High Magnetic Concentration Research Articles

Magnetic detection of anthropogenic fires at Xiaodong Rockshelter, Southwest China

The Xiaodong Rockshelter, located on the southwest edge of Yunnan Province, is known as Southeast Asia's oldest (>43.5 ka) and northernmost Hoabinhian technocomplex site. The rockshelter preserves a rich record of animals, plants, and lithic artifacts excavated from sediments with a thickness of 4.6 m. New dating reported here indicates that the stratigraphic sequence spans from 65 ka to 15 ka. Several layers in the sedimentary sequence show evidence of fire, representative of the earliest evidence of fire by Hoabinhian population in a tropical-subtropical area. Here, we use magnetic methods coupled with mineral analysis to differentiate natural material from anthropogenically fired sediment. Archaeological fire events are characterized by higher magnetic concentrations and coarser magnetic grains compared to natural sediments. Significant magnetic enhancements were caused by the transformation of paramagnetic iron-bearing silicates into ferrimagnetic, spherical-shaped magnetite with increasing temperatures. Notably, a pronounced magnetic enhancement was observed between 1.8 and 2.5 m, spanning between 42 and 34 ka, indicating intense and concentrated heating, with estimated firing temperatures reaching ca. 400 °C. Additionally, three thin layers exhibiting magnetic enhancement were detected at depths of 3.65 m, 4.45 m, and 4.55 m, dating to ca. 55.6 ka, 62.3 ka and 64.8 ka respectively. This suggests three short-term fired ash deposits with minimal vertical magnetic enhancement, indicative of fire temperatures at ca. 350 °C. The magnetic method proves effective in detecting anthropogenic fire in archaeological sediments and potentially estimating ancient fire temperatures.

Enhanced magnetic field concentration using windmill-like ferromagnets

Magnetic sensors are used in many technologies and industries, such as medicine, telecommunications, robotics, the Internet of Things, etc. The sensitivity of these magnetic sensors is a key aspect, as it determines their precision. In this article, we investigate how a thin windmill-like ferromagnetic system can hugely concentrate a magnetic field at its core. A magnetic sensor combined with such a device enhances its sensitivity by a large factor. We describe the different effects that provide this enhancement: the thickness of the device and its unique windmill-like geometry. An expression for the magnetic field in its core is introduced and verified using finite-element calculations. The results show that a high magnetic field concentration is achieved for a low thickness-diameter ratio of the device. Proof-of-concept experiments further demonstrate the significant concentration of the magnetic field when the thickness-diameter ratio is low, reaching levels up to 150 times stronger than the applied field.

Nanomagnetic Elastomers for Realizing Highly Responsive Micro- and Nanosystems.

Evolution has produced natural systems that generate motion and sense external stimuli at the micro- and nanoscales. At extremely small scales, the intricate motions and large deformations shown by these biosystems are due to a tipping balance between their structural compliance and the actuating force generated in them. Artificially mimicking such ingenious systems for scientific and engineering applications has been approached through the development and use of different smart materials mostly limited to microscale dimensions. To push the application range down to the nanoscale, we developed a material preparation process that yields a library of nanomagnetic elastomers with high magnetic particle concentrations. Through this process, we have realized a material with the highest magnetic-to-elastic force ratio, as is shown by an extensive mechanical and magnetic characterization of the materials. Furthermore, we have fabricated and actuated micro- and nanostructures mimicking cilia, demonstrating the extreme compliance and responsiveness of the developed materials.

