Remanent Magnetization Measurements Research Articles

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.

Multisensor Magnetic Scanning Microscope for Remanent Magnetic Field Measurements.

Magnetic Scanning Microscopy (MSM) emerged with the aim of allowing the visualization of magnetic fields of a sample or material through scanning and proved particularly useful for geology, biomedicine, characterization of magnetic materials, and in the steel industry. In this regard, the reading system of an MSM was modified using a μ-metal magnetic shielding structure to analyze remanent fields. The MSM was adapted to perform readings using two different types of sensors. The sensitive area of the sensors was evaluated, and the HQ-0811 (AKM-Asahi KaseiTM Microdevices) and STJ-010 (Micro MagneticsTM) sensors were chosen, with the HQ-0811 standardized on Printed Circuit Boards (PCBs) to facilitate handling and increase the system's robustness. In the shielded chamber, two piezoelectric ANC-150 stepper motors (Attocube Systems) were used, arranged planarly, to allow the movement of the analyzed samples under the mounted sensors. To acquire data from the sensors, the Precision Current Source Model 6220 and the Nanovoltmeter Model 2182A (both from Keithley) were used, along with Keithley's Delta-Mode integrated system. To analyze the system's effectiveness, three distinct samples were analyzed for calibration, and a MATLAB program was written to analyze the images and extract the material's magnetization. Additionally, a rock sample from the Parnaíba Basin was mapped to demonstrate the system's capabilities.

Inverse exchange bias and training effect in Gd2Co0.5Mn1.5O6 with negative magnetization

The present experiments indicate that the phenomena of inverse exchange bias and negative magnetization are observed simultaneously in Gd2Co0.5Mn1.5O6 below the ferrimagnetic compensation point Tcomp. The training effect confirms the intrinsic nature of the inverse exchange bias and reveals that the frozen spins relax more slowly than the rotatable spins according to the fitting of exchange bias field (HEB) vs cycle loops (n) curve. The amplitude of HEB varies inversely with the cooling field Hcool and the inverse exchange bias is found to remain up to 50 kOe. The observed exchange bias is argued to be due to the fact that the inverse ferromagnetic moments below Tcomp can be flipped by adjusting the amplitude or direction of the magnetic field during the M(H) hysteresis loop measurement. The manipulability of the negative magnetization state is demonstrated by the remanent magnetization and magnetic switching measurements.

Analysis of inhomogeneous magnetization using a spinner magnetometer

The assumption for measuring a discrete sample by spinner magnetometer in paleomagnetism is that the sample under study is a magnetic dipole so that the magnetization vector can be calculated by successive measurements of components along three orthogonal axes. This assumption may not hold for samples with inhomogeneous magnetization, irregular shape, or both, where non-dipole components are no longer ignorable. This study draws attention to their effect on the measurement of remanent magnetization based on an offset dipole model using multipole expansion of magnetic potential. Results from this model are compared with the experimental data measured by a new type of spinner magnetometer featured by high spatial resolution and the capability of measuring the fundamental wave component as well as the harmonic wave components. By using the relative amplitude of the harmonic waves to the fundamental wave, the contribution of non-dipole components can be quantified, leading to assessing how dipolar a sample is. The new analyses and instrumentation will be useful as a new diagnostic tool to obtain more reliable data from the samples collected from tectonically active regions with complicated geological histories.

Synthesis, structural and magnetic study of BaFe12O19/CoFe2O4@CoFe2 nanocomposites

