Remanent Research Articles

Sensitivity Analysis of Multi-Parameter Magnetic Control Indicators for determining the Mechanical Properties of Steel

This paper presents the results of a steel magnetic property study using a non-destructive method of determination of the mechanical properties of products made from structural steels 20, 09Mn2Si, and 25CrMoV. The influence of tempering temperature on the change of magnetic properties was analyzed and a statistical analysis of the input parameter significance, including coercive force, residual magnetic induction, and maximum magnetic permeability, was carried out. As a result, it was found that the greatest sensitivity for steels at tempering temperatures up to 400 °C is the coercive force and, above 300 °C, the residual magnetic induction. At the same time, the maximum magnetic permeability provides a correlation over the whole range of tempering temperatures, justifying the use of magnetic properties in the determination of mechanical properties.

Revisiting the assessment of magnetic texture of Rare-Earth Magnets: The role of coercivity

A crucial figure of merit of rare-earth magnets is their magnetic texture, because it is closely related to the maximum remanence a magnet can achieve, hence assessing the magnetic texture is pivotal in terms of magnet’s performance. Fernengel et al. (1996) developed a methodology based on magnetometry, which allows for a quick determination of the texture by calculating the degree of alignment 〈cosθ〉 from the remanent magnetization in directions parallel and perpendicular to the texture axis of the magnet. Although this method provided reliable values, its application was limited to magnets with high degrees of alignment (〈cosθ〉 > 95 %), a restriction that was corrected by Quispe et al. (2020). Nevertheless, recent experiments have indicated that the magnetometry technique can introduce errors in texture assessment when the magnet presents high levels of coercivity. This work presents an approach that incorporates a correction factor into the magnetometry technique, accounting for the effect of the coercivity and circumventing this error source in texture assessment. The proposed methodology has been successfully applied to magnets with varying levels of coercivity.

Characterization of rolling bearing rotation and local defects exploiting their magnetic remanence

Rotational speed and defect monitoring are of crucial relevance for all the rotating machinery. Traditional sensors require to be mounted on or near the rotating bodies, exposing them to significant thermal and mechanical stress. In this work, a method has been developed to measure the angular velocity and to detect the presence of potential bearing defects from the analysis of the magnetic field generated by the residual magnetization of moving parts. To test such an approach, a dedicated experimental setup using a bare induction coil and a magnetoresistive device as separate sensing elements has been developed. This contactless technique provides reliable results and can achieve performance similar to or better than that of accelerometers, which are commonly used for this purpose. The presence of defects has been further assessed using white light interferometry. Finally, the results are discussed and compared with alternative techniques.

Biomagnetic monitoring of the spatial distribution of atmospheric particulate matter in an industrialized city in Japan: Case study at Muroran

<p>Japan has 111 active volcanoes, supplying a great amount of magnetically-enhanced fly ashes. Such fly ashes likely mask anthropogenic magnetic signals; therefore, only a few magnetic biomonitoring studies have been reported in active volcanic regions, including Japan. The environmental magnetic results are reported for the materials deposited on Sasa Kurilensis, also known as dwarf bamboo, in the vicinity of the industrialized Muroran city center in Japan. The dust on the ten leaves at 105 sites was wiped off with a commercial wipe sheet, and their rock magnetic properties were analyzed. Room- and low-temperature magnetic analyses indicate that the major magnetic mineral in the dust is partially oxidized magnetite, ranging from single to pseudo single domain size, and the magnetic mineralogy on the leaves’ surface remains consistent throughout the study area. Much higher saturation isothermal remanent magnetization intensities are observed in the city’s eastern parts. The dominant wind directions in Muroran city are northwest, indicating that the steel companies in the city center are the major source of the fine-grained magnetic minerals on the dwarf bamboo leaves. These results indicate that using the leaves of dwarf bamboo for magnetic biomonitoring can be a non-destructive and rapid method to study the spatial distribution of atmospheric particulate matter from local industrial activities, even in active volcanic areas.<strong></strong></p>

