Enhancement Of Magnetic Susceptibility Research Articles

Optimized magnetic properties of a Terfenol-D alloy in an extended temperature range using a high magnetic field

Tb–Dy–Fe alloys are among the most suitable magnetostrictive materials for high-power transducers. Optimizing magnetic properties in an extended temperature range could ensure the stable operation of transducers. In this work, a high magnetic field is applied to the directional solidification of Tb–Dy–Fe alloys. We study the microstructure, crystallographic orientation, magnetic susceptibility, crystal structure, and magnetic domain of samples. When the content and alignment of the magnetic phase along with crystallographic orientation remain basically invariant, the magnetic susceptibility of samples increases with the magnetic flux density of the high magnetic field throughout the temperature range from 273 K to Curie temperature (T C). At 4 T, the maximum magnetic susceptibility is increased by ∼ 40% compared with the sample without a high magnetic field applied, and the advantage is maintained in the range ∼ 300 K. Analysis shows that the enhancement of magnetic susceptibility is not due to the change in crystal structure, as commonly believed, but to the highly ordered alignment of magnetic domains. This research provides a new method for improving the temperature properties of magnetic materials using a high magnetic field.

Magnetic enhancement in paleosols with hydroclimatic and vegetation cover variabilities (Holocene vs. late MIS 3) in the central Korean Peninsula

Magnetic susceptibility enhancement (kE) is useful for reconstructing terrestrial paleohydroclimate variabilities. However, kE and its driving process(es) in the Korean Peninsula remain uninvestigated. Therefore, this study investigated two kEs of similar magnitudes, dated MIS 1 (Holocene) and late MIS 3 (~ 29–36 ka), from a paleosol sequence in the upland of paleo-fluvial terrace in the central Korean Peninsula. We observed increased ferri- and antiferro-magnetic mineral components,including ultrafine particles, and stronger chlorite weathering for the two kEs, suggesting pedogenic component predominance. The Fe-bearing (phyllo)silicate weathering mechanism proposed for the Chinese Loess Plateau sequences can explain the pedogenesis-induced kEs for the studied site. Superparamagnetic-domain (SPD) to pseudo-single-domain sized particles of pedogenic magnetite are likely major contributors to kEs. Moreover, we recognized the younger kE interval as more SPD contribution but less in total ferrimagnetic contribution, and more antiferromagnetic contribution than the older ones. The magnetic differences between the periods can result from vegetation cover impact and surrounding hydroclimate conditions, consistent with the recent suggestion for part of the southeast Chinese sites with relatively more rainfall. Consequently, our study provides a baseline for improving the relationship between mineral magnetic signals and local/regional hydroclimatic and environmental variabilities.

Enhancement of magnetic susceptibility of Mn<sub>3</sub>Sn single crystal under GPa-level uniaxial stress

