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Different models have been used to evaluate the interfacial Dzyaloshinskii–Moriya interaction (DMI) from the asymmetric bubble expansion method using magneto-optics. Here, we investigate the most promising candidates over a range of different magnetic multilayers with perpendicular anisotropy. Models based on the standard creep hypothesis are not able to reproduce the domain wall (DW) velocity profile when the DW roughness is high. Our results demonstrate that the DW roughness and the interface roughness of the sample layers are correlated. Furthermore, we give guidance on how to obtain reliable results for the DMI value with this popular method. A comparison of the results with Brillouin light scattering (BLS) measurements on the same samples shows that the BLS approach often results in higher measured values of DMI. [ABSTRACT FROM AUTHOR]

In this article, boundary conditions for Landau–Lifshitz equations at the interface between two ferromagnets with different interfacial Dzyaloshinskii–Moriya interactions (iDMIs) are derived. We calculated and verified the analytical expression for the energy flux density continuity for the spin-wave (SW) propagation through the ferromagnet with stepwise iDMI considering the boundary conditions mentioned. Analytical expressions for reflection, transmission coefficients, and the nonreciprocity factor are calculated in the case of SW propagation through a ferromagnet with the stepwise iDMI. Two different types of nonreciprocity effects for SW propagation through a ferromagnet with the stepwise interface Dzyaloshinskii–Moriya interaction are revealed for opposite orientations of Dzyaloshinskii–Moriya vector. The material parameters of a ferromagnet and the stepwise iDMIs are found for which the extremely high nonreciprocity factor (>10) is expected according to the results of calculations. The results of this article deepen the knowledge about the SW propagation control in magnonic devices. [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]

The laser beam melting (LBM) additive manufacturing (AM) technology is used for processing a high silicon steel (Fe 6.5%wtSi). The effects of LBM machine parameters over microstructure and magnetic properties are studied. Particular attention is dedicated to determining the influence of a normalized energy density over the material density, the grain size, and the crystallographic texture and their impact on the magnetic properties: magnetic flux density and coercivity. [ABSTRACT FROM AUTHOR]

In this article, we derive a magnetic dipole model for two identical, electrically conducting, and permeable macroscopic spheres that are exposed to an oscillating homogeneous magnetic field. Our model predicts both amplitude and phase of the induced field outside the spheres. The description is provided for parallel and transverse excitation relative to the axis through the sphere centers. This geometric decomposition allows the application of arbitrary excitation field directions. Our approach is based on one dipole per sphere. The origins of these secondary dipole fields are proposed to be found at positions slightly displaced from the sphere centers to consider the mutual interaction. This displacement and the resulting phase of the dipole moments strongly depend on the distance between the spheres as well as on complex-valued first- and second-order response factors, which contain material properties and the oscillation frequency. We demonstrate the usefulness of our displaced dipole model in terms of efficiency and accuracy compared to other computationally simple approaches. [ABSTRACT FROM AUTHOR]

Cerium-substituted yttrium iron garnet (Ce:YIG) thin films are promising magneto-optical (MO) materials for the application in optical isolators. Ce:YIG can be grown on the YIG seed layer, and the change of layer thickness ratio for Ce:YIG to YIG may result in different magnetic properties. In this work, Ce:YIG (Ce1Y2Fe5O12) to YIG (Y3Fe5O12) bilayer films, with different thickness ratios of 2:1, 4:1, 6:1, and 8:1, were grown by pulsed laser deposition (PLD); 2:1 and 4:1 films consist of pure YIG phase; 6:1 and 8:1 films consist of YIG phase, Y2Fe4O9 phase with hexagonal structure, and Y2O3 phase with cubic structure. Y2Fe4O9 and Y2O3 phases induce the decrease of saturation magnetization ($M_{s}$). The concentration of Fe2+ and Ce4+ ions increases with layer thickness ratio increasing, resulting in the decrease of saturation magnetization ($M_{s}$), coercivity ($H_{c}$), and magnetic anisotropy energy ($E$). It is found that the best magnetic properties, including $H_{c}$ (26.9 Oe), $M_{s}$ (140.6 emu/cm3), and $E$ (257.5 J/cm3), are obtained in the 2:1 film. [ABSTRACT FROM AUTHOR]

To minimize the total film thickness and to make symmetric layer structures, the ultrathin symmetric Ta(1 nm)/Pt(1.7 nm)/ Co($t$)/Pt(1.7 nm)/Ta(1 nm) multilayers, where the Co thickness ($t$) was varied from 0.3 to 1.4 nm, were fabricated on Si substrate with a native oxide layer. The perpendicular magnetic anisotropy (PMA) was observed in the range of $t = 0.3-0.9$ nm. The coercive field of ~16 mT for $t =0.7$ nm and the domain wall velocity of ~ $100 \mu \text{m}$ /s for $t \le0.6$ nm were comparable with those in previous reports. Surprisingly, as the Co thickness approached 0.9 nm, the domain wall velocity dropped dramatically to ~ $0.1 \mu \text{m}$ /s, and the magnetic domain structure shifted from big-circular domains to small-bubble domains. A change from PMA to easy-plane magnetic anisotropy around $t =0.95$ nm could be explained using the classic Kittel’s model. Because of their good PMA, such ultrathin symmetric multilayers could be used in various spintronic applications. [ABSTRACT FROM AUTHOR]

This work delineates the thermally stable, self-biased straintronic nanomagnetic logic (NML) by leveraging the dipole coupling between an array of nanomagnets using only two electrodes that discard the intricate voltage mechanism of multi-electrode systems. For efficient NML operation, the self-biased elliptical nanomagnets with fixed aspect ratio can be designed over a particular thickness range, limited by the thermal stability and shape anisotropy energy. Micromagnetic simulations show that the 180° magnetization switching of the nanomagnet is assisted by an external applied voltage and the dipole coupling, allowing controlled NML operations. The relationship between the critical switching frequency and critical strain is used to select the appropriate nanomagnets for different logic operations. [ABSTRACT FROM AUTHOR]

