Evolution of magnetic domain structure and magnetic properties of Fe-based nanocrystalline powder cores during transverse magnetic field annealing

In this work, transverse magnetic field annealing (TA) was performed to FeSiBNbCu nanocrystalline powder cores (NPCs), and the magnetic properties, microstructure, and magnetic domain structure were in detail studied comparing with those after normal annealing (NA), and the mechanism of the improvement of soft magnetic properties by TA was elucidated. The experimental results show that the core loss of the sample is reduced by 14 % and the coercivity is reduced by 38 % after TA at 450 °C compared to the NA sample. The direct current bias performance of the TA sample is maintained at 67 % under a 100 Oe bias field. TA optimizes the soft magnetic properties of NPCs by optimizing the domain structure, reducing the formation of micro-vortex dots and broadening the size of the domain. These results can provide a good guide for optimizing the performance of NPCs with low core loss at high frequency.     

Influence of additional magnetic field on plasma parameters in magnetron sputtering

With three additional magnetic rings being assembled outside the discharge room and connected with the magnetic field of the conventional unbalanced magnetron sputtering, a closed magnetic field configuration distribution had been formed in the whole discharge room and which can confine discharge plasma more effectively. The spatial distribution of the newly designed magnetic field configuration was simulated using the ANSYS software. Plasma potential, electron temperature, electron density and ion density in the discharge plasma were diagnosed by Langmuir probe and the optical emission line intensity ratios of Ar⁺/Ar and Cu⁺/Cu were studied by optical emission spectroscopy. The structure and morphology of the Cu films are measured by scanning electron microscopy. A comparative study of the new magnetic field configuration with the conventional unbalanced magnetic field configuration was conducted. The results showed that the application of the additional magnetic field can increase the plasma density, enhance the ionization degree of the sputtered Cu and decrease the plasma potential effectively. The characteristics of the deposited Cu film were also influenced by the new magnetic field configuration greatly.     

Diffusion positive column of electric discharge in transverse magnetic field

The effect of a transverse magnetic field on the characteristics of planar diffusion positive column of electric discharge has been studied. It is shown that, as the magnetic induction increases, the distributions of plasma density and particle fluxes to walls become asymmetric; the density maximum shifts in the direction of Ampere’s force action, and the ion flux in this force direction can significantly exceed the reverse flux. It is established that there is a maximum value of magnetic induction, which bounds from above the region of magnetic fields in which a stationary state of the positive column is possible. In the region where a stationary state of the positive column is possible, each value of the magnetic induction corresponds to two positive-column regimes with different values of the electron energy, drift velocity, and electric field strength.     

A positive column of electric discharge in a transverse magnetic field

The influence of a transverse magnetic field on the characteristics of the positive column of electric discharge was investigated in both the diffusion and nondiffusion approximations. All solutions in the diffusion approximation were derived in analytical form. It is shown that with the enhancement of the magnetic field induction, the concentration distributions of the plasma and particle fluxes to insulated walls become nonsymmetric, the concentration maximum displaces in the direction of the magnetic force action, and the ion flux concurrent with this force may exceed substantially the ion flux in the opposite direction. The dependences of discharge parameters on the induction value are defined for helium. It is demonstrated that there is a maximum value of induction which bounds from above the range of magnetic fields, where the stationary state of the positive column is possible. In the range allowed for the stationary state, a single induction value is matched by two different modes of the positive column varying in values of the electron energy, drift speed, and electric-field strength. By means of the transverse magnetic field, it is possible to vary the electron energy within wide limits (from a few electronvolts to several hundred electronvolts).     

Fluctuations of the magnetically-supported dc discharge in coaxial configuration

Floating potential fluctuations have been studied in DC discharge plasma in two cylindrical magnetron systems using the data from single and double cylindrical Langmuir probes. The power spectral density was calculated from the experimental data in the range of magnetic fields 15-35 mT and at different pressures and probe axial positions within the discharge vessel. Plots of power spectral density vs frequency and vs wave number are presented. The possible mechanism of generation of observed fluctuations in relation to their measured properties is discussed.     

不同非平衡度磁场环境中溅射等离子体的诊断与分析

采用Langmuir探针对两种不同非平衡度磁场环境中(K值分别为2.78和6.41)的溅射等离子体进行诊断,并使用高斯仪测量靶材表面的磁感应强度,结合靶材表面磁场分布的Ansys软件模拟,分析了等离子体在非平衡磁场环境中的运动规律。结果表明:磁控阴极内侧(靶材表面中部)的溅射等离子体主要参数(离子密度、电子密度及电子温度)在两种不同非平衡度磁场中都具有随靶基距增大而逐渐减小的趋势,大量带电粒子从磁控阴极外端向远离靶材表面的区域运动;K为2.78时的等离子体参数在靶材表面的刻蚀环正上方60 mm范围内明显高于K为6.41时,前者靶材表面的磁感应强度大于后者;向外发散的磁力线数量随K值的增大而增多。     

Numerical simulation of interaction between arc discharge and transverse magnetic field

An unsteady-state three-dimensional numerical model of radiation magnetogasdynamics is used to calculate the structure of an arc discharge which interacts with an external transverse magnetic field and transverse gas flow. The velocity field and the distribution of gas temperature obtained as a result of calculations agree with experimental data. The difference between the calculated and measured values of temperature in the discharge column is approximately 5%.     

