Single-Layer Magnet Phase in Intrinsic Magnetic Topological Insulators, [MnTe][Bi<sub>2</sub>Te<sub>3</sub>]<sub><i>n</i></sub>, Far beyond the Thermodynamic Limit.

Jain, Deepti; Yi, Hee Taek; Yao, Xiong; Mazza, Alessandro R; Chen, An-Hsi; Kisslinger, Kim; Han, Myung-Geun; Brahlek, Matthew et al. · Nano Lett · 2025

basic_science · Level V

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Abstract

The intrinsic magnetic topological insulator (IMTI) family [MnTe][Bi<sub>2</sub>Te<sub>3</sub>]<sub><i>n</i></sub> has demonstrated magneto-topological properties dependent on <i>n</i>, making it a promising platform for advanced electronics and spintronics. However, due to technical barriers in sample synthesis, their properties in the large <i>n</i> limit remain unknown. To overcome this, we utilized the atomic layer-by-layer molecular beam epitaxy (ALL-MBE) technique and achieved IMTIs with <i>n</i> as large as 15, far beyond that previously reported in bulk crystals or thin films. Then, we discover that the "single-layer magnet (SLM)" phase, primarily determined by intralayer ferromagnetic coupling, emerges for <i>n</i> > ∼4 and remains little affected up to <i>n</i> = 15. Nonetheless, still, nonzero, interlayer ferromagnetic coupling is necessary to stabilize the SLM phase, suggesting that the SLM phase eventually disappears in the <i>n</i> → ∞ limit. This study uncovers the secrets of IMTIs beyond the thermodynamic limit and opens a door to diverse magneto-topological applications.