Dc Bias Magnetic Field Research Articles

Microwave sintering versus conventional sintering of NiCuZn ferrites. Part II: Microstructure and DC-bias superposition characteristics

NiCuZn ferrites with the composition of (Ni0.48Cu0.10Zn0.42O)1.04(Fe2O3)0.96 were consolidated by microwave sintering (MS) and conventional sintering (CS), respectively. The influences of external microwave field and additives (1wt% BSZ glass or 1wt% Bi2O3) on the microstructure and DC-bias superposition characteristics of NiCuZn ferrites were investigated. Experimental results demonstrated that the final grain size was much larger with higher density since applying microwave field. In addition, for undoped ferrites, coarse grains structure obtained from microwave sintering is harmful to the DC-bias superposition characteristics. However, since adding BSZ glass or Bi2O3, the discrepancy on the final grain size obtained from MS and CS methods is not obvious. NiCuZn ferrites with the addition of BSZ glass or Bi2O3 exhibited a stronger ability to inhibit the drop of permeability under the DC-bias magnetic field. Possible mechanisms behind are discussed in this article.

Biasing a ferronematic - a new way to detect weak magnetic field.

The magnetic properties of a ferronematic, i.e., a nematic liquid crystal doped with magnetic nanoparticles in low volume concentration are studied, with the focus on the ac magnetic susceptibility. A weak dc bias magnetic field (a few Oe) applied to the ferronematic in its isotropic phase increases the ac magnetic susceptibility considerably. Passage of the isotropic-to-nematic phase transition resets this enhancement irreversibly (unless the dc bias field is applied again in the isotropic phase).

Computation and Analysis of the DC-Biasing Magnetic Field by the Harmonic-Balanced Finite-Element Method

This paper sought to present harmonic-balanced method for finite element analysis of nonlinear eddy current field. The harmonic-balanced method can be used to compute the time-periodic electromagnetic field in harmonic domain, considering electric circuits coupled with the nonlinear magnetic field. 2-D and simplified 3-D model of laminated core is established and computed to prove the accuracy and validity of the proposed method. The calculated magnetizing current is compared with the measured results and the computed magnetic field is analyzed to investigate the effect of DC bias.

Nonlinear ac stationary response and dynamic magnetic hysteresis of quantum uniaxial superparamagnets

The nonlinear ac stationary response of uniaxial paramagnets and superparamagnets---nanoscale solids or clusters with spin number $S\ensuremath{\sim}{10}^{0}\ensuremath{-}{10}^{4}$---in superimposed uniform ac and dc bias magnetic fields of arbitrary strength, each applied along the easy axis of magnetization, is determined by solving the evolution equation for the reduced density matrix represented as a finite set of three-term differential-recurrence relations for its diagonal matrix elements. The various harmonic components arising from the nonlinear response of the magnetization, dynamic magnetic hysteresis loops, etc., are then evaluated via matrix continued fractions indicating a pronounced dependence of the response on $S$ arising from the quantum spin dynamics, which differ markedly from the magnetization dynamics of classical nanomagnets. In the linear response approximation, the results concur with existing solutions.

Near-Flat Self-Biased Magnetoelectric Response in Three-Phase Metglas/Terfenol-D/PZT-Laminated Composites

Since the piezoelectric/magnetostrictive laminate composite exhibits a strong magnetoelectric (ME) effect, it provides a novel method for detecting ac magnetic field. There are a number of researches on the development of ME composites and their applications in detecting magnetic fields. Dong et al. demonstrates the possibility of fabricating ac magnetic field sensors with high performances[1]. Especially, ME composite sensor can achieve the passive sensing of magnetic field and possesses high sensitivity, which greatly enhances the competitiveness of ME composite sensor against traditional magnetic sensors. ME voltage coefficient varies with H dc owing to the piezomagnetic coefficient's variation as a function of H dc , which shows a peak behavior near an optimum dc bias magnetic field H dc, opti . Hence, the ME composite sensor requires an external dc bias magnetic field to obtain the high ME sensitivity. However, the bias magnetic field is usually generated by using permanent magnets. It will increase the electromagnetic noise and increase the size of the sensor greatly, which is disadvantageous for the realization of high-sensitivity miniature magnetic sensors. Furthermore, the peak point is sharp and fixed, correspondingly small fluctuations of the optimum dc bias magnetic field will lead to a remarkable decrease of the ME voltage coefficient and degrade the ME composite performance significantly. In addressing these issues, the study of self-biased ME composite has provoked a great number of research activities and made progress [2-3]. However, these efforts have not obtained a wide range of dc bias response.

