Group Seminar 2025/26

ABSTRACT: Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted considerable interest not only as an ideal platform for exploring magnetism in the atomically thin limit, but also for their potential for next-generation spintronic applications [1]. In heterostructures involving 2D vdW magnets, novel quantum phenomena can emerge at interfaces, where the magnetic proximity effect from 2D magnets toward adjacent nonmagnetic materials plays a crucial role and has been widely studied [2]. In contrast, proximity effects from nonmagnetic materials on the magnetic properties of 2D vdW magnets, particularly on magnetic anisotropy, remain underexplored.

In this work, we report a reorientation of magnetic anisotropy in monolayer FeCl2 epitaxially grown on a Bi(111) surface –from its natural out-of-plane direction to a predominantly in-plane direction– as revealed by X-ray magnetic circular dichroism (XMCD) measurements [3]. This effect disappears in bilayer FeCl2 on Bi(111), where the magnetic anisotropy reverts to its intrinsic out-of-plane direction. This magnetic anisotropy reorientation is not attributed to the monolayer thickness itself but to a proximity effect from the Bi surface, since the out-of-plane easy axis remains down to the monolayer in FeCl2 films grown on a Au(111) surface [4]. Angle-resolved photoelectron spectroscopy (ARPES) reveals metallic interface states, which are derived from the Bi surface states modified by charge transfer and backfolding according to the Brillouin zone of the moiré superstructure formed by the FeCl2 overlayer, suggesting a strong coupling between FeCl2 and Bi. These findings demonstrate that nonmagnetic materials can exert a strong influence on the magnetic properties and interfacial electronic structure of 2D vdW magnets via proximity effects at the vdW interfaces, offering new strategies for engineering the magnetic and electronic properties of spintronic devices based on 2D vdW magnets and their heterostructures.

References: 

[1] Q. H. Wang, et al., ACS Nano 16, 6960 (2022).

[2] B. Zhang, et al., npj Spintronics 2, 6 (2024).

[3] S. Terakawa, et al., Adv. Mater. 38, e21534 (2026).

[4] A. Aguirre, et al., Adv. Mater. 36, 2402723 (2024).