Dc Bias Field Research Articles

Magnetic and dielectric properties of single-crystalline ErFeMnO4

We report on the growth of single-crystal ErFeMnO4 and its magnetization, resistivity, and dielectric dispersion behaviors for varying temperature and electric field. A clear bifurcation between the in-plane and out-of-plane M(T) curves is observed due to a paramagnetic-ferrimagnetic transition with a transition temperature of ∼301 K, which is higher than for other RFe2O4 or substituted compounds. Over a similar temperature range, sudden changes in both the relative permittivity and resistivity were also observed, indicating a strong connection between the magnetization, resistivity and dielectric properties. It can be concluded that the electron transfer between the Fe-site ions plays an important role in these behaviors. Finally, a large relative tunability of 75.9% for relative permittivity εr and a net polarization P of about ∼408.7 μC/m2 were attained for a DC biased electric field E = 25 kV/m at 390 K, which are promising for the application of tunable ferroelectric devices.

Build Charging Database of Linear-Motor Type Flux Pump and Analyze the Influence of DC-Bias Field Using Fixed Step Size Search Algorithm

The linear-motor type flux pump is a wireless DC power source for high-temperature superconducting coils, which is compact in size, efficient in energy use, fast in output control, etc. It consists of three major parts: DC windings, phase windings and iron circuit, which generates a DC-bias AC travelling wave in its airgap. In theory, there are three controllable parameters such as DC-bias field, amplitude of the AC travelling wave, and the field frequency (travelling speed). By changing those parameters, we change the applied fields and its DC output current into superconducting coils. For studying the impact of those parameters on its DC output, this paper uses a fixed step algorithm to collect the current charging data, by automatically controlling the flux pump device, and then establishes an output database. By using this algorithm, we have searched out the maximum pumped current and analyzed the impact of the three parameters. We have also found out that, in order to get maximum current output, the value of the DC-bias field should be close to the amplitude of AC magnetic field.

Unusual dynamic susceptibility arising from soft ferromagnetic domains in MnBi8Te13 and Sb-doped MnBiTe (n = 2, 3)

MnBiTe (MBT) is the first intrinsic magnetic topological insulator and is promising to host emergent phenomena such as quantum anomalous Hall effect. They can be made ferromagnetic by having or with Sb doping. We studied the magnetic dynamics in a few selected ferromagnetic (FM) MBT compounds, including MnBi8Te13 and Sb doped MnBiTe ( using AC susceptibility and magneto-optical imaging. Slow relaxation behavior is observed in all three compounds, suggesting its universality among FM MBT. We attribute the origin of the relaxation behavior to the irreversible domain movements since they only appear below the saturation fields when ferromagnetic domains form. The very soft ferromagnetic domain nature is revealed by the low-field fine-structured domains and high-field sea-urchin-shaped remanent-state domains imaged via our magneto-optical measurements. Finally, we ascribe the rare ‘double-peak’ behavior observed in the AC susceptibility under small DC bias fields to the very soft ferromagnetic domain formations.

Quantum efficiency of photoemission from biased metal surfaces with laser wavelengths from UV to NIR

This paper studies photoelectron emission from metal surfaces with laser wavelengths from 200 to 1200 nm (i.e., ultraviolet to near-infrared), using a recent quantum model based on the exact solution of time-dependent Schrödinger equation. The dominant electron emission mechanism varies from different multiphoton emission processes to dc or optical field emission, depending on the laser intensity, wavelength, and dc bias field. The parametric dependence of the quantum efficiency (QE) is analyzed in detail. It is found that QE can be increased nonlinearly by the non-equilibrium electron heating produced by intense sub-picosecond laser pulses. This increase of QE due to laser heating is the strongest near laser wavelengths where the cathode work function is an integer multiple of the corresponding laser photon energy. The quantum model, with laser heating effects included, reproduces previous experimental results, which further validates our quantum model and the importance of laser heating.

Thermally stimulated depolarization current measurements on degraded lead zirconate titanate films

