Reduction Of Saturation Magnetization Research Articles

Microstructural defects in hot deformed and as-transformed τ-MnAl-C

In this study, detailed microstructural characterisation has been conducted in both as-transformed and hot deformed samples of τ-MnAl-C using transmission electron microscopy. After hot deformation, true twins, dislocations, intrinsic stacking faults and precipitates of Mn3AlC are the main defects in the recrystallised grains. True twins and order twins were distinguished based on differences in their diffraction patterns. A significant fraction of non-recrystallised grains existed, which had microstructures based on combinations of high densities of true twins, dislocations, and deformation bands. The formation of the Mn3AlC precipitates was confirmed and related to the reduction of saturation magnetization and the increase in the Curie temperature of τ-MnAl-C after hot deformation. Antiphase boundaries, which are believed to act as nucleation sites for reverse domains, were not observed in the hot deformed sample.

Al2O3-10 wt% Fe composite prepared by high energy ball milling: Structure and magnetic properties

In the present work, Al2O3-10 wt% Fe composite powders were manufactured by mechanical alloy using different milling times. The morphology, structure and magnetic properties were carefully investigated and explained through the results of SEM, XRD (with Rietveld refinement), Mössbauer spectroscopy and magnetic measurements at low-temperatures. After 50 h of milling, the results reveal α-Fe particles uniformly distributed in Al2O3 and a decrease of the average particle size of Al2O3–Fe composite. Besides, XRD data show a decrease of crystallite sizes, accompanied by an increase of the lattice micro-strain. For samples milled for 30 h and 50 h, the Mössbauer spectra recorded at 300 K showed a superparamagnetic component related to very fine hematite crystallites with a maximum absorption relative area of 10%. The M − H curves recorded at 6 K showed a small reduction in saturation magnetization, and an improvement in remanence magnetization and coercivity field with milling time, while the M-T curve of the sample milled for 50 h shows a peak at 185 K, related to the Morin transition of the hematite phase.

Permeability Spectral Analysis and Determination of Microstructural Parameters for Mn0.7+xZn0.3SixFe2-2xO4 Series

In this communication, the compositional dependence of the real part (μ′) and an imaginary part (μ″) of complex permeability for polycrystalline compositions of ferrite series, Mn0.7+xZn0.3SixFe2-2xO4 (x = 0.1–0.3), over the wide frequency and temperature ranges has been discussed. The μ′ decrease with Mn-Si concentration (x) is mainly due to the reduction in saturation magnetization (Ms) and average grain size (D). The D decreases due to smaller solid solubility in the spinel structure and segregation of SiO2 at grain boundaries. The μ′(f) plots at 300 K show a relaxed type of spectra. The observed maximum in the vicinity of Neel temperature in μ′(T) curves is due to the relative rate of change of anisotropy constant and Ms values, whereas in μ″(T) plots it is because of the domain wall damping. The derived microstructural parameters related to grain structure have been discussed in a systematic manner.

Microstructure and magnetic properties of MnO2 coated iron soft magnetic composites prepared by ball milling

In this paper, Fe soft magnetic composites (SMCs) coated with MnO2 were prepared successfully by ball milling and following spark plasma sintering. The effect of MnO2 content on microstructure and magnetic properties for the Fe/MnO2 SMCs was investigated in detail. The analysis results show that a uniform MnO2 coating layer can be formed on the surface of the Fe particles via low speed ball milling with agate balls. When the MnO2 content increases from 0.0 wt% to 10.0 wt%, the thickness of the MnO2 coating layer exhibits a growth trend. As a consequence, the increased nonmagnetic phase leads to the magnetic dilution, finally resulting in the reduced saturation magnetization and deteriorated coercivity. Moreover, the enhanced resistivity induced by the increased thickness, significantly reduces the generation of the inter-particle eddy current, which leads to more stable permeability and lower total core loss at high frequencies. This study provides a novel insulating coating layer to reduce total core loss and is advantageous for the development of iron-based SMCs.

