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In this paper, the electromagnetic performance of variable flux memory (VFM) machines with series-magnetic-circuit is investigated and compared for different rotor topologies. Based on a V-type VFM machine, five topologies with different interior permanent magnet (IPM) arrangements are evolved and optimized under same constrains. Based on two-dimensional (2-D) finite element (FE) method, their electromagnetic performance at magnetization and demagnetization states is evaluated. It reveals that the iron bridge and rotor lamination region between constant PM (CPM) and variable PM (VPM) play an important role in torque density and flux regulation (FR) capabilities. Besides, the global efficiency can be improved in VFM machines by adjusting magnetization state (MS) under different operating conditions.

Recently, the application fields using permanent magnet motors have been rapidly expanding. Consequently, research on the production technology of permanent magnet motors is actively progressing, with a particular emphasis on the importance of the magnetization process during assembly after inserting permanent magnets into motors. Traditional designs of post-magnetization systems are tailored to address the issue of increased leakage flux at the corners of permanent magnets in embedded permanent magnet synchronous machines, based on the rotor structure. This involves using more power and designing larger magnetizing yokes to reduce heat generation through compensatory design. This paper proposes a design process that analyzes the effects of incomplete magnetization on motor characteristics and can derive a design that does not adversely affect motor performance during localized incomplete magnetization. The process validated through simulations and experiments can reduce power consumption by approximately 40% compared to traditional methods.

In the present paper, the magnetization processes in amorphous alloys based on iron are discussed in detail. Our main goal was to measure the stabilization energy connected with the presence of microvoids (frozen during rapid cooling from the liquid phase) and to determine the interaction energy of relaxators with spontaneous magnetization vector (the so-called wN Neel) for amorphous Fe78Si13B9 alloys. A structural analysis of the alloys using X-ray measurements at the subsequent stages of crystallization was also performed. [ABSTRACT FROM AUTHOR]

In the present paper, the magnetization processes in amorphous alloys based on iron are discussed in detail. Our main goal was to measure the stabilization energy connected with the presence of microvoids (frozen during rapid cooling from the liquid phase) and to determine the interaction energy of relaxators with spontaneous magnetization vector (the so-called wN Neel) for amorphous Fe78Si13B9 alloys. A structural analysis of the alloys using X-ray measurements at the subsequent stages of crystallization was also performed.

The accurate prediction of iron losses has become a prominent problem in electromagnetic machine design. The basis of all iron loss models is found in the spatial field-locus of the magnetic flux density (B) and magnetic field (H). In this paper the behavior of the measured BH-field-loci is considered in FEM simulation. For this purpose, a vector hysteresis model is parameterized based on the global measurements, which then can be used to reproduce the measurement system and obtain more detailed insights on the device and its local field distribution. The IEM has designed a rotary loss tester for electrical steel, which can apply arbitrary BH-field-loci occurring during electrical machine operation. Despite its simplicity, the proposed pragmatic analytical model for vector hysteresis provides very promising results.

Accurate demagnetization modelling is mandatory for a reliable design of rare-earth permanent magnet applications, such as e.g. synchronous machines. The magnetization of rare-earth permanent magnets requires high magnetizing fields. For technical reasons, it is not always possible to completely and homogeneously achieve the required field strength during a pulse magnetization, due to stray fields or eddy currents. Not sufficiently magnetized magnets lose remanence as well as coercivity and the demagnetization characteristic becomes strongly nonlinear. It is state of the art to treat demagnetization curves as linear. This paper presents an approach to model the nonlinear demagnetization in dependence on the magnetization field strength. Measurements of magnetization dependent demagnetization characteristics of rare-earth permanent magnets are compared to an analytical model description. The physical meaning of the model parameters and the influence on them by incomplete magnetization are discussed for different rare-earth permanent magnet materials. Basically, the analytic function is able to map the occurring magnetization dependent demagnetization behavior. However, if the magnetization is incomplete, the model parameters have a strong nonlinear behavior and can only be partially attributed to physical effects. As a benefit the model can represent nonlinear demagnetization using a few parameters only. The original analytical model is from literature but has been adapted for the incomplete magnetization. The discussed effect is not sufficiently accurate modelled in literature. The sparse data in literature has been supplemented with additional pulsed-field magnetometer measurements.

