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Magnetite is an iron oxide found in rocks. Its magnetic properties are used for paleoclimatic reconstructions. It can also be synthesized in the laboratory to exploit its magnetic properties for bio- and nanotechnological applications. However, although the magnetic properties depend on particle size in a well-understood manner, they also depend on the structure of the oxide, because magnetite oxidizes to maghemite under environmental conditions. The dynamics of this process have not been well described. Here, a study of the alteration of magnetite particles of different sizes as a function of their storage conditions is presented. Smaller nanoparticles are shown to oxidize more rapidly than larger ones, and that the lower the storage temperature, the lower the measured oxidation. In addition, the magnetic properties of the altered particles are not decreased dramatically, thus suggesting that this alteration will not impact the use of such nanoparticles as medical carriers., ChemPlusChem, 79 (8), ISSN:2192-6506

Comparison of the paleomagnetic pole positions of late Paleozoic secondary magnetizations with a time-averaged reference apparent polar wander path for North America shows that sedimentary rocks within the central Appalachians were remagnetized in the later half of the Permian, between ca. 255 and 275 Ma. Ages of remagnetization do not vary for sites distributed along or across strike of the central Appalachian fold and thrust belt or across the Appalachian Plateau in New York, nor do they vary with stratigraphic position of the host rocks. However, the pattern of folding relative to remagnetization across the Valley and Ridge and Great Valley in Pennsylvania, Maryland, and West Virginia shows a distinct temporal variation. Individual fold tests yield postfolding magnetizations near the hinterland margin of the fold and thrust belt, synfolding magnetizations in the central part of the belt, and prefolding magnetizations near the foreland. Because of the similar age of the late Paleozoic magnetization, we conclude that rocks across the central Appalachians were remagnetized in a relatively short period of time as folding and thrusting propagated more slowly toward the foreland. We interpret this pattern to indicate that older folds near the hinterland grew prior to remagnetization, folds in the central region grew during remagnetization, and folds near the foreland grew after remagnetization. Rapid remagnetization relative to folding is also evident from the physical characteristics and magnetic properties of secondary hematite in remagnetized (synfolding) folds. In such folds, rocks were apparently remagnetized during an increment of fold growth, in which there was partial and possibly negligible fold-limb rotation. Collectively, these results may constrain the mechanism for basinal fluid mobilization during deformation. Current models for remagnetization involve the migration of chemically active brines into the foreland during tectonism. If realistic, our results bear on this model by suggesting that brine migration was not directly related to the successive emplacement of individual thrust sheets, as has been suggested for other fold and thrust belts.

For a broad range of values of magnetic monopole mass and charge, the abundance of monopoles trapped inside the Earth would be expected to be enhanced in the mantle beneath the geomagnetic poles. A search for magnetic monopoles was conducted using the signature of an induced persistent current following the passage of igneous rock samples through a SQUID-based magnetometer. A total of 24.6 kg of rocks from various selected sites, among which 23.4 kg are mantle-derived rocks from the Arctic and Antarctic areas, was analysed. No monopoles were found and a 90% confidence level upper limit of $9.8\cdot 10^{-5}$/gram is set on the monopole density in the search samples., 6 pages with references, 1 table, 1 figure

In order to understand mechanisms that maintain and drive the evolution of the Earthʼs magnetic field, a characterization of its behavior on time scales of centuries to millennia is required. We have conducted a search for periodicities in Holocene sediment magnetic records, by applying three techniques: multitaper spectral estimation, wavelet analysis and empirical mode decomposition. When records are grouped according to their geographical locations, we find encouraging consistency amongst the observed periods, especially in nearby inclination records. No evidence was obtained for discrete, globally observed, periods. Rather we find a continuous broadband spectrum, with a slope corresponding to a power law with exponent of − 2.3 ± 0.6 for the period range between 300 and 4000 yr. This is consistent with the hypothesis that chaotic convection in the outer core drives the majority of secular variation.

The magnetic anisotropy of Devonian black shale samples was measured from two cores drilled in the Appalachian Plateau. The mineralogy of the shales is predominantly clay, with small quantities of quartz and minor amounts of opaques and chlorite. Magnetite is the predominant ferromagnetic mineral present in the samples. The magnetic fabric was measured at both room temperature and liquid-nitrogen temperature and is dominated by a well-defined bedding (vertical) compaction and a lesser defined magnetic lineation. Measurements of the anisotropy of magnetic susceptibility (AMS) at liquid-nitrogen temperature, which enhances the paramagnetic contribution in the rock, showed a strong increase in both the bulk susceptibility and susceptibility differences. This increase suggests that the AMS is controlled by the paramagnetic minerals, particularly the clays and chlorite. Strain was measured from the orientation of basal planes of the chlorite crystals by texture goniometry. Good correlations have been found (1) between the orientation of the magnetic lineation and the long axes of the chlorite crystals, and (2) between the degree of magnetic foliation and the amount of vertical compaction. The magnetic lineation also agrees well with the direction of seismic anisotropy over the Plateau. The anisotropy of the anhysteretic remanence, which expresses the anisotropy due to the ferromagnetic component in the rocks, shows a weaker correlation with the amount of vertical compaction. A weak magnetic lineation suggests that the magnetite grains were aligned during a deformation phase which post-dates the main Alleghanian orogeny. The magnetic anisotropy of the Devonian shales mirrors the compaction and tectonic fabric on the Appalachian Plateau.

