Decrease In Magnetic Properties Research Articles

Investigation of BaTiO3/ Cu1-xMgxFe2O4 nano-multiferroic composites

In the present work, the citrate precursor approach has been used to generate nano-particle ferrites with the chemical composition Cu1-xMgxFe2O4 (where x = 0.0, 0.5, and 1). Multiferroic composites of BaTiO3 along with the three samples of Cu-Mg ferrites have been prepared using two percentages of BaTiO3 (30 % and 70 %) with each one of the three ferrites. X-ray fluorescence (XRF) and X-ray diffraction (XRD) have been used to characterize the samples under investigation, indicating that the intended samples have formed without impurities. The average particle size of the samples has been estimated from the XRD patterns (64.1 nm for BaTiO3, 85.8 nm for CuFe2O4, 83.5 nm for Cu0.5Mg0.5Fe2O4 and 89.2 nm for MgFe2O4) and have been fairly verified using a transmission electron microscope (TEM) too. A vibrating sample magnetometer (VSM) has been used to study the magnetic characteristics; where the maximum saturation magnetization is recorded for the Mg ferrite as 26.549 emu/g and the maximum coercive field is found for the Cu ferrite as 1085.13G. A variation of the examined samples from hard to soft ferrite has been noticed by introducing Mg such that we can conclude that the Cu0.5Mg0.5Fe2O4 and MgFe2O4 samples may be suitable for high-frequency devices. The decrease in magnetic properties with introducing BaTiO3 has been recorded too. The ferroelectric properties have been investigated and the results show a ferroelectric behavior of BaTiO3 that reveals its nanostructure. An enhancement of conduction current has been recorded by the addition of CuFe2O4, MgFe2O4, and Cu0.5Mg0.5Fe2O4. The maximum values of conduction current have been achieved the pure Mg ferrite and at the samples containing 70 % ferrites in the composite samples in agreement with literature. Finally, it is worth mentioning that the samples exhibiting lossy capacitor behavior may be used as piezoelectric actuators.

The Role of Concentration, Site, and O Vacancy on Magnetic and Optical Properties of Cu‐Doped Anatase TiO2

Cu‐doped is a dilute magnetic semiconductor with excellent electrical, magnetic, and optical properties. Herein, first‐principles methods are employed to investigate its electronic structure, magnetic properties, and optical behavior. The results demonstrate that Cu‐doped exhibits intrinsic ferromagnetism. The presence of O vacancies facilitates the ferromagnetic exchange between Cu ions by forming bound magnetic polarons (BMPs). This finding validates the BMPs model and explains for the decrease in magnetic properties during annealing under O2 conditions. As the concentration of Cu increases, the system undergoes a transition from a semiconductor to a metal. Cu ions exhibit a preference for a compact configuration and display either paramagnetism or antiferromagnetism. The spin polarization can be effectively controlled from 0% to 100% by adjusting the concentration and site of Cu. Additionally, Cu doping leads to a reduction in the bandgap and an extension of the absorption range into the infrared region. The absorption intensity is positively correlated with the concentration. The presence of a spin‐polarized intermediate band indicates a correlation between the spin of the excited electron and the energy of the absorbed photon. Overall, Cu‐doped shows significant potential for applications in spintronics and spin‐related optics, including photospintronics and spin photocatalysis.

Failure analysis on Nd-Fe-B under the multi-physical field coupling of permanent-magnet synchronous machines

In this paper, the Tesla meter and magnetic force microscope were used to study the open-circuit remanence and magnetic domain structure of Nd-Fe-B permanent magnets (PMs) in high-power density permanent magnet synchronous motors (PMSMs). An experimental platform was built to simulate the internal demagnetization environment of PMSM. Nd-Fe-B PMs were subjected to high temperature, DC demagnetizing field and alternating demagnetizing field. The results show that even when the working point of Nd-Fe-B PM is higher than the knee point, demagnetization still occurs in the simulated motor environment. The relationship between macroscopic magnetic properties and magnetic domain structure is investigated. With the decrease of open-circuit remanence, the average width and the magnetization of the magnetic domain in the magnetization direction decrease. Due to the width of the magnetic domain decreasing, the number of magnetic domains increases, and the area of the domain wall increases. As a transition region with weak magnetism, the increase of the domain wall area will lead to a decrease in magnetic properties. This work is helpful to understand the demagnetization mechanism of Nd-Fe-B magnets in the PMSMs.