AbstractCharge transport mechanisms governing DC resistance degradation in ferroelectric films are influenced by defects, particularly oxygen vacancies. This paper demonstrates that oxygen vacancies migrate in lead zirconate titanate (PZT) films under a DC bias field and contribute to resistance degradation. Model PZT thin films were developed in which the concentration and distribution of oxygen vacancies were controlled via (a) changing the dopant type and concentration from 1%–4% Mn (acceptor) to 1%–4% Nb (donor) or (b) annealing undoped PZT films at varying partial pressures of PbO. The presence of associated (immobile) and dissociated (mobile) oxygen vacancies was distinguished by thermally stimulated depolarization current (TSDC) measurements. The impact of mobile oxygen vacancies on local defect chemistry and associated charge transport mechanisms was explored by electron energy loss spectroscopy (EELS). For Mn‐doped PZT films, following resistance degradation, TSDC studies revealed only one depolarization peak with an activation energy of 0.6–0.8 eV; this peak was associated with ionic space charge presumably due to migration of oxygen vacancies. The magnitude of the depolarization current peak increased with increasing degradation times. A similar depolarization current peak attributed to the existence of mobile oxygen vacancies was also observed for undoped and Nb‐doped PZT films; the magnitude of this peak decreased as the Nb or PbO contents in PZT films increased. An additional TSDC peak associated with polaron hopping between Ti3+ and Ti4+ was found in both Nb‐doped PZT films and undoped PZT films annealed under low PbO partial pressure. Degraded Nb‐doped samples exhibited a chemical shift in the TiL2,3 peak to lower energy losses and the appearance of shoulders on the t2g and eg peaks, implying a reduction of Ti cations in regions near the cathode.

Giant circumferential magnetoelectric effect in Pb(Zr,Ti)O3/Mn-Zn-ferrite cylindrical composite

Giant magnetoelectric effect was observed in Pb(Zr,Ti)O3(PZT)/Mn-Zn-ferrite cylindrical composite with both DC bias and AC magnetic fields along circumferential direction. The circumferential magnetoelectric voltage coefficient αME,C-C at low frequency f = 1 kHz and resonance frequency fr = 73.9 kHz reaches 1 Vcm−1 Oe−1 and 381 Vcm−1 Oe−1, respectively, at low optimum bias field H DC= 0.40 Oe, which is the highest values of circumferential magnetoelectric voltage coefficient in all kinds of magnetoelectric structures reported ever. Combining constitutive equations for piezoelectric phase and magnetic phase under circumferential excitation with equation of motion for continuous medium, the frequency dependence of αME,C-C was derived as a function of material parameters and geometrical sizes, which agrees well with the experimental results. The achieved high circumferential magnetoelectric effect originates from low compliance of Mn-Zn-ferrite, improved interface mechanical coupling and self-bound effect due to cylindrical structure, and absence of effect of demagnetization factor with circumferential excitation and bias. The distinct features including giant circumferential ME effect, extremely low bias field and cheap cost of Mn-Zn-ferrite promise the PZT/Mn-Zn-ferrite cylindrical composite as a competitive device for vortex magnetic field detection and transducers.

Influence of the Azimuthal Angle on the Dynamic Forced Response of the Magnetization of Nanoparticles in Superimposed Ac and Dc Bias Field

A consistent study of the consequence of the azimuthal angle φ on the susceptibility and the hysteresis of the nanoparticles is performed, we treat the problem with Brown’s magnetic equation thereby extending the statistical moment method. The (DMH) loops are obtained, the principal-axis of the magnetization is oriented to the direction of the field under an any azimuthal angle. It’s demonstrated that the hysteresis and the nonlinear ac susceptibility powerfully depend on the Azimuthal angle φ.

The piezoelectric memory effect of PbFe2/3W1/3O3 ceramic

A relaxor shows piezoelectricity with a DC bias electric field because of the field-induced ferroelectric phase transition. The piezoelectricity will disappear if the field is withdrawn. Surprisingly, in relaxor PbFe2/3W1/3O3, after a DC bias field cooling process, it shows piezoelectricity on heating at a particular temperature range without the DC bias field, which is the so-called piezoelectric memory effect. The electrical and structural investigations indicate that the memory effect is closely related to a local polar phase transition and the ‘softening’ of the lattice.

Frequency blue shift of terahertz radiation from femtosecond laser induced air plasmas

The peak frequency of the terahertz radiation generated from the femtosecond laser-induced air plasmas is blue shifted with the increased second harmonics intensity when a high voltage is added upon the air plasmas. This blue shift is the result of the DC-biased field from the high voltage plus the AC-biased field from the second harmonics, indicating that this terahertz radiation frequency peak is tunable by varying the two field components. This tunable frequency peak is significant to various applications such as remote sensing and material characterization.