Investigation of structural, magnetic and morphological properties of Zinc and Cobalt-doped Nickel Ferrites

Abstract Nickel Ferrite nanocrystalline material doped with transition metal ions (Zn2+, Co2+) was obtained by chemical combustion method using respective nitrate hexahydrates and glycine as fuel. The phase purity of the prepared ceramic samples was ascertained using Powder X-ray diffraction (XRD) exhibiting an inverse cubic spinel structure with space group Fd 3 ‾ $\overline{\mathrm{3}}$ m. Lattice parameters follow the Vegard law, indicating a consistent lattice expansion. The formation of porous nanocrystalline ferrite was confirmed by Scanning Electron Microscopy (SEM) images and corroborated by Williamson-Hall analysis. Raman Spectroscopic analysis identified characteristic bands corresponding to vibrational modes of nickel ferrite (NiFe2O4) and revealed shifts in the peak position with doping by zinc (Zn) and cobalt (Co). Vibrating Sample magnetometry (VSM) analysis indicated varied magnetic behaviour with different dopants and concentrations highlighting the influence of cation substitution on magnetic properties. The specific saturation magnetization (M s ), remanent magnetization (M r ) and coercivity (H c ) are improved by the substitution of Zn2+ and Co2+ ions. This simple and cost-effective preparation technique holds promise for synthesizing high-quality nickel ferrite, which could find applications in magnetic and electronic devices.

Paleolatitudinal movements of the eastern Sakarya Zone from Jurassic to Eocene

The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

Magnetic properties of iron ores from two Ordovician deposits in Northern Portugal: Marão and Moncorvo

AbstractThe Vila Cova do Marão Mining Field (VCMF) and the Moncorvo Iron Complex (MIC) in northern Portugal are important geo-resources of iron. Here we provide a detailed characterisation of their mineralogy through petrographic observations and magnetic properties. Petrographic observations show the VCMF ore primarily consists of quartz, magnetite, and chlorite, while the MIC ore of hematite and quartz, with rare magnetite occurrences. The magnetic susceptibility (χ) of the VCMF host rock is ~ 2470 × 10⁻8 m3/kg, while the VCMF ore deposits have χ of ~ 20,500 × 10⁻8 m3/kg. MIC ores show lower χ values of 520–700 × 10⁻8 m3/kg. Isothermal Remanent Magnetisation (IRM) component unmixing of the VCMF host rock indicates that the magnetic population is represented by a single component with B1/2 of 45–55 mT and DP values 0.30–0.35 mT, respectively, typical of magnetite. The VCMF ore is characterised by a single component with B1/2 of 32–44 mT and DP of 0.30–0.35, typical of magnetite. The MIC ore shows two components: component 1 with B1/2 of 50 mT and DP values of 0.31–0.37 mT, typical of magnetite, and component 2 with B1/2 of 500 mT and DP of 0.19–0.26, typical of hematite. IRM at saturation (SIRM) of component 1 is 116–248 A/m for the host rock, 1100–2400 A/m for the VCMF samples, and 209–335 A/m for the MIC samples, providing an approximation of magnetite concentration. The Cisowski test shows the presence of strongly interacting single-domain particles (0.16 < R < 0.24) in all samples. Our data provides useful information for future iron ore resource exploration in the area.

Evaluation of the characteristics of ferrite garnet films for magneto-optical control of materials

