Values Of Coercive Force Research Articles

Structural and magnetic properties of La-substituted strontium W-type hexagonal hexaferrites

W-type strontium hexaferrites with chemical composition of Sr1−xLaxZn2Fe16O27 (x = 0–0.25) were synthesized by traditional ceramics process. Effects of the substituted amount x of La3+ on the ferrites microstructure and magnetic properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and a magnetic properties test instrument. As a result, at x ≤ 0.20, all samples are single phase after the La substitution. At x = 0.25, another phase of La2O3 is present. In addition, the maximum values of the remanence (Br) and maximum energy product ((BH)max) for the magnets have been obtained at x = 0.10. The maximum value of the intrinsic coercive force (Hcj) and magnetic induction coercivity (Hcb) for the magnets has been obtained at x = 0.15.

The Structure and Magnetic Properties of Bronze, Stainless still and Alloy Layers Formed by Direct Laser Welding on Nonmagnetic Substrates

Investigations of crystal structure, microstructure and composition of laser welded coatings of bronze, IN625, PGSR-4 and stainless steel alloys on non-magnetic substrates have shown that from the raw alloy powders (wire) the additional crystalline phases are extracted with new compositions and sizes of units of microns, which randomly distributed in the coating volume. Due to formation of additional phases with increased electron concentration magnetic hysteresis loops have appeared at 4 K and 300 K for all welded coatings. Bronze and stainless steel coatings have demonstrated soft ferromagnetic properties with two type of magnetic domains with small magnetization that resulted in small value of saturation magnetization (Ms = 60-146 emu/cm3 at 300 K and Ms = 107-241 emu/cm3 at 4 K) and low values of coercive force (40 – 90 Oe) at 300 K and (50-170 Oe) at 4 K. En existence of one type of ferromagnetic domains with middle Curie temperatures (230-270 K) in laser welded IN625 and PGSR-4 coatings has determined soft ferromagnetic nature of magnetism at low temperature (Ms =274 – 398 emu/cm3) and transition in paramagnetic conditions at 300 K due to main contribution only paramagnetic grains with different composition.

Магнитный контроль сопротивления усталости сварных соединений

Introduction. Complexity of welded joints nondestructive testing under operation conditions is associated with the heterogeneity of the metal structure within the heat-affected zone, which is a stress concentrator; the metal structure in this zone is being changed under cyclic loads. The work aim was to investigate the possibility of applying a coercimetry method to diagnostics of welds working under cyclic loads.
 Method. At low-cycle fatigue irreversible damage accumulation takes place even in a defect-free weld. The magnetic structurescope KRM-Ts-K2M was used for detection of this damage by the value of the coercive force increase. The impact of load parameters on a coercive force was studied on the basis of static and cyclic testing of samples with butt and fillet (T-shaped) welds.
 Results. Numerous static and cyclic testing of welds and base metal have enabled the author to determine correlation between a coercive force value and weld resource parameters for the conventional steel grades St3sp, 09G2S and 10KhSND. Prospects of small (with the base ≤ 20 mm) sensors application for weld local diagnostics has also been shown in the work.
 Conclusion. Combination of magnetic structural testing by a coercive force method with an ultrasonic inspection makes it possible to predict a physical resource of metal work at the examination of hazardous production facilities.

Ti-doping effects on magnetic properties of dense MgB2 bulk superconductors

We have studied the effects of Ti doping on the magnetic properties of MgB2 superconducting bulks. The trapped field, which was obtained by field-cooled magnetization, , was about 3.6 T at 13 K at the surface of the single Ti5–20% doped MgB2 bulks, which was about 1.3 times larger than that of the non-doped bulk. The of 4.6 T was achieved at 14.1 K in the centre of the doubly stacked Ti-doped MgB2 bulks. The remanent magnetic flux density, which corresponds to the trapped field by zero-field cooled magnetization, , was comparable with the absolute value of coercive force with a very small vortex creep rate of about 2% over 40 h. These results suggested that the MgB2 bulk was an excellent ‘quasi-permanent’ magnet. The critical current density, , under magnetic field was also enhanced by Ti doping; under 3 T at 20 K, the of A cm−2 for the pristine sample was enhanced to that of 1.6–1.8 A cm−2 for the Ti-doped samples. The irreversibility field exceeded 5 T at 20 K for the Ti-doped samples. The existence of nanometric unreacted B and strongly Mg-deficient Mg-B particles and TiB2 layers at the periphery of Ti precipitates was suggested in the Ti-doped bulks by microscopic observation. The improvement of the vortex pinning properties in Ti-doped MgB2 originated from the creation of the nanometric nonsuperconducting particles and TiB2 layers acting as strong vortex pinning centres.

