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In this paper, core loss features of soft magnetic composite (SMC) material from 5 Hz to 1000 Hz have been properly measured and discussed under alternating and three dimensional (3-D) rotational magnetizations. The comparison results show that the rotational core losses are greater than that of the alternating core losses at the same magnitude of magnetic induction densities, especially at relatively higher excitation frequencies. The corresponding rotational hysteresis properties, such as magnetic flux density vector loci, magnetic field strength vector loci are also measured and analyzed. Experimental results show that SMC materials have good 3-D features, and great potential for application in rotational magnetic flux machines. © 2013 IEEE.

This paper presents the magnetic flux distributions in Fe-based superconducting materials including single crystal of Ba(Fe 1.9Ni 0.1)As 2 and Ba(Fe 1.8Co 0.2)As 2, as well as polycrystalline SmFeO 0.75F 0.2As by means of magneto-optical imaging (MOI) technique. The single crystals were grown out of FeAs flux while polycrystalline sample was grown by hot-press. A MOI film with in-plan magnetization was used to visualize flux distributions at the sample surface. A series of magneto-optical images was taken when the samples were zero-field cooled and field cooled. The flux behavior, including penetration into and expelling from the samples, as well as pinning properties were studied. When external fields increase, flux is completely shielded from the crystals, then, gradually penetrates toward the crystal center from the edge. For polycrystalline sample, Meissner state was observed at very low field. With increasing the field further, flux penetrates into the sample easily along grain boundary, then into grain. Compared with high-T c cuprates, it is found that the flux distributions in Fe-based superconducting materials are very similar to that in high-T c cuprates with strong pinning strength. © 2012 American Institute of Physics.

We have investigated the structural, magnetic, and ferroelectric properties of magnetically frustrated multiferroic YMnO 3 single crystals. The ferroelectric domain structures of YMnO 3 samples were studied by piezoresponse force microscopy. Instead of domain vortex structure in stoichiometric crystals, YMnO 3-δ exhibits a random domain configuration with straight domain walls. In magnetic measurements, the YMnO 3-δ crystal shows typical antiferromagnetic behavior with higher Nel temperature and lower magnetization compared to the stoichiometric sample. The ordered oxygen vacancies dominate multiferroicity through tailoring the domain wall structure. © 2012 American Institute of Physics.

This paper systematically reports our recent study on the magnetic hysteresis property of magnetorheological (MR) fluid material under one dimension alternating and two dimension rotating magnetic field. The measurement was completed by a single sheet tester and a MR fluid sample container. The principle of measurement and the calibrating procedure of sensor coil are presented. The experiment results, such as H-B loop, H & B vector loci and lagging angle between H and B are analyzed and discussed. The results will be useful in the design of smart structure using MR material fluid. © 2011 IEEE.

Compared with the conventional fixed speed drive, a major factor that handicaps the wide acceptance of variable speed drive with high efficiency permanent magnet (PM) motors is its high cost. This paper presents an effort to reduce the material and manufacturing costs of PM motors by using the soft magnetic composite (SMC), and the highly matured powder metallurgic technology. Because the SMC's magnetic properties are quite different from that of the traditional silicon steel sheets, special efforts have been made on measurement and modelling of vectorial magnetic properties, electrical machine topologies, and drive schemes in order to make the best use of the material. Various PM SMC motors of transverse flux topologies have been designed, fabricated, and tested. The detailed results are presented and discussed. © 2011 IEEE.

The critical current density, Jc, flux pinning behavior and magneto- resistance results of BaFe2-xNi xAs2 single crystal have been investigated in fields up to 13 T over a temperature range of 2 to 20 K. The magnetoresistance below the superconducting transition temperature (Tc) shows Arrhenius thermally activated behavior: oexp(-Uo(T,H)/kBT), where Uo is the thermally activated energy. BaFe2-xNixAs2 exhibits high thermally activated flux flow energy with a very weak field dependence. Jc is as high as 2 105A/cm2 for zero magnetic field at 2 K. Jc was found to decrease for B 1 T, but showed a very weak field dependence and remained nearly constant with increasing magnetic field for B 1 T at T 2, 5, and 10 K. Flux jumping was also observed in magnetization loops at very low temperature for large sample, which is related to the high Jc in the single crystal. A peak effect was observed at 10 K. © 2011 American Institute of Physics.

