Epitaxial Growth and Magnetic Ordering*

MnBi₂Te₄ (MBT) is a prototypical antiferromagnetic topological insulator (AFMTI), offering a platform to study emergent quantum phases when time-reversal symmetry is intrinsically broken. It is composed of van der Waals stacked septuple Te–Bi–Te–Mn–Te–Bi–Te layers, where the Mn sublattice introduces long-range magnetic order into a topological framework. Thin-film synthesis via molecular beam epitaxy (MBE) is essential for engineering heterostructures and devices that exploit these coupled magnetic and electronic properties.

Here we report the molecular beam epitaxy growth of 18-septuple-layer MBT thin films, epitaxially integrated on insulating Al2O3 (001) substrates with a Bi₂Te₃ buffer layer. Streaky reflection high energy electron diffraction (RHEED) patterns during deposition and X-ray diffraction measurements confirm smooth surfaces, high crystallinity, and well-defined layered ordering. Low temperature magnetization measurements at 3.5 K exhibit a primarily linear dependence of moment on field after substrate background subtraction, with features suggestive of a spin-flop transition, consistent with field-induced metamagnetic behavior previously reported in bulk MnBi₂Te₄ single crystals.

These results demonstrate that the hallmark AFM order is preserved in epitaxial films while offering tunability in the thin-film limit. Ongoing low-temperature magnetoresistance and Hall effect measurements will directly probe the interplay between magnetic transitions and charge carriers. These measurements will provide further insight into the emergent physics of MBT thin films and establish a pathway toward device-compatible AFMTI platforms for exploring topological quantum phenomena.