A setup based on a polarization microscope was developed to study the characteristics of two types of ferrite-garnet films with the chemical composition Lu1.51Ho0.56Bi0.93Fe4.1Al0.9O12. The parameters of the hysteresis loop, values of residual magnetization, and the saturation field of the studied films were determined experimentally. The domain structure period was estab-lished, and a compact device for visualizing defects in steel samples was created. Using this device, a series of experiments were conducted on test samples with cracks of various sizes, and magneto-optical images of the cracks were obtained. The hysteresis loop of the two types of ferrite-garnet films was constructed in the “magnetiza-tion coefficient-magnetic field induction” coordinates. The magnetization coefficient was cal-culated based on the relative change in the area of bright and dark domains when the external magnetic field, directed perpendicular to the film plane, was varied. The efficiency of using two types of films, grown under different technological conditions but having the same chemical composition, in non-destructive testing methods was analyzed. It was found that the investigated films had the same domain period, but their residual magnetization and saturation field values varied significantly. Diagrams of the experimental setup and the developed device, as well as the characteristics of some of their components, are presented. To generate the magnetic field in the test samples, a coil wound on a U-shaped ferrite core was used, pressed against the sample surface on the opposite side relative to the crack location. The experiments were conducted under constant magnetic fields of varying intensity. The device was tested on specially prepared test samples with pre-grown cracks of known sizes. The tests demonstrated that films with higher residual magnetization and saturation field values were more sensitive to detecting defects such as enclosed cracks.

Room-temperature ferromagnetic MnGa nanoparticles in dilute magnetic semiconductor (Ga, Mn)As thin film: preparation and characterization

The GaAs based diluted magnetic semiconductor, (Ga, Mn)As, with the unique advantage of manipulating the spin and charge was widely investigated in the scientific community and considered as a potential material for the spintronic devices. However, its Curie temperature (Tc), which is limited to around 200 K, hinders the research progress of diluted magnetic semiconductors for potential device applications. Herein, we propose an approach to prepare the MnGa nanoparticles embedded in (Ga, Mn)As matrix using the magnetron sputtering deposition of Mn on GaAs surface, followed by the nano-second pulsed laser annealing (PLA), which gives aTcabove 400 K. We demonstrate that the MnGa nanoparticles are only formed in (Ga, Mn) As thin film during the nano-second PLA under a critical range of energy density (0.4-0.5 J cm-2). The highest achieved coercivity, saturation magnetization and remanent magnetization are 760 Oe, 11.3 emu cm-3and 9.6 emu cm-3, respectively. This method for preparing the hybrid system of ferromagnetic metal/dilute magnetic semiconductor builds a platform for exploring the interesting spin transport phenomenon and is promising for the application of spintronic devices.

Forensic-geology-based magnetic analysis of beach sediments from the Shimokita Peninsula, Japan.

The occurrences of various illegal activities on beaches require effective geological and environmental investigation methods. Among these methods, the room-temperature magnetic analysis of soils and sediments represents a nondestructive investigation method for various amounts, types, and grain sizes of magnetic minerals. Here, to verify the usefulness of magnetic analysis in forensic geology research, beach sediment samples from nine sites in the Shimokita Peninsula, Japan, were measured using magnetic analysis to determine the correlations between their concentration-dependent magnetic parameters and actual regional characteristics. The results revealed that the values of various parameters, namely the low-field magnetic susceptibility, anhysteretic remanent magnetization, and isothermal remanent magnetization (IRM), were relatively higher at sites near Ti and Fe sedimentary ore deposits. Further, thermomagnetometry results revealed that magnetite was the main magnetic carrier of the sediments. Moreover, pyrrhotite was detected around Ti-Fe mine sites. Furthermore, the results of the investigated parameters reflected the regional characteristics of the amount of magnetic minerals in the beach sediments. Low-temperature IRM curves and the magnetic grain size parameter also displayed sample-site-reflective characteristics. Thus, we believe that magnetic analysis represents an effective method for estimating the provenance of beach sediments in forensic geology research.

Magnetic diagnosis model for heavy metal pollution in beach sediments of Qingdao, China

