Value Of Initial Permeability Research Articles

Research on the blocking mechanism of oily sewage reinjection based on microfluidic technology

Reinjection into reservoirs to displace oil is an environmentally friendly and efficient way to treat and use produced oily sewage. However, the permeability damage to the reservoir by the small oil droplets in the oily sewage (usually called oil-in-water, OIW) is a huge challenge in oil industry. In this work, microfluidic device is designed to qualitatively and quantitively evaluate the OIW damage using both micro-homogeneous model and micro-heterogeneous model together with core flooding experiments. The results show that OIW can cause serious permeability damage (more than 60%) to the porous media after 50 PV sewage injection due to the adsorption and accumulation of oil drops in four main forms: oil droplet blockage, column oil blockage, cluster oil blockage, and blind oil blockage. To relieve the OIW damage, according to the composition of oil in the produced water, a new oily blockage removal system, which is composed of organic solvent, surfactant, and alcohol, is developed to solve the problem of pore blockage caused by OIW. The three components in blockage removal system cooperate with each other can effectively remove the blockage in pores caused by OIW, and the permeability recovered to more than 96% of the initial permeability values after 20 PV injection of blockage removal system.

Influence of V<SUB>2</SUB>O<SUB>5</SUB> Addition on the Magnetic Properties of Li-Zn Ferrites

The structural property, bulk density and porosity of V₂OSUB5/SUB (0.0, 0.4, 0.8 and 1.2 wt.%) added Li-Zn ferrites are observed along with the surface morphology. The samples have been prepared by the solid-state reaction technique and sintered at 1050 ℃. The X-ray diffraction patterns of the prepared samples have shown the single phase cubic spinel structure. A microstructural study demonstrates that the grain size increases up to 0.8 wt.% V₂OSUB5/SUB and slightly decreased thereafter for 1.2 wt.% V₂OSUB5/SUB addition. The saturation magnetization value increases from 44.0 to 50.3 emu/g as the V₂OSUB5/SUB content increases up to 0.8 wt.%. The decrease of magnetization for 1.2 wt.% V2O5 content is apparent and it is found to be 47.3 emu/g. This may be related to the dilution effect with the excess of non-magnetic V2O5. It is also observed that the value of initial permeability increases up to 0.8 wt.% V₂OSUB5/SUB.

Impact of the Surface Irregularities of NiFeMo Compacted Powder Particles on Irreversible Magnetization Processes.

One specific group of materials with excellent application potential are powder-compacted soft magnetic materials. These materials have been intensively studied by materials scientists to improve their magnetic properties. This work describes the influence of mechanical smoothing applied to Ni80Fe15Mo5 (wt.%) alloy particle surfaces before the process of compaction. The soft magnetic properties of compacted powders prepared from smoothed and non-smoothed particles were investigated using the following measurements: coercive field, permeability, excess loss, and Barkhausen noise analysis. We found that compactions prepared with smoothed powder particles exhibit a lower value of coercivity (4.80 A/m), higher initial (10,850) and maximum relative permeability (27,700), and low-frequency core losses (1.54 J/m3) in comparison with compactions prepared with non-smoothed particles.

Effect of plastic deformation on the phase composition and electromagnetic characteristics of the 321N austenitic steel (08Kh18N10T)

The changes in the phase composition and electromagnetic properties of the 321N chromium-nickel austenitic steel under plastic deformation by uniaxial tension are studied. As strain increases from 0 to 0.37, the content of ferromagnetic α′-martensite in the steel increases monotonically to 60%. The electrical resistivity and the initial magnetic permeability increase monotonically by factors of 1,25 and 18, respectively. To monitor the strain state and the content of α'-martensite in products made of the 321N steel, it is preferable to use initial magnetic permeability rather than electrical resistance. The skin layer thickness of the deformed 321N steel for frequencies from 5 to 1000 kHz is calculated from the experimental values of initial magnetic permeability and electrical resistivity. Eddy current diagnostics of the state of the surface of products made of this steel, hardened by surface plastic deformation, is proposed to be performed at frequencies ranging between 100 and 200 kHz.

