First-order Reversal Curve Research Articles

Improved Preisach Model for the Vector Hysteresis Property of Soft Magnetic Composite Materials Based on the Hybrid Technique of SA-NMS

The two-dimensional hysteresis property of the soft magnetic composite (SMC) material under circular rotational excitation was measured by the experimental platform. The first-order reversal curves and the corresponding scalar Everett functions can be numerically generated by the measured major hysteresis loops along the orthogonal easy axis and hard axis. Different from the classical model, an improved vector Preisach hysteresis model that considers the anisotropic property of the SMC materials under vector magnetic excitation was put forward by introducing two parameters w and z. The two parameters were used to identify the vector Everett functions and adjust the shape of hysteresis curves under different magnitudes of the magnetic flux density. Furthermore, an efficient hybrid algorithm that combines simulated annealing with Nelder-Mead simplex technique was proposed for the accurate extraction of optimal parameters. The simulated results based on the improved model agree well with the measured ones; thus, the effectiveness and accuracy of the proposed method were verified.

Exchange bias training in La0.7Sr0.3FeO3/Ni79Fe21 films with native surface oxide: First-order reversal curve analysis

In conventional magnetometry, exchange bias training (EBT) is mostly evaluated through the major magnetization hysteresis loops (MHLs). We here report a study of EBT by using the first-order reversal curves (FORCs) in the heterostructures of ${\mathrm{SrTiO}}_{3}(001)/{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{FeO}}_{3}(\mathrm{LSFO})/{\mathrm{Ni}}_{79}{\mathrm{Fe}}_{21}(\mathrm{Py})/{\mathrm{PyO}}_{x}$. It was unraveled that the training effect occurs once after exceeding the left coercivity of the first MHL, while the magnetic coupling from the ultrathin native oxide (${\mathrm{PyO}}_{x}$) mainly contributes to an exchange springlike behavior. Besides for the first MHL, the FORCs corresponding to the second MHL and the quasiequilibrium stage were collected, respectively, which provide a detailed picture of how the magnetization reversal evolves in the training process.

In situ transport characterization of magnetic states in Nb/Co superconductor/ferromagnet heterostructures.

Employment of the non-trivial proximity effect in superconductor/ferromagnet (S/F) heterostructures for the creation of novel superconducting devices requires accurate control of magnetic states in complex thin-film multilayers. In this work, we study experimentally in-plane transport properties of microstructured Nb/Co multilayers. We apply various transport characterization techniques, including magnetoresistance, Hall effect, and the first-order-reversal-curves (FORC) analysis. We demonstrate how FORC can be used for detailed in situ characterization of magnetic states. It reveals that upon reduction of the external field, the magnetization in ferromagnetic layers first rotates in a coherent scissor-like manner, then switches abruptly into the antiparallel state and after that splits into the polydomain state, which gradually turns into the opposite parallel state. The polydomain state is manifested by a profound enhancement of resistance caused by a flux-flow phenomenon, triggered by domain stray fields. The scissor state represents the noncollinear magnetic state in which the unconventional odd-frequency spin-triplet order parameter should appear. The non-hysteretic nature of this state allows for reversible tuning of the magnetic orientation. Thus, we identify the range of parameters and the procedure for in situ control of devices based on S/F heterostructures.

Defect-correlated skyrmions and controllable generation in perpendicularly magnetized CoFeB ultrathin films

Skyrmions have attracted significant interest due to their topological spin structures and fascinating physical features. The skyrmion phase arises in materials with a Dzyaloshinskii–Moriya interaction at interfaces or in volume of non-centrosymmetric materials. Although skyrmions have been demonstrated experimentally, the general critical intrinsic relationship among fabrication, microstructures, magnetization, and the existence of skyrmions remains to be established. Here, two series of CoFeB ultrathin films with controlled atomic scale structures are employed to reveal this relationship. The amount of defects was artificially tuned by inverting the growth order, and skyrmions were shown to be preferentially formed in samples with more defects. By utilizing first-order reversal curves, the stable region and the skyrmion densities can be efficiently controlled in the return magnetization loops. These findings establish a general internal link from sample preparation to skyrmion generation and provide a general method for controlling skyrmion density.