Low-field magnetic analysis for sigma phase embrittlement monitoring in thermally aged 22Cr duplex stainless steel

The aim of this study is to evaluate a new nondestructive method designated as Low-Field Magnetic Analysis (LFMA) based on the measurement of magnetic flux density for monitoring sigma (σ) phase precipitation in duplex stainless steel (DSS). In addition, the effect of isothermal aging treatment at 800 °C on the metallurgical degradation of UNS S31803 DSS was investigated. It was found a change in the volume fraction of α-Fe/γ-Fe phases due to α-Fe (ferromagnetic phase) eutectoid decomposition to precipitate sigma and secondary austenite (paramagnetic phases). A significant and gradual reduction of saturation magnetization was observed with the increase of thermal treatment time, indicating a decrease in the quantity of α-Fe phase. Two magnetic methods were used to verify the evolution of the σ phase: M−H measurements at 300 K using a commercial magnetometer and LFMA testing. Both methods were sensitive to small percentages of σ phase in the microstructure. Furthermore, our developed technique presents accurate results for low magnetic fields with high sensitivity and reliability.

Unveiling the Effect of Zn2+ Substitution in Enrichment of Structural, Magnetic, and Dielectric Properties of Cobalt Ferrite

This work reports the detailed structural characterization of Zn2+ ion-substituted cobalt ferrite nanoparticles (CFO NPs; Co1−xZnxFe2O4; x = 0.00, 0.25, 0.50, and 0.75), prepared using a facile sol–gel method. It correlates structural changes with magnetic and dielectric properties. The as-synthesized samples were investigated by X-ray diffraction (XRD) analysis, BET surface area analyzer, energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), Mossbauer spectroscopy, and impedance analyzer. The pristine sample (CFO) comprised of NPs with 25 nm size, which decreased up to 11 nm upon the formation of Zn0.75Co0.25Fe2O4. The N2 adsorption–desorption isotherm of the prepared Zn0.5Co0.5Fe2O4 sample confirmed the presence of a mesoporous structure. SEM images revealed that all prepared samples exhibited porous surface with honeycomb-like structures. The cationic distribution was described by Mossbauer spectra. The increment of Zn ions in the prepared samples resulted in sharp reduction of saturation magnetization and remanence values. The normal dielectric dispersion behavior was recorded and can be ascribed to the Maxwell–Wagner type polarization. Besides, the dielectric parameters varied by increasing Zn content in CFO NPs. This may be ascribed to O2 vacancies and Fe3+ ions in A- and B-sites. Dielectric studies revealed that, content of Zn ions beyond x = 0.25 was sufficient to reduce both dielectric constant and loss at low frequencies.

Ag8+ ion irradiation modulated structural, microstructural, defect, and magnetization in ZnO thin films

The irradiation effect of high energy silver ion (Ag8+) has been investigated on ZnO thin films to understand their impact on structural, microstructural, optical, electronic and magnetic properties. The RF sputtered pristine ZnO/Si thin films are polycrystalline and highly textured along (0 0 2) plane. The irradiated ZnO/Si samples showed enhanced structural and microstructural defects with irradiation time. The lattice parameters have reduced for irradiated ZnO thin films, suggesting structural deformation. The irradiation has resulted into enhanced defect density and strain in these thin films. A weak room temperature ferromagnetic moment (3.24 × 10−4 emu cm−2) has been observed, which has reduced drastically for Ag8+ irradiated samples up to 1.05 × 10−4 emu cm−2. The observed reduction in saturation magnetization has been attributed to the enhanced microstructural defects, lowering the free charge carriers and increasing the recombination centers simultaneously.