Magnetic field sensing performance of centimeter-scale resonator with optimized structure

Applications of magnetometers are affected mainly by their sensitivities and detection bandwidths. Till now, the applications of the centimeter-scale optomechanical magnetometer have been still limited by those two factors. In order to improve its sensing performance in a low frequency regime of the alternating current (AC) magnetic field sensor based on centimeter-scale whispering gallery mode resonator, we design a new centimeter-scale crystalline whispering gallery mode resonator which has different relative distributions of the magnetostrictive material (Terfenol-D) and the optical material (CaF<sub>2</sub>) from the unoptimized centimeter-scale whispering gallery mode resonator. Experimental results show that this new resonator is able to detect the AC magnetic field ranging from 6 Hz to 1 MHz, and a peak sensitivity of 530 pT·Hz<sup>–1/2</sup> at 123.8 kHz is achieved without DC bias field in a magnetically unshielded non-cryogenic environment. On condition that the optical quality factor is at the same level of 10<sup>8</sup> and there is no DC bias magnetic field, the best sensitivity of the optimized resonator is 11 times higher than that of the unoptimized resonator, and the corresponding detection frequency band is expanded by 1.67 times, switching from the frequency band of 10 Hz–600 kHz to 6 Hz–1 MHz. Besides, the device only needs 100 μW light intensity to operate, which offers us a low optical power consumption magnetometer. Within the detection frequency band, the proposed magnetometer can detect both a single frequency alternating magnetic field signal and an alternating magnetic field signal covering a certain frequency range. It can detect 50 or 60 Hz alternating magnetic field signal generated by current in the wire so that the working status of the power system can be monitored. If the sensing performance is further improved, it may be able to detect the magnetic field signal at frequency in a range of 1 kHz–10 MHz generated by the partial discharge current and the extremely low frequency human body magnetic field signal located in a frequency band of [10 mHz–1 kHz]. Further improvement in sensing performance is possible through optimizing the system noise and the magnetic field response capability of the device, which might allow the device to possess the applications in the fields of power system fault monitoring and medical diagnosis.

Direct current tolerant characteristics of FeCuNbSiB nanocrystalline in tensile stress annealing

The effect of relevant factors on the magnetic properties and structures of FeCuNbSiB nanocrystalline alloy in the tensile stress process was investigated. The continuous annealing apparatus was designed to control the tensile stress, annealing temperature, isothermal time, heating rate, and cooling rate. Different levels of relevant factors were performed on the ribbon samples using orthogonal experiments designing and then studied by simple variable controlling. To compare the DC tolerance property, the DC-bias field H0.98 is defined. The results show that during annealing the above relevant factors significantly affects the magnetic property including the DC-bias field and core loss. It is observed that the DC-bias field H0.98 and the unit weight core loss of alloy Pm reach the optimum value in 570 and 590 °C and subsequently deteriorate with the increasing annealing temperature. The DC tolerance property is proportional to the tensile stress and when the tensile stress increasing up to 94 MPa, the DC-bias field H0.98 shows a linear relationship with tensile stress. On the other hand, the DC tolerance property is negligible corresponding to the tensile stress smaller than 94 MPa and conversely, the core loss of alloy decrease significantly. The DC-bias field H0.98 of annealing samples exhibit a comparably stable value in the time range of 90 s to 900 s. In addition, the core loss Pm shows a similarly linear decreasing function with isothermal time from 20 to 900 s. Based on the results, the DC-bias field H0.98 is more than 3500 A/m when the tensile stress exceeds 230 MPa and the unit weight of core loss Pm is about 63 W/kg corresponding to f = 100 kHz and Bm = 300 mT when the isothermal time is 900 s, respectively. Analysis with magneto-optical Kerr microscopy reveals that the width of magnetic domains decreases with an increasing tensile stress and annealing temperature. Besides, when the isothermal time exceed 480 s, the magnetic domain wall shows a transformation from perpendicular to parallel to the direction of magnetization. In addition, the relationship between magnetic properties and relevant factors in the tensile stress process is discussed.

Non-equilibrium magnetic response of canonical spin glass and magnetic glass

Time and history dependent magnetization has been observed in a wide variety of materials, which are collectively termed as the glassy magnetic systems. However, such systems showing similar non-equilibrium magnetic response can be microscopically very different and they can be distinguished by carefully looking into the details of the observed metastable magnetic behavior. Canonical spin glass (SG) is the most well studied member of this class and has been extensively investigated both experimentally and theoretically over the last five decades. In canonical SGs, the low temperature magnetic state obtained by cooling across the SG transition temperature in presence of an applied magnetic field is known as the field cooled (FC) state. This FC state in canonical SG is widely believed as an equilibrium state arising out of a thermodynamic second order phase transition. Here, we show that the FC state in canonical SG is not really an equilibrium state of the system. We report careful dc magnetization and ac susceptibility measurements on two canonical SG systems, AuMn (1.8%) and AgMn (1.1%). The dc magnetization in the FC state shows clear temperature dependence. In addition, the magnetization shows a distinct thermal hysteresis in the temperature regime below the SG transition temperature. On the other hand, the temperature dependence of ac susceptibility has clear frequency dispersion below SG transition in the FC state prepared by cooling the sample in the presence of a dc-bias field. We further distinguish the metastable response of the FC state of canonical SG from the metastable response of the FC state in an entirely different class of glassy magnetic system namely magnetic glass, where the non-equilibrium behavior is associated with the kinetic-arrest of a first order magnetic phase transition.

