoretical models assumed for various semiconductor wires are useful in estimating the steady-state transport characteristics of scaled devices in a practical range of temperatures around room temperature.

Instability of Ion Cyclotron Waves (ICWS) at the Expense of Lower Hybrid Drift Waves (LHDWS) Turbulence Energy

Instability of ion cyclotron waves(ICWs) is investigated in presence of lower hybrid drift waves(LHDWs) turbulence. Plasma inhomogeneity in the Earth’s magnetopause region supports a range of low frequency drift wave turbulent fields due to gradients in density in different regions of the media. One of these drift phenomena is identified as lower hybrid drift waves (LHDWs) which satisfies resonant conditions ω − k · v = 0. We have considered a nonlinear wave-particle interaction model where the resonant wave that accelerates the particle in magnetopause may transfer its energy to ion cyclotron waves through a modulated field. In spite of the frequency gaps between the two waves, energy can be transferred nonlinearly to generate unstable ion cyclotron waves which always do not satisfy the resonant condition Ω−K · v ≠ 0 and the nonlinear scattering condition Ω − ω − (K − k) · v ̸= 0. Here, ω and Ω are frequencies of the resonant and the nonresonant waves respectively and k and K are the corresponding wave numbers. We have obtained a nonlinear dispersion relation for ion cyclotron waves(ICWs) in presence of lower hybrid drift waves(LHDWs)turbulence. The growth rate of the ion cyclotron waves using space observational data in the magnetopause region has been estimated.

Temperature and electric field dependent phase structural evolution in 0.5Bi(Mg1/2Ti1/2)O3-0.2Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 ceramic

A systematic investigation of the temperature dependent strain property in 0.5Bi(Mg1/2Ti1/2)O3-0.2 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (0.5BMT-0.2PMN-0.3 PT) ceramic was performed in this work. Generally, the temperature dependent strain evolution was found to be seriously related to the electric field (E), i.e., with increasing temperature, a monotonic increase in the strain was observed in the low field range (E ≤ 2 kV/mm), a first increase and then decrease in the strain was observed in the middle field range (2<E ≤ 4 kV/mm), and temperature insensitive strain was obtained in the high field range (E > 4 kV/mm). The temperature and electric field dependent evolution of the phase structure was investigated by in-situ synchrotron X-ray diffraction. Overall, the different strain behaviors observed at different temperatures and electric fields are believed to be related to the stability of different phase structures at varying temperatures and electric fields.

Analysis of energy conversion capability among various magnetostrictive materials for energy harvesting

This work addresses vibrational energy harvesting using magnetostrictive materials. In this field, materials with exceptional magneto-mechanical coupling properties (e.g. Galfenol, Terfenol-D) have attracted significant attention. Only a few magnetostrictive materials have been tested in devices, however, leaving the actual influence of these materials’ properties on the energy harvesting device open to question. This work compares an extensive range of ferromagnetic materials through analysis of their magnetic behavior under static stress. To enable fair comparison of the materials, a model was developed to interpolate their magnetic anhysteretic curves under fixed stress of σ = ±50 MPa. The energy harvesting process was then simulated using a theoretical Ericsson thermodynamic cycle, where the area represents the energy density. This approach estimates the ultimate energy density of the materials using a fair approach, without placing conditions on the applied magnetic field. The correlation between ultimate energy density and the magnetoelastic coefficient show that highly magnetostrictive materials achieve higher ultimate energy densities, as expected. In the low field range, it is however concluded that all materials exhibit energy densities of the same order of magnitude. Secondly, the magnetoelastic coefficient versus excitation field characteristics revealed an optimal bias magnetic field for each material. Finally, for realistic implementation, the paper considers a pre-stress in combination with a bias magnetic field and the small dynamic variations that result from currents induced in surrounding coils. A model was developed and revealed an optimum output energy density that was independent of the geometry and the coil. An energy harvesting figure of merit was then defined to enable a final comparison of the materials, encompassing both material characteristics and realistic applications. Under these working conditions and with all costs considered, some low-magnetostriction materials appeared able to compete with giant magnetostriction materials.

