Hysteresis Loop Changes Research Articles

Effect of void geometry and magnetic anisotropy in controlling the vortex in sub-micron annular Permalloy disc

Ferromagnetic rings, particularly asymmetric Permalloy (Py) rings are recognized as promising configurations for spintronic devices, offering additional degrees of freedom for manipulating magnetic states, especially in vortex configurations. Through micromagnetic simulations, our study explores the impact on magnetization states and spin configuration concerning ring symmetry, aligning with the interest in controlling vortex states for information storage. We initially obtained zero-field spin configurations by varying ring thickness (t), observing a 360° domain wall in rings with t < 12 nm and bi-vortex wall in rings with t ∼36 nm during magnetization reversal. Notably, an extended stability of the global-vortex state was observed in rings with t > 36 nm, indicating the dominance of global-vortex nucleation in thick asymmetric rings during domain wall movement. We investigate the hysteresis loops and spin configurations by varying the in-plane and out-of-plane anisotropy values. Our findings reveal the presence of multiple vortex cores with different polarities and sense of rotations in the ring for the in-plane anisotropy ∼30 to ∼40 kJ m−3. Additionally, a global-vortex with two vortex cores was formed due to demagnetization energy. We analysed the energy profile of stable magnetization states for various t and anisotropy values. Interestingly, the shape of the hysteresis loop changes significantly for the disc containing different shapes of void. Circular and square-shaped geometries suggest that the bi-vortex state is a stable configuration during magnetization reversal in both cases. The study also indicates the stability of the vortex with a square-shaped void geometry up to a sufficiently large field. For the case of triangular-shaped voids, the global-vortex state was favored with even the small fields. The estimated spin canting angles are found to be correlated with the presence of vortex spin configurations. Overall, these results are important for the development of magnetization vortex-based spintronics devices.

Exploration of dynamic phase transition of 3D Ising model with a new long-range interaction by using the Monte Carlo method

In this paper, we present a novel interpretation of the long-range interaction for exploring the magnetic characteristics of the 3D Ising model. To describe the long-range interaction, we utilize spin chains, which enable us to explore the dynamic magnetic behaviors of this model. The research investigates the impacts of the amplitude of the time-dependent magnetic field h0 and period τ on the dynamic phase transition by obtaining phase diagrams and midplane cross-sections of the system. Critical exponents are also discussed, which are consistent with other theoretical results. The dynamic hysteresis behaviors are then examined through various physical parameters. As the temperature increases, the area and shape of the dynamic hysteresis loop change. Our theoretical conclusions are consistent with those of other theoretical and experimental studies.

Optimization of Giant Magnetoimpedance Effect of Amorphous Microwires by Postprocessing

Magnetic microwires with amorphous structures can present a unique combination of excellent magnetic softness and giant magnetoimpedance (GMI) effects together with reduced dimensions and good mechanical properties. Such unique properties make them suitable for various technological applications. The high GMI effect, observed in as-prepared Co-rich microwires, can be further optimized by postprocessing. However, unexpected magnetic hardening and a transformation of the linear hysteresis loop into a rectangular loop with a coercivity on the order of 90 A/m were observed in several Co-rich microwires upon conventional annealing. Several routes to improve magnetic softness and GMI effect in Fe- and Co-rich magnetic microwires are provided. We observed that stress annealing could remarkably improve the magnetic softness and GMI ratio of Co-rich microwires. Thus, almost unhysteretic loops with a coercivity of 2 A/m and a magnetic anisotropy field of about 70 A/m are achieved in Co-rich microwires stress annealed at appropriate conditions. The observed change in hysteresis loops and the GMI effect is explained by stress-annealing-induced anisotropy, which is affected by the stresses applied during annealing and by the annealing temperature. While as-prepared Fe-rich amorphous microwires present a low GMI effect, appropriate postprocessing (annealing and stress annealing) allows for a remarkable GMI ratio improvement (an order of magnitude). The evaluated dependence of the maximum GMI ratio on frequency allows the identification of the optimal frequency band for the studied samples. The origin of stress-annealing-induced anisotropy and related changes in hysteresis loops and the GMI effect are discussed in terms of the relaxation of internal stresses, “back-stresses”, as well as structural anisotropy.