A stimuli-responsive material is synthesized that combines the actuation potential of liquid-crystalline elastomers with the anisotropic magnetic properties of ellipsoidal iron oxide nanoparticles. The resulting nanocomposite exhibits unique shape-memory features with magnetic information, which can be reversibly stored and erased via parameters typical of soft materials, such as high deformations, low stresses, and liquid-crystalline smectic-isotropic transition temperatures.

[1] Sediment and archeomagnetic data spanning the Holocene enable us to reconstruct the evolution of the geomagnetic field on time scales of centuries to millennia. In global field modeling the reliability of data is taken into account by weighting according to uncertainty estimates. Uncertainties in sediment magnetic records arise from (1) imperfections in the paleomagnetic recording processes, (2) coring and (sub) sampling methods, (3) adopted averaging procedures, and (4) uncertainties in the age-depth models. We take a step toward improved uncertainty estimates by performing a comprehensive statistical analysis of the available global database of Holocene magnetic records. Smoothing spline models that capture the robust aspects of individual records are derived. This involves a cross-validation approach, based on an absolute deviation measure of misfit, to determine the smoothing parameter for each spline model, together with the use of a minimum smoothing time derived from the sedimentation rate and assumed lock-in depth. Departures from the spline models provide information concerning the random variability in each record. Temporal resolution analysis reveals that 50% of the records have smoothing times between 80 and 250 years. We also perform comparisons among the sediment magnetic records and archeomagnetic data, as well as with predictions from the global historical and archeomagnetic field models. Combining these approaches, we arrive at individual uncertainty estimates for each sediment record. These range from 2.5° to 11.2° (median: 5.9°; interquartile range: 5.4° to 7.2°) for inclination, 4.1° to 46.9° (median: 13.4°; interquartile range: 11.4° to 18.9°) for relative declination, and 0.59 to 1.32 (median: 0.93; interquartile range: 0.86 to 1.01) for standardized relative paleointensity. These values suggest that uncertainties may have been underestimated in previous studies. No compelling evidence for systematic inclination shallowing is obtained from the analysis of the available database of Holocene sediment magnetic records. The analysis highlights the importance of collecting oriented cores, publishing and archiving unprocessed raw paleosecular variation determinations, and presenting a detailed chronology so that changes in the sedimentation rate can be assessed. With regard to future field models, workers should consider rejection of anomalous cores through comparisons to other sources and ensure that realistically large uncertainties are allocated to high-latitude declination records.

Hybrid magnetic/plasmonic nanoparticles possess properties originating from each individual material. Such properties are beneficial for biological applications including bio-imaging, targeted drug delivery, in vivo diagnosis and therapy. Limitations regarding their stability and toxicity, however, challenge their safe use. Here, the one-step flame synthesis of composite SiO2-coated Ag/Fe2O3 nanoparticles is demonstrated. The hermetic SiO2 coating does not influence the morphology, the superparamagnetic properties of the iron oxide particles and the plasmonic optical properties of the silver particles. Therefore, the hybrid SiO2-coated Ag/Fe2O3 nanoparticles exhibit desired properties for their employment in bio-applications.

If produced in high energy particle collisions at the LHC, magnetic monopoles could stop in material surrounding the interaction points. Obsolete parts of the beam pipe near the CMS interaction region, which were exposed to the products of pp and heavy ion collisions, were analysed using a SQUID-based magnetometer. The purpose of this work is to quantify the performance of the magnetometer in the context of a monopole search using a small set of samples of accelerator material ahead of the 2013 shutdown., The European Physical Journal C, 72 (12), ISSN:1434-6044, ISSN:1434-6052

