Mapping Metastable Magnetic Textures in (Fe0.5Co0.5)5GeTe2 with in-situ Lorentz Transmission Electron Microscopy

Abstract

Topologically protected magnetic textures are a promising route to low-energy control of magnetism, but they are most often studied away from ambient conditions, typically at low temperatures and high magnetic fields. Here we use in-situ Lorentz transmission electron microscopy with control of temperature and magnetic field to investigate the skyrmion metastability in (Fe0.5Co0.5)5GeTe2 (FCGT). By field-cooling FCGT in magnetic fields of different magnitude to different base temperatures and then removing the applied field, we create meta(stable) zero-field magnetic states. We use this method to build a phase diagram of the zero-field metastable spin structures in FCGT, which will be critical for selecting the desired topologically-protected spin state for future studies to manipulate magnetism with stimuli such as electric current, electric field, mechanical strain, and more.

Figures (7)

• Figure 1: Magnetic textures in FCGT. Spin arrangement of (a) Néel skyrmions and (b) cycloidal states. In (a) and (b) the gray panels show the spin alignments along a slice through the center of the spin textures. c) Crystal structure of Van-der-Waals layered FCGT. d-g) LTEM images of FCGT showing (d) skyrmions, (e) parallel cycloidal domains, (f) labyrinthine cycloidal domains, and (g) mixed skyrmion-cycloidal state with insets illustrating the expected appearance of each state.
• Figure 2: Field-cooling cycles in FCGT. a) Path through temperature-magnetic field phase space for a single field-cooling cycle. On this path we heat the sample above its Curie temperature (i), place it in a magnetic field (ii), cool it to a temperature of interest T$_i$ (iii) and remove the applied magnetic field (iv). (b) A representation of several field-cooling paths (corresponding to [c-h]) with final temperature plotted on the x-axis and cooling field plotted on the y-axis. The shape and color of the plot points corresponds to the resulting magnetic state. c-h) LTEM images of the magnetic textures resulting from a variety of field-cooling paths (inset in each image).
• Figure 3: Magnetic saturation behavior of FCGT. a) LTEM image of a labyrinthine helical state resulting from field cooling at 1050 Oe (above the saturation magnetization) and 293K. b) A similar labyrinthine helical state resulting from isothermal magnetic saturation after zero-field cooling at 293K. Inset charts describe the paths through temperature-magnetic field phase space.
• Figure 4: FCGT cycled in magnetic field at 323K. a) Initial zero-magnetic-field LTEM image showing helical domains after field cooling from above T$_\textrm{c}$ with B$_\textrm{cool}$ = 350 Oe. b) LTEM image of magnetic skyrmions stabilized by a 350 Oe perpendicular magnetic field. c) Zero-field LTEM image of helical domains that reappeared after removing the perpendicular magnetic field.
• Figure 5: Low temperature magnetic textures in FCGT. a) LTEM image collected at 203K of circular domains in FCGT created by following the field cooling path at 350 Oe inset in (a). b) LTEM image of conventional Néel domains in FCGT created by applying then removing a saturating magnetic field to the texture in (a) (following the path inset in b).