Sm2Co17 rubber magnet is a kind of bonded magnet and can be produced using by-products obtained in the cutting process of sintered compact after Sm–Co system sintered magnets were made. These rubber magnets are still expensive, but they are effectively used for the sensors requiring a small amount of them. Their magnetic properties largely depend on the interaction between the rubber and the magnetic powder. This article describes the effect of the stearic acid and the compacting pressure on the density and magnetic properties of Sm(Co0.6Cu0.08Fe0.3Zr0.02)8.35 rubber magnets. In the case of 1.5 wt% of stearic acid and 850 MPa of compacting pressure, this article shows that the isotropic rubber magnet is 5.51 g/cm3 in density, 0.34 T in remanence, and 22.99 kJ/m3 in energy product. [ABSTRACT FROM AUTHOR]

A modeling method of the anisotropic magnetic characteristics due to compression molding of a soft magnetic composite (SMC) for inductance calculation of an SMC inductor is proposed. First, a particle model with a flattened iron particle and a uniform layer of insulation is constructed to simulate the anisotropic BH curves in arbitrary directions using the measured limited two BH curves in the compress and vertical directions under compression. Then, the proposed particle model is expanded to include the dc-biased characteristic of permeability. Moreover, the proposed model is applied to two inductors with legs having different compress directions. It is shown that the proposed method can be applied to the optimal design of inductors taking account of the compress direction of SMC. [ABSTRACT FROM AUTHOR]

A full-vectorial finite-difference (FD) scheme is proposed in this work to accurately extract the propagating modes on a magnetically biased graphene microstrip. Initially, the anisotropic surface conductivity of graphene is introduced, and the appropriate eigenvalue problem is formulated starting from Maxwell’s equations. In particular, an FD approximation is utilized, while the discretization of the computation domain is based on the popular Yee cell. Then, the relationship between tangential, to the propagation direction, electromagnetic components is derived, leading to a linear eigenvalue problem. The numerical results highlight the expected difference between the propagation properties of the edge modes, thus validating the successful implementation of the featured modal solver. Moreover, it is shown that the number of unknown components is efficiently reduced due to the proper elimination of the longitudinal fields and the linearity of Maxwell’s equations. [ABSTRACT FROM AUTHOR]

A numerical issue arises when we extend the convolutional neural network (CNN) U-net to the anisotropic magnetostatic field computation. The output magnetic field has a significant gradient with respect to the input geometry parameter, which introduces inevitable errors in the training process to degrade the performance of deep learning (DL). To address this issue, the subset selection approach is utilized to divide the whole database into several subsets, where the samples are assigned according to the gradient between the input and output. Then these subsets with different sample densities are combined into a global one. Taking the uniform dataset with the same sample size as a comparison, the influence of subset selection on DL is investigated by comparing the performance of CNN on different datasets. Numerical experiments illustrate that the adaptive subset selection can be employed to improve the accuracy and efficiency of the CNN network. [ABSTRACT FROM AUTHOR]

Soft magnetic composites (SMCs) demonstrate excellent potentials for electromagnetic applications. Isotropy is one critical feature in designing the composite. This work presents a shape optimization algorithm for SMCs subject to isotropy and volume constraints. The maximal isotropic effective permeability is the design target for a fixed volume fraction of the SMCs’ inclusion. Augmented Lagrange is applied to satisfy the volume requirement. In addition, an adaptive weighted sum approach is used to deal with the isotropy constraint. A level-set function is defined on the whole design domain and propagates the shape of the inclusion. Shape derivative is deduced to determine the descent direction. A numerical application is implemented for SMCs in magnetostatics in 2-D for various initial shapes. The local minimum is located at a rapid convergence rate. [ABSTRACT FROM AUTHOR]

MnxAl100-x and MnyGe100−y alloy epitaxial films of 20 nm thickness are prepared on Cr(001) single-crystal underlayers at 300 °C by varying the Mn content, $x$ or $y$ , from 0 to 100 at. %. The formation of crystallographic phase is systematically investigated as a function of composition by reflection high-energy electron and X-ray diffractions. The phases in MnxAl100−x and MnyGe100−y films are determined to vary in the orders of $A 1=> L 1_{0} + A 12=> L 1_{0} => A 2=> A12$ and $A 4=> tP => cP => D 0_{22} => A12$ with increasing the Mn content, respectively. Metastable fct-based ordered $L1$ 0 phase is formed in the MnxAl100−x films with $x $ = 50– $65. L1$ 0 single phase is obtained at an Mn-rich composition of $x $ = 58, whereas bcc-based disordered $A12$ and $A2$ phases are, respectively, involved at the $L1$ 0 stoichiometric composition of $x $ = 50 and at a more Mn-rich composition of $x $ = 65. Employment of a slight Mn-rich composition stabilizes $L1$ 0 phase. On the other hand, metastable fct-based ordered $D0$ 22 phase is formed in the MnyGe100−y films with $y$ = 60– $75. D0$ 22 single phase is obtained in the range from the stoichiometric composition of $y$ = 75 to a slightly Mn-poor composition of $y $ = 68. The $c$ -axis orientation is normal to the film surface for both $L1$ 0 and $D0$ 22 crystals. The present study has clarified the crystal structure and growth of MnxAl100−x and MnyGe100−y films for the respective full compositional ranges and has shown that control of the composition is important to obtain $L1$ 0 and $D0$ 22 ordered Mn-based alloy films with perpendicular magnetic anisotropies. [ABSTRACT FROM AUTHOR]

