Phase Contrast Imaging of Non-Collinear Spin Textures with Lorentz Microscopy

Transmission electron microscopy is a critical asset to basic and applied sciences research as it enables the characterization of, e.g., structural order on the atomic scale. This includes not only crystalline structures and orientation, but also their temporal evolution, behavior at and across interfaces, and disordered, amorphous materials leveraging tomographic imaging. To date, the vast majority of electron microscopy harnesses the superior spatial resolution owing to a de Broglie wavelength of a few picometers. Taking advantage of the wave properties of coherent electrons and their interaction with electromagnetic fields, e.g., matter, allows for enhancing sensitivity and resolution and visualizing the spin degrees of freedom in the form of the in-plane magnetic induction. These experiments are based on the detection of the electron phase using off-axis or in-line holography. The former requires a biprism, the latter works in Fresnel mode/Lorentz mode with post processing involving a phase retrieval algorithm, such as transport-of-intensity or Gerchberg-Saxton. I will discuss the fundamentals, including pros and cons, of phase contrast imaging and review recent applications to visualize non-collinear spin textures in magnetic films in the presence of magnetic bias fields and cryogenic temperatures triggering magnetic phase transitions and spin fluctuations. One focus will be on chiral spin textures in amorphous materials where exit wave reconstruction allows to disentangle electrostatic, magnetization, and magnetic field contributions to the phase shift [1,2]. <br/><br/>[1] RS et al., Adv. Mater. DOI: 10.1002/adma.201800199<br/>[2] RS et al., Adv. Mater. DOI: 10.1002/adma.202004830<br/><br/>Supported by the National Science Foundation, Division of Materials Research under Grant No. 2203933.