Energy storage performance of K0.5Na0.5NbO3-based ceramics modified by Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3

The damage of lead-based ceramics to our environment and health completely hindered their industrial applications. K0.5Na0.5NbO3 (KNN) ceramic material is considered as a good substitute for lead-free ceramics because of its high dielectric constant, excellent piezoelectric properties, high Curie temperature and sustainability. However, it is challenging to achieve their high energy-storage performances because of their large energy loss density (Wloss) under an applied electric field. Thus, this work proposes a combinatorial optimization strategy of inducing polar nano-regions and improving breakdown strength (BDS) to enhance the energy-storage performances of the KNN-based ceramics. As a result, we obtained a record high recoverable energy-storage density (Wrec) value of 7.4 J·cm−3 for the Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3 (BZNT)-modified KNN ceramic mainly due to its enhanced BDS. Furthermore, remarkable temperature stability was obtained for the 0.90KNN-0.10BZNT ceramic over a wide temperature range (20–180 °C). Remarkably, the first-order reversal curve (FORC) confirmed the excellent energy-storage performances of the 0.90KNN-0.10BZNT ceramic, which we ascribed to its enhanced relaxation behavior. Additionally, 0.90KNN-0.10BZNT material exhibited excellent pulsed charge/discharge properties of the high power density (184.84 MW·cm−3) and fast discharge time (46.3 ns). Our results demonstrated a novel strategy for improving the energy-storage performances of dielectric ceramics. This strategy could be used to design other or similar materials for various applications.

Magnetic Reversal in Wiegand Wires Evaluated by First-Order Reversal Curves.

The magnetic structure of Wiegand wires cannot be evaluated using conventional magnetization hysteresis curves. We analyzed the magnetization reversal of a Wiegand wire by measuring the first-order reversal curves (FORCs). A FeCoV Wiegand wire with a magnetically soft outer layer and a hard magnetic core was used in this study. The magnetization reversal of the soft and hard regions in the wire was identified in the FORC diagrams. The magnetization reversal of the dominantly irreversible process of the soft layer and the magnetic intermediate region between the soft and hard regions was clarified.

Fabrication and magnetic characteristics of electrodeposited FeCr nanowire arrays

Fe-based nanowire (NW) arrays have long been investigated due their potential applications in future-generation magnetic nanodevices. However, very few research studies have considered FeCr NWs so far. Herein, FeCr NW arrays with different compositions are fabricated using a pulsed ac electrodeposition technique in porous anodic alumina templates. The Cr electrolyte concentration changed between 2 and 8 mM, influencing morphological, compositional, structural and magnetic properties. As an additive, the element Cr enhanced coercivity and squareness of Fe NWs, inducing the formation of Fe (200) peak in the crystal structure. As an alloying component, although the Cr element kept the structural and magnetic properties almost constant, it considerably affected the NW length compared to Fe NWs. First-order reversal curve analysis showed significant reductions in magnetostatic interactions when increasing the Cr concentration. In this case, local interactions between the FeCr NW arrays were expected to increase compared to pure Fe NWs.

Precise electrical detection of the field and current-induced switching mode of a magnetic nanodisk in a non-local spin valve

In this work, we study the manipulation and the detection of the magnetic state and switching modes of a Permalloy disk, using a non-local spin-valve with dual CoFe injectors and with the disk acting as the detector electrode. Applying simultaneously external magnetic fields and spin currents from the injectors, we demonstrate the possibility to use the spin torque created by the spin current to modulate the switching modes and switching fields of the disk, following the disentanglement of the influence of Joule heating. Moreover, by engineering the device to have a very small overlap of the spin conduit with one side of the disk, we demonstrate how, with the help of a first-order reversal curve analysis, we can extract the precise details of the switching from the monodomain to the vortex state, including the chirality of the system without the need for direct imaging.

Fast and universal approach for quantitative measurements of bistable hysteretic systems

Accurate and fast characterization of hysteretic systems can accelerate progress in fields as diverse as biomedicine, sensors, data storage, and logic devices. Here, we introduce a fast approach to determine magnetic parameters (intrinsic coercivities of elementary domains, interaction fields between the domains, and the variances of both) of bistable hysteretic systems. The approach uses the first few points in first-order reversal curves (FORC) to mathematically and empirically determine the projections of traditional FORC diagrams onto the reversal field and applied field axes. Since this projection approach only requires a few points per each reversal curve (rather than 100+ points for 100+ curves compared to the traditional FORC method), the time of measurement is reduced by 50-100x over traditional FORC measurements. In addition, the projection results do not contain the typical FORC artifacts that have been disputed for decades. As a proof of concept, the projection analysis was used to determine the magnetic parameters of several arrays of bistable magnetic nanowires (MNWs), and the results were compared with the hysteresis loop and FORC results. For non-interacting arrays of MNWs, all three methods give the intrinsic coercivity with minor difference. While, the differences become significant for the interacting arrays of the MNWs that will be discussed in details.