Investigation of structural, magnetic and electrical properties of aluminum substituted Co-Mg ferrite

The effect of nonmagnetic Al3+ substitution on the structural, morphological, magnetic, and dielectric characteristics of Co0.5Mg0.5AlxFe2−x04 ferrite nanoparticles synthesized using the co-precipitation method was investigated. All samples were found to have a single-phase cubic spinel by X-ray diffraction. The decrease in crystallite size from 55 to 29 nm with Al3+ substitution validated the materials nano-crystalline formation. The infrared spectrum exhibits two distinct absorption bands matching to the spinel structure as well as two extra absorption bands and a shoulder between 360 and 265 cm−1. The DSC exothermic peaks around 440 °C may be attributed to the phase shift of the prepared samples from amorphous to the crystalline state. The TEM results were used to investigate the sample shape and quantify particle size demonstrating that increasing the Al3+ content induces a decrease in particle size. The VSM technique revealed a decrease in magnetic properties which was attributable to an increase in nonmagnetic Al3+ ions. The magnetic permeability is found to rise with increasing Al3+ content as the anisotropy constant decreases. Dielectric characteristics were investigated at room temperature in the frequency range of 0.1 Hz–20 MHz. The presence of polaron type conduction in the prepared samples was confirmed by the ac conductivity. These produced nanoparticles dielectric characteristics demonstrate their utility in high-frequency device development applications and electronic device production.

Synthesis of barium hexaferrite templated by nanocrystalline cellulose extracted from luffa acutangula fiber

Nanocrystalline cellulose templated barium hexaferrite has been prepared by sol-gel auto combustion and calcination method. Nanocrystalline cellulose template of 0, 0.5%, 1.0%, and 1.5% (w/v) were used to synthesize barium hexaferrite. The XRD pattern and TEM observation reveal the crystalline phase formation of hexagonal barium ferrite. Cellulose template changes the microstructure and properties of barium hexaferrite. Adding cellulose template of 0.5% (w/v) produce well-defined hexagonal platelet barium ferrite without impurity while adding more template result in barium hexaferrite containing hematite and excess cellulose template causing the decrease in magnetic properties. The crystallite size reduces with the addition of the cellulose template. The saturation magnetization and magnetocrystalline anisotropy are estimated using the Law of Approach to Saturation magnetization. The maximum values of saturation magnetization and magnetocrystalline anisotropy are 57.43 ± 0.25 emu g−1 and (4.64 ± 0.1) × 105 erg cm−3.

Influence of laser powder bed fusion process conditions and resulting microstructures on the electromagnetic properties of a 16MnCr5 steel

Abstract 16MnCr5 steel parts were additively manufactured by laser powder bed fusion in order to investigate the effect of microstructure on electromagnetic properties. As process parameters have a direct impact on the obtained microstructure, different conditions were used to manufacture samples on which magnetic and electrical tests were conducted. The obtained results were presented and discussed in terms of density, microstructure and electromagnetic properties. Finally, correlations have been demonstrated between the microstructure and the electromagnetic performances. Lower magnetic and electric properties were obtained with the higher porosity rates at low volume energy density. The microstructural effects were evidenced, through a decrease in magnetic properties with grain orientation, and an improvement with stress relief annealing.