Electric field sensing and polarisation measurement using advanced multi-pass interrogation type fiber-optic beam deflection probe

We present an experimental demonstration of precise determination of electric field and polarisation properties of the sample using fiber-optic beam deflection transducer. We use a cantilever-deflection fiber probe formed by coating an optimized composition of cobalt-modified bismuth ferrite nanocomposite over a selected length at the tip of deflecting fiber to sense the surrounding electric field. In a chronological development through designing and investigating a series of experiments, we establish a configuration exhibiting a high-performance electric field sensing scheme. First, we devise a Sagnac loop assisted beam deflection assembly that doubly modulates light with the varying electric field. The observed results of the sensor are theoretically modeled using the associated parameters, and the polarisation properties of the probe sample are fairly determined. To deploy a multi-pass signal circulation through the probe for enhanced sensitivity, we then conceive of a promising ring resonator design and tested. Next, incorporating the beam-deflection probe in the resonator circuit, we test and optimize the performance of the transducer. The signal modulation in the resonator cavity caused by electric field-induced deflection of fiber is then accurately analysed to understand its response and interpret the variety of experimental results. We demonstrate a high-performance electric field sensor that operates precisely in the 0–0.75 kV/cm range. The polarisation properties of the probe sample for the low field range of 0–0.8 kV/cm are also determined. The method is all-optical and safe for deployment in any hazardous environment. Also, it enjoys all the advantages of optical fiber-based instrumentation and can be suitably adapted to explore higher-order design for applications based on electric field sensing.

Enhancement of spin–flop-induced magnetic hysteresis in van der Waals magnet (Fe1−xCox)5GeTe2

We have systematically studied magnetotransport properties in van der Waals (vdW) magnetic materials, (Fe1−xCox)5GeTe2, where the magnetic phase changes from the ferromagnetic with the perpendicular magnetic anisotropy (PMA; x = 0 , 0.05) or with the in-plane magnetic anisotropy (IMA; x = 0.19) to the antiferromagnetic (x = 0.46) with the PMA. We have demonstrated that such magnetic properties seen in bulk still remain even in thin film devices. An anomalous Hall resistance with magnetic hysteresis was clearly observed in the low Co substitution ( x = 0 , 0.05). The anomalous Hall effect was still observable for x = 0.19, but the magnetic hysteresis vanishes because of the IMA. In the antiferromagnetic region, there was no anomalous Hall effect in the low magnetic field range, but a clear hysteresis was observed at 2.5 T where the spin–flop transition takes place. This hysteresis can be seen only below 30 K and monotonically decreases with increasing temperature. We argue that the defects at a specific site in this system and also the resistance upturn below 30 K could be related to the hysteric behavior at the spin–flop transition. Our findings provide a recipe for the use of (Fe1−xCox)5GeTe2 with different Co substitutions to construct vdW magnetic devices.

Transport property of topological crystalline insulator SnTe (100) and ferrimagnetic insulator heterostructures

• High quality SnTe/RE3Fe5O12 (RE=Eu, Y) epitaxial heterostructures were prepared. • Domain disorder is induced by Fe atom diffusion in SnTe through magnetic interface. • Two different magnetoelectrical transport in two heterostructures are observed. • Linear magnetoresistance and nonlinear Hall appear in SnTe/Eu 3 Fe 5 O 12 . Topological crystalline insulator (TCI) SnTe is a potential material for quantum electronic devices because of its attractive inherent sensitivity of band topology and highly mobile characteristic of Dirac fermions. The proximity effect at the interface of SnTe film can affect the topological surface transport and may result in novel quantum magneto-electric effects. Here, we study the magnetoelectrical transport properties of SnTe thin films grown on ferrimagnetic insulators Eu 3 Fe 5 O 12 (110) (EuIG (110)) and Y 3 Fe 5 O 12 (111) (YIG (111)) single-crystal underlayers by molecular beam epitaxy. Linear magnetic resistance (LMR) is observed in SnTe/EuIG heterostructures in the low field range, which is different from the weak antilocalization (WAL) characteristic of SnTe/YIG heterostructures. Especially, the double carrier characteristic with the coexistence of holes and electrons in SnTe/EuIG heterostructure is quite different from the holes as main carriers in SnTe/YIG, although the SnTe layer remains the same crystal plane (100) in the two heterostructures. The LMR in SnTe/EuIG is attributed to the topological surface Dirac electrons and disordered domain distribution in the SnTe layer which is in sharp contrast to the WAL of SnTe/YIG with ordered domain distribution in the SnTe layer. The present studies of transport properties not only provide a fundamental understanding of the transport mechanism of TCI and magnetite insulator heterostructure but also display the promising application probability for tunable topological electronic devices.