Anisotropic Congruency-Based Vector Hysteresis Model Applied to Non-Oriented Laminated Steels

A new approach is proposed to model the hysteretic behavior of magnetic materials in 2-D electromagnetic analyses. A scalar congruency-based hysteresis model is developed using the first-order reversal curves (FORCs) and verified by comparing the model results with quasi-static measurements. An anisotropic scalar model is obtained from two scalar hysteresis models using FORCs measured parallel and perpendicular to the material rolling direction. The established anisotropic scalar model is employed as the main building block to determine the vector hysteresis model based on the Mayergoyz vector hysteresis generalization. The obtained vector hysteresis model is coupled with a finite-element solver to analyze the three-limbed transformer core investigated in the TEAM problem number 32. The comparison between the simulation results and experimental data confirms the accuracy of the proposed model with an rms flux density error of less than 0.07 T.

Abstract P-7: NdFeCo-based Nanoparticles for Biomedical Applications

Background: The multifunctional nanoparticles can be promising antitumor materials. The results of a study of synthesized NdFeCoB oxide nanoparticles (NPs) as a basis for drug transportation systems are presented. In the next step, the NPs can be coated by a multifunctional gel shell. Methods: NPs, the composition of NdFexCo1-xB (where x =0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5), were synthesized by a Pechini-type sol-gel method. The synthesis allows tuning of NPs magnet properties by manipulating the microstructure and phase composition. NPs were studied by XRD, SEM, TEM, HRTEM, and VSM. Results: SEM images show that the average size of NPs changed from 280 nm (for x = 0) up to 416 nm (for x = 0.1 – 0.5). At TEM images the NPs of the sample without cobalt (x = 0) have an elongated shape (Fig 1a). Diffraction patterns showed that the NPs consist of single crystal or ordered crystallites. NPs with cobalt mainly consist of crystallites with a size of about 20-50 nm. There are also areas with a complex-grained microstructure. Hysteresis loops and first-order reversal curve analysis indicated that the NPs were ferromagnetic whose coercivity, squareness ratio, and magnetic interactions changed significantly with the cobalt contents.

A novel strategy for the fabrication of high-performance nanostructured Ce-Fe-B magnetic materials via electron-beam exposure

Ce2Fe14B compound has a great potential to serve as a novel permanent magnet alternative thanks to the abundant and inexpensive rare-earth element (cerium), while its low magnetocrystalline anisotropy and energy product severely restrict its applications. In this work, a novel strategy combining melt-spinning and electron-beam exposure (EBE) aiming for fabricating high-performance Ce-Fe-B magnetic materials is reported to solve the above-mentioned problem. Remarkably, this strategy facilitates developing a suitable grain boundary configuration without using any additional heavy rare-earth element. Under the optimal EBE condition, the maximum energy product ((BH)max) of pure Ce-Fe-B alloy is 6.5 MGOe, about four times higher than that obtained after conventional rapid thermal processing method for the same precursor. The enhanced intergranular magnetostatic coupling effect in the EBE sample is validated by mapping the first-order-reversal-curve (FORC) diagrams. The in-situ observation of magnetic domain wall motion for Ce-Fe-B alloy using Lorentz transmission electron microscopy reveals that the boundary layers are very effective in pinning the motion of domain walls, leading to the increased coercivity under EBE, and this pinning effect is further verified by micromagnetic simulations. Our results suggest that CeFeB materials using EBE could be a promising candidate after further processing, which could fill the performance “gap” between hexaferrite and Nd-Fe-B-based magnets.

AMS and rock magnetism in the Caviahue-Copahue Volcanic Complex (Southern Andes): Emission center, flow dynamics, and implications to the emplacement of non-welded PDCs