Demagnetization characteristics of permanent magnets play a central role for the design and optimization process of permanent magnet electrical machines and magnetic actuators. Currently, practical issues, such as loss of performance of electromagnetic energy conversion devices, due to demagnetization effects in permanent magnets or due to reduced servo‐dynamics in magnetic actuators, cannot be addressed by using conventional material models or are investigated by using rough approximations valid in restricted operation regions, if at all. This paper strives to integrate demagnetizing characteristics dependent on previous magnetizing field strength in the finite element method. The discussed examples are a magnetizer of a single permanent magnet and a spoke‐type permanent magnet rotor. [ABSTRACT FROM AUTHOR]

Neutron depolarization experiments have shown that the intragranular magnetic domain structure of polycrystalline ferrites exhibits a marked grain size dependence. Below a grain size of around $3~\mu \text{m}$ , the magnetic domain structure changes from the two-domain to the mono-domain state. Ferrites composed of mono-domain grains exhibit low dissipation at megahertz frequencies. This is attributed to the absence of intragranular domain wall movement, i.e., a microscopic origin for dissipation in ferrites has been identified. The implications of this clear observation and evidence for a transition from the mono- to two-domain state in ferrites for micromagnetic theory when a single particle becomes monodomain, as well as for the initial permeability mechanisms in polycrystalline ferrites, are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a generalized dynamic hysteresis model for estimating the iron loss of complex flux waveforms. A versatile measurement system is developed to experimentally investigate the magnetic and iron loss properties of the studied soft magnetic material over a wide range of ac and dc excitation. With the measured hysteresis loop data available, an improved dynamic hysteresis model is proposed to properly include the impact of the flux density changing rate, instantaneous magnetization state, and time history of magnetic flux on dynamic field modeling. Experimental results have confirmed the desired accuracy of iron loss predictions over broad operating ranges, including conditions of pure sinusoidal fields, non-sinusoidal flux waveforms with superimposed harmonics, and flux waveforms in the presence of pre-magnetized dc-bias fields. The model parameters identified from symmetrical hysteresis loops can be utilized to predict the iron loss over a variety of conditions, making it a generalized tool for the iron loss estimation of complex flux waveforms. [ABSTRACT FROM AUTHOR]

Here, we report the structural and magnetic properties and magnetocaloric effect (MCE) in the SmNi5 compound. The presence of the hexagonal CaCu5-type structure is confirmed by the performed X-ray diffraction analysis. The strong dependence of magnetic properties over the applied external magnetic field is demonstrated. Moreover, the studies of so-called field-cooling and zero-field-cooling curves revealed an unexpected existence of a negative magnetization M in a certain temperature range. The origin of the observed phenomenon may arise from the possible switching effect in spin (M4fS) and orbital (M4fL) moment within 4f sublattice at a certain crossover temperature (Tcross). The MCE is established by the magnetic isotherms collected at different temperatures. The change of magnetic entropy (ΔSm) in the vicinity of a magnetic phase transition at TC = 29 K are reported. The maximum value of ΔSm(T,H) and the relative cooling power under Δμ0H = 1 T is estimated to be 0.59 J/kgK and 4.35 J/kg, respectively. The domination of Sm3+ states is confirmed by the analysis of the Sm 3d core-level line studied by X-ray photoemission. The character of Ni 2p line confirms the magnetic nature of Ni atoms. [ABSTRACT FROM AUTHOR]

Diffusion of the pulse magnetic field into the metal of the toroidal magnetic core wound by a transformer steel strap is considered. The 1-D numerical model has been developed, which takes into account the viscous-type dynamic losses of magnetization, as well as the eddy currents. The parameter of viscous-type dynamic losses of magnetization was measured on samples of cold-rolled anisotropic transformer steel. The processes of magnetic field propagation in the strap, when the transformer is switched to the voltage source, have been analyzed, and the iteration algorithm of calculation of magnetic field in the strap has been developed. The experimental data have confirmed the obtained calculation results. The problems of application of transformer steel in pulse transformers are considered. [ABSTRACT FROM AUTHOR]