Late Paleozoic remagnetizations of central Appalachian clastic and carbonate rocks of Ordovician to Devonian age constrain the structural evolution of the Pennsylvania salient. New paleomagnetic results from 26 sites located on nine folds combined with previously published results from 60 sites yield a mean direction for the northeastern limb of the salient at 172°/1° ( k = 49) and a mean direction for sites southwest of the salient at 173°/1° ( k = 70). These two directions are not statistically different from each other and are not significantly rotated from the expected Permian paleomagnetic direction for North America. Individual fold test results show that this secondary magnetization is synchronous with or even older than folding across the region. These paleomagnetic results suggest that curvature of fold axes around the salient is an original feature of fold growth and not the result of post-orogenic oroclinal bending. In contrast, analysis of the primary magnetization in the Silurian Bloomsburg Formation shows that directions from the two limbs of the salient are significantly different. New results from twenty sites yield a mean direction for the northeastern limb at 4°/−40° ( k = 31), and for the southwestern limb at 338°/ − 8° ( k = 23). Combining these results with previously published directions from the Bloomsburg Formation yields a mean direction for the northeastern limb at 1°/−34° ( k = 32) and for the southeastern limb at 343°/34° ( k = 30). The difference in declination does not appear to be the result of internal deformation of the rocks or acquisition of magnetization during a period of rapid apparent polar wander. Rather, these directions indicate that the northeastern limb has been rotated clockwise 18 ± 9° relative to the southwestern limb. The sense and amount of this rotation is consistent with the curvature of the orogen around the salient. However, within each limb of the salient the primary component declinations do not directly correlate with the orientation of the first-order fold axes. Collectively therefore, these paleomagnetic results suggest that the structural evolution of the salient included pre-orogenic rotations or rotations that occurred early in the Alleghanian orogeny followed by later remagnetization and folding of the central Appalachian foreland.

Identification of the mineral remains of magnetotactic bacteria (MTB), known as magnetofossils, is of particular interest because their occurrence can be used for environmental and climatic reconstructions. Single-domain magnetite particles, which are biomineralized in the cell body of MTB, have characteristic properties that can be used to detect their fossil remains. Acquisition of anhysteretic and isothermal remanent magnetization (ARM and IRM), first-order reversal curve (FORC) diagrams, and ferromagnetic resonance (FMR) spectra were used to detect the magnetic mineral inventory in Holocene lake sediments. A comparative analysis in terms of the discriminatory power of these methods is presented. The FORC diagrams contain two distinct features: a sharp horizontal ridge centered on the horizontal axis Bc and a feature with symmetric spread along the vertical Bb axis. The coercivity spectra derived from the central ridge coincides with that derived from ARM and IRM acquisition curves and is compatible with the presence of noninteracting linear chains of single-domain magnetite. The second feature on FORC diagrams is indicative of interacting particles in clusters. In the FMR spectra from bulk sediment, two populations are separated empirically based on the FORC information. An asymmetric signal is taken to describe the population, which contains single-domain particles in clusters. Empirical spectral separation of this contribution results in FMR spectra that are similar to those of intact MTB, which strongly suggests that a fraction of linear magnetosome chains is present. Combination of FMR and FORC results demonstrates the strong potential of these methods for identifying magnetofossils, based on alignment and interaction patterns of magnetic particles.

The structure of columnar-jointed lava flows and intrusions has fascinated people for centuries and numerous hypotheses on the mechanisms of formation of columnar jointing have been proposed. In cross-section, weakly developed semicircular internal structures are a near ubiquitous feature of basalt columns. Here we propose a melt-migration model, driven by crystallization and a coeval specific volume decrease inside cooling and solidifying columns, which can explain the observed macroscopic features in columnar-jointed basalts. We study basalts from Hrepphólar (Iceland), combining macroscopic observations, detailed petrography, thermodynamic and rheological modelling of crystallization sequences, and Anisotropy of Magnetic Susceptibility (AMS) of late crystallizing phases (that is, titanomagnetite). These are all consistent with our proposed model, which also suggests that melt-migration features are more likely to develop in certain evolved basaltic lava flows (with early saturation of titanomagnetite), and that the redistribution of melt within individual columns can modify cooling processes.

Hybrid plasmonic-magnetic nanoparticles possess properties that are attractive in bioimaging, targeted drug delivery, in vivo diagnosis and therapy. The stability and toxicity, however, of such nanoparticles challenge their safe use today. Here, biocompatible, SiO2-coated, Janus-like Ag/Fe2O3 nanoparticles are prepared by one-step, scalable flame aerosol technology. A nanothin SiO2 shell around these multifunctional nanoparticles leaves intact their morphology, magnetic and plasmonic properties but minimizes the release of toxic Ag+ ions from the nanosilver surface and its direct contact with live cells. Furthermore, this silica shell hinders flocculation and allows for easy dispersion of such nanoparticles in aqueous and biological buffer (PBS) solutions without any extra functionalization step. As a result, these hybrid particles exhibited no cytotoxicity during bioimaging and remained stable in suspension with no signs of agglomeration and sedimentation or settling. Their performance as biomarkers was explored by selectively binding them with live tagged Raji and HeLa cells enabling their detection under dark-filed illumination. Therefore, these SiO2-coated Ag/Fe2O3 nanoparticles do not exhibit the limiting physical properties of each individual component but retain their desired functionalities facilitating thus, the safe use of such hybrid nanoparticles in bio-applications.

