Magnetic History Research Articles

Polyacrylamide Ferrogels with Magnetite or Strontium Hexaferrite: Next Step in the Development of Soft Biomimetic Matter for Biosensor Applications.

Magnetic biosensors are an important part of biomedical applications of magnetic materials. As the living tissue is basically a “soft matter.” this study addresses the development of ferrogels (FG) with micron sized magnetic particles of magnetite and strontium hexaferrite mimicking the living tissue. The basic composition of the FG comprised the polymeric network of polyacrylamide, synthesized by free radical polymerization of monomeric acrylamide (AAm) in water solution at three levels of concentration (1.1 M, 0.85 M and 0.58 M) to provide the FG with varying elasticity. To improve FG biocompatibility and to prevent the precipitation of the particles, polysaccharide thickeners—guar gum or xanthan gum were used. The content of magnetic particles in FG varied up to 5.2 wt % depending on the FG composition. The mechanical properties of FG and their deformation in a uniform magnetic field were comparatively analyzed. FG filled with strontium hexaferrite particles have larger Young’s modulus value than FG filled with magnetite particles, most likely due to the specific features of the adhesion of the network’s polymeric subchains on the surface of the particles. FG networks with xanthan are stronger and have higher modulus than the FG with guar. FG based on magnetite, contract in a magnetic field 0.42 T, whereas some FG based on strontium hexaferrite swell. Weak FG with the lowest concentration of AAm shows a much stronger response to a field, as the concentration of AAm governs the Young’s modulus of ferrogel. A small magnetic field magnetoimpedance sensor prototype with Co68.6Fe3.9Mo3.0Si12.0B12.5 rapidly quenched amorphous ribbon based element was designed aiming to develop a sensor working with a disposable stripe sensitive element. The proposed protocol allowed measurements of the concentration dependence of magnetic particles in gels using magnetoimpedance responses in the presence of magnetite and strontium hexaferrite ferrogels with xanthan. We have discussed the importance of magnetic history for the detection process and demonstrated the importance of remnant magnetization in the case of the gels with large magnetic particles.

Exploring original articles to retreat the history of electricity and magnetism

Exploring original articles to retreat the history of electricity and magnetism

A high-resolution, 60 kyr record of the relative geomagnetic field intensity from Lake Towuti, Indonesia

Past changes in the Earth’s magnetic field can be highlighted through reconstructions of magnetic paleointensity. Many magnetic field variation features are global, and can be used for the detailed correlation and dating of sedimentary records. On the other hand, sedimentary magnetic records also exhibit features on a regional, rather than a global scale. Therefore, the development of regional scale magnetic field reconstructions is necessary to optimize magnetic paleointensity dating. In this paper, a 60 thousand year (kyr) paleointensity record is presented, using the core TOW10-9B of Lake Towuti, located in the island of Sulawesi, Indonesia, as a part of the ongoing research towards understanding the Indonesian environmental history, and reconstructing a high-resolution regional magnetic record from dating the sediments. Located in the East Sulawesi Ophiolite Belt, the bedrock surrounding Lake Towuti consists of ultramafic rocks that render the lake sediments magnetically strong, creating challenges in the reconstruction of the paleointensity record. These sediment samples were subject to a series of magnetic measurements, followed by testing the obtained paleointensity records resulting from normalizing natural remanent magnetization (NRM) against different normalizing parameters. These paleointensity records were then compared to other regional, as well as global, records of magnetic paleointensity. The results show that for the magnetically strong Lake Towuti sediments, an anhysteretic remanent magnetization (ARM) is the best normalizer. A series of magnetic paleointensity excursions are observed during the last 60 kyr, including the Laschamp excursion at 40 kyr BP, that provide new information about the magnetic history and stratigraphy of the western tropical Pacific region. We conclude that the paleointensity record of Lake Towuti is reliable and in accordance with the high-quality regional and global trends.

Kinetic effects in the magnetic and magnetocaloric properties of metamagnetic Ni50Mn35In14.25B0.75

Ni50Mn35In14.25B0.75 is a typical representative of the family of metamagnetic In-based Heusler alloys which shows large magnetocaloric effects generated from first order magnetostructural and ferromagnetic-paramagnetic transitions. For this alloy, a study of the adiabatic temperature change ΔTad by a direct method and through thermomagnetic measurements in magnetic fields up to 14 T has been performed. It has been shown that the rate of heating/cooling can affect the magnitude and sign of ΔTad. The application of magnetic fields larger than 12 T (on cooling) results in the “kinetic arrest” of the ferromagnetic austenitic phase. The effects of the temperature and magnetic history, and kinetic effects, on ΔTad of these Ni-Mn-In-based Heusler alloys in high magnetic fields are discussed.