The magnetic field-dependent remanent magnetization and demagnetization of magnetite nanoparticles dispersed in a frozen isoparaffin oil have been measured as a function of magnetite concentration. Frozen ferrofluid samples with magnetite volume fractions between 7.1% and 0.03% were demagnetized using either thermal or dc demagnetization and were kept frozen at 77 or 4 K during measurement to restrict mechanical rotation and translation of the particles. The magnetization and demagnetization remanences of the frozen ferrofluid were measured and plotted parametrically in the magnetic field magnitude to produce Henkel and $\Delta M$ plots for comparison with the Wohlfarth model. The Henkel and $\mathrm {\Delta }M$ plots of the ferrofluid samples with higher concentrations of magnetite deviated from the predictions of the Wohlfarth non-interacting model, consistent with demagnetizing interactions in the system. The magnitude of this deviation decreased with decreasing magnetite concentration. A simple model is presented that quantitatively explains the deviations from the expected relations and can be used in other systems to characterize magnetic interactions. [ABSTRACT FROM AUTHOR]

This work investigates a 2-D vector field behavioral model to describe the anisotropic magnetic permeability and losses in Grain-Oriented Electrical Steels (GOES) within quasi-static and magneto-harmonic working conditions. The model includes the an-hysteretic magnetic field driven by the total anisotropy, the coercive force responsible for the quasi-static hysteresis losses, and the dynamic damping eddy field responsible for the extra losses. Each field contribution requires the definition of a tensor property whose diagonal and non-diagonal coupling components are experimentally identified as a function of the flux density magnitude $B$ and its angle $\theta $ with the Rolling Direction (RD). The static behavior is identified at low frequency and the dynamic one takes the frequency-dependent field diffusion into account. Diagonalization tools reveal main characteristic magnetic axis for the separate properties with deflections at the macroscale. [ABSTRACT FROM AUTHOR]

This article proposes a methodology for modeling magnetic anisotropy in ferromagnetic materials. This approach was initially used to represent the isothermal remanent magnetization (IRM) acquired by natural mineral assemblages and based on the use of the cumulative distribution function (CDF) of a probability density function (PDF). For the purpose of this work, the anisotropy of electrical steel sheets is modeled by means of CDFs of Gaussians. The methodology is validated by comparisons between numerical and experimental data obtained from an Epstein frame and a Rotational Single Sheet Tester. The outcomes of the study are twofold: first, the parameters defining the CDF follow a polynomial trendline, and second, they can easily be calculated from a limited amount of experimental data which is a key point from an engineering point of view. [ABSTRACT FROM AUTHOR]

We investigated the effects of sputtering conditions for the deposition of an Iridium (Ir) layer in a [Co/Pt]m/Co/Ir/[Co/Pt]n/Co/W/CoFeB synthetic antiferromagnetic reference layer (Ir-SyF) on the magnetic properties and tunnel magnetoresistance ratio (TMR ratio) of magnetic tunnel junctions (MTJs) stacks annealed at 400 °C for 1 h. The exchange coupling field ($H_{\mathrm {ex}}$) of Ir-SyF was improved by reducing the energy of Ir recoil ions and two times larger than that with Ru-SyF. Energy dispersive X-ray (EDX) spectrometry line analysis revealed greater interlayer diffusion in Ir when Ir was sputtered by using a conditions with large recoiled energy. This could cause the deterioration of the $H_{\mathrm {ex}}$ of the Ir-SyF. Despite the larger $H_{\mathrm {ex}}$ , the TMR ratio of the MTJ with Ir-SyF is smaller than that with Ru-SyF. The $m$ – $H$ curve of MTJ with Ru-SyF showed a large plateau region around zero magnetic field, whereas that with Ir-SyF did not. These results indicated the degradation of perpendicular magnetic anisotropy (PMA) in the top part of the Co/Pt multilayer with CoFeB reference layer and a large biquadratic coupling effect in the thin Ir layer. This causes the deterioration of the TMR ratio of the MTJ with Ir-SyF. TEM image of the Co/Pt layer in the MTJ with Ir shows some lattice defects. The EDX line analysis revealed that a large amount of Pt in the top Co/Pt layer diffused toward CoFeB reference layer in the Ir-SyF, resulting in the degradation of PMA. The structural analysis by X-ray diffraction showed the lattice spacing of CoPt (111) in Ir-SyF to be larger than that in Ru-SyF, indicating the occurrence of strain relaxation at the Co/Pt interface. These crystallographic changes in Ir-SyF might be related to a larger Pt diffusion. Suppression of Pt diffusion as well as low damage Ir deposition in the reference layer is crucial to utilize Ir-SyF. [ABSTRACT FROM AUTHOR]

Optimizing the performance of magnetoimpedance (MI) requires controlling the anisotropy of material which is often done with field annealing. However, field annealing needs large-scale equipment with a vacuum environment and consumes a large amount of electricity for heating and generating a large magnetic field. Conversely, Joule heating has advantages of simple, compact, and possible-to-use small current. Thus, we attempted controlling the magnetic anisotropy on thin-film MI elements using Joule heating and the applied field by magnets. Before annealing, the element has an easy axis with a direction parallel to the longitudinal direction of the element owing to shape anisotropy. After Joule heating, the MI behavior showed a double peak profile, which is a typical impedance profile when large impedance changes are obtained. The peak height in the impedance and inductance increases with the heating current up to 100 mA and then becomes constant or slightly increases. The field at which the impedance and inductance have a peak increases monotonically with increasing heat current. We confirm that the magnetic anisotropy direction changes with Joule heating and with a field applied by magnets based on observing the magnetic domain structure using a Kerr effect microscope. [ABSTRACT FROM AUTHOR]

The effect of nanoparticles (NPs) on microwave magnetoresistance in MgO/CoFeB(free)/Ta/CoFeB(fixed)/MgO)/Ta platform and the effect of individual NP on free CoFeB ferromagnetic layer magnetization have experimentally been revealed and analyzed. The area of the platform where magnetization is inverted under scattering field of NPs has been observed. Micromagnetic modeling of dipole magnetic interaction confirms the existence of such areas in “NP-platform” system. The increase in critical field of the platform and the change of resistance under scattering field on NPs have experimentally been revealed. [ABSTRACT FROM AUTHOR]

