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Co3Sn2S2, a ferromagnetic Weyl semi-metal with Co atoms on a kagome lattice, has generated much recent attention. Experiments have identified a temperature scale below the Curie temperature. Here, we find that this magnet keeps a memory, when not exposed to a magnetic field sufficiently large to erase it. We identify the driver of this memory effect as a small secondary population of spins, whose coercive field is significantly larger than that of the majority spins. The shape of the magnetization hysteresis curve has a threshold magnetic field set by the demagnetizing factor. These two field scales set the hitherto unidentified temperature scale, which is not a thermodynamic phase transition, but a crossing point between meta-stable boundaries. Global magnetization is well-defined, even when it is non-uniform, but drastic variations in local magnetization point to a coarse energy landscape, with the thermodynamic limit not achieved at micrometer length scales. [ABSTRACT FROM AUTHOR]

The results of experimental studies of magnetic properties and magnetization reversal processes of a series of alloys Sm-Gd-Zr-Co-Cu-Fe are presented. The studied samples were subjected to prolonged isothermal annealing for 24 hours, which made it possible to achieve the formation of a certain nanostructure that affects the hysteresis properties of the material and allows to achieve a high coercivity state. According to the magnetic measurements data obtained by the method of a vibrating magnetometer, the hysteresis loops are constructed, the dependence of the saturation magnetization, and the coercive force on chemical composition, and the values of the temperature coefficient of magnetization change depending on the relative content of Sm and Gd are determined. It is shown that the substitution of a part of samarium atoms for gadolinium atoms increases the effect of the mechanism of irreversible rotation of the spontaneous magnetization vector on the remagnetization of samples. Application of the studied samples in various devices puts serious demands on the stability of their magnetic properties at high temperatures. Our researches allow us to conclude that compounds with gadolinium concentration x=0,5 have the greatest coercive force, and compounds with gadolinium concentration in the range x=0,5-0,6 have the highest temperature stability.

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the paper, a magneto-mechanic hysteresis model for giant magnetostrictive materials is suggested by considering the effect of the domain rotation and domain wall motion on the magnetization process under prestress and the applied magnetic field. The coercive force, which is magneto-mechanic dependent, is proposed instead of a pinning constant in the Jiles–Atherton model. The model can well predict the characteristics of a magnetization-applied field curve and magnetostrictive strain-applied field curve shown in the experiment, especially the "overturn phenomenon" under different compressive prestresses. Furthermore, the effect of the microstructure parameter, such as the ratio of the domain wall thickness to the internal stress wavelength, the amplitude of internal stress, the ratio of the domain wall thickness to the inclusion radius, and inclusion consistency, on coercive force under applied prestress can also be described by the model. The comparison between the results predicted by the model and experiment shows that the model is suited for a wide-ranging applied magnetic field. [ABSTRACT FROM AUTHOR]

The path dependence of the magnetocaloric effect (MCE) in CoS 1.76 Se 0.24 has been studied. A field-induced paramagnetic (PM)-ferromagnetic (FM) transition results in 4.6 J/kg-K peak value of isothermal entropy change (Δ S th ) for 90 kOe field change. Above 10 K, the temperature dependence of Δ S th calculated from the forward curve (0 kOe–90 kOe) and that calculated from the reverse curve (90 kOe–0 kOe) are found to be similar, whereas at lower temperature, contrasting behaviour is observed due to the kinetic arrest of first-order magnetic transition. [ABSTRACT FROM AUTHOR]

The results of an experimental study of magnetization reversal processes of (R,Zr)(Co,Cu,Fe)Z (R = Sm, Gd) alloys taking into account micro- and nanostructure are presented. To create a highly coercive state in the samples, they were isothermally annealed at 800°C for 8-24 hours. The duration of annealing affects the formation of the nanostructure of alloys of this type. Based on magnetic measurements performed using a vibration magnetometer, magnetic hysteresis loops and graphs of the dependence of the coercive force on the chemical composition and duration of heat treatments were obtained, and the range of changes in the temperature coefficient of magnetic induction was determined depending on the relative content of Sm and Gd in the samples. Data on micro- and nanostructure were obtained using optical and scanning probe microscopy. The correlation relationships between the micro- and nanostructure parameters and the magnetic properties of the studied alloys are described. It was found that the highest values of the coercive force are achieved in an alloy in which the value is x = 0,5.