How to achieve spin control of noncollinear antiferromagnetic Mn<sub>3</sub>Sn at room temperature is a challenge. In this study, we modulate the magnetic structure of Mn<sub>3</sub>Sn single crystals by subjecting them to uniaxial stress at the GPa level using a high-pressure combined deformation method. Initially, the single crystal is sliced into regular cuboids, then embedded in a stainless steel sleeve, and finally, uniaxial stress is applied along the <inline-formula><tex-math id="M4533">\begin{document}$ \text{[11}\bar{2}\text{0]} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M4533.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M4533.png"/></alternatives></inline-formula> direction and <inline-formula><tex-math id="M4534124">\begin{document}$ \text{[01}\bar{1}\text{0]} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M4534124.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M4534124.png"/></alternatives></inline-formula> direction of the Mn<sub>3</sub>Sn single crystal. Under high stress, the single crystal undergoes plastic deformation. Our observations reveal lattice distortion in the deformed single crystal, with the lattice parameter gradually decreasing as the stress level increases. In addition, the magnetic susceptibility of Mn<sub>3</sub>Sn under GPa uniaxial stress (<i>χ</i>) is different from that under MPa uniaxial stress, and its value is no longer fixed but increases with the increase of stress. When 1.12 GPa stress is applied in the <inline-formula><tex-math id="M157485">\begin{document}$ \text{[11}\bar{2}\text{0]} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M157485.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M157485.png"/></alternatives></inline-formula> direction, <i>χ</i> reaches 0.0203 <inline-formula><tex-math id="M45346">\begin{document}$ {\text{μ}}_{\text{B}}\cdot{\text{f.u.}}^{{-1}}\cdot{\text{T}}^{{-1}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M45346.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M45346.png"/></alternatives></inline-formula>, which is 1.42 times that of the undeformed sample. In the case of stress applied along the <inline-formula><tex-math id="M45487">\begin{document}$ \text{[01}\bar{1}\text{0]} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M45487.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M45487.png"/></alternatives></inline-formula> direction, <i>χ</i> ≈ 0.0332 <inline-formula><tex-math id="M45.3458">\begin{document}$ {\text{μ}}_{\text{B}}\cdot{\text{f.u.}}^{{-1}}\cdot{\text{T}}^{{-1}} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M45.3458.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20240287_M45.3458.png"/></alternatives></inline-formula> when the stress is 1.11 GPa. This result is also 2.66 times greater than the reported results. We further calculate the values of trimerization parameter (<i>ξ</i>), isotropic Heisenberg exchange interaction (<i>J</i>), and anisotropic energy (<i>δ</i>) of the system under different stresses. Our results show that <i>ξ</i> gradually increases, <i>J</i> gradually decreases, and <i>δ</i> gradually increases with the increase of stress. These results show that the GPa uniaxial stress introduces anisotropic strain energy into the single crystal, breaking the symmetry of the in-plane hexagon of the kagome lattice, which causes the bond length of the two equilateral triangles composed of Mn atoms to change. Thus, the exchange coupling between Mn atoms in the system is affected, the anisotropy of the system is enhanced, and the antiferromagnetic coupling of the system is enhanced. Therefore, the system <i>χ</i> is no longer a constant value and gradually increases with the increase of stress. This discovery will provide new ideas for regulating the anti-ferromagnetic spin.

Pedogenic effect and the impact of erosion factors on topsoil magnetic susceptibility enhancement

The main aims of this study were to i) investigate the impact of erosion factors including land use, slope position, and lithology on magnetic susceptibility (MS) of soil, and ii) detecting the pedogenic effect on MS enhancement using simple methods, including median absolute deviation (MAD), topsoil-subsoil difference methods, MS magnitude and Dearing’s model. Soil cores were sampled along five slope positions in two transects selected in forested and cultivated lands in a watershed located in north of Morocco. The results showed higher values of MS in the upperslopes in forested land due to soil stability, and lower ones in middleslopes and lowerslopes due to soil erosion. However, MS is higher in cultivated land in middleslopes due to soil deposition and it is lower in the upperslopes due to erosion. The results confirmed the pedogenic effect on MS. This is confirmed by i) enhanced Forster factor and low values of magnetic susceptibility background, ii) dominance of ultrafine super-paramagnetic/stable single-domain ferrimagnetic grains in almost all studied soils, and iii) absence of anomaly in MAD data set and pertinence of the results of MAD and topsoil-subsoil difference methods.

Enhancement of electron magnetic susceptibility due to many-body interactions in monolayer MoSe2

Employing the original, all-optical method, we quantify the magnetic susceptibility of a two-dimensional electron gas (2DEG) confined in the MoSe2 monolayer in the range of low and moderate carrier densities. The impact of electron–electron interactions on the 2DEG magnetic susceptibility is found to be particularly strong in the limit of, studied in detail, low carrier densities. Following the existing models, we derive the value of for the bare (in the absence of the interaction effects) g-factor of the ground state electronic band in the MoSe2 monolayer. The derived value of this parameter is discussed in the context of estimations from other experimental approaches. Surprisingly, the conclusions drawn differ from theoretical ab initio studies.

