First-order Reversal Curve Research Articles

Effects of Mn doping on the conduction mechanism and dielectric nonlinearity of Na0.5Bi0.5TiO3 thin film

In this work, the conduction mechanism and dielectric nonlinearity of undoped and Mn-doped Na0.5Bi0.5TiO3 (NBT) films were investigated. The potential conduction mechanism in relatively low electric fields should be dominated by hopping conduction rather than typical Ohmic conduction. In the high electric field region, the conduction mechanism is dominated by Poole–Frenkel emission and Schottky emission. The enhancement of electrical insulation of NBT films after Mn doping was shown to result from a decrease in oxygen vacancies and elevation of the conduction energy barrier. Furthermore, significant improvements in the nonlinearity of both the dielectric constant and polarization of Mn-doped NBT films were observed, as indicated by the results of Rayleigh fitting and first-order reversal curve distributions. Such enhancements were attributed to the reduction in domain wall pinning, decreased interference from electrostatic potential and improved leakage characteristics.

Contributions and limitations of environmental magnetism to characterize traffic-related particulate matter sources

SUMMARY The chronic exposure to particulate matter (PM) pollution causes societal and environmental issues, in particular in urban areas where most citizen are regularly exposed to vehicular traffic. Since almost two decades, environmental magnetic monitoring has demonstrated its efficiency to successfully map relative concentrations of airborne particle deposition on accumulative surfaces. A better understanding of the magnetic results requires discriminating the main traffic-related sources of the observed signal on particle collectors. To meet this objective, we investigated a sample set of exhaust and non-exhaust sources with respect to their magnetic fingerprints inferred from hysteresis loops, first-order reversal curve (FORC) diagrams, temperature dependency of initial susceptibility and unmixing of isothermal remanent magnetization acquisition curves. The source sample set comprises 14 diesel and gasoline exhaust smoke residues, 12 abrasive-fatigue wear test pieces from worn brake-pads, brake powders, worn tire-tread and three resuspension products: asphalt concrete, street dust and Saharan mineral dust deposited by precipitation after long-range eolian transport. Magnetic properties of the source samples were compared to those from various accumulative surfaces exposed to urban traffic (passive collectors, filters of facemasks for cycling, plant leaves and tree barks). We found some fingerprints of exhaust pipes and brake wear products on these collectors. The findings highlight the relevance of environmental magnetism tools to characterize different traffic-related source signals in accumulative surfaces in urban environment.

The physical origin of inhomogeneous field within HfO2-based ferroelectric capacitor

In this work, the origins of the inhomogeneous field within the HfO2-based ferroelectric (FE) capacitor are investigated. We propose a model to simulate the relationship between the reversed polarization and the applied pulses with different amplitudes and durations. The electric field distribution is considered to be influenced by the ferroelectric layer thickness (tFE) and the built-in field (Eb). Then, the distribution parameters of both two physical factors and the Merz law, which define the switching dynamics, could be obtained by fitting the experimental results. Comparing with the results of high-resolution transmission electron microscope and first-order reversal curve measurements, it can be reasonably concluded that the physical origin of the inhomogeneous field in HfO2-based ferroelectrics is the random distribution of tFE and Eb. This work improves the understanding of the switching dynamics by providing the origins of the inhomogeneous field in an FE film.

Discovery of late Quaternary giant magnetofossils in the Bay of Bengal

Unusually large and enigmatic giant magnetofossils are well-documented in sediments deposited during and surrounding climatic events such as the Paleocene-Eocene Thermal Maximum (~56 Ma) and Middle Eocene Climatic Optimum (~40 Ma). However, the absence of giant magnetofossil modern analogues raises intriguing questions about their origin and formation mechanism. In this study, we report the discovery of giant magnetofossils within late Quaternary sediments retrieved from the Bay of Bengal (BoB), the youngest giant magnetofossils yet reported. First-order reversal curve diagrams of BoB sediments display a central ridge feature, a characteristic magnetic signature of non-interacting single domain magnetofossils. Scanning electron microscopy examinations reveal giant magnetofossils with needle, spindle, bullet, and spearhead shapes. We use high-resolution transmission electron microscopy, with electron diffraction and energy dispersive spectrometry, to confirm their distinctive morphologies and magnetite crystal structure. Our environmental magnetic and geochemical data suggest that an influx of fluvially derived reactive iron and organic carbon, combined with persistent suboxic conditions, supported the proliferation of giant magnetofossil-producing organisms. The discovery of a modern analogue to ancient giant magnetofossils expands our understanding of their temporal distribution within the geological record and is a promising step toward elucidating the nature of the organisms responsible for their formation.