MnZn ferrites that exhibit low core losses at high frequencies are suitable for the integration and miniaturization of power conversion devices. To obtain low core losses at high frequencies, it is important to understand the underlying mechanism. In this work, MnZn ferrites with various grain sizes were produced by changing the sintering temperature. The relationship between domain morphology, dynamic magnetization behavior, and core losses at high frequencies was carefully investigated. As the average grain size approached the critical size of single‐domain state, the contribution of domain wall displacement to complex permeability decreased, while domain wall resonant frequency improved significantly, resulting in the suppression of residual loss at 3 MHz. As the average grain size increased, the domain morphology changed from a single‐domain state to a multidomain state, which increased the initial permeability and decreased hysteresis loss. However, the number of domain walls increased, causing a significant decrease in the domain wall resonant frequency, and resulting in a sharp increase in residual loss. These results provide valuable insights into reducing high‐frequency core losses in MnZn ferrites by domain engineering. [ABSTRACT FROM AUTHOR]

The use of linear transformer drivers (LTDs) is widely considered the most promising technological approach for the development of future pulsed-power accelerators. In large-scale pulsed-power accelerators, abnormal conditions like switch prefire can occur frequently during tests and normal operations due to the presence of a large number of switches. The diagnosis of such faults based on signature waveforms requires further investigation. According to previous research, the characteristics of the magnetic cores greatly influence the fault waveforms. In this paper, a full-cycle mathematical model of the magnetic core is established utilizing a classical Preisach model based on experimental results. This model is coupled with the LTD circuit model in simulations, and simulation results are obtained under the condition of switch prefire. The simulation results are in good agreement with the experimental results from a four-stage LTD module with a sharing shell and de-ionized water insulated transmission line. The magnetization process of the cores is also determined under prefire conditions. Analyses of the magnetization process indicate that the completely demagnetized core shows high permeability under positive excitation and that the permeability abruptly decreases as the excitation is reversed. The hysteresis characteristics result in a phenomenon in which the output voltage in the prefired stage is almost unipolar. Finally, the features of the fault voltages captured in the experiments are also explained. [ABSTRACT FROM AUTHOR]

While studying domain wall (DW) propagation in magnetic nanowires (NWs) may pave the way for future research and technological applications in recording heads and novel sensors, no attention has been paid to the investigation of magnetic reversal modes in multilayered NWs using angular first-order reversal curve (AFORC) analysis. Here, the magnetization reversal process of uniform FeNi/Cu NW arrays with a diameter of 45 nm electrodeposited in the anodic aluminum oxide template is systematically studied by AFORC analysis for the field angle θ (0° ≤ θ ≤ 90°) and compared with the average magnetic behavior of reversal modes based on conventional hysteresis loop measurements. The FeNi segment aspect ratio is kept constant at about 5, whereas the Cu segment length (LCu) increases from 2.5 to 25 nm. AFORC coercivity increases continuously with increasing θ, indicating that the NWs reverse their magnetization by nucleation and propagation of vortex DW (VDW). At θ = 0°, the respective hysteresis loop coercivity and magnetostatic coupling between FeNi segments along the NW length are reduced by increasing LCu from 2.5 to 25 nm, resulting in an enhancement in the reversible fraction of NWs from 10% to 48%. However, the VDW reversal mode is not influenced by the increase in NW reversibility as a function of θ for the different LCu, which arises from constant properties of the FeNi segments. The AFORC analysis of the reversal mechanism is also found to be in agreement with recent angle-dependent anisotropic magnetoresistance measurements in single multilayered NWs. [ABSTRACT FROM AUTHOR]

This paper presents a novel method of waveform generation in a single-sheet tester (SST) for measuring core losses and permeability in a steel sheet. Some improvements and modifications of the apparatus are also described. The improved way of working of a SST is important, especially in the extended range of polarization (up to 1.9 T). The system consists of hardware and software. Everything together was tested and has given good results. The proposed algorithm is described and compared to previously known methods.

In this work, we used the mean-field approximation to investigate the magnetic properties and hysteresis behavior of the ferromagnetic spin-3/2 Blume-Capel model in a graphene monolayer. The effects of crystal field, external magnetic field, and temperature on the system’s magnetizations, phase diagram, and hysteresis loops were examined. Exciting results have been obtained, particularly second- and first-order phase transitions, critical points, and multi-loop hysteresis phenomena. [ABSTRACT FROM AUTHOR]

There are several models for magnetic hysteresis. Their key purposes are to model magnetization curves with a history dependence to achieve hysteresis cycles without a frequency dependence. There are different approaches to handling history dependence. The two main categories are Duhem-type models and Preisach-type models. Duhem models handle it via a simple directional dependence on the flux rate, without a proper memory. While the Preisach type model handles it via memory of the point where the direction of the flux rate is changed. The most common Duhem model is the phenomenological Jiles–Atherton model, with examples of other models including the Coleman–Hodgdon model and the Tellinen model. Examples of Preisach type models are the classical Preisach model and the Prandtl–Ishlinskii model, although there are also many other models with adoptions of a similar history dependence. Hysteresis is by definition rate-independent, and thereby not dependent on the speed of the alternating flux density. An additional rate dependence is still important and often included in many dynamic hysteresis models. The Chua model is common for modeling non-linear dynamic magnetization curves; however, it does not define classical hysteresis. Other similar adoptions also exist that combine hysteresis modeling with eddy current modeling, similar to how frequency dependence is included in core loss modeling. Most models are made for scalar values of alternating fields, but there are also several models with vector generalizations that also consider three-dimensional directions. [ABSTRACT FROM AUTHOR]