Anisotropic magnetotransport properties coupled with spiral spin modulation in a magnetic semimetal EuZnGe

We investigate the thermodynamic, magnetic, and electrical transport properties of a triangular-lattice antiferromagnet EuZnGe using single crystals grown from Eu-Zn flux in sealed tantalum tubes. Magnetic properties are found to be isotropic in the paramagnetic state while we observe an enhancement of in-plane magnetic susceptibility at the temperature near T* =11.3 K, suggesting an easy-plane anisotropy at low temperatures. Magnetic transition temperature is lower than T* as specific heat shows a peak at TN =7.6 K. We reveal the magnetic modulation along the c axis by resonant x-ray scattering at Eu L2 edge, which suggests competing magnetic interaction among Eu triangular-lattice layers. We observe a double-peak structure in the intensity profile along (0, 0, L) below TN, which is mainly composed of a dominant helical modulation with q ~ (0, 0, 0.4) coexisting with a secondary contribution from q ~ (0, 0, 0.5). We reproduce the intensity profile with a random mixture of five- and four-sublattice helices with spin rotation skipping due to hexagonal in-plane anisotropy. The metallic conductivity is highly anisotropic with the ratio rho_zz/rho_xx exceeding 10 over the entire temperature range and additionally exhibits a sharp enhancement of rho_zz at TN giving rise to rho_zz/rho_xx ~ 50, suggesting a coupling between out-of-plane electron conduction and the spiral magnetic modulations. In-plane magnetic field induces a spin-flop like transition, where the q = 0.4 peak disappears and an incommensurate peak of approximately qICM ~ 0.47 emerges, while the q = 0.5 modulation retains a finite intensity. This transition correlates with non-monotonic magnetoresistance and Hall resistivity, suggesting a significant interplay between electrons and spin structures through Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction.

Optically stimulated luminescence dating of loess in South-Eastern China using quartz and polymineral fine grains

Loess deposits distributed in southeastern China play an important role for paleoclimate reconstruction of the subtropical regions. These loess-paleosol deposits are mainly spread within the middle and lower reaches of the Yangtze River as well as in the drainage area of the Huai River. The ages of loess paleosol sequences that are distributed along the Huai River are not well constrained. In this study, the standard single-aliquot regenerative dose (SAR) optically stimulated luminescence (OSL) protocol and two elevated temperature post infrared-infrared stimulated luminescence SAR protocols (pIRIR 225 and pIRIR 290 ) were applied on 4–11 μm quartz and polymineral fine grains, respectively, in order to obtain the first numerical luminescence chronology for a loess-paleosol sequence in northern Jiangsu Province. Our results show a good agreement between quartz SAR-OSL and polymineral pIRIR ages up to ~70 ka. These findings confirm that Xiashu loess accumulated during the Last Glaciation. For samples older than this, the ages increasingly deviate with depth. Fine quartz ages beyond 70 ka are interpreted as underestimates, as previous studies reported that quartz ages >70 ka from various sedimentary origins worldwide may underestimate even if they pass rejection criteria and dose recovery tests. On the other hand, the pIRIR ages are most likely overestimating the true depositional ages as indicated by the results of dose recovery tests, where a 30–60% overestimation of the recovered dose is reported for values larger than ~400 Gy. The overestimation of pIRIR protocols was also confirmed by the results obtained when large beta doses were added on top of the natural accrued dose. Moreover, our dating results suggest that L1/S1 transition (corresponding to MIS 5/4 boundary) occurred much higher in the stratigraphic sequence than may have been interpreted from the magnetic susceptibility enhancement. This inconsistency can be assigned to invalidity of magnetic susceptibility as a chronostratigraphical proxy due to ferrimagnetic minerals dissolution or transformation during paedogenesis processes in this humid subtropical region in the southeastern China.