Research on fatigue failure of SiCf/SiC composites at high temperature based on X-ray computed tomography

The woven architecture of ceramic matrix composites and the existence of pores lead to the anisotropy and non-uniformity of the materials, which affect the mechanical behavior and failure of the materials in service environment. In this paper, tension-tension fatigue behavior of a plain-woven SiCf/SiC composite was investigated via X-ray computed tomography. The meso-scale architecture (pore, woven, etc.) characteristics of the SiCf/SiC specimen were obtained by X-ray computed tomography before and after the tests, and the conclusions can be drawn as following: (1) Changes in hysteresis loops, elastic modulus and area of hysteresis loop are correlated: as the cycle number increases, the elastic modulus decreases and the area of hysteresis loop increases; The larger the area of hysteresis loop, the greater the decrease rate of elastic modulus. (2) the porosity distribution of SiCf/SiC specimen shows the characteristics of both periodic and aperiodic. The periodic phenomenon is related to the meso-woven architecture, while the aperiodic phenomenon is caused by the distribution of stitching holes. (3) The fracture location of the specimen is significantly affected by the location of the stitching holes and the porosity distribution, but not completely determined by them. (4) When the load on the specimen is large, the stepped cracks are more likely to occur, and most cracks initiate from the surface/boundary of the fiber.

Highly stable electrical performances of HfO2-based ferroelectric devices under proton irradiation

The proton irradiation effects on TiN/Zr-doped HfO2 (HZO)/TiN ferroelectric capacitors are investigated in this work. Electrical characterization results show that the change of ferroelectric hysteresis loop and leakage current are negligible under proton irradiation up to fluence 1.0 × 1012 ions/cm2. The decrease of permittivity after irradiation is due to the degradation of the effective carrier concentration in Si substrate induced by displacement damage. The results demonstrate that HZO ferroelectric material is immune to radiation and has the application potential to be used in space system.

Study on Damage Characteristics of Water-Bearing Coal Samples under Cyclic Loading–Unloading

For underground water reservoirs in coal mines, the complex water-rich environment and changing overburden stress can damage coal pillar dams. In this paper, the coal samples from coal seam 22 of Shangwan coal mine were taken as research objects and the damage mechanism and characteristics of coal samples with different moisture content and wetting-drying cycles under cyclic loading were investigated. The results show that as the moisture content and wetting-drying cycles increase, the post-peak stage of the coal samples under cyclic stress becomes obvious, and the hysteresis loop changes from dense to sparse. Compared to the uniaxial compression experiment, when w = 5.28% (the critical water content), mechanical parameters such as peak strength and modulus of elasticity decrease the most. Under cyclic loading, the damage mode of both sets of coal samples was tensile damage, but the increase in wetting-drying cycles promotes the development of shear fractures. For evaluating fracture types, the RA-AF density map is more applicable to wetting-drying cycle coal samples, whereas for the coal samples with different moisture contents this should be carried out with caution. This study can provide some theoretical basis for the stability evaluation of coal pillar dams in underground water reservoirs.

Coupled particle and mesh method in an Euler frame for unsteady flows around the pitching airfoil

Finite difference method (FDM) is a grid-based method which is convenient for implementing multiple resolutions and has high computational efficiency. Smoothed particle hydrodynamics (SPH) is a meshless and particle method which has been widely applied into the fluid flows with free surfaces. In this study, a coupled SPH-FDM approach in an Euler frame is developed to simulate the unsteady flow around a pitching airfoil. In addition, an improved iterative shifting particle technology (IPST) is proposed to satisfy the movement of pitching airfoils. Steady flows around the static airfoils are simulated by SPH-FDM, and the results are compared with results of finite volume mothed (FVM) and literatures. The flows around the pitching airfoil with different conditions are simulated, and the results by coupled SPH-FDM are compared with the results by FVM which uses mesh deformation technology to control the movement of mesh. The numerical results by SPH-FDM in an Euler frame are agreement with the results of FVM or literatures, which verifies the effectiveness of the present method. The results of pithing airfoils show the direction of lift hysteresis loop changes from clockwise to counterclockwise as the pitching axis moves from the leading edge to the trailing edge, which can be well predicted by present SPH-FDM in the Euler frame. In addition, some parameters which may affect the lift hysteresis loop are discussed in this study. The results indicate that the acceleration of the airfoil surface has little effect on the lift hysteresis loop; the shape of airfoil has a weak effect on the lift hysteresis loop; the velocity of the airfoil surface, the position of the pitching axis and the free-stream velocity have predominant effect on the lift hysteresis loop.