Magnetic properties of particles are generally determined from randomly oriented ensembles and the influence of the particle orientation on the magnetic response is neglected. Here, we report on the magnetic characterization of anisotropic spindle-type hematite particles. The easy axis of magnetization is within the basal plane of hematite, which is oriented perpendicular to the spindle axis. Two standard synthesis routes are compared and the effects of silica coating and particle orientation on the magnetic properties are investigated. Depending on the synthesis route we find fundamentally different magnetic behavior compatible with either single domain particles or superparamagnetic sub-units. Furthermore, we show that silica coating reduces the mean blocking temperature to nearly room temperature. The mechanical stress induced by the silica coating appears to reduce the magnetic coupling between the sub-units.

The crystal symmetry of hematite in the basal plane predicts three easy magnetization axes for the sublattice spin orientation above the Morin transition. Spin canting then leads to three preferred magnetization axes perpendicular to these easy axes. By combining detailed crystallographic orientation by EBSD measurements with dense magnetic hysteresis and remanence curves as a function of rotation angle, the relation between crystallography and magnetic properties has been experimentally verified for the basal plane of a natural hematite crystal. The measurements lead to a better understanding of the interplay between spin canting, remanence and magnetic susceptibility at different field strengths. The measurement results coincide qualitatively with theoretical predictions, and provide experimental evidence for quantitative evaluation by more complex micromagnetic modeling.

A differential effective medium (DEM) model is used to predict elastic properties for a set of porous and anisotropic aggregates, comprised of mixtures of calcite and muscovite. The DEM takes into consideration an anisotropic background medium with triclinic or higher symmetry, in which inclusions of idealized ellipsoidal shape are added incrementally. In general, the calculated elastic properties of a solid that contains inclusions representing "dry" pores/cracks are strongly dependent on the orientation and aspect ratio of the inclusions. Aspect ratios of inclusions in the synthetic aggregates, which consist of air-filled pores, are estimated from anisotropy of magnetic susceptibility (AMS) of samples whose pore space has been impregnated with a colloidal ferrofluid. The AMS derived pore shape geometry is used as an input value for inclusions in the DEM. Modeling results are compared with laboratory determined elastic properties, measured with ultrasonic waves. Calculated shear wave velocities agree in general well with laboratory measured S wave velocities, whereas calculated P wave velocities are typically 0.5-1.1 km/s higher than measured values. Differences between calculated and measured P wave velocities are attributed mainly to incomplete and biased ferrofluid saturation of pores. Spherical pores are preferably filled during imbibition, in comparison to thin cracks, which leads to overprediction of the calculated P wave velocities. The amount of ferrofluid that fills the pore space is dependent on the ratio of calcite to muscovite and the load used for compaction during sample synthesis. The permeability decreases with increasing muscovite content and increasing compaction load. Incomplete saturation of samples with high-muscovite content is confirmed by X-ray microtomography density contrast imaging of dry and ferrofluid saturated specimens.

SUMMARY In recent years remagnetization of orogenic belts has been explained by fluid migration through rocks undergoing deformation. A laboratory study of remagnetization is presented in which varying amounts of iron (0-13.5 weight per cent Fe,O,) are adsorbed onto smectite surfaces. All smectite samples contain structural Fe (111) which is located in octahedral sites and is thermally stable up to 700°C. An increase in the amount of iron adsorbed onto the clay surface leads to the formation of ferric nanophases in which parts are magnetic. Mineralogical changes that occur during thermal treatment between room temperature and 700 "C were monitored using electron spin resonance (ESR), bulk susceptibility, acquisition of isothermal remanent magnetization (IRM) and Curie temperature analysis. After heating the samples to 250"C, a new ferrimagnetic phase is created as indicated by ESR and IRM acquisition. ESR spectra, IRM acquisition and Curie analyses suggest that magnetite is the predominant phase that is being created. These grains continue to be created and grow with heating up to 500°C. Above this temperature a decrease in the intensity of the IRM at 1T suggests that the phase is being transformed into haematite. The thermal experiments on iron-loaded smectites show that surfaceinduced processes can lead to the formation of new magnetic minerals under conditions characteristic of low-grade metamorphism.

Measurements of finite strain, the anisotropy of magnetic susceptibility, the magnetic carrier of the susceptibility, and fieldwork have been carried out in the Onaping Formation of the Sudbury Basin, Ontario. The magnetic fabric indicates that changes in the magnitude and type of magnetic susceptibility ellipsoids closely mirror the changing pattern of deformation from northwest to southeast across the Onaping Formation outcrops. A quantitative correlation has been established between finite strain measurements and the magnetic susceptibility results and this allows the number of available strain measurements to be extended by more than 500 samples. The finite strain results suggest a deformation path in which the Onaping Formation was first affected by NW-SE-directed, horizontal, layer-parallel shortening which produced an upright tectonic cleavage. Subsequently, components of overthrust, NW-directed simple shear were superimposed upon the already deformed rocks of the Onaping Formation. The result of removing the strain, according to the sequence of superimposed deformations revealed by the deformation path, suggests that the Sudbury Basin was nearly circular in shape prior to its deformation. Consequently, a major objection to the meteorite impact theory for origin of the Sudbury Structure is eliminated.