Magnetic responses to heavy metal pollution of the industrial soils in Shanghai: Implying the influences of anthropogenic magnetic dustfall on urban environment

Using the magnetic method to detect soil pollution has attracted increasing interest. To study the influence of magnetic dustfall on urban environment, 105 soil samples (0–5 cm) were collected along three equidistant gradient profiles with respect to a major iron and steel industrial complex (ISIC) in the northern suburb of Shanghai, Southeast China. The soils and atmospheric particulate matter (APM) in the area were examined using magnetic and micromorphological analyses. As a result, magnetic susceptibility (χlf) of study soils is commonly significantly enhanced, with a mean of 284.8 × 10−8 m3 kg−1. 68.6% of the soils are higher in χlf than 100 × 10−8 m3 kg−1, more than three times the magnetic background. Moreover, it shows an increasing trend toward the ISIC. Frequency-dependent susceptibility (χfd%) of the soils is mostly less than 2%, and is negatively significantly correlated with χlf, suggesting that the enhancement of soil magnetism is due mainly to coarse anthropogenic magnetic particles (multi-domain (MD) or stable single domain (SSD)). A number of magnetic spheroids were observed in the soils and APM, which are believed to mainly come from the ISIC. The persistent deposition of anthropogenic Fe-borne magnetic dustfall has significantly influenced the urban environment, causing the synchronous enhancement of magnetic susceptibility and heavy metal contents in the soils. The study soils are moderately polluted by Zn and Pb, and the soils of Profile I, the nearest to the ISIC, are heavily polluted by Pb and moderately polluted by Cd and Zn. χlf can reflect the overall level of heavy metal pollution of the soils effectively. Moreover, it is positively significantly correlated with the content of Cd, Cu, Zn, Ni, Cr, Pb and Mn (p < 0.01) in the soils. However, it is difficult to measuring the content of one or more heavy metals in the soils using the magnetic method as locally quantitative correlations between χlf and heavy metal content cannot be established even within this small industrial area.

Preliminary Investigation of Soil and Sediments Using Magnetic Susceptibility Method in Kogi State, Nigeria

Over the years, there has been significant increase in population and urbanization in Kogi State as a result of rural - urban migration. This has become a major threat to soil sustainability which is a natural non-renewable resource. The aim of this research is to carry out magnetic susceptibility mapping on the surface and subsurface soil of Kogi State using environmental magnetism techniques and geochemical analysis. The susceptibility test on rock samples and background soil samples within the study area shows an average of about 112.0 × 10^-5 SI. The magnetic susceptibility measurement on soil from Kogi State shows magnetic susceptibility enhancement of about (450.0 - 700.0) × 10^-5 SI. These values were dominant along the major towns, road pavements and commercial areas at the surface to a depth of about 50.0 cm in soil profiles. The 2D spatial distribution of magnetic susceptibility with depth reveals that these magnetic grains are distributed in the subsurface as a result of anthropogenic loading. The frequency-dependence of magnetic susceptibility (χfd%) values are very low (2 - 10.0 %) in most of the areas on the surface soil. These values indicate that the magnetic properties are predominantly contributed by the coarse multi-domain (MD) and stable single-domain (SSD) grains of anthropogenic origin. Atomic Absorbtion Spectrometer (AAS) analysis of these soil samples indicates the presence of Lead (300.0 - 900.0) mg/l and Cadmium (20.0 - 60.0) mg/l in large concentration at the surface soil in most part of the Kogi State. While Chromium show relatively low concentration on the surface soil. From the statistical correlation analysis, Lead and Cadmium show high positive correlation with magnetic susceptibility. These results suggests that the high enhancement of magnetic susceptibility on the surface and sub-surface soil in most part of Kogi State arise from anthropogenic activities rather than lithological and pedogenic processes and most likely cause by high concentration of Lead and Cadmium.