Interaction of rock-bolt supports while weak rock reinforcing by means of injection rock bolts

Purpose is to analyze changes in shape and dimensions of a rock mass area, fortified with the help of a polymer, depending upon the density of injection rock bolts as well as the value of initial permeability of enclosing rocks to substantiate optimum process solutions to support roofs within the unstable rocks and protect mine workings against water inflow and gas emission. Methods. Numerical modeling method for coupled processes of rock mass strain and filtration of liquid components of a polymer has been applied. The model is based upon fundamental ideas of mechanics of solids and filtration theory. The problem has been solved using a finite element method. Its solution took into consideration both the initial permeability and the permeability stipulated by mine working driving, injection time of reagents and their polymerization, and effect of po-lymer foaming in the process of mixing of its components. Changes in physicomechanical and filtration characteristics of rock mass during polymer hardening were simulated. It has been taken into consideration that a metal delivery pipe starts operating as a reinforcing support element only after the polymer hardening. Findings. If three and five injection rock bolts are installed within a mine working section then stresses, permeability coefficients, pressure of liquid polymeric composition, and geometry of the fortified area of rock mass have been calculated. It has been shown that rock bolt location is quite important to form a rock-bolt arch. It has been demonstrated for the assumed conditions that if five injection rock bolts are installed within the mine working roof then close interaction between rock-bolt supports takes place; moreover, the integral arch is formed within the mine working roof. Originality. Dependence of change in the polymer reinforced area upon a value of initial permeability of enclosing rocks has been derived. It has been shown that in terms of low values of initial permeability, geometry of rock-bolt supports as well as its size is identified only by means of a value of the unloaded zone around the mine working. In this context, initial permeabi-lity increase results in the enlarged diameter of the reinforced rock mass area in the neighbourhood of the injection rock bolt. Practical implications. The findings are recommended to be applied while improving a method to support the mine working roof and decrease water inflow as well as gas emission from the rocks, being undermined, into the working.

Fe–Mn–Ga shape memory glass-coated microwire with sensing possibilities

The structural phase transformation in a non-stoichiometric shape memory Fe42.8Mn27.6Ga29.6 Heusler glass-coated microwire was experimentally observed using indirect magnetic, permeability, and electrical resistance measurements. While the temperature dependence of magnetization revealed hysteresis of magnetization during the heating and cooling process, magnetic hysteresis loops point to the change in the direction of the easy magnetization axis of the low- and high-temperature phase. Additionally, the unusual behavior of the permeability and electrical resistance measurements are in good agreement with the magnetic measurements. The x-ray diffraction profile measured at room temperature revealed the coexistence of a high-temperature L21 phase (a= 5.88 Å) and low-temperature phase with the L12 structure (a = 3.71 Å) and can be considered as another proof of the shape memory effect that is expected in the Fe–Mn–Ga-based Heusler alloys. In the presented glass-coated microwire, it is not only possible to shift the transformation temperature with the external magnetic field, but from its initial permeability value, it is possible to determine whether the alloy has undergone the structural transformation. Therefore, the presented Fe–Mn–Ga-based glass-coated microwire may be considered a suitable candidate for microactuators with sensory capabilities.

Effects of sintering temperature on microstructure, initial permeability and electric behaviour of Ni-Mn-Zn ferrites

The effects of sintering temperature on microstructure, initial permeability, and electrical behaviour of Ni0.5-xMnxZn0.5Fe2O4 (0.0 < x < 0.5) prepared using the precursor combustion method have been investigated. X-ray diffraction analysis confirmed the single phase cubic spinel structure of Ni0.5-xMnxZn0.5Fe2O4 (0.0 < x < 0.4) compositions sintered at 1100 °C. The Mn2+ substituent preferentially occupies tetrahedral sites as indicated by the Rietveld analysis and the increase in the IR absorption frequency of ν1 band with increasing Mn substitution. The SEM measurements have revealed homogeneous microstructures of the ferrites with narrow grain size distribution in the range 0.93μm–1.86 μm. Mössbauer spectra exhibit a superposition of two Zeeman sextets for the compositions x ≤ 0.2, a superposition of two Zeeman sextets, and a paramagnetic doublet for the compositions, x = 0.3 and 0.4, and one sextet and single quadrupole doublet for a composition, x = 0.5. The activation energy in the range 0.258 eV–0.612 eV suggests a polaron hopping type conduction mechanism in all the sintered ferrites. The dielectric constant in the range 0.057–55.21 and lower dielectric loss (10−2) imply better stoichiometry and homogeneity. The initial permeability increases at lower Mn substitution (x = 0.2) and exhibits a decrease as the Mn substitution increases. The dc resistivity, dielectric constant, and initial permeability values suggest the suitability of these ferrites for high frequency device applications.

