Magnetic Properties Of Powders Research Articles

Effects of Misalignment of c-axis on the Properties of Hydrogenation-Disproportionation-Desorption-Recombination Particles.

Hydrogenation-Disproportionation-Desorption-Recombination (HDDR) Nd2Fe14B particles have excellent magnetic properties, but the magnetic properties of powder are not uniform across different particle sizes. The remanence and maximum magnetic energy products of samples with a particle size of 120 μm are 14.0 kGs and 41.35 MGOe, while the products of samples with a particle size of 60 μm are only 13.3 kGs and 36.31 MGOe. The macroscopic morphology of HDDR Nd2Fe14B particles and the gradient distribution of microstructures in different micro-regions were observed. By modifying the macroscopic morphology of the particles, the poorly oriented clusters on the surface of the particles were precisely eliminated, and the remanence and maximum magnetic energy products of the particles increased to 14.5 kGs and 45 MGOe, respectively. Compared with the original particles, the samples after mechanical grinding had better grain arrangement. The effects of the nanocrystalline c-axis and field misalignment angle θ on the magnetic properties of HDDR Nd2Fe14B particles were investigated through micromagnetic simulation. The targeted removal of macroscopic defects on the particle surface contributed to a 3.6% increase in remanence and an 8.8% increase in the maximum magnetic energy product, offering a promising approach to enhance the microstructure of high-performance HDDR Nd2Fe14B particles.

Effects of Cr doping and size reduction on the structural and magnetic properties of α–CoV2O6

We report the effect of Cr-doping on the structural and magnetic properties of powder α–CoV2O6 samples. Samples were synthesized using a wet chemical synthesis method and calcined at temperatures between 350 ℃ and 500 ℃ to promote phase formation. For α–CoV2O6 and Cr-doped α–CoV2O6 samples, a single phase only occurs when the samples are calcined at 450 ℃ and 500 ℃, respectively, as confirmed using powder x-ray diffraction (XRD). Cr-doping results in a compression distortion of the lattice along the c-axis. Transmission electron microscopy (TEM) measurements indicate that Cr-doping causes a reduction in particle size and particle agglomeration. Metamagnetism was observed in field dependence of magnetization, M(μ0H) for α–Co(V1−xCrx)2O6 samples with 0 ≤ x ≤ 0.05. The hysteresis in M(μ0H) curves for μ0H < 5 T at 2 K indicate that the magnetization is metastable and suggests magnetic irreversibility. Zero-field-cooled (ZFC) and field-cooled (FC) temperature dependence of magnetization, M(T), show antiferromagnetic (AFM) ordering of the α–Co(V1−xCrx)2O6 samples at fields, μ0H ≤ 1 T. Increasing field strength to 2.5 T causes a transition from the AFM state to a ferrimagnetic (FI) state, and an introduction of spin-glass (SG)-like behavior. At 5 T, a transition from the FI state to a ferromagnetic (FM) state and a suppression of SG-like behavior is observed.

Two-step combustion synthesis of single-phase mesoporous ScFeO3 with bixbyite structure and magnetically soft behavior

In this paper, we consider the possibility of obtaining cubic bixbyite-type scandium ferrite in the form of phase-pure nanopowders. The samples were obtained by solution combustion method with either lack or excess of fuel and represented an X-ray amorphous phase according to the X-ray diffraction (XRD) results. To obtain cubic scandium ferrite, the samples were subjected to heat treatment at 700 °C, determined using DTA/TGA. The XRD data analysis confirmed the formation of cubic scandium ferrite with an average crystallite size of ∼20 nm for the sample obtained with a lack of fuel and 13 nm with an excess of fuel. According to the low-temperature nitrogen adsorption-desorption technique, the specific surface of the mesoporous samples decreased after annealing from 39.7 m2/g to 20.5 m2/g for the sample obtained with a lack of fuel and from 82.7 m2/g to 34 m2/g for the sample obtained with excess fuel. Scanning electronic microscopy (SEM) results demonstrated the foam-like morphology of nanopowders and no significant changes in their microstructure after heat treatment. The magnetic properties of powders that have undergone heat treatment have been studied. Narrow M-H hysteresis loops and low values of the coercive force indicate ferromagnetic behavior of the synthesized nanoparticles, which is supported by low values of the coercive force (Hc = 345 Oe and 769 Oe), remanent magnetization (Mr = 0.65 emu/g and 0.26 emu /g) and saturation magnetization (Ms = 1.69 emu/g and 0.26 emu/g) for lack and excess of fuel, respectively. The obtained materials are classified as magnetically soft and can potentially be used in the creation of transformers, magnetic screens, magnetic memory systems, radio engineering, and computer technology.