The magneto-resistance, critical current density, Jc, upper critical field, Hc2, and flux pinning properties of LaFeAsO 1-xFx superconductors were investigated systematically by magnetic and magneto-transport measurements in the fields up to 13 T over a temperature range of 5-35 K. It was found that the Hc2 increased with increasing fluorine concentration up to x 0.15, while with higher fluorine doping, Hc2 decreased. A peak effect in the J c as a function of field was observed at T 15 K for both the 5 and 15 fluorine doped samples. The broadening of the superconducting transition in magnetic field can be well understood by the thermally activated flux flow model. The pinning potential, Uo, scales as Uo/k B B-n with n 0.13 for B 1 T and n - 0.68 for B 1 T for LaFeAsO0.85F0.15. © 2011 American Institute of Physics.

Superconductivity has been found in newly discovered iron-based compounds. This paper studies the motion of magnetic vortices in BaFe1.9Ni 0.1As2 single crystal by means of the magneto-optical imaging technique. A series of magneto-optical images reflecting magnetic flux distribution at the crystal surface were taken when the crystal was zero-field cooled to 10 K. The behavior of the vortices, including penetration into and expulsion from the single crystal with increasing and decreasing external fields, respectively, is discussed. The motion behavior is similar to that observed in high-Tc superconducting cuprates with strong vortex pinning; however, the flux-front is irregular due to randomly distributed defects in the crystal. © 2011 American Institute of Physics.

The soft magnetic composite (SMC) is a new type of soft magnetic material made of insulated iron powders. Its special characteristics could enable the development of low cost high performance electrical machines. This paper presents the measurement and modelling of magnetic properties of SMC under 3D magnetizations. Detailed descriptions of the 3D magnetic property tester, principle of measurement, core loss models, and experimental results are included and discussed.

Considering the special characteristics existing in the pulse-width modulated (PWM) switching converter, a general method for the time-stepping finite element analysis based electromagnetic field coupling with its feeding circuit used in the analysis of PWM switching converter considering hysteresis effects is introduced in this paper. Comparing with the electromagnetic field-circuit indirect coupling method (ICM), the proposed method has overcome the drawback that the ICM cannot take the hysteresis effects into account. Compared with the electromagnetic field-circuit direct coupling method (DCM), the proposed method has the similar accuracy but higher efficiency. Furthermore, like the ICM, the proposed method also divides the system with higher state dimensions produced by the DCM into two subsystems with lower state dimensions; this may reduce the algorithm convergence problem which often happens in high dimensional systems. © 2008 American Institute of Physics.

One and two-dimensional hysteresis properties are normally used to characterize soft magnetic materials. However, the results are not informative enough to disclose three-dimensional (3-D) hysteresis behavior under vector excitations. This paper presents a 3-D sensing house for measuring the 3-D property of soft magnetic materials. The fabrication, construction, and calibration are discussed in detail. Test results of 3-D magnetic flux density B and field strength H loci of soft magnetic composite material are presented. © 2007 - IOS Press and the authors. All rights reserved.

Soft magnetic composite (SMC) materials are especially suitable for construction of electrical machines with complex structures and three-dimensional (3D) magnetic fluxes. In the design and optimization of such 3D flux machines, the 3D vector magnetic properties of magnetic materials should be properly determined, modeled, and applied for accurate calculation of the magnetic field distribution, parameters, and performance. This paper presents the measurement of 3D vector magnetic properties and determination of 3D reluctivity tensor of SMC. The reluctivity tensor is a key factor for accurate numerical analysis of magnetic field in a 3D flux SMC motor. © 2007 Elsevier B.V. All rights reserved.