OSL-dating of the Pleistocene-Holocene climatic transition in loess from China, Europe and North America, and evidence for accretionary pedogenesis

Loess deposits intercalated by paleosols are detailed terrestrial archives of Quaternary climate variability providing information on the global dust cycle and landscape dynamics. Their paleoclimatic significance is often explored by quantifying their mineral magnetic properties due to their sensitivity to local/regional hydroclimate variability. Detailed chronological assessment of such regional proxy records around the climatic transitions allow a better understanding of how regional records react to major global climatic transitions such as the Pleistocene-Holocene climatic transition. Logs of high-resolution magnetic susceptibility and its frequency dependence were used as paleoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil as reflected in nine loess-paleosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, USA. The onset of increase in magnetic susceptibility above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. High-resolution luminescence dating was applied on multiple grain-sizes (4–11 μm, 63–90 μm, 90–125 μm) of quartz extracts from the same sample in order to investigate the timing of Pleistocene-Holocene climatic transition in the investigated sites. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. The initiation of this increase, interpreted as recording the initiation of the Pleistocene-Holocene climatic transition at each site, was dated to 14–17.5 ka or even earlier. Our chronological results highlight the need of combining paleoclimatic proxies (magnetic susceptibility) with absolute dating when investigating the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid chronostratigraphic misinterpretations in loess-paleosol records caused by simple pattern correlation. The detailed luminescence chronologies evidence the continuity of eolian mineral dust accumulation regardless of glacial or interglacial global climatic regimes. Coupled with magnetic susceptibility records this indicates that dust sedimentation and pedogenesis act simultaneously and result in a non-negligible accretional component in the formation of Holocene soils in loess regions across the Northern Hemisphere. The luminescence ages allowed the modeling of accumulation rates for the Holocene soil which are similar for European, Chinese and U.S.A. loess sites investigated and vary from 2 cm ka −1 to 9 cm ka −1 . While accretional pedogenesis has often been implicitly or explicitly assumed in paleoclimatic interpretation of loess-paleosol sequences, especially in the Chinese Loess Plateau, our luminescence data add direct evidence for ongoing sedimentation as interglacial soils formed. • High-resolution magnetic susceptibility record as paleoclimate proxy. • High-resolution luminescence dating applied on multiple quartz fractions. • Initiation of magnetic susceptibility enhancement dated prior to ~11.7 ka. • Continuous dust accumulation during Pleistocene-Holocene transition and in Holocene. • Accretional Holocene soils in European, Chinese Loess Plateau and US loess sites.

Magnetic parameters and palaeoclimate: A case study of loess deposits of North-East of Iran

Environmental magnetism techniques enable us to reconstruct paleoclimate conditions in some deposition such as losses. The magnetic properties of minerals are used as proxies for environmental changes. For this study, loess/paleosol sequence of Kolet section at Neka, north-east of Iran were magnetically investigated. We applied environmental magnetism methods, to reconstruct paleoclimate changes. We investigated relationship between paleoclimate changes and environmental magnetism proxies like magnetic susceptibility (?) variation. The laboratory techniques indicated the presence of main factor of magnetic property in loess/paleosol sequence, such as magnetite, maghemite and etc. We also estimated magnetically parameters (like SIRM, HIRM and etc.) to confirm concentrations of both aeolian and pedogenic particles versus variations of magnetic susceptibility enhancement. The ? values show prominent peaks for the three well developed soil and paleosol horizons, Recent Soil (S0), Upper Paleosol (S1) and Lower Paleosol (S2); which refer to warmer and wetter conditions. As result, we concluded that the increase/decreasing of magnetic susceptibility is coinciding with palaeosol/loess sequence, and probably with humid/arid conditions. Moreover, variations of magnetic susceptibility versus lithological column of Kolet section enabled us to recognize paleoclimatically periods known as interglacial/glacial cycles. The obtained magnetic data indicate that during over the past 50 ka, there have been at least two glacial/interglacial periods and since last 20 ka, there was no main glaciation occurrence, in the study area.