Correlation Between Magnetoelectric and Magnetic Properties of Ferromagnetic–Piezoelectric Structures

The magnetoelectric (ME) effect in composite structures consisting of ferromagnetic (FM) and piezoelectric (PE) layers arises due to combination of magnetostriction and piezoelectricity by means of mechanical coupling between the layers [1]. The structures generate ac voltage u being placed in an external dc bias magnetic field H and ac magnetic field h. Amplitude of the voltage is u ∼qd 31 h, where q = dλ/dH is the piezomagnetic coefficient and λ(H) in the magnetostriction of the FM layer, d 31 is the piezoelectric module of the PE layer, and h is the field amplitude. It has been shown that the magnetostriction is related to the FM layer magnetization as λ ∼ M 2. It follows, that field dependence of the ME voltage u(H) can be explained or predicted by measuring the field dependence of magnetization M(H). The aim of the present work is to demonstrate a correlation between magnetoelectric and magnetic properties of the FM-PE composite structures.

A Slice-Type Magnetoelectric Laminated Current Sensor

This paper describes the design and the implementation of a new structure for an ac current sensor based on a magnetoelectric laminated composite slice. Two layers of longitudinally magnetized magnetostrictive material Terfenol-D (Tb0.3Dy0.7Fe1.92) and one layer of transversely polarized piezoelectric material Pb(Zr,Ti)O3 (PZT) were epoxy-bonded and the wire conducting the current coiled along the slice and the output voltage obtained across the two surfaces of the PZT. Compared with the reported ring-type or close-magnetic-circuit-type magnetostrictive current sensor topologies, there was no requirement for any interruption of the power supply to enable the installation and the maintenance of the sensor, which was very convenient and practical. The dimensions of the slice sensor were 30 mm $\times $ 8 mm $\times $ 2.8 mm. An averaging method was used to perform the theoretical analysis and the simulation is carried out using the COMSOL multiphysics software. The analysis, simulation, and experimental results were compared thoroughly. The current sensitivity was 1.03 mV/mA over input currents ranging from 15 mA to 2.1 A. A stable output voltage over a frequency range from 20 Hz to 5 kHz was attained by the slice. Further research on the influence of the dc bias magnetic field and the number of turns of the current coil on the output characteristics of the sensor has been carried out. This current sensor has great potential for further research and applications.

Enhanced Magnetoelectric Effect in Permendur/Pb(Zr0.52Ti0.48)O3 Laminated Magnetostrictive/Piezoelectric Composite

In this work, after investigating three typical magneto-electric (ME) composites, Permendur/Pb(Zr0.52Ti0.48)O3(PZT), Metglas/PZT, and Tefenol-D/PZT, with the same dimensions and different saturation magnetostriction and magnetic permeability, the most excellent ME performance is observed in the Permendur/PZT laminates, which agrees well with the predicted results from the figure of merit. The low-frequency and resonance ME coefficients of Permendur/PZT composite are ~23.1 V/Oe.cm and ~309 V/Oe.cm at the optimal dc bias magnetic field of ~250 Oe, respectively. The strong ME effect of Permendur/PZT composite gives it potential in practical magnetic sensitive device applications.

