First-order Reversal Curve Diagrams Research Articles

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.

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.

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 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.

Magnetic and structural properties of biogenic magnetic nanoparticles along their production process for use in magnetic hyperthermia

Iron-oxide nanoparticles synthesized by magnetotactic bacteria can be used in cancer treatment by means of magnetic hyperthermia. In order to study the structural properties of samples through the successive steps of their production from cultivated magnetotactic bacteria to coated magnetosomes, and their effect on magnetic properties, we performed a combination of (cryo-)Transmission Electron Microscopy observations and magnetic hysteresis as well as First-Order Reversal Curve diagrams at low temperature. The anisotropy of magnetic interactions was investigated by recording field-cooled FORC diagrams with a measuring field either parallel or perpendicular to the field-cooling direction. The results from the various techniques are in very good agreement. We found that magnetosomes in magnetotactic bacteria are arranged in chains and have magnetic properties typical of stable single-domain aligned particles. Extracted magnetosomes form clusters of interacting maghemite particles with some remaining chains, while purified magnetosomes are solely arranged in clusters. Finally, magnetosomes coated with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) are still organized in clusters but with less magnetostatic interactions than in purified magnetosomes, while magnetosomes coated with citric acid tend to recover a chained structure forming loops. The main features observed on the FORC diagrams are consistent with the various arrangement observed. Lastly, hyperthermia properties were measured for the two coated samples and we found that magnetosomes coated with citric acid display a higher Specific Absorption Rate and therefore hold a better potential for biomedical applications.

First-Order Reversal Curves of Sets of Bistable Magnetostrictive Microwires.

Amorphous microwires have attracted substantial attention in the past decade because of their useful technological applications. Their bistable magnetic response is determined by positive or negative magnetostriction, respectively. First-order reversal curves (FORC) are a powerful tool for analyzing the magnetization reversal processes of many-body ferromagnetic systems that are essential for a deeper understanding of those applications. After theoretical considerations about magnetostatic interactions among microwires, this work introduces a systematic experimental study and analysis of the FORC diagrams for magnetostrictive microwires exhibiting an individually bistable hysteresis loop, from a single microwire to sets of an increasing number of coupled microwires, the latter considered as an intermediate case to the standard many-body problem. We performed the study for sets of quasi-identical and different hysteretic microwires where we obtained the coercivity Hc and interaction Hu fields. In the cases with relevant magnetostatic interactions, FORC analysis supplies deeper information than standard hysteresis loops since the intrinsic fluctuations of the switching field generate a complex response. For sets of microwires with very different coercivity, the coercivity distributions of the individual microwires characterize the FORC diagram.

FORC diagram features of Co particles due to reversal by domain nucleation

First Order Reversal Curve (FORC) diagrams are a popular tool in geophysics and materials science for the characterization of magnetic particles of natural and synthetic origin. However, there is still a lot of controversy about the rigorous interpretation of the origin of certain features in a FORC diagram. In this study, we analyze FORCs computed by micromagnetic simulations of Co cubes with dimensions of 50, 100 and 150 nm and uniaxial magnetocrystalline anisotropy. For the larger cubes we observe the formation of a stable two-domain state. The nucleation of a reversed domain and its subsequent annihilation are clearly visible as separate peaks in the FORC diagram. They spread out along the coordinate axis in the FORC diagram, which is associated with the bias field HU of a Preisach hysteron. Based on our findings, we state that a FORC diagram peak spreading along the HU axis can have its origin in the step-wise magnetization reversal driven by nucleation of domains in a single particle. This means that we have identified another mechanism apart from the well-known magnetostatic interaction between a set of particles that leads to features in the FORC diagram extending along the HU-axis. Our study demonstrates that if FORCs shall be used as a quantitative tool to assess the microstructure of samples containing magnetic material, more information from other methods will be required to identify the correct physical mechanism by which a certain “fingerprint” in a FORC diagram is produced.

