First-order Reversal Curve Method Research Articles

Synergy of a Stabilized Antiferroelectric Phase and Domain Engineering Boosting the Energy Storage Performance of NaNbO3-Based Relaxor Antiferroelectric Ceramics.

Relaxor antiferroelectric (AFE) ceramic capacitors have drawn growing attention in future advanced pulsed power devices for their superior energy storage performance. However, state of the art dielectric materials are restricted by desirable comprehensive energy-storage features, which have become a longstanding hurdle for actual capacitor applications. Here, we report that a large energy density Wrec of 5.52 J/cm3, high efficiency η of 83.3% at 560 kV/cm, high power density PD of 114.8 MW/cm3, ultrafast discharge rate t0.9 of 45 ns, and remarkable stability against temperature (30-140 °C)/frequency (5-200 Hz)/cycles (1-105) are simultaneously achieved in 0.7 NaNbO3-0.3 CaTiO3 relaxor AFE ceramics via the synergy of stabilized AFE R phase and domain engineering in combination with breakdown strength enhancement. The structural origin for these achievements is disclosed by probing the in situ microstructure evolution by means of the first-order reversal curve method, piezoelectric force microscopy, and Raman spectroscopy. The highly dynamic polar nanoregions and stabilized AFE R phase synergistically generate a linear-like and highly stable polarization field response over a wide temperature and field scope with concurrently improved energy density and efficiency. This work offers a new solution for designing high-performance next-generation pulsed power capacitors.

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.

Comparison of the evolution of internal bias field of doped hafnia ferroelectric capacitors for the field-cycling reliability

The discovery of ferroelectricity in HfO2 thin films extends the range of research on next-generation electronic devices. However, for commercial applications, reliable ferroelectric switching characteristics under electric field cycling of HfO2 thin films must be secured. Despite recent reports of improved reliability under electric cycling of HfO2 with various dopants, a deep understanding of the experimental results is still needed. Our research has confirmed that finer domains and grains formed in thin films doped with Si than in those doped with Zr. This difference leads to a difference in the size of the domain and the number of domain walls, and a large number of domain walls function to suppress the diffusion of oxygen vacancies, which is known to significantly affect the stability of hafnia. This dependence was verified by the observation of relatively limited changes in the internal electric field of the Si-doped HfO2 films during the progression of cycling, using the first-order reversal curve method and various electrical measurements.

3D Nanomagnetism in Low Density Interconnected Nanowire Networks.

Free-standing, interconnected metallic nanowire networks with densities as low as 40 mg/cm3 have been achieved over centimeter-scale areas, using electrodeposition into polycarbonate membranes that have been ion-tracked at multiple angles. Networks of interconnected magnetic nanowires further provide an exciting platform to explore 3-dimensional nanomagnetism, where their structure, topology, and frustration may be used as additional degrees of freedom to tailor the materials properties. New magnetization reversal mechanisms in cobalt networks are captured by the first-order reversal curve method, which demonstrate the evolution from strong demagnetizing dipolar interactions to intersection-mediated domain wall pinning and propagation, and eventually to shape-anisotropy dominated magnetization reversal. These findings open up new possibilities for 3-dimensional integrated magnetic devices for memory, complex computation, and neuromorphics.

Effect of the repeat number and Co layer thickness on the magnetization reversal process in [Pt/Co(x)]N multilayers

Magnetic properties, domain morphology and magnetization reversal processes were investigated for two sets of [Pt/Co(x)]N multilayers with various (Co/Pt) bilayer repeat numbers (N) and Co layer thicknesses (x) using hysteresis loops, magnetic force microscopy (MFM), and the first-order reversal curve method. When N ranges from 7 to 20, the effective anisotropy, Keff, of the multilayers increases from 0.86 × 106 erg cc−1 to 1.48 × 106 erg cc−1 and the coercivity (Hc) is maintained at approximately 290 Oe. Moreover, when x increases, Keff drops from 0.52 × 106 erg cc−1 to 0.09 × 106 erg cc−1 and Hc decreases from 285 Oe to 75 Oe. According to the switching field distribution, evidence has been found that the magnetization switching is gradually dominated by the reversible process and the portion of the irreversible switching process declines from 86% to 40% and 58% to 10% when N and x are increased, respectively.

Excellent Energy-Storage Properties Achieved in BaTiO3-Based Lead-Free Relaxor Ferroelectric Ceramics via Domain Engineering on the Nanoscale.