Relationship between soil magnetic susceptibility enhancement and precipitation in Cretaceous paleosols

Relationship between soil magnetic susceptibility enhancement and precipitation in Cretaceous paleosols

Alignment and Rotational Disruption of Dust

Abstract We reveal a deep connection between alignment of dust grains by radiative torques (RATs) and mechanical torques (METs) and the rotational disruption of grains introduced by Hoang et al. The disruption of grains happens if they have attractor points corresponding to high angular momentum (high J). We introduce fast disruption for grains that are directly driven to the high-J attractor on a timescale of spin-up, and slow disruption for grains that are first moved to the low-J attractor and gradually transported to the high-J attractor by gas collisions. The enhancement of grain magnetic susceptibility by iron inclusions expands the parameter space for high-J attractors and increases the percentage of grains experiencing the disruption. The increase in the magnitude of RATs or METs can increase the efficiency of fast disruption but, counterintuitively, decreases the effect of slow disruption by forcing grains toward low-J attractors, whereas the increase in gas density accelerates disruption by transporting grains faster to the high-J attractor. We also show that the disruption induced by RATs and METs depends on the angle between the magnetic field and the anisotropic flow. We find that pinwheel torques can increase the efficiency of fast disruption but may decrease the efficiency of slow disruption by delaying the transport of grains from the low-J to high-J attractors via gas collisions. The selective nature of the rotational disruption opens a possibility of observational testing of grain composition and physical processes of grain alignment.

Tracing of traffic-related pollution using magnetic properties of topsoils in Daejeon, Korea

The present study was designed to explore the possibility of roadside pollution screening using magnetic properties of topsoil samples in Daejeon, South Korea. Low-field magnetic susceptibility, frequency dependence of magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, isothermal remanent magnetization (IRM) acquisition and demagnetization, back-field IRM treatment, and thermal demagnetization of composite IRM were determined for roadside topsoil samples. Magnetic susceptibility measured on 238 samples from the upper 5 cm of the topsoils ranged from 8.6 to 82.5 × 10–5 SI with a mean of 28.3 ± 10.8 × 10–5 SI. The proximal zone, 55 m wide area situated on either side of the main street, exhibited an enhancement of magnetic susceptibility. In areas distant from the main street, low magnetic susceptibility (< 50 × 10–5 SI) was observed. The topsoil samples exhibited significant susceptibility contrasts, suggesting that two dimensional magnetic mapping was effective in identifying traffic-related pollution. A few magnetic hotspots with intensities of magnetic susceptibility near or over 50 × 10–5 SI might reflect the difference in topographic elevation and surface morphology. Among various IRM-related parameters, remanence of coercivity was most significant statistically. In most samples, IRM component analysis provided dual coercivity components. Thermal demagnetization of composite IRM and morphological observation of magnetic separates suggest angular magnetite produced by vehicle non-exhaust emissions spherical magnetite derived from exhaust emission to be the dominant contributors to the magnetic signal. It is likely that lower- and higher-coercivity components represent the presence of coarse-grained angular magnetite and fine-grained spherical magnetite, respectively.

Strong enhancement of magnetic susceptibility induced by spin-nematic fluctuations in an excitonic insulating system with spin-orbit coupling

Effects of the spin-orbit coupling (SOC) and magnetic field on excitonic insulating (EI) states are investigated. We introduce the two-orbital Hubbard model with the crystalline field splitting, which is a minimal model for discussing the exciton condensation in strongly correlated electron systems, and analyze its effective Hamiltonian in the strong correlation limit by using the mean-field theory. In the absence of the SOC and magnetic field, the ground state changes from the nonmagnetic band-insulating state to the EI state by increasing the Hund coupling. In an applied magnetic field, the magnetic moment appears in the EI state, which is continuously connected to the forced ferromagnetic state. On the other hand, in the presence of the SOC, they are separated by a phase boundary. We find that the magnetic susceptibility is strongly enhanced in the EI phase near the boundary with a small SOC. This peculiar behavior is attributed to the low-energy fluctuation of the spin nematicity inherent in the high-spin local state stabilized by the Hund coupling. The present study not only reveals the impact of the SOC for the EI state but also sheds light on the role of quantum fluctuations of the spin nematicity for the EI state.

