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Recent paleomagnetic studies have constrained the strength\ud and longevity of the magnetic field generated by the solar nebula, which has broad implications for the early evolution of the solar system. Paleomagnetic evidence was recorded by nanoscale iron inclusions in olivine crystals in the\ud Semarkona LL 3.0 chondrite. These dusty olivines, have been shown to be credible carriers of ancient magnetic remanence. The small scale of the iron inclusions presents several challenges for defining their fundamental magnetic\ud properties. Here we present the first correlative study of the response of these magnetic structures under applied laboratory fields. Results show that the majority of particles are in a single-vortex state and exhibit stable magnetic behavior in applied fields up to 200 mT. Experimental observations using Lorentz microscopy and magnetic transmission X-ray microscopy are shown to compare well with the results of finite-element micromagnetic simulations derived from 3D models of the particles obtained using electron tomography. This correlative approach may be used to characterize the fundamental magnetic behavior of many terrestrial and extraterrestrial paleomagnetic\ud carriers in the single- to multi-vortex size range, which represent the vast majority of stable magnetic carriers in rocks and meteorites.\ud \ud \ud Plain Language Summary:\ud Some of the first solid materials to form in the solar system have been brought to Earth by meteorites. They contain tiny metallic inclusions which record information about the magnetic fields at the earliest stages of our solar sys-\ud tem’s history. Understanding these magnetic fields, and how they are recorded by metallic particles, provides very important information for understanding how our solar system formed and evolved. We have studied some of these particles to image their magnetic structure using microscopes which allow us to see structures a billionth of a metre in size. We have developed a new technique using X-rays to image how the magnetic structure in these particles changes when we apply different magnetic fields in the laboratory. We have also been able to reproduce our results using computer simulations of the magnetic behavior of the particles. This is the first study that has imaged the magnetic structure of these particles under applied fields. We find that the particles are very stable; even under magnetic fields thousands of times stronger than Earth’s, the particles still don’t change the magnetic structure they had in the early solar system.\ud Keypoints:\ud • We show the first experimental results demonstrating the stability of dusty olivines under applied magnetic fields.\ud • We use a novel combination of electron and X-ray microscopy techniques combined with micromagnetic simulations.\ud • We confirm previous results that dusty olivines are capable of recording magnetic fields from the solar nebula.

Tensile tests and microstructural observations were carried out to investigate the influence of aging products on tensile deformation behavior of Al-0.62 mass%Mg-0.32 mass%Si alloy. Solution-treated alloys were aged to form needle-like β″ precipitates or Mg-Si clusters. The aged alloy with β″ precipitates showed higher yield stress than that with Mg-Si clusters. Transmission electron microscopy observations revealed that the β″ precipitates pinned dislocations. It was suggested that the strengthening types of the alloy with β″ precipitates were both Orowan and cutting mechanism, by estimating the Orowan stress and considering crystal structure of β″ precipitates. In contrast, the aged alloys with Mg-Si clusters showed excellent performance of uniform elongation due to large work hardening compared to those of the alloy with β″ precipitates. Dislocations in the alloy with Mg-Si clusters were wavy in morphology. The yield stress of the alloy with Mg-Si clusters was higher than that of the solution-treated alloy and much lower than the estimated Orowan stress. This result indicated that the cutting mechanism was the main strengthening type of the aged alloy with Mg-Si clusters, and this strengthening mechanism gave a good balance of strength and elongation.

Dusty olivine (olivine containing multiple sub-micrometer inclusions of metallic iron) in chondritic meteorites is considered an ideal carrier of paleomagnetic remanence, capable of maintaining a faithful record of pre-accretionary magnetization acquired during chondrule formation. Here we show how the magnetic architecture of a single dusty olivine grain from the Semarkona LL3.0 ordinary chondrite meteorite can be fully characterised in three dimensions, using a combination of Focussed-Ion-Beam nanotomography (FIB-nT), electron tomography and finite-element micromagnetic modelling. We present a three-dimensional (3D) volume reconstruction of a dusty olivine grain, obtained by selective milling through a region of interest in a series of sequential 20 nm slices, which are then imaged using scanning electron microscopy. The data provide a quantitative description of the iron particle ensemble, including the distribution of particle sizes, shapes, interparticle spacings and orientations. Iron particles are predominantly oblate ellipsoids with average radii 242 ± 94 nm by 199 ± 80 nm by 123 ± 58 nm. Using analytical TEM we observe that the particles nucleate on sub-grain boundaries and are loosely arranged in a series of sheets parallel to (001) of the olivine host. This is in agreement with the orientation data collected using the FIB-nT, and highlights how the underlying texture of the dusty olivine is crystallographically constrained by the olivine host. The shortest dimension of the particles is oriented normal to the sheets and their longest dimension is preferentially aligned within the sheets. Individual particle geometries are converted to a finite-element mesh and used to perform micromagnetic simulations. The majority of particles adopt a single vortex state, with ‘bulk’ spins that rotate around a central vortex core. We observed no particles, which are in a true single domain state. The results of the micromagnetic simulations challenge some pre-conceived ideas about the remanence carrying properties of vortex states. There is often not a simple predictive relationship between the major, intermediate and minor axes of the particles and the remanence vector imparted in different fields. Although the orientation of the vortex core is determined largely by the ellipsoidal geometry (i.e., parallel to the major axis for prolate ellipsoids and parallel to the minor axis for oblate ellipsoids), the core and remanence vectors can sometimes lie at very large (tens of degree) angles to the principal axes. The subtle details of the morphology can control the overall remanence state, leading in some cases to a dominant contribution from the bulk spins to the net remanence, with profound implications for predicting the anisotropy of the sample. The particles have very high switching fields (several hundred mT), demonstrating their high stability and suitability for paleointensity studies.