Barium titanate-based energy-storage dielectric ceramics have attracted great attention due to their environmental friendliness and outstanding ferroelectric properties. Here, we demonstrate that a recoverable energy density of 2.51 J cm-3 and a giant energy efficiency of 86.89% can be simultaneously achieved in 0.92BaTiO3-0.08K0.73Bi0.09NbO3 ceramics. In addition, excellent thermal stability (25-100 °C) and superior frequency stability (1-100 Hz) have been obtained under 180 kV cm-1. The first-order reversal curve method and transmission electron microscopy measurement show that the introduction of K0.73Bi0.09NbO3 makes ferroelectric domains to transform into highly dynamic polar nanoregions (PNRs), leading to the concurrently enhanced energy-storage properties by the transition from ferroelectric to relaxor ferroelectric (RFE). Furthermore, it is confirmed by piezoresponse force microscopy that the appearance of PNRs breaks the long-range order to some extent and reduces the stability of the microstructure, which explains the excellent energy-storage performance of RFE ceramics. Therefore, this work has promoted the practical application ability of BaTiO3-based energy-storage dielectric ceramics.

Variation of magnetic anisotropy and temperature-dependent FORC probing of compositionally tuned Co-Ni alloy nanowires

The magnetic microstructure of Co-Ni binary alloy nanowires electrodeposited with controlled composition into nanoporous aluminum oxide templates can be represented as an ensemble of stochastic magnetic domains, whose size is determined by the magnetic correlation length. Using a method based on the approaching of magnetization to saturation, we defined the dimension of regions with magnetic orientation coherency as the stochastic domain size. Based on the experimental measurements of magnetization curves near saturation and first order reversal curves (FORC), we described a relationship between the macroscopic and microscopic parameters of the nanowires depending on the crystal structure observed by high-resolution transmission electron microscopy in terms of the random anisotropy model. The alloy composition strongly determines the crystal structure, in particular, the grain size and hcp/fcc phase distribution, and influences the effective magnetic anisotropy energy providing the direction of easy magnetization in the nanowire arrays. The characterization of Co-Ni arrays by FORC method at room and low temperatures revealed the transformation of magnetic behavior and certain contributions to the energy of the effective magnetic anisotropy.

First order reversal curves and intrinsic parameter determination for magnetic materials; limitations of hysteron-based approaches in correlated systems

The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach.

Self-organization and FORC-based magnetic characterization of ultra-high aspect ratio epitaxial Co nanostrips produced by oblique deposition on an ordered step-bunched silicon surface

Further development of microelectronics requires novel or improved technological approaches for device nanofabrication and functional properties characterization. In this paper, we studied the crystal structure and magnetic properties of epitaxial Co nanostrips with the average width of 32.6, 45.3, and 62.6 nm grown on a step-bunched Si(111)5.55 × 5.55-Cu/Cu surface. Technological conditions, under which the ultra-high aspect ratio (∼104) structurally solid, straight nanostrips of hcp-Co with crystallographic axis [0001] oriented along their long side can be grown, were determined. The dependence of the coercive force on the width of the nanostrips was demonstrated. Magnetization reversal through the transverse domain-wall nucleation and propagation in a Co nanostrip was defined with an analytical approach based on the Stoner–Wohlfarth model. Using the first-order reversal curve method, we analyzed the effect of nanostrip uniformity degree on magnetic behavior and the influence of the magnetostatic interactions on the coercive force of individual nanostrips.

Identifying weakly-interacting single domain states in Ni nanowire arrays by FORC

The control and understanding of magnetization reversal mechanisms and magnetostatic interactions in nanomagnet arrays is a critical point that has to be overcome in order to reach industrial applications. However, usual magnetic characterization techniques can only provide information on the overall array behaviour and are not able to discriminate relevant local properties. In this work, we show that the first-order reversal curve (FORC) method is a unique tool to identify weakly-interacting uniaxial single domain (SD) particles in systems with complex mixed magnetic states. We compare the FORC diagrams of two sets of Ni nanowire (NW) arrays electrodeposited in hexagonally ordered nanoporous alumina templates: A) with a uniform length distribution (interacting SD particles), and B) with a non-uniform length distribution. For non-uniform length distributions, regions of isolated NWs occur in the array, creating a complex mixture of strongly and weakly-interacting SD particles. These weakly-interacting NWs are here identified by a characteristic ridge along the coercive field axis of the FORC diagram. Micromagnetic simulations confirmed the presence of this weakly-interacting magnetic behaviour in the array with non-uniform length distributions. Combining FORC results with micromagnetic simulations, we show that the magnetization reversal of interacting wires occurs by the nucleation of transverse domain walls at the NWs' ends, while isolated wires nucleate vortex domain walls. This work thus highlights the importance of the FORC method for the accurate identification and understanding of local magnetic behaviours in nanomagnet arrays.