Models of ferromagnetic hysteresis are established by following a thermodynamic approach. The class of constitutive properties is required to obey the second law, expressed by the Clausius–Duhem inequality, and the Euclidean invariance. While the second law states that the entropy production is non-negative for every admissible thermodynamic process, here the entropy production is viewed as a non-negative constitutive function. In a three-dimensional setting, the magnetic field and the magnetization are represented by invariant vectors. Next, hysteretic properties are shown to require that the entropy production is needed in an appropriate form merely to account for different behavior in the loading and the unloading portions of the loops. In the special case of a one-dimensional setting, a detailed model is determined for the magnetization function, in terms of a given susceptibility function. Starting from different initial magnetized states, hysteresis cycles are obtained by solving a nonlinear ordinary differential system. Cyclic processes with large and small amplitudes are established for materials such as soft iron. [ABSTRACT FROM AUTHOR]

• Intentionally cracked REBCO split wires were fabricated using V-bending and pressure concentration methods. • We obtained a high critical current that is higher than that of original single core coated conductor by about 15 %. • The AC-loss of the split wire can be reduced to 3 % of original single core coated conductor. • The fabrication method and conditions of split wire have a large effect on its critical current and AC-loss. Tape shape of REBCO-coated conductor with a single-core structure is commercially available. However, the single core leads to a large AC-loss due to magnetization hysteresis. A multi-core structure can be used to reduce this loss. However, it is difficult to fabricate a long multi-core wire made of a REBCO-coated conductor because defects generated during the fabrication process lead to local decreases in the critical current. To obtain a large critical current throughout the wire, the critical current in each core should be maintained. However, local defects in most cores in a long wire reduce the critical current. This study proposes an intentionally cracked REBCO split wire that has a multi-core structure but without complete separation of the cores. [ABSTRACT FROM AUTHOR]

Based on the consideration of the magnetic domain motion under different magnetization levels, an improved J-A model with variable parameters is proposed to solve the problem of significant errors in the process of calculating the inner symmetric small loops. The proposed method introduces a variable scale parameter v(B) to correct the irreversible magnetization component of the J-A model. Meanwhile, based on the magnetic domain theory, a method with variable pinning parameter k(B) and a variable domain wall bending parameter c(B) is proposed. By comparing the measured data of B30P105 Grain-Oriented (GO) silicon steel, the calculation error for each magnetization level of the model is within 7%, which means that the global hysteresis properties of GO silicon steel can be well reproduced. [ABSTRACT FROM AUTHOR]

The influence of the Dzyaloshinskii–Moriya interaction (DMI) on the formation of polar structures in nanoscale magnetoelectric films has been studied. The sequence of micromagnetic structures of different topology at magnetization and remagnetization of a film of limited size in a magnetic field oriented along the normal to the film surface is investigated. It is shown that the formation of polar structures is related to the existence of magnetic structures. Specific features of polar states in dependence of the DMI type and the interface symmetry is analyzed. [ABSTRACT FROM AUTHOR]

Cluster deposited Pd films exhibit ferromagnetism in the temperature range from 1.8 to 400 K. The magnetization properties are found to be dependent on the film thickness. The varying morphology of the resulting Pd film with respect to thickness suggests that cluster size, deposition energy, and substrate type are crucial for the resulting film magnetization. This is demonstrated by the characteristic ferromagnetic hysteresis with the temperature dependent saturation magnetization, remanence, and coercivity of palladium nanocluster aggregates. The temperature dependence of the saturation magnetization, remanence, and coercivity of Pd nanoclusters were measured using an ultra-high-sensitive magnetometer based on a superconducting quantum interference device, and the morphology of the samples was analyzed by tunneling electron microscopy. [ABSTRACT FROM AUTHOR]