Magneto-dielectric effect in relaxor superparaelectric Tb2CoMnO6 film

We report magneto-dielectric properties of partially B-site ordered monoclinic Tb2CoMnO6 double perovskite thin film epitaxially grown by metalorganic aerosol deposition technique. Transmission electron microscopy and electron energy loss spectroscopy mapping shows the presence and distribution of both Co2+ and Co3+ ions in the film, evidencing a partial B-site disorder, which was further confirmed by the observation of reduced saturation magnetization at low temperatures. The ferromagnetic Curie temperature, TC=110 K, is slightly higher as compared to the bulk value (100 K) probably due to an in plane tensile strain. Remarkably, a short range ordering of spins at T*~190 K>>TC was established and assigned to the B-site disorder in the film. Two different dielectric relaxation peaks have been observed; they merge at the same temperature T* of short range spin correlations. Moreover, an unexpected high temperature dipolar relaxor-glass-like transition at T~T* was observed, at which a coupling to short range magnetic correlations results in a 4% magneto-dielectric coupling.

Substitution effect of Y3+ ions on the structural, magnetic and electrical properties of cobalt ferrite nanoparticles

Abstract Y3+-doped cobalt ferrite nanoparticles, CoYxFe2-xO4 (x=0.00, 0.05, 0.10, 0.15), were synthesized using the sol-gel auto-combustion technique. Single-phase cubic spinel structure was confirmed by the X-ray diffraction technique. The lattice parameter increased with the increase of Y3+ content in the cobalt ferrite and varied from 8.3876 to 8.4271 Å. FE-SEM images showed that the samples had distinct crystalline nanoparticles of spherical shape with small agglomeration. EDAX results showed good agreement with the particularized composition. Magnetic measurement using a vibrating sample magnetometer (VSM) recorded a reduction in saturation magnetization (Ms) and coercivity (Hc) by Y3+ substitution. The values of Ms and Hc ranged from 66.61 to 17.52 emu/g and 1168.9 to 801.9 Oe, respectively. The electrical properties of Y3+-substituted cobalt ferrite were studied by measuring the dielectric constant and loss. With increasing frequency, the value of the dielectric constant decreased, as a natural behavior of the ferrite material.

Study of structural, magnetic properties and bandgap of spinel Co1−xFe2+xO4 ferrite

Co1−xFe2+xO4 (x = 0.0–0.8) spinel nano ferrite dry gel powders were synthesized by sol gel auto-combustion method. Synthesized samples were investigated by using X-ray diffraction (XRD), magnetic measurements, Ultraviolet–visible (Uv–Vis); Fourier transform infrared (FTIR) spectroscopy. XRD validates the formation of spinel phase, and incorporation of Co, Fe in spinel lattice. Results reveal that compositional variation leads to: i) cationic re-distribution; ii) allowing fine-tuning of bandgap with strong correlation among Bandgap – Fe3+ ions on B-site; iii) changes in degree of inversion; iv) variation of disorder; v) shows better soft magnetic behavior; vi) surface spin disorder leads to reduction of saturation magnetization; vii) observed changes in Debye temperature suggest modification of lattice vibrations.

Study of structural and magnetic properties of Zinc-Substituted Cadmium ferrite nanocrystals

Polycrystalline CdxZn1-xFe2O4 ferrites with (x = 0.2 and 0.8) have been prepared by conventional microwave induce sol–gel method. The Calcination of samples was performed at 800 OC for 4 h. The prepared powder samples were structural and compositional characterized by XRD and FE-SEM. Rietveld refined XRD patterns exposed the cubic spinel phase. The magnetic property of prepared samples was investigated using VSM. Magnetization measurements have shown that the particles have superparamagnetic behavior at room temperature. The hysteresis curves of the sample exhibited the reduction of saturation magnetization and coercivity by Zn2+ ions substitution.

Modified co-precipitation process effects on the structural and magnetic properties of Mn- doped nickel ferrite nanoparticles

Manganese doped Nickel ferrites nanoparticles (NPs) have been synthesized by modified co-precipitation method for investigating the effects of adding dopant ions after formation of nucleation centers in the reaction medium. The structure and magnetic properties of the as-synthesized samples have been studied by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR) and Vibrating sample magnetometer (VSM). The structural results showed that all the samples have cubic spinel phase with the average 21 nm crystallite size. In addition, variation of the preferred XRD peak from (311) orientation to (440) occurred because of the compressive strain in the structure which was calculated by means of Williamson-Hall method (W–H). Adding dopant ions, after nucleation, caused strain, spin canting and reduction of saturation magnetization.

