The vortex state in geologic materials: a micromagnetic perspective

A wide variety of Earth and planetary materials are very good recorders of paleomagnetic information. However, most magnetic grains in these materials are not in the stable single domain grain size range but are larger and in nonuniform vortex magnetization states. We provide a detailed account of vortex phenomena in geologic materials by simulating first‐order reversal curves (FORCs) via finite‐element micromagnetic modeling of magnetite nanoparticles with realistic morphologies. The particles have been reconstructed from focused ion beam nanotomography of magnetite‐bearing obsidian and accommodate single and multiple vortex structures. Single vortex (SV) grains have fingerprints with contributions to both the transient and transient‐free zones of FORC diagrams. A fundamental feature of the SV fingerprint is a central ridge, representing a distribution of negative saturation vortex annihilation fields. SV irreversible events at multiple field values along different FORC branches determine the asymmetry in the upper and lower lobes of generic bulk FORC diagrams of natural materials with grains predominantly in the vortex state. Multivortex (MV) FORC signatures are modeled here for the first time. MV grains contribute mostly to the transient‐free zone of a FORC diagram, averaging out to create a broad central peak. The intensity of the central peak is higher than that of the lobes, implying that MV particles are more abundant than SV particles in geologic materials with vortex state fingerprints. The abundance of MV particles, as well as their single domain‐like properties point to MV grains being the main natural remanent magnetization carriers in geologic materials

Social media hook sports events: a systematic review of engagement

Social media are nowadays used in all sectors, and likewise frequently within the sports industry. However, there is a lack of studies that offer a holistic understanding of the phenomenon of social media engagement (SME) in this area. Thus, the main object of the present study was the elaboration of a systematic review of the existing literature of the past ten years about SME within the field of sports events. The study was carried out following the PRISMA guidelines. By searching the databases Web of Science, Scopus, ProQuest, and Academic Search Ultimate, we identified 208 studies. After screening and reviewing for eligibility, we finally included 28 articles in the present study. The methodologies, types of analysis applied, main objectives, and the results on SME of the articles included in the synthesis were systematically reviewed. The findings showed that only four articles had as a principal theme the SME. Social media offer a useful tool for engagement, but SME adopts must still gain greater recognition. The need to co-create with users and engage them on social media, due to the great utility of social media in this sector is highlighted based on the results. It was found that SME around sports events remains an emerging and still developing research field which presents a wide range of future research lines

Helium ion microscope – secondary ion mass spectrometry for geological materials

The helium ion microscope (HIM) is a focussed ion beam instrument with unprecedented spatial resolution for secondary electron imaging but has traditionally lacked microanalytical capabilities. With the addition of the secondary ion mass spectrometry (SIMS) attachment, the capabilities of the instrument have expanded to microanalysis of isotopes from Li up to hundreds of atomic mass units, effectively opening up the analysis of all natural and geological systems. However, the instrument has thus far been underutilised by the geosciences community, due in no small part to a lack of a thorough understanding of the quantitative capabilities of the instrument. Li represents an ideal element for an exploration of the instrument as a tool for geological samples, due to its importance for economic geology and a green economy, and the difficult nature of observing Li with traditional microanalytical techniques. Also Li represents a “best-case” scenario for isotopic measurements. Here we present details of sample preparation, instrument sensitivity, theoretical, and measured detection limits for both elemental and isotopic analysis as well as practicalities for geological sample analyses of Li alongside a discussion of potential geological use cases of the HIM–SIMS instrument

Structure of a bacterial cell surface decaheme electron conduit

Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves decaheme cytochromes that are located on the bacterial cell surface at the termini of trans-outer-membrane electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular intercytochrome electron exchange along “nanowire” appendages. We present a 3.2-Å crystal structure of one of these decaheme cytochromes, MtrF, that allows the spatial organization of the 10 hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65-Å octaheme chain transects the length of the protein and is bisected by a planar 45-Å tetraheme chain that connects two extended Greek key split ß-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g., minerals), soluble substrates (e.g., flavins), and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface

Control of primary productivity and the significance of photosynthetic bacteria in a meromictic kettle lake.

During 1986 planktonic primary production and controlling factors were investigated in a small (A0 = 11.8 · 103 m2, Zmax = 11.5 m) meromictic kettle lake (Mittlerer Buchensee). Annual phytoplankton productivity was estimated to ca 120 gC · m–2 · a–1 (1,42 tC · lake–1 · a–1). The marked thermal stratification of the lake led to irregular vertical distributions of chlorophylla concentrations (Chla) and, to a minor extent, of photosynthesis (Az). Between the depths of 0 to 6 m low Chla concentrations (< 7 mg · m–3) and comparatively high background light attenuation (kw = 0,525 m–1, 77% of total attenuation due to gelbstoff and abioseston) was found. As a consequence, light absorption by algae was low (mean value 17,4%) and self-shading was absent. Because of the small seasonal variation of Chla concentrations, no significant correlation between Chla and areal photosynthesis (A) was observed. Only in early summer (June–July) biomass appears to influence the vertical distribution of photosynthesis on a bigger scale. Around 8 m depth, low-light adapted algae and phototrophic bacteria formed dense layers. Due to low ambient irradiances, the contribution of these organisms to total primary productivity was small. Primary production and incident irradiance were significantly correlated with each other (r2 = 0.68). Although the maximum assimilation number (Popt) showed a clear dependence upon water temperature (Q10 = 2.31), the latter was of minor importance to areal photosynthesis

