Circular Magnetization Research Articles

3-D Hybrid Model of the Axial-Flux Motor Accounting Magnet Shape

This article presents a generalization of an analytical model of an axial-flux permanent-magnet machine to any magnet shape. It uses an existing model, which computes the 3-D magnetic-flux density by the separation of variables and a finite-difference method. The original magnet shape is modified by adding a radial dependency to the Fourier series description of permanent magnets (PM) magnetization. The model is then developed for a general complex magnet shape. As an example, the model will be computed for a circular magnet shape and will be compared with finite-element analysis.

Directed-Driven 8-Phase Magnetically Levitated Rotary Table Based on an Analytical-Numerical Model

The magnetically levitated rotary table (MLRT) has the potential to be applied in many industrial applications due to its excellent rotation ability and good positioning accuracy. This paper presents the prototype of a novel MLRT with a simple and compact structure. The table employs a circular permanent magnet (PM) array and a circular coil array to generate large scale rotation around the vertical axis and limited movement in the other directions. This MLRT has a higher current carrying capacity and simpler commutation law than the existing MLRT. Furthermore, different from the previous works, the magnetic force model presented in this paper is obtained by a novel analytical-numerical method that considers the clearances in the circular PM array. Thus, the predicted magnetic force and torque are more accurate than those from the existing modeling method. The translation and rotation of the table are measured by six laser sensors, which are distributed around and below the mover respectively. The PID controller is used to stabilize the system. Experiments related to the motion decoupling, trajectory tracking and load change are carried out to verify the motion performance of the novel rotary table. Compared with the existing magnetic force model, the experimental results illustrate that the novel magnetic force model, which considers the clearances in a circular PM array, is more suitable for motion control of the MLRT.

Semi-Analytical Solution of Magnetic Force and Torque for a Novel Magnetically Levitated Actuator in Rotary Table

This article proposes a fast and accurate semi-analytical calculation method of magnetic force and torque in the magnetically levitated rotary table. Benefited from the high computation efficiency and accuracy, the solution is suitable for the optimization and real-time control of the magnetically levitated system. Different with the existing harmonic method for modeling the magnetic field produced by the circular magnet array in the rotary table, the gaps in circular permanent magnet array are taken into account for the force and torque computation in this article. With the obtained magnetic flux density distribution, the magnetic force and torque can be acquired via the coordinate transformation and Lorenz integral law. Then, the numerical integral method is used to calculate the exact results of complex Lorentz integrals. Finally, the effectiveness and accuracy of the semi-analytical solution are verified by a boundary element software named Radia. Compared with the existing solutions, the new semi-analytical method is more accurate and suitable for the magnetically levitated actuator in the rotary table.

The reason of occurrence of a longitudinal residual induction of steel spindle after circular magnetization

A special attention is paid to the possibility of appearance of a longitudinal residual magnetic flux leakage (MFL) field in the tested ferromagnetic spindle after its circular magnetization. The reasons of appearance of this field and experimental verification of the interpretation are given. When the occurrence of such field is unacceptable, the spindle has to be demagnetized.

Magnet and Pin kit: Connection Symbolic and Submicroscopic Representations of Lewis dot structure and Molecular geometry

This work aims to connect the symbolic and submicroscopic representations of covalent compound’s Lewis dot structure and molecular geometry by using the Magnetic and Pin kit (MP-kit), which was constructed from magnets and pins. The MP-kit was created to facilitate the students. The kit has two sets, the first set, called Magnet set, consists of a 30x30 cm iron plate, an alphabet A with magnet (refer to central atom), 6 alphabets B with magnet (refer to surrounding atom), 18 white circular magnets (refer to valence electron of A), 42 black circular magnets (refer to valence electron of B) and 3 yellow circular magnets (refer to extra electron of molecule, from ion generation). Which was used to create the Lewis dot structure of covalent molecules. The second set, called Pin set, consists of a spherical eraser (refer to central atom), 6 pins (refer to bond and surrounding atom) and 3 droplet pins (refer to lone pair electron of central atom). Which was used to make the molecular geometry of covalent compounds, that predicted by using VSEPR theory. The users can use the Magnet set to create the Lewis dot structure without frequent drawing and rubbing on the papers. The magnets on the plate are moved for anytime when the users know it’s wrong. Moreover, this set can be used to show the number of bond pair electrons, types of bond and number of lone pair electrons on central atom. The Pin set is used to build the 3D molecular structure and specify the bond angles. The kit was used to link the symbolic and submicroscopic representations and encourage the student’s understanding. Finally, the teacher can use the MP-kit to check the student’s misconception, leading to solve problems immediately.