Reorientations, relaxations, metastabilities, and multidomains of skyrmion lattices

Magnetic skyrmions are nano-sized topologically protected spin textures with particle-like properties. They can form lattices perpendicular to the magnetic field and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu$_2$OSeO$_3$ and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history of the sample which can induce metastable lattices. Kinetic measurements show that these metastable skyrmion lattices may or may not relax to their equilibrium positions under macroscopic relaxation times. Furthermore, multidomain lattices may form when two or more equivalent crystallographic directions are favored by spin-orbit coupling and oriented perpendicular to the magnetic field.

Iron snow in the Martian core?

The decline of Mars' global magnetic field some 3.8–4.1 billion years ago is thought to reflect the demise of the dynamo that operated in its liquid core. The dynamo was probably powered by planetary cooling and so its termination is intimately tied to the thermochemical evolution and present-day physical state of the Martian core. Bottom-up growth of a solid inner core, the crystallization regime for Earth's core, has been found to produce a long-lived dynamo leading to the suggestion that the Martian core remains entirely liquid to this day. Motivated by the experimentally-determined increase in the Fe–S liquidus temperature with decreasing pressure at Martian core conditions, we investigate whether Mars' core could crystallize from the top down. We focus on the “iron snow” regime, where newly-formed solid consists of pure Fe and is therefore heavier than the liquid. We derive global energy and entropy equations that describe the long-timescale thermal and magnetic history of the core from a general theory for two-phase, two-component liquid mixtures, assuming that the snow zone is in phase equilibrium and that all solid falls out of the layer and remelts at each timestep. Formation of snow zones occurs for a wide range of interior and thermal properties and depends critically on the initial sulfur concentration, ξ0. Release of gravitational energy and latent heat during growth of the snow zone do not generate sufficient entropy to restart the dynamo unless the snow zone occupies at least 400 km of the core. Snow zones can be 1.5–2 Gyrs old, though thermal stratification of the uppermost core, not included in our model, likely delays onset. Models that match the available magnetic and geodetic constraints have ξ0≈10% and snow zones that occupy approximately the top 100 km of the present-day Martian core.

Is WISEP J060738.65+242953.4 Really a Magnetically Active, Pole-on L Dwarf?

Abstract The interplay of rotation and manifested magnetic activity on ultracool dwarfs (UCDs) is of key importance for gathering clues regarding the operation of the dynamos within these objects. A number of magnetized UCDs host kG-strength magnetic fields. It was recently reported that the L8 dwarf WISEP J060738.65+242953.4 is a radio-emitting UCD that is likely observed pole-on, due to its lack of photometric variability and narrow spectral lines. Follow-up radio observations at Arecibo Observatory, together with a careful analysis of previously published details, however, suggest that the scientific and statistical significance of the radio and spectroscopic data has been overstated. If the UCD is observed along its aligned spin/magnetic axis, the absence of observed Hα activity may present challenges to the auroral model of UCD magnetism, although short-term or long-term cyclic magnetic activity may explain this behavior. The Monte Carlo simulations presented here suggest that the source probably rotates with km s−1, indicating that its inclination angle and rotational velocity are unexceptional and that its angular momentum has evolved as expected for brown dwarfs observed in ∼1 Myr old clusters. The discovery and verification of the most rapidly and slowest rotating brown dwarfs places valuable constraints on the angular momentum evolution and magnetic activity histories of these objects.

Solar Flare Prediction Using Machine Learning with Multiwavelength Observations

AbstractWe developed a flare prediction model based on the supervised machine learning of solar observation data for 2010-2015. We used vector magnetograms, lower chromospheric brightening, and soft-X-ray data taken by Solar Dynamics Observatory and Geostationary Operational Environmental Satellite. We detected active regions and extracted 60 solar features such as magnetic neutral lines, current helicity, chromospheric brightening, and flare history. We fully shuffled the database and randomly divided it into two for training and testing. To predict the maximum size of flares occurring in the following 24 hours, we used three machine-learning algorithms independently: the support vector machine, the k nearest neighbors (kNN), and the extremely randomized trees. We achieved a skill score (TSS) of greater than 0.9 for kNN. Furthermore, we compared the prediction results in a more operational setting by shuffling and dividing the database with a week unit. It was found that the prediction score depends on the way the database is prepared.

Resonant properties of dipole skyrmions in amorphous Fe/Gd multilayers

The dynamic response of dipole skyrmions in Fe/Gd multilayer films is investigated by ferromagnetic resonance measurements and compared to micromagnetic simulations. We detail thickness and temperature dependent studies of the observed modes as well as the effects of magnetic field history on the resonant spectra. Correlation between the modes and the magnetic phase maps constructed from real-space imaging and scattering patterns allows us to conclude the resonant modes arise from local topological features such as dipole skyrmions but does not depend on the collective response of a closed packed lattice of these chiral textures. Using, micromagnetic modeling, we are able to quantitatively reproduce our experimental observations which suggests the existence of localized spin-wave modes that are dependent on the helicity of the dipole skyrmion. We identify four localized spin wave excitations for the skyrmions that are excited under either in-plane or out-of-plane r.f. fields. Lastly we show that dipole skyrmions and non-chiral bubble domains exhibit qualitatively different localized spin wave modes.

