Initial Magnetization Curve Research Articles

Fe 81 Ga 19 合金 取向单晶生长及磁致伸缩性能

The Fe81Ga19 single crystals were grown in a floating zone melting furnace at a growth rate of 4 mm/h by using a seed crystal. A single crystal was grown by using the seed crystal oriented 5◦ from the 〈001〉 orientation. Pole figure tests were taken at different parts of the single crystal and showed that the start and end parts’ axial orientations were 5◦ and 4◦ from the 〈001〉 orientation, respectively. Another single crystal was grown by using the seed crystal oriented 〈001〉 orientation. Magnetostrictive properties along the axis of the crystals λ/ were measured for the single crystal, and the saturated magnetostriction λ/ up to 0.0324% was achieved under the pre–stress of 60 MPa. Initial magnetization curves were measured in single crystals along 〈100〉, 〈110〉 and 〈111〉 axis, respectively. From the magnetization curves, magnetocrystalline anisotropy constants of Fe81Ga19 alloys were calculated, and the values of K1 and K2 were 1.3×104 and −2.6×104 J/m, respectively.

Initial Magnetization and Coercivity Mechanism in Amorphous TbxCo1-xThin Films with Perpendicular Anisotropy

The coercivity mechanism in permanent magnets was analyzed according to the effects of domain nucleation and domain wall pinning. The coercivity mechanism of a TbCo thin film with high perpendicular magnetic anisotropy was considered in terms of the local inhomogeneity in the thin film. The initial magnetization curves of the TbCo thin films demonstrated domain wall pinning to be the main contributor to the coercivity mechanism than domain nucleation. Based on the coercivity model proposed by Kronmuller et al., the inhomogeneity size acting as a domain wall pinning site was determined. Using the measured values of perpendicular anisotropy constant (K u ), saturation magnetization (M s ), and coercivity (H c ), the inhomogeneity size estimated in a TbCo thin film with high coercivity was approximately 9 ㎚.

The magnetization reversal processes of Sm 2Gd 10.5Fe 8Co 64Zr 2.5Cu 13 alloy in the as-quenched state

The magnetization reversal processes of the as-quenched Sm 2Gd 10.5Fe 8Co 64Zr 2.5Cu 13 ribbons obtained by melt-spinning method have been investigated. From the analysis of the initial magnetization curve it was deduced that the main mechanism of magnetization reversal process is the pinning of domain walls at the grain's boundaries. From the dependence of the reversible magnetization components as a function of magnetic field it was found that reversible rotation of magnetic moment vector results in high initial values of this component. The presence of several maxima on the differential susceptibility curves derived from the irreversible magnetization component in both direction of magnetization implies existence of several pinning sites for domain walls. The interaction between the alloy grains have been examined by using the so-called δm( μ 0 H i) plot. The values of δm( μ 0 H) for investigated alloy remains positive for an applied field up to 1.15 T and negative for higher fields. Such behavior of δm( μ 0 H i) dependence certifies that the dominant interaction between grains is the short range exchange interactions but low values of δm( μ 0 H) implies that these interactions are week.

Effect of film morphology on the magnetic properties for Nd–Fe–B thin films

The microstructure and magnetic properties of Nd–Fe–B thin films with a particulate structure were investigated. The nominal thickness of the Nd–Fe–B layer ( t N) was varied from 2 to 50 nm on a (0 0 1) Mo buffer layer. The films were grown with their c-axis perpendicular to the plane, and the morphology of the film with t N=2 nm was shown to be particulate from an atomic force microscope image. The slope of the initial magnetization curve became steeper by increasing the t N value in the initial magnetization curve, indicating that the film morphology composed of single domain particles changed to that of multi-domain particles with growth. The film with t N=8 nm, which had a structure consisting of a mixture of single and multiple domain particles, showed the maximum value of the coercivity measured in the direction perpendicular to the film plane ( H c) as 19.5 kOe.

Fabrication and characterization of highly textured Nd–Fe–B thin film with a nanosized columnar grain structure

We have fabricated a highly textured Nd–Fe–B thin film with a hard magnetic performance: Mr=1.39 T, Hc=827 kA/m, and (BH)max=358 kJ/m3. The microstructure of the film was characterized in detail by cross-sectional and plane-view transmission electron microscopy observations. The film consisted of nanosized columnar grains with an average size of 40 nm and included a strong diffraction contrast along the grain boundary. A high resolution energy filtered image indicated that Nd was enriched discontinuously along the grain boundary, causing an unsuitable decoupling among the Nd2Fe14B grains, which is in agreement with the pinninglike feature of the initial magnetization curve.

