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2020-11-30
Procházka, P..  2019.  Impulse Exciter of Rotating Blades With an Increased Excitation Force. IEEE Transactions on Instrumentation and Measurement. 68:300–302.
This paper deals with electromagnetic vibration excitation of rotating machine blades in a purpose of dynamic measurement and testing. A novel method for increasing the excitation force is presented. At the same time, the suggested method allows to reduce blade remanent induction. Examples of measurements are shown, and obtained results are discussed.
Guerra, Y., Peña-Garcia, R., Padrón-Hernández, E..  2019.  Remanence State and Coercivity in 1-D Chain of Polycrystalline Hollow Cobalt Nanospheres. IEEE Transactions on Magnetics. 55:1–5.
In this paper, we present a study about the remanence state and coercivity in 1-D chain of cobalt hollow nanospheres, by using micromagnetic simulation. The high coercivity values (Hc is determined in the range of 600-1800 Oe) and the monotonic decrease of remanence are attributed to the shape anisotropy effect due to an increase in the aspect ratio value. The configuration of magnetization in remanence showed the onion state for hollow spheres (HSs) with Re = 15 nm, whereas for Re = 30 nm, appear the curling-vortex (CV) state. Finally for a cluster of chains, constituted by cobalt HSs, with random orientations the CV state is preserved.
2020-02-24
Altun, Hüseyin, Sünter, Sedat, Aydoğmuş, Ömür.  2019.  Modeling and Simulation of Magnetizing Inrush Current in A Single-Phase Transformer. 2019 4th International Conference on Power Electronics and their Applications (ICPEA). :1–6.
In this paper, a transformer model has been developed. The model is based on the equivalent electrical circuit used in transient simulation studies which considers the non-linearity of the iron core. The non-linear ferromagnetic behavior of the iron core was obtained by using the Jiles-Atherton hysteresis model. The magnetizing inrush current of a core type single-phase transformer was analyzed under four different energization conditions. The primary winding of the transformer was connected to the supply at various instants while there was either some level of remanent flux or no remanent flux in the iron core. Corresponding simulation results are presented and discussed.
Li, Baiqiang, Ma, Shaohua, Cai, Zhiyuan, Zheng, Yahong.  2019.  A Novel Method for Calculating Residual Magnetic Flux of DC Contactors. 2019 5th International Conference on Electric Power Equipment - Switching Technology (ICEPE-ST). :535–538.
Reliable calculation model of electromagnetic mechanism characteristics of DC contactor is of great significance to its structural optimization. In this paper, the excitation process of contactor magnet is summarized, and a new calculation model of hysteresis-finite element method is proposed. It can effectively calculate the remanence of the electromagnetic mechanism under different excitation conditions, and give the relationship curve between the remanence flux and the anti-remanence gap.
2019-09-30
Elbidweihy, H., Arrott, A. S., Provenzano, V..  2018.  Modeling the Role of the Buildup of Magnetic Charges in Low Anisotropy Polycrystalline Materials. IEEE Transactions on Magnetics. 54:1–5.

A Stoner-Wohlfarth-type model is used to demonstrate the effect of the buildup of magnetic charges near the grain boundaries of low anisotropy polycrystalline materials, revealed by measuring the magnetization during positive-field warming after negative-field cooling. The remnant magnetization after negative-field cooling has two different contributions. The temperature-dependent component is modeled as an assembly of particles with thermal relaxation. The temperature-independent component is modeled as an assembly of particles overcoming variable phenomenological energy barriers corresponding to the change in susceptibility when the anisotropy constant changes its sign. The model is applicable to soft-magnetic materials where the buildup of the magnetic charges near the grain boundaries creates demagnetizing fields opposing, and comparable in magnitude to, the anisotropy field. The results of the model are in qualitative agreement with published data revealing the magneto-thermal characteristics of polycrystalline gadolinium.

Kim, Seung-Wook, Park, Sun Young, Han, Junghyun.  2018.  Magnetization Dynamics for Magnetic Object Interactions. ACM Trans. Graph.. 37:121:1–121:13.
The goal of this paper is to simulate the interactions between magnetic objects in a physically correct way. The simulation scheme is based on magnetization dynamics, which describes the temporal change of magnetic moments. For magnetization dynamics, the Landau-Lifshitz-Gilbert equation is adopted, which is widely used in micromagnetics. Through effectively-designed novel models of magnets, it is extended into the macro scale so as to be combined with real-time rigid-body dynamics. The overall simulation is stable and enables us to implement mutual induction and remanence that have not been tackled by the state-of-the-art technique in magnet simulation. The proposed method can be applied to various fields including magnet experiments in the virtual world.
Davila, Y. G., Júnior, F. A. Revoredo, Peña-Garcia, R., Padrón-Hernández, E..  2019.  Peak in Angular Dependence of Coercivity in a Hexagonal Array of Permalloy Spherical Nanocaps. IEEE Magnetics Letters. 10:1–3.

