Sputter‐Grown MnBi ₂ Te ₄ Thin Films: Magnetic Ground States and Phase Control

The synthesis and magnetic properties of the intrinsic magnetic topological insulator MnBi 2 Te 4 , grown by magnetron sputtering, are investigated. While this growth method enables smoother morphologies than molecular beam epitaxy and is compatible with scalable processing, the metastable nature of MnBi 2 Te 4 presents considerable challenges in phase control and magnetic uniformity. By systematically varying the relative sputter powers of Mn, Bi 2 Te 3 , and Te targets, conditions that favor the formation of near‐stoichiometric MnBi 2 Te 4 , as supported by X‐ray diffraction, atomic force microscopy, and energy‐dispersive X‐ray spectroscopy, are identified. These films exhibit reduce surface roughness and lower twin‐domain density compared to Mn‐rich counterparts, which show evidence of phase separation and structural disorder. Magnetometry and X‐ray magnetic circular dichroism reveal that both film types exhibit sizable Mn moments, although signatures of antiferromagnetic order are only weakly expressed and appear sensitive to composition and morphology. Despite producing structurally well‐ordered films, clear linear dichroism attributable to A‐type antiferromagnetic ordering is not observed, suggesting magnetic inhomogeneity or suppression of interlayer coupling. These results highlight the compositional sensitivity of sputtered MnBi 2 Te 4 and underline the difficulties in stabilizing the intrinsic magnetic topological phase in thin‐film form.