Innovative Techniques in Underground Mining for the Prevention of Gas Dynamic Phenomena

In the last decades, rigorous research has been carried out with the end of understanding the gas dynamic phenomenon and although different preventive techniques have been employed, even today there are numerous accidents even with the loss of life. This work analyses an alternative and innovative method of fracturing and degassing coal, by generating CO2 with a pyrotechnic device called PYROC (Pyrotechnic Break Cartridges). Medium-scale tests of generation of CO2 into coal samples are carried out and their effect is analysed comparing the initial and final permeabilities of the coal samples once the generation of CO2 has finished. These permeabilities are calculated by injecting methane. Besides, the influence of different parameters as the length of the boreholes, the pressure of the gas or the initial permeability of the coal have been analysed with a numerical simulation of one face of one of the sublevels of a mine. The results show that the method increases the safety in mining operations because it fractures and degasses the coal, increases the permeability of the coal in the borehole of injection from 9.5 mD to 31 mD, decreases the methane gas pressure below pre-detonation levels for 1 min, achieves decompressed lengths between 8 and 10 m ahead of the face with pressures of injection of 50 MPa, relaxes the total length of the borehole for initial coal permeability values equal to or greater than 0.002 mD, and allows to work with low permeable coals with high induced stresses and high methane concentrations.

THMCD modeling of carbonate acdizing with HCl acid

Developing a Thermal–Hydrologic–Mechanical–Chemical–Damage (THMCD) coupling model for carbonate rock based on TOUGHREACT–FLAC3D simulator is innovatively put forward in this paper. In present study, a carbonate acidzing model with HCl acid, which considers thermal, fluid flow, mechanics, chemical reaction and mineral dissolution, and damage evolution, is carried out to explore the essence of acid fracturing. To consider the heterogeneity of rock materials, Weibull distribution function is adopted to consider the heterogeneity property of the carbonate in FLAC3D. The investigation results show that, initially the damage zone spreads uniformly within 5 m around the injection hole, then none-uniform propagation of the damage zone occurs due to the heterogeneity of the carbonate. The severely damaged areas are mainly concentrated around the injection hole, and the damaged area may extend about 10 m during carbonate acidizing with HCl acid. Based on the damage propagation principle, PH variation, ions concentration, temperature variation and permeability change are basically consistent with the damage distribution of the carbonate. The PH value within 5 m around the injection hole is relatively high due to the consume of the injected acid, and the minimum PH value is obtained at the periphery of the far damage zone during carbonate acidizing with HCl acid. The concentrations of the generated H + , Cl − , Ca 2 + and HCO 3 − are high in the vicinity of the fracturing hole, basically identical with the damage distribution of the carbonate. The magnitude of carbonate permeability in the damaged carbonate has increased dramatically compared with the initial permeability value. The new THMCD simulator leads to an enhanced elaboration of carbonate acidzing with HCl acid in oil engineering. • THMCD is carried out to explore the aessence of acid fracturing. • PH variation and permeability change are basically consistent with the damage distribution. • Permeability in the damaged carbonate has increased dramatically during acid fracturing.