Pyroclastic deposits can cover significant areas and register major geological events. Despite their importance, understanding depositional dynamics of pyroclastic density currents (PDCs) and linking explosive deposits to their emission centers is still a challenge, especially in the case of non-welded, massive ignimbrites. Located in the Southern Andes, the Caviahue Copahue Volcanic Complex (CCVC) comprises one of the most active volcanic centers in the Andean Belt. This volcanic complex hosts massive ignimbrites with both source emplacement poorly constrained, currently grouped in the Riscos Bayos Ignimbrites (RBI). In this contribution, we perform a full magnetic characterization and anisotropy of magnetic susceptibility (AMS) study on the massive RBI of the CCVC. The magnetic characterization was performed using magnetic experiments including isothermal remanet magnetization, thermomagnetic curves, hysteresis loops, first-order reversal curves, and scanning electron microscopy. Magnetic experiments indicate primary, multi-domain, high Curie temperature titanomagnetites as the AMS carriers. Ellipsoids are predominately oblate, with a low degree of anisotropy and east-southeastward imbrication. This fabric arrangement is consistent with PDC sedimentary fabrics deposited under laminar flow conditions. Despite RBI massive structure AMS data reveals changes in transport capacity of the PDC and particle organization. These changes are marked by increasing AMS dispersion and decreasing degree of anisotropy up-section within flow units. Directional statistics of AMS data implies the Las Mellizas Caldera as the emission center of RBI. The reconstructed flow path also suggests the PDC overrun of the Caviahue Caldera topographic rim. This study highlights the application of AMS to the identification of emission centers of explosive deposits, featuring its application to massive ignimbrites.

Exploring Effects of Magnetic Nanowire Arrangements and Imperfections on First-Order Reversal Curve Diagrams

The first-order reversal curve (FORC) method is one of the most appealing magnetic characterization methods that has been used over decades for detailed analyses of nanoscaled magnetic systems. These detailed analyses are accompanied by numerous magnetic features in FORC diagrams that usually are difficult to explain fully. Here, the FORC diagrams of several magnetic nanowire (MNW) arrays are modeled and discussed. The focus is on how the MNW arrangement (i.e. hexagonal, random, and square) and imperfections (i.e. variation of coercivity, Hc) effects interaction fields (Hu) between MNWs, as well as switching events and FORC diagram features. Hu in hexagonal arrangements is higher than those in square or random arrangements because hexagonal is a close-packed arrangement, so there are more nearest neighbors. Furthermore, the FORC diagrams features were dictated not only by the Hu and Hc values but also by their standard deviation ratios (σu /σc), where “Wish-bone” features were observed for σu /σc ≤ 1 and “T-shape” features were observed for σu /σc ≥ 5.

Effect of sputtering power on the first order magnetization reversal, reversible and irreversible process in Fe71Ga29 thin films

We report on the first-order reversal curves (FORC) of magnetization and effect of defects on magnetization process in Fe71Ga29 thin films with different values of sputtering power (50 – 120 W). Phase purity of the thin films was confirmed by grazing incidence X– ray diffraction (GI-XRD). The reversible and irreversible contributions to the magnetization are evidenced through the minor loop parameter such as pseudo hysteresis loss (WF*) and energy loss coefficient (WF0). In particular, the energy loss coefficient is found to decrease from 28 × 106 (A/m. mT) at 50 W to 21 × 106 (A/m. mT) at 120 W, which signifies a decrease in domain wall resistance. FORC infers narrow switching, which leads to low coercivity distribution at 120 W as a result of less defects.

Multilayer regular hexagonal prism barium ferrite nanodot arrays on a substrate based on an AAO mask

Herein, the multilayer regular hexagonal barium ferrite nanodot arrays have been prepared by pulsed laser deposition through a porous anodic alumina template. The BaM nanodot arrays displayed a c-axis oriented crystal with a multilayer regular hexagonal structure, and the degree of orientation was improved by the post-annealing. Furthermore, the hysteresis loops showed the annealed nanodot arrays have a high squareness ratio of 0.65 along the easy magnetization direction. The first-order reversal curve diagram confirmed that the nanodots have a small interactive field between the particles. Consequently, this effective approach is potentially applied in self-biased microwave devices.

Unexpected Light-Induced Thermal Hysteresis in Matrix Embedded Low Cooperative Spin Crossover Microparticles

The embedding of spin-crossover micro- or nanocrystals in various surroundings dramatically changes their functionalities based on first-order spin transitions. The dampening of their internal cooperativity, together with introducing a new kind of interactions occurring at interfaces between spin-crossover particles and their environment, results in spectacular effects, as an enhanced hysteresis with non-cooperative transitions. In this work, we deal with the influence of the embedding matrix on the light-induced thermal hysteresis (LITH) in the case of spin-crossover microparticles of Fe(phen)2(NCS)2. Despite the low cooperativity of this compound, the competition between the continuous photoexcitation towards the metastable high spin state and the relaxation down to low spin ground state leads to a light-induced thermal hysteresis, with a quasi-static width of around 10 K. This unexpected hysteresis is explained by considering a switch-on/cutoff mechanism of the particle–matrix interactions in the framework of a mean-field approach based on negative external pressures, with Gaussian distributed variations and of an Ising-like model with various interactions with the environment. Additional first-order reversal curves measurements and corresponding calculated distributions are in line with relaxations under light and confirm the existence of a non-kinetic LITH.