Accurate demagnetization modelling is mandatory for a reliable design of rare-earth permanent magnet applications, such as e.g. synchronous machines. The magnetization of rare-earth permanent magnets requires high magnetizing fields. For technical reasons, it is not always possible to completely and homogeneously achieve the required field strength during a pulse magnetization, due to stray fields or eddy currents. Not sufficiently magnetized magnets lose remanence as well as coercivity and the demagnetization characteristic becomes strongly nonlinear. It is state of the art to treat demagnetization curves as linear. This paper presents an approach to model the nonlinear demagnetization in dependence on the magnetization field strength. Measurements of magnetization dependent demagnetization characteristics of rare-earth permanent magnets are compared to an analytical model description. The physical meaning of the model parameters and the influence on them by incomplete magnetization are discussed for different rare-earth permanent magnet materials. Basically, the analytic function is able to map the occurring magnetization dependent demagnetization behavior. However, if the magnetization is incomplete, the model parameters have a strong nonlinear behavior and can only be partially attributed to physical effects. As a benefit the model can represent nonlinear demagnetization using a few parameters only. The original analytical model is from literature but has been adapted for the incomplete magnetization. The discussed effect is not sufficiently accurate modelled in literature. The sparse data in literature has been supplemented with additional pulsed-field magnetometer measurements. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect and magnetization processes of the extended Ising model on the 3-dimensional octahedral lattice are studied by the classical Monte Carlo method with Metropolis algorithm. It is shown that different combinations of antiferromagnetic and ferromagnetic nearest-neighbor interactions J 1 and J 2 (in particular J 1 = − 1 , J 2 = 1 and J 1 = − 1 , J 2 = − 1) lead to the fundamentally different magnetic behaviors at nonzero temperatures, despite the fact that zero-temperature magnetization curves have exactly the same form. The reason is that the spin configurations forming zero-temperature magnetization plateaus for both J 2 = − 1 and J 2 = 1 are different, and different are also their temperature evolutions (controlled by calculations of in-plane and inter-plane sublattice magnetizations), which lead to different results for the magnetic entropy change (the magnetocaloric effect). Due to this fact a much higher positive entropy change is observed for the ferro-antiferromagnetic system compared to the pure antiferromagnetic system. • Magnetocaloric effect and magnetization processes of Ising model on octahedral lattice are studied • Combinations of antiferro/ferromagnetic interactions lead to different behaviors at T¿0 • Higher positive entropy change is observed for the combined ferro-antiferromagnetic system [ABSTRACT FROM AUTHOR]

The effect of plastic deformation on the magnetic parameters of rapid-quenched nanostructured Co66Fe4Nb2.5Si12.5B15 wires was established for the first time, as well as their sensitivity to tensile stresses. Plastic deformation changes magnetic anisotropy induced by the rapid quenching of cobalt-based metal wires, and, as a consequence, determines their magnetic parameters. Remanence is a characteristic that is most sensitive to plastic deformation. A conclusion is drawn that plastic deformation of wires leads to an increase in magnetostriction constant. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) numericalmodels of the electromagnetic behavior of superconductors have been developed, but they are not routinely used yet. This work aims at providing a comparison and validation of three different approaches: theminimum electro-magnetic entropy production method, the H-formulation of Maxwell's equations, and the volume integral equation method for 3-D eddy currents computation. The investigated problem is that of a high-temperature superconductor (HTS) parallelepiped bulk with the magnetic field parallel to two of its faces and making an angle with the other one, without and with a further constraint on the possible directions of the current. The latter constraint allows simulating a stack of thin superconducting tapes, which are electrically insulated in one direction. The results in terms of current density profiles and energy dissipation are compared, and the differences in the two situations of unconstrained and constrained current flow are pointed out. This paper constitutes a concrete result of the collaborative effort taking place within the HTS numericalmodeling community and will hopefully serve as a stepping stone for future joint investigations. [ABSTRACT FROM AUTHOR]

The suppression of flux creep in the central magnetic field of an high-temperature superconducting (HTS) coil is experimentally validated by applying a low ac magnetic field using additional coils. The HTS coil is fabricated using a Gd-based coated conductor, and a pair of the additional coils wound using copper wires, which are connected in series in the opposite direction, are located coaxially inside and outside the HTS coil. These coils are immersed in liquid nitrogen, and the temporal evolutions of the central fields in the axial direction by applying ac fields for short periods of time using the additional coils after the ramping processes of the HTS coil are observed using a Hall probe. The influences of the amplitude and frequency of ac field on the flux creep in the HTS coil are investigated experimentally. [ABSTRACT FROM AUTHOR]

In a development of the next-generation light source such as X-ray free-electron laser (FEL), it is necessary to achieve very intense undulator magnetic field with compact magnets. For this purpose, the pure-type high-Tc superconductor (HTS) undulator was proposed. In general, it is very difficult to adjust the magnetic field distribution after the HTSs are magnetized all together in a cryostat; therefore, a very careful design of the undulator magnets using a numerical analysis is required. The authors have been working on a development of the numerical simulation code of the magnetization process of the HTS undulator by using the current vector potential method ( $T$ -method). In this paper, the previously developed numerical code is modified to be used for much larger scale simulations by using a method of a multipole expansion for calculations of magnetic field aiming a practical FEL undulator design. [ABSTRACT FROM AUTHOR]

We focused on the low and high induction loss separation in soft magnetic composites (SMC), which determine the regions of different predominant magnetization processes. These are the low induction losses which are related to domain wall displacements and the high induction losses related to magnetization vector rotation, domain wall annihilation, and nucleation. The composite samples prepared by replacing of Somaloy 700 (polycrystalline iron powder covered by insulating layer) with Vitrovac 6155 (amorphous co-based alloy) have been investigated. We found out that the porosity remained constant up to 5 wt.% of Vitrovac fraction, which led to slight improvement of magnetic properties of the resulting SMC-the maximum permeability increased and the magnetization process was confirmed to be realized to a greater extent by the processes of domain wall displacement, up to a higher magnetic induction. The higher inner demagnetizing fields caused by higher porosity in sample with 20 wt.% of Vitrovac resulted in lower mobility of domain walls, exhibiting by higher energy losses and lower maximum permeability. [ABSTRACT FROM PUBLISHER]