Cooperative effects in hybrid nanocomposites are an interesting field of research. The behavior of magnetic nanocomposites is the result of spatial arrangements of phases and their magnetic correlations through exchange and dipolar forces. Understanding these influences is an important task in order to produce magnetic composites with improved properties. In this work, we present a study on the structural and magnetic properties of nanocomposites made of barium hexaferrite (BaFe12O19) coated either with cobalt ferrite spinel (CoFe2O4) or core-shell CoFe2O4@CoFe2 nanoparticles, i.e. BaFe12O19/CoFe2O4 or BaFe12O19/CoFe2O4@CoFe2. The BaFe12O19 (BFO) phase was produced using the ionic coordination reaction technique and then coated with CoFe2O4 (CFO) nanoparticles synthesized by the polyol method. Several concentrations of the BFO and CFO phases were considered. The BFO/CFO samples were reduced in hydrogen gas, where partial reductions of cobalt ferrite give rise to the alloy CoFe2 (CF). Thus, we produced a new nanocomposite of the type BFO/CFO@CF. These samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM) and Mössbauer spectroscopy (ME). The XRD and ME analyzes revealed the presence of the phases BFO and CFO, for the non-reduced nanocomposites, and for the partially reduced nanocomposites we found three phases BFO, CFO and CF. TEM images showed that these phases are structurally coupled. Isothermal remanent magnetization (IRM) and direct current remanent demagnetization (DCD) measurements were done and the analyzes through the Henkel and δm plots were performed, providing information about the nature of the interactions among the phases and their magnetic behavior. The samples BFO/CFO and BFO/CFO@CF with the lowest percentage of BFO (∼7 wt%) showed exchange coupling between the phases while the other samples exhibited predominantly magnetic dipolar interactions.

Origin of spin-glass-like magnetic anomaly in the superconducting and multiferroic spin ladder BaFe2Se3

The spin ladder system ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ presents puzzling magnetic behaviors, such as a spin-glass-like phase below $\ensuremath{\sim}50$ K. In this paper, an exchange bias effect with a large vertical shift in the field-cooled hysteresis loop is observed below 50 K. We also evidence the existence of uncompensated spins by susceptibility, magnetic remanence, and hysteresis loop measurements. The thermoremanent and isothermoremanent magnetization curves evidence a two-dimensional diluted antiferromagnet (DAFF) nature. Moreover, a nanometer-sized layered structure is observed by scanning electron microscope (SEM) and confirmed by scanning transmission electron microscope (STEM) coupled with electron energy loss spectroscopy (EELS). The discovery of exchange bias in antiferromagnetic ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ crystals adds a new dimension to the research of its superconducting and multiferroic properties.

Exchange coupling in SrFe12O19/CoFe2O4 composites: Effect of component proportions

(100-x)SrFe12O19/(x)CoFe2O4 composites were prepared by ball milling technique using different fractions of hexagonal and cubic ferrite powders as precursors, namely x = 10, 20, 30, 40 wt%. After grinding in a ball mill, as-prepared composites were annealed at 900 °C for 3 h. X-ray powder diffraction was carried out for structural analysis. Energy dispersive X-ray analysis allowed elemental analysis of the composites. Magnetic properties were studied at room temperature by magnetization versus applied external magnetic field, direct current demagnetization and isothermal remanence magnetization measurements. A relationship has been established between structural parameters (depending on the proportions of fractions of different crystallite size) and magnetic properties of the composites. Composite sample with 10 wt% CoFe2O4 reveals the highest energy product (BH)max = 10.9 kJ/m3, which is approximately 20 % higher than that of pristine SrFe12O19. The presence of the exchange coupling effect extracted from Henkel plots nicely explain the improved magnetic characteristics of composite.

SrFe12O19/CoFe2O4 magnetic composites: Nanoparticle size and effect of annealing temperature on magnetic properties

Nanostructured magnetic composites of hexagonal SrFe12O19 and cubic CoFe2O4 powders were prepared by ball milling technique varying the mean size of CoFe2O4 grains and using 80/20 mass ratio. Subsequently, the composites were divided into two series of distinct annealing conditions: i) at 1000 °C and ii) at temperature at which the corresponding CoFe2O4 phase was synthesized. X-ray powder diffraction was carried out for phase identification and structural analysis. Transmission electron microscopy and/or scanning electron microscopy were applied for morphological monitoring. Energy dispersive X -ray analysis allowed elemental analysis. Magnetic properties were studied at room temperature by magnetization versus the applied external magnetic field, direct current demagnetization and isothermal remanence magnetization measurements. A relation was established between the structural parameters of the composite and the magnetic properties, putting emphasis on the exchange coupling effect. Although the stored energy product for all the composites studied is lower than that of hexagonal SrFe12O19, a visible gain of remanence magnetization of selected composites is observed. In the first series of composites, the one made from the CoFe2O4 grains of the largest mean size exhibits the highest energy product, (BH)max = 9.5 kJ/m3. In the second series of composites the one thermally treated at 900 °C is magnetically the hardest, Hc = 3920 Oe.