Synthesis and Characterisation of Copper Substituted Cobalt Ferrite Nanoparticles by Sol-Gel Auto Combustion Route

In the present study, the structural, functional, morphological and magnetic characteristics of copper substituted cobalt ferrite nanoparticles were investigated. The samples of Co1-xCuxFe2O4 at x = 0.06, 0.08 and 0.1 M were prepared by Sol-gel auto combustion route. X-ray diffraction technique was used to confirm the phase formation and structural analysis which matches with the JCPDS Data. The average crystallite size was found to be ∼25, ∼19 and ∼18 nm for x = 0.06, 0.08 and 0.1 respectively. The Micro Raman Spectroscopy revealed the stretching vibrations at 274 cm−1, 660 cm−1, and 466 cm−1, which are characteristic of Spinel Ferrites. From the FTIR analysis, the band observed at 3457cm−1 and 1650 cm−1 is assigned to hydrogen bonded O-H group and ionic stretching of C-H bond. The band assigned at 1105 cm−1, is due to Co – O and Cu - O or Fe – O vibrations. The existence of water adsorption band and metal oxygen band confirms the existence of Co and Cu in the synthesized sample. The surface morphology of samples was imaged by the field emission scanning electron microscope. The substitution of Cu2+ in the parent systems caused a significant reduction in particle size. The compositional analysis was done, which confirmed that the concentration of copper was increased in the samples. The samples were subjected to magnetic characterization because magnetic behavior is also affected by substitution of Copper in Cobalt ferrite. Magnetic hysteresis study at room temperature confirmed the reduction in saturation magnetization (MS = 14.25 to 8.33 emu/g.) and reduction in coercivity (HC = 602.64 to 380.94 Oe) when size is reduced. As the concentration of Cu into CoFe2O4 matrix increases, particle size decreases and the saturation magnetization decreases.

Tuning the microstructural, optical and superexchange interactions with rare earth Eu doping in nickel ferrite nanoparticles

A methodical study on structural, magnetic and optical properties of Eu doped NiFe2O4 nanoparticles with generic composition NiEuxFe2-xO4 (x = 0.00, 0.02, 0.04 and 0.06), synthesized via co-precipitation technique has been reported in this article. The fabrication of single phase ferrite nanoparticles was verified using X-ray powder diffractograms. The analysis of W–H plots revealed the presence tensile strain in the samples along with an average crystallite size of 20 ± 4 nm. The existence lowering of cubic symmetry at octahedral sublattices was detected by vibrational Raman spectra recorded at 300 K. The values of indirect optical band gap were noted in the range of 1.76 ± 0.02 eV. The hysteresis loops at room temperature supported the paramagnetic character of Eu3+ ions in spinel structure. The evidence of reduced A-O-B superexchange interaction along with reduction of saturation magnetization was also found for higher Eu content nanoparticles at 300 K. The coercivity was observed to increase at 5 K. The blocking temperature and thermo-magnetic irreversibility was reduced with increasing Eu concentration.

Highly Reduced Saturation Magnetization in Epitaxially Grown Ferrimagnetic Heusler Thin Films.

The key of spintronic devices using the spin-transfer torque phenomenon is the effective reduction of switching current density by lowering the damping constant and the saturation magnetization while retaining strong perpendicular magnetic anisotropy. To reduce the saturation magnetization, particular conditions such as specific substitutions or buffer layers are required. Herein, we demonstrate highly reduced saturation magnetization in tetragonal D022 Mn3–xGa thin films prepared by rf magnetron sputtering, where the epitaxial growth is examined on various substrates without any buffer layer. As the lattice mismatch between the sample and the substrate decreases from LaAlO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 to SrTiO3, the quality of Mn3–xGa films is improved together with the magnetic and electronic properties. Especially, the Mn3–xGa thin film epitaxially grown on the SrTiO3 substrate, fully oriented along the c axis perpendicular to the film plane, exhibits significantly reduced saturation magnetization as low as 0.06 μB, compared to previous results. By the structural and chemical analyses, we find that the predominant removal of Mn II atoms and the large population of Mn3+ ions affect the reduced saturation magnetization. Our findings provide insights into the magnetic properties of Mn3–xGa crystals, which promise great potential for spin-related device applications.

