Hydrogen-induced ferromagnetic to antiferromagnetic transition in MnSb₂Te₄

MnSb₂Te₄ (MST) is a layered magnetic topological material with a potential to host exotic electronic states and tunable transport properties. MST can exhibit either ferromagnetic (FM) or antiferromagnetic (AFM) ordering, depending on the level of Sb-Mn antisite disorder. Here we report on the effects of controlled intake of ionic hydrogen (H⁺), which couples to antisite disorder by modifying Mn-Te bonds, thereby transforming the long-range magnetic ordering from FM to AFM, passing through a mixed FM/AFM phase. The hydrogen-converted AFM (H-AFM) state features localization below the Néel temperature T_N ≃ 20 K, a reduction in carrier density, and increased mobility relative to the parent FM state. The H-AFM and as-grown AFM MST states exhibit comparable characteristic field scales — a spin-flop transition field (H₁) and a field (H₂) at which the moments align with the applied magnetic field (H). The ratio H₂/H₁ is only ~10-20% higher in the hydrogenated system but the high-field magnetoconductance σ_xx (H, T) exhibits opposite temperature dependencies above H₂. Low-H polar angle θ scans show maxima at 0^o (|| c-axis) and minima at 90^o in both AFM states, which contrasts with the tilt at low fields of the preferred magnetic axis in FM MST [1]. High-resolution TEM revealing the complex Sb-Mn disorder in FM and AFM MST along with Density Functional Theory (DFT) calculations of the changes in bond lengths, magnetism, and energetics will be presented and the effects of disorder on magneto-transport will be discussed.