Effect of a DC transverse magnetic field on the magnetization dynamics in FeCuNbSiB ribbons and derived nanostructured powder cores

The paper aims to give a comprehensive account of DC transverse bias magnetic field influence on the dynamic magnetization processes in Fe73Cu1Nb3Si16B7 soft magnetic ribbons and nanostructured powder cores based on ribbon precursor. These materials were extensively investigated using an approach of impedance spectroscopy from the viewpoint of complex permeability spectra, which offer the indirect insight into magnetization mechanisms and their frequency relaxation. In order to analyze the dynamic nature of domain wall magnetization mechanism, we carried out complex permeability measurements under combined influence of three independent variables, i.e. magnetizing frequency, various driving AC and DC bias magnetic fields. From this ample matrix of results, it has been found that the DC bias smaller than some critical field can increase the real part of complex permeability in the case of as-quenched and annealed ribbon. Nonetheless, the higher fields play a role of additional anisotropy and consequently domain wall damping mechanism. For nanocrystalline compacted powder cores, only the damping influence of DC transverse field was observed. The results are compared in detail and possible mechanisms of domain wall movement damping are proposed and discussed.

Metamagnetic transition and magnetothermal properties of ErCo4Ge2

Polycrystalline ErCo4Ge2 was investigated by magnetic susceptibility and heat capacity measurements. The results show that ErCo4Ge2 undergoes a transition from the paramagnetic to the antiferromagnetic (AFM) state around 2.6 K. The second order character of this magnetic transition is confirmed from the lambda-like peak of the heat capacity data. Both χ′ and χ″ of ErCo4Ge2 are strongly dependent on the ac magnetic field frequency and bias dc magnetic field. A field induced metamagnetic transition from AFM to ferromagnetic state is observed below TN. Under a magnetic field change of 50 kOe, the maximum value of the magnetic entropy change (magnetocaloric effect) −ΔSM is 14.2 J/kg K at 2.75 K and the adiabatic temperature change ΔTad is 5.7 K. In particular, a large −ΔSM value of 11.7 J/kg K is achieved for a low magnetic field change of 20 kOe.

Hysteretic Magnetization Losses of HTSC Tapes in Coaxial AC and DC Magnetic Fields

In the work we present experimental results of ac magnetization losses measurements performed in the presence of a dc-bias magnetic field. Both ac and dc magnetic fields were coaxial and directed perpendicularly to the flat surface of sample tapes. The HTS tapes used in our experiments are commercially available composite tapes, namely a BSCCO-2223/Ag multifilamentary tape and an YBCO-123 coated conductor tape. The measurements were carried out with a sinusoidally varying magnetic fields at frequency range of about 21-113 Hz, and amplitudes up to 100 mT. The superimposed a dc-bias magnetic field was of the order of up to 50 mT. At a certain magnetic field amplitude, and at a certain dc bias magnetic field, a distinguish minimum in ac losses is observed. Occurrence of the ac loss minima differs considerably for two studied sample tapes.

Enhanced bending-resonance magnetoelectric response in end-bonding magnetostrictive/piezoelectric heterostructure

In this paper, we present a magnetoelectric (ME) heterostructure made by attaching two magnetostrictive Nickel (Ni) plates at the two free ends of a piezoelectric Pb(Zr1-xTix)O3 (PZT) plate. With this configuration, the Ni and the PZT plates vibrate more freely due to the absence of an interfacial epoxy layer, which results in a larger bending deformation of the PZT plate. The Ni and the PZT plates couple to each other by mechanical magnetic forces, instead of shear forces. In addition, the two Ni plates act as proof masses for the PZT plate, which can reduce the bending resonant frequency (f r) the of PZT plate. The experimental results demonstrate that the bendingresonance ME voltage coefficient (aME,r) is 2.82 times larger than that of the traditional bilayer laminate Ni/PZT. As the length of the Ni plates (L) increases, the fr decreases and can be shifted in a range of 34.6 kHz ≤ fr ≤ 61.02 kHz. The maximum aME,r of 49.84 V/cm Oe is observed at dc bias magnetic field H dc = 158 Oe when L = 18 mm. This heterostructure is of interest for high-sensitive dc magnetic-field sensors, ME transducers.