Oriented Magnetite Inclusions in Plagioclase: Implications for the Anisotropy of Magnetic Remanence

AbstractMicron to sub‐micron sized ferromagnetic inclusions in rock forming silicate minerals may give rise to particularly stable remanent magnetizations. When a population of inclusions have a preferred crystallographic or shape orientation in a rock, the recorded paleomagnetic direction and intensity may be biased by magnetic anisotropy. To better understand this effect, we investigated plagioclase grains from oceanic gabbro dredged from the Mid‐Atlantic Ridge at 11°–17°N. The plagioclase grains contain abundant needle and lath shaped magnetite inclusions aligned along specific directions of the plagioclase lattice. Electron back scatter diffraction and anisotropy of magnetic remanence measurements are used to correlate the orientation distribution of the magnetite inclusions in the host plagioclase that contains multiple twin types (Manebach, Carlsbad, Albite, and Pericline) with the bulk magnetic anisotropy of the inclusion‐host assembly. In non‐modified plagioclase, the anisotropy ellipsoid of magnetic remanence has oblate shapes that parallels the plagioclase (010) plane. It is suggested that recrystallization of magnetite inclusions during hydrothermal overprint shifts the relative abundance of the inclusions pertaining to the different orientation classes. We show that the maximum axis of the anisotropy ellipsoid of magnetic remanence parallels the plagioclase [001] direction, which in turn controls the recorded remanent magnetization direction. Our results are relevant for paleointensity and paleodirection determinations and for the interpretation of magnetic fabrics.

3D Joint Inversion of Scanning Magnetic Microscopy Data

AbstractScanning magnetic microscopy (SMM) is a modern magnetometry technique that maps the magnetic anomalies resulting from small‐scale variations of remanent magnetization within a sample. This information is vital to understand the origin of rock behavior in laboratory experiments and in larger scale magnetic surveys. To quantify the fine‐scale remanent magnetization, we used 3D magnetic vector inversion to jointly invert SMM data collected both above and below a 5 mm‐thick norite sample from the Bjerkreim‐Sokndal layered intrusion in South Norway. The sample is from an area with a striking remanent aeromagnetic anomaly which shows a minimum of −13,000 nT below background in the high‐resolution helicopter survey. Inversion results confirm bulk remanent magnetization measurements with calculated median magnetization intensities between 79 and 106 A/m and a strong preferred magnetization direction perpendicular to the slab plane. Furthermore, results indicate that the main source of natural remanent magnetization is in the pyroxenes.

Variation in the concentration and regional distribution of magnetic nanoparticles in human brains, with and without Alzheimer\u2019s disease, from the UK

The presence of magnetic nanoparticles (MNPs) in the human brain was attributed until recently to endogenous formation; associated with a putative navigational sense, or with pathological mishandling of brain iron within senile plaques. Conversely, an exogenous, high-temperature source of brain MNPs has been newly identified, based on their variable sizes/concentrations, rounded shapes/surface crystallites, and co-association with non-physiological metals (e.g., platinum, cobalt). Here, we examined the concentration and regional distribution of brain magnetite/maghemite, by magnetic remanence measurements of 147 samples of fresh/frozen tissues, from Alzheimer’s disease (AD) and pathologically-unremarkable brains (80–98 years at death) from the Manchester Brain Bank (MBB), UK. The magnetite/maghemite concentrations varied between individual cases, and different brain regions, with no significant difference between the AD and non-AD cases. Similarly, all the elderly MBB brains contain varying concentrations of non-physiological metals (e.g. lead, cerium), suggesting universal incursion of environmentally-sourced particles, likely across the geriatric blood–brain barrier (BBB). Cerebellar Manchester samples contained significantly lower (~ 9×) ferrimagnetic content compared with those from a young (29 years ave.), neurologically-damaged Mexico City cohort. Investigation of younger, variably-exposed cohorts, prior to loss of BBB integrity, seems essential to understand early brain impacts of exposure to exogenous magnetite/maghemite and other metal-rich pollution particles.

