High Initial Permeability Research Articles

Hysteresis properties of the amorphous high permeability Co66Fe3Cr3Si15B13 alloy

The scaling law of minor loops was studied on an amorphous alloy Co66Fe3Cr3Si15B13 with a very high initial permeability (more than 150000) and low coercivity (about 0.1 A/m). An analytical expression for the coercive force in the Rayleigh region was derived. The coercive force is connected with the maximal magnetic field Hmax via the reversibility coefficient μi/ηHmax. Reversibility coefficient shows the relationship between reversible and irreversible magnetization processes. A universal dependence of magnetic losses for hysteresis Wh on the remanence Br with a power factor of 1.35 is confirmed for a wide range of magnetic fields strengths.

Soft magnetic properties of rapidly-annealed nanocrystalline Fe-Nb-B-(Cu) alloys

Nanocrystalline Fe-M-B (M = Zr or Nb) alloys (Nanoperm) exhibit excellent soft magnetic properties when M content is 6–7 at%. Lowering the M content below 4 at% usually results in a coarsening of the nanocrystallites and so sets a lower limit on the M content for Nanoperm. In this report we have demonstrated that a highly refined, magnetically soft nanostructure can be achieved for Fe-Nb-B-(Cu) alloys with a Nb content well below 4 at% by employing a rapid annealing process which utilises a heating rate of 150 K s−1. The low Nb-content of these nanocrystalline alloys brings about a high saturation magnetic polarization of 1.85–1.9 T, well above the upper limit of Nanoperm (1.7 T). These newly developed, bcc-Fe based nanocrystalline soft magnetic alloys which have an M content lower than 4 at% are named HiB-Nanoperm. HiB-Nanoperm exhibits excellent soft magnetic properties with a coercivity as low as 2.5 A m−1 and a high initial permeability of ∼104 at 1 kHz. A possible explanation for the rapid annealing induced grain refinement observed for this Fe-M-B system is that the higher annealing temperatures used by this process bring about a lowering of the precursor amorphous phase viscosity which then triggers homogeneous nucleation, thereby considerably increasing the number density of bcc-Fe nucleation sites.

Controllable preparation of large-area arrays of Al-substituted CoCuNi ferrite rods with improvement of saturation magnetization and initial permeability

Co0.5Cu0.3Ni0.2Al x Fe2−x O4 (x = 0, 0.07, 0.14, and 0.21) rods of large-area arrays are synthesized by a solvothermal method, followed by calcination in air. The samples are characterized by powder X-ray diffraction, FT-IR spectra, scanning electron microscope, and vibrating sample magnetometer. The effect of diamagnetic Al3+ ion substitution and calcination temperature on the structure, morphology, and magnetic properties of Co0.5Cu0.3Ni0.2Al x Fe2−x O4 has been investigated. The results indicate that high-crystallized cubic Co0.5Cu0.3Ni0.2Al x Fe2−x O4 rods of large-area arrays are obtained when the precursors are calcined at 750 °C in air for 3 h. The crystallite size of Co0.5Cu0.3Ni0.2Al x Fe2−x O4 increases with the increase in Al3+ content, attributed to the decrease in lattice strain in Co0.5Cu0.3Ni0.2Al x Fe2−x O4 with the increase in Al3+ content. The lattice parameters of Co0.5Cu0.3Ni0.2Al x Fe2−x O4 slightly increase with the increase in Al3+ content. This is due to the transformation from cubic NiFe2O4 phase to cubic CoFe2O4 phase after doping Al3+ ion. Al3+ substitution can improve the magnetic properties of Co0.5Cu0.3Ni0.2Al x Fe2−x O4. Co0.5Cu0.3Ni0.2Al0.14Fe1.86O4, calcined at 950 °C, has the highest specific saturation magnetization (86.36 ± 2.25 emu/g) and magnetic moment (3.586 ± 0.093 μ B ). Co0.5Cu0.3Ni0.2Al0.21Fe1.79O4, calcined at 950 °C, has the highest initial permeability (17.216 ± 0.448). The results are explained by Neel’s two sublattices.