Investigation of radial heat conduction with 1D self-consistent model in helicon plasmas

A 1D radially self-consistent model in helicon plasmas has been established to investigate the influence of radial heat conduction on plasma transport and wave propagation. Two kinds of 1D radial fluid models, with and without considering heat conduction, have been developed to couple the 1D plasma–wave interaction model, and self-consistent solutions have been obtained. It is concluded that in the low magnetic field range the radial heat conduction plays a moderate role in the transport of helicon plasmas and the importance depends on the application of the helicon source. It influences the local energy balance leading to enhancement of the electron temperature in the bulk region and a decrease in plasma density. The power deposition in the plasma is mainly balanced by collisional processes and axial diffusion, whereas it is compensated by heat conduction in the bulk region and consumed near the boundary. The role of radial heat conduction in the large magnetic field regime becomes negligible and the two fluid models show consistency. The local power balance, especially near the wall, is improved when conductive heat is taken into account.

Accuracy Assessment of Simplified Computation of Active and Passive Magnetic Shielding for Optically Pumped Magnetometers

A low residual environmental magnetic field is required for the proper operation of most optically pumped magnetometers (OPMs). This is achieved using a combination of passive and active magnetic shielding. Passive magnetic shielding often uses multiple layers of highly permeable materials. A realistic two-layer magnetically shielded room (MSR) for biomagnetic measurements is numerically studied using the finite element method. A measured B-H characteristic of Mumetal is used, which is linearly extrapolated from the Rayleigh region (RR) into the low magnetic field range. This extension of the magnetization curve yields no significant differences compared to using a constant permeability value for the low magnetic field range. Furthermore, we model the MSR with only one shield and apply a simple analytical method of images (MOI). The MOI yields on average a 100-fold reduction in computation time. The relative difference of the magnetic flux density computed with MOI and finite element method (FEM) is smaller than < 1% at the center of a spherical region of interest (ROI) with a radius of 0.3 m desired from the point of magnetoencephalography (MEG) using OPMs. The achieved accuracy of the MOI makes it suitable for the optimization of active shielding coils.

Systematic investigation of the effect of layer thickness on the linear sensing characteristics of asymmetric structured CoFe/Rh/CoFe/Cu/CoFe fully epitaxial CIP-GMR based magnetic sensors

Giant magnetoresistance (GMR) devices known for their widespread application as magnetic field sensors face challenges owing to their nonlinear resistance response with the magnetic field. Here, we have developed CoFe(3 nm)/Rh(tRh nm)/CoFe(tmidCoFe nm)/bcc Cu(1.6 nm)/CoFe(ttopCoFe nm)/MgO(2 nm) based current in plane (CIP)-GMR devices and demonstrated linear MR curves with tunable characteristics. The MR ratio and saturating magnetic field were tunable between 3.9% and 23.5%, and 0.013 T and 1.5 T. The numerical simulation modeling confirmed biquadratic coupling between the bottom and middle CoFe layers through Rh and antiferromagnetic coupling between the middle and top CoFe layers through a Cu spacer, providing the linear MR. The fine-tuning of thicknesses of the middle and top CoFe layers provides supplementary routes for optimizing the sensitivity and operation field range of the CIP-GMR devices to specific magnetic sensor applications in the low and medium magnetic field range. The above results demonstrate that CIP-GMR devices with the asymmetric structure demonstrated in this study are promising for the next generation linear magnetic sensors.

Spin-Wave Dynamics in an Artificial Kagome Spin IceSupported by the State Grid Corporation of China via the Science and Technology Project: Research on Electromagnetic Measurement Technology Based on EIT and TMR (Grant No. JL71-18-007).