Effect of Cr doping on ferroelectric and magnetic properties of Bi0.8Ba0.2FeO3

Multiferroic ceramics Bi0.8Ba0.2Fe1−xCrxO3 (x=0, 0.05 and 0.1) were synthesized by using the conventional solid state reaction method. The pure phase with rhombohedral structure was confirmed by the X-ray diffraction measurements for all samples. It was shown that the magnetic and the ferroelectric properties were simultaneously improved, and the maximum values of the remnant magnetization (2Mr) and the remnant polarization (2Pr) at room temperature for all samples are around 1emu/g and 1.9μC/cm2, respectively. Furthermore, the leakage current density, the low frequency dispersion in the dielectric constant and the dielectric loss decreased with increasing the Cr concentration from x=0 to 0.1. A remarkable change in the P–E loop was observed whether a bias dc magnetic field was applied or not, approving the existence of the magnetoelectric coupling indirectly therein.

Nonequilibrium magnetic response of anisotropic superparamagnetic nanoparticles and possible artifacts in magnetic particle imaging.

Magnetic responses of superparamagnetic nanoparticles to high-frequency AC magnetic fields with sufficiently large amplitudes are numerically simulated to exactly clarify the phenomena occurring in magnetic particle imaging. When the magnetic anisotropy energy inevitable in actual nanoparticles is taken into account in considering the magnetic potential, larger nanoparticles exhibit a delayed response to alternations of the magnetic fields. This kind of delay is rather remarkable in the lower-amplitude range of the field, where the assistance by the Zeeman energy to thermally activated magnetization reversal is insufficient. In some cases, a sign inversion of the third-order harmonic response was found to occur at some specific amplitude, despite the lack in DC bias magnetic field strength. Considering the attenuation of the AC magnetic field generated in the human body, it is possible that the phases of the signals from nanoparticles deep inside the body and those near the body surface are completely different. This may lead to artifacts in the reconstructed image. Furthermore, when the magnetic/thermal torque-driven rotation of the anisotropic nanoparticles as well as the magnetic anisotropy energy are taken into account, the simulated results show that, once the easy axes are aligned toward the direction of the DC bias magnetic field, it takes time to randomize them at the field-free point. During this relaxation, the third-order harmonic response depends highly upon the history of the magnetic field. This is because non-linearity of the anhysteretic magnetization curve for the superparamagnetic nanoparticles varies with the orientations of the easy axes. This history dependence may also lead to another artifact in magnetic particle imaging, when the scanning of the field-free point is faster than the Brownian relaxations.

Resonance modes of freestanding magnetoelastic resonator and the application in viscosity measurement

The magnetoelastic material possesses several resonance modes, but the magnetoelastic sensors operate in basically the fundamental resonant frequency. This paper investigates the resonance modes of a freestanding ME resonator, tests these modes in liquids with different viscosity and measures the viscosity of human blood. Five resonance modes with different amplitudes appear in the frequency range of 30–280 kHz. The resonance modes are affected by the direction and strength of the DC bias magnetic field. Compared with the width of the resonance peak, the quality factor cannot correctly reflect the sharpness of the resonance peak of different resonance modes. The five modes are affected by liquid. The first mode has better resolution in determining the resonant frequency, but the higher mode is more sensitive to viscosity. The ME resonator can be used to quickly distinguish the viscosity of blood.

A fabrication process for the monolithic integration of magnetoelastic actuators and silicon sensors

This paper describes a microfabrication process that accommodates the design considerations of wirelessly actuated magnetoelastic traveling wave and standing wave motors that are integrated with capacitive position sensors on a silicon substrate. The process—which incorporates AuIn eutectic bonding, multiple deep reactive ion etching steps, and metal electrode deposition and etching—addresses the challenges of magnetoelastic layer attachment, multi-layer structures, and robust electrode isolation. Measurements of successfully fabricated devices show that the typical resonant frequencies of the clockwise and counterclockwise modes for the standing wave stators existed at 12.1 and 22.4 kHz with 0.44 µm and 0.4 µm out-of-plane amplitudes, respectively, when a ≈2 Oe amplitude ac magnetic field and a ≈6.5 Oe dc magnetic bias field were applied. For the as-fabricated traveling wave motors, two desired mode shapes with π/2 spatial phase shift existed at typical frequencies of 28.4 and 29.9 kHz, with typical out-of-plane amplitudes of 74 and 70 nm, respectively, when a ≈6 Oe amplitude ac magnetic field and a ≈3 Oe dc magnetic bias field were applied. The frequencies were tuned with added mass, resulting in a shift to 28.37 and 28.33 kHz with out-of-plane amplitudes of 80 and 60 nm for the two modes, respectively. After tuning, a traveling wave with a continuous direction of propagation was successfully demonstrated. The capacitive position sensing scheme showed a sensitivity of ≈0.5 pF per degree over 8°.