Design and fabrication of plasmonic cavities for magneto-optical sensing (article)

This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this record.The dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32604The design and fabrication of a novel plasmonic cavity, intended to allow far-field recovery of signals arising from near field magneto-optical interactions, is presented. Finite element modeling is used to describe the interaction between a gold film, containing cross-shaped cavities, with a nearby magnetic under-layer. The modeling revealed strong electric field confinement near the center of the cross structure for certain optical wavelengths, which may be tuned by varying the length of the cross through a range that is compatible with available fabrication techniques. Furthermore, the magneto optical Kerr effect (MOKE) response of the composite structure can be enhanced with respect to that of the bare magnetic film. To confirm these findings, cavities were milled within gold films deposited upon a soluble film, allowing relocation to a ferromagnetic film using a float transfer technique. Cross cavity arrays were fabricated and characterized by optical transmission spectroscopy prior to floating, revealing resonances at optical wavelengths in good agreement with the finite element modeling. Following transfer to the magnetic film, circular test apertures within the gold film yielded clear magneto-optical signals even for diameters within the sub-wavelength regime. However, no magneto-optical signal was observed for the cross cavity arrays, since the FIB milling process was found to produce nanotube structures within the soluble under-layer that adhered to the gold. Further optimization of the fabrication process should allow recovery of magneto-optical signal from cross cavity structures.Financial support from the UK Engineering and Physical Science Research Council (EPSRC) grants EP/1038470/I and EP/1038411/1 is gratefully acknowledged. We also acknowledge the support of Seagate Technology (Ireland) under SOW 00077300.0. RMB contribution to project was supported by the Royal Academy of Engineering under the Research Chairs and Senior Research Fellowships Scheme

Nanoscale Imaging of High‐Field Magnetic Hysteresis in Meteoritic Metal Using X‐Ray Holography

Stable paleomagnetic information in meteoritic metal is carried by the “cloudy zone”: ~1–10 μm‐wide regions containing islands of ferromagnetic tetrataenite embedded in a paramagnetic antitaenite matrix. Due to their small size and high coercivity (theoretically up to ~2.2 T), the tetrataenite islands carry very stable magnetic remanence. However, these characteristics also make it difficult to image their magnetic state with the necessary spatial resolution and applied magnetic field. Here, we describe the first application of X‐ray holography to image the magnetic structure of the cloudy zone of the Tazewell IIICD meteorite with spatial resolution down to ~40 nm and in applied magnetic fields up to ±1.1 T, sufficient to extract high‐field hysteresis data from individual islands. Images were acquired as a function of magnetic field applied both parallel and perpendicular to the surface of a ~100 nm‐thick slice of the cloudy zone. Broad distributions of coercivity are observed, including values that likely exceed the maximum applied field. Horizontal offsets in the hysteresis loops indicate an interaction field distribution with half width of ~100 mT between the islands in their room temperature single‐domain state, providing a good match to first‐order reversal curve diagrams. The results suggest that future models of remanence acquisition in the cloudy zone should take account of strong interactions in order to extract quantitative estimates of the paleofield.EC/FP7/320750/EU/Nanopaleomagnetism: a multiscale approach to paleomagnetic analysis of geological materials/NanoPaleoMagEC/FP7/312284/EU/Coordinated Access to Lightsources to Promote Standards and Optimization/CALIPS

Probing microwave fields and enabling in-situ experiments in a transmission electron microscope.

A technique is presented whereby the performance of a microwave device is evaluated by mapping local field distributions using Lorentz transmission electron microscopy (L-TEM). We demonstrate the method by measuring the polarisation state of the electromagnetic fields produced by a microstrip waveguide as a function of its gigahertz operating frequency. The forward and backward propagating electromagnetic fields produced by the waveguide, in a specimen-free experiment, exert Lorentz forces on the propagating electron beam. Importantly, in addition to the mapping of dynamic fields, this novel method allows detection of effects of microwave fields on specimens, such as observing ferromagnetic materials at resonance

On three-dimensional misorientation spaces.

Determining the local orientation of crystals in engineering and geological materials has become routine with the advent of modern crystallographic mapping techniques. These techniques enable many thousands of orientation measurements to be made, directing attention towards how such orientation data are best studied. Here, we provide a guide to the visualization of misorientation data in three-dimensional vector spaces, reduced by crystal symmetry, to reveal crystallographic orientation relationships. Domains for all point group symmetries are presented and an analysis methodology is developed and applied to identify crystallographic relationships, indicated by clusters in the misorientation space, in examples from materials science and geology. This analysis aids the determination of active deformation mechanisms and evaluation of cluster centres and spread enables more accurate description of transformation processes supporting arguments regarding provenance