Steady-State Analysis of Hysteretic Magnetic Field Problems Using a Parallel Time-Periodic Explicit-Error Correction Method

In this paper, we introduce a novel approach for obtaining steady-state solutions in time-periodic magnetic field analyses considering hysteresis. First, we extract the poorly converged error component in transient calculations using the parallel time-periodic explicit-error correction method. Then, tentative steady-state solutions are obtained for each element by correcting the extracted error components. Based on the tentative periodic waveforms of the flux density vectors, the magnetization history of each element is also corrected. Numerical results are presented to demonstrate the effectiveness of the developed approach.

Advancing Precambrian palaeomagnetism with the PALEOMAGIA and PINT(QPI) databases

State-of-the-art measurements of the direction and intensity of Earth’s ancient magnetic field have made important contributions to our understanding of the geology and palaeogeography of Precambrian Earth. The PALEOMAGIA and PINT(QPI) databases provide thorough public collections of important palaeomagnetic data of this kind. They comprise more than 4,100 observations in total and have been essential in supporting our international collaborative efforts to understand Earth's magnetic history on a timescale far longer than that of the present Phanerozoic Eon. Here, we provide an overview of the technical structure and applications of both databases, paying particular attention to recent improvements and discoveries.

Accurate and Easy-to-Obtain Iron Loss Model for Electric Machine Design

Iron loss modeling is crucial for electric machine design. However, current models feature severe drawbacks. They are 1) very complex, and thus, can hardly be applied, 2) require very high effort for measuring and computation, and/or 3) are not very accurate. In this paper, a new modeling technique is introduced for calculating the instantaneous power loss in ferromagnetic materials without taking the magnetization history into account. A standard measurement setup and specimen shape is used. The considered approach comprises the required measurements, the nonlinear loss modeling by itself, and an extensive verification for different flux density waveforms and frequencies. In addition, a detailed qualitative comparison to well-known iron loss models is given. The presented technique gives very accurate results, while obtaining the model is comparably easy. Moreover, as the calculation of the instantaneous losses is not based on the previous magnetization state of the material, a modeling error for a particular instant of time has no impact on the subsequently calculated characteristics. In the future, this model should ensure a more accurate iron loss calculation for electric machine designs.

The Influence of Pulsed Linear Electromagnetic Actuator Magnetization History on Precision and Impact Energy Stability

The influence of pulsed magnetization history in pulsed electromagnetic actuator on system output mechanical parameters has been discussed. Hysteresis behavior of pulsed linear electromagnetic actuators considerably degrades the precision and stability of impact energy system's performance. In this paper, a method is developed to provide stability for the dosed impact energy in pulsed linear electromagnetic actuators. Theoretical conclusions and experimental results have been provided.

The use of neodymium magnets in healthcare and their effects on health.

The strong magnetic field properties of magnets have led to their use in many modern technologies, as well as in the fields of medicine and dentistry. Neodymium magnets are a powerful type of magnet that has been the subject of recent research. This review provides a brief explanation of the definition, history, and characteristics of rare earth magnets. In addition, a broad overview of results obtained in studies performed to date on the effects of magnets, and neodymium magnets in particular, on body systems, tissues, organs, diseases, and treatment is provided. Though they are used in the health sector in various diagnostic devices and as therapeutic tools, there is some potential for harmful effects, as well as the risk of accident. The research is still insufficient; however, neodymium magnets appear to hold great promise for both diagnostic and therapeutic purposes.

Hysteresis Compensation Method for Magnetoresistive Sensors Based on Single Polar Controlled Magnetic Field Pulses

This paper presents an improved hysteresis compensation method based on magnetic field pulses. The magnetic field pulses are generated by current pulses applied to a one-winding coil structure on the top of the sensor element. This configuration allows the sensor electronic to drive a magnetoresistive (MR) sensor in its magnetic saturation. Anisotropic magnetoresistance, giant magnetoresistance, and tunnel magnetoresistance current sensors are chosen for conducting experiments. The magnetic field generated by current pulses and the magnetic field generated by the current to be measured always have to be in the same direction. As a result, the output characteristic of an MR current sensor can always be kept on the negative rising and the positive falling branch of the magnetic major loop during the measurement. Thus, a defined output of the MR current sensor independent from the magnetic history for all current values can be achieved. An electronic mixed signal circuit consisting of a field-programmable gate array, an optoisolator, analog switches, and attention display converters is used to generate the current pulses and to measure the output of the current sensor. Current measurements with and without controlled magnetic field (current) pulses are compared. A hysteresis reduction to nearly 20% of the original value, by using this hysteresis compensation method, was reached.