A Novel In Situ High‐Temperature Magnetometry Method for Radiofrequency Heating Applications

AbstractRadiofrequency heating of magnetic particles promises highly efficient and direct heating of catalytic reactors for coupling of low carbon electricity with energy intensive chemical transformations. In this work, a novel real‐time and in situ magnetometry method is developed to measure minor and major hysteresis loops of soft magnetic nanopowders. It is applied to measure the magnetic properties and hysteresis power absorption of magnetite and maghemite powders up to 500 °C. An arctangent model for saturation magnetization is adapted for minor hysteresis loops. It produces an excellent fit for hysteresis loop power across field strengths up to 18.5 kA m−1 and allows prediction of heating power, remanence, and susceptibility. Samples of magnetite and maghemite are shown to heat rapidly from room temperature at more than 25 °C s−1, with maghemite giving the strongest heating response. The peak heating power occurs at the transition beyond the ellipsoidal Rayleigh law region. These findings suggest that the properties of magnetic powders, coupled with variable magnetic field strengths and frequencies, can be tuned to optimize the heating power for a variety of applications.

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.

Preparation and characterization of Mn–Zn ferrites via nano-in-situ composite method

The polycrystalline Mn–Zn ferrites with different iron concentration were prepared by nano-in-situ composite method. The phase composition, microstructure, mechanical and magnetic properties of powders and bulk materials were investigated. The results showed that the crystallinity of powders decreased with the increasing iron concentration from 46 wt.% to 52 wt.%. The single spinel phase was obtained after sintering at 1200°C of all samples. The best comprehensive performance of Mn–Zn ferrite was achieved with the iron concentration 50 wt.%. This manuscript, explained the findings of novel nano-in-situ composite method, which will provoke new thinking and investigation in the research of Mn–Zn ferrite.

Investigation of the structural and magnetic properties of amorphous/nanocrystalline Fe70Ti10B20 (%at.) alloys by mechanical alloying

In this study, amorphous/nanocrystalline Fe 70 Ti 10 B 20 (at.%) alloys were synthesized by using elemental Fe, Ti and B powders under argon gas atmosphere via mechanical alloying method. The powders were ball milled at 20:1 ball-to-powder ratio and 500 rpm rotating speed up to 70 h. The phase and morphological properties of the synthesized powders were examined by using X-Ray diffractometer and scanning electron microscope with energy-dispersive X-ray spectroscope (SEM/EDX). The magnetic properties of powders were determined by vibrating sample magnetometer (VSM) at room temperature in the range of 0-20 kOe. It is determined that after 2.5 h of milling, Ti and B are started to dissolve in Fe lattice and Fe(TiB) solid solutions formed. XRD analysis revealed that the amorphous structures were formed after 30h of milling and the crystallite size and lattice strain were found ~ 8.2 nm and 1.16%, respectively. SEM images indicated that the particles were mostly agglomerated and the particles size distribution was in the range of 10-48 μm. Magnetic measurements revealed that after 70 h of milling, the saturation magnetization (M s ) and the coercivity (H c ) was about 94 emu/g and 117 Oe.

