Hard magnetic response of exfoliated van der Waals Ferromagnet Fe_5-xGeTe₂, and coexistence between merons and skyrmions

Magnetic two-dimensional materials show very intriguing properties and have recently emerged as a very promising new area in condensed matter physics with significant potential for applications in magnonics, low power spintronics quantum computing, and optical communication. However, Curie temperature (T_c) of many of the known 2D ferromagnets are well below room temperature. For example, Cr₂GeTe₆ (T_c ~ 60 K), CrI₃ (T_c ~ 45 K), and Fe₃GeTe₂ (T_c ~ 220 K). Intriguely, Fe₅GeTe₂ displays a T_c as high as 330 K, which means that it has a great potential for applications. Motivated by the Hall response of exfoliated Fe₃GeTe₂ that is dominated by the anomalous Hall, we measured large magnetic coercivity and found the change in direction of hard magnet in nanoflakes of Fe_5-xGeTe₂. The size of the hysteresis depends on the crystal thickness with magnetic coercive field (H_cr) increasing with decreasing the layer thickness. Furthermore, we will present our result showing the magnetic domain of Fe_5-xGeTe₂ measured via Lorentz Transmission Electron Microscopy (LTEM) measurement with the range of temperature 100 K~300 K. Evidences for coexistence between merons and skrymions, and how they change will be shown with various temperatures.