In-plane magnetic anisotropy and magnetization reversal in phase-separated (La0.5Pr0.5)0.625Ca0.375MnO3 thin films

The dynamics and interaction of different electronic phases near the metal-to-insulator transition of the phase-separated ${({\mathrm{La}}_{0.5}{\mathrm{Pr}}_{0.5})}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$ (LPCMO) thin film grown on NGO substrate was studied using the first-order reversal curves (FORC) diagram method for electric transport measurements. The in-plane angle-dependent remanence and coercivity field in the region of the ferromagnet metallic phase was measured using the macroscopic magnetization technique. These measurements suggest an in-plane uniaxial magnetic anisotropy for the film with a uniaxial anisotropic constant (Ku) of $\ensuremath{\sim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}^{3}$ at 20 K. The angle dependence of the coercivity is best described by 1/cos\ensuremath{\theta} dependence indicating that the magnetization reversal occurs mainly through the depinning of the domain wall, a signature of nucleation and propagation mechanism. The correlation of FORC measurements, resistance relaxation, and macroscopic magnetic measurements indicate a fast reversal of electronic and magnetic phases towards the denser phase region and strong interaction of different phases for the LPCMO system.

Crystalline texture of cobalt nanowire arrays probed by the switching field distribution and FORC diagrams

The crystalline texture of arrays of low diameter Co nanowires (NWs) synthesized by electrodeposition using electrolytes with different acidities (pH in the range 2.0–6.6) was studied by the switching field distribution (SFD) and first order reversal curve (FORC) diagrams. Particularly, the SFD determined as the derivative of the descending part of the major hysteresis loop has proven to be a reliable and powerful method for the identification of different crystalline textures in the NWs and the quantification of their corresponding texture percentages. The presence of the face centered cubic-like texture at low pH values and hexagonal close packed textures with the c-axis perpendicular and parallel to the NWs axis at higher pH values have been identified by performing multiple Gaussian fits to the SFD by virtue of their different magnetic behavior observed during reversal of the magnetization. The field position and size of each curve in the multiple Gaussian fit provide information about the corresponding magnetic contribution and volumetric texture percentage of each crystalline texture in the NWs, respectively. The analysis of the SFD has been complemented and validated with FORC diagram measurements, showing that the width of the coercive field distribution is in good agreement with the width of the SFD. Also, it has been found that the different branches observed in the FORC diagrams along the interaction axis provide further insight on the interaction between magnetocrystalline fields. This work provides a novel methodology for the use of magnetometry as a reliable technique for the study of the interplay between the microstructure and magnetic behavior of arrays of NWs.

The effects of magnetic interactions on first-order reversal curve (FORC) and the origin of the negative region for Nd-Fe-B based magnets

In this study, we investigated the effects of magnetic interactions within Nd-Fe-B magnets on first-order reversal curve (FORC) and the origin of negative regions in FORC diagram. Magnetostatic interaction causes the FORC diagram pattern to expand along the Hu axis, especially in the direction of positive half-axis of Hu. And the negative regions will tend to be embedded in the positive regions when magnetostatic interaction is not negligible. The origin of the negative peaks is the difference of the onset of magnetization and the subsequent magnetization process of adjacent FORCs caused by the different and complex stray fields within magnets at the beginning of the FORCs. Besides, the origin of the positive peaks is analyzed in detail as well.

Microstructure, ion adsorption and magnetic behavior of mesoporous γ-Fe2O3 ferrite nanoparticles.

Magnetic nanoparticles with capacity for surface functionalisation have potential applications in water purification and biomedicine. Here, a simple co-precipitation technique was used to synthesize mesoporous ferrite nanoparticles in the presence of cetyltrimethylammonium bromide (CTAB) micellular surfactant. The as-synthesized ferrite nanoparticles were calcined at 250 °C for 5, 10, 15, and 24 h to remove the surfactant and create a mesoporous structure. The prepared samples were characterised using a wide range of analytical techniques. Microscopical images showed that all uncalcined particles have cauliflower shape without porosity. However, after calcination, surface and deep pores were created on the synthesized nanoparticles. In addition, transmission electron microscope (TEM) images of calcined nanoparticles revealed a wormhole-like structure, which is typical for the mesoporous architectures. Based on X-ray diffraction (XRD), the uncalcined and calcined samples exhibit pure Fe3O4 (magnetite) and γ-Fe2O3 (maghemite) ferrite phases, respectively. The γ-Fe2O3 nanoparticles demonstrated a high Brunauer-Emmett-Teller (BET) surface area with pore diameters smaller than 10 nm and a type IV isotherm similar to the mesopores. Hysteresis loops measured by vibrating sample magnetometry (VSM) showed the superparamagnetic nature for mesoporous γ-Fe2O3 nanoparticles. The first-order reversal curve (FORC) diagram revealed the formation of a mesoporous structure in calcined materials which reduces coercive distribution (Hc) and magnetostatic interaction (Hu) once compared to non-calcined samples. Mesoporous γ-Fe2O3 nanoparticles were successfully employed as an adsorbent for the removal of heavy metal ions of Pb(ii) from an aqueous solution. The highest lead ion adsorption was observed in mesoporous γ-Fe2O3 nanoparticles prepared with 3% CTAB.