Structure and magnetic properties of nanocrystalline dysprosium powders

In this current study, nanocrystalline Dy powders were prepared by melt-spinning and subsequent high-energy ball-milling. The effect of ball-milling time on the structure and magnetic properties of the powders was studied. The crystal structure and microstructure of the melt-spun ribbons and ball-milled powders were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Magnetic measurement of all samples was performed with vibrating sample magnetometer (VSM). XRD results indicate that the average crystal grain size of the powders decreases from 90.09 nm of the ribbons to 10.42 nm of the 4-h ball-milled powders. Further TEM observation shows that the grains are fine and uniform. The Neel temperature (TN) decreases from 182 K of the ribbons to 172 K of the powders, while the Curie temperature (TC) increases from 100 to 130 K, demonstrating that the grain size has substantial influence on the magnetic transition process. Moreover, at 60 K, as the ball-milling time increases, the coercivity of the powders increases first, peaking at 0.48 T for 2-h milling, then drops again, while the remanence of the powders decreases monotonically. As a result, the powders milled for 2 h exhibit an optimal maximum energy product of 64.0 kJ·m−3, demonstrating the good potential of these powders as a permanent magnet at low temperatures.

Microstructure, magnetic properties of hexagonal barium ferrite powder based on calcination temperature and holding time

In this paper, single-phase and fine-grain hexagonal barium ferrite powder was prepared based on the optimal calcination condition. The influence of calcination conditions including temperature and holding time on microstructure and magnetic properties of powder were studied in detail. Firstly, θ–2θ scan X-ray diffraction (XRD) results reveal that it is hard to obtain single phase of powder when the calcination temperature is lower than 850 °C. In addition, the calcination time for single phase of barium ferrite powder was reduced with the increase in calcination temperature. Scanning electron microscopy (SEM) images and magnetic hysteresis loops show that the condition of low temperature and long holding time is beneficial for obtaining homogeneous size of grain and excellent magnetic properties. Consequently, hexagonal barium ferrite powder with uniform grain size of ~ 180 nm, high purity and excellent magnetic properties is obtained at optimal calcination condition of 850 °C–10.0 h.

Microstructure and magnetic properties of SmCo7/Co nanocomposite powders prepared by mechanical alloying

SmCo7/Co nanocomposite powders were prepared by high-energy ball milling of SmCo5 modified by adding Co and annealed at different temperatures. The phase evolution, microstructure and magnetic properties of the nanocomposite powders were analyzed. The results have shown that the annealing temperature and the addition of Co significantly affected the phase structures and magnetic properties of the powders. The nanocomposite powders were completely composed of the SmCo7 phase and the face-centered cubic Co phase. When annealing the SmCo5 powder at 750 °C, the SmCo7 phase decomposed into Th2Zn17-type Sm2Co17 and CaCu5-type SmCo5 phases with an average grain size of 13.9 nm, and the maximum energy product and remanence had maximum values of 10.51 MGOe and 77.92 emu/g, respectively. However, adding 28 wt% Co effectively prevented growth of the grain (11.5 nm) and enhanced the decomposition temperature (850 °C), resulting in a higher maximum magnetic energy product, coercivity, and remanence. The SmCo7 lattice contracted as Co content increased.

Mechano-chemical processing and characterization of nano-structured FeS powder

In this paper, preparation of FeS nano-powder by high energy mechanical milling of Fe–S and FeS2–Fe powder mixtures was studied. Effect of NaCl as a process control agent on the progress of reactions, morphology of particles and magnetic properties was investigated. The structural evolution, morphology and magnetic properties of powders were evaluated using X-ray diffraction, field emission electron microscope and vibrating sample magnetometer. It was found that FeS formed after 15h and 9h milling of Fe–S and FeS2–Fe as starting materials, respectively. Addition of NaCl prolonged the process and changed the combustion reaction mechanism to gradual one in Fe–S mixture. It also reduced the mean particle size to 56nm. Hysteresis parameter indicated the presence of different magnetic phases where antiferromagnetic phase was the dominant phase.