A three-dimensional (3-D) magnetic property measurement system, which can control the three components of the magnetic flux density B vector and measure the magnetic field strength H vector in a cubic sample of soft magnetic material, has been developed and calibrated. This paper studies the relationship between the B and H loci in 3-D space, and the power losses features of a soft magnetic composite when the B loci are controlled to be circles with increasing magnitudes and ellipses evolving from a straight line to circle in three orthogonal planes. It is found that the B and H loci lie in the same magnetization plane, but the H loci and power losses strongly depend on the orientation, position, and process of magnetization. On the other hand, the H vector evolves into a unique locus, and the power loss approaches a unique value, respectively, when the B vector evolves into the round locus with the same magnitude from either a series of circles or ellipses. © 2006 Elsevier B.V. All rights reserved.

Even under one-dimensional (1D) alternating or 2D rotating magnetic excitation, a magnetic material shows 3D magnetic property due to the rotation of magnetic domains. Only when the 3D properties are properly considered the understanding and modelling of the magnetisation process can be complete. This paper summarises our work about the investigation on the magnetic properties of soft magnetic composite (SMC) material under 3D vector magnetisations by using a 3D magnetic property tester. The core loss models under 3D flux density vectors are analysed and applied to predict the core losses of a permanent magnet claw pole/transverse flux motor with SMC core. © 2005 Elsevier B.V. All rights reserved.

To gain insight into the origin of the colossal reduction of resistance in response to magnetic field in colossal magnetoresistance manganite, the magnetic field induced transition in ferromagnetic La0.7 Ca0.3 Mn O3 was studied using a high-resolution magneto-optical imaging (MOI) technique. The MO images were captured in various magnetic fields over a wide temperature range for both highly dense samples with strong-link grain boundaries and porous samples with weak-link boundaries. Formation and evolution of magnetic domains as a function of field or temperature were clearly observed around and far below the Curie temperature TC =240 K. Ferromagnetic areas tend to grow to large sizes and finally join together at the expense of paramagnetic areas as the field increases or temperature decreases for strong-link samples. A sharp magnetoresistive transition is observed when the sample changes from a paramagnetic insulator to a metallic ferromagnetic phase in the vicinity of TC. In contrast, the porous samples showed magnetoresistance over a wide temperature range and exhibited a remarkable grain boundary related magnetization process in addition to magnetization within grains. A close correlation is found between the magnetization process observed by MOI and magnetoresistance measurements. Our MOI results indicate that the strong-link or weak-link grain boundaries are responsible, respectively, for magnetoresistance occurring either only in the vicinity of the ferromagnetic transition or over a very wide temperature range. © 2006 American Institute of Physics.

Hysteresis phenomenon is one of the important characteristics of soft magnetic materials. A three-dimensional (3D) magnetic property measurement system has been developed. This system can effectively control the locus of the time-varying magnetic flux density vector B and measure the corresponding magnetic field strength vector H in a cubic sample of soft magnetic material. The sample involved in this study is a soft magnetic composite sample made of highly pure iron powder. This paper investigates the B and H loci in 3D space and the power loss when the B loci are controlled to become circles and ellipses lying in three orthogonal planes. It is found that the B and H loci lie in the same magnetization plane, but the H loci and losses depend strongly on the orientation, position, and process of magnetization. On the other hand, the H vectors evolve into a unique locus pattern, and the power losses approach a unique value when the B vectors evolve into the same loci through either a series of small circles or ellipses. © 2006 American Institute of Physics.

This paper reports the measurement of magnetic properties of the soft magnetic composite material SOMALOYTM 500 in a square sample under different patterns of flux density with 2D magnetic excitations. The test system, principle of measurement, magnetic power loss calculation, and methods of correction for misalignment of H surface sensing coils are presented. The experimental results show that although nominally isotropic, the SOMALOY TM 500 sample exhibits some anisotropy. The results are useful in the design and performance analysis of rotating electrical machines. © 2005 Elsevier B.V. All rights reserved.

This paper analyzes the effect of the internal field on the measurement with two-dimensional (2-D) rotating fluxes. It is demonstrated that due to the effect of the internal field, the misalignment of H sensing coils, causing the asymmetry of H loci and the discrepancy of the rotational core losses between two opposite rotating directions cannot be corrected completely. A numerical averaging method is employed to eliminate the angular error. Finally, the B and H loci and rotational core losses of a soft magnetic composite (SMC) material were measured under circular rotating magnetic flux density vectors, and the results were corrected by the proposed averaging method. © 2005 IEEE.