Magnetic and Magnetotransport Properties of Fe-NbO System

Magnetoresistive effect and electrotransport properties of Fe-NbO (13 ≤ Fe, at.% ≤ 80) thin films annealed at 600 °C has been investigated. It has been established that the samples structure contains three main phases Fe, NbO2, Fe2.9O4. Maximum of magnetoresistance in the samples does not exceed 0.3%, a coercive force is ranging from 150 to 370 Oe, depending on the Fe concentration. It is assumed that the films have a granular structure. Magnetoresistance and coercive force values, as well as the correlation between the magnetoresistance and the magnetization of the Fe-NbO samples are uncharacteristic for granular systems. It is assumed that uncharacteristic properties are due to the significant influence of ferrite Fe2.9O4 on the magnetic properties and electrotransport of the Fe-NbO films.

Investigation of Nanostructure and Magnetic Properties of Nanocrystalline NiZnCu Ferrites Synthesized by Sol-Gel Method

Nanocrystalline material of ferrites with composition Ni0.5Zn0.35Cu0.15Fe2O4 was successfully synthesized by sol-gel method. This paper investigates nanostructure and magnetic properties of nanocrystaline material Ni0.5Zn0.35Cu0.15Fe2O4. Crystallite size, intensity,d-spacing and lattice parameters of material were investigated by using X-Ray diffractometer (XRD). While nanostructure, size, shape, surface morphology and topography of Ni0.5Zn0.35Cu0.15Fe2O4 were examined by variable pressure field emission scanning electron microscope (VP-FESEM) SUPRA 55VP. Magnetic properties was investigated using vibrating sample magnetometer (VSM). According to thermo gravimetric analysis (TGA) result, it was found that after temperature 600oC there is no more weight loss detected and it was considered as minimum calcination temperature. XRD result shows that the samples is in single-phase cubic spinel structure. Crystallite size of the material is in range of 42.3-163.7nm. Highest intensity was 88.89 arb.units at highest calcination temperature 900oC. The value of d-spacing and FWHM decrease with increasing calcination temperature. Lattice paramenters decrease in the range of 8.4040-8.2458oA. VP-FESEM analysis shows that grain size increase by increasing calcination temperature. Grain size of the material is in the range of 47.6-506.9nm with cubic structure of the Ni0.5Zn0.35Cu0.15Fe2O4. VSM result shows that the highest value of magnetic saturation was at 152.8emu/g. The best value of coercive force (Hc) was in 31.8Oe and magnetic remanence (Mr) was in 2.6emu/g.

Insights into size-dominant magnetic microwave absorption properties of CoNi microflowers via off-axis electron holography.

In this study, CoNi flower-like hierarchical microstructures with different sizes were obtained via a one-step solvothermal method by simply adjusting the concentration of precursors and surfactant. The obtained CoNi microflowers possess uniform and tunable size, good monodispersity, and remarkable magnetic microwave absorption properties as well as electron holography phase images. Characterization results have demonstrated the dependency of properties of CoNi microflowers on their morphologies and sizes. The microflowers exhibit different stray magnetic fields that might be determined by whether the pristine nanoflakes on the flowers' surface was parallel or perpendicular to grid plane. And as the size of microflowers increased, the coercive force (Hc) value decreased while saturation magnetization (Ms) value gradually increased, and it can be also observed that the values of Ms and Hc at 5 K are higher than those at 300 K. In addition, the blocking temperature decreased when size increased. Typically, the 2.5 μm CoNi microflowers achieve the maximum reflection loss (RL) value of -28.5 dB at 6.8 GHz with a thickness of 2 mm, while on the other hand, the 0.6 μm flowers achieved a broader absorption bandwidth below -10 dB of 6.5 GHz. Therefore, it is believable that the CoNi flowers with different sizes and hierarchical structures in this work have great potential for high performance magnetic microwave absorption applications.

