Magnetic phase diagram of two-leg ladder iron-based systems: Exact numerical results

Motivated by growing experimental evidence of exotic magnetism in low-dimensional iron-based systems, we study the magnetic phases of the multi-orbital Hubbard ladder in the orbital-selective Mott phase. To reduce computational effort, we use a low-energy description of the latter model: the generalized Kondo-Heisenberg Hamiltonian. Our main result is the doping- and interaction-dependent magnetic phase diagram. We reproduce the experimental results on the AFe₂X₃ family (A=Cs,Rb,Ba,K; X=S,Se), especially the block magnetism of BaFe₂Se₃ (AFM coupled 2x2 FM islands). In agreement with studies of the chain geometry, we also unveil block magnetism beyond the 2x2 pattern and an interaction-induced block-spiral magnetism (a spiral of rigidly rotating FM blocks). Moreover, we find phases not present on the chain: a robust regime of phase separation, incommensurate AFM, and a new regime of block-like magnetic patterns. Finally, we exploit the bonding/antibonding band occupations to give insight into the structure of the phase diagram.