Artificial spin ice (ASI) structures have significant technological potential as reconfigurable metamaterials and magnetic storage media. We investigate the field/frequency-dependent magnetic dynamics of a kagome ASI made of 25-nm-thick permalloy nanomagnet elements, combining magnetoresistance (MR) and microscale ferromagnetic resonance (FMR) techniques. Our FMR spectra show a broadband absorption spectrum from 0.2 GHz to 3 GHz at H below 0.3 kOe, where the magnetic configuration of the kagome ASI is in the multidomain state, because the external magnetic field is below the obtained coercive field H c ∼ 0.3 kOe, based on both the low-field range MR loops and simulations, suggesting that the low-field magnetization dynamics of kagome ASI is dominated by a multimode resonance regime. However, the FMR spectra exhibit five distinctive resonance modes at the high-field quasi-uniform magnetization state. Furthermore, our micromagnetic simulations provide additional spatial resolution of these resonance modes, identifying the presence of two high-frequency primary modes, localized in the horizontal and vertical bars of the ASI, respectively; three other low-frequency modes are mutually exclusive and separately pinned at the corners of the kagome ASI by an edge-induced dipolar field. Our results suggest that an ASI structural design can be adopted as an efficient approach for the development of low-power filters and magnonic devices.

Oxidative Effects during Irreversible Electroporation of Melanoma Cells-In Vitro Study.

Irreversible electroporation (IRE) is today used as an alternative to surgery for the excision of cancer lesions. This study aimed to investigate the oxidative and cytotoxic effects the cells undergo during irreversible electroporation using IRE protocols. To do so, we used IRE-inducing pulsed electric fields (PEFs) (eight pulses of 0.1 ms duration and 2–4 kV/cm intensity) and compared their effects to those of PEFs of intensities below the electroporation threshold (eight pulses, 0.1 ms, 0.2–0.4 kV/cm) and the PEFs involving elongated pulses (eight pulses, 10 ms, 0.2–0.4 kV/cm). Next, to follow the morphology of the melanoma cell membranes after treatment with the PEFs, we analyzed the permeability and integrity of their membranes and analyzed the radical oxygen species (ROS) bursts and the membrane lipids’ oxidation. Our data showed that IRE-induced high cytotoxic effect is associated both with irreversible cell membrane disruption and ROS-associated oxidation, which is occurrent also in the low electric field range. It was shown that the viability of melanoma cells characterized by similar ROS content and lipid membrane oxidation after PEF treatment depends on the integrity of the membrane system. Namely, when the effects of the PEF on the membrane are reversible, aside from the high level of ROS and membrane oxidation, the cell does not undergo cell death.

Improved Dynamic Magnetostriction measurement method based on M-EMAT for the characterization of residual strain

The Dynamic Magnetostriction (DM) measurement method as a nondestructive testing method of ferromagnetic materials, measures the DM curve using electromagnetic acoustic transducer (EMAT) to characterize material and predict the mechanical properties. Lorentz forces and magnetostriction forces contribute mainly to the ultrasonic generation. Only the range of low field, in which the magnetostriction force mechanism is predominant can be used to measure the DM curve, but the boundaries of this range are uncertain. The improved DM measurement method based on shear wave Magnetostriction EMAT (M-EMAT) is proposed and the theory of generation of shear waves is derived. For the M-EMAT, only magnetostriction force mechanism contributed to the generation of shear waves. A theoretical model for the optimization of the transducer is developed, the model is in good agreement with the experimental results. The microstructure changes caused by residual strain will affect the magnetostriction coefficient and the DM curve. Therefore, the DM curves of low carbon steel specimens with different levels of residual strains are measured by the optimized transducer to characterize the residual strain. The normalized results demonstrate that the slope of the DM curve obviously changes with the residual strain. This leads to the conclusion that the DM measurement method can be used to characterize the residual strain of the low carbon steels.

Deposition-temperature dependence of structure, ferroelectric property and conduction mechanism of BCZT epitaxial films

Ba0·85Ca0·15Zr0·1Ti0·9O3 (BCZT) epitaxial films were successfully deposited on (001) Nb-doped SrTiO3 substrate, and the effects of deposition temperatures on the structure, ferroelectric property, and conduction mechanism were studied. The results of XRD and AFM verified the well epitaxial structure with smooth surfaces of the deposited BCZT epitaxial films. BCZT epitaxial films deposited at 650 °C exhibited the best ferroelectric property (2Pr = 22.91 μC/cm2, 2EC = 1702.11 kV/cm) and relatively low leakage current density (7.91 × 103 A/cm2). The conduction mechanism of BCZT films corresponds to the space-charge-limited current (SCLC) mechanism and the Fowler-Nordheim (F–N) tunneling mechanism in the low and high electric field range, respectively.