Preliminary Quality Control of Magnetic Materials for applications in Restorative Medicine - Quantitative Analysis of Structural Homogeneity of RE-M-B /Polymer Composites

The properties of bonded magnetic materials (RE-M-B /polymer magnetic composites) depend not only on the magnetic properties of powder, but also on the parameters of the consolidation process and the type of binder. Increasing the binder content in RE-M-B /polymer composites could be very beneficial from the cor-rosion resistance point of view, which, unfortunately, is not conducive to the magnetic properties improve-ment. Therefore, a compromise between both trends is necessary to obtain a material with adequate corro-sion resistance with an acceptable decrease in magnetic properties. In the paper the results of research un-der Nd12Fe77Co5B / biotolerant-polymer composites with different binder content have been presented. The research has been carried out on Nd12Fe77Co5B / biotolerant-polymer composites with 20 and 10 wt. % of binder. Due to the possibility of using the magnetic material in restorative medicine, as a binder the bio-tolerable polymeric material has been used (acrylate). All results has been compared to previously deter-mined measurements for composite with a binder content about 3 % wt.. It has been found that the content of 10 % wt. bio-tolerable polymeric material in the magnetic composite is the most favorable (optimal) - the binder material is evenly distributed throughout the composite volume.

Effect of punching edge deformation on the magnetic properties of Fe49-Co49-V2 alloy

The rotor and the stator of electrical machines consists of an assembly of soft magnetic laminates typically fabricated by punching from the thin sheets. In this work, the effect of edge deformation on the magnetic properties of laminates resulting from the punching of Fe49-Co49-V2 alloy thin sheets is investigated. Ring samples with varying circumference to area ratios, defined by a CTAR index, were made by punching and subsequently annealed to optimize the magnetic properties. The magnetic properties of the annealed samples were investigated for its correlation with the microstructure. It was found that the magnetic performance of Fe49-Co49-V2 alloy decreases with increasing volume of edge deformation, corresponding to an increasing CTAR index. The deterioration in the magnetic properties can be attributed to the high density of recrystallized grains along the edges of the Fe49-Co49-V2 samples. These recrystallized grains are significantly smaller than those away from the edges and pose a higher degree of restriction to the magnetic domain wall movement. The decrease in magnetic properties from edge damage can be mitigated by increasing the annealing time to allow for grain growth at the edges.

Magnetic transformation of Zn‑substituted Ni–Co ferrite nanoparticles

A series of ferrite samples with the compositional formula, Ni0.2ZnxCo0.8−xFe2O4 (x = 0.0, 0.2, 0.4, 0.6 and 0.8), was prepared using the citrate-based sol–gel method for the better understanding of zinc doping on the structural and magnetic properties. X-ray diffraction (XRD) studies of the samples showed single-phase ferrite cubic structure without any secondary phases, with the average crystallite size D = 103–130 nm for the samples heat-treated at 950 °C. TEM micrograph shows nearly sphere-shaped particles with particle size consistent with the XRD results. The lattice parameter increased linearly with increasing Zn2+ ion content. Fourier transform infrared (FT-IR) measurements also confirm the formation of the cubic spinel structure of ferrite. The ferrite samples were observed by scanning electron microscopy (SEM) to be spherical nanoparticles. The surface morphology and stoichiometric ratio of the compositional elements were analyzed by scanning electron microscopy equipped with energy-dispersive spectroscopy (EDS). EDS showed that the elemental ratios were stoichiometric. The static magnetism of the magnetometer was studied by using a vibrating sample magnetometer (VSM). An examination of the magnetic properties revealed an increase in saturation magnetization with increasing Zn concentration up to x = 0.2 and a decrease thereafter. These results could be explained using Neel’s collinear two-sub-lattice model and three-sub-lattice non-collinear model suggested by Yafet and Kittel. The magnetic cubic anisotropy constant determined by the law of approach to saturation decreased with increasing Zn content. For Zn-substituted Ni–Co ferrites, the magnetic properties decrease obviously with the increase in Zn2+ ion content. This rapid decrease in magnetic properties reveals that the magnetic properties of Zn-substituted nickel–cobalt ferrite have realized the transition from hard magnetism to soft magnetism. The smaller coercivity value confirms that soft ferrite has been obtained. Meanwhile, this transition from hard magnetism to soft magnetism can be used as a potential high-frequency soft magnetic material.