Holocene evolution of the Banni Plain at the north‐east margin of the Arabian Sea: Constraints from a ca 50 m long sediment core

AbstractHolocene evolutionary history of the Banni Plain in the Great Rann of the Kachchh Basin is reconstructed from a subsurface sediment core of ca 50 m. Detailed data on textural and lithofacies variations, grain‐size analysis, environmental magnetism and accelerator mass spectrometry 14C dates on seven samples were generated on the sediment core retrieved from the Banni Plain near Berada. A high‐resolution record extending back to 10 ka has been reconstructed from the top ca 40 m of the core section comprising shallow marine sediments. The core is divisible into five depositional units. The basal part is a fluvial depositional unit followed upward by estuarine, sub‐tidal, intertidal and supra‐tidal environments. The sediment accumulation rate is highest in the sub‐tidal to intertidal facies (1.9 cm year−1) and decreases towards the supra‐tidal facies to 0.09 cm year−1. Environmental magnetic analysis, χlf coupled with the S‐ratio, indicates high magnetic mineral concentrations during the Early Holocene, suggesting a wet period accompanied by high monsoon precipitation. This is followed by the onset of semi‐arid conditions in the Great Rann of the Kachchh Basin as indicated by the low values of the χlf and S‐ratios. A westward and northward shift in the shoreline towards the deeper part of the basin is suggested during the Late Holocene, which is coupled with aridity and reduced monsoonal conditions. The change in depositional pattern from the retrogradational deposit of fluvial (Unit 1) to estuarine sediment (Unit 2), progressing to sub‐tidal (Unit 3), is attributed to sea‐level transgression followed by regressive intertidal (Unit 4) to supra‐tidal deposition (Unit 5), culminating in complete withdrawal of the sea, aided by tectonic uplift, during the Late Holocene. The results reveal that the sediment accumulation rates and depositional environments changed over time in response to changes in sea level from minima to maxima and then eventually to the present level.

A study of the propagation of magnetoacoustic waves in small-scale magnetic fields using solar photospheric and chromospheric Dopplergrams: HMI/SDO and MAST observations

In this work, we present a study of the propagation of low-frequency magneto-acoustic waves into the solar chromosphere within small-scale inclined magnetic fields over a quiet-magnetic network region utilizing near-simultaneous photospheric and chromospheric Dopplergrams obtained from the HMI instrument onboard SDO spacecraft and the Multi-Application Solar Telescope (MAST) operational at the Udaipur Solar Observatory, respectively. Acoustic waves are stochastically excited inside the convection zone of the Sun and intermittently interact with the background magnetic fields resulting into episodic signals. In order to detect these episodic signals, we apply the wavelet transform technique to the photospheric and chromospheric velocity oscillations in magnetic network regions. The wavelet power spectrum over photospheric and chromospheric velocity signals show a one-to-one correspondence between the presence of power in the 2.5–4 mHz band. Further, we notice that power in the 2.5–4 mHz band is not consistently present in the chromospheric wavelet power spectrum despite its presence in the photospheric wavelet power spectrum. This indicates that leakage of photospheric oscillations (2.5–4 mHz band) into the higher atmosphere is not a continuous process. The average phase and coherence spectra estimated from these photospheric and chromospheric velocity oscillations illustrate the propagation of photospheric oscillations (2.5–4 mHz) into the solar chromosphere along the inclined magnetic fields. Additionally, chromospheric power maps estimated from the MAST Dopplergrams also show the presence of high-frequency acoustic halos around relatively high magnetic concentrations, depicting the refraction of high-frequency fast mode waves around vA≈vs layer in the solar atmosphere.

Rapid light carbon releases and increased aridity linked to Karoo\u2013Ferrar magmatism during the early Toarcian oceanic anoxic event

Large-scale release of isotopically light carbon is responsible for the carbon isotope excursion (CIE) of the Toarcian Oceanic Anoxic Event during the Lower Jurassic. Proposed sources include methane hydrate dissociation, volcanogenic outgassing of carbon dioxide and/or thermogenic methane release from the Karoo‐Ferrar magmatic province (southern Africa). Distinct small-scale shifts superimposed on the long-term CIE have been interpreted as rapid methane pulses linked to astronomically forced climate changes. In the Peniche reference section (Portugal), these small-scale shifts correspond to distinct brownish marly layers featuring markedly high mercury (Hg) and magnetic mineral concentration. Total organic carbon and Hg increase are uncorrelated, which suggests input of Hg into the atmosphere, possibly released after the intrusion of the Karoo-Ferrar sills into organic-rich sediments. Enhanced magnetic properties are associated with the presence of martite, washed-in oxidized magnetite, inferred to be due to increased aridity on the continental hinterland. This study provides strong evidence for a direct link between the Karoo-Ferrar magmatism, the carbon-isotope shifts and the resulting environmental changes.