Interactive Studies on Synthetic Nanopolymer decorated with Edible Biopolymer and its Selective Electrochemical determination of L-Tyrosine

Herein, an edible biopolymer amine Modified Gum Acacia (MGA), successfully encumbered with Electron Beam irradiated Polypyrrole Nanospheres (EB-PPy NSs), was investigated for the effective role in L-Tyrosine (Tyr) biosensing application. The morphology of EB-PPy NSs decorated MGA (EB-PPy/MGA) hybrid nanobiocomposite has been studied by Scanning electron microscopy and its affirmed interactions were characterized by X-ray diffraction, Raman, FT-IR spectroscopy, UV-Visible spectroscopy, Thermo Gravimetric Analysis and Vibrating Sample Magnetometer. The hybrid nanobiocomposite manifested diamagnetic behavior with reduced saturation magnetization (Ms = 1.412 × 10−4 emu/g) to produce more adhesive surface. Amine chains in EB-PPy NSs and hydroxyl groups of MGA contributed to effective immobilization, thus enabling suitable orientation for Tyr determination. The electrochemical analysis illustrated that the proposed nanobiocomposite based sensor exhibited an excellent electrocatalytic activity toward selective determination of Tyr in the linear range of 0.4 to 600 µM with a lower detection limit of 85 nM, low oxidation potential of 0.72 V and good selectivity. Finally, the reliability of the constructed EB-PPy/MGA for Tyr detection was demonstrated in real samples.

Structural and magnetic properties of single domain CoFe2O4 magnetic nanoparticles dispersed in SiO2 matrix

Uniformly dispersed CoFe2O4 nanoparticles in SiO2 matrix have been synthesized in two-step process by a co-precipitation route at lower temperature (70 °C). Phase purity and average crystallite size of cobalt ferrite (CFO) and CoFe2O4 nanoparticles dispersed in SiO2 matrix (Si-CFO) have been evaluated to be 17.6 nm and 15.2 nm respectively. Bond edges and bond lengths were evaluated from Rietveld refinment confirms the existence of compressed and tensile strain in CFO and Si-CFO nanoparticles. The average particle sizes evaluated from transmission electron microscope (TEM) were found to be 16 and 17.3 nm respectively. Functional groups present in CFO and Si-CFO nanoparticles were investigated from Fourier transform infrared spectra (FTIR). Magnetic properties were investigated by vibrating sample magnetometry (VSM). Lower saturation magnetization (25.6) with enhanced coercivity (977) at room temperature has been observed for Si-CFO nanoparticles and attributed to the increased number of disordered surface spins with reduced effective magnetic anisotropy, enhanced stress and surface anisotropy. Strain in CFO and Si-CFO nanoparticles have been evaluated from magnetic measurements and corroborate well with the strain evaluated from Williamson-Hall-Isotropic strain model (W-H-ISM) and Williamson-Hall-Anisotropic strain model (W-H-ASM). Effect of specific saturation magnetization specific surface area and dead magnetic layer thickness on magnetic properties of pristine CFO and Si-CFO nanoparticles have been investigated. The enhanced specific surface area and dead magnetic layer thickness resulted in increased strain in Si-CFO with reduced saturation magnetization. The dead layer thickness is evaluated to be 1.34 nm and 1.96 nm for CFO and Si-CFO nanoparticles respectively.