Element-specific first order reversal curves measured by magnetic transmission x-ray microscopy

The first-order reversal curve (FORC) method is a macroscopic measurement technique that can be used to extract quantitative and microscopic properties of hysteretic systems. Using magnetic transmission x-ray microscopy (MTXM), local element-specific FORC measurements are performed on a 20 nm thick film of CoTb. The FORCs measured with microscopy reveal a step-by-step domain evolution under the magnetic field cycling protocol and provide a direct visualization of the mechanistic interpretation of FORC diagrams. They are compared with magnetometry FORCs and show good quantitative agreement. Furthermore, the high spatial resolution and element-specific sensitivity of MTXM provide new capabilities to measure FORCs in small regions or specific phases within multicomponent systems, including buried layers in heterostructures. The ability to perform FORCs on very small features is demonstrated with the MTXM-FORC measurement of a rectangular microstructure with vortex-like Landau structures. This work demonstrates the confluence of two uniquely powerful techniques to achieve quantitative insight into nanoscale magnetic behavior.

Magnetic Structure of Wiegand Wire Analyzed by First-Order Reversal Curves.

Various coercive force field components in Wiegand wire exhibit a significant magnetization reversal under an applied magnetic field. A fast magnetization reversal is accompanied by a large Barkhausen jump, which induces a pulse voltage in a pickup coil wound around the Wiegand wire which serves as a power source for the devices or sensors. This study aims to elucidate the magnetization reversal in the Wiegand wire by using a first-order reversal curve (FORC) diagram method. The magnetic structure of the Wiegand wire typically comprises three layers: a soft layer, middle layer, and hard layer. In this study, we analyze the coercive and interactive force fields between the adjacent layers. The results demonstrate a high coercivity of the center core and a lower coercivity of the outer layer of the wire.

Interwire and Intrawire Magnetostatic Interactions in Fe-Au Barcode Nanowires with Alternating Ferromagnetically Strong and Weak Segments.

Metallic barcode nanowires (BNWs) composed of repeating heterogeneous segments fabricated by template-assisted electrodeposition can offer extended functionality in magnetic, electrical, mechanical, and biomedical applications. The authors consider such nanostructures as a 3D system of magnetically interacting elements with magnetic behavior strongly affected by complex magnetostatic interactions. This study discusses the influence of geometrical parameters of segments on the character of their interactions and the overall magnetic behavior of the array of BNWs having alternating magnetization, because the Fe and Au segments are made of Fe-Au alloys with high and low magnetizations. By controlling the applied current densities and the elapsed time in the electrodeposition, the dimension of the Fe-Au BNWs can be regulated. This study reveals that the influence of the length of magnetically weak Au segments on the interaction field between nanowires is different for samples with magnetically strong 100 and 200 nm long Fe segments using the first-order reversal curve (FORC) diagram method. With the help of micromagnetic simulations, three types of magnetostatic interactions in the BNW arrays are discovered and analy. This study demonstrates that the dominating type of interaction depends on the geometric parameters of the Fe and Au segments and the interwire and intrawire distances.

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

Wiegand wires exhibit a unique fast magnetization reversal feature in the soft layer that is accompanied by a large Barkhausen jump, which is also known as the Wiegand effect. However, the magnetic structure and interaction in Wiegand wires cannot be evaluated by conventional magnetization hysteresis curves. We analyzed the magnetic properties of Wiegand wires at various lengths by measuring the first-order reversal curves (FORCs) and by evaluating the FORC diagram from a series of FORCs. In particular, we used a FeCoV Wiegand wire with a magnetic soft outer layer, an intermediate layer, and a hard core. The magnetization of the various layers in the wire could be identified from the FORC diagrams. Furthermore, based on the interaction between multiple layers, the positive and negative polarity of the FORC distribution was clarified.