Angular dependence of coercivity and remanence in 1-D chain of soft permalloy thin truncated conical disks of height 20 nm has been investigated by using finite-element micromagnetic modeling. Base radius ($R$) of the conical disk is varied between 50 and 100 nm. Top radius ($r$) of the conical nanodisk is also varied, such that the ratio $\sigma =r/R $ lies between 0.1 and 1. When the magnetic field is applied along the axis of the 1-D chain, almost square hysteresis loops are exhibited, and corresponding coercive field increases monotonically with $\sigma $. Correspondingly, the remanent magnetization state shifts from $c$ -state to homogeneous magnetization state when $\sigma $ is decreased from 0.9 to 0.5 and then to buckled magnetization state as $\sigma $ is reduced to 0.1. The remanent magnetization and coercive field monotonically decrease with an increase in the angle $\theta $ of applied magnetic field with respect axis of the 1-D chain. This behavior is due to dominating dipolar interaction along the axis of the chain, which makes it the easy axis. The Stoner–Wohlfarth (SW) model is used to approximately estimate the effective uniaxial anisotropy constant arising due to the demagnetization effect of the 1-D chain of conical nanodisks. [ABSTRACT FROM AUTHOR]

This article presents an improved algorithm for identification of the excess loss statistical parameter to get more accurate prediction of multiple harmonic magnetic hysteresis and loss properties of grain-oriented silicon steel sheets. Magnetic hysteresis characteristics of a specimen are measured on a magnetic measurement platform. Static hysteresis property can be simulated accurately by the Preisach model. The excess loss field expression under multiple harmonic magnetizations is constructed based on an extraction algorithm for the statistical parameters of excess loss. According to the equivalence of loss separation and field separation, a new dynamic model is established. In the case of different multiple harmonic magnetizations, the magnetic hysteresis characteristics obtained by predictions are compared with the test results. Also, the influences of peaked flux density, harmonic order, and harmonic content upon the total iron loss are investigated. [ABSTRACT FROM AUTHOR]

In this paper, a simple magnetization model convenient for engineering applications is presented based on the expressions of the first-order LTI system model. Considering the trade-off between the nonlinearity of anhysteretic magnetization and the hysteresis width, the proposed model employs two different equations with different magnetic field amplitudes. Furthermore, the proposed model utilizes the first-order LTI system model with a low magnetic field amplitude and a simple nonlinear function, based on the amplitude–frequency function, with a high magnetic field amplitude. Two important characteristic parameters for engineering applications, namely, amplitude and the equivalent phase lag, were exacted and analyzed to validate the computation precision of the proposed model. Then, the model was verified through comparisons to the validated Jiles–Atherton model. For easy use, similar to a physics-based model instead of a fitting method, empirical expressions for the model parameters were given, and applicable ranges of these equations were determined using the parameters of the Jiles–Atherton model. Finally, an example of the magnetization model applied to an on/off type device was computed to further verify the effectiveness of the proposed model with quite a simple expression. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a novel method of waveform generation in a single-sheet tester (SST) for measuring core losses and permeability in a steel sheet. Some improvements and modifications of the apparatus are also described. The improved way of working of a SST is important, especially in the extended range of polarization (up to 1.9 T). The system consists of hardware and software. Everything together was tested and has given good results. The proposed algorithm is described and compared to previously known methods. [ABSTRACT FROM AUTHOR]

The magnetic properties and anomalous Hall effect of the Mn4N (002) film mixed with the (111) phase were investigated. The lessened magnetization of hysteresis loops at a low field and the peak at about 50 K of the temperature-dependent magnetization curves display that magnetocrystalline anisotropies play a significant role in the magnetic properties of the film. Moreover, the centres of the anomalous Hall loops are shifted to the left for positive currents and show the opposite shift for negative currents, which may indicate the presence of current-induced effective fields. It is proposed that the (111) phase in the film could not only supply the magnetization m derivation from the c aixs but also afford asymmetric interfaces to induce effective fields. The effective perpendicular field arises from the perpendicular components of the effective fields. [ABSTRACT FROM AUTHOR]

An advanced eddy current (EC) sensor incorporating with direct current (dc) magnetizing unit is presented, and its sensor signals are evaluated numerically considering hysteresis behavior. In this article, we propose an efficient method to calculate sensor signals while considering both a moving magnetizer and a high-frequency alternating current (ac) excitation. The calculation process is divided into two sequential analyses. The first step is a time-domain simulation to calculate a gradual change of dc magnetic field from the moving magnetizer. Then, its solution of the magnetic flux density is stored and used to make a subsequent magnetization curve based on the fitting equation-based hysteresis model. The obtained sub-magnetization curve is used for a time-harmonic simulation, and the sensor signal can be finally obtained. We applied the calculation method to a prototype sensor, and it enables to evaluate sensor signals quantitatively at the different magnetizing field and defect size. [ABSTRACT FROM AUTHOR]

Wiegand wires exhibit a unique fast magnetization reversal feature in the soft layer that is accompanied by a large Barkhausen jump, which is also known as the Wiegand effect. However, the magnetic structure and interaction in Wiegand wires cannot be evaluated by conventional magnetization hysteresis curves. We analyzed the magnetic properties of Wiegand wires at various lengths by measuring the first-order reversal curves (FORCs) and by evaluating the FORC diagram from a series of FORCs. In particular, we used a FeCoV Wiegand wire with a magnetic soft outer layer, an intermediate layer, and a hard core. The magnetization of the various layers in the wire could be identified from the FORC diagrams. Furthermore, based on the interaction between multiple layers, the positive and negative polarity of the FORC distribution was clarified. [ABSTRACT FROM AUTHOR]