Magnetic flux biasing of magnetostrictive sensors

The performance of magnetostrictive materials, especially those with high initial magnetic permeability and associated low magnetic reluctance, is sensitive to not just the amount of magnetic bias but also how the bias is applied. Terfenol-D and Galfenol have been characterized under constant magnetic field and constant magnetomotive force, which require active control. The application of a magnetic flux bias utilizing permanent magnets allows for robust magnetostrictive systems that require no active control. However, this biasing configuration has not been thoroughly investigated. This study presents flux density versus stress major loops of Terfenol-D and Galfenol at various magnetic flux biases. A new piezomagnetic coefficient is defined as the locally-averaged slope of flux density versus stress. Considering the materials alone, the maximum is 18.42 T GPa−1 and 19.53 T GPa−1 for Terfenol-D and Galfenol, respectively. Compared with the peak piezomagnetic coefficient measured under controlled magnetic fields, the piezomagnetic coefficient is 26% and 74% smaller for Terfenol-D and Galfenol, respectively. This study shows that adding parallel magnetic flux paths to low-reluctance magnetostrictive components can partially compensate for the performance loss. With a low carbon steel flux path in parallel to the Galfenol specimen, the maximum increased to 28.33 T GPa−1 corresponding to a 45% improvement compared with the case without a flux path. Due to its low magnetic permeability, Terfenol-D does not benefit from the addition of a parallel flux path.

Structural and optical properties of Mn0.5Zn0.5Fe2O4 nano ferrites: Effect of sintering temperature

Mn-Zn ferrites have shown various remarkable applications e.g. in magnetic amplifiers, power transformers and electromagnetic interference etc. due to their high initial permeability. Mn–Zn ferrite powder (Mn0.5Zn0.5Fe2O4) has been prepared by the co-precipitation method and subsequently sintered at three different temperatures i.e. 973 K, 1173 K, 1373 K. Optical properties have been correlated with the structural properties. For structural properties X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) have been employed. It has been observed that there is an increase in crystallite size with sintering from 973 K to 1373 K and FTIR confirms the formation of bond between metal ion and oxygen ion at the octahedral site and tetrahedral site. A red shift has been confirmed from UV–visible absorption spectra and photoluminescence spectra have been reported with an increase in sintering temperature.

Effect of MoO3 Addition on the Magnetic Properties and Complex Impedance of Mn–Zn Ferrites with High B s and High Initial Permeability

Mn–Zn ferrites with high initial permeability (μ i) and high saturation magnetic flux density (B s) were successfully synthesized by using a conventional ceramic processing route with addition of MoO3. The structure, morphology, magnetic properties, and complex impedance of all samples were investigated by X-ray diffraction, scanning electron microscopy, DC magnetic instrument, and precision LCR meter. The addition of MoO3 promotes the growth of larger and more uniform grains and therefore enhances the μ i. Meanwhile, it improves the density and hence the B s. Through the analysis of complex impedance spectra by an equivalent circuit model, it is demonstrated that MoO3 mainly exists at grain boundaries and improves the impedance in a wide frequency range.

Effect of sintering on structural and electrical properties of co-precipitated Mn-Zn ferrites

Mn-Zn ferrite is one of the important class of soft ferrites. These are famous for possessing high initial permeability. In the present work, we have studied the effect of sintering on Mn-Zn nano particles. The particles were synthesized using co-precipitation method. The structural characterization of the prepared sample after each sintering step were done by using XRD. The XRD analysis showed the spinel structure. The electrical properties were studied as a function of temperature. It was observed that dielectric constant, loss tangent and AC conductivity varies with respect to temperature. The prepared composition is useful in microwave devices.

