Structural evolution and electronic properties of (Sr_(1-x)Ca_x)_(2_y)IrO_(4+z) spin-orbit-assisted insulators

摘要

The effect of isoelectronic substitution within single crystals of (Sr_(1-x)C_x)_(2_y)IrO_(4+z) is explored. The nominal n = 1 Ruddlesden-Popper phase with y = 0, z = 0 remains stable from x = 0 until x = 0.11, where the antiferromagnet spin-orbit Mott-insulating state persists. An increase in the saturated moment is observed with increasing Ca substitution, suggesting a modified coupling of the in-plane moments relative to the in-plane rotation of IrO_6 octahedra. Beyond x = 0.11, the x = 1/4, y = 0, z = 1/2 structural phase Sr_3CaIr_2O_9, consisting of a three-dimensional network of corner-sharing octahedra, begins to intermix and eventually nucleates phase-pure crystals at higher starting Ca content. An insulating, nonmagnetic ground state is observed in this phase attributable to the J = 0 state and is consistent with a recent powder study. At higher Ca concentrations beyond x = 0.75, crystals begin to stabilize in the y = 1/3, z = 0 quasi-one-dimensional Ca_5Ir_3O_(12) structure. The low-temperature transport in this chain-based structure is well described via variable range hopping, and an antiferromagnetic ordering transition appears below T_N = 9 K. Our data provide a detailed mapping of the electronic and structural properties accessible as the structural framework of the canonical spin-orbit Mott insulator Sr_2IrO_4 is destabilized via isovalent chemical substitution.