NanoPaleoMagnetism

Huge congratulations to Joy on passing her viva. Her fantastic (award winning) work on the development of FORC diagrams as a tool for unmixing rock magnetic signals was suitably celebrated with a giant ‘FORC’ cake. Joy’s thesis has shed new light on the role Fe reduction plays in controlling the magnetic properties of sediments, and lead to the discovery of a new type of magnetite – trabecular magnetite – that has an internal nano-porous structure resembling that of trabecular bone. Joy will now be heading off to Peking University to work with Liao Chang. So long Joy, and thanks for all the FORCs!

Huge congratulations to Joy for being awarded a prize for outstanding student presentation at the 16th Castle Meeting, Chęciny, Poland, June 15th 2018. Her talk entitled “New insights into iron reduction processes using FORC-PCA” summarised her PhD work on using FORC-PCA, electron holography and tomography to unravel the magnetic carriers in sediments.

It’s time once again for the annual trip to the American Geophysical Union meeting – the largest gathering of geoscientists on the planet. This year the meeting moves to  New Orleans, and to celebrate we have a bumper crop of NPM group talks and posters, as well as several contributions involving our international collaborators. In no particular order, our contributions are listed below. They include mineralogical and paleomagnetic studies of the oldest materials on Earth, the discovery of the mechanism controlling the formation of ultra fine magnetite in sediments, a study of the response of magnetotactic bacteria to one of Earth’s most extreme past climate change events, and the most detailed analysis to date of the chemical and crystallographic architecture of iron-nickel meteorites. Click on the links to find out what we’ve been up to. Better still, come and see us in New Orleans (if we can drag the PI out of the blues clubs!).

GP23B-0924 Why do Hematite FORCs Look Weird?

GP13A-05 From the ocean to a salt marsh: towards understanding iron reduction processes with FORC-PCA

GP23B-0923 Magnetic and microstructural characterisation of FeNi: Insight into the formation and impact history of the IAB parent body

GP13A-02 A new magnetofossil approach to trace paleoenvironmental changes across the Paleocene-Eocene Thermal Maximum

DI33B-0417 Paleomagnetism of Hadean to Neoarchean Detrital Zircons from the Jack Hills, Western Australia

GP22A-06 In-field imaging of the ‘cloudy zone’ of the Tazewell IIICD iron-nickel meteorite using X-ray holography

GP33C-01 Isolating magnetic moments from individual grains within a magnetic assemblage

V53B-02 Revealing the sub-nanometere three-dimensional microscture of a metallic meteorite

V51G-08 Can Inclusions Survive To The Ends Of The Earth?

Congratulations to Claire Nichols on passing her viva. Claire’s work on the nanopaleomagnetism of iron-nickel meteorites (or ‘tiny space magnets’ as they will forever more be known…) has cast new light on the magnetic history of the pallasite parent body using new X-ray methods developed as part of the ERC project. Claire’s continuing quest to answer the question “What is magnet…?” will now move to M.I.T., where she will (among other things) turn her attention to the magnetism of the Moon. We wish her all the best!

Magnetic imaging is one of the central tasks in nanopaleomagnetic research. A number of Transmission Electron Microscopy (TEM) methods for magnetic imaging with nanoscale spatial resolution are available (e.g. Electron Holography, Lorentz Microscopy, Differential Phase Contrast imaging). However, they all suffer from one key drawback: electrons are strongly deflected by applied magnetic fields, so measurements normally have to be performed under near field-free conditions – great if you want to image remanence states, but not so great if you are interested in hysteresis properties…

The problem of magnetic imaging in strong fields can be solved by using X-rays instead of electrons to probe the magnetic state of the sample. X-rays are unaffected by magnetic fields, but this freedom comes at a price: unlike electrons, X-rays cannot be focussed using electromagnetic lenses, making imaging with X-rays a particular challenge.

X-ray holography is a high-resolution imaging technique that circumvents the need for lenses entirely. Instead it uses coherent diffraction from the sample and a known reference object to form a holographic interference pattern. Using Fourier transforms, an image of the sample (convoluted with the reference object) is extracted from the hologram. This approach yields spatial resolution down to 30 nm, and the ability to image in applied magnetic fields up to 2 Tesla.

Principle of X-ray holography, as pioneered by Eisebitt et al. (2004) Lensless imaging of magnetic nanostructures by X-ray spectro-holography. Nature 432, 885-888.