GM2/GD2 synthase gene knockout mice lack all complex gangliosides, which are abundantly expressed in the nervous systems of vertebrates. In turn, they have increased precursor structures GM3 and GD3, probably replacing the roles of the depleted complex gangliosides. In this study, we found that 9-O-acetyl GD3 is also highly expressed as one of the major glycosphingolipids accumulating in the nervous tissues of the mutant mice. The identity of the novel component was confirmed by neuraminidase treatment, thin layer chromatography-immunostaining, two-dimensional thin layer chromatography with base treatment, and mass spectrometry. All candidate factors reported to be possible inducer of 9-O- acetylation, such as bitamine D binding protein, acetyl CoA transporter, or O-acetyl ganglioside synthase were not up-regulated. Tis21 which had been reported to be a 9-O-acetylation inducer was partially down-regulated in the null mutants, suggesting that Tis21 is not involved in the induction of 9-O-acetyl-GD3 and that accumulated high amount of GD3 might be the main factor for the dramatic increase of 9-O-acetyl GD3. The ability to acetylate exogenously added GD3 in the normal mouse astrocytes was examined, showing that the wild-type brain might be able to synthesize very low levels of 9-O-acetyl GD3. Increased 9-O-acetyl GD3, in addition to GM3 and GD3, may play an important role in the compensation for deleted complex gangliosides in the mutant mice. J. Neurochem. (2008) 105, 1057–1066.

We demonstrate that images of flux vortices in a superconductor taken with a transmission electron microscope can be used to measure the penetration depth and coherence length in all directions at the same temperature and magnetic field. This is particularly useful for MgB2, where these quantities vary with the applied magnetic field and values are difficult to obtain at low field or in the c direction. We obtained images of flux vortices from a MgB2 single crystal cut in the ac plane by focused ion beam milling and tilted to 45 degrees. with respect to the electron beam about the crystallographic a axis. A new method was developed to simulate these images that accounted for vortices with a nonzero core in a thin, anisotropic superconductor and a simplex algorithm was used to make a quantitative comparison between the images and simulations to measure the penetration depths and coherence lengths. This gave penetration depths Lambda(ab) = 100 +/- 35 nm and Lambda(c) = 120 +/- 15 nm at 10.8 K in a field of 4.8 mT. The large error in Lambda(ab) is a consequence of tilting the sample about a and had it been tilted about c, the errors on Lambda(ab) and Lambda(c) would be reversed. Thus obtaining the most precise values requires taking images of the flux lattice with the sample tilted in more than one direction. In a previous paper [J. C. Loudon et al., Phys. Rev. B 87, 144515 (2013)], we obtained a more precise value for Lambda(ab) using a sample cut in the ab plane. Using this value gives Lambda(ab) = 107 +/- 8 nm, Lambda(c) = 120 +/- 15 nm, xi(ab) = 39 +/- 11 nm, and xi(c) = 35 +/- 10 nm, which agree well with measurements made using other techniques. The experiment required two days to conduct and does not require large-scale facilities. It was performed on a very small sample, 30 x 15 mu m and 200-nm thick, so this method could prove useful for superconductors where only small single crystals are available, as is the case for some iron-based superconductors.

Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (g-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards g-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information.

Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information., Magnetite provides a valuable record of the Earth's geomagnetic history. Here, Almeida et al. combine electron microscopy and energy-loss spectroscopy to study the effects of in situ oxidation on the magnetization fidelity and crystalline phase of pseudo-single domain magnetite grains.