Textured Z-type hexaferrites Ba3Co2Fe24O41 ceramics with high permeability by reactive templated grain growth method

The c-axis oriented Ba3Co2Fe24O41 (Co2Z) ceramic with high permeability was successfully prepared by reactive templated grain growth (RTGG) method using reactive template BaFe12O19 (BaM) and complementary Ba2Co2Fe12O22 (Co2Y). The microstructure and magnetic property of the textured ceramic sample in different orientations were investigated. The sample presents both structural and magnetic anisotropic characteristics. The obtained (00h) textured Co2Z ceramic exhibits a favorable combination of easy magnetization plane orientation, high initial permeability of 19.0±1.2 (much higher than that from conventional ceramic method (CCM) (μi=12)), and high cut-off frequency (fr>1GHz), indicating the potential for high frequency application in novel electronic devices.

Strong coercivity reduction and high initial permeability in NiCoP coated BaFe12O19–polystyrene bilayer composite

Soft-magnetic NiCoP coated hard-magnetic M-type ferrite BaFe12O19 (BaM)–polystyrene (PS) bilayer composite film was successfully synthesized. X-ray diffraction peaks exhibited no change in the structure of BaM after coating with PS. The NiCoP coated BaM–PS composite exhibited a wasp-waisted magnetic hysteretic loop with remarkable reduction in the coercivity, remanence and squareness with respect to BaM–PS, which is useful for the core of a magnetic switching device to control currents so large that they are unmanageable. Moreover, the initial permeability measurement exhibits initial permeability of around 100 000 and thermal stability up to 558 K, which is good for flux-amplifying components of smaller inductors.

High Magnetic Loss Mg–Cu Ferrites for Ultrahigh Frequency EMI Suppression Applications

Spinel ferrites have been extensively used in the design and implementation of electromagnetic interference (EMI) suppressors and EM wave absorption materials in the megahertz frequency range. It is well known that EMI absorbing magnetic materials require high initial permeability and loss factor. MnZn and NiZn spinel ferrites are often used in the lower frequency range (< 300 MHz) due to the limit of Snoek's law. Therefore, it is of scientific and technological importance to explore new materials with high EMI suppression performances in the ultra-high frequency range (UHF, 300 MHz-1 GHz). Recently, Mg-Cu ferrites have received attention due to their attractive magneto-dielectric properties and high-density polycrystalline growth at relatively low temperatures. Either complex permeability or permittivity is sensitive to chemical composition, sintered density and the microstructure. Control of the process makes it possible to achieve high permeability and large loss factor simultaneously in Mg-Cu ferrites for high performance EMI suppression. In this study, the influences of Cu as a substitute for Mg and sintering temperature upon microstructure and high frequency properties of Mg-Cu ferrites were investigated for their ability to suppress EMI.

Improvement of microstructure, initial permeability, magnetization and dielectric properties of nanocrystalline LixCu0.1Co0.1Zn0.8−2xFe2+xO4

Structural, magnetic and dielectric properties of Li substituted LixCu0.1Co0.1Zn0.8−2xFe2+xO4 (where x=0.00–0.40) prepared by auto combustion method have been investigated. The X-ray diffraction patterns of these compositions confirmed the formation of the single phase spinel structure. Disc- and toroid-shaped samples are prepared from each composition and sintered at various temperatures (1100–1300°C) in air for 1h. The lattice parameter decreases with the increase in Li1+ content obeying Vegard's law. The particle size of the starting powder compositions varied from 24 to 46nm. The bulk density and permeability increases up to a certain level of Li1+ substitution, beyond that all these properties decrease with increase in Li1+ content. The bulk density increases with increase in sintering temperatures up to 1150°C both for the parent and substituted compositions. Due to substitution of Li1+, the real part of the initial permeability increases from 18 to 61 for x=0.10 for the samples sintered at 1150°C. The ferrites with higher initial permeability have relatively lower resonance frequency which obey Snoek's law. The initial permeability strongly depends on average grain size and intragranular porosity but at higher sintering temperatures some voids are present in the samples which reduce the density and hence permeability of the samples. The ferri to paramagnetic transition temperature, TC, for the parent sample is below room temperature. The TC increases almost linearly with increasing Li content.The saturation magnetization, Ms, and the number of Bohr magneton, n(µB), increases up to x=0.30 due to the enhancement of the A–B interaction in the AB2O4 spinel type ferrites. Beyond that value of x, the Ms and the n (µB) values are decreased. The substitution of Li1+ influences the magnetic parameters due to modification of the cation distribution. Dielectric constant (ε′) decreases with increase in frequency which is rapid at lower frequencies and slower at higher frequencies which may be due to the Maxwell–Wagner interfacial polarization.