Improvement of microstructure and initial permeability of Mn0.5Ni0.1Zn0.4GdxFe2-xO4 with sintering temperature

This article reports the effect of sintering temperatures on microstructure and magnetic properties of Mn0.5Ni0.1Zn0.4GdxFe2-xO4 synthesized by conventional solid state reaction technique and the sintering was performed in the temperature range of 1150 to 1350 °C. The sintered samples were characterized using several techniques. Initial permeability, RQF and magnetic loss factor were measured using impedance spectroscopy. Microstructural analysis and phase identification were analyzed using field emission scanning electron microscope and X-ray diffractometer, respectively. XRD patterns reveal the formation of spinel ferrites phase of all the compositions sintered at 1300 °C, as optimum TS. Average grain size and relative quality factor are found increased with the rise of TS and the highest value of average grain size and RQF are observed for TS = 1300 °C, beyond this temperature average grain size and RQF are found decreased slightly. Magnetic loss factor (tanδ) decreases gradually with the rise of TS. The initial permeability increases with TS and it is found that the value of initial permeability for TS = 1350 °C is more than 5 times higher than that of the value obtained for TS = 1150 °C.

Rietveld refined structure, ferroelectric, magnetic and magnetoelectric response of Gd- substituted Ni-Cu-Zn ferrite and Ca, Zr co-doped BaTiO3 multiferroic composites

The room temperature magnetoeletric coupling was investigated thoroughly in various xNi0.48Cu0.12Zn0.40Gd0.04Fe1.96O4 + (1-x)Ba0.985Ca0.015Zr0.10Ti0.90O3 multiferroic composites. Ferrite and ferroelectric phase of the composites have been prepared by the standard solid state reaction technique. Structural study was conducted by the X-ray diffraction (XRD) and the Rietveld refinement was adopted for further analysis of the structure. The refined XRD patterns confirmed all composites having a biphasic spinel-perovskite structure with Fd3¯m, and P4mm space group, respectively. Microstructural characteristics of all samples have been analyzed using Field Emission Scanning Electron Microscopy images. The magnetoeletricaly coupled composites is illustrated by an obvious modification in lattice, dielectric, ferroelectric and magnetic properties as a function of ferrite content. The dielectric constant of the composites was found to decrease with the addition of ferrite content in line with the theoretical estimations of the Bruggeman, Maxwell-Garnett, Lichtencker and Looyenga models, respectively. The dielectric constant and initial permeability were calculated theoretically using the different models and compared with the experimental values. The discrepancy between the calculated and experimental values of dielectric constant and initial permeability might be attributed to the diffusion of ions and interaction between two phases of the composites. The ac conductivity analysis revealed that the conduction mechanism is attributed to the small polaron hopping and also obeyed the Jonscher’s power law. Complex impedance was evaluated using the Nyquist plot which ensured the dominance of both grain and grain boundary resistance. The hysteresis loops (M-H and P-E) ensured the typical ferromagnetic and ferroelectric nature for all composites at room-temperature. Magnetic studies show an improvement of initial permeability, relative quality factor and magnetization, whereas magnetic loss gradually reduces with the increment of ferrite content. The maximum magnetoelectric response (~173 mVcm−1Oe−1) was found for x = 0.10 composite that could be utilized in the future multifunctional devices.

Impact of Sn4+ substitution in Mg–Zn ferrites: Deciphering the structural, morphological, dielectric, electrical and magnetic properties

From the viewpoint of enormous applications and research, ferrite materials have already been achieved the status of one of the important branches of materials science. In this report, we have tuned the physical properties of Mg–Zn ferrites by Sn substitution investigated using X-ray diffraction, field emission scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, electrical and dielectric properties and quantum design physical properties measurement system. The Mg0·5Zn0.5SnxFe2-xO4 (0 ≤ x ≤ 0.10) samples have been synthesized by the conventional ceramic technique. The studied ferrites exhibits the single-phase up to x = 0.08 where an increase in lattice constant was observed. The FESEM images revealed the microstructure and the energy dispersive spectroscopy (EDS) confirms the absence of any unwanted elements. The increase (decrease) in bulk density (porosity) was associated with the variation of average grain size. FTIR spectra confirmed the formation of spinel structure. The dielectric polarization or conduction mechanism in these materials is due to the hopping of charge carriers at the octahedral sites. The common dielectric behavior of studied compositions is also observed. The substitution of Sn ions leads to enhanced dielectric constant and ac conductivity due to increased hopping of charge carriers. Complex impedance spectroscopy study revealed the non-Debye type of relaxation process within the studied compositions with a dominant contribution from grain boundary resistance. The dynamic magnetic hysteresis loops are measured to obtain the magnetic parameters. The low values of coercivity revealed the soft magnetic nature of the studied compositions. The obtained saturation magnetization (Ms) for Mg–Zn ferrite (x = 0.00) is comparable with the prior result. Non-linear decrease of Ms (62-44 emu/g) due to Sn substitution is explained based on the variation of magnetic moments over A- and B-sites. The squareness ratio (Mr/Ms) revealed that the magneto-statical interaction is present within the synthesized samples. The constant value of initial permeability (μʹ) over a wide range of frequencies revealed the compositional stability and quality of the prepared ferrite. The variation of μʹ with Sn content is similar to that of Msvs Sn contents. Moreover, theoretical cation distribution and the effect of Sn substitution on the related parameters have also been studied. The studied parameters are compared with the reported results, where available.