Development of a High Current Density Distributed Tin Method Nb3Sn Wire

We have developed a high-performance (high-J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire via a distributed tin (DT) method. Non-Cu J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> of 1100 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 16 T, 4.2 K has been achieved by improving the Sn diffusion and optimizing the Ti content. With the future circular collider magnet planned by European Organization for Nuclear Research (CERN), the target of non-Cu J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> is set to 1500 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 4.2 K, 16 T. For this target, we have chosen the DT method, which is a type of internal Sn method, and because it has no limitation of Sn solubility, higher J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> can be expected. This paper finds that further improvement of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> can be realized by controlling the Sn diffusion condition and the ternary additive elements. By setting the Sn diffusion distance to lower than 48 μm, the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn composition in multi-Nb modules becomes uniform and fine. In addition, by controlling the ternary element content (Ti) for improving the characteristics of the middle magnetic field, it is possible to achieve high J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> at 16 T.

Design of an Innovative Downhole NMR Scanning Probe

Currently, commercial downhole nuclear magnetic resonance (NMR) tools can measure depth (along with borehole axis) and radial (perpendicular with borehole axis) profile information simultaneously. However, in many cases, the lack of information due to the strong heterogeneity, partial invasion of the drilling mud around the borehole or borehole collapse will have a serious impact on applications. In order to ensure the validity of each measurement, acquisition of azimuthal information is as important as the depth and radial profile information. In this paper, we described the performance and response simulation of an innovative centralized downhole NMR scanning probe (SMRT). This probe uses hollow cylinder magnets as main magnets to produce azimuthally symmetrical polarized (related to the $z$ -axis) static magnetic field ${B} _{0}$ . Circular focusing magnets and high permeability materials are added between the main magnets to simultaneously adjust the field homogeneity along with $z$ -axis, increase the height of sensitive region and enhance the strength of ${B} _{0}$ field in sensitive region. Coil array is composed of eight independent coil units with the same performance but different azimuthal selection function used to scan the formation around the probe so that eight azimuthally distinguishable sensitive regions can be investigated. Magnets and coil array configuration are optimized with the finite-element method, and ${B} _{0}$ field and ${B} _{1}$ field is calculated to obtain the spin dynamic response. Numerical simulation results show that NMR signals from different azimuthal sections had no overlapped feature (sensitive volume of each azimuthal direction is thin shell of arc length approximate 45°) and high azimuthal resolution is feasible.

P-bits for probabilistic spin logic

We introduce the concept of a probabilistic or p-bit, intermediate between the standard bits of digital electronics and the emerging q-bits of quantum computing. We show that low barrier magnets or LBMs provide a natural physical representation for p-bits and can be built either from perpendicular magnets designed to be close to the in-plane transition or from circular in-plane magnets. Magnetic tunnel junctions (MTJs) built using LBMs as free layers can be combined with standard NMOS transistors to provide three-terminal building blocks for large scale probabilistic circuits that can be designed to perform useful functions. Interestingly, this three-terminal unit looks just like the 1T/MTJ device used in embedded magnetic random access memory technology, with only one difference: the use of an LBM for the MTJ free layer. We hope that the concept of p-bits and p-circuits will help open up new application spaces for this emerging technology. However, a p-bit need not involve an MTJ; any fluctuating resistor could be combined with a transistor to implement it, while completely digital implementations using conventional CMOS technology are also possible. The p-bit also provides a conceptual bridge between two active but disjoint fields of research, namely, stochastic machine learning and quantum computing. First, there are the applications that are based on the similarity of a p-bit to the binary stochastic neuron (BSN), a well-known concept in machine learning. Three-terminal p-bits could provide an efficient hardware accelerator for the BSN. Second, there are the applications that are based on the p-bit being like a poor man's q-bit. Initial demonstrations based on full SPICE simulations show that several optimization problems, including quantum annealing are amenable to p-bit implementations which can be scaled up at room temperature using existing technology.

