Hydrogen-tuned magnetotransport anisotropy and bandstructure of MnSb₂Te₄

In low dimensional systems magnetic anisotropy is at the root of long-range magnetic order and is vital in spintronic applications, most strikingly when the nontrivial topology of electronic bands is at play. Recent focus has been on the layered low-disorder antiferromagnet (AFM) MnBi₂Te₄ (MBT), shown to host topological surface Dirac bands supporting quantum anomalous Hall (QAH) and axion insulator states. Both, the band topology and magnetic anisotropy can be strongly affected by magnetic disorder, and current debate has centered around the topological nature of the isostructural to MBT yet a largely antisite-disordered MnSb₂Te₄ (MST). Depending on the level of Mn disorder, MST can be grown as an AFM or a ferromagnet (FM). Here we report on the post-growth tuning of magnetic anisotropy and the bandstructure of MST by injecting/extracting ionic hydrogen (H⁺). Our magnetotransport studies of MST under different field orientations reveal that hydrogenation tilts the spin direction from the out-of-plane (H||c) towards in-plane (H||ab), inducing a noncollinear spin structure that leads to transforming the initially an FM MST to canted AFM. Removal of H⁺ reverts MST to an FM state featuring topological chiral channels. This transition, investigated by DFT calculations, is due to hydrogen weakly binding to Mn. The role of hydrogen-healed Mn-Te dangling bonds will be discussed.