Electronic structure and magnetic properties of graphene/Co composite

The results of measurements of XPS spectra and magnetic properties of powder graphene/Co composite prepared by hydrogen reduction of CoCl2·6H2O deposited on few-layers graphene matrix are presented. XPS Co 2p measurements show two sets of 2p3/2,1/2-lines belonging to oxidized and metallic Co-atoms. This means that metal in composite is partly oxidized. This conclusion is confirmed by magnetic measurements which show the presence of the main (from the metal) and shifted (from the oxide) hysteresis loops. The presence of oxide layer on the metal surface prevents the metal from the full oxidation and (as shown by magnetic measurements) provides the preservation of ferromagnetic properties after long exposure in ambient air which enables the use of graphene/metal composites in spintronics devices.

Structure and Magnetic Properties of NdFeB Powder Prepared by Hydrogen Decrepitation and High-Energy Ball Milling

An ingot of NdFeB alloy was disintegrated by hydrogen decrepitation (HD). High-energy ball milling technique with hard metal milling elements and balls was employed to refine HD powders down to particle size optimum for magnet processing. The experiments were performed according to experimental plan to optimize the milling parameters regarding particle size, contamination and magnetic properties of the powder. The effect of milling time, speed of rotation, ball-powder weight ratio (BPR) and amount of wet agent was investigated. The highest influence was shown to be from attritor speed of rotation, ball-to powder ratio and combined effect of milling wet agent and rotating speed. Unified parameter of estimated number of total ball impacts was calculated, which allows predicting the final particle size of the powder at different milling speeds. Magnetic moments of powders were measured.

The Magnetic Properties of Fe-6.5wt.%Si Alloy Powders Produced by High Pressure Gas Atomization

The soft magnetic properties of Fe-6.5wt.%Si alloy powders produced via high pressure gas atomization under different powder sizes, environments (atmospheric and vacuum) and heat-treatment were presented by vibrating sample magnetometer (VSM), respectively. It is found that the soft magnetic properties of powder gradually grow up as the increasing of the powder size under atmospheric and vacuum environments. However, the using of vacuum environment has an optimal capacity to strengthening the properties rather than atmospheric environment. The heat-treatment of 1000°C for 2 hours offers considerable potential for improving the soft magnetic properties of the powders.

Irreversible magnetic properties of carbon nanoparticles

Magnetic properties of powder and glassy samples with carbon nanoparticles. not intentionally doped and doped with Ag, Au and Co, are investigated at temperatures T ~ 3 — 300 K in magnetic fields B up to 5 T. Magnetization M (T) exhibits in low fields of B = 1 — 50 mT a strong irreversibility, which is suppressed above B ~ 1 T. The high-temperature (T ~ 200 — 300 K) dependence of M on B demonstrates a saturation above B ~ 2 T. Magnetic hysteresis is observed already at 300 K. exhibiting a power-law temperature decay of the coercive field. Analysis of the experimental data suggests a concentration of the magnetization close to the surface of the carbon nanoparticles. This is consistent with the origin of magnetism in nanocarbon due to intrinsic surface defects. Deviations of macroscopic and microscopic parameters in the Co-doped sample from those in the other samples imply an influence of the Co ions and/or clusters.

Structural characteristics and magnetic properties of bulk nanocrystalline Fe84Zr2Nb4B10 alloy prepared by mechanical alloying and spark plasma sintering consolidation

Magnetic properties of Fe84Zr2Nb4B10 sample were investigated. The sample was produced from nanocrystalline powders made by the mechanical alloying (MA) and consolidation using the spark plasma sintering (SPS) technique. Effects of milling time on phase transformation, structural characteristics, and magnetic properties of powders were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and physical property measure system (PPMS), respectively. Results show that nanostructured α-Fe supersaturated solid solution is obtained in the final MAed products. The saturation magnetization (Ms) increased with increasing milling time and became constant at 130 h, but the coercivity (Hc) increased firstly and then decreased. The consolidated bulk sample exhibited a high density of 6.893 g·cm−3, there was no phase change during SPS process, and the saturation magnetization and susceptibility of the SPSed bulk sample improved in comparison with the milled powders. The variation of magnetic parameters can be explained by nano-scale effect and Herzer model.