The role of the electric field on the magnetic ground state in thin disks is investigated. The equation governing the magnetic equilibrium in the case of rotational symmetry is derived and solved by varying electric and magnetic fields. The equilibrium states so obtained are classified in a phase diagram, which divides the plane of the electric and magnetic fields in regions where the magnetization profile has certain shape. Full micromagnetic simulations are used to confirm our analysis. [ABSTRACT FROM AUTHOR]

The effect of Fe-rich content on the microstructure, phase structure, elements distribution, and magnetic properties of Sm(Co $_{0.91-\mathit {x}}$ FexCu0.07Zr0.02)7.6 ($x$ = 0.22, 0.30, and 0.35) magnets has been investigated systematically. With the increase of Fe content, the 2:17H, 2:17R, and 1:3R phases appeared in the Fe-rich solid solution. The different phase structures in the high-resolution transmission electron microscopy (HRTEM) images showed a locally short-range ordered state with dislocations. The presence of 2:17R phase and 1:3R phase was negative to the spinodal decomposition during the aging stage. In addition, the high Fe content caused Cu element enrichment in some area of the final state magnet, which further affected the formation of cellular structure. The Fe content increased from $x$ = 0.22 to $x$ = 0.35, the average cell size increased from 83.67 to 112.46 nm, the thickness of cell boundary increased from 9.6 to 18.25 nm, and the density of Zr-rich platelets increased from 0.036 to 0.06 nm. Furthermore, the defective cellular structures in the magnet ($x$ = 0.35) with incomplete and discontinuous cell boundaries had weak pinning field and poor coercivity. Moreover, the magnetooptical Kerr optical microscope observation revealed that the domain width of magnet ($x$ = 0.35) was significantly higher than that of magnet ($x$ = 0.22), and the reversal magnetic domain was formed first in the magnet ($x$ = 0.35), which caused a poor coercivity. [ABSTRACT FROM AUTHOR]

As a device that realizes the “static-to-motion” transformation which influences the national economy and people’s livelihood, the electric machine (EM) has put forward higher requirements for the torque/power density with the development of industry. It is difficult to meet the new requirements by using traditional silicon steel. Therefore, the application of “new” materials has become a breakthrough point. This article studied the properties and the application of Fe-Co-V alloys (1J22) which has a high saturation magnetic polarization, then analyzed its performance in high torque density EMs. Since the stator field is a rotating magnetic field which changes with time, the variable-angle magnetic performance test was carried out on 1J22 to discuss the influence of the magnetic performance under different shear angles on the stator magnetic flux. The EM’s design and prototype production were carried out for the unique properties of the 1J22 material itself. Compared with the EM model using traditional non-grain-oriented (NGO) silicon steel 35ADG1900, the use of 1J22 material can solve the temperature rise problem under special working conditions. At the same time, the feasibility of 1J22 in high torque density traction motor has been verified. [ABSTRACT FROM AUTHOR]

The dependence of double magnet master (DMM) printing characteristics on master thickness and non-magnetic separator (NMS) thickness is investigated using micromagnetic simulation. It is found that the recording field difference saturates when the master thickness reaches the bit length. The NMS, which separates the two magnetic materials of the DMM, shifts the maximum points of the recording field distribution into the softer magnet regions, decreasing the island-like non-reversed regions, thus enhancing the printing performance. The effective switching field is important for understanding magnetic printing characteristics. The printed magnetization distributions are in accordance with the switching field distribution of the recording field generated by the DMM. Therefore, optimizing the master thickness and NMS thickness effectively improves the DMM printing characteristics for various servo patterns. [ABSTRACT FROM AUTHOR]

Magnetic properties and nanostructure for FePt-30 vol% BN granular films deposited while flowing N2 gas with ratio between 0% and 5% with respect to the total flow of N2 + Ar are investigated. Here is a list of the results: 1) A maximum coercivity ($H_{\mathrm {c}}$) of 18.9 kOe, a saturation magnetization ($M_{\mathrm {s}}$) of 600 emu/cm3, a perpendicular magnetic anisotropy ($K_{\mathrm {u\bot }}$) of $1.7\times 10^{\mathrm {7}}$ erg/cm3, and a magnetic anisotropy field ($H_{\mathrm {k}}$) of 58 kOe, with smaller grain size and higher degree of grain separation are obtained when N2 gas with a ratio of around 2% is added; 2) higher fraction of N2 gas ratio leads to an increase of the amount of magnetic grains with $c$ -axis parallel to the film plane; 3) lattice constant $a$ remains constant, a minimum value of lattice constant $c$ and the ratio $c/a$ are also observed for a N2 ratio of around 2%; 4) there are two phenomena observed in nanostructure and magnetic properties defined by the N2 ratio. For N2 ratios under 2%, changes in the $c/a$ ratio, the degree of order, and the agglomeration suppression of grains enhance $M_{\mathrm {s}}$ , $K_{\mathrm {u\bot }}$ , and $H_{\mathrm {k}}$. This indicates that the segregation of B into grain boundaries as the result of the N2 addition. For N2 ratios over 2%, the change of tetragonal into cubic FePt magnetic grains, the reduction of the degree of order, and the decrease of $M_{\mathrm {s}}$ and $K_{\mathrm {u\bot }}$ suggest that excess nitrogen dissolves into the FePt magnetic grains; and 5) another consequence of the 2% N2 ratio is the enhancement of the magnetic grain decoupling along with the increase of $H_{\mathrm {k}}$ , this results in the maximization of $H_{\mathrm {c}}$. [ABSTRACT FROM AUTHOR]