Magnetic mineral tracing of sediment provenance in the central Bengal Fan

We present a comprehensive magnetic mineral analysis of surface sediments from 110 sites in the central Bengal Fan to trace sediment provenance. Multiple magnetic parameters, including magnetic mineralogy, concentration, and grain size were generated. Rock magnetic measurements indicate that the dominant magnetic minerals within the studied sediments are detrital magnetite and titanomagnetite, which is further confirmed directly by scanning electron microscope (SEM) and transmission electron microscope (TEM) observations on magnetic extracts. Fuzzy c-means clustering analysis of magnetic parameters indicates that the study area can be divided into three clusters. Considering the position of ‘active valley’, we further divide cluster 1 into clusters 1A and 1B. Cluster 1A primarily covers the west side of the ‘active valley’ with relatively high magnetic concentrations and dominantly coarse-grained magnetic minerals, which likely correspond to basaltic materials derived from the Deccan Plateau. From the Godavari river mouth to the inner Bay of Bengal, magnetic concentration gradually decreases with a fining trend of magnetic grain size. Clusters 1B, 2, and 3 are on the east side of the ‘active valley’, where magnetic concentration and magnetic grain size decrease with increasing distance to the ‘active valley’. Combined with published data in the Indian region and the upper Bengal Fan, we suggest that the main provenances are the Himalayan and the Deccan Plateau, whose contributions to sediment distribution are quantitatively assessed. Our analysis suggests that the position of ‘active valley’ plays a key role in sediment distribution in the central Bengal Fan, while the effect of ocean currents is negligible.

Spin jam induced by quantum fluctuations in a frustrated magnet

Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.

DETECTION OF COHERENT STRUCTURES IN PHOTOSPHERIC TURBULENT FLOWS

We study coherent structures in solar photospheric flows in a plage in the vicinity of the active region AR 10930 using the horizontal velocity data derived from Hinode/SOT magnetograms. Eulerian and Lagrangian coherent structures are detected by computing the Q-criterion and the finite-time Lyapunov exponents of the velocity field, respectively. Our analysis indicates that, on average, the deformation Eulerian coherent structures dominate over the vortical Eulerian coherent structures in the plage region. We demonstrate the correspondence of the network of high magnetic flux concentration to the attracting Lagrangian coherent structures (a-LCS) in the photospheric velocity based on both observations and numerical simulations. In addition, the computation of a-LCS provides a measure of the local rate of contraction/expansion of the flow.

Experimental Study on Recovery of Kronos from Iron-Separation Tailings

It is determined through analysing the feature of tailings of Hebei iron stone, which contains TiO2 7.18%, adopting“high intensity magnetic separation-shaking table concentration. The results show that the concentrate with a TiO2 grade of 27.31%, recovery87.75% and productivity 23.07% and the tailing with a TiO2 grade of 1.14%, recovery12.25% and productivity 76.93%.

Synthesis of Functionalized Microspheres with High Magnetic Concentration for Microscale Force Application

Magnetic microspheres are commercially available in a wide range of diameters and with a variety of chemical functionalities for applications such as cell sorting, protein isolation, or microscale force spectroscopy. The most commonly-used products are magnetic spheres one micron in diameter or larger. These spheres generally consist of a polymer core which is swollen in a solvent and saturated with a solution of iron oxide nanoparticles. This top-down process tends to result in incomplete saturation of the polymer spheres and therefore a diminishing magnetic concentration as spheres grow larger since the magnetic content does not scale with volume.We present here a bottom-up approach to microsphere fabrication which begins with a high-permeability magnetic fluid consisting of magnetite nanoparticles complexed with poly(dimethyl siloxane-co-aminopropylmethyl siloxane). The magnetic content of the fluid may be adjusted smoothly from 0 - 50% wt. without any nanoparticle aggregation, resulting in a highly-magnetic silicone fluid which is homogenous at scales well below 100 nm. Using this material, we demonstrate the production of solid, spherical microbeads in diameters ranging from 2 - 30 microns. Since magnetic nanoparticles are distributed uniformly throughout the material, magnetic content scales directly with volume, resulting in a significant advantage over competitors in terms of magnetic force application at larger sizes. Controlling for diameter, the high magnetic content of these spheres results in nearly four times the force-generating capabilities of the leading 2.8-micron competitor, with advantages increasing in larger spheres. In addition, we use a cell-targeting assay to demonstrate our ability to functionalize the microsphere surface with a variety of ligands.