Unusual anomalous Hall effect in SrRuO3 films with linear out-of-plane Ru vacancies gradient

The manipulation of magnetic transport properties has been one of the central problems in spintronics. However, the modulation of Hall signals in thin films has stringent requirements on their thickness and means of growth. Here, a series of inhomogeneous SrRuO3 thin films with different paths of linear out-of-plane Ru vacancies gradient was designed to generate an unusual anomalous Hall effect (UAHE) under broad growth conditions. Combining x-ray diffraction and magnetic data, it was concluded that the appearance of UAHE was not a simple superposition of AHE caused by multiple magnetic phases. The interaction between these magnetic phases in the linear-vacancies-gradient SrRuO3 films was analyzed by the first-order reversal curve (FORC) method, and it was found that the change trend of FORC was the same as that of UAHE. Such out-of-plane linear-vacancies-gradient thin film provides a way to regulate the different phases by introducing the cation vacancies distribution in an orderly way to control their magnetic and transport properties in oxide films. Furthermore, a distinctive perspective on the origin of UAHE was obtained by combining FORC with UAHE.

Restoration and Transformation: The Response of Shocked and Oxidized Magnetite to Temperature

AbstractLarge impact craters on Earth are associated with prominent magnetic anomalies, residing in magnetite of the shocked target rocks and impactites. Shock experiments on magnetite suggest that up to 90% of magnetic susceptibility is lost at pressures >5 GPa, but can be partially restored by post‐shock thermal annealing. The magnetic property changes are caused by shock induced grain size reduction and fragmentation, as well as domain wall‐pinning at crystal lattice defects. A recent study of granitoids from the peak‐ring of the Chicxulub crater found that annealing may occur naturally, but can also be overprinted by high‐temperature hematite‐to‐magnetite transformation in non‐oxidizing environments. In this study, we isolate the effect of defect annealing and hematite‐to‐magnetite transformation using the evolution of hysteresis, isothermal remanent magnetization components and first order reversal curve (FORC) diagrams at different high‐temperature steps. We used a laboratory‐shocked magnetite‐quartz ore, a non‐shocked naturally oxidized granite, and a naturally shocked and oxidized granite. Our findings suggest that annealing of shock‐induced lattice defects partially restores some pre‐shock magnetic behavior and causes an apparent average bulk‐sample domain state increase. Hematite‐to‐magnetite transformation creates new fine‐grained magnetite that strongly overprints the original signal, and decreases the average bulk‐sample domain state. Where annealing and hematite‐to‐magnetite transformation both occur, the new magnetite masks the annealing‐induced property restoration and apparent domain state modification in the shocked magnetite. As magnetite oxidation is a ubiquitous process in surface rocks, these findings are fundamental to understand hematite‐to‐magnetite transformation as a potential overprint mechanism, and could have broad implications for paleomagnetic interpretations.

Combination of hysteresis models for accuracy improvement and stabilised electromagnetic calculations

An interpolation strategy based on pre-evaluated integrals of the first-order reversal curves is presented. The proposed approach allows the seamless integration of different hysteresis models into a single calculation in a way that the most appropriate curve is picked up for particular subdomains of the Preisach plane. It can be shown that this approach can contribute to the stabilisation of numerical field calculations.

Coercivity mechanism of La–Nd–Fe–B films with Y spacer layer

The effect of the Y spacer layer on the phase composition, coercivity, and magnetization reversal processes of La–Nd–Fe–B films has been investigated. The addition of a 10 nm Y spacer layer increases the coercivity of the film to 1.36 T at 300 K and remains 0.938 T at 380 K. As the thickness of the Y spacer layer increases, Y participates in the formation of the main phase in the film, and further regulates the formation of La–B phases. The results of the first-order reversal curve (FORC) and micromagnetic fitting show that the coercivity of all the films is dominated by nucleation mechanism. The c-axis preferred orientation, good magnetic microstructure parameters and the largest dipole interaction enhance the coercivity. Therefore, the introduction of the Y spacer layer can be an effective way to improve the coercivity of La–Nd–Fe–B film over a wide temperature range of 150 K–380 K.

