Simulation of Remanent, Transient, and Induced FORC Diagrams for Interacting Particles With Uniaxial, Cubic, and Hexagonal Anisotropy

The diagnostic power of first‐order reversal curve (FORC) diagrams has recently been enhanced by an extended measurement protocol that yields three additional FORC‐like diagrams: the remanent (remFORC), induced (iFORC), and transient (tFORC) diagrams. Here, we present micromagnetic simulations using this extended protocol, including numerical predictions of remFORC, iFORC, and tFORC signatures for particle ensembles relevant to rock magnetism. Simulations are presented for randomly packed single‐domain (SD) particles with uniaxial, cubic, and hexagonal anisotropy, and for chains of uniaxial SD particles. Noninteracting particles have zero tFORC, but distinct remFORC and iFORC signals, that provide enhanced discrimination between uniaxial, cubic, and hexagonal anisotropy types. Increasing interactions lessen the ability to discriminate between uniaxial and cubic anisotropy but reproduces a change in the pattern of positive and negative iFORC signals observed for SD‐dominated versus vortex‐dominated samples. Interactions in SD particles lead to the emergence of a bi‐lobate tFORC distribution, which is related to formation of flux‐closure in super‐vortex states. A predicted iFORC signal associated with collapsed chains is observed in experimental data and may aid magnetofossil identification in sediments. Asymmetric FORC and FORC‐like distributions for hexagonal anisotropy are explained by the availability of multiple easy axes within the basal plane. A transition to uniaxial switching occurs below a critical value of the out‐of‐plane/in‐plane anisotropy ratio, which may allow FORC diagrams to provide insight into the stress state of hexagonal minerals, such as hematite

Multiscale X-ray imaging using ptychography

The success of ptychography and other imaging experiments at third-generation X-ray sources is apparent from their increasingly widespread application and the improving quality of the images they produce both for resolution and contrast and in terms of relaxation of experimental constraints. The wider availability of highly coherent X-rays stimulates the development of several complementary techniques which have seen limited mutual integration in recent years. This paper presents a framework in which some of the established imaging techniques \u2013 with particular regard for ptychography \u2013 are flexibly applied to tackle the variable requirements occurring at typical synchrotron experiments. In such a framework one can obtain low-resolution images of whole samples and smoothly zoom in on specific regions of interest as they are revealed by switching to a higher-resolution imaging mode. The techniques involved range from full-field microscopy, to reach the widest fields of view (>mm), to ptychography, to achieve the highest resolution (<100 nm), and have been implemented at the I13 Coherence Branchline at Diamond Light Source

Ptychotomography at DLS Coherence Beamline I13

We describe the implementation and execution of ptychotomography at I13-1, the coherence branchline at Diamond Light Source. The data collection and image reconstruction protocol is demonstrated with the three dimensional reconstruction of a nanoporous gold sample

Simulation of Remanent, Transient, and Induced FORC Diagrams for Interacting Particles With Uniaxial, Cubic, and Hexagonal Anisotropy

The diagnostic power of first-order reversal curve (FORC) diagrams has recently been enhanced by an extended measurement protocol that yields three additional FORC-like diagrams: the remanent (remFORC), induced (iFORC), and transient (tFORC) diagrams. Here we present micromagnetic simulations using this extended protocol, including numerical predictions of remFORC, iFORC, and tFORC signatures for particle ensembles relevant to rock magnetism. Simulations are presented for randomly packed single-domain (SD) particles with uniaxial, cubic, and hexagonal anisotropy, and for chains of uniaxial SD particles. Non-interacting particles have zero tFORC, but distinct remFORC and iFORC signals, that provide enhanced discrimination between uniaxial, cubic, and hexagonal anisotropy types. Increasing interactions lessen the ability to discriminate between uniaxial and cubic anisotropy but reproduces a change in the pattern of positive and negative iFORC signals observed for SD-dominated versus vortex-dominated samples. Interactions in SD particles lead to the emergence of a bi-lobate tFORC distribution, which is related to formation of flux-closure in super-vortex states. A predicted iFORC signal associated with collapsed chains is observed in experimental data and may aid magnetofossil identification in sediments. Asymmetric FORC and FORC-like distributions for hexagonal anisotropy are explained by the availability of multiple easy axes within the basal plane. A transition to uniaxial switching occurs below a critical value of the out-of-plane/in-plane anisotropy ratio, which may allow FORC diagrams to provide insight into the stress state of hexagonal minerals, such as hematite.European Research Counci