Nanocomposites of ZnO mixed with different Ni-ferrite contents: Structural and magnetic properties

In this study two methods, solid-state (S–S) and sol-gel (S-G), were used to prepare ZnO/NiFe2O4 (assigned as ZnO/NF) hetero nanocomposites with different NF contents (0, 5, 10, 15, 20 and 25 wt %). The prepared composites were investigated using XRD, EDX, HR-TEM to study their structural and morphological properties. The obtained XRD patterns have been analyzed by employing the Rietveld refinement technique. The results confirmed the formation of ZnO/NF composites with individual characteristic peaks corresponding to both ZnO and NF, and no impurities were detected. HR-TEM images showed nearly spherical particles for all samples with an average particle size of 23–72 nm. The magnetic parameters were estimated from the measured hysteresis loops using a vibrating sample magnetometer (VSM). The samples showed typical ferromagnetic behavior with different saturation magnetization (Ms) and coercivity (Hc) depending on the NF contents and the preparation route. The values of initial permeability (μi) showed independent behavior on the frequency and its correlation with saturation magnetization Ms and particle size was discussed. The study may help in enhancing the magnetic properties of ZnO by doping with NF. The comparison between two preparation techniques may provide optimum conditions to be used in development of multiphase materials for various applications.

Effect of sintering temperature on the structural, morphological, electrical, and magnetic properties of Ni–Cu–Zn and Ni–Cu–Zn–Sc ferrites

Polycrystalline Ni0.3Cu0.2Zn0.5Fe2O4 and Ni0.3Cu0.2Zn0.5Sc0.05Fe1.95O4 compounds have been prepared by standard solid-state reaction technique and sintered at 1000, 1100, 1150, 1200, and 1250 °C for 5 h in air. The effect of sintering temperature on the structural, morphological, magnetic, dielectric, and electrical properties of these spinel ferrites has been studied thoroughly and comparatively. Formation of the single-phase cubic spinel structure of these compositions is confirmed by X-ray diffraction analysis. The lattice constant increases with sintering temperature as well as with 5% scandium (Sc3+) doping in Ni–Cu–Zn ferrite. Surface morphology reveals that the grain size increases with sintering temperature. Among the prepared ferrites, Ni0.3Cu0.2Zn0.5Sc0.05Fe1.95O4 has the maximum density (5.05 × 103 kg/m3) at sintering temperature 1150 °C, which gives the highest value of initial permeability. It is observed that initial permeability varies with sintering temperature, and it gives the maximum value at optimum sintering temperature. It is noted that Curie temperature decreases with 5% Sc3+ ions doping, whereas it slightly increases with increasing sintering temperature for both compositions. Ni0.3Cu0.2Zn0.5Fe2O4 compound shows the highest Curie temperature 418 °C. Dielectric constant, dielectric loss factor and AC electrical conductivity decrease with 5% Sc3+ ions doping in Ni–Cu–Zn ferrite. The initial permeability decreases sharply at Curie temperature, which indicates a high degree of compositional homogeneity. The ‘Hopkinson’ peak is observed just below the Curie temperature in the real part of initial permeability versus temperature graphs. The mechanism of dielectric polarization and electrical conductivity has been explained based on the electron hopping between Fe3+ and Fe2+ ions. The variation trend of complex impedance and AC electrical conductivity reveals the semiconducting behavior of the ferrite samples. Formation of partial semicircles in the Z/-axis indicates that relaxation process is non-Debye type. The investigated ferrites show relatively high initial permeability, low magnetic loss, and low electrical conductivity in a wide frequency range, which make them potential candidate for various practical applications such as small and compact power suppliers for computers, microprocessors, microwave electronic devices, etc.

