Self-Assembly Design of a Robust 2D Frustrated Magnet with Bilayer Tetragonal Spin-Lattice

We intentionally designed a stable two-dimensional (2D) bilayer dimer system, OsFeP₄, which serves as a tunable spin-5/2 J₁-J₂ anisotropic Heisenberg-like model to investigate frustrated magnetism. The frustrated state of 2D OsFeP₄ originates from the robust intradimer ferromagnetic (FM) exchange coupling (J_⊥) and a subtle competition between P₄ molecules mediating interdimer ferromagnetic (J_∥) and antiferromagnetic (AFM) exchange coupling (J_×). This is further supported by a significant broadening of the specific heat peak, a high frustration factor (θ_CW/T_N) of 4.17, the peak at the gamma point in the static structural factor, and short-range spin textures. Moreover, we employ strain to modulate the frustration parameter J_×/J_∥ from 0.23 to 0.4 and spin direction from in-plane to out-of-plane. The FM, AFM, and frustrated phase transitions are identified in the J_⊥-J_×-J_∥ ternary phase diagram. This work will enrich our understanding of the frustration mechanisms in the 2D limit.