[1] Knowledge on forced magma injection and magma flow in dykes is crucial for the understanding of how magmas migrate through the crust to the Earth's surface. Because many questions still persist, we used the long, thick, and deep-seated Foum Zguid dyke (Morocco) to investigate dyke emplacement and internal flow by means of magnetic methods, structural analysis, petrography, and scanning electron microscopy. We also investigated how the host rocks accommodated the intrusion. Regarding internal flow: 1. Important variations of the rock magnetic properties and magnetic fabric occur with distance from dyke wall; 2. anisotropy of anhysteretic remanent magnetization reveals that anisotropy of magnetic susceptibility (AMS) results mainly from the superposition of subfabrics with distinct coercivities and that the imbrication between magnetic foliation and dyke plane is more reliable to deduce flow than the orientation of the AMS maximum principal axis; and 3. a dominant upward flow near the margins can be inferred. The magnetic fabric closest to the dyke wall likely records magma flow best due to fast cooling, whereas in the core the magnetic properties have been affected by high-temperature exsolution and metasomatic effects due to slow cooling. Regarding dyke emplacement, this study shows that the thick forceful intrusion induced deformation by homogeneous flattening and/or folding of the host sedimentary strata. Dewatering related to heat, as recorded by thick quartz veins bordering the dyke in some localities, may have also helped accommodating dyke intrusion. The spatial arrangement of quartz veins and their geometrical relationship with the dyke indicate a preintrusive to synintrusive sinistral component of strike slip.

Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles are determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a core−shell model for the form factor. The particles are found to align with their long axis perpendicular to the applied field. The orientational order is determined from the SAXS data and compared to the orientational order obtained from magnetometry. The direct access to both, the orientational order of the particles, and the magnetic moments allow one to determine the magnetic properties of the individual spindle-type hematite particles. We study the influence of the silica coating on the magnetic properties and find a fundamentally different behavior of silica-coated particles. The silica coating reduces the effective magnetic moment of the particles. This effect is enhanced with field strength and can be explained by superparamagnetic relaxation in the highly porous particles.

Paleomagnetic directions have been determined at 17 Cambrian and 28 Carboniferous limestone sites distributed along the Asturian arc of the Hercynian fold belt in northwestern Spain. The stable vectors are carried by hematite in all cases, and also by magnetite in some grey Carboniferous limestones. A secondary component of magnetization is usually removed well below 400°C, and the higher-temperature component is taken to be the characteristic direction. The structure at each site was carefully evaluated in order to make optimum local tectonic corrections. In addition the data must be corrected for rotations about a vertical axis to allow for a phase of radial folding superimposed on earlier structures. The corrected paleomagnetic declinations are found to vary systematically along the arc of the fold belt. Consequently, paleomagnetic data from the Asturian arc should not be included in compilations used for the construction of a Paleozoic apparent polar wander path. The paleomagnetic data allow us to distinguish between different tectonic models for the evolution of the Asturian arc. A two-stage model for the development of the present curvature is favored. Part of the curvature appears to be primary, preceding the Hercynian deformation. The first stage of the model involved rotations of thrust sheets during their emplacement, producing a more tightly curved arc than the original form. In a second stage, the development of radial folds further tightened the curvature of the arc. Both stages result in clockwise rotations in the north and anticlockwise rotations in the south.

Geophysical Journal International, 173 (1), ISSN:0956-540X, ISSN:1365-246X

[1] Biomonitoring of magnetic properties of tree leaves has been postulated to be a good approach to measure particulate matter (PM) pollution levels. We studied the variation of magnetic hysteresis parameters on leaves of Quercus ilex, an evergreen oak previously used for magnetic biomonitoring of air pollution in Rome (Italy). The hysteresis parameters (MRS, MS, BCR and BC) measured on specimens collected at a close spacing on the surface of two single leaves show variances that are smaller than those observed on a collection of Q. ilex leaves sampled from several trees distributed along high-traffic roads. The variability is higher for magnetizations than for coercivities. This suggests a uniform source for the magnetic particles, such that variations are due mainly to changes in concentration. The normalized hysteresis cycles are remarkably similar for all the specimens. Normalization of magnetic moments by mass appears however more efficient than normalization by volume.

Geophysical Journal International, 168 (1), ISSN:0956-540X, ISSN:1365-246X

We calculate the torque and force generated by an arbitrary magnetic field on an axially symmetric soft-magnetic body. We consider the magnetization of the body as a function of the applied field, using a continuous model that unifies two disparate magnetic models. The continuous torque and force follow. The model is verified experimentally, and captures the often neglected region between weak and saturating fields, where interesting behavior is observed. We provide the field direction to maximize torque for a given field magnitude. We also find an absolute maximum torque, for a given body geometry and material, which can be generated with relatively weak applied fields. This paper is aimed at those interested in systems-level analysis, simulation, and real-time control of soft-magnetic bodies.

