Fig. 6. Magnetic phase diagram of FeTe from Heisenberg model.

a Definition of the Heisenberg model parameters. Gray solid lines denote the prime square lattice, whereas brown dots denote the sublattice. J₁ and J₂ are nearest-neighbor (NN) and next nearest-neighbor (NNN) exchange interactions, respectively, on the prime lattice. J_K denotes NN exchange interaction between the prime lattice and sublattice. K is the NN biquadratic exchange interaction. b, c Magnetic phase diagram calculated from the model Hamiltonian (Eq. (1)) with K = 0.1 and 0.4, respectively.