The thermomagnetic behavior of remanence-induced magnetite (Fe3O4) particles in the pseudo-single-domain (PSD) size range (similar to 0.1-10 mu m), which dominate the magnetic signature of many rock lithologies, is investigated using off-axis electron holography. Construction of magnetic induction maps allowed for the visualization of the vortex domain state in an individual Fe3O4 grain (similar to 200nm in diameter) as a function of temperature. Acquisition of a series of electron holograms at 100 degrees C intervals during in situ heating up to 700 degrees C demonstrates the vortex state of the Fe3O4 grain, in this instance, remains thermally stable close to its unblocking temperature and exhibits a similar in-plane remanent state upon cooling; i.e., the particle is effectively behaving like a uniaxial single-domain particle to temperatures near T-C. Such particles are thought to be robust magnetic recorders. It is suggested that evidence for PSD behavior should therefore not preclude paleomagnetic investigation.

The realization of high-mobility 2DEGs in epitaxially grown heterostructures made of traditional semiconductors is at the heart of present electronics, which has led to a wealth of new physical phenomena as well as new electronic and photonic devices over the past few decades. 2DEGs at the interface between insulating complex oxides not only provide a wealth of opportunities to study mesoscopic physics with strongly correlated electrons confined in nanostructures, but also show promise for multifunctional all-oxide devices with probably even richer behavior than those we experienced in semiconductor devices.

Core-shell GaN nanowires are expected to be building blocks of future light emitting devices. Here we apply off-axis electron holography to map the electrostatic potential distributions in such nanowires. To access the cross-section of selected individual nanowires, focused ion beam (FIB) milling is used. Furthermore, to assess the influence of FIB damage, the dopant potential measured from an intact NW is compared with a FIB prepared one. It is shown that in addition to the built-in potential between the p-type shell and unintentionally n-type under-layer there is a potential barrier between the core and under-layer which are both unintentionally n-type doped.

The magnetic properties of olivine-hosted Fe-Ni particles have been studied to assess the potential of "dusty olivine" to retain a pre-accretionary remanence in chondritic meteorites. Both body-centered (bcc) and face-centered cubic (fcc) Fe-Ni phases were formed by reduction of a terrestrial olivine precursor. The presence of Ni complicates the magnetic properties during heating and cooling due to the fcc-bcc martensitic transition. First-order reversal curve (FORC) diagrams contain a central ridge with a broad coercivity distribution extending to 600 mT, attributed to non-interacting single-domain (SD) particles, and a "butterfly" structure extending to 250 mT, attributed to single-vortex (SV) states. SD and SV states were imaged directly using electron holography. The location of the SD/SV boundary is broadly consistent with theoretical predictions. A method to measure the volume of individual SD particles using electron holography is presented. Combining the volume information with constraints on coercivity, we calculate the thermal relaxation characteristics of the particles and demonstrate that the high-coercivity component of remanance would remain stable for 4.6 Ga, even at temperatures approaching the Curie temperature of pure Fe. The high coercivity of the particles, together with the chemical protection offered by the surrounding olivine, is likely to make them resistant to shock remagnetization, isothermal remagnetization and terrestrial weathering, making dusty olivine a credible recorder of pre-accretionary magnetic fields. Copyright 2011 by the American Geophysical Union.

Mc 2009. Microscopy Conference, Graz, Austria. 30 August - 4 September 2009. First Joint Meeting Of Dreiländertagung And Multinational Congress On Microscopy.

Bistable flux closure (FC) states in Co nanoparticle rings can be switched reversibly by applying a coaxial magnetic field (H-z). The FC switching phenomena can be reproduced by micromagnetics simulations, which also reveal novel magnetic states at intermediate applied field strengths.

In this article, a comprehensive study of head-to-head domain wall spin structures in Ni80Fe20 and Co nanostructures is presented. Quantitative domain wall type phase diagrams for NiFe and Co are obtained and compared with available theoretical predictions and micromagnetic simulations. Differences to the experiment are explained taking into account thermal excitations. Thermally induced domain wall type transformations are observed from which a vortex core nucleation barrier height is obtained. The stray field of a domain wall is mapped directly with sub-10nm resolution using off-axis electron holography, and the field intensity is found to decrease as 1/r with distance. The magnetic dipolar coupling of domain walls in NiFe and Co elements is studied using X-ray magnetic circular dicroism photoemission electron microscopy. We observe that the spin structures of interacting domain walls change from vortex to transverse walls, when the distance between the walls is reduced. Using the measured stray field values, the energy barrier height distribution for the nucleation of a vortex core is obtained.

We report the direct transmission electron microscopy observation of spin structure transformations in nanoscale Permalloy zigzag wires due to Joule heating during the injection of current pulses. This heating is sufficient to overcome the energy barriers separating the different metastable domain wall spin structures. Due to the large energy barriers these are stable and observable at room temperature by off-axis electron holography and Fresnel imaging. The interaction between different domain walls is probed and the main pinning mechanism is determined to be the edge roughness. In addition to transformations, we also report on thermally assisted domain wall hopping between two pinning sites and structural changes that occur when the samples are subjected to even higher current pulses.