Metastable zero-field skyrmion lattice at room temperature in van der Waals (Fe₀.₅Co₀.₅)₅GeTe₂

Ying-Ting Chan^1*, Hongrui Zhang², Rui Chen², Xiang Chen³, Jie Yao², Robert J. Birgeneau³, Ramamoorthy Ramesh², Weida Wu¹

¹Department of Physics and Astronomy, Rutgers University, NJ, USA
²Department of Materials Science and Engineering, University of California, Berkeley, CA, USA
³Materials Sciences Division, Lawrence Berkeley National Laboratory, CA, USA

* Presenter:Ying-Ting Chan, email:ytchan@physics.rutgers.edu

Recently, zero-field skyrmions at room temperature were discovered in a van der Waals 50% Co-doped Fe₅GeTe₂ (FCGT) with a high Curie temperature (Tc = 365 K) and novel non-centrosymmetric structure. [1] Here, we visualize the magnetic domains near room temperatures in FCGT thin flakes using a variable-temperature magnetic force microscope. The skyrmion lattice can be induced from stripe domains by a small external magnetic field and persists as a metastable state in zero field at room temperature. Interestingly, the skyrmion lattice gradually “melt” into the stripe domains with annealing temperature above 320 K. The metastable skyrmion lattice and its annealing behavior can be explained by a phenomenological picture of the free energy landscape. [2]

[1] H. Zhang et al., Phys. Rev. Mater. 6, 044403 (2022).
[2] H. Zhang et al., Sci. Adv., 8, eabm7103 (2022).

Keywords: Skyrmions, Magnetic vdW materials, Variable-temperature magnetic force microscopy