High-frequency induction heating of Ti-coated mild steel rod for minimally invasive ablation therapy of human cancer

For application as a novel ablation therapy of human cancer, the heating property of a Ti-coated mild steel rod was studied in an AC magnetic field at 300kHz. When the Ti-tube thickness was as low as 0.1mm, the specimen, when placed parallel to the magnetic flux direction (θ=0°), exhibited a significant increase in temperature; however, its value gradually decreased with the increasing Ti thickness. In computer simulation images, the high magnetic flux concentration and concurrent large current density were observed around the interface between the mild steel rod and the Ti-tube. The heating property was drastically different at the three inclination angles (θ=0°, 45°, and 90°) to the magnetic flux direction. However, the effect of the inclination angle was markedly reduced in the mild steel rod surrounded by a 0.3mm thick Ti-tube, suggesting that the non-oriented heating property will be achieved for the prototype ablation needle coated with a Ti layer having the optimum thickness.

Humid medieval warm period recorded by magnetic characteristics of sediments from Gonghai Lake, Shanxi, North China

Variations in monsoon strength, moisture or precipitation in eastern China during the MWP reflected by different climatic records have shown apparent discrepancies. Here, detailed environmental magnetic investigations and mineralogical analyses were conducted on lacustrine sediments of Core GH09B1 (2.8 m long) from Gonghai Lake, Shanxi, North China, concerning the monsoon history during the MWP. The results demonstrate that the main magnetic mineral is magnetite. The sediments with relatively high magnetic mineral concentrations were characterized by relatively fine magnetic grain sizes, which were formed in a period of relatively strong pedogenesis and high precipitation. In contrast, the sediments with low magnetic mineral concentrations reflected an opposite process. The variations of magnetic parameters in Gonghai Lake sediments were mainly controlled by the degree of pedogenesis in the lake drainage basin, which further indicated the strength of the Asian summer monsoon. The variations in the χ and S −300 parameters of the core clearly reveal the Asian summer monsoon history over the last 1200 years in the study area, suggesting generally abundant precipitation and a strong summer monsoon during the Medieval Warm Period (MWP, AD 910–1220), which is supported by pollen evidence. Furthermore, this 3–6-year resolution environmental magnetic record indicates a dry event around AD 980–1050, interrupting the generally humid MWP. The summer monsoon evolution over the last millennium recorded by magnetic parameters in sediments from Gonghai Lake correlates well with historical documentation (North China) and speleothem oxygen isotopes (Wanxiang Cave), as well as precipitation modeling results (extratropical East Asia), which all indicate a generally humid MWP within which centennial-scale moisture variability existed. It is thus demonstrated that environmental magnetic parameters could be used as an effective proxy for monsoon climate variations in high-resolution lacustrine sediments.

A continuous palaeosecular variation record of the last four millennia from the Augusta Bay (Sicily, Italy)