The paper presents results of validation of the anhysteretic magnetization model for a soft amorphous alloy with significant perpendicular anisotropy. The validation was carried out for the Jiles-Atherton model with Ramesh extension considering anisotropy. Due to the fact that it is difficult to measure anhysteretic magnetization directly, the soft magnetic core with negligible hysteresis was used. The results of validation indicate that the Jiles-Atherton model with Ramesh extension should be corrected to allow accurate modeling of the anhysteretic magnetization. The corrected model may be applied for modeling the cores of current transformers operating in a wide range of measured currents.

The single hysteron model is identified to reconstruct the magnetization processes of a grain-oriented electrical steel and it is implemented in a finite-element scheme. The model involves the Zeeman energy and the anisotropy energy of the material and an interaction field to take into account others terms, such as the magnetoelastic energy, the exchange energy, inclusions, and crystallographic discontinuities. The interaction field is evaluated experimentally using a round rotational single sheet tester, where a disk sample of the material is excited for several rotational magnetization processes. Details about the finite-element scheme, the computational time, and the memory allocations involved in the simulations are presented and discussed. [ABSTRACT FROM AUTHOR]

The analytical expression for the initial magnetization curve for Fe-phenolphormaldehyde resin composite material was derived based on the already proposed ideas of the magnetization vector deviation function and the domain wall annihilation function, characterizing the reversible magnetization processes through the extent of deviation of magnetization vectors from magnetic field direction and the irreversible processes through the effective numbers of movable domain walls, respectively. As for composite materials the specific dependences of these functions were observed, the ideas were extended meeting the composites special features, which are principally the much higher inner demagnetizing fields produced by magnetic poles on ferromagnetic particle surfaces. The proposed analytical expression enables us to find the relative extent of each type of magnetization processes when magnetizing a specimen along the initial curve. [ABSTRACT FROM AUTHOR]

For the spherical kagome system {W72V30}, which is a magnetic cluster with 30 V4+ ions, recent experimental and theoretical studies on the magnetization process at low temperatures have indicated that Dzyaloshinskii–Moriya interaction is an important ingredient in this material. In this paper, we use microcanonical thermal pure quantum (mTPQ) states to calculate the temperature dependence of the magnetic susceptibility and compare our calculated results with an existing experimental susceptibility. These mTPQ states are generated to reproduce the smooth microcanonical ensemble, which is difficult from the canonical ensemble. We show that adequate choice of a parameter in the generation procedure of mTPQ states leads to the same temperature dependence as the canonical ensemble. [ABSTRACT FROM AUTHOR]

The Monte Carlo methods are used to examine effects of various factors, like the geometrical frustration, the spin–electron coupling and the increasing spin values, on the ground states and magnetocaloric effect in the two-dimensional coupled double Ising model. A number of remarkable results are found and compared with experimental behaviors observed in rare-earth tetraborides. It was shown that the geometrical frustration in a combination with different spin values S of rare-earth ions leads to the formation of a wide spectrum of magnetization sequences with fractional magnetizations and the enhanced magnetocaloric effect manifested by the appearance of heating and cooling regions in the adiabatic temperature change. A comparison of numerical results obtained for frustrated and non-frustrated lattices shows that the better cooling (heating) effects are observed in the case of the frustrated (non-frustrated) lattice and that the fractional magnetization plateaus can be surprisingly stabilized even in the absence of geometrical frustration. [ABSTRACT FROM AUTHOR]

Electrical engineers rely on analytical models to design industrial induction motors for different customer-driven applications. These models are fundamental and do not normally consider additional core losses due to stamping or welding or the impact of being inverter fed. To overcome the resulting gap between analytical results and measured data, these equivalent circuit models are traditionally adapted by correction factors. This paper presents a methodology allowing the parameterization of such an analytical model based on inverter-fed load and no-load measurements carried out for several frequencies. The results show a fair agreement over a wide range of operating points, which is acceptable for daily regular industrial applications. [ABSTRACT FROM AUTHOR]

Hysteresis properties and magnetization processes in exchange coupled Fe 10 Ni 90 /Tb 27 Co 73 bilayers separated by ultrathin Ti spacers of different thicknesses were investigated in temperature range from 79 to 450 K. Magnetization process in most samples with exchange bias took place by magnetization rotation. Exchange bias field decreased monotonously with thickness of Ti spacer increasing while coercivity had a distinguished maximum at critical value of exchange bias disappearance. Exchange bias field was shown to decrease almost linear with temperature increasing until the irreversible fall to zero at blocking temperature, demonstrating very similar behavior for bilayers with ultrathin Ti spacer of different thicknesses. [ABSTRACT FROM AUTHOR]