Magnetic properties’ modification and coercivity enhancement of NdFeB sintered magnets prepared by the dual-alloy (DA) sintering together with grain boundary diffusion (GBD) treatment are demonstrated. For the original NdFeB magnet, (BH)max of 51.4 MGOe and ${_{i}}H_{\mathrm {c}}$ of 14.9 kOe are obtained. For the magnet made with the same composition as the former but doped with Ce85Al15 (CeAl) powders, magnetic isolation due to the distribution of Ce and Al at GB increases the coercivity effectively, yet few Ce entering into grain interior decreases $B_{\mathrm {r}}$ , (BH)max, and Curie temperature slightly. In addition, the coercivity of the above magnets can be further enhanced to 22.7–25.1 kOe by GBD with different amounts of Tb70Cu30 (TbCu) powders. The clear core–shell structure, which consists of (Nd, Tb)2Fe14B phase with higher magnetocrystalline anisotropy field ($H_{\mathrm {A}}$) as the shell and Nd2Fe14B phase as the core, is observed. CeAl helps to form a continuous and smooth GB. The diffusion source of TbCu could infiltrate into the magnet along such smooth GB and form a homogeneous core–shell structure. As a result, coercivity is remarkably enhanced from 14.9 kOe for DA sintered magnet with 2 wt% CeAl to 25.1 kOe for the magnet GBD with TbCu. Most importantly, various levels of NdFeB magnets, such as 52M, 35–50SH, and 45UH, could be easily attained by modifying the amounts of CeAl for DA sintered magnets and/or GBD with TbCu powders. [ABSTRACT FROM AUTHOR]

To cope with the increasingly serious microwave radiation pollution, an extensive search for efficient microwave absorption materials (MAMs) has attracted great attention recently. Herein, a thin layer of SiO2 with high dielectric permittivity on the surfaces of MnFe2O4 (MnFO) nano-hollow spheres (NHSs) is found to be an effective strategy to improve electromagnetic (EM) wave attenuation for a larger reflection loss (RL) along with a larger bandwidth (BW) within a widely used frequency range. Larger interfacial area, higher magnetic anisotropy, internal reflections, and scattering from NHS along with higher magnetic permeability of MnFO are responsible for superior absorption properties of MnFO NHS. The MnFO (~550 nm)/SiO2 (~35 nm) bi-layered NHS results in a sufficiently high RL ~ −61.02 dB with a composite absorber of a thickness of only 4.40 mm and filler concentration of 20%. The above study on the variation of SiO2 thickness over MnFO NHSs helps us to optimize for maximum BW and absorption with minimum composite absorber thickness. This study demonstrates the optimized MnFO/SiO2 NHS as a highly promising low-cost and lightweight EM wave absorber suitable for high-frequency applications. [ABSTRACT FROM AUTHOR]

We provide a comparative first-principles investigation of the structural, electronic, vibrational, and thermodynamic properties of the full Heusler compounds, cubic Fe2NiAl, and tetragonally distorted Co2NiAl. In both cases, we find the inverse Heusler structure to be in close competition with a layered arrangement of the elements, which breaks cubic symmetry and is accompanied by significant absolute values for the magnetocrystalline anisotropy energy. While for Fe2NiAl the layered arrangement is predicted as a new ground state, we show evidence that it might become dynamically stable around room temperatures also for Co2NiAl. We identify in both systems subtle differences in the electronic and vibrational density of states between the different structures, which might be related to their particular stability. [ABSTRACT FROM AUTHOR]

Variable flux memory machines (VFMMs) can have their level of magnet flux density modified by the injection of $d$ -axis current pulses in the armature windings. The use of Fe-Cr-Co magnets as a source of the magnetic field in these machines is still little explored, even if these magnets present interesting thermal and mechanical properties. In this context, this article explores the validation of a standstill magnetization strategy applied in a non-salient single pole pair Fe-Cr-Co-based VFMM designed for high-speed applications in the transportation electrification field. Due to the absence of a well-defined knee on the second quadrant of the hysteresis loop of the magnet used, the methodology commonly seen in the literature for describing the behavior of the recoil lines defining the working points cannot be directly used. Therefore, by the experimental results obtained from the standstill magnetization of the VFMM studied, a new methodology is developed based on the estimation of the remanence in terms of the excitation field characterizing the internal hysteresis loops of the Fe-Cr-Co. The achieved results are compared with the reference obtained from a HysteresisGraph, which represents a closed and ideal magnetic circuit of measurement. The effects of a stator geometry designed with closed slot wedges in the VFMM and the anisotropy shape are explored for justifying the differences observed. [ABSTRACT FROM AUTHOR]

Motivated by the recent experiment done by Yu et al. [X. Z. Yu, et. al., Sci. Adv., 6, 25, eaaz9744 (2020)] on magnetic skyrmion creation and annihilation by electric currents in FeGe devices with a notch structure, we examine the interaction between the electric current vorticity near the notch and localized spins, and obtain three effects of the current vorticity on the localized spins. The first one is an effective Zeeman field induced by the current vorticity. This effective Zeeman field is responsible for skyrmion creation. The second effect is a vorticity-induced Dzyaloshinskii–Moriya (DM) interaction with the direction of the DM vector being parallel to the vorticity direction and is different from the vector of the intrinsic DM interaction. This vorticity-induced DM interaction makes the skyrmions distorted. The third effect is a spin current due to the gradient of the vorticity and the spin current drives the magnetic skyrmions far from the notch. Our theory opens a new path to design the magnetic textures by using structural settings. [ABSTRACT FROM AUTHOR]

We have systematically investigated the spin-orbit torque (SOT)-induced effective magnetic field in a structure consisting of a Ta heavy metal layer and an antiferromagnetically coupled Mn1.8Ga1/Co2MnSi (CMS) bilayer around the magnetization compensation point by varying CMS film thickness. The efficiency of SOT generation takes the maximum around the compensation point, and it is approximately six times as large compared with that in the devices with a MnGa single structure. The enhancement of SOT efficiency can be explained mainly by the reduction in saturation magnetic moment around the compensation point. Moreover, a significant enhancement of the effective spin Hall angle was observed around the compensation point because of the inversion of the magnetization configuration before and after the compensation point. [ABSTRACT FROM AUTHOR]

