Correction of temperature dependency of a standard; case-study – magnetic flux density standard

Temperature dependence of measuring instruments represents one of the most influential error sources in measurement of most physical quantities. There are several methods of reducing or cancelling substantial temperature influence on instruments.

In this paper we are describing a calculative correction method in the field of precision magnetic flux density measurements, which involves mathematical correction of the instrument properties. For dc magnetic fields under 5 mT, nuclear magnetic resonance (NMR) measurements are both impractical and time-consuming and in some environments even impossible. To avoid complex NMR measurements, field coils as magnetic flux density transfer standards are often used. A method for correction of an air-cored field coil’s coil-constant in order to take into account its temperature dependence is presented. As a result, instead of a complex NMR measurement only a simple current and temperature measurement were needed to calculate the generated magnetic flux density with relative uncertainty of 0.025%.     

径向磁力轴承定子结构参数的确定

通过分析径向磁力轴承的结构形式、磁极数以及线圈槽形，针对径向磁力轴承定子的结构设计，在充分考虑材料的电磁性能的基础上，提出了一种结构参数的确定方法，为磁力轴承的优化设计及参数驱动的智能设计提供了参考。     

Characterization of LSMO/C60 spinterface by first-principle calculations

Spinterface between fullerene C₆₀ and La_{0 7}Sr_{0 3}MnO₃ (LSMO) was studied by means of density functional theory. Co-existence of many different configurations was shown, and probabilities of their appearance were estimated. Dependence of composite properties on configuration and temperature was also investigated. Key role of transition metal atoms in both binding between composite compartments and magnetic ordering in C₆₀ molecule was discussed. The latter was suggested to be responsible for spin-polarized charge transport while overall magnetic moment of fullerene molecule is relatively small.     

Measuring magnetic anisotropy with a rotatable ac electromagnet

Magnetic anisotropy of magnetic thin films was determined from a series of hysteresis loops measured via a rotatable alternate current (ac) electromagnet, the rotation angle of which could be continuously tuned at 360° with a high resolution. Co₂FeAl Heusler alloy films grown by molecular beam epitaxy were used to show the benefits of the method for measuring magnetic anisotropy.     

Adsorption studies of Pb (II) by two different magnetic MnFe2O4 materials synthesized with sol-gel process

Abstract

The spherical nanomaterials of MnFe-Ac and MnFe-Na can be synthesized with sol-gel method. The adsorption test of Pb (II) was carried out with two kinds of synthesized nanomaterials, and discussed their adsorption effects of Pb (II). The characteristic was analyzed by SEM, XRD, XPS and magnetic measurements. As the results showeed, the particles size of the material became smaller, but the morphology did not change after adsorption. The change of Ms was from 42.7 and 62.0?emu/g to 25.6 and 89.4?emu/g, respectively. By Langmuir and Freundlich models, the maximum adsorption amounts of Pb (II) were 23.40 and 41.56?mg/g, respectively, and analysis demonstrated that the adsorption of Pb (II) on samples was monolayer adsorption. The kinetic analysis showed that the adsorption of Pb (II) on the two materials was more in accordance with the pseudo-second-order model, which indicated that adsorption process of the materials for Pb (II) were primarily limited by the chemical adsorption.     

A Stokesian dynamics approach for simulation of magnetic particle suspensions

The dynamic behaviour of μm-scale ferromagnetic particles in suspension is of interest for various mineral beneficiation processes. It is, however, difficult to experimentally study such processes at the particle-level. In these instances it can be advantageous to resort to suitable particle simulation methods.Stokesian dynamics is a mesh-free numerical technique developed for suspensions of nm to mm size particles. The method inherently considers hydrodynamic interactions, but additional interaction models can be included depending on the system under investigation. We here present a Stokesian dynamics (SD) implementation, which allows for simulation of the motion of suspended magnetic particles in presence of an external magnetic field. The magnetic interaction model includes particle-field interactions as well as pairwise interactions between magnetised particles.Simulations are compared with experiments using a laboratory-scale flow cell. The method is shown to be realistic for studying ferromagnetic suspensions in mineral processing applications, and can be useful in understanding and predicting the efficiency of mineral separation processes.     