We report the influence of interface antiferromagnetic coupling on magnetoelectric properties of ferromagnetic bi-layers. Electric polarization arising at magnetic ingomogeneity in bi-layered ferromagnetic structure with antiferromagnetic coupling at interface in applied magnetic field has been explored. Diagrams representing dependences of electric polarization on magnetic field P ( H ) have been constructed for two magnetic field geometries (in-plane and out-of plane fields). It has been found out that P ( H ) dependences demonstrate non-monotonic behavior. Peculiarities of polarization in an in-plane-oriented magnetic field have been explained by magnetization processes. It has been shown that a variety of magnetic configurations of Bloch, Neel and mixed Bloch–Neel types can be realized in antiferromagnetically coupled film due to cubic anisotropy contribution. In the area of Bloch magnetic configuration electric polarization vanishes. The critical values of magnetic fields suppressing polarization have been estimated. [ABSTRACT FROM AUTHOR]

The magnetic structure of MnSn 2 and magnetic phase transitions in this compound have been investigated by magnetic measurements on single crystals. The results show that two antiferromagnetic (AFM) states exist below 325 K and that a transition between these two phases occurs at 74 K. Applying a magnetic field ( H ) has great influence on the transition temperature. An anomalous magnetization process at low fields occurs when the magnetic field applied along the [110] direction, which is ascribed to the contribution of the basal anisotropy. Based on the data for the magnetization processes and the phase transition of the present single crystal, the H–T phase diagram has been established. [ABSTRACT FROM AUTHOR]

A specially developed setup for precise measurement of magnetic hysteresis and Barkhausen noise is presented in this paper. A novelty of the setup consists in a unique combination of two main features: 1) an accurate local determination of the magnetic field and 2) an improved feedback control of the magnetization process. First, the magnetic field is measured by two Hall sensors at different distances above the sample. The sample field is determined by a linear extrapolation of these measured profiles of the tangential fields to the sample surface. Second, a digital feedback loop for precise control of the ac magnetization process is proposed. The feedback algorithm combines two methods of magnetizing signal adjustment: linear corrections of the magnetizing voltage amplitude and phase. The presented system is able to adjust the waveform of the magnetic induction or field to the prescribed sinusoidal or triangular shape. This provides stable and physically accurate results, which are independent of a specific experimental configuration. [ABSTRACT FROM AUTHOR]

This paper deals with the post-assembly magnetization process of motors using ferrite permanent magnets (PMs). In order to meet the needs of mass production, most motors are magnetized post assembly. However, increasing complex shapes are required to maximize the flux of PMs. As a result, certain locations in the magnet are not fully magnetized by the magnetizing fixture due to insufficient magnetomotive force. Therefore, an analysis concerning the post-assembly magnetization is needed. In this paper, the concentrated flux spoke-type synchronous motor is analyzed with regard to the magnetization process. Owing to more flux, this motor is designed as a V-shape PM. Therefore, it is not fully magnetized according to magnet shape. By identifying the effect of the magnet shape, the magnetization level is compared by the amount of flux linkage between post assembly and at full magnetization. Finally, the back electromotive force is estimated by the post-assembly magnetization method according to the magnet shape. [ABSTRACT FROM AUTHOR]

A simple, but very realistic, spin–electron model is used to study the influence of mixed spins (from electron and spin subsystems) on a formation of fractional magnetization plateaus in rare-earth tetraborides. The spin subsystem is described by the ordinary Ising model and the electron subsystem by the ordinary Hubbard model. Moreover, both subsystems are coupled by the anisotropic spin-dependent interaction of the Ising type. To model the most realistically situation in rare-earth compounds we study the following combination of mixed spins: S = 1 , 3 / 2 and 2 in the spin subsystem and s d = 1 / 2 in the electron subsystem. It is shown that the mixed spins, in a combination with the Coulomb interaction U , have the significant impact on the formation and stabilization of different magnetization plateaus. In particular, we have found that the Coulomb interaction for S = 1 and S = 3 / 2 stabilizes the 1/2 plateau and strongly suppresses the 1/3 plateau which is in perfect agreement with the experimental measurements in TmB 4 and ErB 4 compounds. At nonzero temperatures our numerical results predict one high-temperature peak (of the Ising type) in the temperature dependence of the specific heat capacity, which accords with specific heat capacity measurements in TmB 4 and ErB 4 , and one low-temperature electron peak, which is not, however, seen in experiments. The reason is probably the fact that the electron peak appears at a several times lower temperature than the spin peak and thus the experiments, made only to 2 K, did not catch it. • A new spin–electron model with mixed spins is proposed. • Mixed spins in a combination with the Coulomb interaction stabilize 1/2 plateau. • Specific heat curves exhibit single- and double-peaked structure. • Predictions of our model are in a very good agreement with experiments in TmB 4 and ErB 4. [ABSTRACT FROM AUTHOR]