Effect of divalent metal ions substitution on structural and magnetic properties of Li0.25Mn0.5-xMxFe2.25O4 (M = Co2+, Ni2+, Cu2+) spinel ferrites

In the existing study, substitution of different divalent metal ions in Li0.25Mn0.5-xMxFe2.25O4 (where, M = Co2+, Ni2+, Cu2+; x = 0.0, 0.1, 0.3 and 0.5) was performed to improve the magnetic properties. Their structural and magnetic features were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD analysis proved the presence of single phase cubic spinel structure in all prepared compositions. The lattice parameter decreased linearly with increasing doping concentrations. The crystallite size values vary from 60 to 101 nm. VSM studies revealed that saturation magnetization values of Li0.25Mn0.5-xMxFe2.25O4 were strongly affected by different metal ions substitutions, which is credited to the cationic arrangement on the lattice sites. The change in the magnetization with metal substitution was discussed by using Neél's two-sublattice model. Among the three investigated series, Li0.25Mn0.5-xCoxFe2.25O4 ferrite revealed a synergistic effect in improving the magnetic properties making it suitable for applications in microwave devices and magnetic recording media. The initial permeability μi was measured at elevated temperatures from 300 up to 890 K. The composition Li0.25Mn0.4Ni0.1Fe2.25O4 gave the highest value of initial permeability, indicating the material potential utility in TV deflection yokes. Curie temperature increased with the replacement of manganese ions by different metal ions. In general, the replacement of different divalent transition metal ions plays an important role in changing the structural and magnetic properties of Li0.25Mn0.5Fe2.25O4 ferrites.

Experimental measurement of permeability evolution in sandstone during hydrostatic compaction and triaxial deformation

The permeability of sandstone during hydrostatic compaction and triaxial deformation was measured using a rock triaxial servo-controlled system. The gas permeability was also measured using an integrated permeability and porosity test system to study the difference between gas and water permeability. The experimental results suggested that gas permeability is larger than water permeability by almost one order of magnitude. This phenomenon is due to the slippage effect. The modified permeability is much closer to the water permeability. An empirical exponential relationship can describe the stress-dependent permeability of sandstone, while a power law is suitable to describe the relationship between porosity and effective confining pressure. During triaxial deformation, permeability initially decreases and then begins to increase at an accelerating rate. The peak value of permeability is hysteretic to peak stress. The initial permeability, lowest permeability, peak permeability, and stable value of permeability all decrease with the increase of effective confining pressure. The volumetric strain has a great effect on permeability. The turning point where permeability starts to increase coincides well with the onset of dilatancy.

Effects of second milling time to the core loss of MnZn ferrites for high frequency application

The effect second milling time on the electromagnetic properties of MnZn ferrites has been studied up to MHz range. The average particle sizes of powder ranging from 1.49 to 1.16 μm were obtained by varying the second milling time from 72 to 324min. It is found that the total losses (Pcv) deteriorate when the second milling time over 252 min and the limit particle size is 1.21 μm. The value of initial permeability (μi) reduces by 20% when the particle size is 1.16 μm due to the uneven distribution of grain size, indicating that uniform microstructure demands suitable particle size. Meanwhile, the eddy current loss (Pe) and residual loss (Pr) dominate the total loss at 3 MHz playing a significant role in total losses. The hysteresis loss (Ph) and eddy current loss (Pe) deteriorate gradually at 3 MHz when the particle size is 1.21 μm at 100 °C. The residual loss increases greatly with the particle size decreasing at 3 MHz. An excellent MnZn power ferrite possessing high initial permeability (μi = 887), high saturation magnetic flux density (Bs = 531 mT) and low total losses (Pcv = 1940 kW/m3) at 3 MHz-50 mT is synthesized in this research.