Cylindrical single grains of Gd Ba2 Cu3 Oy (Gd-123) with a diameter of 25 mm were successfully fabricated by melt-texture growth (MTG) process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density (Jc) showed that it was possible to fabricate large Gd-123 single grain with a high Jc at high temperatures and fields by means of properly controlling the starting powders of Gd2 O3, BaC O3, and CuO before the MTG process. © 2005 American Institute of Physics.

This paper presents a vector model of magnetization based on the three-dimensional (3-D) Stoner-Wohlfarth elemental operator. To account for the magnetic interactions between particles, a phenomenological mean-field approximation is employed. The paper also illustrates the numerical simulation results of the magnetization in 3-D. This model will be useful to simulate the magnetization process of complicated topology flux electromagnetic devices. © 2005 IEEE.

This paper, as a pioneering work, presents measurement techniques to characterize soft magnetic materials in three-dimensional (3D) space. A novel 3D magnetic property tester using cubic sample has been constructed and calibrated. Some phenomena and problems of measurement caused by the imperfect winding and misalignment of coils are analyzed. The correction methods are proposed and employed. The new soft magnetic composite SOMALOY™ 500 is investigated. © 2004 Elsevier B.V. All rights reserved.

Soft magnetic composite (SMC) materials are especially suitable for construction of low-cost high-performance motors with three-dimensional (3-D) magnetic fields. The 3-D finite-element analysis (FEA) conducted in the design of a claw pole transverse flux motor (CPTFM) with an SMC core reveals very complicated B (flux density) loci in the core when the motor rotates. In order to understand and account for the effects of the patterns of B loci on motor parameters and performance such as core losses, a 3-D magnetic property testing system was built for magnetic measurement on a cubic SMC sample. 3-D rotational core loss models in SMC materials and rotating motors are developed. © 2005 IEEE.

To investigate the magnetic properties of electrical contact between the superconducting filaments in a multifilament tape, this paper studies the vortex motion across a simpler planar model of the tape, namely an array of superconducting film strips with shorted ends, a 'shunted-x-array'. The vortex motion visualized by magneto-optical imaging is discussed when external currents, magnetic fields, and both simultaneously are applied. When transport current alone is applied, the flux distribution in the shunted-x-array strips is very similar to that in a single strip. However, the behaviour is completely different in the presence of an external magnetic field. The induced current flows around the entire sample to shield the inner region, while the vortices penetrate first into the outermost strips, and then into the next strips in turn as the field increases. For this case, the flux distribution is symmetrical about the central vertical line of the sample. When current and field are simultaneously applied, the vortex penetration into the sample is no longer symmetrical because the resultant current is not a simple linear superposition of the induced and applied currents.

The magneto-optical imaging (MOI) technique is widely employed to characterize the magnetic properties of superconductors and other magnetic materials because it can easily show the variation of flux density over a plane with relatively high resolution. In this paper, flux profiles visualized by the MOI technique will be presented for different experimental conditions. The sample investigated is a high-temperature superconducting single strip. Three cases are investigated: 1) application of external currents; 2) application of external magnetic fields; and 3) simultaneous application of external magnetic field and current. The behavior of complicated vortex penetration into the samples for different conditions will be discussed in detail. The magnetic flux profiles are calculated taking into account the sample thickness, as well as the interval between the sample and the MOI indicator film. The calculated and the experimental results are compared and discussed.

In a magnetic material, even under an alternating or a two-dimensional rotating magnetic excitation, the magnetic flux is three dimensional (3-D) due to the rotation of magnetic domains. For measurement of 3-D magnetic properties of materials, a novel tester has been developed. The test principle, construction, and calibration of the 3-D magnetic property tester will be presented. Experimental results of B and H Loci and core losses with 3-D magnetic fluxes are included and discussed. The system is working and the results are validated.