HfO2-ZrO2 Ferroelectric Capacitors with Superlattice Structure: Improving Fatigue Stability, Fatigue Recovery, and Switching Speed.

HfO2-ZrO2 ferroelectric films have recently gained considerable attention from integrated circuit researchers due to their excellent ferroelectric properties over a wide doping range and low deposition temperature. In this work, different HfO2-ZrO2 superlattice (SL) FE films with varying periodicity of HfO2 (5 cycles)-ZrO2 (5 cycles) (SL5), HfO2 (10 cycles)-ZrO2 (10 cycles) (SL10), and HfO2 (15 cycles)-ZrO2 (15 cycles) (SL15) were studied systematically. The HfZrOx (HZO) alloy was used as a comparison device. The SL5 film demonstrated improved ferroelectric properties compared to the HZO film, with the 2 times remnant polarization (2Pr) values increasing from 41.4 to 48.6 μC/cm2 at an applied voltage of 3 V/10 kHz. Furthermore, the first-order reversal curve diagrams of different SL and HZO capacitors at different states (initial, wake-up, fatigue, and recovery) were measured. The SL capacitors were found to effectively suppress the diffusion of defects during P-V cycling, resulting in improved fatigue stability characteristics and fatigue recovery capability compared to the HZO capacitor. Moreover, an improved switching speed of the SL films compared to the HZO capacitor was concluded based on the inhomogeneous field mechanism (IFM) model. These results indicate that the SL structure has a high potential in future high-speed ferroelectric memory applications with excellent stability and recovery capability.

Enhanced soft-to-hard magnetic switching ratio in grain-oriented Fe–Si cores induced by helical anisotropy

The non-segmented shifted design of magnetic cores made of grain-oriented electrical steels, which induces the helical anisotropy, has been highly effective in reducing magnetic losses and minimizing acoustic noise in rotating machines. In order to address the challenges associated with precise theoretical modeling of complex underlying magnetization process, we have introduced angle-dependent first-order reversal curve diagrams. These diagrams offer significant insights into the microscopic properties of magnetization switching. By analyzing the distribution of coercive and interaction fields, we can identify distinct features that correspond to different domain wall processes and local coercivities, highlighting the magnetic behavior's heterogeneity. Through experimental measurements and theoretical analysis, we have gained quantitative understanding of the competing contributions from 90° and 180° domain wall processes in shifted structures. At shifting angles near the location of the hard magnetization axis, a notable transition in the magnetization process is observed by promoting the activation of the softer 180° domain wall processes. Among the different shifting angles tested, the structure with a shifting angle of 90° exhibits the highest ratio of soft-to-hard magnetization switching.

Reconstruction of thermomagnetic and phase transformation loops in magnetostructural transitions using selective integration of temperature first-order reversal curves (TFORC) distributions

The temperature variant of the first-order reversal curves (TFORC) analysis technique is emerging as a useful tool for the study of the thermal hysteresis in magnetocaloric alloys undergoing first-order phase transitions. This work demonstrates the capabilities of the TFORC technique for reconstructing and deconvoluting the reversible and irreversible components of thermomagnetic transitions through the integration of the TFORC distributions. Through numerical simulations, the influence of applying smoothing protocols, the presence of noise in the magnetization curves or the distance between the hysteretic first-order phase transition and the Curie transitions of the phases have been tested. By employing the appropriate integration protocol of TFORC distributions, the transformed phase fraction can be separated from the total thermomagnetic behavior. The results obtained from the numeric simulations have been confirmed by applying the proposed analysis methods to the experimental TFORC results of a Ni-Mn-In Heusler alloy sample undergoing magnetic first-order phase transition. In this way, the TFORC technique can be stablished as a valuable characterization method for magnetostructural phase transition materials.