Determination of AC losses in segmented rare earth permanent magnets

Segmenting rare earth permanent magnets into thin slices is an effective means for avoiding eddy current losses in oscillating magnetic fields. However, the large surface areas created by segmentation can give rise to severe hysteresis losses. The surface hysteresis may lead to increasing rather than decreasing AC losses for narrower segmentation. Increasing losses were observed in NdFeB samples for segment thicknesses below 4 mm, in an AC field of ±80 kA/m at 1000 Hz. In contrast, Sm2Co17 magnets showed no significant hysteresis losses. The strong hysteresis losses in NdFeB were observed for AC fields oscillating around H = 0. DC bias fields of >100 kA/m reduced the hysteresis losses by more than one order of magnitude. Determining the hysteresis losses from quasi-static minor loop measurements gave similar results as found in the AC measurements. An evaluation of the hysteresis losses is thus possible by hysteresisgraphs, which are more widely available.

OPM magnetorelaxometry in the presence of a DC bias field

Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNP’s magnetic moments is measured by sensitive magnetometers and an inverse problem is solved. To remove or minimize the magnetic shielding in which MRX imaging is carried out today, the knowledge of the influence of background magnetic fields on the MNP’s relaxation is a prerequisite. We show MRX measurements using an intensity-modulated optically pumped magnetometer (OPM) in background magnetic fields of up to 100~upmu mbox{T}. We show that the relaxation parameters alter or may be intentionally altered significantly by applying static fields parallel or antiparallel to the MNP’s alignment direction. Further, not only the relaxation process of the MNP’s magnetic moments could be measured with OPM, but also their alignment due to the MRX excitation field.

Dielectric, piezoelectric and dc bias characteristics of Bi-doped PZT multilayer ceramic actuator

In this study, the microstructure, dielectric, piezoelectric and dc bias properties of the Bi-doped PZT (PZTB) multilayer piezoelectric actuators, have been discussed. The thickness of the dielectric monolayer was about 70 μm, and a relatively uniform distribution of the grain size was developed. The application of a large dc bias field resulted in a decrease in the dielectric constant and dielectric loss of the multilayer piezoelectric ceramics. The shift of the Curie temperature (Tc) towards a higher value and stabilized temperature-dependent dielectric properties were observed under the dc bias field. The increase in parameter γ suggested the enhancement of the degree of diffuseness of the phase transition. The large displacement reached 0.11% of the thickness of the multilayer piezoelectric ceramic under a low driving voltage of 150 V, indicating the potential of commercial applications of the studied multilayer piezoelectric actuators. This study provides specific experimental data to evaluate the practical application of the Bi-doped PZT multilayer piezoelectric actuators.

Geochemical and magnetic data on anthropogenic ashes from municipal solid waste incineration (MSWI).

This paper reports supplementary information to “Understanding room-temperature magnetic properties of anthropogenic ashes from municipal solid waste incineration to assess potential impacts and resources” [1]. The sample-set is composed of 47 samples of bottom (BA) and fly (FA) ashes from Municipal Solid Waste Incineration (MSWI), including eight magnetic extracts of selected BA and FA materials. The sampling relies on a simple random sampling strategy at four different MSWI sites in Northern Italy [2]. X-Ray Fluorescence (XRF) analysis on pressed powder pellets, microscopic observations on thin sections and stubs, and magnetic analysis were carried out.Various magnetic measurements are presented: the magnetic susceptibility measured at two different frequencies (0.47 and 4.7 kHz); the mass-specific susceptibility of ARM (χARM), expressed in m3/kg, calculated after mass-normalization and bias DC field correction; experiments for isothermal remanent magnetization (IRM) experimented were also conducted. The latter measurement allowed the calculation of additional parameters, such as the coercivity of remanence (B0cr) and the S-ratio [3]. The IRM acquired in a field of 1.0 T was regarded as the saturation IRM (SIRM). Mass-specific magnetic susceptibility (χ) was calculated by dividing the volume susceptibility by the sample mass. Finally, hysteresis loops and backfield curves at room temperature were measured on selected samples and are available. Data can be reused as groundwork information in future studies on MSWI residues. It would be essential to produce new data on geochemical and magnetic characteristics of MSWI residues to assure good coverage of data for enhanced sustainability of these heterogeneous streams of anthropogenic materials. This combination of methods will contribute to paving the way for quick and reliable resource assessment as well as to promote environmental sustainability.