From fast magnetic memories with low-power consumption to recording media with high densities, realizing the magnetization reversal and interaction of magnetic layers would allow for manipulating the ultimate properties. Here, we use a pulsed electrochemical deposition technique in porous alumina templates (50 nm in pore diameter) to fabricate arrays of nanowires, consisting of FeNi layers (26âˆ'227 nm in thickness) with disk to rod-shaped morphologies separated by ultra-thin (3 nm) Cu layers. By acquiring hysteresis curves and first-order reversal curves (FORCs) of the multilayer nanowire arrays, we comprehensively investigate magnetization reversal properties and magnetostatic interactions of the layers at different field angles (0° ≤ θ ≤ 90°). These involve the extraction of several parameters, including hysteresis curve coercivity (H c Hyst ), FORC coercivity (H c FORC ), interaction field distribution width (Î" H u ), and irreversible fraction of magnetization (IF m ) as a function of θ. We find relatively constant and continuously decreasing trends of H c Hyst when 0° ≤ θ ≤ 45°, and 45° < θ ≤ 90°, respectively. Meanwhile, angular dependence of H c FORC and IF m shows continuously increasing and decreasing trends, irrespective of the FeNi layer morphology. Our FORC results indicate the magnetization reversal properties of the FeNi/Cu nanowires are accompanied with vortex domain wall and single vortex modes, especially at high field angles. The rod-shaped layers also induce maximum Î" H u during the reversal process, owing to enhancements in both magnetizing and demagnetizing-type magnetostatic interactions. [ABSTRACT FROM AUTHOR]

Magnetic energy loss P of soft magnetic laminations like SiFe sheets tends to be expressed through an integral over the power product H · dB/dt. Already in earlier papers, we stressed that distinctions are needed for the quantities H and B. However, they are not considered in practically consistent ways, in the so far literature. Here, we discuss these distinctions in closer ways, comparing loss determination by calculation and measurement, respectively. A physically consistent procedure is described for the determination of loss and magnetization power functions through measurement of bi-located quantities HS and BC (S surface, C cross section). On the other hand, it is concluded that corresponding quantitative calculations—based on co-located quantities H and B—are impeded by the high amount of technological parameters of modern steel products. For example, they result from chemical additions, and—in particular—also from specific technologies of rolling, annealing, coating or scribing. [ABSTRACT FROM AUTHOR]

The Jiles–Atherton (JA) model is widely used in real-time hysteresis estimation for its better physical understanding and less experimental efforts. However, the inherent defects of JA model may lead to some nonphysical solutions, including negative differential permeability, non-closure of minor loops, and asymmetry of centered minor loops. To deal with such problems, a limiter for differential permeability and a scaling factor for loop closure are generally adopted. However, the existing methods may cause loops’ edges overlapping and cannot solve the asymmetry of centered minor loops. Therefore, a new equation for irreversible magnetization is proposed to solve the negative differential permeability and the edges overlapping. Also, to improve the fitting performance, the JA coefficients are adjusted for different fields and different loops’ turning points. In addition, a scaling factor for centered minor loops is developed to deal with the asymmetry. The factor only needs prior knowledge of minor loops’ starting points. Besides, a modified stack model is proposed, which can extract enough information for coefficients lookup and scaling factors calculation and can realize real-time hysteresis estimation for arbitrary field. Finally, the estimation results are verified by experiments on a toroidal transformer. [ABSTRACT FROM AUTHOR]

Alloy nanoparticles are a potential candidate for research among different types of nanoparticles, due to their simple synthesizing method, promising features and diverse applications. Here, we have studied truncated octahedron FeCo alloy nanoparticles using atomistic simulations. The work is carried in the framework of classical spin Hamiltonian. Monte-carlo method and Landau Lifshitz Gilbert (LLG) equation are employed for sampling of chosen atomistic system. In this study, it has been observed that magnetic ordering temperature in the FeCo alloy is dependent on the composition of alloy in addition to the size of the system. The magnetic ordering temperature is calculated for each composition and size. Moreover, switching of the magnetic field in the FeCo alloy is studied using the combination of classical spin Hamiltonian and LLG equation as a function of composition of alloy and temperature of system. [ABSTRACT FROM AUTHOR]

A model for an equivalent electrical circuit designed for a ferrite (3C90) inductor usually used in power converters excited by a non-sinusoidal current appropriate for use in power electronics is proposed. This study, based on 3D finite element analysis, leads to significant precision advantages over 2D analysis for non-symmetric inductors. The frequency range of the analysis for the toroidal core was between 15 kHz and 1 GHz, with different levels of excitation in non-saturation and saturation status focusing on the power loss.