We present a high-resolution palaeomagnetic and rock magnetic study of two cores, MS06 and MS06-SW (6.7 and 1.1 m long, respectively), collected at 72 m below sea level in the Augusta Bay shelf (Eastern Sicily, Ionian Sea, Italy) about 2.3 km from the coastline. Geophysical surveying carried out in the sampling area highlighted the presence of a homogeneous sedimentary sequence that most likely was deposited after the Last Glacial Maximum and was not affected by anthropogenic disturbances. The two cores penetrated a monotonous mud sedimentary sequence, interrupted at ∼3 m depth by a 3–4-cm-thick volcanic sandy layer that is correlated with the tephra fallout deposit produced by the 122 BC plinian eruption of Mt Etna. This tephra, along with radiocarbon dating of nine marine shells and with radioactive tracers for the uppermost 0.3 m (210Pb and 137Cs), provide the chronological constraints for the stratigraphic sequence that resulted younger than 4500 yr BP. Palaeomagnetic and rock magnetic data show that the sample sequence is magnetically homogeneous. A single peak of high magnetic mineral concentration is present and corresponds to the volcanic sandy layer. Palaeomagnetic data allowed the identification of a well-defined characteristic remanent magnetization that provides a high-resolution record of palaeosecular variation (PSV) at the sampling site. The reconstructed PSV curve is in good agreement with the available regional reference PSV curves and with the prediction from recent PSV modelling for Europe. The palaeomagnetic data obtained in this study on the one hand support and refine the age model for the cores, derived from other independent constraints, and on the other hand provide an original high-resolution PSV curve that can serve as a reference for the central Mediterranean over the last 4 ka.

Magnetic parameters, trace elements, and multivariate statistical studies of river sediments from southeastern India: a case study from the Vellar River

This contribution constitutes a new study using magnetic parameters and trace element determinations of pollutants in river sediments from the Tamil Nadu state. The Vellar River covers a total length of about 200 km and flows into the Bay of Bengal. Sediment samples were collected at different sediment depths (up to 90 cm) from 12 sites to investigate their magnetic properties (27 samples) and the contents of trace elements (21 out of 27 samples) along the river; as well as to perform magnetic studies for various grain size fractions (16 sub samples). The magnetic results of magnetic susceptibility and remanent magnetizations suggest that the magnetic signal of these sediments is controlled by ferrimagnetic minerals magnetite-like minerals and a minor contribution of antiferromagnetic carriers (such as hematite minerals). Detailed studies of selected samples showed a higher magnetic concentration in finer grain-sized fractions and a slightly different magnetic mineralogy. Magnetic concentration-dependent parameters evidenced high values, which, together with the background values, allowed us to identify magnetic enhancement at some sites. The Pearson correlation and multivariate statistical studies (Principal Component Analysis, Canonical Correlation Analysis) supported the relationship between the magnetic and chemical variables; in particular, magnetic susceptibility, anhysteretic and isothermal remanent magnetization are closely correlated to Co, Cr, Cu, Fe, V, Zn, and the pollution load index. In addition, Principal Coordinate Analysis and fuzzy C-means cluster analysis allowed us to make a classification and to perform a magnetic-chemical characterization of the data into four groups, thereby identifying critical (possibly polluted) sites from the Vellar River.

Beach sediment magnetism and sources: Lake Erie, Ontario, Canada

Measurements were made along the northwestern shore of Lake Erie, Canada to determine whether grain magnetic properties can be used to identify and distinguish sources of beach sediment. Although surface magnetic susceptibilities were highly variable, ranging from 56 to 9867×10−5 SI (Bartington MS2D), there was generally a gradual increase from the low beach (near the waterline) towards the high beach; there were also narrow, shore-parallel bands with high susceptibility at various points on the beach surface. Magnetic mineralogy on the beaches was dominated by low-Ti magnetite (570°<Tc<580°C), and the effective grain-size varied from pseudosingle domain in the low beach to multidomain on the high beach. Sandy bluff sediments in the eastern part of the study area had magnetic properties (e.g. S-ratios, hysteresis loops, thermomagnetic curves) that were similar to those on the beaches, whereas the magnetic properties of the extensive till bluffs and river basin sediments were quite different. The data suggested that, whereas the beaches in the western part of the study area are supplied with sediment from bluffs several tens of kilometres to the east, the source of the high magnetic concentrations on the eroding beaches of eastern Point Pelee remains to be determined.

