Room-temperature Ferromagnetism of Cobalt Ultrathin Films Covered on a Monolayer MoS₂

MoS₂ has been shown a widely application, including spintronics: ferromagnetic (FM) materials/MoS₂ spin-valve devices [1]. However, a direct observation of the magnetic properties of such interface is still lack. In this report, we focus on the FM behavior of the Co thin films cover on a monolayer (ML) MoS₂. First, a series of magneto-optical Kerr effect (MOKE) experiments of Co on an amorphous MoS₂ surface confirm that the in-plane magnetization signal exists when the Co's thickness is above 5 ML. Therefore, we performed a series of in-situ experiments with different thicknesses of Co on monolayer MoS₂ triangular islands at the X-ray photoemission electron microscopy (XPEEM) endstation at BL05B2 of Taiwan Light Source. Clear spatially-resolved magnetic domain images were obtained, and the tendency of thickness-invariance and the preferred directions of domain boundary are observed. We further covered 3 ML of Fe on the Co surface. The domain images of Fe and Co indicate the ferromagnetically coupled with each other.

[1] W. Wang, A. Narayan, L. Tang, K. Dolui, Y. Liu, X. Yuan, Y. Jin, Y. Wu, I. Rugger, S. Sanvito, and F. Xiu, Nano Lett. 15, 5261 (2015)