Defects engineered ferroelectricity and electrocaloric effect in Pb0.7Ba0.3ZrO3 ceramics

Point defects play a versatile role in modulating ferroelectricity and piezoelectricity, however, the decisive role of point-defect concentration/species in controlling macroscopic performance remains unknown. In this work, defects are implanted by reduced atmosphere annealing and/or Mn doping in Pb0.7Ba0.3ZrO3 ceramics. i) defects induce lattice distortion, internal lattice strain and accordingly, phase structure is changed (Williamson-Hall analysis and Rietveld refinement); ii) ferroelectricity is enhanced for 0 MN and 1 MA sample with contribution of defect polarization (first-order reversal curves). iii) Joule heat is depressed as an enhanced resistivity by carrier annihilation/forming defect complex; iv) ECE behaves distinctly among 0 MN, 1 MA and 1 MH, respectively. 0 MN sample exhibits a ΔTmax of 0.39 K and 1 MA possesses a ΔTmax of 0.34 K. Interestingly, a broad temperature span with a low instability of ∼20 % within 288 K–423 K is obtained in 1 MH sample. This work not only provides a guideline for defects enhancing ferroelectricity and ECE, but also clarifies the reduction-resistant properties of (Pb, Ba)ZrO3 system that are suitable for constructing base-metal multilayer ceramic capacitors in solid-state cooling devices.

Angular first-order reversal curve analysis of FeNi/Cu multilayered nanowire arrays with different diameters

The main goal of the emerging field of spintronics is the shrinkage of materials and devices while improving their magnetic performance for a variety of applications, especially three-dimensional information storage. This stipulates the understanding of fundamental magnetic mechanisms such as magnetization reversal and switching events in multilayer systems with tunable size. Here, a porous anodic alumina membrane-assisted electrochemical deposition method is employed to fabricate FeNi/Cu multilayered nanowire arrays (MNWAs) with diameters in the range of D = 35–80 nm. Angular magnetic properties of these MNWAs are investigated via hysteresis loop and first-order reversal curve (FORC) measurements for angle fields of 0° ≤ θ ≤ 90°. While the former indicates the existence of different contributions of vortex domain wall propagation for smaller (D ≤50 nm) and larger (D >50 nm) diameters, the latter reveals the occurrence of single vortex states, depending on θ and D. Moreover, at θ = 0°, a transition from single domain to multidomain-like behavior appears to occur with increasing D from 35 to 80 nm based on FORC diagrams, significantly influencing magnetization reversibility of magnetic FeNi segments with relatively high aspect ratios (>5). The variation of magnetostatic interactions with respect to θ is discussed and compared at each diameter as an effective factor in determining angular magnetic properties. Also, the axial variation behavior of coercivity as a function of D is correlated with changes in the reversible percentage, shedding light on the expectations from the vortex domain wall propagation.

Magnetization processes in two-dimensional arrays of iron nanowires

Arrays of iron nanowires (NWs) obtained by template-assisted electrodeposition constitute a promising composite material characterized by a combination of high magnetization in the filler and perpendicular magnetic anisotropy. The properties of these composites arise from the interplay between the behavior of individual NWs and their magnetostatic interactions. In this study, we investigated NW arrays with identical wire diameters but varying spatial arrangements. Major hysteresis loops were studied under various field directions relative to the NW axis. Key parameters such as the slope of the magnetization curve, saturation magnetization, and coercive force were quantified. Additionally, FORC (First Order Reversal Curve) measurements were conducted with the field oriented longitudinally with respect to the NW, offering insights into the inhomogeneity of the demagnetizing field influenced by the NW array's configuration. In the sample with the highest NW density, we observed isotropic behavior of the effective demagnetizing field, and we proposed an explanation for this phenomenon using the effective media approach. Micromagnetic simulations revealed that the magnetic behavior of individual NWs with a 100 nm diameter can be described as an interchange between volumes characterized by vortex and uniform magnetization patterns. Calculations of the demagnetizing field using the effective medium model demonstrated excellent agreement with experimental data across arrays featuring different NW densities. Remarkably, the quantitative consistency of coercive field values obtained from micromagnetic simulations and experimental measurements in the range of angles from 0° to 45° for the studied samples underscores the structural homogeneity of the obtained NWs.

