Lorentz transmission electron microscopy is a unique characterization technique that enables the simultaneous imaging of both the microstructure and functional properties of materials at high spatial resolution. The quantitative information such as magnetization and electric potentials is carried by the phase of the electron wave, and is lost during imaging. In order to understand the local interactions and develop structure-property relationships, it is necessary to retrieve the complete wavefunction of the electron wave, which requires solving for the phase shift of the electrons (phase retrieval). Here we have developed a method based on differentiable programming to solve the inverse problem of phase retrieval, using a series of defocused microscope images. We show that our method is robust and can outperform widely used \textit{transport of intensity equation} in terms of spatial resolution and accuracy of the retrieved phase under same electron dose conditions. Furthermore, our method shares the same basic structure as advanced machine learning algorithms, and is easily adaptable to various other forms of phase retrieval in electron microscopy.
Magnetic bubbles are remarkable spin structures that developed in uniaxial magnets with strong magnetocrystalline anisotropy. Several contradictory reports have been published concerning the magnetic bubble structure in a metallic magnet MnNiGa: Biskyrmions or type-II bubbles. Lorentz microscopy in polycrystalline MnNiGa was used to explain the magnetic bubble structure. Depending on the connection between the magnetic easy axis and the observation plane, two types of magnetic bubbles were formed. Magnetic bubbles with 180° domains were formed if the easy axis was away from the direction perpe…
Transmission electron microscopy is one of the most powerful techniques to characterize nanoscale magnetic structures. In light of the importance of fast control schemes of magnetic states, time-resolved microscopy techniques are highly sought after in fundamental and applied research. Here, we implement time-resolved Lorentz imaging in combination with synchronous radio-frequency excitation using an ultrafast transmission electron microscope. As a model system, we examine the current-driven gyration of a vortex core in a 2 $\mathrmμ$m-sized magnetic nanoisland. We record the trajectory of the…
We consider the case of a chiral soliton lattice subjected to uniaxial elastic strain applied perpendicular to the chiral axis and derive through analytical modelling the phase diagram of magnetic states supported in the presence of an external magnetic field. The strain induced anisotropies give rise to three distinct non-trivial spin textures, depending on the nature of the strain, and we show how these states may be identified by their signatures in Lorentz transmission electron microscopy (TEM). Experimental TEM measurements of the Fresnel contrast in a strained sample of the prototypical …
Chiral magnetic textures in ultrathin perpendicularly magnetised multilayer film stacks with an interfacial Dzyaloshinskii-Moriya interaction have been the focus of much research recently. The chirality associated with the broken inversion symmetry at the interface between an ultrathin ferromagnetic layer and a heavy metal with large spin-orbit coupling supports homochiral Néel domain walls and hedgehog (Néel) skyrmions. Under spin-orbit torques these Néel type magnetic structures are predicted, and have been measured, to move at high velocities. However recent studies have indicated that some…
The study of nanoscale chiral magnetic order in polycrystalline materials with a strong Dzyaloshinkii-Moriya interaction (DMI) is interesting for the observation of magnetic phenomena at grain boundaries and interfaces. One such material is sputter-deposited B20 FeGe on Si, which has been actively investigated as the basis for low-power, high-density magnetic memory technology in a scalable material platform. Although conventional Lorentz electron microscopy provides the requisite spatial resolution to probe chiral magnetic textures in single-crystal FeGe, probing the magnetism of sputtered B2…
Quantification of magnetic interactions in van der Waals heterostructures using Lorentz transmission electron microscopy and electron holography
Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich（尤利希研究中心恩斯特·鲁斯卡电子显微镜与谱学中心）；Peter Grünberg Institute, Forschungszentrum Jülich（尤利希研究中心彼得·格林贝格研究所）；Department of Inorganic Chemistry, University of Chemistry and Technology Prague（布拉格化学技术大学无机化学系）
Topological magnetic textures are of great interest in various scientific and technological fields. To allow for precise control of nanoscale magnetism, it is of great importance to understand the role of intrinsic defects in the host material. Here, we use conventional and time-resolved Lorentz microscopy to study the effect of grain size in polycrystalline permalloy films on the pinning and gyration orbits of vortex cores inside magnetic nanoislands. To assess static pinning, we use in-plane magnetic fields to shift the core across the island while recording its position. This enables us to …
Domain Switching on the Pareto Front: Multi-Objective Deep Kernel Learning in Automated Piezoresponse Force Microscopy
University of Tennessee（田纳西大学）；Institute of Science Tokyo（东京科学大学）；University of California, Berkeley（加州大学伯克利分校）；Rice University（莱斯大学）；Pacific Northwest National Laboratory（太平洋西北国家实验室）
Physics-aware global Rietveld refinement for high-energy X-ray diffraction microscopy with application to reconstructing intragranular orientation and strain fields
California Institute of Technology（加州理工学院）；Massachusetts Institute of Technology（麻省理工学院）
Understanding the fundamental dynamics of topological vortex and antivortex naturally formed in micro/nanoscale ferromagnetic building blocks under external perturbations is crucial to magnetic vortex based information processing and spintronic devices. All previous studies have focused on magnetic vortex-core switching via external magnetic fields, spin-polarized currents, or spin waves, which have largely prohibited the investigation of novel spin configurations that could emerge from the ground states in ferromagnetic disks and their underlying dynamics. Here, we report in situ visualizatio…
We report differential phase contrast scanning transmission electron microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet Fe$_3$Sn$_2$ nanostructures. This technique can directly detect the deflection angle of a focused electron beam, thus allowing clear identification of the real magnetic structures of two magnetic objects including three-ring and complex arch-shaped vortices in Fe$_3$Sn$_2$ by Lorentz transmission electron microscopy imaging. Numerical calculations based on real material-specific parameters well reproduced the experimental results, showing that the magnetic o…
We show that magnetic skyrmions can be stabilized at room temperature in continuous Ir/Co/Pt multilayers on SiO2/Si substrate without prior application of electric current or magnetic field. While decreasing the Co thickness, tuning of the magnetic anisotropy gives rise to a transition from worm-like domain patterns to long and separate stripes. The skyrmions are clearly imaged in both states using Magnetic Force Microscopy. The density of skyrmions can be significantly enhanced after applying the in-plane field procedure. In addition, we have investigated the phase diagram of a sample deposit…
