Structure and Magnetism of EuS on Bi₂Se₃(0001)

Abstract

The rocksalt‐type ferromagnetic (FM) insulator EuS (bulk T C = 17 K) grown on Bi 2 Se 3 with well‐matched (111) plane of the film and (0001) plane of the substrate is studied. The system may feature magnetic proximity effect breaking the time‐reversal symmetry and opening a bandgap in the metallic topologically protected surface state of Bi 2 Se 3 . The experimental X‐ray diffraction studies are combined with ab initio calculations to resolve contradictory results concerning the enhancement of the T C up to 300 K and the degree of induced magnetization in the system. It is concluded that previous studies relied on idealized and unconfirmed structure models. Herein, it is shown by surface X‐ray diffraction (SXRD) with ab initio calculations that a two double layer‐thick EuS film grows with a sharp interface and without chemical intermixing in a single domain state in an FCC‐type stacking on the Bi 2 Se 3 (0001) surface in which the topmost layer is metallic, thereby lifting polarity. A large p z ‐orbital‐derived top‐layer sulfur magnetic moment of 0.6 μ B is found, whereas for europium, μ Eu = 6.9 μ B throughout the film is found. No magnetization within the first Bi 2 Se 3 quintuple layer is found. The calculation of the exchange parameters J ij indicates a complex FM and antiferromagnetic ordering between europium and sulfur with a maximum Néel temperature of 226 K.