Micromagnetic simulations of coercivity as a function of external magnetic field direction were performed for a hexagonal array of hemispherical Permalloy nanocaps. The analysis was based on hysteresis loops for arrangements of nanocaps of variable thickness (5 nm and 10 nm). The angular dependence of coercivity had a maximum at about 80° with respect to the arrangement plane. An increase in coercivity with nanocap thickness is related to the magnetization reversal mechanism, where the dipole energy of individual caps generates an effective intermediate axis, locking the magnetic moments. The coercivity has maximum values of 109 Oe for 5 nm and 156 Oe for 10 nm thickness. The remanence decreases monotonically with angle. This is associated with the influence of shape anisotropy, where the demagnetizing field in the plane of the array is much smaller than the demagnetizing field perpendicular to the plane.

2019-01-16
Yang, H. F., Hu, X. K., Sievers, S., Bohnert, T., Costa, J. D., Tarcquzzaman, M., Ferreira, R., Bieler, M., Schumacher, H. W..  2018.  Coherent Control of Acoustic-Wave-Induced Magnetization Dynamics in Magnetic Tunnel Junctions. 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018). :1–2.
We report time-domain measurements of acoustic-wave-induced magnetization dynamics in magnetic tunnel junctions. The acoustic pulses are generated by femtosecond laser excitation and interact with the magnetization through magnetoelastic coupling. The induced magnetization precession is not only dependent on the externally applied magnetic field, but also on the laser excitation position. The presented method even allows us to coherently control the precession using two laser pulses at various magnetic fields and excitation positions.
2018-05-16
Kim, M., Park, H., Kim, C., Park, S. K., Ri, H. C..  2017.  The Relation Between Local Hysteresis Losses and Remanent Magnetic Fields in HTSC Films. IEEE Transactions on Applied Superconductivity. 27:1–4.

Various critical state models have been developed to understand the hysteresis loss mechanism of high-temperature superconducting (HTSC) films. The analytic relation between the hysteresis loss and the remanent field was obtained based on Bean's critical state model for thin films in the full-penetration case. Furthermore, numerical calculation of local hysteresis loops was carried out by Kim's critical state model. In this paper, we investigated local hysteresis losses for a GdBCO coated conductor by using low-temperature scanning Hall probe microscopy and reproduced the experimental results by applying the critical state model. Because of the demagnetizing effect in thin films, analysis of local hysteresis losses can be useful approach to understand of total hysteresis losses.

Maity, T., Roy*, S..  2017.  Manipulation of Magnetic Properties by Tunable Magnetic Dipoles in a Ferromagnetic Thin Film. IEEE Magnetics Letters. 8:1–4.
We demonstrate how a unique nanomodulation within a continuous ferromagnetic film can induce magnetic dipoles at predefined, submicrometer scale locations, which can tune the global magnetic properties of the film due to dipole-dipole interactions. Arrays of tunable magnetic dipoles are generated with in-plane and out-of-plane directions, which can be rotated in-plane within the three-dimensional (3-D) modulated structure of a continuous film. In-plane magnetic dipole rotation enables a methodology to control overall magnetic properties of a ferromagnetic thin film. Formation of magnetic dipoles and their tunability were studied in detail by magnetic force microscopy, high-resolution magnetic measurements, and micromagnetic simulation of a nanomodulated Ni45Fe55 alloy film. A pattern larger than a single magnetic domain would normally form a vortex in the remanent state. However, here the unique 3-D nanostructure prevents vortex formation due to the competition between in-plane and out-of-plane dipole-dipole interaction giving rise to a metastable state. Experimentally, at zero remanence, the magnetization goes through a transformation from a metastable to a stable state, where the dipole-dipole interaction depends on their geometrical arrangement. Thus, the magnetic properties of the continuous film can be varied by the proposed pattern geometry. A detail analytical study of the dipolar energy for the system agrees well with the experimental and simulated results.
Chandrasekaran, S. K., Crawford, A. C..  2017.  Demagnetization of a Complete Superconducting Radiofrequency Cryomodule: Theory and Practice. IEEE Transactions on Applied Superconductivity. 27:1–6.