Giant coercivity in single crystal Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; film

Van der Waals (vdW) layered ferromagnetic materials provide a unique platform for fundamental spintronic research, and have broad application prospects in the next-generation spintronic devices. In this study, we synthesize high-quality single crystals of vdW intrinsic ferromagnet Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; by the chemical vapor transport method. We obtain thin layer samples of Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; with thickness values ranging from 19 to 100 nm by the mechanical exfoliation method, and find that their corresponding Curie temperatures are between 176 and 133 K. The anomalous Hall measurement shows that the Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; has out-of-plane ferromagnetism with the coercivity reaching 7.6 T at 1.5 K, which is the largest value in those of the layered vdW ferromagnetic materials reported so far. In addition, we observe that the reversal polarity of the hysteresis loop changes sign with temperature increasing. Our work provides an opportunity to construct stable and miniaturized spintronic devices and present a new platform for studying spintronics based on van der Waals magnetic materials.

Magnetic Properties of a Ni Nanonet Grown in Superfluid Helium under Laser Irradiation

A nanonet consisting of ultrathin Ni nanowires (diameter &lt;4 nm) and Ni nanoballs (diameter &lt;20 nm) has been grown through laser ablation of a Ni target in superfluid helium. At a low Ni concentration, the nanonet consists mainly of nanowires and manifests a rectangular magnetic hysteresis loop, while an increase in the Ni concentration results in an increase in both the concentration and diameter of the nanoballs. A decrease in hysteresis loop rectangularity is observed as the concentration of the nanoball increases. We show that the composition of the system can be determined from the changes in the magnetic hysteresis loop and the temperature dependence of magnetization. The significance of the work consists of the observation of evolution of magnetic properties of the ferromagnetic nanonet, while its composition varies from nanowires to a combined nanowires–nanoballs system.

Oxygen vacancies induced room temperature ferromagnetism and enhanced dielectric properties in Co and Mn co-doped ZnO nanoparticles

We investigated the influence of oxygen vacancies (varying) on the structure and properties (dielectric and magnetic) of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles (NPs) fabricated using the chemical precipitation technique. The oxygen vacancies in the lattice increased with an increase in dopants (Co, Mn) concentration. Annealing of the doped nanoparticles decreased their dielectric properties due to reduced grain boundaries caused by enhanced grain growth. Replacement of Zn ions with dopants in the lattice enhanced the samples' electrical conductivities due to the reduction in grain boundaries and increase of charge carriers. The co-doped nanoparticles annealed at 600 °C exhibited some hysteresis loop changes and became ferromagnetic (FM). The magnetization increased with an increase in dopants content in the ZnO matrix, while coercivity decreased. This shows that the properties of the doped samples are strongly related to the number of oxygen vacancies. These results demonstrated that the enhanced dielectric and magnetization responses of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles are strongly correlated with the oxygen vacancies. The enhancement in optical, dielectric, and magnetic properties make transition metals (TM)-doped ZnO nanoparticles suitable for spintronics, and optoelectronic-based applications.

Passive piezomagnetic monitoring of structures subjected to in-service cyclic loading: Application to the detection of fatigue crack initiation and propagation

In this research, the evolution of the piezomagnetic field of a low carbon steel under cyclic tensile stress was investigated. The objective was to explore the correlations between piezomagnetic signal measured by a fluxgate magnetometer with progressive changes that take place during the fatigue tests. Experiments show first that the piezomagnetic hysteresis loop changes drastically with the propagation of fatigue crack. A multiscale magneto-elastic model of the piezomagnetic behavior allows secondly the experimental cycles evolution to be explained.

An Evolutionary Computation-Based Method for Nondestructive Tensile Force Measurements in Two Materials Using Hysteresis Loop

In traditional methods, features extracted from the hysteresis loop are manually analyzed to establish a model for predicting tensile force in one ferromagnetic material. However, the hysteresis loop is sensitive to material type, thus increasing the difficulty in predicting tensile forces in two materials. Moreover, manual feature extraction is time consuming. It is necessary to complete automatic feature extraction and elimination of the influence of material type on the hysteresis loop in order to automatically establish a prediction model for tensile force prediction in two materials. In this article, an evolutionary computation-based method was proposed to perform the above-mentioned two tasks simultaneously. The proposed method involves three steps. First, hysteresis loops of two materials under different tensile forces were measured. Second, the measured hysteresis loops were transformed into corresponding transformed ascending hysteresis curves through a transformation operation of the curve of hysteresis loop change (CHLC) for eliminating the influence of material type on the hysteresis loop. Third, an improved bat algorithm was proposed to eliminate further the influence of material type on the transformed ascending hysteresis curve. The improved bat algorithm iteratively gave the position of a material type-insensitive feature on the transformed ascending hysteresis curve. The material type-insensitive feature-based neural network was used to predict tensile forces in two materials. Experimental results verified the proposed method. The motivation of obtaining a general tensile force prediction model, the applicability of the proposed method in more than two materials, and the influence of CHLC transformation operation on the improved bat algorithm and neural network are also discussed.

