Doping driven spin-flop transition in mixed 3d-5d compounds

The in-plane magnetization of the layered iridate Sr₂IrO₄ turns to out-of-plane upon partial substitution of ruthenium or manganese atoms for iridium. Based on first-principles electronic structure analysis, we present an effective low-energy Hamiltonian to model this doping effect. We found that the spin-flop transition originates from the M-Ir bond direction changes from the local easy axis to the hard axis as M changes from Ir to Ru or Mn.