Low-Barrier Magnet Design for Efficient Hardware Binary Stochastic Neurons

Binary stochastic neurons (BSN's) form an integral part of many machine learning algorithms, motivating the development of hardware accelerators for this complex function. It has been recognized that hardware BSN's can be implemented using low barrier magnets (LBM's) by minimally modifying present-day magnetoresistive random access memory (MRAM) devices. A crucial parameter that determines the response of these LBM based BSN designs is the \emph{correlation time} of magnetization, $\tau_c$. In this letter, we show that for magnets with low energy barriers ($\Delta \approx k_BT$ and below), circular disk magnets with in-plane magnetic anisotropy (IMA) lead to $\tau_c$ values that are two orders of magnitude smaller compared to $\tau_c$ for magnets having perpendicular magnetic anisotropy (PMA) and provide analytical descriptions. We show that this striking difference in $\tau_c$ is due to a precession-like fluctuation mechanism that is enabled by the large demagnetization field in IMA magnets. We provide a detailed energy-delay performance evaluation of previously proposed BSN designs based on Spin-Orbit-Torque (SOT) MRAM and Spin-Transfer-Torque (STT) MRAM employing low barrier circular IMA magnets by SPICE simulations. The designs exhibit sub-ns response times leading to energy requirements of $\sim$a few fJ to evaluate the BSN function, orders of magnitude lower than digital CMOS implementations with a much larger footprint. While modern MRAM technology is based on PMA magnets, results in this paper suggest that low barrier circular IMA magnets may be more suitable for this application.

Giant Magneto Impedance Effect of Co-Based Metallic Fiber Under Bias Magnetic Field

The giant magneto impedance, GMI, effect of Co-based metallic fibers prepared by melt-extracted technology is investigated under different bias direct electrical current Ib. The GMI curves have single peaks which are symmetric about zero field at and below 1MHz. However, the bimodal GMI curves which have asymmetric peaks are observed when Ib is over 2mA at 0.1MHz. And asymmetric GMI, AGMI, effect is also appeared at 1MHz when Ib just is 1mA and the field sensitivity of GMI effect is increased 5.6 times. The GMI effect and magnetization process is affected by the bias magnetic field profoundly induced by Ib, which is correlated with the outer shell domain structures with circumferentially magnetization easy axis existed in the outer shell of Co-rich magnetic wires with low and negative magnetostriction. Below 1 MHz, only if the bias current is over 1.5mA which induces a magnetic circumferential magnetic field is above the coercivity of 14.4A/m, the circumferential magnetization and GMI effect can experience the bias magnetic field effect. Above 1MHz, the skin effect gets stronger and significantly decreases the total participants of circular magnetization process in the fibers and consequently, the circular outer shell magnetization process gets much sensitive to circular bias magnetic field. AGMI effect with high field sensitivity is realized due to the bias current.

Electronic structure by X-ray absorption spectroscopy and observation of field induced unusually slow spin relaxation from magnetic properties in pyrochlore Eu2−xFexTi2O7

X-ray absorption spectroscopy (XAS) as well as x-ray magnetic circular dichroism (XMCD) and magnetization of hybrid pyrochlore Eu2-xFexTi2O7 were investigated, where the rare earth Eu (4f) was replaced with transition metal Fe (3d) to introduce competing 4f-3d interactions. It is confirmed that the valence states of Eu and Fe ions are formally trivalent while that of Ti ions are tetravalent (3d0). The analysis yielded that the tetravalent Ti ions occupy octahedral sites with distorted Oh symmetry which is triggered by the presence of vacant 8a anionic site adjacent to TiO6 octahedra. Further study with Fe doping revealed that it essentially reduces the octahedral distortion by introducing anionic disorder (migration of 48f oxygen ions to 8a site). Analysis of O K edge XAS spectra further confirmed the Fe substitution causing the systematic change in the ligand (O2-) coordination of the Ti4+ cations. On the other hand, a new field induced transition (with Fe doping) at low temperature T* (4 K<T*< 8 K) in ac susceptibility with unusually slow spin relaxation was observed. The transition shifted towards higher temperatures both with increasing applied field and Fe concentration. However, the single ion spin freezing (Tf ~35 K) appears to be suppressed with Fe substitution. Interestingly, small amount of Fe3+ ion substitution showed significant enhancement in the dc magnetization at lower temperatures (<100 K). Analysis further indicated rise of dipolar FM exchange interaction with Fe doping.

Ab initio study of the role of defects on the magnetic response and the structural, electronic and hyperfine properties of ZnFe2O4

In this work the effects of defects (oxygen vacancies, cationic inversion) on the structural, electronic and the magnetic response of the spinel ZnFe2O4 (ZFO) are studied by using a density functional theory (DFT) based ab initio method (the Full-Potential Linearized Augmented Plane Waves plus Local Orbitals, LAPW+lo) on the framework of the Generalized Gradient Approximation plus U (GGA+U) level. The changes induced by the defects in the hyperfine interactions at the Fe sites of the structure are also presented. In order to discuss the magnetic ordering and the electronic structure of the system we considered different spin arrangements. We found that, similar to the normal and pristine case, reduced and partially inverted ZFO presents an energy landscape characterized by a large number of metastable states. Our calculations successfully describe the hyperfine properties (isomer shift, magnetic hyperfine field and quadrupole splitting) at the Fe sites that are seen by Mössbauer Spectrocopy (MS) at 4 and 300 K, enabling us to characterize the local structure around Fe atoms. Our LAPW+lo predictions also demonstrate the relevance of both oxygen vacancies and antisites (cationic inversion) in the formation of local ferromagnetic coupling between Fe ions, giving rise to a ferrimagnetic ordering in an otherwise antiferromagnetic compound. This results support conclusions based in experimental results obtained in x-ray magnetic circular dichroism and magnetization measurements performed on zinc ferrites with different cation distributions and oxygen vacancy concentrations reported in the literature.