Repolarization of Ferroelectric Superlattices BaZrO3/BaTiO3

With the use of the modified Sawyer-Tower scheme and Merz technique, studies were conducted on the repolarization characteristics of ferroelectric (BaZrO3/BaTiO3) superlattices on monocrystalline MgO substrate. Studies of temperature changes in the dielectric hysteresis loops indicated a sufficiently smooth decrease in spontaneous polarization compared with homogeneous barium titanate near the phase transition temperature of the superlattice. Experimental studies of switched currents have shown that the switching processes in the synthesized superlattices are implemented in two stages: activation motion (“creep” mode) and non-activation motion (slip mode). The presence of the activation switching stage and the numerical estimates show that with high probability, the movement of domain boundaries accomplishes the processes of switching in the studied superlattice. The threshold field separating the stated stages decreases with increasing temperature up to the Curie point of the superlattice, similar to the coercive field. Detection of the non-strictly exponential dependence of the switching current on the reverse field strength in the activation stage was modulated by the dependence with the power-law exponent for the applied electric field. Both techniques indicate that the studied superlattices have a small internal displacement field directed from the superlattice to the substrate.

Chemical tuning of the magnetic properties of epitaxial BaFe12-xScxO19 (0≤x≤2.1) hexaferrite thin films

The composition dependent magnetic structure in epitaxial BaFe12-xScxO19 (0 ≤ x ≤ 2.1, BaScM) thin films have been investigated. Results show that with increasing Sc3+ content, the out-of-plane c-axis lattice constants of BaScM films increase but do not follow the Vegard's law. The changes in hysteresis loops indicate a variation of magneto-crystalline anisotropy from the uniaxial-type for BaFe12O19 to the near-planar type for BaFe10.2Sc1.8O19. The remanent magnetic domains change from a mixture of dots and maze-like structure to more maze-like structure as the Sc3+ content increases. The above magnetic results can be explained by a composition dependent magnetic structure transition from collinear-type ferrimagnetic magnetic structure to the non-collinear conical magnetic structure which appears at Sc3+ content x ≥ 0.6. The ZFC/FC curves further show that the conical magnetic structure transition temperature (Tcone) of the films increases with the Sc3+ content until x ≥ 2.1. The above results may help better apply BaScM films in the electromagnetic devices.

Polarization energy storage effect of ferroelectrics

The dipole of a three-dimensional ferroelectric is distributed homogeneously in specific polarization directions related to its lattic orientations. Upon applied electric field, dipoles in all directions respond differently to electric field, resulting in various field-induced effects.The most basic effect is polarization induction effect by electric field sharply in the phase transition temperature region, which results in higher energy storage density in the corresponding temperature region. Based on the relationship between the three-dimensional Gibbs free energy and polarization in ferroelectrics from the Devonshire theory, the influences of the induced effect and reorietation of the dipole of ferroelectric on the polarization energy storage density and discharge energy density are obtained. The results show that the peak temperature of energy storage density under low electric field is lower than the Curie’s temperature, and it approaches and exceeds the Curie’s temperature with the increase of electric field. The ratio of two ferroelectric parameters has significant influence on the polarization behavior, hysteresis loop and energy storage density of ferroelectrics and causes their correlations, in which the temperature width of the dielectric peak corresponds to the temperature width of the shape change of hysteresis loop and the temperature width of the energy storage density peak. The higher the energy storage density peak is, the narrower the temperature area of the peak is.

Instability of magnetization and resistivity in La0.5Ca0.5Mn1-xAlxO3 (0 ≤ x ≤ 0.025) ceramic manganites

A detailed investigation of the thermal hysteresis, electrical and magnetic properties of La0.5Ca0.5Mn1-xAlxO3 manganites was carried out by resistivity and magnetization measurements. Rietveld refinement of X-ray diffraction patterns indicates an orthorhombic structure with Pnma space group for all samples. The magnetic susceptibility measurements on samples with Al doping up to x = 0.0125 indicated that the charge and orbitally ordered CE-type antiferromagnetic (AFM) state is suppressed and the ferromagnetic (FM) phase increases. With further increase in Al content the FM phase is also suppressed and an A-type AFM insulating state is stabilized. The thermal hysteresis decreases in the samples up to x = 0.0125 whereas it increases by further enhancement of doping up to x = 0.025. The rotation direction of the thermal hysteresis loop changes from counterclockwise to clockwise with increasing of Al doping. Also, the magnetization measurement indicates that saturation magnetization is initially enhanced by increasing doping level up to 0.0125 whilst it is slightly reduced by further increasing doping content. Magnetization versus magnetic field loops of samples at zero field cooled (ZFC) and field cooled (FC) modes at 5 K showed an instable behaviour in the low doping, while in high doping the magnetization curve of ZFC and FC overlapped, demonstrating the stable FM and AFM phases. The results of the resistivity measurements confirmed change in thermal hysteresis and thermal cycling. The thermal hysteresis and cycling behaviour are attributed to the interfacial elastic energy in the boundary between FM and CO–AFM phases.

