# Biblio

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.

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.

Having significant role in the storing, delivering and conversion of the energy, the permanent magnets are key elements in the actual technology. In many applications, the gap between ferrites and rare earths (RE) based sintered permanent magnets is nowadays filled by RE bonded magnets, used in more applications, below their magnetic performances. Therewith, the recent trends in the RE market concerning their scarcity, impose EU to consider alternative magnets (without RE) to fill such gap. The paper presents the chemical synthesis of the exchange coupled SrFe12O19/CoFe2O4 nanocomposites, based on nanoferrites. The appropriate annealing leads to the increasing of the main magnetic characteristics, saturation magnetization MS and intrinsic coercivity Hc, in the range of 49 - 53 emu/g, respectively 126.5 - 306 kA/m. The value reached for the ratio between remanent magnetization and saturation magnetization is higher than 0.5, fact that proved that between the two magnetic phases occurred exchange interaction.

Alternatives to rare earth permanent magnets, such as alnico, will reduce supply instability, increase sustainability, and could decrease the cost of permanent magnets, especially for high-temperature applications, such as traction drive motors. Alnico magnets with moderate coercivity, high remanence, and relatively high-energy product are conventionally processed by directional solidification and (significant) final machining, contributing to increased costs and additional material waste. Additive manufacturing (AM) is developing as a cost effective method to build net-shape 3-D parts with minimal final machining and properties comparable to wrought parts. This paper describes initial studies of net-shape fabrication of alnico magnets by AM using a laser engineered net shaping (LENS) system. High-pressure gas atomized pre-alloyed powders of two different modified alnico “8” compositions, with high purity and sphericity, were built into cylinders using the LENS process, and followed by heat treatment. The magnetic properties showed improvement over their cast and sintered counterparts. The resulting alnico permanent magnets were characterized using scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, and hysteresisgraph measurements. These results display the potential for net-shape processing of alnico permanent magnets for use in next generation traction-drive motors and other applications requiring high temperatures and/or complex engineered part geometries.

In order to investigate the relationship and effect on the performance of magnetic modulator among applied DC current, excitation source, excitation loop current, sensitivity and induced voltage of detecting winding, this paper measured initial permeability, maximum permeability, saturation magnetic induction intensity, remanent magnetic induction intensity, coercivity, saturated magnetic field intensity, magnetization curve, permeability curve and hysteresis loop of main core 1J85 permalloy of magnetic modulator based on ballistic method. On this foundation, employ curve fitting tool of MATLAB; adopt multiple regression method to comprehensively compare and analyze the sum of squares due to error (SSE), coefficient of determination (R-square), degree-of-freedom adjusted coefficient of determination (Adjusted R-square), and root mean squared error (RMSE) of fitting results. Finally, establish B-H curve mathematical model based on the sum of arc-hyperbolic sine function and polynomial.

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.

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.