A significant advance in magnetic field management in a fully assembled superconducting radiofrequency cryomodule has been achieved and is reported here. Demagnetization of the entire cryomodule after assembly is a crucial step toward the goal of average magnetic flux density less than 0.5 μT at the location of the superconducting radio frequency cavities. An explanation of the physics of demagnetization and experimental results are presented.

2017-12-20
Auerbach, E., Leder, N., Gider, S., Suess, D., Arthaber, H..  2017.  Characterization of dynamic nonlinear effects in MTJ-based magnetic sensors. 2017 Integrated Nonlinear Microwave and Millimetre-wave Circuits Workshop (INMMiC). :1–3.

The MgO-based magnetic tunnel junction (MTJ) is the basis of modern hard disk drives' magnetic read sensors. Within its operating bandwidth, the sensor's performance is significantly affected by nonlinear and oscillating behavior arising from the MTJ's magnetization dynamics at microwave frequencies. Static I-V curve measurements are commonly used to characterize sensor's nonlinear effects. Unfortunately, these do not sufficiently capture the MTJ's magnetization dynamics. In this paper, we demonstrate the use of the two-tone measurement technique for full treatment of the sensor's nonlinear effects in conjunction with dynamic ones. This approach is new in the field of magnetism and magnetic materials, and it has its challenges due to the nature of the device. Nevertheless, the experimental results demonstrate how the two-tone measurement technique can be used to characterize magnetic sensor nonlinear properties.

2017-12-04
Chen, Zhiwei, Bai, Baodong, Chen, DeZhi, Chai, Wenping.  2016.  Design of distribution devices for smart grid based on nanocomposite magnetic material. 2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia). :3546–3553.

This paper design three distribution devices for the strong and smart grid, respectively are novel transformer with function of dc bias restraining, energy-saving contactor and controllable reactor with adjustable intrinsic magnetic state based on nanocomposite magnetic material core. The magnetic performance of this material was analyzed and the relationship between the remanence and coercivity was determined. The magnetization and demagnetization circuit for the nanocomposite core has been designed based on three-phase rectification circuit combined with a capacitor charging circuit. The remanence of the nanocomposite core can neutralize the dc bias flux occurred in transformer main core, can pull in the movable core of the contactor instead of the traditional fixed core and adjust the saturation degree of the reactor core. The electromagnetic design of the three distribution devices was conducted and the simulation, experiment results verify correctness of the design which provides intelligent and energy-saving power equipment for the smart power grids safe operation.

Guerra, Y., Gomes, J. L., Peña-Garcia, R., Delgado, A., Farias, B. V. M., Fuentes, G. P., Gonçalves, L. A. P., Padrón-Hernández, E..  2016.  Micromagnetic Simulation in Hexagonal Arrays of Nanosized Hollow Nickel Spheres. IEEE Transactions on Magnetics. 52:1–6.

Arrays of nanosized hollow spheres of Ni were studied using micromagnetic simulation by the Object Oriented Micromagnetic Framework. Before all the results, we will present an analysis of the properties for an individual hollow sphere in order to separate the real effects due to the array. The results in this paper are divided into three parts in order to analyze the magnetic behaviors in the static and dynamic regimes. The first part presents calculations for the magnetic field applied parallel to the plane of the array; specifically, we present the magnetization for equilibrium configurations. The obtained magnetization curves show that decreasing the thickness of the shell decreases the coercive field and it is difficult to obtain magnetic saturation. The values of the coercive field obtained in our work are of the same order as reported in experimental studies in the literature. The magnetic response in our study is dominated by the shape effects and we obtained high values for the reduced remanence, Mr/MS = 0.8. In the second part of this paper, we have changed the orientation of the magnetic field and calculated hysteresis curves to study the angular dependence of the coercive field and remanence. In thin shells, we have observed how the moments are oriented tangentially to the spherical surface. For the inversion of the magnetic moments we have observed the formation of vortex and onion modes. In the third part of this paper, we present an analysis for the process of magnetization reversal in the dynamic regime. The analysis showed that inversion occurs in the nonhomogeneous configuration. We could see that self-demagnetizing effects are predominant in the magnetic properties of the array. We could also observe that there are two contributions: one due to the shell as an independent object and the other due to the effects of the array.