Research and development of technology for laser configuration of sensitive element of fluxgate inclinometer

The paper presents the results of thermodynamic analysis of oxidation processes occurring during laser treatment of amorphous magnetically sensitive ribbon (71KNSR) in air and in the atmosphere of argon. Kinetic assessment of the rate of chemical reactions is based on the Arrhenius equation. The results of analytical calculations show that the decrease of magnetic properties of the alloy after laser treatment in the air is mostly determined by the formation of iron oxides Fe2O3 and Fe2O4. Chemical elemental analysis of the composition of the samples after laser configuration in argon shows a significant decrease in their composition of oxygen compared to samples configured in the air. Analysis of samples using scanning electron and magnetic force microscopy confirms the preservation of the magnetic properties after treatment in argon. The developed technology is used for the manufacture of a sensitive element of a fluxgate inclinometer.

Effect of WC addition and cooling rate on microstructure, magnetic and mechanical properties of Ti(C0.6,N0.4)-WC-Mo-Ni cermets

Ti(C0.6,N0.4)-8Mo-xWC-25Ni (x = 0, 3, 6 and 9 wt%) cermets were synthesized under different cooling rates by vacuum sintering. The influence of WC addition and cooling rate on microstructure, magnetic and mechanical properties of the as-prepared Ti(C,N)-based cermets was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The results revealed that the grain size of the Ti(C,N)-based cermets became finer with WC addition. Furthermore, room-temperature saturation magnetization (Ms), remanence (Mr) and Curie temperature (Tc) of the Ti(C,N)-based cermets initially decreased with increasing WC content, followed by a gradual increase. Cermets bacame paramagnetic at x = 6 under the cooling rate of 2 °C/min, x = 6 and 9 under the cooling rate 35 °C/min, respectively. The decrease in magnetic properties could be ascribed to the enhanced solid solubility of alloy elements in Ni-based binder phase. Moreover, the hardness and transverse rupture strength (TRS) of the Ti(C,N)-based cermets initially increased and followed by a gradual decrease, whereas the fracture toughness initially decreased followed by an increase with increasing WC content. At the same value of x, the Ti(C,N)-based cermets exhibited better magnetic and mechanical properties at the cooling rate of 35 °C/min than that at the cooling rate of 2 °C/min, which could be attributed to the grain refinement strengthening and solid-solution strengthening of the binder phase.

Optical, magnetic and structural properties of Cr-doped ZnO thin films by sol–gel dip-coating method

Cr-doped ZnO thin films are deposited by sol–gel dip coating. The effect of Cr on the structural, magnetic and optical parameters of zinc oxide films is studied. X-ray diffraction patterns of Cr-doped ZnO thin films are found to have a hexagonal wurtzite structure of ZnO. The bandgap energy of the Cr-doped ZnO thin films is calculated by the Tauq method. Crystallite size is evaluated by the Scherrer and Williamson–Hall relation. Both show that crystallite size enhances with an enhancement in Cr doping. The bandgap energy of the Cr-doped ZnO thin films is decreased by increasing the Cr dopant. The films are found to be ferromagnetic with a decrease in magnetic properties with an increase in Cr content.

Characterization of the interface reaction zone between iron and NiZn ferrite in a composite material - Study of a silica layer as a diffusion barrier

Iron-ferrite composites fabricated by powder metallurgy processes were studied for electromagnetic and large band microwave absorption applications. The sintering behavior of such composites is not well-understood, and these materials have been found to lose their magnetic properties or mechanical properties. Different systems of Fe/NiZn ferrite composites were investigated in order to better understand the chemical reactions that occur between oxide spinel and iron particles during the fabrication process. Three different systems, two models and one reference material were studied to analyze the chemical reactions in the aforementioned fabrication process. The first model consisted of iron films deposited by Physical Vapor Deposition (PVD) onto an NiZn-ferrite substrate. The reference material was made of a mixture of hot pressed iron and ferrite powders. In the second model, a SiO2 layer was deposited by PVD onto the NiZn-ferrite substrate, followed by iron deposition by PVD to study the role of SiO2 as a diffusion barrier. The materials were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dilatometry, electron probe microscopy analysis (EPMA) and X-ray diffraction (XRD). For the Fe/NiZn ferrite systems, the experimental results showed (i) an oxido-reduction reaction above 600 °C that produced FeO and FexNi1-x phases and (ii) a diffusion process of Ni and Zn. The combination of diffusion and oxido-reduction reaction induced the total consumption of the initial phase and a considerable decrease in magnetic properties. By adding a silica layer between the iron and ferrite layers, the redox interfacial reaction and iron diffusion were prevented at temperatures up to 800 °C.