Syntheses and Fundamental Properties of Fe-rich Metastable Phase Alloys with Saturation Magnetization Exceeding 1.9 T

A melt-spun Fe90Si5B5 alloy ribbon consists of bcc-Fe(Si) + Fe3B + amorphous phase and exhibits good bending ductility, high tensile fracture strength above 1000 MPa, high corrosion resistance and unique magnetic properties as exemplified for high saturation magnetization exceeding 1.9 T, moderately high initial permeability of about 150 and low coercivity of 745 A/m which are attractive for magnetic sensors utilizing a nearly constant high permeability with applied field up to coercivity. Besides, the tensile fracture strength and elongation increase significantly to 1286 MPa and 0.62%, respectively, after annealing for 900 s at 823 K. The Fe-Si-B alloy ribbons are attractive as a new type of sensor material with features of high bending ductility, high tensile strength and elongation, relatively good corrosion resistanceand unique soft magnetic properties with very high saturation magnetization.

Geotechnical and geophysical characteristics of muskeg samples from Alberta, Canada

A series of laboratory tests have been performed to explore the geotechnical and geophysical characteristics of fibrous muskeg (i.e., grassy bog), using undisturbed block samples obtained from Alberta, Canada. The basic index properties of muskeg show similar values to the reference data for other organic soils, and they significantly differ from those of typical inorganic soils. Due to high organic content, muskeg has high water content, high compressibility, and high initial permeability. The effective stress and porosity play a major role in controlling the stress-dependent geophysical properties of shear wave velocity, real permittivity, and electrical conductivity. The values of peak drained friction angle obtained in the direct shear tests are in the range of 26° to 51°.

DC-Bias-Superposition Characteristics of Ni0.4Zn0.2Mn0.4Fe2O4 Nanopowders Synthesized by Auto-Combustion.

Ni0.4Zn0.2Mn0.4Fe2O4 nanopowders were prepared by auto-combustion method. The as-synthesized powders were characterized using X-ray diffraction (XRD) and thermo-gravimetric-differential thermal analysis (TG-DTA), and the powders were densified at different temperatures 400 degrees C, 500 degrees C, 600 degrees C and 700 degrees C/4 hrs using conventional sintering method. The sintered samples were characterized by XRD and transmission electron microscope (TEM). The bulk densities of the samples were increased with an increase of sintering temperature. The grain sizes of all the samples vary in between 18 nm to 30 nm. The hysteresis loops show high saturation magnetization and low coercivity, indicates that it is a soft material. The incremental permeability (permeability with magnetic field superposition) was influenced by both ΔM and H(c). A sample with higher initial permeability and favoured the attainment of a higher incremental permeability. The Q-factor was mainly determined by the sintered density and microstructure. To summarize, a uniform and dense microstructure with relatively small average grain size is favourable for obtaining better dc-bias-superposition characteristics, including permeability and Q-factor.

Structural and magnetic properties of Ni0.15Mg0.1Cu0.3Zn0.45Fe2O4 ferrite prepared by NaOH-precipitation method

Abstract The Ni 0.15 Mg 0.1 Cu 0.3 Zn 0.45 Fe 2 O 4 ferrite powders have been prepared by NaOH co-precipitation method and characterized by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The XRD patterns confirm the single phase spinel structure of synthesized nanoparticles. The average crystallite size of the particles increases from 12 to 36 nm with calcining temperature ( T a ) from 500 to 800 °C. The saturation magnetization ( M s ) of the superparamagnetic particles was deduced by Langevin theory. Subsequently, the densification characteristics and magnetic properties of the low-temperature 950 °C-sintered ferrite bulk samples were also investigated. The magnetic measurement showed that the sintered bulk sample of T a = 600 °C has the highest initial permeability ( μ i ), lowest coercivity ( H c ), largest saturation magnetization ( M s ) and satisfactory thermal stability of μ i . The microstructures of sintered samples were examined using field emission scanning electric microscope (FESEM). The T a has significant influence on the bulk density, initial permeability, saturation magnetization and coercivity of Ni 0.15 Mg 0.1 Cu 0.3 Zn 0.45 Fe 2 O 4 ferrite.