Magnetic relaxation phenomena in the chiral magnet Fe1−xCoxSi : An ac susceptibility study

We present a systematic study of the ac susceptibility of the chiral magnet Fe$_{1-x}$Co$_x$Si with $x$ = 0.30 covering four orders of magnitude in frequencies from 0.1 Hz to 1 kHz, with particular emphasis to the pronounced history dependence. Characteristic relaxation times ranging from a few milliseconds to tens of seconds are observed around the skyrmion lattice A-phase, the helical-to-conical transition and in a region above $T_C$. The distribution of relaxation frequencies around the A-phase is broad, asymmetric and originates from multiple coexisting relaxation processes. The pronounced dependence of the magnetic phase diagram on the magnetic history and cooling rates as well as the asymmetric frequency dependence and slow dynamics suggest more complicated physical phenomena in Fe$_{0.7}$Co$_{0.3}$Si than in other chiral magnets.

On the correct estimation of the magnetic entropy change across the magneto-structural transition from the Maxwell relation: Study of MnCoGeBx alloy ribbons

An accurate calculation of the different magnetocaloric-related magnitudes derived from the temperature dependence of the magnetic entropy change in materials exhibiting first-order magnetocaloric effect is imperative to correctly estimate the true potential of a specific material for refrigeration purposes. In this contribution, we present a meticulous study of two different thermal procedures to measure the set of isothermal magnetization curves from which the total field induced magnetic entropy change, ΔST, is calculated using the adequate Maxwell relation. If the accurate determination of ΔST for any temperature is pursued the thermal and magnetic history of the materials must be taken into account, and then, the unidirectional measurement of reversible isothermal magnetization curves after a thermal cycle is required. The analysis was conducted on MnCoGeB0.01 alloy ribbons that show a giant ΔST at the coupled magneto-structural transition, from a ferromagnetic (TiNiSi-type) phase to a paramagnetic (NiIn2-type) one, owing to the concomitant abrupt magnetization change. We suggest that the conclusions reached can be applicable to any other system displaying magnetocaloric effect originated at a first-order phase transition.

Influence of Magnetic Prehistory on the Exchange Bias in Fe20Ni80/FeMn/Fe20Ni80 Films

<p>In this work peculiarities of the hysteresis properties formation in permalloy layers included in Fe<sub>20</sub>Ni<sub>80</sub>/FeMn/Fe<sub>20</sub>Ni<sub>80</sub> films were investigated. Temperature dependencies of magnetization reversal parameters were analyzed in the temperature range 5-300 K for samples with various FeMn thickness (2÷4 nm). Conditions of the exchange bias emergence were determined. Magnetic history was shown to have a significant effect on the magnitude and the character of the exchange bias.</p>

New constraints on the magnetic history of the CV parent body and the solar nebula from the Kaba meteorite

Recent paleomagnetic studies of Allende CV chondrite as well as thermal modeling suggest the existence of partially differentiated asteroids with outer unmelted and variably metamorphosed crusts overlying differentiated interiors. To further constrain the magnetic history of the CV parent body, we report here paleomagnetic results on Kaba CV chondrite. This meteorite contains 11 wt% pseudo-single domain magnetite, making it a rock with an excellent paleomagnetic recording capacity. Kaba appears to carry a stable natural remanent magnetization acquired on its parent body upon cooling in an internally generated magnetic field of about 3 μT from temperatures below 150 °C during thermal metamorphism about 10 to several tens of Myr after solar system formation. This strengthens the case for the existence of a molten advecting core in the CV parent body. Furthermore, we show that no significant magnetic field (i.e. lower than ∼0.3 μT) was present when aqueous alteration took place on the Kaba parent body around 4 to 6 Myr after solar system formation, suggesting a delay in the onset of the dynamo in the CV parent body and confirming that nebular fields had already decayed at that time.

Extended skyrmion lattice scattering and long-time memory in the chiral magnetFe1−xCoxSi

Small angle neutron scattering measurements on a bulk single crystal of the doped chiral magnet Fe$_{1-x}$Co$_x$Si with $x$=0.3 reveal a pronounced effect of the magnetic history and cooling rates on the magnetic phase diagram. The extracted phase diagrams are qualitatively different for zero and field cooling and reveal a metastable skyrmion lattice phase outside the A-phase for the latter case. These thermodynamically metastable skyrmion lattice correlations coexist with the conical phase and can be enhanced by increasing the cooling rate. They appear in a wide region of the phase diagram at temperatures below the $A$-phase but also at fields considerably smaller or higher than the fields required to stabilize the A-phase.