Investigation of the polarization dependence of the transient current in polycrystalline and epitaxial Pb(Zr,Ti)O3 thin films

The polarization dependence of the current in epitaxial and polycrystalline (with conductive grain boundaries) Pb(Zr,Ti)O3 (PZT) films is studied using direct-current (dc) measurements and scanning spreading current microscopy. Both methods show identical results in micro- and nanoscale ranges. The current response from the film to the applied bias contains a long relaxation component that depends on the bias rise rate and polarization direction, exhibiting current peaks near the coercive force value. The polarization dependences of the current for polycrystalline and epitaxial films are found to be fundamentally different. The current of the polycrystalline film is much higher when the bias is directed against the polarization, whereas the current of the epitaxial film is higher if the bias and polarization directions coincide. All films exhibit current hysteresis of non-ferroelectric (clockwise) direction with decreasing bias. It is also shown that the polarization dependences of the transient current in both polycrystalline and epitaxial films are similar to the polarization dependence of the photovoltaic current in these films.

Microstructure and magnetic properties of Ca-substituted M-type SrLaCo hexagonal ferrites

M-type strontium hexaferrites with chemical composition of Sr0.80−xCaxLa0.20Fe11.85Co0.15O19 (x=0−0.15) were prepared by the ceramic process. The samples were sintered at temperatures of 1175, 1185 and 1195 °C for 2 h in air. Effects of the substituted amount x of Ca2+ on the ferrites microstructure and magnetic properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and B–H hysteresis curve measurements. As a result, at x≤0.12, all samples are single phase after the Ca substitution. At x=0.15, another phase of hematite (α-Fe2O3) is present. In addition, the maximum values of the remanence (Br) and maximum energy product ((BH)max) for the magnets have been obtained at x=0.08 for sintering temperature=1185 °C. The maximum value of the intrinsic coercive force (Hcj) for the magnets has been obtained at x=0.12 when the magnets were sintered at 1185 °C.

Crystal structure, magnetic and electric properties of highly coercive ferrites Sr1 − x Sm x Fe12 − x Zn x O19 (0 ≤ x ≤ 0.4)

The samples of highly coercive ferrites Sr1 − xSmxFe12 − xZnxO19 (0 ≤ x ≤ 0.4) with the structure of magnetoplumbite have been obtained by the solid-phase method. It has been determined that the samples Sr1 − xSmxFe12 − xZnxO19 are single-phase at x ≤ 0.2 and contain the impurity phases of α-Fe2O3, SmFeO3, and ZnFe2O4 at x ≥ 0.3. In the magnetic fields up to 14 T, the specific magnetization has been measured and the values of coercive force (σHc) have been determined at 5 and 300 K. It has been shown that semiconductor electroconductivity of single-phase samples Sr1 − xSmxFe12 − xZnxO19 gradually decreases with the increase in the degree of substitution of x from 0 to 0.2.

Evolution from amorphous to nanocrystalline and corresponding magnetic properties of Fe-Si-B-Cu-Nb alloys by melt spinning and spark plasma sintering

Abstract The nanocrystalline Fe-Si-B-Cu-Nb alloys were prepared by firstly melt spinning and then spark plasma sintering process. The microstructure and magnetic properties of the samples obtained were investigated by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The body-centered cubic α-Fe(Si) phase precipitated from the amorphous matrix when the sintering temperature was increased to 800 K. The Fe23B6 phase started to form at the sintering temperature of 950 K. The grain size and densities of the sintered Fe-Si-B-Cu-Nb alloys increased with increasing the sintering temperature. Moreover, the saturation magnetizations of the samples obtained increased first and then decreased as the sintering temperature was increased from 750 K to 1050 K, while the values of coercive force changed in the opposite direction. The Fe-Si-B-Cu-Nb alloys sintered at 900 K exhibited a nanocrystalline structure with a grain size of ∼34 nm. It also displayed excellent soft magnetic properties with saturation magnetization at 137.5 emu/g, coercivity at 5 Oe and remanence at 1.0 emu/g.