Temperature Dependence of Magnetic Hysteresis Loop of NdFeB with Uniaxial Anisotropy by LIBS Technique

Laser-induced breakdown spectroscopy (LIBS) has been investigated as a potential analytical tool for better understanding the role of sample temperature and magnetization on the optical emission of laser-induced plasma for NdFeB sample. The mechanism of optical emission by increasing of sample temperature (Ts) and plasma confinement including shock wave in the presence of magnetic field is discussed. The heated samples show a significant decrease in magnetic properties, especially the coercivity and saturation of magnetization. The coercivity and saturation of magnetization of NdFeB were 15000 Oe and 95 emu/g, respectively. The intensity of emission lines decreased with an increase in Ts for NdFeB sample. The coercivity and saturation of magnetization of samples was monotonically decreased and caused to decrease in LIBS signal intensities.

Influence of annealing temperature on the Dy diffusion process in NdFeB magnets

Sintered NdFeB magnets were coated with a layer of Dy metal using electron beam evaporation method and then annealed at various temperatures to investigate the temperature dependence of Dy diffusion process in NdFeB magnets. A Dy-rich phase was observed along the grain boundaries after the grain boundary diffusion process, the diffusion coefficients of various temperatures were obtained, the diffusion coefficients of Dy along the grain boundaries at 800°C and 900°C were determined to be 9.8×10−8cm2s−1 and 2.4×10−7cm2s−1, respectively. The diffusion length depended on the annealing temperature and the maximum diffusion length of approximately 1.8mm and 3.0mm can be obtained after annealing at 800°C and 900°C for 8h. Higher diffusion temperature results in the diffusion not only along the grain boundaries but also into grains and then decrease in magnetic properties. The optimum annealing conditions can be determined as 900°C for 8h. The coercivity was improved from 1040kA/m to 1450kA/m and its magnetization has no significant reduction after the grain boundary diffusion process at the optimum annealing conditions.

Ferromagnetic composites with polymer matrix consisted of nanocrystalline Fe-based filler

ObjectiveThe paper intends to present structural and magnetic behavior of ferromagnetic composites consisted of nanocrystalline powders obtained by annealing and milling of Fe78Si9B13 and Fe73,5Cu1Nb3Si13,5B9 metallic glasses. MethodsThe as-cast ribbons were subsequently milled using a high-energy ball mill. The prepared powders were separated into fractions with a particle mean diameter range of 200–500µm, 75–200µm and 25–75µm and then annealed to obtain the nanocrystalline powder materials. The powder particles were mixed and consolidated with a polymer to obtain composites in the form of the toroidal cores. The following experimental techniques were used: scanning and transmission electron microscopy, X-ray diffraction and vibration sample magnetometry. ResultsThe analysis of magnetic properties of the powders and the composites prepared from the powders revealed that the preparation process caused significant decrease in magnetic properties in a relation to ribbons in as-cast state. ConclusionThe structure and magnetic properties of the examined materials could be improved by means of a right choice of milling time as well as a thermal treatment and by a decrease of the demagnetization effect. Practice implicationsThe amorphous and nanocrystalline powders obtained by a milling of metallic glasses are an alternative to solid alloys and make it possible to obtain the ferromagnetic nanocomposites with controlled magnetic properties.