This study is focused on the possibility to extend the use of the first-order reversal curve (FORC) diagram method to rate-dependent hysteresis observed experimentally on soft magnetic wires. The FORC system of an amorphous magnetic wire was measured with an inductometric experimental setup in which the field-rate was maintained constant. The FORC experiment was performed for four different field-rates. We have developed and implemented a model based on the hypothesis that the magnetization processes in the samples are mainly due to the movement of a domain wall between the central domains of the wire. The differential equation of the domain wall movement is able to give a remarkably accurate description of the experimental FORC diagrams for all the field rates used in the experiment. The experimental FORCs, the FORC susceptibility diagram, and the classical FORC diagram show, however, a number of details that the model is not able to describe. In each such case, one discusses the possible physical cause of the observed behavior. [ABSTRACT FROM AUTHOR]

In this work, and by means of micromagnetic simulations, we study the magnetic properties of toroidal nanomagnets. The magnetization ground state for different values of the aspect ratio between the toroidal and polar radii of the nanotorus has been obtained. Besides, we have shown that the vortex and the in-plane single domain states can appear as ground states for different ranges of the aspect ratio, while a single domain state with an out-of-plane magnetization is not observed. The hysteresis curves are also obtained, evidencing the existence of two reversal modes depending on the geometry: a vortex mode and a coherent rotation. A comparison between toroidal and cylindrical nanoparticles has been performed evidencing that nanotori can accommodate a vortex as the ground state for smaller volume than cylindrical nanorings. [ABSTRACT FROM AUTHOR]

Strong ferromagnetic interlayer exchange couplings J in perpendicularly magnetized systems are becoming increasingly desirable for applications.We study whether ferromagnetic interlayer exchange couplings can be measured by a combination of broadband ferromagnetic resonance methods and magnetometry hysteresis loops. For this, we model the switching and the eigenexcitations in bilayer systems comprising a soft layer coupled to a thicker harder layer that possesses higher perpendicular magnetic anisotropy. For large J>0, the switching fields are essentially independent of J but the frequency of the optical eigenmode of the bilayer and the linewidth of the acoustical and optical eigenmode are directly sensitive to the coupling. We derive a corpus of compact analytical expressions to analyze these frequencies, their linewidth and discuss the meaning thereof. We illustrate this corpus on a system mimicking the fixed layers of a magnetic tunnel junction meant for spin torque applications. [ABSTRACT FROM AUTHOR]

A class of operators based on a Prandtl-Ishilinskii operator with inverse in a closed form is presented. Conversely to those considered in the past, they describe the B − H constitutive equation and not the usual J − H link. This allows its application in numerical schemes for the description of nonlinear dynamic circuits in transient conditions, with low formulation effort and computational weight, with respect to the standard inversion of the operator. The model has been implemented into a numerical scheme describing a RL nonlinear and hysteretic circuit, outlining the effects of residual magnetization and coercive field on the global current dynamics. The model performances are preliminary compared to numerical model based on the standard numerical inversion of the operator, along with the experimental results of transient current analysis. [ABSTRACT FROM AUTHOR]

A model of exchange bias in a polycrystalline bilayer based on thermal fluctuations was extended to account for an arbitrary magnetization angle of the ferromagnetic (FM) layer. It allows for a more accurate description of the thermally activated reversal of the Néel vector in antiferromagnetic (AFM) grains since the extended model takes into account the variation of barrier height resulting from the magnetization angle of the FM layer. Field-annealing (setting of the exchange bias) and further relaxation of the FM/AFM bilayer was simulated using a sequence of iterations based on this model. An array of AFM grains is generated based on a lognormal distribution of their volume. Chosen parameters of distribution are based on the fit to the experimentally measured temperature dependence of exchange bias in sputter-deposited CoFe/IrMn films. The angular deviation of the exchange bias and the degradation of its amplitude in an applied field, with relative angle varied from 0° to 180°, are calculated. Hysteresis of the exchange bias with field exposure is observed. A temperature–time ($T$ – $\tau$) diagram of the deviation angle, predicting the stability of the exchange bias under specific temperature and time, is presented. [ABSTRACT FROM AUTHOR]