Magnetization process of cubic Fe3O4 submicron particles: First-order reversal curves and neutron diffraction studies

We have studied magnetization process of 260 nm sized cubic Fe3O4 particles below and above the Verwey transition temperature Tv∼ 110 K, by measurements of magnetic first-order reversal curves (FORCs) and high-resolution power neutron diffraction. The FORC diagram exhibits two distinct FORC distribution peaks below Tv, which shift towards the origin, merge into a single peak on heating, whereas only a single FORC peak appears above Tv. Neutron diffraction measurements under magnetic fields revealed a minimum of the magnetic intensity at a magnetic field of ∼−300 Oe, being close to the reversal field where the FORC peak is located. These results were interpreted as due to a reorientation and reversal of a spin vortex core, which accompany a large magnetic irreversibility.

Fabrication and magnetic properties of pulse electrodeposited FeSn nanowire arrays

When it comes to fabricating efficient nanomaterials for magnetic recording media and spintronic devices, Fe-based nanowires (NWs) containing nonmagnetic elements can represent themselves as one of ideal candidates. Here, a pulse electrodeposition method in porous anodic alumina membranes is employed to fabricate Fe100-xSnx (2 ≤ x ≤ 68) NW arrays with a diameter of about 35 nm. During the NW fabrication, Sn electrolyte concentration (CSn) and off-time (Toff) between pulses change in the range from 0.0025 to 0.02 M and 0–75 ms, respectively. As a general trend, magnetic properties including coercivity and squareness values decrease with increasing the Sn content. Meanwhile, first-order reversal curve diagrams show single domain and pseudo-single domain states of the FeSn NWs, depending on the Sn content in the structure dominated by Fe or FeSn alloy crystal phase. Magnetostatic interactions and coercive field distributions are also observed to significantly change by varying CSn and Toff, providing magnetically tunable FeSn NW arrays induced by the nonmagnetic element addition.

Effect of PEG nanoparticle surface coating on the magnetic and structural properties of CoFe2O4/PVDF composites

This research focuses on the impact of polyethylene glycol (PEG) coating on the magnetic and structural properties of composites consisting of an electroactive polyvinylidene fluoride matrix and CoFe2O4 nanoparticles. The intrinsic piezoelectric and magnetic properties of the constituents fundamentally determine the properties of composites, but the microstructure and particle packing of the composite are equally crucial for enhancing magnetoelectric coupling. Our findings reveal that PEG coating promote a more uniform spatial distribution of particles agglomerates within the polymer matrix, which achieved by strengthening of the interfacial coupling and reducing of the filler density during the solvent casting process. Together with reduced agglomerates size from an average of 28 ± 3 μm to 17 ± 1 μm uniform spatial distribution leads to decrease of magnetic dipolar interactions from ∼ 900 Oe to ∼ 800 Oe - tendence confirmed from the first-order reversal curve (FORC) analysis. Additionally, the root mean square roughness of the composite surface decreases from 185 nm to 74 nm, indirectly confirming increased sample uniformity. Local electrical properties, measured through Piezoresponse Force Microscopy (PFM), show a substantial enhance of the local piezoelectric response by ∼ 40 %. Results can be used for the enhancing of magnetoelectric effect in biocompatible materials, utilized at low frequency.

Exploring the magnetic, optical and dielectric properties of Cr- doped hematite (α-Fe(2−x)CrxO3): A comprehensive study

Magnetic, dielectric, and optical properties of Cr-doped hematite (α-Fe2O3) i.e. α-Fe(2−x)CrxO3 (x = 0.00, 0.03, 0.06, 0.10, 0.20) have been investigated in the present work. The nanospheres with excellent mono dispersity have been synthesized successfully by facile hydrothermal treatment at 160 °C. Rhombohedral structure with space group R3C for all the nanostructures have been revealed from X-ray diffraction patterns and the spectrum is compatible with the Raman active phonon modes. Raman spectra in response to the effects of doping indicated microscopic structural disarray. The α-Fe(2−x)CrxO3 nanostructures have exhibited enhanced ferromagnetic characteristics comparable to undoped hematite(α-Fe2O3). The potential of coercivity in the α-Fe(2−x)CrxO3 system has not been fully excavated, which restricts its practical application to a certain extent. With the increase of Cr3+ doping level in α-Fe2O3 and decrease in the particle size. we have successfully attained the highest coercivity values as it increases from 1481.98–5273.75 Oe, with good signatures of remnant magnetization indicating the capability of Cr3+ doping in boosting the magnetic properties of α-Fe2O3 for magnetic applications such as magnet tapes, magnetic data storage devices, and permanent magnets. The domain state of magnetization and interaction fields were comprehensively investigated by first-order reversal curve analysis (FORCs). With Cr doped α-Fe2O3, we observed an enhanced dielectric constant with the highest dielectric constant of 25.10 in Fe1.85Cr0.15O3. and extremely low dielectric losses. Due to their incredibly low dielectric losses, these nanostructures are ideally suited for implementation in high-frequency microwave device applications. The absorption edges have been reinforced to higher wavelengths, in addition to enhanced visible absorption in the visible region and reduced optical bandgaps. The lowest bandgap 1.66 eV is observed in α-Fe1.85Cr0.15O3 due to additional levels introduced between valence and conduction bands. This study suggests that the magnetic, dielectric, and optical properties of hydrothermally prepared α-Fe2O3 systems can be largely tailored with Cr content making them suitable candidates for spintronics, optoelectronic and magneto-optical devices.