Electrocodeposition of magnetic nickel matrix nanocomposites in a static magnetic field

The effect of an external magnetic field on the electrocodeposition of composites consisting of either Co or magnetite nanoparticles in a Ni matrix has been studied. An alkaline Ni pyrophosphate bath containing citrate was used. The magnetic particles were prepared by thermal decomposition (Co) or chemical precipitation (magnetite) and characterized by transmission electron microscopy, X-ray diffraction, dynamic light scattering, zeta potential and vibrating sample magnetometry measurements. The particle incorporation showed a distinct dependency on the orientation of an externally applied magnetic field. While the particle incorporation increased in a perpendicular field (perpendicular with regard to the electrode surface), it decreased in a parallel orientation. This result is explained with the dominating action of the magnetophoretic force. The structure and the properties of the Ni layers were significantly affected by the particle codeposition. A refinement of the Ni grains was found with increasing plating current density and as a result of the nanoparticle incorporation. The magnetic hardness and the Vickers microhardness of the films increased significantly due to the incorporation of the nanoparticles.     

Performance of CAMAC TDC and ADC in magnetic field

The performance of a LeCroy CAMAC 2228A TDC and a 2249A ADC have been studied in presence of magnetic fields up to 5000 G. The conversion gains of the TDC and ADC increased with magnetic field in a non-linear fashion which can be adequately parameterized by a fourth-order polynomial. The behavior of both the TDC and ADC can be completely understood in terms of a change in the inductance of a ferromagnetic core inductor in the 20 MHz clock circuit of these units.     

Plasma parameters in the vicinity of the quartz window of a low pressure surface wave discharge produced in O2

Plasma parameters in the vicinity of the dielectric window of a low density, microwave discharge produced in O₂ at 915 MHz are investigated by a spherical probe and optical emission spectroscopy while the microwave field distribution is measured by a spectrum analyzer. The electron energy distribution function is found to be strongly dependent on the position with respect to the slot antenna, exhibiting a group of energetic electrons at locations where the electric field and the optical intensity exhibit maximum values. The density of energetic electrons decreases sharply just a few cm away from the dielectric.     

Template-free synthesis of nickel nanowires by magnetic field

Nickel nanowires were prepared by a template free method combined with chemical reduction and magnetic field. The application of an external magnetic field resulted in the formation of self-aligned metallic nickel nanowires of about 50 nm in diameter. Nickel particles were prepared in the absence of a magnetic field to better illustrate the structure directing role of the magnetic field. Physical properties of the nickel nanochains were examined by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. This study provides a simple method to prepare Ni nanowires in large scale which broads their practical applications.     

Unique properties of polyaniline in the presence of applied magnetic field and ferric chloride

Fe-contained polyaniline (abbreviated as PANI–Fe) was prepared by chemical oxidation of aniline with ammonium peroxydisulfate oxidant in 0.5 mol dm⁻³ HCl and an adequate content of FeCl₃·6H₂O solution in the presence of an applied magnetic field at room temperature. The X-ray photoelectron spectroscopy (XPS) and UV–vis and FTIR spectra suggest that there is an interaction between FeCl₃ and PANI chains, but PANI–Fe backbone is essentially identical with that of parent polyaniline. The electron paramagnetic resonance (EPR) spectrum shows that there were unpaired electrons in PANI–Fe synthesized in the presence of an applied magnetic field, the spin density and the conductivity of which are 7.308 × 10²⁰ spins g⁻¹ and 0.891 S cm⁻¹, respectively. The plot of magnetization (M) vs. the applied magnetic field (H) displays that the PANI–Fe possesses soft ferromagnetic behavior at room temperature. The results of cyclic voltammogram show that the PANI–Fe film is of excellent electrochemical activity.     

The influence of the magnetic field on the performance of an active magnetic regenerator (AMR)

The influence of the time variation of the magnetic field, termed the magnetic field profile, on the performance of a magnetocaloric refrigeration device using the active magnetic regeneration (AMR) cycle is studied for a number of process parameters for both a parallel plate and packed bed regenerator using a numerical model. The cooling curve of the AMR is shown to be almost linear far from the Curie temperature of the magnetocaloric material. It is shown that a magnetic field profile that is 10% of the cycle time out of sync with the flow profile leads to a drop in both the maximum temperature span and the maximum cooling capacity of 20-40% for both parallel plate and packed bed regenerators. The maximum cooling capacity is shown to depend very weakly on the ramp rate of the magnetic field. Reducing the temporal width of the high field portion of the magnetic field profile by 10% leads to a drop in maximum temperature span and maximum cooling capacity of 5-20%. An increase of the magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by 30-50% but the maximum temperature span by only 20-30%. Finally, it was seen that the influence of changing the magnetic field was more or less the same for the different regenerator geometries and operating parameters studied here. This means that the design of the magnet can be done independently of the regenerator geometry.     