Magnetic and RF-electromagnetic absorbing study of aluminum doped nickel ferrites prepared by two techniques

Pure phase aluminum doped nickel ferrite nanoparticles [NiAlxFe2−xO4] with x = 0.0, 0.25 and 0.5 have been investigated for magnetic and electromagnetic absorbing properties in S band and influence of Al3+ ions has been studied. Nickel aluminum ferrites have been synthesized by co-precipitation and sol–gel auto combustion routes. Magneto-dielectric properties were measured in terms of complex permeability (μ*) and complex permittivity (ϵ*) at 300 K in the frequency range of 1 MHz to 3 GHz using RF material/impedance analyzer. Dielectric permittivity (ϵ′ and ϵ″) has been observed to decrease with the increase in applied frequency and concentration of aluminum ions (x = 0.0–0.5). Magnetic permeability (μ′ and μ″) has been found to decrease with the increase in aluminum ions concentration. Electromagnetic absorbing properties were studied for all the samples by calculating the reflection losses (RL) in the frequency range of 1 MHz–3 GHz using the permittivity and permeability measurements in accordance with the transmission line theory. RL (dB) values lie in the range of −42 dB to −57 dB. RL values (> −10 dB) confirm more than 90% absorption of electromagnetic waves incident normal to the material surface. Aluminum doping has increased the RL values from −45 dB to −57 dB along with the shift of RL dip towards the higher frequency side for the samples prepared by sol–gel auto combustion technique. Magnetic properties have been studied by vibrating samples magnetometer (VSM) at room temperature and a decrease in magnetic properties has been observed due to increase in x from 0.0–0.5.

A large domain wall pinning effect on the magnetic properties of ZrO2 added Mn–Zn ferrites

The effect of ZrO2 addition on the microstructure and magnetic properties of Mn–Zn ferrites was investigated. The results indicated that the initial permeability (μi), saturation induction (Bs) and power loss (PL) were significantly improved when the ZrO2 concentration was 0.02wt%. A number of irregular particles were well dispersed on the surfaces of grains when the ZrO2 concentration exceeded 0.02wt%. The irregular particles were considered to be agglomerated ZrO2 particles, and their precipitation process was observed. The pores along with ZrO2 particles on the surfaces of grains had a large pinning effect on the domain wall, which thus caused the decrease of magnetic properties. Non-magnetic Al element was detected, which indicates that a small amount of Al2O3 may dissolve in ZrO2. The optimal values of μi (2322), Bs (522mT) and PL (386kW/m3) were obtained, which shows a great promise for switched-mode power supply (SMPS) applications.

Effect of aluminum substitution on the structural and magnetic properties of cobalt ferrite synthesized by sol–gel auto combustion process

Aluminum substituted cobalt ferrite powders (CoFe2−xAlxO4) with varying composition from 0.0 to 1.0 in the step of 0.2 have been obtained by sol–gel auto combustion technique using citric acid as a fuel. The metal nitrate to fuel ratio was maintained 1:4 throughout the synthesis of CoFe2−xAlxO4. The thermal analysis of as prepared samples is done by TGA technique. The compositional stoichiometry of the prepared samples is confirmed by Energy dispersive X-ray analysis technique. Single phase cubic spinel structure and nano phase structure of the synthesized powders were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallite size of 16–26nm was obtained using Scherrer formula. SEM analysis shows the formation of uniform grain growth. The grain size obtained from SEM results is of the order of 30nm. Maximum specific surface area was observed to be of the order of 52m2/gm. The highest value of saturation magnetization and coercivity was observed for pure cobalt ferrite sample and it decreases as the aluminum content x increases. A strong co-relation between the saturation magnetization and aluminum content was observed. The decrease in magnetic properties is due to the substitution of aluminum ions in place of Fe3+.

Microstructure and magnetic properties of NdFeB magnet prepared by spark plasma sintering

Nd 15Dy 1.2Fe balAl 0.8B 6 magnet was prepared by spark plasma sintering (SPS) technique. Sintering between 810 and 830 °C and consequent tempering result in relatively high magnetic properties and sintering density, which are comparable to the conventionally sintered ones. Further increase of sintering temperature gains a slight increase in sintering density and decrease in magnetic properties. Grain size of NdFeB prepared by SPS is fine and uniform, which is much smaller than that of conventionally sintered ones. Continuous thin film of the Nd-rich phase is formed along the grain boundary and the density of magnet is increased through tempering, which is the main reason for improving the magnetic properties. Furthermore, TEM observations indicate a conversion of crystal structure of the Nd-rich phase at triple junction site after tempering.