Structural, optical and magnetic properties of α- and β-MnO2 nanorods

Herein, we synthesise various polymorphs of MnO2 through hydrothermal technique. Formation of pure tetragonal structured α-, β- and mixture of α and β phase of MnO2are identified through Fourier transform infrared spectroscopy (FTIR) and X-Ray diffraction (XRD).Rietveld refinement reviles 73% of α-MnO2 and 27% of β-MnO2 present in αβ-MnO2. From Field emission scanning electron micrographs (FESEM), average diameter of α- and β-MnO2nanorods is found to be 36 nm and 23 nm, respectively, while in αβ-MnO2, nanorods of two different sizes, 28 and 116 nm are observed. Among all polymorphs, small size of nanorods in β-MnO2 results high specific capacitance. Through UV–visible absorption spectra, the optical band gap of α-, β- and αβ-MnO2nanorods are estimated to be 1.53, 1.30 and 1.45 eV, respectively. XPS confirms the presence of large concentration of Mn3+ in α- and αβ-MnO2 nanorods results high effective magnetic moment in comparison to the theoretical one which is almost same in β-MnO2. Henceforth, we evaluate the accurate composition of MnO2 as α-MnO1.48, β-MnO1.86 and αβ-MnO1.15. Spin-glass/cluster-glass behavior is confirmed from ac susceptibility and remanent magnetization measurements in β-MnO2and αβ-MnO2which is absent in α-MnO2 depending on a critical concentration of Mn3+ions.

Prolific shedding of magnetite nanoparticles from banknote surfaces

Here, we use magnetic methods first to quantify the content of strongly magnetic particles of banknotes (US dollars, USD, and British pounds sterling, GBP), and then examine the possibility of their release from handled banknote surfaces. The content of magnetic particles, from magnetic remanence measurements, for the USD and paper GBP banknotes is high; greater, for example, than that in vehicle engine-exhaust emissions, and similar to that for airborne roadside particulate matter (PM). Our magnetic analyses of USD and GBP banknotes, and of the ink pigment widely used in their printing, reveal not only that the banknotes are highly magnetic, but also that strongly magnetic, nano-sized particles are readily and prolifically shed from their surfaces (especially from the USD banknotes). A common practice, prior to increased automation, was for bank tellers to count banknotes by licking a finger to adhere to each successive counted note, and thus speed up the manual counting process. Given the rate of particle shedding reported here, this traditional manual counting procedure must have resulted in prolific transfer of iron-rich nanoparticles both to the fingers and thence to the tongue. We hypothesise that, pre-automation, magnetite and other metal-bearing nanoparticles were repetitively and frequently ingested by bank tellers, and subsequently entered the brain directly via the taste nerve pathway, and/or indirectly via the systemic circulation and the neuroenteric system. This hypothesis may plausibly account for the reported and currently unexplained association between elevated neurodegeneration-related mortality odds ratios and this specific occupation.

Spin glass effects in the (Cr84Re16)99.6Mn0.4 alloy

The possible existence of the spin glass (SG) state in the (Cr84Re16)99.6Mn0.4 alloy was investigated using magnetisation measurements. The temperature dependence of magnetisation, M(T), indicated a splitting of the M(T) data in the zero-field-cooled (ZFC) and field-cooled (FC) curves at the pinning temperature, Tp which is an indication of magnetic anisotropy in the system. The (Cr84Re16)99.6Mn0.4 alloy showed time dependence of isothermal remanent magnetisation (IRM) measurements, which is a signature associated with canonical SG. Measurement of field dependence of magnetisation did not show saturation at the lowest temperature or highest magnetic field because of the lack of long-range magnetic ordering which is also a SG signature. Preliminary measurements indicate the possible existence of magnetic frustration leading to the SG state in the (Cr84Re16)99.6Mn0.4 alloy.