Apatite-forming ability and magnetic properties of glass-ceramics containing zinc ferrite and calcium sodium phosphate phases

Fine particles of zinc ferrite (ZnFe 2O 4) and calcium sodium phosphate [NaCaPO 4] were crystallized in bulk x(ZnO, Fe 2O 3)(65− x)SiO 220(CaO, P 2O 5)15Na 2O (6 ≤ x ≤ 21 mol %) glassy matrix by heat treatment. Initial magnetization curves reveal that samples with x = 6 and 9 mol % zinc–iron oxide exhibit both ferrimagnetic and paramagnetic contributions, whereas, samples with x > 9 mol % zinc–iron oxide exhibit only ferrimagnetic contribution. This observation is supported by the disappearance of the electron paramagnetic resonance (EPR) absorption line centered at g ≈ 4.3 in samples with x > 9 mol % zinc–iron oxide. Apatite-forming ability of the glass-ceramic samples was investigated by examining apatite formation on the surface of the samples treated in simulated body fluid (SBF). Increase in apatite-forming ability was observed with an increase in zinc–iron oxide content. The results obtained have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass-ceramic composition. A good correlation has also been observed between the magnetic nature of the samples and their apatite-forming ability. These materials are expected to find application as thermo-seeds in hyperthermia treatment of bone cancer.

Magnetic properties of [formula omitted]-based diluted magnetic semiconductors

Polycrystalline Sn 1− x Ni x O 2 samples were prepared in single-phase form for x = 0.02 and 0.07 and were characterized using several experimental techniques. Room-temperature ferromagnetism with transition temperature, T c , as high as 770 K was observed from the temperature variation of magnetization measurements. Nanoparticles of uniform crystalline phase and composition were identified from the transmission electron microscope images. The initial magnetization curves recorded at 80 and 300 K for both samples could be analyzed based on the bound magnetic polaron (BMP) model, where the size of the BMP is found to increase with temperature. The magnitude of electrical resistivity is found to decrease with doping, and its temperature dependence could be explained based on the variable range hopping mechanism.

A New Technique for Modeling Hysteresis Phenomenon in Soft Magnetic Materials

A major part of power systems consists of ferromagnetic materials, and investigation of their parameters and magnetic characteristics in various operating conditions is necessary. Hysteresis in ferromagnetic materials is a complicated physical phenomenon, and its modeling is a challenging problem. In fact, the basic problem in this modeling is that for a given value of the magnetic field intensity, there are unlimited possible magnetic flux density values that depend on the history of the material. A class of the hysteresis models as physical models is expressed based on the physics theories. In the present article, a new model for hysteresis phenomenon is proposed. This model is a combination of mathematical equations and models that have been obtained based on the experimental observations and a series of the magnetic paths macroscopic properties extracted from the Preisach model. The proposed model generates symmetrical and asymmetrical hysteresis loops with high accuracy. In this model, an artificial neural network is used to present the descending path of the major DC hysteresis loop and initial magnetization curve based on a set of experimental data. In this model, it is necessary to extract some major properties of the magnetic paths from the well-known Preisach model. These features and also the proposed mathematical equations, obtained based on the experimental observations, are then used to generate the symmetrical and asymmetrical hysteresis paths.

Influence of rare earth (Gd, Dy or Sm) dopants on the magnetic properties and microstructure of Nd60‐xRExFe30Al10 alloys

AbstractThe effect of partial substitution of Gd, Dy and Sm for Nd in Nd60‐xRExFe30Al10 alloys for the magnetic properties and microstructure was studied. Each of the elements used has different influence on the magnetic properties of the (Nd, RE)‐Fe‐Al alloys. Gd substantially increases the coercivity, even at as high concentrations as 20%. Addition of Gd does not change neither the initial magnetization curve nor the initial susceptibility. Similarly high coercivity increase can be achieved by addition of up to 5% of Dy. For higher Dy contents a dramatic drop of the coercivity was observed. Introduction of Sm leads to deterioration of the magnetic properties, even at as small concentrations as 1%. All the additional elements studied decrease the saturation magnetization and remanence. Additions of Dy, Gd and Sm, which partly substitute Nd in the Nd60Fe30Al10 alloy, leads to formation of crystalline precipitates. In the case of Dy these precipitates are formed by MgCu2 type phase. In the Sm doped alloy the size of the crystalline precipitates, visible in the amorphous matrix, are about twice of those, which are present in the dopant free alloy. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of annealing time on the structural and magnetic properties of L1 0 FePt thin films

Thermal annealing of [Fe 1.65 nm/Pt 1.84 nm] 50 multilayers at 673 K for various annealing times between 60 and 12000 s leads to the direct formation of the fully ordered L1 0 FePt phase with (111) texture. The average grain sizes, determined from X-ray diffraction size–strain analysis, are smaller than the critical size for multi-domain FePt particles, suggesting the presence of single-domain (SD) grains. The coercivity increases with annealing time and increasing grain size and reaches values of about 955 kA/m. The remanence values are typical for randomly oriented weakly-interacting particles. A decrease of the remanence with annealing time suggests a decrease of the intergrain exchange interactions with annealing time. Analysis of minor loops and the initial magnetization curves shows the presence of a broad distribution of critical fields, which the individual SD particles have to overcome for the magnetization reversal.

