Frustration in square lattice of Iridium Jeff=1/2 moments at high pressure

We study the evolution of magnetic order in the weakly ferromagnetic, insulator Sr2IrO4 under applied pressure using x-ray resonant magnetic scattering and x-ray magnetic circular dichroism techniques in the diamond anvil cell. The weak inter-layer coupling is readily tunable with pressure giving rise to a change in magnetic structure followed by coexisting and competing magnetic phases with different inter-layer coupling. Application of moderate magnetic fields stabilizes one of the magnetic phases. Higher pressures drive the system into a magnetically disordered state, possibly a quantum paramagnetic state. We discuss the results in the context of a J1-J2 model where the increasing strength of next-nearest-neighbor exchange coupling with pressure leads to frustration of in-plane interactions