[1] A low-coercivity phase, identified as magnetite and/or maghemite, is the main iron oxide in brain tissue. Measurement of susceptibility as a function of temperature (χ–T) in brain tissue samples does not show a Verwey transition but instead shows a perturbation around 50 K. A susceptibility anomaly has been reported at this temperature in several studies of multidomain magnetite crystals, which, however, also display a Verwey transition. We have investigated the magnetic characteristics of this 50 K anomaly further in brain and tumor tissue. The magnetic measurements consist of χ–T curves, measured after cooling in zero field (ZFC) or in a field (FC), as well as hysteresis loops. The 50 K anomaly is expressed as a bump in χ–T curves over a 20 K temperature range, with a peak between 44 and 58 K. The magnetic intensity of the samples is weak; however, the anomaly signal is an order of magnitude larger than known effects related to the magnetic ordering of oxygen at 43 K. A phase transition, or magnetic ordering of another phase, does not seem a likely explanation, because both the ZFC and FC curves follow the perturbation, rather than showing a bifurcation at peak susceptibility. This explanation also precludes magnetic blocking of a superparamagnetic component. Hysteresis loops at temperature of the peak perturbation show a splitting of the descending and ascending limbs at the maximum starting field. The magnetic behavior observed in these experiments is consistent with a change in electron activity.

Geophysical Journal International, 165 (1), ISSN:0956-540X, ISSN:1365-246X

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BioMetals, 18 (2), ISSN:0966-0844, ISSN:1572-8773

[1] The anisotropy of magnetic susceptibility (AMS) is an integral measure of the preferred orientation of all minerals present in a rock. When the AMS is carried by paramagnetic minerals alone, the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals. The relationship between the AMS and deformation depends on several factors, which control the development of lattice-preferred orientation (LPO) in a rock. A mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase. Measurements of the AMS are compared with fabric-based anisotropy models for black slates from the Navia-Alto Sil slate belt in northern Spain. The AMS is carried by paramagnetic minerals, as has been confirmed by high-field torque magnetometry, low-temperature AMS and magnetization curves. The LPO of mica and chlorite has been determined by X-ray texture goniometry. Pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates. The models have been tested in samples displaying three types of pole figures: a high-intensity point maximum, a medium-intensity elliptical maximum, and a girdle-shaped distribution. At one site displaying kink bands the LPO shows variations between these types at the outcrop scale. The case studies illustrate the success in modeling different LPO types.

In extensional sedimentary basins fine-grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern. The origin of the magnetic lineation, which is often found in extensional basins, is not yet well understood. In clays from extensional basins in southern Italy, the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults. A combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings. Low-field, high-field and low-temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy. The magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates. Neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes. Results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite, lying parallel to the common axis of differently oriented basal planes. A quantitative correlation between the magnetic and rock fabric was made comparing the low- and high-field magnetic anisotropy (AMS, HFA) to the theoretical anisotropy calculated from the chlorite-preferred orientation. A good linear correlation is found between the degree of theoretical anisotropy and the AMS and HFA. Results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins, where macroscopic evidence of deformation is often not visible. fabric consistent with the regional deformation pattern. The origin of the magnetic lineation, which is often found in extensional basins, is not yet well understood. In clays from extensional basins in southern Italy, the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults. A combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings. Low-field, high-field and low-temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy. The magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates. Neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes. Results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite, lying parallel to the common axis of differently oriented basal planes. A quantitative correlation between the magnetic and rock fabric was made comparing the low- and high-field magnetic anisotropy (AMS, HFA) to the theoretical anisotropy calculated from the chlorite-preferred orientation. A good linear correlation is found between the degree of theoretical anisotropy and the AMS and HFA. Results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins, where macroscopic evidence of deformation is often not visible.

The magnetic fabric of a rock, defined by the anisotropy of magnetic susceptibility (AMS), is often used as a tectonic indicator. In order to establish a quantitative relationship between AMS and mineral texture, it is important to understand the single crystal intrinsic AMS of each mineral that contributes to the AMS of the rock. The AMS and crystallographic preferred orientation (CPO) of amphiboles, olivine and pyroxenes has been analyzed in a series of amphibolites, peridotites and pyroxenites that do show preferred mineral alignment. The CPO of each mineral phase was determined based on electron backscatter diffraction (EBSD). Whole- rock AMS was computed based on the CPO and single crystal AMS of the respective minerals. A comparison between measured and modelled magnetic anisotropy shows that the directions of the principal susceptibility axes agree well in amphibolite and peridotite. Pyroxenite is a good example for competing AMS fabrics in polyphase rocks.

Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

Superparamagnetic nanoparticles are employed in a broad range of applications that demand detailed magnetic characterization for superior performance, e.g., in drug delivery or cancer treatment. Magnetic hysteresis measurements provide information on saturation magnetization and coercive force for bulk material but can be equivocal for particles having a broad size distribution. Here, first-order reversal curves (FORCs) are used to evaluate the effective magnetic particle size and interaction between equally sized magnetic iron oxide (Fe2O3) nanoparticles with three different morphologies: (i) pure Fe2O3, (ii) Janus-like, and (iii) core/shell Fe2O3/SiO2 synthesized using flame technology. By characterizing the distribution in coercive force and interaction field from the FORC diagrams, we find that the presence of SiO2 in the core/shell structures significantly reduces the average coercive force in comparison to the Janus-like Fe2O3/SiO2 and pure Fe2O3 particles. This is attributed to the reduction in the dipolar interaction between particles, which in turn reduces the effective magnetic particle size. Hence, FORC analysis allows for a finer distinction between equally sized Fe2O3 particles with similar magnetic hysteresis curves that can significantly influence the final nanoparticle performance.

Magnetic nanoparticles encompass a wide range of scientific study and technological applications. The success of using the nanoparticles in various applications demands control over size, dispersibility, and magnetics. Hence, the nanoparticles are often characterized by transmission electron microscopy (TEM), X-ray diffraction, and magnetic hysteresis loops. TEM analysis requires a thin layer of dispersed particles on the grid, which may often lead to particle aggregation thus making size analysis difficult. Magnetic hysteresis loops on the other hand provide information on the bulk property of the material without discriminating size, composition, and interaction effects. First order reversal curves (FORCs), described as an assembly of partial hysteresis loops originating from the major loop are efficient in identifying the domain size, composition, and interaction in a magnetic system. This study presents FORC diagrams on a variety of well-characterized biogenic and synthetic magnetite nanoparticles. It also introduces deconvoluted reversible and irreversible components from FORC as an important method for obtaining a semi-quantitative measure of the effective magnetic particle size. This is particularly important in a system with aggregation and interaction among the particles that often leads to either the differences between physical size and effective magnetic size. We also emphasize the extraction of secondary components by masking dominant coercivity fraction on FORC diagram to explore more detailed characterization of nanoparticle systems.

The room temperature co-precipitation of ferrous and ferric iron under alkaline conditions typically yields superparamagnetic magnetite nanoparticles below a size of 20 nm. We show that at pH = 9 this method can be tuned to grow larger particles with single stable domain magnetic (> 20–30 nm) or even multi-domain behavior (> 80 nm). The crystal growth kinetics resembles surprisingly observations of magnetite crystal formation in magnetotactic bacteria. The physicochemical parameters required for mineralization in these organisms are unknown, therefore this study provides insight into which conditions could possibly prevail in the biomineralizing vesicle compartments (magnetosomes) of these bacteria. ISSN:1932-6203

We combine tensile strength analysis and X-ray scattering experiments to establish a detailed understanding of the microstructural coupling between liquid-crystalline elastomer (LCE) networks and embedded magnetic core-shell ellipsoidal nanoparticles (NPs). We study the structural and magnetic re-organization at different deformations and NP loadings, and the associated shape and magnetic memory features. In the quantitative analysis of a stretching process, the effect of the incorporated NPs on the smectic LCE is found to be prominent during the reorientation of the smectic domains and the softening of the nanocomposite. Under deformation, the soft response of the nanocomposite material allows the organization of the nanoparticles to yield a permanent macroscopically anisotropic magnetic material. Independent of the particle loading, the shape-memory properties and the smectic phase of the LCEs are preserved. Detailed studies on the magnetic properties demonstrate that the collective ensemble of individual particles is responsible for the macroscopic magnetic features of the nanocomposite.

Magnetotactic bacteria produce chains of magnetite nanoparticles, which are called magnetosomes and are used for navigational purposes. We use these cells as a biological template to prepare a hollow hybrid material based on silica and magnetite, and show that the synthetic route is nondestructive as the material conserves the cell morphology as well as the alignment of the magnetic particles. The hybrid material can be resuspended in aqueous solution, and can be shown to orient itself in an external magnetic field. We anticipate that chemical modification of the silica can be used to functionalize the material surface in order to obtain multifunctional materials with specialized applications, e.g. targeted drug delivery.

The growth of the nanotechnology industry has led to an increased interest in characterizing magnetic nanoparticles. A natural material with well-defined grain size in the nanoparticle range is commercially available—horse spleen ferritin, an iron storage protein. Modeling of the magnetic properties of commercial horse spleen ferritin is often based on the assumption of a single-phase core of ferrihydrite (5Fe2O3∙9H2O). Low temperature hysteresis measurements indicate, however, that the ferritin cores contain at least two magnetic phases. Initial magnetization curves measured at temperatures between 50 and 300K have been modeled using four methods. A model that used a sum of two Langevin functions fitted the data 70% better on average than a model that used a single Langevin function. It was also superior to both a random mean orientation model and a model that takes account of crystalline anisotropy. The two-phase model consists of a phase with a high coercivity that does not undergo saturation and a sec...