To perform an X-ray holography experiment, the sample (normally a thin film, but in our case a < 100 nm thick TEM lamella) is placed on a silicon nitride membrane. The reverse side of the membrane is coated in 600 nm of gold, which is opaque to soft X-rays. A circular window, 5 µm in diameter, is milled into the gold mask, exposing the region of the sample to be imaged. A small reference hole (~30-80 nm in diameter) is drilled adjacent to the sample window. The sample and reference are illuminated with a coherent beam of circularly polarised soft X-rays, tuned to the Fe L3 absorption edge, and the resulting holographic interference pattern is recorded on a high-resolution CCD camera. The inverse Fourier transform of the interference pattern is calculated and the image of the sample extracted from one of the resulting side bands. The magnetic signal is separated from non-magnetic contributions by subtracting the left- and right-circularly polarised images, yielding dark or light contrast which is proportional to the out-of-plane component of magnetisation.

Bastian Fau and Roberts Blukis: searching for high resolution hysteresis measurements using X-ray holography.

Overview of the X-ray holography end station on beam line UE52-SGM at BESSY II.

Close-up of the sample chamber. A series of 4 coils (two visible in the lower part of the image) allow magnetic fields up to 2 T to be applied in directions parallel, perpendicular and at 45° to the sample plane.

Collaborating with X-ray holography experts Bastian Fau, Christian Günther and Stefan Eisebitt, we recently applied this method for the first time to image the nanomagnetic state of the cloudy zone in an iron meteorite at the synchrotron BESSY II in Berlin. The cloudy zone is a nanoscale intergrowth containing islands of tetrataenite in an Fe-rich matrix. The high coercivity and dense packing of tetrataenite islands makes it a natural target for nanopaleomagnetic studies, but we know little about how the cloudy zone responds to strong magnetic fields, and in particular how magnetic interactions between adjacent islands might influence their collective behaviour. Using X-ray holography we were able to image the switching behaviour of the cloudy zone as the magnetic field was swept from + 1 T to -1 T and back again (click on the image below to see the movie). The movie shows the sequence of magnetic states obtained through a full hysteresis cycle. Switching of individual tetrataenite islands and groups of islands can be seen as a sudden change from black to white contrast. Sweeping of magnetic domain walls across the tetrataenite rim are also clearly resolved, as well as evidence for the interaction of magnetic domain walls and crystallographic twin walls in the rim.

We are only just beginning the process of analysing these measurements. Eventually we hope to extract hysteresis loops from individual tetrataenite islands, and examine them for evidence of inter particle interactions. Comparison of the observations with micromagnetic simulations will help us understand the underlying physics of these unique nanostructures, with the ultimate aim of deciphering the true nature of the magnetic signals they acquire during formation on the meteorite parent body. In the mean time, enjoy this sneak peak of what can be achieved using X-ray holography – watch this space!

X-ray holographic image of the cloudy zone. The horizontal field of view is 5 µm. Dark and light regions correspond to magnetisation pointing either into or out of the plane of the sample. The region containing large magnetic domains on the left corresponds to the tetrataenite rim. The fine-scale features correspond to the island/matrix structure of the cloudy zone, with the size of the islands decreasing from left to right across the image. CLICK ON THE IMAGE TO SEE THE MOVIE!

I am pleased to announce that the latest update to FORCulator is now available for download from the NPM software site. This update fully integrates FORCulator into FORCinel 3.0 universe, enabling your simulated FORC diagrams to be treated in exactly the same way as your experimental FORC diagrams. The new version also incorporates FORCem, which turns this release into a fully integrated package for processing, simulating and analysing multiple FORC diagrams. As well as the enhanced integration, FORCulator 3.0 bring some new features, such as the ability to generate FCC arrays and scattered clusters of interacting particles. The FCC option enables packing fractions up to 74% to be generated – extreme magnetostatic interactions!

Happy FORCulating!

Rich

We are pleased to announce our latest NPM paper applying synchrotron Mössbauer spectroscopy to obtain the highest spatial resolution measurements of iron and stony-iron meteorites is now available via Open Access.

http://onlinelibrary.wiley.com/doi/10.1111/maps.12841/full

Metallic phases in the Tazewell IIICD iron and Esquel pallasite meteorites were examined using 57Fe synchrotron Mössbauer spectroscopy. Spatial resolution of ~10–20 μm was achieved, together with high throughput, enabling individual spectra to be recorded in less than 1 h. Spectra were recorded every 5–10 μm, allowing phase fractions and hyperfine parameters to be traced along transects of key microstructural features. The main focus of the study was the transitional region between kamacite and plessite, known as the “cloudy zone.” Results confirm the presence of tetrataenite and antitaenite in the cloudy zone as its only components. However, both phases were also found in plessite, indicating that antitaenite is not restricted exclusively to the cloudy zone, as previously thought. The confirmation of paramagnetic antitaenite as the matrix phase of the cloudy zone contrasts with recent observations of a ferromagnetic matrix phase using X-ray photoemission electron spectroscopy. Possible explanations for the different results seen using these techniques are proposed.