This article presents the potential contribution of segmented stator magnetic circuits of rotating permanent magnet electrical machines with concentric winding. Two magnetic materials are mixed: FeSi non-oriented electrical steel and FeSi grain-oriented electrical steel (GOES). The choice of using GOES is based on the high performance it offers in terms of permeability and iron losses compared to conventional non-oriented grain electrical steel (NOES), particularly when GOES is magnetized in the rolling direction (RD). The goal is to analyze the contribution of the mixed magnetic circuit on the losses and electromagnetic torque but also the drawbacks due to the cut process and the assembly. The behavior of the magnetic field at the junction between the segments is studied by comparing different geometrical connection shapes and compared to a reference magnetic circuit fully made with NOES sheets. This comparison is experimentally made with a model representative of the existing phenomena in an electrical machine. In addition, numerical calculations using finite elements software are carried out by considering both the magnetic anisotropy and the saturation of the GOES. [ABSTRACT FROM AUTHOR]

Current-induced domain wall motion (CIDWM) shows promising prospects with low power, high density, high speed, and so on. Recent studies have demonstrated that magnetic tunnel junction (MTJ) based on CIDWM has great potential in mimicking a non-volatile artificial neuron and synapse. By combining the effect of the interfacial Dzyaloshinskii–Moriya interaction (DMI) to stabilize the Néel-type domain wall (DW) and the high-speed low-power advantages of spin orbit torque (SOT), the novel MTJ device is experimentally demonstrated with low threshold current and high propagation speed, which shows potential applications in the field of the artificial neuron and synapse. In this article, a compact model for CIDWM-MTJ based on SOT and DMI is presented. The model integrates the SOT mechanism for magnetization reversal and DW nucleation, CIDWM behaviors, and tunnel resistance theory of MTJ nanopillar. The micromagnetic simulation and the temporal evolution of the DW position are implemented by solving the Landau–Lifshitz–Gilbert (LLG) equation and the 1-D model. Based on the developed model, a hybrid CIDWM-MTJ/CMOS circuit is simulated for verification. The presented model combines the CIDWM dynamics and the MTJ magnetic dynamics, showing potential application for the simulation of all-spin artificial neural network (ANN). [ABSTRACT FROM AUTHOR]

In this study, bulk Pr2Fe14B/ $\alpha $ -Fe nanocomposite magnets were fabricated from amorphous Pr9Fe86-x ${\text {Cu}}_{x}\text{B}$ 5 ($x$ = 0–1.5 at.%) precursors by a rapid high-pressure thermal compression (HPTC) technique, and the effects of Cu content on the texture and magnetic properties of the deformed magnets were investigated systematically. Results showed that the magnetic anisotropy $A_{m}$ and remanence $B_{r}$ of the deformed magnets increase evidently with increasing Cu content, whereas the coercivity $H_{\mathrm {ci}}$ decreases dramatically, thereby resulting in the maximum energy product (BH)max initial increase and then decrease. A magnetic anisotropy of $A_{m}$ = 0.44 and the optimal magnetic properties of (BH)max = 21.4 MGOe, $B_{r}$ = 13.1 kG, and $H_{\mathrm {ci}}$ = 3.52 kOe were achieved at x = 1.0 at.%, which can mainly be attributed to the strong ($00l$) crystallographic alignment of Pr2Fe14B nanocrystals and excellent exchange coupling between hard and soft nanocrystals. The present research is important for developing anisotropic bulk nanocomposites with high-energy products. [ABSTRACT FROM AUTHOR]

Based on spark plasma sintered (SPS) Nd-Fe-B magnets with PrCu sintering aid, hot deformed (HD) magnets are prepared through hot deformation technique. After that, using PrCu as the diffusion source, grain boundary diffusion (GBD) is implemented on HD magnet. Eventually, GBD magnet is subjected to hot deformation to regulate the distribution of RE-rich phase and increase $c$ -axis orientation, referred to as the secondary deformation (SD). The results show that hot deformation processes have an important influence on magnetic properties and microstructure, among which the deformation condition of 700 °C/0.5 h is the most favorable to obtain optimal magnetic properties. Through GBD, the coercivity, as high as 2117 kA/m, can be obtained, increasing by 7.5% comparing with that of the initial SPS sample. Moreover, it is found that the SD can effectively optimize the distribution of RE-rich phase, and improve $c$ -axis orientation of grains. Eventually, a good balance between coercivity and remanence is achieved. In addition, both GBD and SD can increase the thermal stability of HD magnets. [ABSTRACT FROM AUTHOR]

This article theoretically solves the problem of the thermally activated motion of gas of non-interacting magnetic vortices/skyrmions in the field of defects located randomly, i.e., anchoring centers. The properties of the anchoring centers can also fluctuate. The factor that drives the gas of quasiparticles can be of any physical nature (fields, currents, gradients of the magnetic characteristics of the magnet, and so on). The process of vortices motion is described as a sequence of thermally activated separation of vortices from the attracting centers. The cases of some model distribution functions of the energy barriers are considered: 1) the barriers are of the same height; 2) the heights of the barriers are distributed evenly; and 3) the heights are distributed according to the normal law. Within these models, analytical expressions for the drift velocity and the diffusion gas coefficient of quasiparticles are obtained. [ABSTRACT FROM AUTHOR]

At deep sub-micrometer technology, CMOS circuits suffer from high leakage and have reliability issues due to process variation. Hybrid magnetic tunnel junction (MTJ)/CMOS circuits have been proposed to overcome these challenges. MTJs have zero standby power and are compatible with CMOS technology. In this article, a dynamic logic-based hybrid MTJ/CMOS magnetic full adder (MFA) has been proposed, which eliminates the error voltage appearing on output due to charge injection and clock feedthrough phenomenon, thereby enhancing the performance of MFA and making it more reliable. This effect is induced by the pMOS transistor, which is used as a switch to precharge the output nodes. The proposed MFA uses two dummy transistors, whose drain and source terminals are shorted to make them act as MOS capacitors, to absorb the error voltage introduced by the switch pMOS transistor due to charge injection and clock feedthrough, when turned OFF. Eliminating the error induced due to charge injection and clock feedthrough makes the amplification process faster and reduces the dynamic power consumption. Results are verified by performing transient and Monte Carlo simulations using cadence virtuoso with UMC 40 nm CMOS technology kit and compact model of perpendicular magnetic anisotropy (PMA) MTJ, which validates that the proposed MFA is highly reliable as it provides the error-free output and imparts better power–delay product (PDP) compared to previously proposed MFA. [ABSTRACT FROM AUTHOR]