Environmental magnetic characterization for the Pialli Level and the Cretaceous Oceanic Red Bed 7 (late Albian, Poggio le Guaine core, central Italy)

The mid-Cretaceous is known as the most extreme greenhouse period in the last 150 Myr and was punctuated by repeated environmental perturbations. The mid-Cretaceous was also characterized by the emplacement of major Large Igneous Provinces and the deposition of organic-rich layers known as Oceanic Anoxic Events. Here, we present a high-resolution environmental magnetic and stable isotopic records of the western Tethyan pelagic interval in the Poggio le Guaine (PLG, Italy) core, deposited during the late Albian. Environmental magnetic data are here applied to detect redox and paleoproductivity variations across the OAE 1d and CORB 7 events. Combing the magnetic data and geochemical data from carbon (δ13C) and oxygen (δ18O) isotopic records, we document changes in the paleoenvironmental conditions across the Pialli Level and CORB 7 events in the Tethyan realm. The magnetic properties of the 10-m-thick pelagic marine sediments of the PLG core record the onset between upper part of Cretaceous Oceanic Red Bed 7 (CORB 7) and the Pialli Level that is a part of the Oceanic Anoxic Event (OAE) 1d. An increase in the magnetic mineral concentrations with hematite and goethite as the main magnetic carrier characterizes the upper CORB 7 sediments. Variations in “hard” isothermal remanent magnetization and the S-ratio during the upper CORB 7 are interpreted as changes in aeolian dust input into the Umbria-Marche Basin. During the interval between the upper part of CORB 7 and OAE 1d (Pialli Level), the magnetic mineral concentration decreases, and the magnetic mineralogy changes from hematite to magnetite, suggesting a change in the oceanic system. This change might be associated to an increase in orbital forcing capable of modulating the monsoon activity at the onset of the Pialli Level. First-order reversal curves for all samples from the PLG core are similar and indicate a dominance of detrital magnetite. The absence of magnetically non-interacting single domain biogenic particles suggests that an increase in primary productivity was not significant or variation of the anoxic-oxic boundary could have also occurred. Finally, our records show cyclic alterations that reflect changes in the terrigenous input that was triggered by a period of enhanced orbital forcing paced by monsoonal systems.

Fine-tuning magnetic and hyperthermia properties of magnetite (Fe3O4) nanoparticles by using ammonia as a reducing agent

The tunable control of heat produced by magnetic nanoparticles (NPs) when placed in an alternating magnetic field can prevent undesirable concurrent heating of healthy tissues for magnetic hyperthermia. Here, magnetite (Fe3O4) NPs are synthesized by a co-precipitation method with different concentrations of ammonia (CA = 7–30 ml) as a reducing agent. By changing CA, increasing and decreasing trends of structural, morphological and magnetic properties are observed. Superparamagnetic (SPM) behavior of Fe3O4 NPs is studied by first-order reversal curve analysis, indicating fine-tuned SPM percentages. By dispersing these NPs in water medium, specific loss power (SLP) is investigated. The variation of SLP as a function of CA is found to follow that of SPM percentage, reaching a maximum value of 93 W/g for a ferrofluid containing Fe3O4 NPs synthesized with CA = 23 ml. In this case, SPM percentage is maximized to about 60 %, facilitating the heat production by Néel and Brownian mechanisms.