Crystal-like microstructural Finemet/FeSi compound powder core with excellent soft magnetic properties and its loss separation analysis

The Finemet/FeSi compound powder cores with crystal-like microstructure were successfully fabricated by adding micron-size gas-atomized FeSi powders into the thick Finemet flaky-powders. Loss-separation fitting model for the compound cores mixed with different mass fractions of FeSi powders was built to analyze the relative loss mechanism and source of each part loss. Due to the fact that the magnetic powders were coated with high-quality electrical-insulating layer, the inter-particle eddy current energy loss is only 1/400–1/800 of total energy loss. The volume fraction of non-magnetic phase and pinning effect, which are found to be sensitive to density of cores, play a significant role on both hysteresis loss and excess loss. As compared to the pure Finemet based powder cores, the Finemet/FeSi compound cores mixed with 10–14 wt% of FeSi powders exhibit a higher permeability and a greater retained permeability at a DC-bias field of 7960 A/m. The total core loss reduced from 788 kW/m3 to 614 kW/m3 at 300 kHz, 0.05 T. These results indicated that the Finemet/FeSi compound powder cores with crystal-like microstructure have a great advantage in power electronics applications, and suggested that the powder micro-structure design is a promising method to further improve magnetic performances for soft magnetic composites.

Iron Loss Modelling of Electrical Traction Motors for Improved Prediction of Higher Harmonic Losses

A Finite Element (FE) modelling approach is presented to account for the core losses in electrical machines that are generated by higher harmonic frequencies, for example those caused by Pulse Width Modulation (PWM) switching or by space harmonics due to the machine geometry. The model builds further on a post-processing calculation tool that was recently developed to take into account the magnetic skin effect in electrical steel laminations at high frequencies, and extends this by a more detailed loss analysis of the minor hysteresis loops that are caused by the higher harmonics. Further, these tools for high-frequency loss analysis are integrated into a complete electrical machine model with separate consideration of the major and minor loops. The modelling approach relies strongly on extensive magnetic measurement data of the electrical steel, in order to accurately predict the different loss components for minor hysteresis loops as a function of the DC bias field, frequency and amplitude of the minor loop. Results from the model are shown for an automotive traction motor, illustrating the losses caused by PWM harmonics and demonstrating the relevance of including the skin effect in these calculations.

Significant Non-Bias-Field Magnetoelectric Response and High Output Power in a Novel Combination Based on Terfenol-D and Electrets

A new magnetoelectric (ME) sensing combination based on a magnetostrictive Terfenol-D rod and electret membrane has been proposed. AC signal and dc bias magnetic field dependences of the induced ac voltage were investigated using the traditional dynamic ME measurement. The results show that the induced ac voltage is strongly dependent on the applied ac signal and dc bias magnetic field. A significant ME response with high sensitivity and high tunability was obtained, and the optimized ME voltage output with high output power is observed for a zero bias dc magnetic field. The minimum limit of detection and maximum dc bias field tunability are 0.056 mA (or 5.27 $\times \,\,10^{-{7}}$ T) and 98.42%, respectively. In addition, both the induced ac voltage and output power are strongly dependent on the frequency of the driving ac signal magnetic field. A wide working frequency range and high energy conversion efficiency are observed with this combination. These findings not only provide insight into the dynamic measurement of ME response beyond ME materials but also provide a new type of sensing combination, possessing potential application in ME sensors, energy converters, switches, and magnetic detectors.

Magnetostrictive Characteristics of the Grain-Oriented Electrical Steel in an Epstein Frame Magnetized with a DC Biased Magnetic Field

The presence of direct current (dc) biased magnetic field enhances the vibration and noise in the transformer cores due to magnetostrictive effect in the grain-oriented electrical steel laminations. Based on an Epstein frame, an experimental setup was built to measure the in-plane magnetostriction, the principal magnetostriction was computed under a dc bias, and the influence of dc bias magnetic field on the magnetostrictive property of electrical steel sheet was investigated. A model based on a back propagation neural network (BPNN) method assisted with the Levenberg–Marquardt algorithm was proposed to describe the magnetostrictive behaviour in the presence of dc bias. Finally, the BPNN model was verified by comparing the measured magnetostriction and the computed one. This research is helpful to make an accurate estimation to deformation of iron core under a dc bias.