Resolving the Ferromagnetism of alpha-Sn/Co/Cu(111) by Spin-polarized Scanning Tunneling Microscopy

Chia-Ju Chen^1*, Yi-Hao Zhuang¹, Shih-Tang Huang¹, Guan-Yu Chen¹, Nitin Kumar¹, Yen-Hui Lin¹, Pin-Jui Hsu¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Chia-Ju Chen, email:s109022803@m109.nthu.edu.tw

By introducing spontaneous magnetization next to the topological insulator lead to the modification of the surface electronic structure. The magnetic spin order via exchange interaction will break the time-reversal symmetry and cause an exchange gap. Theoretical studies predicted that when the Fermi level is located inside the exchange gap gives rise to the quantum anomalous Hall (QAH) effect, the so-called magnetic topological insulator. In this study, we have successfully grown flat α-Sn (stanene) islands on top of the triangular ferromagnetic Co islands on the Cu(111) substrate at the low temperature. By utilizing spin-polarized scanning tunneling microscopy/spectroscopy (SP-STM/STS) techniques, we can obtain spin-sensitive electronic information on the sample surface. The topography measurements with line profiles show the protruding heights are 0.15 and 0.22 nm form a single atomic layer on the substrate and top of Co islands, respectively. Besides, the differential conductance maps show the same size and orientation of different Sn/Co islands with opposite magnetization states, which present ferromagnetism. Moreover, we investigated the reversal magnetization process and observed that the hysteresis loop and the switching field would depend on the island's size. These results provide an artificial way to synthesize heterostructure leads to spontaneous magnetization.

Keywords: Spin-polarized Scanning Tunneling Microscopy, Ferromagnetic Nanoislands, Stanene