Swelling of clay minerals in unconsolidated porous media and its impact on permeability

This work combines core-flood experiments with X-ray μ-computed tomography (μ-CT) to investigate the swelling of clay minerals and its impact on permeability of unconsolidated porous media. Both swelling (montmorillonite) and non-swelling (kaolinite) clay were added as coatings on soda lime beads and quartz grains. Clay content varied from 1.4 to 5.5wt.% in the montmorillonite-coated samples and from 2.0 to 6.8wt.% in the kaolinite-coated samples. Permeability changes were monitored as a function of time using pure water. Visualization of coated bead and grains columns by μ-CT provided quantitative information on morphological changes of clay grains/coatings among dry and water-saturated samples. All clay-coated samples showed a 10–40% decrease in permeability as compared to uncoated samples. In general, permeability decreases with increasing clay content. A 39% volume increase of montmorillonite particles was observed by μ-CT immediately after the sample was saturated with water, i.e. swelling occurred almost instantaneously after water–clay contact. In contrast, kaolinite particles had a 15% volume increase, which was primarily attributed to the hydration of clay pellets by water. The calculated porosity reduction associated with clay swelling ranged from 0.4% to 1.7% including both montmorillonite- and kaolinite-coated samples. This decrease in porosity was estimated to cause only a 2–5% reduction in permeability, primarily due to the high initial porosity and permeability of the selected samples. This study presents a baseline to estimate changes in permeability as a result of clay swelling for samples with variable clay content, grain size, and porosity.

Changes in porosity, permeability, water retention curve and reactive surface area during carbonate rock dissolution

Chemical reactions between fluids and the solid phase change porous media by dissolution and precipitation processes that modify the pore space geometry and associated hydraulic and chemical properties (saturated and relative permeability, porosity, capillary pressure curve, pore size distribution, reactive surface area). Knowledge of these properties and how they evolve with time is important for understanding and modelling multi-phase flow or reactive transport. Most published studies for reservoir rocks concentrate on the changes of porosity and saturated liquid permeability, but few data are available on the other parameters, and even less on their evolution during interaction with acidic solutions.We investigate the joint evolution of transport parameters of sedimentary carbonate rocks upon reaction with dilute acid (HCl). We first characterize the initial permeability, porosity and pore size distribution. We then attack the rock samples by permeation with HCl (pH3.5 or 4.1) and characterize them again after partial dissolution. Several dissolution-characterization cycles were performed on each sample in order to study the evolution and interaction of the different parameters.In two coarse calcite cores C1 (dissolved at pH3.5) and C2 (pH4.1) with high initial permeability, significant dissolution occurred only in pores with diameters greater than 0.022mm. Permeability increased very little even though porosities increased by 2.6–5.8%. In fine-grained dolomite cores, dissolution affected a broader range of pore sizes, down to 0.001mm in D1 (pH3.5), and down to 0.0066mm in D2 (pH4.1). A wormhole broke through in D1 after percolation of only 5000 pore volumes of acid. Effective reactive surface areas decreased by a factor of 240–250 in the cores dissolved at pH3.5, but only by a factor of 2–25 in the cores dissolved at pH4.1. A simple 1-D model was unable to simulate the evolution of the reactive surface during wormhole formation. Effective reactive surface area correlated negatively with permeability, and was consistent with the geometric area of the pores that carried most flux, which was calculated from the retention curves.