Magnetic properties of upper Paleozoic loessite-paleosol couplets in the Western USA: The role of pedogenic hematite in magnetic enhancement

The sequence of loessite-paleosol couplets in the Western USA consists of more than 700 m of lithified loessite with more than 200 m of paleosols which are interpreted as Protosols or Argillisols. The sequence provides one of the highest resolution terrestrial records of late Paleozoic climate. Several previous investigations have suggested that the magnetic susceptibility enhancement model of the loessite is similar to that of the loess of the Chinese Loess Plateau, since the concentration of fine-grained superparamagnetic (SP) magnetite is higher in the paleosols than in the parent material. However, this is not evident in all sequences, and in some cases hematite, rather than magnetite, dominates the high-field magnetic behavior. In this study, four soil units were selected to investigate the origin of the magnetic mineralogy of the loessite deposits, based on magnetic analysis of two Protosol units and two Argillisol units. The results reveal the presence of two major coercivity components in the loessite: a soft magnetic component with a saturating field below 100 mT, and a hard component with a saturating field higher than 300 mT. These components correspond to magnetite and/or maghemite and hematite, respectively. The magnetic enhancement of Argillisols is mainly due to the pedogenic formation of magnetite and/or maghemite particles, and that of Protosols is mainly due to the pedogenic formation of hematite.

Using magnetic susceptibility for predicting hydrocarbon pollution levels in a petroleum refinery compound in Isfahan Province, Iran

Nowadays through the world as well as in Iran, petroleum hydrocarbons have majority contribution in environmental ricks for human and other organisms. Therefore, this study evaluates hydrocarbon pollution effects on soil chemical properties, as well as soil magnetic susceptibility on a petroleum refinery compound in Isfahan province, Iran. It also examines the efficacy of using magnetic signatures to predict hydrocarbon pollution of soils. Two sites (polluted and unpolluted) with similar intrinsic soil properties and environmental attributes were selected. A total of 120 soil samples were collected at two depths of 0–10 and 10–30 cm. Laboratory analysis included measurement of electrical conductivity (EC), pH, aqua regial extractable Fe (FeA), dithionite extractable Fe (Fed), magnetic susceptibility at low frequency (χlf), total petroleum hydrocarbon (TPH), as well as powdery X-ray characterization. Polluted soils by petroleum hydrocarbons had significantly higher EC, χlf, FeA and Fed and lower pH values compared to the unpolluted soils. Positive significance (r = 0.88, p < .01) was obtained between TPH and magnetic susceptibility. Enhancement of magnetic susceptibility presumably attributed to formation of ferrimagnetic minerals such as magnetite because of degradation of hydrocarbon compounds. A multiple linear regression model was developed between magnetic susceptibility and TPH, and the results showed that the developed pedotransfer function could explain 86% of the variability of TPH in the studied area, and provided a reliable function to predict TPH in polluted soils, as a cost-effective and fast technique to be implemented in the polluted sites by petroleum hydrocarbons. It seems that inclusion of additional magnetic measures may improve the accuracy of the predictive model.

