Pressure-Tuned Intralayer Exchange in Superlattice-Like MnBiTe/(BiTe) Topological Insulators.

The magnetic structures of MnBiTe(BiTe) can be manipulated by tuning the interlayer coupling via the number of BiTe spacer layers , 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 = 1 and 2. MnBiTe stays at A-type antiferromagnetic (AFM) phase with a decreasing Néel temperature and an increasing saturation field. In sharp contrast, MnBiTe 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 MnBiTe because of the in-plane lattice compression.