E. T. Simpson

Three-Dimensional Tomographic Imaging and Characterization of Iron Compounds within Alzheimer's Plaque Core Material

Although it has been known for over 50 years that abnormal concentrations of iron are associated with virtually all neurodegenerative diseases, including Alzheimers disease, its origin, nature and role have remained a mystery. Here, we use high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray (EDX) spectroscopy and electron energy-loss spectroscopy (EELS), electron tomography, and electron diffraction to image and characterize iron-rich plaque core material - a hallmark of Alzheimers disease pathology - in three dimensions. In these cores, we unequivocally identify biogenic magnetite and/or maghemite as the dominant iron compound. Our results provide an indication that abnormal iron biomineralization processes are likely occurring within the plaque or the surrounding diseased tissue and may play a role in aberrant peptide aggregation. The size distribution of the magnetite cores implies formation from a ferritin precursor, implicating a malfunction of the primary iron storage protein in the brain.

Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the Verwey transition using electron holography

Off-axis electron holography in the transmission electron microscope is used to record magnetic induction maps of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the sample using liquid nitrogen. The magnetic microstructure is related to the morphology and crystallography of the particles, and to interparticle interactions. At room temperature, the magnetic signal is dominated by interactions and shape anisotropy, with highly parallel and straight field lines following the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction undulates along the length of the chain. This behaviour may result from a competition between interparticle interactions and an easy axis of magnetisation that is no longer parallel to the chain axis. The quantitative nature of electron holography also allows the change in magnetisation in the crystals with temperature to be measured.

The application of Lorentz transmission electron microscopy to the study of lamellar magnetism in hematite-ilmenite

Abstract Lorentz transmission electron microscopy has been used to study fine-scale exsolution microstructures in ilmenite-hematite, as part of a wider investigation of the lamellar magnetism hypothesis. Pronounced asymmetric contrast is visible in out-of-focus Lorentz images of ilmenite lamellae in hematite. The likelihood that lamellar magnetism may be responsible for this contrast is assessed using simulations that incorporate interfacial magnetic moments on the (001) basal planes of hematite and ilmenite. The simulations suggest qualitatively that the asymmetric contrast is magnetic in origin. However, the magnitude of the experimental contrast is higher than that in the simulations, suggesting that an alternative origin for the observed asymmetry cannot be ruled out. Electron tomography was used to show that the lamellae have lens-like shapes and that (001) planes make up a significant proportion of the interfacial surface that they share with their host.

Properties of Rocks and Minerals – Magnetic Properties of Rocks and Minerals

This review describes the current state of the art in the field of computational and experimental mineral physics, as applied to the study of magnetic minerals. The review is divided into four sections, describing new developments in the study of mineral magnetism at the atomic, nanometer, micrometer, and macroscopic length scales. We begin with a description of how atomistic simulation techniques are being used to study the magnetic properties of minerals surfaces and interfaces, and to gain new insight into the coupling between cation and magnetic ordering in Fe–Ti-bearing solid solutions. Next, we review the theory of off-axis electron holography, and its application to the study of magnetotactic bacteria and minerals containing nanoscale transformation-induced microstructures. Then, we review the theory and application of micromagnetic simulations to the study of nonuniform magnetization states and magnetostatic interactions in minerals at the micrometer length scale. Finally, we review recent developments in the use of macroscopic magnetic measurements for characterizing and quantifying the microscopic spectrum of coercivities and interaction fields present in rocks and minerals.

Off-Axis Electron Holography of Magnetic Fields in Biological Materials

* Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark ** Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom *** Department of Earth and Environmental Sciences, University of Pannonia, Veszprém, POB 158, H8200 Hungary **** Institute of Science and Technology in Medicine, Keele University, Thornburrow Drive, Hartshill, Stoke-on-Trent ST4 7QB, United Kingdom