Magnetic domain structure and crystallographic orientation of electrical steels revealed by a forescatter detector and electron backscatter diffraction

Tailoring the Anisotropic Oxygen Transport Properties in Bulk Ceramic Membranes Based on a Ruddlesden-Popper Oxide by Applying Magnetic Fields

Textured Nd2NiO4+ δ bulk ceramic membranes are fabricated via slip casting in a 0.9 T magnetic field generated by neodymium magnets. This process aligns the oxide grains with their easy-magnetization c-axis parallel to the applied magnetic field. Depending on the magnetic field's direction relative to the slip casting, grains orient either with their a,b-plane or c-axis parallel to the normal direction of the disk-shaped ceramic, thus aligning with the oxygen permeation direction. Without the magnetic field, a non-textured bulk membrane is formed. The microstructure and texture of the ceramic membranes are meticulously analyzed using advanced techniques, including X-ray diffraction, scanning and transmission electron microscopy, as well as related methods. Evaluation of the texturing effect on the oxygen permeation performance shows that the a,b-plane textured Nd2NiO4+ δ bulk membrane achieves the highest oxygen permeation fluxes between 1023-1223 K. Additionally, it demonstrates impressive CO₂ stability, maintaining effective performance for at least 140 h due to preferential oxygen transport along the a,b-plane. These characteristics make Nd2NiO4+ δ an auspicious material for industrial applications as an oxygen transport membrane, outperforming more susceptible perovskite-based materials. Magnetic alignment thus proves to be an effective method for achieving membrane texturing, enabling precise regulation of oxygen transport properties.

Effect of sub-micron deformations at opposing strain rates on the micromagnetic behaviour of non-oriented electrical steel

We are entering an era of re-electrification, seeking high-power density electrical machines with minimal resource use. Significant performance gains in electrical machines have been achieved through precise manufacturing processes, including the shaping/cutting of soft magnetic materials. However, most studies have evaluated magnetic performance at a macro level, focusing on components, while the fundamental mechanisms, e.g., how the micromagnetic behaviour is affected by mechanical interference, remain unclear. In this study, we examine the impact of sub-micron deformations at opposing strain rates (10-2 to 101 s-1) on the micromagnetic behaviour of soft magnetic non-oriented electrical steel. Using a diamond probe to indent within a single grain of polycrystalline material at different velocities, we induce quasi-static and dynamic mechanical loading. Our analysis, employing magnetic force microscopy, transmission Kikuchi diffraction, and scanning transmission electron microscopy with a pixelated detector, reveals that magnetic texture disturbances rely on the time-dependent dislocation dynamics of the Fe-BCC material. Additionally, we compress micro-pillars to further investigate these effects under bulk-isolated deformation. These findings highlight the importance of considering even ultra-small loads, such as nano-indentations and micro-pillar compressions, in the manufacturing of next-generation electric machines, as they can affect magnetic texture and performance.

An EBSD camera as a tool to characterise in-plane magnetisation vectors on Fe-Si (001) surface

Previous studies have shown that type-II magnetic-domain contrasts are caused by differences in the backscattering yields of magnetic domains of opposite magnetisation. Imaging the magnetic domains when the magnetisation vectors in the opposite-magnetisation domains are perpendicular to the tilt axis of the specimen has been considered difficult, because of the lack of change in the backscattering yields between the domains. An alternative way to obtain the type-II magnetic-domain contrasts is to utilise the difference in the exit angular distribution of the backscattered electrons from different magnetic domains. In this study, it is found that an electron backscatter diffraction (EBSD) camera can be used to obtain the type-II magnetic-domain contrasts caused by the above two mechanisms simultaneously. We verify this by distinguishing all four possible in-plane magnetisation vectors on a Fe-Si (001) surface without a sample rotation, using an EBSD detector as an array of electron detectors. The change in contrast between the magnetic domains, with respect to the location of a virtual electron detector, can provide information on the directions of the magnetisation vectors. A method to suppress the topographic contrast superimposed on the magnetic-domain contrast is also demonstrated.

Assessing the influence of crystallographic orientation, stress and local deformation on magnetic domains using electron backscatter diffraction and forescatter electron imaging

The magnetic properties of non-oriented electrical steel (NOES) used in an electrical engine play an important role in the transformation process from electric to mechanic energy. In this process the NOES is subjected to cyclic loading and strong tensile forces. Until now the dependence of the magnetic properties with respect to a through stress changing microstructure is not fully understood. In this paper a setup for a quasi-static in situ deformation experiment with a SEM is presented in which the surface magnetic domains of a NOES were captured by revealing type 2 magnetic contrast with forescatter diodes, the crystallographic texture was mapped through EBSD and the local relative strains and rotations were calculated with CrossCourt. The magnetic domains were related to the angles between the easy axes and the surface as well as the angle differences between the easy axes of neighboring grains. For small differences wide boundary-crossing domain patterns occurred. In contrast, for high ones predominantly compensating domains emerged. Thus a distinct influence of neighboring grains was present. Reaching a certain stress level, a strong tendency of domain alignment along the easy axes closest to the stress direction could be observed. Locally exceeding the elastic limit, slip lines appeared but had no visible influence on the domains. After unloading, in those areas a clear hindrance of domain alignment was apparent, which was attributed to the dislocation accumulations. CrossCourt enables the estimation of GND accumulations, which can be used to detect domain wall pinning. In conclusion, the presented method provides a way to link the magnetic properties of NOES to the texture and a through stress changing microstructure.

Information or resolution: Which is required from an SEM to study bulk inorganic materials?

Significant technological advances in scanning electron microscopy (SEM) have been achieved over the past years. Different SEMs can have significant differences in functionality and performance. This work presents the perspectives on selecting an SEM for research on bulk inorganic materials. Understanding materials demands quantitative composition and orientation information, and informative and interpretable images that reveal subtle differences in chemistry, orientation/structure, topography, and electronic structure. The capability to yield informative and interpretable images with high signal-to-noise ratios and spatial resolutions is an overall result of the SEM system as a whole, from the electron optical column to the detection system. The electron optical column determines probe performance. The roles of the detection system are to capture, filter or discriminate, and convert signal electrons to imaging information. The capability to control practical operating parameters including electron probe size and current, acceleration voltage or landing voltage, working distance, detector selection, and signal filtration is inherently determined by the SEM itself. As a platform for various accessories, e.g. an energy-dispersive spectrometer and an electron backscatter diffraction detector, the properties of the electron optical column, specimen chamber, and stage greatly affect the performance of accessories. Ease-of-use and ease-of-maintenance are of practical importance. It is practically important to select appropriate test specimens, design suitable imaging conditions, and analyze the specimen chamber geometry and dimensions to assess the overall functionality and performance of an SEM. For an SEM that is controlled/operated with a computer, the stable software and user-friendly interface significantly improve the usability of the SEM. SCANNING 38:864-879, 2016. © 2016 Wiley Periodicals, Inc.

Mapping the magnetic and crystal structure in cobalt nanowires

Using off-axis electron holography under Lorentz microscopy conditions to experimentally determine the magnetization distribution in individual cobalt (Co) nanowires, and scanning precession-electron diffraction to obtain their crystalline orientation phase map, allowed us to directly visualize with high accuracy the effect of crystallographic texture on the magnetization of nanowires. The influence of grain boundaries and disorientations on the magnetic structure is correlated on the basis of micromagnetic analysis in order to establish the detailed relationship between magnetic and crystalline structure. This approach demonstrates the applicability of the method employed and provides further understanding on the effect of crystalline structure on magnetic properties at the nanometric scale.