Domain wall coupling in thin film sandwiches of permalloy/Cu/permalloy, obtained by sputtering, of thickness from 2000Å/200Å/2000Å up to 200Å/50Å/200Å has been studied to determine the coupling field between domain walls. To perform this study samples were cut in a size small enough to obtain a value of magnetostatic energy of the same order than the domain wall energy. Results show the possibility of obtaining magnetic dots with bistable behaviour of microns size.Se ha estudiado el acoplamiento entre paredes magnéticas en películas tipo sandwich de permalloy/Cu/permalloy, obtenidas por pulverización catódica, de espesores comprendidos entre 2000Å/200Å/2000Å, para evaluar el campo de acoplamiento entre las paredes. Para realizar este estudio se han cortado la muestras de un tamaño lo suficientemente pequeño para conseguir que la energía magnetostática de la muestra sea del mismo orden de magnitud que la energía de la pared magnética. Los resultados obtenidos muestran la posibilidad de conseguir dots magnéticos de tamaños de micrómetros con un comportamiento biestable.

The magnetic and magnetotransport properties have been investigated in a family of multilayer glass-coated microwires with a soft CoFeSiB nucleus and magnetically harder Co and CoPtRh deposited outer layers. Their magnetic properties are mainly determined by the magnetic interactions between the magnetic phases, i.e., the magnetoelastic coupling generated by the supplementary mechanical stresses induced by the deposited layers and by the magnetostatic interactions between the soft magnetic inner core and the hard magnetic deposited layers. The deposition of 900 nm-thick hard magnetic layers (Co and CoPtRh) on the soft magnetic CoFeSiB glass-coated microwire leads to a biphase magnetic character. Isothermal annealing at 300 °C for 1 h of multilayer microwires determines a slight decrease of the coercive field, an increase in the relative magnetic permeability, and to an increase in the magnetoimpedance response, more significant for the CoFeSiB/Co multilayer microwires. The possibility to design the magnetic and magnetotransport properties through magnetic coupling and annealing makes these materials very competitive as the functional sensing elements. [ABSTRACT FROM AUTHOR]

Microstructure and magnetic entropy changes in amorphous and partially crystallized Fe86−x Pt x Zr7Nb1Cu1B5 (x=0 or 5) alloys are studied. The transmission Mössbauer spectrum for the as-quenched Fe86Zr7Nb1Cu1B5 alloy is typical of weak amorphous ferromagnets with the average hyperfine field of (4.78±0.02)T. The replacing of 5% of Fe atoms by Pt increases the average hyperfine field up to (13.12±0.02)T. High resolution electron microscopy and transmission Mössbauer spectroscopy do not reveal the existence of medium range ordering regions. In the as-quenched state of both alloys the maximum magnetic entropy change occurs near the Curie points and is equal to 0.51Jkg−1 K−1 and 0.85Jkg−1 K−1 for Fe86Zr7Nb1Cu1B5 and Fe81Pt5Zr7Nb1Cu1B5, respectively. The maximum magnetic entropy change decreases after partial crystallization of the alloys. Both alloys in the as-quenched state above their Curie points behave like Curie–Weiss paramagnets with the paramagnetic Curie temperature equals to Θ 1=(330±1)K for Fe86Zr7Nb1Cu1B5 alloy and Θ 2=(370±1)K for Fe81Pt5Zr7Nb1Cu1B5 alloy. [ABSTRACT FROM AUTHOR]

The paper presents results of validation of the anhysteretic magnetization model for a soft amorphous alloy with significant perpendicular anisotropy. The validation was carried out for the Jiles-Atherton model with Ramesh extension considering anisotropy. Due to the fact that it is difficult to measure anhysteretic magnetization directly, the soft magnetic core with negligible hysteresis was used. The results of validation indicate that the Jiles-Atherton model with Ramesh extension should be corrected to allow accurate modeling of the anhysteretic magnetization. The corrected model may be applied for modeling the cores of current transformers operating in a wide range of measured currents. [ABSTRACT FROM AUTHOR]