Temperature affecting the magnetic properties of the Co79−xFe3Cr3Si15Bx amorphous alloy

The paper studies the effect the temperature has on the magnetic properties of the Co79−xFe3Cr3Si15Bx amorphous alloy with different boron content. Magnetic saturation induction Bs and Curie temperature TC decrease as the boron content increases. Within the range of relatively high temperatures, magnetic saturation induction Bs=μ0Ms is related to the temperature by Bs(T)∼(TC−T)0.38. In the Co79−xFe3Cr3Si15Bx amorphous alloys with the Curie temperature of lower than 180°С the initial permeability of 200,000 and the coercive force of 0.1A/m were obtained. The high initial permeability of the amorphous alloy is attributed to the absence of the crystalline, magnetoelastic and induced magnetic anisotropy in this alloy. Low Curie temperature near which the permeability appreciably increases (Hopkinson effect) is another approach to the ideal magnetic softness.

Effects of co-dopants on the magnetic properties of Ni–Zn ferrites

Abstract In this study, substitution of co-dopants into the Ni 0.4 Zn 0.6 Fe 2 O 4 ceramic was performed. Al 3+ , Sn 4+ and Ti 4+ ions were added to the Ni 0.4 Zn 0.4 Li 0.10 Fe 2.10 O 4 ceramic to improve magnetic properties. After sintering, all samples were indexed on a spinel structure and no detectable second phase was observed. When the concentration of dopants increased, the grain size of the Ni–Zn ferrites increased from 1.40 to 6.05 μm and the saturation magnetization declined from 428.8 emu/cm 3 to 374.0 emu/cm 3 . Amongst the systems investigated, the Ni 0.4 Zn 0.4 Li 0.10 Al 0.050 Fe 2.050 O 4 , Ni 0.4 Zn 0.425 Li 0.10 Ti 0.025 Fe 2.050 O 4 , and Ni 0.4 Zn 0.450 Li 0.10 Ti 0.050 Fe 2.000 O 4 ceramics revealed promising magnetic properties for applications. The measured initial permeability and quality factor were respectively 291.9 and 45.1 for the Ni 0.4 Zn 0.4 Li 0.10 Al 0.050 Fe 2.050 O 4 ceramic, 316.9 and 42.5 for the Ni 0.4 Zn 0.425 Li 0.10 Ti 0.025 Fe 2.050 O 4 ceramic, 429.4 and 34.8 for the Ni 0.4 Zn 0.450 Li 0.10 Ti 0.050 Fe 2.000 O 4 ceramic. The high initial permeability and quality factor values associated with good electrical resistivity (>10 6 Ω-cm) qualify the ceramics for high frequency applications.

A Passive Impedance Matching Interface Using a PC Permalloy Coil for Practically Enhanced Piezoelectric Energy Harvester Performance at Low Frequency

This paper presents an analytical and experimental study of a passive impedance matching interface based on a large inductive reactance but with a centimeter-scaled size for practically enhanced piezoelectric energy harvester performance at low frequency. Low frequency vibration normally leads to a large capacitive reactance value for small-sized piezoelectric energy harvesters and it is impractical to achieve the maximum power transfer condition by use of a conventional inductor as its volume would be of a few cubic meters. In this paper, PC permalloy material was used to implement a passive impedance matching interface in order to reduce the size of the inductor to a few cubic centimeters as it has a very high initial magnetic permeability of 6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> H/m. The implemented interface is capable to practically perform the complex conjugate load matching of a macrofiber composite energy harvester at a frequency ≤10 Hz. The effects of the interface on the voltage, current, and power transferred to resistive loads were examined through comparisons of the results between configurations with and without the interface for applied strain levels and frequencies in the range between 480-1170-με peak-to-peak and 2.5-10 Hz, respectively. An increment of the power around 94.6% was obtained under an excitation of 480 με at 10 Hz in correspondence to an optimal resistive load reduced by over 70%. Compared with the state-of-the-art active impedance matching techniques, which use additional power sources to control the signal generated by piezoelectric energy harvesters, the developed interface is totally passive, easier to be implemented, and can be potentially used for the enhancement of vibration energy harvesting performance.