High enhanced magnetization in carbon-doped Mn3Ga thin films

Carbon-doped Mn₃Ga thin films were grown on Si/SiO₂ substrates using rf magnetron sputtering technique. The tetragonal D0₂₂–type crystalline structure of ferrimagnetic Mn₃Ga is preserved on the Mn₃GaC_x films upon carbon concentrations up to x = 0.5, whereas higher concentrations lead to the formation of the antiperovskite Mn₃GaC phase. Geometry optimization calculations using the density functional theory were performed on a 2 × 2 × 2 Mn₃GaC_0.25 supercell with C in different positions in order to find that the most stable position for the C is interstitial octahedral site. Magnetic M(H) loops show that saturation magnetization M_s of Mn₃GaC_0.25 is enhanced to 200 kAm⁻¹ (from M_s = 90 kAm⁻¹ for undoped films). The increase of the C concentration leads to a reduction of the Curie temperature from 770 K to ∼420 K at the same time that the lattice cell suffers an expansion. The enhancement of M_s is explained in terms of a 90° ferromagnetic superexchange Mn-C-Mn interaction.     

Subspace identification analysis of RFX and T2R reversed-field pinches

Input–output datasets from two magnetic confinement fusion (MCF) experiments of the reversed-field pinch (RFP) type are examined. The RFP datasets, which are samples of the distributed magnetic field dynamics, are naturally divided into many smaller batches due to the pulsed-plasma operation of the experiments. The two RFP experiments considered are (i) EXTRAP T2R (T2R) with 64 inputs and 64 outputs and (ii) RFX-mod (RFX) with 192 inputs and 192 outputs. Both T2R and RFX are magnetohydrodynamically unstable and operates under magnetic feedback with optional dither injection. Using subspace system identification techniques and randomised cross-validation (CV) methods to minimise the generalisation error, state-space orders of the empirical systems are suggested. These system orders are compared to “stabilisation diagrams” commonly used in experimental modal analysis practice. The relation of the CV system order to the decay of the singular values from the subspace method is observed. Both (i) stable vacuum diffusion and (ii) unstable plasma response datasets are analysed. Apparent simulation and prediction errors are quantified for both cases using a deviation-accounted-for index. These results are purely data-driven. A simple approach towards exploitation of the subspace techniques for finite-element model refinement and data confrontation is presented.     

Tailorable magnetic properties of ε-Fe2O3/SiO2 hybrid via alkaline etching

In this study, conventional silicon alkaline-etching procedure was utilized to tailor magnetic properties of ε-Fe₂O₃/SiO₂ hybrid. It was found that the saturation magnetization, coercivity and exchange bias field can be readily changed and tailored by altering the etching time and frequency in a set of sodium hydroxide solutions. The relative quantity of ε-Fe₂O₃ phase, the proximity or pinning effect derived from SiO₂ phase as well as the phase transformation from ε-Fe₂O₃ to α-Fe₂O₃ during etching treatment were three main factors to its controllable magnetic properties. This work will shed new light on the development of functional ε-Fe₂O₃/SiO₂ composites with tailorable magnetism in practical magnetically-relevant applications.     

The cation inversion and magnetization in nanopowder zinc ferrite obtained by soft mechanochemical processing

Two zinc ferrite nanoparticle materials were prepared by the same method – soft mechanochemical synthesis, but starting from different powder mixtures: (1) Zn(OH)₂/α-Fe₂O₃ and (2) Zn(OH)₂/Fe(OH)₃. In both cases a single phase system was obtained after 18 h of milling. The progress of the synthesis was controlled by X-ray diffractometry (XRD), Raman spectroscopy, TEM and magnetic measurements. Analysis of the XRD patterns by Rietveld refinement allowed determination of the cation inversion degree for both obtained single phase ZnFe₂O₄ samples. The sample obtained from mixture (1) has the cation inversion degree 0.3482 and the sample obtained from mixture (2) 0.400. Magnetization measurements were confirmed that the degrees of the inversion were well estimated. Comparison with published data shows that used method of synthesis gives nano powder samples with extremely high values of saturation magnetizations: sample (1) 78.3 emu g⁻¹ and sample (2) 91.5 emu g⁻¹ at T = 4.5 K.