Magnetism of Body‐Centered Cubic Fe‐Ni Alloys Under Pressure: Strain‐Enhanced Ferromagnetism at the Phase Transitions

AbstractWe investigated the magnetism of body‐centered cubic (bcc) FeNi alloys (Fe92Ni08, Fe87Ni13, and Fe84Ni16) as a function of pressure at room temperature through the bcc to hexagonal closed packed (hcp) phase transition. In each case, the fully saturated magnetic remanence attained maxima, 3–6 times higher than the initial value, at the hysteretic bcc → hcp and hcp → bcc transition boundaries upon compression and decompression. Magnetization maxima generally shifted to lower pressures with increasing Ni, concurrent with the phase transition. In Fe84Ni16, X‐ray magnetic circular dichroism (XMCD) at the K‐edge of Fe measured in a 2.5 T field together with X‐ray absorption spectroscopy indicate that the magnetism defined by XMCD divided by the proportion of bcc also attains a maximum in the transition regions, similar to the magnetic remanence measurements. Enhanced remanence is attributed to a lattice mismatch between bcc‐Fe and hcp‐Fe phases together with defect‐riddled martensite. This mechanism also explains why the remanence of bcc FeNi is 2–4 times stronger at full decompression than initially, which bears on the interpretation of paleointensity records of meteorites containing bcc FeNi alloys (kamacite). Only techniques that probe magnetic states carried out in fully saturating external fields detect magnetic signals in bcc‐Fe residing in the hcp stability region, thereby explaining the discrepancy among the experimental results. How far in pressure bcc‐Fe persists into the hcp stability field, especially at elevated temperatures, remains open.

Evergreen Needle Magnetization as a Proxy for Particulate Matter Pollution in Urban Environments.

We test the use of magnetic measurements of evergreen needles as a proxy for particulate matter pollution in Salt Lake City, Utah. Measurements of saturation isothermal remanent magnetization indicate needle magnetization increases with increased air pollution. Needle magnetization shows a high degree of spatial variability with the largest increases in magnetization near roadways. Results from our magnetic measurements are corroborated by scanning electron microscopy of needle surfaces and by inductively coupled plasma mass spectrometry of metal concentrations in residues collected from sampled needles. Low‐temperature magnetic analysis suggests the presence of small (<20 nm) partially oxidized magnetite particles on needles collected adjacent to a major roadway. Magnetization may be a low‐cost proxy for certain metal concentrations (including lead) during periods of increased particulate pollution. The spatial resolution of our method appears capable of resolving changes in ambient particulate matter pollution on the scale of tens to hundreds of meters. Questions remain regarding the timescales over which evergreen needles retain particulate matter accumulated during atmospheric inversion events in Salt Lake City. Results presented here corroborate previous studies that found needle magnetization is a fast, cost‐effective measure of particulate matter pollution. This method has the potential to provide high spatial resolution maps of biomagnetically monitored particulate matter in polluted urban environments year‐round.

Consequences of switching field angular dependence for applications of anhysteretic remanent magnetization

The measurement of anhysteretic remanent magnetization (ARM) is an easy nondestructive means of evaluating many important rock properties. This involves applying an alternating magnetic field (AF) along with a direct biasing field (DF) to magnetize rock samples. Various techniques employing ARM have been widely used with notable success to help solve problems in tectonics, volcanology, sedimentology, environmental and paleoclimate studies and to better understand geomagnetic field behavior. Often, however, too little attention is paid to the effects of switching field angular dependence, which has important influence on the coercivity and angular distributions of grains that actually carry the ARM. As a result, commonplace methods of ARM measurement are not ideally designed for their intended purposes. For example, differentiation of a progressive ARM acquisition or turning on the direct field within a narrow AF window (i.e. partial ARM) are unable to isolate the ARM contribution from a specified coercivity grain fraction. Instead, the optimal method of measuring ARM in a targeted coercivity grain fraction is to differentiate a progressive tumble demagnetization of a total ARM generated with a peak AF high enough to fully activate the coercivity range of interest. Ignoring the activation property can lead to overestimation of relative paleointensity, underestimation of high coercivity grain concentrations, amplification of ARM anisotropy (e.g. error in natural remanence corrections), and unwanted mixing of anisotropy fabric components held in separate coercivity grain fractions.