Absence of structural correlations of magnetic defects in the heavy-fermion compoundLiV2O4

Magnetic defects arising from structural imperfections have pronounced effects on the magnetic properties of the face-centered cubic normal-spinel structure compound ${\text{LiV}}_{2}{\text{O}}_{4}$. High-energy x-ray diffraction studies were performed on ${\text{LiV}}_{2}{\text{O}}_{4}$ single crystals to search for superstructure peaks or other evidence of spatial correlations in the arrangement of the crystal defects present in the lattice. Entire reciprocal lattice planes were mapped out with the help of synchrotron radiation. No noticeable differences in the x-ray diffraction data between a crystal with high magnetic defect concentration and a crystal with low magnetic defect concentration were found. This indicates the absence of any long-range periodicity or short-range correlations in the arrangements of the crystal/magnetic defects.

Origin of ferromagnetic response in diluted magnetic semiconductors and oxides

This paper reviews the present understanding of the origin of ferromagnetic response thathas been detected in a number of diluted magnetic semiconductors (DMSs) and dilutedmagnetic oxides (DMOs) as well as in some nominally magnetically undoped materials. Itis argued that these systems can be grouped into four classes. To the first belongcomposite materials in which precipitations of a known ferromagnetic, ferrimagnetic orantiferromagnetic compound account for magnetic characteristics at high temperatures.The second class forms alloys showing chemical nanoscale phase separation into the regionswith small and large concentrations of the magnetic constituent. Here, high-temperaturemagnetic properties are determined by the regions with high magnetic ion concentrations,whose crystal structure is imposed by the host. Novel methods enabling a controlof this spinodal decomposition and possible functionalities of these systems aredescribed. To the third class belong (Ga, Mn)As, heavily doped p-(Zn, Mn)Te,and related semiconductors. In these solid solutions the theory built on the p–dZener model of hole-mediated ferromagnetism and on either the Kohn–Luttingerkp theory or the multi-orbital tight-binding approach describes qualitatively, and oftenquantitatively, thermodynamic, micromagnetic, optical, and transport properties.Moreover, the understanding of these materials has provided a basis for the development ofnovel methods, enabling magnetization manipulation and switching. Finally, in anumber of carrier-doped DMSs and DMOs a competition between long-rangeferromagnetic and short-range antiferromagnetic interactions and/or the proximity of thelocalization boundary lead to an electronic nanoscale phase separation. Thesematerials exhibit characteristics similar to colossal magnetoresistance oxides.

Phase relations in theLi2O−V2O3−V2O5system at700°C: Correlations with magnetic-defect concentration in heavy fermionLiV2O4

The phase relations in the Li2O-V2O3-V2O5 ternary system at 700 C for compositions in equilibrium with LiV2O4 are reported. This study clarified the synthesis conditions under which low and high magnetic defect concentrations can be obtained within the spinel structure of LiV2O4. We confirmed that the LiV2O4 phase can be obtained containing low (0.006 mol%) to high (0.83 mol%) magnetic defect concentrations n{defect} and with consistently high magnetic defect spin S values between 3 and 6.5. The high n{defect} values were obtained in the LiV2O4 phase in equilibrium with V2O3, Li3VO4, or LiVO2 and the low values in the LiV2O4 phase in equilibrium with V3O5. A model is suggested to explain this correlation.

Monte Carlo study of the random-exchange–Ising-model behavior in a diluted antiferromagnet:Fe0.48Zn0.52F2

We present a microscopic Monte Carlo description of the site-diluted b.c.c. frustrated Ising antiferromagnet ${\mathrm{Fe}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{F}}_{2}$, with an emphasis on the random exchange Ising model (REIM) phase observed at high and intermediate magnetic concentrations, $0.3\ensuremath{\lesssim}x&lt;1.0$, in a zero magnetic field. Thermodynamical, microscopic, and critical properties of the $x=0.48$ system are found to be in good agreement with both zero-field experimental measurements and previous Monte Carlo results on the site-diluted s.c. nonfrustrated ferromagnetic Ising model. In particular, we contrast the results of the REIM behavior at $x=0.48$ with those of the zero-field spin-glass phase observed at $x=0.25$.