Magnetic techniques have been widely used in recent decades to determine heavy metal pollution in sediments due to their high sensitivity to magnetic particles and considerable measurement convenience. Beaches are usually greatly influenced by human activities, but pollution problems such as heavy metal pollution due to sewage discharge, nearby factories, and garbage disposal have reduced the tourism value and ecological environmental quality of beaches. In this study, three beaches in Qingdao city were chosen as examples, and a magnetic diagnostic model for heavy metal pollution in beach sediments was established using statistical methods. The results showed that beach No. 1 in Qingdao was not polluted, while the pollution level of beach No. 2 was lower than that of beach No. 3. Beach No. 2 exhibited slight Cr and Zn pollution and slight Fe enrichment, while beach No. 3 exhibited slight to severe Cr, Ni, and Zn pollution and severe Fe enrichment. The statistical model results indicated that χ, saturation isothermal remanent magnetization (SIRM), SOFT, and χARM are more suitable for establishing magnetic diagnostic models, and the pollution level, pollution source and diffusion range of heavy metal elements could be detected with this model. The main causes of pollution are sewage outlets and the disposal of artificial coal ash. When the magnetic susceptibility value of the 0.063–0.125 mm particle size fraction of Qingdao beach sediments is greater than 6000 × 10−8 m3kg−1, attention should be given to possible contamination by heavy metals. In this study, we revealed that environmental magnetic methods can be employed to effectively determine the pollution level, source, and diffusion of heavy metals in beach sediments, which can facilitate the management of heavy metals and other pollutants in beach sediments and ecological environmental protection.

Biomagnetic Monitoring of Urban Pollution: The Case of Aburrá Valley, Colombia

This study aims to identify the most polluted areas and sites using the magnetic signal of ornamental plant leaves as an indicator of environmental pollution. Systematic sampling was conducted with 98 sampling sites described according to urban land use, such as road hierarchy and road surface, soil group, collected plant species, and municipality. The magnetic parameters analyzed were low- and high-frequency magnetic susceptibility and the isothermal remanent magnetization acquisition curves in order to calculate the magnetic enhancement factor. For the analysis of variance, a Kruskal–Wallis test was performed to compare urban land uses. Subsequently, the magnetic enhancement factor in dust and surface soil was used to prepare maps of environmental pollution for each urban area. Analyses of the different magnetic parameters of the dust deposited on leaves show that low-coercivity ferrimagnetic minerals dominated the magnetic signal, probably magnetite of anthropic origin, and were closely linked to vehicular traffic and, to a lesser extent, industrial activities.

Paleomagnetic study of Tres Vírgenes Volcanic Complex, Baja California, Mexico

While the great majority of paleomagnetic studies come from Central Mexico (Trans Mexican Volcanic Belt), still few works are available from Baja California peninsula. Twelve lava and domes from the Tres Vírgenes Volcanic Complex were sampled, and 96 standard paleomagnetic cores were analyzed. Available isotope ages range from 22 ka to 300 ka. Magnetic mineralogy analysis indicates that titanium-poor titanomagnetite is the main carrier of remanent magnetization, although some sites also contain Ti-rich titanomagnetites commonly observed in recent volcanic eruptions. Nine of the studied lavas yielded normal polarity magnetization with site mean declination ranging D=349°−28.1° and inclination I=32.4°−55.4° as expected for the Bruhnes chron. Mean paleodirections show remarkable coincidence with previously reported data from the nearby San Quintín volcanic field. The scatter parameter of the virtual geomagnetic poles SB=15.1213.8716.60 agrees, under uncertainties, with the latitude-dependent G Model of paleosecular variation for the Bruhnes chron. Both Thellier double heating and Tsunakawa-Shaw absolute paleointensity methods were applied, however, the success rate was relatively low with 4 reliable values ranging from 21.46μTto56.4μT. One of the lava domes that we dated at 253 ± 24 ka using the U-Th systematics demonstrated the worldwide observed Calabrian Ridge 0 short-lived geomagnetic event.

Iterative algorithm for computing magnetic field considering remanent magnetization and demagnetization