Large-Area Nanopillar Arrays by Glancing Angle Deposition with Tailored Magnetic Properties.

Ferromagnetic films down to thicknesses of tens of nanometers and composed by polycrystalline Fe and Fe2O3 nanopillars are grown in large areas by glancing angle deposition with magnetron sputtering (MS-GLAD). The morphological features of these films strongly depend on the growth conditions. Vertical or tilted nanopillars have been fabricated depending on whether the substrate is kept rotating azimuthally during deposition or not, respectively. The magnetic properties of these nanopillars films, such as hysteresis loops squareness, adjustable switching fields, magnetic anisotropy and coercivity, can be tuned with the specific morphology. In particular, the growth performed through a collimator mask mounted onto a not rotating azimuthally substrate produces almost isolated well-defined tilted nanopillars that exhibit a magnetic hardening. The first-order reversal curves diagrams and micromagnetic simulations revealed that a growth-induced uniaxial anisotropy, associated with an anisotropic surface morphology produced by the glancing angle deposition in the direction perpendicular to the atomic flux, plays an important role in the observed magnetic signatures. These results demonstrate the potential of the MS-GLAD method to fabricate nanostructured films in large area with tailored structural and magnetic properties for technological applications.

Biomagnetic Characterization of Air Pollution Particulates in Lahore, Pakistan

AbstractWe report the characterization of anthropogenic magnetic particulate matter (MPM) collected on leaves from roadside Callistemon (bottlebrush) trees from Lahore, Pakistan, and on known sources of traffic‐related particulates to assess the potential of first‐order reversal curve (FORC) diagrams to discriminate between different sources of anthropogenic magnetic particles. Magnetic measurements on leaves indicate the presence of surface‐oxidized magnetite spanning the superparamagnetic (<30 nm) to single domain (∼30–70 nm) to vortex size range (∼70–700 nm). Fe‐bearing particles are present both as discrete particles on the surface of larger mineral dust or carbonaceous particles and embedded within them, such that their aerodynamic sizes may be decoupled from their magnetic grain sizes. FORC diagrams of brake‐pad residue specimens show a distinct combination of narrow central ridge, extending from 0 to 200 mT, and a low‐coercivity, vertically spread signal, attributed to vortex and multi‐vortex behavior of metallic Fe. This is in agreement with scanning electron microscopy results that show the presence of metallic as well as oxidized Fe. Exhaust‐pipe residue samples display a more conventional “magnetite‐like” signal comprising a lower coercivity central ridge (0–80 mT) and a tri‐lobate signal attributed to vortex state and/or magnetostatic interactions. The FORC signatures of leaf samples combine aspects of both exhaust residue and brake‐pad endmembers, suggesting that FORC fingerprints have the potential to identify and quantify the relative contributions from exhaust and non‐exhaust (brake‐wear) emissions. Such measurements may provide a cost‐effective way to monitor the changing contribution; of future particulate emissions as the vehicle fleet is electrified over the coming years.

FORC analysis of magnetically soft microparticles embedded in a polymeric elastic environment

First-order reversal curve (FORC) analysis allows one to investigate composite magnetic materials by decomposing the magnetic response of a whole sample into individual responses of the elementary objects comprising the sample. In this work, we apply this technique to analysing silicone elastomer composites reinforced with ferromagnetic microparticles possessing low intrinsic coercivity. Even though the material of such particles does not demonstrate significant magnetic hysteresis, the soft matrix of the elastomers allows for the translational mobility of the particles and enables their magnetomechanical hysteresis which renders into a wasp-waisted major magnetization loop of the whole sample. It is demonstrated that the FORC diagrams of the composites contain characteristic wing features arising from the collective hysteretic magnetization of the magnetically soft (MS) particles. The influence of the matrix elasticity and particle concentration on the shape of the wing feature is investigated, and an approach to interpreting experimental FORC diagrams of the MS magnetoactive elastomers is proposed. The experimental data are in qualitative agreement with the results of the simulation of the particle magnetization process obtained using a model comprised of two MS particles embedded in an elastic environment.