Optimizing direct magnetoelectric coupling in Pb(Zr,Ti)O3/Ni multiferroic film heterostructures

Polycrystalline Pt thin films of different thicknesses (0–75 nm) were introduced using magnetron sputtering in Pb(Zr0.52Ti0.48)O3 (PZT, 400 nm in thickness)/Pt/Ni multiferroic film heterostructures, aimed at optimizing the transfer efficiency of magnetostrictive strain from the bottom Ni foil to the top PZT film and thus the direct magnetoelectric (ME) coupling. The ME voltage coefficient αE31 was directly measured, while the strain transfer efficiency k was obtained by combined experimental and theoretical analysis. At the optimum Pt-thickness of 30 nm, the polycrystalline film heterostructure shows the largest αE31 of 772 mV cm−1 Oe−1 at a low dc magnetic bias field of 86 Oe, as well as the highest k of 83% that is comparable to that in epitaxial quasi-2-2 film heterostructures.

Jump effect based magnetically tunable resonance of PZT-ring/TDF-strip composite with improved sensitivity

By considering the jump effect of magnetostrictive materials, a novel structure of PZT-ring/TDF-strip magnetoelectric composite is proposed to achieve magnetically tunable electromechanical resonance with a DC bias magnetic field. With the jump effect induced piezomagnetic coefficient of the Tb0.3Dy0.7Fe1.92 strip, the resonance properties of the Pb(Zr,Ti)O3 ring are theoretically studied and experimentally measured. The highly consistent results prove that the proposed composite has two resonant frequencies with improved sensitivity (133Hz/Oe) and enhanced resolution (722ppm/Oe) of resonance shift, which provide the feasibility of magnetically tunable electromechanical resonance with a low magnetic field and suggest the application potential for controllable sonar transducer.

The giant magnetoelectric effect in Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites

The Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites with excellent magnetoelectric (ME) coupling effect were synthesized by electrostatic spray depositing. The ME coupling characteristics of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites were investigated. It is found that the appropriate thickness ratio between magnetostrictive layers and piezoelectric layers (tm/tp) will be favorable to raise the resonance ME field output performance. The resonance frequency of ME field coefficient can be tuned by controlling tm/tp. The optimum resonance ME field coefficient of Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites achieves 259.2 V/cm Oe at mechanical resonance frequency at 11.5 kHz with the dc bias magnetic field is 60 Oe. Remarkably, the proposed composites exhibit a giant ME effect and a higher ME voltage coefficient than the previous Terfenol-D/PZT laminated composites. It indicates that the mentioned Fe73.5Cu1Nb3Si13.5B9/PZT thick film composites have great potential for the application of highly sensitive magnetic field sensing and vibration energy harvesting.

Electromagnetic Sensors Based on Magnonic Crystals for Applications in the Fields of Biomedical and NDT

An exploratory investigation of high sensitivity sensors based on magnonic crystals for the measurement of weak magnetic fields at room temperature is presented. The samples are YIG crystals on GGG substrate (Gadolinium-Gallium-Garnet) on which a periodic structure of shallow grooves are etched or gold stripes are deposited. The excitation of surface magnetostatic spin waves (MSSW) which should appear in these structures is obtained by means of microstrip transmission line or microstrip planar antenna.The measurement of the magnonic structure by complex transmission coefficient (S12) shows a significant shift in frequency of the maximum absorption peak related to magnonic band gap which depends on the magnitude of the DC magnetic bias field applied. It shows the possibility of magnonic high Q-value band gap implementation with respect to spin wave propagation band (GHz band) in magnonic crystals applied to spin waves detection of magnetic fields.The influence of the characteristics of the microstrip line or the microstrip antenna on sensor performance (sensitivity and resolution) is studied.