We present a comprehensive model for a description of magnetization processes in rare-earth tetraborides (RET). The model is based on the coexistence of two subsystems, and namely, the spin subsystem described by the XXZ Heisenberg model and the electronic subsystem described by the generalized Hubbard model on the Shastry–Sutherland lattice. Moreover, both subsystems are coupled locally by the anisotropic double-exchange interaction, which besides the usual J z term of the Ising type takes into account also the J x y term representing the spin-flip processes. The model is solved numerically using the exact Lanczos method on the cluster of L = 12 sites and the truncated Lanczos method on the cluster of L = 36 sites. The special attention is paid on a description of individual and combined effects of the double-exchange interaction J x y and the Heisenberg J x y ′ interaction on the stabilization of magnetization plateaus with fractional magnetization. We have found that the J x y and J x y ′ interaction terms exhibit fully opposite effects on the stability of the main 1/2 and 1/3 plateau phases. While the J x y interaction destroys the 1/2 plateau and stabilizes the 1/3 plateau, the J x y ′ interaction stabilizes the 1/2 plateau and destroys the 1/3 plateau. For J x y > 0 and J x y ′ > 0 only small combined effects of J x y and J x y ′ on the stability of the 1/3 and 1/2 plateaus are found in the weak coupling limit ( J x y / J z ≤ 0. 5 and J x y ′ / J z ′ ≤ 0. 5), but in the opposite limit the significant effects of these terms on the suppression of the 1/3 plateau and the stabilization of 1/2 plateau are observed. • The influence of double-exchange and Heisenberg interaction on magnetization processes are examined. • It is found that they exhibit fully opposite effects on the stability of the main 1/2 and 1/3 plateaus. • Double-exchange interaction destroys the 1/2 plateau and stabilizes the 1/3 plateau. • Heisenberg interaction stabilizes the 1/2 plateau and destroys the 1/3 plateau. [ABSTRACT FROM AUTHOR]

In the vicinity of the first-order transition temperature, the \Ni50{\Mn}35{\In}15 Heusler alloy exhibits interesting magnetizing processes. The virgin curve at 280 K lies entirely outside the major loop, and the area of the MH loop formed by the virgin curve and the sequential descending curve is significantly larger than that of the major loop. At 275 K, the virgin curve lies slightly outside the major loop, and the area of the loop containing the virgin curve is slightly larger than that of the major loop. These differences are attributed to the different initial magnetic states of the alloy at the two temperatures. The initial state at 280 K is a mixed state, consisting of a low magnetization majority phase and a high magnetization minority phase. The initial state at 275 K is almost all the low magnetization phase. At both temperatures, a strong enough field converts the low magnetization phase to the high magnetization phase. The initial state affects the reverse transition from high to low magnetization phase upon cycling the field back to zero. The behavior of the virgin curve, major loop, and related properties is a complex function of the field and initial state. Similar behavior is expected in other Heusler alloys and other materials exhibiting first-order magneto structural transitions. [ABSTRACT FROM PUBLISHER]

There are two main thrusts towards new permanent-magnet materials: improving extrinsic properties by nanostructuring and intrinsic properties by atomic structuring. Theory—both numerical and analytical—plays an important role in this ambitious research. Our analysis of aligned hard-soft nanostructures shows that soft-in-hard geometries are better than hard-in-soft geometries and that embedded soft spheres are better than sandwiched soft layers. Concerning the choice of the hard phase, both a high magnetization and a high anisotropy are necessary. As an example of first-principle research, we consider interatomic Mn exchange in MnAl and find strongly ferromagnetic intralayer exchange, in spite of the small Mn-Mn distances. [ABSTRACT FROM AUTHOR]

The paper presents a micromagnetic solver, where the long-range contributions to the magnetostatic field are computed by a multipole expansion technique and the spatial distribution of the exchange field is reconstructed via a finite difference scheme able to handle non-structured meshes. In this way, large samples having complex geometries can be simulated. The numerical accuracy, the computational efficiency and the flexibility of the proposed solver are investigated by comparison to standard approaches. [ABSTRACT FROM PUBLISHER]

A finite difference scheme suitable for unstructured meshes is here applied to the spatial reconstruction of the exchange field in Landau-Lifshitz-Gilbert equation. This method determines second-order derivatives by solving a over-determined set of linear equations through norm minimization of a Taylor series expansion functional. In this way, the local character of the exchange field computation typical of standard finite difference schemes is preserved, but similarly to finite element schemes irregular meshes can be handled. In this paper, the accuracy and computational efficiency of the proposed approach is tested in comparison with finite element and structured mesh based finite difference schemes. [ABSTRACT FROM AUTHOR]

Cables in superconducting magnets are subjected to field-dependent losses, i.e., induced interstrand and interfilament coupling losses, and superconductor hysteresis losses. For the two kinds of induced eddy currents, analytical and numerical models are available, allowing calculating the dissipated power under various operating conditions. For the losses stemming from the superconductor magnetization, the literature only gives formulas for the dissipated energy over closed excitation cycles. We derive an expression for the instantaneously dissipated hysteresis losses during an arbitrary ramp profile using a simplified geometry and hysteresis model. This allows estimating the losses dissipated in nonclosed excitation loops. [ABSTRACT FROM PUBLISHER]

