Structural evolution and electronic properties of (Sr1-xCax)2-yIrO4+z spin-orbit assisted insulators

TL;DR

This study investigates how isoelectronic Ca substitution affects the structure and electronic properties of Sr2IrO4, revealing phase transitions, magnetic behavior changes, and transport mechanisms in related iridate compounds.

Contribution

It provides a detailed mapping of structural and electronic evolution in (Sr1-xCax)2-yIrO4+z as Ca replaces Sr, including phase stability, magnetic states, and transport properties.

Findings

Stable Ruddlesden-Popper phase up to x=0.11 with persistent spin-orbit Mott insulator

Transition to nonmagnetic J=0 state in Sr3CaIr2O9 phase

Variable range hopping conduction in Ca5Ir3O12 structure

Abstract

The effect of isoelectronic substitution within single crystals of (Sr1-xCax)2-yIrO4+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 IrO6 octahedra. Beyond x=0.11, the x=1/4, y=0, z=1/2 structural phase Sr3CaIr2O9, 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 Ca5Ir3O12 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 Sr2IrO4 is destabilized via isovalent chemical substitution.