Assessment of local magnetization in objects exhibiting hysteresis is crucial to the accurate design and performance estimation for a wide range of electromagnetic devices. In the past, different efforts have been carried out to incorporate hysteresis models in field computation approaches. While those models varied in methodologies, they shared a common goal of offering an accurate and computationally efficient field computation tool. Recently, it was demonstrated that a two-dimensional (2-D) vector hysteresis operator may be realized using a tri-node Hopfield neural network (HNN). The purpose of this article is to offer a novel 2-D field computation approach in media exhibiting hysteresis that uses the aforementioned hysteresis operator. The approach is based on incorporating domain-to-domain interactions in the overall network energy formulation while using typical HNN energy minimization algorithms. Details of the proposed model, numerical simulations, and comparisons with finite-element calculations are given in the article. [ABSTRACT FROM AUTHOR]

This study details the effect of the co-substitution of Ni4+ ions for Mn4+ ions on the structural, morphological, electrical, and magnetic parameters of BaMn1−xNixO3 (x = 0.1, 0.3, 0.5, 0.7, and 0.9) synthesized by the co-precipitation route. XRD pattern confirmed the hexagonal (P63/mmc (194), z = 2) phase for all samples and an additional significant secondaries phases, such as BaMn2O3, Mn2NiO3, Mn3O4, Mn2NiO4, and NiO for all doping levels. The crystallite size is obtained to be 36.8 to 90.2 nm and independent of Ni content; such a trend in SEM images presented the regular hexagonal platelets of sizes ~ 84–390 nm. Also, the ratio of Gs/Cs varies between 2 and 5. EDX revealed the presence of constituent elements with their weight percentages in BaMn1−xNixO3 products. ρXRD and ρexp are estimated to be around 5.9370 g/cm3. The porosity, P, decreases by 60% with increasing Ni-90%. The σDC increases with increasing temperature impress semiconductor behavior. SPH model is the best fit for the conductivity data. The activation energy is calculated to be (0.21–0.33) eV and increased 3 times with increasing Ni content. The magnetic hysteresis loops demonstrate the paramagnetic (PM) behavior for the tested manganite compound, where BaMn1−xNixO3 possesses paramagnetic phases and increment of Ni-content affects the magnetic parameters as Ms, remnant Mr, Hc, and magnetic moment nB. Hc increases to 2%; inversely, Ms decreases to 2%, increasing Ni-90%. The attractive electromagnetic properties suggest that BaMn1−xNixO3 could be a promising potential material in the fabrication of magnetic devices on an industrial scale. [ABSTRACT FROM AUTHOR]

We investigate the quasi-static magnetic behavior of ensembles of ferromagnetic nanoparticles consisting of MnP nanoclusters embedded in GaP(001) epilayers grown at 600, 650, and 700 °C. We use a phenomenological model, in which surface effects are included, to reproduce the experimental hysteresis curves measured as a function of temperature (120-260K) and direction of the applied field. The slope of the hysteresis curve during magnetization reversal is determined by the MnP nanoclusters size distribution, which is a function of the growth temperature. Our results show that the coercive field is very sensitive to the strength of the surface anisotropy, which reduces the energy barrier between the two states of opposite magnetization. Notably, this reduction in the energy barrier increases by a factor of 3 as the sample temperature is lowered from 260 to 120K. [ABSTRACT FROM AUTHOR]

The (Tb0.3Dy0.7Fe1.9)1-x(Tb0.15Ho0.85Fe1.9)x alloys were prepared in an arc furnace under high purity argon. The as-cast samples wrapped in Mo foil were sealed in a silica tube filled with high purity argon and were homogenized at 1000 °C for 1 day and at 950 °C for 5 days. Then, the homogenized specimens with 5mm in diameter and 8mm in length were annealed under the magnetic field of 320 kA/m. The static measurement of magnetostriction (λ//, λ⊥) was made by standard strain gauge, and the magnetization M was measured by a vibrating sample magnetometer. It is found that the main phase of annealed (Tb0.3Dy0.7Fe1.9)1-x(Tb0.15Ho0.85Fe1.9)xalloys is the (Tb,Dy,Ho)Fe2 phase with the MgCu2-type structure. The magnetostriction λ// and magnetization M of (Tb0.3Dy0.7Fe1.9)1-x(Tb0.15Ho0.85Fe1.9)x alloys increases with increasing x from x=0.1 to x=0.3 when H<240 kA/m. The hysteresis becomes small with increasing x when x⩽0.3. For magnetically annealed rod alloys, the magnetostriction markedly increases and reaches 1080 × 10-6> for x=0.3 when H=240 kA/m. [ABSTRACT FROM AUTHOR]

Memory machines with both high-power-density and wide-speed-range are becoming very attractive most recently. The purpose of this paper is to propose a novel type of memory machine, namely, claw pole memory machine. It engages an axially magnetized AlNiCo PM ring on the claw pole rotor to build the main magnetic flux in air-gap which is responsible for the electromechanical energy conversion. A magnetizing coil is equipped to online regulate the magnetization level of the permanent magnet ring, so as to achieve wide-speed-range operation. The operating principle is analyzed. The Preisach hysteresis model is combined with 3D finite element method to conduct performance assessment of the proposed claw pole memory machine. Calculation results demonstrate that the air-gap flux density can be readily adjusted by injecting DC pulse into the magnetizing coil, and the speed-range of the proposed machine can be extended as wide as six times of its base speed. [ABSTRACT FROM AUTHOR]