SUMMARY Efficient and high-precision methods for performing large-scale numerical calculations under high magnetic susceptibility conditions are essential for magnetic exploration applications. This paper proposes an algorithm for magnetic field modelling considering both demagnetization and remanent magnetization. The 3-D partial differential equation of magnetic potential is reduced to a 1-D ordinary differential equation in the space-wavenumber domain through a 2-D Fourier transform in the horizontal direction. Using the quadratic interpolation finite element method to obtain the pentagonal equation, the chasing method is used to solve the equation efficiently, and a contraction operator based on electromagnetic integral equation method is introduced to ensure stable iteration convergence. The validity of the algorithm was confirmed by comparing it with analytical solutions. Numerical examples demonstrate the importance of considering demagnetization under high magnetization conditions. Test results reveal that magnetic susceptibility is the sole factor affecting convergence among the factors examined. Further analysis showed that, for the same magnetic susceptibility, the algorithm converges with the same number of iterations and higher precision is achieved with an increasing number of nodes. Under the same grid configuration, higher magnetic susceptibility requires more iterations to converge and results in lower algorithm precision. The algorithm presented in this paper shows higher efficiency compared to those based on integral equations. Moreover, we demonstrate the algorithm's high accuracy when applied to models with anomalies near boundaries. Finally, the adaptability of the algorithm to complex geological models and undulating topography is verified by combining model tests with DEM data. This algorithm presents an efficient and high-precision method for magnetic field calculations under conditions of high susceptibility and strong remanent magnetization, offering promising prospects for geoscience applications.

Novel Mo: CoFe2O4 nanoparticles combustion synthesis for opto-magneto-electrochemical applications: A systematic analysis

In current work, various concentrations (0.0 wt%, 0.10 wt%, 0.25 wt%, 0.50 %,0.75 wt%, and 1 wt%) of Molybdenum (Mo) - doped cobalt ferrite (CFO) nanoparticles (Mo:CFO NPs) were synthesized using the flash combustion approach. The structural analysis of the prepared Mo:CFO was examined by the XRD patterns, and the obtained crystallite size 48.64, 46.72, 22.81, 21.05, 18.03, and 19.31 nm for 0.0 wt%, 0.10 wt%, 0.25 wt%, 0.50 wt%, 0.75 wt%, and 1 wt% Mo:CFO NPs, respectively. The presence of stoichiometry and homogeneity of the prepared Mo:CFO NPs was confirmed by the EDX analysis. The five phonon modes of the prepared Mo:CFO NPs were recorded by FT-Raman spectra, and the phonon modes were observed around 220, 312, 479, 624, and 685 cm−1 that corresponded o T2g(2), Eg, T2g(1), A1g(2), and A1g(1) symmetries, respectively. The grain sizes of the pure CFO and Mo:CFO NPs were evaluated using the images of scanning electron microscopy (SEM) and obtained in the range of 39–61 nm, respectively. The presence of valence states Co (2p), Fe (2p), O (1 s), and Mo (3d) in the prepared 1 wt% Mo:CFO NPs were examined by XPS spectra. The particle sizes ∼26.4 nm and ∼ 16.7 nm were obtained for pure CFO and 1 wt% Mo:CFO NPs using lognormal function fitting. The emission peaks at 445 ± 3, 521 ± 3, and 620 ± 2 nm in the PL spectra were observed by PL spectroscopy. The decrease in saturation magnetization Ms. (70.80–66.54 emu/g) and reduced remanent magnetization Mr. (24.22–18.64 emu/g) of prepared Mo: CFO NPs was observed in the MH analysis by SQUID analysis. The electrochemical study of Mo: CFO NPs (0.0 %, 0.25 %, 0.50 %, and 1.0 %) was done in a three-electrode assembly cell. The capacitance of values 650.0 Fg−1, 800.0 Fg-1, and 810.0 Fg−1 for pure CFO, 0.25 % Mo: CFO, and 0.50 % Mo: CFO were recorded in electrochemical analysis. The highest capacitance of 840.0 Fg−1 was observed for the electrode with 1.0 % Mo: CFO NPs. It was analyzed that the increase in CFO electrodes enhances their performance, and therefore, it can be utilized for multifunctional devices.