Combined first-order reversal curve and x-ray microscopy investigation of magnetization reversal mechanisms in hexagonal antidot lattices

The magnetization reversal in nanoscaled antidot lattices is widely investigated to understand the tunability of the magnetic anisotropy and the coercive field through nanostructuring of thin films. By investigating highly ordered focused ion beam milled antidot lattices with a combination of first-order reversal curves and magnetic x-ray microscopy, we fully elucidate the magnetization reversal along the distinct orientations of a hexagonal antidot lattice. This combination proves especially powerful as all partial steps of this complex magnetization reversal can be identified and subsequently imaged. Through this approach we discovered several additional steps that were neglected in previous studies. Furthermore, by imaging the microscopic magnetization state during each reversal step, we were able to link the coercive and interaction fields determined by the first-order reversal curve method to true microscopic magnetization configurations and determine their origin.

Thermal hysteresis kinetic effects of spin crossover nanoparticulated systems studied by FORC diagram method on an Ising-like model

The scientific community is manifesting a high research interest on spin crossover compounds and their recently synthesized nanoparticles, due to their various appealing properties, such as the bistability between a diamagnetic low spin state and a paramagnetic high spin state (HS), inter-switchable by temperature or pressure changes, light irradiation or magnetic field. The utility of these compounds showing hysteresis covers a broad area of applications, from the development of more efficient designs of temperature and pressure sensors to automotive and aeronautic industries and even a new type of molecular actuators. We are proposing in this work a study regarding the kinetic effects and the distribution of reversible and irreversible components on the thermal hysteresis of spin crossover nanoparticulated systems. We are considering here tridimensional systems with different sizes and also systems of nanoparticles with a Gaussian size distribution. The correlations between the kinetics of the thermal hysteresis, the distributions of sizes and intermolecular interactions and the transition temperature distributions were established by using the FORC (First Order Reversal Curves) method using a Monte Carlo technique within an Ising-like system.

Analysis of first order reversal curves in the thermal hysteresis of spin-crossover nanoparticles within the mechanoelastic model

The recently obtained spin-crossover nanoparticles are possible candidates for applications in the recording media industry as materials for data storage, or as pressure and temperature sensors. For these applications, the intermolecular interactions and interactions between spin-crossover nanoparticles are extremely important, as they may be essential factors in triggering the transition between the two stable phases: the high-spin and low-spin ones. In order to find correlations between the distributions in size and interactions and the transition temperatures distribution, we apply the FORC (First Order Reversal Curves) method, using simulations based on a mechanoelastic model applied to 2D triangular lattices composed of molecules linked by springs and embedded in a surfactant. We consider two Gaussian distributions: one is the size of the nanoparticles and another is the elastic interactions between edge spin-crossover molecules and the surfactant molecules. In order to disentangle the kinetic and non-kinetic parts of the FORC distributions, we compare the results obtained for different temperature sweeping rates. We also show that the presence of few larger particles in a distribution centered around much smaller particles dramatically increases the hysteresis width.

Enhanced exchange bias in IrMn/CoFe deposited on self-organized hexagonally patterned nanodots

Exchange biased nanostructures of IrMn/CoFe were deposited on anodized alumina with hexagonally patterned nanodot surface structures. Nanodots with diameters of 20, 70, and 100 nm were fabricated to investigate the size effect on the magnetic properties. Magnetometry and the first-order reversal curve method revealed significant enhancements of the exchange bias and coercivity in the nanodots compared with flat films. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes and increased random fields due to the nanostructure morphology and domain wall pinning by the boundaries between adjacent nanodots.

Effect of doping on surface reactivity and conduction mechanism in samarium-doped ceria thin films.

A systematic study by reversible and hysteretic electrochemical strain microscopy (ESM) in samples of cerium oxide with different Sm content and in several working conditions allows disclosing the microscopic mechanism underlying the difference in electrical conduction mechanism and related surface activity, such as water adsorption and dissociation with subsequent proton liberation. We have measured the behavior of the reversible hysteresis loops by changing temperature and humidity, both in standard ESM configuration and using the first-order reversal curve method. The measurements have been performed in much smaller temperature ranges with respect to alternative measuring techniques. Complementing our study with hard X-ray photoemission spectroscopy and irreversible scanning probe measurements, we find that water incorporation is favored until the doping with Sm is too high to allow the presence of Ce3+. The influence of doping on the surface reactivity clearly emerges from all of our experimental results. We find that at lower Sm concentration, proton conduction is prevalent, featured by lower activation energy and higher electrical conductivity. Defect concentrations determine the type of the prevalent charge carrier in a doping dependent manner.