It is important to explore better alternatives to CMOS to sustain Moore’s law far in the future. One option is to integrate non-volatile spin devices, such as magnetic tunnel junction (MTJ), with the existing CMOS technology to augment its capability. This article presents five approximate 1 bit full adders for applications where accuracy can be traded for energy, speed, and area. The application of an approximate adder is demonstrated in image processing for smoothening an image. Three of these adders are fully non-volatile, one is partially volatile, and one is fully volatile. All the adders use SRAM-based sense amplifier (SA) to reduce sensing energy and hardware count. To reduce the delay, some of the adders utilize the parallel connection of logic devices (MTJ or MOSFET) in the logic tree. All the adders are simulated using 45 nm CMOS predictive technology model (PTM) and perpendicular magnetic anisotropy (PMA) CoFeB/MgO/CoFeB MTJ model with HSPICE simulator. After performing simulations, results show that the proposed fully non-volatile approximate adder (AXFA4) performs exceptionally well against its existing counterpart AX_MFA2 in terms of the energy-delay product (EDP) and the area-delay product (ADP) with a decrement of 84% and 80%, respectively. All the adder designs compute sum at 75% and carry at 100% accuracy, respectively. [ABSTRACT FROM AUTHOR]

Indirect exchange coupling mediated by the conduction electrons (Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange) is studied in the multiwall carbon nanotubes (MWCNTs) of diameters of tens of nanometers with single domain ferromagnetic nanoparticles (FNPs) embedded inside. By adapting the Klinovaja-Loss (KL) model [Phys. Rev. B 87, 045422 (2013)] for single-wall carbon nanotube (CNT) and applying the parameters of MWCNTs, we show that the static spin susceptibility can propagate up to tens of micrometers. The main condition for the long-range exchange interaction is the adjustment of the Fermi level to the gap opened by the spin–orbit interaction (SOI). At typical diameters of the inner shell of MWCNTS of 20–30 nm, the required shift of the Fermi level is much smaller than that for single-wall CNT and does not exceed tens of meV. The proposed approach allows evaluating the energy of the exchange interaction between FNPs belonging to the same CNT. The obtained results open up good opportunities for the realization and implementation of MWCNT-based spintronic devices. [ABSTRACT FROM AUTHOR]

Multifunctional materials with high magnetic, electrical, and magnetoelectric (ME) characteristics play an important role in development of data storage devices. Herein, multi-phase ($0.95- x$)Ba0.9Ca0.1TiO3 (BCT)-0.05Na0.5Bi0.5TiO3 (NBT)- $x$ CoFe2O4 (CFO) ceramics were prepared by a two-stage mechanochemical activation technique. The objective of this study is to develop a multifunctional material with improved multiferroic characteristics. The structural analysis by the Rietveld method shows the presence of heterogeneous structure without any impurity phase. The incorporation of CFO in 0.95BCT-0.05NBT has resulted in significant improvement in magnetic and ME characteristics without significantly hampering the electrical properties. The sample with $x =0.11$ has shown high saturation magnetization of 8.26 emu/g along with moderately high ME coefficient of 5.411 mV/cm $\cdot $ Oe. In addition, the energy storage performance of all the studied samples has also been investigated and the optimized sample $x =0.11$ presents a large discharge energy density of 2.249 J/cm3 and moderately high energy efficiency of 63.8% at 388 kV/cm. The results obtained in this work suggest a significant influence of CFO substitution on the magnetic characteristics of BCT-NBT ceramics, which subsequently indicate their potential applications in spintronics, magnetic memory storage, and electrical energy storage devices. [ABSTRACT FROM AUTHOR]

Hard magnets are key components in the evolution of transportation technologies and renewable energies. In particular, in automobile industry, the anticipated switch to full electric drive in the next 30 years will create a strong demand for magnets. Unfortunately, present high-performance hard magnets use critical elements, either rare-earth (RE), or cobalt, so we can foresee a big stress on the market. In this article, we will review all existing hard magnets having functional properties adapted to automobile electric drives, the evolution of present material to reduce the critical elements content or to get rid of them. Finally, a functional cost criterion will be set and discussed. [ABSTRACT FROM AUTHOR]

We used standard micro-electro-mechanical systems (MEMS) fabrication techniques (lithography, etching, and sputtering) to the batch fabrication of out-of-plane textured $50~\mu \text{m}$ -thick Nd–Fe–B micro-magnets on Si substrates of 100 mm diameter. Pre-patterning of the Si substrate serves to structure the in-plane dimensions of the micro-magnets and affords stress relief in the magnetic layer. Two protocols were applied to grow the films: a one-step process, in which the film is directly crystallized and a two-step process, where the film is amorphous in the as-deposited state and crystallized during post-deposition annealing. Both processing routes result in micro-magnets with magnetic properties (texture and coercivity) comparable to sintered Nd–Fe–B bulk magnets. We report on how substrate patterning and film thickness affect the very distinctive microstructures of our films. Finally, the stray magnetic field patterns produced above these topographically patterned films were characterized by scanning Hall probe microscopy (SHPM). [ABSTRACT FROM AUTHOR]

A porous polymer loaded with segmented nanorods of magnetic metal is very promising for the design of novel microwave devices. Arrays of bi-segmented Ni/Co and core–shell Ni@Co rods were prepared by electroless deposition into porous of polycarbonate track-etched membrane. An intrinsic effective magnetic field of the magnetic composite nanorods aligned in the nonmagnetic template was studied by magnetization curves and ferromagnetic resonance (FMR). The effect of the interface boundaries for two types of bi-segmented rods with coaxial and along-axis Co/Ni segmentation to effective field was established. [ABSTRACT FROM AUTHOR]