Dynamical scaling analysis of symmetry breaking for the antiferromagnetic triangular Heisenberg model in a uniform magnetic field

Phase transitions for the two-dimensional antiferromagnetic triangular Heisenberg model in a uniform field are primarily analyzed using dynamical scaling analysis. The system has ${Z}_{3}$ and $O(2)$ symmetries. The transition temperatures and types of transition are investigated using the relaxation of order parameters and the asymptotic behaviors of relaxation time around transition temperatures. In the low-field range, the order parameters for the ${Z}_{3}$ and $O(2)$ symmetries exhibit the behavior typical of a second-order transition and Kosterlitz-Thouless (KT) transition, respectively, with distinct transition temperatures. In the high-field range, an order parameter for the ${Z}_{3}$ symmetry exhibits the behavior of a second-order transition, while another order parameter related to the components perpendicular to the field demonstrates that the relaxation time diverges with an asymptotic form, indicating a second-order transition rather than a KT transition. These transition temperatures are estimated to be close. Critical exponents for these two order parameters are estimated separately by calculating the relaxation of fluctuations in the high-field range. It was confirmed that the critical exponents for both of these order parameters change continuously as a function of field, and they are distinct from each other.

Quantum oscillations in nanowires of topological insulator Bi0.83Sb0.17

Three dimensional topological insulators (TIs) are novel materials with a conducting surface covering an insulating bulk interior. We examine the topological properties of nanowires of TI Bi0.83Sb0.17 and observed that they display oscillations of the magnetoresistance (MR) that can be interpreted as topological surface electronic transport. In this work, we study the nanowires at various magnetic field orientations, at low temperatures (1.5 K ≤ T < 5 K), and for field strengths up to 14 T. In the 4 T < B < 10 T range we observe B-periodic, Aharonov–Bohm (AB) oscillations of longitudinal MR with two periods, namely, one flux quantum Φ0 and half of flux quantum Φ0/2 (ΔB1 = Φ0/S, ΔB2 = Φ0/2S, where S is the cross-sectional area of the nanowire). The periods depend on the angle α between the magnetic field and the wire axis according to a cosine law that indicates that the phenomenon is governed by the axial flux enclosed by the nanowire. In additional to the high magnetic field oscillations, in the low magnetic field range, B < 4 T, we observe a conductance maximum for zero magnetic field and the first magnetoresistance maximum for Φ = Φ0/2.

Control of spin dynamics in artificial honeycomb spin-ice-based nanodisks

We report the experimental and theoretical characterization of the angular-dependent spin dynamics in arrays of ferromagnetic nanodisks arranged on a honeycomb lattice. The magnetic field and microwave frequency dependence, measured by broadband ferromagnetic resonance, reveal a rich spectrum of modes that is strongly affected by the microstate of the network. Based on symmetry arguments with respect to the external field, we show that certain parts of the ferromagnetic network contribute to the detected signal. A comparison of the experimental data with micromagnetic simulations reveals that different subsections of the lattice predominantly contribute to the high-frequency response of the array. This is confirmed by optical characterizations using microfocused Brillouin light scattering. Furthermore, we find indications that nucleation and annihilation of vortex-like magnetization configurations in the low-field range affect the dynamics, which is different from clusters of ferromagnetic nanoellipses. Our work opens up new perspectives for designing magnonic devices that combine geometric frustration in gyrotropic vortex crystals at low frequencies with magnonic crystals at high frequencies.

Investigation of Rayleigh region in strip like amorphous FINEMET samples after different heat treatments

In this paper we have investigated the influence of thermal treatment on magnetization processes in the low magnetic field range (Rayleigh region). For this study, rapidly quenched FINEMET ribbons in the as-prepared amorphous state were used. It has been observed that the various annealing temperature lead to the different behavior of a studied material as a consequence of a relaxation of the quenched-in internal stresses in the investigated samples. However, neither of the effects of the atomic diffusion has been observed after low temperature heat-treatments. Moreover, it was detected that the partial elimination of internal stresses has a reduction effect on total magnetic anisotropy.