Investigation of Room Temperature Mössbauer Spectroscopy and Initial Permeability Properties of Al3+ Substituted Cobalt Ferrites

In the present work, Al[Formula: see text] substituted cobalt ferrites (CoFe[Formula: see text]AlxO4, [Formula: see text], 0.4, 0.6, 0.8) have been synthesized via standard solid-state reaction technique. The incorporation of Al[Formula: see text] ions in cobalt ferrite has been shown to play an important role in modifying the magnetic properties. The room temperature (300[Formula: see text]K) [Formula: see text]Fe Mössbauer spectra reveals that the studied samples show two characteristic ferromagnetic zeeman sextets at A and B-sites at lower Al[Formula: see text] ion concentration (i.e., up to [Formula: see text]). However, a paramagnetic relaxation has been noted for higher Al[Formula: see text] substitution (for [Formula: see text] and 0.8) samples. The dependence of the Mössbauer parameters such as isomer shift, quadrupole splitting, line width and magnetic hyperfine field on Al[Formula: see text] ion concentration has also been noted. The variations in initial permeability over a wide frequency range (125[Formula: see text]kHz to 30[Formula: see text]MHz) at 300[Formula: see text]K have been recorded. The fairly constant values of initial permeability and the low values of the relative loss factor of the order of 10[Formula: see text] to 10[Formula: see text] over the wide frequency range are the important findings of the present work. The observed low values of relative loss factor at high frequencies suggest that the studied ferrites are promising materials to be used in microwave applications.

Low temperature ferromagnetic behavior and temperature dependent anomalous dielectric relaxation of Zn0.90Ni0.05Mn0.05O diluted magnetic semiconductor

We report structural, magnetic and temperature dependent dielectric properties of diluted magnetic semiconductor Zn0.90Ni0.05Mn0.05O prepared by solid state reaction technique. X-ray diffraction analysis revealed formation of single phase hexagonal wurtzite structure. Scanning electron microscopy and atomic force microscopy images indicated increase in grain size and roughness respectively with increasing sintering temperature. Field dependent DC magnetization at low temperature exhibited ferromagnetic ordering with coercivity ~ 6 × 104 A/m and remanence ~ 17 A/m. Complex initial permeability values were found to be positive for the measurement frequency range (1 kHz–120 MHz) with a relaxation at lower frequency. Temperature dependent DC magnetization and AC susceptibility followed curie law with curie temperature below 65 K. Temperature dependent dielectric constants ($$\varepsilon ^{\prime}\,\& \,\varepsilon ^{\prime\prime}$$) and loss tangents ($$tan\delta$$) measured for selected frequencies were found to be an increasing function of temperature and decreasing function of frequency. AC conductivity ($${\sigma }_{ac}$$) values were found to be an increasing function of frequency and temperature. Clear signatures of relaxations were observed in $$\varepsilon ^{\prime},\,\varepsilon ^{\prime\prime},$$ $$tan\delta$$ and $${\sigma }_{ac}$$ for temperatures above 200 °C.

Correlation between the magnetic properties and phase constitution of FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) high-entropy alloys

The as-cast FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) high-entropy alloys (HEAs) were produced by vacuum arc melting. The correlation between the magnetic properties and phase constitution of the HEAs was thoroughly investigated. The results reveal that all samples contain BCC plus FCC duplex phases and the addition of Ga can promote the formation of BCC phases. Energy dispersive spectroscopy (EDS) results revealed that Cu and Ga elements are enriched in the BCC phases and they are more seriously in the phase boundary regions. Furthermore, the magnetic properties are closely related to the phase constitution of the as-cast FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) HEAs. The values of saturated magnetization (Ms), maximum magnetic flux density (Bm), remanence (Br), coercivity (Hc) and hysteresis losses (Pu) increase with the increase of the volume fraction of BCC phases, while the values of initial permeability (μi) and maximum permeability (μmax) increase with the increase of the volume fraction of FCC phases. In addition, the mechanical property of FeCoNi(CuAl)0.8Gax (0 ≤ x ≤ 0.08) HEAs was also discussed in the work.