High-frequency GMI hysteresis effect analysis by first-order reversal curve (FORC) method

In this work, we investigate the giant magnetoimpedance (GMI) hysteresis at high-frequency (10 MHz – 1 GHz) of Co-based amorphous magnetic ribbons. The first-order reversal curve (FORC) method was used to analyze their hysteretic behavior present at a low magnetic field (below 7 Oe). Results show that the GMI hysteresis is related to both the system magnetic anisotropy and the current frequency (through the skin depth). The GMI hysteresis gradually decreases upon frequency increase before disappearing, while a clockwise rotation of the FORC distributions is observed. These results are attributed to a heterogeneous magnetic structure in the magnetic ribbon volume. On the other side, while the cut-off frequency depends on the magnetic anisotropy strength, an inverted GMI hysteresis revives for the higher anisotropy ribbon. Above this frequency inversion, FORC results indicate a hardening of the effective switching field as a thicker region is probed. We propose that in this case, the stronger perpendicular anisotropy creates important differences between the superficial and volumetric anisotropy, enough to induce interaction between the two regions of different magnetization directions. This sensitive FORC protocol can be applied for investigating the GMI hysteresis, and thus the complex magnetic structure of several soft magnetic systems.

Magnetic Properties of a Holocene Sediment Core from the Yeongsan Estuary, Southwest Korea: Implications for Diagenetic Effects and Availability as Paleoenvironmental Proxies

The sensitivity of magnetic properties, which characterize the mineralogy, concentration, and grain size distribution of magnetic minerals, to environmental processes may provide useful information on paleoenvironmental changes in estuarine environments. Magnetic property studies of estuaries are less common than other environments and, due to the west coast of South Korea having an abundance of estuaries, it provides a good place to study these processes. In this study, we analyzed a variety of magnetic properties based on magnetic susceptibility, hysteresis parameters, progressive acquisition of isothermal remanent magnetization and first-order reversal curve data from a Holocene muddy sediment core recovered from the Yeongsan Estuary on the west coast of South Korea. We examined diagenetic effects on magnetic properties and tested their availability as proxies of paleoenvironmental change. The presence of generally low magnetic susceptibility, ubiquitous greigite-like authigenic magnetic component, and very fine magnetic particle occurrence suggested that the analyzed sediments had undergone considerable early diagenetic alteration. Electron microscopic observations of magnetic minerals support this suggestion. Our results confirm that the use of initial bulk susceptibility as a stand-alone environmental change proxy is not recommended unless it is supported by additional magnetic analyses. We recognized the existence of ferromagnetic-based variabilities related to something besides the adverse diagenetic effects, and have examined possible relationships with sea-level and major climate changes during the Holocene. The most remarkable finding of this study is the two distinct intervals with high values in magnetic coercivity (Bc), coercivity of remanence (Bcr), and ratio of remanent saturation moment to saturation moment (Mrs/Ms) that were well coincident with the respective abrupt decelerations in the rate of sea-level rise occurred at around 8.2 and 7 thousand years ago. It is then inferred that such condition with abrupt drop in sea-level rise rate would be favorable for the abrupt modification of grain size distribution toward more single-domain-like content. We modestly propose consideration of the Bc, Bcr, and Mrs/Ms variability as a potential indicator for the initiation/occurrence of sea-level stillstand/slowstand or highstand during the Holocence, at least at estuarine environments in and around the studied area.

Magnetic characterization of magnetoactive elastomers containing magnetic hard particles using first-order reversal curve analysis

Abstract The use of new types of intelligent materials is becoming increasingly widespread. These include magnetoactive elastomers with hard magnetic filling components, which offer the unique chance to adapt active and passive material properties. In this context, this paper presents an overview of the experimental results on the study of the magnetic properties of elastic composites with a magnetic hard component. First-order reversal curves, which are recorded with a vibrating sample magnetometer, are used as method to characterize the magnetic material behavior. The influence of various parameters on the process of magnetization of composites is considered, including the stiffness of the polydimethylsiloxane-based matrix polymer, the particle ratio and the particle size as well as the so-called training effect.