Remarkable magnetic properties of amorphous hydrogenated carbon nanostructured thin films

AbstractAmorphous hydrogenated carbon thin films with 3d metal nanoparticles were deposited on Si and glass‐ceramic substrates by reactive ion‐plasma magnetron sputtering. Thin films have a high complex permittivity ε * and permeability µ * (ε ′ ≈ 1000–10000, ε″ ≈ 100–1500, μ ′ ≈ 10–70, µ ″ ≈ 0.4–10), what can stipulate by anomalous electromagnetic microwave radiation absorption effect. The magnetic parameters as shape of hysteresis loop, values of coercive force, remanence and saturation magnetization were determined from vibrating‐coil magnetometer measurements. The mechanism of absorption in the material under study is described. Obtained results demonstrate a good promise to use this material for the absorption of electromagnetic microwave radiation. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Succession law of Nd–Fe–B alloys with different coercivities

In order to establish a succession law of every phase in sintered Nd–Fe–B magnets marked as 38/38H/38SH/38UH, four alloys of Nd33−x Dy x Al0.7Nb0.6Cu0.1B1.05Febal. (at%) were investigated after smelting processing, sintering processing, high-temperature tempering processing, and high- and low-temperature tempering processing. It is found that the four phases: the Nd2Fe14B matrix phase, Nd-rich phase, B-rich phase, and defect phase can be inherited by means of the subsequent processing. These phases might have the special constitution and appearance in the different states. Magnetic properties also have succession law. In every processing except smelting one, the values of remanence and maximum energy product hardly alter, but the value of coercive force increases gradually.

Perpendicular coercive force of thick CoFeB thin films grown on silicon substrate

The room-temperature magnetic properties of CoFeB thin films grown on silicon substrate were investigated. Large perpendicular coercive forces in CoFeB thin films with thickness up to 172nm were observed. The value of the perpendicular coercive force is 1850Oe as the thickness of the CoFeB layer is 38nm. The large perpendicular coercive force indicates the presence of intrinsic perpendicular magnetic anisotropy in thick CoFeB layer with thickness up to 172nm, which originates from (300) texture in CoFeB layer. The strength of perpendicular magnetic anisotropy of CoFeB depends on annealing temperature.

Magnetic and electronic properties of bimagnetic materials comprising cobalt particles within hollow silica decorated with magnetite nanoparticles

Bimagnetic materials were fabricated by decorating the external surface of rattle-type hollow silica microspheres (which themselves contain metallic cobalt nanoparticles) with magnetite nanoparticles; thus, each magnetic substance was spatially isolated by the silica shell. The amount of magnetite decoration on the co-occluded hollow silica was varied from 1 to 17 mass %. Magnetic and electronic properties of the resulting bimagnetic materials were characterized by superconducting quantum interference device measurements and X-ray absorption spectroscopy, respectively. The ferrous iron in the bimagnetic sample was slightly more oxidized than in the magnetite reference, probably from some charge-transfer because of the SiO2 surface contact, although the overall oxidation state of the samples is very similar to that of magnetite. The temperature dependence of the sample magnetization recorded with Zero Field Cooling and Field Cooling resulted in blocking temperatures for the bimagnetic materials that were close to that of magnetite nanoparticles (176 K) and were lower than that for the bare Co-occluded hollow silica (which was above room temperature). Values of coercive force and exchange bias at 300 K became quite small after decoration with only minimal amounts of magnetite nanoparticles (1–3 mass %) and were lower than those of magnetite. This is the first example of enhancing superparamagnetism by spatial separation of both Co and magnetite magnetic nanoparticles using a thin wall of diamagnetic silica.

Nanocrystalline Soft Magnetic Toroidal Cores of the Highest Relative Magnetic Permeability and Low Coercive Force

All the technologies of the melt quenching preparation ensure its time-temperature treatment to not only improve but also stabilize the metal structure and properties with every melt. The influence of annealing temperature of nanocrystalline alloy Fe72.5Cu1Nb2Mo1.5Si14B9 on the structure and magnetic properties has been investigated. The relation between numerical values of the coercive force, the initial magnetic permeability and the magnetic hysteresis loop rectangularity factor allows optimizing a mode of nanocrystalline alloy heat treatment.

Preparation and Magnetic Properties of CuFe2O4 Nanoparticles

CuFe2O4 nanoparticles have been obtained by heat treatment of coprecipitation product, which were synthesis by reaction of Cu2+ ions and Fe3+ in alkaline condition. The morphology and microstructure of the synthesized urchin-like superstructures have been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the CuFe2O4 nanoparticles were polycrystal with cubic jacobsite structure and a size distribution from 20 to 40 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc) value of 86.83Oe, saturation magnetization (Ms) value of 37.98 emu/g and remanent magnetization (Mr) value of 2.68 emu/g. The IR spectrum of peak at 586 cm−1 was corresponding to the vibration modes of CuFe2O4 nanoparticles.