Impurity band conduction in group-IV ferromagnetic semiconductor Ge1-xFex with nanoscale fluctuations in Fe concentration

We study the carrier transport and magnetic properties of group-IV-based ferromagnetic semiconductor Ge1-xFex thin films (Fe concentration x = 2.3%–14%) with and without boron (B) doping, by measuring their transport characteristics: the temperature dependence of resistivity, hole concentration, mobility, and the relation between the anomalous Hall conductivity versus conductivity. At relatively low x (=2.3%), the transport in the undoped Ge1-xFex film is dominated by hole hopping between Fe-rich hopping sites in the Fe impurity levels, whereas that in the B-doped Ge1-xFex film is dominated by the holes in the valence band in the degenerated Fe-poor regions. As x increases (x = 2.3%–14%), the transport in the both undoped and B-doped Ge1-xFex films is dominated by hole hopping between the Fe-rich hopping sites of the impurity band. The magnetic properties of the Ge1-xFex films are studied by various methods including magnetic circular dichroism, magnetization, and anomalous Hall resistance and are not influenced by B-doping. We show band profile models of both undoped and B-doped Ge1-xFex films, which can explain the transport and the magnetic properties of the Ge1-xFex films.

Lorentz Transmission Electron Microscopy Image Simulations of Experimental Nano-Chessboard Observations in Co-Pt Alloys.

The magnetization configuration of a novel nano-chessboard structure consisting of L10 and L12 phases in a Co40Pt60 alloy is investigated using Lorentz transmission electron microscopy (LTEM) and micro-magnetic simulations. We show high-resolution LTEM images of nano-size magnetic features acquired through spherical aberration correction in Lorentz Fresnel mode. Phase reconstructions and LTEM image simulations are carried out to fully understand the magnetic microstructure. The experimental Fresnel images of the nano-chessboard structure show zig-zag shaped magnetic domain walls at the inter-phase boundaries between L10 and L12 phases. A circular magnetization distribution with vortex and anti-vortex type arrangement is evident in the phase reconstructed magnetic induction maps as well as simulated maps. The magnetic contrast in experimental LTEM images is interpreted with the help of magnetic induction maps simulated for various relative electron beam-sample orientations inside the TEM.

In vivo study of non-invasive effects of non-thermal plasma in pressure ulcer treatment

According to high incidence and prevalence of pressure ulcers worldwide, the purpose of this study is using of non-thermal atmospheric plasma as a novel therapy for pressure ulcers. Cold plasma was produced by applying a high-voltage (5 kV) and high-frequency (25 kHz), to helium gas. Under general anesthesia and sterile conditions, two circular magnets were used to create pressure ulcers on the dorsal skin of adult rats. The wounds were divided randomly into control and plasma-treated groups. Animals in the plasma-treated group received plasma radiation for 5 days, each day 3 times and every time 60 s. Mechanical assays were performed to determine plasma effects on the mechanical strength of the repaired tissue. The results showed that mechanical strength of repaired wound in the plasma-treated group was significantly higher than that in the control group (p < 0.05). In addition, evidence from histological studies indicates a significantly accelerated wound re-epithelialization in comparison with the control group; angiogenesis and fibrosis (collagen synthesis) were also significantly increased and the inflammation phase of wound healing was shorter in the plasma-treated group. The plasma treatment also resulted in significant wound contraction and acceleration of wound healing. The findings of present study indicate the effects of cold plasma on pressure ulcer treatment.

Reading Nanomagnetic Energy Minimizing Coprocessor

Nanomagnetic coprocessor enacts an energy minimization framework to solve the quadratic optimization problem often arisen in a computer vision paradigm. Our approach relies on the fact that the Hamiltonian of a system of coupled nanomagnets is quadratic. Therefore, a wide class of quadratic energy minimization can be solved directly by the relaxation physics of a grid of nanomagnets. The solutions of such problems are obtained from reading the magnetic state of the cells, in other words, the resistance. This monograph explores the methods to detect the magnetic states, and also considers the dimensional variation of each cell of the coprocessor and inspects the resultant change in resistance. We measure at most ${\text{7.8}}$ % change in resistance due to the process imperfection of in-house fabrication processes. This requires a read circuitry that can handle the largest deviation. Unlike STT-MRAM, the circular magnets do not have shape anisotropy but, here we show that with an additional preamplifier circuit, we are able to improve sense margin by at least ${\text{73}}$ %.