Soil and dust magnetism in semi-urban area Truskavets, Ukraine

The objective of this paper was to study pollution in the semi-urban area of Truskavets (Ukraine) using low-cost and energy-efficient magnetic measurements. Soil magnetic properties were measured near a railway station (transect) and near a road (transect and grid). To compare the magnetic properties of the soils from the urban areas, we sampled in a forest area located 2–3 km from Truskavets. Additionally, ten dust samples were taken 150 cm above the ground from the smooth surface of the tree bark. Near the Stebnyk Ring (the end of the second transect), we established a grid (20 × 20 m) and measured the soil magnetic susceptibility MS (mass-specific χ, and volume κ). There were taken 55 soil samples within the upper 0–5 cm of the topsoil. The results showed that low-frequency MS of the natural soil was within the range of 8–10 × 10–8 m3/kg, a low value for the Ukraine soils. The urban soils collected near the roadway and the railway had high MS values. Soil pollution was confirmed by the frequency dependence of magnetic susceptibility: χfd = 2–3%. Our results, based on the thermomagnetic, hysteresis, isothermal (IRM), and anhysteretic remanent magnetization (ARM) measurements, suggested that magnetite is responsible for the increase in the magnetic signal of the urban soils. Natural soils normally contain a single domain (SD) grains. It has also been found that the high coercivity haematite and goethite are stable pedogenic minerals in the Truskavets natural soil. Overall, the magnetic measurements have proven to be a rapid, low cost, non-destructive and efficient technique for soil monitoring and air quality assessment.

Room temperature exchange bias in antiferromagnetic composite BiFeO3-TbMnO3

The magnetic property of a 0.7BiFeO3-0.3TbMnO3 composite has been studied in detail and compared with that of 0.8BiFeO3-0.2TbMnO3. The magnetic properties in 0.7BiFeO3-0.3TbMnO3 are improved in manifold compared to BiFeO3. An exchange bias (HEB) is observed in both the compositions of these antiferromagnetic composites, which varies between 5 and 180 Oe with a maximum at ∼275 K. Isothermal remanent magnetization measurements at room temperature indicate the presence of an interfacial layer of a 2-dimensional dilute uniaxial antiferromagnet in a uniform magnetic field (2D DAFF). The presence of exchange bias can be explained on the basis of a strong strain-mediated magnetoelectric coupling induced exchange interaction and the creation of a 2D DAFF layer at the interface. The properties of this layer are defined by canting and pinning of BiFeO3 spins at the interface with TbMnO3 due to Fe and Mn interaction. X-ray magnetic circular dichroism confirms the presence of canted antiferromagnetic ordering of BiFeO3, charge transfer between Mn ions, and different magnetically coupled layers that play a vital role in the exchange bias.

Diagenesis of magnetic minerals at the Southwest Pacific DSDP Site 277

ABSTRACTWe present a paleomagnetic and rock magnetic record from a 465.2 m long drill core recovered at DSDP Site 277 in the Southwest Pacific. Our study sought to construct a magnetostratigraphy and thus enable further paleoenvironmental work on this sedimentary succession. Magnetic remanence measurements revealed a stable magnetisation in the upper 34.8 m and lower 58.7 m of the core. However, between 34.8 and 397.5 m sediments are very weakly magnetised, do not carry a stable magnetisation, and rock magnetic analyses revealed a lack of remanence carrying minerals in this interval. We suggest that during the period spanning Paleocene to Oligocene sufficiently high organic matter (reagents) accumulation resulted in complete reduction and dissolution of ferri/ferromagnetic grains.