We have employed the Monte Carlo (MC) simulation technique to study the aging effect on the Zero-Field-Cooled (ZFC) magnetization curves of ultra-small CoFe2O4 nanoparticles (mean size \sim 3 nm) embedded in a Si matrix. We consider spherical nanoparticles consisting of an ordered ferrimagnetic core and a ferrimagnetic disordered surface. The spins in the particles interact with nearest neighbors Heisenberg exchange interaction. Our simulations show that the spin-glass like disorder at the surface affects the magnetic properties to the extent that they exhibit aging effect: the low temperature ZFC magnetization depends on the time (waiting time, tW) spent before applying the magnetic field at a temperature at which most of the surface moments are frozen. The results of our MC simulations are in good agreement with the experimental findings confirming that the random freezing of surface spins is responsible for the aging effect. [ABSTRACT FROM PUBLISHER]

Measurements of magnetic properties have been performed on commercially available low carbon steels (Armco and non-oriented electrical steels) in order to construct and test a Preisach model for materials under stress. The measurements include hysteresis loops of samples under tensile stress taken during loading and after unloading at given strain levels. A vector Preisach model using the SW model as the elementary operator, superposition to account for easy axes dispersion and a weighed mixture of normal distributions to account for the long-range interactions established through the magnetoelastic coupling is proposed. The model reproduces the effect of applied stress, verifying the experimental finding that the permeability of a material under tensile stress decreases. The Preisach density is constructed in such a way as to account for the strong magnetostatic interactions observed in the high induction regions in the case of built-in stresses, so the model is also able to capture the effect of the residual compressive stresses in unloaded materials. The use of the differential permeability and its first derivative are proposed as parameters to be monitored in NDT applications. [ABSTRACT FROM PUBLISHER]

This paper aims to tackle the general problem of increasing the performances of small permanent-magnet (PM) machines, through the use of bonded magnets instead of the more diffused ferrite magnets. In particular, the study is developed for a fractional-slot concentrated winding PM machines for automotive applications. Neodymium bonded magnets with different and unconventional resins are realized in the internal laboratories. The rotors with the different magnet technologies are experimentally characterized, and the experimental values are compared with the simulation ones. The obtained results allow to define the possible performance increment. Finally, this paper analyzes the possible improvement of the rotor magnetic circuit for a better exploitation of the bonded magnets, without altering the stator structure and the motor housing. [ABSTRACT FROM PUBLISHER]

The magnetoimpedance effect is attractive for thin film-based magnetic sensor applications. Recently a significant progress has been made in the development of appropriate theories, preparation and characterization of MI thin film-based structures. In the present work FeNi(100\ nm)/Cu(3.2\ nm)]4/FeNi(100\ nm)/Cu(L_Cu)/[FeNi(100\ nm)/Cu(3.2\ nm)]4/FeNi(100\ nm) multilayered structures with open magnetic flux have been prepared by rf-sputtering. Their magnetic properties and MI were studied as a function of the thickness of the central Cu lead. It was shown that the thickness of the Cu lead is an important parameter. The highest sensitivity (\approx50%/Oe, f=160\ MHz) was observed for the sample with a central Cu layer thickness of about a half-thickness of a magnetic layer (LCu\approx 250\ \rm nm). The maximum sensitivity of the real part of the impedance was also obtained for this thickness (\approx75%/Oe). [ABSTRACT FROM AUTHOR]

The study of unusual influence of Ru substitution for Fe on magnetic properties of \Lu2{\Fe}17 is extended to a series of R2{\Fe}17. The work is performed on single-crystalline samples of \Lu2{\Fe}16{\Ru}, \Y2{\Fe}17-x{\Ru}x(0\leq x\leq 1) and \Er2{\Fe}17-x{\Ru}x (x=0, 1) compounds. The collinear ferromagnetic ground state present in the R2{\Fe}17 (Y and Lu) parent alloys is destroyed in R2{\Fe}17-x{\Ru}x, and antiferromagnetism is stabilized in the whole temperature range of magnetic order. The ordering temperatures of R2{\Fe}16{\Ru} (R=\Y, Lu, Er) are 120 K, and no evidence of spontaneous magnetization is found in any of the alloys. The Fe sublattice in \Er2{\Fe}16{\Ru} is most likely to be antiferromagnetic as well, however the type of magnetic order of the Er sublattice is not clear. All the compounds under study possess an easy-plane type of magnetic anisotropy and exhibit wide field-induced hysteretic transitions at low temperatures. [ABSTRACT FROM AUTHOR]