Congratulations to Roberts Blukis on his first paper from his PhD!

Rich

It will be a bumper year for NPM research at this year’s AGU. The whole gang will be there, with one notable exception: our glorious leader :-(. Given the choice of either going to AGU or missing my daughter play the starring role in the school Christmas show (Ariel in the “The Little Mermaid”), there was no real contest. The team will be there, however, with a total of 3 talks (two invited) and 5 posters (including mine, thanks to Nono and Joy). In fact there is a slice of NPM action happening on each day, so come and say hi!

MR13A-2379: Multi-Scale and Multi-Dimensional Mineralogical Mapping using Machine Learning

Joshua Franz Einsle, Richard J Harrison, Duncan Johnstone, Ben Martineau, Sean M Collins, Iris Buisman, Zineb Saghi, Alexander Eggeman, Alexander M Piotrowski, Joseph L Kirschvink, Paul A Midgley

Session: MR13A Advanced Experimental, Computational, and Analytical Techniques for Mineralogy and Mineral Physics III Posters

Day: Monday, 12 December 2016

GP13A-05: Pallasite Paleomagnetism: Quiescence of a Core Dynamo (Invited)

Claire Isobel O’Bryen Nichols, James Francis Joseph Bryson, Benjamin P Weiss, Julia Herrero-Albillos, Florian Kronast, Francis Nimmo, Richard J Harrison

Session: GP13A Planetary Magnetism and Paleomagnetism I
Day: Monday, 12 December 2016

GP22A-01: What does it mean to be pseudo single domain? Demystifying the PSD state

Ioan Lascu, Richard J Harrison, Joshua Franz Einsle, Matthew Ball

Session: GP22A Fundamental Mineral and Rock Magnetism I
Day: Tuesday, 13 December 2016

GP23C-1353: A High spatial Resolution Synchrotron Mössbauer Study of the Tazewell IIICD and Esquel Pallasite Meteorites

Roberts Blukis, Richard Harrison

Session: GP23C Planetary Magnetism and Paleomagnetism II Posters
Day: Tuesday, 13 December 2016

GP31A-1289: FORCinel Version 3.0: An Integrated Environment for Processing, Analysis and Simulation of First-Order Reversal Curve Diagrams

Richard J Harrison, Ioan Lascu

Session: GP31A Fundamental Mineral and Rock Magnetism II Posters
Day: Wednesday, 14 December 2016

GP43D-05: Research strategies and quantitative methods in environmental magnetism (Invited)

Ioan Lascu, Joy R. Muraszko, Richard J Harrison, Kendra K McLauchlan

Session: GP43D Recent Advances in Environmental and Biogeomagnetism I
Day: Thursday, 15 December 2016

P51A-2125: Paleomagnetic and compositional insight into the formation and impact history of the IAB parent body

Claire Isobel O’Bryen Nichols, Geraint Northwood-Smith, Julia Herrero-Albillos, Florian Kronast, Richard J Harrison

Session: P51A Accretion, Differentiation, and Early Planetary Evolution II Posters
Day: Friday, 16 December 2016

GP51C-1392: Climate variability in the southwestern Iberian Margin: new insights from FORC-PCA

Joy R. Muraszko, Ioan Lascu, Richard Harrison

Session: GP51C Recent Advances in Environmental and Biogeomagnetism II Posters
Day: Friday, 16 December 2016

We are pleased to announced the release of FORCinel 3.0, a major update to our suite of FORC processing and analysis tools. Virtually every aspect of FORCinel has been rewritten or optimised to provide a dramatically improved workflow, a host of new features optimised for processing and analysing multiple FORCs, and full integration with both FORCem and FORCulator. A list of new features can be found here, along with an introductory video tour. Look out for more video tutorials appearing soon. The software can be downloaded here, and is compatible with both Igor Pro 6 and the recently released Igor Pro 7.