An improved cleaning protocol for foraminiferal calcite from unconsolidated core sediments: Hypercal—a new practice for micropaleontological and paleoclimatic proxies

Paleoclimatic and paleoceanographic studies routinely rely on the usage of foraminiferal calcite through faunal, morphometric and physico-chemical proxies. The application of such proxies presupposes the extraction and cleaning of these biomineralized components from ocean sediments in the most efficient way, a process which is often labor intensive and time consuming. In this respect, in this study we performed a systematic experiment for planktonic foraminiferal specimen cleaning using different chemical treatments and evaluated the resulting data of a Late Quaternary gravity core sample from the Aegean Sea. All cleaning procedures adopted here were made on the basis of their minimum potential bias upon foraminiferal proxies, such as the faunal assemblages, degree of fragmentation, stable isotope composition (δ18 O and δ13 C) and/or Mg/Ca ratios that are frequently used as proxies for surface-ocean climate parameters (e.g., sea surface temperature, sea surface salinity). Six different protocols were tested, involving washing, sieving, and chemical treatment of the samples with hydrogen peroxide and/or sodium hexametaphosphate (Calgon®). Single species foraminifera shell weighing was combined with high-resolution scanning electron microscopy (SEM) and synchrotron X-ray microtomography (SµCT) of the material processed by each of the cleaning protocols, in order to assess the decontamination degree of specimen’s ultrastructure and interior. It appeared that a good compromise between time and cleaning efficiency is the simultaneous treatment of samples with a mixed hydrogen peroxide and Calgon solution, while the most effective way to almost completely decontaminate the calcareous components from undesirable sedimentary material is a two-step treatment—initially with hydrogen peroxide and subsequently with Calgon solutions. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Simulation of Remanent, Transient, and Induced FORC Diagrams for Interacting Particles With Uniaxial, Cubic, and Hexagonal Anisotropy

The diagnostic power offirst‐order reversal curve (FORC) diagrams has recently beenenhanced by an extended measurement protocol that yields three additional FORC‐like diagrams: theremanent (remFORC), induced (iFORC), and transient (tFORC) diagrams. Here, we present micromagneticsimulations using this extended protocol, including numerical predictions of remFORC, iFORC, and tFORCsignatures for particle ensembles relevant to rock magnetism. Simulations are presented for randomlypacked single‐domain (SD) particles with uniaxial, cubic, and hexagonal anisotropy, and for chains ofuniaxial SD particles. Noninteracting particles have zero tFORC, but distinct remFORC and iFORC signals,that provide enhanced discrimination between uniaxial, cubic, and hexagonal anisotropy types. Increasinginteractions lessen the ability to discriminate between uniaxial and cubic anisotropy but reproduces achange in the pattern of positive and negative iFORC signals observed for SD‐dominated versus vortex‐dominated samples. Interactions in SD particles lead to the emergence of a bi‐lobate tFORC distribution,which is related to formation offlux‐closure in super‐vortex states. A predicted iFORC signal associated withcollapsed chains is observed in experimental data and may aid magnetofossil identification in sediments.Asymmetric FORC and FORC‐like distributions for hexagonal anisotropy are explained by the availability ofmultiple easy axes within the basal plane. A transition to uniaxial switching occurs below a critical value ofthe out‐of‐plane/in‐plane anisotropy ratio, which may allow FORC diagrams to provide insight into thestress state of hexagonal minerals, such as hematite.This work was supported financially by the National Institute of Advanced Industrial Science and Technology, Ministry of Economy, Trade and Industry, Japan (APR, HO, DH, XZ, RJH, ARM, PXH, and TS), the Australian Research Council through grant DP160100805 (APR, DH, RJH, ARM, and PXH), and by the European Research Council under the European Union's Seventh Framework Programme (FP/2007–2013)/ERC grant agreement number 320750 (RJH)