Inrush Current Modeling in a Single-Phase Transformer

This paper introduces a proper model for ferromagnetic core which includes hysteresis, saturation, eddy current losses, and anomalous losses. This model can generate symmetrical and asymmetrical loops with high accuracy. An artificial neural network is used to present the major dc hysteresis loop and initial magnetization curve based on a set of experimental data. This ferromagnetic core model is then used to estimate the inrush current of a single-phase transformer. Differential equations system obtained based on the equivalent circuit is converted into a nonlinear algebraic system of equations and then solved by Newton-Raphson routine. The predicted results are in good agreement with the experimental results.

Permeability of Soft Magnetic FeCoV-Composites for Varying Filler Fractions

The dependence of permeability on the magnetic field in the initial magnetization curve for different Fe49 Co49V2-polymer composites is investigated. For a measurement frequency of f = 1 Hz and a low filler fraction of x = 0.1 the permeability is nearly constant with increasing magnetic field with a small maximum at H = 26100 A/m. Increasing filler fraction causes an increase of initial permeability and also the maximum permeability becomes more and more distinctive. Additionally the position of the maximum shifts to a lower magnetic field of H = 3027 A/m for filler fraction x = 0.8. At this filler fraction the maximum permeability is ?max = 57 and the initial permeability is ?i = 36. At the magnetic field where the maximum permeability was found also the frequency dependence from 1 Hz to 2000 Hz of the permeability was estimated. While the permeability is nearly constant in the whole examined frequency range for a filler fraction x ? 0.2, a higher filler fraction causes a reduction of permeability at higher frequencies. For the composite with 80-vol. % Fe49Co49V2 content the permeability is decreased for frequencies f > 100 Hz.

Microstructure and magnetic properties of bulk magnets Nd 14– xFe 76+ xCo 3Zr 1B 6 ( x=0, 0.5, 1) prepared by spark plasma sintering

Melt-spun ribbons with nominal composition of Nd 14– x Fe 76+ x Co 3Zr 1B 6 ( x=0,0.5,1) were consolidated into isotropic bulk magnets by spark plasma sintering method. It was found that the Nd content and sintering temperature had significant influence on the density and magnetic properties of the sintered magnets. Homogeneous microstructure and fine grain (50–100 nm) were obtained when sintering below 700 °C, and the initial magnetization curve showed that the coercivity was controlled by the pinning mechanism. However, abnormally large grains and inhomogeneous microstructure in magnets were observed after sintering at 750 °C, furthermore, the grains were found to be multi-domain structure and the coercivity was mainly controlled by nucleation mechanism.

Electrodeposition of coercive L1 0 FePt magnets

We report the preparation, characterization of structure and magnetic properties of electrodeposited L1 0 FePt films with high coercivity. Equiatomic as-deposited films are nanocrystalline, soft and magnetically isotropic. The transition from the disordered to the ordered phase was studied by varying the annealing time and annealing temperature. The as-deposited nanocrystalline deposits were treated in forming gas and developed the tetragonal L1 0 structure only at temperatures above 500 °C. The coercivity increases with both annealing temperature and annealing time reaching a value of 1.5 T at 900 °C. The magnetization reversal mechanism was identified as nucleation type from the initial magnetization curve of a thermally demagnetised sample.

Crystal Structure and Magnetic Properties of Sm2 Fe17Nδ Thin Films Deposited on Si (100) Substrates

This work focuses on the crystal structure and magnetic properties of the hard magnetic Sm2Fe17Nδ films prepared by dc magnetron sputtering and the subsequent nitriding process. The XRD, EDS, M-H and M-T data show that N enters the cell structure and the films with the single Th2Zn17 phase are obtained when the nitriding temperature varies from 300 to 400° C, thus the maximum value of the coercivity HC reaches 2561.7 Oe. However, the Sm2Fe17 phase decomposes to the SmN nonmagnetic phase and the α-Fe soft magnetic phase with further increasing nitriding temperature, which corresponds to the decreasing HC. Furthermore, the easy magnetization direction (EMD) is found to locate randomly in the film plane. This texture can not give an excellent MR/MS higher than the Stoner-Wohlfarth limitation (MR/MS = 0.5), which agrees well with the observed low MR/MS (0.58). It is suggested that the magnetization reversal process is dominated by the nucleation mechanism according to the initial magnetization curve and the dependence of HC on the field H.

