Lorentz electron ptychography for imaging magnetic textures beyond the diffraction limit

• Published in: Nature nanotechnology Vol. 17; no. 11; pp. 1165 - 1170
• Main Authors: Chen, Zhen, Turgut, Emrah, Jiang, Yi, Nguyen, Kayla X., Stolt, Matthew J., Jin, Song, Ralph, Daniel C., Fuchs, Gregory D., Muller, David A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2022; Nature Publishing Group
• Subjects: 639/766/119/1001; 639/925/930/2735; Chemistry and Materials Science; Crystal defects; Crystal dislocations; Damping; Diffraction; Electron microscopy; Electron radiation; High resolution; High resolution electron microscopy; Hypothetical particles; Image resolution; Letter; Magnetic fields; Magnetic measurement; Materials Science; Microscopes; Microscopy; NANOSCIENCE AND NANOTECHNOLOGY; Nanotechnology; Nanotechnology and Microengineering; Optics; Particle theory; Scattering angle; Sensitivity; Single crystals; Spatial discrimination; Spatial resolution
• ISSN: 1748-3387; 1748-3395; 1748-3395
• DOI: 10.1038/s41565-022-01224-y

Nanoscale spin textures, especially magnetic skyrmions, have attracted intense interest as candidate high-density and power-efficient information carriers for spintronic devices 1 , 2 . Facilitating a deeper understanding of sub-hundred-nanometre to atomic-scale spin textures requires more advanced magnetic imaging techniques 3 – 5 . Here we demonstrate a Lorentz electron ptychography method that can enable high-resolution, high-sensitivity magnetic field imaging for widely available electron microscopes. The resolution of Lorentz electron ptychography is not limited by the usual diffraction limit of lens optics, but instead is determined by the maximum scattering angle at which a statistically meaningful dose can still be recorded—this can be an improvement of up to 2–6 times depending on the allowable dose. Using FeGe as the model system, we realize a more accurate magnetic field measurement of skyrmions with an improved spatial resolution and sensitivity by also correcting the probe-damping effect from the imaging optics via Lorentz electron ptychography. This allows us to directly resolve subtle internal structures of magnetic skyrmions near the skyrmion cores, boundaries and dislocations in an FeGe single crystal. Our study establishes a quantitative, high-resolution magnetic microscopy technique that can reveal nanoscale spin textures, especially magnetization discontinuities and topological defects in nanomagnets 6 . The technique’s high-dose efficiency should also make it well suited for the exploration of magnetic textures in electron radiation-sensitive materials such as organic or molecular magnets 7 . Magnetic textures at the nanoscale are usually hard to resolve. This high-resolution electron microscopy method enables the imaging of the internal structure of magnetic textures with higher resolution and precision than the optical limit of the instrument.