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TT: Fachverband Tiefe Temperaturen
TT 9: 2D Materials: Electronic structure, excitations, etc. I (joint session O/HL/TT)
TT 9.1: Hauptvortrag
Montag, 9. März 2026, 10:30–11:00, TRE/MATH
Magnetic Order in 2D Materials Beyond Bulk Constraints — •Jeison Fischer — II. Physikalisches Institut, Universität zu Köln
Even though exfoliated microflakes remain widely used in 2D magnetism research, their bulk origin restricts access to many potentially interesting phases, an obstacle that molecular beam epitaxy (MBE) can overcome. MBE enables the controlled synthesis of single-layer materials directly related to, yet often distinct from, their bulk counterparts.
In my talk, I will present structural characterization and discuss the mechanisms behind the formation of such novel 2D materials grown via MBE on graphene. [1-2] The emerging magnetic properties of these new 2D materials will be exemplified with two cases: Cr2S3-2D and Fe2S2-2D. Cr2S3 forms a covalently bonded NiAs-type structure without van der Waals gaps. Using spin-polarized scanning tunneling microscopy (STM) and X-ray magnetic circular dichroism (XMCD), we show that it hosts ferromagnetic coupling within the plane with magnetic moments pointing out-of-plane, combined with A-type antiferromagnetic coupling between different Cr planes. Fe2S2 exhibits a unique hexagonal phase, in which Fe atoms occupy tetragonally coordinated sites. Spin-polarized STM reveals that the moments are noncollinear within the plane. We map the in-plane components of two distinct magnetic configurations and find that the moments are confined to the 2D plane, forming a Néel state and a 2Q state.
[1] Knispel et al. Small, 2025 21, 2408044.
[2] Safeer et al. Adv. Funct. Mater. 2025, 202500907.
Keywords: 2D magnetic materials; Molecular beam epitaxy; spin-polarized STM; chromium sulfide; iron sulfide