Optimized model for magnetic hysteresis in silicon-iron sheets by using the simulated annealing algorithm

To characterize magnetic materials it is very important to take into account the initial magnetization curve and the magnetic hysteresis loop. Several approaches have been used to model these characteristics. However, some problems related to the accuracy of the results, especially at the knee of the curves have been encountered. This paper presents a contribution to solve this problem using both a simulated annealing algorithm to optimize the parameters of the Jiles-Atherton magnetic hysteresis model and the Brillouin theory to express the anhysteritic magnetization. The obtained results are in good agreement with measurements performed on silicon- iron sheets.

Synthesis of Metal and Ceramic Magnetic Nanoparticles by Levitational Gas Condensation (LGC)

Nickel (Ni) and ferrite (<TEX>$Fe_3O_4$</TEX>, <TEX>$NiFe_2O_4$</TEX>) nanoparticles were synthesized by LGC using both wire feeding (WF) and micron powder feeding (MPF) systems. Phase evolution and magnetic properties were then investigated. The Ni nanopowder included magnetic-ordered phases. The LGC synthesis yielded spherical particles with large coercivity while the abnormal initial magnetization curve for Ni indicated a non-collinear magnetic structure between the core and surface layer of the particles. Since the XRD pattern cannot actually distinguish between magnetite (<TEX>$Fe_3O_4$</TEX>) and maghemite (<TEX>${\gamma}-Fe_2O_3$</TEX>) as they have a spinel type structure, the phase of the iron oxide in the samples was unveiled by <TEX>$M{\ddot{o}}ssbauer$</TEX> spectroscopy. The synthesized Ni-ferrite consisted of single domain particles, including an unusual ionic state. The synthesized nanopowder bore an active surface due to the defects that affected abnormal magnetic properties.

Abstract: P835 CHARACTERIZATION OF THE LOW DENSITY LIPOPROTEIN RECEPTOR (LDLR) GENE MUTATION IN ALBANIA

Rapidly solidified nanocomposite Nd9Fe77−xB14Tix alloys, consisting of magnetic Nd2Fe14B phase and soft magnetic phases, were investigated. The effect of titanium addition on the structure and magnetic properties was studied. It was found that 2–4 at% Ti addition leads to substantial increase of the coercivity and maximum energy product, maintaining the remanence unchanged. The highest properties: Jr=0.81 T, JHc=907 kA/m, (BH)max=99 kJ/m3, were achieved for the Nd9Fe73B14Ti4 alloy. This effect we attribute to the formation of fine and homogeneous grain structure and a change of the phase morphology in the Ti-containing alloys. The initial magnetization curve indicates a change of the coercivity mechanisms giving rise to pinning of domain walls, which is caused by reduction of the crystallite size.

Nanocrystalline Y0.5Sm0.5Co5 ribbons obtained by melt spinning

Nanocrystalline Y0.5Sm0.5Co5 ribbons were obtained by melt spinning using a copper wheel surface speed of 40 m/s. X-ray diffraction patterns from the as-cast ground alloy and from the melt-spun ribbons were indexed as CaCu5-like hexagonal structure. Crystallographic texture was observed and a dendritic microstructure with a dendrite size between 1 and 5 μm from the noncontacting ribbon surface was measured. In addition, a finer microstructure on the contacting surface was observed. Magnetic measurements, corrected for the demagnetizing field, show a nonsaturated magnetization curve. An initial magnetization curve typical of a nucleation-type magnetization mechanism was observed and an intrinsic coercivity of 1.2 T and a Mr/Ms ratio equal to 0.67 were measured.

Initial Magnetization Curves for Powder Cores Taking into Account Distribution of Demagnetizing Field

The authors did some experiments and calculations on the initial magnetization curves for Fe-3mass%Si powder cores. The initial magnetization curves of the powder cores with gas-atomized and water-atomized powders were measured. The magnetic flux density was high for water-atomized powder cores at low magnetic fields, but it was high for gas-atomized powder cores at high magnetic fields like 10 kA/m. The initial magnetization curves were calculated taking into account the distribution of the demagnetizing field, which was supposed to have a log-normal distribution. The calculated curves were found to be in good agreement with the measured curves by adjusting the mean and standard deviation of the demagnetizing factor. The gas-atomized powder cores were estimated to have smaller standard deviations than the water-atomized powder cores. This suggested that dispersions of the gaps between the particles and the particle shapes largely affected the demagnetizing factors of the powder cores.