Plasma parameter analysis of Ag sputter deposition using cathodes with different magnetic flux densities

The effects of the magnetic flux density of the Ag sputter target surface on plasma parameters were investigated using the Langmuir probe system in this work. It was found that the electron energy and electron density near the substrate clearly decreased at a high magnetic flux density. In addition, the difference between plasma potential and floating potential (V_p−V_f) decreased at the high magnetic flux density relative to the potentials at the low magnetic flux density. The changes in plasma parameters could be interpreted as the result of many electrons being trapped in the neighborhood of the target surface (cathode sheath) at the high magnetic flux density; hence, the number of electrons in the space near the substrate is reduced. The Ag thin films exhibited low resistivity at a high magnetic flux density. The reduction in resistivity was attributed to the following factors: the low electron energy and electron density near the substrate; the low kinetic energy of positive argon ions; the low kinetic energy of argon atoms backscattered onto the target surface.     

Induced magnetic anisotropy and strain in permalloy films deposited under magnetic field

Field induced magnetic-anisotropy is a very important but poorly understood property. There have been many hypotheses on the origin of the phenomenon, e.g. strain, atomic pair ordering, etc., but little experimental evidence exist. This study prepares 100 nm thick Permalloy films having the field-induced-magnetic-anisotropy and carefully measure strains, i.e. interplanar distance of crystallographic (111) planes in various directions, using high power synchrotron radiation and precise Grazing Incidence X-Ray Diffraction method. The result delineates that the field-induced-magnetic-anisotropy has a strong correlation with the strain-anisotropy in the film.     

Magnetic chains of Co spheres synthesized by hydrothermal process under magnetic field

Hydrothermal process under magnetic fields is successfully used to synthesize Co chains using reduction approach by carefully controlling the reaction conditions. The formation of the chain structure might be that magnetic fields drive the nanoscale crystals of Co to form chains. The Co sphere size and chain length are analyzed by X-ray diffraction (XRD) and scan electron microscopy (SEM). The result of the vibrating sample magnetometer (VSM) shows that the magnetic chains possess the saturation magnetization of 102 emu/g. The factors on the magnetic properties of the magnetic nanochains are discussed.     

Studies of the magnetic field intensity on the synthesis of chitosan-coated magnetite nanocomposites by co-precipitation method

Chitosan-coated magnetite nanocomposites (Fe₃O₄/CS) were prepared under different external magnetic field by co-precipitation method. The effects of the magnetic field intensity on phase composition, morphology and magnetic properties of the Fe₃O₄/CS nanocomposites were investigated by X-ray diffractometer (XRD), Fourier transform infrared analysis (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results showed that the intensity of the magnetic field in the co-precipitation reaction process did not result in the phase composition change of the magnetic chitosan but improved the crystallinity of magnetite. The morphology of Fe₃O₄/CS nanocomposites was greatly changed by the magnetic field. It was varied from random spherical particles to chain-like cluster structure and rod-like cluster structure with the magnetic field intensity increased in the synthetic process. The VSM results indicated that all the products had excellent superparamagnetic properties regardless of the presence or the absence of the magnetic field, and the saturation magnetization values of the Fe₃O₄/CS nanocomposites were significantly improved by the magnetic field.     

Design of a new magnetic refrigeration field source running with rotating bar-shaped magnets

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a prime candidate for the next generation of cooling systems. The essential components of magnetic refrigeration are the magnetic field generator and the magnetocaloric material. Although, several permanent magnet systems (magnetic field sources) for MR have been developed, recent development in magnetic refrigeration technology has encouraged researchers all over the world to think about new and original systems. This paper aims to describe a new and original magnetic refrigeration system based on a simple principle of magnetism called the Halbach effect. The proposed system is running with rotating bar-shaped magnets. This structure provides the desired varying magnetic field to the magnetocaloric material. Several configurations for the proposed systems have been investigated and presented in this paper. The design and modeling have been accomplished by using the finite elements method.     

A new semi-analytical method analyzing the magnetic field in unbalanced magnetron sputtering system

A new method, semi-analytical method (SAM), is first applied to calculate and analyze the magnetic filed in unbalanced magnetron sputtering system, and introduced in detail. An analytic solution of the scalar magnetic potential in the system can be acquired by the SAM. Its unknown number is much less than that in the numerical method. The analytic series expression of magnetic flux density can be easily obtained directly by differentiating the scalar magnetic potential function, and it can also easily ensure the precision of solving the magnetic flux density. The comparison of results between the values measured by experiment and the values calculated by the SAM has shown correctness and effectiveness of this method. The SAM cannot only accurately describe the distribution of magnetic flux density and optimize magnetic field in unbalanced magnetron sputtering system, but also be conveniently used for the simulation about plasma distribution and thin film growth.