Degradation of Tributyl Phosphate Using Nanopowders of Iron and Iron–Nickel under the Influence of a Static Magnetic Field

A novel method for the degradation of tributyl phosphate was investigated through the use of nanopowders of iron and iron–nickel. A combination of magnetic field and sonication was used to induce degradation. Using a tributyl phosphate concentration of 300 ppm at pH 4, the Fenton reaction was initiated in the presence of sonication and a reduction in organic carbon content of up to 50% could be created under an induced magnetic field of 0.7 T. The magnetic properties of powders after sonication treatment, in the presence and absence of a magnetic field, were observed to be different. Different degradation mechanisms were proposed under the influence of varying induced magnetic field for iron and iron–nickel.

Effect of sintering temperature on magnetic and electrical properties of nano-sized Co 2W hexaferrites

Nano-sized and single phase W-type hexaferrite (BaCo 2Fe 16O 27) powders synthesized by sol–gel autocombustion method have been investigated. The samples were sintered in a temperature range of 1000–1200 °C for 5 h. The thermal decomposition behavior of as-prepared powder was studied by thermogravimetry (TG), differential thermal analysis (DTA) and infrared spectra (IR). The structural and magnetic properties of powders were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The grain size calculated by Scherer equation was found in the range of 36–47 nm which is small enough to obtain a suitable signal-to-noise ratio in high density recording media. Hysteresis loop measurements show that the coercivity values lie in the range of 210.61–1602.6 Oe with increasing sintering temperature. Magnetization studies show a significant increase in the values from 15 to 22 emu/g. The dc electrical resistivity is observed to decrease up to a certain value as the temperature increases and then rises at higher temperature.

Enhancing magnetic properties of anisotropic NdDyFeCoNbCuB powder by applying magnetic field at high temperature during hydrogen desorption

Anisotropic powder was prepared with precursor (NdDy)-(FeCoNbCu)-B sintered magnets by hydrogen decrepitation, desorption, and subsequent annealing treatment. The hydrogen desorption was performed in magnetic fields of 0, 1, 3, and 5 T. The orientation of tetragonal phase grains of the powder was evaluated from the hysteresis loops measured by extraction magnetometer. Residual hydrogen content of the powder was evaluated by thermal-magnetic analysis. The powder with H(cj), B(r), and (BH)(max) of 1138 kA.m(-1), 1.029 T, and 172.5 kJ.m(-3), respectively, was achieved under the condition of the magnetic field of 3 T. Magnetic properties of the powder, especially, the remanence of the powder, are enhanced upon magnetic fields, which is due to better orientation of powder particles and less residual hydrogen in the powder resulted from the magnetic field during the hydrogen desorption process.

Effect of Nitridation Magnetic Properties of Nanocrystalline Fe-Co Alloy Powders

Nanocrystalline Fe-Co alloy powders, which were prepared by high-energy mechanical milling, were nitrided under the mixing gas of NH3/H2 in the temperature range from 380°C to 510°C. X-ray diffraction (XRD) was used to analyze the grain size and reaction during the processing. The magnetic properties of the nitrided powders were measured by Vibrating Sample Magnetometer (VSM). The results show that with the appearance of Fe4N phase after nitride treatment, and the grain-size of FeCo phase decreases with the increase of nitridation temperature between 380°C to 450°C.The saturation magnetization of nitrided alloy powder treated at 480°C is about 18% higher than that of the initial Fe-Co alloy powder, accompanied by the reduction of the coercivity. Transmission electron microscope (TEM) was used, attempting to further analyze the effect of Fe4N phase on microstructure and magnetic properties of the powder mixtures.