Integration by design: driving mineral system knowledge using multi-modal, collocated, scale-consistent characterisation

Abstract. Recent decades have seen an exponential rise in the application of machine learning in geoscience. However, fundamental differences distinguish geoscience data from most other data types. Geoscience datasets are typically multi-dimensional, and contain 1D (drill holes), 2D (maps or cross-sections), and 3D volumetric and point data (models/voxels). Geoscience data quality is a product of the data's resolution and the precision of the methods used to acquire them. The dimensionality, resolution, and precision of each layer within a geoscience dataset translate into limitations to the spatiality, scale, and uncertainty of resulting interpretations. Historically, geoscience datasets were overlaid cartographically to incorporate subjective, experience-driven knowledge and variances in scale and resolution. These nuances and limitations that underpin the reliability of automated interpretation are well understood by geoscientists but are rarely appropriately transferred to data science. For true integration of geoscience data, such issues cannot be overlooked without consequence. To apply data analytics to complex geoscience data (e.g. hydrothermal mineral systems) effectively, methodologies that characterise the system quantitatively at a common scale, using collocated analyses, should be sought. This paper provides research and exploration insights from an innovative district-wide, scale-integrated geoscience data project, which analysed 1590 samples from 23 mineral deposits and prospects across the Cloncurry district, Queensland, Australia. Nine different analytical techniques were used, including density, magnetic susceptibility, remanent magnetisation, anisotropy of magnetic susceptibility, radiometrics, conductivity, automated mineralogy based on scanning electron microscopy (SEM), geochemistry, and short-wave infrared (SWIR) hyperspectral data with 561 columns of scale-integrated data (+2151 columns of SWIR data). All data were collected on 2.2 cm × 2.5 cm sample cylinders, a scale at which the confidence in the coupling of data from techniques can be high. These data are integrated by design to eliminate the need to downscale coarser measurements via assumptions, inferences, inversions, and interpolations. This scale-consistent approach is critical to the quantitative characterisation of mineral systems and has numerous applications in mineral exploration, such as linking alteration paragenesis with structural controls and petrophysical zonation. The Cloncurry METAL dataset is made freely available via the AuScope Data Repository: https://doi.org/10.60623/82trleue (Austin et al., 2024).

Machine Learning-Enhanced Fabrication of Three-Dimensional Co-Pt Microstructures via Localized Electrochemical Deposition

This paper presents a novel method for fabricating three-dimensional (3D) microstructures of cobalt–platinum (Co-Pt) permanent magnets using a localized electrochemical deposition (LECD) technique. The method involves the use of an electrolyte and a micro-nozzle to control the deposition process. However, traditional methods face significant challenges in controlling the thickness and uniformity of deposition layers, particularly in the manufacturing of magnetic materials. To address these challenges, this paper proposes a method that integrates machine learning algorithms to optimize the electrochemical deposition parameters, achieving a Co:Pt atomic ratio of 50:50. This optimized ratio is crucial for enhancing the material’s magnetic properties. The Co-Pt microstructures fabricated exhibit high coercivity and remanence magnetization comparable to those of bulk Co-Pt magnets. Our machine learning framework provides a robust approach for optimizing complex material synthesis processes, enhancing control over deposition conditions, and achieving superior material properties. This method opens up new possibilities for the fabrication of 3D microstructures with complex shapes and structures, which could be useful in a variety of applications, including micro-electromechanical systems (MEMSs), micro-robots, and data storage devices.

High-resolution sedimentary cyclostratigraphy and astronomical signals in the Upper Ordovician of Southwest China