Regularly used in power transformers, grain-oriented (GO) steels are also usually chosen for the manufacturing of the stator cores of hydro generator and turbogenerator. These steels are renowned for their high magnetic performances in the rolling direction (RD) (high permeability and low magnetic losses). Nevertheless, in a turbogenerator where GO steels are employed to reduce the size of the stator core, the magnetic flux flows through several successive directions within the plane of the steel. So, the anisotropic behavior of the GO steel has to be considered in the design step of the related devices in order to improve their energy efficiency as well as their diagnosis based on modeling. In this article, an anisotropic phenomenological iron loss model, quite recently developed, has been studied and successfully implemented in a finite element method (FEM) simulation environment. The implementation has been validated against experimental data achieved on an industrial conventional GO grade typically used in turbogenerators. The results show a good agreement of the computational results with the experiments for both quasi-static and dynamic regimes. [ABSTRACT FROM AUTHOR]

The unmet demand for data privacy and brand protection in anti-counterfeiting has urged heavyweight industries to develop new nanomaterials for barcoding. Here, we tailor the remanence spectra of magnetic nanowires (MNWs) to make 23 new unique magnetic nanobarcodes signatures. Using arrays of 30 and 100 nm diameter MNWs, composed of FeCo, Ni, or Co, we establish design rules for generating diverse codes followed by the description of a simple decoding algorithm. When used together, remanence spectra and our decoding algorithm enabled unambiguous identification of 14 of 15 combinations of two nanobarcodes. When three nanobarcodes were present at the readout simultaneously, our algorithm was able to successfully identify 9 of 20 combinations. Our approach opens a promising path toward expandable encoding and reliable decoding of MNWs. [ABSTRACT FROM AUTHOR]

Magnetic skyrmions have the potential for a wide range of applications in the next generation of spintronics since they are topologically protected spin configurations in the nanometer length scale. In order to be used in the logic gate, it is necessary to consider how to manipulate magnetic skyrmions. At present, the current drive is the mainstream drive, but this method could consume enormous energy for large Joule heating. In this work, the potential well is introduced to drive skyrmion to reduce energy consumption. The potential well is generated by voltage-controlled magnetic anisotropy (VCMA). We study the possibility of the potential well-induced skyrmion movement within a certain distance, the relevant factors that affect the distance of skyrmion induction, and propose a switched-voltage driving structure within the well-established framework of micromagnetics. Its processes have been theoretically investigated and demonstrated, in which the switched-voltage driving structure can be used to drive skyrmions. Our results provide guidance for the design of low energy consumption voltage-driven skyrmion driving method and a new concept for track memory. [ABSTRACT FROM AUTHOR]

Amorphous glass-coated Fe-Si-B-P microwires with an induced gradient of perpendicular magnetic anisotropy are studied. The angular dependence of the domain wall mobility in the perpendicular magnetic field is present in as-cast sample. After thermal annealing below the crystallization temperature, the effect of the perpendicular magnetic field is suppressed due to the relaxation of internal mechanical stresses. Moreover, the domain wall mobility decreases, and the critical field increases. The results are explained in terms of the release of mechanical stresses induced during production after annealing. Furthermore, a new mechanical stress distribution is induced due to the slow cooling rate after thermal annealing. Scanning electron microscopy images of annealed samples below and above the crystallization temperature suggest the presence of the gradient of perpendicular magnetic anisotropy. Directional growth of the crystals after annealing above the crystallization temperature follows the induced stresses and shell-like structure in the cross section is recognized. [ABSTRACT FROM AUTHOR]

The synthesis of mixed iron–gallium borates, FexGa1–xBO3, and the results of modeling intracrystalline interactions, namely exchange, Dzyaloshinskii–Moriya, and dipole–dipole couplings in these crystals by means of the Monte Carlo technique using laboratory-developed codes are presented. The dipole–dipole contribution to basal magnetocrystalline anisotropy is calculated considering extended dipoles as Ampérian currents. The dependences of the intracrystalline interaction constants on iron contents, ${x}$ , are obtained at 0 K. [ABSTRACT FROM AUTHOR]

Single-layer magnetoresistive sensors were designed in a Wheatstone bridge configuration using La2/3Sr1/3MnO3 ferromagnetic oxide thin film. Uniaxial anisotropy was induced by performing epitaxial deposition of the films on top of vicinal SrTiO3 substrate. X-ray scan confirms the high crystalline quality of the films and the magnetic anisotropy was checked by magneto-optical Kerr effect measurements. Thanks to the anisotropic magnetoresistive effect and the very low noise measured in the devices, sub-nT resolution was achieved above 100 Hz at 310 K. [ABSTRACT FROM AUTHOR]

Effects of the ferromagnetic layer thickness and annealing temperature were studied in Pt-/Co-/MgO-based systems grown on thermally oxidized Si substrates using magnetron sputtering system. The Co thicknesses were varied in the range of 1–6 nm and the samples were annealed ex situ at 200 °C, 300 °C, and 400 °C. Vibrating sample magnetometry was used to determine the magnetization at saturation and the magnetic dead layer thickness that were found to be insignificantly affected by the annealing. Brillouin light scattering, in Damon–Eshbach configuration, was used to measure the thermally excited spin wave (SW) frequencies versus the in-plane applied magnetic field and the SW vector which were used to investigate the perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii–Moriya interaction (iDMI), respectively. The Co effective thickness dependence of the effective magnetization ($M_{\mathrm {eff}}$), which provides information on the PMA constants, shows the existence of two linear regimes with different slopes due to misfit strain-induced magnetoelastic anisotropy contributions to volume and surface terms. The volume magnetocrystalline anisotropy constant increases monotonously with annealing temperature, whereas the pure surface (Néel type) constant increases with annealing up to 300 °C and degrades at 400 °C. The surface iDMI constant decreases with increasing annealing temperature and no obvious correlation with interface PMA constant has been found, suggesting different interfaces contribution to PMA and iDMI. [ABSTRACT FROM AUTHOR]