Enhanced magnetism and persistent insulating state in Mn doped Sr 2 IrO 4 .

The influences of Mn substitution at the Ir site of Sr 2 IrO 4 are investigated via a comprehensive study of the variation of structural parameters, the transport and magnetic properties of the Sr 2 Ir 1- x Mn x O 4 samples. The incorporation of Mn leads to an increase of the in-plane Ir-O-Ir bond angle, while it is not sufficient to drive the Mott-insulating state to a metallic state. Interestingly, we find a coexistence of Ir 4+ -O 2- -Ir 4+ super-exchange interaction and Mn 3+ -O 2- -Mn 4+ double exchange interaction in x ⩾ 0.06 samples. The Mn 3+ -O 2- -Mn 4+ ferromagnetic domains are isolated by the Ir 4+ -O 2- -Ir 4+ antiferromagnetic areas, leading to a severely localized electronic and magnetic states. The electron hopping between the localized states dominates the conductivity of the Sr 2 Ir 1- x Mn x O 4 samples.