Chlorite weathering linked to magnetic enhancement in Red Clay on the Chinese Loess Plateau

Magnetic parameters are widely used in the loess-palaeosol sequence tracing Quaternary climate change on the Chinese Loess Plateau (CLP). However, the climatic implication and magnetic enhancement mechanism in aeolian Red Clay on the CLP is still debated. Chlorite is a common Fe-bearing silicate in Red Clay and it is easily to be weathered. The transformation of weakly magnetic ferrihydrite, a product in chlorite weathering process, into strongly magnetic iron oxides has been linked to magnetic enhancement in many soils. Here, we present a complete chlorite weathering record within the Red Clay sequence through a detailed mineralogical investigation, from a 125-m thick eolian Red Clay deposit in the Chaona section (~8.1 to 2.6 Ma) of the central CLP to explore the link between changes in chlorite geochemical composition and magnetic susceptibility enhancement and regional climate. The results suggest a concomitant evolution of chlorite Fe content and magnetic susceptibility, indicating that Fe released from chlorite brucite-like interlayers, which induced ferrihydrite formation, is responsible for the enhanced magnetic susceptibility in the CLP Red Clay deposits. Moreover, the results also show that the chlorite Fe content exhibited a stepwise decrease, with two accelerated stages at ~6.2 Ma and ~3.6 Ma. The post-6.2 Ma evolution of chlorite Fe content is related to increased precipitation caused by phased enhancement of the East Asian summer monsoon (EASM). Our study also suggests that changes in chlorite chemical composition and crystallinity linked to soil weathering are useful proxies in tracing past weathering intensity and climate change within arid-less humid regime.

Laacher See tephra discovered in the Bohemian Forest, Germany, east of the eruption

Abstract We present a geochemically confirmed finding of the Laacher See tephra (LST), directly east of the Laacher See volcano (LSV). European lake sediment (Rachelsee, Germany) contains the time period of the Laacher See volcanic explosion (LSE) ca. 12900 yr cal BP in the East Eifel volcanic field. This eruption significantly affected the local environment but its impact in regions far east from its source is poorly known. The lake sediment sequence showed an enhancement in magnetic susceptibility and an increase in concentration in niobium and phosphorus. These enhancements correlated with direct tephra particle observations whose geochemical analysis compared well with the published LST data from proximal sites. Detailed analyses revealed a most likely match with tephra known to have been deposited during the middle phase of the eruption. We suggest that contrary to other published studies, the LST cloud traveled directly east, as far as 470 km, from the volcano,. The pollen record shows minimal change during the tephra deposition, thus indicating that the LSE had no noticeable influence on vegetation in eastern Bavaria and the southern part of the Czech Republic. The discovery of the LST at Rachelsee, opens the potential of further tephrochronological studies in regions to the east of the LSV.

Assessing Magnetic Susceptibility Profiles of Topsoils under Different Occupations

Magnetic susceptibility measurements at low and high frequencies (χlf, χhf) were carried out on topsoil samples from reforested, cultivated, and pasture lands from a catchment located at the north of Morocco. The aims of this study were to investigate the impact of land use or human activity on χlf of soil overlying the same substrate, to discriminate allochthonous material or pollution from autochthonous or inherited ones, and to assess the origin and contribution of superparamagnetic (SP) grains to the global magnetic susceptibility χlf. Measurements of χlf indicated significant enhancement, with values ranging from 12.4 to 252.82 × 10-8 m3 kg−1 with a mean value of 107.087 × 10-8 m3 kg−1 for the reforested lands. In the cultivated lands, χlf were from 8.4 to 88.65 × 10-8 m3 kg1 with a mean value of 42.69 × 10-8 m3 kg−1, while in the pasture lands, χlf was comprised between 14.34 × 10-8 m3 kg−1 and 133.35 × 10-8 m3 kg−1 with a mean value of 57.33 × 10-8 m3 kg−1. The magnetic enhancement indicates high concentration of ferrimagnetic minerals in the top soil. The magnetic susceptibility enhancement decreases as the human activity increases, while the underlying bedrock is almost the same: reforested land &gt; pastures land &gt; cultivated land. The analysis of the variations of χlf and frequency dependent susceptibilities (χfd and %χfd), along the profiles of soil, indicate a pedogenic origin of the topsoil magnetic susceptibility enhancement.