Pressure-Tuned Intralayer Exchange in Superlattice-Like MnBi₂Te₄/(Bi₂Te₃)<i>_n</i> Topological Insulators

Abstract

The magnetic structures of MnBi₂Te₄(Bi₂Te₃)_<i>n</i> can be manipulated by tuning the interlayer coupling via the number of Bi₂Te₃ spacer layers <i>n</i>, while the intralayer ferromagnetic (FM) exchange coupling is considered too robust to control. By applying hydrostatic pressure up to 3.5 GPa, we discover opposite responses of magnetic properties for <i>n</i> = 1 and 2. MnBi₄Te₇ stays at A-type antiferromagnetic (AFM) phase with a decreasing Néel temperature and an increasing saturation field. In sharp contrast, MnBi₆Te₁₀ experiences a phase transition from A-type AFM to a quasi-two-dimensional FM state with a suppressed saturation field under pressure. First-principles calculations reveal the essential role of intralayer exchange coupling from lattice compression in determining these magnetic properties. Such magnetic phase transition is also observed in 20% Sb-doped MnBi₆Te₁₀ because of the in-plane lattice compression.