The NQPI Seminar Series presents Tiancong Zhu of The Ohio State University, on “Epitaxial Growth of Room Temperature 2D vdW Ferromagnet MnSe2 and Its Integration with Topological Insulators”, on Thursday, Feb. 14, at 4:10 p.m. in Clippinger Labs 194.
Tiancong Zhu
Abstract: Magnetism in two-dimensional (2D) systems is a fascinating topic. Although long range magnetic order is theoretically prohibited at finite temperature for isotropic spins (i.e. 2D Heisenberg models) [1], the presence of magnetic anisotropy has enabled the observation of ferromagnetic ordering with 2D Ising critical exponents [2,3]. Further, the nature of magnetism in 2D ultrathin films has been investigated by spin-polarized scanning tunneling microscopy (STM) [4,5]. The advent of 2D van der Waals (vdW) magnets [6,7] provides exciting new opportunities, including magnetic phenomena that can be strongly tuned by electrostatic gates, proximity effects, strain, and Berry curvature. Initial work on intrinsic ferromagnetism in monolayer vdW materials observed magnetic ordering only at low temperatures [6,7], but more recent studies (including from our group) using molecular beam epitaxy (MBE) have discovered intrinsic ferromagnetism up to room temperature [8,9]. In this talk, I will present our demonstration of room temperature ferromagnetism in vdW material MnSe2 [9]. Because vdW crystals of MnSe2 do not exist, we utilize MBE to epitaxially stabilize the material at the monolayer limit. Magnetometry measurements of monolayer MnSe2 films show ferromagnetic ordering at room temperature, with saturation magnetization (~4μB/Mn) comparable to density functional theory calculations. Continued growth of MnSe2 leads to the formation of α-MnSe(111), which brings insight in understanding the origin of the magnetism. Furthermore, I will talk about our attempts in integrating 2D magnet MnSe2 onto topological insulator Bi2Se3 via MBE. Such systems have a lot of potential in studying spin-transfer torque, exploring magnetic skyrmions, and searching for quantum anomalous Hall effect. By performing spin-polarized STM measurement, we observe direct evidence of ferromagnetic ordering of monolayer MnSe2 on Bi2Se3. The attempt of growing MnSe2 on Bi2Se3 also leads to the synthesis of magnetic topological insulator Bi2MnSe4. Some preliminary structural and magnetic characterization of this new material will also be discussed.
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