Direct current bias related hysteresis loss characteristics of three commercially available magnetic materials: (1) an iron based Metglas tape core, (2) a Sendust powder core, and (3) a Mn-Zn based ferrite in both un-gapped and gapped configurations were studied. The measurements are conducted for a fixed external field Hext, a fixed flux swing (ΔB), and a fixed maximum forward magnetization (Bmax) as a function of the external bias field. In all the measurements, a direct correlation is found between permeability and measured loss values as a function of dc bias field. Increased hysteresis losses are measured in the magnetization rotation region in which classical domain theory predicts minimal losses. The observed trends are discussed within the frame work of classical domain theory. [ABSTRACT FROM AUTHOR]

Hysteresis loss of magnetic nanoparticles (MNPs) has been widely studied for magnetic-hyperthermia application. On the basis of the numerical simulation for the AC magnetization curve of immobilized MNPs, we obtain an analytical expression for the hysteresis loss that is applicable to a wide range of MNP parameters and excitation conditions. This expression is more general and includes the previously obtained ones. It can be used to quantitatively study how MNP parameters and excitation conditions affect the hysteresis loss. We also use the expression to show an optimization method for hyperthermia application. First, the MNP core size that maximizes the loss is obtained as a function of the excitation conditions. For the optimum core size, the expression for the loss becomes very simple, and we can quantitatively evaluate the loss. Then, a numerical example is shown in which we obtain a condition that yields a loss as large as 1 kW/g Fe. We also discuss the hysteresis loss of MNPs suspended in liquid. The obtained results will be useful for hyperthermia application. [ABSTRACT FROM AUTHOR]

As a continuation of previously published work [A. Erdinç and M. Keskin, Int. J. Mod. Phys. B 18, 1603 (2004), doi:10.1142/S0217979204024823] the hysteretic properties of magnetization (m) and quadrupolar moment (q) have been investigated for the spin-1 Blume–Emery–Griffiths model using pair approximation. The magnetic field (h) dependence of m is produced for different values of the lattice coordination number (z), biquadratic interaction (k) and single-ion anisotropy (d). The (m , h) loops show different and novelty properties when d < 0. We also observed the hysteresis cycles in the (q , d) , (q , h) and (m , d) planes. These curves strongly depend on biquadratic interaction k. Our results are found to be in good agreement with the other theoretical findings. [ABSTRACT FROM AUTHOR]

Magnetotactic bacteria (MTB) intact cells have been applied in magnetic hyperthermia therapy of tumor, showing great efficiency in heating for tumor cell inhibition. However, the detailed magnetic hyperthermia properties and optimum heat production conditions of MTB cells are still poorly understood due to lack of standard measuring equipment. The specific absorption rate (SAR) of MTB cells is often measured by home-made equipment at a limited frequency and magnetic field amplitude. In this study, we have used a commercial standard system to implement a comprehensive study of the hyperthermic response of Magnetospirillum gryphiswaldense MSR-1 strain under 7 frequencies of 144–764 kHz, and 8 field amplitudes between 10 and 45 kA/m. The measurement results prove that the SAR of MTB cells increases with magnetic field frequency and amplitude within a certain range. In combination with the magnetic measurements, it is determined that the magnetic hyperthermia mechanism of MTB mainly follows the principle of hysteresis loss, and the heat efficiency of MTB cells in alternating magnetic field are mainly aff ected by three parameters of hysteresis loop, saturation magnetisation, saturation remanent magnetisation, and coercivity. Thus when we culture MTB in LA-2 medium containing sodium nitrate as source of nitrogen, the SAR of MTBLA-2 cells with magnetosomes arranged in chains can be as high as 4 925.6 W/g (in this work, all SARs are calculated with iron mass) under 764 kHz and 30 kA/m, which is 7.5 times than current commercial magnetic particles within similar size range. [ABSTRACT FROM AUTHOR]

Magnetostrictive behavior is characterized by a complex coupling between magnetic and mechanical quantities. While this behavior can be quite easily exploited for both actuation and sensing or energy conversion purposes, the complex hysteresis interaction between magnetization and magnetic field and mechanical stress and strain is hard to model. Nevertheless, magnetic and magnetostrictive experimental curves are quite self-similar, assuming stress as self-similarity parameter. The quantification of this concept would help modeling. Here, this concept is quantified and experimentally confirmed over different types of magnetostrictive samples. [ABSTRACT FROM AUTHOR]