Dynamic levitation performance of Gd–Ba–Cu–O and Y–Ba–Cu–O bulk superconductors under a varying external magnetic field

We report that the dynamic levitation force of bulk high temperature superconductors (HTS) in motion attenuates when exposed to an inhomogeneous magnetic field. This phenomenon has significant potential implications for the long-term stability and running performance of HTS in maglev applications. In order to suppress the attenuation of the levitation force associated with fluctuations in magnetic field, we compare the dynamic levitation performance of single grain Y–Ba–Cu–O (YBCO) and Gd–Ba–Cu–O (GdBCO) bulk superconductors with relatively high critical current densities. A bespoke HTS maglev dynamic measurement system (SCML-03) incorporating a rotating circular permanent magnet guideway was employed to simulate the movement of HTS in a varying magnetic field at different frequencies (i.e. speed of rotation). The attenuation of the levitation force during dynamic operation, which is key parameter for effective maglev operation, has been evaluated experimentally. It is found that GdBCO bulk superconductors that exhibit superior levitation force properties are more able to resist the attenuation of levitation force compared with YBCO bulk materials under the same operating conditions. This investigation indicates clearly that GdBCO bulk superconductors can play an important role in suppressing attenuation of the levitation force, therefore improving the long-term levitation performance under dynamic operating conditions. This result is potentially significant in the design and application of HTS in maglev systems.

AC-current-induced magnetization switching in amorphous microwires

We studied the influence of AC current flowing through microwires, on magnetization dynamics. We used a previously developed Sixtus-Tonks modified setup to evaluate the domain wall (DW) velocity within the microwire. However, instead of a magnetizing solenoid, we used a current flowing through the microwire. We observed that the AC current flowing through the annealed Co-rich microwire leads to remagnetization by fast domain wall propagation. The estimated DW velocity was approximately 4.5 km/s, which is similar to and even higher than that reported for the magnetic-field-driven domain wall propagation in Fe- and Co-rich microwires. We measured the DW velocity under tensile stress, and found that the DW velocity decreases under applied stress. An observed DW propagation induced by the current flowing through the microwire is explained considering the influence of an Oersted magnetic field on the outer domain shell. This field has a circular easy magnetization direction and magnetostatic interaction between the outer circumferentially magnetized shell and the inner axially magnetized core.

Numerical Simulation of Magnetization and Demagnetization Processes

The purpose of this paper is to describe a finite-element method for the numerical simulation of magnetization and demagnetization processes in ferromagnetic pieces with hysteresis. In particular, the proposed methodology will be applied to compute the remanent flux density after a magnetic particle inspection test on specimens with cylindrical symmetry consisting of three stages: longitudinal magnetization, circular magnetization, and demagnetization.

RF magnetized ring-shaped plasma for target utilization obtained with circular magnet monopole arrangement

We proposed a new setup for generating outer ring-shaped radio frequency (RF) magnetized plasma near the chamber wall using monopole magnet setups. Three monopole magnet setups with (a) R = 5 mm, (b) R = 20 mm, and (c) R = 35 mm were investigated, where R is the gap between the magnets in consecutive circles. The distributions of the two dimensional magnetic flux lines, the absolute value of the horizontal magnetic flux density, and the discharge voltage were investigated for the proposed setups to produce outer ring-shaped plasma. A highly luminous ring-shaped plasma was observed for the setup (a), whereas multi-ring discharges were observed for the setups (b) and (c). It was found that the electron temperature decreases with increasing gas pressure for all cases. The electron temperatures were 2.42, 1.71, and 1.15 eV at an Ar gas pressure of 4 Pa for setups (a), (b), and (c), respectively. The plasma density was approximately the same for setups (b) and (c) at all gas pressures. The highest plasma densities were 6.26 × 1015, 1.06 × 1016, and 1.11 × 1016 m−3 at 5 Pa for setups (a), (b), and (c), respectively. It was found that the electron mean free path was 41.4, 63.17, and 84.66 mm at an Ar gas pressure of 5 Pa for setups (a), (b), and (c), respectively. The electron neutral collision frequency for setup (a) was higher than those for setups (b) and (c) at a constant RF power of 40 W and an axial distance of z = 13 mm from the target surface. The radial profile of the ion saturation current for setup (b) was more uniform than those for setups (a) and (c).