Co/Pt Multilayers on Self-Organized Hexagonal Patterned Nanodots

Anodic alumina with surface of hexagonal patterned nanodots was prepared by a two-step anodizing procedure. Scanning electron microscope and atomic force microscopy results clearly showed the formation of self-organized hexagonal patterned nanostructure. Diameters of the nanodots were controlled by choosing different anodization voltage and types of electrolyte acids. Co/Pt multilayers deposited on the nanodots with different diameters of 20, 70, and 100 nm lead to the formation of magnetic nanostructures with perpendicular anisotropy. Magnetometry and the first-order reversal curve method were used to study the magnetic properties of Co/Pt nanostructures. An out-of-plane magnetic easy axis was observed for the continuous films and the nanodots with diameters of 100 and 70 nm. The magnetic multilayers deposited on 20 nm nanodots appeared to have taken on a hard axis type behavior. The curvature of nanodot arrays induces strong modifications on the magnetic properties of the nanostructures.

Hysteretic giant magnetoimpedance effect analyzed by first-order reversal curves

We applied the first-order reversal curve method to hysteretic giant magnetoimpedance (GMI) of soft magnetic amorphous ribbons with a well-defined transversal domain structure and quasi-anhysteretic magnetization behavior. In opposition to major curve, it gives access to the distribution of local irreversible changes of the transverse permeability, which undergo a gradual transition. Results show that hysteretic GMI effect consists of three distinct regimes depending on the applied field. An interlinked hysteron/anti-hysteron model is proposed to analyze the obtained results, which allows one to follow the influence of frequency and anisotropy upon the irreversible switches probed by GMI.

Interactions and reversal-field memory in complex magnetic nanowire arrays

Interactions and magnetization reversal of Ni nanowire arrays have been investigated by the first-order reversal curve (FORC) method. Several series of samples with controlled spatial distribution were considered including simple wires of different lengths and diameters (70 and 110 nm) and complex wires with a single modulated diameter along their length. Subtle features of magnetic interactions are revealed through a quantitative analysis of the local interaction field profile distributions obtained from the FORC method. In addition, the FORC analysis indicates that the nanowire systems with a mean diameter of 70 nm appear to be organized in symmetric clusters indicative of a reversal-field memory effect.

Pressure effect investigated with first-order reversal-curve method on the spin-transition compounds [FexZn1−x(btr)2(NCS)2] · H2O (x=0.6,1)

In this work we present results obtained by the first-order reversal-curve (FORC) method for finding the effect of pressure on a spin transition. The FORC data were recorded by diffuse reflectivity measurements for the spin-transition compounds [Fe(btr)${}_{2}$(NCS)${}_{2}$]$\ifmmode\cdot\else\textperiodcentered\fi{}$H${}_{2}$O and [Fe${}_{0.6}$Zn${}_{0.4}$(btr)${}_{2}$(NCS)${}_{2}$]$\ifmmode\cdot\else\textperiodcentered\fi{}$H${}_{2}$O (btr $=$ 4,4${}^{\ensuremath{'}}$-bis-1,2,4-triazole) under constant pressure in the range 1--1600 bars. The joint distributions in coercivity-bias coordinates, obtained by the FORC method, were expressed in energy gap $\ensuremath{\Delta}$ and interaction parameter $J$ coordinates for a complete discussion of the pressure effect in terms of physical parameters, including their average values, distribution widths, and $\ensuremath{\Delta}\ensuremath{-}J$ correlation parameter. Pressure increases both $\ensuremath{\Delta}$ and $J$, as expected. Pressure has a negligible effect on the distribution widths but sizably decreases the correlation parameter value of the diluted system, an unexpected feature which suggests that the diluted system has multiple-domain behavior with pressure-dependent domain size. This deduction is supported by inspection of the samples using optical microscopy at room temperature. Simulations of the metal distribution in a two-dimensional lattice are performed in order to estimate the pressure-induced change in domain size.

Mechanically clamped PZT ceramics investigated by First-Order Reversal Curves diagram

The First Order Reversal Curves (FORC) diagrams method was developed for characterizing the switching properties of ferroelectrics. In the present paper, the FORC method was applied for hard Pb(Zr,Ti)O3 ceramics with symmetric and asymmetric clamping. An ideal high-oriented single-crystalline ferroelectric with rectangular P(E) loop would be characterised by a delta-function FORC distribution, while real ferroelectrics and mostly the polycrystalline ceramics show dispersed FORC distributions. All the investigated ceramics show FORC distributions with non-Gaussian shape, slightly elongated along the coercitive axis, meaning a high dispersion of the energy barriers separating the two bi-stable polarizations ?P. The degree of dispersion is enhanced by clamping. The maximum FORC coercivity is located at ~ (1.9-2) MV/m for all the hard ceramics. The FORC cycling experiment causes the reversal of the initial poling and result in a positive/negative bias on the FORC diagrams. According to the observed features, it results that FORC coercivity is more related to the nature of the material, while the bias field is more sensitive to the electrical and mechanical boundary conditions in which the ferroelectric ceramics evolves while switching.