The detection, fabrication, use, and understanding of fine magnetic particulates and structures provides an interdisciplinary platform which crosses a diverse number of science areas, including geophysics, environmental science, medicine, biology data storage media, and semiconductor devices. Natural and laboratory-grown magnetic particulates and fabricated structures at the scale of 5-100 nm have a wide number of applications, including interpreting environmental change and paleomagnetic signatures; disease diagnosis and drug delivery in humans; locating and understanding the production of biomagnets in a variety of organisms; and designing the next generation of data storage devices and nanoscale information technology components.

[1] The magnetic properties of synthetic lepidocrocite (γ-FeOOH) were investigated between 5 and 300 K. The purity of the samples was verified by X-ray diffraction and Mossbauer spectra at room temperature. The lepidocrocite is paramagnetic at room temperature with a low field susceptibility of 57.8 × 10−8 m3 kg−1. It undergoes magnetic ordering at low temperature and a peak in in-phase susceptibility occurs around 52 K, where it is antiferromagnetic. Thermal demagnetization of low-temperature remanence after cooling in zero field and in a 2.5-T field display a large loss in remanence from 5 to 30 K. Hysteresis loops are open and symmetric about the origin below 50 K; the remanent magnetization probably arises from a defect magnetic moment. The field-cooled hysteresis loop at 5 K is shifted along the field axis, which implies an exchange bias between antiferromagnetic and ferrimagnetic alignment in the lepidocrocite.

The Northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite. The magnetic fabric of this sedimentary rock, as defined by the anisotropy of magnetic susceptibility, is controlled by bedding compaction but is inverse (i.e., the maximum susceptibility axes are normal to the bedding plane). This inverse fabric is attributed to the dominating presence of siderite. The rocks were incrementally heated to 600°C, and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step; cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric. After heating the samples above 250°C, the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane. The low-temperature magnetic fabric remains inverse until the samples are heated to about 500°C. After heating to higher temperatures a normal fabric was observed at both room temperature and low temperature. Rock magnetic evidence shows that magnetite is created during the heating. The start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy, powder X ray diffraction, and acquisition of isothermal remanence. Berthierine starts to break down at approximately 250°C and is totally oxidized by 500°C. The creation of magnetite in the heating experiments corresponds with this mineralogical change. The change in the room temperature magnetic fabric is associated with the decomposition of berthierine, part of which alters to magnetite. The new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite.

Cleavage formation in the Precambrian Chelmsford Formation of the Sudbury Basin, Ontario, is directly related to the finite strain and deformation path. Finite strain was measured at the outcrop scale from the shapes and orientations of deformed concretions within sandstones, at the microscopic scale from the relative positions of quartz grain centers, and via quantitative correlations between the anisotropy of magnetic susceptibility and strain. Two-dimensional strains measured in different sections at each site were combined into three-dimensional strain ellipsoids at 16 sites distributed throughout the Chelmsford Formation outcrop. Using the magnetic susceptibility correlation, a further 527 individual strain ellipsoids were obtained throughout the sites. A prominent strain gradient is mirrored by the progressive development of cleavage in the Chelmsford Formation, with strain and fabric development increasing in intensity from NW to SE. At the least deformed sites, cleavage is weak or absent. The finite strain reflects a combination of vertical compaction followed by coaxial, tectonic layer-parallel shortening acting in a subhorizontal, NW-SE direction. Pressure solution is the dominant deformation mechanism responsible for the formation of cleavage. Material removed by pressure solution is redeposited as pressure fringes on quartz grains, an observation which is compatible with the form of the deformation path which indicates little effect due to volume loss in cleavage formation in these sandstones. Folds within the Chelmsford Formation indicate formation by buckling but have very low limb dips. Decomposition of the finite strain tensor into a compactional part and a layer-parallel shortening part suggests that fold initiation and amplification was preceded by about 38% layer-parallel shortening. The large number of strain ellipsoids obtained from the Chelmsford Formation provide a significant data base from which a number of important tectonic problems can be examined including the predeformational shape of the Sudbury structure.

During folding of the Scaglia Rossa limestone in Umbria, Italy, deformation was mainly accommodated by pressure solution cleavage. Fossils between the cleavage planes appear visibly undeformed, yet the limestone possesses a weak magnetic fabric. The maximum and intermediate principal axes of the magnetic anisotropy ellipsoid define a distinct magnetic foliation plane within which a weak concentration of the maximum axes forms a magnetic lineation. Neither of these features is of sedimentary origin. Results from a slumped outcrop, where bedding and a cleavage induced by overburden compaction have different attitudes, show that the magnetic foliation is caused by the compaction. Comparisons with field-derived structural data suggest that the magnetic lineation was produced tectonically during deformation of the Apennine fold belt.