During the Late Ordovician, a series of significant biotic and geological events occurred globally and more specifically in South China. The development of a high-resolution orbital cyclostratigraphic framework and a precise radioisotope dating has greatly enhanced our understanding of the factors controlling these events. In this study, quantitative proxies for palaeo-water depths, derived from sedimentological analyses, serve as indicators for orbital cyclostratigraphic assessment.Relatively shallow-marine carbonates with well-developed shallowing-upward cycles were deposited in the western Yangtze Platform during the Late Ordovician. High-resolution geochronological data were obtained from high-precision isotope dilution thermal ionization mass spectrometry (ID-TIMS) zircon dating of K-bentonite beds at the studied section. This facilitated sedimentary facies and environmental analyses, as well as the recognition of sedimentary cycles. Based on mud content, bioclastic content, and laminations, four sedimentary facies, twelve sedimentary microfacies, and forty-eight shallowing-upward sedimentary cycles were identified in the Daduhe Formation.Through comparative time series analysis of depth rank, lime mudstone-calcareous mudstone binary data, non-carbonate content, and anhysteretic remanent magnetization (ARM), astronomical cycles and trends in sedimentation rates have been identified. This study confirms the reliability of radioisotope dating, establishing a 0.46 Myr duration for the Dicellograptus complexus graptolite biozone and a 0.96 Myr duration for the Paraorthograptus pacificus graptolite biozone, both with an empirical uncertainty of 0.1 Myr. This research proposes a reliable method for identifying astronomical cycles through high-precision sedimentary microfacies and cyclostratigraphy, in comparison with rock magnetic cyclostratigraphy studies.

Petrophysical cobalt exploration indicators in Kuusamo, northern Finland

The increasing global demand for cobalt, a critical green transition metal, encourages the development of improved exploration workflows, as Co typically occurs as a by-product of other metals, and the exploration and processing methods are rarely optimised for it. This paper investigates the possibility of extracting geophysical cobalt exploration indicators from petrophysical properties in Kuusamo, one of the most prominent cobalt-enriched areas in the largest European Co producer, Finland. The study region hosts 20 Au–Co deposits and occurrences classified as orogenic gold deposits with atypical metal association. Two separate mineralization stages have been distinguished: a pyrrhotite-dominated Co-stage and a pyrite-dominated Au–Co stage. The assumption in this study was that Co-enriched samples could be distinguished from Au-enriched samples and host rocks in petrophysical data due to the mineral associations. The investigation used an extensive previously acquired petrophysical and geochemical drill hole dataset from six targets complemented with new thermomagnetic data for magnetic mineral phase detection. The samples were divided into ore classes for the petrophysical data analysis. The results indicate that cobalt’s association with monoclinic pyrrhotite is a key factor for geophysical applications: the high remanent magnetisation characteristic of monoclinic pyrrhotite suggests that Co-enriched ores should typically associate with magnetic anomaly sources. Co enrichment is also related to higher electrical conductivities in comparison to Au. The workflow applied in this study illustrates how key petrophysical parameters can be connected with ore-bearing minerals and rocks, and the results indicate how cobalt could be explored more directly and effectively in the study area.

Size effects on the magnetic properties of a system of ε-Fe2O3 nanoparticles embedded in a SiO2 xerogel matrix

A representative series of samples consisting of fine ε-Fe2O3 nanoparticles uniformly distributed over the SiO2 xerogel matrix with an iron oxide content of 5–33 wt % has been synthesized and studied by mutually complementary physical methods. It has been shown by the X-ray diffractometry and high-resolution electron microscopy examination that, with increasing iron oxide concentration, the average particle size <d> increases from 4 to 11 nm. According to the X-ray diffractometry and Mӧssbauer spectroscopy data, the samples with an iron oxide content of 5–20 wt % are single-phase, while at the highest Fe2O3 concentration (33 wt %), the β-Fe2O3 and α-Fe2O3 phases arise. As the average particle size <d> increases, a monotonic increase in coercivity HC and remanent magnetization MR of the synthesized systems at room temperature is observed, which is indicative of their magnetic hysteresis. The magnetic transition known to occur in the ε–Fe2O3 oxide manifests itself in all the investigated samples as a drastic change in the HC and MR values at 150–75 K. At the same time, a thorough analysis of the temperature dependence of the real part of the ac magnetic susceptibility χ′ has shown that the particles with a size smaller than a critical value of dC ∼6.5 nm do not undergo the magnetic transition and have a much lower magnetic anisotropy constant as compared with coarser particles (d > dC). It has been found that, in the low-temperature region, the magnetic moments of these fine particles experience superparamagnetic blocking. It has been established that the size effects that arise in ultra-fine ε–Fe2O3 particles has a serious impact on the macroscopic magnetic properties of the highly dispersed systems based on them.