Mechanical Model of a Hybrid Non-linear Viscoelastic Material Damping Device With Its Verifications

This paper proposes a new viscoelastic (VE) material damping device with hybrid nonlinear properties. Compared with traditional linear material dampers, the new nonlinear VE material damping device is characterized by its better energy dissipation and deformation capability. The series performance tests of the VE device are conducted, based on which the sources and variation law of material nonlinearities are analyzed. Five aspects of material nonlinearities are summarized, including the shape change of hysteresis loop caused by phase difference, the initial stiffness caused by large loading rate, the softening effect caused by high temperature and fatigue, and the softening and stiffening effect under large strain deformation. Then, a mechanic model for this device is proposed which considers multiple nonlinear effects of the material. For the verifications of the proposed mechanic model, a shaking table test on a steel frame equipped with the new VE devices is designed and performed. Based on the proposed mathematic mechanic model, the numerical mechanic model is implemented in the OpenSees software. The accuracy of the mechanic model is firstly verified by comparing the performance tests data with the simulation results. Then numerical model is also used to calculate the time history response of the shake table tested steel frame under earthquake loading. It is concluded that the mechanic model can well depict several nonlinear material behaviors of the new VE device, and the corresponding numerical model created in the open source calculation platform is reliable to be used to calculate nonlinear time history response of a structure equipped with the new VE material damping devices.

Smart composites with embedded magnetic microwire inclusions allowing non-contact stresses and temperature monitoring

A novel sensing technique for non-destructive and non-contact monitoring of the composites utilizing ferromagnetic glass-coated microwire inclusions with magnetic properties sensitive to tensile stress and temperature is proposed. We provide in-situ studies of the evolution of the hysteresis loop of arrays consisting of Co- and Fe-rich microwires, as well as transmission and reflection parameters of the composites with microwire inclusions during the composites matrix polymerization. We observed remarkable change of the hysteresis loops upon matrix polymerization: remarkable coercivity change and transformation of linear hysteresis loop to rectangular or from rectangular to linear for arrays with Co-rich and Re-rich microwires respectively. Using the free space technique we observed considerable variation of the reflection in the range of 4–7 GHz and transmission upon the matrix polymerization. Observed dependencies are discussed considering variation of temperature and stresses during the thermoset matrix polymerization and their influence on magnetic properties of glass-coated microwires.

Complex Dynamical Behaviors of a Fractional‐Order System Based on a Locally Active Memristor

A fractional‐order locally active memristor is proposed in this paper. When driven by a bipolar periodic signal, the generated hysteresis loop with two intersections is pinched at the origin. The area of the hysteresis loop changes with the fractional order. Based on the fractional‐order locally active memristor, a fractional‐order memristive system is constructed. The stability analysis is carried out and the stability conditions for three equilibria are listed. The expression of the fractional order related to Hopf bifurcation is given. The complex dynamical behaviors of Hopf bifurcation, period‐doubling bifurcation, bistability and chaos are shown numerically. Furthermore, the bistability behaviors of the different fractional order are validated by the attraction basins in the initial value plane. As an alternative to validating our results, the fractional‐order memristive system is implemented by utilizing Simulink of MATLAB. The research results clarify that the complex dynamical behaviors are attributed to two facts: one is the fractional order that affects the stability of the equilibria, and the other is the local activeness of the fractional‐order memristor.

Experimental and numerical studies of bolted joints subjected to torsional excitation

The dynamic response of bolted joints subjected to torsional excitation is investigated experimentally and numerically. First, the effects of the initial preload and the angular amplitude on axial force loss of the bolt were studied. Second, the change of hysteresis loops with the increasing number of loading cycles was found under a larger torsional angle. At last, a fine-meshed three-dimensional finite element model was built to simulate the bolted joint under torsional excitation, from which the hysteresis loops were obtained under varying angular amplitudes. The results of numerical analysis are in good agreement with those of experiments.