Solvothermal preparation of cobalt nanorods

Cobalt nanorods have been prepared through solvothermal process with hydrazine hydrate and dimethylglyoxime (DMG) as reducing and morphology directing agents. The phase structure, morphology and magnetic properties of the as-prepared product were extensively characterized by X-ray diffraction, transmission electron microscopy and superconducting quantum interference device magnetometer. X-ray diffraction pattern revealed that the as-synthesized product was cobalt with face-centered cubic structure. Transmission electron microscopy observation showed that the as-prepared product composed of rod-like shape with size around 10 nm. The presence of DMG molecules on the surface of Co nanostructures was confirmed by the FTIR spectra. Magnetic measurements revealed that the nanorod exhibit ferromagnetic behavior at 300 K. The coercive force value of cobalt nanorods is 340 Oe at 300 K. Compared with bulk cobalt, the nanorods exhibit significant increase in coercive force as a reflection of shape anisotropy. The saturation magnetization value of Co nano rod is 150 emu/g at room temperature.

Structural Characterization, and Magnetic Morphological Study of Ni<sup>+2</sup> Doped ZnO Synthesized by Combustion Reaction Application for DMS

ZnO is a semiconductor that can be doped with transition metal ions, and thus becomes feasible to use in the diluted magnetic semiconductor (DMS), or semiconductor with magnetic properties. In this work we have studied the influence of doping of Ni+2on the structural, morphological and magnetic properties of Zn1-xNixO system, to x = 0.07, 0.1 and 0.2 mol of Ni+2synthesized by combustion reaction. The systems were characterized by XRD, SEM and VSM. The maximum temperatures ranged from 639 K and 683 K. All systems showed a majority phase formation of ZnO, with the presence of the second phase NiO. The crystallite size for the majority phase varied between 49 and 56nm. All systems have resulted in samples with a morphology consisting of dense clusters, formed by particles pre-sintered and shaped roughly hexagonal plates. The magnetic measurements showed that the values of saturation magnetization lies between 4.6 to 28.5emu/g, remanent magnetization of 0.01 to 0.3 emu/g, coercive force values varies between 12.7 and 62.4 Oe and Curie temperature ranging from 308 to 311K.

Magnetic properties of 1 : 4 complexes of CoCl2 and pyridines carrying carbenes (S0 = 4/2, 6/2, and 8/2) in diluted frozen solution; influence of carbene multiplicity on heterospin single-molecule magnets

The microcrystalline sample of a parent complex, [CoCl(2)(py)(4)], showed a single-molecule magnet (SMM) behavior with an effective activation barrier, U(eff)/k(B), of 16 K for reversal of the magnetism in the presence of a dc field of 3 kOe. Pyridine ligands having 2-4 diazo moieties, DYpy; Y = 2, 3l, 3b, and 4, were prepared and confirmed to be quintet, septet, septet, and nonet in the ground state, respectively, after irradiation. The 1 : 4 complexes, CoCl(2)(DYpy)(4); Y = 2, 3l, 3b, and 4 in frozen solutions after irradiation showed the magnetic behaviors of SMMs with total spin multiplicity, S(total) = 17/2, 25/2, 25/2, and 33/2, respectively. Hysteresis loops depending on the temperature were observed and the values of coercive force, H(c), at 1.9 K were 12, 8.4, 11, and 8.1 kOe for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively. In dynamic magnetic susceptibility experiments, ac magnetic susceptibility data obeyed the Arrhenius law to give U(eff)/k(B) values of 94, 92, 93, and 87 K for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively, while the relaxation times for CoCl(2)(CYpy)(4); Y = 2 and 3l, obtained by dc magnetization decay in the range of 3.5-1.9 K slightly deviated downward from Arrhenius plots on cooling. The dynamic magnetic behaviors for CoCl(2)(CYpy)(4) including [CoCl(2)(py)(4)] and CoCl(2)(C1py)(4) suggested that the generated carbenes interacted with the cobalt ion to increase the relaxation time, τ(q), due to the spin quantum tunneling magnetization, which became larger with increasing S(total) of the complex.