Crystalline Co–Fe–B nanoparticles: Synthesis, microstructure and magnetic properties

A new approach for in-situ synthesis of crystalline Co–Fe–B nanoparticles was presented in which low temperature methods were developed by using metal chlorides and NaBH4 in an inorganic molten salt environment. Effects of different reaction systems/conditions on the phase formation, thermal behavior and microstructure were investigated. The melting point of reactants and impurities in final powders were reduced by the use of molten salt technique. After a reaction of CoCl2, FeCl3 and NaBH4 at 850 °C in sealed tubes, CoB and Fe3B phases formed separately. After a reaction under Ar flow; however, CoFeB2 solid solution nano powders were obtained in one step at 850 °C with an average size of 60 nm. After annealing at 1100 °C, stable and highly crystalline (CoFe)B2 solid solution phase with a Co:Fe molar ratio of 1:1 was achieved. As-synthesized particles exhibited ferromagnetic property, and possessed a narrow hysteresis curve characteristic of soft magnetic materials. Extended reaction temperature from 650 to 850 °C is seen to produce coercivity enhancement up to 500 Oe without significant reduction in saturation magnetization. On the other hand, after an annealing process and subsequent phase and chemical change, crystalline (CoFe)B2 particles exhibited superparamagnetic property.

An investigation of structural and magnetic properties of Ce–Nd doped strontium hexaferrite nanoparticles as a microwave absorbent

Ce-Nd-substituted M-type strontium hexaferrite nanoparticles, Sr(CeNd)x/2Fe12-xO19 (SCNH)(x = 0, 0.5, 1, 1.5, 2) can be successfully synthesized using co-precipitation method. The synthesized nanocomposites are characterized by X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FESEM), vibrating sample magnetometer (VSM). The vector network analyzer (VNA) were used to analyze microwave absorption property. For comparison, the microwave absorption properties of the samples were measured by two simulation and metal back methods. The XRD and FT-IR analysis confirmed the existence of the M-type strontium hexaferrite phase in all samples. FESEM shows that the morphology of the particle in all of the samples was roughly hexagonal shape and they had uniform distribution. The VSM results indicated that increasing amounts of doped Ce3+ and Nd3+ reduced saturation magnetization (Ms) and coercivity (Hc). The minimum Hc for Sr (CeNd)x/2 Fe12-xO19 (SCNH) (x = 0, 0.5, 1, 1.5, 2) was 2700 Oe. The VNA results showed that by measuring the permittivity and permeability at 5 mm thickness and simulating the RL for <5 mm thicknesses the maximum RL would be obtained as −8.7 dB at d = 2.5 mm and f = 11 GHz in X = 2 sample. While using the metal back approach by direct measurement of RL from S11 at d = 2.5 mm thickness, results in maximum reflection loss of −37 dB at 9.62 GHz with 1.93 GHz bandwidth in X = 2 sample. This could be attributed to microstructural non-uniformities, which have not been taken into account in RL simulating method, while the direct calculation of RL at each specific thickness (by measuring the S11) yields more realistic results. Totally the results showed that Ce–Nd doped strontium hexaferrite nanoparticles are suitable candidates as microwave absorbers.

PVA-doped NiNd Fe2-O4 nanoferrites: Tuning of dielectric and magnetic properties

Abstract Polyvinyl alcohol (PVA)-blended spinel phase NiNdxFe2-xO4 nanoferrites were successfully prepared with a different composition (x = 0.01, 0.03, 0.05, 0.07, and 0.09). The spinel cubic structure was revealed from X-ray diffraction pattern. These nanoferrites showed insulating behavior with an enhanced energy bandgap when compared with PVA-unblended nanoferrites. The obtained dielectric loss and real and complex dielectric constants were in the microwave region (frequency ∼2.9–5.95 GHz). Pseudocapacitance and resistive behavior were explored from impedance analysis. The magnetization hysteresis plot of nanoferrites showed a soft ferromagnetic nature. It was found that reduction in saturation magnetization of NiNdxFe2-xO4 nanoferrites obtained by PVA doping has the strong microwave absorption capacity.